POLYMER COMPOSITES REINFORCED BY INORGANIC NANOPARTICLES AND LIGNOCELLULOSE By LETIAN WANG A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DE GREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2014
Â© 2014 Letian Wang
To my parents Li Wang and Yunju Li, I am here only because you gave me your strong shoulders to stand on and my wife Yuebing Li u for everything
4 ACKNOWLEDGMENTS I express my sincerest gratitude to my advisor, Dr. Zhaohui Tong , for her support, guidance, patience, and inspiration throughout my graduate study at the University of Florida. Their genuine interest and enthusiasm for this field are very contagious and I always feel energized, op timistic and eager to solve problems . I also thank the other members of my committee, Dr. Bruce Welt , Dr. Eric Mclamore , Dr. Luisa Amelia Dempere and Dr. Guodong Liu for their valuable advice, help and support in the past four years. Special thanks go to Dr. Yulin Deng (Georgia Institute of Technology) for bring me into scientific research; my group members Dr. Fei Wang, Dr. Jijiao Zeng, Nusheng Cheng and Suguna Jairam l Lab ( University of Florida) ; Dr. Lonnie Ingram, Dr. Ismael Nieves, Joe Sagues at the Biorefinery Pilot Plant ( University of Florida) ; Dr. Art Texeira, Dr. Bin Gao, Dr. Pratap Pullammanappallil ( University of Florida) ; Dr. Anthony Brennan and his group m embers ( University of Florida) ; Dr. Delong Song (Ingredion), Dr. Zhihong Fu (Texas A&M) , Dr. Siobhan Matthews ( SCF Processing Ltd ) for their thoughtful suggestions and their insight to my research problems. My colleagues also friends in the Agricultural & Biological Engineering department, especially Zhijiang Ni and Tian Di, they deserve special acknowledgement. They not only gave me help and support to my research, but also helped me to remember that there is more to life than research. I would also like t o thank the entire office staff, technicians, each of whom has helped me throughout the past 4 years.
5 TABLE OF CONTENTS page ACKNOWLEDGMENTS ................................ ................................ ................................ .. 4 LIST OF TABLES ................................ ................................ ................................ ............ 9 LIST OF FIGURES ................................ ................................ ................................ ........ 10 LIST OF ABBREVIATIONS ................................ ................................ ........................... 13 ABSTRACT ................................ ................................ ................................ ................... 16 CHAPTER 1 GAP OF KNOWLEDGE A ND SCOPE OF STUDY ................................ ................. 20 2 BACKGROUND AND MOTIVATION ................................ ................................ ...... 25 Biomaterials ................................ ................................ ................................ ............ 25 Lignocellulosic Biomass ................................ ................................ ................... 26 Lignocellulosic Residue from Biofuel Production ................................ .............. 27 Reinforcing material in biocomposite. ................................ ........................ 31 Soil amendment ................................ ................................ ......................... 32 Biobased Polymer and Biodegradable Polymer ................................ ............... 33 Biobased poly mers ................................ ................................ .................... 34 Biodegradable polymer ................................ ................................ .............. 38 Biocomposites ................................ ................................ ................................ ........ 40 Introduction of B iocomposites ................................ ................................ .......... 40 Lignocellulosic Biomass Reinforced Biocomposites ................................ ......... 41 Pristine natural fiber reinforced biocomposite ................................ ............ 41 Post processing lignocellulosic residue reinforced biocomposite ............... 43 Inorganic Material Reinforced Bionanocomposites ................................ .......... 48 Nanoclay reinforced nanocomposites ................................ ........................ 49 Graphene and graphene oxide reinforced nanocomposites ...................... 52 Biocomposite Preparation Methods ................................ ................................ ........ 57 Melt Mixing ................................ ................................ ................................ ....... 58 Solution Blending ................................ ................................ ............................. 61 Miniemulsion Polymerization ................................ ................................ ............ 64 3 RESEARCH OBJECTIVES ................................ ................................ ..................... 72 Green Composites of Poly (lactic acid) and Sugarcane Bagasse Resi dues from Bio refinery Processes ................................ ................................ ......................... 72 Disk Refining and Ultrasonication Treated Sugarcane Bagasse Residues for Poly (Vinyl Alcohol) Bio Composites ................................ ................................ ... 72
6 Synthesis of poly methyl methacrylate encapsulated nanolignin graphene oxide nano composite latex via miniemulsion polymerization ................................ ....... 73 Characterization of Biorefinery Residues as Sandy Soil Amendments ................... 73 4 GREEN COMPOSITES OF POLY (LACTIC ACID) AND SUGARCANE BAGASSE RESIDUES FROM BIO REFINERY PROCESSES .............................. 74 Introductory Remarks ................................ ................................ .............................. 74 Materials and Experiments ................................ ................................ ..................... 76 Materials ................................ ................................ ................................ ........... 76 Bagasse Residues Characteristics ................................ ................................ ... 77 Compositions of bagasse residues ................................ ............................ 77 Fiber length measurement for bagasse residues ................................ ....... 78 Composite Preparation ................................ ................................ ..................... 78 Mechanical Properties Measurements ................................ ............................. 79 Tensile test ................................ ................................ ................................ . 79 Flexural property test ................................ ................................ ................. 79 Thermal Analysis ................................ ................................ .............................. 79 Molecular Weight M easurement ................................ ................................ ....... 80 Scanning Electron Microscopy ................................ ................................ ......... 80 Statistical Analysis ................................ ................................ ............................ 81 Results and Discussions ................................ ................................ ......................... 81 Bagasse Residues Characteristics ................................ ................................ ... 81 Mechanical Properties ................................ ................................ ...................... 82 Tensile properties ................................ ................................ ...................... 82 Flexural properties ................................ ................................ ..................... 84 Thermal Properties ................................ ................................ ........................... 84 Molecular Weight ................................ ................................ .............................. 85 Morphologies of PLA and its Composites ................................ ......................... 86 Conclusions ................................ ................................ ................................ ............ 86 5 DISK REFINING AND ULTRASONICATION TREATED SUGARCANE BAGASSE RESIDUES FOR POLY (VINYL ALCOHOL) BIO COMPOSITES ...... 100 Introductory Remarks ................................ ................................ ............................ 100 Experiment ................................ ................................ ................................ ............ 103 Materials ................................ ................................ ................................ ......... 103 Dis k Refining (DR) Treatment ................................ ................................ ........ 103 Ultrasonication (US) Treatment ................................ ................................ ...... 104 Characterization o f Bagasse Residues ................................ .......................... 104 Film Casting of Composites ................................ ................................ ............ 105 Characterization of film composites ................................ ................................ 106 Results and Discussion ................................ ................................ ......................... 107 SEM Analysis o f Untreated and Treated Fermentation Residues .................. 107 Size Analyzer Analysis o f Treated Bagasse Residues ................................ ... 107 Tensile Mechanical Properties of the Composites ................................ .......... 108 Thermal Properties of the Composites ................................ ........................... 110
7 SEM Observation o f t he Composite s Fracture Surfaces ................................ 111 Conclusions ................................ ................................ ................................ .......... 112 6 NANOCOMPOSITES OF POLY METHYL METHACRYLATE ENCAPSULATED GRAPHENE OXIDE PREPARED BY MINIE MULSION POLYMERIZATION ....... 126 Introductory Remarks ................................ ................................ ............................ 126 Materials and Experiment ................................ ................................ ..................... 129 Materials ................................ ................................ ................................ ......... 129 Experiments ................................ ................................ ................................ ... 129 Preparation of graphene oxide (GO) ................................ ........................ 130 Synthesis of quaternary ammonium lignin (QAL) ................................ ..... 130 Modification of GO ................................ ................................ ................... 131 Miniemulsion polymerization of methyl met hacrylate (MMA) in the presence of graphene oxide (GO) ................................ ........................ 132 Characterization ................................ ................................ ................................ .... 132 Fourier Transform Infrared Spectrometry (FTIR) ................................ ............ 132 X Ray Diffraction (XRD) ................................ ................................ ................. 133 Molecular Weight ................................ ................................ ............................ 133 Thermal Stability Analysis ................................ ................................ .............. 134 Particle Size ................................ ................................ ................................ ... 134 Electron Microscopy ................................ ................................ ....................... 134 Results and Discussion ................................ ................................ ......................... 134 Visual Comparison of GO Modification by Different Surfactants .................... 134 Fourier Transform Infrared Spectrometry (FTIR) ................................ ............ 135 X Ray Diffraction (XRD) ................................ ................................ ................. 136 Thermal Stability Analysis ................................ ................................ .............. 137 Parti cle Size Distribution of Latex Droplets ................................ ..................... 138 Morphology of Graphene Oxide, Polymer Droplets in Latex and Melt Film .... 139 Molecular We ight ................................ ................................ ............................ 141 Stability of Latex ................................ ................................ ............................. 142 Conclusion ................................ ................................ ................................ ............ 143 7 CHARACTERIZATION O F BIOREFINERY RESIDUES AS SANDY SOIL AMENDMENTS ................................ ................................ ................................ .... 157 Introductory Remarks ................................ ................................ ............................ 157 Material and Methods ................................ ................................ ........................... 159 Materials ................................ ................................ ................................ ......... 159 Soil and Leachate Samples Preparation ................................ ........................ 160 Biorefinery Residues Characterization ................................ ........................... 161 Composition a nalysis ................................ ................................ ............... 161 Specific surface area measurement ................................ ......................... 161 S canning electron microscopy ( SEM ) for morphology analysis ............... 161 Fourier transform infrared spectroscopy (FTIR) ................................ ....... 162 Water Retention V alue (WRV) ................................ ................................ ........ 162 Nutrient Solution Concentration Analysis ................................ ....................... 163
8 Statistical Analysis ................................ ................................ .......................... 163 Result & Discussion ................................ ................................ .............................. 164 Fiber Compositions ................................ ................................ ........................ 164 Specific Surface Areas (SSAs) ................................ ................................ ....... 164 Morphologies of Biorefinery Residues ................................ ............................ 16 5 Nutrient Ions Sorption ................................ ................................ ..................... 165 Water Retention Values (WRVs) ................................ ................................ .... 165 Nutrient Retention in Leachate ................................ ................................ ....... 166 Conclusions ................................ ................................ ................................ .......... 167 8 OVERALL CO NCLUSION ................................ ................................ .................... 175 APPENDIX SUPPORTING INFORMATION FOR CHAPTER 7 ................................ ..................... 178 LIST OF REFERENCE ................................ ................................ ................................ 183 BIOGRAPHICAL SKETCH ................................ ................................ .......................... 200
9 LIST OF TABLES Table page 4 1 Temperature profile of the twin extruder for composite processing .................... 88 4 2 Composition and fiber characteristics of three types of bagasse residues ......... 89 4 3 Effect of different residues and DVKS on the mechanic al properties of neat PLA and PLA composites ................................ ................................ ................... 90 4 4 Effect of three types of bagasse residues and DVKS on the thermal properties of neat PLA and its composites ................................ ......................... 91 4 5 The molecular weight of neat PLA and its composites ................................ ....... 92 5 1 The main components of the fermentation bagasse residue ............................ 114 5 2 TGA data for neat PVA and its composites containing 2%, 5%, and 10% disk refining (DR) and DR plus ultrasonication (US) treated bagasse residues ....... 115 6 1 The defaul t recipe for the miniemulsion polymerization of PMMA latex. ........... 144 6 2 Molecular weight of polymerized latex of PMMA with different GO loading. ..... 145 7 1 Compositions of BM and FB residues ................................ .............................. 169 7 2 Effects of fiber loadings on the relative WRV%, ammonium retention% and phosphate retention% of residue fiber mixtures and correspo nding statistical analysis ................................ ................................ ................................ ............ 170 A 1 Effects of fiber sizes on the relative WRV%, ammonium retention% and phosphate retention% of residue fiber mixtures and corresponding statistical analysis ................................ ................................ ................................ ............ 180
10 LIST OF FIGURES Figure page 1 1 Sustainable biomass cycle based on lignocellulosic materials from agricultural and bioethanol industry. ................................ ................................ ... 24 2 1 Scheme of three main types of layere d silicates in polymer matrix .................... 69 2 2 Schematic and relationship of graphene to other graphitic co mpounds. ............ 70 2 3 Structure of graphene oxide and its surface functional groups. ................. 71 4 1 Schematic diagram of the twin screw extruder ................................ ................... 93 4 2 SEM images of three types of bagasse residues. ................................ ............... 94 4 3 Effect of three types of residues and DVKS on tensile stren gth and tensile elastic modulus of neat PLA and its composites ................................ ................. 95 4 4 Effect of three types of residues and DVKS on elongation at break of neat PLA and its composites. ................................ ................................ ..................... 96 4 5 Effect of three types of residues and DVKS on flexural strength and flexural modulus of neat PLA and its composites. ................................ ........................... 97 4 6 DSC Thermograms of neat PLA, PLA with 2% DVKS and its composites (1 st Scan). ................................ ................................ ................................ ................. 98 4 7 SEM images of tensile fracture surfaces. ................................ ........................... 99 5 1 SEM images of the baga sse residues, before disk refining .............................. 116 5 2 Particle size distribution of disk refining (DR) bagasse residues ...................... 117 5 3 Particle size distribution of disk refining plus ultrasonication (DR+US) treated bagasse residues. ................................ ................................ ............................ 118 5 4 Particle size distribution of disk refining and ultrasonication treated bagasse residues (DR+US) me asured by Zetasizer (six duplicates). ............................. 119 5 5 Tensile moduli and maximal stress of PVA and its bagasse residue composites with 2%, 5%, and 10% substitution ................................ ................ 120 5 6 The maximal tensile strain (elongation) of PVA and its bagasse residue composites ................................ ................................ ................................ ....... 121 5 7 TGA diagrams of neat PVA, neat disk refining (DR) treated bagasse res idue, and PVA composites containing DR treated bagasse residue ......................... 122
11 5 8 TGA diagrams of neat PVA, neat disk refining (DR) and ultrasonication (US) treated bagasse residue, and PVA composites con taining DR+US treated bagasse residues ................................ ................................ ............................. 123 5 9 SEM images of the fractured cross sections of neat PVA and PVA composites. ................................ ................................ ................................ ...... 124 5 10 SEM images of the fractured cross sections of PVA composites with 2% DR+US bagasse residue ................................ ................................ .................. 125 6 1 Chemical reactions of the preparation of quaternary ammonium lignin.. .......... 146 6 2 Photo of 0.02 g GO and GO treated with 0.01 g different surfactants in water, 10 minutes after agitation was stopped ................................ ............................ 147 6 3 Photo of 0.02 g diff erent surfactant treated GO in water and MMA mixture, 10 minutes after 10 minutes sonication. ................................ ................................ 148 6 4 FTIR spectra of raw graphite, raw GO, VBTAC treated GO and reduced GO. . 149 6 5 FTIR spectra of raw graphite, raw GO, lignin, QAL and QAL treated GO. ........ 150 6 6 XRD spectra of raw graphite, GO, QAL treated GO, and VBTAC treat ed GO. . 151 6 7 XRD spectra of raw graphite, GO, VBTAC treated GO, nanocomposites with 0%, 0.5% and 2% GO. ................................ ................................ ..................... 152 6 8 TGA thermograms of (a) raw graphite, (b) GO and (c) GO after treated with VBTAC ................................ ................................ ................................ ............. 153 6 9 Effect of different PVA and GO content on the particle size distribution of latex of PMMA and GO prepared via miniemulsio n polymerization. ................. 154 6 10 SEM and TEM images of GO and nanocomposites ................................ ......... 155 6 11 Photo of latex after miniemulsion polymerization a nd set still for more than 3 months ................................ ................................ ................................ .............. 156 7 1 BET specific surface area (SSA) analysis of FB and BM. Three size classes .. 171 7 2 Scan ning Electron Microscopy (SEM) images of biorefinery residue, FB and BM. ................................ ................................ ................................ ................... 172 7 3 Water retention tests results ................................ ................................ ............. 173 7 4 Nutrient re tention tests results. ................................ ................................ ......... 174 A 1 Schematic diagram of the modified centrifuge tube to determine water retention value (WRV). ................................ ................................ ..................... 181
12 A 2 Fourier Transform Infrared Spectroscopy (FTIR) spectra of nutrient soluti on treated biorefinery residues . ................................ ................................ ............. 182
13 LIST OF ABBREVIATIONS AIBN Azoisobutyronitrile AMPS 2 acrylamido 2 methyl 1 propanesulfonic acid BM Br own mill residues CMC Carboxymethylcellulose CNT Carbon nanotube DLS Dynamic light scattering DMA Dynamic mechanical analysis DR Disk Refining DVKS DesmodurÂ® VKS 20, a coupling agent EB Elongation at break ECH Epichlorohydrin ETAC Epoxypropyl trimethylammonium chloride FB Ferment ed sugarcane bagasse FM Flexural modulus FS Flexural strength FTIR Fourier Transform Infrared Spectroscopy HD Hexadecane HPLC High pressure liquid chromatography cc Cold crystallization enthalpy m Melting en thalpy mc Non isothermal melt crystallization enthalpy H 2 SO 4 Sulfuric acid LRB Lignocellulose residues from biofuel production MDI Diphenylmethane diisocyanate
14 MFC Microfibrillated cellulose MMA Methyl methacrylate Mw Molecular weight MWD Multiple wavelength detector NC Nanocellulose NREL National Renewable Energy Laboratory PB Pretreated sugarcane bagasse PET Polyethylene terephthalate PLA Polylactic acid PLLA Poly(L lactic acid) PLR Post processing lignocellulosic residue PMMA P oly methyl methacrylate PP Polypropylene PPF Pristine plant fiber PSt Poly styrene P(St BA) Poly styrene butyl acrylate PVA Polyvinyl alcohol QAL Quaternary ammonium lignin RB Raw sugarcane bagasse RID Refractive index detector SDBS Sodium dodec yl benzene sulfonate SEC S ize e xclusion c hromatography SEM Scanning electron microscope SSAs Specific surface areas SScF Simultaneous saccharification and co fermentation
15 T cc Cold crystallization temperature TEB T ensile elongation at break (cross head displacement) TEM Transmission electron TEMs Tensile elastic modulus T g G lass transition temperature T m Melting temperature T mc Non isothermal melt crystallization temperature TMA Trimethylamine TS Tensile strength (strength at break) TX 40 5 Triton 405 US Ultrasonication VBTAC (Vinyl benzyl) trimethyl ammonium chloride WRV Water retention value
16 Abstract of Dissertation Presented to the Graduate School of the University of Florida in Partial Fulfillment of the Requiremen ts for the Degree of Doctor of Philosophy POLYMER COMPOSITES REINFORCED BY INORGANIC NANOPARTICLES AND LIGNOCELLULOSE By Letian Wang August 2014 Chair: Zhaohui Tong Major: Agricultural and Biological Engineering Lignocellulosic residues from biochemic al production (ethanol or butanol) (LRB) are renewable, sustainable, potentially abundant, and inexpensive materials that could be utilized to produce an array of biobased products including fuels, chemicals, or biobased composites . H owever, they have been under utilized , and most of them were burned or gasified to generate power or heat. The development of biobased composites from biorefinery residues is expected to add value to current biorefinery pro cess, and the biocomposites may serve as alternative to conventional petroleum based plastic products. However, there are two main challenges that need to be solved in order to produce lignocellulosic based biocomposites with competitive properties against conventional plastics. The first challenge is the com patibility issue between LRB (including its individual component such as lignin) and polymer matrix. And the second challenge is that the wide particle size distribution and the presence of large fiber bundles result in inhomogeneous dispersion of the fill ers within the polymer matrix. This Ph.D. dissertation systematically investigated various fabrication techniques to prepare biocomposites using biorefinery residues as feedstock , with the focus on
17 exploring possible solutions to two main technical challen ges. To tackle the challenges, the conventional top down and the new bottom up approaches were employed. The top down approach in this dissertation consists of two fabrication routes. The first route includes simultaneous mechanical size reduction, homogen ization and mixing of different LRBs with poly lactic acid (a hydrophobic polymer resin) by melt mixing and with the aid of Desmodur VKS20 (DVKS), a chemical compatibilizer between hydrophilic lignocellulosic residues and hydrophobic polymer matrix. It was expected that size reduction mechanical treatment could increase surface areas of biorefinery residues and the compatibility between LRB and polymer at the aid of compatibilizer DVKS. The effects of different LRB characteristics on mechanical properties, crystallization behaviors, and morphologies of PLA composites were investigated. The results indicated that in the presence of 2 % DVKS, PLA composite with different LRBs exhibited as high as 98.94 % tensile strength and 93.91 % flexural strength of pristi ne PLA. The second route involves separated mechanical size reduction and homogenization (disk refining and ultrasonication) of LBR prior of solution blending with poly vinyl alcohol (PVA, a hydrophilic polymer). The results showed that the particle size of LBR was reduced by disk refining and ultrasonication to the range of tens of nanometers to several micro meters . It was found that the tensile modulus of the biocomposites was significantly improved and the tensile strength was slightly improved with the incorporation of the size reduced LRB. The biocomposites also had better thermal stability compared to neat PVA .
18 Although the top down approach could improve the compatibility of lignocellulosic residues with polymer matrix to some extent, the properties of obtained bio composites were still not satisfactory because poor dispersion of the filler in the polymer matrix and interfacial adhesion between different components . Therefore, in the second part of this dissertation, we will consider a bottom up appro ach, which focused on self assembly of nanocomposites through in situ m iniemulsion polymerization and encapsulation techniques on nanoscale . Our previous research demonstrated that the application of nanoscale self assembly via miniemulsion polymerization was able to prepare stable latex of nanocomposites consisted of polymer encapsulated nanoclay that was modified by quaternary ammonium lignin (QAL, a synthetic lignin surfactant). The obtained nanocomposites had dramatically improved physical, thermal and gas barrier properties because of the excellent filler dispersion and interfacial adhesion 1 . Therefore, in this approach, we focused on self assembl y of a different inorganic particle , graphene oxide ( GO ), into the polymer droplets through miniemulsion pol ymerization because of the superior properties of GO and graphene . If the nanocomposites of polymer encapsulated QAL GO can be successfully prepared, it will bring a new horizon to the preparation of conductive bio nanocomposite with superior mechanical and thermal properties via miniemulsion polymerization. Furthermore, it will open another avenue for utilizing LBR, which adds value to the bioethanol production, as lignin we used in both projects was extracted from LBR. This task is very challenging since to the best of my knowledge, polymer encapsulated exfoliated GO has never been synthesized before. I n this dissertation , we first prepared QAL and vinyl benzyl trimethyl ammonium chloride (VBTAC, a
19 commercial surfactant) treated GO s. Then attempted to fabr icate nanocomposites consisted of polymer encapsulated treated GOs via miniemulsion polymerization. XRD results showed that VBTAC increased the interlayer space of GO, and GO was exfoliated during the subsequent miniemulsion polymerization. More importantl y, microscopic evaluation revealed that GO was encapsulated in polymer droplets successfully and the latex was stable for more than 3 months. In summary, the top down approach can be very effective in preparing low cost bio nano composites with properties t hat match or exceed the pristine polymer matrix. The bottom up approach can be utilized to prepare high value bionanocomposites via self assembly by miniemulsion polymerization in nanoscale .
20 CHAPTER 1 GAP OF KNOWLEDGE AND SCOPE OF STUDY Biobased materia ls have proven potential to provid e solutions to alleviate our dependence on petroleum resources while minimize their own environmental impacts 2, 3 . Petroleum resources are limited, therefore alternatives are requ ired to maintain the health growth of our society. Moreover, petroleum based consumables such as commodity plastics are known to leave large environmental footprints for extended period of time. Consequently, the demand of biobased materials (both fuel and commodity products) is growing steadily over past decades 3 6 . Besides the emerging biofuels, completely or partially biobased polymer and polymer composites have been extensively studied. Some of the biobased pol ymers such as poly (lactic acid) (PLA) and polymer composites reinforced with lignocelluloses such as pristine plant fibers (PPF) have already been employed in packaging, automobile, and agricultural applications. Lignocellulose is the most abundant natur al polymer, and it is a potentially important feedstock for the production of various forms of bioproducts due to its widespread availability, sustainability, and low starting value 7 . Previously, researchers have made it possible to produce 2 nd generation bioethanol or biobutanol from post processing lignocellulosic residues (PLR) 8 and many pilot plants have been under constr uction in the US. However, the production cost of 2 nd generation bioethanol/biobutanol is still too high to compete with gasoline. Therefore the production of value added byproducts from waste stream of bioethanol process could be an effective approach to reduce total cost of biochemical refinery processes. The waste stream is still rich in lignocelluloses which are essentially composed of two components,
21 cellulose and lignin. The residue cellulose from bioethanol process has high crystallinity and good mec hanical properties, whereas lignin has very complex aromatic structure which gives it excellent anti oxidation and antibacterial ability 9, 10 . Therefore, polymer composites incorporated with lignocellulose residu es from biofuel production (LRB) and their derivatives could have mechanical and thermal properties comparable to other biocomposites reinforced with PPF but with lower cost . Moreover, the encapsulation of inorganic based lignin hybrid in polymer matrix vi a miniemulsion polymerization will further improve the properties and uniformity as well as eliminating abrasive damage to the equipment from singly inorganic particles. A new renewable process cycle (Figure 1 1.) could be established if LRBs and their der ivatives can be utilized to reinforce polymer composites effectively . Therefore, t he focus of this study is the investigation of polymer biocomposites incorporated with LRB and lignin extracted from LRB. Although there exists a number of researches for th e preparation of polymer biocomposite reinforced with PPF, the study that cover s the incorporation of PLR or LBR is very limited. In this study, two approaches including top down and bottom up approaches were employed for composites preparation. The top do wn approach consists of simultaneous size reduction and mixing of LRB with a hydrophobic polymer resin by melt mixing at the aid of a chemical compatibilizer and the separated mechanical size reduction/homogenization of PBR followed by a solvent casting wi th a hydrophilic polymer. The bottom up approach involves the self assembly of nanocomposites via in situ miniemulsion polymerization to encapsulate lignin inorganic hybrid into polymer matrix to form stable latex nanocomposite. The initial study for the synthesis of stable
22 latex of polymer encapsulated nano inorganic particles (GO) was elaborated in this study. In addition, to pursue other application of PLR, this dissertation also includes the use of biomass residues as soil amendment materials. Synthet ic petroleum based polymer, synthetic cellulose derivatives have been studied as high efficiency soil amendments to improve water and nutrient retention. These materials either tend to release toxins upon degradation or suffer from prohibitive high cost wh ich kept them from being used in the field. Compare to those aforementioned materials, PLR and LRB are more favorable because of their environmental benign characteristics and low starting value. More importantly, PLR and LRB are plant parts which are resp onsible of storing or transporting water and nutrients by nature. After bio ethanol processing, they have more surface area while still containing a considerable amount of cellulose, which is an excellent water holding material. In this dissertation , the ef fects of water and nutrient retention ability were evaluated in terms of PLR and LRB fiber composition, length, specific surface area and their loading levels in soil. ORGANIZATION OF THE DISSERTATION This Ph.D. dissertation has the following eight chapt ers: Chapter 1: Summarized the gap of knowledge and the scope of study Chapter 2: Discussion of the background and current status of relevant biomaterials and techniques, and the motivation of conducting the four research projects Chapter 3: Outlined the specific objectives of the four research projects
23 Chapter 4: Biocomposites consisting of PLA and three types of sugarcane bagasse residues (up to 30 wt. %) from different steps of a bioethanol process were prepared. The effect of different residue characte ristics and addition of a compatibilizer on mechanical properties, thermal stability, crystallization behaviors and morphologies of PLA composites were investigated. Chapter 5: Biocomposites of disk refined and ultrasonication treated sugarcane bagasse re sidue reclaimed from a bioethanol process with poly vinyl alcohol by film casting. The effects of various fiber length and surface morphology of residues (as a result of mechanical treatment) on mechanical properties, thermal stability and morphologies of PVA composites were studied. Chapter 6: Stable latex of nanocomposites of graphene oxide (GO) encapsulated by poly methyl methacrylate (PMMA) were synthesized via miniemulsion polymerization. GO was obtained from vigorous oxidation of graphite and functio nalized prior of polymerization. The effect of the amount of GO and co stabilizer on GO encapsulation, exfoliation and dispersion, polymer droplet size and the stability of the latex were evaluated. Chapter 7: The efficiency of two types of lignocellulosi c residues (residues from a bioethanol process, and a pulping process) as amendments for sandy soil was accessed. The characteristics of these residues including composition, specific surface areas, morphologies and nutrient sorption capacity were evaluate d and analyzed against the water and nutrient retention results. Chapter 8: Overall conclusion of this dissertation
24 Figure 1 1 . Sustainable biomass cycle based on lignocellulosic materials from agricultural and bioethanol industry.
25 CHAPTER 2 BACKGROUND AND MOTIVATION In recent years, fuels and materials derived from renewable sources have attracted a lot of attentions due to the limited of geological reserve of fossil fuels 11 an d its long term negative impacts on the environment such as greenhouse gas emissions, air pollution, and the associated effects of climate change 2 . Meanwhile, a large amount of petroleum derived materials (chemicals, plastics) t hat are made from fossil fuels further aggravate the depletion of these nonrenewable energy resources. Most petroleum based plastics remain stable at ambient conditions for hundreds or thousands of years after being discarded. This further aggravates the growing need for landfill space and adds to the environmental pollution caused by toxic fumes produced through combustion of these materials. Therefore, it is necessary to develop bio based products (biofuel and biomaterials) from renewable biomass resou rces. Biomass means the biodegradable fraction of products, wastes and residues from biological origin from agriculture, forestry and related industries including fisheries and aquaculture, as well as the biodegradable fraction of industrial and municipal waste. Biomass has been utilized by us for thousands of years for energy and materials. There are many other new sources of energy like solar, wind and fuel cells. They are all capable of providing the energy we need, whereas only biomass is able to offe r a huge selection of bioproducts which can be used as substituent of petroleum based materials Biomaterials Biomass can not only provide us the fuel, but it also offers countless biomaterials which can be used in many applications. Biomaterials are agricu ltural, forestry and marine feed stocks (that include lignocellulosic biomass such as plants, trees, wood
2 6 waste, grasses, agricultural residues and fungi, algae etc.) and the ones, which are derived from natural renewable resources. Conventional biomateria ls like wood, linen and stubble were used to build homes and make clothes. In textile industry, half of fiber comes from natural materials such as cotton, wool, flax etc. Paper industry uses lignocellulosic biomass to make paper and packaging materials. In polymer industry, some of the polymers, such as poly lactic acid (PLA) and polyhydroxyalkanoates (PHAs) are synthesized from starch or sugars, respectively. Biocomposites completely or partially composed of biobased materials have been studied extensively as well. B iomaterials such as lignocellulosic biomass, biobased and biodegradable polymers as well as Biocomposites will be discussed in detail. Lignocellulosic Biomass Lignocellulosic biomass can be divided into two types based on the source: pristine p lant fiber (PPF) and post processing lignocellulosic residues (PLR). Plant fibers such as cotton, linen and jute have been playing important roles in our daily life. Cotton is the most widely planted and is the dominant material for clothing. Linen has bet ter strength, durability and absorb/give off moisture more rapidly compare to cotton. Jute is one of the cheapest natural fibers, and is second among other textile plants in the amount produced and variety of uses. Jute is in the middle between textile fib er and wood, it has long, soft, shiny vegetable fibers that can be spun into coarse, strong threads, and it is used chiefly to make sacks coarse cloth and furnishing 12 . Aside from these well known pristine plant fibers (PPF) which are relatively expensive, post processing lignocellulosic residues (PLR) such as sugarcane bagasse and sweet beet pulp from sugar mill and corn stalk, wheat straw from agricultural industry are abundant, renewable and have very low starting value. However, PLR are
27 burnt in the field or in the processing plant for energy g eneration purpose only. With the vast demand of bioethanol and incentives provided by US government, there would be increasing amount of PLR available for subsequent utilization. It would be a significant contribution to the sustainable biomass cycle prese nted earlier (Figure 1 1), if PLR and LRB can be converted to valuable products. The constituents of PLR and LRB varies, for raw sugarcane bagasse and its subsequent LRB , there are about 27 % or 40 % of lignin, 40 % or 45 % of cellulose, 28 % or 12 % of h emicellulose, respectively 13 . T he characteristics of lignin, cellulose and hemicellulose, as well as their applications will be discussed in this section . Lignocellulosic Residue from Biofuel Production Lignocellulosic residue from biofuel production (LRB) is the main starting material of this study. Biofuel are one of the viable alternatives to supplement or replacement to the conventional petroleum based fuel. The current total global production of renewable fuels is 50 billion liters a year, about 40% of that is bioethanol which is d erived from extracted sugarcane juice 14 . However, there has been growing criticism about using food commodities (sugar, starch) for fuel production because it may lead to higher prices for both food and fuel. This criticism might be addressed by using cellulose (instead of sugar or starch) to make bioethanol. This process does not use the edible part of the crop, but the lignocellulosic part, which is inedible and is typically not used, such as wood, agricultural g rasses, and agricultural residues such as sugarcane bagasse, can be used to produce ethanol. Using low cost agricultural waste can minimize the impact of fuel production on the food supply and reduce production costs. Sugarcane bagasse is the waste mater ial of sugarcane after sucrose extraction. The current total global production of renewable fuels is 50 billion liters a year, about
28 40% of which comes from sugarcane. With US Department of Energy (DOE) call for 2030, the production of sugarcane should be greatly increased 15 . Sugarcane bagasse has primarily been used as animal feed or disposed as solid waste. Ingram et. al. have been developing a novel approach of converting the lignocellulosi c waste to bioethanol via a process called simultaneous saccharification and co fermentation (SSCF). The cellulose based bioethanol process has great potential because the PLR is abundant and inexpensive. In the bioethanol process developed by Ingr am et al . , raw bagasse was pretreated by a low level of phosphoric acid concentration followed by the steam explosion treated then the pretreated bagasse can be effectively fermented by liquefaction plus SSCF process using hydrolyze resistant Escherichia Coli 8, 16 20 . There are no commercial cellulosic based bioethanol facilities in the United States yet, but there are many cellulosic ethanol projects under development and construction 21 . The complex lignocellulosic b ioethanol production process results in a high cost (approximately US$3.03 $4.163 per gallon) 22 . Although it is more economical than biodiesel, it is still not as competitive as fossil fue ls. A promising approach to reduce total cost of bioethanol derived from lignocellulose is to produce value added and high functionality byproducts from its waste. LRB from bioethanol production usually consists of a large quantity of lignin, some residue cellulose and a small amount of protein. It may be used directly as soil amendment material or for the production of a collection of bioproducts such as biocomposites and lignin derivatives with unique properties at competitive cost. Next, lignin, cellulos e and hemicellulose will be discussed individually.
29 Lignin is the most abundant constituent in LRB. Lignin is a cross linked aromatic polymer comprising hydroxyphenyl , guaiacyl, and syringyl units 23 . Depending on the different resources and extraction methods, lignin has a variety of chemical structures. The current major source of lignin (kraft lignin, lignosulphonates, and soda lignin) is from the waste stream of the pulping and sugar mills and it has been used as the energy sources by direct combustion. Purified lignin is extracted or separated from lignocellulosic feedstock by alkaline, acid solution, organic solvent or ionic liquids in a relative smaller quantity. Lignin derivatives have numerous applications, such as resins 24 , polymer composites 10, 25, 26 ; colloidal dispersants or surfactants 1, 27, 28 ; additives for ink and paint 29 ; feedstock of vanillin, hydroxylated aromatics, q uinines, aldehydes, and aliphatic acids 30 ; environmental friendly dust suppression agent 31 ; carbon fiber and active carbon 32, 33 ; adhesives; fertilizers and pesticides delivery 34 . In previous studies conducted in our group, lignin is extracted from LRB and converted to a cationic surfactant which was used to modify nanoclay from hydrophilic to organophilic. The obtained organoclay was able to be dispersed in organophilic monomer phase and exfoliated by the in situ miniemulsion polymerization process. As a result, nanoclay polymer nanocomposites were successfully obtained 1 . In this study, lignin was converted to the same cationic surfactant and used as a modification agent to modify graphene oxide from hydrophilic to organophilic. Cellulose is a main component of plant biomass (90% of cotton, 40% of wood and 30 40% of non wood plant). Cellulose is a polysaccharide with a liner chain consisting 4) linked D glucose units 35, 36 . In the fully extended cellulose molecule, the repeating units are at an angle of 180 degrees to the adjacent
30 ones. The degree of polymerization, the length of the polymer chain varies from plant to plant. The deg ree of polymerization of natural cellulose can be as high as 14000, but purification processes reduces it to around 37 . Solid cellulose has a microcrystalline structure, with crystalline and amorphous regions. The molecular structure of cellulose decides its supramolecular structure, and its physical and chemical properties. Man made cellulose has been sour ced mainly from wood and cotton, by employing lignin separation methods as discussed previously. The major applications of cellulose are: paper products, textiles, additives in drugs and foods, sustainable building materials. More importantly, cellulose is the major usable portion of the feedstock in lignocellulosic bioethanol production. Hemicellulose is actually not a form of cellulose, it is composed of xyloglucan, 3,1 4) glucan. Hemicellulose has two primary functions in plants, the first is strengthening the cell wall by interaction with cellulose and lignin, the second is function of seed storage carbohydrate 38, 39 . The structure and content of the hemicellulose varies widely between plants and cells. There are three major differences between hemicellulose and cellulose. The first is hemicellulose c onsists of several different hetero 4) linked D glucose units. In the second place, the degree of polymerization of natural hemicellulose is 10 to 100 times lower than that of natural cellulose. Last but not least, hemicellulose is highly branched compare to the linear structure of cellulose. The commercial significance of hemicellulose is not as big as lignin or cellulose. Some types of hemicelluloses are used directly in the food industry, e.g., guar and l ocust bean gums (galactomannan), konjak gum (glucomannan), and tamarind gum
31 (xyloglucan) 40 . Cholesterol 3,1 4) glucan for hyper cholesterolemic patients was reported previously 41 and the U.S. Food and Drug Administration recommends the dai 3,1 4) glucan. While cellulose is crystalline, strong, and resistant to hydrolysis, hemicellulose has a random, amorphous structure with little strength. It is easily hydrolyzed by dilute acid or base as well as myriad hemicellulase enz ymes 5 . However, hemicelluloses affect the saccharification of biomass in lignocellulosic biofuel production, due to the released pentoses are less desirable for fermentation than hexoses 40 . Reinforcing material in biocomposite . There are many ways to utilize the vast amoun t of the PLR and LRB other than directly burning. Two of the promising approaches are to use the residues directly is as the reinforcement in Biocomposites or as a low cost soil amendment. Numerous studies regarding using pristine fiber as reinforcing ma terial in polymer composites have been reported. Many researchers have reported the enforcement of PLA by the incorporation of natural fibers such as jute fiber 42 , flax fiber, kenaf fiber 43 47 or lignocelluloses such as pine wood flour 48 and sweet beet pulp (SBP ) 49 . The benefits of using natural fibers and lignocelluloses include their widespread availability, low density, biodegradability, high stiffness and better thermal stability. However, natural fibers cost much more compare to LRB be cause they are normally used in textile and paper manufacturing. For this reason, the industrial application of using pristine nature fiber such as cotton in polymer biocomposite is limited. In contrary, LRB has negligible cost in the first place because i t is normally burned or disposed as solid waste. More importantly, as we discussed earlier, the lignocellulosic biofuel process could benefit from the utilization of LRB to produce value added byproducts. The detailed discussion
32 of using lignocellulosic bi omass in polymer composite will be presented in Chapter 2, Soil amendment Only a few investigations regarding the application of lignocellulosic residues such as PLR or LRB in soil amendme nt have been reported. In contrary, many s ynthetic hydrophilic polymers have been investigated as soil amendment materials to retain water and nutrient in arid area. It has been reported that hydrophilic polymers such as polyacrylic acid and polyacrylamide gels were able to retain water up to 500 times of their weight 50 . These synthetic polymers could improve water retention in sandy soils 51 , therefore facilitated the gr owth of plants 52, 53 . However, despite the superior water retention capacity, their wide applications as soil amendments have been limited by a variety of factors such as non renewable, non biodegradable, low salt tolerance, possibility of releasing toxic residues and high cost 50, 54 . Bio based materials such as manures, starch, PPF , cellulose (including carboxymethylcellulose, CMC), and chitosan have been studied as soil amendments as well. The drawbacks for their use include low retention, high price, low salt tolerance and their competitiveness with food 54 57 . As previous reported, the addition of organic matters improved wat er holding capacity of a soil 58 . In addition, the removal of lignocellulosic residues from agricultural fields or forests to biomass processing locations instead of leaving in the crop field had adverse impact on soil quality and productivity, and led to accelerated evaporation, water and nutrient losses 59, 60 . It is essential to return part of biomass residues back to soil as approximately 41% of biomass should be kept in all major land use areas in order to prevent soil erosion according to previous studies 60, 61 .
33 The use of lignocellulosic residues ( PLR or LRB ) as soil amendments not only adds an avenue to biomass processing industries but also offsets the negative impacts rties. Johnson et al. reported that corn stove fermentation residues were capable to improve properties of severely eroded soil such as water stable aggregates and decreased bulk density without adverse impacts on crop growth 58 . Galvez et al. claimed that bioethanol by products led to N 2 O emissions and larger inc reases in soil respiration, N availability and enzymatic activity in comparison with other amendments such as sewage sludge and composts 62 . 63 reported that no crop phytot oxicity was significant after seven day application of bioethanol residues. Biobased Polymer and Biodegradable Polymer Biobased polymer and biodegradable polymer are two important members in the polymer family. The first man made plastic was derived from plant wall cellulose in 1855, but the natural sourced plastics were overwhelmed by the invasion of petroleum derived plastics. With the ever growing concerns of the limited petroleum source and our environment, the biobased polymers and biodegradable polym ers have been attracting more and more interests. Biobased polymers are the naturally occurring polymeric materials as well as the high molecular weight synthetic polymers prepared by chemical or biological methods (or both). Biodegrada ble polymer can deco mpose as a result of activities caused by living organisms, and may also involve factors of hydrolysis, oxidation, photo degradation or elevated temperature. However, biobased polymers are not necessarily biodegradable and biodegradable polymer are not all biobased. The most important task is to choose the appropriate polymer for the specific application.
34 Biobased and biodegradable polymers have been used in more and more commercial products. Many cold drink cups and fast food cutleries are made of biobase d and biodegradable polylactic acid (PLA), and biodegradable polymers such as polyvinyl alcohol (PVA) has been used as additive in paint and coating. Several major commercialized biobased or biodegradable polymers will be discussed in detail below. Biobas ed polymers There are three major types of biobased polymers which differ from their origin in the market at this moment. They are starch, sugar and microorganism based biopolymers. Talking about starch based biopolymers, the one has to be mentioned is th e Polylactic Acid (PLA). PLA is a hydrophobic thermoplastics made from the renewable agricultural feedstock (corn starch) through fermentation followed by the polymerization process of the lactic acid 64 . PLA is normally derived from starch. Manufacturing method can be gen eralized as bacterial fermentation of starch to form lactic acid, followed by condensation polymerization of the D or L lactic acid or ring opening polymerization of the lactide to obtain PLA. High molecular weight PLAs with tunable rigidity, moisture r esistant and biodegradability were prepared by the manufacturers. Such tunable properties of PLA could be achieved by incorporating a comonomer of hydroxy acids, or racemization of D or L isomer. PLA homopolymer such as poly(L lactic acid) (PLLA) is a ha rd, transparent and crystalline polymer having a melting point of 170 180 Â°C and a glass transition temperature of about 53 Â°C 64 66 . H.Tsuji developed the stereo complexation method of these two isomers. He foun d that 1:1 ratio gives the highest melting temperature of 220Â°C which is 40Â°C higher than the different types of the homo crystalline PLA derived from L lactic acid (PLLA) 67 .
35 Like most thermoplastics, PLA can be processed by techniques including thermoforming, injection and blow molding, foaming, film extrusion and fiber extrusion. PLA is reasonably transparent and has high gloss and low haze. The tensile strength, red to standard thermoplastics such as polypropylene (PP), polyethylene terephthalate (PET) 68 , which are widely used in packaging, medical applications and automobile interior components 43, 69 . The specific gravity of PLA (1.24 g/cm3) is lower than that of PET (1.34 g/cm3), but higher than many other conventional polymers which have a specific gravity in the range of 0.8 to 1.1 g/cm3 (e.g. polypropylene (PP) is 0.92 and low density polyethylene (LDPE) is 0.90). PLA has high odor and flavor barrier properties. It also has high resistance to grease and oil, thus finding application in the packaging of viscous oily liquids. In terms of packaging material, PLA is suitable for dry and short shelf life products but not suitable for the packaging of carbonated beverages and other liquids due to its poor O2 , CO2 and water vapor barrier 70 . Because PLA is biodegradable and biocompatible, it used in the biomedical application as sutures and drug delivery devices as well as in tissue engineering 70 . The two major manufacturers of PLA are Natural Works and PURAC, they had total production capacity of 250,000 tones per annual. The selling estimated to be around 1.3 1.6 per kg in 2007 dollar 71 . Apart from starch based biopolymers, sugar based biopolymers, such as polyethylene (PE) can be produced form the ethanol derived from sugarcane juice. After fermentation, the ethanol is distilled and dehydrated to ethylene. Nevertheless, biobased PE is not biodegradable, but it would be great if biobased ethylene can
36 replace the petroleum based ethylene, as the g lobal consumption of all ethylene derived polymers were approximately 185 million tones including polymers and fibers in 2007 alone. The application of PE spun from packaging, cosmetics, automotive parts, and toys to agricultural and industrial purposes 70 . Until recently, the production of ethylene from biomass was not considered to be cost competitive compared with petroleum derived ethylene 20 . Prices for bio based polyethylene may be 30% higher compared to petrochemical polyethylene. Prices for petrochemical LDPE, for ex ample, were around US$ 1.7 per kg in 2008 72 . On e of the most noticeable emerging sugar based biopolymers is the polyglycolide Acid (PGA) which is biodegradable thermoplastic polyester. It can be prepared by polycondensation of glycolic acid which is commonly isolated from sugar crops. PGA has high st rength and stiffness but low hydrolytic stability, like PLA, PGA can be used as a material for the absorbable sutures, controlled drug delivery and tissue engineering applications due to its biodegradability 12 . In addition to the starch and sugar based biopolymers, microorganism based biopolymers has made its way to the market place as well. Poly hydroxyalkanoate (PHA) is a type of polyesters and is primarily a product of carbon assimilation (from glucose, coming from starch) and is employed by microorganisms as a form of energy storage molecule to be metabolized when other common energy sources are not available. Industrial bacterial fermentation consists of fermentation, isolation and purification and blending and palletizing 12 . Many other microorganism based biolastics are produced by a variety of organisms, for instance, poly 4 hydroxy butyrate (PHB) and polyhydroxyvalerate (PHV).
37 PHV has attracted much commercial interest to be the alternative polymer because its physical properties are remarkably similar to those of PP. PHB appears stiff and brittle, it also has a high degree of cryst importantly, PHB is rapidly biodegradable. For this reason, PHB is being evaluated as a material for tissue engineering scaffolds and for controlled drug release carriers. The manufacturers of mic roorganism based plastics are mainly located in the USA, China and Brazil. With the complex purification process and low worldwide production capacity of just 2300 tones. Among the biobased polymers described above, PLA is the best choice at this point du e to its relatively low cost, comparable mechanical properties to petroleum based polymers, and rapid biodegradability. In comparison with petroleum based polymers, one of the most significant obstacles for the wide applications of PLA is the cost. Based o n current market, PLA will not be considered competitive in current US market unless its cost can be reduced from about $2 per lb to $0.40 0.80 per lb 42 . One promising way to reduce the cost of PLA while maintain its advantageous properties is to incorporate lignocellulosic materials such as LRB to the polymer matrix to produce biocomposites. The merits of this approach are: the entire composite is still biobased and biodegradable; the price of PLA can be reduced; and this type of composite would be a significant value added product of the lignocellulosic biofuel process. This biocomposite preparation approach can also be applied to different polymer materials. In this study, PLA will be employed as the matrix materials for preparation of biocomposites reinforced by different types of LRB.
38 Biodegradable polymer There are many biodegradable polymers available currently, however, they are not necessary biobased. Several examples are: polyvinyl alcohol (PVA), Biomax (an ethylene copolymer, manufactured by DuPont), poly hydroxyalkanoate and poly alkylene dicarboxylate. PVA is a petroleum based but biodegradable polymer, unlike most vinyl polymers, PVA i s not synthesized by polymerizing its monomer, vinyl alcohol. PVA instead is prepared by first polymerizing vinyl acetate, and the resulting polyvinyl acetate is converted to PVA. PVA has excellent film forming, emulsifying and adhesive properties while c ost around half compare to PLA. PVA is also resistant to oil, grease and some solvents. It has high tensile strength and flexibility, as well as high oxygen and aroma barrier properties. PVA has many applications including paper coatings, release liner, CO 2 barrier film, emulsion or latex stabilizer, paper adhesives and textile sizing agent 73 75 . PVA can be dissolved in hot water and form films by casting. However, a common feature of PVA is their low mechanical st rength and integrity 76 78 . Biomax is formulated to mimic polyethylene (PE) or polypropylene (PP) but biodegradable. Biomax resins have a large range of melting points from 72 to 226 Â°C, which allows them to be pr ocessed by a large selection of techniques. Biomax is based on existing polyethylene terephthalate (PET), so it can be manufactured from the same plant which produces PET. DuPont also claims that Biomax is only marginally expensive than PET and cheaper tha n other biodegradable polymers. Biomax can be used as a modified of PLA, according to DuPont, it improves the impact strength, toughness and brittleness of PLA upon 2% addition 79 . Other potential applications could be agricultural films, disposable plates and cups, etc.
39 Poly hydroxya lkanoates, such as poly caprolactone (PCL) are biodegradable polymers that not primarily derived from biobased feedstock. PCL is synthesized from cyclic ester monomer, lactone, by a ring opening reaction with a catalyst such as stannous octanoate in the presence of an initiator that contains an active hydrogen atom 65 , by manufacturers including Union Carbide, Solvay, and Daicel. PCL is a partially crystalline linear polyester with a low T g of 60 Â°C and a low T m of 60 Â°C, and having a modulus between those of low density and high density polyethylene at room temperature. PCL is degradable by the enzymes and lipases secreted from microorganisms, according to Potts and Tokiwa et al. 80, 81 . Although PCL is biodegradable, most of its current applications are not based on its biodegradability. PCL is used in many polymer formulations as compatibilizer because it is compatible with many organic materials and polymers. It is also used as a solfe blocks for segmented polyurethanes due to its low T g . In addition to the above current applications, PCL may be blended in starch based polymers such as PLA to improve their water resistance 82 . Polyalkylene dicarboxylates (PADC) are a family of biodegradable polymers that derived from polycondensation of glycols with aliphatic dicarboxylic acids. Examples in this family are polybutylene succinate, poly ( butylene succinate co butylene adipate) and polyethylene succinate. PDACs has T m ranges from 90 120 Â°C, T g ranges from 45 to 10 Â°C. They have density around 1.25 g/cm 3 which is close to PET, stiffness between LDPE and HDPE and tensile strength between PE and PP 83 . PDACs can be extruded, injected or molded by existing polyolefin processing equipments. The
40 degradation of PDAC has been studied, it was found t hat they can be degraded in activated sludges, soils and compost 84, 85 . Apart from the above synthesized biodegradable polymers, biodegradable aliphatic polyester amides (PEA) have been developed and commercialized. PEAs are generally derived from 1,6 hexanediol, glycine, and diacids with a 2 8 methylene groups 86, 87 . The degradation of PEAs was studied by Saotome et al. and they claimed that the PEAs can be degraded with proteolitic enzymes 88, 89 . Bayer commercialized a ser ies of heavy metal, halogens and aromatic compounds free PEAs such as BAK 1095 and BAK 2195, where are based from Nylon 6, butanediol, adipic acid and butanediol, adipic acid, diethylene glycol respectively. BAK 1095 and 2195 have crystallization temperatu re and T m of 66 Â°C, 125 Â°C and 130 Â°C, 175 Â°C, respectively. Upon aerobic conditions, BAK 1095 and 2195 release water, carbon dioxide and biomass. Both of the BAKs can be processed with normal polyolefin processing equipments, and they can be used in agric ultural and packaging industry. From the biodegradable polymers discussed above, PVA is the most economical and wide used polymer. However, a common feature of PVAs is their low mechanical strength and integrity. In this study, LRB will be used to reinfor ce PVA via a solution mixing approach. In addition, PVA is also used as a costabilizer in latex system and the details will be discussed in the miniemulsion polymerization section. Biocomposites Introduction of Biocomposites As early as 1908, the first ph enol or melamine formaldehyde resin and cotton reinforced composite materials were fabricated for application in electronics. In 1989,
41 seats and fuel tank of the early airplane were composites which consisted of natural fibers and polymer resins 5 . The definition of biocomposite various in the literature, generally, it means a composite material with one or all components which are derived from biomaterials. This this study, if one or more of the polymer matrix, reinforcing filler, compati bilizer or modification agent are biobased or biodegradable, then this composite is considered to be a biocomposite. There are many types of biocomposites that design for different applications, with various polymers and reinforcing fillers. The polymer m atrix can be PLA, PVA, poly styrene butyl acrylate or PMMA etc. The reinforcing fillers can be organic or inorganic, such as PPF, synthetic biobased fibers, PLR, LRB or clay, carbon fiber, graphene, or graphene oxide (GO). Lignocellulosic B iomass Reinforc ed Biocomposites Numerous studies have been conducted regarding the reinforcing of biocomposite by lignocellulosic biomass. Although improvements in mechanical, thermal and barrier properties of the biocomposite upon the incorporation of lignocellulosic bi omass were demonstrated, the majority of the studies were concentrated on using PPFs which are not economical as the reinforcing material. In this section, previous biocomposite reinforced with both PPF, post processing lignocellulosic residues (PLR) and l ignocellulosic residues from biofuel production (LRB) are discussed. Pristine natural fiber reinforced biocomposite Pristine plant fibers (PPF) include Kenaf, cotton, bamboo, hemp and flax etc. and they have relatively high strength, high stiffness and low density 90 . Kenaf fiber (KF) and
42 polymer bio composite was fabricated from by Pan et al . The effect s of the KF loading on crystallization behavior biocomposite morpholo gy , mechanical and dynamic mechanical properties were investigated. It was reported that the nucleation density increases dramatically with the presence of KF. With the 30 wt % KF fiber loading, the half times of isothermal crystallization were reduced to less than half of pristine polymer, the tensile and storage modulus of the composite were improved by 30% and 28%. Scanning electron microscopy (SEM) observation showed that there are some irregularities and voids between KF fiber and polymer matrix. It is expected that the crystallization rate and mechanical properties could be further improved if interfacial interaction and compatibility between the KF and polymer matrix can be optimized 91 . Polymer and bamboo fib er (BF) bio composites were prepared and studied . The tensile properties, water resistance, and interfacial adhesion of this bio composites were improved by the addition of LDI, but thermal flow was hindered due to cross linking between polymer matrix and BF whereas there was no significant change in T m . Thermal degradation temperature was lower than those of pristine polymer, but the composites with LDI showed higher degradation temperature than those without LDI. Enzymatic biodegradability study showed tha t addition of LDI delayed the biocomposite degradation 92 . The mechanical and degradation properties of polymer hemp fiber (HF) bio composite were investigated. Modulus of elasticity significantly increased with the hemp content, reaching 5.2 GPa in the case of crystallized polymer reinforced with 20 wt.% hemp, whereas the elongation and stress at break decreased with an increasing amount of fib er . The presence of poly e thylene g lycol (PEG) as plastici z er did not affect
43 the rate of degradation of the this bio c omposite, whereas higher HF content accelerated the degradation 93 . Jute and polymer biocompo site was studied by Karmaker et al. They reported that the biocomposite with jute fiber had slightly better tensile strength and about six times of the elastic modulus of the pristine polymer. The coupling agent improved the tensile strengths to around two times, however the elastic and bending moduli were not affected 94 . In conclusion, when inco rporating PPF in biocomposite, they can improve mechanical, thermal properties or at least keep these properties very close to those of the pristine polymers. However, due to the high cost of PPF, the application of biocomposites made with these fibers is limited. PLR have very low starting value and may have better compatibility with polymer, which will be discussed in the next section. Post processing lignocellulosic residue reinforced biocomposite Post processing lignocellulosic residues (PLR) are chief ly residues from sugar, paper, oil, and bioethanol production (LRB). These residues have been through different types of treatments such as hydrothermal, chemical, mechanical, and biological or any combination of them with various intensity. These treatmen ts could cause isolation and surface modification of fibers, which could be beneficial for improving the interfacial adhesion between fiber and polymer. According to previous reports, pretreatment of pristine plant fibers (PPF) is preferred prior of incor porating them in polymer matrix due to two reasons. The first one is the isolated cellulose fibers in plant fiber is much stronger than the bulk pristine fiber if the length of the fiber can be preserved during the isolation process. The elastic modulus of bulk wood is about 10 GPa, while that of cellulose fibers and micro fibrils are
44 40 and 70 GPa, respectively 95 . The other reason is the hydrophilic nature of PPF, which cause the fiber to swell when absorbing wat er and also causes compatibility problem with hydrophobic polymers. The incompatibility problem could cause poor interfacial adhesion between the polar hydrophilic lignocellulosic fiber and the non polar polymer matrix 96, 97 . Mechanical size reduction, washing and steam explosion process (such as the commercialized Duralin process) have been employed to pretreat the PPF. Mechanical size reduction can increase specific surface area to improve interfacial adhesion, w hile washing can reduce the amount of soluble components in the PPF to improve its durability. Steam explosion, such as the Duralin treatment of fiber generally consists of a steam or water heating step of the pristine plant fiber at temperatures above 160 Â°C in an autoclave, followed by a drying and a curing step above 150 Â°C. The pectin and nonstructural carbohydrates are removed, while hemicellulose and lignin are depolymerized into lower molecular aldehyde and phenolic compounds. These compounds could b e combined by the curing to form a water resistant resin, which is capable of binding the cellulose microfibrils together 98, 99 . PLR such as sugar beet pulp (SBP), fiber of oil palm pulp (FOP) and raw sugarcane ba gasse (RB) have generally been through mechanical size reduction and hydrothermal treatment which resembles of the steam explosion pretreatment for PPF to different degree, therefore the interfacial adhesion of these two types of fibers and polymer matrix should be improved. Notably, the number of reports regarding using PLR as reinforcement of biocomposites is far less than using PPF. SBP and PLA biocomposites were prepared via compression molding and studied by Liu et al. The composition of SBP is approx imately 75% carbohydrate
45 (pectin, cellulose, and hemicellulose), 9% protein, 6% ash, 9% lignin, and less than 1% biocomposites. The effects of increasing SBP loading on the mechanica l properties were investigated. It was found that for the fracture energy, tensile strength and tensile modulus were the highest when 10% SBP used. Notably, the biocomposite with 10% SBP had 5 20% higher mechanical properties across the board than the pr istine PLA. The effect of water content in SBP on the mechanical properties of PLA biocomposites were also studied, and the results demonstrated water had detrimental effect on mechanical properties. Biodegradability was investigated. SBP/PLA biocomposites were buried in soil at 40 Â°C for 4 weeks and the changed in molecular weight of PLA, as well as the physical weight were recorded. It was reported that SBP was degraded far quicker than PLA matrix, and the more SBP loading the higher the weight loss was. PLA matrix did not lose weight in 4 weeks, but its molecular weight was drastically reduced 42 . Blend with Higher SBP content up to 45% were studie d as well. It was reported that with SBP loading higher than 10%, SBP tends to form aggregates therefore reduces all mechanical properties 49 . Processed fiber of oil palm (FOP) contents chiefly 25 % lignin and 48 % cellulose and 22 % hemicellulose 100 . FOP and phenol formaldehyde (PF) biocomposites were studied by Sreekala et al. Various chemically treated FOP (40% by weight) and PF biocomposites were prepared by compression molding of FOP mat impregnated in PF. Mechanical performance of the matrix is greatly enhanced by fiber reinforcement. Oxidized FOP improved tensile strength of the biocomposite by 10%, flexural strength
46 about 50% compare to composite with untreated FOP. All chemi cal treatments significantly improved impact properties of biocomposites 101 . Hill et.at. also studied the reinforcing effect of FOP on biocomposites with polystyrene and a commercial polyester. Acetylated and silane treated FOP demonstrated significant improvement in interfacia l shear strength with polystyrene and polyester. The tensile strength, tensile modulus, elongation at break, impact strength of biocomposites were all improved by less than 10% when incorporated with acetylated and silane treated FOP. These changes are due to a combination of a change in the mechanical properties of the modified fibers and the increased hydrophobicity of the surface allowing for improved wettability of the fiber by the polystyrene and polyester 100 . Raw sugarcane bagasse (RB) is the waste material from sugar mill, and it has been through multiple stages of mechanical size reduction and washing which removes a lot of the soluble components. The composition of RB is generally 25% lignin, 40 % cellulose, 28 % hemicellulose and 3% of ash plus acetic acid 13 . Saini et al. prepared grounded RB and poly vinyl chloride (PVC) biocomposites by compression molding. The effects of filler content, particle size, and alkali treatment of bagasse powder on the properties of PVC were eva luated. Tensile strength, elongation at break, and impact strength decreased whereas stiffness, modulus, and hardness of the composites increased with increasing RB loading. More specifically, upon 30 % RB loading, tensile modulus was increased about 48%, thermal stability increased about 10 %, and impact strength was increased 14% compare with pristine
47 modulus, and about 20 % higher elongation at break as well as impact streng th compare to composites with RB of 100 resistance of biocomposites slightly, increased thermal stability significantly, increased stre ngth compare to composites with untreated RB 102 . RB and an unsaturated polyester biocomposites was prepared and studied by vilay et al. Alkali and acrylic acid treatments of RB were conducted to modify the fiber p roperties. The effect of different fiber treatments and the fiber loading on the composites properties were investigated. Composites with alkali and acrylic acid treated RB had 70 % and 130% higher tensile strength, 5 % and 25 % higher tensile modulus and about 33 % and 30 % higher elongation at break compare to composite incorporated with untreated RB. Surprisingly, even for composites with untreated RB, the tensile and flexural properties were improved with the increasing RB loading compare to pristine po lyester. Scanning electron microscope (SEM) investigations showed that the alkali and acrylic acid modifications of RB improved the fiber matrix interaction. Storage modulus and water absorption of the biocomposites with alkali and acrylic acid treated RB were greatly improved compare to that of biocomposites with unmodified RB 103 . From previous literature, there is very limited number of reports regarding the utilization of LRBs in biocomposites. In this study, a series of LRBs from a simultaneous saccharification co fermentation bioethanol process w ith RB as feedstock will be incorporated in polymer matrix. LRBs have been through one or multiple of the acid, steam and microbial treatments during the bioethanol process. Particularly, steam
48 explosion is expected to improve the mechanical properties of fibers because it removes the pectins and nonstructural carbohydrates in pristine plant fibers (PPFs). The reinforcing efficiency of LRBs will be studied regarding fiber loading and fiber type will be investigated. Inorganic Material Reinforced Bionanocomp osites Apart from the lignocellulosic biomass reinforced biocomposites, inorganic materials have also been used for polymer reinforcements. Since 1980s, there has been a strong interest on the development of polymer nanocomposites reinforced by inorganic n anofillers such as nanoclay, carbon nanotube (CNT) and graphene. The final nanocomposite does not have to be in nanoscale, but can be micro or macroscopic in size, whereas at least one of the dimensions of the filler material is of the order of a nanomete r 104 . The transition from macroscale to nanoscale yields dramatic changes in physical properties, because of nanoscale materials have a large specific surface area and many important chemical an d physical interactions are governed by inter surfaces properties 104, 105 . Therefore, the properties of composite constructed by nanoscale materials can be significantly different from composite constructed by mac roscale materials with the same composition. Moreover, only a very low filler loading level will be necessary to change the properties of a composite constructed with nanoscale fillers. An early example of a nanocomposite is the Nylon 6 and nanoclay nanoco mposite that Toyota Central Research Laboratories developed, for which a very small amount of nanoclay loading resulted in a significant improvements in thermal and mechanical properties 106 . Not only the size, but also the morphology, dispersion and interfacial adhesion between nanoscale filler and polymer matrix can decide the properties of the nanocomposite 104 .
49 Polymer nanocomposites incorporated with nanoclay, graphene, carbon nanotubes (CNT) and carbon black have been studie d intensively due to the improvements of the mechanical and electrical properties provided by those nanoscale filler materials 1, 107 109 . This this study, we will be focusing on polymer nanocomposites with nanocla y, graphene, graphene oxide (GO) and one or more biobased or biodegradable components. Nanoclay reinforced nanocomposites Depending on the nature of the nanoclay and polymer matrix used and the method of preparation, the properties of the polymer nanoclay nanocomposite could be significantly different 110 . There are three main types of arrangements of layered silicate filler and matrix in composites, phase separat ed, intercalated and exfoliated, as illustrated in Figure 2 1. 111 . If the layered filler is not penetrated by the polymer matrix, the composite is considered as a phase separat ed composite which has the same properties compare to the traditional composites. If the each layer of the filler is penetrated by a single polymer chain, the resulting morphology is referred as an intercalated structure. For the scenario of each layer of the filler is completely isolated and uniformly dispersed in the polymer matrix, this structure is considered as a composite with exfoliated filler 111 . The polymer nanocomposites with exfoliated nanoclay demonstrated better mechanical properties, thermal stability and barrier properties with far less nanoclay content compare to equivalent conventional polymer c omposites. Generally speaking, the reinforcement effect of the nanoclay is proportional to the degree of exfoliation of the nanoclay 112 .
50 Clays are composed of layered crystalline silicate minerals. An important feature of clay is their cation exchange ability between the interlayer and a n aqueous solution. In this dissertation, we will focus on the smectite family of clay minerals such as montmorillonite (MMT) and saponite. The ga ps between the silicate layers are called interlayer space or galleries., which is the result of Van der Waals force. Because clay is highly hydrophilic, water are usually presents in the interlayer spaces. MMT and saponite have very similar structure, how ever there are differences in their compositions and particle sizes. The general chemical composite of MMT is [(Al Mg )(Si 8 )O 20 (OH 4 )]Na 113 The ideal chemical composite of saponite is [(Mg 6.00 )(Si Al )O 20 (OH 4 )]Na 114 Bionanocomposites of nanoclay with one or more biobased compone nts have been studied by only a few researchers. Pranger et al. prepared a poly furfuryl alcohol (PFA) and nanoclay (MMT) bionanocomposite. PFA is a biobased hydrophobic polymer, however, its monomer furfuryl alcohol (FA) is hydrophilic and completely solu ble in water because of the hydroxyl group of the side chain and the oxygen heteroatom of the furan ring. These characteristics of FA allow the formation of a stable suspension of hydrophilic nanoclay in FA. The result showed that both onset of degradation (5% Weight Loss) and weight retained after nonoxidative degradation in nitrogen gas were improved by 20% and 10% compare to pristine PFA. The improvement in thermal stability could be attributed to fully exfoliation of nanoclay by the PFA polymer chain, w hich was confirmed in the report 115 .
51 Hybrid bionanocomposite of nanoclay, kenaf fiber (KF) and PLA was prepared by Kaiser et al. previously. Impact strength, fracture toughness and thermal stability are the main disadvantages of short fiber filled biocomposite. Nanoclay is known to significantly improve the thermal and mechanical properties of the nanocomposites. Nanoclay and KF were employed at the same time because it is expected that the hybrid composite can have the advantages of both of these two fillers. Mechanical analysis showed improvements with incorporation of KF and nanoclay, specifically the impact strength increased by 50% compare d with unreinforced PLA. Addition of nanoclay to KF and PLA composite increased decomposition and melting temperatures (T m ) by 27 Â°C and 3 Â°C, respectively 116 . A family of epoxy nanoclay nanocomposites was studied by Wang et. al. A soybean oil based epoxidized fatt y acids (EGS) as the epoxy monomer and 4 methyl 1,2 cyclohexanedicarboxylic anhydride as the comonomer and a commercial modified nanoclay (organo nanoclay) were used in the study. Mechanical analysis showed that 1 wt % incorporation of clay improved nanoco mposite tensile strength and modulus by 22% and 13% compared to neat epoxy, respectively. Tensile modulus was further increased by 34% without any reduction in strength by incorporating 6 % organo nanoclay. The glass transition temperature (T g ) was also in creased by 4 6 Â°C for all clay loading. X ray scattering results demonstrated that intercalation and exfoliation of organo nanoclay was induced by high speed shear mixing and sonication, respectively. Nanocomposites with exfoliated organo nanoclay showed improved mechanical and thermal properties across the board than those of nanocomposites with intercalated organo nanoclay. If combined, high speed shear mixing with sonication induced a much
52 higher degree of exfoliation, which provided better properties compared to a high shear mixing method alone 117 . Although there are a few reports regarding nanoclay polymer biocomposites, the biobased or biodegradable components are either polymer matrix or lignocellulosic fiber. Lignocellulosic fibers such as PLR or LRB have always been studi ed as structure components, which limits their application in the biocomposites. Lignin, the most abundant component in LRB is hydrophobic in nature. In our previous study, lignin was extracted from LRB and used as starting material of quaternary ammonium lignin (QAL), a synthetic cationic surfactant . QAL was then used to modify the hydrophilic clay to organophilic, and the modified lignin clay was able to be dispersed in the organophilic styrene monomer phase. QAL stays in the polymer bionanocomposite in t he form of QAL clay nanohybrid. In this study, lignin extracted from LRB was converted to a QAL for modifying graphene oxide (GO). GO is hydrophilic, therefore it needs to be modified to be dispersed in organophilic monomer or polymer phase. Graphene and graphene oxide reinforced nanocomposites Polymer nanocomposites incorporated with carbon nanotubes (CNT), carbon black and graphene have been studied intensively. Especially graphene, ever since its discovery in 2004 118 , it has been incorporated in nanocomposites due to the improvements of the mechanical and electrical properties provided 1, 107 109 . Graphene has similar layered lattice structure like nanoclay, therefore it is expected it can be incorporated in polymer nanocomposite via similar methods which used for incorporating clay. Graphene is the primal building block of other graphitic allotropes, with thickness of a single atom, structure of hexagonally arranged sp 2
53 hybridized carbon atoms in a 2 D sheet like morphology (as shown in Figure. 2 2 ) 119 . Graphene sheets are held together by weak Van der Waals force, t herefore they can be exfoliated readily. Graphene has been attracting more and more attention of researchers, because its superior properties even if compared with CNT. Researchers f 130 GPa 120 ; thermal conductivity of 5000 W/(m.K) 121 ; electrical conductivity of up to 6000 S/cm 122 ; specific surface area of up to 2630 m 2 /g and gas impermeability 123 . Graphene can be prepared via a collection of techniques such as chemical oxidation and exfoliation 124, 125 followed by chemical or thermal reduction, micromechanical 126 and chemical vapor depositions 127 . Chemical oxidation and exfoliation to yield graphene oxide (GO) followed by reduction is widely considered to be the most feasible method for industrial application due to the wide availability of graphite and the less complex, scale up capable processes 119 . More importantly, unlike graphene which has no accessible functional groups on its surface, GO has multiple oxygen containing functional groups on its surface, such as hydroxyl, carboxyl and epoxy groups (as shown in Figure. 2 3 ) 128 , which are crucial for the subsequent functionalization or processing with polymers 119 . If the superb properties of graphene can be transferred to polymer composites, these composites could have wide potential applications in vehicles, aircrafts, electronics, and packaging. GO sheets are hydrophilic in nature and they tend to restack so that they have to be functionalized and stabilized before they can be d ispersed in monomer 129, 130 . Several methods were investigated previously, for instance, reduction of GO in a stabilization medium 131 , covalent modification of GO by using amines, alkyl Lithium
54 reagents, is ocyanate and diisocyanate 132 134 , non covalent functionalization of GO in presence of polymer/polymeric anions, amphiphilic polymers such as poly(sodium 4 styrenesulfonate), 7,7,8,8 tetracyanoquinodimethane, or wi th sulfonated polyaniline 135, 136 and diazonium salt coupling of GO which consists of reduction of GO with hydrazine followed by functionalization with aryl diazonium salts 137 . Many researchers prepared and studied mechanically sound and conductive graphene nanocomposites with vario us types of graphene and polymer matrix. Nanocomposites reinforced with graphite platelets and thermally exfoliated graphite sheets (FGS) prepared by partial pyrolysis of GO were fabricated and analyzed by Kim et al. The nanocomposites have conductivity p ercolation threshold of 0.3 volume % and 3 volume % with FGS and graphite, respectively. The threshold concentrations of FGS and graphite for rigidity percolation threshold determined with melt rheology and elastic moduli estimation were in good agreement with conductivity percolation. For gas barrier properties, hydrogen permeability of nanocomposites with 4 volume % FGS and graphite was reduced by 60 % and 25 %, respectively. As the concentration of FGS and graphite increases in the nanocomposite, a linea r viscoelastic was deduced from the reduction in critical strain and the increase in shear modulus 138 . Thermally reduced graphite oxide (TRGtO) from graphite oxide (GtO) was used to fabricate conductive nanocomposite as we ll. Thermally reduced graphite oxide (TrGO) was prepared by chemical oxidation of graphite followed by thermal expansion content of it was increased from 81 to 97 wt. % by a further thermal treatments at 700 Â°C and 1000 Â°C. Nanocomposite of TrGO with isotactic polypropylene (iPP), poly
55 styrene co acrylonitrile (PSAN), polyamide 6 (PA6) and polycarbonate (PC) were fabricated and analyzed regarding mechanical and electrical p erformances. The electrical percolation threshold of nanocomposites with iPP, PSAN, PA6 and PC were 4, 2.5, 5, 7.5 wt. %, which are considerably less than that of the nanocomposite incorporated with carbon black (CB) and multi wall carbon nanotube (MWCNT) fabricated at the same conditions. The tensile modulus of nanocomposites with TrGO and these 4 types of polymer are significantly higher than nanocomposites reinforced with BC or MWCNT. The report attributed the better electrical and mechanical properties caused by incorporating of TrGO to the 600 m 2 g 1 specific surface area and the partially exfoliated structure of TrGO in different polymer matrix 139 . Stankovich et al. prepared a conductive graphene nanocomposite with 0.1 volume % percolation threshold. GO was first modified by phenyl isocyanate before incorporated in polystyrene matrix, and then red uced by dimethylhydrazine 140 . This graphene nanocomposite has a conductivity of 0.1 Sm 1 with only 1 volume % graphene loading, which is sufficient for many electrical applications 141 . GO poly methyl methacrylate (PMMA) nanocomposites were prepared and studied by Jang et al. They compared the effects in exfoliation of GO by a macroazoinitiat azobisisobutyronitrile (AIBN) regarding the morphological, mechanical, thermal, electrical conductivity and rheological properties of corresponding nanocomposite. The MAI with a poly ethy lene oxide segment was intercalated between the interlayer space of GO and induce further exfoliation during polymerization. In their report, nanocomposite with exfoliated GO had conductivity of 1.78 Ã— 10 5 Sm 1 when 2.5
56 volume % GO was incorporated which is close to 50 times higher than that of the nanocomposites with intercalated GO. The thermal, mechanical and rheological properties also confirmed that GO with a high degree of exfoliation has better reinforcing capability than intercalated GO 142 . Graphene bionanocomposites with biobased polymer were studied by Ca o et al. They synthesized a bio based epoxy monomer (GA II) from biobased gallic acid, which is expected to be able to absorb to the surface of graphene by its aromatic group via a II graphene complex was able to be dispersed in GA II epox y solution in dichloromethane via sonication. With the addition of only 2 wt% GA II graphene complex, the tensile strength and modulus, flexural strength and modulus of the nanocomposites were improved by 27%, 47%, 9% and 21%, respectively. The thermal and electrical conductivities were also improved from 0.15 to 1.8 W m 1 K 1 and from 7.0 x 10 15 to 3.28 x 10 5 s cm 1 , respectively 143 . An environmentally friendly freeze dried grap hene nanosheet (GNS) which based from graphite oxide (GtO) was prepared. Cao et al. claimed that this type of freeze dried GNS was much lighter and more loosely packed compare to the vacuum filtration separated GNS, and it can be dispersed in N,N dimethylf ormamide (DMF) with PLA. The GNS was completely exfoliated by the freeze dry process according to their XRD results. With 0.2 wt. % of GNS incorporated in PLA matrix, the tensile strength was increased from 47.7 to 60 Mpa (about 25 % increase) and the stor age modulus was increased from 2862 to 3385 Mpa (about 18 % increase). The thermal stability was also improved, the 5 % weight loss temperature was increased from 323 to 334 Â°C 144 .
57 There are numerous reports regarding the preparation of graphene nanocomposites, and a few of them were prepared with biobased monomer and polymers. However, there are no reports about utilizing low value lignocellulosic biomass such as LRB. Lignin, the most abundant component in LRB is hydrophobic in nature. In this study, we are planning to convert lignin to a cationic lignin surfactant for dispersing GO in hydrophobic phases. Biocomposite Prepara tion Methods The preparation methods of biocomposite s and bionanocomposite s are the same methods that used for preparing conventional polymer composites. In general, three main approaches were employed, which are the top down methods melt mixing and solu tion blending and the more advanced bottom up method miniemulsion polymerization. Melt mixing of filler with polymer resin by mechanical treatment such as extrusion followed by injection or compression molding, and it has been employed extensively in rep orts of biocomposites reinforced with macroscopic lignocellulosic fibers 13, 139, 145 149 . Melt mixing has already been used in many industrial polymer applications, it provides filler size reduction, filler and po lymer mixing at the same time, continuous processing and process integration capability with different molding process. In this study, melt mixing was used to prepare LRB PLA biocomposites. Solution blending of micro or nanoscale fillers and polymer in a solvent, followed by solvent removal is another technique that employed by many researchers 150 155 . The fillers are often subjected to a size reduction step to reduce their size to micro or nanoscale before blende d with polymer in a solvent. Although this process often requires an organic solvent, it is very simple to use and can be applied to many different
58 polymer and filler combinations. In this study, solution blending was used to prepare size reduced LRB and p olyvinyl alcohol (PVA) biocomposite with water as solvent. Miniemulsion polymerization involves the dispersion of micro or nanoscale filler particles in monomer suspension in water and then polymerized. It has been used in the industry for neat polymer be ads production, also it has attracting more and more attentions in nanocomposite research because the controllable particle size, better mixing, better filler and polymer interfacial bonding and the lack of harmful organic solvents 1, 109, 156 159 . In this study, miniemulsion polymerization, a type of in situ polymerization, was employed to prepare graphene oxide (GO) poly methyl methacrylate (PMMA) nanocomposites. All in all, these methods are designed to improve the filler dispersion and interfacial bonding, the two most important factors that deciding the properties of the product composite. In this section, previous reports regarding preparing lignocellulosic fiber reinforced biocomposite by melt mixing, lignoce llulosic fiber with micro/nanoscale size incorporated biocomposites by solution blending and inorganic nanoparticle incorporated nanocomposites by miniemulsion polymerization will be discussed. Melt Mixing Melt mixing is the most studied method for prepar ing polymer composites. In general, filler material and polymer resin are premixed and the mixture is then subject to mechanical shear at high pressure and temperature. The extrudate is then cooled and pelletized for subsequent molding. An extruder is ofte n used and plasticizer is normally added to facilitate the interfacial adhesion between the filler and polymer. Beldzki et. al. compared two roll mill, high speed mixer and twin screw extruder by analyzing the properties of the wood fiber and polypropylen e (PP) composites
59 prepared with those machines and compression molding. It was shown that twin screw extruder processed composites had higher mechanical properties than those compounded in a two roll mill or a high speed mixer. Although twin extrusion caus ed some fiber fragmentation, it provided better filler dispersion which is crucial for preparing mechanically sound composites. The use of maleated PP (used as a compatibilizer) in the melt mixing step improved the mechanical properties of the composites a nd the hydrophobicity of the wood fibers in dry conditions. However, when processes in wet conditions, the tensile and flexural strength were reduced 160 . Melt mixing was used to prepare biocomposite of plant derived kenaf fiber (KF) and PLA. The KF fiber and PLA resin were extruded and pell etized before compression molding was used to make the composites. Crystallization, morphology, mechanical, and dynamic mechanical properties of the biocomposites were investigated. It was found that the KF fiber improves the crystallization as it was comp leted during the melt cooling at 5Â°C/min, as well as increases the nucleation density during isothermal crystallization. The composite with 30% KF loading had 30 % and 28 % higher tensile and storage modulus compare to pristine PLA. SEM observation of frac ture surface showed that many fibers were pulled out during tensile tests, which indicating the interfacial adhesion could be further improved 91 . Biocomposites with post processing lignocellulosic residues (PLR) prepared by melt mixing were reported only in a few literatures. Liu et. al. conducted a series of studies regarding incorporating sugar beet pulp (SBP) in PLA matrix 42, 44, 49, 161, 162 . SBP after sucrose extrac tion was incorporated in PLA matrix by twin screw extrusion followed by injection molding. The SBP is rich in carbohydrate (75% is pectin, cellulose,
60 and hemicellulose combined), it also has about 9% protein and 9% lignin. The SBP was pre grounded to 300 Âµ m powder before mixed with PLA resin and a compatibilizer, Polymeric diphenylmethane diisocyanate (pMDI). The 8 temperature control zones of the twin extruder was set at 150 to 170 Â°C, whereas the injection molding zone temperatures were set between 165 to 170 Â°C, respectively. Tensile, flexural and thermal properties, molecular weight of the PLA matrix and the morphology of the fracture surface of the tensile tested biocomposites were analyzed. With the increase of SBP loading increased (from 7% to 45%), t he tensile strength was reduced from 70 to loading. The thermal properties were not affected as much as the tensile properties. With the SBP loading increased up to 30%, the difference in glass transition temperature (T g ), cold crystallization temperature (T c ) and melt temperature (T m ) were just about 1 Â°C. However, at 45% SBP loading, the T g , T c and T m were reduced 7, 10 and 9 Â°C. This was attributed to the high moisture content in the 45% SBP, as moisture at high processing temperature could causes degradation of the PLA matrix 49 . The effects of the compatibilizer in melt m ixing were also studied. Liu et al. reported that pMDI was very significant for tensile and thermal properties of the biocomposite, also the molecular weight of the PLA matrix. The tensile strength of the biocomposite with 30% SBP was increased from 56.9% to 80.3% and 93.8% of pristine PLA by addition of 0.5 % and 2 % pMDI. With 50% SBP and 2% pMDI, the tensile strength was 87.8 % of that of pristine PLA. The pMDI also demonstrated slight effect to the molecular weight (Mw) of the PLA matrix. With addition of pMDI, the Mw of PLA was increased about
61 13% for the sample without SBP, whereas the Mw of PLA was not changed for more than 5%. However, addition of pMDI reduced the polydispersity index (PDI). This indicated that pMDI is capable of causing chain exte nsion for shorter polymer chains, which could be the reason for the improvement in tensile properties when pMDI is added. Conversely, pMDI was not affecting the thermal properties significantly. The micro morphology of the fracture surfaces demonstrated th at the addition of pMDI greatly facilitated the wetting of SBP by PLA. Therefore, the SBP fibers were torn apart fracture plain for the biocomposites with pMDI instead of pulled out of the fracture plain for the biocomposites without pMDI 44 . Although there are numerous reports regarding preparation of PPF or PLR reinforced polymer biocomposites by using melt mixing. There is little attention has been paid to study the properties of the polymer biocomposites reinfo rced with LRB fabricated by melt mixing. In this study, melt mixing was used to fabricate LRB PLA biocomposite to study the effect of the LRB fibers composition, size, and surface characteristics on the mechanical and thermal properties of the final biocom posite. Solution Blending The other top down method for preparing polymer biocomposite that will be discussed here is the solution blending method. The reason of referring solution blending a top down method is because the filler fiber is often pre proce ssed before blending with polymer solution to reduce its fiber length, disintegrate fiber bundles and to increase specific area by inducing fibrillation. Solution blending is particular potent for preparing composites when both filler and polymer matrix ar e hydrophilic. First, there is no dispersibility issue between two miscible compounds. In addition, strong hydrogen bonding can form between
62 hydrophilic fillers and polymers. Furthermore, there is no organic solvent required for the process, which makes it environmental friendly. Last but not least, the simplicity of the method allows the establishment of related economical industrial processes. Water soluble hydrophilic polymers such as poly (vinyl alcohol) (PVA) are particularly promising to be employed in the biocomposite with lignocellulosic fibers prepared by solution blending. Firstly, PVA is resistant to organic solvents and is biodegradable. Secondly, lignocelluloses are able to be dispersed in it without chemical modifications. PVA has broad applic ations including coatings, detergents, adhesives, paints and solution cast films 73, 74 . But, a disadvantage of PVA is the low mechanical strength. Recently, many high purity micro or nanoscale fibers such as cellulosic nanofibers, nanocrystals, and fibrils were extracted from bulk lignocellulosic fibers and used to reinforce PVA to further improve the mechanical and thermal pro perties of PVA films 76 78 . Solution blending was employed to prepare PVA nanocellulose (NC) biocomposite by Lee. et al. High crystalline (87 92 %) NC with nanoscale diameter and microscale length was obtained b y acid hydrolysis of microcrystalline cellulose (MCC). The biocomposites were prepared by blending PVA and NC in water solution at 80 Â°C, followed by drying and film casting. Tensile strength and modulus were significantly improved by the increasing NC loa ding, for as much as 61 % and 79 % at 3% and 5% NC loading, compare to pristine PVA. The improved tensile properties and thermal stability might be due to the strong intermolecular forces between nanocellulose and the base PVA matrix. The intermolecular fo rces keep the inherent stiffness, brittleness and tensile strength of the NC intact and results in enhancement of the
63 mechanical strength of the films 163 . Besides, the improvements could be caused by the uniform distribution of the NC thro ughout the PVA matrix. Furthermore, it might be also caused by the strong hydrogen bonding between the hydroxyl groups of nanocellulose and the PVA matrix 77 . Solution blending was also used to prepare a fully biodegradable biocomposites with microfibrillated cellulose (MFC) and PVA. Chemical crosslinking of MFC and PVA was ca rried out by using glyoxal to further improve the interfacial bonding. Crosslinking by glyoxal was confirmed by the presence of acetal linkages between MFC and PVA. It was also found that the MFC was well dispersed and bonded to PVA by analysis of the comp osite surfaces, which suggested that solution blending with chemical crosslinking is an effective way to prepare MFC and PVA composites. The mechanical properties and thermal stability of the MFC reinforced PVA film were superior compare to pristine PVA, a nd they were further improved by the acetal linkages induced by crosslinking 164 . Although there is a depth of knowledge regarding the solution blending preparation of PVA biocomposites reinforced by these purified nanocellulose , little attention has been given to the use of low value PLR and LRB in biocomposites prepared by solution blending. Extremely low cost and renewable PLR and LRB has been through various physiochemical and biological treatments, which could result in the fragmentation of the large fiber bundle, reduced size, in creased fibrillation and increased crystallinity. These characteristics are crucial for the strong interfacial bonding between fiber and polymer matrix of the composite prepared by solution blending. In this study, PLR and LRB were first characterized and then incorporated in PVA via
64 solution blending. Mechanical and thermal properties of the biocomposites were studied. Miniemulsion Polymerization In situ polymerization includes suspension, emulsion and miniemulsion polymerization. Suspension polymerization resulted in large and unstable polymer droplet (0.1 10 mm in diameter), where heterogeneous blocking agent has to be employed to stabilize this system, and the resulting polymer has lower molecular weight compare to the other two polymerization methods 165 . Large droplet size also allows filler particles reside in a single drople t, which could lead to particle aggregation. Emulsion polymerization is capable of achieving decent dispersion of filler particles and the intercalation of polymer into the inter layer space of graphitic material 16 6 169 . However, there are some inherent disadvantages. For conventional emulsion polymerization, micellar nucleation generally dominates which means monomer has to diffuse through the organic aqueous interface to form micelle before polymerization occurs 165 . This phenomenon limits the rate of reaction, and also leads to exposed pa rticles of graphitic material. For instance, the reported final latex is mainly consisted of polymer droplet attached on filler particles, or filler particles armored on polymer droplet 166, 167, 170 173 . With no f ull coverage of graphitic material by polymer droplets (no encapsulation), filler particles is exposed to outside environment, also they have high tendency to aggregate which could leads to wide particle size distribution. For miniemulsion polymerization, monomer is generally dispersed in aqueous phase with the aid of mechanical methods such as ultrasonication and highly organophilic surfactant, prior of polymerization. The loci of polymerization is the monomer droplets which means each dispersed monomer d roplets are polymerized
65 with no further mass transfer 174, 175 . Stable nano droplet with diameter 50 500 nm with narrow particle size distribution is generally obtained, while high molecular weight could be achie ved due to the segregation effects where bimolecular termination by the polymer chains is suppressed as the small tendency of two chains are in the same droplet 165 . Encapsulation of filler particles by polymer droplets is also achievable as result of monomer droplet nucleation. With those inherent advantages, miniemulsion polymeriz ation is one of the most viable approaches to encapsulate nanoparticles in polymer droplets and form stable aqueous dispersion with narrow particle size distribution 1, 109, 176 . There is very limited number of re ports about utilizing miniemulsion polymerization to prepare GO polymer nanocomposites. Some improvements of physical properties upon addition of graphitic materials were observed, however, the investigation of particle size distribution, intercalation, ex foliation or encapsulation was often overlooked. About half of the reports were focusing on using graphitic material as surfactant to prepare GO armored polymer droplets 177 180 . By employing this approach, the gra phitic material is exposed to outside environment therefore limited the application of such latex. Also, intercalation and exfoliation of polymer chain between the interlayer spaces of GO was not studied. Furthermore, the particle size distribution was qui te broad (0.2 1 um), which exceeded the common upper range of miniemulsion. Several reports were focusing on the investigating of the effect of the presence of graphitic particles with various sizes on the physical properties of the casted film prepared from latex that made via miniemulsion polymerization. In the study of Viet Hung et. al., miniemulsion polymerization was used to prepare neat poly vinyl chloride
66 (PVC) latex, followed by the addition of reduced GO 181 . The percolation threshold was close to t he region of polymer graphitic material composites prepared through melt or solvent blending 119 . The reduced GO has almost no surface functional groups and it tends to agglomerate, simple blending is not ideal for the efficient dispersion, intercalation or encapsulation of gr aphitic materials. Yu et. al. used miniemulsion polymerization to prepare polystyrene (PSt) based GO nanocomposites. Although improvements in anti corrosion property of the nanocomposite were observed, particle size distribution and encapsulation were not studied 182 . Tan et. al. synthesized GO nanocomposite via a simultaneous miniemulsion polymerization of styrene (St) and methyl methacrylate (MMA ), and the double percolation of the two immiscible polymers reduced the percolation threshold significantly. However, polymer droplets were grafted on the surface of the GO sheets, therefore no encapsulation was achieved. Moreover, the size distribution of the polymer droplets was unclear due to the large size of the GO sheets in the miniemulsion samples 183 . Encapsulation of GO by Poly (styrene butyl acrylate) ( P ( St BA)) via miniemulsion polymerization was studied by Etmimi et al. 184 . They modified GO with a reactive surfactant, 2 acrylamido 2 methyl 1 propanesulfonic acid (AMPS) and then dispersed AMPS GO in monomer. Bonding and intercalation of AMPS with GO were claimed without verifi resonance (NMR) analysis. Complete encapsulation was claimed as well. However, the image of the polymer droplets encapsulated GO is not clear enough to rule out the possibility of having the size distribution of AMPS GO, neat P(St BA) latex and final latex with GO was not
67 measured by quantitative methods such as dynamic light scattering (DLS) or by graphic software based on tran smission electron microscope (TEM) images, which could provide information of whether the size of the AMPS GO and polymer droplets are suitable for encapsulation to take place. Moreover, potassium persulfate (KPS), a water soluble initiator was used to sta rt the polymerization. Water soluble initiators are suitable for initiating micellar and homogeneous nucleation 185 . For miniemulsion polymerization, the loci of nucleation is the monomer droplets which means an oil soluble initiator is far more efficient, as it does not need to diffuse through aqueous/oil boundary to initiate the nucleation. Furthermore, KPS is a strong oxidation and bleaching agent, its aqueous solution is acidic which could post detrimental effects to the stability of miniemul sion 186 . For the purpose of functionalizing GO for the subsequent miniemulsion polymerization, a polymerizable modifying agent is more favorable. 2 acrylamido 2 methyl 1 propane sulfonic acid (AMPS) was employed by several researchers previously. The amine group of AMPS can react with the hydroxyl groups on the GO to form hydrogen bond, so that the AMPS can enter and increase the int er layer space of GO and accelerate the insertion of monomers into the interlayer space resulting exfoliated structure 187, 188 . AMPS can also participate in the polymerization reaction initiated by potassium persu lfate (KPS) which facilitates the exfoliation of GO 184, 189 . From our previous research of the synthesis of nanocomposite with nanoclay via miniemulsion polymerization, (Vinyl benzyl) trimethyl ammonium chloride (VBTAC) was used to modify clay which also rich in hydroxyl group similar to GO. VBTAC is a short chain cationic surfactant with unsaturated reactive group. It can be polymerized with
68 other monomers such as styrene, and it does not increase the viscosity o f the monomer with VBTAC treated clay 109 azobis (2 methylpropion itrile) (AIBN) was chosen over water soluble initiators such as KPS due to the nature of miniemulsion polymerization that we discussed earlier. In this study, stable latex of polymer encapsulated nano size GO were synthesized via miniemulsion polymerizati on. GO was subjected to pre exfoliation by ultrasonication followed by reaction with VBTAC or QAL to yield exfoliated organophilic nanohybrids, which are expected to be well dispersed into organophilic monomer. MMA will be used as the monomer instead of st yrene because of the better mechanical properties which will be crucial for future applications.
69 Figure 2 1 . Scheme of three main types of layered silicates in polymer matrix. [ A dapted from Alexandre, M.; Dubois, P. Materials Science & Engin eering R Reports 2000, 28, (1 2), 1 63 . C opyright permission granted by Elsevier Limited, UK ] 111
70 Figure 2 2 . Schematic and relationship of graphene to other graphitic compounds. A) graphene, B) buckey ball, C) carbon nanotube, D) graphite. [ A dapted from Kim, H.; Abdala, A. A.; Macosko, C. W. Macromolecules 2010, 43, (16), 6515 6530 . Copyright permission granted by American Chemical Society , US ] 119 A B C D
71 Figure 2 3 . Structure of graphene oxide and its surface functional groups. [ A dapted from He, H. Y.; Klinowski, J.; Forster, M.; Lerf, A. Chemical Physics Letters 1998, 287, (1 2) . Copyright perm ission granted by Elsevier Limited, UK ] 128
72 CHAPTER 3 RESEARCH OBJECTIVES The overall research objective of this study is utilizing and converting reclaiming lignocellulosic residues from a bioethanol process (LRB). LRB ca n be used as starting materials in preparing composites, or it can be used directly as soil amendment materials. The prepared biobased or/and biodegradable composites are expected to possess competitive properties which allows them to become the candidate for supplement or replacement of the petroleum based counterparts. The applications of the composites can be light weight structural materials, packaging and coating. The factors that affect the interfacial bonding between the lignocellulosic materials and the polymer matrix are studied as well. The specific objectives of the four projects will be discussed in this section. Green Composites of Poly (lactic acid) and Sugarcane Bagasse Residues from Bio refinery Processes To study the effects of the differen t treatments during the bioethanol process on the composition, fiber length and morphologies of three types of bagasse residue from different s teps of the bioethanol process To investigate the effects of different residue characteristics on mechanical and thermal properties, crystallization behaviors, molecular weight and morphologies of PLA composites To evaluate the improvement caused by the coupling agents on the interfacial bonding between the lignocellulosic residues and the polymer matrix by analyzing physical and thermal properties, crystallization behaviors, molecular weight and morphologies of PLA composites Disk Refining and Ultrasonication Treated Sugarcane Bagasse Residues for Poly ( Vinyl Alcohol) Bio Composites To study the effect of the disk re fining and ultrasonication treatments on the morphology and particle size distribution of lignocellulosic residues from bioethanol process and paper mill
73 To investigate the effects of various fiber length and surface morphology of residues on mechanical pr operties, thermal stability and morphologies of PVA composites Synthesis of poly methyl methacrylate encapsulated nanolignin graphene oxide nano composite latex via miniemulsion polymerization To study the change in chemical structure of extracted lignin and synthesized quaternary ammonium lignin (QAL) through the mannish reaction To compare the interaction between GO and two different surfactants (QAL and VBTAC), and study the exfoliation of GO caused by these two surfactants To develop a stable latex of poly methyl methacrylate (PMMA) encapsulated nanolignin GO nanocomposite via miniemulsion polymerization To study effect of the amount of GO and co stabilizer on GO encapsulation, exfoliation and dispersion, polymer droplet size and the stability of the latex Characterization of Biorefinery Residues as Sandy Soil Amendments To evaluate and compare the differences in composition, fiber length and specific surface area of lignocellulosic residue from bioethanol and pulping process To investigate the effect s of residue variables on water retention value (WRV) and nutrient retention (P and N) of Florida sandy soil
74 CHAPTER 4 GREEN COMPOSITES OF POLY (LACTIC ACID) AND SUGARCANE BAGASSE RESIDUES FROM BIO REFINERY PROCESSES 1 Introductory Remarks In recent year s, there has been a great interest in the use of bio based materials derived from renewable resources due to concerns of the depletion of petroleum resources, greenhouse gas emission, and the environmental problems related to non biodegradable petroleum ba sed materials. PLA is a hydrophobic thermoplastic polymer made from renewable agricultural feedstock (corn starch) through fermentation followed by the polymerization of the lactic acid 64 . Because of its high strength and modulus, PLA has been a promising alternative to so me petroleum based polymer, which has been widely used in packaging, medical applications and automobile interior components 43, 69 of wide usa ge. The cost of PLA is not considered competitive in current US market. Unless its cost can be reduced from about $2 per lb to $0.40 0.80 per lb 42 , its use in a greater number of applications will not occur. Many researchers have reported the enforcement of PLA by th e incorporation of natural fibers such as jute fiber 190 , flax fiber, kenaf fiber 43 47 or lignocelluloses such as pine wood flour 48 and sweet beet pulp (SBP). The benefits of using natural fibers and lignocelluloses include their low cost, widespread availabi lity, low density, biodegradability, high stiffness and better thermal stability 42, 44, 49, 191 . 1 Reprinted with permission from L. Wang, Z. Tong, L. O. Ingram, Q. Cheng, S. Matthews, Green Composites of Poly (Lactic Acid) and Sugarcane Bagasse Residues from Bio refinery Processes. Journal of Polymers and the Environment, 21, 780 788 (2013).
75 Sugarcane is one of the most important lignocellulosic biomass resources in the world as it can be used as a food r esource (e.g. sugar and sugary food products) or feedstock to produce renewable fuels (e.g. ethanol) 192 . The current total global production of renewable fuels is 50 billion liters a year, about 40% of which is derived from extracted sugarcane juice 14 . Meanwhile, the use of the sugarcane bagasse residue after sugar extraction to produce second generation biofuel (e.g. ethanol) has been extensively studied recently due to its wid e availability and low cost 16, 18 20 . However, the process of using sugarcane bagasse residues to produce ethanol is not cost effective due to the high energy consumption required for a harsh pretreatment process, a complicated detoxification process and the use of expensive enzyme. This study aims to produce PLA composites by incorporating PLA and the low cost residue from the bioethanol process (the hard to hydrolyzed fibers and un reacted lignin components) via twin screw extrusion. The use of hard to hydrolyzed residues is expected to not only reinforce the PLA composite but also allow a cost effective bioethanol process by using mild pretreatment condition, generating less inhibitor, eliminating the expensive detoxification process and using less expensive enzyme. To achieve this goal, in this work, PLA based composites were prepared using a twin screw extruder followed by injection molding. Three types of sugarcane bagasse residues were used; the first was di rectly collected after the sugar extraction process, the second after pretreatment and the third after fermentation of a bioethanol process with a mild pretreatment process. During the bioethanol process, bagasse residues were subjected to chemical, physi cal or biological treatments (e.g. microbe, enzyme). These variations resulted in the residues of different compositions, surface activities,
76 residue fiber quantities, and microstructures. In this study, we investigated the effects of bagasse residues fro properties. When incorporating hydrophilic fibers(or lignin) with hydrophobic PLA, the incompatibility between two materials results in the insufficient interfacial bonding and undesirabl e mechanical properties of composites 45 . Interfacial bonding between fibrous additives and the polymer matrix significantly affects mechanical strength of composites 48, 91, 191, 193 195 . The interfacial bonding could be im proved through fiber surface modification by physical or chemical pretreatments 196, 197 and the use of coupling agents 44, 198 . It was reported that PLA composites incorpo rated with diluted sodium dioxide treated fibers had slightly improved tensile, impact and fracture properties while composites with steam exploded fibers showed very significant improvements in mechanical properties 199 . Isocyanate type agents have been used as coupling agents in wood composites 200 , natural fiber based composites 43 , and PLA blends with bio based additive s including starch and sugar beet pulp 44 . In this study, a small amount of an isocyanate type coupling agent D esmodurÂ® VKS 20 (DVKS), a mixture of diphenylmethane diisocyanate (MDI), was used to improve the interfacial bonding of PLA with lignocellulosic residues. The effects of DVKS on properties and the molecular weight of PLA and its composites were exami ned in this study as well. Materials a nd Experiments Materials Bagasse residues from different steps of a bioethanol process were collected, which included (1) Raw bagasse (RB): bagasse residues provided by Florida Crystals Corporation (Okeelanta, FL) an d used without further size reduction; (2) Pretreated
77 bagasse (PB): the bagasse after a mild acid pretreatment (1% w/w phosphoric acid solution, 4 hours) and a steam explosion process ( 180Â°C, 10 minutes); (3) Fermentation residue (FB): bagasse residue col lected from the fermentation broth after a fermentation process at 37Â°C for 144 hours. All bagasse residues were washed with US standard test sieve #270 under warm tap water until effluent became clear and then dried in an oven at 70Â°C for at least 24 hou rs. The PLA 6202D pellets were purchased from NatureWorks LLC (Minnesota, USA). DesmodurÂ® VKS 20 (DVKS), was generously provided by Bayer MaterialScience LLC (Leverkusen, Germany). It is a mixture of diphenylmethane diisocyanate (MDI) with isomers an d higher functional homologues, which has a NCO content of about 31.5Â±1.0%. Acetic acid (glacial, certified ACS), hydrogen peroxide (30%, certified ACS), chloroform (HPLC grade) were purchased from fisher Scientific, USA. Bagasse Residues Characteristics Compositions of bagasse residues Compositions of three types of bagasse residues (RB, PB and FB) were analyzed according to the National Renewable Energy Laboratory (NREL) method 201 . Monomer sugar contents after cellulose hydrolyzation were measured by High Pressure Liquid Chromatography (Agilent Technologies HPLC 1200 series, Santa Clara, CA, USA) equippe d with BioRad Aminex HPX 87H column (Hercules, CA, USA). The acid soluble lignin was determined by UV Vis spectroscopy (Beckman DU800 UV/Vis Spectrophotometer, Brea, CA, USA). Both the acid insoluble lignin content and the ash content were obtained by grav imetric analysis. According to the NREL method 202 , crude protein content was calculated from total nitrogen content, which was measured by Elementar vario MAX CNS elemental analyzer (Hanau, Germany) .
78 Fiber length measurement for bagasse resid ues A maceration method described by Franklin 203 was used to disintegrate the fiber bundles for the following fiber length analysis. In a m aceration process, 99% acetic acid and hydrogen peroxide with a volume ratio of 1:2 were mixed together to form a maceration solution. Then 5 grams of each bagasse sample was transferred into 150 mL of this solution and heated at 60 Â°C for 48 hour reactio n. After maceration, bagasse residues were washed extensively with DI water until a pH 7 was obtained. The fiber lengths of bagasse residues were measured by Fiber Quality analyzer (FQA, OpTest Equipments Inc, Hawkesbury, Ontario, Canada) at a consistency of 2mg/l. Composite P reparation A co rotating twin screw extruder (Prism TSE 24HC, Thermo Electron Corporation, Stone, UK), located at SCF Processing Ltd. (Drogheda, Ireland), and a pelletizer, was used to prepare the PLA/ bagasse residue composites. The twin extruder has a screw diameter of 24 mm and a length to diameter ratio of 40:1. The extruder has ten temperature controlled zones along its barrel as shown in Figure 4 1. Table 4 1 lists the temperatures of each zone. The screw speed of 100 rpm was us ed for all the experiments. Before extrusion, the PLA was dried at 80Â°C for 2 hours and the weight loss of the PLA before and after drying was noted at less than 3 wt.%. The bagasse residues were also dried at 80Â°C overnight in a vacuum oven and re dried at 80Â°C for 2 hours in a convection oven immediately before processing. PLA, bagasse residues, and 2 wt. % of coupling agent DVSK were pre mixed in a blender and then the mixture was put in the extruder. After extrusion, the extrudate was cooled for 20 mi nutes and subsequently pelletized. The pellets were injection molded at melting temperature of
79 170Â°C, injection pressure of 120 bars, and mold temperature of 38 Â°C at holding time of 2 minutes. The strips with the nominal dimensions of 100Ã—12Ã—4 mm were ma de. Mechanical Properties Measurements Tensile test Tensile test was performed on an Instron test frame with MTS renew package (model 1122, MA, USA) and the procedure were designed according to ASTM D 638 10 204 . The frame was equipped with a 1000 lb load cell and air grips for reproductive gripping. Each specim en was machined to type V shape and conditioned according to ASTM D 638 and ASTM 618 205 respectively. Five replicates were tested for each specimen at a crosshead moving speed of 2 mm/min. Tensile strength (TS, strength at break), ten sile elongation at break (TEB, cross head displacement) were recorded. Tensile elastic moduli of all composites were determined from the linear portion of stress strain curves. Flexural property test Flexural properties of pure PLA and its composites were measured according to ASTM D 790 206 using an Instron testing machine (Model 5566, load cell capacity of 100N, Grove city, PA, USA) and conditioned as described in ASTM D 618. The nominal width and thickness are 12 mm and 4 mm, respectively. And the support span is 64 mm. Five replicates were tested for each specimen at a crosshead speed of 1.9 mm/min. Fl exural modulus was the tangent modulus from the linear portion of the stress strain curves. Thermal A nalysis The thermal behavior of PLA and its composites was analyzed by Differential Scanning Calorimeter (DSC 220C, Seiko instruments Inc, Japan). Samples were crimp
80 sealed in 40 a heating rate of 10 Â°C /min to examine the glass transition, the cold crystallization and the melting temperature (T g , T cc and T m ) as well as their enthalpy cc and m ) . After that, samples were kept at 190 Â°C for 5 minutes and then cooled to 25 Â°C at a cooling rate of 10 Â°C/min to study the non isothermal melt crystallization temperature and enthalpy (T mc mc ). The heating and cooling cycles were repeated 3 times under constant gaseous nitrogen flow. Molecular W eight M easurement The m olecular weight (Mw) of the PLA and its composites was measured by s ize e xclusion c hromatography (SEC), an Agilent Technologies 1260 series HPLC systems equipped with a refractive index detector (RID) and a multiple wavelength detector (MWD) (CA, USA). Three columns were connected in series including PLgel mixed B, PLgel mixed E 5 Âµm with a pore size of 10000A and PLgel mixed E 5 Âµm with a pore size of 100A. The PLA and its composite samples were dissolved in HPLC grade chloroform for 8 hours at a concentration of approximately 0.5 wt. %. Then the solution was filtered through 0.22 Âµm syringe filter before injections to remove the un dissolved materials such as c ellulose and lignin. 50 ÂµL filtered solution was injected in each run and thermostat temperature was set at 25 Â°C and the flow rate was 1 mL /min. All results were processed using ChemStation software package with GPC analysis (Rev.B.04.03). The molecular w eight was calculated based on a universal calibration using a set of polystyrene standard. Scanning E lectron M icroscopy Scanning e lectron m icroscopy (SEM) (JOEL JSM 6400, operating voltage of 5KV 15KV, JEOL, Peabody, MA, USA) was used to examine the morph ologies of
81 bagasse residues from different steps of the bioethanol process and the topographies of fracture surfaces of composites after tensile testing. All samples were coated with gold before scanning. Statistical A nalysis Analysis of variance (ANOVA) was used to analyze the results of tensile tests, flexural tests and the molecular weight measurements. General linear model with a pair software package was used. Results and Discussions Bagasse Residues Characteristics Table 4 2 summarizes all the compositions and the average fiber lengths of bagasse residues (RB, PB and FB). The pretreated bagasse residues (PB) had the highest percentage of cellulose fibers because most h emicelluloses were broken down to soluble monomer sugars during pretreatment. This result agreed well with a lower percentage of hemicellulose in PB. The lignin content was increased and the fiber length was decreased with enhanced hydrolysis severity and progressive digestion of polysaccharides to monomer sugars during the bioethanol process. As shown in Table 4 2, the fiber length of PB was almost half of that of RB, while the fiber length of FB was approximately half of PB, which indicated that cellulose fiber chains were cut to shorter chains during the hydrolysis process. The residues (PB and FB) were collected by washing them under warm tap water on US standard test sieve #270 until effluent became clear. Soluble components (enzyme, dead cells, solubl e lignin and original protein, approximately 15 wt. %) and insoluble lignin components with a small particle size (approximately total 10 wt. %) were lost in the filtrate, which resulted in a relatively
82 high percentage of cellulose for PB (53.29 wt. %) and FB (44.81wt. %) samples. The loss of relatively large quantity of lignin is due to the large sieve size. We used this sieve to efficiently collect plenty of residues for our experiment due to small particle sizes of residues and the formation of aggregate s due to large surface areas. Figure 4 2 shows the morphologies of three types of bagasse residues. The raw bagasse (RB) was composed of fiber bundles with near smooth surfaces without any significant surface fibrillation (Figure. 4 2 A ). In PB, fiber bun dles disappeared and individual fiber layers with large surface areas and significant surface fibrillation were observed (Figure. 4 2 B ). The fermentation bagasse residues (FB) (Figure. 4 2 C ) were composed of large quantity of particles with a very low asp ect ratio. As depicted in Table 4 2, these particles could consist of a large quantity of lignin particles and a small amount of residue carbohydrates after most polysaccharides were hydrolyzed to monomer sugars, which were further converted to ethanol du ring bioethanol process. Mechanical Properties Tensile properties Figure. 4 2, Figure. 4 3 and Table 4 3 demonstrate tensile properties and flexural properties including the tensile strength (TS), flexural strength (FS), tensile elongation at break (EB) , tensile elastic modulus (TEM s ), flexural modulus (FM) for neat PLA, PLA with 2 wt. % DVKS, PLA composites with the substitution of 30 wt. % PB and PLA composites with the substitution of 30 wt. % RB, PB and FB and in the addition of 2 wt. % DVKS. ANOVA a nd Tukey method under 95% confidence level were used to identify differences of tensile and flexural properties among different samples. Different letters in TM columns of Table 4 3 represe For example, tensile properties shown in Table. 4 3 indicated that the addition of DVKS
83 s of neat PLA. However, the addition of pretreated bagasse residu es without the coupling agent DVKS significantly decreased the TS and slightly increased the TEM s (A/AB). This can be explained by the incompatibility between hydrophobic PLA and hydrophilic bagasse residues. Also, Residual bagasse tends to form agglomerat es which could become the weak point in composites and causes early fracture 44 . However, the addition of 2 wt. % coupling agent DVKS resumed TS and TEB of PLA composites with 30 % PB to 99 % and 116% of neat PLA, respectively. It suggested that DVKS acted as a coupling agent between bagasse residue and PLA because the CNO group of DVKS could react with the surfac e hydrogen bonding, the residue water in bagasse residues and the carbonyl group of the PLA 198, 207 . The TS and the TEB of PLA composites with 30% residues (RB and PB FB) substitution and in the addition of 2% DV those of pure PLA. We observed that PLA composite with PB had higher TEM than the composite with RB even though RB had twice longer fiber length than PB. It indicated that more specific surface areas generated through chem thermal pretreatment could provide more interfacial bonding between the PLA and the bagasse residue. FB exhibited the least reinforcing to PLA composites. The TS, TEB and modulus of the PLA composite with FB were 88.58%, 91.35% and 93.62% of those of neat PLA, respectively. As we mentioned before, FB consisted of a large quantity of lignin particles with a low aspect ratio, which result in lower strength properties of the residue itself. The moduli of all the composites were higher than that of neat PLA, which suggested that the bagasse residue provided the additional nature of modulus in the
84 PLA composite. This result agreed well with modulus results in the addition of lignocellulosic fillers 44 . Flexural properties As shown in Figure. 4 4 and table 4 3, the effects of different residues and DVKS on the flexural strength (FS) and flexural modulus (F M) of PLA and its composites follow the similar trend as their effects on the tensile strength (TS) and tensile elastic modulus (TEM s ). As shown in Table 4 but decreased flexural modulus (FM) of ne also observed that all the PLA composites had a significantly increased FM in between PLA and the filler, which led to a higher i mpact resistance of PLA composites in the addition of the coupling agent. As shown in Table 4 3, there was no significant difference in flexural strength (FS) of PLA composites with PB and RB and Pure PLA in the presence of DVKS. However, the FS of PLA com posite with FB was much lower Thermal Properties Figure. 4 5 shows DSC thermograms of PLA and its composite samples and Table 4 4 summaries all the DSC data shown in Figure. 4 5. While the addition of P B and DVKS individually decreased the glass transition temperature (T g ) of PLA polymer, T g was in the same level of that of neat PLA when incorporating both PB and DSVK in the PLA matrix. The increase of T g for PLA composites in the presence of both PB an d coupling agent DSVK may be attributed to the confined polymer chain formed by interfacial reaction among bagasse hydroxyl groups, NCO group of DVKS, and PLA carbonyl groups. The T m of PLA composites and the PLA in the presence of DVKS were
85 lower than th at of neat PLA. It is because that DVKS has plasticization effects and lignin (main component of the residues) can also act as natural adhesives as previously reported 208 . The cold crystallization was observed for both the neat PLA and its composites. But the melt crystallization of neat PLA was undetectable in DSC thermograms. Neat PLA was not able to crystalize during the injection molding process. This could be caused by rapid cooling during the molding process. Melt crystallization was detected in all the PLA composites and the PLA in the presence of DVKS. PLA composites with PB and DVKS exhibited maximum melting crystallization ( maximum T mc mc ) b ecause the maximum surface areas of this composite allowed more heteronucleation and growth of PLA crystals. Molecular Weight The molecular weight (Mw) of the PLA and its composites measured by SEC are shown in Table 4 5. Without DVKS, bagasse residues gr eatly decreased the MW of PLA. There are two reasons for this decrease. One reason is that hydrophobic PLA and hydrophilic residues are not compatible with each other. The second reason is that PLA may be hydrolyzed by the residue water and acetic acid in bagasse residues at high temperature 209 211 . In the presence of 2% DVKS, the Mw of PLA was slightly increased. DVKS extended the PLA chain because that the isocyanate group of DVKS reacted with carbonyl group and hydroxyl group of PLA molecules 44 . Regarding PLA composites with different types of residues, PLA composites w ith PB had the highest molecular weight and the composite with RB had the lowest molecular weight. This result indicated that chain extending is directly correlated with the exposed surface areas. PB had the most exposed surfaces, which generated more act ive reaction sites to aid the formation of more bonding between PLA, the coupling agent and PB. RB had an intact
86 cell wall structure, which prevented the formation of inter bonding and resulted in a low Mw. The strength of the PLA composite with RB mainly derived from the strength of fiber bundles themselves. FB also had some exposed areas due to the biological, chemical and mechanical treatments that it was subjected to. It had the molecular weight close to PB but higher than RB. Morphologies of PLA and i ts Composites As shown in Figure 4 6, the fractural surfaces of neat PLA and PLA composites were examined by SEM. The fracture surface of neat PLA was relatively smooth and uniform (Figure 4 6 A ). In the presence of 30% RB (Figure 4 6 B ), intact fiber bundl es were clearly shown in the plane. Some interstices were observed in the areas between the PLA and fibers, especially at the sites where fibers were pulling out of the plane during the tensile test. The intact fiber bundles could not provide more surfaces to facilitate inter bonding between PLA and bagasse residues but had good mechanical strength by themselves. The fracture surfaces of PLA composites with PB and FB had no visible interstices, which could be caused by better inter bonding between the PLA a nd fibrils. A large number of fibrils were clearly shown in the SEM image of PLA composite with PB, which resulted in better strength of this composite. The results agreed well with the previous analysis. Large quantity of lignin particles and the residue fibers with a low aspect ratio were seen in the PLA composite with FB. Conclusions In this study, t win screw extrusion followed by injection molding was used to prepare green PLA composites with the substitution of three types of sugarcane bagasse residue characteristics in terms of their components, residue fiber lengths and morphologies.
87 The fiber length was gradually decreased (FB
88 Table 4 1 . Temperature profile of the twin extruder for composite processing Zone 1 2 3 4 5 6 7 8 9 10 Die Barrel Temp (Â°C) 30 155 160 165 165 162 164 165 165 160 165
89 Table 4 2 . Com position and fiber characteristics of three types of bagasse residues: RB the raw bagasse residues; PB the pretreated bagasse residues; FB the bagasse residues after fermentation Material Lignin% Cellulose % Hemicellulos e % Protein % Ash % Acetic acid% Fiber Length (mm) RB 26.70 39.72 27.85 2.75 1.91 1.15 1.23 PB 29.33 53.29 14.90 1.43 1.05 0 0.63 FB 40.19 44.81 11.52 2.51 0.95 0 0.28
90 Table 4 3. Effect of different residues and DVKS on the mechanical properties of neat PLA and PLA composites Sam ple Tensile Properties Flexural Properties TS 1 (Mpa) TM 2 TEB 3 (%) TM 2 TEM 4 (Mpa) TM 2 FS 5 (Mpa) TM 2 FEB 6 (mm) TM 2 FM 7 (Mpa) TM 2 a 62.0 Â± 1.9 A 2.1 Â± 0.1 AB 4013.2 Â± 271.8 A 104.0 Â± 1.1 A 25.2 Â± 3.1 A 1816.3 Â± 39.9 A b 64.2 Â± 1.9 A 2.5 Â± 0.5 A 3885.7 Â± 3 21.1 A 105.3 Â± 4.9 A 15.6 Â± 1.91 B 1753.6 Â± 98.4 A c 49.9 Â± 1.9 B 1.4 Â± 0.2 C 4408.7 Â± 134.8 AB 81.1 Â± 1.5 B 6.36 Â± 0.2 C 2439.6 Â± 28.8 B d 60.5 Â± 1.6 AC 2.2 Â± 0.3 AB 4668.3 Â± 268.8 B 97.9 Â± 2.0 A 8.3 Â± 0.14 C 2507.8 Â± 49.2 B e 61.4 Â± 0.7 A 2.4 Â± 0.2 AB 4272.5 Â± 193.5 AB 97.7 Â± 9.8 A 8.9 Â± 0.3 C 2301.0 Â± 225.7 B f 54.9 Â± 6.9 BC 1.9 Â± 0.2 BC 4069.1 Â± 419.5 A 85.2 Â± 2.7 B 7.2 Â± 0.4 C 2330.0 Â± 55.1 B a. Neat PLA; b. PLA with 2% DVKS; c. 70% PLA 30%PB; d. 70% PLA, 30% RB, 2% DVKS; e. 70% PLA, 30% PB, 2% DV KS; f. 70% PLA, 30% FB, 2% DVKS 1. Tensile Strength (TS); 2. Tukey Method 95% Confidence Interval (TM); 3. Tensile Elongation at Break (TEB); 4. Tensile Elastic Modulus (TEM); 5. Flexure Strength (FS); 6. Flexural Elongation at Break (FEB); 7. Flexural Mod ulus (FM).
91 Table 4 4. Effect of three types of bagasse residues and DVKS on the thermal properties of neat PLA and its composites cold crystallization melting melt crystallization T g (Â°C) 1 T cc (Â°C) 2 cc (J/g) 3 T m (Â°C) 4 m (J/g) 5 T mc (Â°C) 6 mc (J/g) 7 PLA 0% DVKS 59.6 95.7 21.7 169.9 47.7 PLA 2% DVKS 59.1 94.2 20.9 168.7 45.4 110.3 10.9 30%PB 57 96.8 17.2 168.3 34.7 95.6 9.0 30%RB 2% DVKS 59.7 98.4 14.7 168.5 31.5 112.3 13.1 30%PB 2% DVKS 59.9 93.6 13.7 167.9 31.7 115.3 21.8 3 0%FB 2% DVKS 57.7 97.2 17.6 168.3 31.3 110.8 10.0 1. Glass transition temperature (T g ); 2. Cold crystallization temperature (T cc ); 3. Enthalpy of cold crystallization ( cc ); 4. Melting temperature (T m ); 5. Enthalpy of melting ( m ); 6. Temperature of melt crystallization ( T mc ); 7. Enthalpy of melt crystallization ( mc ).
92 Table 4 5. The molecular weight of neat PLA and its composites 1.Mw: weight weighted molecular w eight, 2. Mn: number weighted molecular w eight , 3. PDI: polydispersity index Material Mw 1 Mn 2 PDI 3 Neat PLA 1.16E+05 6.02E+04 1.92 PLA 2% DVKS 1.17E+05 5.99E+04 1.96 70% PLA 30%PB 9.93E+04 5.24E+04 1.90 70% PLA 30%RB 2% DVKS 1.09E+05 5.58E+04 1.95 70% PLA 30%PB 2% DVKS 1.28E+05 7.01E+04 1.82 70% PLA 30%FB 2% DVKS 1.25E+05 6.56E+04 1.91
93 Figure 4 1 . Schematic diagram of the twin screw extruder
94 Figure 4 2 . SEM images of three typ es of bagasse residues . A) raw bagasse residues, RB (scale =100Âµm), B) pretreated bagasse residues, PB (scale = 100Âµm), C) fermentation bagasse residues, FB (scale =10Âµm).
95 Figure 4 3 . Effect of three types of residues an d DVKS on tensile strength and tensile elastic modulus of neat PLA and its composites. (a. Neat PLA; b. PLA with 2% DVKS; c. 70% PLA, 30% PB; d. 70% PLA, 30% RB, 2% DVKS; e. 70% PLA, 30% PB, 2% DVKS; f. 70% PLA, 30% FB, 2% DVKS)
96 Figure 4 4 . Effect of three types of residues and DVKS on elongation at break of neat PLA and its composites. (a. Neat PLA; b. PLA with 2% DVKS; c. 70% PLA, 30% PB; d. 70% PLA, 30% RB, 2% DVKS; e. 70% PLA, 30% PB, 2% DVKS; f. 70% PLA, 30% FB, 2% D VKS)
97 Figure 4 5 . Effect of three types of residues and DVKS on flexural strength and flexural modulus of neat PLA and its composites. (a. Neat PLA; b. PLA with 2% DVKS; c. 70% PLA, 30% PB; d. 70 % PLA, 30% RB, 2% DVKS; e. 70% PLA, 30% PB, 2% DVKS; f. 70% PLA, 30% FB, 2% DVKS)
98 Figure 4 6 . DSC Thermograms of neat PLA, PLA with 2% DVKS and its composites (1 st Scan).
99 Figure 4 7 . SEM images of tensile fracture surfaces . A ) neat PLA , B ) PLA with 30% RB and 2% DVKS , C ) PLA composites with 30% PB and 2% DVKS; D ) PLA composite with 30% FB and 2% DVKS. PLA PB Fiber FB Fibril ( A ) ( B ) ( C ) ( D )
100 CHAPTER 5 DISK REFINING AND ULTRASONICATION TREATED SUGARCANE B AGASSE RESIDUES FOR POLY ( VINYL ALCOHOL) BIO COMPOSITES 2 Introductory Remarks Bio based products (e.g. bioenergy, bio based materials) from renewable resources are receiving ever growing attention due to the concerns about the depletion of petroleum resour ces, the price escalation of crude oil, and the aggravation of climate change . As an abundant natural resource, lignocelluloses are potentially important feedstock for the production of various forms of bio based products. There are many other advantages f or using lignocelluloses such as being renewable, environmentally friendly (less greenhouse gas emissions), allowing independence of foreign oil, and helping rural economic development 7, 212 . Sugarcane bagasse residue derived after sugarcane juice extraction has primarily been used as animal feed or disposed as a solid waste. It has been studied for bio ethan ol production through simultaneous saccharification and co fermentation (SScF) 16, 18, 19 . In our previous work, sugarcane bagasse residues from different steps of laboratory ethanol production, i.e. raw bagasse re sidues, pretreated bagasse residues, and bagasse residues after fermentation, were used to reinforce poly(lactic acid) (PLA) matrix through twin screw extrusion 13 . The results of this work indicated that the application of fermentation residues lowered the physical properties of bio com posites compared with those reinforced by residues taken from up stream of fermentation steps, i.e. raw bagasse and pretreated bagasse residues. This reduction in 2 Reprinted with permission from Cheng, Q., Tong, Z., Dempe re, L., Ingram, L., Wang, L., Zhu, J.Y. 2013. Disk Refining and Ultrasonication Treated Sugarcane Bagasse Residues for Poly(Vinyl Alcohol) Bio composites. Journal of Polymers and the Environment, 21(3), 648 657.
101 physical properties could be caused by significantly increased lignin content (about 60 70%) and the reduction in the aspect ratio of residue fibers (about 10 20%) in the fermentation residues 13 . In this study, we attempted to increase total surface area of fermentation bagasse residues and the aspect ratio of their residue fiber segments via multiple mechanical treatments incl uding disk refining and/or ultrasonication. These treatments are expected to improve the interaction between biomass residues and the polymer matrix. The modified residues can then be used with poly ( vinyl alcohol) (PVA) to produce a biodegradable composit e with improved mechanical and thermal properties. Disk refining (or super grinding) can generate very high shear force that is usually used to prepare micro or nano fibrils from lignocellulosic fibers. Two disks with bars and grooves are parallelly place d with a small gap to crush and shear fibers by the repeated cyclic stresses. This mechanical treatment results in the irreversible change of fiber structures and reduces fibers to micro or nano scale 213 216 . T he ultrasonication treatment, as another important mechanical treatment approach, has been used in many processes, such as emulsification, catalysis, homogenization, disaggregation, scission, and dispersion 217 . For example, several researchers used the ultrasonication treatment to break down cellulose fibers to small fibrils for the application of polymer reinforcements 76, 218 220 . During an ultrasonication treatment, a very strong mechanical oscillating power produced by ultrasonic wave generates cavitation. Within the cavitation bubble and its immediate vicinity, violent shock waves are produced wh ich can generate a high temperature and a high pressure
102 field to coherently act on materials, which results in the rupture of the material structures 221 . Poly ( vinyl alcohol) (PVA) has various advantages such as being biodegradable, resistance to solvents, being able to chemically bond with cellulose and lignin. PVA can also form films by casting because it is solu ble in hot water. PVA has broad applications including protective colloids in the manufacture of polymer emulsions, the bindings of pigments and fibers, dip coated products, protective strippable coatings, the production of detergents and cleansing agents, adhesives, emulsion paints and solution cast films 73, 74 . However, a common feature of PVA is their low mechanical strength and integrity. Recently, many micro or nano scale fibers such as cellulosic nanofibers, nanocrystals, and fibrils were used to reinforce PVA to further improve the mechanical and thermal properties of PVA films 76 78, 222, 223 . Although there is a depth of knowledge regarding the extraction of these materials from cellulosic fibers, little attention has been paid to the use of low value lignocellulosic biomass, such as residues (mainly lignin) reclaimed from the wa ste stream of bioethanol fermentation process, for PVA reinforcement. Therefore, the focus of this study was to prepare PVA composite film reinforced with low cost fermentation bagasse residues, after a size reduction treatment by disk refining (DR) alone or followed by a high intensity ultrasonication (DR+US). We characterize the DR and the DR+US treated fermentation residues by Scanning Electronic Microscopy (SEM) and different particle size analyzers. Then, we investigate the influence of the addition o f DR and DR+US treated bagasse residues on the mechanical and thermal properties, and surface morphologies of the reinforced PVA composites.
103 Experiment Materials The fermentation bagasse residues used as raw materials are solids separated from the ferment ation broth of a bioethanol process, liquefaction plus simultaneously saccharification and fermentation process (L+SScF). At first, the raw bagasse underwent a multi step hydrolysis process including steam explosion plus mild acid pretreatment and a liquef action step, followed by a fermentation process at 37 Â°C for 144 hours 18, 19 . The fermentation broth was collected and washed with standard test sieve #270 under warm water until effluent became clear, and then dr ied in an oven at 70Â°C for at least 24 hours. The components of the fermentation residues including lignin, cellulose, and a small amount of hemicellulose (Table 5 1) were analyzed according to a standard National Renewable Energy laboratory (NREL) procedu re 201 . The higher percentage of cellulose (34%) is due to the loss of significant amount of small sized lignin particles and protein during the washing steps. Poly ( vinyl alcohol) (PVA) (Acros Organics, 99 100% hydrolyzed, average molecular weight of 86000) was used as the matrix material in the composites. Dis k Refining (DR) T reatment The fermentation bagasse r esidues were suspended in water (~3.14% consistency) and refined using a Super Mass Colloider (model: MKZA6 2, Disk model: MKGA6 80#, Masuko Sangyo CO., Ltd, Japan) at 1500 rpm. The SuperMassCollider is equipped with a power meter to record electrical ener gy input. Two stone disks were positioned on top of each other. The bottom disk rotates while the top one is stationary. Refining started with 210 g oven dried fermentation residue. Pulp feeding was achieved by gravity. Pulp suspension was fed into the disk refiner continuously through a loop
104 consisting of a peristaltic pump (Cole Parmer, Chicago, IL) and plastic tubing. The refiner disk gap setting was gradually changed from 300 to ~ 100 Âµm within one hour. The zero position was determined right at the contact position between the two refining disks before loading pulp. Due to the presence of pulp, there is no direct contact between the two stone disks even at a negative setting of disk gap position. The disk refiner was kept running for another 4 hours 10 minutes. The total energy consumed for refining was approximately 6.61 kWh/kg. Ultrasonication (US) T reatment The water suspension of the disk refined bagasse residue was further treated for 30 minutes by high intensity ultrasonication at 80% of the s ystem maximal power scale and under a continuous mode to further reduce the size of the residue particles and fibrils. The ultrasonic (US) processor (Sonic Newtown, CT, 20 kHz, Model 1500 W, Newtown, CT) was directly applied to the water suspension of DR t reated residues in a 500 mL beaker. During the US treatment, the DR treated suspension was diluted to 0.52% consistency to improve stirring. The resultant sample after 30 minute US treatment is referred to as DR+US in this study. Characterization o f Bagass e Residues Scanning Electron Microscopy (SEM) (JEOL JSM 6400, operating voltage 5 or 15 kv, JEOL, USA) was used to examine the morphologies of the fermentation residue samples (DR and DR+US). All samples were coated with Au Pd (~10 nm) before SEM imaging. A Coulter Counter Multisizer 4 (MS4, Beckman, CA) was used to measure the particle size and its size distribution (under the maximum bin size of 400) of the DR and
105 to detect the particles for DR and DR+US bagasse residues, respectively. MS4 with 100 n be used to measure the particle sizes of water suspension of bagasse residues were diluted to the desired concentration level (about 5 10% in a volume basis) with a ba lanced electrolytic solution (Isoton II, Beckman, CA) in a 100 mL measurement beaker. Then the samples were measured using the MS4 immediately with stirring. Five replicates were conducted for both DR and DR+US particles. Dynamic light scattering (DLS) (Ze tasizer ZS3600 with a non invasive back scatter under 500 mw, 532 nm laser, Malven, UK) was used to estimate the size and the size distribution of the DR+US bagasse residues in a smaller size range. The DR+US samples were further diluted to about 0.1wt.%. A few drops of the dilut ed sample were suspended in 1 mL deionized water and measured immediately. Film Casting o f Composites PVA in a water solution (10 wt.%) and bagasse residues (DR and DR+US) in a water suspension (3.14 wt.% and 0.52 wt.%, respectivel y) were mixed and stirred manually and then dispersed by ultrasonication treatment (Model 300V/T, Biologics, Inc., Manassas, VA) for three minutes at a 50% maximum power scale and under a continuous mode. The mixtures were degassed in a desiccator with vac uum and evaporated in petri dishes at room temperature ( ~22Â°C) and the relative humidity (RH) of ~30% until films were formed. After that, these films were thermally treated in an oven at 70 Â°C for more than 4 hours. The samples were kept in a desiccator more than three days for conditioning before the mechanical and thermal properties were tested. A saturated solution of magnesium nitrate (Mg(NO 3 ) 2 ) was placed in the desiccator to
106 regulate the desiccator RH to approximately 53% at room temperature (~22Â°C) . According to American Society for Testing and Materials (ASTM) D1708 224 , the conditioning RH is 50Â±5% and the condition time is more than 40 hours. The composites were prepared at four levels (0%, 2%, 5% and 10%) of PVA substitution using fermentation residue of DR and DR+US. The nominal thickness of the composite Characterization of film composites Mechanical testing of the composites was performed on an Instron test machine (Model 5566, load cell capacity of 100 N, Grove City, PA) with the crosshead speed of 10 mm/min. The crosshead extension was used as specimen deformation. Samples were cut to dog bone shapes with the widths of 5 mm, the lengths of 20 mm for the narrow portions (gauge length 20 mm) and total lengths of 40 mm. In accordance with ASTM D1708 08, five specimens were tested for each composite 224 . Tensil e elastic modulus of all composites was determined from the linear portion of the stress strain curves (tangent modulus). Multiple comparisons by the Statistical Analysis System (SAS) (t Tests (LSD)) were used to detect the overall significant differences of the tensile modulus, tensile strength, and maximal strain at the break point of the The thermal analysis process utilized a Thermogravimetric Analyzer (TGA/DSC1, Stare system, Mettler Toledo, Schwerzenbach, Switzerland) to determine the thermal behaviors of the composites, neat PVA, and neat bagasse residues. A 10 mg sample was placed in the TGA and heated from 50 Â°C to 500 Â°C at a 20 Â°C/min heating rate. The tests were conducted under nitrogen gas with flow at 20 mL /min to avoid oxi dation.
107 Scanning electron microscopy (SEM) was also used to examine the topography of the fracture surface of the neat PVA and bagasse residues reinforced PVA composites after tensile tests. All samples were coated and scanned using the same process as des cribed above. Results and Discussion SEM Analysis o f Untreated and Treated Fermentation Residues SEM images of the fermentation residues before and after disk refining (DR) and after DR plus ultrasonication (DR+US) treatments are shown in Figure 5 1. Parti cle size reduces upon DR treatment and further reduces upon ultrasonication. The dimensions of most untreated fermentation residues ranged from hundreds of microns to 1 mm. After DR treatment, the sizes of most particles were smaller than tens of microns. Particle size of bagasse residues were further reduced to sub micron upon 30 minute US treatment, due to the strong available hydrodynamic force generated by ultrasonication 221 . Size Analyzer Analysis o f Treated Bagasse Residues Figures 5 2 and 5 3 show the number and volume distributions of the DR and the DR+US treated fermentation residues measured by Beckman Co ulter Multisizer 4. This multisizer diameter. The size range of measured particles is 2% to 60% of an aperture diameter 2, residue particles treated with DR had an average diam observed (Figure 5 2), which was consistent with particle sizes shown in the SEM images (Figures. 5 1 C and 5 1 C ). As shown in Figure. 5 1 D, some small particles (<
108 2Âµm) were present in the residue but were not detected by the multisizer aperture. A smaller aperture was used but was found ineffective perhaps because the aperture was clogged by larger particles. It is speculated that the smaller particles of less than 2 Âµm are mainly lignin particles which can associate with the larger residue cellulosic fibril surface, which is agreed well with SEM results that small spherical particles (lignin particles) attached in fiber (large aspect ratio) surfaces. Figure 5 3 shows the average particle size and the size distribution of DR+US treated bagasse residues. It was observed that particles had an average diameter o to their larger diameters. This agrees well with the SEM im ages (Figure 5 1 E and 5 1 F ). (Figure 5 1 F ). These particles were not detected by the multisizer when using a dynamic light scattering (DLS) based Zetasizer. The results showed the sample had a size ranging 4). The results in Figure 5 4 clearly show a bi modal distribution in particle size. The large peak is most likely associated with the cellulosic fibrils. Tensile Mechanical Properties of the C omposites Figure 5 5 summarizes the tensile moduli and tensile strengths (maximal stress) for neat PVA and PVA composites with the substitution of 2%, 5%, and 10% DR and DR+US treated bagasse residues, respectively. The tensile modulus of PVA increased by 20%, 61%, and 154%, respectively, by varying DR treated bagasse residues (2%, 5%, and 10%). The introduction of both DR and DR+US treated particles significantly
109 oves PVA modulus (Figure 5 5). Although DR+US produced smaller bagasse residue particles (Figure 5 2 and 5 3), the advantage of DR+US treatment over DR alone in improving tensile moduli was not statistically significant (p=0.21 0.52). This is partly becaus e of the aggregation of smaller particles and cellulose fibrils, as seen in the SEM images of cross sections of the composites, which will be discussed in the following section. The aggregation of smaller particles and/or fibrils might influence the reinfo rcement of their composites 76, 218 . Tensile strength of neat PVA was increased significantly by substituting 2% PVA within one standard deviation. Additions of 2%, 5% and 10% DR and 5% DR+US treated bagasse residues did not affect PVA tensile strength. The substitution of 10% DR+US bagasse residues decreased PVA tensile strength (P<0.0001). One of the possible explanations that most all the levels and treatments did not improve tensile strength was that the residue fibers have high lignin content (Table 5 1) and low aspect ratios (Figure 5 1). The long fibers, the most important reinforcement component, were digested and shortene d significantly by hydrolysis and fermentation. These fibers are different from microfibers and nanofibers directly produced from wood pulp 225 and soybean 226 that had high aspect ratios and could greatly improve the mechanical properties of their PVA composites. Another possible reason is that the aggregation of smaller particles at high concentrations (e.g. 10%) can affect the mechanical properties of composites 76, 218 . The advantage of DR+US treatment over DR in improving tensile oadings (Figure 5 5) because DR+US produced smaller bagasse residue particles and fibrils
110 (Figure 5 2 and 5 as described above. The maximal tensile strain (elongation) at the break point of ne at PVA was increased significantly (P<0.0001) by 17% and 19% at 2% substitution with DR and DR+US treated bagasse residues, respectively (Figure 5 6). However, the change in maximal strain was minimal at increased substitution levels of 5% and 10% DR and 5 % DR+US treated bagasse residues. The maximal tensile strain was reduced by more than 30% at 10% substitution with DR+US treated residues (P<0.0001), suggesting the higher stiffness of the PVA composite with residue particles at a high concentration which resulted in the aggregation of smaller particles and therefore a brittle composite. Thermal Properties of the Composites Thermogravimetric Analysis (TGA) was used to investigate the effect of treated fermentation residues on the thermal stability of the P VA composites. The TGA and derivative TGA (DTGA) thermograms are shown in Figure 5 7 (the neat PVA, the DR treated residue, the composites with DR treated residue) and Figure 5 8 (the neat PVA, the DR+US treated residue, and the composites with DR+US resid ue). There were three main weight loss regions for PVA and PVA composites with both DR and DR+US particles. Similar results were obtained by others 77, 227 . All samples exhibited an initial weight loss from 70 to 1 50 Â°C, which was attributed to the evaporation of water. The second degradation region (max weight loss region) was located between 250 to 400 Â°C with a weight loss from 50 to 70% for different materials, which was attributed to the pyrolysis of bagasse re sidues and PVA degradation. The third weight loss region occurred above 400 Â°C, due to the decomposition of carbonaceous matter from PVA and lignin 77 .
111 Table 5 2 shows the moisture contents, the max weight loss in the second region and their temperature ranges for all samples. The water content of the DR and DR+US bagasse part icles were low because they were not conditioned after drying, while the PVA and all other composites had relative high water contents since they were conditioned at the RH about 53% for more than three days. The neat PVA had about 2% of water content and the composites had 2.6 to 2.9% of water content as the biomass absorbed more water during the conditioning process. This water includes both physically bound and free water, which were reported to have strong plasticizing effect, and improve the movement o f PVA chains 227 . Figures 5 7 A and 5 8 A indicate that PVA exhibit s thermal degradation at a lower temperature than neat DR and DR+US fermentation residues. It was also observed that the composites of PVA with both DR and DR+US bagasse residues degraded at a lower temperature than the neat residues, but at a higher tempe rature than PVA. This agrees well with DTGA curves shown in Figure 5 7 B and 5 8 B. Similar results have been reported in literature 228, 229 . The max degradation temperature of PVA increased after adding DR and DR+U S treated residues because of the different degradation temperatures of the composite constituents. It was reported that PVA degradation occurred first, followed by cellulose and lignin thermal decomposition 228, 22 9 . Therefore, we can conclude that the inclusion of cellulosic materials improves the thermal stability of PVA and the degradation temperature of the composites 77 . SEM Observation o f t he Composites Fracture Surfaces The SEM images of the fractured cross sections of neat PVA and PVA composites reinforced with 5% DR treated an d 5% DR+US treated bagasse residues are shown in Figur e 5 9. The fracture surfaces of neat PVA film were relatively smooth
112 (Figure 5 9 A and 5 9 B ), while those of PVA composites with DR (Figures 5 9 C and 5 9 D ) and DR+US (Figure 5 9 E and 5 9 F ) treated bagass e residues were very rough. There were clear gaps between the larger bagasse particles and the polymer matrix for both DR and DR+US composites (Figure 5 9 D and 5 9 F ). The fractured surfaces also revealed that some particles and fibrils were aggregated, mor e significant for DR+US treated bagasse composites. Figure 5 10 shows the SEM images of the fractured cross sections of PVA composites reinforced with 2% and 10% DR+US treated bagasse residues. The particles were dispersed well at 2% loading (Figure 5 10 A ) , while particle aggregations were observed at 10% loading (Figure 10 B ). The non uniform dispersion and aggregation of DR+US treated particles in the PVA matrix could explain that even the DR+US treated residues had smaller particles than DR treated residu es, there are no significant difference in most of the tensile properties (Figures 5 5 and 5 6) 76 . Conclusions The preparation of PVA composites through the combination of biodegradable plastic PVA and a low value fermentation residue reclaimed from the waste stream of bioethanol process was described. The residue had a high content of lignin and a low aspect ratio of residue fibers due to the multiple hydrol ysis steps in the bioethanol process. At first, the residues were broken down to hundreds of nanometers to tens of microns after disk refining (DR) treatment and tens of nanometers to several microns after further ultrasonication (US) treatment in order to increase their surface areas and aspect ratios. The morphologies of these treated residues illustrated that most particles still had a low aspect ratio compared with cellulose fibrils reported in the literature. The results indicated that the PVA tensile modulus was significantly improved with the substitution of DR and DR+US treated bagasse residues, and the PVA tensile strength
113 and maximal strain were slightly increased at 2% DR+US substitution. Thermal property data revealed that the composites had high er thermal degradation temperature compared to neat PVA, and that decomposition temperature increased with the increase in the amount of residues used for substitution.
114 Table 5 1 . The main components of the fermentation bagas se residue AIL* % ASL* % Total Lignin% Total ash % Glucan % Xylan % Galactan % Arabinan % Mannan % Acetic acid% Total % 47.9Â±0.1 1.0Â±0.1 49.0Â±0.0 1.2Â±0.0 33.9Â±0.9 7.1Â±0.0 6.7Â±0.1 1.2Â±0.0 0.0Â±0.0 0.8Â±0.0 99.8Â±0.8 (Note: *AIL: acid insoluble lignin, ASL: acid soluble lignin)
115 Table 5 2 . TGA data for neat PVA and its composites containing 2%, 5%, and 10% disk refining (DR) and DR plus ultrasonication (US) treated bagasse residues Sample PVA DR2 DR5 DR10 US2 US5 US10 DR DR+US Water content (%) 1.98 2.64 2.62 2.93 2.73 2.70 2.91 0.48 0.63 Temperature range at max weight loss (ÂºC) 250 310 250 335 250 355 250 350 250 342 250 360 250 356 250 390 250 390 Max weight loss (%) 69 64 65 69 67 63 65 52 57
116 Figure 5 1 . SEM images of the bagasse residues, before disk refining . A) Scale = 1mm B) Scale = 200 Âµm), after disk refining C) Scale = 20 Âµm, D) Scale = 5 Âµm), and after disk refining and ultrasonication treatment E) Scale = 20 Âµm, F) Scale = 5 Âµm).
117 Figure 5 2 . Particle size distribution of disk refining (DR) bagasse residues . M easured
118 Figure 5 3 . Particle size distribution of disk refining plus ultrasonication (DR+US) treated bagasse residues . M easured by Beckman Coulter Multisizer 4 with 20
119 Figure 5 4 . Particle size distribution of disk refining and ultrasonication treated bagasse residues (DR+US) measured by Zetasizer (six duplicates).
120 Figure 5 5 . Tensi le moduli and maximal stress of PVA and its bagasse residue composites with 2%, 5%, and 10% substitution (DR: disk refining alone, DR+US: ultrasonication after DR).
121 Figure 5 6 . The maximal tensile strain (elongation) of P VA and its bagasse residue composites (DR: disk refining alone, DR+US: ultrasonication after DR).
122 Figure 5 7 . TGA diagrams of neat PVA, neat disk refining (DR) treated bagasse residue , and PVA composites containing DR treated bagasse residue , a ) TGA and b) DTGA.
123 Figure 5 8 . TGA diagrams of neat PVA, neat disk refining (DR) and ultrasonication (US) treated bagasse resid ue , and PVA composites containing DR+US treated bagasse residues , a ) TGA and b) DTGA.
124 Figure 5 9 . SEM images of the fractured cross sections of neat PVA and PVA composites . A) Scale = 20 Âµm, B) Scale = 5 Âµm, PVA composites reinforced with 5% DR C) Scale = 20 Âµm, D) Scal e = 5 Âµm, and 5% DR+US E) Scale = 20 Âµm, F) Scale = 5 Âµm bagasse residues.
125 Figure 5 10 . SEM images of the fractured cross sections of PVA composites with 2% DR+US bagasse residue . A) Scale = 2 Âµm) , and 10% DR+US B) Sc ale = 5 Âµm.
126 CHAPTER 6 NANOCOMPOSITES OF POLY METHYL METHACRYLATE ENCAPSULATED GRAPHENE OXIDE PREPARED BY MINIEMULSION POLYMERIZATION Introductory Remarks Recently, nanocomposites consisted of polymer matrix and carbon nanotubes (CNT), carbon black or si licates have attracted a lot attention because of the improvements of the mechanical and electrical properties provided by those reinforcing materials 1, 107 109 . Particularly graphene, b ecause of its excellent mec hanical, thermal, electrical and gas barrier properties even if is compared with CNT 120 123 , it has become one of the most studied nanomaterial. Graphene consists of 6 hexagonally arranged sp 2 hybridized carbon at oms in a 2 D sheet like morphology with atomic thickness. Graphite is formed by graphene sheets held together in parallel by weak Van der Waals morphology. If the superb proper ties of graphene can be transferred to polymer composites, these composites could have wide potential applications in vehicles, aircrafts, electronics, and packaging. For preparing nanocomposite, graphene oxide (GO), one of the precursors of graphene, is m ore favorable than graphene. Unlike graphene which has no accessible functional groups on its surface, GO has multiple oxygen containing functional groups on its surface, such as hydroxyl, carboxyl and epoxy groups which are crucial for the subsequent fun ctionalization treatments, as well as incorporation with polymers 119 . After incorporation, GO can be chemically reduced to graphene. In order to incorporate graphene in polymer matrix, many methods were employed and studied. In this study, miniemulsion polymerization was emplo yed. In miniemulsion polymerization process, monomer phase is dispersed in continuous
127 aqueous phase in nano sized droplet form by mechanical methods such as ultrasonication and stabilized with highly organophilic surfactants and co stabilizers, and then th e monomer droplet is polymerized. Compare to melt mixing, solution blending, suspension and emulsion polymerization, miniemulsion polymerization has the following advantages. Firstly, the loci of polymerization is the monomer droplets which means no furthe r mass transfer which enables filler encapsulation by the polymer droplets 174, 175 . Secondly, stable latex of nano droplets with diameter of 50 500 nm and narrow particle size distribution are generally obtained . Thirdly, high molecular weight could be achieved due to the bimolecular termination is suppressed 165 . Last but not least, there is no organic solvent required which means less cost and more environmental friendly. With those inherent advantages, miniemulsion polymerization is a viable approach to encapsulate nanoparticles in poly mer droplets and form a stable aqueous dispersion with narrow particle size distribution 1, 109, 176 . Miniemulsion polymerization has been utilized to prepare GO polymer nanocomposites by only few researchers. Fur thermore , a fair portion of those studies were concentrated on the improvements of physical properties upon addition of GO or partially reduced GO, whereas investigation of effects of different surfactants, particle size distribution, intercalation, exfoli ation or encapsulation were often overlooked 177 183 . Etmimi and Sanderson reported exfoliated Poly (styrene butyl acrylate ) (P(St BA))/GO nanocomposites via miniemulsion polymerization and GO was firstly modif ied by a reactive surfactant, 2 acrylamido 2 methyl propanesulfonic acid (AMPS) to aid the intercalation of monomer. Exfoliated GO/P(St BA) nanocomposite was obtained. However, the stability of latex was not mentioned and the whether the modified GO was
128 en capsulated was not clearly discussed 184 . Man et al. claimed that GO nanosheets could be ar mored on polystyrene nanoparticles via miniemulsion polymerization but reduction occurred during polymerization, which resulted in the loss of colloidal stability 177 . Tan and Zeng reported that conductive reduced graphene oxide (RGO) was produced thro ugh reduction of GO through functioned with r methacryloxypropyl trimethoxysilane (MPS) and then grafted on copolymer P (St co MMA) as conducted filler to solution mix with polystyrene (PS)/ poly (methyl methacrylate) to prepare conductive polymer composi tes 183 . In particular, there is no research to use miniemulsion polymerization for the synthesis of stable latex of poly mer encapsulated exfoliated GO nanocomposites. If this system can be obtained, the uniform distribution of exfoliated GO will result in significant property improvement and stable latex will benefit for long term storage as well. In previous studies of mi niemulsion polymerization, stable latex es of nanoclay encapsulated by polymer droplets as a core shell structure and with narrow particle size distribution were successfully synthesized 1, 109 . Two distinctive sur factants, VBTAC and QAL were employed to modify nanoclay from hydrophilic to hydroph ob ic , and also increase clay interlayer space for subsequent penetration of monomer. Therefore, in this study, we plan to use these two organophilic surfactants, VBTAC or QAL, to modify GO to form organophilic nanohybrid, which can disperse into MMA monomer and follow a miniemulsion polymerization to achieve complete exfoliation and encapsulation of GO. S table latex es of polymer encapsulated nano size GO via miniemulsion p olymerization were synthesized. GO was prepared from low cost 125 . Low value raw graphite with
129 average size of 20um was used instead of specially processed high end graphitic material. Graphite oxide was subjected to pre exfoliation by ul trasonication to yield GO. Extracted lignin from LRB was converted to QAL by the incorporation of quaternary ammonium groups. GO was treated by VBTAC and QAL prior of miniemulsion polymerization. Several common surfactants were also used to modify GO as c omparison. Methyl methacrylate (MMA) was used as the monomer instead of St BA because of its rigid mechanical properties which will be crucial for future applications. Materials and Experiment Materials The lignin was extracted from fermentation broth of a bioethanol process, which involves liquefaction plus simultaneous saccharification and fermentation process (L+SScF) using sugarcane bagasse as raw materials 43 . Raw graphite flake (average from Sigma Aldrich Co. LLC. (U.S.A.) and used as received. Monomer methyl methacrylate (MMA) 99%, was purchased from Sigma Aldrich Co. LLC. (U.S.A.), the inhibitor (mono methyl ether hydroquinone) was removed by passing through a glass column filled with a luminum oxide powder. (Vinyl benzyl) trimethyl ammonium chloride (VBTAC) 99%, sodium dodecyl benzene sulfonate (SDBS) technical grade, Triton 405 (TX 405) 70% solution in water, hexadecane (HD) 99%, Azoisobutyronitrile (AIBN) 98%, 4 methoxyphenol, 99% , were purchased from Sigma Aldrich Co. LLC. (U.S.A.) and used as received. Poly vinyl alcohol (PVA, 99%, Mw = 86000) granules, trimethylamine (TMA, 50% aqueous solution) and epichlorohydrin (ECH, 99%) were purchased from Acros Organics (Thermo Fisher Scie ntific, NJ, U.S.A.). Sulfuric acid, 98%, potassium permanganate, 99% and hydrogen
130 peroxide, 30% were purchased from Fisher Scientific (U.S.A.) and used as received. Silver nitrate, 0.025 M, was purchased from Ricca Chemicals (U.S.A.). Experiments Preparati on of graphene oxide (GO) GO was prepared according to Hummers Method 125 with some modification. In an ice bath, powdered flake graphite (10 g) and sodium nitrate (5 g) were added to 98% sulfuric acid (230 mL) in a 1.5 L flask that was previously cooled to 5 Â°C in a freezer. While ke eping the temperature below 20 Â°C, potassium permanganate (30 g) was slowly stirred into the above mixture. The ice bath was then removed, and the mixture was heated to and kept at 35Â°C for 30 min. Deionized water (460 mL) was then slowly added to the mixt ure, causing an increase in temperature to about 100 Â°C. The diluted mixture was maintained at 100 Â°C for 15 min before it was further diluted with warm deionized water (420 mL) and hydrogen peroxide (3%, 100 mL). The yellow brownish GO was separated by va cuum filtration then washed repeatedly with deionized water until effluent became neutral. The purified GO was then redispersed in water and freeze dried (Freeze Dryer 8, Labconco, MO, U.S.A.) to produce GO which preserve d their original structure and prop erties for the subsequent experiments . Synthesis of q uaternary a mmonium l ignin (QAL) The synthesis of e poxypropyl t rimethylammonium c hloride (ETAC) from trimethylamine (TMA) and epichlorohydrin (ECH) was demonstrated as Figure 6 1 (a). According to Wu et 46 , the mixture of TMA and ECH with a molar ratio of 10:7 were transferred to a tri neck flask installed with a condenser and a stirrer in an ice salt bath (NaCl/ice = 1:3 by weight) for 1 hour. After tha t, the reactants were left overnight for complete reaction. ETAC can be detected by silver nitrate with the
131 appearance of white precipitate and ready for preparation of quaternary ammonium lignin. 2.5 g of lignin was reacted with 25 mL of sodium hydroxide (NaOH) (20 wt.%) solution in a warm bath at 80 Â° C for 20 minutes. Then, ETAC was added into the mixture and reaction was conducted under constant magnetic stirring for 5 hours until brown red emulsion was obtained. The chemical reaction refers to scheme F igure 6 1 (b). The obtained products were dried under vacuum and stored in the refrigerator prior to use. Modification of GO The dry weight of the GO was determined gravimetrically. To further exfoliate the GO, the GO (before any further treatments) was d ispersed in deionized water to form a suspension with 1% consistency. Ultrasonication was then applied to the 1% GO suspension (energy equivalent of 1.35 kWh, with a 300V ultrasonic homogenizer, BioLogics, Inc., VA, U.S.A., on 90% power and 90% pulse setti ng), which was kept in an ice bath while deionized water was added to the suspension accordingly to ensure constant solid content. After Sonication, certain amount of VBTAC, QAL , and other surfactants (as comparison) was added to the GO suspension separat ely and the concentration of surfactant is approximately 20 wt. % of GO. The suspension was stirred for 24 hours to allow reaction of surfactant and GO. After that, the treated GO suspension was dialyzed in deionized water (3.5kD dialysis tube, Spectrum Lab oratories, INC, TX, U.S.A.) until no chlorine could be detected by silver nitrate (about 3 4 days). All GO samples were freeze dried (Freeze Dryer 8, Labconco, MO, U.S.A.) to preserve their original structure and properties.
132 Miniemulsion polymerization o f methyl methacrylate (MMA) in the presence of graphene oxide (GO) In a typical run (recipe in Table 6 1), the oil phase composed of 0.5 g of co stabilizer hexadecane, 0.1 g of AIBN, 6 g of monomer MMA, and varying quantities of GO was mixed by 30 min magn etic stirring and followed by ultrasonication (energy equivalent of 0.27 kWh, with a 300V ultrasonic homogenizer, BioLogics, Inc., VA, U.S.A., on 90% power and 90% pulse setting) in an ice bath. The water phase mixture composed of 0.17g of TX 405, various amount of PVA , and nano filtered deionized water . It was then magnetically stirred in an ice bath for 30 min. PVA was used as a co stabilizer of latex. The ultrasonicated monomer phase was transferred to the water phase, the mixture was then ultrasonicated again (energy equivalent of 0.08 kWh, with a 300V ultrasonic homogenizer, BioLogics, Inc., VA, U.S.A., on 90% power and 90% pulse setting) to form a miniemulsion . The obtained miniemulsion was transferred into a three neck flask equipped with a condenser, a mechanical overhead stirrer and a temperature control unit. The miniemulsion was stirred for another 30 min at room temperature and degased with nitrogen. The polymerization was initiated by increasing the temperature to 70 Â± 2 Â°C and reaction was allow ed to taken place for 8 h under continuous mechanical stirring. Upon 8 h reaction, several drops of 2% 4 ethoxyphenol was added to terminate the polymerization. Characterization Fourier Transform Infrared Spectrometry (F TIR ) Fourier transform infrared sp ectrometry (FTIR) spectra were recorded on a Thermo Nicolet Magna 760 FTIR spectrometer (Thermo Scientific, MA, U.S.A.). 0.1 2 mg of each sample was mixed with 160 mg potassium bromide to prepare a pellet form
133 ready for FTIR measurement. 32 scans for eac h sample were taken with the scanning range from 400 to 4000cm 1 , with resolution of 4. X Ray Diffraction (XRD) X Ray Diffraction (XRD) measurements were performed on Phillips XPert MRD instrument (PANalytical, Almelo, Netherlands ) with Cu K radiation so Ã…) at a voltage of 45 V, step size of 0.016Â°, scan step time of 5 s, scan angle from 5Â° to 60Â°. The d (001) basal spacing of the raw graphite, GO, and polymerized samples is the interlayer Ray sour ce (Cu K the diffraction angle. Molecular Weight The molecular weight (Mw) of the PMMA and its nanocomposites with GO was measured by size exclusion chromatograp hy (SEC), an Agilent Technologies 1260 series HPLC systems equipped with a refractive index detector (RID) and a multiple wavelength detector (MWD) (CA, USA). Three columns (Agilent Technologies, CA, USA) were connected in series, including a PLgel mixed B , a PLgel a pore size of 10,000 Ã…), and a PLgel samples were dissolved in HPLC grade tetrahydrofuran at a concentration of 0.2 wt. %. After that, solution was filtered through a 0.22 Âµm syrin ge filter. In each run, 50 ÂµL filtered solution was injected, the thermostat temperature and flow rate was set at 25 Â°C and 1 mL/min, respectively. All results were processed using ChemStation software with GPC analysis package (Rev.B.04.03). Molecular wei ght was calculated based on a universal calibration using a set of polystyrene standard.
134 Thermal Stability Analysis Thermogravimetric analysis (TGA) was performed using a Mettler Toledo (OH, U.S.A.) thermal analyzer. 3 10 mg samples were heated at a heat ing rate of 10 Â°C/min from 30 to 1000 Â°C with 100 mL/min constant nitrogen flow. Particle Size Dynamic light scattering (DLS) was used to estimate the size and size distribution of the graphite samples and miniemulsions after polymerization. A Zetasizer with noninvasive back scatter under 500 mw and 532 nm laser (ZS3600, Malven, U.K.) was used. All samples were made to 0.05 or 0.1% concentration and transferred to the standard 3.5 mL square cuvettes for analysis. Electron Microscopy Scanning electron m icroscopy (SEM) and transmission electron microscopy (TEM) were utilized to study the morphologies of graphite, graphene oxide, polymerized particles in miniemulsion and melting latex films. SEM was carried out on a FEI XL 40 FEG SEM (FEI instruments, OR, U.S.A.) at an operation voltage of 10 keV. Miniemulsion samples were dried on conductive carbon tabs then coated with gold palladium coating (Au/Pd). TEM was conducted on a JEOL 200CX TEM (JEOL instruments, MA, U.S.A.) with 100 keV accelerating voltage. Mi niemulsion samples were dried on carbon type A grids and air dried prior of analysis. Melt film samples were dried in air first, and then melt at 160 Â°C in a laboratory oven for 6 hours. Results and Discussion Visual Comparison o f GO Modification by Diffe rent Surfactants From Figure 6 2, we observed that GO treated with AMPS (c) and SDBS (d) behaved quite similar as neat GO (a) through the formation of stable dispersion in
135 water . The good dispersion of GO in water is because that GO has significantly small er size and many surface functional groups a fter oxidation and exfoliation. The hydrophilic surfactant may further aid this dispersion. Meanwhile, GO treated with organophilic surfactants VBTAC, OTAB , and MTAB were precipitated on the bottom of the vials, which indicated that GO treated by these surfactants lost its hydrophilicity. VBTAC was chosen as the surfactant for further miniemulsin polymerization because of two reasons. First VBTAC has shorter carbon chain than OTAB and MTAB, which could not signif icantly increase the viscosity of emulsion. Second, VBTAC has the reaction group (double bonds), which could react with monomer MMA to further increase the interaction between GO and monomer MMA 109 . In order to un derstand the hydrophilicity of the modified GO, three modified GO by VBTAC, SDBS , and QAL was tested through dispersion in monomer and water mixture. MMA has 0.94 g/cm 3 , which is float ed on top of aqueous phase. SDBS is used because it is an anionic surfac tant which is expected to provide electrostatic stabilization for GO 230, 231 . From Figure 6 3, it is clearly shown that VBTAC treated GO has been converted from hydrophilic to organophilic, as the GO stayed on top MMA phase. GO treated with SDBS is still mainly hydrophilic but beca me slightly organophilic. Unfortunately, GO treated with QAL is still hydrophilic, as the GO was completely stayed in aqueous phase. This could be caused by the interference of hydrophilic functional groups of lignin. Fourier Transform Infrared Spectromet ry (FTIR) Figure 6 4 shows the FTIR spectra of grapheme, GO, GO with VBTAC and the reduced GO. T he stretching vibration of the carboxyl groups ( COOH) around 1700 cm 1 , the vibration of in plane tertiary hydroxyl groups ( OH) at 1400 cm 1 , and the vibratio n
1 36 of alkoxy (C O) around 1050 cm 1 indicate raw graphite was highly oxidized to form GO 232 235 . The double bond C=C stretching around 1600 cm 1 indicated the successful grafting of VBTAC on GO surface 109 . After reaction of lignin with ETAC, a strong peak of amine group can be observed on the FTIR spectra (Figure 6 5), which indicates the successful formation of QAL. The signal for this amine group becomes weak in GO QAL hybrid, which can be attributed to the formation of hydrogen bonding with the hydroxyl group on GO. X Ray Diffraction (XRD) The interlayer spacing (d) of the GO and composite samples was measured by 6 , nm, the (002) structure 236 . The oxidation of graphite is expected to increase this interlayer distance (d spacing), which can be observed from the XRD spectra of GO. spacing of 0.803 nm compare to raw graphite. This change was due to the addition of oxygen containing groups and water molecules into the interlayer space between the graphene sheets. Moreover, the strong characteristic peak of graphite disappeared entirely, which indicates the complete disruption of t he original stacked (002) structure of raw graphite 237 . A highly oxidized GO was obtained, which is in agreement with the FTIR spectra. VBTAC is expected to enter the interlayer space and its cationic ammonium group would bond with the oxygen containing groups, which cause further increase in the interlayer space of GO. From Figure 6 6, after reaction of GO with QAL, the characteristic peak of GO c ompletely disappeared. Moreover, there is no clear layered structure can be observed, which can be caused by the restacking of
137 the layers caused by QAL. Based on the FTIR and the XRD spectra, it can be explained that the lack of hydrogen bonding between QA L and GO and the interruption from lignin function groups such as hydroxyl groups, may resulted in the poor dispersion of QAL treated GO in the monomer phase. As a result, QAL was not able to fully enter the interlayer space of GO to convert GO to organoph ilic, therefore QAL treated GO was not able to disperse into monomer phase to form stable miniemulsion. In contrary, a fter GO treated by to a d spacing = 0.981. T he increase in the d spa cing is expected to facilitate the intercalation of monomer. For the polymerized samples ( Figure 6 7) , the diffraction peaks are quite different from the GO samples. As we can observe from Figure 6 correspond s to pristine and VBTAC treated GO disappeared completely. This change in diffraction behavior indicates that the GO was well exfoliated by the introduction of polymer chains. Similar changes in clay and its nanocomposites were reported by other researchers as well 109, 238 . For polymerized PMMA with 0% GO, there is a characteristic peak of PMMA at 18. 239 , which became less intensiv formulations with 0.5% and 2% GO. This change may be caused by the presence of the exfoliated GO in the polymer matrix. Thermal Stability Analysis Thermal stability of raw graphite, GO and VBTAC treated GO was analyzed by TGA (Figure 6 8 ). Raw graphite did not exhibit weight loss below 600 Â°C, and it only lost about 8% of its weight at 1000 Â°C. In the case for GO and VBTAC treated GO, about 10% weight loss can be observed at 100 Â°C might be attributed to the evaporation of water molecules trapped between the GO sheets, which suggests that there are many
138 oxygen containing functional groups on the GO plane. An addition of 30% weight loss occurred between 150 Â°C and 250 Â°C, which could be caused by the removal of the labile oxy gen containing functional groups 240 242 . When the temperature increased from 300 Â°C to 1000 Â°C, GO and VBTAC treated GO lost another 10% and 25% of their weight, respectively. The 10% Weight loss of GO can be attr ibuted to the combustion of the exfoliated carbon skeleton of GO 243 . Furthermore, VBTAC treated GO lost another 15% of its weight when compar ing to GO between 300 Â°C to 1000 Â°C, which indicates that there are 15 wt. % of VBTAC entered the GO galleries and bonded with GO sheets. Particle Size Distribution of Latex Droplets PVA has been studied for stabilizing emulsions and miniemulsions in combination with other surfactants or by itself. When PVA was applied with other surfactants, the resulted latex showed better emulsion fluidity and stability, and added some performance characteristics, such as excellent tackiness for adhesives, and better freeze thaw stability 244 247 . PVA was used in our latex formulation to increase the stability . Firstly, hig h viscosity reduces the collision between particles caused by mechanical processing , so that particle size can be more precisely controlled. Because semi vigorous agitation has to be employed to suspend and disperse all nano sized droplets, and the agitation could cause droplets to collide, merge and lose the encapsulated core. From Figu re 6 9A , it is shown that the average particle size is decreasing slightly with the increase of PVA content in the latex, which agreed with previous report 244 246 . Latex with 10% and 20% PVA had average size of 25 0 and 230 nm. For latex with 0% and 5% PVA, a second peak that representing particles with size more than 4um appeared, which could be the result of particle aggregation induced by collision.
139 The particle size of latex droplets was increasing with the ad dition of more GO in the formulation, as shown in Figure 6 9B . A t GO loading of 0 %, the average particle size is about 200nm . When GO loading is increased to 0.25% and 0.5%, the particle size increased to around 290 nm. This could be caused by the encapsu lation of GO particles by the polymer droplets. When GO loading increased to 0.75 % and 1%, the average particle size increased to about 400 and 480 nm, this implies that there might be some slight GO aggregation took place, by the excessive GO that cannot be encapsulated by polymer droplets. When GO loading was increased to 2%, particle size increased to about 520 nm. This could be due to the higher level of aggregation of GO particles. Notice particle size at GO loading of 0.25 % and 0.5 % was very close, however the size increased significantly when GO loading reached 0.75%, which indicates that GO loading of 0.5 % is the most optimum loading level among all recipes. The particle size distribution is also related to the GO content in the latex, as indicat ed by Figure 6 9B . With the increasing GO loading, the particle size distribution is increased . There are three possible reasons . F irstly, the encapsulation of GO resulted in a lot of much smalle r than droplets with GO inside. Thirdly, the GO sheets that were not encapsulated could aggregate and form large clusters , which further increased the overall particle sizes of miniemulsion . Morphology of Graphene Oxide, Polymer Droplets in Latex , and M elt Film GO sheets in Figure 6 10 A are obtained after graphite oxide was sonicated and treated with VBTAC. Although the GO sheets are overlapping on top of each other, it is clearly shown that the majority of the GO is only several layers thick. The layer ed structure of graphite was disrupted by oxidation, sonication and intercalation of VBTAC,
140 as it was confirmed by XRD results. The size of GO sheets is around 200 nm and the thickness is in the order of several nanometers, which will be further reduced du ring pre sonication with monomer. AS shown in Figure 6 10 B and C , for the neat PMMA latex (0% GO), all droplets had spherical shape with about 200 nm in size, and the droplet size distribution was very uniform. This indicates that a stable latex with narr ow particle size distribution was synthesized by the default recipe (Table 6 1). For the nanocomposite of VBTAC treated GO (0.5%) encapsulated by PMMA (Figure 6 10 D and E ), some large particles with size about 300 nm were observed in both TEM and SEM imag es. In the TEM image (Figure 6 10 E ), these large particles have dark core that can be attributed to the presence of modified GO nanosheets inside the PMMA shell. In addition, the absence of un encapsulated GO sheets, suggested that GO sheets were completel y encapsulated by PMMA. Melted film of this nanocomposite was also imaged by TEM (Figure 6 10 F ). GO nanoplatelets with thickness of several nanometer can be observed, which indicating the exfoliation of GO by the polymer chain was very extensive, as the G O encapsulated is only several layers thick 248 . This is because of the VBTAC modification, which increases the interlayer spacing of GO and facilitated the intercalation of monomer into the GO galleries, and the subsequent exfoliation by the polym erized monomer. In contrary, the images of nanocomposites prepared with untreated GO (0.5%) is presented as Figure 6 8 G , H and I . From the SEM image (Figure 6 10 G ), it is clearly shown that the polymer droplets were aggregated together, with almost no sphe rical
141 should be the un exfoliated or aggregated GO sheets. From TEM image Figure 6 10 H , t Without the VBTAC treatment, monomer was not able to cover or enter the galleries of the hydrophilic GO, which prohibited the subsequent exfoliation and encapsulation of GO by the polymer. Hydrophilic GO might be stayed in the water phase during the entire polymerization process. The melted film image of this nanocomposite revealed that majority of the GO sheets were not exfoliated, with only few of exfoliated GO nanoplatel ets. This implies that the untreated GO was not well dispersed in the polymer phase and not exfoliated by the polymer. The size of the droplets and GO sheets from the images agrees well with the particle size results obtained by DLS analysis. Molecular We ight As we can see from Table 6 2, at 0% GO loading, miniemulsion polymerization yielded PMMA with Mw close to 130000. It is very close to the middle Mw range among the commercial grade PMMA (15000, 120000, 350000 and 996000, Sigma Aldrich), which demonstr ated miniemulsion polymerization is a viable method to synthesis high molecular weight polymer. With the increasing amount of GO, Mw of PMMA decreased then started to increase slightly, and the polydispersity index (Pdi) increased. The existence of GO nan oparticles in the miniemulsion could obstruct the polymer chain growth. Similar findings were observed in miniemulsion polymerization of nanoclay with monomers. Previous researcher attributed this to the irreversible reaction between the surface functional groups of the nanoclay and the growing radicals, where this reaction reduced radical concentration therefore directly affect the polymerization 249, 250 . The reason
142 caused the increase of Mw at GO loading 1 %, and 2 % might be the aggregation of excessive GO. With GO aggregated and formed larger particles, there are fewer GO particles with appropriate size and surface functionalities to interfere the growth of polymer chain. With the existence of both short and lon g polymer chain, the Pd I increases with the increase of GO loading. Tong and Roghani mamaqani assigned the increase of Pdi with increasing amount of nanoclay in the miniemulsion to the disturbance to the polymerization equilibrium, as well as the chain tra nsfer and termination of propagation radicals caused by the nanoclay 251, 252 . Stability of Latex Figure 6 11 demonstrate that the stability of latex varie s due to the different amount of GO and PVA in the formulat ion. Latex with 0.5 % GO (Figure 6 11A ) showed good stability over three month time, no visible separation or sedimentation can be observed. As comparison, the same latex without any GO (Figure 6 11G ) showed slight separation. This suggested that exfoliate d GO sheets can be effectively encapsulated by polymer droplets, which are much more stable than un encapsulated GO. With amount of GO was increased from 0.5 % to 1% and 2%, the polymer droplets seems separated from aqueous phase and settled on the bottom. This might be due to the disturbance of the latex equilibrium caused by aggregation of excessive GO nanoparticles as discussed in previous sections. From Figure 6 11 (D F) , the stabilizing effect of PVA was clearly confirmed. The increase in viscosity cau sed by addition of PVA reduces the collision between particles. Mechanical agitation could cause droplets to collide, merge and lose the encapsulated core. The large black particles in Figure 6 9 D and E , could be the aggregated polymer droplets of GO due t o collision.
143 Conclusion Stable latex es of graphene oxide (GO) encapsulate by poly methyl methacrylate (PMMA) nanocomposite was synthesized by miniemulsion polymerization. Lignin was extracted from LRB and chemically converted to quaternary ammonium lignin (QAL, a cationic surfactant). QAL and a commercial surfactant (Vinyl benzyl) trimethyl ammonium chloride (VBTAC) was used to modify the graphite oxide obtained after oxidation of graphite and pre sonication. QAL and VBTAC modification was expected to not o nly change GO surfaces from organophobic to organophilic, but also to increase the interlayer spacing between GO layers therefore initiate the intercalation of monomer with GO. Unfortunately, it was found that the QAL treated GO was not able to be disperse d in monomer phase and intercalate with GO as expected . This could be caused by the lack of hydrogen bonding, high molecular weight of lignin and its inherent complex functional groups which hindered the surface bonding and intercalation with GO. However, (Vinyl benzyl) trimethyl ammonium chloride (VBTAC) treated GO was successfully dispersed in monomer phase. Moreover, it was found that VBTAC could increase the interlayer space of GO, and GO could be exfoliated during the subsequent miniemulsion polymeriza tion. More importantly, microscopic evaluation revealed that VBTAC treated GO (0.5 % GO loading as of weight of monomer) was encapsulated in polymer droplets. T he latex is stable even after more than 3 month sitting .
144 Table 6 1 . The recipe for the miniemulsion polymerization of PMMA latex . Mixt ures Component Amount Added (g) Percentage/ total (wt.%) Percentage/ Monomer (wt.%) Oil Phase Methyl Methacrylate 6 20.00% 100.00% Hexadecane 0.5 1.67% 8.33% AIBN 0.1 0.33% 1.67% Poly Vinyl Alcohol (10% solution) 0.6 2.00% 10.00% Water Phase Triton 405 0.17 0.57% 2.83% Deionized Water 24 80.00% 400.00%
145 Table 6 2 . M olecular weight of polymerized latex of PMMA with different GO loading . Mw Mn Pdi 0% GO 1.28E+06 4.14E+05 3.106 0.5% GO 2.15E+05 4.49E+04 4.796 1% GO 2.99E+05 6.55E+04 4.567 2% GO 3.93E+05 6.14E+04 6.395
146 Fig ure 6 1 . C hemical reactions of the preparation of quaternary ammonium lignin . A) Synthesis of epoxypropyl trimethylammonium chloride (ETAC), and scheme B) Synthesis of quaternary ammonium lignin (QAL).
147 Figure 6 2 . Photo of 0.02 g GO and GO treated with 0.01 g different surfactants in water, 10 minutes after agitation was stopped . A ) neat GO, B ) GO with VBTAC, C ) GO with AMPS, D ) GO with SDBS, E ) GO with OTAB, F ) GO with MTAB . A) B) C) D) E) F)
148 F igure 6 3 . Photo of 0.02 g different surfactant treated GO in water and MMA mixture, 10 minutes after 10 minutes sonication . A ) VBTAC, B ) SDBS, C ) QAL A B C
149 Figure 6 4 . FTIR spectra of raw graphite , raw GO, VBTAC treated GO an d reduced GO . ( Note: a = 1700 cm 1 , b = 1400 cm 1 , c = 1050 cm 1 , d = 1600 cm 1 )
150 Figure 6 5 . FTIR spectra of raw graphite , raw GO, lignin, QAL and QAL treated GO .
151 Figure 6 6 . XRD spectra of raw graphite, GO, QAL treated GO, and VBTAC treated GO .
152 Figure 6 7 . XRD spectra of raw graphite, GO, VBTAC treated GO, nanocomposites with 0%, 0.5% and 2% GO .
153 Figure 6 8 . TGA thermograms of (a) raw graphite, (b) GO and (c) GO after treated with VBTAC 30.00% 40.00% 50.00% 60.00% 70.00% 80.00% 90.00% 100.00% 50 100 150 200 250 300 350 400 450 500 550 600 650 700 750 800 850 900 950 1000 Weight Loss (%) Temperature ( Â° C) (a) (b) (c)
154 Figure 6 9 . Effect of different PVA and GO content on the particle size distribution of latex of PMMA and GO prepared via miniemulsion polymerization . A ) different PVA content with constant GO content of 0.5%; and B ) different GO content with constant PVA content of 10% A) B)
155 Figure 6 10 . SEM and TEM images of GO and nanocomposites. A ) TEM of GO, obtained after sonication and VBTAC treatment; B ) SEM and C ) TEM of neat PMMA nano dro plets; D ) SEM and E ) TEM and F ) TEM of melted film of nanocomposites of VBTAC treated GO(0.5%) encapsulated by PMMA; G ) SEM and H ) TEM and I ) TEM of melted film of nanocomposites of untreated GO(0.5%) with PMMA A B C D E F G H I 100 nm 0.5 m
156 Figure 6 1 1 . Photo of latex afte r miniemulsion polymerization and set still for more than 3 months. A ) 0.5% GO, 10% PVA, B ) 1% GO, 10% PVA, C ) 2% GO, 10% PVA, D ) 0.5% GO, 0% PVA, E ) 0.5% GO, 5% PVA, F ) 0.5% GO, 20% PVA, G ) 0% GO, 10% PVA A) B) C) D) E) F) G)
157 CHAPTER 7 CHARACTERIZATION OF BIOREFINERY RESIDU ES AS SANDY SOIL AMENDMENTS 3 Introductory Remarks The use of low cost crop residues (e.g. sugarcane bagasse residue after sugar extraction) to produce second generation biofuel (e.g. ethanol) is a promising sustainable approach to partially offset current petroleum dominant energy market 3, 4, 8 . As a result, a large number of biorefinery residues will be produced in newly built biorefinery processes. Meanwhile, large quantity of bio based wastes from current bioma ss related processes (e.g. pulp and paper processes) also need better utilization instead of burning. One of the promising approaches to use bio based waste is as a low cost soil amendment. As previous literature reported, the addition of organic matters improved water holding capacity of a soil 58 . In addition, the removal of bio based waste from agricultural fields or forests to biomass processing locations instead of leaving in the crop field had adverse impact on soil quality and productivity, and led to accelerating evaporation, water and nutrient losses 59, 60 . It is essential to return part of biomass residues back to soil as approximately 41% of biomass should be kept in all major land use areas in order to prevent soil erosion according to previous studies 60, 61 . Productivity of sandy soils, characterized by low water and nutrient holding capacity, is limited by the lack of available water as well as nutrients that are required by plant growth 54 . Meanwhile, in arid area, it is imperative to use water efficiently because 3 Reprinted with permission from Wang, L., T ong, Z., Liu, G., Liu, Y. 2014. Characterization of biomass residues and their amendment effects on water sorption and nutrient leaching in sandy soil. Chemosphere, 107, 354 359.
158 of water shortage. Synthetic hydrophilic polymers have been investigated as soil amendment materials to retain water and nutrient in arid area. It has been reported that hydrophilic polymers such as polyacrylic acid and polyacrylamide gels were able to retain water up to 500 times of their weight 50 . These synthetic polymers could i mprove water retention in sandy soils 51 , therefore facilitated the growth of plants 52, 53 . However, despite the superior water retention capacity, their wide applications as soil amendments have bee n limited by a variety of factors such as non renewable, non biodegradable, low salt tolerance, possibility of releasing toxic residues and high cost 50, 54 . Bio based materials such as manures, starch, pristine p lant fiber, cellulose (including carboxymethylcellulose, CMC), and chitosan have been studied as soil amendments as well. The drawbacks for their use include low retention, high price, low salt tolerance and their competitiveness with food 54 57 . The use of biomass residues (biorefinery and pulping residues) as soil amendments not only adds an avenue to biomass processing industries but also offsets es. Johnson et al. reported that corn stove fermentation residues were capable to improve properties of severely eroded soil such as water stable aggregates and decreased bulk density without adverse impacts on crop growth 58 . Galvez et al. claimed that bioethanol by products led to N 2 O emissions and larger increa ses in soil respiration, N availability and enzymatic activity in comparison with other amendments such as sewage sludge and composts 62 . 63 reported that no crop phytotoxi city was significant after seven day application of bioethanol residues.
159 The impact of biorefinery residues and their characteristics on water and nutrient retention capacity of sandy soil remains unclear. Therefore, in this study, we aim to evaluate the efficiency of biomass residues as sandy soil amendments according to their characteristics, particle size ranges and loading levels. These two distinctive biomass residues (fermentation residues (FB) from a cellulosic bioethanol process using sugarcane ba gasse as raw materials; brown mill residues (BM) from waste stream of a papermaking process) are different in compositions (lignin dominated or cellulose dominated), particle sizes, and specific surface areas. The understanding for the correlation between characteristics of these two residues and water and nutrient retention capacity of sandy soil is very beneficial for the large scale use of bio wastes as soil amendments in the field in the future. Material and Methods Materials Fermentation sugarcane ba gasse residues (FB) were collected from waste stream of a bioethanol pilot plant. The collected residues were placed in a sieve (US standard test sieve #270) and washed with warm tap water until effluent became clear and then dried in an oven at 70 Â° C fo r 24 hours. Brown mill residues (BM) were collected from waste stream after screening in a papermaking process using slash pine as the raw material (Buckeye Technologies, Perry, FL, USA). BM residues were dried at 70 Â° C for 24 hours and then milled in a laboratory mill (Model 4, Thomas Willey, Swedesboro, NJ, USA) equipped with a screen with a mesh opening size of 2 mm. Both FB and BM were separated into three size ranges (A: 0.297 0.5 mm, B: 0.178 0.297 mm, C: 0.089 0.178 mm) by using a set of ASTM standard test sieves (#35, 50, 80 and 170) and a Octagon 200 test sieve shaker at an amplitude of 8 for 15 minutes. The
160 soil was collected from Hastings, Florida. It is classified as Ellzey fine sand series (sandy, siliceous, hyperthermic, Arenic Endoaqua lf) 253 . Boric acid, sodium hydroxide, sodium tetraborate, sulfuric acid, phenol, ethylenedia mine tetraacetic acid disodium salt dehydrate, sodium nitroprusside, ammonium chloride, antimony potassium tartrate, ammonium molybdate, ascorbic acid, ammonium persulfate, potassium phosphate monobasic were purchased from fisher scientific (USA) and used as received. Sodium hypochlorite solution (Clorox House bleach) was purchased in local grocery store (The Clorox Company, Oakland, California, USA). The nutrient solution at a concentration of 3000 ppm was prepared by dissolving anhydrous ammonium chloride and potassium phosphate monobasic in autoclaved deionized water and stored at 4 Â°C to prevent microbial growth. Soil and Leachate Samples Preparation Soil (150 grams as dry weight equivalent) and FB or BM (1, 3, 5, and 10% dry weight of soil) were man ually mixed in a beaker before loading to soil columns. Basically, nutrient solution was transferred to columns loaded with soil and FB/BM mixtures and the leachates were collected (for detailed description of soil column and the leachate collection proced ure, please refer to Appendix ). All leachate samples were then stored at 4 Â°C in the refrigerator and the pH is kept less than 2 by adding sulfuric acid (H 2 SO 4 ) before analysis . The soil FB or BM residue mixtures were temporarily stored in zip bags and us ed for water retention value (WRV) analysis.
161 Biorefinery Residues Characterization Composition a nalysis Compositions of biorefinery residues (FB and BM) were analyzed according to the National Renewable Energy Laboratory (NREL) method 201 . Monomer sugar contents after cellulose hydrolyzation were measured by High Pressure Liquid Chromatography (Agilent Technologies HPLC 1200 series, Santa Clara, CA, USA) equipped with BioRad Aminex HPX 87H column (Hercules, CA, USA). The acid soluble lignin was determined by UV Vis spectroscopy (Beckman DU800 UV/Vis Spectrophotometer, Brea, CA, USA). Both acid insoluble lignin and ash content were obtained by gravimetric analysis. Specific surface area mea surement Specific surface areas (SSAs) of FB and BM at different particle sizes were determined by N 2 sorption isotherms on a NOVA 1200 series volumetric gas adsorption instrument (Quantachrome, FL, USA). Samples were loaded in a specific glass cells and the cell was submerged in liquid nitrogen. The densities of all the samples were pre measured by a multipycnometer (Quantachrome, FL, USA) and used as a parameter for further SSA analysis. The specific surface area was calculated by multipoint nitrogen ad sorption in a relative pressure range of 0.05 0.2 P/P 0 in accordance to BET method developed by Brunauer et al. 254 . Scanning electron microscopy ( SEM ) for morphology analysis Scanning Electron Microscopy ( SEM) with a field emission gun (FEI XL 40 FEG SEM, operating voltage of 30 KV, FEI, Hillsboro, Oregon, USA) was used to examine the morphologies of both biomass residues FB and BM. All samples were coated with platinum before scanning.
162 Fourier transform i nfrared spectroscopy (FTIR) Fourier Transform Infrared Spectroscopy (FTIR) was used to investigate the sorption of nutrient ions on biorefinery residues (FB and BM). FTIR spectra were recorded on Spectrum BX spectrometer from PerkinElmer (Massachusetts, U SA) (for detailed sample preparation and testing parameters, please see Appendix . Water R etention V alue (WRV) Relative water retention values (WRVs) for both soil alone as control and soil residue mixture at different sizes (size groups A, B and C) and loading levels of FB and BM (1, 3, 5, and 10%) were measured according to a modified TAPPI Method UM256 255 . In each column, approximately 15 grams of soil or soil mixture was collected and then loaded into a stainless steel centrifuge holder equipped with a pre weighed membrane filter (pore size 0.45 Âµm) and a fine metal mesh located on its perforated bottom. The holder was located inside a 50 mL ce ntrifuge tube (detailed schematic in Appendix, Figure A 1 ). This provides a space on the bottom of the centrifuge cup to collect water for 30 min at room temperature, w here the operating speed (2600 RPM) was calculated according to Eq uation 1 . After centrifugation, each sample with membrane filter together was transferred to a pre weighed aluminum tray and the gross weight of wet sample with tray was recorded immediately. After that, it was dried at 50 Â°C for 24 hours until constant weight was reached. The gross weight of dry sample with tray was recorded as well. The WRV of each sample was calculated according to Equation 2. Eq uation 1 acceleration due to gravity)
163 Where, W = revolutions per minute, r = radius of centrifuge, g 0 = acceleration due to gravity (9.8 m/s 2 ) Equation 2 . Water retention value (WRV) (ratio of total water content to dry weight of sam ple) Where, W 1 = gross weight of wet sample, tray and membrane filter after centrifugation, W 2 = gross weight of wet sample, tray and membrane filter after drying, W 3 = weight of tray and membrane filt er Nutrient Solution Concentration Analysis Ammonium (NH 3 ) concentration in leachates was determined by the AQ 2 Discrete Automated Analyzer (AQ2, Seal Analytical, Mequon, WI, USA) according to USEPA colorimetric method 350.1 256 . Phosphorus concentration was determined by the AQ 2 Discrete Automated Analyzer (AQ2, Seal Analytical, Mequon, WI, USA) according to EPA method 365.1 257 . Statistical Analysis All experiments were carried out in triplicate. Analysis of variance (ANOVA) was used to analyze the results of water retention values and nutrient solution concentrations. General linear model with a pairwise comparison, Tukey test under a 95 d. Different letters shown in Tukey method column in both Table 7 2 and 7 3 represent significant
164 Result & Discussion Fiber Compositions Lignocellulose is generally composed of three main compon ents 15 30% of lignin, 30 45% of cellulose and 10 15% of hemicellulose, which are combined together to form a firm and compact network structure 258 . The compositions of biorefinery residues FB and BM are summarized in Table 7 1. FB had much higher percentage of lignin (50%) than original lignocellulose because most of carbohydrates were converted to ethanol through hydrolysis and fermentation processes while lignin could not be utilized through biorefi nery process and left as residues 8 . BM was exclusively made of cellulose (80%) while lignin occupied as low as 8.5% in the residue. This indicated that mos t of lignin was removed through papermaking process 259 . Specific Surface Areas (SSAs) The specific surface areas (SSAs) of FB and BM are illustrated in Fig ure . 7 1. We observed that pa rticle size ranges (A: 0.297 0.5mm; B: 0.178 0.297mm; C: 0.089 0.178mm) had no significant effect on SSAs for both FB and BM. This indicated that bulk sizes might not affect specific surface areas which were determined by both surface area and density. In addition, the residues had a large aspect ratio, which resulted in a larger deviation for the use of screen size as classification standard. Previous research also claimed that different types of fibers passed through the same test sieve might have distinc tive SSAs 260 . As shown in Figure . 7 1, the SSA of BM (76 m 2 /g of the avera ge SSA) was more than twice that of FB (32 m 2 /g of the average SSA ). The larger SSA of BM might be derived from cellulose fibers, which occupied as high as 80% in this residue. FB with a greater percentage of low aspect ratio lignin resulted in a reduced SSA, which agreed well with other researchers 261 . In fiber dominant BM
165 residues, cellulose crystallinity was greatly reduced and a large number of fibrils with larger SSA were produced during the process to remove lignin 262 . Morphologies of Biorefinery Residues The morphologies of FB and BM were examined by the Scanning Electron Microscope (SEM). As shown in Figure . 7 2 (a) and (c), in general, BM had smaller size and larg er aspect ratio than those of FB, which agreed well with the result of specific surface areas. FB was made of irregular lignin bundles with a diameter larger than ure . 7 2 (a, b)), which might facilitate water and nutrient transfer. BM was composed of uniform and platy fiber bundles with a width of several micrometers but a large aspect ratio (Fig ure . 7 2 (c, d)). Nutrient Ions Sorption In order to study the sorption of nutrient ions (a mmonium and phosphate) onto FB and BM residues, FTIR was used to characterize untreated and nutrient solution treated FB and BM samples. Many changes in peaks and vibrations were presented, which can prove the sorption of the nutrient ions onto the FB and BM. Detailed discussion and the FTIR spectra can be found in Appendix . Water Retention Values (WRVs) The addition of merely 1% FB and BM improved WRV by approximately 10 and 35% in comparison with the control soil, respectively (Fig ure . 7 3 (a)). Statis tical analysis of WRV of FB (see Appendix , Table A 1 ) showed that there was no significant difference of WRV between the control and all three fiber size groups in the addition of 1% of FB. Addition of 1% BM from all three size groups significantly improve d WRV in comparison with the soil control and there was no significant difference of WRVs among
166 three size groups. These results agreed well with the previous SSA results. It indicated that the residues with larger SSAs had higher WRVs. As shown in Figu re . 7 3 (b), the WRV of the soil was increased by approximately 55, 75, and 150% with the addition of 3, 5, and 10% of FB, respectively. The addition of 3 and 10% of BM, the WRV of sandy soil was doubled, even tripled comparing with the soil control. Stati stical analysis (Table 7 2) also indicated that the WRV of soil residue samples was significantly improved in the addition of 3, 5, and 10% of FB or BM. There was significant difference in WRV among samples with 3, 5, and 10% residue loading. The differenc e of WRV between FB and BM was attributed to their differences in surface properties and compositions. As previously mentioned, BM had larger SSA as that of FB, which resulted in more available sites for holding water. Laird and his coworkers stated that b iomass amendment with greater SSA had improved water and nutrient retention of soil and biomass mixture 263 . FB had about 5 times of lignin content of BM but less cellulose content. Cellulose was highly hydrophilic due to the existence of a large number of hydroxyl groups and carbonyl groups. The surfaces of BM residues were greatly fibrillated through pulping process 259 , which could further facilita te water absorption of BM in soil as well. In FB, cellulose fibers were removed from residue surfaces and surfaces in the presence of large amount of hydrophobic lignin possibly reduced water retention. The results agreed well with several previous studi es, that stated plant fiber residues with larger percentage of cellulose or smaller percentage of lignin had greater water sorption or water retention 58, 260, 261, 264, 265 . Nutrient R etention in Leachate The s oil nutrient retention by incorporating FB and BM was studied in terms of different fiber types, particle size ranges and residue loadings. The effectiveness was
167 evaluated by nutrient concentration in the leachate, which was presented in Fig ure . 7 4 (a d ). In general, soil mixture with FB and BM demonstrated excellent nutrient absorption capacity for both ammonium and phosphate ions. The addition of 1% FB with the particle size range of 0.297 0.5mm in the soil could reduce ammonium and phosphate concentra tion in the leachate to about 40% and 60% of the soil control (Fig ure . 7 4 (a)), respectively. While the addition of 1% BM with the same particle size range in the soil reduced ammonium and phosphate concentration to approximately 15% and 30% of the contro the nutrient retention for both FB and BM ( Appendix , Table A 1, Fig ure . A 4 (a and c)), which was similar as the WRV study. This can be explained by the identical SSAs in three different siz e ranges. Kithome, Li and their coworkers claimed that one of the dominating factors of ionic sorption on to coir and activated carbon was the SSA 266, 267 . The residue loadings significantly affected the nutrient retention for both ammonium and phosphate ions (Table 7 2, Fig. 7 4 (b and d)). As shown in Fig ure . 7 6b, in the addition of 3, 5, and 10% FB or BM in the soil, the ammonium concentration in the leachate were reduced to about 3, 0.9, and 0.7% for FB and 2 .5, 2, and 1.5% for BM as compared with that of the soil control respectively. The phosphate concentration changes in the leachate followed the similar trend (Fig ure. 4 d)). When the loading levels of two residues were higher than 5%, nutrient concentrati on in the leachate was extremely low. Conclusions Bio based wastes, FB and BM were able to significantly improve water and nutrient retention of sandy soil. In 1% and 10% loading levels, FB and BM was able to improve WRV by approximately 10 and 35% to 150 % and 300%, while reduce 50% to
168 99% of ammonium and phosphate concentration in the leachate compare to the soil control, respectively. The ability of FB and BM on water and nutrient retention was correlated with their characteristic properties especially s pecific surface areas and surface functional groups. The results of this study will be beneficial to biorefinery, pulping and agricultural industries.
169 Table 7 1 . Compositions of BM and FB residues Lignin % Cellulose % Hemicellulose% Ash% BM 8.5Â±2.9 80.4Â±2.4 10.4Â±0.6 0.8Â±0.0 FB 49.8Â±1.7 40.1Â±0.4 9.5Â±1.5 0.7Â±0.2
170 Table 7 2 . Effects of fiber loadings on the relative WRV%, ammonium retention% and phosphate retention% of residue fiber mixtures and corresponding statistical analysis Sample Relative WRV % Tukey Method 95% Relative NH4 Retention % Tukey Method 95% Relative P Retention % Tukey Method 95% soil only 100 A 100 A 100 A FB 1% A 110.07Â±8.57 AB 37.60Â±3.18 B 46.48Â±2.31 B FB 3% A 157.90Â±5.93 C 2.56Â±0.29 C 2.91Â±0.94 C FB 5% A 182. 76Â±9.62 D 1.04Â±0.18 C 0.32Â±0.09 C FB 10% A 239.28Â±8.68 E 0.70Â±0.08 C 0.30Â±0.15 C BM 1% A 133.86Â±5.18 BC 15.16Â±0.84 D 22.43Â±2.08 D BM 3% A 200.84Â±4.31 D F 2.08Â±0.58 C 0.41Â±0.10 C BM 5% A 220.70Â±18.44 DE 1.63Â±0.25 C 0.40Â±0.01 C BM 10% A 309.46Â±3.08 G 1.24Â±0.37 C 0.37Â±0.03 C
171 Figure 7 1 . BET specific surface area (SS A) analysis of FB and BM . T hree size classes: A: 0.297 0.5 mm B: 0.178 0.297 mm C: 0.089 0.178 mm.
172 Figure 7 2 . Scanning Electron Microscopy (SEM) images of biorefinery residue, FB and BM. A) and B) FB with 100X and 1000X magnification respectively , C) and D) BM with 100X and 1000X magnification respectively) (A) (B) D) (C)
173 Figure 7 3 . Water retention tests results. A) Effects of fibe r sizes on the relative water retention value (WRV) of FB and BM soil mixture in the presence of 1% residue, with soil only control as 100% and three size classes: A: 0.297 0.5 mm B: 0.178 0.297 mm C: 0.089 0.178 mm, B) Effects of different fiber loa dings on the relative water retention value (WRV) of the FB and BM soil mixtures, with soil only control as 100% and one size class: A: 0.297 0.5 mm (based on 1, 3, 5, and 10% loadings) A) B)
174 Figure 7 4 . Nutrient retention tests results . A) Effects of different fiber sizes on the relative ammonium ion concentration in the leachate of FB and BM soil mixture in the presence of 1% residue and with th ree size classes: A) 0.297 0.5 mm B: 0.178 0.297 mm C: 0.089 0.178 mm, B) Effects of different fiber loadings on the relative ammonium ion concentration in the leachate of FB and BM soil mixture with one size c lass: A: 0.297 0.5 mm ( based on1, 3, 5, and 10% residue loadings) , C) Effects of different fiber sizes on the relative phosphorus concentration in the leachate from FB and BM soil mixture in the presence of 1% residue, with three size classes: A: 0.297 0.5 mm B: 0.178 0.297 mm C: 0.089 0.178 mm; D) Effects of different fiber loadings on the logarithmic relative phosphorus concentration in the leachate from FB and BM soil mixture, with one size class: A: 0.297 0.5 mm (based on 1, 3, 5, and 10% residue loadings). All results was calculated based on 100% for soil control sampl e A) B) C) D)
175 CHAPTER 8 OVERALL CONCLUSION The overall goal of this dissertation was to produce polymer biocomposites incorporated with lignocellulosic residues from bioethanol proces s (LRB) or the lignin extracted from LRB and its hybrids with inorganic base (graphene oxide, GO), as the alternatives for conventional petroleum based polymer products. The synthesized biocomposites are expected to have competitive physical or thermal pro perties with their petroleum based counterparts but with low cost and sustainability. In order to achieve this overall goal, both top down ad bottom up approaches are employed to tackle two main challenges for the preparation of bionanocomposites: 1) the c ompatibility issue between hydrophilic LRB and hydrophobic polymer matrix; 2) large fiber bundles and broad particle size distribution of biorefinery residues. In C hapter 4, the top down approach was utilized to prepare biocomposites. Three types of LRBS f rom different biorefinery steps were mixed with poly lactic acid (PLA) resin in the addition of compatibilizer Desmodur VKS20 (DVKS) (a chemical compatibilizer) in a twin extruder, which provides simultaneous mechanical size reduction, homogenization, and mixing. The results indicated that in the presence of 2 % DVKS, PLA composite with different LRBs exhibited as high as 98.94 % tensile strength and 93.91 % flexural strength of pristine PLA. In addition, it was found that the LRB with the highest cellulose content had the best physical properties among all samples . The results also demonstrated that melt mixing by extrusion and the application of the crosslinker DVKS are effective methods to prepare lignocellulosic biocomposites.
176 In C hapter 5, we further d ecreased particle sizes of LRB to further improve the compatibility between lignocellulosic residues and polymer matrix. LRB was first subjected disk refining and ultrasonication for size reduction and homogenization to size range from tens of nanometer to several micrometers. The treated LRB was then blended with poly vinyl alcohol (PVA) solution through film casting process. It was found that both tensile properties and thermal stability were improved with the incorporation of the size reduced LRB. The st udy of C hapter 5 indicated that mechanical size reduction / homogenization of LRB could be a vital step in preparing biocomposites reinforced with lignocellulosic residues. In C hapter 6, the bottom up approach was evaluated by conducting bionanocomposite se lf assembly of quaternary ammonium lignin (QAL) modified graphene oxide (GO) encapsulated by poly methyl methacrylate (PMMA) via miniemulsion polymerization. QAL was chemically derived from lignin which was extracted from LRB. A commercial surfactant (Viny l benzyl) trimethyl ammonium chloride (VBTAC) was used as comparison. Modification of these two surfactants was expected to increase the organophilicity, and the interlayer spacing of GO. It was shown that only VBTAC treated GO was successfully dispersed i n monomer phase. Moreover, it was found that VBTAC could increase the interlayer space of GO, and GO could be exfoliated during the subsequent miniemulsion polymerization. More importantly, microscopic evaluation revealed that VBTAC treated GO (0.5 % GO lo ading as of weight of monomer) was encapsulated in p olymer droplets, and t he latex was stable after more than 3 month. But the further synthesis of GO lignin hybrid has not been successfully obtained due to high molecular weight of lignin which prohibited its entry to
177 the interlayer space of GO and its inherent complex functional groups which hindered the surface bonding and intercalation with GO. This work will be further explored in future study in our group.
178 APPENDIX SUPPORTING INFORMATION FOR CHAPTE R 7 Soil and l eachate s amples p reparation . Soil column is composed of a cylinder shaped top and a funnel shaped bottom finish. The cylindrical top has an inner diameter of 40 mm and a height of 165 mm. A metal mesh with a diameter of 40 mm is placed at the end of cylindrical top and a detachable plug is attached at the smaller end of the funnel shaped bottom. A membrane filter (GE* Magna* Nylon Membrane filter, pore size 10 Âµm) is placed on the metal mesh and replaced for each sample to minimize soil loss. During the experiment, 200 mL of autoclaved deionized (DI) water was added into columns with soil mixture together and then stirred for uniform distribution. The columns were at first sealed by applying the plugs and filled up by autoclaved DI water and f inally sealed on the top by parafilm. The columns were left stand for 24 hours at room temperature to remove soluble contaminants. After that, the plugs were removed to initiate a 24 hour draining process while the columns were kept sealed from the top. A fter that, 50 mL nutrient solution (3000 ppm of ammonium chloride and potassium phosphate monobasic) was transferred to each column and the leachates were immediately collected from the bottom of columns. Each leachate sample was filtered by a membrane fi lter with a pore size of 0.45 Âµm (Fisher Sci, USA) and then transferred to a sterilized 50 mL centrifuge tube. Fourier transform infrared spectroscopy (FTIR) . Fourier Transform Infrared Spectroscopy (FTIR) was used to investigate the sorption of nutrient i ons on biorefinery residues (FB and BM). At first, 0.5 g FB or BM was mixed with 50 mL of nutrient solution and placed in an incubator/shaker (180 rpm) at room temperature for 24 hours. Each treated sample was then filtrated by a membrane filter with a por e size of 0.45 Âµm to
179 remove liquid part and dried at 50 Â°C for 24 hours. After that, 2 mg of each sample (untreated and treated) was mixed with 160 mg potassium bromide to prepare a pellet form ready for FTIR measurement. FTIR spectra were recorded on Spec trum B X spectrometer from PerkinElmer (Massachusetts, USA). FTIR took 32 scans for each Nutrient ions sorption . The FTIR spectra for untreated FB and BM are very identical due to the similar chemical composit ions of FB and BM. The changes in absorbance caused by ammonium sorption can be observed around 1500 cm 1 (peak a and e in Appendix , Figure. A 2 (a and b), respectively). This peak is attributed to the stretching vibration of the asymmetric and symmetric C OO of deprotonated carboxylate functional groups of cellulose , which might be initiated by the electrostatic attraction between ammonium ions and carboxylate anion 268 . Ammonium sorption might also cause the change in absorbance between 1750 cm 1 and 1650 cm 1 (peak d in Appendix , Figure. A 2 (b)) which might ind uced by stretching vibration of C O bonds due to non ionic carboxyl groups ( COOH, COOCH3) and may be assigned to hydrogen bonding between carboxylic acids or their esters and ammonium ions 268 . Phosphate sorption may also cause several changes in FTIR spectra, for instance, between 1300 cm 1 and 1200 cm 1 (peak b and f in Appendix, Figure. A 2 (a and b), respectively) and the peak around 1150c m 1 (peak c and g in Appendix, Figure. A 2 (a and b), respectively). This peak is attributed to the bending of the out of plane aliphatic C H groups and P O C stretching, res pectively 269 .
180 Table A 1 . Effects of fiber sizes on the relative WRV%, ammonium retention% and phosphate retention% of residue fiber mixtures and corresponding statistical analysis Sample Rel ative WRV % Tukey Method 95% Relative NH4 Retention % Tukey Method 95% Relative P Retention % Tukey Method 95% Soil Only Control 100 A 100 A 100 A FB 1% A 110.07Â±8.57 A 40.94Â±4.34 B 57.85Â±2.63 B FB 1% B 112.89Â±4.09 A 47.37Â±2.53 B 64.79Â±2 .79 B FB 1% C 113.61Â±8.10 A 43.13Â±6.92 B 57.79Â±4.78 B BM 1% A 133.86Â±5.18 B 15.16Â±0.84 C 29.09Â±3.92 C BM 1% B 132.60Â±3.47 B 14.42Â±0.98 C 31.79Â±1.09 C BM 1% C 133.12Â±8.06 B 20.41Â±1.08 C 33.73Â±6.24 C
181 Figure A 1 . Schematic diagram of the modified centrifuge tube to determine water retention value (WRV).
182 Figure A 2 . Fourier Transform Infrared Spectroscopy (FTIR) spectra of nutrient solution treated biorefinery residues, A) FB , B) BM . A) c 1150 a 1500 b 1300 1200 B) g 1150 e 1500 d. 1750 1650 f 1300 1200
183 LIST OF REFERENCE 1. Jairam, S.; Tong, Z.; Wang, L.; Welt, B. Acs Sustainable Chemistry & Engineering 2013, 1, (12), 1630 1637. 2. Dincer , I. Renewable & Sustainable Energy Reviews 2000, 4, (2), 157 175. 3. Farrell, A. E.; Plevin, R. J.; Turner, B. T.; Jones, A. D.; O'Hare, M.; Kammen, D. M. Science 2006, 311, (5760). 4. Balat, M.; Balat, H.; Oz, C. Progress in Energy and Combustion Scien ce 2008, 34, (5), 551 573. 5. Bledzki, A. K.; Gassan, J. Progress in Polymer Science 1999, 24, (2), 221 274. 6. Hoffert, M. I.; Caldeira, K.; Benford, G.; Criswell, D. R.; Green, C.; Herzog, H.; Jain, A. K.; Kheshgi, H. S.; Lackner, K. S.; Lewis, J. S.; Lightfoot, H. D.; Manheimer, W.; Mankins, J. C.; Mauel, M. E.; Perkins, L. J.; Schlesinger, M. E.; Volk, T.; Wigley, T. M. L. Science 2002, 298, (5595). 7. Oak Ridge National Laboratory(ORNL), Biomass as feedstock for a bioenergy and bioproducts industry: the feasibility of a billion ton annual supply. 2005. 8. Geddes, C. C.; Nieves, I. U.; Ingram, L. O. Current Opinion in Biotechnology 2011, 22, (3), 312 319. 9. Boudet, A. M.; Goffner, D. P.; GrimaPettenati, J. Comptes Rendus De L Academie Des Sciences Serie Iii Sciences De La Vie Life Sciences 1996, 319, (4), 317 331. 10. Cazacu, G.; Pascu, M. C.; Profire, L.; Kowarski, A. I.; Mihaes, M.; Vasile, C. Industrial Crops and Products 2004, 20, (2), 261 273. 11. Aguilera, R. F., How Long Will Petroleum Resou rces Last? In EU Energy Policy (blog) , 2008. 12. Clark, J., Introduction to Chemicals From Biomass. Deswarte, F., Ed. Wiley: 2008; p 170. 13. Wang, L.; Tong, Z.; Ingram, L. O.; Cheng, Q.; Matthews, S. Journal of Polymers and the Environment 2013, 21, (3) , 780 788. 14. Lam, E.; Shine, J.; Da Silva, J.; Lawton, M.; Bonos, S.; Calvino, M.; Carrer, H.; Silva Filho, M. C.; Glynn, N.; Helsel, Z.; Ma, J.; Richard, E.; Souza, G. M.; Ming, R. Global Change Biology Bioenergy 2009, 1, (3), 251 255. 15. Department of Energy(DOE), Improving Hybrid Poplars as a Renewable Source of Ethanol Fuel. 2010.
184 16. Asghari, A.; Bothast, R. J.; Doran, J. B.; Ingram, L. O. Journal of Industrial Microbiology 1996, 16, (1), 42 47. 17. Geddes, C. C.; Peterson, J. J.; Mullinnix, M. T .; Svoronos, S. A.; Shanmugam, K. T.; Ingram, L. O. Bioresource Technology 2010, 101, (23), 9128 9136. 18. Geddes, C. C.; Peterson, J. J.; Roslander, C.; Zacchi, G.; Mullinnix, M. T.; Shanmugam, K. T.; Ingram, L. O. Bioresource Technology 2010, 101, (6), 1851 1857. 19. Geddes, C. C.; Mullinnix, M. T.; Nieves, I. U.; Peterson, J. J.; Hoffman, R. W.; York, S. W.; Yomano, L. P.; Miller, E. N.; Shanmugam, K. T.; Ingram, L. O. Bioresource Technology 2011, 102, (3), 2702 2711. 20. Patel, M. A.; Ou, M. S.; Ingr am, L. O.; Shanmugam, K. T. Biotechnology Progress 2005, 21, (5), 1453 1460. 21. (RFA), R. F. A., Ethanol Industry Outlook. 2009. 22. Balat, M. Energy Conversion and Management 2011, 52, (2). 23. Kim, H.; Ralph, J.; Akiyama, T. BioEng Res 2008, 1, (1), 56 66. 24. Tejado, A.; Pena, C.; Labidi, J.; Echeverria, J. M.; Mondragon, I. Bioresource Technology 2007, 98, (8), 1655 1663. 25. Gosselink, R. J. A.; de Jong, E.; Guran, B.; Abacherli, A. Industrial Crops and Products 2004, 20, (2), 121 129. 26. Le Di gabel, F.; Averous, L. Carbohydrate Polymers 2006, 66, (4). 27. Areskogh, D.; Henriksson, G. Process Biochemistry 2011, 46, (5), 1071 1075. 28. Areskogh, D.; Li, J.; Gellerstedt, G.; Henriksson, G. Biomacromolecules 2010, 11, (4), 904 910. 29. Belgacem, M. N.; Blayo, A.; Gandini, A. Industrial Crops and Products 2003, 18, (2), 145 153. 30. Holladay, J.; Bozell, J.; White, J.; Johnson, D., Top value added chemicals from biomass volume II results of screening forpotential candidates from biorefinery ligni n Pacific Northwest National Laboratory, Oak Ridge, TN, USA: 2007. 31. Han, C., Dust Control on Unpaved Roads. Wisconsin Transportation Information Center: 1992.
185 32. Kadla, J. F.; Kubo, S.; Venditti, R. A.; Gilbert, R. D.; Compere, A. L.; Griffith, W. Ca rbon 2002, 40, (15), 2913 2920. 33. Carrott, P. J. M.; Suhas; Carrott, M. M. L. R.; Guerrero, C. I.; Delgado, L. A. Journal of Analytical and Applied Pyrolysis 2008, 82, (2), 264 271. 34. Zhang, Y. H. P. Journal of Industrial Microbiology & Biotechnology 2008, 35, (5), 367 375. 35. Zeng, J.; Tong, Z.; Wang, L.; Zhu, J. Y.; Ingram, L. Bioresource Technology 2014, 154, 274 281. 36. Ragauskas, A., Chemical Composition of Wood. Institute of Paper Science and Technology, Georgia Institute of Technology. 37. Nevell TP, Z. S., Cellulose chemistry and its applications. Wiley: New York, 1985. 38. Meier, H.; Reid, J. S. G. Encyclopedia of plant physiology. New series. Volume 13 A. Plant carbohydrates. I. Intracellular carbohydrates [Loewus, F.A.; Tanner, W. (Edi tors)] 1982 , 418 471. 39. Reid, J. S. G. Advances in Botanical Research Incorporating Advances in Plant Pathology 1985, 11, 125 155. 40. Scheller, H. V.; Ulvskov, P. Annual Review of Plant Biology, Vol 61 2010, 61, 263 289. 41. Keogh, G. F.; Cooper, G. J. S.; Mulvey, T. B.; McArdle, B. H.; Coles, G. D.; Monro, J. A.; Poppitt, S. D. American Journal of Clinical Nutrition 2003, 78, (4), 711 718. 42. Liu, L. S.; Fishman, M. L.; Hicks, K. B.; Liu, C. K. J. Agric. Food Chem. 2005, 53, (23), 9017 9022. 43. Grau pner, N.; Herrmann, A. S.; Mussig, J. Compos. Pt. A Appl. Sci. Manuf. 2009, 40, (6 7), 810 821. 44. Chen, F.; Liu, L. S.; Cooke, P. H.; Hicks, K. B.; Zhang, J. W. Industrial & Engineering Chemistry Research 2008, 47, (22), 8667 8675. 45. Huda, M. S.; Drz al, L. T.; Misra, M.; Mohanty, A. K.; Williams, K.; Mielewski, D. F. Industrial & Engineering Chemistry Research 2005, 44, (15), 5593 5601. 46. Ryntz, R. A. JCT Res. 2006, 3, (1), 3 14. 47. John, M. J.; Thomas, S. Carbohydr. Polym. 2008, 71, (3), 343 364 . 48. Pilla, S.; Gong, S.; O'Neill, E.; Rowell, R. M.; Krzysik, A. M. Polymer Engineering and Science 2008, 48, (3), 578 587.
186 49. Liu, L. S.; Finkenstadt, V. L.; Liu, C. K.; Coffin, D. R.; Willett, J. L.; Fishman, M. L.; Hicks, K. B. Journal of Biobased M aterials and Bioenergy 2007, 1, (3), 323 330. 50. Holliman, P. J.; Clark, J. A.; Williamson, J. C.; Jones, D. L. Science of the Total Environment 2005, 336, (1 3), 13 24. 51. Aldarby, A. M.; Elshafei, Y. Z.; Shalaby, A. A.; Mursi, M. Arid Soil Research a nd Rehabilitation 1992, 6, (2). 52. Flannery, R. L.; Busscher, W. J. Communications in Soil Science and Plant Analysis 1982, 13, (2). 53. Johnson, M. S. Journal of the Science of Food and Agriculture 1984, 35, (11). 54. Andry, H.; Yamamoto, T.; Irie, T.; Moritani, S.; Inoue, M.; Fujiyama, H. J. Hydrol. 2009, 373, (1 2), 177 183. 55. He, Z. L.; Calvert, D. V.; Alva, A. K.; Li, Y. C.; Banks, D. J. Plant and Soil 2002, 247, (2), 253 260. 56. Radwan, M. A.; Farrag, S. A. A.; Abu Elamayem, M. M.; Ahmed, N. S . Biology and Fertility of Soils 2012, 48, (4), 463 468. 57. Mamilov, A. S.; Byzov, B. A.; Zvyagintsev, D. G.; Dilly, O. M. Applied Soil Ecology 2001, 16, (2), 131 139. 58. Johnson, J. M. F.; Sharratt, B. S.; Reicosky, D. C.; Lindstrom, M. Soil Science S ociety of America Journal 2007, 71, (4), 1151 1159. 59. Blanco Canqui, H.; Lal, R. Critical Reviews in Plant Sciences 2009, 28, (3). 60. Lindstrom, M. J. Agriculture Ecosystems & Environment 1986, 16, (2). 61. Holt, R. F. Nutrient cycling in agricultura l ecosystems 1983, 23, 428 438. 62. Galvez, A.; Sinicco, T.; Cayuela, M. L.; Mingorance, M. D.; Fornasier, F.; Mondini, C. Agriculture Ecosystems & Environment 2012, 160, 3 14. 63. Gell, K.; van Groenigen, J. W.; Cayuela, M. L. J. Hazard. Mater. 2011, 18 6, (2 3), 2017 2025. 64. Lunt, J. Polym. Degrad. Stabil. 1998, 59, (1 3), 145 152. 65. Mochizuki, M.; Hirami, M. Polymers for Advanced Technologies 1997, 8, (4), 203 209.
187 66. Enomoto, K. K., JP), Ajioka, Masanobu (Kanagawa, JP),; Yamaguchi, A. K., JP) P olyhydroxycarboxylic acid and preparation process thereof. 5310865 1994. 67. Tsuji, H. Macromolecular Bioscience 2005, 5, (7), 569 597. 68. Pickering, K. L.; Sawpan, M. A.; Jayaraman, J.; Fernyhough, A. Composites Part a Applied Science and Manufacturi ng 2011, 42, (9), 1148 1156. 69. Auras, R.; Harte, B.; Selke, S. Macromolecular Bioscience 2004, 4, (9), 835 864. 70. Shen, L., present and future development in plastic from biomass. Wiley InterScience: 2010. 71. Vink, E. T. H.; Rabago, K. R.; Glassne r, D. A.; Gruber, P. R. Polymer Degradation and Stability 2003, 80, (3), 403 419. 72. Shen, J.; Hu, Y.; Shi, M.; Lu, X.; Qin, C.; Li, C.; Ye, M. Chemistry of Materials 2009, 21, (15), 3514 3520. 73. Hassan, C. M.; Peppas, N. A. Biopolymers/Pva Hydrogels/ Anionic Polymerisation Nanocomposites 2000, 153, 37 65. 74. C.A.Finch, Poly(vinyl alcohol): properties and applications . Wiley: New York, 1987. 75. Hallensleben, M. L., Polyvinyl Compounds, Others. In Ullmann's Encyclopedia of Industrial Chemistry , Wiley : 2000. 76. Cheng, Q. Z.; Wang, S. Q.; Rials, T. G. Composites Part a Applied Science and Manufacturing 2009, 40, (2), 218 224. 77. Lee, S. Y.; Mohan, D. J.; Kang, I. A.; Doh, G. H.; Lee, S.; Han, S. O. Fibers and Polymers 2009, 10, (1). 78. Peresin, M. S.; Habibi, Y.; Zoppe, J. O.; Pawlak, J. J.; Rojas, O. J. Biomacromolecules 2010, 11, (3). 79. http://www.dupont.com/content/dam/assets/products and services/packaging materials solutions/assets/biomax_strong_120.pdf 80. Potts, J. E.; Clendinn.Ra; Ackart, W. B.; Neigisch, W. D. Abstracts of Papers of the American Chemical Socie ty 1972, 164, (AUG S), 4 &. 81. Tokiwa, Y.; Suzuki, T. Nature 1977, 270, (5632), 76 78.
188 82. D.Bloor, M. C. F., R.J.Brook, S.Mahajan, The Encyclopedia of Advanced Materials . Pergamon: 1994. 83. Fujimaki, T. Polymer Degradation and Stability 1998, 59, (1 3 ), 209 214. 84. M. Nishioka, T. T., Y. Wanajyo, H. Oonami, T. Horiuchi, In Biodegradable Plastics and Polymers , Elsevier: Amsterdam, 1994; p 584. 85. E.Takiyama, T. F., In Biodegradable Plastics and Polymers , Elsevier: Amsterdam, 1994; p 150. 86. Parede s, N.; Rodriguez Galan, A.; Puiggali, J. Journal of Polymer Science Part a Polymer Chemistry 1998, 36, (8), 1271 1282. 87. Huang, S. J.; Ho, L. H. Abstracts of Papers of the American Chemical Society 1992, 204, 214 POLY. 88. Saotome, Y.; Tashiro, M.; Miy azawa, T.; Endo, T. Chemistry Letters 1991 , (1), 153 154. 89. Saotome, Y.; Miyazawa, T.; Endo, T. Chemistry Letters 1991 , (1), 21 24. 90. Bledzki, A. K.; Gassan, J. Angewandte Makromolekulare Chemie 1996, 236, 129 138. 91. Pan, P. J.; Zhu, B.; Kai, W. H .; Serizawa, S.; Iji, M.; Inoue, Y. Journal of Applied Polymer Science 2007, 105, (3), 1511 1520. 92. Lee, S. H.; Wang, S. Q. Composites Part a Applied Science and Manufacturing 2006, 37, (1), 80 91. 93. Masirek, R.; Kulinski, Z.; Chionna, D.; Piorkowska , E.; Pracella, M. Journal of Applied Polymer Science 2007, 105, (1), 255 268. 94. Karmaker, A. C.; Youngquist, J. A. Journal of Applied Polymer Science 1996, 62, (8), 1147 1151. 95. Moloney, T. M., International Encyclopedia of Composites . VCH Publisher s: New York, 1995. 96. John, M. J.; Anandjiwala, R. D. Polymer Composites 2008, 29, (2), 187 207. 97. Mitra, B. C.; Basak, R. K.; Sarkar, M. Journal of Applied Polymer Science 1998, 67, (6), 1093 1100. 98. Stamboulis, A.; Baillie, C. A.; Garkhail, S. K.; van Melick, H. G. H.; Peijs, T. Applied Composite Materials 2000, 7, (5 6), 273 294.
189 99. Kessler, R. W.; Becker, U.; Kohler, R.; Goth, B. Biomass & Bioenergy 1998, 14, (3), 237 249. 100. Hill, C. A. S.; Khalil, H. Journal of Applied Polymer Science 2000, 78, (9), 1685 1697. 101. Sreekala, M. S.; Kumaran, M. G.; Joseph, S.; Jacob, M.; Thomas, S. Applied Composite Materials 2000, 7, (5 6), 295 329. 102. Saini, G.; Narula, A. K.; Choudhary, V.; Bhardwaj, R. Journal of Reinforced Plastics and Composites 2010, 29, (5), 731 740. 103. Vilay, V.; Mariatti, M.; Taib, R. M.; Todo, M. Composites Science and Technology 2008, 68, (3 4), 631 638. 104. Oriakhi, C. Chemistry in Britain 1998, 34, (11), 59 62. 105. Lu o, J. J.; Daniel, I. M. Composites Science and Technology 2003, 63, (11), 1607 1616. 106. Usuki, A.; Kawasumi, M.; Kojima, Y.; Okada, A.; Kurauchi, T.; Kamigaito, O. Journal of Materials Research 1993, 8, (5), 1174 1178. 107. Moniruzzaman, M.; Winey, K. I. Macromolecules 2006, 39, (16). 108. Huang, J. C. Advances in Polymer Technology 2002, 21, (4). 109. Tong, Z. H.; Deng, Y. L. Polymer 2007, 48, (15), 4337 4343. 110. Il Park, C.; Park, O. O.; Lim, J. G.; Kim, H. J. Polymer 2001, 42, (17), 7465 7475. 111. Alexandre, M.; Dubois, P. Materials Science & Engineering R Reports 2000, 28, (1 2), 1 63. 112. Carrado, K. A. Applied Clay Science 2000, 17, (1 2), 1 23. 113. Bechthold, N.; Landfester, K. Macromolecules 2000, 33, (13), 4682 4689. 114. Bechthold, N.; Tiarks, F.; Willert, M.; Landfester, K.; Antonietti, M. Macromolecular Symposia 2000, 151, 549 555. 115. Pranger, L.; Tannenbaum, R. Macromolecules 2008, 41, (22), 8682 8687. 116. Kaiser, M. R.; Anuar, H. B.; Samat, N. B.; Razak, S. B. A. Iranian Pol ymer Journal 2013, 22, (2), 123 131.
190 117. Wang, R. P.; Schuman, T.; Vuppalapati, R. R.; Chandrashekhara, K. Green Chemistry 2014, 16, (4), 1871 1882. 118. Novoselov, K. S.; Jiang, D.; Schedin, F.; Booth, T. J.; Khotkevich, V. V.; Morozov, S. V.; Geim, A. K. Proceedings of the National Academy of Sciences of the United States of America 2005, 102, (30). 119. Kim, H.; Abdala, A. A.; Macosko, C. W. Macromolecules 2010, 43, (16), 6515 6530. 120. Lee, C.; Wei, X.; Kysar, J. W.; Hone, J. Science 2008, 321, (58 87). 121. Balandin, A. A.; Ghosh, S.; Bao, W.; Calizo, I.; Teweldebrhan, D.; Miao, F.; Lau, C. N. Nano Letters 2008, 8, (3). 122. Du, X.; Skachko, I.; Barker, A.; Andrei, E. Y. Nature Nanotechnology 2008, 3, (8). 123. Bunch, J. S.; Verbridge, S. S.; Alde n, J. S.; van der Zande, A. M.; Parpia, J. M.; Craighead, H. G.; McEuen, P. L. Nano Letters 2008, 8, (8). 124. Brodie, B. C. Philosophical Transactions of the Royal Society of London 1859, 149, 249 259. 125. Hummers, W. S.; Offeman, R. E. Journal of the American Chemical Society 1958, 80, (6). 126. Novoselov, K. S.; Geim, A. K.; Morozov, S. V.; Jiang, D.; Zhang, Y.; Dubonos, S. V.; Grigorieva, I. V.; Firsov, A. A. Science 2004, 306, (5696). 127. Wang, X.; You, H.; Liu, F.; Li, M.; Wan, L.; Li, S.; Li, Q .; Xu, Y.; Tian, R.; Yu, Z.; Xiang, D.; Cheng, J. Chemical Vapor Deposition 2009, 15, (1 3). 128. He, H. Y.; Klinowski, J.; Forster, M.; Lerf, A. Chemical Physics Letters 1998, 287, (1 2). 129. He, H. K.; Gao, C. Chemistry of Materials 2010, 22, (17), 50 54 5064. 130. Kuilla, T.; Bhadra, S.; Yao, D.; Kim, N. H.; Bose, S.; Lee, J. H. Progress in Polymer Science 2010, 35, (11). 131. Park, S.; An, J.; Piner, R. D.; Jung, I.; Yang, D.; Velamakanni, A.; Nguyen, S. T.; Ruoff, R. S. Chemistry of Materials 2008, 20, (21), 6592 6594. 132. Worsley, K. A.; Ramesh, P.; Mandal, S. K.; Niyogi, S.; Itkis, M. E.; Haddon, R. C. Chemical Physics Letters 2007, 445, (1 3).
191 133. Niyogi, S.; Bekyarova, E.; Itkis, M. E.; McWilliams, J. L.; Hamon, M. A.; Haddon, R. C. Journal of the American Chemical Society 2006, 128, (24), 7720 7721. 134. Zhang, D. D.; Zu, S. Z.; Han, B. H. Carbon 2009, 47, (13), 2993 3000. 135. Stankovich, S.; Piner, R. D.; Chen, X. Q.; Wu, N. Q.; Nguyen, S. T.; Ruoff, R. S. Journal of Materials Chemistry 2006, 16, (2). 136. Hao, R.; Qian, W.; Zhang, L.; Hou, Y. Chemical Communications 2008 , (48), 6576 6578. 137. Lomeda, J. R.; Doyle, C. D.; Kosynkin, D. V.; Hwang, W. F.; Tour, J. M. Journal of the American Chemical Society 2008, 130, (48). 138. Kim, H.; Macosko, C. W. Macromolecules 2008, 41, (9). 139. Steurer, P.; Wissert, R.; Thomann, R.; Muelhaupt, R. Macromolecular Rapid Communications 2009, 30, (4 5). 140. Stankovich, S.; Dikin, D. A.; Dommett, G. H. B.; Kohlhaas, K. M.; Zimney, E. J.; Stach, E. A .; Piner, R. D.; Nguyen, S. T.; Ruoff, R. S. Nature 2006, 442, (7100). 141. Chung, D. D. L. Journal of Materials Science 2004, 39, (8). 142. Jang, J. Y.; Kim, M. S.; Jeong, H. M.; Shin, C. M. Composites Science and Technology 2009, 69, (2). 143. Cao, L. J.; Liu, X. Q.; Na, H. N.; Wu, Y. G.; Zheng, W. G.; Zhu, J. Journal of Materials Chemistry A 2013, 1, (16), 5081 5088. 144. Cao, Y. W.; Feng, J. C.; Wu, P. Y. Carbon 2010, 48, (13), 3834 3839. 145. Kim, H.; Macosko, C. W. Polymer 2009, 50, (15). 146. Z hang, H. B.; Zheng, W. G.; Yan, Q.; Yang, Y.; Wang, J. W.; Lu, Z. H.; Ji, G. Y.; Yu, Z. Z. Polymer 2010, 51, (5), 1191 1196. 147. Mahmoud, W. E. European Polymer Journal 2011, 47, (8), 1534 1540. 148. Li, M. L.; Jeong, Y. G. Composites Part a Applied Sci ence and Manufacturing 2011, 42, (5), 560 566. 149. Wissert, R.; Steurer, P.; Schopp, S.; Thomann, R.; Mulhaupt, R. Macromolecular Materials and Engineering 2010, 295, (12), 1107 1115. 150. Yoonessi, M.; Gaier, J. R. Acs Nano 2010, 4, (12), 7211 7220.
192 15 1. Liu, Q.; Liu, Z. F.; Zhong, X. Y.; Yang, L. Y.; Zhang, N.; Pan, G. L.; Yin, S. G.; Chen, Y.; Wei, J. Advanced Functional Materials 2009, 19, (6), 894 904. 152. Matyba, P.; Yamaguchi, H.; Eda, G.; Chhowalla, M.; Edman, L.; Robinson, N. D. Acs Nano 2010, 4, (2), 637 642. 153. Vadukumpully, S.; Paul, J.; Mahanta, N.; Valiyaveettil, S. Carbon 2011, 49, (1), 198 205. 154. Yang, J. T.; Wu, M. J.; Chen, F.; Fei, Z. D.; Zhong, M. Q. Journal of Supercritical Fluids 2011, 56, (2), 201 207. 155. Cheng, Q.; Tong , Z.; Dempere, L.; Ingram, L.; Wang, L.; Zhu, J. Y. Journal of Polymers and the Environment 2013, 21, (3), 648 657. 156. Kim, H.; Miura, Y.; Macosko, C. W. Chemistry of Materials 2010, 22, (11). 157. Zhang, K.; Zhang, L. L.; Zhao, X. S.; Wu, J. Chemistry of Materials 2010, 22, (4), 1392 1401. 158. Yan, J.; Wei, T.; Fan, Z.; Qian, W.; Zhang, M.; Shen, X.; Wei, F. Journal of Power Sources 2010, 195, (9), 3041 3045. 159. Xu, Z.; Gao, C. Macromolecules 2010, 43, (16), 6716 6723. 160. Bledzki, A. K.; Letman , M.; Viksne, A.; Rence, L. Composites Part a Applied Science and Manufacturing 2005, 36, (6), 789 797. 161. Finkenstadt, V. L.; Liu, L. S.; Willett, J. L. Journal of Polymers and the Environment 2007, 15, (1), 1 6. 162. Finkenstadt, V. L.; Liu, C. K.; C ooke, P. H.; Liu, L. S.; Willett, J. L. Journal of Polymers and the Environment 2008, 16, (1), 19 26. 163. Favier, V.; Dendievel, R.; Canova, G.; Cavaille, J. Y.; Gilormini, P. Acta Materialia 1997, 45, (4), 1557 1565. 164. Qiu, K. Y.; Netravali, A. N. C omposites Science and Technology 2012, 72, (13), 1588 1594. 165. Schork, F. J.; Luo, Y. W.; Smulders, W.; Russum, J. P.; Butte, A.; Fontenot, K., Miniemulsion polymerization. In Polymer Particles , Okubo, M., Ed. 2005; Vol. 175, pp 129 255. 166. Zhang, L. Y.; Shi, T. J.; Wu, S. L.; Zhou, H. O. High Performance Polymers 2014, 26, (2), 156 165.
193 167. Hu, H.; Wang, X.; Wang, J.; Wan, L.; Liu, F.; Zheng, H.; Chen, R.; Xu, C. Chemical Physics Letters 2010, 484, (4 6). 168. Kuila, T.; Bose, S.; Khanra, P.; Kim, N. H.; Rhee, K. Y.; Lee, J. H. Composites Part a Applied Science and Manufacturing 2011, 42, (11), 1856 1861. 169. Gu, Z. M.; Zhang, L.; Li, C. Z. Journal of Macromolecular Science Part B Physics 2009, 48, (2), 226 237. 170. Das, S.; Wajid, A. S.; Shelbu rne, J. L.; Liao, Y. C.; Green, M. J. Acs Applied Materials & Interfaces 2011, 3, (6), 1844 1851. 171. Xie, P. F.; Ge, X. P.; Fang, B.; Li, Z.; Liang, Y.; Yang, C. Z. Colloid and Polymer Science 2013, 291, (7), 1631 1639. 172. Gudarzi, M. M.; Sharif, F. Soft Matter 2011, 7, (7), 3432 3440. 173. Song, X. H.; Yang, Y. F.; Liu, J. C.; Zhao, H. Y. Langmuir 2011, 27, (3), 1186 1191. 174. Pan, G. F.; Sudol, E. D.; Dimonie, V. L.; El Aasser, M. S. Macromolecules 2001, 34, (3). 175. Taden, A.; Landfester, K. M acromolecules 2003, 36, (11), 4037 4041. 176. Asua, J. M. Progress in Polymer Science 2002, 27, (7), 1283 1346. 177. Man, S. H. C.; Thickett, S. C.; Whittaker, M. R.; Zetterlund, P. B. Journal of Polymer Science Part a Polymer Chemistry 2013, 51, (1). 1 78. Thickett, S. C.; Zetterlund, P. B. Current Organic Chemistry 2013, 17, (9), 956 974. 179. Thickett, S. C.; Zetterlund, P. B. Acs Macro Letters 2013, 2, (7), 630 634. 180. Man, S. H. C.; Yusof, N. Y. M.; Whittaker, M. R.; Thickett, S. C.; Zetterlund, P. B. Journal of Polymer Science Part a Polymer Chemistry 2013, 51, (23), 5153 5162. 181. Viet Hung, P.; Thanh Truong, D.; Hur, S. H.; Kim, E. J.; Chung, J. S. Journal of Nanoscience and Nanotechnology 2012, 12, (7), 5820 5826. 182. Yu, Y. H.; Lin, Y. Y. ; Lin, C. H.; Chan, C. C.; Huang, Y. C. Polymer Chemistry 2014, 5, (2), 535 550. 183. Tan, Y.; Fang, L.; Xiao, J.; Song, Y.; Zheng, Q. Polymer Chemistry 2013, 4, (10), 2939 2944.
194 184. Etmimi, H. M.; Sanderson, R. D. Macromolecules 2011, 44, (21). 185. Aldu ncin, J. A.; Forcada, J.; Asua, J. M. Macromolecules 1994, 27, (8), 2256 2261. 186. Chen, M.; Wu, L. M.; Zhou, S. X.; You, B. Macromolecules 2004, 37, (25), 9613 9619. 187. Xu, M. Z.; Choi, Y. S.; Kim, Y. K.; Wang, K. H.; Chung, I. J. Polymer 2003, 44, (20 ), 6387 6395. 188. Greesh, N.; Hartmann, P. C.; Cloete, V.; Sanderson, R. D. Journal of Colloid and Interface Science 2008, 319, (1), 2 11. 189. Nadim, E.; Bouhendi, H.; Ziaee, F.; Bazhrang, R. Polymer Bulletin 2012, 68, (2), 405 414. 190. Plackett, D.; An dersen, T. L.; Pedersen, W. B.; Nielsen, L. Compos. Sci. Technol. 2003, 63, (9), 1287 1296. 191. Ochi, S. Mech. Mater. 2008, 40, (4 5), 446 452. 192. Waclawovsky, A. J.; Sato, P. M.; Lembke, C. G.; Moore, P. H.; Souza, G. M. Plant Biotechnology Journal 201 0, 8, (3), 263 276. 193. Bax, B.; Muessig, J. Compos. Sci. Technol. 2008, 68, (7 8), 1601 1607. 194. Ganster, J.; Fink, H. P. Cellulose 2006, 13, (3), 271 280. 195. Shibata, M.; Oyamada, S.; Kobayashi, S.; Yaginuma, D. J. Appl. Polym. Sci. 2004, 92, (6), 3 857 3863. 196. Satyanarayana, K. G.; Arizaga, G. G. C.; Wypych, F. Prog. Polym. Sci. 2009, 34, (9), 982 1021. 197. Ibrahim, N. A.; Yunus, W. M. Z. W.; Othman, M.; Abdan, K. Journal of Reinforced Plastics and Composites 2011, 30, (5), 381 388. 198. Smith, G . D. Wood Fiber Sci. 2004, 36, (2), 228 238. 199. Tokoro, R.; Vu, D. M.; Okubo, K.; Tanaka, T.; Fujii, T.; Fujiura, T. J. Mater. Sci. 2008, 43, (2), 775 787. 200. Bao, S. C.; Daunch, W. A.; Sun, Y. H.; Rinaldi, P. L.; Marcinko, J. J.; Phanopoulos, C. For. Prod. J. 2003, 53, (6), 63 71.
195 201. Sluiter, A., Hames, B., Ruiz, R., Scarlata, C., Sluiter, J., Templeton, D., Crocker, D, Determination of Structural Carbohydrates and Lignin in Biomass (NREL/TP 510 42618). National Renewable Energy Laboratory, Golden, C O.: 2008. 202. B. Hames, C. S., and A. Sluiter, Determination of Protein Content in Biomass. National Renewable Energy Laboratory: 2008. 203. Franklin, G. L. Nature 1945, 155, (3924), 51 51. 204. International, A., D638 10 Standard Test Method for Tensil e Properties of Plastics. United States, 2010. 205. International, A., ASTM Standard D618 "Standard Practice for Conditioning Plastics for Testing". ASTM International: West Conshohocken, PA, 2008. 206. International, A., ASTM Standard D790 "Standard Test Methods for Flexural Properties of Unreinforced and Reinforced Plastics and Electrical Insulating Materials". ASTM International: West Conshohocken, PA, 2003. 207. Wang, H.; Sun, X. Z.; Seib, P. J. Appl. Polym. Sci. 2001, 82, (7), 1761 1767. 208. Le Digabe l, F.; Averous, L. Carbohydrate Polymers 2006, 66, (4), 537 545. 209. Yang, L. X.; Chen, X. S.; Jing, X. B. Polym. Degrad. Stabil. 2008, 93, (10), 1923 1929. 210. Jung, J. H.; Ree, M.; Kim, H. Catal. Today 2006, 115, (1 4), 283 287. 211. Felipe, M. G. A.; Vitolo, M.; Mancilha, I. M.; Silva, S. S. Biomass & Bioenergy 1997, 13, (1 2), 11 14. 212. U.S.Congress, O., Potential Environmental Impacts of Bioenergy Crop Production Background Paper, . U.S. Government Printing Office: Washington, DC, 1993. 213. Nakagai to, A. N.; Yano, H. Applied Physics a Materials Science & Processing 2004, 78, (4), 547 552. 214. Nakagaito, A. N.; Yano, H. Applied Physics a Materials Science & Processing 2005, 80, (1), 155 159. 215. Henriksson, M.; Berglund, L. A. Journal of Applied Po lymer Science 2007, 106, (4), 2817 2824. 216. Karande, V. S.; Bharimalla, A. K.; Hadge, G. B.; Mhaske, S. T.; Vigneshwaran, N. Fibers and Polymers 2011, 12, (3), 399 404.
196 217. O.V.Abramov , High Intensity Ultrasonic Theory and Industrial Applications . Gordo n and Breach Science Publishers : Amsterdam, 1998. 218. Cheng, Q.; Wang, S. Q.; Rials, T. G.; Lee, S. H. Cellulose 2007, 14, (6), 593 602. 219. Wang, S. Q.; Cheng, Q. Z. Journal of Applied Polymer Science 2009, 113, (2), 1270 1275. 220. Cheng, Q. Z.; Wang, S. Q.; Han, Q. Y. Journal of Applied Polymer Science 2010, 115, (5), 2756 2762. 221. Suslick, K. S. Science 1990, 247, (4949). 222. Qingzheng Cheng, D. D., Jingxin Wang and Siqun Wang, Advanced Cellulosic Nanocomposite Materials. In Advances in Composite M aterials for Medicine and Nanotechnology , Attaf, B., Ed. InTech: 2011; pp 547 564. 223. J. Wang, Q. C., A. B. Adebayo and S. Difazio, Fiber Reinforced Composites . Nova Science Publishers Inc: New York, 2012. 224. International, A., D1708 10 Standard Test M ethod for Tensile Properties of Plastics by Use of Microtensile Specimens. ASTM International: United States, 2010. 225. Chakraborty, A.; Sain, M.; Kortschot, M. Holzforschung 2006, 60, (1). 226. Wang, B.; Sain, M. Composites Science and Technology 2007, 6 7, (11 12). 227. Frone, A. N.; Panaitescu, D. M.; Donescu, D.; Spataru, C. I.; Radovici, C.; Trusca, R.; Somoghi, R. Bioresources 2011, 6, (1). 228. Yang, H.; Yan, R.; Chen, H.; Lee, D. H.; Zheng, C. Fuel 2007, 86, (12 13). 229. Holland, B. J.; Hay, J. N. Polymer 2001, 42, (16), 6775 6783. 230. Deryagnin, B.; Landau, L. Acta Phys Chim URSS 1941, 14, 633 662. 231. Verwey, E.; Overbeek, J., Theory of the stability of lyophobic colloids . Elsevier: New York, 1943. 232. Liu, H. T.; Zhang, L.; Guo, Y. L.; Cheng, C.; Yang, L. J.; Jiang, L.; Yu, G.; Hu, W. P.; Liu, Y. Q.; Zhu, D. B. Journal of Materials Chemistry C 2013, 1, (18), 3104 3109. 233. Zangmeister, C. D. Chemistry of Materials 2010, 22, (19), 5625 5629. 234. Nethravathi, C.; Rajamathi, M. Carbon 2008, 46, (14).
197 235. Titelman, G. I.; Gelman, V.; Bron, S.; Khalfin, R. L.; Cohen, Y.; Bianco Peled, H. Carbon 2005, 43, (3). 236. Uhl, F. M.; Yao, Q.; Nakajima, H.; Manias, E.; Wilkie, C. A. Polymer Degradation and Stability 2005, 89, (1). 237. Park, S.; An, J.; Po tts, J. R.; Velamakanni, A.; Murali, S.; Ruoff, R. S. Carbon 2011, 49, (9), 3019 3023. 238. Khezri, K.; Haddadi Asl, V.; Roghani Mamaqani, H.; Salami Kalajahi, M. Journal of Polymer Research 2012, 19, (5). 239. Lan, F.; Liu, K. X.; Jiang, W.; Zeng, X. B.; Wu, Y.; Gu, Z. W. Nanotechnology 2011, 22, (22). 240. Li, C. B.; Wang, X. R.; Liu, Y.; Wang, W.; Wynn, J.; Gao, J. P. Journal of Nanoparticle Research 2012, 14, (6). 241. Wu, T.; Wang, X.; Qiu, H.; Gao, J.; Wang, W.; Liu, Y. Journal of Materials Chemistry 2012, 22, (11), 4772 4779. 242. Wang, X. L.; Wen, X. H.; Liu, Z. P.; Tan, Y.; Yuan, Y.; Zhang, P. Nanotechnology 2012, 23, (48). 243. Wang, P. H.; Tang, Y. X.; Dong, Z. L.; Chen, Z.; Lim, T. T. Journal of Materials Chemistry A 2013, 1, (15), 4718 4727. 244 . Kim, N.; Sudol, E. D.; Dimonie, V. L.; El Aasser, M. S. Macromolecules 2003, 36, (15), 5573 5579. 245. Kim, N.; Sudol, E. D.; Dimonie, V. L.; El Aasser, M. S. Macromolecules 2004, 37, (7), 2427 2433. 246. Yuki, K.; Nakamae, M.; Sato, T.; Maruyama, H.; Ok aya, T. Polymer International 2000, 49, (12), 1629 1635. 247. Robeson, L. M.; Vratsanos, M. S. Macromolecular Symposia 2000, 155, 117 138. 248. Choi, K. S.; Liu, F.; Choi, J. S.; Seo, T. S. Langmuir 2010, 26, (15), 12902 12908. 249. Samakande, A.; Sanderso n, R. D.; Hartmann, P. C. Journal of Polymer Science Part a Polymer Chemistry 2008, 46, (21), 7114 7126. 250. Zhong, Y.; Zhu, Z. Y.; Wang, S. Q. Polymer 2005, 46, (9), 3006 3013.
198 251. Roghani Mamaqani, H.; Haddadi Asl, V.; Najafi, M.; Salami Kalajahi, M. A iche Journal 2011, 57, (7), 1873 1881. 252. Tong, Z. H.; Deng, Y. L. Macromolecular Materials and Engineering 2008, 293, (6), 529 537. 253. Baillie, I. C. Soil Taxonomy 2001, 17, (1), 60. 254. Brunauer, S.; Emmett, P. H.; Teller, E. Journal of the American Chemical Society 1938, 60, 309 319. 255. TAPPI, Useful Method 256 Water Retention Value. 1991. 256. O'Dell, J. W., EPA method 350.1 Determination of ammonia nitrogen by semi automated colorimetry. U.S. Environmental Protection Agency: Cincinnati, Ohio, 1993. 257. O'Dell, J. W., EPA method 365.1 Determination of phosphorus by semi automated colorimetry. U.S. Environmental Protection Agency: Cincinnati, Ohio, 1993. 258. Ververis, C.; Georghiou, K.; Christodoulakis, N.; Santas, P.; Santas, R. Industrial Cro ps and Products 2004, 19, (3). 259. Hubbe, M. A.; Venditti, R. A.; Rojas, O. J. Bioresources 2007, 2, (4). 260. Driemeier, C.; Oliveira, M. M.; Mendes, F. M.; Gomez, E. O. Powder Technol. 2011, 214, (1), 111 116. 261. Spence, K. L.; Venditti, R. A.; Rojas, O. J.; Habibi, Y.; Pawlak, J. J. Cellulose 2010, 17, (4), 835 848. 262. da Silva, A. S.; Lee, S. H.; Endo, T.; Bon, E. P. S. Bioresource Technology 2011, 102, (22), 10505 10509. 263. Laird, D. A.; Fleming, P.; Davis, D. D.; Horton, R.; Wang, B. Q.; Karlen , D. L. Geoderma 2010, 158, (3 4), 443 449. 264. Said, A.; Ludwick, A. G.; Aglan, H. A. Bioresource Technology 2009, 100, (7), 2219 2222. 265. Pejic, B. M.; Kostic, M. M.; Skundric, P. D.; Praskalo, J. Z. Bioresource Technology 2008, 99, (15). 266. Kithome , M.; Paul, J. W.; Kannangara, T. Communications in Soil Science and Plant Analysis 1999, 30, (1 2), 83 95. 267. Li, K. Q.; Li, Y.; Zheng, Z. J. Hazard. Mater. 2010, 178, (1 3), 553 559.
199 268. Wahab, M. A.; Jellali, S.; Jedidi, N. Bioresource Technology 201 0, 101, (14). 269. Riahi, K.; Ben Thayer, B.; Ben Mammou, A.; Ben Ammar, A.; Jaafoura, M. H. J. Hazard. Mater. 2009, 170, (2 3), 511 519.
200 BIOGRAPHICAL SKETCH Letian Wang was born 198 5 in Nanjing , China. H e received the combined bachelor and master of engineering in chemical engineering from University College London in the UK in 20 09 . H e enrolled as a PhD student in the Agricultural and Biological Engineering Department at University of Florida in 20 10 , and received his Ph.D. from the University of Fl orida in the summer of 201 4 . His doctoral research, under the direction of Dr. Zhaohui Tong , focused on utilizing lignocellulosic residues from bioethanol production to prepare value added biocomposites, particularly with respect to using both conventional mechanical and novel miniemulsion polymerization . He has published five peer review journal articles in top ranking international journals. After graduation, he will pursue industrial career in the US .