The microstructure of a wood pulp fiber

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Title:
The microstructure of a wood pulp fiber
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Book
Creator:
Ritter, George J
Chidester, G. H
Forest Products Laboratory (U.S.)
University of Wisconsin
Publisher:
USDA, Forest Service, Forest Products Laboratory ( Madison, Wis )
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THI MICIOSTRUCTUI OF A

WO)OD PULP I fIR
October 1928

No. 1911
UNITED STATES DEPARTMENT OF AGRICULTURE
FOREST SERVICE
FOREST PRODUCTS LABORATORY
Madison, Wisconsin
In Cooperation with the University of Wisconsin




T.HE MICROSTRUCTLE OF A W00D PULP FIBER*

GEC.VC J. RITTER, Chemist
and
G. H. CHIDESTER, Assistant Engineer
The results presented in this paper were obtained in fundamental
study that the Forest Products Laboratory is making in its investigation of
the behavior of uood, largely for the purpose of bettering the utilization
of ,ood. These results will here be considered in connection with the prob-
lems that confront the pulp and paper manufacturer.
I. Constituents of Wood
Constituents Comm.ionly Wasted
The manufacturer of pulp and naper naturally is interested in the
nature and the location of the constituents of wood that are removed during
the preparation of wood Tulp.
Lignin is the major component (28.0 percent) of the part of the
wood that is removed during the manufacture of sulphite pulp. It exists in
two forms,- which differ somewhat in chemical composition.
One form is the binding material (middle-lamella lignin) between
the wood fibers; the other is a finely divided amorph-ous material (cell-wall
lignin) in the cell wall. ho other the cell-wall form is chemically combined
with the cellulose in the vall or is physically distributed throughout is not
known definitely. If all the constituents except lignin are removed from a
transverse section of wood, the two forms may be sooeen with the aid of a micro-
scope. One form, the middle lamella, is revealed as a network; the other,
the cell-uall form, appears as a finely divided agglomorated residue in the
space formerly occupied by the lignified cellulose in the cell wall. (Plates
1 and 2.)
Further, if all the constituents except lignin are removed from
transverse sections, which have been cut thicker than those which were used
in Plates 1 and 2 so that the network might remain intact during washing, the
two forms of lignin may be separated. By imprgnating the network residue
with par,-raffin, thin sections of the middle-lamella lignin may be cut and
photographed. (Plates 3 and 4.)
1Rittcr, Ind. Enr. Chem. 19, 1194 (1925).
-Publishied in Paper Trade Journal, October 25, 1928.
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In addition, two other groups of components, tho pentosane not in
cellulose and -he extractives, approximately G percent Oach, -Lre a total loss
to the manufacturer of chemical pulp and raper and, still, fl-rther, tlie dif-
forenc "etwcen coimcrcill'y bleached sulfite cellulose and chkrinated cellu-
lose (20 percent of the wood) is -,nothr loss of lignin-fre material that in
all probability is an excellent Pa-per-making material. From ork dcrn in the
Pulp and Paper Section of the Forest Products Laboratory, it is known that the
unbleachod suifito inilp yields can be increased from the 1sul 40 nercont to
approximtely 50 percent with si 'ltanecus im-provement of tho quality of the
pulp.
Lastly, the viscose manufacturer in using the sulfite cellulose
wastes vaother 7 percent of the spruce wood, leaving but 34 pCrccnt to be
utilized,
Constituents Commonly Utilized
Cellulose, which is practically the eolo constituent of chemical
wood -,ulp, consists of vnxious carbohydrates wher it is prepared from wood.
When isol-ted h"r chlorination, it constitutes approximately 60 percent of the
total ood forming the major portion of the cell wall. In cner.l, it consists
of pointed capsular fibcrs. A '=owlode of the minute structure and the
properties of these fibers is of importnncD to the p-per maker, to enable him
to best adapt his processes to work in hira rmony with them rather tha,7n against
them.
II. 1,icrostriucture of the tIood Fiber
Separation of layers in the Cell -all
The cellulosic material used in exa-ining the microstructure of the
wood fiber was 1 reared from tin longitudinal wood shavings. These shavings
were delignified b-- th.e Cross and Beva--n method, were dehydrated withV alcohol
for several da:,s, and were kept in alcohol until required for use.
Examination of deligrif ed fibers after they had received alternate
swelling and sihinling, treatments with alkali and with acids indicated that
the cell wall is in a rranner similar to that of the cell-wall layers of cot-
ton- con-poscd of several layers packed together closely. These layers are so
close together or else are so embedded in a cementing material of such an
index of refractior. th)at t he layers are invisible in the orij-*nal wood. But,
b- chemical end hi-sical treat!i-lents, w.-iich the fibers receive through deligni-
fication, swelling, and shrinkriln:, the binding matoiial can be reminvod or the
lay ers can be -oushed aT)art, so that t'. a spacings become visible. The presence
of several layers in the cell wall can- also be show%n.--1 plainly by treating
delignifid fibers iith phosphoric acid
2
On neutralization of the alkali within dilute acid the wcod sections shrink.
3Van Iterson, Chem. 'cekblad, 24E, 175 (1927).

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If fibers that have been treated properly with alkali and acid are
examined with the aid of a microscope, stratifications that define the various
layers can be seen in the cell wall. (Plate 5.) Since the layers form
pointed capsules that are nested, complete layers can not be separated by
sliding certain ones endwise over the others, even though they may have been
properly loosened. If short sections of such fibers are used, however, it is
possible to remove the loosened, concentric, tube-like sections of the layers
by sliding them endwise. (Plate 6.)
At present, the chemical composition of the binding material between
the various layers in the cell wall is unknown. it may be compcsed of an
easily hydrolyzable portion of the cellulose. The quantity of this substance
may be so minute that it will be necessary to determine it by difference in
the composition of the residue before and after its removal, rather than to
isolate, recover, and identify the binding material itself. This phase of
the study will be undertaken later. The accomplishment reported here is the
actual separation of the layers in the secondary thickening of the cell wall
in wood fibers.
Orientation and Se-Daration of the Fibrils
in the Cell-wall Layers
The swelling properties of bordered pits reported in Part III of
this paper, the optical properties observed between N~icol prisms, and the re-
sults that will be described in Part II indicate that not only do tiny -fibrils
form the various layers of the cell wall of wood fibers, but that these
fibrils can be separated by chemical means.
The fibrils that compose the outer layers are oriented at approxi-
mately 900 to the long axis of the wood fiber. Immediately under the outside
layer of some fibers there are occasional stray bands of fibrils w-ound about
the inner layers at approximately 450 to the fiber's axis. Such fibrils do
not form a continuous layer. In the remaining layers the fibrils are oriented
from 00 to 300 to the axis of thc fiber.
A study of the orientation of the fibrils in the various cell-wall
layers and of the separation of the fibrils in each layer vas made by two
methods, alkali-acid and phosphoric acid treatments.
(1) Alkali-acid method.--After alternate alkali and acid treatment
of fibers, faint stratifications became prominent and more and more striations
became visible. In places at which the outer layer had been dissolved, there
was extreme outward swelling of the inner layers. Such selling made apparent
the pronounced constrictions at the places where the outer layer was still
intact, and also the less prominent constrictions on the fibers that had stray
fibril bands wound about their inner layers at an angle of 45'. (Plate 7.)
Continued treatment, with the aid of slight pressure on the cover glass,
broke thec constricting bands and the inner layers separated into fibril bun-
dles. (Plato 8.) It was possible to separate these bundles into individual
fibrils, w;hic', naturally have a dipameter smaller than that of the bundles.
Unfortulr-tcly, no satisfactory photomicrographs were obtained.

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(2) Phosphoric acid method.--It is possible to control the reaction
of the nhosphoric acid method upon cellulose letter than that of the alkali-
acid method. Further, it is possible to reveal the minute structural arrange-
ment of the layers in a manner that can not be accomplished by the alkali-
acid method, Phosphoric acid seems to hnave a specific propert for develop-
ing striations in wood fibers by loosening the layers and the fibrils before
the skeleton structure dissolves.
Fibers treated by the phosphoric acid method show that solution of
the outer layer at intervals is accompanied by extreme outward swelling, of
the inner layers; such fibers are constricted at the places where the outer
layer is still intact. (Plate 9.) Extremely high magnification shous that
the cell-uall layers separate in the transverse direction. (Plate 10.) Such
photographs suggest that the orientation of the fibrils in the outer 7nd in
the inner layers is radically different.
Through slowly dissolving the outer layer, it became apparent that
striation and separation of the fibrils precede the ultimate solution of the
layer as an entirety. Since the fibrils in the outer layer are oriented at
approximately 900 to the axis of the ,wood fiber (pl. 11), it is obvious that
the fibers can not swell outwardly beyond the maximum limits that they assume
in a water medium, unless the fibrils in the outer layer expand lengthwise or
break. Such a structure also accounts for delignified fibers swelling inwardly
when the outer layer is still intact. (Plate 18.)
On account of the convexity of the surface of the bead-like swell-
ings in Plate 10, the minute structure of the inner layers is not visible. A
swollen surface both flatter -nd longer must be examined if the tiny fibrils
are to be seen in their proper orientation. By proper focusing of the micro-
scope the orientation of the fibrils in the various layers can be studied.
(Plate 12.) If the acid treatment is continued, the fibrils are loosened to
a greater extent. (Plate 13.) By allow ing the reaction to proceed still
further, the individual fibrils are isolated. (Plate 14.)
If the minute structural arrangement of the outer layer is contrasted
with that of the inner layers, it will be seen that wood fibers are designed
to witstsand both transverse and loniitudinal stresses.
This separation of the cll wall of the wood fiber into fibrils
confirms some findings of ;aenti7.-
Separation of the "Fusiform bodies" in the Fibrils
A careful examination of the isolated fibrils from the inner layers
of the cell wall under the high power of the microscope revealed that they
were made up of units, the ends of :I'hich taper to saro points; the lunits are
held together by. a slight overlapning of the pointed ends- so as to form the
W'aentig. Papierfabrikant 25, 115 (1927),
5T
-These units differ from the dermatosomes described by. Wiesner in his
Elementar Structur, Alfred Holder, Vien, 1892, T. 162.

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tiny, slender fibrils of a diameter practically uniform throughout their entire
lengthl. The lon axis of each. unit is parallel to the long axis of the fibril.
The reaction of the phosphoric acid under proper conditions slowly opens up
the natural planes of cleavage between the tiny units, which are of fusiform
s are. (Plate 15.) Since, as far as the senior author knows, these are newly
discovered u nits, which have been separated and photographed for the first
time in the investigation now reported, they have been given the descriptive
name "fusiforlm bodies."
III. Properties of Wood
Physical Pro-eorties
Some of the swelling properties of wood have been known for a long
time through everyday experiences with the increased external dimensions that
are produced in wood products when they are changed from dry and vet condi-
tions by soaking in liquids, such as uater, and solutions of acids and alka-
lis. Later swells dry wood approximately to its green volume. Strong acids
and alkalis swJell dry wood beyond its green volume.
!!ith the aid of a microscope, it may be seen that the cell walls of
wood also swell internally, and that the internal swelling, when an alkali or
a strong acid is used as the reagent, may be sufficiently severe to fill the
cell cavities. If a section of wood in its original state is swollen, the
fibers retain their external shape, which in cross section s:ows definite
angles. (Plates 16 and 17.)
From Plate 17 it is evident that a swollen condition retards the
movement of impregnating liquors, prior to cooking, through the pits and the
cell cavities, On the other hand, a condition such as that shown in this
plate indicates that the fibers have been impregnated by diffusion of the
alk1li throu'. the actual cell walls. The appearance of the section showm
su:,!ests that apreontion of wood chips with alkali liquors takes place
principally y ilff on through the cell wall itself rather than through the
various n- t.ra. oe, r:ic in the wall.
Acid solut~c of ordinary concentration produce very little swell-
ing of the cell ll l >nd its green volume. The original sizes of thlie open-
inrs, therefore, remae-_, rractically unaltered. Siuch a condition suggests
ternt impregration of chips with an acid cooking liquor takes place prin-
cipally a.n .: t,-:, rnd cell cavities.
7f < 'i. fibers are treated with alkali or with strong acids,
th : too, ,: .7 "ing the cell wall into the lumen, but their cross-
si : Cn 1 c,... uit the 3drnstic reacnts, the fibers become slightly plastic and
t I to 0... e .Niapes that have the minimum external surface in both the
tr:..::: :v 0isnd thoe lorn.itudinal dimensions.

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By alternately swelling wood fibers beyond their green volume and
thenshrnkig tem uiclymark.ings are developed that suggest the minute
microstructure described in Part II of this paper.
Sodium hydroxide solution (15.6 percent concentration) was used for
swelling the -fibers shown in Plate 18. The appearance of those fibers gives
an idea of the appearance of wood fibers in cross section after the alkaline
treatment in the viscose process, and also in the alpha-cellulose determina-
tion. The numerous pit openings of the swollen cell walls, which do not ap-
pear in -the rhotomicrograph, are charged to oblong slits that axe practically
closed.
Optical properties that suggest the structure of the cell wall
about the bordered pits are manifested when the nits are examined in polarized
light. It has been known. for a long time that the secondary layer of the
cell wall rotates the plane of polarized light and that the face of a bordered
pit shows the commonly observed dark cross when it is placed between NTicol
prisms that are crossed at 90. The optical properties of the secondary layer
are commonly considered to be due to an orderly arrangement of cellulose mole-
cules in chains_. (Tagelits hypothesis); X-ray diagrams of Sponsler and Dore8
suggest that those chains are, in general, parallel to the longitudinal axis
of the fiber. The fibrils in the secondary layer about the pit are bent
around the opening, making their arrangement somewhat circular. The fibrils
in the outside layer are present and arc oriented at 900 to the fiberls axis.
Bending around the opening they superpose a layer of concentric rings over
the slight distortions in the circular !tructurc of the inner layers. It is
because of this involved total structure that the bordered pits exhibit a
symmetrical dark cross through a complete rotation of the microscope stage.
(Plates 21 and 22.)
IV. _Significance of Fiber 11icrostructure
to Chemical Pulping
Treatments that tend to separate wood fibers into fibrils and, in
turn, tend to separate the fibrils into the fusiform. bodies, are of interest
to the paper maker. If a definite -percentage of the fibers in a pulp are in
a physical condition similar to the conditions in Plates 5, 6, 7, 11, _!nd 12,
it may aid immensely in the felting qualities of the pulp. On the other hand,
if the reaction should be carried on sufficiently to put a large percentage
of the fibers in the condition shown in Plate 13, the -pulp might be useless
for making papor.
6'-Dippc!, "Das 1ikroskop,"1 2, p. 264.
7Sachs, "History of Botany," p. 350.
8--"Fourth Colloid Symposium," Monograph, p. 174 (1926).

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Further, from the results already presented in this paper, it
appears that pulps of different qualities and varying yields, produced by
different cooking conditions, should show some difference in the microstruc-
ture of the fibers. Also, pulps cooked under the more drastic of the usual
commercial conditions might respond more readily to the treatments previously
described than pulps cooked under milder conditions. In addition, pulps
beate for varying periods might show a tendency to respond to the acid treat-
ments more readily as the beating time increased.
,he physical properties of the wood fibers determine to a large
degree the ease with which phosphoric acid reacts wJith the cell wall. A
slight ruptvre of the woody tissues, such as frayed ends, aids in starting
the reaction. This fact may be demonstrated by treating short sections of
fibers with the acid. With such a section, the solution of the outer layer
begins at the frayed ends, and progresses toward the middle. By arresting
the reaction '-efore all the outer layer is removed, it is possible to obtain
a residue that consists of loosened bundles tied with the spiral bands that
form the remainder of the outer layer. (Plate 19.)
Optical Properties
Isolated "fusiform bodies," fibrils, and fibril bundles between
Nicol prisms exhibit the same property as wood fibers, in that they transmit
polarized light when they are oriented at an angle to the axes of the crossed
prisms, but do not do so when oriented parallel to either of the axes.
(Plate 20.)
The bead-like swelling showr in Plate 10, if placed between Nicol
prisms, exhibit a "dark cross" when the axis of the fiber is parallel to the
axis of one of the prisms. dhen the microscope stage is rotated 450, the dark
cross becomes slightly distorted. The bead-like swellings disappear, in gen-
eral, as spherical bodies with a slight distortion in the direction of the
fiber's axis. A cross section of such a body is composed of an approximate
circle made up of concentric rin-s of visible fibrils, which are distorted in
Sannr similar to tht of the swellings. With such a structure, the opti-
a manner similar to t liat ofthe swellings
cal phenomenon of the swellings can be explained.
Some tests were made to determine whether such relationships could
be shown. Preliminary experimental work was done on two series of sulfite
cooks of white spruce and Eastern hemlock, respectively. Each series consisted
of a pulp showing high strength and high yie!d in contast to one showing low
stren::th and low yield. These pulps were subjected to the Laboratory standard
strength-development procedure by use of the ball mill.
The bleachabilities of the pulps were also determined. The essential
data are recorded in Table 1.
The differences in the two spruce pulps are greater than those in
the hemlock p-ulps. In maximum bursting strength, the second spruce pulp is
0.55 point il- er than the first; the yield is 8.6 percent higher. The maxi-
mum bursting strength of the second hemlock pulp is 0.21 point higher, while
the yield is 2.9 percent higher than the first,

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The spruce pulns were stained with Bismarck brown, air dried, treated
with a solution of phosphoric acid, heated for 4 minutes at 600 C., a. cod ed.
Slides were then made and photomicrographs taken. The hemlock pulbs were
treated in the same way except that they were heated for 3 minutes instead of
4. In addition, 4 of the initial samples were treated with a slightly stronger
acid, at room temperature, to show more clearly the differences in the fibers
before milling, The photomicrographs of these fibers appear in Plates 26, 27,
28, and 29.
Untreated fibers, both milled and not milled, of Pulp 3236-I are
shown in Plates 23, 24, and 25. Fibers of the 4 pulps, milled and not milled
and treated with phosphoric acid, are shown in Plates 30 to 49, inclusive.
The results show that pulps prepared under mild cooking conditions
are less susceptible to the attack of phosphoric acid than those prepared by
drastic cooking conditions. Differences in the susceptibility to the attack
appear when plates prepared from the two unmilled spruce pulps and the two
unmilled hemlock pulps are compared. For example, contrast Plates 26 and 27;
28 and 29; 30 and 31; and 40 and 41.
The results further show that the binding material and the helical
winding of fibrils forming the outer layer of the fiber have been partially
or wholly dissolved, allowing the inner portion of the fiber to expand. In
some cases, the inner fibrils may be seen slightly separated, forming an ex-
tended helix.
The effect of the acid is also noticeable as the milling progresses.
When the outer portion of the fiber has been ruptured mechanically, the inner
part is attacked by the acid at the rupture and swelling takes place. In the
refined pulps, also, the stronger pulp shous, in general, less effect of the
acid.
By treating fibers from various sulfite pulps with1 phosphoric acid
and examining them under the microscope, it is possible to observe differences
in the quality of the pulp. Just how fine a distinction can be made remains
to be worked out. It may be possible to evaluate the pulp numerically by using
phosphoric acid solutions of different concentrations, noting the strength at
which the pulp is attacked.
Although a rapid qualitative test may be developed from the method,
more important is the information it gives on the fundam:*n tal relation of the
microstructure of the fiber to different cookng condit,)-is, ielcds, and
strength properties.
Summary
The location in the wood of the two forms of lignin is described.
The two forms are shown in photomicrographs.




The possibility of obtaining a yield of 60 percent of ligin-free
fibers for paper material is suggested.
The cell ,wall of ood fibers is composed of several layers, which
can be se-parated 'by chemical means.
The layers in the cell wall of a wood fiber can be separated into
fibrils chemical means. The fibrils in the outer layer are oriented at
approximately, right angles to the fiber's axis, while those in the remaining
layers are from 00 to 300 thereto.
The fibrils can be separated into regularly shaped "fusiform bodies"
with optical properties similar to those of the fibrils.
" 7hen either- lignified or delignified wood fibers are treated with
swelling reagents, the fiber walls thicken outwardly and also inwardly. The
polygonal shape of the cross section of delignified fibers is unaltered, but
the cross section of delignified fibers is limited by the outer layer of
fibrils, which are oriented at 900 to the fiber's axis.
The optical phenomenon, when bordered pits are observed between
N icol prisms, is explained on the basis of the ring-like structural arrange-
ment of the cellualosic Material of the cell wall.
The effect of -phosnohoric acid on pulps obtained from two series of
cooks of spruce and he-ilock is described. Its effect is more severe or, the
pulps from the more drastic cooks, both in the raw and refined condition.
The effect increases as the period of milling increases.
The swelling and dissecting action of the phos phoric acid on the
fibers is explained on the assumption that part of the outer layer and more
of the building material between the fibrils in the various layers of the cell
wall are removed by the more drastic cooking conditions. Milling )as the
m li~aleffect of progressively rupturing the outer layer of fibrils and
of -the inner fibrils. Such an effect permits a more rapid attack
by t p'}oric aci d.
s suggested that the phosphoric acid treatment developed in the
study L r ;j d in this paper may be further standardized to provide a new
Mevd 7, t evaluation of pulp quality.

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Legends for Plates on Following Pages

Plate l--The middle-lamella lignin and the cell-wall lignin of red alder.
Plate 2.--Another transverse section of red alder which also shows the two
forms of lignin. Some of the middle-lamella lignin is slightly
out of focus because of making visible larger quantities of the
cell-wall lignin.
Plate 3.--A cross section cut from a block of yellow pine middle-lamella
lignin which was first impregnated with paraffin. The rough
appearance of the paraffin is due to a slight melting and re-
solidifying of the paraffin on the surface.
Plate 4.--A cross section of yellow pine middle-lamella lignin similar to
that of Plate 3. The section shows that the cellulose and the
cell-wall lignin can be removed with very little injury to the
middle lamella.
Plate 5.--Shows a separation of the delignified cell wall of elm into four
distinct layers by means of a 68 percent solution of phosphoric
acid.
Plate 6.--Short sections of dclignified elm fibers in which the cell wall
layers have been separated and slipped endwise.
Plate 7.--Delignified elm fiber which has received alternated treatments
with alkali and acid. The outer layor has been removed from a
large portion of the fiber. A helical band at approximately
450 koops the cell wall from rupturing.
Plate 8.--Delignified elm fiber treated alternately with alkali and acid.
Shows a separation of the cell wall into fibril bundles.
Plate 9.--Shows the transverse swelling of the inner layers of elm in places
at which the outer layer has been dissolved.
Plate 10.--Shows three separate layers of a delignificd olm fiber at the con-
stricted places and the transverse swelling of two inner layers.
Plate ll.--Section of the outside layer, showing helical striations extend-
ing around the fiber at right angles to the fiber's axis.
Plato 12.--Shows minute fibrils of the inner cell wall layers. The fibrils
have been loosened by phosphoric acid treatment.
Plate 13.--Shows appearance of a fiber after the fibrils have been well
loosened.
Plato 14.--Shows a more nearly complete separation of the cell wall layers
into fibrils.

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Plate 15.--Shous how the "fusiform" bodies in the fibrils can be separated.
Plate 16.--Cross section of Western yellow pine soaked in water. Note the
general rectangular shape of the cells.
Plate 1?.--Cross section of Western yellow pine which has been swollen with 15
percent alkali. Note the puffy appearance of the surface, the
thickening of the cell wall, and the general rectangular shape
of the cells,
Plate 18.--Cross section of Western yellow pine which has been delignified so
as to obtain isolated cells. On treatment with 15 percent alkali
the isolated cells assume a cylindrical shape with the lumen
closed.
Plate 19.--Short sections of delignified elm fibers, showing the bundle-like
residue obtained when the dissolving action of phosphoric acid
is arrested before the outer layer is removed completely.
Plato 20.--Shows that the fibrils between 1'icol prisms are luminous when
oriented at an angle to the axis of either Nicol prism, but
dark when parallel thereto.
Plate 21.--Radial face of Western yellow pine. The fibers are oriented par-
allel to the axis of one Nicol prism. The fibers are dark;
lines of the "dark cross" are parallel to the corresponding axes
of the Nicol prisms.
Plato 22.--Radial face of Western yellow pine between Nicol prisms, The
fibers are oriented at approximately 450 to the axes of the
Ticol prisms. The fibers are luminous; lines of the "dark cross"
are parallel to the corresponding axes of the Nicol prism.
Plato 23.--Spruce sulphite pulp. Pulp 3236; high yield; not milled.
Plato 24.--Sprucc sulphite pulp. Pulp 3236; high yield; milled 40 minutes.
Plate 25.--Sprucc sulphite pulp. Pulp 3236; high yield; milled 80 minutes.
Plato 26.--Sprucc sulphite pulp. Pulp 3236; high yield; not milled; treated
with phosphoric acid.
Plato 27.--Spruce sulphite pulp. Pulp 3226; low yield; not milled; treated
with phosphoric acid.
Plate 28.--Homlock sulphite pulp. Pulp 3317; high yield; not milled; treated
with phosphoric acid.
Plate 29.--Homlock oulphite pulp. Pulp 3314; lowi yield; not milled, treated
with phosphoric acid.
PFlto 30.--Spruce sulphite pulp. Pulp 3236; high yield, not milled; treated
with phosphoric acid.

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_n2.~~iosr,~I c f (-4 d.
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trc t c d Wi4t> C) S T)ori o cid.

-. O-,)--r:,c acid.
rulD. Pulp 3223;
p '-os-, -or- c acid..
pulp. Palp 32.3,27;
p.0 C. 0 ICi ,Cd.
.rrcs-OCr:Ic acid.
c-' ru I 25c
s 0 1-r1c acid,
-,no~ s or c acid.

lo'- ;'iold;

SI e'.

i.1 d;
y ield;

not m4.Iled; t( re--tce.
not milled; treated
killedd 20 i1:;
milled 2'in;s
milleI 40 ir ;
mile 0 m~ts

10 ld;milIc'd 80 miautc.~s;

10% 4 l'~d; zllod K0 minut :s;

low yi-ld; rn'lled 20 min-,,.es;
nihyiele_; milled 410 a~~
LL~ ~i'1 lled C ~'es;
lc-w --ield: milled C"C :n-*__, ,ts;
hiJ yeld;Milled 80 matc
low iold; mU-led SO mirues;




..A& w ..
AV
10
tz

12

13 14

is

t WTI
i 4




~L,

16 17

1

20

22

9 v

23

25

_; 4
27

26

29

30 3J 01

A!
''

P- 4

,Y 4
33 i




~4~

34 (

36 37

35rrr

40 41

38 E

39

42i t

43 44 4Si

\ rai
r
.-*;1--i
~-- ~
i i
.I !- i

46

H i . (I ? r 47 486

49)




Table l.--Strength and yield characteristics of experimental sulfite pulps
: : ::: ::
Pulp :Species:Yield in: Bleach : Bursting strength :: Tearing strength :: Folding strength
number : :percent :require- : --- --------------- ------------------- -------------------
:: of :ment in ::Milling time in min.::Milling time in min.::Milling time in min.
: :oven-dry:percent ::-------------------- -------------------- :--------------------
: : weight : :: 20 : 40 : 60 : o80 :: 20 : 40 : 60 : 80 :: 20 : 40 : 60 : 80
:: Points/lb./ream :: Grams/lb./ream ::Number double folds
: :hit :: :: ::
3226-I:hite : 45.2 : 10 ::O.50:o.73:0.77:0.72 ::1.47:1.61:1.81:1.66 :: 11: 4s: 154: 213
:spruce : : :: : : : :: : : : ::
3236-1: Do...: 53-8 : 28 :: .97:1.18:1.32:1.23 ::1.62:1.47:1.41:1.53 :: 577:1930:22S0:1167
34I~sen :4 :: : :: :: :
3314-I:Eastern: 43.4 : 28 :: -57: .66: .81: .78 ::2.17:2.40:2.25:2.04 :: 47: 246: 270: 289
:hemlock: : : : : :: : : : :: : :
3317 : Do...: : :: 72: .86:1.02: .96 ::2.10:2.45:213:2.00 :: 60: 170: 612: 87
3317 Do... : 46.3 : 28 :: .72: .86:1.02: .96 ::2.10:2.45:2.13:2.00 :: 60: 170: 612: 878
:: : :: : : :: : :::: :




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