USES OF WOOD WSTES IN PULP xND PAPER PRODUCTS
C. E. HRUBESKY, Chemist
, ~Forest Products Laboratory,p Forest Service..
U, S., Department of Agriculture
-j .. .
Wood waste from logging and the manufacture of wood products often presents
a problem of disposal. Since the quantities produced in single operations
are frequently too small to consider developing a new pulping operation, a
logical procedure in such cases is to investigate the possibilities of
supplying the material to pulp and paper mills that may be operating in the
Wood waste in.the form of slabs, edgings, trim, chips, shavings, and veneer-
mill waste as produced in various woodworking operations, is acceptable to
many mills*- This type of waste is likely to be more acceptable if it is
prepared or processed to a uniform size or graded into different sizes,
Shipping distance is also an important factor in determining the accepta-
bility of a waste wood material. Methods of handling, bundling, baling, and
the like, must be considered with the view to reducing transportation and
The types of products in which wood wastes are being utilized at present
are chemical, semichemical, and groundwood pulps, and coarsely fiberized
wood, all of which are used in the manufacture of various kinds of paper,
roofing and saturating felt, container board, insulating board hard-
board. ., .__I
D ,- T v 1 97 2
Although wood wastes frequently produce pul inferior to those made rom
round wood, they may offer an important sour of raw material to su element
the wood supply of a pulpmill. This waste wi1 generally.rn W.yte@rl ies
less desirable for pulping and will come to t Fmi. '1-yvg r such as
S slabs, edgings, trims, chips, shavings,and venee acres from plywood plants.
Some of the waste material can undergo routine barking and chipping and be
maintained at iadison, Wis., in cooperation with the University of
-Various uses of these wood wastes are described in Forest Products Laboratory
,Reports Nos. R1666-1, "Uses for Sawdust and Shavings" and R1666-2, "Uses
for Slabs, Edgings, and Trims."
& May 1953
Report No, R1666-6
used along with the regular supply of pulpwood chips. It may be necessary,
however, to subject material that is difficult to bark and chip to a
separate digestion under conditions adjusted to the material at hand.
A waste material available in the pulpmill itself is a residue of coarse
sawdust and pin chips from the slashing and chipping operations. This
material has received only limited consideration because it is dirty and
contains only short fibers. Although the fiber loss in operations subsequent
to pulping may be high, low-quality pulp can be obtained from sawdust.1 It
appears advisable, however, to mix sawdust with at least 25 percent of
ordinary-sized chips for satisfactory operation. Experiments at the Forest
Products Laboratory and elsewhere have shown that the pulp from sawdust is
strong enough to be used in mill wrap and low-grade board.
Soda pulp is being produced from both hardwood and softwood veneer-mill waste.
Veneer trim is passed through special chippers, usually at the veneer mill,
and is sold to pulpmills in the form of chips. The veneer cores, being
easily handled in round form, are sold to pulpmills where they are chipped in
the mill chippers.
The sawmill waste used by sulfite mills in the Pacific Northwest in 1951
amounted to about 5 percent of their total wood supply.!i Approximately 1-1/4
million air-dry tons of sulfite pulp were produced; the amount of pulp derived
from sawmill waste was estimated at 60,000 air-dry tons.
A considerable tonnage of kraftpulp is being produced from sawmill waste in
the form of slabs and edgings,/ W h is unsuited for lumber because of low
grade or decay, and the residue from plywood plants. This material is either
chipped at the wood mill and sold to the pulpmill as chips or is transported
to the pulpmill in whole form where it is chipped in special chipper and
made into pulp for use in bag stock, toweling, and kraft specialty papers.
In 19522, sulfate mills in the Pacific Northwest replaced much of their log
and pulpwood requirements by chips from mill residues that would otherwise
have been burned.
ILn utilizing slabs and edgings for chemical pulps, the amount of bark present
affects the type of pulp and the end product for which the waste material can
be used. For the production of clean light-colored pulps by the sulfite
process, a very little bark is objectionable, For the production of kraft
pulp to be used in container board and cheap wrappings, where cleanliness of
the pulp is not of major importance, considerable bark can be tolerated.
hill, ,. H. Substitutes for Round Pine jood in Making Klkaline Pulps.
Paper Trade J. Vol. 119, No. 19, pp. 185-187, 19U44.
-4dammond, k. N. The Utilization of Wood Waste in the Manufacturing of
Chemical iulps in the Pacific Northwest* Forest Products res. Soc. Proc.
Vol. 5, pp. 150-154. 1951.
4Pacific Northwest Forest and Range Experiment Station. Annual Report -
1952, pp. 9-10.
Report No. Nl666-6
In sulfate pulping tests at the Forest Products Laboratory6- on kraft-type,
bleaching sulfate, and sulfate semichemical pulps, the presence of bark
caused (1) an increased in yield of pulp from a cord of rough pulpwood,
(2) an increased in consumption of active chemicals during cooking, and
(3) a decrease in brightness of the pulp, or darker-colored pulps. Over a
range of 0 to 25 percent bark, the active alkali required per ton of pulp
is directly related to the percentage of bark, and increases at the rate of
13*4 pounds of active alkali for each 1 percent of bark.7
Semichemical pulping can be broadly defined as a two-stage pulping process
involving chemical treatment to remove part of the lignocellulose fiber-
bonding material and mechanical refining to complete the pulping action.
This process has been found particularly well suited to the pulping of
certain litte-used hardwoods, often termed "waste woods," although excellent
pulps have also been made from softwoods.
As the result of work at the Forest Products Laboratory some 20 years ago,
the first applicLtion of the semichemical process to the production of
corrugating boards from extracted chestnut chips has developed into an
industry which supplies a considerable tonnage of this material today.
Large quantities of semichemical pulps from other species are used for
insulating board and container board.
Experiments at the Forest Products Laboratory-8 have shown that oak slabs
containing as much as 20 percent of bark can be used for the manufacture of
corrugating board through the semichemical process. Other forms of wood
waste are also used in making this product in one or two commercial opera-
tions. With some woods a considerable amount of bark can be tolerated and
with others, very little reduces pulp quality.
Groundwood pulp made from veneer cores, wood-mill slashings, bolts of solid
wood that are unsuitable for lumber, and from presteamed Douglas-fir slab wood
is used in the manufacture of corrugating board, bags, and toweling paper.2
-luartin, J. S., and Brown, K. J. Effect of Bark on Yield and Quality of
Sulphate Pulp from Southern Pine. Tappi Vol. 35, No. 1, pp. 7-10, 1952.
-%llo, G. F. Review of Alkaline Pulping Procedures in Canadian Mills. Pulp
and Paper Ind. Vol. 20, No. 2, pp. 62-63. 1946.
-Kel]er, L. L. Effect of Bark in the Neutral Sulfite Semichemical Pulping
of Aspen, Hickory, and Slash Pine. Tappi Vol. 33, No. 11, pp. 556-560.
2Anonymous. Waste wood a Challenge that Built the Longview Fibre Company,
Pacific Pulp and Paper Ind. Vol. 15, No. 3, p. 10. 191l.
Report No. R1666-6
There is considerable demand at present for coarse fibers for upe in roofing
and saturating felts. Roofing felt mills procure their wood in several forms
logs, mill waste, chips, and coarse fiber. Where it is obtained as log and
mill waste, it is first reduced to chips, then reduced to coarse fiber in an
Asplund Defibrator. dhen received in chip form, the wood goes directly to
the fiberizing machine. Although Asplund fiber can be pressed to remove free
water and be baled for shipment in a damp condition, it is not known that
this is being done at present. The fiber is ordinarily used in the felt mill
where it is produced.
Several plants in this country supply to roofing felt mills in their vicinity
a coarsely fiberized wood product, which is produced by a dry shredding
Among manufacturers of machines adaptable to the manufacture of coarsely
fiberized wood are:l0
Allis-Chalmers bufg. Co., West qllis, wis.
American Defibrator, Inc., Chrysler Bldg., New York, N. Y.
Bauer Bros Co., Springfield, Ohio
Pandia, Inc., 122 E. Forty-second St., ,iew York, N. Y.
Sprout-Jaldron and Co., iuncy, Pa.
Sutherland Refiner Corp., Trenton, N. J.
Fine sawdust (6 to 8 mesh) is finding some use in saturating felts where it
acts as a filler and probably increases the absorptive power of the felt for
For making these fibers, it is said to be desirable that the wood waste be in
a green or moist condition rather than dry. Some manufacturers claim that
the fiber obtained from air-dry wood causes the felt to be brittle and weak.
Insulating Board and Structural Board
Wood waste has assumed importance in the production of insulating board and
hardboards. Low-density softwoods and hardwoods are mostly used. ,ith new
developments in fiber processing equipment, the denser types of hardwoods
will probably come into greater use. The wood wastes used consist of cull
sawlogs and pulpwood logs, slabs and edgings, byproduct chips from naval
stores extraction, and pulpmill screenings. In addition to wood, several
agricultural waste materials and vaste paper are used in the manufacture of
some wall boards.
A modern insulating-board plant usually requires from 150 to 200 cords of
wood per day and costs from 2 to 3 million dollars. The output of such a
mill will be from hOO to 500 thousand square feet of 1/2-inch board per day.
-Inclusion of names in this list, which is undoubtedly incomplete, implies
no endorsement as to quality or prices.
report ;o. R1666-6
Sawmill waste in the form of chips is being supplied to several insulating-
board mills as raw material for insulating-board stock. In some instances
wood chips are steamed or given a mild digestion for a short time in a
digester and then passed through refiners. Asplund pulp is also used for
Processed raw w od offers possibilities as a cheap component of insulating
board or hardboard. The waste in the form of slabs, edgings, or round wood
can be fiberized, or chips or hogged wood can be passed through a disk
refiner without any previous treatment other than wetting with water.
Although fibers produced directly by these methods may have low strength
characteristics, they are suitable as fillers for boards where strength is
of secondary importance. One advantage of this type of material is that
wood wastes can be fiberized in small quantities, baled, and shipped to mills
for conversion into boards.
Work at the Forest Products Laboratory-! has a own that pulps suitable for
insulating board and hardboard can be made from slabs, edgings, planer ends,
and hogged veneer of Western hemlock, iDouglas-fir, or white fir. The waste
was chipped, steamed mildly to soften the chips, and fiberized in a disk
In 1952, ten hardboard plants in operation or under construction in Oregon
and '.'ashington, with a rated capacity of approximately 450 million square
feet of 1/8-inch board per year, based their production on a raw material
supply otherwise wasted.-_ One plant will operate on cull white fir timber,
while the rest will use either sawmill or plywood residues.
A satisfactory insulating board can be made from wood-mill sawdust held
together with a binder of highly beaten wood pulp.13 Following methods
described in United States patents issued to Howard iieiss in 1927, boards
were made at the Forest Products Laboratory containing as much as 85 per-
cent sawdust previously processed in an attrition mill, and 15 percent
hydrated pulp. Since these boards were hand made on a small scale, no major
difficulties were encountered in their formation, pressing, and drying. Be-
cause of the low drainage and felting properties of this type of material,
these mixtures might not run well on conventional continuous board machines
but probably would be suitable for small-scale batch operations.
Although the effect of heat-treating structural board (hardboard) to increase.
its breaking strength has been recognized for many years, it is only recently
that it has been applied in general practice._ In this treatment the board
is carried from the press and held for 4 to 5 hours in a chamber heat-d at
llSchwartz, S. L., Pew, J. C., and Schafer, E. R. Production of insulating
Board and Hardboard from Sawmill and Logging 'jiaste. Abstract in Paper
Trade J. Vol. 124, No. 8, p. 36. 1947.
12Pacific Northwest Forest and Range Experiment Station. Annual Report -
1952, pp. 9-10.
-1U. S. Forest Products Laboratory. Insulating Boards from Mill Wastes,
Forest Thinnings, and Cull Trees. Forest Products Laboratory Report
No. R1762, 15 pp. 1950.
IL4owgren, Uno. ViJallboard manufacture in Sweden by the Defibrator System.
Pulp and Paper Ind. Vol. 21, No. 1, p. 50. 1946.
Report No. R1666-6 -5-
120* to ihO" C. It is then passed through a section with circulating moist
air to stabilize it for atmospheric conditions. The heat treatment usually
increases the modulus of rupture about 25 to 30 percent, but at the same time
increases the brittleness. *ith prolonged heat treatment, the modulus of
rupture increases to a maximum, after which it drops rapidly. The rate of
increase and drop in strength increases as the temperature increases.
Hardboard can also be made by a dry-forming process. The pulp, instead of 11 2
being carried as a water suspension onto a screen for formation, can be -
formed in a dry or semidry condition and hot pressed into a board which is o _
usually given an additional heat treatment. The properties of the board cm
are greatly influenced by additives such as waxes and resins. p-B
In preliminarj work at the Forest Products Laboratory, several structural a
boards were rm;.e by dry-forming mixtures of sawdust with rosin and coal-tax I
pitch. nIlthough the strength of these boards was below that required by
Federal Specification LLL-F-311 for a Class A hard-pressed fiberboard, the
product had a resistance to abrasion equal to that of eak wood, which might
make it suitable for molded tiles to be used as a prefinished floor covering.
Since strength and color can be quite variable in a satisfactory corrugating
board, this type of product forms a ready outlet for wood wastes. As
mentioned previously, kraft and semichemical pulps from wastes are being used
for large tonnages of corrugating board.
Current experiments at the Forest Products Laboratory indicate that
furniture-mill waste, mostly hardwoods, can be made into a product comparing
favorably with commercial corrugating board by converting the waste into a
semichemicdl pulp and processing it in a disk refiner.
It is reported15 that a satisfactory fiber for conversion into boxboard
and coarse papers was prepared from wood waste, shavings, and sawdust by
treatme:nt in an Asplund Defibrator-Chemipulper followed by refining in a
Report N"o. R1666-6
-1hurch, J. 1ti Fibre from '.Waste '.iood. Pulp i Paper bag. Can. Vol. 47,
No. 3, p. 275. 1946.