Note: Descriptions are shown in the official language in which they were submitted.
648~9
This invention relates to a method of converting
lignocellulosic materials into use~ul products wi~hout waste,
and products of this method.
In the past th~re has been a great deal o~ waste in
the utilization of lignocellulosi~ materials, and particularly
wood. During logging operations, the limbs of trees are cut o~f
and are burned or left around to decay. In the mills a large
percentage of the wood is lost in sawdust, trimmings or cuttings,
and the like. Soma effort has been made to reduce the amount of
sawdust, and to convert the trimmings and cuttings into chips
for use in the manufacture of pulp. However, the waste is still
very great. In addition to this, many small trees are left
bahind in logging operations since it is uneconomical to cut and
handle them, and many species o~ trees and shrubs are not used
at all since they are not considered to be suitable for the
manufacture of lumber. ~ -
Many sources of lignocellulosic ~iber are not commer~
cially utilized for construction purposes because of inherent
characteristics that make them economically unattractive, such
as small diameter, low density, low resistance to decay, poor
grain properties, and poor strength properties. In many areas
or countries such weed species can constitute a significant, if
not the major, part of the available wood resource. In British
Columbia, Canada, Western red cedar constitutes a significant
part of the coastal ~orest, something o~ the order of 22%. -
However, its strength properties and pulp yield characteristics
are such as to make it of little commercial value compared to
such contiguous species as Douglas ~ir and hemlock. In some
tropical areas, such as Malasia, the desired species may occur
at such a low frequency per acre as to allow for only the most
; . . .
primitive segregation and cutting operations. In other areas,
the dominaDt vegetation consists of bushes, reeds, and other ~ -
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woody plants, not suited ~or conventional conversion into con-
struction products. In addition to this non utilization o~ non-
processed wood ~iber, is the very :Large amount of waste wood
generated in the most highly automated, high yield log conver-
sion systems. It is estimated that the waste wood amounts to
about 45% of the total tree, taking into account all low value
uses of residues for fuel and soil conditioning.
The present invention contemplates the production of
construction materials, such as lumber, various types of panels,
and the production of pulp, from any source of lignaceous
cellulosic fiber. The general idea is to break down any ligno-
cellulosic material into slivers, fibers or strands by any suit-
able means, such as by slicing, crushing, shaving, peeling or
the like. The aim in the breakdown is generally to produce as
long fibers as possible. During the breakdown there are pro-
duced small or fine particles, medium length strands and long
length strands. The fine particles are utilized in the manu-
facture of pulp and/or fiber boards, the medium lengths are used -
~
in the manufacture of strand boards, chip boards and/or particle
boards, and the long lengths are manufactured into dimensionedlumber and/or board products. It is this production of $he di-
mentioned lumber that makes the process or method practical,
since the lumber is engineered to give desired characteristics,
regardless of the type of the basic lignocellulosic material.
An important feature of this process is the ~act that it can be
operated to produce the various products in accordance with the
markat demand. If the demand for pulp is up and fol tha other
products is down, more of the material can be converted into
short lengths or particles. on the other hand, i~ the demand `~
for strand boards, chip boards or particle boards is up, the
percentage of medium lengths can be increased at the expense of
the long lengths. Howeuer, if the demand ~or lumber is up, as
3~ - 2 -
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~648~
many long lengths are produced as possible. As the lumber pro-
ducts have the highest com~ercial value, it is usually desirable
to aim to produce the highest possible amount of long length
fibers.
~he general advantages resulting from this process
carry on into the dimensioned lumber field. The lumber can be ~ ~
produced in size and characteristics in accordance with the -
market demand. For exampleJ if there is a ralatively great de-
mand for two by fours, a large percentage of the long fibers can
be converted into these. On the other hand, if other boards or
timbers are particularly required, the production can be concen- `
trated on these. - -
This is a concept that caD revolutionize the wood ~ ~-
product producing industry. Heretofore9 the trees were converted ~ ; ~
: into the best or highest paying products possible. However, with ~ -;
the prior production methods, the control of the type o~ lumber
produced-is very limited so-that if a large number of, say, two ~
by fours are in demand, the operation will also result in ths
production of large number of boards or lumber of different sizes ~ ;
:- .
which may not be required at the moment. Thus, a producer can
end up with a large inventory of boards not needed at the moment
when he tries to fulfill the sudden demand for boards or lumber ~ ;~
of other dimensions.
The main product of this process is the dimensioned
lumber. It is possible to make any number of boards of the
same or dif~erent dimensions, and these can be given desired
characteristics regardless of the original source of matsrial.
The term "board" as used herein is intended to include all kinds
of boards, timbers and lumber of any desired dimensions.
As stated above, the lignocellulosic materials can be
broken down in any desired manner. The fibers are separated by
length into those fractions most suitable for the required end
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~0~;~809
use, treated with such additives as may be needed to give the
required resistance to decay and ~ire, dried either before or
after the addition of adhesives, or they can be left undried,
and then combined with a binding material, and, possibly, com-
bined with non-cellulosic fibers, such as glass, metals and
plastics, and formed into a mass and either cast, molded, extruded
or pressed into the desired end product.
Any method of breaking up the raw lignacious cellulos
material into fibers will develop a wide range of fiber lengths
and diameters. The most profitable and useful end use is a lum-
ber product suitable for CODstruCtiOn purposes, followed by a
strand panel board with strength properties similar to plywood, ;~
chip boards, and lastly the particle board for essentially non~
structural usas. A possible segregation of the particles in the -~
following lengths for the specified purposes is as follows: -
Dimensioned lumbar 6" to 4 feet
Strand board 2" to 6"
Chip board ~" to 2"
Particle board Less than ~"
Pul~ Less than ~"
An excess of any ~raction can be broken down into lower lengths.
All of the products than can be produced by the
present process, excepting the dimensioned lumber, are produced
by known processas.
~ owever, this invention contemplates tha production
of dimensioned lumber from any lignacious cellulosic ~aterial.
Use of this concept will significantly affect the conventional
forestry practices from the present emphasis upon mer~hantable
lumber to that of a maximum yield of woody fiber per acre, and
will result in a true tree farming approach utilizing fast grow-
ing, short cycle, high vield species rather than the present
slow growing long cycle species.
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As stated above, one of the advantages of the present
process is the utilization on non-commercial "weak" specias in
the production of good grade lumber. Some species of wood, such
as aspen and alder, are considered low value species and little
used for commercial purposes because of their very low yield
of merchantable lumber per/unit/acre of logs. This low yield
is due to the small size of log, the low strength properties
and the incidents of compr~ssion and tension wood causing warp-
ing and twisting. Utilization of these species in the manufacture
of the various products in accordance with this process makes
very large volumes of wood available for commercial use. A ~;
large percentage of the wasts from the standard logging sawmill
and manufacturing procadures can be converted to dimensioned
lumber having more value than the use of these materials for
pulping. Smaller trees and shorter harvesting cycles can be used
in order to give an increase in wood yield from given acreag~
The present process lsnds itself to the production of
a uniform density material with guaranteed strength and durabil-
ity properties, free from the inherent defects of normal lumber-
knots, splits and density variations.
The strength properties of wood increase with increas-
ing density. All species for which data is at present available ;
show this increaseO This relationship of strength properties to
density is of major commercial significance in the use of lumber, - ;~
resulting in allowable design stress values significantly below
that of the average strength values of the species involved.
Variations in the density of wood are due to variations in its
structure and the presence of extraneous constituents. The
structure is characterized by the proportional amoLInts of
different cell types, such as fibers, tracheids, vessel ducts,
and rays, and by their dimensions. Hereditary tendencies,
physiological and mechanical factors, position in the tree trunk,
; - 5 -
1064~
all affect the density of the wood. The relationships are very
complex and not well understood. The result is a wide variation
in density within any ona species which can be as large as a
factor of 2 to 2~. The dimensionad lumber of the present inven- -
tion overcome these inherent variations in normal lumber proper-
ties.
By choice of compressed density, resin solids and
strand geometry, particular properties can be imparted to an-
gineered or dimensioned lumber. A range o~ lumber-like products
can thus be engineered to use specifications, and these are com-
petitive on an engineering basis with solid lumber, metals,
plastic and concrete.
If desired, fire retardants, preservatives, colorants
and the like can be added to the particles or strands used in
the production of the dimensioned lumber. `
The engineered or dimensioned lumber produced by this
process-is-made-up of callulosic-~ibers-or strands ranging from
about 6 inches to about 4 feet in length, and having a width of
about 0.05 to 0.25 and a thickness of about 0.05 to about 0.5
inch. These fibers are coated with adhesive in standard coating
equipment, such as drum applicators or curtain applicators. A
water insoluble structural glue, such as phenol formaldshyde, is
used to coat the fibers, although any suitable type of glue can
be used. The coated fibers are arranged in bundles and then
subjected in presses to pressures sufficient to produce a fin- ; ~
ished product having predetermiDed dimensions and density. The ~ ;
pressures and temperatures used are sufficient to produce the
desired density. For e~ample, pressuras of from about 100 to
about 400 psi have been found to be suitable, and the ~ibers ara
subjected to a high enough temperature for a time sufficient to
produce a temperatura of at least 212F within the product. For
example, a temperature of 300F for up to 30 minutes has pro-
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106480~
duced desirable products, but this time can be reduced. Ifhigh ~requency energy is used for providing the heat, the press-
ing can be done in around one minute.
Referring to the accompanying drawings,
Figure 1 diagrammatically illustrates apparatus ~or
carrying out the method in accordance with this invention,
Figure 2 illustrates one way of producing lignocellu- ;
losic material to useful fiber lengths,
Figure 3 illustrates a piece o~ dimensioned lumber
made in accordance with this invention,
Figure 4 is a graph comparing the modulas of elastici$y -
~to density in engineered lumber,
Figure 5 is a graph illustrating the relationship o~
the resin solids used relative to the modulas of elasticity,
Figure 6 is a graph illustrating the ef~ect of strand
or fiber length,
Figure 7 dia_rammatically illustrates the direction of
springback oi some forms of dimensioned lumber, and .
Ei~gures 8, 9 and 10 ara graphs illustrating specified
charactsristics of the dimensioned lumber.
Figure 1 diagrammatically illustrates apparatus for
carrying out the present invention. The lignocellulosic material
such as logs, roots, branches, waste wood, shrubs and the like,
are ~ed to a brsakdown device 10 where they are sliced, crushed
or otherwise broken d~wn into fibers. It is desirable to produce
long strands or fibers for USQ in the manufacture of dimensioned
lumber. For example, these can be f~om 6 inches to 4 feet in
length, 0.05 to 0.~5 inch in width, and 0.1 to 0.5 inch in thick- ~ -
ness. In the general breakdown there will be fibers o~ medium
length and very short fibers. The general aim is to produce as
many long fibers as possible since these are used in the produc-
tion of dimensioned lumber which is ths most valuable product
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~0648~g
for the market. It is at this point that the final output of
the process can be controlled. The short or fine fibers are used
for pulping or fiber boards, while the medium length fibers are
used in the manufacture of strand boards, chipboards, particle
boards and the like. If the demand for pulp and/or these differ-
ent boards goes up relative to the demand for dimensioned lumber,
more short fibers and/or medium fibers are produced at the break-
down device 10.
The fibers from device 10 go to a separator 12 which
separates out the short length fibers to be used in the manu-
facture of fiber boards or pulp, or for any other purpose for
which short length fibers are suitable.
Some or all of the medium length and long length fibers
may be directed to an applicator 14 where they are treated with
fire proofing material, insecticides, preservatives, stains or
the like before being sent on to a dryer 16. Some or all of
these fibers can be by-passed directly to dryer 16. The moisture
content of the fibers is reduced to the desired extent for the ~-~
production of the final product. If desired, the medium length
fibers may be separated ~rom the long length fibers before they
reach dryer 16, in which case the different groups of fibers
would be separately dried in accordance with the demand. ~
In this example, the fibers from dryer 16 go to a ?
separator 18 which separates them into the long fibsrs and the
medium fibers. The long fibers go to a glue applicator 20 which
may be in any desired form, such as a drum applicator or a
curtain applicator, and from here they go to a prass or mold 22
which presses them under heat and pressure into lumber of desired
dimensions and the desired density. There is another control at
this point, that is, the dimensions of the lumber produ~ed is in
accordance with the demand. For example, if there is a great
demand for two by fours, the percentage of these would be high
. ~.
ILCl 6~
relative to boards of other dimensions ~or which the demand was
not so ~reat. Although this diagram merely shows one press or
mold 22, it is obvious that there cDuld be several presses so
that boards of different dimensions could be made at the same
time.
Separator 18 separates out the medium fibers from the
long fibers, and these are directed to a glue applicator 24,
whence they travel to a press 26 which produces the type of
boards required, such as strand boards, chipboards, particle-
boards, and the like. Here again, although one press only is
shown, there may be several. In addition to this, the "press"
is intended to mean any system necessary to produce the desired
particle-type board.
What actually happens in this method or process is
that ths original material is broke~ down into fibers of di~fer-
ent lengths, and then these are reconstituted into dimensioned
lumber, particle-type boards, pulp and the like. With this ~ -
arrangement, there is no waste. In addition, the process is
geared to handle all of the particles produced from the original
material, regardless of their length, and regardless of whe~her
the lengths are accidentally or intentionally produced.
Figure 2 illustrates one way of reducing lignocellu-
losic material, such as a log, to useful fiber leDgths. A log
30 is cut by suitable slicing material into slices 31, and then
each slice 31 is cut into relatively thin pieces 32 which extend
the length of slice 31. Each piece 32 has a desired width, such
as 0~05 to 0.25 inch. Then each piece is cut transversely into
strands 33 of desired thicknesses, for example, 0.05 to 0.5 inch.
These preferably are the length of the pieces 32. It is obvious
that during this slicing or cutting process~ there will be a lot
of fibers which are considerably shorter than the strands or
iibers 33. As stated above, the medium length fibers can be used
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in the production of particle-type boards, and the short fibers
can be used in the production of pulp, or ~or other desired
purposes. ;
Figure 3 illustrates a piece of dimensioned lumber or
board 38 made up of strands or fibers 33. These strands or
fibers, after being coated with a suitable adhesive, are laid
side by side and then pressed under heat and pressure into a
board of desired dimensions, such as, for axample, a two by four.
These strands can extend the full length o~ the board, as shown,
1~ or each strand may extsnd only part way through-out the length
of the board. The strands are laid side by side, but as these
are of random dimensions and lengths, they interlock to a degree
so that there are no straight glue lines extending from one sur-
face to the other of the board. The density of the finished pro-
duct is determined by the amount of pressure and heat used in
the press. This is another advantage of this method, that is
the boards produced can be not only of desired dimensions, but -
they can be made in desired densities in accordance with the ~-
purpose for which they are designsd. In addition, it is po~sible
to subject the long strands to a continuous pressing operation so ;~
that boards of any desired length can be produced. As the strands
are interlaced to a certain degree, any length of board can be
produced.
Although the lengths of the strands for dif~erent
purposes can vary, the following is an indication of practical
leDgths for the different pUrpQSeS~
Engineered lumber 6 inches to 48 inches `~
Strand board 2 inches to 6 inches
Chipboard ~ inch to 2 inches ~ -
Particle board Less than a ~ inch
Pulp chips and
sawdust
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~0648~
In the manufactured or dimensioned lumber, the re~
sistance of the glueline to horizontal shearing ~orces is pro-
portional to tha length of the fiber to which the stress îs being
transmitted to the glueline. It i5 also inversely proportional
to the thickness of the glueline wh:ich is rel~ted to ths ~iber
thickness to the extand that the degree to which a "closest
packing" condition of the fibers is achieved. The optimum resin ;~;
content for any set of variables is that at which maximum strength
properties are obtained, all else being equal. Theoretically,
too little resin gives insufficient coverage, and too much resin
causes thick gluelines, thereby reducing strength. Variables
affecting the optimum resin content are the fiber geometry and
the pressure applied during the curing of the resin.
The thing that makes this process an economical success
is the fact that engineered or dimensioned lumber can be made
with equal strength to that of top structural grade Douglas fir
lumber. This can be either on an equal density basis using ~- ;
optimum fiber geometry ~nd adhesive content, or it can be on an ;
increased density basis using less favourable fiber geometry and
adhesive content. The strength of the engineered lumber is
essentially independent of the raw material species, but in-
creased "springback" with moisture absGrption occurs with the ~`
use of low dansity species. The durability and stability are
mainly controlled by adhesive content.
Strength-Density Relationship for Engineered Lumber
Figure 4 shows plots of the strengths (Modulus of
Elasticity,MOE) against compressed density for engineered lumber
made from 1/8" Douglas fir strands under the following con-
ditions:
Strand length 6", 12", 24"
Resin solids 1, 3, 5% (Phenol formaldehyde
solids to dry wood percentage)
Press pressures 100 to 400 psi
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8091
These plots show that for any givan condition of
strand length and resin solids the strength of tlle engineered
lumber increases with increasing compressed density. The rates
of increase, i.e. the slope of the strength with density are
equal (the lines are parallel). This linear increase of strength
with the density is characteristic of ~ood, i.e. if the clear
wood strengths of the commercial western softwoods (USDA "Wood
Handbook", p. 75-77) are plotted against ovendry density, a
straight line is obtained shown by the heavy straight line in
Figure 4. This line has the same slope as the engineered lumber
lines and acts as an upper limit of those lines.
It will be seen that the 24", 5% line is coincident
with the limiting wood strength line. It is believed that no
engineerad lumber can be made with graater strength at a given
density than this clear wood strength limiting line.
In Figure 4 the MOE requirements of two grades of
Douglas fir lumber, select structural and No. 3 structural are
shown by horizontal lines (Standard Grading Rules No. 16, WCLIP,
p. 135). This shows how engineered lumber can be made with ~-~
equal strength to these grades for all conditions of strand
length and resin solids which cross the horizontal strength -
lines. For a given grade increased density is required to com~
pensate for shorter strand lengths and reduced resin solids.
Strength Versus % Resin Solids
Figure 5 shows that the optimum resin solids percentage
is in the range 3-5%. The plots at equal press pressure (and
resulting density) level off in this range, any increment in
resin solids giving only a marginal increase in strength. This ~i ;
resin solids range is for 1/8" square cross section strands.
Increasing rasin solids would be required for smaller strand
section because of increasing specific surface area in the
engineered lumber and vice versa with large strand cross sections.
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1~;4~9
Ef~ect of Strand Length on Strength
Lines taken from Figure 4 are plotted in Figure 6
to show the effect of strand leng-th on strength at equal resin
solids (5%). Tha 24" line is almost coincident with the clear
wood strength line, the 12" line is about 20% below the clear
wood strength line, and the 6" line is about 50% below. The
clear western softwoods MOE density line can be assumad equi-
valent to engineered lumber with infinitely long strands. Thus
the 24" strand lengths are the best approximation to infinite
strand lengths. The 24" length on an 1/8" square cross section
corresponds to a length to diameter ratio of 200:1 which has
been established as the optimum fiber geometry for glass ~iber
composites. (Motavkin, A.V., et al "Choice of Optimu~ Structure
of Glass Fiber Based Materials", Mekhanika Polimerov 5 (2):
288-297 (1969).
Thickness Swell of Engineered Lumber
After Moisture Absorption
The compression of the engineered lumber to any
desired density has a disadvantage of "springback", the permanent
residual thickness swelling which occurs on release of the com-
pressive stress with moisture absorption. This "springback" ~`
phenomenon is also experienced in particleboard type products. `~
In angineered lumber the thickness swelling and "springback" is
dependent on the overcompression above the unco~pressed density
of the strand bundles (extrapolate the lines back to the density
X-axis), the resin solids and the strand geometry. This
permanent "springback" of about 5% for optimum strand length and
resin solids is not disadvantageous in lumber type applications
of floor joists and wall studs where the swelling would be re-
stricted to the smaller dimension direction as shown in Figure ~.
Effect o~ Species on Thickness Swell and "Springback"
Figure 10 shows the comparison of residual thickness
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11)648~9
swell in tha compressed direction ("springback") of aspen with
that of Douglas fir for equal strand length and resin solids
conditions. It will be seen from the Figure that aspen has a
greater "springback" than Douglas fir (about 7% more swell for
all densities). This difference can be accounted for if the two
5% 24" lines are extrapolated back to the density X-axis at 20
and 26 lb/cu. ft. for aspen and Douglas fir, respectively. The
6 lb./cu. ft. difference is approximately equal to the differ-
ence clear wood dry densities (30.4 23.2 = 7.2) between ~
Douglas fir and aspen. `;
Thus the influence of species on swelling character-
istics can be predicted with reference to the Douglas fir data
by comparison of clear wood dry densities and drawing lines para- ~
llel to the established Douglas fir standard swell lines. ~ ;
Engineered or dimensional lumber can be made with any
desired strength to above that of the structural ~rade of a ;~
high strength wood species, such as Douglas fir, by using wood
fibers obtained from low quality logs and combining fiber length, `~
resin content and final product density. The exact combination
of fiber length, resin solids and final pressed density chosen
will depend upon the econo~ic and technical situation, such as ;~
the fiber length in stock, the co~t of the raw materials, and
the wood species available. Examples of such combinations to -~;
meet various grades are shown in the following Table: -
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TABLE
Group Grade MOE Species Fiber Resin Density
1,000,000 Length In. Solids Lbs/Cu/
% Ft.
A Douglas Fir
Structural
Selsct and
No. 1 1.93 24 5 30
24 3 31.2
2~ 1 35.5 -
Douglas Fir 12 5 32.6 :
12 3 35.6
12 1 40.0
6 5 36.0 ~i
Aspen 24 5 35
W. Red Cedar 24 5 31
12 5 32
Douglas Fir
Structural
No. 2 1.74 24 5 27.O ~.:
24 3 29
24 1 34.5
12 5 30.5 :~.
Douglas Fir 12 3 32.7 -.
12 1 3~.5 ~-
6 5 34.2
6 3 37
Aspen 24 5 31.5 :~:
Douglas Fir W. Red Cedar 24 5 31.5
Structural 12 5 30.5 .: :
No. 3 and
Light Framing 24 5 25.0
Construction 1.54 24 3 27
Standard and 24 1 31.5 --
UXility Douglas Fir 12 5 28
12 3 30.5 ;:
6 5 34 : :
6 3 34.5
6 1 40 .
Aspen 24 5 28.5
W.Red Cedar 24 5 28
12 5 23.5 ~`
B Pacific Hemlock 1.30 24 5 23
Structural No.3 24 3 25 : .
and Light Framing 24 1 29
Construction. Douglas Fir 12 5 26 -
Standard and 12 3 28 ::
Utility. 12 1 33.5 ~:~
6 5 31
3 32.5
6 1 38
Aspen 24 5 25
W.Red Cedar 24 5 23.5
12 5 25~5
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As can be seen, the strength of the engineered lumber can be
independent of the raw material species so that weak species,
such as Aspen and Western Red Cedar, can be used in the manu-
facture of the highest strength lumber grades, even though their
natural occurring densities of 23.7 and 20.6 lbs/cu. ft., re-
spectively, would normally relegate them to the lowast strength
grade of 1.00 MM psi MOE. The actual volume of dry fiber re-
quired per MFBM of engineered lumber will depend upon the re~
quired grade, tha density of the wood specias, the required
density of the engineered lumber for that species, and the length
of the fibers. In practice, it is possible to mix species and
fiber lengths in various proportions to make the most effect-
lve use of the available raw material.
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