Medium density, high strength lignocellulose composition board including exhaustively hydrated cellulosic gel binder

A medium density, high strength lignocellulose composition board comprises on a dry weight basis from 60 to 95% lignocellulose particles and from 5 to 40% exhaustively hydrated cellulosic gel binder, the gel binder being characterized in its gel condition by a TAPPI drain time of at least 350 seconds.

BACKGROUND AND BRIEF DESCRIPTION OF THE INVENTION 
This invention relates to lignocellulose composition boards. It pertains 
particularly to wood composition boards of high strength and medium 
density, e.g. a density of 20 to 50 pounds per cubic foot. 
In the building trades need exists for a composition board, specifically a 
wood fiber board, of medium density and increased strength which retains 
the other necessary and desirable fiber-board properties of dimensional 
stability, thickness swelling, water absorption, uniformity, and the like. 
If such a fiber board product were to be available commercially, it could 
be substituted in building materials specifications for fiber boards of 
substantially higher density. This would result in significant savings of 
raw materials, as well as in important economies in building material 
costs and transportation costs. 
Accordingly, it is the general purpose of the present invention to provide 
a composition board product of medium density and greatly increased 
strength which is characterized also by acceptable properties of 
dimensional stability, thickness swelling, water resistance, and 
uniformity. 
It is a further purpose of the present invention to provide a composition 
board product of low cost which can be produced in high yield from its 
original starting materials. 
A further object of the present invention is the provision of a composition 
board product which does not require the inclusion together with its 
primary fibrous lignocellulose component of an excessively large quantity 
of an exotic binder of high cost. 
Still another object of the present invention is the provision of a 
composition board product including a low cost binder which serves the 
ancillary functions of acting as a dispersant for the lignocellulose fiber 
component of the board, as a fines retention agent, and also as a board 
density control agent. 
A still further object of the present invention is the provision of a rapid 
and economical process for the manufacture of composition boards having 
the above noted qualities of medium density and high strength. 
I now have discovered that the foregoing and other objects of the present 
invention are achieved by the provision of a medium density composition 
board comprising broadly, on a dry weight basis, from 60 to 95% by weight 
of lignocellulose fiber and from 5 to 40% by weight of a unique cellulosic 
gel binder. As will be described in detail hereinafter, the cellulosic gel 
binder employed is exhaustively hydrated so that it is characterized in 
its gel condition by a TAPPI drain time of at least 350 seconds, 
preferably at least 900 seconds, and specifically from 900 to 2000 
seconds. 
The medium density board product of the invention has a density of from 20 
to 50 pounds per cubic foot. However, it has strength properties which are 
characteristic of prior art fiber boards having a much higher density. For 
example, a medium density fiber board of the invention at a density of 30 
pounds per cubic foot meets the current product standards of the American 
Hardboard Association for building siding and furniture cores for wood 
fiber boards having a density of 42 pounds per cubic foot. The standards 
met include modulus of rupture, tensile strength, thickness swelling and 
water absorption. The savings in raw material use, transportation costs, 
and product cost resulting from the substitution of the hereindescribed 
medium weight product in building specifications are immediately apparent. 
The noted improvement in strength is achieved, furthermore, at no sacrifice 
of the other important properties required of fiber board products. 
This desirable result is achieved as a direct consequence of the inclusion 
in the hereindescribed fiber board products of an exhaustively hydrated 
cellulosic gel binder as a major component of the board-making furnish. In 
the forming of the board product, the gel component not only acts as an 
efficient binder in a quick pressing operation to bind the particles of 
lignocellulose into an integral board, it also acts as a dispersant for 
the fibers so that a uniform board free from the presence of bunched fiber 
aggregates is obtained. It also shrinks during drying of the board with 
the result that it compacts and integrates the other board components. 
Being water resistant per se, it augments the water resistant 
characteristics of the finished board product.

DESCRIPTION OF SPECIFIC EMBODIMENTS 
The medium density, high strength, lignocellulose composition boards of my 
invention are illustrated by the following general and preferred 
formulations, wherein percent is given in percent by weight, on a dry 
weight basis: 
______________________________________ 
General Preferred 
Composition (%) 
Composition (%) 
______________________________________ 
Lignocellulose 
Particles 60 to 95 70 to 90 
Hydrated cellulosic 
gel binder 5 to 40 10 to 30 
______________________________________ 
The lignocellulose which is the primary structural component of the 
hereindescribed medium density composition boards may be derived from a 
wide variety of sources. Representative sources include bagasse and such 
woods as the wood of the eucalyptus, cottonwood, willow, alder, Douglas 
fir and pine. 
Where woody materials are employed they may be used in the form of chips, 
planer shavings, flakes or sawdust. Whatever their source, the materials 
first are size reduced, preferably by being defibrated to the form of 
lignocellulosic fibers and fiber bundles. This is accomplished in suitable 
apparatus, such as Bauer or Sprout-Waldron mechanical refiners. A 
preferred defibrating system includes the conventional Asplund defibrator 
wherein wood pieces are subjected to abrasive reduction in an environment 
of steam under pressure of from 40 to 150 pounds per square inch. If 
desirable or necessary, the fibrous product of the Asplund machine may be 
passed to a secondary refiner such as an Asplund raffinator for ultimate 
reduction to a particle size of 10% maximum plus 12 mesh, U.S. Sieve 
Series. 
The second primary constituent of the hereindescribed medium density high 
strength lignocellulose composition boards is an exhaustively hydrated 
cellulosic gel binder used in an amount of from 5 to 40%, preferably 10 to 
30% by weight, dry board basis. 
This material distinguishes from the hydrated cellulosic gels of the prior 
art in that it is exhaustively hydrated to a condition in which it has 
substantially no fiber structure at all. The difference becomes evident 
when the gels are subjected to the conventional Schopper-Riegler freeness 
test, or TAPPI Standard T221-OS-63. 
In accordance with TAPPI Standard T221-OS-63, used to measure the freeness 
of various slow pulps such as are under consideration here, a pulp sample 
is formed into a sheet 61/4" in diameter in a Williams sheet mold. The 
sheet formed in the mold contains 1.2 grams of dry pulp or gel. The 
drainage time required to form the sheet is measured and becomes an 
indication of the degree of hydration of the stock. 
In using this test, it readily is possible to distinguish the 
hereindescribed highly hydrated cellulosic gel binders from the hydrated 
cellulosic gel products of the prior art, such as those employed in the 
manufacture of glassines paper, and those employed in the manufacture of 
prior art composition board products such as are disclosed in Roberts U.S. 
Pat. No. 3,379,608-9. Both of these made use of hydrated cellulosic gels 
having a drain time, as measured by the above mentioned TAPPI standard 
T221-OS-63 of about 300 seconds. 
I have discovered, however, that it is possible to hydrate cellulosic gel 
to a degree much more highly advanced than that characteristic of the gels 
employed in either glassines paper or the composition boards of the 
aforesaid patents. Thus, whereas the named prior art gels have a TAPPI 
standard freeness measured by a drain time of about 300 seconds, the gels 
employed in my invention have drain times of at least 350 seconds, 
preferably above 900 seconds, and in particular from 900-2000 seconds. 
Other test methods may be employed to identify and characterize the 
hereindescribed exhaustively hydrated cellulosic gel binders. 
One such is to determine the shrinkage upon drying of the hand sheet 
produced by the above described TAPPI T221-OS-63 test. A suitably hydrated 
gel will form a hand sheet which shrinks upon drying to bone-dry condition 
to a diameter which is at least 20% smaller than its original diameter. In 
making this determination, a wet TAPPI handsheet measuring 61/4" in 
diameter is rolled up, oven dried to bone-dry condition, and the length of 
the dried roll measured. From the difference between these two 
measurements the percent of shrinkage is calculated. 
In a second method, the handsheet is dried and a small flame applied to its 
underside. If the cellulose is sufficiently hydrated, the flame 
instantaneously will produce a blister on the sheet. 
In a fourth test method, 250 ml. of the refined pulp slurry is dried into a 
solid ball. If the gel is sufficiently hydrated for the present purposes, 
the ball will sink when dropped into water and thereafter will remain hard 
without swelling for an indefinite period of submergence. 
The use of the thus characterized exhaustively hydrated cellulosic gel 
binders in the medium density composition boards of my invention is 
critically significant for several reasons. 
In the first place, the gel serves as a highly efficient binder which binds 
the lignocellulose fibers together in an integrated product. Upon drying, 
the gel binder shrinks materially, pulling the particles together and 
locking them irreversibly in their consolidated condition. This factor is 
of primary importance in determining the increased strength of the board 
product. 
The gel also serves as a binder, which acts very rapidly to set the 
thickness and density of the felted sheet when it is introduced into the 
press. This makes possible a quick pressing operation, i.e. one requiring 
a press time of only 10 seconds to three minutes, preferably from 10 
seconds to 60 seconds. This in turn produces significant economies in 
requiring only a relatively inexpensive single opening press, which easily 
is adaptable to inclusion in conventional plant production lines. 
Several other important advantages stem from the use of the novel 
cellulosic gel binder described above. The binder imparts water resistance 
to the board product in which it is contained. As noted, such products 
contain from 5 to 40% by weight of the binder and the binder is so highly 
hydrated as to be substantially insoluble in water. This imparts a high 
degree of binder water resistance to the board product. The gel binder is 
superior in this respect to conventional fiber board binders such as the 
urea formaldehyde thermosetting resins. 
Still further, the gel is a highly efficient dispersion aid in the 
formulation of the fiber slurries from which the boards are made. In this 
application, it disperses into individual fibers wood fiber clumps which 
may be contained in the slurry. It also thickens the slurry so that as it 
is run on the wire at a consistency of about 5% there is little tendency 
for any light particles contained in the slurry to float, or any heavy 
particles to sink. Still further, it is responsible for the formation of a 
very stable slurry which is converted to a finished board product of 
completely homogeneous cross section. 
Fourth, the gel serves as a fines retention agent. This is of particular 
importance during vacuum forming of the board from a pulp slurry run onto 
the screen. During this procedure, finely divided particles present in the 
slurry tend to be extracted from the formed sheet by the run-off water. As 
a retention aid, the gel serves the valuable function of retaining these 
fines within the sheet, thereby conserving raw materials, improving the 
properties of the board, and minimizing a waste disposal problem. 
The hydrated cellulosic gels suitable for the intended purpose are products 
in which water of hydration is added to cellulose molecules by the 
substantially complete beating or refining of cellulose in aqueous medium. 
The cellulose thereby is converted from a fluffy, fibrous condition into a 
gelatinous condition, the degree of conversion being dependent upon such 
variables as the duration of the refining, the nature of the refining 
equipment, the presence or absence of extraneous chemicals, etc. 
Conventionally, the conversion is effectuated by mechanically treating 
cellulose pulp in aqueous medium in disc type refiners equipped with lava 
tackle or in conical refiners such as the Jordan. 
The cellulose pulp for the gel manufacture may be derived from any one of 
several sources, such as the bleached or unbleached wood or bagasse pulps 
manufactured by the conventional sulphate or sulphite papermaking 
processes. If bagasse is employed as the ultimate raw material, it 
preferably is depithed before being pulped. The pulps are available on the 
large commercial scale in the form of dried pulp sheets. 
In the manufacture of the hereindescribed gel products, the cellulose pulp 
is refined and hydrated exhaustively to a high degree at which fiber 
structure is almost completely destroyed. This is accomplished by breaking 
down the cellulose pulp sheets to their component individual fibers or 
fiber clumps, preferably by adding the dry sheets and water to a 
conventional hydrapulper, and hydrapulping at a stock consistency of from 
1 to 10%, preferably from 6 to 8%. This requires about 30 minutes. 
The resulting pulp then is pumped to a storage tank and fed in controlled 
flow to the selected disc type or conical type primary refiner. There 
preferably are three such refiners arranged in series with a 
flow-restricting valve downstream from the last refiner to insure an 
adequate pressurized refiner dwell time. These abrade the pulp and hydrate 
it to a high degree by forcing water into the cellulosic structure. 
The resulting partially refined and hydrated pulp is passed into a second 
storage tank which supplies a secondary refiner of the same general class 
as the primary refiner, but which is effective to complete the hydration 
and size reduction of the pulp to values imparting to the pulp TAPPI 
standard drain times of at least 350 seconds, preferably above 900 
seconds. This is accomplished by a shearing action which almost completely 
destroys the fiber structure of the pulp and hydrates it exhaustively. 
This supplemental and exhaustive refining greatly improves the qualities 
of the pulp as a binder, dispersing agent, and retention agent when used 
in the manufacture of the hereindescribed medium density composition 
boards of high strength. 
In particular, it makes of the gel an "irreversible" binder. This means 
that a composition board made with the hereindescribed highly refined gel 
binder can be subjected to the action of boiling water for several hours, 
with little softening or relaxing of the adhesive bond present between the 
bonded fibers. If the board is dried after having been subjected to such a 
boil test, it is just as strong as it was before boiling. This is the same 
characteristic exhibited by phenolic resins when they are used as binders. 
It no doubt is responsible for the improved water resistance of the 
composition boards of my invention. 
In addition to the lignocellulose fiber and hydrated cellulosic gel binder 
which are the principal constituents of the hereindescribed composition 
boards, there may be included in the boards varying amounts of 
supplemental materials such as sizing material used in the amount required 
to develop desired properties in the board product. In particular, there 
may be incorporated in the boards from 0.5 to 3% by weight of conventional 
wax sizes such as Petrolatum or Hercules Paracol wax, in order to improve 
the water resistance of the boards. 
Other additives which may be added are fire retardants such as borax, boric 
acid and ammonium phosphate; supplemental fibers such as sisal or 
fiberglass used in an amount of from 5 to 15% to increase toughness and 
impact resistance; pigments; and supplemental binders such as starch and 
phenolic resin binders, used in amount appropriate to the development of 
desired properties. 
In the manufacture of the high strength, medium density composition boards 
of my invention, there are compounded together flows of three separate 
furnish components: Lignocellulose fiber slurry, hydrated cellulosic gel, 
and wax emulsion and/or other additives. 
The lignocellulose fiber slurry is prepared as indicated above. In a 
typical instance, pulp logs with or without preliminary debarking are 
reduced to chips in a conventional chipper. The chips are fed to an 
Asplund Defibrator followed by a conventional Asplund type Raffinator 
which reduces the chips to a fiber slurry having a particle size of 10% 
maximum plus 12, U.S. Sieve Series. The slurry has a consistency of about 
40% through the Defibrator and about 30% through the Raffinator. 
In a preferred manner of operation the hydrated cellulosic gel component is 
prepared by feeding Kraft pulp to a conventional hydrapulper in which it 
is disintegrated into a fibrous slurry having a consistency of from 1 to 
10%, preferably from 6 to 8%. 
The resulting slurry is fed to a battery of three or four conventional 
refiners such as Jones refiners or modified Jordan refiners with straight 
steel tackle, or preferably with lava linings. The charge passes from one 
of these refiners to another and ultimately to a disc type refiner such as 
a Jones duo-flow disc refiner. 
The flow through the sequence of refiners is throttled down by appropriate 
valving to give a pressurized dwell or residence time sufficient to 
develop a hydrated cellulosic gel product having a drain time by the above 
described TAPPI drainage test T221-OS-63 of at least 350 seconds, 
preferably at least 900 seconds, and specifically from 900 to 2000 
seconds. This result is achieved by controlling the operating conditions 
in the refiner in such a manner as to beat and abrade the pulp for a total 
refining period of from 1 to 10 minutes at a pressure of from 20 to 120 
psi using an energy input of from 25 to 50 horespower days per ton (HPD/T) 
of pulp. 
The additive emulsion is prepared by emulsifying in water a conventional 
industrial wax such as Hercules Paracol or petrolatum, and mixing in 
predetermined amounts of any other selected additives. 
The three foregoing constituents, i.e. the lignocellulose fiber slurry, the 
cellulosic gel slurry, and the additive emulsion, are fed together in 
metered flows into a mixing tank where they are intimately mixed together 
in the desired proportions. 
The mix tank charge then is transferred to the chest of a forming machine 
which preferably is of the Fourdrinier type providing a high degree of 
suction for dewatering the stock. In the forming machine, the charge is 
run into a wet sheet having a pressed thickness of about one and one-half 
inches, pressed, in a rotary press section, and cut to length. Thereafter 
the resulting sheet is quick pressed to a thickness of from 1/4 inch up to 
one inch on wire in a heated flat press, depending on the desired ultimate 
board thickness. 
It is a particular feature of the invention that use of the hereindescribed 
novel cellulosic gel binder makes possible carrying out the press 
operation in a relatively inexpensive single opening press. This is for 
the reason that the gel acts to set the thickness and density of the sheet 
in the press during a very short press time of from 10 seconds to 3 
minutes, preferably from 10 seconds to 60 seconds, at a pressure of 50 to 
150 psi and a platen surface temperature of from 150.degree. to 
300.degree. F. Exemplary conditions for pressing are 30 seconds at 100 psi 
and 240.degree. F. 
Other advantages flow from the application of the quick pressing procedure. 
Quick pressing dries out the water to a tipple moisture content of about 
35% by weight, vs. a conventional level of 55% so that less kiln time is 
required. This is accomplished without altering the properties of the gel 
binder. 
Quick pressing also preheats the sheet so that less drying time is required 
subsequently in the kiln. Also, it forms a smooth top surface on the sheet 
which remains when the sheet is dried into a board. 
Still further, the quick pressing operation permits control of the density 
of the finished board to within the desired 20 to 50 pounds per cubic foot 
range. Using the gel binder, it may be carried out without splitting of 
the sheet when the sheet is released from the press. This result clearly 
is attributable to the effective adhesive qualities of the gel binder. 
It is followed by a kiln drying operation effectuated in three zones at 
successive zone temperatures of from 500.degree. to 600.degree. F., 
400.degree. to 500.degree. F., and 300.degree. to 400.degree. F., with the 
higher temperatures at the head end of the kiln. Drying is continued to a 
final board moisture content of less than 2%, preferably about 1/2% by 
weight. Drying removes not only the free water from the board, but also 
most of the water of hydration from the cellulosic gel. 
The resulting boards are cooled, trimmed, finished as needed for the 
contemplated product, and packaged, ready for shipping. 
The presently described medium density, high-strength composition boards 
and their method of manufacture are illustrated in the following examples: 
EXAMPLE 1 
Eucalyptus wood chips were defiberized in an Asplund Defibrator operated at 
150 psi, followed by refining in an Asplund type Raffinator to a fiber 
product size of less than 10% plus 12 mesh U.S. Sieve Series. The fibers 
were mixed with sufficient water to form a fiber stock having a 
consistency of 4%. 
An exhaustively hydrated cellulosic gel was produced by hydrapulping 
unbleached kraft pulp to a consistency of 8%. The resulting pulp was 
passed through a series of three Jones Fiber-master No. II conical 
refiners followed by a Jones Duo Flow shearing type disc refiner. In their 
operation, the refiners were controlled by valving their discharge ports 
to achieve residence times within the refiners adequate to produce three 
types of gel, one having a drain time of 355 seconds, another of 1200 
seconds and another of 1800 seconds, all as measured by TAPPI test 
standard T221-OS-63. 
The foregoing constituents were mixed in a mix tank with 1% Hercules 
Paracol wax. 
The three components of the furnish were mixed to uniformity, transferred 
to the chest of a Fourdrinier type forming machine and run into board. The 
board was pressed to thickness, dried, and tested for modulus of rupture. 
Three sets of boards were thus manufactured and tested, using the gels 
having drain times of 355, 1200 and 1800 seconds, respectively. In each 
set of tests, three boards were prepared having gel contents of 10, 15 and 
20% by weight respectively, dry board basis. 
When pressing the first two groups of boards, the press pressure was 150 
psi, the press temperature was 240.degree. F., and the press duration 40 
seconds. In the third group of boards, a press pressure of 100 psi, a 
press temperature of 240.degree. F., and a press duration of 25 seconds 
were employed. 
The results are given in the table below: 
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Gel Stock Modulus 
Board Board Drain Gel Drain of 
Ex. Thickness Density Time Usage Time Rupture 
No. (inches) lbs/cu/ft 
(sec) (%) (Sec) (psi) 
______________________________________ 
1 .517 24.7 355 10 10 870 
2 .509 27.2 355 15 14 1085 
3 .496 29.6 355 20 30 1470 
4 .525 31.8 1200 10 20 1150 
5 .528 30.0 1200 15 55 1900 
6 .500 32.6 1200 20 123 2500 
7 .505 30.1 1800 10 63 1620 
8 .510 29.8 1800 15 97 2550 
9 .495 30.0 1800 20 220 3060 
______________________________________ 
It is apparent from the foregoing that the inclusion of the exhaustively 
hydrated cellulosic gel binder in the stipulated proportions exerts a 
profound and most remarkably beneficial effect on the strength properties 
of the composition boards of my invention. Thus, as shown in Example 9, 
including 20% of a gel having a drain time of 1800 seconds results in the 
production of a board having a density of only 30 pounds per cubic foot, 
but a modulus of rupture of over 3,000 pounds per square inch. This 
extraordinarily high modulus of rupture value is characteristic normally 
of boards not of the medium density 30 pounds per cubic foot class, but of 
boards of much higher density, i.e. boards having densities of the order 
of 45 pounds per cubic foot. 
The resulting saving in raw material costs, transportation costs and board 
manufacturing costs are apparent. These are achieved, furthermore, while 
retaining the other properties of light weight, dimensional stability, 
uniformity, water resistance and workability which necessarily must 
characterize structural composition boards to render them suitable for 
their various uses. 
EXAMPLE 2 
Kraft cellulosic pulp was refined at a consistency of 4% in a "Bauer #442" 
refiner. This refiner was of the double disc plate type having one 
stationary and one rotating stainless steel disc. The spacing between the 
bars was about 1/4". 
Two series of runs were made, one without pressurizing the refiner and the 
other with the application of pressure to the pulp during refining. 
In the first series, the outlet valve on the discharge side of the refiner 
was left wide open, with the result that the pressure in the refiner was 
only 5 psi. The TAPPI drain time of the processed pulp after two passes 
through the refiner was only 10 seconds. The drain time of the unprocessed 
pulp was 7 seconds. 
In the second series, the valve on the discharge side of the refiner was 
throttled to develop a pressure of 65 psi in the refiner. The TAPPI drain 
time of the pulp after two passes through the refiner was 160 seconds; 
after three passes, 385 seconds; and after four passes, 590 seconds. 
Total refining time for the four passes was about four minutes and total 
energy consumption was about 49 HPD/T. A handsheet made from the finished 
gel after the fourth pass blistered when a match was applied to its 
underside. A dried ball of the same gel sank when dropped into water.