Method of bonding particle board and the like using polyisocyanate/phenolic adhesive

A method of forming particle board characterized by the use of an adhesive comprising a polyisocyanate and a phenolic adhesive. Enhanced adhesive characteristics and other advantages are associated with the method in which the polyisocyanate is added to the wood particles, etc. prior to application of the phenolic adhesive.

BACKGROUND OF THE INVENTION 
I. Field of the Invention 
This invention relates generally to a method of forming particle board and 
the like, using an exterior grade resin adhesive, specifically a 
polyisocyanate and a phenolic, e.g., phenol/formaldehyde adhesive. 
II. Description of the Prior Art 
Phenolic resole resins prepared by the alkaline condensation of a phenol 
and formaldehyde such as disclosed in U.S. Pat. Nos. 2,360,376 to VanEpps, 
2,437,981 to Stephan, and 2,457,493 to Redfern have long been used in 
plywood adhesive technology. Similar basic formulations and technology has 
been employed in formulation of an economical fast-cure phenolic resin for 
exterior hardwood flakeboard, such as described by Chung-Yun Hse in 
Formulation of an Economical First Cure Phenolic Resin for Exterior 
Hardwood Flakeboard, Proceedings of the Ninth Particleboard Symposium, 
Washington State University, Pullman, Washington, 1975. 
It has also been shown that the wide variation in hardwood density and 
process variables, such as moisture content of wood chips or flakes 
significantly affects resin performance. Additionally, it has been noted 
that the wood absorbs water from the adhesive glue during the mat forming 
process. Thus, with highly absorbent hardwood species such as, for 
example, the oaks, rapid dehydration of the glue line occurs with 
resultant inadequate glue flow and penetration during the subsequent hot 
press cure cycle. With a less absorptive species, such as, for example, 
sweetgum, an aqueous glue line dries more slowly, thereby causing 
unacceptable flow and penetration during hot pressing. Either of these 
latter conditions causes a substandard flakeboard. 
Advantageously, a good hardwood flakeboard adhesive must not only be 
capable of producing specification-grade flakeboard over a broad range of 
wood species and density, but must also be tolerant of the variable wood 
absorptivity. The adhesive should also be characterized by tolerance of 
high flake moisture content and temperature, high temperature and humidity 
of the working area, low resin application, and press pre-cure time, etc. 
Various adhesives and adhesive compositions have been previously proposed 
for use in fabricating flake board, particle board and the like, for 
example U.S. Pat. No. 3,919,017 to Phillip D. Shoemaker et al discloses 
the bonding of cellulosic materials to form particle board and the like 
with a binder system comprising an organic polyisocyanate and 
formaldehyde. The use of this adhesive system is said to allow the 
cellulosic materials containing up to about 22% moisture to be pressure 
consolidated without predrying. With regard to this combined adhesive of a 
polyisocyanate and formaldehyde, the patentees suggest that the binder 
system components can be separately added, although the order of addition 
is unimportant and the components may be added simultaneously. The 
patentees further indicate that typical adhesive systems for fabrication 
of particle board have included such thermosetting resins as 
phenolformaldehyde resorcinol-formaldehyde, melamine-formaldehyde and 
others. 
U.S. Pat. No. 3,440,189 to John Arthur Sharp discloses the fabrication of 
particle board using as the adhesive a thermoset adhesive containing an 
organic polyisocyanate and "Vinsol" resin. The "Vinsol" resin is described 
as a resinous hydroxyl group containing component derived from pine wood. 
The use of this combination adhesive is said to produce a water resistant 
particle board suitable for outdoor applications. 
Other U.S. Pat. Nos. which show typical adhesive compositions for the 
fabrication of particle board and the like include: 3,821,056 to Joseph 
Edward Wierden-polyisocyante/polyol reaction product; 3,632,734 to John G. 
Haygreen-application of phenol/formaldehyde resin to green particles; 
3,736,275 to Nicholas J. Iamnarino-Xanthomonas hydrophilic colloid and 
cross linking agent; 3,874,990 to Lyle V. Surdyk-flame retardant 
phosphoric acid-dicyandiamide formaldehyde resin; and 3,968,308 to Aldoph 
Buschfeld et al-a phenol or urea condensation resin. 
Typical processes for fabricating particle board and the like are shown in 
the foregoing patents as well as the following: U.S. Pat. Nos. 3,492,388 
to J. England-Kanusel; 3,557,263 to Allen A. Marra; 3,649,396 to B. J. 
Carlsson and 3,899,559 to Fred E. Johnanson et al. 
In an environment unrelated to the fabrication of particle board and the 
like, the combination of a polyisocyanate and a formaldehyde condensate 
has been proposed. Thus U.S. Pat. No. 3,268,467 to Grover W. Rye et al 
proposes the blocking of a polyisocyanate with a formaldehyde condensate 
resin in bonding a rubber reinforcing element to rubber, such as for 
example in bonding rayon, nylon, dacron or a metal such as steel to rubber 
in the tire industry. 
SUMMARY OF THE INVENTION 
In accordance with the present invention a method is provided whereby an 
improvement is achieved in the fabrication of particle board and the like. 
This method involves the use of an adhesive system which comprises a 
polyisocyanate as a minor component and, as the major component, a 
phenolic resin e.g., a phenol-formaldehyde condensation product. The 
polyisocyanate is present in the amount of from about 10 to about 50% by 
weight of the adhesive and the phenol-formaldehyde condensation product is 
present in an amount of from about 50 to about 90% by weight. 
To achieve the advantages of the method of the present invention, the 
polyisocyanate is applied to the wood furnish prior to the application of 
the phenolic resin. Thereafter, the combined adhesive is reacted by 
heating in situ to obtain an improved thermosetting adhesive resin and the 
attended advantages in the environment of the present invention. 
In accordance with the method of the present invention the prior 
application of the polyisocyanate creates enhanced adhesive 
characteristics as well as improved tolerance of the adhesive to wood 
species and process variables. 
DESCRIPTION OF THE PREFERRED EMBODIMENT 
The method of the present invention utilizes an adhesive composition 
comprising a minor amount of polyisocyanate and a major amount of a 
phenolic resin in the fabrication of particle board and the like. 
The expression "particle board and the like" as used throughout is meant to 
embrace those boards known as particle board, chipboard, wafferboard and 
fiberboard as well as other similar names wherein the board is prepared by 
application of an adhesive to cellulosic particles, chips or fibers, 
specifically wood particles, chips and fibers and subsequently formed into 
the desired board through application of heat and pressure. While 
reference will be made generally to particle board throughout the 
remainder of this application, it should be understood that this invention 
is applicable to other equivalent forms of this type of product. 
Similarly, the method of the present invention and its attended advantages 
can be achieved with respect to various forms of cellulosic starting 
material and is not limited to any particular form. The use of wood chips, 
however, in the formation of a typical particle board comprises the 
preferred environment for the method of the present invention. 
The method of the present invention utilizes an adhesive composition which 
comprises a polyisocyanate and a phenolic resin. Generally, the 
polyisocyanates employed in the method of the present invention are those 
which have an isocyanato group functionality of at least about two. 
Preferably, this functionality ranges from 2.3 to 3.5 with an isocyanate 
equivalent of 132 to 135. The isocyanato functionality can be determined 
from the percent available NCO groups and the average molecular weight of 
the polyisocyanate composition. The percent available NCO groups can be 
determined by the procedures of ASTM test method D1638. 
Suitable polyisocyanates may be commercially obtained in several viscosity 
or molecular grades. The polyisocyanates which can be employed in the 
method of the present invention can be those that are typically employed 
in adhesive compositions, including typical aromatic, aliphatic and 
cycloaliphatic polyisocyanates. Representative aromatic polyisocyanates 
include 2,4-tolylene diisocyanate, 2,6-tolylene diisocyanate, 
4,4'-methylene bis(phenyl isocyanate), 1,3-phenylene diisocyanate, 
triphenylmethane triisocyanate, 2,4,4'-triisocyanatodiphenyl ether, 
2,4-bis(4-isocyanatobenzyl) phenylisocyanate and related polyaryl 
polyiscocyanates, 1,5-naphthalene diisocyanate and mixtures thereof. 
Representative aliphatic polyisocyanates include hexamethylene 
diisocyanate, xylylene diisocyanate, 1,12-dodecane diisocyanate and lysine 
ethyl ester diisocyanate. Representative cycloaliphatic polyisocyanates 
include 4,4'-methylenebis(cyclohexyl isocyanate), 1,4-cyclohexylene 
diisocyanate, 1-methyl-2,4-cyclohexylene diisocyanate and 
2,4-bis(4-isocyanatocyclohexylmethyl) cyclohexyl isocyanate. Particularly 
suitable in the present invention is polymethylene polyphenyl isocyanate, 
with a functionality of about 2.7. The polyisocyanate is applied in its 
liquid form; preferably polymethylene polyphenyl isocyanate having a 
viscosity of about 200 to 275 cps at 25.degree. C. 
The major component of the resin composition utilized in the method of the 
present invention is a phenolic resin. The term "phenolic resin" refers to 
the products resulting from the reaction of phenols with aldehydes. In 
addition to phenol itself, cresols, xylenols, p-tertbutylphenol, 
p-phenylphenol and the like may be used as the phenol component. 
Formaldehyde is the most common aldehyde, but acetaldehyde, furfuraldehyde 
and the like may also be used. These resins are fully described in the 
Kirk-Othmer Encyclopedia, Volume 15, Pages 176 to 207. 
The phenolic resin preferably used in the method of the present invention 
is obtained by the alkaline condensation of phenol and formaldehyde as an 
aqueous dispersion and has 40% to 45% resin solid with a pH of 9.5 to 11.5 
and a viscosity of 200 to 325 cps at 25.degree. C. 
Generally, when a phenol-formaldehyde resin is used as the phenolic resin 
it is present in the adhesive composition used in the method of the 
present invention within the range of about 50 to 90% by weight, 
preferably within the range of about 70 to 80% by weight of the total 
amount of adhesive. Generally, the polyisocyanate is present in an amount 
of about 10% to 50%. In these amounts a significant increase in bond 
strength is obtained in accordance with the present invention. 
The most preferred composition for use in the method of the present 
invention comprises 70 to 80% by weight phenolformaldehyde resin and 20 to 
30% by weight polyisocyanate. When the adhesive system is used according 
to these percentages, one achieves a commercially attractive combination 
of desired board properties and economic advantages. 
In the method of the present invention, the adhesive system, as previously 
described, is ordinarily applied to wood particles or wood fibers 
(collectively and alternatively referred to as wood furnish), by standard 
techniques. To achieve the advantages of the present invention, in 
application of the adhesive system, it is necessary that the 
polyisocyanate be applied to the wood furnish prior to application of the 
phenolic resin. Such application sequence imparts enhanced strength 
characteristics to the resulting particle board as compared to 
simultaneous application of the polyisocyanate and phenolic resin or 
application of the phenolic resin prior to the polyisocyanate. 
It has been discovered that upon initial application, the polyisocyanate 
reacts readily with hydroxyl groups or water on the surface of or among 
the wood particles to form strong molecular bonding. Subsequently, a 
cross-linking reaction between isocyanate groups and the phenolic resin 
occurs upon the introduction of the phenolic resin, thereby reinforcing 
the functionalities of the phenolic adhesive. The initial rapid reaction 
of the polyisocyanate gives the combined resin system its improved 
tolerance to wood species and process variables. 
The method of the present invention and the attended advantages are not 
dependent upon the particular method utilized in the fabrication of the 
particle board, except, of course, the requirement that the polyisocyanate 
be applied prior to the phenolic resin. Accordingly, any of the prior art 
methods illustrated in the patents previously recited can be utilized. In 
general, the method for fabricating the particle board involves the 
application of the adhesive composition, polyisocyanate first, to the wood 
chips with subsequent application of heat and pressure to form the board 
into its desired configuration. It should be appreciated that the adhesive 
composition can be applied to the wood chips in any conventional means 
such as spray coating, coating or other dispersion of the adhesive and 
wood. 
In a typical process of fabricating particle board a first layer of wood 
chips and adhesive is generally layed down on a caul plate. This first 
layer is termed the face mix and forms the face of the finished particle 
board. After the face mix is layed on the caul a second layer of wood 
chips and adhesive is then layed down on top of the face mix. This second 
layer is termed the core mix since it will form the core of the finished 
particle board. Following this a third layer of wood chips and adhesive is 
layed down on top of the core mix. This third layer is also a face mix and 
will form the opposite face of the finished particle board. The three 
layers so layed down on the caul plate are termed the mat. 
The mat, including a plurality of caul plates are loaded into a press and a 
pressing operation is carried out in order to form the desired particle 
board. By way of example a mat which has an initial thickness of about 
31/2 inches may be pressed down to a thickness of about 0.7 inch or a mat 
which has an initial thickness of 7 inches may be pressed down to a final 
thickness of approximately 17/8 inches. During the pressing operation the 
mats are generally heated to a temperature such as 250.degree.-400.degree. 
F. as they are being compressed at about 100-600 psi. The exact conditions 
utilized in the pressing and heat curing of the particle board can, of 
course, be easily selected by one skilled in the art depending, of course, 
upon the desired characteristics of the final product. 
When utilizing such a procedure in the fabrication of particle board it is 
only necessary in accordance with the present invention that each 
application of adhesive comprise an initial application of the 
polyisocyanate, followed by application of the phenolic resin. Generally, 
the polyisocynate is applied in its liquid form, and the resin as an 
aqueous dispersion. 
Furthermore, although in accordance with the present invention the 
application of the phenolic resin after the polyisocyanate application 
significantly minimizes the binding of wood particles to the caul plates, 
it is generally preferred to apply a typical release agent such as for 
example, glycerin or wax emulsion on the caul plates to minimize any 
sticking. This, of course, is conventional in the formation of particle 
board using the caul plate technique. 
As indicated previously, when utilizing the method of the present invention 
the particular wood starting material is not critical and, enhanced wood 
tolerance is achieved by the present method. Accordingly, any type of 
species of wood is suitable for preparing the particleboard of the present 
invention including both hard and soft woods with high density woods and 
low density woods being suitably applicable. 
When carrying out the method of the present invention, the amount of 
adhesive can be that amount which is typically utilized in fabrication of 
particle board. Generally, it has been found that effective fabrication of 
particle board is achieved with an adhesive spread rate of about 3 to 
about 6% by weight based upon the dry wood weight of the wood furnish. 
Here again, however, amounts both above and below this range can be 
tolerated in preparing particle boards having outstanding characteristics. 
The method of the present invention will now be illustrated by the 
following examples which are in no way intended to limit the invention. 
In the examples the materials utilized were prepared as follows: 
Preparation of the Phenol-formaldehyde Resin 
Table I lists the formulation used in preparing the phenol-formaldehyde 
resin. 
TABLE I 
______________________________________ 
Ingredients Parts Per Thousand 
______________________________________ 
First 37% formaldehyde 
316 
Water 234 
90% phenol 280 
50% sodium hydroxide 
96 
Second 37% formaldehyde 
74 
______________________________________ 
To prepare each resin, the first formaldehyde portion, all of the phenol 
and water was placed in the reaction kettle. The sodium hydroxide was 
added as a catalyst at a rate of 20 ml every ten minutes to gradually 
increase the pH from about 8.5 to about 10.5. At the end of the sodium 
hydroxide addition, the reation mixture was heated and maintained at 
95.degree.to 100.degree. C. The second formaldehyde component was added 
after 2.5 hours of reaction time. When the viscosity reached the 
Gardner-Holt viscosity C the temperature was reduced to 70.degree. C. When 
viscosity reached the Garner-Holt viscosity H the reaction was terminated 
by rapidly cooling the mixture to 25.degree. C. 
Particleboard Construction Conditions 
Table II lists the typical conditions and characteristics of particle 
boards manufactured in the following examples. 
TABLE II 
______________________________________ 
Panel density: 46 lb/cu. ft. 
Panel thickness: 1/2 inch. 
Resin content: 4% 
Hot press temperature: 
300.degree. F. 
Hot press time: 4.5 minutes 
______________________________________ 
All wood flakes or chips were produced by a shaping-lathe headrig with 
average flake dimension of 3 inches long by 0.015 inch thick and random 
width. The mixed hardwood flakes consist of 40% sweetgum (Liquidambar 
styraciflua L.) and 60% southern red oak (Quercus falcata Michx.).

EXAMPLE I 
A series of flake or particle boards are fabricated according to the 
following adhesive blending processes: 
(1-A) applying polyisocyanate prior to the phenol-formaldehyde resin 
adhesive; 
(1-B) Applying polyisocyanate and phenol-formaldehyde resin adhesive 
simultaneously; 
(1-C) Applying phenol-formaldehyde resin adhesive prior to the 
polyisocyanate. 
Both phenol-formaldehyde resin and polyisocyanate are applied by 
conventional air-atomizing nozzles in a rotating drum-type blender. Of the 
total amount of adhesive, the phenol-formaldehyde resin constitutes 75 
percent and the polyisocyanate constitutes 25 percent. Standard internal 
bond specimens measuring 2 by 2 inches are cut from the final product and 
tested in accordance with ASTM Standards for evaluating the properties of 
wood-bare fiber and particle panel materials (ASTM D-1037-64). 
Table 3 gives typical results of adhesive bond strength in pounds per 
square inches of Example 1. 
TABLE 3 
______________________________________ 
Relationships between adhesive 
blending process and integral bond 
strength (Example 1) 
Internal bond 
Test Adhesive blending process 
psi 
______________________________________ 
1-A Polyisocyanate* prior to 
127 
phenolic** 
1-B Polyisocyanate* and phenolic 
89 
simultaneously** 
1-C Phenolic** prior to 67 
polyisocyanate* 
______________________________________ 
*polymethylene polyphenyl isocyanate functionality about 2.7 
**as prepared above based on Table I 
The significantly higher internal bond with the method of the applying 
polyisocyanate prior to the phenolic resin is evident. No significant 
difference is observed in these tests between the processes of spraying 
phenolic resin prior to polyisocyanate and that of the polyisocyanate and 
phenolic resin simultaneously. 
EXAMPLE 2 
Evidence as shown in Example 1 of the superior performance of method of 
applying the polyisocyanate prior to the phenol-formaldehyde resin leads 
to the study of the constituent ratio of polyisocyanate to 
phenol-formaldehyde resin. The following test conditions are investigated. 
TABLE 4 
______________________________________ 
Ratio of Polyisocyanate 
to Phenolic Resin 
Polyisocyanate, % 
Phenolic Resin, % 
______________________________________ 
(2-A) 0 100 
(2-B) 10 90 
(2-C) 20 80 
(2-D) 30 70 
(2-E) 40 60 
(2-F) 50 50 
(2-G) 60 40 
______________________________________ 
The panel fabrication and testing are similar to that of Example 1 except 
the hot press time is 5.5 minutes and total resin content is 5 percent. 
Typical internal bond strengths are given in Table 5. 
TABLE 5 
______________________________________ 
Effects of Constituent Ratio of Polyisocyanate 
to Phenolic Resin on Internal Bond Strength 
Percent constituent 
ratio polyisocyanate/ 
Internal bond (psi) 
Test phenolic resin 1-A.sup.1 
1-B.sup.2 
1-C.sup.3 
______________________________________ 
2-A 0/100 72 72 72 
2-B 10/90 99 83 75 
2-C 20/80 152 97 80 
2-D 30/70 192 112 83 
2-E 40/60 208 123 92 
2-F 50/50 216 131 100 
2-G 60/40 173 139 113 
______________________________________ 
.sup.1 1-A application of polyisocyanate prior to phenolic resin 
.sup.2 1-B application of polyisocyante and phenolic simultaneous 
.sup.3 1-C application of phenolic resin prior to polyisocyanate 
The superiority of the method of applying polyisocyanate prior to phenolic 
resin is again apparent. Also, the increased constituent ratio of 
polyisocyanate to phenolic resin results in increased bond strength. 
However, in the application of polyisocyanate prior to phenolic resin, 
increased amount of polyisocyanate above about 50 percent has been found 
to give less advantageous bond strength. 
EXAMPLE 3 
To measure the tolerance of the method of application under high moisture 
content of wood furnish, the following test conditions are chosen: 
______________________________________ 
Flake Constituent Ratio 
Moisture Polyisocyanate/ 
Test Content, % phenolic Resin, %/% 
______________________________________ 
3-A 4 0/100 
3-B 4 10/90 
3-C 4 30/70 
3-D 4 50/50 
3-E 11 0/100 
3-F 11 10/90 
3-G 11 30/70 
3-H 11 50/50 
______________________________________ 
The panels are prepared as described in Example 2, again using a hot press 
time of 5.5 minutes and total resin content of 5 percent. The average 
internal bond strengths of the panels are summarized in Table 6. 
TABLE 6 
______________________________________ 
Effects of Flake Moisture Content 
on Internal Bond Strength 
Flake Constituent Ratio 
Moisture Polyisocyanate/ 
Content phenolic Resin Internal 
Test % %/% psi 
______________________________________ 
3-A 4 0/100 72 
3-B 4 10/90 104 
3-C 4 30/70 169 
3-D 4 50/50 208 
3-E 11 0/100 0 
3-F 11 10/90 72 
3-G 11 30/70 135 
3-H 11 50/50 174 
______________________________________ 
Table 6 clearly demonstrates the superiority of applying polyisocyanate 
prior to phenolic resin over phenolic resin alone (Tests 3-A and 3-E). It 
is noted that satisfactory bond strength is obtained for the flake with 
high moisture content at 11 percent by applying as little as 10 percent of 
polyisocyanate prior to the phenolic, whereas in a conventional phenolic 
resin system steam generated from high moisture content flakes during the 
hot press cycle results in panel delamination. 
EXAMPLE 4 
The high wood density of hardwood species such as oaks and hickory has 
contributed to the difficulty in fabrication of low density panels. To 
measure the tolerance of the present adhesive system to the high density 
hardwood species, particles boards made from southern red oak with the 
following variables are investigated: 
______________________________________ 
Constituent Ratio 
Panel Polyisocyanate/ 
Density phenolic Resin 
Test pcf %/% 
______________________________________ 
4-A 41 0/100 
4-B 41 20/80 
4-C 45 0/100 
4-D 45 20/80 
4-E 49 0/100 
4-F 49 20/80 
______________________________________ 
4-A, 4-C, and 4-E panels are fabricated with conventional 
phenol-formaldehyde resin adhesive without polyisocyanate, whereas 4-B, 
4-D, and 4-F panels are fabricated according to the present invention, 
i.e., applying polyisocyanate prior to phenolic resin. The constituent 
ratio of polyisocyanate to phenolic resin is maintained at 20/80 in 4-B, 
4-D and 4-F. The hot press time and total resin content is 5.5 minutes and 
5 percent, respectively. The panels are prepared and tested as described 
in Example 1. Table 7 gives the typical internal bond strength in pounds 
per square inch. 
TABLE 7 
______________________________________ 
Internal Bond Strength 
of Southern Red Oak Panels 
Constituent Ratio 
Panel Polyisocyanate/ Internal 
Density Phenolic Resin Bond 
Test pcf %/% psi 
______________________________________ 
4-A 41 0/100 21 
4-B 41 20/80 84 
4-C 45 0/100 44 
4-D 45 20/80 124 
4-E 49 0/100 92 
4-F 49 20/80 116 
______________________________________ 
The panels fabricated according to the method of the present invention 
yield consistently higher internal bond strength. It is noted that 
satisfactory panels are produced even at low panel density of 41 pounds 
per cubic foot which is not possible with the conventional phenolic resin 
system. 
EXAMPLE 5 
In the manufacture of particle board panels, the resin content level not 
only strongly affects panel performance but also is the most expensive 
single item in the manufacturing cost. To measure the efficiency of the 
adhesive system of the present invention, the following test conditions 
are investigated: 
TABLE 8 
______________________________________ 
Relationship of Resin Content 
and Internal Bond Strength 
Constituent Ratio 
Resin Polyisocyanate Internal 
Content Phenolic Resin Bond 
Test % %/% psi 
______________________________________ 
5-A 3 0/100 43 
5-B 3 20/80 71 
5-C 4 0/100 56 
5-D 4 20/80 139 
5-E 5 0/100 68 
5-F 5 20/80 152 
______________________________________ 
The 5-A, 5-C, 5-E panels are fabricated with conventional 
phenol-formaldehyde resin adhesive without polyisocyanate while 5-B, 5-D, 
and 5-F panels are fabricated according to the present invention, i.e., 
applying polyisocyanate prior to phenolic resin; the constituent ratio of 
polyisocyanate to phenolic resin is maintained at 20/80. The hot press 
time and panel density are 5.5 minutes and 44 pcf, respectively. The 
panels are prepared and tested as described in Example 1. Typical internal 
bond strengths are given in Table 8. 
The superiority of the resin system containing polyisocyanate is again 
apparent for all resin content levels in the test. 
These tests confirm the unexpected superiority of applying polyisocyanate 
prior to the phenolic resin in fabrication of particle board and the like. 
The tests also confirm the improvement of the method of the present 
invention when called upon for use under adverse veneer moisture content 
conditions and resin content levels. Satisfactory particle boards are 
formed from high density species such as southern red oak at significantly 
lower panel density which is not attainable with conventional methods and 
systems. 
While the invention disclosed herein has been described with reference to 
preferred embodiments and representative examples thereof, the invention 
is not deemed to be so limited. Accordingly, modifications to the present 
method may be made while still falling within the intent and scope of the 
invention.