METHOD OF MAKING DIMENSIONALLY STABLE COMPOSITE BOARD AND COMPOSITE BOARD PRODUCED BY SUCH METHOD

METHODE DE FABRICATION D'UN PANNEAU COMPOSITE DIMENSIONNELLEMENT STABLE, ET PRODUIT AINSI OBTENU

English Abstract

ABSTRACT
This invention relates to a novel composite board made from
a mixture of particles of a cellulose material and binder and a
method of making same whereby the composite board so produced
displays improved dimensional stability (resistance to thickness
swellling) when the board is subjected to high humidity or
moisture conditions. As a result, the novel method and
composite board produced thereby can be employed as a
construction material in locations hitherto regarded as
unacceptable or questionable due to the undesired thickness
swelling characteristic of conventional composite panels such as
particlehoard or waferboard. The method and composite board
displaying the attribute of improved dimensional stability
involves subjecting a composite board that is conventionally
formed by heat and pressure treatment to a secondary heat
treatment for a predetermined period of time and at preselected
temperature range. When compared to conventional composite
board that has not been subjected to secondary heat treatment,
the difference in thickness swelling is significant. The board
surfaces and board edges are preferably subjected to the
secondary heat treatment. Admixtures of regular resins and a
slower curing binder such as spent sulphite liquor, hitherto
regarded as unsuitable in the production of composite board, can
now also be employed.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of producing an improved composite board made from
a mixture of particles of a cellulosic material and a binder,
wherein the composite board is conventionally formed by heat and
pressure treatment, said method comprising subjecting the formed
composite board to a secondary heat treatment for a
predetermined period of time and at a preselected temperature
range, said secondary heat treatment resulting in a board having
improved dimensional stability when subjected to an environment
of high humidity or moisture.
2. The method as claimed in Claim 1 wherein the said composite
board is trimmed to a predetermined size prior to said secondary
heat treatment.
3. The method as claimed in Claim 1, wherein said secondary
heat treatment is applied to at least one of the panel surfaces
and the edges of said board.
4. The method as claimed in Claim 3, wherein said secondary
heat treatment is applied only to the side edges of said board.
5. The method as claimed in Claim 3, wherein said secondary
heat treatment is applied to the opposite panel surfaces of said
board.
6. The method as claimed in Claim 1, 2 or 3, wherein the
secondary heat treatment comprises directly contacting the board
with an element having a termperature higher than the
temperature of said board.
7. The method as claimed in claim 1, 2 or 3 wherein said
predetermined period is from about 2 to 15 minutes and said
preselected temprature ranges from about 230°C to about 270°C.
-12-

8. The method as claimed in Claim 1, 2 or 3 wherein the
secondary heat treatment is carried out while said board still
contains residual heat from originally being formed.
9. the method as claimed in Claim 1, 2 or 3 wherein said
secondary heat treatment is carried out by means of one of a
heating chamber, a hot press and a set of hot platens.
10. The method as claimed in Claim 1, 2 or 3, wherein the
period of said secondary heat treatment is no greater than the
time required to conventionally form said board.
11. The method as claimed in Claim 1, 2 or 3, wherein said
particles of cellulosic material comprise at least one of
fibers, particles, flakes, chips, wafers and strands of wood.
12. The method as claimed in Claim 1, 2 or 3 wherein said
binder is a thermo-setting resin.
13. The method as claimed in Claim 1, 2 or 3, wherein said
binder is at least one of phenol formaldehyde, esocyanate and
spend sulphite liquor.
14. The method as claimed in Claim 1, 2 or 3, wherein said
secondary heat treatment is carried out in an oxygen reduced
environment.
15. A method of producing bond-durable wood-based composite
boards having improved resistance to swelling when subjected to
high humidity comprising the steps of:
(a) forming a mat which primarily consists of wood particles
and a binder;
(b) heat-pressing said mat to form a composite panel; and
-13-

(c) subjecting said composite panel to secodary heating at a
temperature in a range from about 230°C to about 270° for a
period of time from about 2 to about 15 minutes.
16. The method as claimed in Claim is wherein the edges of said
composite panel are trimmed to provide a panel of a
predetermined size prior to said secondary heating.
17. The method as claimed in claim 16 wherein said secondary
heating is applied to at least one of the panel faces and
applied to the trimmed edges of said composite panel.
18. The method as claimed in Claim 15, 16 or 17, wherein said
secondary heating is carried out while said composite panel
still contains residual heat from the heat-pressing of said
mat.
19. The method as claimed in Claim 15, 16 or 17, wherein said
secondary heating is carried out by means of one of a heating
chamber, a hot press and a set of hot platens.
20. The method as claimed in Claim 15; 16 or 17, wherein the
time of said secondary heating is no greater than the time
required for heat-pressing said mat and said wood particles are
wafers and said binder is a phenol formaldehyde resin.
21. The method as claimed in Claim 15, 16 or 17, wherein said
wood particles include at least one of fibers, chips, flakes,
wafers and strands and said binder is at least one of phenol-
formaldehyde, isocyanate and spent sulphite liquor.
22. The method as claimed in Claim 15, 16 or 17, wherein said
secondary heating is carried out in an oxygen reduced
environment.
23. An improved bond-durable wood-based composite board which
has improved resistance to moisture swelling and which is
primarily composed of a cured mixture of a thermosetting resin
-14-

and wood particles, said board being characterized by first
being formed into a hot-pressed substantially thermally cured
wood-based composite panel and thereafter subjected to a
secondary heat treatment.
24. A board as claimed in Claim 23, wherein said secondary heat
treatment is in a temperature range from about 230°C to about
270°C for a period of time from about 2 minutes to about 15
minutes.
25. The wood-based composite board as claimed in Claim 23,
wherein said thermosetting resin is at least one of phenol
formaldehyde, isocyanate and spent sulphite liquor and said wood
particles comprises at least one of fibers, flakes, chips,
wafers and strands.
26. The wood-based composite board as claimed in Claim 23, 24
or 25, wherein said secondary heating of said wood-based
composite panel is carried out by means of one of a heating
chamber, a hot press and a set of hot platens.
27. A method as claimed in Claim 1, 2 or 3, wherein the
cellulosic material comprises particles of wood subjected to a
steam-pressure treatment prior to being formed into the
composite board.
28. A method as claimed in claim 15, 16 or 17, wherein said
wood particles prior to said mat forming are subjected to a
steam-pressure treatment.
29. The composite board as claimed in Claim 23, 24 or 25,
wherein said wood particles are characterized by being subjected
to a steam-pressure treatment prior to being formed into said
panel.
-15-

ABSTRACT
This invention relates to a novel composite board made from
a mixture of particles of a cellulose material and binder and a
method of making same whereby the composite board so produced
displays improved dimensional stability (resistance to thickness
swellling) when the board is subjected to high humidity or
moisture conditions. As a result, the novel method and
composite board produced thereby can be employed as a
construction material in locations hitherto regarded as
unacceptable or questionable due to the undesired thickness
swelling characteristic of conventional composite panels such as
particleboard or waferboard. The method and composite board
displaying the attribute of improved dimensional stability
involves subjecting a composite board that is conventionally
formed by heat and pressure treatment to a secondary heat
treatment for a predetermined period of time and at preselected
temperature range. When compared to conventional composite
board that has not been subjected to secondary heat treatment,
the difference in thickness swelling is significant. The board
surfaces and board edges are preferably subjected to the
secondary heat treatment. Admixtures of regular resins and a
slower curing binder such as spent sulphite liquor, hitherto
regarded as unsuitable in the production of composite board, can
now also be employed.
-16-

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY
OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. A method of producing an improved composite board made from
a mixture of particles of a cellulosic material and a binder,
wherein the composite board is conventionally formed by heat and
pressure treatment, said method comprising subjecting the formed
composite board to a secondary heat treatment for a
predetermined period of time and at a preselected temperature
range, said secondary heat treatment resulting in a board having
improved dimensional stability when subjected to an environment
of high humidity or moisture.
2. The method as claimed in Claim 1 wherein the said composite
board is trimmed to a predetermined size prior to said secondary
heat treatment.
3. The method as claimed in Claim 1, wherein said secondary
heat treatment is applied to at least one of the panel surfaces
and the edges of said board.
4. The method as claimed in Claim 3, wherein said secondary
heat treatment is applied only to the side edges of said board.
5. The method as claimed in Claim 3, wherein said secondary
heat treatment is applied to the opposite panel surfaces of said
board.
6. The method as claimed in Claim 1, 2 or 3, wherein the
secondary heat treatment comprises directly contacting the board
with an element having a termperature higher than the
temperature of said board.
7. The method as claimed in claim 1, 2 or 3 wherein said
predetermined period is from about 2 to 15 minutes and said
preselected temprature ranges from about 230°C to about 270°C.
-17-

8. The method as claimed in Claim 1, 2 or 3 wherein the
secondary heat treatment is carried out while said board still
contains residual heat from originally being formed.
9. the method as claimed in Claim 1, 2 or 3 wherein said
secondary heat treatment is carried out by means of one of a
heating chamber, a hot press and a set of hot platens.
10. The method as claimed in Claim 1, 2 or 3, wherein the
period of said secondary heat treatment is no greater than the
time required to conventionally form said board.
11. The method as claimed in Claim 1, 2 or 3, wherein said
particles of cellulosic material comprise at least one of
fibers, particles, flakes, chips, wafers and strands of wood.
12. The method as claimed in Claim 1, 2 or 3 wherein said
binder is a thermo-setting resin
13. The method as claimed in Claim 1, 2 or 3, wherein said
binder is at least one of phenol formaldehyde, esocyanate and
spend sulphite liquor.
14. The method as claimed in Claim 1, 2 or 3, wherein said
secondary heat treatment is carried out in an oxygen reduced
environment.
15. A method of producing bond-durable wood-based composite
boards having improved resistance to swelling when subjected to
high humidity comprising the steps of:
(a) forming a mat which primarily consists of wood particles
and a binder;
(b) heat-pressing said mat to form a composite panel; and
-18-

(c) subjecting said composite panel to secodary heating at a
temperature in a range from about 230°C to about 270° for a
period of time from about 2 to about 15 minutes.
16. The method as claimed in Claim 15 wherein the edges of said
composite panel are trimmed to provide a panel of a
predetermined size prior to said secondary heating.
17. The method as claimed in claim 16 wherein said secondary
heating is applied to at least one of the panel faces and
applied to the trimmed edges of said composite panel.
18. The method as claimed in Claim 15, 16 or 17 I wherein said
secondary heating is carried out while said composite panel
still contains residual heat from the heat-pressing of said
mat.
10. The method as claimed in Claim 15, 16 or 17, wherein said
secondary heating is carried out by means of one of a heating
chamber, a hot press and a set of hot platens.
20. The method as claimed in Claim 15, 16 or 17, wherein the
time of said secondary heating is no greater than the time
required for heat-pressing said mat and said wood particles are
wafers and said binder is a phenol formaldehyde resin.
21. The method as claimed in Claim 15, 16 or 17, wherein said
wood particles include at least one of fibers, chips, flakes,
wafers and strands and said binder is at least one of phenol-
formaldehyde, isocyanate and spent sulphite liquor.
22. The method as claimed in Claim 15, 16 or 17, wherein said
secondary heating is carried out in an oxygen reduced
environment.
23. An improved bond-durable wood based composite board which
has improved resistance to moisture swelling and which is
primarily composed of a cured mixture of a thermosetting resin
-19-

and wood particles, said board being characterized by first
being formed into a hot-pressed substantially thermally cured
wood-based composite panel and thereafter subjected to a
secondary heat treatment.
24. A board as claimed in Claim 23, wherein said secondary heat
treatment is in a temperature range from about 230°C to about
270°C for a period of time from about 2 minutes to about 15
minutes.
25. The wood-based composite board as claimed in Claim 23,
wherein said thermosetting resin is at least one of phenol
formaldehyde, isocyanate and spent sulphite liquor and said wood
particles comprises at least one of fibers, flakes, chips,
wafers and strands.
26. The wood-based composite board as claimed in Claim 23, 24
or 25, wherein said secondary heating of said wood-based
composite panel is carried out by means of one of a heating
chamber, a hot press and a set of hot platens
27. A method as claimed in Claim 1, 2 or 3, wherein the
cellulosic material comprises particles of wood subjected to a
steam-pressure treatment prior to being formed into the
composite board.
28. A method as claimed in claim 15, 16 or 17, wherein said
wood particles prior to said mat forming are subjected to a
steam-pressure treatment.
29. The composite board as claimed in Claim 23, 24 or 25,
wherein said wood particles are characterized by being subjectd
to a steam-pressure treatment prior to being formed into said
panel.
-20-

Description

3~
- 1
TITLE OF INVENTION
-
Improved method of making dimensionally stable composite
board and composite board produced by such method.
BACKGROUND OF INVENTION
This invention relates to a novel method of producing
composite board made from a mi~ture of particles of cellulosic
material and a binder such as wood~based particle board or wafer
board and which exhibits improved dimensional stability over
conventional composite board when exposed to high humidity or
moisture conditionsO Additionally, ~he invention is directed
towards a novel composite board which exhibits resistance to
moisture swelling when produced or manufactured in accordance
with the methology of this invention.
The dimensional stability of a composite board or panel is
normally determined by measuring the thickness swelling the of
panel following controlled exposure to moisture. Conventional
wood-based composite boards or panels can experience a thickness
swelling ranging from 10 to 25 percent of the panel's thickness
following a ~4 hour cold water soak and which can range from 2
to 40 percent iE subjected to a vertical 2~ hour cold water
soak. When sub~ecting a conventional panel to a 2 hour boiling
period followed by a l hour cold water soak, thickness swelling
in the range of 50 to 60 percent can be anticipated. As a
result, the use of conventional composite boards and panels as a
construction material is limited to installations and
environments where the moisture conditions are controlled or
anticipated in advance. Consequently, wood-based composites are
regarded as undesirable for exterior applications and
particularly ground contact applications because of differential
dimensional changes between the wet and dry portions of the
material below and above the ground.
~r~

~2~3~
The moisture and moisture cycling effect experienced by
composite panels subjected to variations in humidity or exposure
to water also contribute to the breakdown or degradation of the
panel rendering it unfit as a construction material for the
purpose intended. Indeed, building contractors are reluctant to
use wood-based composite panels as a flooring or sub-flooring
since the marginal edges of a panel can exhibit greater
thickness swelling over its central portion which detracts from
a substantially planer abutment joint with neighboring panels.
Where used as a flooring, it is not uncommon for composite board
installers to plane or shave down to swollen panels adjacent
their side edges.
The novel composite panel of this invention displays
improved dimensional stability and hence improved bond
durability of the cellulosic particles which, together with a
binder, make up the composite panel. As a consequence,
composite panels produced in accordance with this invention, can
be employed in areas hitherto regarded as not recommened or open
to question and, additionally, can be further treated with
preservatives, fire retardants or other chemicals without
causing significant deleterious damage to the panel from the
standpoint of excessive thickness swelling or loss of strength
as heretofore encountered.
Although not employed commercially, it is known that
composite products such as boards will display improved
dimensional stability if subjected to high temperature ranges in
the order of 450 degrees fahrenheit or higher. There is,
however, a very real risk of fire when operating at this
temperature due to the accumulation of wax, dust and loose wood
particles around the hot press. It has, hitherto, also been
recognized that dimensional changes can be reduced by placing
wood composites in a heating chamber or oven for a relatively
long period of time in order to obtain improved dimensional
stability. This procedure, however, results in deterioration of

-- 3 ~
the panel strength and again constitutes a fire hazzard.
Furthermore, it contrlbutes significantly to a slow-down in a
line production run and is not regarded as being commercially or
economically viable.
SUMMARY OF INVENTION
In accordance with this invention, I have surprisingly and
unexpectedly found that a composite board made Erom mixture oE
particles of cellulosic material and a binder which is
conventionally formed by heat and pressure treatment will
display significantly improved dimensional stability through the
simple expedient of subjecting the conventionally formed
composite board to a secondary heat treatment for a
predetermined period of time and at a preselected temperature.
Preferably, the composite board subjected ~o the secondary heat
treatment step is first trimmed to a predetermined size. By
doing so, the entire board, the board faces or the board edges,
can be subjected to the secondary heat treatment, as desired.
Trimming of the composite board prior to the secondary heat
treatment is desired as it removes the loose particles and thus
prevents fire hazard and additionally renders these exposed
edges of the final board available for secondary treatment.
The preferred predetermined period of time and preselected
temperature when practicing the method and producing the final
composite board embodied by my invention is from about 2 to 15
minutes and a temperature range from 230C to about 270C.
From a production run standpoint, the secondary heat
treatment step can be carried out by, say, a heating chamber, a
hot press or a set of hot plates downstream in the production
line oE the equipment: used in initially heat-pressing the mat.
In this type of arrangement, the exposure time to the secondary
heat treatment can be made to correspond with the initial press
period of the mat in order to render the sequential steps

3';~C3~
-- 4 --
harmonious Additionally, following initial heat pressing of
the mat to form the composite board or panel, the residual heat
following the initial mat pressing can be advantageously carried
over to reduce the temperature differen~ial and hence the energy
required during the second heat treatment in order to bring the
panel during this secondary heat treatment step up to its
preselected temperature. Where only edge treatment is desired,
the panels can be merely piled up and the edges treated with hot
plantens for a predetermined time and temperature.
While any suitable heating means in order to carry out the
secondary heat ~reatment step can be employed such as, say, a
heating chamber, a hot press or at least one set oE hot platens,
physical contact of the board surface or edge to be treated is
preferred in order to reduce the oxygen environment during this
step as it has been recognized that when the panel is heated in
the presence of oxygen, thermal degradation can take place
affecting a loss in board or panel strengthc As is used in the
production of conventional composite panels, the preEerred
binder is a heat resistant or thermosetting one such as phenol
formaldehyde resins or isocyanate binders. I`he particles oE
cellulosic material employed in the composite panel and as is
known can be any one or a combination of fibers, flakes, chips,
wafers and strands.
As the preferred operating temperature used in the
secondary treatment step is from 230~C to about 270C, I have
also found that admixture of regular resin such as phenol
formaldehyde (PF) resin, and a slower curing binder, such as
spent sulphite liquor (SSL) hitherto regarded as unpractical and
unfeasable is now a viable alternative and thus can contribute
to a significant reduction in resin costs.
Exactly why the secondary heat treatment emparts to
conventional composite board improved dimensional stability and
thus its bond durability in high humidity or wet environments is

~3~
-- 5 ~
yet unknown. ~owever, in attempting to explain this unexpected
phenonomen, it is believed that high wood temperatures as
previously practiced in an attempt to achieve dimensional
stability, by analogy, can be applied to the secondary heat
treatment step of this invention operating at a significantly
lower temperature range which preferably is Erom 230C to about
270C. In this regard, high wood temperature is believed to
cause a plastic Elow of lignen "in situ' and thus reduces
internal (pent up) stresses in the wood compared to wood
compressed at a lower temperature~ Further, high wood -
temperature causes thermal degradation of hemicelluloses which
is the most hygroscopic component of wood, to furfural and
various sugars~ These tend to react with each other to form
insoluable polymers, and thus the hygroscopicity of the wood
tends to decrease. Additionally, high wood temperatures in the
absence of oxygen can cause a small loss of constitution water
which leads to a reduction of hygroscopicity of cellulose and
perhaps provides a lignin-rich fused surface that is analagous
to a hot-melt adhesive.
In a companion patent application being filed concurrently
with this application, I disclose an alternative improved method
of making dimensionally stable composite board and composite
board produced by such method and which essentially comprises
subjecting the wood particles IEurnish) to a steam-pressure step
prior to the mat or composite board forming. It will be
recognized, therefor, that this alternative method can usefully
and advantageously be combined with my secondary heat treatment
technique of the subject invention in order to further enhance
the dimensional stability of composite board.
The following e~amples illustrate the marked improvement
imparted to conventional composite boards or panels when same
have been subjected to the secondary heat treatment step of this
inven-tion and as compared to panels which have not undergone
secondary treatment. It should also be recognized that the

-- 6 --
secondary heat treatment technique can be practiced on composite
panels that have been produced and stored for some significant
period of time without appreciable differences in resul-ts.
EXAMPLE 1
___
Conventional waferboards measuring l" x 24" x 24" were
fabricated with the following parameters.
1. Wafers: commercial disk-cut wafers
2. Resin type and content: powdered phenol-formaldehyde
3. Wax type and content: slack wax 1.5~
4. Mat moisture content: 6~ in face, 3~ in core
5. Press time and panel thickness: 2 min. 40 sec., 4 min.
10 sec., 5 min. and 10 min. 30 sec. for 5/16 in., 7/16 in.,
1/2 in. and 3/4 in. thick boards respectively
6. Press temperature: 410F (210C)
After the boards were made, their edges were trimmed and the
trimmed boards were divided into three groups. The first group
was used as control; the panels of second and third groups were
subjected to secondary heat treatment, being treated at 464~F
(240~C) forthe times stiplulated. The treatments were done by
placing each panel between two hot platens. The boards were not
hot-stacked. the result of this e~periment is shown in Table 1.

TABLE 1
Thickness Swelling after 24-hour Water Immersion of Untreated
and Treated WaferboardS
_ _ _ . _ _
Location Percent Increase in
Test of Heat ~oard Thickness
Method* Measure- Treat-
ment** ment 5/16" 7/16" 1/2" 3/4"
Horizontal 1" in from No(control)16.7 11.5 10.6 6.7
adjacent edge Yes6.3 3.9 4.0 2.3
Vertical 1" down from No(control~1504 9.3 7.4 5.7
top edge Yes 7.14.0 4.0 1.4
Vertical 1" in up from No(control)27.5 18.0 18.1 12.6
bottom edge Yes9.1 5.3 5.S 2.8
Vertical Average No(control)21.513~6 12.7 9.2
Yes 8.14.7 4.8 2.1
* specimen size 4" x 4"
** for vertical test 3 points 1" from top edge and 3 points 1'
from bottom edge
EXAMPLE 2
Boards were made in a similar manner described in Example 1 but
they were conditioned at 20 ~/- 3C and 65 ~/- 1% relative
humidity to reach equilibrium moisture content (about 7~). They
were heated at 244C between hot p]atens or various lengths in
time. The results are shown in Table 20

3.f~7~
TABLE 2
__
Effect of Heat Treatment on Board Properties
Treatment Time~ ~5~n~ 5
Properties 0 2.5 3.
(Untreated)
Density lb/ft2 43.0 41.4 41~1 40.5
Thickness swelling
(TS) after 24 hour
soak 13.0(T)b 9.5(T)b 7.7(T)b 6.7(T)b
Vertically 33.6(B)C 29.0(B)C 23.5(B)C 21.0(B)C
23 3(A)d 19.3(A)d 15.6(A)d 13.9(A)d
MOE, 103 psi 739 723 762 719
MOE, psi 4426 4153 4258 3996
Wet MORe, psi 2207 2236 2305 2201
_
MOE - modulus of elasticity; MOR - modulus oE rupture
b TS at the points 1 in. from the top edge and 2 in. below water
surface
c TS at the points 1 in. from teh bottom edge and 6 in. below
water surEace
d Average of (b) and (c)
e MOR after 2 hour boil and 1 hour cold water soak

~37~3Y~
g
EXAMPLE 3
Boards were made in a similar manner as described in Example 1.
They were cut into 7 in. x 10 in. strips and piled up. Fi~e
minutes after hot pressingt the pile of 7 in. x 10 in. strips
was heated at 240C on edges for 5 minutes. Commercial (i.e,
third party manufactured) waEerboard were also used and treated
as mentioned prevously except the boards were heated up from
room temperature at 240C for 10 and 15 minutes. The results
are summarized in Table 3.
TABLE 3
Thickness Swelling of edged treated Waferboard after 5 days Cold
Water Soak and then Re-Dry
Conditions Duration
of Speci- of Heat
mens before Treat- Thickness Swelling % Ratio of
Heat Treat- ment Treated Untreated 1" in Thickness
ment min. Edges(A) Edges(B) from Swelling
Edges(C) C/A C/B
_
Coola 10 23.1 30.2 21.3 .922 .705
Coola 15 15.4 20.6 15.9 1.032 .772
Hotb 5 19.3 37.7 24.5 1027 .650
_
a Room temperatue at 5% moisture content (commercial waferboard)
b 5 minutes after hot pressing
EXAMPLE 4
Boards were made in a similar manner as described in
Example 1, except that the binder used an admixture of 40%
phenol-formaldehyde (PF) resin and 60% powdered spent sulphite
liquor (SSL).

~2~L3'71D~
~ 10 -
% Thickness Swelling after 24 hr~ Water Immersi.on of 7/16" thick
Waferboards Bonded with an Admixture of Phenol Formaldehyde (PF)
Resin and 5pent Sulfite Liquor (SSL)
_ _ _ _ =
Location
Test of Measure- Resin Type and Content
Method ment 2.25% PF* core 1% ~ +
2O25%PF* 1% PF* + 1.5~ 1.5~
SSL*** in faces SSL***
Horizontal 1" from every 3.9% 4.4% 4.8%
two adjacen-t
edge
Vertical 1" down from 4~0% 4.0% 3.7
top edge
Vertical 1" up from 5.3~ 7.6% 7.4%
bottom edge
Vertical Average 4.7% 5.8% 5.6
_ _
* PF: phenol formaldehyde resin
** SSL: powdered spent sulfite liquor
An examination of Table 1 clearly indicates that improved
dimensional stability (resistance to thickness swelling) is
achieved employing the secondary heat step and or a 464F
(240C) heat application, an exposure time of 5 minutes is
preferred. Table 2 confirms secondary heat treatment can also
be applied to the cool panels, but a prolonged treatment time is
preferredO Table 2 also suggests that it is more effective to
treat boards containing residual heat (Table 1) than conditioned
boards (Table 2) which may be due to the existing board heat and
reduced moisture content of the board itself.

~ 3~ 37
Table 2 also indicates that the mechanical properties of
the boards were not impaired by the secondary heat treatment as
contemplated by this invention.
Table 3 indicates that thickness swelling of board edges
that have no~ undergone secondary heat treatment is
significantly greater than comparable panel edges that have
undergone this secondary step. Moreover, the thickness swelling
measured 1" in from the board edges when compared to the
thickness swelling at the treated edges is significantly less
than that tabulated when comparing the thicXness swelliny 1" in
from the edges to the swelling occasioned at the untreated
edges; the result being that the edges oE composite boards or
panels when viewed in cross-section are less likely to be Elared
at the edges if the edges have undergone the secondary heating
step.
Table 4 indicates that waferboard can be made from an
inexpensive admixture of phenol formaldehyde resin (40%) and
spent sulphite liquor (SSL) with significantly improved
dimensionally improved stability when compared with the control
specimens of Table I.
While specified embodiments of this invention have been
disclosed herein, those skilled in the art will appreciate that
changes and modifications may be made therein without departing
from the concept and scope of this invention as defined in the
appended claims.