Note: Descriptions are shown in the official language in which they were submitted.
34
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PRODUCTION OF STRUCTURAL PANELS
USING ISOCYANATE/FURFURAL BINDER
BACKGROUND OF THE INVENTION
Many products are manufactured by the basic
process of consolidating or joining together bodies of
cellulosic materials using pressure, heat and a chemical
binder. Included among them are wood-base products
such as plywood, hardboard, particleboard and veneer-
faced particleboard, and pressed or molded products
made from vegetable fibers, such as cornstalks, straw
or bagasse, or from other cellulosic materials such
as pulp, shredded paper or the like. Typically, the
binders used in making such products are thermosetting
resins such as phenol-formaldehyde, resorcinol-
formaldehyde, melamine-formaldehyde,urea-formaldehyde,
urea-furfural and condensed furfuryl alcohol resins.
Other known binders include organic polyisocyanates,
which have been used for gluing plywood and, either
alone or together with urea- or melamine-formaldehyde
resins, as particleboard adhesives. Typical of the
types of binders disclosed in the art are polyisocyanate-
formaldehyde mixtures (see U.S. Patents 3,919,017 and
3,930,110); polyisocyanates (see U.S. Patent 4,046,952
and British Patent 1,148,016); polyisocyanates in
combination with urea-formaldehyde resin and/or
phenol-formaldehyde resins (see U.S. Patent 4,209,433
and British Patent 1,148,016).
The use of furfural as a smoke suppressant in
polyurethane foams is also known (see K. Ashida,
"Novel Methods of Smoke Suppression in Isocyanurate
Foams (1)", Advances in Urethane Science and Tech-
nology, Volume 5, 1978). Finally, it has been suggested
to blend furfural and/or furfuryl alcohol with an
isocyanate which is a phosgenation product of
an aniline-formaldehyde condensate and to there-
after simultaneously trimerize the isocyanate
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and polymerize the furfural and/or furfuryl alcohol
to thereby produce a furan-modified isocyanurate foam
(see U.S. Patent 4,232,127).
As noted earlier, isocyanates have demonstrated
a capability as a binder in the production of struc-
tural panels from cellulosic particles. Isocyanates,
and particularly polymethylene polyphenylisocyanates,
can yield products with properties generally equal or
superior to products produced from phenol-formaldehyde
resins. However, one of the major problems associated
with such isocyanates is their relatively higher cost
when compared to phenol-formaldehyde resins. While
there are many cost-saving advantages built into an
isocyanate binder (such as faster press times, lower
spread rates and low~r panel densities), the initial
cost of the isocyanate has been a deterrent to their
use.
DESCRIPTION OF THE INVENTION
The present invention is directed to the dis-
covery that highly useful binders for the productionof panels, and particularly structural panels, from
cellulosic particles can be provided by merely mixing
polyisocyanates based on methylene di(phenylisocyanate)
with an aldehyde which is soluble in the polyisocyanate
and which is reactive therewith at a temperature of
above 250F. It has been found that the addition of
such aldehydes to the polyisocyanates not only
significantly reduces the cost of the isocyanate binder,
but also allows for the production of structural panels
with improved physical properties when compared to
panels produced using the isocyanate alone.
The present invention is thus directed to novel
binder compositions and the use thereof in the pro-
duction of structural panels from cellulosic particles.
The present invention is also directed to mixtures of
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the binder of the present invention with cellulosic
particles.
The isocyanate component of the binder of the
present invention may be substantially any polyiso-
cyanate based on methylene di(phenylisocyanate). By"polyisocyanate based on methylene di(phenylisocyanate)"
as used herein is meant polymethylene polyphenyl
isocyanates, polyisocyanates having urethane groups
which are obtained by reacting relatively small amounts
of low molecular weight diols with methylene di(phenyl-
isocyanate) [see, e.g., U.S. Patents 3,644,457;
3,394,164 and 4,115,429], carbodiimide group-containing
polyisocyanates derived from methylene di(phenyl-
isocyanate) [see, e.g., U.S. Patents 3,152,162;
3,384,653; 3,449,256; 4,014,935; 4,088,665 and
4,154,752], and mixtures thereof. Such isocyanates
are well known in the art and are commercially available.
It is presently preferred to utilize polymethylene
polyphenyl isocyanates (e.g., such as are produced by
phosgenating an aniline-formaldehyde condensate) and
it is most preferred to use a mixture of such
isocyanates, wherein the mixture has the following
average structure:
NCO ~ NCO NCO
~ CH2 - ~ CH2 n
whérein n has a value of from 0.5 to 4 and preferably
0.5 to 3. Such isocyanate mixtures are known in the
art and are commercially available.
As noted above, the aldehyde used in the present
invention must be soluble in the isocyanate and must be
reactive with said isocyanate. Specific aldehydes
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found to be useful include furfural, benzaldehyde,
pelargonaldehyde, cinnamaldehyde, nonylaldehyde, butyr-
aldehyde, salicyaldehyde, chlorobenzaldehyde, ortho-
tolylaldehyde, 2-naphthaldehyde, piperonal and vanillan.
The presently preferred aldehyde is furfural. While the
aldehydes used herein have been described as being
reactive with the isocyanate component, it is not known
with certainty that the aldehyde is reactive with the
isocyanate~ When the aldehydes herein are heated with
the isocyanates herein, no characteristic aldehyde odor
is detected. Thus, it is believed that the aldehyde
and isocyanate do indeed react.
The aldehyde used in the present invention is
used as such. The ratio of isocyanate to aldehyde is
not critical and the optimum ratio for a given applica-
tion can be determined by routine experimentation. In
general, the amount of aldehyde can range from 1 to 50
parts by weight per 100 parts by weight of the mixtllre of
aldehyde and isocyanate. The most preferred amount of
aldehyde is from 3 to 30 parts by weight. It is pre-
ferred that the amount of aldehyde added be such that
the viscosity of the mixture is below 1,000 cP and
preferably below 500 cP (Brookfield at 25C). It is
most preferred that the viscosity of the mixture be
between 25 and 300 cP. Of course, it is possible to
use even higher amounts of aldehyde (e.g., up to 60%
or higher) if inert fillers such as fumed silica are
added.
The binder system may be added or applied in any
suitable manner, such as by brushing, dipping, spraying,roller coating, etc. In the preferred practice of the
invention, the polyisocyanate and the aldehyde solution
are added or applied together since they are inherently
miscible. The quantity of binder needed in a particular
application can be determined by simple experimentation.
Amounts in the range of 2-5% by weight, based on the
dry weight of cellulosic material, have been used with
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good results, although amounts of up to 20% by weight
can also be used to advantage.
As will be appreciated, the novel isocyanate-
aldehyde binder system may be used in the manufacture
of a wide variety of products from many different
cellulosic materials or mixtures of such materials.
By way of illustration, however, the invention will
be described hereinafter particularly with respect to
the manufacture of particleboard.
Particleboard is produced according to the
invention by bonding together particles of wood or
other cellulosic material using heat, pressure and a
binder system comprising an isocyanate and aldehyde.
As mentioned above, the polyisocyanate component of the
binder system may be substantially any polyisocyanate
based on methylene di(phenylisocyanate). The preferred
polyisocyanates are polyphenyl isocyanate and most
preferably are of the average structure noted above.
The starting material for the particleboard
comprises particles of cellulosic material, typically
wood particles derived f~om lumber manufacturing waste
such as planer shavings, veneer chips and the like, and
engineered particles such as flakes, strands, wafers
and the like. The methods for producing suitable
particles are well known and conventional. If desired,
mixtures of cellulosic particles may be used. Particle-
board has been successfully produced, for example, from
wood particle mixtures containing up to about 30% bark.
Typically, particles must be dried to between 4 and 10%
moisture content, thus causing substantial drying costs.
According to the present invention, particles may be
used at moisture contents up to 20~. Generally,
particles made from lumber waste materials contain
about 10-20% moisture and may be used without further
drying. Particles containing lesser amounts of moisture
may be used; however, such generally needlessly adds
to dryer cost.
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Particleboard is fabricated, according to pre-
ferred practice, by spraying the particles with binder
as they are tumbled or agitated in a blender. The
amount of binder system used can generally range from 1
to 20% by weight depending upon the properties desired
for the final product. Preferably, about 2-5% by weight
of the binder system is added, based on the "oven dry"
weight of the particles. The binder system components
are added as a preformed mixture, although they may be
added separately and simultaneously, if desired. Other
materials, such as wax sizing or fire retardant, may
also be added to the particles during the blending
step.
After sufficient blending to produce a uniform
mixture, the coated cellulosic particles are formed
into a loose mat or felt, preferably containing
between about 6 and 20% moisture by weight. The mat
is then placed in a heated press between caul plates
which may, if necessary, be treated with a release
composition and compressed to consolidate the particles
into a board. Pressing '.imes, temperatures and
pressures vary widely depending on the thickness of
the board produced, the desired density of the board,
the size of the particles used and other factors well
known in the art. By way of example, however, for
1/2 inch thick particleboard of medium density,
pressures of about 350-700 psi and temperatures of
about 270-425F are typica~. Pressing times for
1/2 inch particleboard are typically about 2 to 7
minutes. As is generally known in the art, these
parameters will vary depending on the desired thick-
ness of the finished product. Because a portion of
the moisture present in the mat will react with poly-
isocyanate to form polyur~a, it does not have to be
evaporated during the pressing cycle.
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The invention is further illustrated, but is
not intended to be limited by the following Examples
in which all parts and percentages are by weight unless
otherwise specified.
EXA~IPLES
EXAMPLES 1-24
In the Examples which follow, the isocyanates
used were all phosgenation products of aniline-
formaldehyde condensates and can be characterized as
follows:
(a) Polyisocyanate A: a polymethylene poly-
phenyl isocyanate having a weight average molecular
weight of 410, a Brookfield viscosity at 25C of 225
centipoises (cP~, and an NCO content of 31.5%.
(b) Polyisocyanate B: a polymethylene poly-
phenyl isocyanate having a weight average molecular
weight of 410, a Brookfield viscosity at 25C of 291
cP and an NCO content of 31.5%.
(c) Polyisocyanate C: a polymethylene poly-
phenyl isocyanate having a weight average molecular
weight of 480, a Brookfie;d viscosity at 25C of 558
cP and an NCO content of 31.3%.
(d) Polyisocyanate D: a polymethylene poly-
phenyl isocyanate having a weight average molecular
weight of 510, a Brookfield viscosity at 25C of
2180 cP and an NCO content of 30.8%.
(e) Polyisocyanate E: a polymethylene poly-
phenyl isocyanate having a weight average molecular
weight of 610, a Brookfield viscosity at 25C of
4525 cP and an NCO content of 30.2%.
(f) Polyisocyanate F: a polymethylene poly-
phenyl isocyanate having a weight average molecular
weight of 720, a Brookfield viscosity at 25C of
11,350 cP and an NCO content of 29.9~.
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In the Examples which follow, the four viscosity
values noted in Table I were selected and the amounts
of furfural necessary to achieve each viscosity with
each isocyanate were added in the amounts shown in
Table I.
Panels were prepared by spraying the binder
noted into a rotary drum blender which had previously
been charged with Douglas fir ring-cut flakes. The
binder was applied at a rate of 3 parts by weight
binder per 97 parts of wood flakes. After sufficient
tumbling to obtain a uniform distribution of the
binder, the coated particles were removed from the
blender and formed into a 24 inch by 28 inch by 1/2
inch panel in an electrically heated, hydraulically
operated laboratory press. The press was maintained
at a temperature of about 350F and a five-minute press
cycle was used. Caul plates bound each side of the
panel while it was being pressed. To prevent the
panel from sticking to these plates, a 10% aqueous
zinc stearate solution was sprayed on each plate. The
resultant particleboards all had densities of 42 pounds
per cubic foot.
The panels were then maintained at 72F, 65%
relative humidity until no change in weight was noted
(this ge~erally took from 3 to 10 days). The panels
were then tested using ASTM D-1037-72 to determine
modulus of rupture (MOR), modulus of elasticity (MOE),
tensile strength perpendicular to the surface (IB),
6-cycle MOR and wet MOR (MOR after a two-hour water
boil and one-hour cold water soak). The results of
such tests are as set forth in Table I.
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g
0 ~ J\ O O 1~ n ~1 ~ N ~ ~ ~ ~ N ~ N O CO
~1 ~ I` N ~ Ct~ _I N O il~ 0 O ~ O
m ~o u~o~~Or~oo~ o~u ct)~
o
~
o
~l
,~1
a~ ~o I
1~t o ~ o ~ co 1` ~ O ~I CO U~
O ~ ~ ~ ~ ~/ ~ ~ ~ ~1
~D ~
O U~ ,1 ~ ~ r~ r~ l~ O O ~ ~ ~9 ~ O ~ ~ ~D OD ~ CO 1~ ~t ~ u~ a)
H~ O . V~ ~ ~ L') ~ t-- O 0 1~'1 ~ ~ ~5
_ ~ ~ ~ ~ ~ ~ ~ ~ N ~ N ~ ) ~ ~ ~ N ~ N t~
Ir) O O L"l 1l ) 0 0 n ul 0 0 u~ O O u~ In O O u ) ~ 0 O u
O .~ ~`1 O U l ~ ~ O ~ `1 N O l~r) N t~l O 11~ ~ N O L') t~ 1 O ~o N
~a
~1
O
O
h ~ U)
~ ~I) H
14 1~4
. O N ~D ~ L~ D ~ CD ~r r N CO ~ ~D N ~D CD r ~ O
n .......................
~U J~ ~D ~`J N ~1 ~-- ~r ~r Lr) _I CO 1` N a) Il ~ ~ 0 1` ~ 'D N a~ CO
~/ ~ 0~ _I N --1 N --1 ~I N --1 ~I N Ir1 .--1 N N ~ --1 N N ~)
,a ~a
~ ~8
_,
J~
>~ D ~ m m m ~ a ~ a
o
U~
H
'a I ~-~ N tr~ D 1` CO ~ O ~--1 N ~ ~ 1~ ~ 1` 00 ~ O ~1 N (~) ~r
~ ~ ~1 _I ~ ~1 ~ ~ _I H ~I N ~ N N N
.,1
m
--10--
EXAMPLE 25
The binder in this Example comprised a blend of
25 parts of Polyisocyanate D and 6 parts of benzaldehyde.
Three parts of the blend were mixed with 97 parts of
wood chips as set forth in the previous Example. A
panel was produced as set forth in the previous Example.
The resultant panel had a specific gravity of 0.67, an
IB of 111 psi, a MOR of 2500 psi and a wet MOR of
1866 psi.
EXAMPLES 26-30
The binder in these Examples comprised a blend
of 25 parts of Polyisocyanate D and 6 parts of the
aldehyde noted in Table II. Thirty-one parts of the
blend were mixed with 1036 parts of wood chips as set
forth in Example 1. Panels were produced as set forth
in Example 1, with the exception that the press cycle
was seven minutes instead of five minutes. The panels
were tested for IB, MOR and wet MOR, with the results
set forth in Table II being obtained.
TABLE II
IB MOR Wet MOR
Example Aldehyde (psi) (psi) (psi)
26 Cinnamaldehyde92 2366 1203
27 Salicyaldehyde90 2179 1089
28 Tolylaldehyde 110 2359 1209
29 Nonylaldehyde 99 2296 859
Butyraldehyde 72 1917 832
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