Organic polyisocyanate-alkylene oxide adhesive composition for preparing lignocellulosic composite products

An improved adhesive binder composition is provided for the preparation of lignocellulosic composite molded articles, especially flake or particleboard, made from moldable compositions which comprises an organic polyisocyanate-alkylene oxide or halogenated alkylene oxide and optionally lignin, for application to the lignocellulosic material prior to the molding process to form the composite product.

FIELD OF THE INVENTION 
The present invention relates generally to the compression molding of 
lignocellulosic materials into composite bodies, sheets and the like and 
more particularly to an improved organic di- or polyisocyanate binder 
system for the lignocellulosic material which imparts equivalent or 
improved properties to the molded pressed composite product at 
substantially reduced isocyanate binder levels. 
BACKGROUND OF THE INVENTION 
The molding of lignocellulosic and lignocellulosic-containing fibers, 
particles or layers to form composite articles is known. The binders which 
normally are used are the synthetic resin glues such as a solution of 
urea-formaldehyde or phenol-formaldehyde resin in water. Composite 
products containing lignocellulose produced in this way lack durability 
and are susceptible to moisture conditions and deterioration in certain 
building purposes to which they may be subjected. 
Di- and polyisocyanates as binders for lignocellulose materials have been 
proposed and are known to give products of increased stability and 
mechanical strength. Process technical advantages of polyisocyanates have 
been disclosed in German Offenlegungsschrift No. 2,109,686. Two problems 
associated with the use of polyisocyanate binders are (1) even at reduced 
binder use levels, the cost of the polyisocyanates as compared to the 
urea-formaldehyde or phenol-formaldehyde resin binders is unfavorable and 
(2) the viscosity of the normally employed polyisocyanate binders are much 
higher than the synthetic glue resins and are therefore difficult to apply 
to the lignocellulose with current application equipment or methods. The 
advent of technology to emulsify the polyisocyanates in water provided a 
binder product with reduced viscosity but with a service life of only 2 to 
4 hours. 
The present invention which comprises an improved polyisocyanate based 
adhesive binder composition that has been extended through the addition of 
alkylene oxides or halogenated alkylene oxides and optionally lignin, 
avoids the above mentioned disadvantages. 
SUMMARY OF THE INVENTION 
This invention relates to the preparation of a polyisocyanate-alkylene 
oxide or halogenated alkylene oxide binder composition and its use for the 
preparation of lignocellulosic composite molded products. 
It is the principal object of this invention to provide an improved 
lignocellulosic binder and composition which gives properties equivalent 
to or better than prior molded pressed composite products at dramatically 
reduced di- or poly-isocyanate (referred to generally as polyisocyanates) 
levels and cost. 
The advantages of the present invention is that reduced levels of the di- 
or poly-isocyanate necessary to produce a cured pressed composite 
lignocellulosic product can be substantially reduced while maintaining 
equivalent or superior composite board physical properties. By employing 
the di- or polyisocyanate-alkylene oxide or halogenated oxide combination, 
with or without the use of lignin as a diluent, the binder resin economics 
are equivalent or better than the synthetic glue resin economics. The 
composite products made with the adhesive binders of the present invention 
have superior physical properties to those prepared with the 
urea-formaldehyde or phenol-formaldehyde binder systems. The addition of 
the alkylene or halogenated alkylene oxides to the di- or polyisocyanates 
substantially reduces the overall viscosity of the binder system while 
exhibiting a marked increase in service life of greater than seven (7) 
days. The binder system of the present invention has viscosities 
equivalent to or lower than the formaldehyde type resin systems in water, 
which allows the instant binder system to be applied to the 
lignocellulosic chips, particles, etc., using present application 
technology. As a further advantage, the binder system of the present 
invention can be employed with high molecular weight or solid di- or 
polyisocyanates which by themselves would have properties which would 
preclude their use as adhesives for lignocellulosic products with current 
application techniques. 
DESCRIPTION OF THE INVENTION 
In accordance with the present invention an adhesive binder composition 
comprising an alkylene oxide or halogenated alkylene oxide having from 3 
to 12 carbon atoms and an organic di- or polyisocyanate, with or without 
the addition of lignin, is provided for the preparation of lignocellulosic 
composite bodies or sheets which comprises shaping in a mold or between 
mold surfaces in the form of a caul plate or platen a mixture of the 
lignocellulosic material and the isocyanate based binder of the present 
invention generally at temperatures of from about 140.degree. C. to 
220.degree. C., preferably 160.degree. C. to 190.degree. C., at pressures 
of from about 100 to 600 psi for a period of from 1 to 10 preferably 3 to 
5 minutes, there being provided at the interface of the mixture and mold 
surface or surfaces a release agent such as a metallic soap. 
The organic polyisocyanates are generally applicable as binders in the 
present invention. Organic polyisocyanates which may be used include 
aliphatic alicyclic and aromatic polyisocyanates characterized by 
containing two or more isocyanate groups. Such polyisocyanates include the 
diisocyanates and higher functionality isocyanates, particularly the 
aromatic polyisocyanates. Mixtures of polyisocyanates may be used which 
for example are the crude mixtures of di- and higher functionality 
polyisocyanates produced by phosgenation of aniline-formaldehyde 
condensates or as prepared by the thermal decomposition of the 
corresponding carbamates dissolved in a suitable solvent as described in 
U.S. Pat. Nos. 3,962,302 and 3,919,279 both known as crude MDI or PMDI. 
The organic polyisocyanate may be isocyanate-ended prepolymers made by 
reacting under standard known conditions, an excess of a polyisocyanate 
with a polyol which on a polyisocyanate to polyol basis may range from 
about 20:1 to 2:1 and include for example polyethylene glycol, 
polypropylene glycol, diethylene glycol monobutyl ether, ethylene glycol 
monoethyl ether, triethylene glycol, etc. as well as glycols or 
polyglycols partially esterfied with carboxylic acids including polyester 
polyols and polyether polyols. The organic polyisocyanates or isocyanate 
terminated prepolymer may also be used in the form of an aqueous emulsion 
by mixing such materials with water in the presence of an emulsifying 
agent. The isocyanates may also contain impurities or additives such as 
carbodiimides, isocyanurate groups, urea, hydrolyzable chlorides and 
biurets as well as certain release agents. Illustrative of such di- or 
polyisocyanates which may be employed include, for example, toluene-2,4- 
and 2,6-diisocyanates or mixtures thereof, 
diphenylmethane-4,4'-diisocyanate (a solid) and 
diphenylmethane-2,4'-diisocyanate (a solid) or mixtures of same, i.e., 
containing about 10 parts by weight 2,4'- or higher, which are liquid at 
room temperature, polymethylene polyphenyl isocyanates, 
naphthalene-1,5-diisocyanate, 3,3'-dimethyl 
diphenylmethane-4,4'-diisocyanate, triphenylmethane triisocyanate, 
hexamethylene diisocyanate, 3,3'-ditolylene-4,4-diisocyanate, butylene 
1,4-diisocyanate, octylene-1,8-diisocyanate, 4-chloro-1,3-phenylene 
diisocyanate, 1,4- 1,3-, and 1,2-cyclohexylene diisocyanates and in 
general the polyisocyanates disclosed in U.S. Pat. No. 3,577,358. The 
preferred polyisocyanates are the diphenylmethane diisocyanate 2,4' and 
4,4' isomers including the 2,2' isomer and the higher functional 
polyisocyanate and polymethylene polyphenyl isocyanate mixtures, which may 
contain from about 20 to 85 weight percent of the diphenylmethane 
diisocyanate isomers. Typical of the preferred polyisocyanates are those 
sold commercially as "Rubinate-M" (Rubicon Chemicals Inc.) and "Papi" 
(The Upjohn Co.). In general the organic polyisocyanates will have a 
molecular weight in the range between about 100 and 10,000 and will be 
employed in amounts of from about 20 to 95 parts by weight, preferably 40 
to 60 parts by weight based on the polyisocyanate-oxide mixture. 
The alkylene oxides and halogenated alkylene oxides employed in the present 
invention in amounts of from about 5 to 80 preferably 60 to 40 parts by 
weight based on the isocyanate-oxide binder mixture contain from 3 to 12 
carbon atoms and include, for example propylene, butylene, amylene, 
heptylene, octylene, decene, dodecene oxides, etc. as well as the 
corresponding halogenated alkylene oxides such as 2-chloropropylene oxide 
(epichlorohydrin), trichlorooctylene oxide, 2-bromopropylene oxide, 
trichloro-, tribromo-, triiodobutylene oxides, 2-bromopropylene oxide, 
2-chlorododecene oxide, etc. 
As indicated hereinabove the addition of the alkylene or halogenated 
alkylene oxides substantially reduces the overall viscosity of the binder 
system providing ease of application. Typical of the viscosities attained 
in centipoise, (c.p.) at 25.degree. C. are as follows using a 
diphenylmethane diisocyanate-polymethylene polyphenyl isocyanate mixture, 
sold commercially as "Rubinate-M" by Rubicon Chemicals Inc. and having a 
viscosity of 230 c.p. at 25.degree. C. The viscosities were run for 30 
minutes, 60 minutes and 4 hours, respectively at various ratios by weight 
of polyisocyanate to oxide. 
______________________________________ 
Propyl- 
230 c.p. lene Centipoise After 
Isocyanate Oxide 30 min. 60 min. 
4 hr. 
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3.0 0.5 17.6 17.9 19.2 
2.5 1.0 5.1 5.1 5.8 
2.0 1.5 1.6 1.9 1.9 
1.5 2.0 1.0 1.0 1.0 
Epichloro- 
hydrin 
3.0 0.5 42.9 42.9 43.5 
2.5 1.0 14.7 14.7 15.6 
2.0 1.5 6.7 6.7 6.7 
1.5 2.0 3.7 3.7 3.7 
Butylene 
Oxide 
3.0 0.5 21.4 22.4 23.5 
2.5 1.0 6.1 6.4 6.4 
2.0 1.5 1.9 1.9 1.9 
1.5 2.0 1.3 1.3 1.3 
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In addition a solid diphenylmethane-4,4'-diisocyanate was mixed with 
propylene oxide at a parts by weight ratio of the 4,4' isomer to propylene 
oxide of 2.5:1.0, 2.0:1.5 and 3.0:0.5 and gave a cloudy liquid mixture 
with less than 50 c.p., a clear liquid mixture of 10 c.p. and liquid 
containing solids respectively. 
The lignin which may be employed as a diluent in the binder system of the 
present invention are used in amounts of from 0 to 60 weight percent, 
preferably from 20 to 35 weight percent based on the total 
polyisocyanate-oxide-lignin mixture. The exact composition of lignin 
varies. Lignin derived from a variety of sources may be used in the binder 
system of the present invention to form the adhesive mixture. One source 
is a mixture of waste liquors resulting from the chemical pulping of 
ligno-cellulose. Suitable lignin which may be employed include, for 
example, purified pine wood lignin, kraft waste liquor, soda waste liquor, 
calcium, magnesium, sodium and ammonium base sulfite liquors, chlorinated 
waste liquors, etc. Lignins from hardwood and softwood sources may be used 
as well as lignins from acid-precipitated and alkali-reconstituted kraft 
liquors. The abundant and available chlorinated waste liquors derived from 
paper mill bleach may be used. The waste liquors may be used in their 
original condition in the adhesive binder composition of the instant 
invention. The lignin may also have a wide range of pH and a solids 
content of from about 10 to 90 weight percent. When employed, the lignin 
is simply physically mixed with the isocyanate-oxide adhesive when 
prepared or applied directly to the lignocellulosic material. 
Lignocellulose, according to the present invention, used to prepare the 
lignocellulosic-containing composite articles include wood chips, wood 
fibers, shavings, sawdust, wood wool, cork, bark and the like products 
from the wood-working industry. Fibers, particles, etc. from other natural 
products which are lignocellulosic such as straw, flax residues, dried 
weeds and grasses, nut shells, hulls from cereal crops such as rice and 
oats and the like may be used. In addition, the lignocellulosic materials 
may be mixed with inorganic flakes or fibrous material such as glass 
fibers or wool, mica and asbestos as well as with rubber and plastic 
materials in particulate form. The lignocellulose may contain a moisture 
(water) content of up to about 25 percent by weight but preferably 
contains between 4 and 12 percent by weight. 
In manufacturing lignocellulosic composite products for the purpose of this 
invention, such as flakeboard for example, a small amount of the binder 
(with or without lignin) along with the lignocellulosic material is simply 
milled or mixed uniformly together. Generally the isocyanate-oxide binding 
agent (with or without lignin) is sprayed onto the material while it is 
being mixed or agitated in suitable and conventional equipment. Various 
type mixing equipment such as an intensive-shear mixer may be employed. 
The binder use levels according to the present invention, based on the 
weight of oven dried (0% moisture content) lignocellulosic material is 
from about 1.5 to 12 preferably 2.5 to 6.5 weight percent. The 
lignocellulose-adhesive binder mixture is generally sprinkled or formed in 
the desired proportions onto a caul plate of aluminum or steel which 
serves to carry the "cake" into the press to give the desired thickness 
of product, the plates having been sprayed or coated with a release agent 
such as the metal soaps like the iron, calcium or zinc stearate compounds. 
Other conventional release agents such as sodium phenolate and certain 
tertiary amines may also be employed.

The following examples are provided to illustrate the invention in 
accordance with the principles of this invention but are not to be 
construed as limiting the invention in any way except as indicated by the 
appended claims. 
In the Examples which follow, the test results set forth are expressed as 
ASTM D 1037 values and wherein 
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M.C. is Moisture Content (%) 
I.B. is Internal Bond (psi) 
T.S. is cold water (25.degree. C.) thickness swell, 
24 hr. immersion (%) 
PMDI is a mixture of liquid diphenylmethane 
diisocyanate-polymethylene polyphenyl 
isocyanate having a 46.5% diphenyl- 
methane diisocyanate content 
P.O. is propylene oxide 
B.O. is butylene oxide 
C.P.O. is 2-chloropropylene oxide 
C.B.O. is trichlorobutylene oxide 
T.B.O. is tribromobutylene oxide 
H.O. is heptylene oxide 
C.D.O. is chlorodecene oxide 
D.D.O. is dodecene oxide 
TDI is toluene-2,4-diisocyanate 
TPMI is triphenylmethane triisocyanate 
CDI is cyclohexylene-1,3-diisocyanate 
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EXAMPLE 1 
580 g. of pine wood chips dried to a moisture content of 6 percent are 
placed in an open tumbler-mixer. During tumbling, 3.5 parts based on 
weight of the wood of an isocyanate based binding agent prepared by mixing 
70 parts crude liquid diphenylmethane diisocyanate-polymethylene 
polyphenyl isocyanate (PMDI) mixture having 46.5 percent diphenylmethane 
diisocyanate content and 30 parts propylene oxide are sprayed over the 
chips by an air pressurized system. Two caul plates 12 inches square are 
sprayed evenly with a zinc stearate external release agent. Using a former 
box, a 10.5 inches square "cake" of the chip-binder mixture is formed on 
the caul plate. The second caul plate is placed over the cake which is 
pressed to stops at a thickness of 13 mm at 190.degree. C. for 41/2 
minutes after which the pressed cake is released from between the press 
plates and cut into specimens for physical testing. Test results of the 
composite board is 132 psi I.B. and a T.S. of 22 percent. 
EXAMPLE 2 to 5 
The procedure of Example 1 is repeated except that different levels of 
oxide are substituted with crude liquid diphenylmethane 
diisocyanate-polymethylene polyphenyl isocyanate (PMDI) mixture having 
46.5 percent diphenylmethane diisocyanate content while maintaining the 
total binder level constant at 3.5 percent based on the weight of the 
wood. 
TABLE 1 
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Ex. PMDI P.O. I.B. T.S. 
No. (%) (%) (psi) 
(%) 
______________________________________ 
2 85 15 173 18 
3 78 22 141 21 
4 43 57 114 25 
5 100 0 161 17 
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EXAMPLES 6 to 9 
The procedure of Examples 1 to 5 is repeated except with the following 
changes. The total binder level is held constant at 4.5 percent based on 
the weight of the wood. A third component, lignin, a product resulting 
from the chemical pulping of lignocellulose, is added to the binder 
mixture. The liquid diphenylmethane diisocyanate-polymethylene polyphenyl 
isocyanate (PMDI) mixture having a 46.5 percent diphenylmethane 
diisocyanate content and oxide content varies over the range specified in 
Table 2 below. 
TABLE 2 
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Ex. PMDI Lignin P.O. I.B. T.S. 
No. (%) (%) (%) (psi) 
(%) 
______________________________________ 
6 66.8 22.2 11.0 149 23 
7 61.0 22.2 16.8 165 22 
8 55.5 22.2 22.3 142 19 
9 44.4 22.2 33.4 143 24 
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EXAMPLES 10 to 15 
The procedure of Examples 1 to 9 is repeated with the following changes. 
The crude liquid diphenylmethane diisocyanate-polymethylene polyphenyl 
isocyanate (PMDI) mixture having a 46.5 percent diphenylmethane 
diisocyanate content and lignin are varied over the ranges specified in 
Table 3 below while the oxide content is varied from 0 to 25 percent of 
the total binder which is based on weight of the wood. 
TABLE 3 
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Total 
Ex. PMDI Lignin P.O. Binder I.B. T.S. 
No. (%) (%) (%) (%) (psi) 
(%) 
______________________________________ 
10 66.8 11.0 22.2 4.5 170 20 
11 61.0 16.8 22.2 4.5 155 22 
12 44.4 33.4 22.2 4.5 149 23 
13 37.5 37.5 25.0 4.0 110 28 
14 100.0 -- -- 4.5 218 18 
15 72.0 28.0 -- 3.5 128 28 
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EXAMPLES 16 to 20 
The procedure for Examples 1 to 15 are repeated except for the following 
changes: butylene oxide is substituted for propylene oxide. The binder 
level for 16 to 19 is held constant at 3.5 percent based on the weight of 
the wood. Example 20 includes 22 weight percent lignin with a 4.5 weight 
percent binder level. The liquid diphenylmethane 
diisocyanate-polymethylene polyphenyl isocyanate (PMDI) mixture having 
46.5 percent diphenylmethane diisocyanate content and oxide percentages 
are varied according to Table 4 below. 
TABLE 4 
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Ex. PDMI B.O. I.B. T.S. 
No. (%) (%) (psi) 
(%) 
______________________________________ 
16 100.0 -- 147 25 
17 78.5 21.5 150 25 
18 71.0 29.0 135 27 
19 57.0 43.0 111 29 
20 55.0 22.3 115 28 
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EXAMPLE 21 (Comparative) 
The procedure for Examples 1 to 20 are repeated except phenol formaldehyde 
resin (6 percent) is used as the binder and the pressing time is 9 minutes 
and pressing temperature 220.degree. C. The following are the test results 
which indicates that a wax must be added to the material pressed to give 
desired properties. 
______________________________________ 
I.B. T.S. 
(psi) 
(%) 
______________________________________ 
101 32.3 
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EXAMPLES 22 to 32 
A number of runs are made in accordance with the procedure of Examples 1 to 
5, utilizing various alkylene or halogenated alkylene oxides and 
polyisocyanate compositions. The binder level is maintained at 3.5 weight 
percent based on the weight of the wood. The oxides and isocyanates with 
test results are set forth in Table 5. 
TABLE 5 
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Poly- 
Ex. Alkylene Isocyanate I.B. T.S. 
No. Oxide (%) (psi) 
(%) 
______________________________________ 
22 C.P.O. PMDI 138 20 
23 C.B.O. PMDI 125 24 
24 T.B.O. PMDI 120 25 
25 H.O. PMDI 130 21 
26 C.D.O. PMDI 125 23 
27 D.D.O. PMDI 125 24 
28 P.O. TDI 110 30 
29 B.O. TPMI 132 21 
30 C.P.O. TDI 105 31 
31 P.O. CDI 105 29 
32 C.B.O. CDI 100 30 
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