CA2392876C - Adhesive system containing tannin for binding lignocellulosic materials - Google Patents

Abstract

An adhesive system for use in binding lignocellulosic materials into a composite product, the adhesive system consisting essentially of (1) an effective amount of at least one powdered tannin; and (2) an effective amount of at least one additional adhesive component chosen from powdered aldehyde polymers, liquid solutions of aldehyde polymers, and liquid solutions of polymeric isocyanate. The invention also provides a method of making a composite product using the present adhesive system and a composite product made using the present adhesive system.

Description

ADHESIVE SYSTEM CONTAINING TANNIN FOR BINDING LIGNOCELLULOSIC
MATERIALS
Field of the Invention This invention relates to adhesive systems for binding lignocellulosic materials in the manufacture of composite products.
Background of the Invention Composite products made from lignocellulosic materials include "composite boards", which term is used herein to mean oriented strand boards ("OSBs"), wafer boards, straw boards, fibre boards, chip boards and particle boards wherein the board substrate is prepared by applying an adhesive to lignocellulosic particles, chips or fibres, specifically wood particles, wood chips and lignocellulosic particles, and subsequently forming the lignocellulosic material into the desired board through application of heat and pressure.
Adhesives currently used by manufacturers of various wood composite products include aldehyde polymers such as urea-formaldehyde, phenol-formaldehyde, and melamine-urea-formaldehyde, melamine-formaldehyde resins ("UF", "PF", "MUF", "MF"), and isocyanate polymers. For example, US 6,297,313 to Hsu teaches a sprayable liquid adhesive system comprising an aldehyde polymer resin and an isocyanate polymer which are combined prior to being sprayed onto lignocellulosic particles.
These adhesives suffer from a number of disadvantages. For example, the ill-effects of formaldehyde on human health are well known. Many of the above adhesives contain free formaldehyde or release formaldehyde during the manufacturing process. In the case of some adhesives formaldehyde is even released from composite boards over their useful life.
Isocyanate polymers tend to be safer once the composite board has been through the press, but are still not entirely free of health risks prior to and during application as an adhesive binding system. They can react with moisture on the skin or moisture in the lungs if inhaled as atomized isocyanate polymer or isocyanate polymer-coated wood dust. Also, isocyanate polymers can cause manufacturing problems, since they can bond to metals (i.e., metal plates and presses), and are more expensive than other conventional adhesives per unit weight basis.
In addition, the above aldehyde polymers are derived from non-renewable petroleum based resources via multiple step chemical processes that often release carbon dioxide and other emissions into the environment. !t is therefore desirable to limit their use where possible for environmental reasons. Furthermore, raw materials used to manufacture many aldehyde polymers include phenol, formaldehyde and caustic soda, all chemicals that are considered dangerous to handle in the workplace.
Also, liquid adhesive systems tend to suffer from a limited storage life or pot life. "Pot life" means the amount of time, following the addition of a catalyst, in which the liquid adhesive system is useful for the desired application catalyzed.
Liquid systems consist of components which, when mixed, begin to react and cure.
After a certain period of time, the system may lose its utility, i.e. cannot be used.
In US 5,407,980 to Pizzi et al., tannin is used as an accelerator to speed up the curing process. This patent teaches a liquid adhesive composition for manufacturing plywood for exterior application including: a) 121 parts by weight phenolic resin; b) 5 to 121 parts by weight isocyanate polymer; c) 1 to 40 parts by weight tannin selected from the group consisting of pine, quebracho, mimosa, and combinations thereof; d) 1 to 15 parts by weight paraformaldehyde or formaldehyde solutions in water; e) 5 to 50 parts by weight of water; and f) and amount of filler comprising inorganic andlor organic materials for providing the composition with the desired viscosity. Pizzi et al. further teaches that the added formaldehyde or paraformaldehyde is necessary to achieve the required hard gel.
Manufacturers of adhesive systems for composite panels continue to search for supplements to or replacements for adhesives presently used, especially those which are based on aidehyde polymer resins (e.g. urea- and phenol-formaldehyde resins) and isocyanate polymers because of environmental, health, cost, and performance concerns. There is still a need for new adhesive compositions or systems which (1 ) can be formulated and used with relative ease while providing a composite board having the desired physical properties; (2) are less harmful to the environment by employing products derived from natural and renewable resources;
(3) are less harmful to human health by reducing or eliminating the amount of free formaldehyde released from composite boards and presses; and (4) are relatively cost-effective to manufacture and use. An object of the present invention is to at least partially address one or more of these needs.
Summary of the Invention Tannin has been used as an adhesive component for at least 50 years. It is derived from natural renewable resources (i.e. trees and plants). Certain kinds are widely available, are extracted from the bark of trees cut for lumber, and are not known to cause problems to health. However, the use of tannins in adhesives is not widespread, especially for OSB board manufacture, since most liquid aldehyde tannin adhesives systems suffer from pot life constraints.
It has been found that natural extracted unmodified tannins, and post extraction modified tannins, in dry powder form, and preferably in spray dried powder form, can be used to replace a portion of certain adhesives known to have better binding properties, to provide an adhesive system which serves to overcome, at least partially, one or more of the problems associated with prior art adhesive systems. Surprisingly, unmodified and modified tannins may be used in dry form and without any externally added formaldehyde generating "donor" catalyst to provide an adhesive system which is useful in the production of commercially acceptable composite products.
The present invention provides, in accordance with one aspect, an adhesive system for use in binding lignocellulosic materials into a composite product, the adhesive system consisting essentially of (1 ) an effective amount of at least one powdered tannin; and (2) an effective amount of at least one additional adhesive component chosen from powdered aldehyde polymers, liquid solutions of aldehyde polymers, and liquid solutions of polymeric isocyanate.
In one embodiment, the adhesive system consists essentially of at least one powdered tannin and at least one powdered aldehyde polymer, in a weight ratio of tannin to aldehyde polymer of from 6:94 to 80:20, preferably from 10:90 to 65:35, more preferably from 20:80 to 60:40, and even more preferably from 40:60 to 50:50.
In another embodiment, the adhesive system consists essentially of at least one powdered tannin and at least one liquid polymeric isocyanate, in a weight ratio of tannin to isocyanate of from 5:95 to 90:10, preferably from 10:90 to 80:20, and more preferably from 35:65 to 75:25.
In yet another embodiment, the adhesive system consists essentially of at least one powdered tannin, at least one powdered aldehyde polymer, and at feast one liquid polymeric isocyanate. The tannin is present in an amount of from 5%
w/w to 80% w/w, preferably from 20% w/w to 40% w/w, and more preferably 20% w/w to 30% w/w. The aldehyde polymer is present in an amount of from 5% w/w to 80%
w/w, preferably from 20% w/w to 40% w/w, and more preferably from 20% wlw to 30% w/w. Finally, the isocyanate is present in an amount of from 15% w/w to 90 w/w, preferably from 40% w/w to 60% w/w, and more preferably from 50% w/w to 60% w/w. These figures are based on the total weight of the adhesive system.
In a still further embodiment, the adhesive system consists essentially of at least one powdered tannin, at least one powdered aldehyde polymer, and at least one liquid solution of aldehyde polymer having an aldehyde polymer concentration of from 10% w/w to 82% wlw, based on the total weight of the aldehyde polymer solution. The tannin is present in an amount of from 6% w/w to 82% w/w, and preferably from 45% w/w to 55% w/w. The powdered aldehyde polymer is present in an amount of from 6% w/w to 82% w/w, and preferably from 10% w/w to 20% w/w.
Finally, the liquid solution of aldehyde polymer is present in an amount of from 12%
w/w to 88% w/w, and preferably from 35% w/w to 45% w/w. Again, these figures are based on the total weight of the adhesive system.
In another embodiment, the adhesive system consists essentially of at least one powdered tannin, at least one powdered aldehyde polymer, at least one liquid solution of aldehyde polymer having an aldehyde polymer concentration of from 10% w/w to 65% wlw aldehyde polymer based on the total weight of the aldehyde polymer solution, and at least one liquid solution of polymeric isocyanate.
The tannin is present in an amount of from 5% w/w to 80% w/w, the powdered aldehyde polymer is present in an amount of from 5% w/w to 80% w/w, the liquid solution of aldehyde polymer is present in an amount of from 5 % w/w to 80% w/w, and the liquid solution of polymeric isocyanate is present in an amount of from 10%
wlw to 85% w/w, all based on the total weight of the adhesive system.
In yet another embodiment, the adhesive system consists essentially of at least one powdered tannin, at least one liquid solution of aldehyde polymer having an aldehyde polymer concentration of from 10% w/w to 65% w/w aldehyde polymer based on the total weight of the aldehyde polymer solution, and at least one liquid solution of polymeric isocyanate. The tannin is present in an amount of from 10%
w/w to 80% w/w , the liquid solution of aldehyde polymer is present in an amount of 10% w/w to 80% w/w, and the liquid solution of polymeric isocyanate is present in an amount of from 10% w/w to 80% w/w, all based on the total weight of the adhesive system.
In one embodiment of an adhesive system containing powdered tannin and powdered aldehyde polymers, 90% w/w of each of the powdered tannins and powdered aldehyde polymers, based on their respective total weights, have a size which is 100 mesh or smaller, and the remaining 10% w/w, based on their respective total weights, have a size which is between 100 mesh and 30 mesh. In another embodiment, 90% w/w of each of the powdered tannins and powdered aldehyde polymers, based on their respective total weights, have a size which is 200 mesh or smaller, and the remaining 10% w/w, based on their respective total weights, have a size which is between 200 mesh and 30 mesh. In a still further embodiment, the median size of each of the powdered tannins and powdered aldehyde polymers is about 400 mesh, In yet another embodiment, the median size of each of the powdered tannins and powdered aldehyde polymers is about 350 mesh.
The aldehyde polymers may be chosen from phenol-formaldehyde polymers, resorcinol-formaldehyde polymers, urea-formaldehyde polymers, melamine-urea-formaldehyde polymers, melamine-formaldehyde polymers, and phenol-formaldehyde polymers modified with at least one member chosen from kraft lignin, kraft black liquor, lignin, lignosulfonates, cashew shell extract, pecan shell extract, urea, melamine-formaldehyde polymers, urea-formaldehyde polymers, protein, and tannin.
The tannins may be chosen from mimosa (wattle) tannin, pine tannin, quebracho tannin, hemlock tannin, mangrove bark tannin, and gambler tannin, and are preferably mimosa (wattle) tannins and, more preferably, modified mimosa (wattle) tannins.
Preferably, the tannins and powdered aldehyde polymers are spray dried.

The aldehyde polymers are preferably at least one phenol-formaldehyde polymer having a formaldehyde/phenol mole ratio of 1.1:1 to 3:1, and preferably 1.5:1 to 2.4:1 The isocyanate polymer preferably has an isocyanate group (-NCO) content of at least 20% w/w based on the total weight of the isocyanate polymer.
Each of the liquid solutions of aldehyde polymers preferably comprises at least one aldehyde polymer and water. Preferably, the at least one aldehyde polymer is present in a concentration of from 25 to 65% w/w, and more preferably in a concentration of from 50 to 55% w/w, based on the total weight of the solution.
The at least one aldehyde polymer is preferably chosen from phenol-formaldehyde polymers, resorcinol-formaldehyde polymers, urea-formaldehyde polymers, melamine-urea-formaldehyde polymers, melamine-formaldehyde polymers, and phenol-formaldehyde polymers modified with at least one member chosen from kraft lignin, kraft black liquor, lignin, lignosulfonates, cashew shell extract, pecan shell extract, urea, melamine-formaldehyde polymers, urea-formaldehyde polymers, protein, and tannin, said at least one aldehyde polymer being present in a concentration of from 10% solids w/w to 65% solids w/w in each liquid solution, based on the total weight of the solution. Furthermore, the at least one liquid solution of aldehyde polymer may further comprise at least one further diluent chosen from methanol, ethanol, butanol, ethylene glycol, propylene glycol, and triethylene glycol.
In accordance with another aspect, the invention provides a method of making a composite product comprising applying an adhesive system to lignocellulosic material to coat and bind the material to form the composite product, the adhesive system consisting essentially of (1 ) an effective amount of at least one powdered tannin; and (2) an effective amount of at least one additional adhesive component chosen from powdered aldehyde polymers, liquid solutions of aldehyde polymers, and liquid solutions of polymeric isocyanate.
In accordance with a further aspect, the invention provides a composite product comprising lignocellulosic material bound together with a cured adhesive system, the adhesive system, prior to curing, consisting essentially of (1 ) an effective amount of at least one powdered tannin; and (2) an effective amount of at least one additional adhesive component chosen from powdered aldehyde polymers, liquid solutions of aldehyde polymers, and liquid solutions of polymeric isocyanate.
Preferably, the lignocellulosic material comprises wood strands, wood wafers, or straw particles. The composite product may be a composite board (e.g. oriented strand board or OSB, wafer board, straw board, etc.) or a layer thereof. While a multi-layer composite board can be made with the same lignocellulosic material and adhesive system employed throughout, typically, composite boards comprise a plurality of different layers in which different wood products and/or different adhesives are employed. The amount of adhesive system binder used in each layer, and the composition of the adhesive used in each layer, may vary, as is known in the art of composite board manufacture.
To avoid the problem of limited pot life, any liquid component of the system is kept separate from the other components until application of all components to lignocellulosic material in situ. It will be appreciated that the powdered components may be pre-blended in certain ratios to suit the particular application and applied to the material in one step. Also, the components may be added in stages or all at once. If added in stages, the order of addition is not critical. What is required is that all components being used are properly combined in situ to achieve the required curing reactions.
The amount of adhesive system used to coat and bind the lignocellulosic material is preferably from 1.5 to 15% w/w based on the weight of the lignocellulosic material. The actual amount to be used is dependent on various factors readily apparent to the person skilled in the art. These factors include the composition of the adhesive system, the type of lignocellulosic material used, including its geometry and size, and the temperature, pressure and time parameters used in the press operation. These parameters are readily determinable by the person skilled in the art using simple experimentation and are themselves dependent on the amount of adhesive system applied and the composition of the adhesive system. Typically, the coated lignocellulosic material is heated to a temperature in the range of from 160°C
to 230°C and more preferably from 200°C to 220°C. Also, the material is typically subjected to a gauge pressure in the press which is in the range of from 750 psi to 2000 psi, and more preferably from 1400 psi to 1700 psi.

The relative amounts of the components in the adhesive system can also be determined through simple experimentation and depend on the identity of the components present.
The amount of time used in the pressing operation affects the properties of the final composite product. The press may be a single opening press, multiple opening press, or a press which uses a continuous process. Typically, the press time is from 100 seconds to 600 seconds, and more preferably from 120 seconds to 240 seconds.
There are many advantages associated with the present adhesive system.
As mentioned above, the present invention uses a harmless, natural, and renewable resource (i.e. modified or unmodified tannin from trees) to replace a portion of prior art binders which have a number of disadvantages, some of which have been noted above. Thus, the invention helps to minimize the negative impact of such prior art binders and/or reduce the cost of the adhesive system.
Adhesive systems according to the invention containing only powdered components have been found to give rise to lower formaldehyde emissions from the blender, forming line, press, and final composite product, as compared to prior art adhesives which contain added formaldehyde or paraformaldehyde. Without being bound by theory, it is believed that, as the present adhesive system cures, the tannin attaches itself to active and unstable methylol groups in the other adhesive components and to excess free formaldehyde present in the system or to aldehyde groups present in the other components of the system, thereby Ncapping" or "catching" these molecules and/or groups to prevent formaldehyde release.
An adhesive system consisting only of powdered components (e.g. powdered tannin and aldehyde polymer) is stable in storage and performs in a predictable manner. The components do not react until actually used in the press.
Furthermore, the time required to cure the adhesive system can be adjusted to suit the application on site. This can be done by varying the amount of the tannin relative to the aldehyde polymer. When the ratio of the weight of the tannin to the aldehyde polymer is less than 1:4, increasing the amount of the tannin relative to the aldehyde polymer will result in an increase in the cure time and plastic flow rate of the adhesive system, and vice versa. Adhesive systems having slower cure times are desirable when forming an outer layer of a composite board. As the outer layer receives more heat in the press than inner layers, a slower curing adhesive in the outer layer prevents the outer layer from curing prior to curing of the inner layer(s).
When the weight ratio of the first part to the second part is greater than 1:4 (e.g.
1:1 ), it has been observed that the cure time and plastic flow rate will decrease as the amount of the first part is increased relative to the amount of the second part, and vice versa.
The powdered system is also easier to use than prior art liquid adhesive systems which require an additional step of premixing of the components by batch process or continuous means prior to use at the composite board manufacturing mill. In prior art liquid systems containing tannin and a formaldehyde generating 'donor' catalyst, the catalyst must be measured accurately to achieve the desired cure properties. The present system is more forgiving when it comes to measuring out the components. The manufacturing process is further simplified by pre-mixing the powdered components and applying them to lignocellulosic material in one step.
On the other hand, the powdered tannin and powdered aidehyde polymer may be added in separate steps, in which case, their relative amounts may be adjusted at the mill to vary the cure time and board properties.
An adhesive system according to the invention can be used to produce commercially acceptable composite boards. The properties of these composite boards will vary with the actual composition of the adhesive system used, the temperature of press platens, the time in the press, the pressure applied, and the time the board spends in hot post-curing.
The invention may be better understood with reference to the following description of the preferred embodiments.
Detailed Description of the Preferred Embodiments Whenever the term Ncomprising" is used herein, it is used to mean "including but not limited to".
The term "about", when used in connection with a numerical figure, means that figure and minor variations therefrom which do not have a material effect on the way the embodiment of the invention works. For the sake of clarity, when "about" is used in connection with a numerical figure, this is meant to include that figure plus or minus 5%.
For the sake of convenience, the term "tannin" when used herein means both modified and unmodified tannin, unless otherwise specified. "Unmodified tannins"
are natural high molecular weight complex molecular substances sourced from various trees and plants and composed mainly of condensed flavonoids and their precursors, the balance being non-flavonoid molecules which may comprise carbohydrate gums, sugars, and amino acids.
"Modified tannins" are unmodified tannins which have been modified by hydrolysis, sulfonation, methylation, acetylation (acylation), or conversion to a metal salt.
Tannins fall into two groups: the pyrogallol group and the catechol group. The tannins useful herein as adhesive components come from the catechol group. The molecular weight of catechol tannins range from 200 - 2500 depending on the natural source, and the extraction and post extraction modification processing techniques. The actual molecular structure of a tannin, its reactivity, and pertormance as an adhesive varies.
The term "aldehyde polymers" when used herein means polymers made with an aldehyde and a compound with reactive hydroxyl or amino groups. Aldehydes include formaldehyde, acetaldehyde, proprionaldehyde, butyraldehyde, furturaldehyde, and benzaldehyde. Compounds with reactive hydroxyl or amino groups include phenols, ureas, and melamines. Aldehyde polymers include phenolic resoles and modified phenolic resoles.
"Phenolic resole" means a condensation product of phenol (or derivatives of phenol) with an aldehyde, formed under basic (i.e. alkaline) conditions in the presence of a catalyst, and which has a mole ratio of aldehyde to phenol greater than 1:1. The term phenolic resole is used interchangeably herein with "phenolic resole resin" or "phenolic resin".
The phenolic component can include any one or more of the phenols which have heretofore been employed in the formation of phenolic resins and which are not substituted at either the two ortho-positions or at one ortho- and the para-position, such unsubstituted positions being necessary for the polymerization reaction. Any one, all, or none of the remaining carbon atoms of the phenol ring can be substituted. The nature of the substituent can vary widely, and it is only necessary that the substituent not interfere in the polymerization of the aldehyde with the phenol at the ortho- and/or para- positions. Substituted phenols employed in the formation of the phenolic resins include: alkyl-substituted phenols, aryl-substituted phenols, cyclo-alkyl-substituted phenols, alkenyl-substituted phenols, alkoxy-substituted phenols, aryloxy-substituted phenols, and halogen-substituted phenols, the foregoing substituents containing from 1 to 26 and preferably from 1 to 12 carbon atoms. Specific examples of substituted phenols include: phenol, 2,6 xylenoi, o-cresol, m-cresol, p-cresol, 3,5-xylenol, 3-4-xylenol, 2,3,4-trimethyl phenol, 3-ethyl phenol, 3,5-diethyl phenol, p-butyl phenol, 3,5-dibutyl phenol, p-amyl phenol, p-cyclohexyl phenol, p-octyl phenol, 3,5-dicyclohexyl phenol, p-phenyl phenol, p-crotyl phenol, 3,5-dimethoxy phenol, 3,4,5-trimethoxy phenol, p-ethoxy phenol, p-butoxy phenol, 3-methyl-4-methoxy phenol, and p-phenoxy phenol.
The aldehydes reacted with the phenol can include any of the aldehydes heretofore employed in the formation of phenolic resins such as formaldehyde, acetaldehyde, propionaldehyde, butyraldehyde, furfuraldehyde, and benzaldehyde.
In general, the aldehydes employed have the formula R'CHO wherein R' is a hydrogen or a hydrocarbon radical of 1 to 8 carbon atoms. The most preferred aldehyde is formaldehyde.
"Modified phenolic resole" is a phenolic resole which has been modified by other formaldehyde reactive components such as kraft lignin, kraft black liquor, lignin, lignosulfonates, cashew shell extract, pecan shell extract, urea, melamine-formaldehyde polymers, urea-formaldehyde polymers, protein, and tannin, In the art, the term "MD/" is often used generically to mean any one of a number of isocyanate polymers or polymeric urethanes. An example is polymeric 4,4'-Biphenyl methane diisocyanate which has been used in wood binders systems for 20 years. For the sake of convenience and clarity, when used herein, the term "MD/" shall mean isocyanate polymer(s), unless otherwise specified. The terms "MD/" and "isocyanate polymer(s)" are used herein interchangeably with the term "polymeric isocyanate". Isocyanate polymers are typically applied in their liquid form.

The isocyanate polymer of the present adhesive system may suitably be any organic isocyanate polymer compound containing at least 2 active isocyanate groups per molecule, or mixtures of such compounds. Generally, the isocyanate polymers employed in the method of this 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 isocyanate polymer composition. The percent available NCO groups can be determined by the procedures of ASTM test method D1638.
The isocyanate polymers 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 isocyanate polymers.
Representative aromatic isocyanate polymers 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 isocyanate polymers include hexamethylene diisocyanate, xylylene diisocyanate, 1,12-dodecane diisocyanate and lysine ethyl esterdiisocyanate. Representative cycloaliphatic isocyanate polymers include 4,4'-methylenebis (cyclohexyl isocyanate), 1,4-cyclohexylene diisocyanate, 1-methyl-2,4-cyclohexylene diisocyanate and 2,4-bis(4-isocyanatocyclohexylmethyl) cyclohexyl isocyanate.
"Liquid solution of aldehyde polymer" is a solution of at least one aldehyde polymer dissolved in an aqueous solution. The solution may include at least one further diluent chosen from methanol, ethanol, butanol, ethylene glycol, propylene glycol, and triethylene glycol.
Powdered components of the present adhesive system are either micropulverised or spray dried, as is known in the art.
Commercially available unmodified and modified tannins, aldehyde polymers (including phenolic resoles and modified phenolic resoles) typically include fillers or extenders. Examples of typical extenders/fillers include calcium carbonate, water (in small amounts), and starches. In addition, powdered aldehyde polymers may contain cross-linking accelerants, as are known in the art. Thus, all references herein to components of the present inventive adhesive system are references to commercially available forms of the components which include such additional ingredients as are typically included in their commercial forms.
In one embodiment, the adhesive system consists essentially of a spray dried tannin and a spray dried phenolic resin. The spray dried components are either pre-mixed off site, mixed on site prior to addition in one step to the lignocellulosic material, or added in stages or series to coat lignocellulosic material in the OSB
blender. This and other embodiments of the present adhesive system according to the invention does not contain added cross-linking accelerants. Examples of such accelerants include paraformaldehyde, hexamine tetramine (hexa), or urea-formaldehyde concentrate (UFC 80T"", UFC 85T""). Without being bound by theory, it is believed that the formaldehyde defrcient tannin molecule is forced to 'scavenge' free formaldehyde from the dry phenolic resin and reactive methylol groups on the phenolic resin molecule. In another embodiment, the adhesive system also includes liquid MDI which is added to the furnish (i.e. lignocellulosic material) in situ to avoid the problem of pre-cure or limited pot life of the adhesive system.
A preferred method of making a composite product, in the form of an oriented strand board, using a preferred embodiment of the present adhesive system, will now be described. The person skilled in the art will readily understand how to adapt the below described method to make other composite boards, such as wafer boards, straw boards, fibre boards and chip boards.
In order to make OSB, bark is first stripped from wet logs. Then, the debarked logs are cut into suitable lengths and fed into a flaker where they are reduced into thin flakes which are fractured to produce narrow, thin strands of wood.
These wood strands are dried to reduce their moisture content from roughly 40-percent to about 3-11 percent of the total mass.
Next, in a rotating blender/mixer, the dried strands are treated with a suitable petroleum based "slack" wax or wax em~rlsion. A suitable wax emulsion is sold in association with the trade-mark Cascowax EW-58A by Borden Chemical, U.S.A.
The wax helps repel water in the finished OSB board as well as seal some of the uneven surfaces of the strands to prevent excess absorption of the adhesive by the wood strands. The person skilled in the art will appreciate that wax is normally not required in the manufacture of straw board because of its waxy surface nature.
A preferred embodiment of the present adhesive system is then added to coat the wax coated wood strands. The preferred embodiment consists of a mixture of first, second and third parts. The first part is unmodified tannin and modified tannin derived from mimosa (wattle) bark. The tannin and modified tannin are spray dried to a powdered state and is sold in association with the trade-mark "Bondtite 345 Mimosa A" (hereinafter referred to as "Mimosa A") by Bondtite Inc. of South Africa. More specifically, Mimosa A is modified by hydrolysis to increase the reactivity of the original unmodified tannin. The second part is a base catalyzed spray dried phenol-formaldehyde resole resin and available commercially from Tembec, Inc. of Temiscaming, Quebec and sold under product code SP007.
This resin and other phenol-formaldehyde resole resins used in the examples herein have a formaldehyde to phenol mole ratio in the range of from 2.2:1 to 1.5:1.
However, it has been found that phenol-formaldehyde resole resins having a formaldehyde to phenol ("F/P") mole ratio of from 3:1 to 1.1:1 will also work in the context of the present invention. Such phenol-formaldehyde resole resins are available from a number of commercial sources other than Tembec, Inc. and also can be readily made in the laboratory by the person skilled in the art. For example, Canadian patent number 1,074,004 to Gres et al discloses a methods) of preparing modified phenol-formaldehyde resins in solid particulate form useful in the context of the present invention.
The third part is a polymeric isocyanate sold in association with the trade-mark BASF Lupranate M20SB by BASF, Inc., U.S.A. and Tembec, Inc. The polymeric isocyanate supplies reactive -NCO (i.e. isocyanate) groups.
The first, second and third parts of the system are added in that order consecutively and in separate steps. It will be appreciated, however, that two or more parts may be added in a single step. As mentioned above, the first and second parts may be pre-mixed and added in one step. The first and second particulate parts are blown or dropped onto the wood strands, while the liquid third part is sprayed onto the wood strands. Fresh strands are fed in at one end of the rotating blender and adhesive coated strands leave at the other end. The amount of adhesive that is applied can be varied by adjusting the meters of the adhesive delivery systems.
The adhesive coated strands are then laid in mats which will form respective layers of the final OSB. When forming mats which will become outer layers of the OSB, the strands are normally aligned in the long direction of the board. For inner layers, the strands are made to cross or are randomly aligned. The OSB's strength comes mainly from the uninterrupted wood fibre, interweaving of the long strands and wafers, and the degree of orientation in the surface layers. The result is a five layer composite mat of oriented strands which is 7" to 10" thick. It will be appreciated that the composite mat may have anywhere from three to seven layers, though five layers is used in the present example. Thereafter, the strand-laden continuous mat is loaded into a single opening press where heat and pressure are applied simultaneously for a specific period of time (in this case 240 seconds) in order to compress the mat to the desired thickness and activate the curing of the adhesive system, thereby bonding the strands into structural strand board panels.
Again, it will be appreciated that the heat and pressure may be applied for a different time period, such as from 120 seconds to 360 seconds, though 120 seconds is used in the present example.
Instead of a single opening press, a multi opening press (example 12 sets of platens, and 12 openings) or a continuous press system may be used. The "master"
or large panels coming out of the press are then cut to size.
It will be appreciated that the components or parts of the adhesive system can be used concurrently or sequentially in a series of blenders, rather than in a single blender, to achieve specific results for the mill or OSB panel grade being run.
An OSB board line may have from 3 to 5 blenders and forming lines prior to the OSB
press, one or more for each layer of the final board. Each blender may empty into its own oriented strand forming section prior to all lines sandwiching into the final panel layer configurations at the press. Typically, there are multiple blenders and forming lines converging to form one final multi-layer mat to produce a layered OSB
board.
It will also be appreciated that the furnish may contain wood components other than strands, such as fines.
The manufacture of other composite boards apart from straw boards, such as wafer boards and chip boards, follows a similar process. Straw board is made by a different process and is not detailed herein. Other composite boards are made with starting lignocellulosic materials which differ from the wood strands used in OSBs in terms of their size and geometry. Typically, such materials are wood components such as wood chips, wood fibres, shavings, veneers, wood wool, cork, bark, sawdust, and the like. Particles of other lignocellulosic material such as shredded paper, pulp or vegetable fibres such as corn stalks, straw, bagasse and the like may also be used. Optionally, non-lignocellulosic materials such as shredded scrap rubber, polyurethane, polyisocyanate and like cellular and non-cellular polymers can be added.
Example I
Trials were conducted with a dry particulate adhesive system according to a first preferred embodiment of the invention. The system consisted of a spray dried commercial grade modified (i.e. by hydrolysis) tannin powder derived from the mimosa tree and sold commercially in association with the trade-mark Bondtite by Bondtite Inc. of South Africa (hereinafter referred to as "Mimosa A").
Mimosa A
belongs to a group of tannins referred to generically as mimosa tannins which are derived from the mimosa (or wattle) tree. Different mimosa tannins are available from a variety of commercial sources including Bondtite, Inc. Mimosa A is reported by Bondtite, Inc. to have a molecular weight of between 900 and 1000.
The system also consists of a production grade spray dried modified phenol-formaldehyde resole resin powder (referred to hereinafter as "Resin A"), available commercially from Tembec, Inc. of Temiscaming, Quebec and sold under product code SP007 and having a formaldehyde to phenol ("F/P") mole ratio of from 2.2:1 to 1.5:1.
Resin A is normally used as a surface layer OSB resin and has the following product specifications:
Amount of free formaldehyde : 1.0% w/w based on the weight of Resin A

Fusion melt disc diameter (150°C): 33-43 mm Hot plate (150°C) spatula knead cure time of powder: 30-40 seconds Phenol-formaldehyde resole resins having similar properties to the above properties can be readily made in the laboratory by the person skilled in the art and would also work in the context of the present invention.
"Fusion melt disc diameter" is a measure utilized in a standard test procedure used by resin suppliers and mill technical personnel. The test is used to determine the fluidity of a fusible heat reactive resin when heated on a hot plate at a temperature of 150°C and at a pressure of 68 psi. The hot plate is a thermoelectric stainless steel hot plate, preheated to 15011°C. 0.5 grams t 0.01 grams of resin is weighed onto a piece of transfer paper. Using a ParrT"" pellet press, a pellet is made from the resin having a diameter of 12.7 mm and a height of 6.0 mm. The pellet is then transferred onto the preheated hot plate which is fined with aluminum foil. A
glass plate having a length of 4", a width of 3", and a height of 1/16", is placed on top of the pellet and an aluminum or steel cylinder weighing 6 kg is placed on top of the glass plate. After 3 minutes, the glass plate and weight are removed and the diameter of the melted pellet is measured at four places. The "fusion melt disc diameter" is the average diameter resulting from the measurements.
"Hot plate (150°C) spatula knead cure time of powder" is the time required to cure a spray dried powdered resin under the following conditions. A hot plate is heated to 15011°C as in the case of the above "fusion melt disc diameter" test. 0.25 grams ~ 0.01 grams of powdered resin is weighed, transferred onto a stainless steel spatula, and then transferred onto the hot plate. The resin is slowly kneaded with a spatula and the time, in seconds, taken for the powder to melt, plasticize and then fully cure, with no remaining signs of plasticity, is measured. The resulting measurement is the "hot plate (150°C) spatula knead cure time of powder".
Mimosa A was dry blended via a metering auger into a continuous air conveyed stream of the spray dried phenolic resin powder (Resin A) to achieve a thoroughly mixed adhesive system having a weight ratio of tannin to Resin A of 1:10.
The following properties of the adhesive system and of the individual components thereof were noted and are shown in Table i below.

TABLE I
Mimosa Resin A Adhesive System (Mimosa A A and Resin A

Free formaldeh de 0.0% 1.0% w/w 0.95% w/w wlw Fusion melt disc no flow 34 mm 39 mm diameter measurable Hot plate (150C) 5 seconds31 seconds35 seconds spatula cure time The free formaldehyde amount is based on the total weight of the tested components or adhesive system, as the case may be.
Without being bound by theory, it is believed that the increases in the plastic flow rate (i.e. the larger fusion melt disc diameter) and in the hot plate cure time of the adhesive system versus Resin A alone, are due to inter-reactions between the tannin and the phenolic resin. It is believed that when the adhesive system is used in an OSB press mill, the tannin will react with free formaldehyde in the phenolic resin powder to form tannin methylol groups and subsequently the methylol groups in the phenolic resin molecule will condense with hydroxyl phenol sites on the tannin molecule and the tannin methylol groups will further polymerize with the phenolic resin molecules.
Free formaldehyde is normally present in spray dried phenolic resins (including Resin A) to facilitate a faster cure in the press. The initial increase in plasticity and cure time of the adhesive system as compared to Resin A alone is believed to be a result of the tannin "scavenging" the free formaldehyde at the expense of the phenolic resin's reactivity, thereby slowing down the rate of cure of the phenolic resin. Continued heat input over a longer elapsed time is believed to activate the final cross-linking, via methylene bridges, of tannin to phenolic resin, phenolic resin to phenolic resin, and tannin to tannin. The result is a lower over-all weight ratio of formaldehyde to the adhesive system as compared to systems consisting only of a phenolic resin or a phenolic resin in combination with a isocyanate polymer. Thus, the present system can be used without any additional formaldehyde or paraformaldehyde being added to produce a composite product which has a lower amount of free formaldehyde in the cured adhesive.
In the manufacture of composite boards, the boards are typically "hot stacked" after the pressing operation. "Hot stacking" refers to the process of removing the pressed boards from the press and stacking them in a pile at a specified temperature for a specified time (e.g. at 130°C for one hour). The stacked boards are then allowed to cool overnight in a controlled humidity (84%) chamber.
Prior art OSB boards manufactured with a phenolic resin alone or in combination with MDI normally improve in terms of their mechanical strength and water resistance properties during hot stacking. There is typically a 20%
improvement in these properties resulting from continued cross-linking (curing) of the aldehyde containing part of the adhesive system. The inventor believes that the present invention improves on this process of continued cross-linking. It is believed that the tannin "scavenges" or reacts with additional fugitive formaldehyde molecules which would otherwise escape from the OSB panel, as well as with the methylol groups on the phenolic resin molecules to cap those groups to reduces the number of sites where future formaldehyde emissions can originate. Thus, it is expected that formaldehyde emissions from composite boards made using the present adhesive system will be reduced.
Alternative embodiments of the present adhesive system consisting only of Resin A and Mimosa A in a weight ratio of 4:1 and 1:1 were tested and found to achieve similar or good results relative to the above described embodiment.
Furthermore, additional testing revealed that adhesive systems containing only Mimosa A and Resin A were as stable in storage as Resin A alone.
Example II
Adhesive systems according to two further embodiments of the invention (Formulations A and B) were formulated and tested against a control (Formulation C) in the production of OSB boards made from strands of southern yellow pine and sweet gum wood species. The same amount of adhesive was used in all tests.
Similarly, blender conditions, forming conditions, and press conditions were kept constant throughout the tests. These parameters will be described in more detail below. The OSB boards produced each had identical top and bottom surface layers bound together using one of Formulations A, B, and C, and a core layer bound together using only a spray dried phenolic resole resin (Formulation D).
All formulations are summarized in Table Ila below. Table Ila also lists the amount of adhesive system used (% w/w based on the total weight of the furnish).
TABLE Ila Adhesive SystemComposition W a i g h Adhesive Dosage %
t r a t w/w i o tannin/resinbased on wei ht of furnish Formulation Resin B 0:100 3 C

(control) surface la er adhesive Formulation Mimosa A 1:4 3 A

surface layerResin B

adhesive Formulation Mimosa B 1:4 3 B

surface layerResin B

adhesive Formulation Resin C 0:100 3 D

core layer adhesive Resin B is a production grade spray dried phenol-formaldehyde resole resin powder available commercially from Tembec, Inc. of Temiscaming, Quebec and sold under product code SP900 and normally used as a surface layer OSB resin. Resin B has an F/P mole ratio of from 2.2:1 to 1.5:1.
Resin C is a spray dried phenol-formaldehyde resole resin available commercially from Tembec, Inc. of Temiscaming, Quebec under product code CP820 (Resin C), and having an F/P mole ratio of from 2.2:1 to 1.5:1.
Mimosa A, as described above, is a modified tannin sold in association with the trade-mark Bondtite 345 by Bondtite, Inc. of South Africa. Mimosa A has a molecular weight of approximately 900-1000 and is derived from the mimosa tree (i.e. wattle).
Mimosa B is a modified tannin (modified to a lower degree of effective hydrolysis than Mimosa A) and is sold in association with the trade-mark Bondtite 645, also by Bondtite, Inc. Mimosa B has a molecular weight of approximately and is less reactive with formaldehyde than Mimosa A.
The production of the OSB boards will now be described. All % w/w figures are % based on the total weight of the furnish.

Step A - Core Layer Production yu_sinq Formulation D) 1.5 % w/w Cascowax EW-58AT"" wax emulsion (sold by Borden Chemical, U.S.A.) was sprayed onto wood strands consisting of 50% w/w strands from sweet gum and 50% w/w strands from southern yellow pine. 3% wlw of Resin C was added to the wax emulsion coated strands and the mixture was tumbled for 4 minutes in a blender. Afterwards, the adhesive coated mixture was stored for mat forming and pressing.
Step B - Surface LaXer Production (usina Formulation A) 1.5 % w/w Cascowax EW-58AT"" wax emulsion was sprayed onto wood strands consisting of 30% strands from sweet gum and 70% w/w strands from southern yellow pine. Formulation A was then added at a dosage of 3% w/w to a blender full of the wax coated emulsion strands which were then tumbled for 4 minutes. Afterwards, the adhesive coated strands were stored for mat forming and pressing.
Step C - Surface t-aKer ProductiQn,~usina Formulation Bl 1.5 % wlw Cascowax EW-58AT"" wax emulsion was sprayed onto wood strands consisting of 30% strands from sweet gum and 70% w/w strands from southern yellow pine. Formulation B was then added at a dosage of 3% w/w to a blender full of the wax coated emulsion strands which were then tumbled for 4 minutes. Afterwards, the adhesive coated strands were stored for mat forming and pressing.
Step D - Surface Layer Production ~(using~ Formulation C) - Control 1.5% w/w Cascowax EW-58AT"" wax emulsion was sprayed onto a mixture of strands identical to the strand mixture used in forming the surface layers in Steps B
and C. Formulation C was then added at a dosage of 3% w/w to a blender full of the wax coated strands which were then tumbled for 4 minutes. Afterwards, the adhesive coated strands were stored for mat forming and pressing.
Six 24"x 24" OSBs, each having a thickness of 7/16" were made, two to test each of formulations A, B and C. Each OSB had three layers: a core layer (50%
w/w) and two identical surface layers (each 25% w/w), one on either side of the core layer. The furnish moisture in the surface layers of all OSBs formed was 6.6%
w/w.
The furnish moisture in the core layer of all OSBs formed was 4.0 % w/w. All OSBs had a core layer formed from the strands resulting from Step A above.
OSB 1 a and OSB 1 b were made using adhesive coated strands formed in Step B using Formulation A above as the two identical surface layers. OSB 2a and OSB 2b were made with surface layers using the adhesive coated strands made in Step C above using Formulation B. OSB 3a and OSB 3b were made using adhesive coated strands formed in Step D and therefore had surface layers containing only Resin B in the surface and no tannin. OSB 3a and 3b served as controls.
All OSBs were formed under conditions summarized in Table Ilb below.
TABLE Ilb Support: Screen at the bottom, ring on top 3'10 Stop bars: '/2+1/900+1/100 Press temperature:190 C

Pressure: 1450 psi Press time: 190 seconds The OSBs were cut into test specimens and the specimens were then tested for mechanical and weathering properties. The actual and average results are summarized in Table Ilc below.

c O

.

O

y N n ~ ~ ~ M
~
N

. c~
M M N~ ~ MC M~ M M
c 7m N

N

N
N

C

V 0 ~ ~ ~ 0 ~ N f~
d c t c ~O n ~
F t c ~ n ~
- m m t C
. O

a a m~

v d~

_ p M p~ (O ~ tn ~ i i i o o ao of n v <o u Sr ir M M M M M M

(n etM M

N

y N
o C

CY7 d'O~ N M n N r' ~

O ~ CO ~ 01 00 CO (O CD n N N N N N N

f- N N N
fn O

N
Y o . n ~ ~ io M
y d i i U U U U
Qm U U

v c m N
-fl.

L

C
~

N
~ N 00 M ~ ~1 T

w U

-a N
J

n M U7 n ~ ll)st .

'' d' ~ ~ d' ~

0 ~ ~ ~
m .i TW

f.
N

fn Y
~' N ~ N O~ h ~ c0 N a0 O
v ~ ~ ~ V due'V
D

fn .t/) ~ 01 U M M

O ~ ~ dM' ~ d V ~ V ~
D ' ' J

c4 M

U U U a ~ Q m m m N

V ~ 0 o o A ' ~ u~ m '- d ~ '~ ~ m a cv "' LIJ m .a m c o m N ~N ~
J o -aM a,~a - ~~ Cf ~ ~ ~~

~ ~c p ~m ~m ~ ~tmn d ~ ~ ~ O O ~ ~~
~
c U cg OQ~yCg~ ti Qii vO v Qu O .

O ~ O ~ O ._..
N N
i;:_.

The above results indicate that boards made with tannin and phenolic resin exhibited properties which were the same as or superior to the properties of boards made with phenolic resin alone. Specifically, Formulation A (OSB 1 a and 1 b) containing Mimosa A and Resin B produced internal bond strength values of from 82.2 to 85.4 psi which is higher than the values obtained for the control, Formulation C (OSB 3a and 3b) (internal bond strength from 78 to 79.9 psi).
Formulation B, containing Mimosa B and Resin B, produced internal bond strength values of from 74.5-83.3 psi which is, on average, comparable to the average results obtained for the control, Formulation C.
Formulations A and B gave rise to better results in water absorption in the 24 hour soak test as compared to the control Formulation C. Other test results were approximately equivalent to the results obtained for the control. It is believed that the internal bond strength and water resistance of the OSB boards containing Formulations A and B are enhanced by the action of the tannin scavenging (i.e.
reacting with and "catching") the formaldehyde being released by the phenolic resole resin during pressing and curing.
Example III - Adhesive system containing MDI
An adhesive system according to a further preferred embodiment was tested in the manufacture of a straw board composite fibre panel. It was found that a panel formed using 2.4% w/w MDI and 1 % w/w Mimosa A (based on the total weight of the furnish) produced a commercially viable product. The MDI used was an isocyanate polymer available commercially from BASF, Inc. of Geismar, Louisiana and sold in association with the trade name BASF Lupranate M20SBT"". Furthermore, the MDI
had an isocyanate group (-NCO) content of about 31.5 % w/w based on the weight of the isocyanate polymer. It is believed that adhesive systems containing MDI
with an isocyanate group (-NCO) content of at least 20% w/w would still be effective in adhesive systems according to the invention.
In this example and all subsequent examples, the MDI used is the BASF
Lupranate M20SBT"".
Example IV
Further embodiments of adhesive systems according to the present invention containing 48 to 49% w/w of BASF Lupranate M205BT"" MDI, based on the total weight of the adhesive system, were used to make additional OSBs which were then tested. The OSBs consisted of six, three layer boards, made from 100% poplar wood strands. Each board was 7/16" thick. The binder systems used in the layers of each board are summarized in Table IVa below. The % w/w values are based on the total weight of the furnish.
For the sake convenience, P1 (Part 1 ) refers to the tannin component of the system (if any), P2 (Part 2) refers to the phenolic resin component (if any), and P3 (Part 3) refers to the MDI component. The actual components used are given below in Table IVa.
The formulations were made up such that the weight ratio of the total of Parts 1 and 2 (tannin plus phenolic resin) to Part 3 (MDI) ranged as follows (note that numbers have been rounded in Table IVa):
Formulation Ratio (Part 1+Part 2):Part 3 (w/w) Surface Layers: 48.3:51.7 Core Layers: 49.2:50.8 T r ~

UJ pr .oa d ~
a> ~
co o -E-~, a>

If N O
.
.

t C
u~ D 00 a ~ a o 0 0 ~ ~ r ~ o .~
N O Z
r N

W

Q
J 0 Q p p p O

y 3 ~ M i"~
cn M m r N

D U ~ o e- r r uJ

a'~ c U' ~

LIJ O o..' ~ ~' N

N 3 N C~

V d a r ' r W

Z N a l9 f0 N

C ~ ~ O
E E

m . o n .

~ C N ~I O

$ c ~
h o O ~ ~ Q N a ~ Q O

N

G d o O
O

o U
~, m yc ~ N

fV CV fV CV N N
h GI

~t d U Q

v O Q ~ ~ ~ ~ ~ e- N
r r V~ J r r N v U IL ~ I

LLI U N . IlJ C C C
.

W 'O O i tll d ~ d ~3mc~~ ~

aosd3a ''. a~
r c . :
~ ~ , '-~na.a~

~ r-Q,~aa a E ~
o ~ ~ o _ .
.
N

I- ~ ~ 3 c 3 E E_ E
~
o ~

~ o H~ oQ o~.-~ .~ .
a cnn.

Z ~

_ m p .L

d Q~

a3N NNN N ~
~

N .
+

O

O d ' O ~ a ~ ~ ~ ~ $ 3 ~
~ ~

a ~a c,.C
v Z >. ~ g O dN

> C y ~

cC ' $ o ~ z o Q s d a a r ~
N

7 Q~~o a o - o J r N

a E E
L

v . n ~
o o ~ o m CO r fD N
G1 eh t0 ~ CO tf 1 m (D

r Resin E is a commercial core type spray dried phenol-formaldehyde resole resin sold under product code CP777 by Tembec, Inc., having an F/P mole ratio of approximately from 2.2:1 to 1.5:1.
Resin F is a commercial surface type spray dried modified phenol-s formaldehyde resole resin sold under product code SP906 by Tembec, Inc., having an FIP mole ratio of from 2.2:1 to 1.5:1. approximately 1.9:1.
Resin G is a developmental spray dried modified phenol-formaldehyde resole resin sold under product code # G-1-12-B by Tembec, Inc., having an FIP mole ratio of from 2.2:1 to 1.5:1.
Resin H is a developmental spray dried modified phenol-formaldehyde resole resin sold under product code # G-1-14-C by from Tembec, Inc., having an F/P
mole ratio of from 2.2:1 to 1.5:1.
The six boards were produced under the following conditions to produce a target density of 38-39 Iblcubic feet (or "cu. ft.").
Platen temperature 215°C
Gauge pressure 1620 psi Press time 125 seconds Hot stacking I hr at 130°C
Further details of the OSBs produced and tested are given in Table IVb below.
TABLE IVb BOARD LAYER CONFIGURATION FOR ALL 6 FORMULATIONS
Moisture Cascowax Binder in 3 Mass distribution content EW- layer in furnish 58ATM % wlw**board wlw***
%

w/w**

Top layer 8.1 1.5 Binders in 25 Top Board la er as r below Core layer 4.3 1 Binders in 50 Core layer as er below Bottom layer8.1 1.5 Binders in 25 Bottom layer same as Top as er below ** based on the total weight of the furnish in the subject layer *** based on the total weight of the board.

Various properties of the boards were measured using ASTM standard test methods ("ASTM 1037-99). A first test measured the internal bond strength of the board in psi. A second test measured the "thickness swell" of the board, i.e.
the percentage increase in thickness of the board relative to the original board thickness after the board was placed in water at an ambient temperature of 24°C
for 24 hours.
A third test measured the amount of water absorbed by the board (determined by measuring the percentage increase in weight of the board relative to the original weight after the board was placed in water for 24 hours at an ambient temperature of 20°C.
The results are summarized in Table IVc below.
TABLE IVc Board Binder in De n InternalNumber T h i c Waterabsorption24 Test s ity k n a s s D r y B o of coreswell 24 hr soak %***
n d hr.

Lblcu. Strengthfailures*soak %**
ft.

si 1 Resin FJMDI37.9 54.8 C=6 9.5 19.9 2 M i m o 39.7 60.7 C=5 9.9 20.6 s a B=1 A/Resin F/MDI

3 Mimosa A 39.2 64.9 C=6 8.5 20 /MDI

4 M i m o 38.7 58.1 C=7 9.3 22.3 s a A/ResinGl MDI

5 M i m o 38.8 58.5 C=5 9.3 21.4 s a A/Resin H MDI

6 MDI 38.9 89.5 C=6 6.7 15.3 * "C" means the core layer. "C=6" means there were 6 breaks in the core layer of the board.
"B" means the interface between the core and the bottom layer. "8 = 1" means there was one break in the interface between the core and bottom layer of board.
** Thickness swell board % (wet thickness incremental over original dry thickness) after 24 hour soak at ambient temperature (20°C) *** Water absorption % (weight absorbed/weight panel dry) after 24 hour soak in water at ambient temperature (20°C).
MDl substituted board binder formulations all reached acceptable performance levels for certain grades of OSB. The substituted MDI boards had internal bond strength values ranging from 54.8 psi to 64.9 psi. The tannin:MDl board had the highest internal bond strength of the substituted MDI boards. All other tannin containing formulations in combination with phenolic resole resins and MDI
produced higher internal bond strength values than the values produced from boards made with a binder containing only phenolic resole resin and MDI.
The thickness swell % measured by the 24 hour soak tests gave rise to a thickness swell of from 8.5% to 9.9% for the substituted MDI board. The tannin:MDl board showed the lowest thickness swell % of the substituted MDI board. The lower the thickness swell value, the more the board is resistant to water absorption and therefore thickness changes in high moisture atmospheres.
The 24 hour soak Water Absorption Test Results for the MDI substituted boards produced values of from 19.9 to 22.3%. The tannin:MDl board produced a value of 20% water absorption vs. 19.9% absorption for the phenolic resin:MDl board. Thus similar properties were observed. The type of phenolic resole resin used in the core and surface layers did not seem to affect the results.
An additional experiment identical to the above experiment was run with boards pressed for 140 seconds instead of 125 seconds. This test produced boards having internal bond strength values which were higher for all 6 boards as compared to the boards pressed for 125 seconds. Also, the % water absorption values and swell values were either unchanged or slightly better for all six boards.
As can be seen from the above results, binder formulations according to the present invention can be used to achieve results comparable to or better than results achieved by prior art aldehyde containing adhesive formulations (phenolic resin +
MDI ). The relative amount of MDI could be reduced further to reduce costs while producing OSB boards with comparable properties to phenolic resin:MDl adhesive system OSB boards.
Example V: ADHESIVE SYSTEM CONTAINING LIQUID PHENOLIC RESOLE
RESINS
Seven, three layer OSB panel boards were made from 100% poplar wood strands and tested. Each board was 23/32" thick. The binder systems used are summarized in Table Va below. Boards 1 to 4 were made using prior art adhesives in the surface layers. Boards 5 to 7 were made using adhesives according to further preferred embodiments of the invention in the surface layers. All boards had a core layer made using MDI only. All % w/w values are based on the total weight of the furnish.

d v Q' O D

Q D
a ~ ~

3 ~ ~ 0 0 0 i v 3 0 0 0 ~ ~ ,ri u U o ~ p c _ L. tlf N N

3~
U

O

U d 0 0 0 0 ' 3 c0 ~ c O

a'>' v v c c a m a~ ~

m U 3 .~ 3 yn ~Wn U 1-0 o m ,..
w 'n c C
c N

d ~ p M
~

t7 U
.

n '13 .fl ~ ~ +O.
'M C y ._ d _ m L _ ~.J ~ ~ o 0 + ~

OC _ ~~ ~ N
~ ~

~Q C~j ~ ~ N

~ L ~ O CV O ~r <n m a p :J ~
3 Sri o N

N

O
~N G lL
T

G ~y N

u' " G N ~ ~ a '' v c c a~ ~
O ~ ~ ~
' ~ ~ ~ ~ ~ cV o C

c a ~ ~ e- O
G o tn d 3 0 'c N Or C
Q Q O

N N Q
N

3~ Q m Q E ~ E

E E E E '~' N 3 ~ c ~ ~ ~ o ~ ~n N '' o ~~ 0 0 0 G C

o (~

N
d .

,.~ C O t(7 C
Il) a i1') 17 o Wn -v) l a ~ '" ~

u~ ~~ D$ ~~ ~ ~

~ ~c~ m3 m ~ m ~ ~
m Q o c m c E-Resins E and F have been described above under Example IV.
Resin J is a commercial surface type liquid modified phenol-fom~aidehyde resole resin sold under product code SL-612 containing 55% solids (i.e.
solutes) dissolved in water (the solvent). Resin J has an F/P mole ratio of approximately from 2.2:1 to 1.5:1.
The MDI, as mentioned above, is the BASF Lupranate M20SB described under Example III. Once again, it is believed that adhesive systems containing MDI
with an isocyanate group (-NCO) content of at least 20% w/w would still be effective in adhesive systems according to the invention.
Mimosa A is described above under Example I1.
All adhesives were applied in situ to the OSB wafers and particles. When used, the spray dried Mimosa A and Resin F were mixed together prior to use and applied separately from the other components of the system. When both MDI
(which is a liquid) and Resin J (which is an aqueous solution) were used, they were not pre-mixed but applied separately.
The. seven boards were produced under the following conditions to produce a target density of 42 Ib/cubic ft.
Platen temperature 210°C
Gauge pressure 1400 psi Press time 230 seconds Hot stacking I hr at 130°C
Further details of the OSBs produced and tested are given in Table Vb below.
TABLE Vb BOARD LAYER CONFIGURATION FOR ALL 7 BOARDS

Moisture contentCascowax Binder in 3 Mass distribution in EW- layer w/w***
furnish % w/w**58AT"" % board wow**

Top 5 1 Same as for 30 bottom -See Table Va above Core 5 1 See Table Va 40 above Bottom 5 1 Same as for 30 top - See Table Va above ** based on the total weight of the furnish in the subject layer *** based on the total weight of the board Tests to indicate the relative effect on properties by replacing 0-100% of the MDI in the surface layers of the control binder system were conducted as described above under Example IV. The results are summarized in Table Vc below.
TABLE Vc Board Binder DensityInternalNumber of ThicknessWater in Test Dry Bond core failures*swell absorption Lb/cu.ft.Strength hr. soakhr soak %***

si %**

1 MDI 42.2 104.4 C=3 5.6 11.6 Control B=3 T=2 2 ControlResin 42 96.9 C=5 F=2 10.3 19.9 F

9 0 3 Resin 42.1 110.6 C=1 8.3 17.4 F

plus liquid B=5 Phenolic T=3 Resin J

4 MDI plus 42.2 105.7 C=3 6.4 14.1 Control Resin B=2 T=2 F

5 R a s 42.1 112 C=1 8.9 18.7 i n F

Preferredp I a B=2 T=4 s System Mimosa A

plus liquid Phenolic Resin J

6 Mimosa 42.3 92.2 C=5 7.6 15.4 A

Prefen-edplus MDI F=4 B=2 System T=3 7 Mimosa 42 95.8 C=3 6.9 14.3 A

Preferredplus Resin B=3 T=1 System F plus MDI

* "C" means the core layer. "C = 1" means that there was one break in the core layer.
"B" means the interface between the core and the bottom layer of board. "B=2"
means that there were 2 breaks in this region.
"F" means the face or top layer. "F=4" means there were 4 breaks in the face layer.
"T" means the interface between the core and the face or top layer. "T=3"
means there were 3 breaks in this region.
** Thickness swell board % (wet thickness incremental over original dry thickness) after 24 hour soak at ambient temperature (20°C) *** Water absorption % (weight absorbed/weight panel dry) after 24 hour soak in water at ambient temperature (20°C).

All seven OSBs produced were of a commercial grade.
The substituted MDI boards (Boards 2 to 7) had internal bond strength values ranging from 92.2 psi to 112.0 psi. In comparison, Board 1, made with MDI
alone, had an internal bond strength of 104.4 psi. Board 5, the tanninapray dried phenoiic resin:liquid phenolic resin board, had the highest internal bond strength (112.0 psi).
This internal bond strength value is slightly higher than the internal bond strength value of Board 3 (110.6 psi), which was made with a binder containing only spray dried phenolic resole resin and liquid phenolic resin. Board 6, the tannin:MDI
board, had the lowest internal bond strength (92.2 psi).
The thickness swell % measured by the 24 hour soak tests gave rise to a thickness swell of from 6.4% to 10.3% for the substituted MDI board vs. a thickness swell 5.6 % for MDI alone. The tanninapray dried phenolic resin:MDl board (Board 7) and the spray dried phenolic resin:MDl board (Board 4) showed the lowest thickness swell % of the substituted MDI boards. The lower the thickness swell value, the more the board is resistant to water absorption and therefore thickness changes in high moisture atmospheres.
The 24 hour soak water absorption test results for the MDI substituted boards produced values of from 14.1 to 19.9%. The tanninapray dried phenolic resin:MDl board (Board 7) produced a value of 14.3% water absorption vs. 14.1 % water absorption for the spray dried phenolic resin:MDl board (Board 4). Thus similar water absorption properties were observed when tannin replaced some of the MDI in the binder formulation.
As can be seen from the above results, addition of Resin J (liquid phenolic resole resin) in situ led to improved internal bond strength values.
Some loss in comparable relative water swell % and water absorption properties resulted in all formulations as the relative amount of MDI w/w was reduced.
However, alternative preferred formulations containing tannin powder can be used to make OSB boards with better or comparable properties relative to the properties of phenolic resin or phenolic resin:MDl adhesive system boards. Since MDI, on a weight basis, is more expensive than tannin or phenolic resole resins, cost savings can be obtained by replacing some of the MDI in adhesive systems with tannin.
While reference has been made in the Examples to OSBs, 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 associated advantages can be achieved with respect to various forms of lignocellulosic starting material and is not limited to any particular form. However, wood strands, wood wafers and straw particles comprise the preferred embodiments of lignoceliuiosic materials used in the method of the present invention.
It will be appreciated that various modifications to the preferred embodiments can be made and will be apparent to the person skilled in the art. The invention shall not be limited to the preferred embodiments but is defined in accordance with the following claims.

Claims (18)

1. An adhesive system for use in binding lignocellulosic materials into a composite product, the adhesive system comprising (1) at least one powdered tannin; (2) at least one liquid solution of polymeric isocyanate, and (3) at least one powdered aldehyde polymer, wherein said adhesive system does not comprise an external crosslinker.

2. An adhesive system according to claim 1 wherein said tannins are chosen from modified or unmodified mimosa tannin, pine tannin, quebracho tannin, hemlock tannin, mangrove bark tannin, and gambier tannin.

3. An adhesive system according to any one of claims 1 to 2 wherein said tannins are mimosa tannins.

4. An adhesive system according to any one of claims 1 to 3 wherein said tannins are modified.

5. An adhesive system according to any one of claims 1 to 3 wherein said tannins are unmodified.

6. An adhesive system according to any one of claims 1 to 5 wherein said powdered tannins are spray dried.

7. An adhesive system according to any one of claims 1 to 6 wherein the isocyanate polymer has an isocyanate group (-NCO) content of at least 20%
w/w based on the total weight of the isocyanate polymer.

8. The adhesive system according to any one of claims 1-7 wherein the tannin is present in an amount of from 5% w/w to 80% w/w, the aldehyde polymer is present in an amount of from 5% w/w to 80% w/w, and the isocyanate is present in an amount of from 15% w/w to 90 % w/w, all based on the total weight of the adhesive system.

9. An adhesive system according to claim 8 wherein the tannin is present in an amount of from 20% w/w to 40% w/w, the powdered aldehyde polymer is present in an amount of from 20% w/w to 40% w/w, and the isocyanate is present in an amount of from 40% w/w to 60% w/w, all based on the total weight of the adhesive system.

10. An adhesive system according to claim 9 wherein the tannin is present in an amount of from 20% w/w to 30% w/w, the powdered aldehyde polymer is present in an amount of from 20% w/w to 30% w/w, and the isocyanate is present in an amount of from 50% w/w to 60% w/w, all based on the total weight of the adhesive system.

11. An adhesive system of any one of claims 7 to 10 consisting essentially of the tannin, the powdered aldehyde polymer and the isocyanate.

12. A method of making a composite product comprising applying an adhesive system to lignocellulosic material to coat and bind said material to form the composite product, the adhesive system comprising (1) at least one powdered tannin; (2) a liquid solution of polymeric isocyanate, and (3) at least one powdered aldehyde polymer wherein said method does not comprise use of an external crosslinker.

13. A method according to claim 12 wherein each liquid adhesive component is kept separate from the other adhesive components of the system until application of the components to the lignocellulosic material.

14. A method according to claim 12 or 13 wherein said at least one powdered tannin and at least one powdered aldehyde polymer are pre-mixed together for simultaneous application to said lignocellulosic material.

15. A method according to any one of claims 12-14 wherein the amount of adhesive system used to coat and bind said lignocellulosic material is 1.5 to 15% w/w based on the weight of said lignocellulosic material.

16. A method according to any one of claims 12-14 wherein said lignocellulosic material comprises wood strands, wood wafers, or straw particles.

17. A composite product comprising lignocellulosic material bound together with a cured adhesive system, said adhesive system, prior to curing, consisting essentially of (1) at least one powdered tannin; (2) a liquid solution of polymeric isocyanate, and (3) at least one powdered aldehyde polymer.

18. A composite product according to claim 17 wherein said lignocellulosic material comprises wood strands, wood wafers, or straw particles.