WO1997002135A1

WO1997002135A1 - Modified wood with surface coatings

Info

Publication number: WO1997002135A1
Application number: PCT/US1996/012356
Authority: WO
Inventors: Darrel D. Nicholas; Charles U. Pittman; Lichang Wang; Ahmed Kabir; Tor P. Shultz; Leonard L. Ingram; Moon G. Kim; Eugene M. Ivankoe
Original assignee: Individual
Current assignee: Individual
Priority date: 1995-07-06
Filing date: 1996-07-03
Publication date: 1997-01-23
Anticipated expiration: 1998-01-06
Also published as: AU6508696A; AU6602996A; WO1997002136A1; WO1997002134A1; AU6680696A

Abstract

A method and process for treating wood. The steps include preparing isocyanate-based reactive prepolymer resins for impregnation, impregnating wood with these impregnation resins, curing the impregnated wood at elevated temperatures, preparing isocyanate resin-based coating materials and applying these coating materials on the cured impregnated wood and curing the coatings at room or elevated temperatures. The resulting treated wood has substantially improved de-contaminability of the chemical warfare agent VX both initially and after long exposure to degradation effects from sunlight.

Description

MODIFIED WOOD WITH SURFACE COATINGS

SUBTITLED

PREPARATION OF LIGHTFAST. DECONTAMINATABLE WOOD AND THE IMPREGNATION AND SURFACE COATING COMPOSITIONS

THEREOF

The invention described herein may be made, used, or licensed by or for the Government for Governmental purposes without the payment to me of any royalties thereon or therefor. FIELD OF THE INVENTION

The present invention relates to impregnated, surface coated wood products. More particularly, the present invention relates to the use of isocyanate-based polymers that are highly lightfast and de-contaminatable to impregnate and surface coat solid wood products with tight film formation via polymer grafting on wood cell surfaces when the prepolymers cure.

BACKGROUND OF THE INVENTION

An important goal in wood research has been to improve performance properties of wood for use in harsh environments and demanding conditions comparable to those which steel is exposed to for use for various reasons. One specific case of interest is the decontaminability of various chemical warfare agents that use a strong alkaline solution. This decontamination performance quality, especially that of the chemicai warfare agent VX due to its unique affinity to many surfacesftnas been considered to be highly necessary in military uses of wood for pallets and other packaging components. Use of raw or surface-coated wood has been severely limited in this application because of the inherently poor de-contaminability arising from the porosity of wood, inadequate performance of available surface coatings materials, and environmental degradation, especially from sunlight, of wood and surface coating materials in general.

As of now, surface coatings materials for wood that can meet the relevant U. S. Military requirements are not available. The coatings approach has also been considered to be of limited utility because of the likelihood of abrasion In use, suggesting that wood properties through the entire wood thickness need to be improved.

Accordingly, materials and methods . for impregnating and coating wood to attain lightfast and de-contaminatable properties have been a highly desirable development objective in military logistics. Conventional wood impregnation prepolymers such as phenol-formaldehyde or melamine-formaldehyde were shown to have effects of decreasing the wood strength due to the brittle nature of the polymer structures. These prepolymers were unacceptable in addition due to the unknown de-contaminability of the warfare agent VX on wood with these polymers impregnated therein.

One object of the present invention is therefore to provide wood impregnation and coatings materials for enhancing various wood properties including the de-contaminability of the chemical warfare agent VX before and after a long exposure to the degradation effect of sunlight.

Another object of the present invention is to provide impregnation and coating procedures for manufacturing the treated wood products using the impregnation and coatings materials of this invention.

Still another object of the present invention is to provide various impregnated and coated wood materials that have various enhanced properties including the de-contaminability of the chemical warfare agent VX before and after long exposure to the degradation effect of sunlight.

Other Objects will appear hereinafter.

SUMMARY OF THE INVENTION

It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, the invention comprises a method and process for treating wood.

The steps of the method include preparing isocyanate-based reactive prepolymer resins for impregnation, impregnating wood with these impregnation resins, curing the impregnated wood at elevated temperatures, preparing isocyanate resin-based coating materials and applying these coating materials on the cured impregnated wood and curing the coatings at room or elevated temperatures. The final product is novel and useful in a variety of applications including those applications described herein.

This invention is intended for use with a variety of woods.

Preferred is lumber derived from either Aspen, Southern Yellow Pine or Red Oak.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As noted above the present invention involves a series of steps to accomplish the objects of the invention. The first step comprises the preparation of isocyanate-based reactive prepolymer resins for wood impregnation. This may be accomplished using various commercially available isocyanate materials such as toluene diisocyanates (TDI). methylene-bisphenylene diisocyanates (MDI). and low molecular weight derivatives of MDI or other aliphatic isocyanates.. All are suitable for the present invention.

Preferred are those materials that have a functionality close to 2.0. Higher functionality isocyanates can be used, but they are less suitable for synthesis of the impregnation prepolymers of this invention.

Polyols suitable for reaction with these isocyanates are linear polyols having a molecular weight range from about 500 to about 5000 daltons and a hydroxyl group functionality of about 2.0. Also polyols having a major amount of hydrophobic segments, such as propylene oxide or butadiene groups, are preferred over those of the more hydrophilic groups, such as ethylene oxide groups. Polyols suitable^ for this invention are linear polyols. such as. for example, ethylene oxide-propylene oxide copolymers, polytetrahydrofurans, and hydroxyl group-terminated polybutadienes.

For the synthesis of the prepolymer of this invention, the isocyanate/polyol ration should be in a range that will keep the amount of isocyanate (NCO) functional groups, left unreacted at the end of the synthesis reaction, at a level between about 3% and 20% by weight based on the total weight of the isocyanate and polyol materials used in the reaction. This excess isocyanate functionality is designed for later reactions with hydroxyl groups and moisture in the wood during the curing process, so that a tightly coupled wood-polymer composite material is obtained. Too high levels of isocyanate group are not desirable because of the slow curing rate in the wood and also because of the rough cured surfaces caused by excessive curing with the moisture in the air.

The prepolymer resin synthesis reaction must be conducted in the absence of moisture, preferably under a stream of dry nitrogen, and at an elevated temperature until all hydroxyl groups of the polyol are reacted. This completeness of reaction is determined when no further increase in viscosity is occurring. The reaction mixture is then cooled to room temperature and may at that time be diluted with a suitable water-dry solvent such as methyl ethyl ketone or Cellosolve Acetate, or the like. The mixture should be stored in a dry. closed container.

The preferred prepolymer resin is a polyurethane resin identified as L-18. L-18 is manufactured by reacting a methylene diphenyl diisocyanate resin, a hydroxy-terminated polypropylene glycol and a hydroxy-terminated polybutadiene resin. The resulting polymer is diluted with methyl ethyl ketone.

Methylene diphenyl diisocyanate resin consists of a mixture of monomeric and oligomeric methylene diphenyl diisocyanates in liquid form, having 29% by weight -NCO group content, an equivalent weight of 144.5 (g/more) and a functionality of 2.1 per mole. The resis should contain less than 2.0% of triethylphosphate as a viscosity reducing agent. The methylene diphenyl diisocyanate resin should exhibit a viscosity of about 35 cP at 25 °C and the resin may he stored In glass, plastic or metal vessels, as long as water is rigorously excluded, so that it is preferably stored under slight dry nitrogen pressure.

The polypropylene glycol has a molecular weight of 2000 g/mole, a functionality of 2/mole and an equivalent weight of 1000 g/mole. It too is stored under slight dry nitrogen pressure to prevent moisture uptake. The water content should be less than 0.05% and the pH value measured in a 10: 1 methanol /water solution should be less than 3.0.

The hydroxy-terminated polybutadiene resin has a molecular weight of 2800 g/mole and a functionality of 2.4 to

2.6/mole. This viscous liquid, having a viscosity of 50P at 30 °C, is stored under a slight pressure of dry nitrogen. It has a hydroxy value of 0.83 meg/g and the polymer structure contains olefin groups (iodine value of 398), composed of 60% trans- 1 ,4 unites, 20%S cis-1.4 unites and 20% vinyl 1.2 units. The nonvolatile content should be greater than 99.9%. The methyl ethyl ketone (MEK) is a solvent having a boiling point of 79.6 °C and is used to reduce the L-18 viscosity. MEK that has no more than 0.1% water is then dried over 4 or 5 A molecular sieve before use. Care should be taken to keep water from the MEK as water will cause the -NCO groups to react with the water, which in turn will cause uncontrolled polymer formation and loss of isocyanate functionality.

The three components, methylene diphenyl diisocyantate resin, hydroxy-terminated propylene glycol and hydroxy-terminated polybutadiene are used in a weight ratio of 41.0% to 13.80% to 45.20%, respectively. Then MEK is added after prepolymer formation so that the MEK constitutes @5-35% by weight of the final solution. If more MEK is used in the formulation, the resulting solution viscosity will be lower; however, a larger void volume fraction will remain inside the - wood after treatment and other treatment difficulties might arise.

Preparation of the L- 18 prepolymer solution is accomplished in a chemical reactor equipped with an agitator, thermometer, condenser, dry nitrogen cover, and heating and cooling mechanisms. Both the reactor and the storage containers or drums should be clean, dry and cool before work is begun. Presented below is an example of the preparation of a drum of prepolymer.

PREPARATION ONE

A reactor is filled with a slow stream of dry nitrogen and maintained at a positive pressure of nitrogen throughout the entire procedure. 1501 pounds of methylene diphenyl diisocyanate resin is charged into the reactor. The agitator is operated at about 15-20 rpm and heat is applied to reach 60 °C in about 20-30 minutes. Next, 505 pounds of hydroxy-terminated polypropylene glycol is charged, followed by 1654 pounds of hydroxy-terminated polybutadiene under heat so that the temperature reaches 80 °C at about 20 minutes from the polybutadiene charge. This temperature is maintained for the entire charging period which may take 90 minutes or more. Upon completion of the charge step, the reactor contents are heated to 85°C in ten minutes and held at that temperature for an additional 20 minutes. Then the contents are cooled to room temperature over 30 to 60 minutes. 1220 pounds of MEK are charged and mixed for 10 minutes. The mixed resin is then discharged into dry drums and covered with dry nitrogen. Viscosity should be between 275 and 300 cP for this resin, which is a 75% solids level.

The second step comprises the impregnation of wood with the prepolymer resins, followed by curing them. The wood should first be dried to a moisture content ranging from about 2% to 14%. based on the oven dry wood weight and the free isocyanate group content of the prepolymer resin should be adjusted to approximate the wood moisture content level. Any wood impregnation procedure may be used as long as the impregnation is sufficiently complete. One such process is generally described as a 'full cell' process, used here to illustrate the process using the prepolymers of the present invention.

As noted above, the preferred lumber is derived from either Aspen. Southern Yellow Pine or Red Oak. Wood quality should be good, being free of decay which can easily be detected visually or by abnormal brashness when picked with a sharp instrument. The lumber should be free from insects, beetles, powder post beetle deterioration and other infestation at the time of treatment. To ensure that the wood is completely free of the oak wilt fungus, all would used in the present invention should be absolutely free from bark.

A wood sample is placed on a plan in a cylinder and a vacuum is applied to the cylinder, preferably 26 inches of Hg up to about 28 inches of vacuum for a minimum of 20 minutes. Dry nitrogen is introduced to break the vacuum and a second vacuum is applied and held for a minimum of 30 minutes. A prepolymer is introduced to the pan through an opening to completely cover the wood sample. The vacuum is then continued for about 30 minutes and, after release of the vacuum, a positive pressure of a minimum of 50 psig to about

150 psi is applied for about 60 minutes or until the intended gross resin injection has been achieved. After the pressure is released, excess resin solution is blown back to the storage tank with dry nitrogen gas and the wood sample is taken out, wiped and dried in a ventilated hood for several hours or more. Samples can then be cured in a heated oven, at about 40 °C for 20 to 24 hours, more or less. The resin solids content or retention of resin is determined by measuring the N content, which should be at the minimum 1.3% for pine and aspen and 0.65% for oak.

The third step includes preparation of surface coating materials for use in the present invention. Two package formulations based on aliphatic isocyanates and multi-functional polymeric polyols are preferred for this invention. Aliphatic isocyanates such as hexane diisocyanate and isophorone diisocyanate or their oligomeric adduct products are suitable. The isocyanate is formulated as one part of the coating system with suitable solvents for adjustment of the viscosity and other properties. The multi-functional polyol is the major component of the second part of the coating system, again with suitable solvents for adjustment of the viscosity. It is preferred that the polyol should be polymeric molecules with a molecular weight range from about 500 to about 15,000 daltons and having more than two hydroxyl groups per molecule with a background structure of either aliphatic or aromatic carbon chains.

Various additives that are normally needed for many coating formulations may be added to this polyol part if desired. The additives particularly useful for the coating system of this invention are flow promoters such as certain acrylic copolymers. hydroxy group-cross linking additives such as methylolated melamine-formaldehyde resins, pigment hydrophobicizing and cross linking agents such as epoxyalkylsilanes. and graft promoters between the polymer and wood surface such as acrylic ester monomers with attendant initiators.

The hydroxyl groups of the polyol are mostly cured with the isocyanate groups by forming urethane bonds but also they are cured by forming bonds with the melamine formaldehyde and epoxysilane components. The two part coating system should be mixed well before its application in a proportion such that the number of isocyanate functionality should be somewhat higher than the number of available hydroxyl groups. This is done to assure adequate self-cross linking by reacting with moisture in the air and for forming urea bonds. Excess isocyanate functionality as well as any deficiency of it in this final mixed coating system should be avoided.

A preferred coating composition is formed from an aliphatic polyisocyanate, melamine resis, acrylic resin, epoxy silane and other additives designed to bind tightly and provide a uniform coverage of porous surfaces. The preferred two part system is identified herein as P- 13 and includes the following individual components.

A high molecular weight epoxy resin is employed. This resin is a hydroxyl group containing, high molecular weight bisphenol-A-based epoxy resin that provides a good flexible coating. Resin solids should be about 40% to 50%, with non-chlorine type solvents such as MEK, monoproply glycol, monomethyl ether acetate and cyclohexane. The epoxy- resin shall have a hydroxyl group content of 1.80- 1.90 meg/g, based on solid resin weight. The solvents for the first part should be technical grade or better but with a water content less than 0.10% and dried over 4-5 Angstrom molecular sieves before use. Xylene and Cellosolve acetate are useful solvents for the second part of this component.

An acrylic resin based flow promoter may be used. One preferred flow promoter is Modaflow, supplied in a 10% solid solution by Monsanto Co. An epoxyalkyl silane to promote adhesion may be used, such as the epoxy group containing silyl ester supplied by Union Carbide Corp. The cross linking agent is a multifunctional acrylate cross liking agent such as propane trimethylmethacrylate, supplied by Sartorner Co. The preferred melamin-formaldehyde resin based thermosetting component is hexamethoxymethyl melamine resin supplied by American Cyanamid Co. Cross linking is initiated by use of benzoyl peroxide and silver perchlorate, in 1% and 0.1% MEK respectively. An aliphatic polyisocyanate is also employed in the preferred composition. An 1 ,6-hexamethylene diisocyanate-based adduct that has less than 1.6% monomer concentration, dissolved in a mixed solvent of an aliphatic ester and an aromatic solvent is used to control the evaporation rate when applied as a coating. The -NCO group content needs to be 16.5% and the resin solids content shall be 75% or more.

Preparation of the P-13 coating solution is also accomplished in a chemical reactor equipped with an agitator. thermometer, condenser, dry nitrogen cover, and heating and cooling mechanisms. Both the reactor and the storage containers or drums should be clean, dry and cool before work is begun. Presented below is an example of the preparation of a drum of prepolymer.

PREPARATION TWO

The coating formula used in this preparation is as follows:

The above formulation was used to prepare the preferred coating formulation. First Part A was prepared, then Part B. In both cases a reactor was filled with a slow stream of dry nitrogen and maintained at a positive pressure of nitrogen throughout the entire procedure. For Part A, the high MW epoxy resin is charged and agitation at about 15-20 rpm started. While agitating at that speed, all the other materials are charge in the order given above. After charging, agitation is continued for 20 minutes so that viscosity is 50 cP +/- 10 cP. Similarly Part B components are charged in sequence as listed above to reach a mixed solution with a viscosity of 5- 10 cP. Both parts are then stored in dry drums until needed. When the coating material is to be used, they are combined is a mixing tank filled with dry nitrogen. 33 parts of Part A are added with mixing at 15-20 rpm, followed by 10 parts of Part B, followed by 20 minutes agitation as a smooth solution is obtained. The viscosity of the mixed solution should be 30 cP +/- 10 cP initially, but will increase as the mixture stands to 60-70 cP over a period of about 10-15 hours.

The next step is the application of the surface coating materials followed by curing it. The surface coating materials prepared as described above should be applied within an hour or two of preparation. The viscosity may be adjusted to some extent by adding a solvent such as methyl ethyl ketone or Cellosolve Acetate. Application of the coating is done using a brush, or preferably, by spraying methods. Of course, the fumes in the application area are to be well controlled. The spraying should not continue once the viscosity has reached about 150 cP. although dilution with up to about 10% MEK is allowed. The treated wood should have a minimum film thickness of 0.3 mils.

After the application of the coating, the coated object should be kept in a well ventilated area until all solvent evaporates and the system cures completely. Alternatively, a faster curing can be achieved by using slightly elevated temperatures such as up to about 40°C to 60°C. in a properly ventilated oven.

EXAMPLES OF THE PREFERRED EMBODIMENT

The following examples demonstrate how the objects of the present invention are accomplished. These are presented for illustrative purposes and not as limitations on the scope of the invention. Where parts are mentioned, they are parts by weight, based on the total weight of the mixture or formulation.

EXAMPLE ONE

A material charge formula comprising 55 parts of isocyanate (Isonate 1143L, from Dow Chemical Co.) and 45 parts of polymeric polyol (Voranol 220- 1 19, from Dow Chemical Co.) were charged in a dry reactor under dry nitrogen and reacted for two hours at 75-80°C. After cooling to room temperature, the prepolymer resin was diluted with methyl ethyl ketone to a 90% resin solids level resulting in a viscosity of about 200 cP. The free NCO group content of the prepolymer resin was calculated to be 15.0%, based on the total resin solids.

EXAMPLE TWO

41.0 parts of Isocyanate (Isonate 1 143L. from Dow Chemical Co.), 13.8 parts of polymeric polyol # 1 (Voranol 220-056, from Dow Chemical Co.) and 45.2 parts of polymeric polyol #2 (Poly bd R-45HT, from Atochem, Inc.) were charged in a dry reactor under dry nitrogen and reacted for two hours at 80°C. After cooling down to room temperature, the prepolymer resin was diluted with methyl ethyl ketone to a 80% resin solids level resulting in a viscosity of 275 cP. The free NCO group content of the resin was calculated to be 10.0% based on the total resin solids.

EXAMPLE THREE

57.2 parts of Isocyanate (Isonate 1143L, from Dow Chemical Co.), 11.8 parts of polymeric polyol # 1 (Voranol 220-056, from Dow Chemical Co.) and 31.0 parts of polymeric polyol #2 (Poly bd R-45HT, from Atochem, Inc.) were charged in a dry reactor under dry nitrogen and reacted for two hours at 80°C. After cooling down to room temperature, the prepolymer resin was diluted with methyl ethyl ketone to a 80% resin solids level resulting in a viscosity of 125 cP. The free NCO group content of the resin was calculated to be 15.0% based on the total resin solids.

EXAMPLE FOUR

Four six inch by six inch by 1 /2 inch pieces of southern pine dried to a 12% moisture content were placed on a pan in a cylinder. A 28 inch vacuum was applied and the prepolymer resin from Example One was introduced to fill the pan and the vacuum was continued for about 30 minutes. After the vacuum was released, a 150 psi air pressure was applied to the cylinder for about 60 minutes. After the pressure was released, samples were taken out and the excess resin on the surface was wiped away. Samples were dried in a ventilated hood for 24 hours and then cured in a heated oven at about 40°C for five hours. The polymer weight gain was 80% and the toughness test result performed according to ASTM C143 with a sample length of 5.5 inches showed a 39% improvement over an untreated control sample.

EXAMPLE FIVE

Four six inch by six inch by 1 /2 inch pieces of southern pine dried to a 12% moisture content were placed on a pan in a cylinder. A 28 inch vacuum was applied and the prepolymer resin from Example Two was introduced to fill the pan and the vacuum was continued for about 30 minutes. After the vacuum was released, a 150 psi air pressure was applied to the cylinder for about 60 minutes. After the pressure was released, samples were taken out and the excess resin on the surface was wiped away. Samples were dried in a ventilated hood for 24 hours and then cured in a heated oven at about 40°C for five hours. The polymer weight gain was 30% and the toughness test result performed according to ASTM C143 with a sample length of 5.5 inches showed a 31% improvement over an untreated control sample.

EXAMPLE SIX

Four six inch by six inch, by 1/2 inch pieces of southern pine dried to a 12% moisture content were placed on a pan in a cylinder. A 28 inch vacuum was applied and the prepolymer resin from Example Three was introduced to fill the pan and the vacuum was continued for about 30 minutes. After the vacuum was released, a 150 psi air pressure was applied to the cylinder for about 60 minutes. After the pressure was released, samples were taken out and the excess resin on the surface was wiped away. Samples were dried in a ventilated hood for 24 hours and then cured in a heated oven at about 40°C for five hours. The polymer weight gain was 86% and the toughness test result perfoπned according to ASTM C143 with a sample length of 5.5 inches showed a 1 1% improvement over an untreated control sample.

EXAMPLE SEVEN

In this experiment a two-package system was prepared that consisted of Part A and Part B, of which material charges were as follows:

Part A and Part B were made, separately, by mixing the materials in the given order in a dry reactor. The final coating composition was obtained by mixing 33 parts of Part A and 10 parts of Part B to a uniform mix in a blender.

EXAMPLE EIGHT

A six inch by 1 /2 inch piece of southern pine was coated with Example Seven material using a soft-bristled brush to give a dried film thickness of four to five mil. The coating was dried in a ventilated hood for 24 hours and cured at 40°C for 24 hours, resulting in a uniform clear glossy coating.

EXAMPLE NINE

Part A of Example Seven was tinted with a solvent-borne white tinting base and a green pigment base by mixing in, respectively. 1.5 parts and 1.0 parts to 98.5 parts of Example Seven. Part A. Mixing this tinted material and Example Seven, Part B, in a ration of 33 parts to 10 parts resulted in a pigmented coating formulation. Coating a piece of southern pine and solvent cleaned mild steel with this coating formula to a three to five mil dry film thickness resulted in a green coating with a good hiding and film adhesion properties.

EXAMPLE TEN

A phenol-formaldehyde resol resin was prepared by reading 64.2 parts of 90% phenol and 35.2 parts of 50% formaldehyde in the presence of 1.1 parts sodium hydroxide at 75°C for eight hours. The resulting resin showed a viscosity of 50 cP and a solids content of 60.0%. The resin was impregnated into southern pine wood in the exact way as in Example Three and the sample was cured in a hot press at 194°C for 10 minutes under a platen pressure of 50 psi. The polymer weight gain was 46.0% and the sample surface showed a shiny coating with the cured PF polymer resin and the toughness test result obtained according to the ASTM C 143 using a sample length of 5.5 inches showed a decrease to a 58% of the untreated control sample.

EXAMPLE ELEVEN

A six inch by 1/2 inch piece of southern pine was coated using a soft-bristled brush with a two-package epoxy resin system,

Devcon 2-ton Epoxy, obtained from Devcon Corporation of Wood Dale,

Illinois. This coating produced a dried film thickness of four to five mils. The coated sample was dried in a ventilated hood for 24 hours and cured at 40°C for 24 hours resulted in a uniform clear glossy coating.

EXAMPLE TWELVE

A melamine-formaldehyde resin. Product #PC-6N, was obtained from Astro Industries. Its formaldehyde/melamine mole ratio was reported to be five to six, solids content was 80.0%, and its pH value was 8.8. The resin was catalyzed with a 0.3% ammonium chloride in the laboratory and impregnated into southern pine wood in the exactly same way as described in Example Three and cured in an oven for four hours with a temperature schedule of gradually increasing from 40°C to 150°C during the curing period. The polymer weight gain was 25% and the toughness test result, obtained according to ASTM D143 using a sample length of 5.5 inches, showed an improvement of 6% over an untreated control sample.

EXAMPLE THIRTEEN

Impregnated wood samples obtained using the procedure and materials of Example Five were coated with the coating formula of Example Seven using the procedure of Example Eight. Pine, aspen, and oak were used in this experiment.

EXAMPLE FOURTEEN

Selected impregnated and/or coated wood samples obtained in the above Examples were tested for de-contaminated efficiency of the chemical warfare agent VX according to the U.S. Military standard by the Midwest Research Institute, Kansas City, Kansas. For the pine sample of Example Thirteen and a steel control sample, de-contamination efficiency was tested also after subjecting them to the simulated sunlight weathering procedure according to ASTM G-26, MIL STD 810 E, Procedure II. The followin results were obtained:

The results show the superiority of the impregnation and coatings formulations of this invention over conventional systems in de-contamination ability before and after a long sunlight degradation procedure! Also, wood strength properties were shown to be improved over the untreated wood by the impregnation materials and methods of this invention.

From the data and examples above, it is obvious that the impregnation and coatings formulations and procedures of this invention afford many desirable results and excellent performance for wood in various applications over conventional systems. Obviously many variations and ramifications can be made in the products and processes of this invention set forth above without departing from the spirit and scope of this invention. While particular embodiments of the present invention have been illustrated and described herein, it is not intended that these illustrations and descriptions limit the invention. Changes and modifications may be made herein without departing from the scope and spirit of the following claims.

Claims

CLAIMS 1. A method for treating wood comprising the steps of:

preparing an isocyanate-based reactive prepolymer resins for impregnation,

impregnating wood with said impregnation resins.

curing said impregnated wood at elevated temperatures for sufficient time to effect said cure;

preparing an isocyanate resin-based coating material; and applying said coating material on the cured impregnated wood and curing the coatings at room or elevated temperatures.

2. The method of claim 1, wherein said prepolymer has a functionality close to 2.0.

3. The method of claim 2, wherein said prepolymer comprises an isocyanate materials selected from the group consisting of toluene diisocyanates. methylene-bisphenylene diisocyanates, low molecular weight derivatives of methylene-bisphenylene diisocyanates and other aliphatic isocyanates, and mixtures thereof.

4. The method of claim 1, which-includes a linear polyol having a molecular weight range from about 500 to about 5000 daltons and a hydroxyl group functionality of about 2.0 for reaction with an isocyanates.

5. The method of claim 4. wherein said polyol has a major amount of hydrophobic segments, such as propylene oxide or butadiene groups.

6. The method of claim 5. wherein said linear polyols are selected from the group consisting of ethylene oxide-ppopylene oxide copolymers, polytetrahydrofurans, hydroxyl group-terminated polybutadienes and mixtures thereof.

7. A treated wood composition, comprising: wood impregnated with an isocyanate-based reactive prepotymer resin and cured at an elevated temperature for sufficient time to effect said cure, said wood further including an isocyanate resin-based coating applied and thereafter cured on the cured impregnated wood.

8. The composition of claim 7, wherein said reactive prepolymer resin has a functionality of about 2.0 or less.

9. The composition of claim 7, wherein said reactive prepolymer resin comprises an isocyanate/polyol having the NCO functional groups at from about 3% to 20%, based on the weight of isocyanate and polyol materials.

10. The composition of claim 7, wherein said isocyanate resin-based coating is a coating formulation formed from a two part system of coating components.

11. The composition of claim 7, which further includes a tinting pigment base admixed therein.

12. The composition of claim 7, wherein said reactive prepolymer resin has a functionality of about 2.0 or less.

13. A coating formulation providing improved de-contamination properties for wood, comprising:

a quantity of an isocyanate-based reactive prepolymer resin for impregnating said wood and subsequent curing at elevated temperature; and

a quantity of an isocyanate resin-based coating material for application to said cured impregnated wood and subsequent curing.

14. The composition of claim 13, wherein said reactive prepolymer resin has a functionality of about 2.0 or less.

15. The composition of claim 13, wherein said reactive prepolymer resin comprises an isocyanate/polyol having the NCO functional groups at from about 3% to 20%, based on the weight of isocyanate and polyol materials.

16. The composition of claim 13. wherein said isocyanate resin-based coating is a coating formulation formed from a two part system of coating components.

17. The composition of claim 13. which further includes a tinting pigment base admixed therein.

18. The composition of claim 13. wherein said reactive prepolymer resin has a functionality of about 2.0 or less.