WO1997002136A1

WO1997002136A1 - Mofified wood with surface coatings

Info

Publication number: WO1997002136A1
Application number: PCT/US1996/012357
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: Nicholas Darrel D; Pittman Charles U; Lichang Wang; Ahmed Kabir; Shultz Tor P; Ingram Leonard L; Kim Moon G; Ivankoe Eugene M
Priority date: 1995-07-06
Filing date: 1996-07-03
Publication date: 1997-01-23
Also published as: AU6680696A; WO1997002135A1; AU6508696A; AU6602996A; WO1997002134A1

Abstract

The present invention relates to resin-impregnated, surface coated wood products. More particularly, the present invention relates to polyurethane prepolymer resin wood impregnation and coating materials that impart to wood a highly lightfast and decontaminatable surface and inner wood structures and their methods of manufacture and applications.

Description

TITLE: MODIFIED WOOD WITH SURFACE COATINGS

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 therefore.

FIELD OF THE INVENTION

The present invention relates to resin-impregnated, surface coated wood products. More particularly, the present invention relates to polyurethane prepolymer resin wood impregnation and coatings materials that impart to wood a highly lightfast anddecontaminatable surface and inner wood structures and their methods of manufacture and applications. BACKGROUND OF THE INVENTION

An important goal in wood products research has been to improve various performance properties of wood for use in. harsh environments and demanding conditions comparable to those which steel is exposed to for various applications. The present invention addresses with the military uses of wood where decontamination of chemical warfare agents before or after weathering by sunlight and other environmental elements must be done efficiently using the standard washing procedure in which a strong alkaline decontaminating solution is used. Wood surfaces having the necessary decontamination quality, especially for the chemical warfare agent VX due to its uniσue affinity to many surfaces, have been considered to be highly difficult to obtain. The high porosity of wood, inadequate performance of available surface coatings materials, and environmental and abrasive degradation of wood and surface coating materials, especially by sunlight, are the key problems in using wood in this application.

As of now, surface coating materials for wood that can meet the relevant U.S. Military requirements for the decontaminatability of various chemical warfare agents are not available. Although the coatings approach for wood for this application is an essential component because of the pigmentation requirement, it is of limited utility due to the likelihood of abrasion in use. Thus, property improvements by an impregnation with appropriate materials through the entire wood structure need to be carried out to obtain the decontaminatability. Such impregnation materials are not currently available. Such materials and methods for impregnating and coating of wood to attain the decontaminatability throughout the lifetime of wood product have been a highly desirable development objective in military logistics as well as for many other commercial applications. Improved toughness and lightfastedness of such wood products are also essential.

The conventional wood impregnation materials based on certain inorganic metallic compounds or organic preservative materials are not likely to give the decontamination quality to wood since they hardly reduce tne porosity of wood. Wood impregnated with phenol- formaldehyde or melamine-formaldehyde prepolymer resins were shown to reduce the porosity, but increase the brittieness of wood and their decontaminatability of chemical warfare agents has not been demonstrated. In the co-pending invention disclosure application by us, isocyanate group-terminated polyurethane prepolymer resins prepared with a combination of certain linear polyether or polyester polyols of 500-7,000 molecular weights and isocyanate materials which have an isocyanate (NCO) group content of between 7-20% were found to impart improved toughness to wood. These improved properties are probably due to the more favorable polymer structure resulting from the curing of the reactive isocyanate groups with the moisture and hydroxyl groups in the wood. This development is a highly desirable one since no polymer wood impregnation resin system has been known to improve the toughness. Such a polymer resin system is the pre-requirement for the type of development envisioned in the present invention. In the course of this development, it became apparent that attaining an adequate decontaminatability of chemical warfare agents would need a more elaborate control of the polyurethane polymer structure, within the framework of the principles of the co-pending disclosure application. In addition to the linearity and molecular weight of the polyether or polyester polyols used, the major parameter to be considered is the functionality of the isocyanate materials. As the isocyanate group functionality increases above 2, the polymer chain branching will increase and result in an increased amount of soft segments in the cured polyurethane structure. The soft segments would be more porous and absorb low molecular weight chemicals such as chemical warfare agents and make the decontamination washing more difficult. It is believed that once the chemical warfare agents permeate the polymer structure, the standard decontamination procedure would not be adequate. On the other hand, isocyanate materials having lower functionalities will increase the hard segments in the cured polymer structure, which would prevent the chemical warfare agents from penetrating into the structure. Otherwise, the same resin formulation parameters as those used in the co-pending invention disclosure application would be useful. That is, the mole ratio of isocyanate and polyol (s; materials should be in a range that will keep the amount of unreacted isocyanate (NCO) functional groups at the end of the synthesis reaction at a level between about 7% and 20% by weight based on the total weight of the isocyanate and polyol materials used. This excess isocyanate functionality is designed to react with the moisture and wood hydroxyl groups in the wood during the curing process. Control of the moisture content of wood between 4-20% based on dry wood weight is also important.

A surface coating material having an adequate decontaminatability of chemical warfare agents for application to the impregnated wood of adequate decontaminatability is also necessary. Curable polyurethane resin coatings based on aliphatic isocyanate materials are known to be lightfast. The curable coating systems are mostly manufactured as two-package systems the polyol and pigment package and the ocyanate material paocage for better storage stability. Again, a low permeability of the coating film coated on the wood would be the key in minimizing the permeation of chemical warfare agents. Toward this objective, the compatibility factor of pigments and other additives with base polymers of the coating is important, and the coating film's integrity and toughness would also be important to abrasion resistance in use. Incompatibility of pigments and additives will create cracks around the pigments' particles for permeation of chemical warfare agents. Therefore, an entirely different approach from that of the impregnation polyurethane resin systems should be preferred: use of multi-functional isocyanates and multi-functional polyol materials packaged into a two-package coating system. The first package would contain a combination of multi-functional polymeric polyols and other crosslinking agents and the second package a multi-functional aliphatic isocyanate material, both packages being diluted in suitable non-hydroxylic solvents. The additional crosslinking agents would be necessary to obtain a tightly crosslinked but tough film structure.

One object of the present invention is therefore to provide wood impregnation and coating materials and methods that impart to wood decontaminatability of the chemical warfare VX and other agents before and after a long exposure to the degradation by sunlight and also that do not make the wood brittle.

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

Still another object of the present invention is to provide various impregnated and coated wood products that have enhanced decontaminatability of chemical warfare agents before and after abrasion or long exposure to the degradation by sunlight and also have improved wood toughness properties.

Other objects will appear hereinafter.

SUMMARY OF THE INVENTION

It has been discovered that the above and other objectives of the present invention may be accomplished in the following manner. Firstly, a specific isocyanate group-terminated polyurethane prepolymer resin is formulated, then impregnated into wood, and the resin impregnated wood is cured, resulting in a resin-impregnated wood product that has a highly lightfast and decontaminatable wood structure, as well as improved toughness properties.

Secondly, a curable, pigmentable polyurethane resin coating system is formulated in which a novel combination of isocyanate and polyol materials are employed, applied on the resin-impregnated wood product obtained above, and the surface coating is cured, resulting in a surface film of very tight structure that allows the standard decontamination procedure of chemical warfare agents to be effective.

The impregnation and coating resin formulations and methods of the present invention are novel in that no such technologies have been known prior to this date. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention involves a series of steps to accomplish the objectives of the invention. The first step comprises the preparation of specific isocyanate group-terminated, thus reactive and curable, polyurethane prepolymer resins for wood impregnation. This is accomplished by selecting specific isocyanates and polyol materials and conducting specific condensation reactions between them at specific isocyanates/poiyol mole ratios so that specific amounts of isocyanate groups are remained unreacted after most of the hydroxyl groups have reacted to form urethane bonds.

The suitable isocyanate materials are those isocyanate materials that have an isocyanate group functionality of between 2 and 2.15, available as toluene diisocyanate (TDI), methylene-bis-phenylene diisocyanates (MDI), hexane diisocyanate (HDI), isophorone diisocyanate (IPDI), and their oligomeric materials or their adducts made by reacting with water, such as Desmodur from Miles Corp., or with polyhydroxyl compounds, such as Isonates from Dow Chemical Co. The suitable polyols are polyether, polyester, and other linear polyols having a hydroxyl group functionality of 2 and a molecular weight range of about 500 - 7,000 daltons. The polyether polyols include polyethylene oxides, polypropylene oxides, ethylene oxide-propylene oxide copolymers, and polytetrahydrofurans, and polyester polyols include those made by reacting adipic or sebacic acid with ethylene glycol or propylene glycol. Hydroxyl group-terminated polybutadiene-based linear polyols are also useful. These polyols can be used in combinations within certain ratio ranges to obtain balanced hydrophobic and hydrophilic properties. Also, important for the reactive polyurethane prepolymer resins of this invention is the mole ratio of isocyanate groups and polyol(s); they should be in a range that will keep the amount of isocyanate (NCO) functional groups left unreacted at the end of resin synthesis at a level between about 7% and 20% by weight based on the combined weight of the isocyanate and polyol materials used. The purpose of this requirement is to increase the toughness of wood" as discovered in the co-pending invention disclosure application by us.

Thus, a polyurethane resin composition formulated with 35-60 parts of an isocyanate material having an isocyanate group functionality between 2 and 2.15, 40-65 parts of a combination of linear polyols having a molecular weight range of between 500-7,000 can be used in the present invention as impregnation resins as long as the mole ratio in the resin is such that the level of the remaining isocyanate groups after the resin synthesis reaction is in the range of 7-20% range based on the total resin solids.

The manufacturing process of the polyurethane prepolymer resins of this invention must be conducted in the absence of any significant amount of extraneous moisture, that is, the stirred reactor and all other equipment that come in contact with the resin materials must be dry and it is also preferable to cover the reactant materials in the reactor under a stream of dry nitrogen to prevent undesirable reactions with the atmospheric moisture. The manufacturing process, that is, the condensation polymerization the wood structure. For reasons mentioned above, wood should first be dried to a moisture content in the range of about 3-20% based on the oven dry wood weight.

Any known wood treatment procedure can be used as long as the resin impregnation is sufficiently complete to obtain the desired extent of resin loading level. Thus, the selection of impregnation process depends on the porosity of wood and the dimensions of wood samples. Small and thin samples of permeable wood species such as aspen can be adequately impregnated simply by soaking it in the resin. Evacuation of wood before resin introduction and application of pressure in a closed cylinder greatly increase the resin impregnation extent and rate. One such process is generally described as a 'full-cell' process and used here to illustrate the impregnation processes using the prepolymer resins of the present invention. In this process, wood pieces are placed in a pan in a cylinder and a vacuum is applied to the cylinder, up to about 28 in.-Hg of vacuum. A prepolymer resin is introduced into the pan through an opening until the resin completely covers the wood. The vacuum is then continued for about 30 minutes and, after release of the vacuum, a positive pressure of about 150 psi is applied for about 60 minutes. After the pressure is released, the wood sample is removed, wiped, and dried in a ventilated hood for several hours.

The resin-impregnatid wood is then cured, preferably in a ventilated area to avoid human exposure to the evolving solvent vapor when the impregnated resin conta. is a diluent solvent. A heated, ventilated oven can be advantageously used with the temperature set in the range of 30-90 °C. Curing for 3-24 hours or more at this temperature range is preferred. At lower temperatures the curing takes longer times. The resin impregnated, cured wood thus obtained is novel with an excellent decontaminatability of chemical warfare agents as well as an improved toughness. The enhanced visual appearance would also make them aptly suitable in many decorative applications.

The next step of the present invention includes the preparation of a surface coating material. A tightly-crosslinkable, sunlight weathering-resistant, pigmentable, and highly decontaminatable surface is to be provided by this coating resin. The coating of the present invention is based on the use of multi-functional isocyanates and multi-functional polyols, packaged into a two-package system. The first package contains a combination of polymeric polyols and other crosslinking agents and the second package contains an aliphatic isocyanate material, both packages diluted in suitable non-hydroxylic solvents. The aliphatic isocyanate materials of high functionality useful in the second package are the oligomeric or adduct materials made by reacting hexane diisocyanate or isophorone diisocyanate with water or polyhydroxyl compounds in such mole ratios that the isocyanate group functionality of the resulting adducts ranges between 3.0 and 4.0. Typical such isocyanate materials are "Desmodur" prepolymers manufactured by Miles Corp. The multi-functional polyols useful for the first package are the epoxy resin polymers derived from diglycidyl-bis-phenol-A having a molecular weight range of 1,500-15,000 daltons. Typical such polyols are "Araldite" epoxy prepolymers manufactured by Ciba-Geigy Corp. The multi-hydroxyl functionality of these polyols is essential for the tight - crosslinking necessary for the coating film, while the aliphatic isocyanates impart flexibility and lightfastedness. Also, the second package contains a group of additives to increase the crosslink density of the polyurethane film through ether bond formation with the hydroxyl groups of the polyol used. Additives that undergo this ether bond formation, only at elevated temperatures, such as melamine-formaldehyde resins, are an essential component. A typical material is "Cymel" resins manufactured by American Cyanamid Co. Another essential additive in the second package is the flow promoting agent that help attain a more uniform film structure: certain acrylic copolymer resin-based materials, for example "Modaflow" resins manufactured by Monsanto Co. are satisfactory. Another useful component in the second package is the hydrophobicizing agent for pigment materials: certain epoxyalkylsilanes, for example "Monomer Silanes" manufactured by Union Carbide Corp. Another useful component in the second package is monomers that promote grafting reactions on wood and other solid surfaces; certain multi-functional acrylic ester monomers with appropriate initiators are satisfactory for this use. A typical material is "Sartomer" monomers manufactured by Sartomer Co. Tinting pigment bases can be any kind as long as they are relatively inert and compatible witn the coating polymers. The two-package system is to be combined before use in such a mole ratio that about 40-75% of the hydroxyl groups of the epoxy polyol are cured by the isocyanate groups, and the rest of hydroxyl groups, 25-60%, are cured by the melamine-formaldehyde resin in the later stage of film formation. Both packages of the coating system are diluted with suitable non-hydroxylic solvents for adjustment of the viscosity and other coatings properties.

The manufacturing of the coating system of the present invention can be done by thorough mixing of components and diluent solvents, separately for each package, in a moisture-free environment to avoid unwanted side reactions. Thus, the first package is comprised of aliphatic prepolymer isocyanates, diluted to any resin solids level with any dry non-hydroxylic solvents, and the second package is comprised of 15-25 parts of a diglycidyl bis-phenol-A polyether polyol, 3-8 parts of a melamine- formaldehyde condensate, and up to 2 parts of various coatings additives mentioned above, and diluted to any resin solids level with dry non-hydroxylic solvents, and then said first and second packages are mixed before use in a proportion range of 2.2-3.2 : 1 by weight of respective resin solids content.

The next step of the pr2sent invention is application of the surface coating system prepared, and curing the applied coating. The mixed coating material should be applied within a given period of time after mixing because the reaction of isocyanate groups with hydroxyl groups of polyols will start to occur after mixing. The viscosity is adjusted by adding a non-hydroxylic solvent if necessary, but resin solids levels above about 20% are recommended. Application of the coating can be done using a brush, sprayer, or any other methods. The solvent fumes from the coating have to be controlled. After the application of the coating, the coated object should be kept in a well ventilated area until all solvent evaporates and the coating cures completely. Alternatively, a faster curing rate can be achieved by using elevated temperatures, up to about 75 °C, in a ventilated oven.

EXAMPLES OF THE PREFERRED EMBODIMENT

The following examples demonstrate how the objectives 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.

Examples 1a-1c. Syntheses of isocyanate group-terminated impregnation polyurethane resins of varying free isocyanate group contents using isocyanate materials having a functionality of 2.1.

Example 1a. Forty-one (41.0) parts of Isonate 1143L, a methylene-bis-phenylene diisocyanate (MDI) material with a functionality of 2.1 (Dow Chem. Co.), 13.8 parts of Voranol 220-056, a polypropylene oxide polyol with a molecular weight of 2000

(Dow Chem. Co.), and 45.2 parts of R-45HT, a polybutadiene-based polyol with a functionality of 2 and a molecular weight of 2800

(Athochem Co) were charged in a dried reactor under dry nitrogen and reacted for two hours at 75-80 C to a stable resin viscosity of about 1100 cP. The free isocyanate (NCO) group content of the resulting prepolymer resin was calculated to be 10.0% by weight based on the total resin solids, and the number-average molecular weight was calculated to be 891. After cooling to room temperature, methyl ethyl ketone was added to the finished resin to attain a 80% resin solids level, resulting in a prepolymer resin with a viscosity of about 275 cP.

Example 1b. A synthesis reaction similar to Example 1a was carried out using 57.2 parts of Isonate 1143L (Dow Chemical Co.), 11.8 parts of Voranol 220-056 (Dow Chemical Co.), and 31.0 parts of R-45HT (Atochem, Inc.). The free isocyanate (NCO) group content of the resin was calculated to be 15.0% based on the total resin solids, and the number-average molecular weight was calculated to be 582. After cooling to room temperature, the resin was diluted with methyl ethyl ketone to a 80% resin solids level, resulting in a resin with a viscosity of 125 cP.

Example 1c. A synthesis reaction similar to Example 1a was carried out for using 55.0 parts of Isonate 1143L (Dow Chemical Co.) and 45.0 parts of Voranol 220-110 (Dow Chemical Co.), a polypropylene oxide polyol. The free isocyanate (NCO) group content of the prepolymer resin was calculated to be 15.0%, based on the total resin solids and the number-average molecular weight was calculated to be 628. After cooling to room temperature, the prepolymer resin was diluted with methyl ethyl ketone to a 90% resin solids level resulting in a resin with a viscosity of about 165 cP. Examples 2a-2c. Syntheses of comparative isocyanate group-terminated impregnation polyurethane resins of varying free isocyanate group contents using isocyanate materials having a functionality of 2.3.

Example 2a. A synthesis reaction similar to Example la was carried out using 80.0 parts of Papi 1094, a methylene-bis-diphenylene diisocyanate material having a functionality of 2.3 (Dow Chemical Co.), and 20 parts of Voranol 220-110, a polypropylene oxide polyol having a molecular weight of 1000 (Dow Chemical Co.). The free isocyanate (NCO) group content of the resin was calculated to be 23.7% based on the total resin solids, and the number-average molecular weight was calculated to be 380. After cooling to room temperature, the resin was diluted with methyl ethyl ketone to a 70% resin solids level, resulting in a resin with a viscosity of 50 cP.

Example 2b. A synthesis reaction same as Example 1a was carried out using 46.0 parts of Papi 1094, 14.9 parts of Voranol 220-056, and 39.1 parts of R-45HT. The free isocyanate (NCO) group content of the resin was calculated to be 12.5% based on the total resin solids, and the number-average molecular weight was calculated to be 767. After cooling to room temperature, the resin was diluted with methyl ethyl ketone to a 75% resin solids level, resulting in a resin with a viscosity of 300 cP.

Example 2c. A synthesis reaction similar to Example 1a was carried out using 60.0 parts of Papi 1094, 11.1 parts of Voranol 220-056, and 26.9 parts of R-45HT. The free isocyanate (NCO) group content of the resin was calculated to be 17.5% based on the total resin solids, and the number-average molecular weight was calculated to be 545. After cooling to room temperature, the resin was diluted with methyl ethyl ketone to an 80% resin solids level, resulting in a resin with a viscosity of 125 cP.

Example 3. A comparative, phenol-formaldehyde thermosetting-type impregnation resin.

A phenol-formaldehyde resol resin was prepared by reacting 64.2 parts of 90% phenol and 35.2 parts of 50% formaldehyde in the presence of 1.1 parts of sodium hydroxide at 75 °C for eight hours. The resulting resin showed a viscosity of 50 cP and solids content of 60.0%.

Examples 4a-4l. Wood impregnation and curing experiments using the polyurethane impregnation resins of Examples la-lc. Examples 2a-2c, and Example 3.

Wood impregnation and curing experiments were carried out using the respective prepolymer resins on southern pine wood, and selectively on oak and aspen wood. The full-cell impregnation procedure was used. Wood pieces dried to a 12.0% moisture content were placed in a pan in a closed cylinder. A 28-inch vacuum was applied to the cylinder and the resin was introduced through an opening until wood pieces are fully submerged, and tne vacuum was maintained for about 30 minutes. Then, tne vacuum was released and dry nitrogen at 150 psi was applied to tne cylinder for 60 minutes. After the pressure was released, the cylinder was opened and wood samples were removed and the excess resin on the surface was wiped off. The polyurethane resin-impregnated wood samples were then dried in a ventilated hood for 24 hours and cured in a heated oven at about 40 °C for five hours. Phenol-formaldehyde resin impregnated wood samples were cured in a hot press at 194 °C for 10 minutes under a platen pressure of 50 psi. The polymer resin loading was measured by weighing wood samples before and after the treatment and calculated as percents based on the dry wood weight. Several 1/2-inch thick, 6-inch wide, and 6-inch long wood pieces were treated for toughness and various decontaminatability tests. The following impregnated wood samples and resin loading levels in relation to the untreated wood controls were obtained:

Example 5. Toughness tests of resin-impregnated wood samples of Examples 4a-4g.

To measure toughness of the resin impregnated wood samples obtained in Examples 4a-4g, the Forest Products Laboratory Toughness Testing Machine (Testing Machines Inc.) was used according to the ASTM D143 procedure. Square stick samples (0.5 × 0.5 × 5.5") were cut the impregnated samples of Examples 4a-4g. In this test, the load is applied to the specimen by means of a small yoke pulled by a roller-type steel chain fastened around a drum. The drum is mounted on the axis of the pendulum and, for testing, the pendulum is raised to an angle and allowed to swing back to break the sample. The angle is increased until the sample is broken, and the load weight can also be increased. The sample toughness (T) is calculated by the equation T = w × l × (cos A2 - cos A1), where w is the weight of pendulum, 1 represents the distance from supporting axis to center of pendulum, and A1 is the initial and A2 is the final angle. The toughness value is read directly from the supplied table and the average value from four impact specimens was calculated in percentages with respect to the average value of four matched, untreated control samples. The toughness values thus obtained are reported in Table 1.

Example 6. A two-package polyurethane resin coating system. The polyol and additives package was prepared by mixing the ingredients shown below, with the suppliers indicated in parenthesis, in the order given in a dry mixing tank under dry nitrogen:

The polyol and additives package:

The isocyanate package was prepared by mixing the ingredients shown below, with the supplier indicated in parenthesis, in the order given in a dry mixing container under dry nitrogen:

The isocyanates package:

The final coating composition was obtained by mixing 33 parts of the polyol and additives package and 10 parts of the isocyanates package to a uniform mix in a blender.

Example 7. A tinted coating system of Example 6.

Ninety-seven and one-half parts of the polyol and additives package of Example 6 was thoroughly mixed with 2.5 parts of a green pigment base, Phtahlogreen 853-5510 (Huels America). Mixing this tinted polyol component package with the isocyanates package of Example 6 in a ratio of 33 parts to 10 parts resulted in a pigmented coating formulation. Coating a piece of southern pine and a solvent-cleaned mild steel with this coating formula to a three to five mil dry film thicknesses resulted in a green coating with a good film adhesion and color.

Examples 8h-81. Coating experiments with the polyurethane coating resin system of Example 6 on wood samples of Examples 4h-41.

6 × 6 × 1/2-inch thick pieces of southern pine, oak and aspen wood samples obtained in Examples 4h-4l were coated with the polyurethane coatings resin system of Example 6 using a soft-bristled brush to give a dried film thickness of 3 - 5 mils. The polyurethane coatings were dried in a ventilated hood for 24 hours and cured at 40 ºC for 24 hours, resulting in a uniform clear glossy coating. The following five polyurethane resin-coated wood samples were obtained:

Example 6h: Coated Ex. 4h; pine with no resin impregnation.

Examples 9j and 9m. Weathering experiments with artificial sunlight on a polyurethane resin-impregnated and coated wood sample of Example 8j and a steel control sample.

In order to examine the sunlight weatherability and the decontaminatability of chemical warfare agent VX of the resulting surfaces, selected samples were subjected to the simulated sunlight weathering procedure according to the ASTM G-26, MIL STD 810 E, Procedure II. In this procedure, one test cycle consisted of irradiating the sample surface with a xenon-arc lamp at an energy level of 60W/m² at 340 nm for 8 hours while maintaining the temperature of sample surface at about 120°F, followed by a resting period of 4 hours. The test-cycle was repeated for a total of 28 days. The experiment was performed at the South Florida Testing Service, Miami, Florida.

Two samples were obtained:

Example 9j: Example 8j; pine impregnated with Resin Ex. la, coated with coating Ex. 7.

Example 9m: steel control; Grade TT-C-490, 0.03-inch thick, zinc phosphate coated, which was coated at a 3-5 mil thickness with the current metal coating material used by the U. S. Army. Examples 10a-10m. VX decontamination tests of impregnated and coated wood samples and steel control samples.

Impregnated and/or coated wood samples and control steel samples obtained in the above Examples were tested for decontamination efficiency of the chemical warfare agent VX (O-ethyl S-(2-diisopropyl aminoethyl)methylphosphonothiolate). The test procedure was the U.S. Military standard (Small-Scale Chemical Agent Tests), defined in the Test Operating Procedure (TOP) 8-2-111, "NBC Contamination Survivability of Small Items of Equipment" of the U. S. Army. The test protocol is described in detail in the Midwest Research Institute procedure, "CSM-119, Environmental Chamber Operation (378N1) with Bubbler Collection and GC Analysis of TGD, VX and HD." In this test, the impregnated wood sample was first cut to an appropriate size to provide a circular exposure area of 100 cm² with a short stainless steel circular tube. All the remaining wood surfaces were sealed to avoid any secondary contamination during the test procedure. Droplets of a chemical warfare agent were then uniformly applied on the exposure area at a loading level of 10g/m² and allowed to sit for one hour. The test piece was then submerged in the standard decontaminating solution ("DS2" solution) for 2 minutes, scrubbed with a brush for 5 minutes, allowed to sit for 30 minutes, and finally rinsed thoroughly with distilled water. Then, over the exposed area of the test piece, a stream of air (30°C and 70-85% RH) was passed for 12 hours at a rate of 5.7 L/minute. The exiting air was scrubbed with two bubblers connected in series. Each bubbler was charged with 12 ml of water at a pH of 3.5. The amount of VX was determined by a spectrophotometric enzymatic assay using acetyl cholinesterase and presented in micrograms per square centimeter of surface area. Triplicate analyses were made along with spiked controls. The tests were conducted by the Midwest Research Institute, Kansas City, Missouri. Fourteen samples, Example 10a- 10n, were subjected to this test. The test results and histories of the samples are reported in Table 1.

Discussion

Toughness data: The pine wood test samples of Examples 10a-10f, which were impregnated with the isocyanate group-terminated polyurethane impregnating resins of Examples 1a-1c and Examples 2a-2c , showed toughness values higher than 100, while the wood sample of Example 10g, which was impregnated with a phenol-formaldehyde resin of Example 3, showed a value appreciably lower than 100. This toughening of wood by polyurethane resins indicates the general utility of the polyurethane resins of this type in the intended applications of the present invention.

VX test results: The pine wood test samples of Examples 10a-10c, which were impregnated with the isocyanate group-terminated polyurethane impregnating resins of Examples 1a-1c showed low, very acceptable VX values in the range of 4.8-14 micrograms per square centimeter, but the wood samples of Example 10d-10f, which were impregnated with the isocyanate group-terminated polyurethane impregnation resins of Examples 2a-2c. showed high, unacceptable VX values in the range of 96-780 micrograms per square centimeter. These results indicate the superiority of the impregnation resins of Examples 1a-1c which are made with an isocyanate material having a functionality of 2.1, over those of Examples 2a-2c which are made with an isocyanate material having a functionality of 2.3. This finding of the beneficial effect of the isocyanate materials having a low functionality of 2.1 on the decontaminatability of chemical agent VX is novel, and is one of the major discoveries of the present invention. As discussed in tne Background of the Invention above, the authors of the present invention believe that the lower functionality of the isocyanate materials, along with the linear polyols used for the prepolymer formation, effected the formation of principally linear polymer chains, and result in a tightly overlapping polymer structure in the wood and prevents the chemical warfare agent from penetrating into the structure. A high isocyanate group functionality, by its very nature, will form branched polymer chains even with linear polyols and result in a cured polymer structure of soft segments that have many molecular spacings remained unfilled to allow easy penetration of chemical warfare agent molecules into the structure. Once this type of penetration occurs, the standard decontamination washing procedure will net be adequate to meet the requirements.

The VX test result of Example 10h is also novel in that very little of the chemical agent VX was detected on the surface of the un- impregnated pine wood which was coated with tne coating resin of Example 7. in Examples 10i,10k and 10l, the coating resin system of Example 7 showed a high decontamnatability on pine, oak, and aspen wood which were impregnated with the impregnation resin of Example 1a. A similarly good decontamination result was obtained in Examples 10j, the same sample as Example 10i but after the sunlight weathering. In Examples 10m-10n, the steel control samples, which were coated with the current coating material being used in the U. S. Army, performed very well before the sunlight weatnenng out very poorly after weathering. This superior decontaminatability of the coating resin system of Example 7 indicates not only excellent degradation resistance against sunlight, but also the good adhesion to the wood substrate. The authors of the present invention believe that these superior film characteristics of the coating system of Example 7 have arisen from the unique combination of the component materials used as discussed in the Background of the Invention.

From the data and discussions presented above, it is obvious that the impregnation and coating formulations and application procedures resulted in many desirable properties not exhibited by conventional and other systems shown in the examples. Obviously, many variations 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.

1. A polyuretnane prepolymer resin composition formulated with 30-60 parts of an isocyanates material and 40-70 parts of a combination of linear polyols, and reacted under any temperature and other conditions for such a duration that the finished prepolymer resin contains an unreacted isocyanate (NCO) group content of between 7-20% based on the resin solids weight, in that

Claims

Said prepolymer isocyanate is any selected from the group consisting of toluene diisocyanate (TDI), methylene-bis-phenyiene diisocyanate (MDI), hexane diisocyanate (HDI), isophorone diisocyanate (IPDI), and their oligomeric materials or their adducts made by reacting them with water or any polyhydroxyl compounds, wherein said prepolymer isocyanate has a functionality of 2 - 2.15, and said polyol is any linear polyol selected from the group consisting of polyethylene oxides, polypropylene oxides, ethylene oxide-propylenp oxide copolymers, and polytetrahydrofurans, hydroxyl group-terminated polybutadienes, and polyester polymers derived from adipic or sebacic acids and ethylene glycol or propylene glycol, and have a molecular weight range of 500-7,000,

Said synthesized polyurethane prepolymer resin is diluted with any dry non-hydroxylic solvents to any resin solids level in the range of 1-100%.

2. The composition of Claim 1, wherein the polyhydroxyl compounds used in making isocyanates adducts are low molecular weight dihydroxyl materials that include ethylene glycol, propylene glycol, and butanediol; and wherein the resin diluent is acetone, methyl ethyl ketone, tetrahydrofuran, toluene, xylene, methylene chloride, and cellosolve acetate.

3. A composition of a resin-impregnated and cured wood product obtained by a resin impregnation and curing procedure,

In that a polyurethane prepolymer resin composition formulated with 30-60 parts of an isocyanate material ana 40-70 parts of a combination of linear polyols, and reacted under any temperature and other necessary conditions for such a duration that the finished prepolymer resin contains an unreacted isocyanate (NCO) group content of 7 - 20% based on the resin solids weight, in that said isocyanate material is any selected from the group consisting of toluene diisocyanate (TDI), methylene-bis-phenyiene diisocyanate (MDI), hexane diisocyanate (HDI), isophorone diisocyanate (IPDI), and their oligomeric materials or their adducts made by reacting them with water or any polyhydroxyl compounds, wherein said prepolymer isocyanate has a functionality of 2 - 2.15, and said polyol is any linear polyol selected from the group consisting of polyethylene oxides, polypropylene oxides, ethylene oxide-propylene oxide copolymers, and polytetrahydrofurans, hydroxyl group-terminated polybutadienes, and polyester polymers derived from adipic or sebacic acids and ethylene glycol or propylene glycol, and have a molecular weight range of 500-7,000,

Said polyurethane prepolymer resin is diluted with any dry, non-hydroxylic solvents to any resin solids level in the range of 1-100%, and then introduced into the inner structure of the wood of any species that is pre-dried at 3-20% moisture contents based on dry wood weight, at any resin loading level in the wood in the range cf 1-150% of the dry wood weight, and finally the resulting resin-impregnated wood is cured at room or any elevated temperatures for any length cf time.

4. The composition of Claim 3, wherein the dihydroxyl compounds used in making isocyanates adducts are low molecular weight polyols that include ethylene glycol, propylene glycol, and butanediol; and wherein the resin diluent is acetone, methyl ethyl ketone, tetrahydrofuran, toluene, xylene, and methylene chloride, cellosolve acetate; and wherein the wood used for resin impregnation is any wood species that include but not limited to various southern pine, jack pine, D. fir, various oaks, gum, yellow poplar, maple, aspen, cotton wood, ponderosa pine, luan, and lodgepole pine.

5. A polyurethane resin coating composition obtainable as a two-package system to be combined before use,

In that the first package is comprised of 15-20 parts of a polyether polyol derived from the polymerization of diglycidyl-bis-phenol-A to a high molecular weight, 2-8 parts of a melamine-formaldehyde condensate having a formaldehyde/melamine ratio of 2.0-6.0, and up to 2 parts of various coatings additives, such as flow and crosslink promoting agents and tinting pigment bases, and diluted to any resin solids level in the range of 1-100% with any dry, non-hydroxylic solvent, the second package is comprised of any aliphatic prepolymer isocyanates selected from the group consisting of the oligomeric materials or adducts made by reacting water or any polyhydroxyl compounds with hexane diisocyanate (HDI) or isophorone diisocyanate (IPDI), wherein the isocyanate material has an isocyanate functionality of 3.0-4.0, and diluted to any resin solids level in the range of 1-100% with any dry non-hydroxylic solvents, and said first and second package are mixed before use in a proportion range cf 2.2-3.2:1 by weight based on the respective resin solids contents.

6. The composition of Claim 5, wherein the additives for the polyol package are polyacrylic flow promoting materials, silane coupling agents, crosslinking agents that include trimethyl propane trimethylolate containing initiators such as benzoyl peroxide and silver perchlorate, and tinting pigment bases of any kind.

7. A process of manufacturing a polyurethane resin composition obtainable as a two-package system to be combined before use,

In that the first package is manufactured by thoroughly mixing 15-20 parts of a polyether polyol derived from the polymerization of diglycidyl-bis-phenol-A to a high molecular weight, 2-8 parts of a melamine-formaldehyde condensate having a formaldehyde/melamine ratio in the range of 2.0-6.0, and up to 2 parts of various coatings additives such as flow and crosslink promoting agents and tinting pigment bases, diluted to any resin solids level in the range of 1-100% with any dry, non-hydroxylic solvents, preferably all in a moisture-free environment, and the second package is manufactured by thoroughly mixing an aliphatic prepolymer isocyanate selected from the group consisting of the oligomeric materials or adducts made by reacting water or any polyhydroxyl compounds with hexane diisocyanate (HDI) or isophorone diisocyanate (IPDI), wherein the isocyanate material has an isocyanate functionality of 3.0-4.0, in any dry non-hydroxylic solvents, at any resin solids level in the range of 1-100%, preferably all in a moisture-free environment, and finally said first and second package are thoroughly mixed before use in a proportion range of 2.2-3.2:1 by weight based on the resin solids contents, preferably in a moisture-free environment.

8. A composition of polyurethane resin-impregnated, polyurethane resin-coated wood obtainable by consecutive resin-impregnation, curing, and resin-coating, and curing procedures,

In that a polyurethane prepolymer resin composition formulated with 30-60 parts of an isocyanate material and 40-70 parts of a combination of polyols, and reacted under any temperature and other necessary conditions for such a duration that the finished prepolymer resin contains an unreacted isocyanate (NCO) group content of between 7-20% based on the resin solids weight, in that

Said prepolymer isocyanate is any selected from the group consisting of toluene diisocyanate (TDI), methylene-bis-phenyiene diisocyanate (MDI), hexane diisocyanate (HDI), isophorone diisocyanate (IPDI), and their oligomeric materials or their adducts made by reacting them with water or any polyhydroxyl compounds, wherein said prepolymer isocyanate has a functionality of 2 - 2.15, and said polyol is any linear polyol selected from the group consisting of polyethylene oxides, polypropylene oxides, ethylene oxide-propyl ene oxide copolymers, and polytetrahydrofurans, hydroxyl group-terminated polybutadienes, and polyesters derived from adipic or sebacic acids and ethylene glycol or propylene glycol and having a molecular weight range of 500-7,000,

Said polyurethane prepolymer resin is diluted with any dry, non-hydroxylic solvents to any resin solids levex in the range of 1-100%., and the resulting resin introduced into the inner structure of the wood that is pre-dried at 3-20% moisture contents based on dry wood weight, at any resin pickup level in the range of 1-150% of the dry wood weight, the resulting resin-impregnated wood cured at room or at any elevated temperature for any length of time,

And, subsequently, coated at a film thickness of 0.1 mil or higher with a polyurethane resin, formulated initially as a two-package system to be mixed before use, in that the first package is comprised of 15-20 parts of a polyether polyol manufactured by the polymerization of diglycidyl-bis-phenol-A to a high molecular weight, 2-8 parts of a melamine-formaldehyde condensate having a formaldehyde/melamine ratio of 2.0-6.0, and up to 2 parts of various coatings additives such as flow and crosslink promoting agents and tinting pigment bases, and diluted to any resin solids level in the range of 1-100% with any dry, non-hydroxyl solvents, and the second package is comprised of the oligomeric materials or adducts made by reacting water or any polyhydroxyl compounds with hexane diisocyanate (HDI) or isophorone diisocyanate (IPDI), wherein said isocyanate material has an isocyanate functionality of 3.0-4.0, diluted to any resin solids levels in the range of 1-100% with any dry non-hydroxylic solvents, and finally said first and second package are mixed in a proportion range of 2.2-3.2:1 by weight based on the respective resin solids contents,

And, finally, the coating resin composition resulted by mixing the first and second package is applied on said polyurethane resin- impregnated and cured wood at a film thickness of 0.1 mil or higher and cured at any temperature for any duration of time.

9. The composition of Claim 8, wherein the polyhydroxyl compound used in making the isocyanate adduct materials are low molecular weight polyols that include ethylene glycol, propylene glycol, and butanediol, and wherein the resin diluent is acetone, methyl ethyl ketone, tetrahydrofuran, toluene, xylene, methylene chloride, cellosolve acetate, and wherein the wood used for polyurethane resin impregnation is any wood species that include but not limited to various southern pines, jack pine, D. fir, various oaks, gum, yellow poplar, maple, aspen, cotton wood, ponderosa pine, and lodgepole pine, and wherein the additives for the first package of the coating system are polyacrylic flow promoting materials, silane coupling agents, crosslinking agents that include trimethyl propane trimethylolate containing initiators such as benzoyl peroxide and silver perchlorate, and the tinting pigment base material is any pigment and filler materials of any kind.

10. A process of manufacturing a polyurethane resin-impregnated, cured, and polyuretnane resin-coated and cured wood,

In that a polyurethane prepolymer resin composition formulated with 30-60 parts cf an isocyanate material and 40-70 parts of a combination of polyols and reacted under any temperature and other necessary conditions for such a duration that tne finished prepolymer resin contains an unreacted isocyanate (NCO) group content of between 7-20% based on the resin solids weight, in that Said prepolymer isocyanate is any selected from the group consisting of toluene diisocyanate (TDI), methylene-bis-phenylme diisocyanate (MDI), hexane diisocyanate (HDI), isophorone diisocyanate (IPDI), and their oligomeric materials or their adducts made by reacting them with water or any polyhydroxyl compounds, wherein said prepolymer isocyanate has an isocyanate group functionality of 2-2.15, and said polyol is any linear polyol selected from the group consisting of polyethylene oxides, polypropylene oxides, ethylene oxide-propylene oxide copolymers, and polytetrahydrofurans, hydroxyl group-terminated polybutadienes, and polyesters derived from adipic or sebacic acids and ethylene glycol or propylene glycol and having a molecular weight range of 500-7,000,

Said polyurethane prepolymer resin is diluted with any dry non-hydroxylic solvents to any resin solids level in the range of 1-100%, and the resulting resin introduced into the inner structure of the wood that is pre-dried at 3-20% moisture contents based on dry wood weight at any resin pickup level in the range of 1-150% of the dry wood weight, the resulting resin-impregnated wood cured at room or at any elevated temperature for any length of time, Followed by manufacturing a polyurethane resin composition attainable by formulating initially as a two-package system to be combined before use, in that the first package is manufactured by thoroughly mixing 15-20 parts of any polyether polyol derived from the polymerization of diglycidyl-bis-phenol-A to a high molecular weight, 2-8 parts of any melamine-formaldehyde resin having a formaldehyde/melamine ratio of 2.0-6.0, and up to 2 parts of various additives such as flow and crosslink promoting agents and tinting pigment bases, and by diluting the mixture to any resin solids level in the range between 1-100% with any dry non-hydroxylic solvents, preferably all in a moisture-free environment, r.he second package is manufactured by thoroughly mixing an aliphatic prepolymer isocyanate selected from the group consisting of the oligomeric materials or adducts made by reacting with water or aι>y polyhydroxyl compounds with hexane diisocyanate (HDI) or isophorone diisocyanate (IPDI), wherein said isocyanate material has an isocyanate group functionality cf 3.0-4.0, in any dry non-hydroxyl solvents at any resin solid level in the range of 1-100%, preferably in a moisture-free environment, and finally said two packages are thoroughly mixed before use in a proportion range of 2.2-3.2:1 by weight based on the resin solids contents, preferably in a moisture-free environment,

Followed by applying the mixed coating compositxon on said polyurethane resin-impregnated and cured wood at any film thicknesses of 0.1 mil or higher using any application methods, and the applied polyurethane resin coating film cured at any temperature for any duration of time.