WO1997002134A1

WO1997002134A1 - Polyurethane impregnated wood, impregnation methods thereof, and articles

Info

Publication number: WO1997002134A1
Application number: PCT/US1996/012283
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: AU6602996A; WO1997002135A1; AU6508696A; WO1997002136A1; AU6680696A

Abstract

The present invention relates to wood products having improved impact resistance or toughness effected by impregnating wood with a polyurethane resin-based prepolymer material and to the processing methods thereof.

Description

TITLE: POLYURETHAME IMPREGNATED WOOD,

IMPREGNATION METHODS THEREOF, AND ARTICLES

The invention described herein may be made, used, or licensed by or for the Governmant for Governmantal perposes without the payment to me of any royalties thereon or therefore.

The present invention relates to wood produces having improved impact resistance or toughness effected by impregnating wood with a polyurethane resin-based prepolymer material and to the processing methods thereof.

An important goal of the current wood products research activities is to improve the strength properties for more demanding uses. The impact resistance or toughness of wood is often the critical parameter in exterior, harsh uses of wood with respect to the extent of wood deterioration that occurs during the course of use. Currently, low cost materials based on inorganic metallic compounds are used widely for wood impregnation to extend the life of wood in outdoor applications. However, this type of impregnated wood has limitations in applications and disposal methods due to the toxicity of the metallic compounds, and various organic polymeric materials have beer, investigated and used as wood impregnation materials to limited extents, with certain health and safety and aesthetic advantages being apparent as well as the weathering durability improvement. Organic polymeric materials used thus far are vinyl monomers such as methyl methacrylate and phenol-formaldehyde and melamine- formaldehyde thermosetting resins. These organic polymeric materials are currently not being used widely, however. Certain advantages and disadvantages are known, but one common disadvantage of these known organic polymeric materials is the reduced toughness, or brittleness, of impregnated wood materials. While the reasons for this weakening of wood by these known organic polymeric materials are not clear, we discovered that wood impregnated with certain isocyanates-based prepolymer resins show increased toughness properties as well as other common beneficial attributes of organic polymer impregnations. Such materials and processing methods have been a highly desirable development objective for many commercial applications of wood.

One object of the present invention is therefore to provide impregnated wood that has enhanced toughness properties as well as improvements on other common wood properties.

Another object of the present invention is to provide wood impregnation methods and procedures for manufacturing these resin impregnated wood products using the appropriate impregnation resin materials.

SUMMARY OF THE INVENTION

The present invention specifically relates to the use of isocyanate group-terminated polyurethane prepolymer resins having isocyanate (NCO) group contents of 2 or higher as wood impregnation materials to impart to wood improved toughness and other more common properties. This approach is novel by itself in that no such prior technology has been known, especially with respect to the appropriate uses of these polyurethane resins in relation to the wood moisture content control necessary since moisture in wood acts as the resin curing catalyst.

The steps of the present invention include preparing, or securing an appropriate reactive isocyanate group-terminated polyurethane prepolymer resin, impregnating wood with the resin, and curing the impregnated wood. The resulting wood products are novel and useful in a variety of applications.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The objectives of the present invention are achieved by a series of steps. The first seep comprises the preparation or securing of an appropriate isocyanate group-terminated, thus reactive, polyurethane prepolymer resin. The resin preparation is accomplished by selecting appropriate isocyanates and polyol materials and reacting them at such an isocyanate group/polyol mole ratio that the amount of isocyanate groups remained unreacted at the end of reaction is in the range of 7-20% of the total resin weight, while most of the hydroxyl groups have reacted to form urethane bonds. Appropriate polyurethane resins can be also obtained from resin suppliers if appropriate isocyanates and polyol materials are used in manufacture in appropriate mole ratios, resulting in appropriate isocyanate group contents and molecular weights for the resin. The suitable isocyanates are various commercially available isocyanate materials such as toluene diisocyanates (TDI), methylene-bis-phenylene diisocyanates (MDI) , hexane diisocyanate (HDD, isophorne diisocyanate (IFDI), and their oligomeric materials. Also the adduct materials made by reacting these isocyanates materials with water, such as "Desmodur" (Mobay Chemical Co.), or made by reacting them with polyhydroxyl compounds such as certain "Isonates" (Dow Chemical Co) are useful. The suitable polyols are various linear polyols having a molecular weight in the range of 500 to about 7,000 daltons, based on polyethylene oxides, glycol-initiated polypropylene oxides, ethylene oxide-propylene oxide copolymers, polytetrahydrofurans, hydroxyl group-terminated polybutadiene polyols, and various polyester polyols made from adipic or sebacic acids and ethylene or propylene glycols. These polyols can also be used alone or in combinations.

The mole ratios of isocyanate/polyol(s) used in the resin formulation should be in a range that will maintain the amount of the unreactεd isocyanate (NCO) functional groups at the end of the resin synthesis reaction, at a level between about 7-20% by weight based on the total weight of the isocyanate and polyol materials used. This range of the unreacted isocyanate group content in the finished resin is one key feature of this invention. The free isocyanate groups in the resin are designed to react with moisture in the wood and, to a limited extent, with the hydroxyl groups of wood structure during the resin curing process. The range of the unreacted isocyanate groups content claimed in the present invention, 7-20%, is to accommodate the varying moisture contents of wood. Since slightly more than two isocyanate groups are needed to react with one molecule of water and cure the polyurethane resin system, wood moisture contents of 3-8% are theoretically needed to cure isocyanate groups in the 7-20% content range when the resin impregnation level is about 100% based on the wood weight. In actuality, some water in the wood would escape without reacting with isocyanate groups, and it was found that moisture contents up to about 20% can be used within the isocyanate (NCO) group content range although moisture contents of 5-15% are preferred. Wood moisture contents lower than about 3% will be deficient of moisture to cure the resins systems in the present invention. Another benefit of having an ample amount of free isocyanate groups in the resin, or of using lower wood moisture contents is to help promote the reaction between wood hydroxyl and isocyanate groups. The level of the available wood hydroxyl groups in wood is difficult to determine, and considering the generally known fact of limited accesses of resin molecules to inner wood structures, the amount of available hydroxyl groups would be a relatively minor amount. However, the effect of the relatively small amount of the reaction occurring between these groups would still be a significant benefit for the objectives of the present invention, especially in comparison to phenol-formaldehyde or melamine formaldehyde resin systems in which such resin-wood inter-reactions are unlikely to occur.

Another key feature of the polyurethane prepolymer resins of this invention is their appropriate number-average molecular weights. The molecular weight, unreacted isocyanate (NCO) group content, and the molecular weights of isocyanates and polyol materials used in the resin synthesis are inter-related parameters. The molecular weight of resin is calculated during the resin formulation stage by considering the latter two parameters. The calculated number-average molecular weights of the prepolymer resins of the present invention are in the range of 420-1350 daltons. Resins with molecular weights below 410 daltons tend to penetrate wood inner structures too much and because of the entailing high isocyanate (NCO) group contents of the resins, a high crosslinking density and, therefore, a reduced toughness resulted.

Also, the polyurethane prepolymer resins of this invention have the isocyanate (NCO) group functionality of 2 or higher, since NCO group functionalities less than 2 would lead to the formation of incompletely cured polyurethane structures, thus resulting in reduced strength properties. Isocyanates materials having a functionality of 1, such as phenyl and certain alkyl isocyanates, have been used for wood impregnation, but they were found to be ineffective for strength improvement because the materials do not crosslink. Also, the polyurethane prepolymer resins of the present invention can have viscosities too high for impregnation of wood and lowering them would be necessary, for which any dry non-hydroxylic solvents are useful.

Thus, the polyurethane prepolymer resin composition formulated with 35-60 parts of an isocyanate material and 40-65 parts of a polyether or polyester polyol can be used in the present invention as impregnation resins as long as the mole ratios of resins are such that the level of the remaining isocyanate (NCO) groups after the resin synthesis reaction are in the range of 7-20% based on the total resin solids, the resins' isocyanate (NCO) group functionality is 2 or higher, and the calculated number-average molecular weight is in the range of 450-1350 daltons. The finished resin can be diluted to any desired viscosity, or resin solids levels, using dry non-hydroxylic solvents such as acetone, methyl ethyl ketone, and others.

The manufacturing process of the polyurethane prepolymer resins of the present 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 to the extent that it is practically possible, and it is also preferable to cover the reactant materials in the reactor under a stream of dry nitrogen to prevent undesirable reactions with atmospheric moisture. The manufacturing process, that is, the condensation polymerization reaction between the isocyanates and polyol hydroxyl groups, can be conducted at any reasonable temperature above about 35 degree C, although as for many chemical reactions, elevated temperatures would be preferred over lower temperatures for reactor economy. The condensation reaction must be complete at the end of resin manufacturing, that is, most hydroxyl groups of the polyols used must have reacted with isocyanate groups, which can be determined by viscosity measurements conducted at regular time intervals during manufacturing. The end point is when the viscosity of the reaction mixture does not increase any more. Viscosity of polymeric resins increases as the polymer molecular weights increase as the result of polymer condensation reactions. If some hydroxyl groups remain unreacted at the end of resin manufacturing, the reaction will proceed in the subsequent storage period and can result in an uncontrolled reaction to give a less effective or even useless product. When all hydroxyl groups have reacted during the resin synthesis, there will be no more molecular weight increase and the viscosity will not increase further even though the formulated level of isocyanate groups remained unreacted. At this stage, the resin is then cooled to room temperature and may be diluted with any suitable dry non-hydroxylic solvent. For similar reasons, the manufactured resin should be stored in a dry, closed container.

The second step of the present invention comprises the impregnation of wood with the polyurethane prepolymer resin, followed by curing the impregnated wood to fix the resin into the wood structure. For the reasons mentioned above, the wood should first be dried to a moisture content in the range of about 3-20%, based on the oven dry wood weight. The wood moisture content and the available amount of free isocyanate groups in the impregnated wood should be balanced in a range that the urethane-bond forming curing reactions with water can occur adequately. In addition, a slight excess amount of isocyanate group should be present to cure with wood hydroxyl groups and among themselves. Excess water present in the wood will contaminate the excess resin in the impregnation container due to the partly reversible nature of the resin impregnation process and should be avoided. The resin loading in wood, or resin absorption rate, can be calculated by weighing the wood sample before and after the impregnation treatment, and the impregnated wood of the present invention were found to contain up to 150% of cured polyurethane resin based on the dry wood weight.

Any wood treatment procedure can be used as long as the impregnation can be made to be sufficiently complete to obtain the desired resin loading level. Thus, selection of the impregnation process depends on the porosity of wood and the dimensions of wood sample. Small thin wood samples, or low density wood such as aspen can be adequately impregnated simply by soaking it in the resin if the resin's viscosity is kept below about 100 cP. Evacuation of wood before resin introduction and application of pressure, both in a closed cylinder, greatly increase the resin impregnation extent and rate. One such process is generally described as a 'full-cell' process, used here to illustrate the impregnation processes in the present invention. In this process, a wood sample is placed in a pan in a cylinder and a vacuum is applied to the cylinder and a prepolymer resin is introduced into the pan through a small opening until the resin completely covers the sample. The vacuum is then continued for a while and, after release of the vacuum, a positive pressure is applied for a period of time. Then, the wood sample is removed.

The resin-impregnated wood samples are then cured preferably in a ventilated oven to avoid human exposure to the evolving solvent vapor when the impregnation resin contains a diluent solvent. The curing can be done in a temperature range of 30-90 °C for 3-24 hours or more. At lower temperatures the curing takes longer times. The resin impregnated, cured wood samples thus obtained are novel with an excellent aesthetic appearance as well as improved toughness properties, making them aptly suitable in many useful wood applications. Curing of traditional treatments such as phenol-formaldehyde or melamine-formaldehyde resin impregnated wood needs more elaborate methods as will be shown later.

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 are not intended 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.

Examples 1a-1j. Polyurethane and other prepolymer resin systems used.

Examples 1a-1f represent laboratory syntheses of polyurethane prepolymer resins having increasing amounts of unreacted isocyanate (NCO) group contents.

Example 1a: Eighty (80.0) parts of Papi 1094, a methylene-bis-phenylene diisocyanate (MDI) material with a functionality of 2.3 (Dow Chem. Co.), and 20.0 parts of E-900, a polyethylene oxide polyol with a molecular weight of 900 (Dow Chem. 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 435 cP. The free isocyanate (NCO) group content of the resulting prepolymer resin was calculated to be 23.5 0% by weight based on the total resin solids and the number-average molecular weight was calculated to be 410. After cooling to room temperature, methyl ethyl ketone was added to the finished resin to a 95% resin solids level, resulting in a prepolymer resin with a viscosity of about 165 cP.

Similar synthesis reactions were carried out for Examples 1b-1f using the necessary materials as described below:

Example 1b: Sixty (60.0) parts of Papi 1094, 11.1 parts of Voranol 220-056, a polypropylene oxide polyol with a molecular weight of 2000 (Dow Chem. Co.), and 28.9 parts of R-45HT, a polybutadiene-based polyol with a functionality of two and a molecular weight of 2800 (Athochem Co) were used. The free isocyanate (NCO) group content was calculated to be 17.5% and the number-average molecular weight was calculated to be 545. Methyl ethyl ketone was added to the finished resin to a 80.0% resin solids level, resulting in a prepolymer resin with a viscosity of about 125 cP.

Example 1c: Sixty (60.0) parts of Papi 1094 and 40.0 parts of E 900 were used. The free isocyanate (NCO) group content was calculated to be 15.3% and the number-average molecular weight was calculated to be 646. Methyl ethyl ketone was added to the finished resin to a 90.0% resin solids level, resulting in a prepolymer resin with a viscosity of about 165 cP.

Example 1d: Fifty-eight and two tenths (58.2) parts of Papi 1094 and 41.7 parts of Voranol 220-110, a propylene oxide polyol with a molecular weight of 1000 (Dow Chem. Co.) were used. The free isocyanate (NCO) group content was calculated to be 15.0% and the number-average molecular weight was calculated to be 659. Methyl ethyl ketone was added to the finished resin to a 91.0% resin solids level, resulting in a prepolymer resin with a viscosity of about 230 cP.

Example 1e: Forty-six parts of Papi 1094, 39.1 parts of R-45HT, and 14.9 parts of Voranol 220-056 were used. The free isocyanate (NCO) group content was calculated to be 12.5% and the number-average molecular weight was calculated to be 761. Methyl ethyl ketone was added to the finished resin to a 75.0% resin solids level, resulting in a prepolymer resin with a viscosity of about 300 cP.

Example 1f: Thirty-six (36.0) parts of Isonate 1143L, a low viscosity methylene-bis-phenylene diisocyanate (MDI) material with a functionality of 2.1, 14.7 parts of Voranol 220-056, and 49.3 parts of R-45HT were used. The free isocyanate (NCO) group content was calculated to be 8.0% and the number-average molecular weight was calculated to be 1072. Methyl ethyl ketone was added to the finished resin to a 75.0% resin solids level, resulting in a prepolymer resin with viscosity of about 250 cP.

Examples 1g-1h represent polyurethane prepolymer resins obtained from a supplier.

Example 1g: Airthane XPC-500, a prepolymer polyurethane resin reported to be synthesized from toluene diisocyanate (TDI) and a polypropylene oxide polyol, with a functionality of 2.2 and an equivalent weight of 500, made by Air Products and Chem. Co. The number-average-molecular weight was calculated to be 1100.

Example 1h: Airthane XAPC-504: a prepolymer polyurethane resin reported to be synthesized from isophorone diisocyanate (IPDI) and polytetrahydrofuran polyol, with a functionality of 2.6 and an equivalent weight of 504, made by Air Products and Chem. Co. The number-average molecular weight was calculated to be 1310.

Examples 1i-1j represent thermosetting-type prepolymer resins obtained from suppliers.

Example 1i: Plenco 761, a phenol-formaldehyde resol resin obtained from Plenco Co., suggested to be useful for wood impregnation, was catalyzed with a 0.20% sodium hydroxide before use. The number-average molecular weight was calculated to be 140.

Example 1j: PC-6N, a melamine-formaldehyde resin from Astro Co., with a reported formaldehyde/melamine ratio of five to six, solids content of 80.0%, and pH value of 8.8. The number-average molecular weight was calculated to be 296. The resin was suggested to be useful for wood impregnation and catalyzed with 0.3% ammonium chloride before use.

Examples 2a-2j. Wood impregnation and curing experiments carried out using the polyurethane and other prepolymer resins of Examples 1a-1j.

Preparation of resin impregnated wood samples was performed with southern pine wood using the full-cell impregnation procedure. 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 the vacuum was maintained for about 30 minutes. Then, the vacuum was released and dry nitrogen at 150 psi was applied to the cylinder for 60 minutes. After the pressure was released, the cylinder was opened and wood samples were taken out and the excess resin on the surface was wiped away. The polyurethane resin impregnated wood samples of Examples 2a-2h were then dried in a ventilated hood for 24 hours and cured in a heated oven at about 40 °C for five hours. The polymer resin loading was determined by weighing wood samples before and after the treatment and then calculating the percentages based on the dry wood weight. For phenol-formaldehyde resin impregnated samples, Example 2i, the impact samples were cured in an oven at 70-100 °C for 5 hours and the toughness samples were cured in a hot press at 190 °C for 3,0 minutes under a pressure of 50 psi. For melamine-formaldehyde resin impregnated samples, Example 2j, the impact samples were cured in an oven at 40-150 °C for 4 hours and the toughness samples were cured in a hot press at 175 °C for 11 minutes under a pressure of 30 psi.

Five 0.78-inch thick, 1.25-inch wide, and 4.00-inch long wafer-type wood pieces were treated for the impact tests and four 1/2-inch thick, 6.00-inch wide, and 6.00-inch long wood pieces were treated for toughness test, independently in most cases. Resins and resin loading levels in relation to untreated wood controls were as follows:

Example 2a: Resin, Example 1a; 128% loading for impact

samples; 65% loading for toughness samples.

Example 2b: Resin, Example 1b; No impact samples; 60% loading for toughness samples.

Example 2c: Resin, Example 1c; 95% loading for impact samples;

75% loading for toughness samples.

Example 2d: Resin, Example 1d; 95% loading for impact samples;

72% loading for toughness samples.

Example 2e: Resin, Example 1e; 64% loading for impact samples;

75% loading for toughness samples.

Example 2f: Resin, Example 1f; 61% loading for impact samples;

37% loading for toughness samples.

Example 2g: Resin, Example 1g; 60% loading for impact samples;

35% loading for toughness samples.

Example 2h: Resin, Example 1h; 37% loading for impact samples;

51% for toughness samples. Example 2i: Resin, Example 1i; 83% loading for impact samples;

44% loading for toughness samples.

Example 2j: Resin, Example 1j; 109% loading for impact

samples; 25% for toughness samples. Example 3. Impact resistance and toughness teats of resin- impregnated wood samples of Examples 2a-2j.

Toughness of the resin impregnated wood samples was measured using two different methods. In the first method, a BYK-Gardener heavy duty impact tester (Model IG-1120) was used on the wafer-type samples (0.78 × 1.25 x 4"). The impact was made using 6- and 8-inch-pound loads on two different spots, 1 inch apart. All five wafer-type samples were impacted the same way along with an equal number of matched untreated control samples. Resistance to failure was rated visually, from 1 to 5 in increasing severity, and the average value was calculated in percentages with respect to the value of control samples, and the value was defined as impact resistance. The impact resistance values for samples of Examples 2a-2j are reported in Table 1.

In the second method of toughness evaluations, the Forest Products Laboratory Toughness Testing Machine (Testing Machines Inc.) was used according to the ASTM C143 procedure. For this test, square stick samples (0.5 × 0.5 × 5.5") were cut from the toughness test samples prepared in Examples 2a-2j. 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 or the load weight is increased until the sample is broken. 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 for samples of Examples 2a-2j are reported in Table 1.

The data in Table 1 indicate comparative samples made by impregnating with phenol-formaldehyde or melamine-formaldehyde resins showed poor performances, in agreement with the generally known fact that these type of resins result in increased brittleness. All polyurethane resin-impregnated wood samples, except Example 2a, showed impact resistance and toughness values greater than untreated control samples, with the most effective value coinciding at a 15% isocyanate group content in the resin. Example 2a showed poor toughness properties apparently due to the relatively high free isocyanate (NCO) group content and low molecular weight values, both tend to promote excessive crosslinking and brittle failure. This result also indicates that impact resistance and toughness values decreased as the isocyanate (NCO) group content of the resins decreased to about 7.6%, Example 2h. although other use properties such as appearance and water absorptions were observed to be improved over the untreated control. The result of Example 2h is due to an excessively high molecular weight resin which was the result of the formulation parameters that were required to obtain the low isocyanate (NCO) group content. As mentioned above, the optimum range of isocyanate (NCO) content in the resin is partly related to the moisture content of the wood, and the results of Examples 2a-2j indicates that the optimum isocyanate group content of resin ranges between about 7-20% based on the resin solids weight when wood of 12% moisture content wood is used for impregnation. Although 12% moisture content is a nominal value for many structural applications in the United States, moisture content can be lowered rather readily down to about 4% based on dry wood weight during the lumber drying stage. This would extend the effective range of the isocyanate group content of resin to below 7.6% level. However, the high molecular weights of prepolymer resins that result when the isocyanate (NCO) group contents are decreased do not still favor moisture contents below about 7%.

Thus, the Examples and discussions given above showed that impregnation with isocyanate group (NCO) -terminated polyurethane resins having unreacted isocyanate (NCO) contents in the range of about 7-20% result in wood with improved toughness strength properties over the untreated control as well as over the phenol-formaldehyde or melamine-formaldehyde resin impregnated wood. This improvement of toughness of wood is very useful in many applications where wood is put to harsh treatments such as in pallets and food processing. Obviously many variations and modifications 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

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

In that a polyurethane resin formulated with 30-65 parts of an isocyanates material and 35-70 parts of a combination of polyols and reacted under such temperature and other necessary reaction conditions for such durations that the resulting resin contains 7-20% unreacted isocyanate (NCO) groups based on the resin solids weight, wherein said isocyanates material is any selected from the group consisting of toluene diisocyanate (TDD, methylene-bis-phenylene diisocyanate (MDI), hexane diisocyanate (HDD, isophorone diisocyanate (IPDI), their oligomeric materials, or their adducts made by reacting them with water or any polyhydroxyl compounds, and said polyol is any selected from the group consisting of polyethylene oxides, glycol-initiated polypropylene oxides, ethylene oxide-propylene oxide copolymers, polytetrahydrofurans, hydroxyl group-terminated polybutadienes, and polyester polyols made from adipic or sebacic acids and ethylene glycol or propylene glycol, all in the molecular weight range of 500 - 7000, wherein the resulting prepolymer resin has a functionality of 2 or higher and diluted to any resin solids level in the range of 1-100% using any dry non-hydroxylic solvents,

And then the resin introduced into the inner structure of wood of any species that is pre-dried at 3-20% moisture contents based on dry wood weight, at any resin pickup level in the wood in the range of 1-150% based on the dry wood weight, and finally the resulting resin-impregnated wood cured at room or any elevated temperatures for any lengths of time.

2. The composition of Claim 1, wherein the polyhydroxyl and amine compounds used in making isocyanates adduct materials are low molecular weight materials that include ethylene glycol, propylene glycol, butanediol, glycerol, ammonia; and wherein the resin diluent is acetone, methyl ethyl ketone, tetrahydrofuran, toluene, xylene, methylene chloride, cellosolve acetate, and butyl acetate; and wherein the wood used for resin impregnation is any wood species that include but is not limited to various southern pines, jack pine, D. fir, various oaks, gum, yellow poplar, maple, aspen, cotton wood, ponderosa pine, luan, and lodgepole pine.

3. A process of manufacturing a polyurethane resin-impregnated and cured wood,

in that a polyurethane resin formulated with 30-65 parts of an isocyanates material and 35-70 parts of a combination of polyols and reacted under such temperature and other necessary reaction conditions for such durations until the resin does not show any further viscosity advancement and the resulting resin contains 7-20% unreacted isocyanate (NCO) groups based on the resin solids weight, wherein said isocyanates material is any selected from the group consisting of toluene diisocyanate (TDI), methylene-bis-phenylene diisocyanate (MDI), hexane diisocyanate (HDI), isophorone diisocyanate (IPDI), their oligomeric materials, or their adducts made by reacting them with water or any polyhydroxyl compounds, and said polyol is any selected from the group consisting of polyethylene oxides, glycol-initiated polypropylene oxides, ethylene oxide-propylene oxide copolymers, polytetrahydrofurans, hydroxyl group-terminated polybutadienes, and polyester polyols made from adipic or sebacic acids and ethylene glycol or propylene glycol, all in the molecular weight range of 500 - 7000, wherein the resulting prepolymer resin has a functionality of 2 or higher and diluted to any resin solids level in the range of 1-100% using any dry non-hydroxylic solvents,

And then the resulting resin introduced into the inner structure of the wood pre-dried at 3-20% moisture contents based on dry wood weight, under any ordinary, vacuum, or pressure conditions until the resin solids weight impregnated in the wood reaches 1-150% of the dry wood weights, and finally the resulting resin-impregnated wood cured at room or any elevated temperatures for any length of time.

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