Outdoor polyurethane wood composite board with long service life and preparation method thereof

Abstract

The invention discloses an outdoor polyurethane wood composite board with long service life and a preparation method thereof, and belongs to the field of polyurethane composite materials. The polyurethane wood composite board comprises a main body layer, a reinforcing layer and / or a protective layer, the main body layer is of a structure formed by compounding polyurethane resin and modified wood particles, and a modifier is composed of nano silicon dioxide, a silane coupling agent, hexaethyl pyrosilicate and a copper azole preservative according to the mass ratio of (1-3): (0.5-1.5): (0.6-2.0): (0.2-0.8). Wood particles are pretreated through a composite modifier, so that the core layer wood component is endowed with excellent corrosion resistance, mildew resistance and dimensional stability, the weather resistance is improved from the source of the material, and the strength retention rate after accelerated aging (boiling in boiling water for 6 hours) is up to 90% at most. Meanwhile, the copper azole preservative is adopted, the mildew-proof grade of the polyurethane wood composite board can reach 0 grade, and the lowest weight loss rate of a decay fungus test in 28 days is 1.1%.

Description

Technical Field

[0001] This invention relates to the field of building materials, and in particular to an outdoor polyurethane wood composite board with a long service life and its preparation method. Background Technology

[0002] As people's demands for the aesthetics, practicality, and durability of outdoor buildings continue to increase, the performance and quality of outdoor building materials have become crucial. Traditional outdoor building materials, such as ordinary wood, while possessing a natural texture, are easily affected by environmental factors such as humidity, temperature, and ultraviolet radiation, leading to problems such as rot, deformation, and cracking, resulting in a relatively short service life. Common wood-plastic composite boards, on the other hand, are insufficient in terms of strength, toughness, and weather resistance, making them unsuitable for long-term outdoor use. The demand for building materials in outdoor construction projects is constantly increasing. Traditional outdoor composite wood-based panels, such as OSB and particleboard, are often prepared using urea-formaldehyde and phenolic resins. These resins require high-temperature reactions, limiting the thickness of the boards and resulting in poor water resistance, making them prone to swelling and cracking outdoors. Simultaneously, wood itself is susceptible to strong ultraviolet radiation and moisture erosion outdoors, leading to degradation, powdering, mold, and fading, and may also be affected by termites and other insect infestations, further impacting its lifespan.

[0003] Polyurethane-wood composites combine the environmentally friendly and renewable properties of wood with the high adhesion and foaming properties of polyurethane resin, making them widely used in construction and decoration. However, traditional polyurethane / wood composites suffer from two major bottlenecks: firstly, wood itself is prone to decay and mold, significantly shortening its lifespan in humid environments; secondly, the overall mechanical properties, especially bending and impact resistance, of pure resin-wood composites sometimes fail to meet the requirements of load-bearing or long-term dynamic loads. Existing technologies include single-treatment of wood with preservatives or simple addition of reinforcing fibers, but these often suffer from insufficient durability of preservatives, weak interfacial bonding, or complex processes. Currently, while some polyurethane-wood composite boards exist on the market, there is still room for improvement in addressing these issues. For example, some existing patents improve performance by adding specific additives or changing the preparation process, but these still struggle to achieve a comprehensive improvement in overall performance and a significant extension of lifespan. Therefore, developing a long-life, high-performance outdoor polyurethane-wood composite board and its preparation method is of significant practical importance.

[0004] Limitations and Improvement Needs of Existing Technologies: While polyurethane materials offer numerous advantages, conventional polyurethane composite panels still face challenges such as poor weather resistance and susceptibility to aging when used outdoors. Some polyurethane composite panels using fiberglass or similar reinforcing fibers also suffer from high density and high energy consumption during production. Therefore, there is a need to develop a new type of outdoor panel that leverages the advantages of both polyurethane and wood while overcoming the shortcomings of existing materials, thereby improving the panel's service life and mechanical properties outdoors.

[0005] Purpose of the invention: The purpose of this invention is to provide a formula for an outdoor polyurethane wood composite board with a long service life; another purpose of this invention is to provide an outdoor polyurethane wood composite board with a long service life and its preparation method.

[0006] Technical solution: In view of the shortcomings of the existing technology, the purpose of this invention is to provide an outdoor polyurethane wood composite board with a long service life and its preparation method, which can solve the existing problems.

[0007] To achieve the above objectives, the technical solution of the present invention is as follows:

[0008] This invention is achieved through the following technical solution: a long-life outdoor polyurethane wood composite board, comprising a main layer and a reinforcing layer, wherein the main layer is a structure composed of polyurethane resin and modified wood particles; the modified wood particles are wood particles treated with a composite modifier containing nano-silica, silane coupling agent, hexaethyl pyrosilicon, and copper azole preservatives.

[0009] Preferably, the polyurethane resin is prepared by mixing component A and component B; wherein, by weight, component A comprises the following components: 100 parts polyol, 0.3-2.5 parts water, 0.2-1.0 parts catalyst, 1.0-3.0 parts surfactant, 0.1-0.5 parts light stabilizer, 5-10 parts flame retardant, and 10-100 parts inorganic powder; component B is 100 parts of diphenylmethane diisocyanate or polymethylene polyphenyl isocyanate, or a combination thereof; the polyol is one of polyoxypropylene polyol or phthalic anhydride polyester polyol, with a hydroxyl value of 350-600 mg. KOH / g; the catalyst is one or a combination of triethylenediamine, dimethylbenzylamine, bismuth naphthenate, and zinc isooctanoate; the surfactant is an organosilicon, such as AK8805 from Mester or B6900 from Degussa; the light stabilizer is one or more of UV absorbers and hindered amine light stabilizers such as UV-9, UV-24, UV-531, and UV-328; the flame retardant is a phosphorus-based flame retardant such as BK-69 or FL-76 from Albemarle; and the inorganic powder is one or more of silicate cement, calcium carbonate, kaolin, and wollastonite.

[0010] Preferably, the reinforcing layer can be located at the bottom of the polyurethane wood composite board, and the reinforcing material is selected from one of polyurethane fiberglass cloth, iron strip, and polyurethane pultruded strip; the reinforcing layer can also be located in the middle of the polyurethane wood composite board, and the reinforcing material is selected from one of polyurethane fiberglass board and bamboo; the reinforcing layer can also be located at both the bottom and the middle.

[0011] The thickness of polyurethane pultruded strips, fiberglass boards, bamboo, iron strips, etc., shall not exceed 1 / 3 of that of polyurethane wood composite boards.

[0012] Preferably, the average particle size of the nano-silica is 50-100 nm.

[0013] Preferably, the main components of the copper azole preservative include copper and azoles, wherein the copper is basic copper and the azoles are one or a combination of tebuconazole and propiconazole, and the model is one of CA-B, CuAz-2, or CuAz-3.

[0014] Preferably, in the composite modifier, the mass ratio of nano-silica, silane coupling agent, hexaethyl pyrosilicon ester and copper azole preservative is (1-3):(0.5-1.5):(0.6-2.0):(0.2-0.8).

[0015] Preferably, the silane coupling agent can be one of KH550, KH560, and KH570.

[0016] A long-life outdoor polyurethane wood composite board and its preparation method include the following steps:

[0017] S1. Preparation of composite modifier solution: It is prepared by dispersing nano silica, silane coupling agent, hexaethyl pyrosilicon, and copper azole preservative in an ethanol-water mixed solvent;

[0018] S2. Wood Particle Modification Treatment: The dried wood particles are immersed in a composite modifier solution, the pH of the system is adjusted to 2-4 with glacial acetic acid, ultrasonically treated for 20-40 minutes, then drained and dried at 80-120℃ to constant weight to obtain modified wood particles;

[0019] S3. Preparation of mixture: The modified wood particles obtained in step S2 are mixed evenly with polyurethane resin A and B in a high-speed mixer to obtain the main layer mixture;

[0020] S4. Laying and molding: (1) When the reinforcing layer is at the bottom, at the bottom of the mold, lay one of the following: polyurethane fiberglass cloth, iron strip, or polyurethane pultruded strip at a preset interval on the lower layer, and then evenly spread the main layer mixture obtained in S3 into the mold; (2) When the reinforcing layer is in the middle, evenly spread the main layer mixture obtained in S3 to 1 / 3-1 / 2 of the mold height, and then lay one of the following: polyurethane fiberglass board or bamboo at a preset interval on the main layer, and finally evenly spread the main layer mixture into the mold; the reinforcing layer material can be laid horizontally, vertically, or both horizontally and vertically;

[0021] S5. Hot pressing curing: Close the mold and hot press it at a pressure of 5-6 MPa and a temperature of 50-60℃ for 20-60 minutes to allow the polyurethane to fully foam and bond and cure with the modified wood particles and reinforcing layer.

[0022] S6. Post-processing: After depressurization, the polyurethane wood composite board is obtained by cooling, trimming, and sanding.

[0023] Preferably, in step S1, the ethanol-water mixed solvent is 90% ethanol, and the volume of the solvent is 15-20 times the weight of the nano-silica.

[0024] Preferably, in step S3, the weight ratio of modified wood particles to polyurethane resin is 100:10-100.

[0025] Beneficial effects:

[0026] (1) Long outdoor service life: By pretreating the wood particles with a composite modifier, the core wood components are endowed with excellent anti-corrosion, anti-mildew and dimensional stability, which improves the weather resistance from the material source and the strength retention rate after accelerated aging (boiling water for 6 hours) is up to 90%. At the same time, copper azole preservatives are used, and the anti-mildew grade of polyurethane wood composite board can reach 0, and the weight loss rate of decay fungus test after 28 days is as low as 1.1%.

[0027] (2) Strong interfacial bonding: Silane coupling agent acts as a "molecular bridge" to improve the interfacial compatibility and bonding strength between organic (wood, resin) and inorganic (nano SiO2) materials. At the same time, the one-step hot pressing process ensures a strong chemical bond between modified wood particles and polyurethane, avoids the risk of delamination, and improves the mechanical properties of the material. Attached Figure Description

[0028] Figure 1 Example 1 shows the polyurethane fiberglass cloth reinforced polyurethane wood composite board.

[0029] Figure 2 Iron-reinforced polyurethane wood composite board prepared in Example 2.

[0030] Figure 3 Example 3 shows the polyurethane pultruded strip reinforced polyurethane wood composite board.

[0031] Figure 4 Example 4 shows the polyurethane fiberglass reinforced polyurethane wood composite board.

[0032] Figure 5 Example 5 shows the bamboo-reinforced polyurethane wood composite board prepared. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention are described clearly and completely. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0034] Example 1:

[0035] Weigh 20 kg of nano silica (average particle size 70 nm), 10.0 kg of silane coupling agent KH550, 12 kg of hexaethyl pyrosilicate, and 5.0 kg of copper azole preservative (CuAz-3) and disperse them in 350 L of 90% ethanol aqueous solution, stirring until the dispersion is uniform.

[0036] 70 kg of dried wood pellets were immersed in 350 L of the above-mentioned composite modifier solution, the pH of the system was adjusted to 3 with glacial acetic acid, ultrasonic treatment was performed for 30 minutes, then drained for 2 hours, and dried at 100 °C to constant weight to obtain modified wood pellets.

[0037] Weigh out 70 kg of modified wood particles, 35 kg of polyurethane resin A (the formulation of A is 100 parts of polyoxypropylene with a hydroxyl value of 350 mg KOH / g, 0.3-2.5 parts of water, 0.2-1.0 parts of triethylenediamine and bismuth naphthenate mixed catalyst, 1.0-3.0 parts of surfactant AK8805 from Mesode, 0.1-0.5 parts of light stabilizers UV-9 and UV-24, 5-10 parts of flame retardant BK-69 from Albemarle, and 10-100 parts of inorganic powder silicate cement and calcium carbonate), and 35 kg of B (B is 100 parts of diphenylmethane diisocyanate). Mix them evenly in a high-speed mixer to obtain the main layer mixture.

[0038] At the bottom of the mold, polyurethane fiberglass cloth is laid on the lower layer, and the above-mentioned main layer mixture is quickly and evenly spread to 85% of the mold volume.

[0039] The mold is closed, and the product is hot-pressed at a pressure of 6MPa and a temperature of 60℃ for 20 minutes.

[0040] After depressurization, cooling, trimming, and sanding, polyurethane fiberglass cloth reinforced polyurethane wood composite board is obtained.

[0041] Example 2:

[0042] Weigh out 30 kg of nano-silica (average particle size 100 nm), 15.0 kg of silane coupling agent KH560, 20 kg of hexaethyl pyrosilicate, and 8.0 kg of copper azole preservative (CuAz-2) and disperse them in 600 L of 90% ethanol aqueous solution. Stir until the dispersion is uniform to obtain a composite modifier solution.

[0043] 70 kg of dried wood pellets were immersed in 490 L of the composite modifier solution prepared above. The pH of the system was adjusted to 2 with glacial acetic acid. The pellets were ultrasonically treated for 40 minutes, drained for 2 hours, and dried at 120 °C to constant weight to obtain modified wood pellets.

[0044] Weigh out 70 kg of modified wood particles, 35 kg of polyurethane resin A (the formulation of A is 100 parts of phthalic anhydride polyester polyol with a hydroxyl value of 600 mg KOH / g, 0.3-2.5 parts of water, 0.2-1.0 parts of dimethyl benzylamine and zinc isooctanoate mixed catalyst, 1.0-3.0 parts of surfactant Degussa B6900, 0.1-0.5 parts of light stabilizers UV-531 and UV-328, 5-10 parts of flame retardant FL-76, and 10-100 parts of inorganic powder kaolin and wollastonite), and 35 kg of B (B is 100 parts of polymethylene polyphenyl isocyanate). Mix them evenly in a high-speed mixer to obtain the main layer mixture.

[0045] At the bottom of the mold, lay iron bars (not exceeding 1 / 10 of the finished plate thickness) at certain intervals in the same direction on the lower layer, and quickly spread the above-mentioned main layer mixture evenly to 85% of the mold volume.

[0046] Close the mold and hot press it at a pressure of 5-6 MPa and a temperature of 50-60℃ for 60 minutes.

[0047] After depressurization, cooling, trimming, and sanding, iron-reinforced polyurethane wood composite boards are obtained.

[0048] Example 3:

[0049] Weigh 10 kg of nano-silica (average particle size 50 nm), 5.0 kg of silane coupling agent KH570, 6.0 kg of hexaethyl pyrosilicate, and 2.0 kg of copper azole preservative (CA-B) and disperse them in 150 L of 90% ethanol aqueous solution, stirring until the dispersion is uniform.

[0050] 35 kg of dried wood pellets were immersed in 105 L of the above-mentioned composite modifier solution, the pH of the system was adjusted to 4 with glacial acetic acid, ultrasonic treatment was performed for 20 minutes, then drained for 2 hours, and dried at 100 °C to constant weight to obtain modified wood pellets.

[0051] Weigh out 35 kg of modified wood particles, 5 kg of polyurethane resin A (the formulation of A is 100 parts of polyoxypropylene with a hydroxyl value of 350 mg KOH / g, 0.3-2.5 parts of water, 0.2-1.0 parts of triethylenediamine and bismuth naphthenate mixed catalyst, 1.0-3.0 parts of surfactant AK8805 from Mesode, 0.1-0.5 parts of light stabilizers UV-9 and UV-24, 5-10 parts of flame retardant BK-69 from Albemarle, 10-100 parts of inorganic powder silicate cement and calcium carbonate), and 5 kg of B (B is 100 parts of diphenylmethane diisocyanate). Mix them evenly in a high-speed mixer to obtain the main layer mixture.

[0052] At the bottom of the mold, polyurethane pultruded strips (not exceeding 1 / 5 of the finished board thickness) are laid in the lower layer at certain intervals in the same direction, and the above-mentioned main layer mixture is quickly spread evenly to 85% of the mold volume.

[0053] The mold is closed, and the product is hot-pressed at a pressure of 6MPa and a temperature of 60℃ for 20 minutes.

[0054] After depressurization, cooling, trimming, and sanding, polyurethane pultruded strip reinforced polyurethane wood composite board is obtained.

[0055] Example 4:

[0056] The preparation of the main layer mixture is the same as in Example 1.

[0057] At the bottom of the mold, spread the main layer mixture evenly to 1 / 3-1 / 2 of the mold height, then lay polyurethane fiberglass boards (not exceeding 1 / 5 of the finished board thickness) in the same direction at certain intervals on the lower layer, and finally use the main layer mixture to evenly spread the mold to 85% of the mold volume; the reinforcing layer material can be placed horizontally, vertically, or both.

[0058] Close the mold and hot press it at a pressure of 5-6 MPa and a temperature of 50-60℃ for 40 minutes.

[0059] After depressurization, cooling, trimming, and sanding, polyurethane fiberglass reinforced polyurethane wood composite board is obtained.

[0060] Example 5:

[0061] The difference from Example 4 is that the reinforcing layer material is bamboo, which is sheet-shaped and its thickness does not exceed 1 / 6 of the finished board thickness. A bamboo-reinforced polyurethane wood composite board is thus prepared.

[0062] Comparative Example 1:

[0063] Weigh 20 kg of nano silica (average particle size 70 nm), 12 kg of hexaethyl pyrosilicate, and 5.0 kg of copper azole preservative (CuAz-3) and disperse them in 350 L of 90% ethanol aqueous solution, stirring until the dispersion is uniform.

[0064] 70 kg of dried wood pellets were immersed in 350 L of the above-mentioned composite modifier solution, the pH of the system was adjusted to 3 with glacial acetic acid, ultrasonic treatment was performed for 30 minutes, then drained for 2 hours, and dried at 100 °C to constant weight to obtain modified wood pellets.

[0065] Weigh out 70 kg of modified wood particles, 35 kg of polyurethane resin A (the formulation of A is 100 parts of polyoxypropylene with a hydroxyl value of 350 mg KOH / g, 0.3-2.5 parts of water, 0.2-1.0 parts of triethylenediamine and bismuth naphthenate mixed catalyst, 1.0-3.0 parts of surfactant AK8805 from Mesode, 0.1-0.5 parts of light stabilizers UV-9 and UV-24, 5-10 parts of flame retardant BK-69 from Albemarle, and 10-100 parts of inorganic powder silicate cement and calcium carbonate), and 35 kg of B (B is 100 parts of diphenylmethane diisocyanate). Mix them evenly in a high-speed mixer to obtain the main layer mixture.

[0066] At the bottom of the mold, polyurethane fiberglass cloth is laid on the lower layer, and the above-mentioned main layer mixture is quickly and evenly spread to 85% of the mold volume.

[0067] The mold is closed, and the product is hot-pressed at a pressure of 6MPa and a temperature of 60℃ for 20 minutes.

[0068] After depressurization, cooling, trimming, and sanding, polyurethane fiberglass cloth reinforced polyurethane wood composite board 1 is obtained.

[0069] Comparative Example 2:

[0070] Weigh out 10.0 kg of silane coupling agent KH550, 12 kg of hexaethyl pyrosilicon, and 5.0 kg of copper azole preservative (CuAz-3) and disperse them in 350 L of 90% ethanol aqueous solution, stirring until the dispersion is uniform.

[0071] 70 kg of dried wood pellets were immersed in 350 L of the above-mentioned composite modifier solution, the pH of the system was adjusted to 3 with glacial acetic acid, ultrasonic treatment was performed for 30 minutes, then drained for 2 hours, and dried at 100 °C to constant weight to obtain modified wood pellets.

[0072] Weigh out 70 kg of modified wood particles, 35 kg of polyurethane resin A (the formulation of A is 100 parts of polyoxypropylene with a hydroxyl value of 350 mg KOH / g, 0.3-2.5 parts of water, 0.2-1.0 parts of triethylenediamine and bismuth naphthenate mixed catalyst, 1.0-3.0 parts of surfactant AK8805 from Mesode, 0.1-0.5 parts of light stabilizers UV-9 and UV-24, 5-10 parts of flame retardant BK-69 from Albemarle, and 10-100 parts of inorganic powder silicate cement and calcium carbonate), and 35 kg of B (B is 100 parts of diphenylmethane diisocyanate). Mix them evenly in a high-speed mixer to obtain the main layer mixture.

[0073] At the bottom of the mold, polyurethane fiberglass cloth is laid on the lower layer, and the above-mentioned main layer mixture is quickly and evenly spread to 85% of the mold volume.

[0074] The mold is closed, and the product is hot-pressed at a pressure of 6MPa and a temperature of 60℃ for 20 minutes.

[0075] After depressurization, cooling, trimming, and sanding, polyurethane fiberglass cloth reinforced polyurethane wood composite board 2 is obtained.

[0076] Comparative Example 3:

[0077] Weigh 20 kg of nano-silica (average particle size 70 nm), 10.0 kg of silane coupling agent KH550, and 12 kg of hexaethyl pyrosilicate and disperse them in 350 L of 90% ethanol aqueous solution, and stir until uniformly dispersed.

[0078] 70 kg of dried wood pellets were immersed in 350 L of the above-mentioned composite modifier solution, the pH of the system was adjusted to 3 with glacial acetic acid, ultrasonic treatment was performed for 30 minutes, then drained for 2 hours, and dried at 100 °C to constant weight to obtain modified wood pellets.

[0079] Weigh out 70 kg of modified wood particles, 35 kg of polyurethane resin A (the formulation of A is 100 parts of polyoxypropylene with a hydroxyl value of 350 mg KOH / g, 0.3-2.5 parts of water, 0.2-1.0 parts of triethylenediamine and bismuth naphthenate mixed catalyst, 1.0-3.0 parts of surfactant AK8805 from Mesode, 0.1-0.5 parts of light stabilizers UV-9 and UV-24, 5-10 parts of flame retardant BK-69 from Albemarle, and 10-100 parts of inorganic powder silicate cement and calcium carbonate), and 35 kg of B (B is 100 parts of diphenylmethane diisocyanate). Mix them evenly in a high-speed mixer to obtain the main layer mixture.

[0080] At the bottom of the mold, polyurethane fiberglass cloth is laid on the lower layer, and the above-mentioned main layer mixture is quickly and evenly spread to 85% of the mold volume.

[0081] The mold is closed, and the product is hot-pressed at a pressure of 6MPa and a temperature of 60℃ for 20 minutes.

[0082] After depressurization, cooling, trimming, and sanding, polyurethane fiberglass cloth reinforced polyurethane wood composite board 3 is obtained.

[0083] Performance testing:

[0084] Performance tests were conducted on each embodiment and comparative example: flexural strength was tested according to GB / T1449; compressive strength was tested according to GJB1585A; mildew resistance (28 days) was tested according to GB / T18261; and corrosion resistance (28-day decay fungus test weight loss %) was tested according to GB / T 13942.1. After boiling in water for 6 hours, the strength retention rate of each sample was tested. The results are shown in the table below.

[0085]

[0086] Comparing Example 1 and Comparative Example 1, it can be seen that without the addition of silane coupling agent, the flexural strength of polyurethane wood composite board decreases by 12.6%. Comparing Example 1 and Comparative Example 2, it can be seen that without the addition of nano-silica, the flexural strength of polyurethane wood composite board decreases by 37%, and the strength retention rate decreases by 47.1% after accelerated aging (boiling in water for 6 hours). This indicates that silane coupling agent and nano-silica can significantly improve the strength of polyurethane wood composite board, and nano-silica can also greatly improve the moisture-proof performance of the reinforcing agent. Silane coupling agent, acting as a "molecular bridge," can improve the interfacial compatibility and bonding strength between organic (wood, resin) and inorganic (nano-SiO2) materials, thereby achieving the above-mentioned effects.

[0087] As can be seen from the comparison between Examples 1-5 and Comparative Example 3, the addition of copper azole preservatives resulted in polyurethane wood composite boards with a mildew resistance rating of 0 and a weight loss rate as low as 1.1% in the 28-day decay fungus test. This indicates that copper azole preservatives can provide highly efficient and environmentally friendly anti-corrosion and anti-mildew properties in polyurethane wood composite boards.

[0088] By employing the synergistic effect of nano-silica, silane coupling agent, and copper azole preservative, a polyurethane wood composite board with a long service life and suitable for outdoor use is prepared.

[0089] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A long-life outdoor polyurethane wood composite board, characterized in that: It includes a main layer, a reinforcing layer and / or a protective layer, wherein the main layer is a structure composed of polyurethane resin and modified wood particles; the modified wood particles are wood particles treated with a composite modifier containing nano-silica, silane coupling agent, hexaethyl pyrosilicon, and copper azole preservatives.

2. The polyurethane wood composite board according to claim 1, characterized in that: The polyurethane resin is prepared by mixing component A and component B. Component A, by weight, comprises the following components: 100 parts polyol, 0.3-2.5 parts water, 0.2-1.0 parts catalyst, 1.0-3.0 parts surfactant, 0.1-0.5 parts light stabilizer, 5-10 parts flame retardant, and 10-100 parts inorganic powder. Component B is 100 parts of one or a combination of diphenylmethane diisocyanate and polymethylene polyphenyl isocyanate. The polyol is one of polyoxypropylene polyol or phthalic anhydride polyester polyol, with a hydroxyl value of 350-600 mg KOH / g.

3. The polyurethane wood composite board according to claim 1, characterized in that: The reinforcing layer may be located at the bottom of the polyurethane wood composite board, and the reinforcing material may be selected from polyurethane fiberglass cloth, iron strip, or polyurethane pultruded strip; the reinforcing layer may also be located in the middle of the polyurethane wood composite board, and the reinforcing material may be selected from polyurethane fiberglass board or bamboo; the reinforcing layer may also be located at both the bottom and middle of the polyurethane wood composite board.

4. The polyurethane wood composite board according to claim 1, characterized in that: In the composite modifier, the average particle size of nano-silica is 50-100 nm.

5. The polyurethane wood composite board according to claim 1, characterized in that: In the composite modifier, the main components of the copper azole preservative include copper and azoles, wherein the copper is basic copper and the azoles are one or a combination of tebuconazole and propiconazole.

6. The polyurethane wood composite board according to claim 1, characterized in that: In the composite modifier, the mass ratio of nano-silica, silane coupling agent, hexaethyl pyrosilicate, and copper azole preservative is (1-3):(0.5-1.5):(0.6-2.0):(0.2-0.8).

7. A method for preparing polyurethane wood composite panels as described in any one of claims 1-5, characterized in that, Includes the following steps: S1. Preparation of composite modifier solution: It is prepared by dispersing nano silica, silane coupling agent, hexaethyl pyrosilicon, and copper azole preservative in an ethanol-water mixed solvent; S2. Wood Particle Modification Treatment: The dried wood particles are immersed in a composite modifier solution, the pH of the system is adjusted to 2-4 with glacial acetic acid, ultrasonically treated for 20-40 minutes, then drained and dried at 80-120℃ to constant weight to obtain modified wood particles; S3. Preparation of mixture: The modified wood particles obtained in step S2 are mixed evenly with polyurethane resin A and B in a high-speed mixer to obtain the main layer mixture; S4. Laying and molding: (1) When the reinforcing layer is at the bottom, at the bottom of the mold, lay one of the following: polyurethane fiberglass cloth, iron strip, or polyurethane pultruded strip at a preset interval on the lower layer, and then evenly spread the main layer mixture obtained in S3 into the mold; (2) When the reinforcing layer is in the middle, evenly spread the main layer mixture obtained in S3 to 1 / 3-1 / 2 of the mold height, and then lay one of the following: polyurethane fiberglass board or bamboo at a preset interval on the main layer, and finally evenly spread the main layer mixture into the mold; the reinforcing layer material can be laid horizontally, vertically, or both horizontally and vertically; S5. Hot pressing curing: Close the mold and hot press it at a pressure of 5-6 MPa and a temperature of 50-60℃ for 20-60 minutes to allow the polyurethane to fully foam and bond and cure with the modified wood particles and reinforcing layer. S6. Post-processing: After depressurization, the polyurethane wood composite board is obtained by cooling, trimming, and sanding.

8. The method for preparing outdoor polyurethane wood composite panels according to claim 6, characterized in that: In step S1, the ethanol-water mixed solvent is 90% ethanol, and the volume of the solvent is 15-20 times the weight of the nano-silica.

9. The method for preparing outdoor polyurethane wood composite panels according to claim 6, characterized in that: In step S3, the weight ratio of modified wood particles to polyurethane resin is 100:10-100.

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