Anti-cracking and moisture-resistant low-swelling and shrinking solid wood floor for floor heating and preparation method thereof

Abstract

The application discloses a kind of anti-cracking moisture-proof low swelling and shrinking solid wood floor for floor heating and a preparation method thereof, the present application mainly uses poplar as base material, after pretreatment by gamma rays, the impregnation solution containing silane coupling agent, nano-silicon dioxide and hydroxyl acrylate is used for hydroxyl modification, forming honeycomb-pore composite structure, improving impermeability;Aluminum nitride-bamboo fiber directional composite layer is used as sandwich layer, and graphene-aramid reinforced cloth is bidirectionally reinforced, to build superimposed heat conduction network, while enhancing crack resistance;Through four-stage drying, water content and stress are precisely controlled, and electrostatic field is used to assist the directional distribution of nanoparticles, to provide stable base material for forming;Nano zinc oxide modified hydroxyl acrylate is used as primer, nano-montmorillonite modified hydroxyl polysiloxane is used as sealant, and UV epoxy-silane is used as topcoat, to form an integrated barrier.The wood board prepared by the present application realizes the functional superposition from internal modification to surface protection, realizes the integrated protection of impermeability, crack resistance, moisture resistance and wear resistance.

Description

Technical Field

[0001] This invention relates to the field of underfloor heating equipment technology, specifically to a crack-resistant, moisture-resistant, low-expansion / shrinkage solid wood flooring for underfloor heating and its preparation method. Background Technology

[0002] Solid wood flooring has become a mainstream choice due to its natural texture and comfortable feel underfoot. However, its insufficient crack resistance, moisture resistance, and low expansion and contraction performance become apparent under conditions such as long-term underfloor heating at 40-60℃, extreme temperature changes from -15℃ to 65℃, and alternating dry and humid environments.

[0003] Existing manufacturing processes for wood panels used in underfloor heating suffer from multiple structural defects and challenges. The choice of substrate presents a dilemma: high-end processes rely on hardwoods aged over 20 years, accounting for over 60% of raw material costs and being scarce resources, thus failing to meet green development requirements; while fast-growing woods, due to their low density and open pores, exhibit a radial shrinkage rate of 5%-7% without modification, resulting in a cracking rate exceeding 15% under underfloor heating conditions. More importantly, neither hardwoods nor fast-growing woods undergo targeted modification for the underfloor heating environment; their cell wall hydroxyl content is low and disordered, leading to a reaction rate of less than 50% for subsequent modifiers, and they remain prone to water absorption and deformation under high temperature and humidity.

[0004] The fragmented operation of the pretreatment process exacerbates performance risks. The degreasing stage often uses a single vacuum steam treatment, which can only remove 60%-70% of the surface resin. Residual resin inside volatilizes at high temperatures, easily forming oil spots and clogging pores, affecting the impregnation effect. Furthermore, after degreasing, the substrate is exposed to atmospheric pressure, increasing surface moisture content and drying energy consumption. Further, impregnation modification is mostly carried out under atmospheric or simple negative pressure, lacking a design adapted to the wood's pore structure. Nanoparticles easily aggregate, offering limited improvement in impermeability, and the adsorption to the substrate is only physical, resulting in a subsequent loss rate exceeding 30%. Secondly, the two-stage hot air process in the drying stage is crude, failing to match the differences in impregnation liquid content. Excessive dehydration rate leads to cracking of the impregnated layer, resulting in a large deviation in final moisture content, poor matching with the equilibrium moisture content of the underfloor heating environment, and excessively high residual internal stress, with an expansion of up to 2.1 mm per meter.

[0005] This invention represents a breakthrough in the process, using modified fast-growing wood and composite structures to reduce costs and improve stability. Through closed-loop parameter control and an integrated protection system, a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating is prepared, thus addressing a core pain point in the industry. Summary of the Invention

[0006] The purpose of this invention is to provide a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating and its preparation method, so as to solve the problems existing in the prior art.

[0007] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating and its preparation method, comprising the following preparation steps: (1) Select poplar wood as the main material and cut it into timber squares according to the standard; (2) Place the timber obtained in step (1) into a γ-ray irradiation device, adjust the parameters, and let it stand after irradiation to obtain γ-ray modified timber; (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate, heat up, turn on the ultrasound, introduce ethanol and water vapor, and degrease; switch to plasma treatment mode, introduce argon gas, clean, and obtain degreased wood. (4) Weigh out silane coupling agent, nano silica, and hydroxy acrylate in proportion, add deionized water and pH adjuster to the container, adjust the pH, add silane coupling agent and stir, then add hydroxy acrylate and stir evenly, then add nano silica, ultrasonically disperse, let stand, and obtain modified impregnation solution. (5) Place the degreased wood obtained in step (3) into an impregnation tank, vacuum it, add the modified impregnation liquid, pressurize it, heat it, impregnate it, and dry it to obtain impregnated modified wood. (6) Place the impregnated modified timber into a multi-functional drying tank, evacuate, control the humidity, adjust the microwave power and electrostatic field strength, and dry to obtain a section of dried timber. (7) Continue to heat up, adjust humidity, increase pressure, adjust microwave power and electrostatic field strength, and dry to obtain two sections of dried wood; (8) Cooling, depressurizing, controlling humidity, adjusting microwave power and electrostatic field strength to obtain three sections of dried wood. (9) Transfer the three sections of dried timber obtained in step (8) into a drying oven, adjust the parameters, and dry to obtain modified impregnated dried timber; (10) Coat the back of the modified impregnated and dried wood with water-based adhesive, place it in a hot press composite machine, composite aluminum nitride-bamboo fiber oriented composite layer, adjust the parameters, and obtain aluminum nitride-bamboo fiber oriented composite layer modified wood; (11) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood square obtained in step (10) with water-based adhesive, place it in a hot press composite machine, composite graphene-aramid reinforcing cloth, and adjust the parameters to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood square. (12) The composite layer modified wood obtained in step (11) is processed with tenons and mortises, coated with sealant, primer and topcoat, cured, dried and left to stand to obtain the crack-resistant, moisture-resistant and low-expansion-shrinkage solid wood flooring for underfloor heating.

[0008] Furthermore, preferably, the poplar wood used in step (1) is 12-year-old poplar wood; the density is 0.65-0.70 g / cm³. 3 The initial moisture content is 18-20%; the standard size of the timber is 2000mm×150mm×50mm. Preferably, in step (4), the mass ratio of silane coupling agent, nano-silica, and hydroxyacrylate is 8-10:12-14:5-6; the pH range is 4.9-5.4; the silane coupling agent is KH-570; and the pH adjuster is analytical grade glacial acetic acid. Preferably, in step (6), the temperature is 50-60℃, humidity is 60-70%, vacuum pressure is -0.06~-0.08Mpa, microwave power is 180-220W, electric field strength is 45-55kV / m, and drying time is 18-20h; in step (7), the temperature is 65-75℃, humidity is 40-50%, vacuum pressure is -0.08~-0.09Mpa, microwave power is 330-360W, and electric field strength is 180-220W. The strength is 75-85kV / m, and the drying time is 24-28h; the temperature of step (8) is 60-70℃, the humidity is 48-55%, the vacuum pressure is -0.075~-0.085Mpa, the microwave power is 150-200W, the electric field strength is 50-70kV / m, and the drying time is 18-22h; the temperature of step (9) is 50-54℃, the humidity is 55-60%, and the drying time is 14-18h. Preferably, in step (12), the primer is nano-zinc oxide modified hydroxy acrylate with a thickness of 8-10 μm; the sealant is nano-montmorillonite modified hydroxy polysiloxane with a thickness of 0.15-0.20 mm; and the topcoat is UV epoxy-silane with a thickness of 25-30 μm. Further, in step (2), the γ-ray irradiation device is a cobalt-60 γ-ray irradiation device; the irradiation dose is 48-52 kGy; the dose rate is 1.6-2.4 kGy / h; the temperature is 25-30℃; and the humidity is 40%-50%.

[0009] Furthermore, in step (5), the method of placing the timber is to place it in layers with intervals; the spacing between the timbers is 30-35mm, and a 5mm thick breathable steel mesh is laid between the layers.

[0010] Furthermore, the aluminum nitride-bamboo fiber oriented composite layer in step (10) is prepared by the following method: (1) Take aluminum nitride whiskers, ultrasonically wash and dry them, add resin and curing agent, mix and stir evenly, and ultrasonically disperse them to obtain modified aluminum nitride whiskers; (2) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent modified KH-570, dry them, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers longitudinally with the fibers, hot press, and cure them twice to obtain an aluminum nitride-bamboo fiber oriented composite layer. The aluminum nitride whiskers have an aspect ratio of 9-12:1; the resin is a water-based epoxy resin, and the curing agent is polyamide, with a mass ratio of 3-4:1. The graphene-aramid reinforced fabric in step (11) is prepared by the following method: (1) Take a single layer of graphene, add NMP, and ultrasonically disperse to prepare a graphene dispersion; (2) Take aramid fabric, immerse it in graphene dispersion, apply pressure with rollers, spray adhesive, hot press, and let it stand to obtain a graphene-aramid reinforced fabric composite layer. The graphene sheet diameter is 5-10 μm; the graphene dispersion has a mass percentage of 0.5%; and the binder is waterborne polyurethane with a solid content of 40-45%.

[0011] Furthermore, the water-based adhesive in steps (11) and (12) is a water-based polyurethane adhesive.

[0012] Furthermore, the nano-zinc oxide modified hydroxy acrylate is prepared by the following method: (1) Add nano zinc oxide, hydroxy acrylate, deionized water and dispersant to a container, stir and sonicate to obtain nano zinc oxide modified hydroxy acrylate; The mass ratio of the nano zinc oxide, hydroxy acrylate, and dispersant is 2:100:0.5; The nano-montmorillonite-modified hydroxyl polysiloxane was prepared by the following method: (1) Mix nano-montmorillonite, KH-550 and anhydrous ethanol, stir and dry to obtain pretreated nano-montmorillonite; (2) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane, stir, sonicate, and let stand to obtain nano-montmorillonite modified hydroxyl polysiloxane. The nano-montmorillonite, KH-550, and hydroxyl polysiloxane are present in a weight ratio of 1-3:1:100.

[0013] Furthermore, a type of crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating is provided, wherein the solid wood flooring is prepared by the method described above.

[0014] Compared with the prior art, the beneficial effects achieved by the present invention are: 1) This invention uses 12-year-old poplar wood as the main substrate. Pretreatment with gamma rays improves pore closure rate and reduces radial shrinkage. Simultaneously, it breaks some ether bonds in the lignin molecules, exposing more hydroxyl sites for subsequent hydroxyl modification. This invention uses a silane coupling agent, nano-silica, and hydroxyl acrylate to prepare an impregnation solution for hydroxyl modification of the wood board. The silane coupling agent hydrolyzes under weakly acidic conditions to form stable Si-OC covalent bonds. The hydroxyl acrylate in the impregnation solution forms hydrogen bonds with the remaining hydroxyl groups in the substrate, strengthening the interfacial bonding. Furthermore, microscopically, the hydroxyl-modified poplar wood forms a honeycomb-pore composite structure, achieving precise size matching with the nano-silica in the impregnation solution. The nanoparticles first fill the micropores, forming a nanoscale impermeability barrier. Then, through the bridging effect of the silane coupling agent, a continuous inorganic-organic composite layer is formed with the honeycomb structure wall. This synergistic structure reduces water absorption and improves impermeability, laying a microscopic foundation for crack resistance and low shrinkage under underfloor heating conditions.

[0015] 2) This invention uses an aluminum nitride-bamboo fiber oriented composite layer as the core layer, forming a bidirectional reinforcement with graphene-aramid reinforcing fabric. The longitudinal bamboo fiber bundles are composited with the transverse aluminum nitride whisker network. The bamboo fiber bundles are arranged along the length of the floor to form the longitudinal main heat conduction channel; the transverse aluminum nitride whisker network fills the gaps between the bamboo fiber bundles to construct the transverse secondary heat conduction channel. The two work together to improve the thermal conductivity of the core layer. The graphene-aramid reinforcing fabric, which is subsequently composited, has graphene sheets that are bonded to the aluminum nitride whiskers of the core layer through van der Waals forces, forming a heat conduction relay between the core layer and the reinforcing fabric. Furthermore, the 0.8% nano-aluminum nitride added to the top coating is connected to the graphene sheets of the reinforcing fabric through coating penetration, ultimately forming a superimposed network of longitudinal heat conduction of the core layer, transverse heat conduction of the reinforcing fabric, and three-dimensional heat conduction of the top coating. The overall heat conduction efficiency is greatly improved, solving the pain points of slow heat conduction and large temperature difference in the traditional wood floor heating environment.

[0016] Furthermore, the graphene sheets in the reinforcing fabric can bridge microcracks inside the substrate. When microcracks appear in the substrate due to changes in temperature and humidity, the graphene sheets prevent crack propagation through van der Waals forces. The high tensile strength of the aramid fibers can offset the radial shrinkage stress of the wood, reducing the risk of cracking. At the same time, the bamboo fiber bundles in the sandwich layer intersect with the reinforcing fabric fibers at a 90° angle, compensating for the anisotropy of the wood, reducing the radial expansion and contraction rate of the substrate, and improving the crack resistance of the wood board.

[0017] 3) This invention designs a four-stage drying process based on the liquid content of the impregnated substrate. In the preheating and equilibration stage, the substrate is slowly dehydrated to 10-12%, with an electrostatic field promoting the migration of nanoparticles towards the cell wall. In the deep dehydration stage, internal moisture migration is accelerated to prevent cracking of the impregnated layer, and the substrate is dehydrated to 8-10%, matching the moisture content of the underfloor heating environment. In the stress release stage, drying stress is released, and the internal stress is tested to be ≤1.5MPa to ensure that the substrate does not deform during molding. In the precise equilibration stage, the moisture content is controlled. This invention controls the slow migration of moisture through temperature and humidity gradients to prevent cracking of the impregnated layer. Simultaneously, an electrostatic field assists in the directional distribution of nanoparticles in the impregnating liquid, ensuring that the moisture content after drying precisely matches the equilibrium moisture content of the underfloor heating environment, providing a stable substrate for the molding process.

[0018] 4) This invention uses hydroxyl-modified acrylate modified with nano-zinc oxide as a primer, which works synergistically with hydroxyl-modified polysiloxane sealant modified with nano-montmorillonite to form a continuous moisture barrier. The -OH groups of the primer react with the Si-OH groups of the substrate impregnation layer, and simultaneously form hydrogen bonds with the hydroxyl-modified polysiloxane in the sealant, eliminating interfacial gaps. The nano-montmorillonite in the sealant can fill the gaps in the tenon and mortise joints, forming a nanoscale sealing layer, significantly improving water resistance and sealing performance. Furthermore, the UV epoxy-silane composite coating on the topcoat forms a high-hardness coating through a cross-linking reaction, and its silane functional groups can form chemical bonds with the primer, preventing the coating from peeling off. This integrated barrier designed by the invention, which combines internal impermeability, structural crack resistance, and surface moisture resistance and wear resistance, significantly improves the performance of wood panels and greatly extends the lifespan of the flooring under underfloor heating conditions. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] To more clearly illustrate the method provided by the present invention, the following embodiments are provided in detail. The test methods for various indicators of the solid wood flooring for underfloor heating that is crack-resistant, moisture-resistant, and has low expansion and contraction are as follows: Moisture content: As specified in 3.3 of GB / T 15036.2-2018. Heat resistance dimensional stability: Complies with the requirements of 6.2 in GB / T 35913-2018. Moisture resistance dimensional stability: As specified in section 6.2 of GB / T 35913-2018. Thermal conductivity: As specified in 6.3.7 of LY / T 1700-2018. Surface crack resistance: As specified in 6.3.5 of LY / T 1700-2018. Example 1 (1) Select a density of 0.68 g / cm³ for 12 years. 3 Poplar wood with an initial moisture content of 18% is used as the main material and is cut into 2000mm×150mm×50mm squares according to standard. (2) The wood obtained in step (1) was placed into a cobalt-60 γ-ray irradiation device, the irradiation dose was adjusted to 50 kGy, the dose rate was 2.2 kGy / h, the temperature was 30℃, the humidity was 45%, and it was left to stand for 2 hours to obtain γ-ray modified wood. (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate to -0.095MPa, heat to 80℃, turn on 400W ultrasound, introduce ethanol-water vapor with a volume ratio of 1:1, and degrease for 3h; switch to plasma treatment mode, introduce 150sccm argon gas, treat with 120W power for 5min, and use 60℃ deionized water to circulate and clean for 15min to obtain degreased wood. (4) Weigh out silane coupling agent KH-570, nano silica, and hydroxy acrylate in a mass ratio of 8:12:5. Add deionized water to a container, adjust the pH to 5.2 with analytical grade glacial acetic acid, add KH-570 and stir, then add hydroxy acrylate and stir evenly. Then add nano silica, disperse by ultrasonication at 400W, and let stand for 2 hours to obtain the modified impregnation solution; (5) Place the degreased and activated wood in layers with intervals, controlling the spacing between the wood to be 30mm. Lay a 5mm thick breathable steel mesh between the layers, place them in an impregnation tank, evacuate to -0.095MPa, maintain for 30min, inject the modified impregnation liquid, pressurize to 0.2MPa, turn on 450W ultrasonic, heat to 55℃ and impregnate for 2h, take out the wood and put it into a hot air circulating oven, cure at 60℃ and 50% humidity for 1 hour, and dry to obtain impregnated modified wood; (6) Place the impregnated modified wood into a microwave-electrostatic field drying tank according to the original arrangement, heat to 55℃, 65% humidity, -0.07MPa vacuum, 200W microwave, 50kV / m electrostatic field, for 18h, to obtain a section of dried wood; (7) Heat to 70℃, 45% humidity, -0.085MPa vacuum, 350W microwave, 80kV / m electrostatic field for 24h to obtain two sections of dried wood; (8) Three sections of dried timber were obtained by cooling to 65℃, 52% humidity, -0.08MPa vacuum, 180W microwave, 60kV / m electrostatic field for 20h; (9) Transfer the three sections of dried wood obtained in step (8) to a constant temperature and humidity drying oven according to the original placement method, dry at 52°C and 56% humidity for 16 hours to obtain modified impregnated dried wood. (10) Take aluminum nitride whiskers with an aspect ratio of 10:1, ultrasonically wash and dry them, add waterborne epoxy resin and curing agent polyamide with a mass ratio of 3:1, mix and stir evenly, and ultrasonically disperse at 300W to obtain modified aluminum nitride whiskers. (11) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent KH-570, dry them at 80℃ for 30 min, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers longitudinally with the fibers, press them at 80℃ and 0.6MPa for 30 min, and then cure them at 120℃ for a second time to obtain an aluminum nitride-bamboo fiber oriented composite layer. (12) Take a single layer of graphene with a sheet diameter of 10 μm, add NMP, and disperse it by ultrasonication at 400 W to prepare a graphene dispersion with a mass percentage of 0.5%. (13) Take aramid fabric, immerse it in a 0.5% graphene dispersion, press it with rollers, spray it with a waterborne polyurethane with a solid content of 40%, press it at 80℃ and 0.6MPa for 30min, and then cure it at 120℃ to obtain a graphene-aramid reinforced fabric composite layer. (14) A water-based polyurethane adhesive was coated on the back of the modified impregnated and dried wood, and then placed in a hot press composite machine to form an aluminum nitride-bamboo fiber oriented composite layer. The composite layer was hot-pressed at 120℃ and 1.2MPa for 60s to obtain the aluminum nitride-bamboo fiber oriented composite layer modified wood. (15) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood square obtained in step (10) with water-based polyurethane adhesive, place it in a hot press composite machine, composite graphene-aramid reinforced cloth, and hot press at 110℃ and 0.9MPa for 50s to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood square. (16) Add nano zinc oxide, hydroxy acrylate and BYK-110 to a container in a mass ratio of 2:100:0.5, stir at 300r / min, sonicate at 300W for 30min to obtain nano zinc oxide modified hydroxy acrylate. (17) Mix nano-montmorillonite and KH-550 at a mass ratio of 3:1, add anhydrous ethanol, stir at 60°C for 30 min, and dry to obtain pretreated nano-montmorillonite; (18) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane at a mass ratio of 1:100, stir at 2000 r / min for 1 h, sonicate at 300 W, and let stand for 2 h to obtain nano-montmorillonite modified hydroxyl polysiloxane. (19) The composite layer modified wood obtained in step (15) is processed with tenons and mortises, coated with nano-montmorillonite modified hydroxy polysiloxane as sealant with a thickness of 0.18 mm, and cured for 24 h; then nano-zinc oxide modified hydroxy acrylate is sprayed as primer with a thickness of 9 μm and dried at 85℃ for 25 min; then commercially available UV epoxy-silane is sprayed as topcoat with a thickness of 28 μm, at 90℃ for 15 min, and then left to stand at room temperature for 48 h to obtain the crack-resistant, moisture-resistant, low-expansion and shrinkage solid wood flooring for underfloor heating.

[0021] Example 2 (1) Select a density of 0.68 g / cm³ for 12 years. 3 Poplar wood with an initial moisture content of 18% is used as the main material and is cut into 2000mm×150mm×50mm squares according to standard. (2) The wood obtained in step (1) was placed in a cobalt-60 γ-ray irradiation device, the irradiation dose was adjusted to 52 kGy, the dose rate was 2.4 kGy / h, the temperature was 30℃, the humidity was 50%, and it was left to stand for 2 hours to obtain γ-ray modified wood. (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate to -0.095MPa, heat to 80℃, turn on 400W ultrasound, introduce ethanol-water vapor with a volume ratio of 1:1, and degrease for 3h; switch to plasma treatment mode, introduce 150sccm argon gas, treat with 120W power for 5min, and use 60℃ deionized water to circulate and clean for 15min to obtain degreased wood. (4) Weigh out silane coupling agent KH-570, nano silica, and hydroxy acrylate in a mass ratio of 10:14:5. Add deionized water to a container, adjust the pH to 5.4 with analytical grade glacial acetic acid, add KH-570 and stir, then add hydroxy acrylate and stir evenly. Then add nano silica, disperse by ultrasonication at 400W, and let stand for 2 hours to obtain the modified impregnation solution; (5) Place the degreased and activated wood in layers with intervals, controlling the spacing between the wood to be 35mm. Lay a 5mm thick breathable steel mesh between the layers, place them in an impregnation tank, vacuum to -0.095MPa, maintain for 30min, inject the modified impregnation liquid, pressurize to 0.2MPa, turn on 450W ultrasonic, heat to 55℃ and impregnate for 2h, take out the wood and put it into a hot air circulating oven, cure at 60℃ and 50% humidity for 1 hour, and dry to obtain impregnated modified wood; (6) Place the impregnated modified wood into a microwave-electrostatic field drying tank according to the original arrangement, heat to 60℃, 70% humidity, -0.08MPa vacuum, 220W microwave, 55kV / m electrostatic field, for 18h, to obtain a section of dried wood; (7) Heat to 75℃, 50% humidity, -0.09MPa vacuum, 360W microwave, 85kV / m electrostatic field for 24h to obtain two sections of dried wood; (8) Three sections of dried wood were obtained by cooling to 70℃, 55% humidity, -0.075MPa vacuum, 200W microwave, 70kV / m electrostatic field for 20h; (9) Transfer the three sections of dried wood obtained in step (8) to a constant temperature and humidity drying oven according to the original placement method, dry at 54℃ and 60% humidity for 16 hours to obtain modified impregnated dried wood. (10) Take aluminum nitride whiskers with an aspect ratio of 10:1, ultrasonically wash and dry them, add waterborne epoxy resin and curing agent polyamide with a mass ratio of 3:1, mix and stir evenly, and ultrasonically disperse at 300W to obtain modified aluminum nitride whiskers. (11) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent KH-570, dry them at 80℃ for 30 min, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers longitudinally with the fibers, press them at 80℃ and 0.6MPa for 30 min, and then cure them at 120℃ for a second time to obtain an aluminum nitride-bamboo fiber oriented composite layer. (12) Take a single layer of graphene with a sheet diameter of 10 μm, add NMP, and disperse it by ultrasonication at 400 W to prepare a graphene dispersion with a mass percentage of 0.5%. (13) Take aramid fabric, immerse it in a 0.5% graphene dispersion, press it with rollers, spray it with a waterborne polyurethane with a solid content of 40%, press it at 80℃ and 0.6MPa for 30min, and then cure it at 120℃ to obtain a graphene-aramid reinforced fabric composite layer. (14) A water-based polyurethane adhesive was coated on the back of the modified impregnated and dried wood, and then placed in a hot press composite machine to form an aluminum nitride-bamboo fiber oriented composite layer. The composite layer was hot-pressed at 120℃ and 1.2MPa for 60s to obtain the aluminum nitride-bamboo fiber oriented composite layer modified wood. (15) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood square obtained in step (10) with water-based polyurethane adhesive, place it in a hot press composite machine, composite graphene-aramid reinforced cloth, and hot press at 110℃ and 0.9MPa for 50s to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood square. (16) Add nano zinc oxide, hydroxy acrylate and BYK-110 to a container in a mass ratio of 2:100:0.5, stir at 300r / min, sonicate at 300W for 30min to obtain nano zinc oxide modified hydroxy acrylate. (17) Mix nano-montmorillonite and KH-550 at a mass ratio of 3:1, add anhydrous ethanol, stir at 60°C for 30 min, and dry to obtain pretreated nano-montmorillonite; (18) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane at a mass ratio of 1:100, stir at 2000 r / min for 1 h, sonicate at 300 W, and let stand for 2 h to obtain nano-montmorillonite modified hydroxyl polysiloxane. (19) The composite layer modified wood obtained in step (15) is processed with tenons and mortises, coated with nano-montmorillonite modified hydroxy polysiloxane as sealant with a thickness of 0.20 mm, and cured for 24 h; then nano-zinc oxide modified hydroxy acrylate is sprayed as primer with a thickness of 10 μm and dried at 85℃ for 25 min; then commercially available UV epoxy-silane is sprayed as topcoat with a thickness of 30 μm, at 90℃ for 15 min, and then left to stand at room temperature for 48 h to obtain the crack-resistant, moisture-resistant, low-expansion and shrinkage solid wood flooring for underfloor heating.

[0022] Example 3 (1) Select a density of 0.68 g / cm³ for 12 years. 3 Poplar wood with an initial moisture content of 18% is used as the main material and is cut into 2000mm×150mm×50mm squares according to standard. (2) The wood obtained in step (1) was placed into a cobalt-60 γ-ray irradiation device, the irradiation dose was adjusted to 48 kGy, the dose rate was 1.6 kGy / h, the temperature was 25℃, the humidity was 40%, and it was left to stand for 2 hours to obtain γ-ray modified wood. (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate to -0.095MPa, heat to 80℃, turn on 400W ultrasound, introduce ethanol-water vapor with a volume ratio of 1:1, and degrease for 3h; switch to plasma treatment mode, introduce 150sccm argon gas, treat with 120W power for 5min, and use 60℃ deionized water to circulate and clean for 15min to obtain degreased wood. (4) Weigh out silane coupling agent KH-570, nano silica, and hydroxy acrylate in a mass ratio of 8:13:6. Add deionized water to a container, adjust the pH to 4.9 with analytical grade glacial acetic acid, add KH-570 and stir, then add hydroxy acrylate and stir evenly. Then add nano silica, disperse by ultrasonication at 400W, and let stand for 2 hours to obtain the modified impregnation solution; (5) Place the degreased and activated wood in layers with intervals, controlling the spacing between the wood to be 35mm. Lay a 5mm thick breathable steel mesh between the layers, place them in an impregnation tank, vacuum to -0.095MPa, maintain for 30min, inject the modified impregnation liquid, pressurize to 0.2MPa, turn on 450W ultrasonic, heat to 55℃ and impregnate for 2h, take out the wood and put it into a hot air circulating oven, cure at 60℃ and 50% humidity for 1 hour, and dry to obtain impregnated modified wood; (6) Place the impregnated modified wood into a microwave-electrostatic field drying tank according to the original arrangement, heat to 50℃, 60% humidity, -0.06MPa vacuum, 180W microwave, 45kV / m electrostatic field, for 18h, to obtain a section of dried wood; (7) Heat to 65℃, 40% humidity, -0.08MPa vacuum, 330W microwave, 75kV / m electrostatic field for 24h to obtain two sections of dried wood; (8) Three sections of dried wood were obtained by cooling to 60℃, 48% humidity, -0.075MPa vacuum, 150W microwave, 50kV / m electrostatic field for 20h; (9) Transfer the three sections of dried wood obtained in step (8) to a constant temperature and humidity drying oven according to the original placement method, dry at 50°C and 55% humidity for 16 hours to obtain modified impregnated dried wood. (10) Take aluminum nitride whiskers with an aspect ratio of 10:1, ultrasonically wash and dry them, add waterborne epoxy resin and curing agent polyamide with a mass ratio of 3:1, mix and stir evenly, and ultrasonically disperse at 300W to obtain modified aluminum nitride whiskers. (11) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent KH-570, dry them at 80℃ for 30 min, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers longitudinally with the fibers, press them at 80℃ and 0.6MPa for 30 min, and then cure them at 120℃ for a second time to obtain an aluminum nitride-bamboo fiber oriented composite layer. (12) Take a single layer of graphene with a sheet diameter of 10 μm, add NMP, and disperse it by ultrasonication at 400 W to prepare a graphene dispersion with a mass percentage of 0.5%. (13) Take aramid fabric, immerse it in a 0.5% graphene dispersion, press it with rollers, spray it with a waterborne polyurethane with a solid content of 40%, press it at 80℃ and 0.6MPa for 30min, and then cure it at 120℃ to obtain a graphene-aramid reinforced fabric composite layer. (14) A water-based polyurethane adhesive was coated on the back of the modified impregnated and dried wood, and then placed in a hot press composite machine to form an aluminum nitride-bamboo fiber oriented composite layer. The composite layer was hot-pressed at 120℃ and 1.2MPa for 60s to obtain the aluminum nitride-bamboo fiber oriented composite layer modified wood. (15) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood square obtained in step (10) with water-based polyurethane adhesive, place it in a hot press composite machine, composite graphene-aramid reinforced cloth, and hot press at 110℃ and 0.9MPa for 50s to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood square. (16) Add nano zinc oxide, hydroxy acrylate and BYK-110 to a container in a mass ratio of 2:100:0.5, stir at 300r / min, sonicate at 300W for 30min to obtain nano zinc oxide modified hydroxy acrylate. (17) Mix nano-montmorillonite and KH-550 at a mass ratio of 3:1, add anhydrous ethanol, stir at 60°C for 30 min, and dry to obtain pretreated nano-montmorillonite; (18) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane at a mass ratio of 1:100, stir at 2000 r / min for 1 h, sonicate at 300 W, and let stand for 2 h to obtain nano-montmorillonite modified hydroxyl polysiloxane. (19) The composite layer modified wood obtained in step (15) is processed with tenons and mortises, coated with nano-montmorillonite modified hydroxy polysiloxane as sealant with a thickness of 0.15 mm, and cured for 24 h; then nano-zinc oxide modified hydroxy acrylate is sprayed as primer with a thickness of 8 μm and dried at 85℃ for 25 min; then commercially available UV epoxy-silane is sprayed as topcoat with a thickness of 25 μm, at 90℃ for 15 min, and then left to stand at room temperature for 48 h to obtain the crack-resistant, moisture-resistant, low-expansion and shrinkage solid wood flooring for underfloor heating.

[0023] Comparative Example 1 (1) Select a density of 0.68 g / cm³ for 12 years. 3 Poplar wood with an initial moisture content of 18% is used as the main material and is cut into 2000mm×150mm×50mm squares according to standard. (2) Place the wood obtained in step (1) into a multi-functional vacuum reactor, evacuate to -0.095MPa, heat to 80℃, turn on 400W ultrasound, introduce ethanol-water vapor with a volume ratio of 1:1, and degrease for 3 hours; switch to plasma treatment mode, introduce 150sccm argon gas, treat with 120W power for 5 minutes, and clean with 60℃ deionized water for 15 minutes to obtain degreased wood. (3) Weigh out silane coupling agent KH-570, nano silica, and hydroxy acrylate in a mass ratio of 8:12:5. Add deionized water to a container, adjust the pH to 5.2 with analytical grade glacial acetic acid, add KH-570 and stir, then add hydroxy acrylate and stir evenly. Then add nano silica, disperse by ultrasonication at 400W, and let stand for 2 hours to obtain the modified impregnation solution; (4) The degreased and activated wood blocks are placed in layers with intervals, and the spacing between the wood blocks is controlled to be 30 mm. A 5 mm thick breathable steel mesh is laid between the layers. The wood blocks are placed in an impregnation tank, vacuumed to -0.095 MPa, and kept for 30 min. Modified impregnation liquid is injected, pressure is increased to 0.2 MPa, 450 W ultrasonic is turned on, and the temperature is raised to 55℃ for 2 h of impregnation. The wood blocks are taken out and placed in a hot air circulating oven at 60℃ and 50% humidity for 1 hour of curing. The wood blocks are then dried to obtain impregnated modified wood blocks. (5) Place the impregnated modified wood into a microwave-electrostatic field drying tank according to the original arrangement, heat to 55℃, 65% humidity, -0.07MPa vacuum, 200W microwave, 50kV / m electrostatic field, for 18h, to obtain a section of dried wood; (6) Heat to 70℃, 45% humidity, -0.085MPa vacuum, 350W microwave, 80kV / m electrostatic field for 24h to obtain two sections of dried wood; (7) Three sections of dried timber were obtained by cooling to 65℃, 52% humidity, -0.08MPa vacuum, 180W microwave, 60kV / m electrostatic field for 20h; (8) The three sections of dried wood obtained in step (8) are transferred to a constant temperature and humidity drying oven according to the original arrangement. They are dried at 52°C and 56% humidity for 16 hours to obtain modified impregnated dried wood. (9) Take aluminum nitride whiskers with an aspect ratio of 10:1, ultrasonically wash and dry them, add waterborne epoxy resin and curing agent polyamide with a mass ratio of 3:1, mix and stir evenly, and ultrasonically disperse at 300W to obtain modified aluminum nitride whiskers. (10) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent KH-570, dry them at 80℃ for 30 min, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers on the fibers longitudinally, press them at 80℃ and 0.6MPa for 30 min, and then cure them at 120℃ to obtain an aluminum nitride-bamboo fiber oriented composite layer. (11) Take a single layer of graphene with a sheet diameter of 10 μm, add NMP, and disperse it by ultrasonication at 400 W to prepare a graphene dispersion with a mass percentage of 0.5%. (12) Take aramid fabric, immerse it in a 0.5% graphene dispersion, press it with rollers, spray it with a waterborne polyurethane with a solid content of 40%, press it at 80℃ and 0.6MPa for 30min, and then cure it at 120℃ to obtain a graphene-aramid reinforced fabric composite layer. (13) A water-based polyurethane adhesive was coated on the back of the modified impregnated and dried wood, and then placed in a hot press composite machine to form an aluminum nitride-bamboo fiber oriented composite layer. The composite layer was hot-pressed at 120℃ and 1.2MPa for 60s to obtain the aluminum nitride-bamboo fiber oriented composite layer modified wood. (14) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood square obtained in step (10) with water-based polyurethane adhesive, place it in a hot press composite machine, composite graphene-aramid reinforced cloth, and hot press at 110℃ and 0.9MPa for 50s to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood square. (15) Add nano zinc oxide, hydroxy acrylate and BYK-110 to a container in a mass ratio of 2:100:0.5, stir at 300 r / min, sonicate for 30 min to obtain nano zinc oxide modified hydroxy acrylate. (16) Mix nano-montmorillonite and KH-550 at a mass ratio of 3:1, add anhydrous ethanol, stir at 60°C for 30 min, and dry to obtain pretreated nano-montmorillonite; (17) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane at a mass ratio of 1:100, stir at 2000 r / min for 1 h, sonicate at 300 W, and let stand for 2 h to obtain nano-montmorillonite modified hydroxyl polysiloxane. (18) The composite layer modified wood obtained in step (15) is processed with tenons and mortises, coated with nano-montmorillonite modified hydroxy polysiloxane as sealant with a thickness of 0.18 mm, and cured for 24 h; then nano-zinc oxide modified hydroxy acrylate is sprayed as primer with a thickness of 9 μm and dried at 85℃ for 25 min; then commercially available UV epoxy-silane is sprayed as topcoat with a thickness of 28 μm, at 90℃ for 15 min, and then left to stand at room temperature for 48 h to obtain the crack-resistant, moisture-resistant, low-expansion and shrinkage solid wood flooring for underfloor heating.

[0024] Comparative Example 2 (1) Select a density of 0.68 g / cm³ for 12 years. 3 Poplar wood with an initial moisture content of 18% is used as the main material and is cut into 2000mm×150mm×50mm squares according to standard. (2) The wood obtained in step (1) was placed into a cobalt-60 γ-ray irradiation device, the irradiation dose was adjusted to 50 kGy, the dose rate was 2.2 kGy / h, the temperature was 30℃, the humidity was 45%, and it was left to stand for 2 hours to obtain γ-ray modified wood. (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate to -0.095MPa, heat to 80℃, turn on 400W ultrasound, introduce ethanol-water vapor with a volume ratio of 1:1, and degrease for 3h; switch to plasma treatment mode, introduce 150sccm argon gas, treat with 120W power for 5min, and use 60℃ deionized water to circulate and clean for 15min to obtain degreased wood. (4) Place the degreased and activated wood in layers with intervals, control the spacing between the wood to be 30mm, lay a 5mm thick breathable steel mesh between the layers, place them in an impregnation tank, evacuate to -0.095MPa, maintain for 30min, inject commercially available bisphenol A formaldehyde resin impregnation liquid, pressurize to 0.2MPa, turn on 450W ultrasonic, heat to 55℃ for 2h impregnation, take out the wood and put it into a hot air circulating oven, cure at 60℃ and 50% humidity for 1 hour, and dry to obtain impregnated modified wood; (5) Place the impregnated modified wood into a microwave-electrostatic field drying tank according to the original arrangement, heat to 55℃, 65% humidity, -0.07MPa vacuum, 200W microwave, 50kV / m electrostatic field, for 18h, to obtain a section of dried wood; (6) Heat to 70℃, 45% humidity, -0.085MPa vacuum, 350W microwave, 80kV / m electrostatic field for 24h to obtain two sections of dried wood; (7) Three sections of dried timber were obtained by cooling to 65℃, 52% humidity, -0.08MPa vacuum, 180W microwave, 60kV / m electrostatic field for 20h; (8) The three sections of dried wood obtained in step (8) are transferred to a constant temperature and humidity drying oven according to the original arrangement. They are dried at 52°C and 56% humidity for 16 hours to obtain modified impregnated dried wood. (9) Take aluminum nitride whiskers with an aspect ratio of 10:1, ultrasonically wash and dry them, add waterborne epoxy resin and curing agent polyamide with a mass ratio of 3:1, mix and stir evenly, and ultrasonically disperse at 300W to obtain modified aluminum nitride whiskers. (10) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent KH-570, dry them at 80℃ for 30 min, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers on the fibers longitudinally, press them at 80℃ and 0.6MPa for 30 min, and then cure them at 120℃ to obtain an aluminum nitride-bamboo fiber oriented composite layer. (11) Take a single layer of graphene with a sheet diameter of 10 μm, add NMP, and disperse it by ultrasonication at 400 W to prepare a graphene dispersion with a mass percentage of 0.5%. (12) Take aramid fabric, immerse it in a 0.5% graphene dispersion, press it with rollers, spray it with a waterborne polyurethane with a solid content of 40%, press it at 80℃ and 0.6MPa for 30min, and then cure it at 120℃ to obtain a graphene-aramid reinforced fabric composite layer. (13) A water-based polyurethane adhesive was coated on the back of the modified impregnated and dried wood, and then placed in a hot press composite machine to form an aluminum nitride-bamboo fiber oriented composite layer. The composite layer was hot-pressed at 120℃ and 1.2MPa for 60s to obtain the aluminum nitride-bamboo fiber oriented composite layer modified wood. (14) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood square obtained in step (10) with water-based polyurethane adhesive, place it in a hot press composite machine, composite graphene-aramid reinforced cloth, and hot press at 110℃ and 0.9MPa for 50s to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood square. (15) Add nano zinc oxide, hydroxy acrylate and BYK-110 to a container in a mass ratio of 2:100:0.5, stir at 300 r / min, sonicate for 30 min to obtain nano zinc oxide modified hydroxy acrylate. (16) Mix nano-montmorillonite and KH-550 at a mass ratio of 3:1, add anhydrous ethanol, stir at 60°C for 30 min, and dry to obtain pretreated nano-montmorillonite; (17) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane at a mass ratio of 1:100, stir at 2000 r / min for 1 h, sonicate at 300 W, and let stand for 2 h to obtain nano-montmorillonite modified hydroxyl polysiloxane. (18) The composite layer modified wood obtained in step (15) is processed with tenons and mortises, coated with nano-montmorillonite modified hydroxy polysiloxane as sealant with a thickness of 0.18 mm, and cured for 24 h; then nano-zinc oxide modified hydroxy acrylate is sprayed as primer with a thickness of 9 μm and dried at 85℃ for 25 min; then commercially available UV epoxy-silane is sprayed as topcoat with a thickness of 28 μm, at 90℃ for 15 min, and then left to stand at room temperature for 48 h to obtain the crack-resistant, moisture-resistant, low-expansion and shrinkage solid wood flooring for underfloor heating.

[0025] Comparative Example 3 (1) Select a density of 0.68 g / cm³ for 12 years. 3 Poplar wood with an initial moisture content of 18% is used as the main material and is cut into 2000mm×150mm×50mm squares according to standard. (2) The wood obtained in step (1) was placed into a cobalt-60 γ-ray irradiation device, the irradiation dose was adjusted to 50 kGy, the dose rate was 2.2 kGy / h, the temperature was 30℃, the humidity was 45%, and it was left to stand for 2 hours to obtain γ-ray modified wood. (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate to -0.095MPa, heat to 80℃, turn on 400W ultrasound, introduce ethanol-water vapor with a volume ratio of 1:1, and degrease for 3h; switch to plasma treatment mode, introduce 150sccm argon gas, treat with 120W power for 5min, and use 60℃ deionized water to circulate and clean for 15min to obtain degreased wood. (4) Place the degreased and activated wood in layers with intervals, control the spacing between wood to be 30mm, lay a 5mm thick breathable steel mesh between the layers, place them in an impregnation tank, vacuum to -0.095MPa, maintain for 30min, inject commercially available nano-titanium ester composite impregnation liquid, pressurize to 0.2MPa, turn on 450W ultrasound, heat to 55℃ for 2h impregnation, take out the wood and put it into a hot air circulating oven, cure at 60℃ and 50% humidity for 1 hour, and dry to obtain impregnated modified wood; (5) Place the impregnated modified wood into a microwave-electrostatic field drying tank according to the original arrangement, heat to 55℃, 65% humidity, -0.07MPa vacuum, 200W microwave, 50kV / m electrostatic field, for 18h, to obtain a section of dried wood; (6) Heat to 70℃, 45% humidity, -0.085MPa vacuum, 350W microwave, 80kV / m electrostatic field for 24h to obtain two sections of dried wood; (7) Three sections of dried timber were obtained by cooling to 65℃, 52% humidity, -0.08MPa vacuum, 180W microwave, 60kV / m electrostatic field for 20h; (8) The three sections of dried wood obtained in step (8) are transferred to a constant temperature and humidity drying oven according to the original arrangement. They are dried at 52°C and 56% humidity for 16 hours to obtain modified impregnated dried wood. (9) Take aluminum nitride whiskers with an aspect ratio of 10:1, ultrasonically wash and dry them, add waterborne epoxy resin and curing agent polyamide with a mass ratio of 3:1, mix and stir evenly, and ultrasonically disperse at 300W to obtain modified aluminum nitride whiskers. (10) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent KH-570, dry them at 80℃ for 30 min, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers on the fibers longitudinally, press them at 80℃ and 0.6MPa for 30 min, and then cure them at 120℃ to obtain an aluminum nitride-bamboo fiber oriented composite layer. (11) Take a single layer of graphene with a sheet diameter of 10 μm, add NMP, and disperse it by ultrasonication at 400 W to prepare a graphene dispersion with a mass percentage of 0.5%. (12) Take aramid fabric, immerse it in a 0.5% graphene dispersion, press it with rollers, spray it with a waterborne polyurethane with a solid content of 40%, press it at 80℃ and 0.6MPa for 30min, and then cure it at 120℃ to obtain a graphene-aramid reinforced fabric composite layer. (13) A water-based polyurethane adhesive was coated on the back of the modified impregnated and dried wood, and then placed in a hot press composite machine to form an aluminum nitride-bamboo fiber oriented composite layer. The composite layer was hot-pressed at 120℃ and 1.2MPa for 60s to obtain the aluminum nitride-bamboo fiber oriented composite layer modified wood. (14) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood square obtained in step (10) with water-based polyurethane adhesive, place it in a hot press composite machine, composite graphene-aramid reinforced cloth, and hot press at 110℃ and 0.9MPa for 50s to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood square. (15) Add nano zinc oxide, hydroxy acrylate and BYK-110 to a container in a mass ratio of 2:100:0.5, stir at 300 r / min, sonicate for 30 min to obtain nano zinc oxide modified hydroxy acrylate. (16) Mix nano-montmorillonite and KH-550 at a mass ratio of 3:1, add anhydrous ethanol, stir at 60°C for 30 min, and dry to obtain pretreated nano-montmorillonite; (17) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane at a mass ratio of 1:100, stir at 2000 r / min for 1 h, sonicate at 300 W, and let stand for 2 h to obtain nano-montmorillonite modified hydroxyl polysiloxane. (18) The composite layer modified wood obtained in step (15) is processed with tenons and mortises, coated with nano-montmorillonite modified hydroxy polysiloxane as sealant with a thickness of 0.18 mm, and cured for 24 h; then nano-zinc oxide modified hydroxy acrylate is sprayed as primer with a thickness of 9 μm and dried at 85℃ for 25 min; then commercially available UV epoxy-silane is sprayed as topcoat with a thickness of 28 μm, at 90℃ for 15 min, and then left to stand at room temperature for 48 h to obtain the crack-resistant, moisture-resistant, low-expansion and shrinkage solid wood flooring for underfloor heating.

[0026] Comparative Example 4 (1) Select a density of 0.68 g / cm³ for 12 years. 3 Poplar wood with an initial moisture content of 18% is used as the main material and is cut into 2000mm×150mm×50mm squares according to standard. (2) The wood obtained in step (1) was placed into a cobalt-60 γ-ray irradiation device, the irradiation dose was adjusted to 50 kGy, the dose rate was 2.2 kGy / h, the temperature was 30℃, the humidity was 45%, and it was left to stand for 2 hours to obtain γ-ray modified wood. (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate to -0.095MPa, heat to 80℃, turn on 400W ultrasound, introduce ethanol-water vapor with a volume ratio of 1:1, and degrease for 3h; switch to plasma treatment mode, introduce 150sccm argon gas, treat with 120W power for 5min, and use 60℃ deionized water to circulate and clean for 15min to obtain degreased wood. (4) Weigh out silane coupling agent KH-570, nano silica, and hydroxy acrylate in a mass ratio of 8:12:5. Add deionized water to a container, adjust the pH to 5.2 with analytical grade glacial acetic acid, add KH-570 and stir, then add hydroxy acrylate and stir evenly. Then add nano silica, disperse by ultrasonication at 400W, and let stand for 2 hours to obtain the modified impregnation solution; (5) Place the degreased and activated wood in layers with intervals, controlling the spacing between the wood to be 30mm. Lay a 5mm thick breathable steel mesh between the layers, place them in an impregnation tank, evacuate to -0.095MPa, maintain for 30min, inject the modified impregnation liquid, pressurize to 0.2MPa, turn on 450W ultrasonic, heat to 55℃ and impregnate for 2h, take out the wood and put it into a hot air circulating oven, cure at 60℃ and 50% humidity for 1 hour, and dry to obtain impregnated modified wood; (6) The impregnated modified wood obtained in step (5) is transferred to a constant temperature and humidity drying oven according to the original placement method, and dried at 52°C and 56% humidity for 16 hours to obtain modified impregnated dried wood. (7) Take aluminum nitride whiskers with an aspect ratio of 10:1, ultrasonically wash and dry them, add waterborne epoxy resin and curing agent polyamide with a mass ratio of 3:1, mix and stir evenly, and ultrasonically disperse at 300W to obtain modified aluminum nitride whiskers. (8) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent KH-570, dry them at 80℃ for 30 min, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers longitudinally with the fibers, press them at 80℃ and 0.6MPa for 30 min, and then cure them at 120℃ for a second time to obtain an aluminum nitride-bamboo fiber oriented composite layer. (9) Take a single layer of graphene with a sheet diameter of 10 μm, add NMP, and disperse it by ultrasonication at 400 W to prepare a graphene dispersion with a mass percentage of 0.5%. (10) Take aramid fabric, immerse it in a 0.5% graphene dispersion, press it with rollers, spray it with a waterborne polyurethane with a solid content of 40%, press it at 80℃ and 0.6MPa for 30 minutes, and then cure it at 120℃ to obtain a graphene-aramid reinforced fabric composite layer. (11) A water-based polyurethane adhesive was coated on the back of the modified impregnated and dried wood, and then placed in a hot press composite machine to form an aluminum nitride-bamboo fiber oriented composite layer. The composite layer was hot-pressed at 120℃ and 1.2MPa for 60s to obtain the aluminum nitride-bamboo fiber oriented composite layer modified wood. (12) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood square obtained in step (11) with water-based polyurethane adhesive, place it in a hot press composite machine, composite graphene-aramid reinforced cloth, and hot press at 110℃ and 0.9MPa for 50s to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood square. (13) Add nano zinc oxide, hydroxy acrylate and BYK-110 to a container in a mass ratio of 2:100:0.5, stir at 300r / min, sonicate for 30min to obtain nano zinc oxide modified hydroxy acrylate. (14) Mix nano-montmorillonite and KH-550 at a mass ratio of 3:1, add anhydrous ethanol, stir at 60°C for 30 min, and dry to obtain pretreated nano-montmorillonite; (15) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane at a mass ratio of 1:100, stir at 2000 r / min for 1 h, sonicate at 300 W, and let stand for 2 h to obtain nano-montmorillonite modified hydroxyl polysiloxane. (16) The composite layer modified wood obtained in step (12) is processed with tenons and mortises, coated with nano-montmorillonite modified hydroxy polysiloxane as sealant with a thickness of 0.18 mm, and cured for 24 h; then nano-zinc oxide modified hydroxy acrylate is sprayed as primer with a thickness of 9 μm and dried at 85℃ for 25 min; then commercially available UV epoxy-silane is sprayed as topcoat with a thickness of 28 μm, at 90℃ for 15 min, and then left to stand at room temperature for 48 h to obtain crack-resistant, moisture-resistant, low-expansion and shrinkage solid wood flooring for underfloor heating.

[0027] Comparative Example 5 (1) Select a density of 0.68 g / cm³ for 12 years. 3 Poplar wood with an initial moisture content of 18% is used as the main material and is cut into 2000mm×150mm×50mm squares according to standard. (2) The wood obtained in step (1) was placed into a cobalt-60 γ-ray irradiation device, the irradiation dose was adjusted to 50 kGy, the dose rate was 2.2 kGy / h, the temperature was 30℃, the humidity was 45%, and it was left to stand for 2 hours to obtain γ-ray modified wood. (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate to -0.095MPa, heat to 80℃, turn on 400W ultrasound, introduce ethanol-water vapor with a volume ratio of 1:1, and degrease for 3h; switch to plasma treatment mode, introduce 150sccm argon gas, treat with 120W power for 5min, and use 60℃ deionized water to circulate and clean for 15min to obtain degreased wood. (4) Weigh out silane coupling agent KH-570, nano silica, and hydroxy acrylate in a mass ratio of 8:12:5. Add deionized water to a container, adjust the pH to 5.2 with analytical grade glacial acetic acid, add KH-570 and stir, then add hydroxy acrylate and stir evenly. Then add nano silica, disperse by ultrasonication at 400W, and let stand for 2 hours to obtain the modified impregnation solution; (5) Place the degreased and activated wood in layers with intervals, controlling the spacing between the wood to be 30mm. Lay a 5mm thick breathable steel mesh between the layers, place them in an impregnation tank, evacuate to -0.095MPa, maintain for 30min, inject the modified impregnation liquid, pressurize to 0.2MPa, turn on 450W ultrasonic, heat to 55℃ and impregnate for 2h, take out the wood and put it into a hot air circulating oven, cure at 60℃ and 50% humidity for 1 hour, and dry to obtain impregnated modified wood; (6) Place the impregnated modified wood into a microwave-electrostatic field drying tank according to the original arrangement, heat to 55℃, 65% humidity, -0.07MPa vacuum, 200W microwave, 50kV / m electrostatic field, for 18h, to obtain a section of dried wood; (7) Heat to 70℃, 45% humidity, -0.085MPa vacuum, 350W microwave, 80kV / m electrostatic field for 24h to obtain two sections of dried wood; (8) Three sections of dried timber were obtained by cooling to 65℃, 52% humidity, -0.08MPa vacuum, 180W microwave, 60kV / m electrostatic field for 20h; (9) Transfer the three sections of dried wood obtained in step (8) to a constant temperature and humidity drying oven according to the original placement method, dry at 52°C and 56% humidity for 16 hours to obtain modified impregnated dried wood. (10) Take a single layer of graphene with a sheet diameter of 10 μm, add NMP, and disperse it by ultrasonication at 400 W to prepare a graphene dispersion with a mass percentage of 0.5%. (11) Take aramid fabric, immerse it in a 0.5% graphene dispersion, press it with rollers, spray it with a waterborne polyurethane with a solid content of 40%, press it at 80℃ and 0.6MPa for 30min, and then cure it at 120℃ to obtain a graphene-aramid reinforced fabric composite layer. (12) A water-based polyurethane adhesive was coated on the back of the modified impregnated and dried wood, and then placed in a hot press composite machine to composite the graphene-basalt fiber composite layer oriented composite layer purchased from the market. The composite layer was hot-pressed at 120℃ and 1.2MPa for 60s to obtain the graphene-basalt fiber oriented composite layer modified wood. (13) Coat the other side of the graphene-basalt fiber oriented composite layer modified wood obtained in step (12) with water-based polyurethane adhesive, place it in a hot press composite machine, composite graphene-aramid reinforced cloth, and hot press at 110℃ and 0.9MPa for 50s to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood. (14) Add nano zinc oxide, hydroxy acrylate and BYK-110 to a container in a mass ratio of 2:100:0.5, stir at 300 r / min, sonicate for 30 min to obtain nano zinc oxide modified hydroxy acrylate. (15) Mix nano-montmorillonite and KH-550 at a mass ratio of 3:1, add anhydrous ethanol, stir at 60°C for 30 min, and dry to obtain pretreated nano-montmorillonite; (16) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane at a mass ratio of 1:100, stir at 2000 r / min for 1 h, sonicate at 300 W, and let stand for 2 h to obtain nano-montmorillonite modified hydroxyl polysiloxane. (17) The composite layer modified wood obtained in step (13) is processed with tenons and mortises, coated with nano-montmorillonite modified hydroxy polysiloxane as sealant with a thickness of 0.18 mm, and cured for 24 h; then nano-zinc oxide modified hydroxy acrylate is sprayed as primer with a thickness of 9 μm and dried at 85℃ for 25 min; then commercially available UV epoxy-silane is sprayed as topcoat with a thickness of 28 μm, at 90℃ for 15 min, and then left to stand at room temperature for 48 h to obtain the crack-resistant, moisture-resistant, low-expansion and shrinkage solid wood flooring for underfloor heating.

[0028] Comparative Example 6 (1) Select a density of 0.68 g / cm³ for 12 years. 3 Poplar wood with an initial moisture content of 18% is used as the main material and is cut into 2000mm×150mm×50mm squares according to standard. (2) The wood obtained in step (1) was placed into a cobalt-60 γ-ray irradiation device, the irradiation dose was adjusted to 50 kGy, the dose rate was 2.2 kGy / h, the temperature was 30℃, the humidity was 45%, and it was left to stand for 2 hours to obtain γ-ray modified wood. (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate to -0.095MPa, heat to 80℃, turn on 400W ultrasound, introduce ethanol-water vapor with a volume ratio of 1:1, and degrease for 3h; switch to plasma treatment mode, introduce 150sccm argon gas, treat with 120W power for 5min, and use 60℃ deionized water to circulate and clean for 15min to obtain degreased wood. (4) Weigh out silane coupling agent KH-570, nano silica, and hydroxy acrylate in a mass ratio of 8:12:5. Add deionized water to a container, adjust the pH to 5.2 with analytical grade glacial acetic acid, add KH-570 and stir, then add hydroxy acrylate and stir evenly. Then add nano silica, disperse by ultrasonication at 400W, and let stand for 2 hours to obtain the modified impregnation solution; (5) Place the degreased and activated wood in layers with intervals, controlling the spacing between the wood to be 30mm. Lay a 5mm thick breathable steel mesh between the layers, place them in an impregnation tank, evacuate to -0.095MPa, maintain for 30min, inject the modified impregnation liquid, pressurize to 0.2MPa, turn on 450W ultrasonic, heat to 55℃ and impregnate for 2h, take out the wood and put it into a hot air circulating oven, cure at 60℃ and 50% humidity for 1 hour, and dry to obtain impregnated modified wood; (6) Place the impregnated modified wood into a microwave-electrostatic field drying tank according to the original arrangement, heat to 55℃, 65% humidity, -0.07MPa vacuum, 200W microwave, 50kV / m electrostatic field, for 18h, to obtain a section of dried wood; (7) Heat to 70℃, 45% humidity, -0.085MPa vacuum, 350W microwave, 80kV / m electrostatic field for 24h to obtain two sections of dried wood; (8) Three sections of dried timber were obtained by cooling to 65℃, 52% humidity, -0.08MPa vacuum, 180W microwave, 60kV / m electrostatic field for 20h; (9) Transfer the three sections of dried wood obtained in step (8) to a constant temperature and humidity drying oven according to the original placement method, dry at 52°C and 56% humidity for 16 hours to obtain modified impregnated dried wood. (10) Take aluminum nitride whiskers with an aspect ratio of 10:1, ultrasonically wash and dry them, add waterborne epoxy resin and curing agent polyamide with a mass ratio of 3:1, mix and stir evenly, and ultrasonically disperse at 300W to obtain modified aluminum nitride whiskers. (11) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent KH-570, dry them at 80℃ for 30 min, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers longitudinally with the fibers, press them at 80℃ and 0.6MPa for 30 min, and then cure them at 120℃ for a second time to obtain an aluminum nitride-bamboo fiber oriented composite layer. (12) A water-based polyurethane adhesive was coated on the back of the modified impregnated and dried wood, and then placed in a hot press composite machine to form an aluminum nitride-bamboo fiber oriented composite layer. The composite layer was hot-pressed at 120℃ and 1.2MPa for 60s to obtain the aluminum nitride-bamboo fiber oriented composite layer modified wood. (13) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood obtained in step (12) with water-based polyurethane adhesive, place it in a hot press composite machine, and composite it with commercially available PE-graphene modified aramid cloth composite layer. Hot press at 110℃ and 0.9MPa for 50s to obtain aluminum nitride-bamboo fiber and PE-graphene modified aramid cloth modified wood. (14) Add nano zinc oxide, hydroxy acrylate and BYK-110 to a container in a mass ratio of 2:100:0.5, stir at 300 r / min, sonicate for 30 min to obtain nano zinc oxide modified hydroxy acrylate. (15) Mix nano-montmorillonite and KH-550 at a mass ratio of 3:1, add anhydrous ethanol, stir at 60°C for 30 min, and dry to obtain pretreated nano-montmorillonite; (16) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane at a mass ratio of 1:100, stir at 2000 r / min for 1 h, sonicate at 300 W, and let stand for 2 h to obtain nano-montmorillonite modified hydroxyl polysiloxane. (17) The composite layer modified wood obtained in step (13) is processed with tenons and mortises, coated with nano-montmorillonite modified hydroxy polysiloxane as sealant with a thickness of 0.18 mm, and cured for 24 h; then nano-zinc oxide modified hydroxy acrylate is sprayed as primer with a thickness of 9 μm and dried at 85℃ for 25 min; then commercially available UV epoxy-silane is sprayed as topcoat with a thickness of 28 μm, at 90℃ for 15 min, and then left to stand at room temperature for 48 h to obtain the crack-resistant, moisture-resistant, low-expansion and shrinkage solid wood flooring for underfloor heating.

[0029] Comparative Example 7 (1) Select a density of 0.68 g / cm³ for 12 years. 3 Poplar wood with an initial moisture content of 18% is used as the main material and is cut into 2000mm×150mm×50mm squares according to standard. (2) The wood obtained in step (1) was placed into a cobalt-60 γ-ray irradiation device, the irradiation dose was adjusted to 50 kGy, the dose rate was 2.2 kGy / h, the temperature was 30℃, the humidity was 45%, and it was left to stand for 2 hours to obtain γ-ray modified wood. (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate to -0.095MPa, heat to 80℃, turn on 400W ultrasound, introduce ethanol-water vapor with a volume ratio of 1:1, and degrease for 3h; switch to plasma treatment mode, introduce 150sccm argon gas, treat with 120W power for 5min, and use 60℃ deionized water to circulate and clean for 15min to obtain degreased wood. (4) Weigh out silane coupling agent KH-570, nano silica, and hydroxy acrylate in a mass ratio of 8:12:5. Add deionized water to a container, adjust the pH to 5.2 with analytical grade glacial acetic acid, add KH-570 and stir, then add hydroxy acrylate and stir evenly. Then add nano silica, disperse by ultrasonication at 400W, and let stand for 2 hours to obtain the modified impregnation solution; (5) Place the degreased and activated wood in layers with intervals, controlling the spacing between the wood to be 30mm. Lay a 5mm thick breathable steel mesh between the layers, place them in an impregnation tank, evacuate to -0.095MPa, maintain for 30min, inject the modified impregnation liquid, pressurize to 0.2MPa, turn on 450W ultrasonic, heat to 55℃ and impregnate for 2h, take out the wood and put it into a hot air circulating oven, cure at 60℃ and 50% humidity for 1 hour, and dry to obtain impregnated modified wood; (6) Place the impregnated modified wood into a microwave-electrostatic field drying tank according to the original arrangement, heat to 55℃, 65% humidity, -0.07MPa vacuum, 200W microwave, 50kV / m electrostatic field, for 18h, to obtain a section of dried wood; (7) Heat to 70℃, 45% humidity, -0.085MPa vacuum, 350W microwave, 80kV / m electrostatic field for 24h to obtain two sections of dried wood; (8) Three sections of dried timber were obtained by cooling to 65℃, 52% humidity, -0.08MPa vacuum, 180W microwave, 60kV / m electrostatic field for 20h; (9) Transfer the three sections of dried wood obtained in step (8) to a constant temperature and humidity drying oven according to the original placement method, dry at 52°C and 56% humidity for 16 hours to obtain modified impregnated dried wood. (10) Take aluminum nitride whiskers with an aspect ratio of 10:1, ultrasonically wash and dry them, add waterborne epoxy resin and curing agent polyamide with a mass ratio of 3:1, mix and stir evenly, and ultrasonically disperse at 300W to obtain modified aluminum nitride whiskers. (11) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent KH-570, dry them at 80℃ for 30 min, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers longitudinally with the fibers, press them at 80℃ and 0.6MPa for 30 min, and then cure them at 120℃ for a second time to obtain an aluminum nitride-bamboo fiber oriented composite layer. (12) Take a single layer of graphene with a sheet diameter of 10 μm, add NMP, and disperse it by ultrasonication at 400 W to prepare a graphene dispersion with a mass percentage of 0.5%. (13) Take aramid fabric, immerse it in a 0.5% graphene dispersion, press it with rollers, spray it with a waterborne polyurethane with a solid content of 40%, press it at 80℃ and 0.6MPa for 30min, and then cure it at 120℃ to obtain a graphene-aramid reinforced fabric composite layer. (14) A water-based polyurethane adhesive was coated on the back of the modified impregnated and dried wood, and then placed in a hot press composite machine to form an aluminum nitride-bamboo fiber oriented composite layer. The composite layer was hot-pressed at 120℃ and 1.2MPa for 60s to obtain the aluminum nitride-bamboo fiber oriented composite layer modified wood. (15) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood square obtained in step (10) with water-based polyurethane adhesive, place it in a hot press composite machine, composite graphene-aramid reinforced cloth, and hot press at 110℃ and 0.9MPa for 50s to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood square. (16) The composite layer modified wood obtained in step (15) is processed with tenons and mortises, coated with nano-silica modified silane modified polyether as sealant with a thickness of 0.18 mm, and cured for 24 h; then nano-titanium dioxide modified water-based epoxy reagent is sprayed as primer with a thickness of 9 μm and dried at 85℃ for 25 min; then commercially available UV epoxy-silane is sprayed as topcoat with a thickness of 28 μm, at 90℃ for 15 min, and then left to stand at room temperature for 48 h to obtain the crack-resistant, moisture-resistant, low-expansion and shrinkage solid wood flooring for underfloor heating.

[0030] Example of effect Table 1 below presents the performance analysis results of the high-temperature oxidation resistant hard carbon fiber coatings of Examples 1 to 3 and Comparative Examples 1 to 7 of the present invention.

[0031] Table 1 The difference between Comparative Example 1 and Example 1 lies in the γ-ray pretreatment; the difference between Comparative Examples 2 and 3 and Example 1 lies in the impregnation solutions, which are commercially available bisphenol A formaldehyde resin impregnation solution and nano-titanium ester composite impregnation solution, respectively; the difference between Comparative Example 4 and Example 1 lies in the four-stage drying method; the difference between Comparative Examples 5 and 6 and the Example lies in the composite layers, which are aluminum nitride-bamboo fiber and graphene-aramid composite layer and aluminum nitride-bamboo fiber and PE-graphene modified aramid fabric composite layer, respectively; the difference between Comparative Example 7 and Example 1 lies in the sealant, which is commercially available nano-silica modified silane modified polyether, and the primer, which is commercially available nano-titanium dioxide modified waterborne epoxy reagent. Comparison of data from the examples and comparative examples shows that this invention uses poplar wood as the main substrate. After pretreatment with gamma rays, it undergoes hydroxyl modification using an impregnation solution containing silane coupling agent, nano-silica, and hydroxyl acrylate to form a honeycomb-porous composite structure, improving impermeability. An aluminum nitride-bamboo fiber oriented composite layer is used as the sandwich layer, bidirectionally reinforced with graphene-aramid fabric, constructing a superimposed thermally conductive network while simultaneously enhancing crack resistance. Moisture content and stress are precisely controlled through four-stage drying, and an electrostatic field is used to assist the directional distribution of nanoparticles, providing a stable substrate for molding. A nano-zinc oxide-modified hydroxyl acrylate is used as the primer, nano-montmorillonite-modified hydroxyl polysiloxane as the sealant, and UV epoxy-silane as the topcoat, forming an integrated barrier. The wood board prepared by this invention achieves a functional superposition from internal modification to surface protection, realizing integrated protection of impermeability, crack resistance, moisture resistance, and wear resistance.

[0032] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention, and no designations in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating, characterized in that, The preparation steps include the following: (1) Select poplar wood as the main material and cut it into timber squares according to the standard; (2) Place the timber obtained in step (1) into a γ-ray irradiation device, adjust the parameters, and let it stand after irradiation to obtain γ-ray modified timber; (3) Place the γ-ray modified wood obtained in step (2) into a multi-functional vacuum reactor, evacuate, heat up, turn on the ultrasound, introduce ethanol and water vapor, and degrease; switch to plasma treatment mode, introduce argon gas, clean, and obtain degreased wood. (4) Weigh out silane coupling agent, nano silica, and hydroxy acrylate in proportion, add deionized water and pH adjuster to the container, adjust the pH, add silane coupling agent and stir, then add hydroxy acrylate and stir evenly, then add nano silica, ultrasonically disperse, let stand, and obtain modified impregnation solution. (5) Place the degreased wood obtained in step (3) into an impregnation tank, vacuum it, add the modified impregnation liquid, pressurize it, heat it, impregnate it, and dry it to obtain impregnated modified wood. (6) Place the impregnated modified wood into a multi-functional drying tank, vacuum it, control the humidity, adjust the microwave power and electrostatic field strength, and dry it to obtain a section of dried wood. (7) Continue to heat up, adjust humidity, increase pressure, adjust microwave power and electrostatic field strength, and dry to obtain two sections of dried wood; (8) Cooling, depressurizing, controlling humidity, adjusting microwave power and electrostatic field strength to obtain three sections of dried wood. (9) Transfer the three sections of dried timber obtained in step (8) into a drying oven, adjust the parameters, and dry to obtain modified impregnated dried timber; (10) Coat the back of the modified impregnated and dried wood with water-based adhesive, place it in a hot press composite machine, composite aluminum nitride-bamboo fiber oriented composite layer, adjust the parameters, and obtain aluminum nitride-bamboo fiber oriented composite layer modified wood; (11) Coat the other side of the aluminum nitride-bamboo fiber oriented composite layer modified wood square obtained in step (10) with water-based adhesive, place it in a hot press composite machine, composite graphene-aramid reinforcing cloth, and adjust the parameters to obtain aluminum nitride-bamboo fiber and graphene-aramid composite layer modified wood square. (12) The composite layer modified wood obtained in step (11) is processed with tenons and mortises, coated with sealant, primer and topcoat, cured, dried and left to stand to obtain the crack-resistant, moisture-resistant and low-expansion-shrinkage solid wood flooring for underfloor heating. The aluminum nitride-bamboo fiber oriented composite layer in step (10) is prepared by the following method: (1) Take aluminum nitride whiskers, ultrasonically wash and dry them, add resin and curing agent, mix and stir evenly, and ultrasonically disperse them to obtain modified aluminum nitride whiskers; (2) Take bamboo fiber bundles of silicon, impregnate them with alkyl coupling agent KH-570 for modification, dry them, lay the bamboo fiber bundles in parallel along the longitudinal direction, coat the modified aluminum nitride whiskers longitudinally with the fibers, hot press, and cure them twice to obtain an aluminum nitride-bamboo fiber oriented composite layer. The aluminum nitride whiskers have an aspect ratio of 9-12:1; the resin is a water-based epoxy resin, and the curing agent is polyamide, with a mass ratio of 3-4:

1. The graphene-aramid reinforced fabric in step (11) is prepared by the following method: (1) Take a single layer of graphene, add NMP, and ultrasonically disperse to prepare a graphene dispersion; (2) Take aramid fabric, immerse it in graphene dispersion, apply pressure with rollers, spray adhesive, hot press, and let it stand to obtain a graphene-aramid reinforced fabric composite layer. The graphene sheet diameter is 5-10 μm; the graphene dispersion has a mass percentage of 0.5%; and the binder is waterborne polyurethane with a solid content of 40-45%.

2. The method for preparing a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating according to claim 1, characterized in that, The poplar wood in step (1) is 12-year-old poplar wood with a density of 0.65-0.70 g / cm3 and an initial moisture content of 18-20%; the standard size of the timber is 2000mm×150mm×50mm.

3. The method for preparing a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating according to claim 1, characterized in that, In step (4), the mass ratio of silane coupling agent, nano silica, and hydroxy acrylate is 8-10:12-14:5-6; the pH range is 4.9-5.4; the silane coupling agent is KH-570; and the pH adjuster is analytical grade glacial acetic acid.

4. The method for preparing a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating according to claim 1, characterized in that, In step (6), the temperature is 50-60℃, humidity is 60-70%, vacuum pressure is -0.06~-0.08Mpa, microwave power is 180-220W, electric field strength is 45-55kV / m, and drying time is 18-20h; in step (7), the temperature is 65-75℃, humidity is 40-50%, vacuum pressure is -0.08~-0.09Mpa, microwave power is 330-360W, and electric field strength is... 75-85kV / m, drying time is 24-28h; the temperature of step (8) is 60-70℃, humidity is 48-55%, vacuum pressure is -0.075~-0.085Mpa, microwave power is 150-200W, electric field strength is 50-70kV / m, drying time is 18-22h; the temperature of step (9) is 50-54℃, humidity is 55-60%, drying time is 14-18h.

5. The method for preparing a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating according to claim 1, characterized in that, The primer in step (12) is nano zinc oxide modified hydroxy acrylate with a thickness of 8-10 μm; the sealant is nano montmorillonite modified hydroxy polysiloxane with a thickness of 0.15-0.20 mm; and the topcoat is UV epoxy-silane with a thickness of 25-30 μm.

6. The method for preparing a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating according to claim 1, characterized in that, The gamma irradiation device in step (2) is a cobalt-60 gamma irradiation device; the irradiation dose is 48-52 kGy; the dose rate is 1.6-2.4 kGy / h; the temperature is 25-30℃; and the humidity is 40%-50%.

7. The method for preparing a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating according to claim 1, characterized in that, The method for placing the timber in step (5) is to place it in layers with intervals; the spacing between the timbers is 30-35mm, and a 5mm thick breathable steel mesh is laid between the layers.

8. The method for preparing a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating according to claim 1, characterized in that, The water-based adhesive used in steps (11) and (12) is a water-based polyurethane adhesive.

9. The method for preparing a crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating according to claim 1, characterized in that, The nano-zinc oxide modified hydroxy acrylate was prepared by the following method: (1) Add nano zinc oxide, hydroxy acrylate, deionized water and dispersant to a container, stir and sonicate to obtain nano zinc oxide modified hydroxy acrylate; The mass ratio of the nano zinc oxide, hydroxy acrylate, and dispersant is 2:100:0.5; The nano-montmorillonite-modified hydroxyl polysiloxane was prepared by the following method: (1) Mix nano-montmorillonite, KH-550 and anhydrous ethanol, stir and dry to obtain pretreated nano-montmorillonite; (2) Add the pretreated nano-montmorillonite to the hydroxyl polysiloxane, stir, sonicate, and let stand to obtain nano-montmorillonite modified hydroxyl polysiloxane. The nano-montmorillonite, KH-550, and hydroxyl polysiloxane are present in a weight ratio of 1-3:1:

100.

10. A crack-resistant, moisture-resistant, and low-expansion / shrinkage solid wood flooring for underfloor heating, wherein the solid wood flooring is prepared by the preparation method according to any one of claims 1-9.

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