A method for processing wood material

Abstract

This invention relates to the field of wood processing technology, specifically a method for processing and preparing wood materials. The invention first involves eliminating permeability barriers in the wood material by removing starch granules from the cell cavities to form continuous permeation channels, followed by drying to a moisture content of 6%–12%. A eutectic solvent is prepared by mixing choline chloride with an organic acid hydrogen bond donor at a molar ratio of 1:2. The eutectic solvent is then impregnated into the wood material using a vacuum negative pressure impregnation process, and held at 65–75°C for 2–4 hours to increase the content of active hydroxyl groups in lignin while ensuring the loss rate does not exceed 8%. A bio-based crosslinking agent is directly added during the impregnation process, resulting in the in-situ formation of a crosslinked network within the cell wall through esterification. After hot-press curing and gradient drying, the eutectic solvent is recovered and recycled. This invention achieves a synergistic improvement in the mechanical properties, dimensional stability, and durability of the wood material, with formaldehyde emissions meeting the requirements of GB18580 standard, and a eutectic solvent recovery rate of not less than 85%.

Description

Technical Field

[0001] This invention relates to the field of wood processing technology, specifically a method for processing and preparing wood materials. Background Technology

[0002] Wood materials are widely used in construction, furniture and decoration due to their advantages such as being renewable and easy to process. However, natural wood generally has defects such as poor dimensional stability, insufficient mechanical properties and susceptibility to humid and hot environments, which to some extent limit its application in high-performance scenarios.

[0003] Existing wood material modification technologies mainly include three categories: resin impregnation, heat treatment, and chemical modification. Resin impregnation modification, represented by urea-formaldehyde resin and phenol-formaldehyde resin, can improve mechanical properties to some extent, but it suffers from formaldehyde release, which has adverse effects on human health and the indoor environment, making it difficult to meet increasingly stringent environmental protection requirements. Heat treatment modification does not require chemical additions, but lignin degradation is more pronounced under high-temperature conditions, resulting in some loss of mechanical properties. Modification with bio-based crosslinking agents such as citric acid has been a research hotspot in recent years, but existing methods mostly involve impregnation followed by drying and then hot pressing. The crosslinking reaction tends to accumulate on the cell wall surface, and there is still room for improvement in the depth and durability of modification.

[0004] As a fast-growing tropical timber, rubberwood has a high content of starch granules in its cell cavities, which hinders the penetration of modifiers into the cell walls and is a significant factor affecting the modification effect of rubberwood. Eutectic solvents, as novel green solvents, have swelling and activating effects on lignin; however, current research mainly focuses on the dissolution and extraction of lignin. Further exploration is needed to explore how to achieve targeted activation and synergistic effects with subsequent cross-linking reactions while preserving the structural integrity of lignin. Summary of the Invention

[0005] This invention provides a method for processing and preparing wood materials, which achieves a synergistic improvement in the mechanical properties and dimensional stability of wood materials by directionally activating lignin with a eutectic solvent and crosslinking in situ within the cell wall with a bio-based crosslinking agent.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention discloses a method for processing and preparing wood-based materials, comprising: S1: The wood material is treated to eliminate permeability barriers, removing starch grains from the cell cavities to form continuous permeability channels, and then the wood material is dried to a moisture content of 6% to 12%; S2: Choline chloride and organic acid hydrogen bond donors are mixed in a molar ratio of 1:2 and stirred at 55-65°C until a homogeneous transparent liquid is formed to obtain a eutectic solvent. S3: Place the wood material treated in step S1 into a sealed impregnation tank, evacuate the tank to a pressure of -0.08 to -0.09 MPa and maintain this pressure for 20 to 30 minutes. Inject a eutectic solvent preheated to 60 to 70°C under negative pressure. After restoring to normal pressure, raise the temperature to 65 to 75°C and hold for 2 to 4 hours. The mass ratio of the eutectic solvent to the wood material is 5:1 to 8:1, which increases the content of active hydroxyl groups in lignin while ensuring that the lignin loss rate does not exceed 8%. S4: After the impregnation treatment in step S3 is completed, without removing the wood material, add the bio-based crosslinking agent directly to the system and crosslink it through esterification reaction for 2 to 3 hours at 80 to 100°C, so that the crosslinking network is generated in situ inside the cell wall. S5: Take out the reacted wood material and heat-press it at 120-150℃ and 0.5-2MPa for curing. The time is calculated as 20-25 minutes per 10mm board thickness. S6: Gradually dry the cured wood material to a moisture content of 8% to 12%, collect the used eutectic solvent, remove moisture by filtration and vacuum evaporation, and then recycle it.

[0007] As a preferred embodiment of the present invention, in S1, the wood material is rubberwood, and the permeability barrier elimination treatment reduces the residual starch content to less than 30% of the original content.

[0008] As a preferred embodiment of the present invention, in S1, the permeability barrier elimination treatment is a hot water extraction treatment, in which the rubberwood is soaked in hot water at 80-90°C for 2-4 hours; or the permeability barrier elimination treatment is an enzymatic hydrolysis treatment, in which an α-amylase solution is used to treat the rubberwood at 50-60°C and pH 6.0-6.5 for 2-3 hours.

[0009] As a preferred embodiment of the present invention, in S2, the organic acid hydrogen bond donor is lactic acid, the water content of the eutectic solvent is 5% to 8%, and the glass transition temperature of the eutectic solvent is below -20°C.

[0010] As a preferred embodiment of the present invention, in S3, the FTIR spectrum of the wood material after heat preservation treatment is 3400-3500 cm⁻¹ -1 The intensity of the hydroxyl characteristic peak increased by 15% to 30% compared with that before treatment, while the lignin loss rate did not exceed 6%.

[0011] As a preferred technical solution of the present invention, in S3, after restoring normal pressure, the pressure is further increased to 0.3-0.5 MPa and maintained for 20-30 minutes, so that the eutectic solvent can further penetrate into the middle layer of the secondary cell wall under positive pressure, and then the temperature is raised to 65-75°C for heat preservation treatment.

[0012] As a preferred embodiment of the present invention, in S4, the bio-based crosslinking agent is a composite system of citric acid and sodium hypophosphite, wherein the amount of citric acid is 5% to 10% of the oven-dry weight of the wood material, and the amount of sodium hypophosphite is 10% to 15% of the weight of citric acid; the esterification reaction occurs between the lignin hydroxyl groups activated after treatment with a eutectic solvent and the polycarboxyl groups of citric acid, forming a lignin-citric acid-cellulose ternary crosslinking network inside the cell wall.

[0013] As a preferred technical solution of the present invention, in S4, boric acid and borax are added to form a composite flame retardant system, the mass ratio of boric acid to borax is 1:1, and the total amount is 2% to 4% of the oven-dry mass of the wood material; the added boric acid and borax coordinate with the lignin hydroxyl and cellulose hydroxyl groups that have not participated in the esterification reaction during the formation of the cross-linking network, so as to realize the coordination anchoring of the flame retardant component with the cross-linking network.

[0014] As a preferred technical solution of the present invention, in S5, the hot pressing curing is carried out in two stages: the first stage is pre-pressed for 10 to 15 minutes at 120 to 130°C and 0.5 to 0.8 MPa to initially cure the cross-linked network while retaining the elasticity of the cell wall; the second stage is heated to 140 to 150°C and pressed for 20 to 25 minutes per 10 mm plate thickness to complete the deep curing.

[0015] As a preferred technical solution of the present invention, in S6, the collected eutectic solvent is evaporated under reduced pressure at 60°C to remove moisture. The choline chloride or organic acid component is added to the initial ratio by detecting the molar ratio of the recovered solvent and then recycled. The recovery rate is not less than 85%, and the moisture resistance of the modified material obtained after the third cycle decreases by no more than 5% compared with the result of the non-cycled treatment.

[0016] The beneficial effects of this invention are: 1. This invention, through the synergistic combination of permeation barrier elimination treatment and vacuum negative pressure impregnation, allows the eutectic solvent to penetrate deep into the cell wall, thereby directionally activating the active hydroxyl groups of lignin while controlling the loss rate within a reasonable range, achieving a balance between lignin activation and structural preservation, and laying the foundation for subsequent in-situ crosslinking.

[0017] 2. This invention employs an in-situ crosslinking process, directly introducing bio-based crosslinking reagents under a continuous eutectic solvent permeation state, causing the esterification crosslinking reaction to occur inside the cell wall, forming a ternary crosslinking network. Compared with non-in-situ crosslinking methods, the esterification crosslinking reaction is more complete and the degree of crosslinking is more sufficient, resulting in a better improvement in the mechanical properties and dimensional stability of wood materials.

[0018] 3. This invention uses a bio-based material system throughout the process. The low eutectic solvent is recyclable and reusable. The bio-based crosslinking agent replaces the traditional aldehyde resin. The formaldehyde emission of the modified material meets the requirements of GB18580 standard and has good green and environmentally friendly characteristics. Detailed Implementation

[0019] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present application, and not all of the 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] The rubberwood lumber used in the embodiments of this invention has a specification of 200mm × 100mm × 20mm and an initial moisture content of approximately 35%–45%. Lignin loss rate was determined according to the Klason lignin method, following the TAPPI T222 standard. The calculation formula is the difference in absolute lignin mass before and after treatment divided by the absolute lignin mass before treatment, and the result is expressed as a percentage. The oven-dry weight of the wood material was obtained by weighing after drying in an oven at 103℃ until the mass became constant. The resistance to moisture swelling (ASE) was calculated using the following formula: , This represents the total volumetric swelling of the untreated material. The total volumetric swelling of the treated material is calculated by dividing the difference between the volume of the sample after water saturation and the volume under absolute dry conditions by the absolute dry volume.

[0021] Example 1: The present invention discloses a method for processing and preparing wood materials, which specifically includes the following steps: S1: Treatment to Eliminate Osmotic Barriers. Rubberwood was soaked in 85℃ hot water for 3 hours to fully dissolve the starch granules within the cell cavities. After soaking, the rubberwood was removed and dried in a 60℃ forced-air drying oven until the moisture content reached 8%–10%. Iodine staining analysis showed that the residual starch granule content was 22% of the original content, meeting the control requirement of less than 30%, and continuous osmotic channels were formed within the cell cavities.

[0022] S2: Weigh choline chloride and lactic acid in a molar ratio of 1:2, mix them, and place them in a 60°C water bath with continuous stirring for 40 minutes until a homogeneous and transparent liquid is formed. Add an appropriate amount of deionized water to the resulting liquid to adjust the water content of the eutectic solvent to 6%. Differential scanning calorimetry (DSC) analysis showed that the glass transition temperature of the resulting eutectic solvent was -28°C, which is lower than -20°C, confirming that the eutectic solvent system was fully formed.

[0023] S3: Place the rubberwood treated in step S1 into a sealed impregnation tank, start the vacuum pump to evacuate the tank to a pressure of -0.085 MPa, and maintain this pressure for 25 minutes. While maintaining negative pressure, inject a preheated eutectic solvent (heated to 65°C) into the tank, with a mass ratio of eutectic solvent to rubberwood of 6:1. After injection, restore normal pressure, then heat the system to 70°C and hold for 3 hours. After the holding period, the lignin loss rate is measured to be 5.2%, meeting the control requirement of no more than 8%; Fourier transform infrared spectroscopy analysis shows that the lignin loss rate is within the range of 3400–3500 cm⁻¹. -1 The intensity of the characteristic peak of hydroxyl groups increased by 21% compared with that before treatment, confirming that the content of active hydroxyl groups in lignin increased.

[0024] S4: After the heat preservation process, without removing the rubberwood, directly add citric acid and sodium hypophosphite to the sealed impregnation tank system. The amount of citric acid is 8% of the oven-dry weight of the rubberwood, and the amount of sodium hypophosphite is 12% of the weight of citric acid. Heat the system to 90℃ and crosslink through esterification for 2.5 hours. The esterification crosslinking reaction occurs between the activated lignin hydroxyl groups after treatment with a eutectic solvent and the polycarboxyl groups of citric acid, forming a lignin-citric acid-cellulose ternary crosslinking network inside the cell wall. After the reaction, Fourier transform infrared spectroscopy was performed, and the result was measured at 1735 cm⁻¹. -1 The characteristic peaks of the ester bond were significantly enhanced, confirming that the esterification and crosslinking reaction had occurred.

[0025] S5: Remove the rubberwood that has completed the cross-linking reaction from the sealed impregnation tank and place it in a hot press for hot pressing and curing at 145°C and 1.5MPa. In this embodiment, the rubberwood board is 20mm thick, and the hot pressing time is calculated at 22 minutes per 10mm of board thickness, for a total hot pressing and curing time of 44 minutes.

[0026] S6: The rubberwood after hot-press curing has formed a stable cross-linked network, significantly improving dimensional stability. Drying was carried out using the following temperature gradient: 60℃ for 12 hours, then increased to 80℃ for 8 hours, and finally equilibrated at room temperature for 48 hours. No cracking occurred during the drying process, and the final moisture content was 9.5%, meeting the control requirement of 8%–12%. The remaining eutectic solvent in the sealed impregnation tank and the condensate collected during hot pressing were collected. After filtering to remove solid impurities such as wood chips, the solvent was evaporated under reduced pressure at 60℃ to remove moisture. The molar ratio of choline chloride to lactic acid in the recovered solvent was measured. The corresponding components were added to the initial molar ratio of 1:2 for recycling. The eutectic solvent recovery rate was 91%. After replenishing the components with the recovered solvent in the manner described above, the solvent was recycled for the first, second, and third cycles. The resulting modified rubberwood exhibited a water swelling resistance of 58.1%, 57.1%, and 55.6%, respectively. These values ​​were 0.3%, 2.1%, and 4.6% lower than the results before recycling (58.3%), respectively, all within the range of 5%. This demonstrates that the treatment effect did not significantly decrease after three cycles of recycling the eutectic solvent.

[0027] The modified rubberwood obtained in Example 1 was subjected to performance testing, and the results are shown in the table below.

[0028] Table 1 Performance test results of Example 1

[0029] Example 2: The difference between Example 2 and Example 1 lies in steps S1 and S3, while the remaining steps are the same as in Example 1.

[0030] Step S1: Permeability Barrier Elimination Treatment. Rubberwood was placed in an α-amylase solution (0.5% concentration) and enzymatically hydrolyzed for 2.5 hours at 55°C and pH 6.2 to ensure complete degradation of starch granules within the cell cavities. After treatment, the rubberwood was removed and dried to a moisture content of 8%–10%. Iodine staining analysis showed that the residual starch content was 18% of the original content, lower than that obtained with hot water extraction, indicating a more uniform permeability channel.

[0031] Step S3: Place the rubberwood treated in Step S1 into a sealed impregnation tank, evacuate to a pressure of -0.085 MPa and maintain for 25 minutes. Inject a preheated eutectic solvent (preheated to 65°C) under negative pressure, with a mass ratio of eutectic solvent to rubberwood of 6:1. After restoring to normal pressure, further pressurize to 0.4 MPa and maintain for 25 minutes, allowing the eutectic solvent to further penetrate into the secondary cell wall layer under positive pressure. Then, raise the temperature to 70°C and hold for 3 hours. After the holding period, the lignin loss rate is measured at 4.8%, meeting the control requirement of no more than 8%. Fourier transform infrared spectroscopy is used to detect the lignin loss rate at 3400–3500 cm⁻¹. -1 The intensity of the hydroxyl characteristic peak increased by 26% compared to before treatment.

[0032] The performance comparison results between Example 2 and Example 1 are shown in the table below.

[0033] Table 2 Performance Comparison of Example 1 and Example 2

[0034] Example 3: Example 3 is based on Example 1, but in step S4, boric acid and borax are additionally introduced to form a composite flame retardant system, and the remaining steps are the same as in Example 1.

[0035] Step S4: After the insulation is complete, without removing the rubberwood, add citric acid, sodium hypophosphite, boric acid, and borax simultaneously to the sealed impregnation tank system. The amount of citric acid is 8% of the oven-dry weight of the rubberwood, the amount of sodium hypophosphite is 12% of the mass of citric acid, the mass ratio of boric acid to borax is 1:1, and the total amount of boric acid and borax is 3% of the oven-dry weight of the rubberwood. Heat the system to 90℃ and crosslink through esterification for 2.5 hours. During the formation of the ternary crosslinking network, the added boric acid and borax coordinate with the lignin and cellulose hydroxyl groups that did not participate in the esterification reaction, achieving coordination anchoring between the flame-retardant component and the crosslinking network.

[0036] Table 3. Flame retardant performance test results of Example 3

[0037] After water immersion, the boron retention rate reached 87.3%, proving that the added boric acid and borax are combined in the cross-linked network through coordination anchoring rather than physical filling, thus exhibiting significant durability and flame retardancy.

[0038] Comparative Example 1: Step S1, the process of eliminating permeability barriers, is omitted.

[0039] Rubberwood that had not undergone penetration barrier removal treatment was directly subjected to step S3 vacuum impregnation treatment, with the remaining steps being the same as in Example 1. Results: The lignin loss rate was 9.8%, exceeding the control requirement of no more than 8%; Fourier transform infrared spectroscopy was used to detect the lignin loss at 3400–3500 cm⁻¹. -1 The intensity of the hydroxyl characteristic peak increased by only 9% compared to before treatment; the resistance to swelling was only 31.2%; and the static bending strength was 82.4 MPa. Starch granules blocked the permeation channels within the cell lumen, preventing the eutectic solvent from uniformly penetrating the cell wall. This resulted in a significant decrease in the increase in the content of active hydroxyl groups in lignin, and a substantial reduction in the modification effect. This demonstrates that the elimination of permeation barriers in step S1 is an important prerequisite for achieving uniform impregnation.

[0040] Comparative Example 2: In step S3, the insulation temperature is raised to 85℃.

[0041] The insulation temperature after restoring normal pressure in step S3 was increased from 65-75℃ to 85℃, with the remaining steps the same as in Example 1. Results: The lignin loss rate was 13.6%, exceeding the control requirement of no more than 8%; the intensity of the hydroxyl characteristic peak detected by Fourier transform infrared spectroscopy increased by 28% compared to before treatment, but the static bending strength was only 84.3 MPa, lower than the result of untreated rubberwood cross-linked with citric acid. Excessive insulation temperature led to excessive lignin dissolution and damage to the cell wall structure. Although the degree of hydroxyl activation was improved, the total amount of lignin hydroxyl groups that could participate in subsequent esterification cross-linking decreased due to structural damage, resulting in a moisture swelling resistance rate of only 38.6%, and ultimately a decrease in mechanical properties. This demonstrates that the insulation temperature range of 65-75℃ is a reasonable parameter range for balancing the increase of lignin active hydroxyl content and controlling the lignin loss rate.

[0042] Comparative Example 3: In-situ crosslinking in step S4 was omitted.

[0043] After completing the vacuum impregnation treatment in step S3, without adding a bio-based crosslinking agent, the hot-pressing curing in step S5 was performed directly, with the remaining steps being the same as in Example 1. Results: The resistance to moisture swelling was only 28.4%, and the static bending strength was 79.6 MPa. The mechanical properties decreased significantly after the hygrothermal cycling treatment. Treatment with a eutectic solvent alone could not form a stable crosslinking network inside the cell wall, and the dimensional stability and durability were significantly inferior to those in Example 1, proving that the in-situ crosslinking in step S4 is the key step to obtain a durable modification effect.

[0044] Comparative Example 4: After removing the rubberwood in step S4, non-in-situ crosslinking was performed.

[0045] After the heat preservation in step S3, the rubberwood was removed from the sealed impregnation tank and immersed in a citric acid solution for crosslinking. The amount of citric acid, crosslinking temperature, and time were the same as in Example 1, and the remaining steps were the same. Results: Fourier transform infrared spectroscopy was used to detect the crosslinking at 1735 cm⁻¹. -1 The intensity of the characteristic peak of the ester bond was 34% lower than that in Example 1; the resistance to swelling was 41.2%; and the static bending strength was 88.7 MPa. After the rubberwood was removed, the impregnation state of the eutectic solvent in the cell wall was disrupted, the exposure of the activated lignin hydroxyl groups decreased, and the crosslinking density decreased, proving that the in-situ operation method of adding the bio-based crosslinking agent directly without removing the rubberwood in step S4 has substantial technical effects.

[0046] The comparative data are summarized in the table below: Table 4. Performance Comparison of Each Example and Comparative Example

[0047] The experimental results from the above embodiments and comparative examples demonstrate the inherent technical correlation and synergistic effect among the steps of this invention. Step S1, the permeation barrier elimination treatment, removes starch granules from the cell lumen to form continuous permeation channels. For woody materials with high starch granule content in the cell lumen, such as rubberwood, this is a crucial prerequisite for achieving uniform penetration of the eutectic solvent into the cell wall. Step S3, under a heat preservation condition of 65–75℃, achieves a balance between increasing the content of active hydroxyl groups in lignin and controlling the loss rate. Excessive temperature will damage the integrity of the cell wall structure, leading to a decrease in mechanical properties. Step S4 uses an in-situ operation to form a lignin-citric acid-cellulose ternary crosslinking network inside the cell wall. Non-in-situ crosslinking or omitting this step will result in a significant decrease in crosslinking density. The organic combination of these three key technical steps achieves a synergistic improvement in the mechanical properties, dimensional stability, and durability of woody materials, while the formaldehyde emission is below the detection limit of GB18580, demonstrating significant advantages in green chemistry.

[0048] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for processing and preparing wood-based materials, characterized in that, include: S1: The wood material is treated to eliminate permeability barriers, removing starch grains from the cell cavities to form continuous permeability channels, and then the wood material is dried to a moisture content of 6% to 12%; S2: Choline chloride and organic acid hydrogen bond donors are mixed in a molar ratio of 1:2 and stirred at 55-65°C until a homogeneous transparent liquid is formed to obtain a eutectic solvent. S3: Place the wood material treated in step S1 into a sealed impregnation tank, evacuate the tank to a pressure of -0.08 to -0.09 MPa and maintain this pressure for 20 to 30 minutes. Inject a eutectic solvent preheated to 60 to 70°C under negative pressure. After restoring to normal pressure, raise the temperature to 65 to 75°C and hold for 2 to 4 hours. The mass ratio of the eutectic solvent to the wood material is 5:1 to 8:1, which increases the content of active hydroxyl groups in lignin while ensuring that the lignin loss rate does not exceed 8%. S4: After the impregnation treatment in step S3 is completed, without removing the wood material, add the bio-based crosslinking agent directly to the system and crosslink it through esterification reaction for 2 to 3 hours at 80 to 100°C, so that the crosslinking network is generated in situ inside the cell wall. S5: Take out the reacted wood material and heat-press it at 120-150℃ and 0.5-2MPa for curing. The time is calculated as 20-25 minutes per 10mm board thickness. S6: Gradually dry the cured wood material to a moisture content of 8% to 12%, collect the used eutectic solvent, remove moisture by filtration and vacuum evaporation, and then recycle it.

2. The method for processing and preparing wood-based materials according to claim 1, characterized in that, In S1, the wood material is rubberwood, and the permeability barrier elimination treatment reduces the residual starch granules to less than 30% of the original content.

3. The method for processing and preparing wood-based materials according to claim 2, characterized in that, In S1, the permeability barrier elimination treatment is a hot water extraction treatment, in which the rubberwood is soaked in hot water at 80-90°C for 2-4 hours; or the permeability barrier elimination treatment is an enzymatic hydrolysis treatment, in which α-amylase solution is used to treat the rubberwood at 50-60°C and pH 6.0-6.5 for 2-3 hours.

4. The method for processing and preparing wood-based materials according to claim 1, characterized in that, In S2, the organic acid hydrogen bond donor is lactic acid, and the water content of the eutectic solvent is 5% to 8%; the glass transition temperature of the eutectic solvent is below -20°C.

5. The method for processing and preparing wood-based materials according to claim 1, characterized in that, In S3, the FTIR spectrum of the wood material after heat preservation treatment is 3400–3500 cm⁻¹. -1 The intensity of the hydroxyl characteristic peak increased by 15% to 30% compared with that before treatment, while the lignin loss rate did not exceed 6%.

6. The method for processing and preparing wood-based materials according to claim 1, characterized in that, In S3, after restoring normal pressure, the pressure is further increased to 0.3-0.5 MPa and maintained for 20-30 minutes, allowing the eutectic solvent to further penetrate into the middle layer of the secondary cell wall under positive pressure. Then, the temperature is raised to 65-75°C for heat preservation treatment.

7. The method for processing and preparing wood-based materials according to claim 1, characterized in that, In S4, the bio-based crosslinking agent is a composite system of citric acid and sodium hypophosphite. The amount of citric acid is 5% to 10% of the oven-dry weight of the wood material, and the amount of sodium hypophosphite is 10% to 15% of the weight of citric acid. The esterification reaction occurs between the lignin hydroxyl groups activated after treatment with a eutectic solvent and the polycarboxyl groups of citric acid, forming a lignin-citric acid-cellulose ternary crosslinking network inside the cell wall.

8. The method for processing and preparing wood-based materials according to claim 7, characterized in that, In S4, boric acid and borax are added to form a composite flame retardant system. The mass ratio of boric acid to borax is 1:1, and the total amount is 2% to 4% of the oven-dry weight of the wood material. During the formation of the cross-linking network, the added boric acid and borax coordinate with the lignin hydroxyl and cellulose hydroxyl groups that have not participated in the esterification reaction, thereby achieving coordination anchoring between the flame retardant components and the cross-linking network.

9. The method for processing and preparing wood-based materials according to claim 1, characterized in that, In S5, the hot-press curing is carried out in two stages: the first stage is pre-pressed for 10 to 15 minutes at 120 to 130°C and 0.5 to 0.8 MPa to initially cure the cross-linked network while retaining the elasticity of the cell wall; the second stage is heated to 140 to 150°C and pressed for 20 to 25 minutes per 10 mm plate thickness to complete the deep curing.

10. A method for processing and preparing wood-based materials according to claim 1, characterized in that, In S6, the collected eutectic solvent is evaporated under reduced pressure at 60°C to remove moisture. The molar ratio of the recovered solvent is detected, and choline chloride or organic acid components are added to the initial ratio before recycling. The recovery rate is not less than 85%, and the moisture resistance of the modified material obtained after the third cycle decreases by no more than 5% compared with the result before non-recycling.

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