High-strength wood-like PU plastic-wood integrated composite material

Abstract

The invention relates to the technical field of plastic-wood materials, in particular to a high-strength wood-imitating PU plastic-wood integrated composite material which is prepared from a component A and a component B. The component A is prepared from, by mass, 32-38 parts of acetylated wood powder; 11 to 16.5 parts of modified lignin; 237 to 260 parts of polyether polyol; 3.8 to 6 parts of a compatilizer; 2.4 to 2.6 parts of a catalyst; 12.5 to 14.2 parts of a foaming agent; 4.9-7 parts of a composite flame retardant; 4.9-7 parts of an auxiliary agent; the component A is polyphenyl polymethylene polyisocyanate, and the component B is polyphenyl polymethylene polyisocyanate; the component A and the component B are subjected to blending, stirring, foaming, injection molding, curing and demolding to obtain the high-strength wood-like PU plastic-wood integrated composite material with good compatibility, and the high-strength wood-like PU plastic-wood integrated composite material has a wide application prospect.

Description

Technical Field

[0001] This invention relates to the field of wood-plastic composite materials technology, and in particular to a high-strength wood-imitation PU integrated wood-plastic composite material. Background Technology

[0002] Polyurethane wood-like material is a rigid polyurethane foam with a smooth, tough, high-density outer skin and a low-density inner core. It belongs to the self-skinning type of rigid polyurethane foam. It is produced by processing polyurethane composites through blending, stirring, foaming, injection molding, curing, and demolding. Due to its wood-like properties and high rigidity and mechanical strength, it is often called "synthetic wood" or "PU wood-like material." Since the 1960s, rigid polyurethane foam has been widely used as a wood-like material for decorative components in furniture. In recent years, to address the timber shortage problem, rigid polyurethane foam wood-like material has become a new area of ​​research and development in my country's furniture industry, and has rapidly developed and been applied in high-end export furniture and interior decoration projects.

[0003] Compared to traditional composite materials, polyurethane wood-like materials are lightweight, low-cost, renewable, and biodegradable. Compared to wood, they are easier to clean and have better water resistance. However, in current technology, the strength of polyurethane wood-like materials is not high, and the interfacial compatibility between wood flour and polyurethane needs further improvement.

[0004] Therefore, based on the relevant technologies mentioned above, there is an urgent need to develop a high-strength wood-imitation PU wood-plastic composite material. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a high-strength wood-imitation PU wood-plastic composite material to solve the problems of low strength and poor compatibility between wood powder and polyurethane materials in the prior art.

[0006] To achieve the above objectives, the present invention provides a high-strength wood-imitation PU wood-plastic composite material.

[0007] A high-strength wood-imitation PU wood-plastic composite material comprises the following raw materials in parts by weight: Component A: 84-97 parts; Component B: 75-90 parts; Component A comprises the following parts by weight of raw materials: Acetylated wood flour 32-38 parts; modified lignin 11-16.5 parts; polyether polyol 237-260 parts; compatibilizer 3.8-6 parts; catalyst 2.4-2.6 parts; foaming agent 12.5-14.2 parts; composite flame retardant 4.9-7 parts; additives 4.9-7 parts; The acetylated wood powder was prepared from poplar wood powder, perchloric acid, and acetic anhydride. The poplar wood powder has a particle size of 0.08-0.1 mm; The modified lignin was prepared from wood flour, dimethyl sulfate, N,N-dimethylbenzylamine and diglycidyl ether; The compatibilizer was prepared from isophorone diisocyanate, octadecyl alcohol and dibutyltin dilaurate; The additive is obtained by mixing silanized nano-silica and cellulose nanocrystals in a mass ratio of 5-8:14-19.2; The polyether polyol is obtained by mixing polyoxypropylene glycerol ether and polyoxypropylene diol in a mass ratio of 25.3-29:7.6-9; The viscosity of the polyoxypropylene glycerol ether is 3000-3500 mPa·s; The viscosity of the polyoxypropylene glycol is 800-1100 mPa·s; Component B is polyphenyl polymethylene polyisocyanate.

[0008] Preferably, the acetylated wood flour is prepared as follows: Poplar wood powder was placed in a vacuum drying oven and dried at 95-105℃ for 6-7 hours. Then, glacial acetic acid and poplar wood powder were added to a three-necked flask and stirred at room temperature for 1.5-2 hours. An acetylation solution was then added dropwise and the mixture was heated to react. After the reaction was completed, deionized water was added to the flask and the mixture was allowed to stand for 20-30 minutes. The mixture was then separated, filtered, and dried to obtain acetylated wood powder.

[0009] Preferably, the ratio of glacial acetic acid, poplar wood powder, acetylation solution and deionized water is 20-26 mL: 2-3 g: 9-13 mL: 30-42 mL; The volume ratio of perchloric acid to acetic anhydride in the acetylation solution is 40-65:1.3-2.3; The heating reaction is carried out at a temperature of 48-55℃ for 2-3 hours.

[0010] Preferably, the compatibilizer is prepared by the following method: Add octadecyl alcohol to xylene and stir until homogeneous. Then add isophorone diisocyanate and continue stirring for 20-30 minutes. Subsequently, add 3 drops of dibutyltin dilaurate and heat to react. After the reaction is complete, wash with toluene and distill to obtain the compatibilizer.

[0011] Preferably, the ratio of octadecyl alcohol, xylene, and isophorone diisocyanate is 52-60.8g:85-100mL:48-50g; The heating reaction is carried out at a temperature of 42-48℃ for 3-4 hours.

[0012] Preferably, the foaming agent is dichlorofluoroethane; The catalyst was obtained by mixing pentamethyldiethylenetriamine and N,N-dimethylcyclohexane in a mass ratio of 9.3-12:0.8-1; The composite flame retardant is obtained by mixing ammonium polyphosphate, 4A molecular sieve and trichloroethyl phosphate in a mass ratio of 18-24.3:3.7-5:2.7-5.

[0013] Preferably, the method for preparing the silanized nano-silica is as follows: Nano-silica was dispersed in toluene, γ-aminopropyltriethoxysilane was added, and the mixture was stirred at 60-80℃ for 2-4 hours. After centrifugation and drying, silanized nano-silica was obtained. The ratio of nano-silica, toluene, and γ-aminopropyltriethoxysilane is 4.5-6g:20-28mL:0.22-0.5g.

[0014] Preferably, the modified lignin is prepared by the following method: Step A1. Add wood flour, deionized water and acetone to a high-pressure reactor, heat and reflux at 185-200℃ for 110-130 min, extract with dichloromethane at 30-40℃ for 30-40 min, collect the extract by rotary evaporation, and dry to obtain lignin powder. Step A2. Place lignin powder and dimethyl sulfate in a flask, heat under reflux at 72-78℃ for 130-150 min, then add 2 mol / L hydrochloric acid solution, and wash twice with deionized water to obtain mixture A; Step A3. Mixture A is heated under reflux with diglycidyl ether and N,N-dimethylbenzylamine, filtered, washed with a mixture of petroleum ether and deionized water, and dried at 50-60℃ for 48-55h to obtain modified lignin.

[0015] Preferably, the ratio of wood flour, deionized water and acetone used in step A1 is 2-3g: 12-15mL: 30-36mL; The ratio of lignin powder to dimethyl sulfate and hydrochloric acid solution in step A2 is 1 mol: 2.4-2.7 mol: 8-13 mL; The mass ratio of mixture A to diglycidyl ether and N,N-dimethylbenzylamine in step A3 is 126-142:45-68:1.4-2; The volume ratio of petroleum ether to deionized water in the petroleum ether-deionized water mixture is 1:1-1.2; The temperature during the heating and reflux process is 90-100℃, and the time is 5-6 hours.

[0016] Preferably, the preparation method of the high-strength wood-imitation PU wood-plastic composite material is as follows: Step S1. Add polyether polyol, foaming agent and catalyst to the reaction vessel in sequence, mix evenly and then heat to react to obtain polyether; Step S2. Add acetylated wood powder and modified lignin to polyether to obtain component A. Then add component B and immediately stir at high speed. After casting and curing for 20-30 minutes, demold to obtain high-strength wood-imitation PU wood-plastic composite material. The heating reaction in step S1 is carried out at a temperature of 55-62°C for 3.5-4.5 hours. The high-speed stirring speed mentioned in step S2 is 2700-2900 r / min and the time is 10-15 min; The temperature during the curing of the injection film is 36-40℃.

[0017] The beneficial effects of this invention are: This invention provides a high-strength wood-like PU-wood composite material. The invention achieves this by blending, stirring, foaming, molding, curing, and demolding components A and B, resulting in a high-strength, compatible wood-like PU-wood composite material. In the additives, silanized nano-silica is well dispersed in the matrix, effectively dispersing external stress and thus improving the tensile strength and other mechanical properties of the composite material. Meanwhile, cellulose nanocrystals contain a large number of hydroxyl groups, which can combine with the active groups in the polyurethane. Therefore, the silanized nano-silica and cellulose nanocrystals in the additives, through an organic-inorganic synergistic effect, effectively improve the interfacial compatibility of the composite material. The high-viscosity polyoxypropylene glycol ether in polyether polyols has high functionality; the higher the hydroxyl value, the better the mechanical properties of the resulting composite material, but the flowability is poor. The flowability is improved after mixing with low-viscosity polyoxypropylene glycol. Furthermore, the lignin modified by dimethyl sulfate, N,N-dimethylbenzylamine and diglycidyl ether has reduced polarity, which improves its compatibility in composite materials and reduces stress concentration inside the composite material. In addition, the rigid aromatic ring structure contained in the molecule has certain heat resistance. When added to the composite material as a filler, the stability of the system is further improved. Compared with the existing technology, it has broad application prospects. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0019] The sources and properties of some of the raw materials used in this invention are as follows: γ-aminopropyltriethoxysilane was purchased from Jinan Xingfeilong Chemical Co., Ltd.; ammonium polyphosphate was purchased from Shenzhen Haicheng Xingye Technology Co., Ltd.; poplar wood powder was purchased from Xingtai Development Zone Jinye Wood Fiber Powder Factory; and 4A molecular sieve was purchased from Shanghai Jiuzhou Chemical Products Co., Ltd.

[0020] Example 1: A method for preparing a high-strength wood-plastic composite material, comprising the following steps: S1. Poplar wood powder was placed in a vacuum drying oven and dried at 95℃ for 6 hours. Then, 20 mL of glacial acetic acid and 2 g of poplar wood powder were added to a three-necked flask and stirred at room temperature for 1.5 hours. Next, 9 mL of acetylation solution was added dropwise, wherein the volume ratio of perchloric acid to acetic anhydride in the acetylation solution was 40:1.3. The mixture was heated at 48℃ for 2 hours. After the reaction was completed, 30 mL of deionized water was added to the flask and allowed to stand for 20 minutes. The mixture was then separated, filtered, and dried to obtain acetylated wood powder. S2. Add 52g of octadecyl alcohol to 85mL of xylene, stir well, then add 48g of isophorone diisocyanate, continue stirring for 20min, then add 3 drops of dibutyltin dilaurate, heat at 42℃ for 3h, after the reaction is complete, wash with toluene and distill to obtain the compatibilizer; S3. Disperse 4.5g of nano-silica in 20mL of toluene, add 0.22g of γ-aminopropyltriethoxysilane, stir and react at 60℃ for 2h, then centrifuge and dry to obtain silanized nano-silica; S4. Add 2g of wood powder, 12mL of deionized water and 30mL of acetone to a high-pressure reactor, heat and reflux at 185℃ for 110min, extract with dichloromethane at 30℃ for 30min, collect the extract by rotary evaporation, dry and obtain lignin powder. S5. Place 1 mol of lignin powder and 2.4 mol of dimethyl sulfate in a flask, heat under reflux at 72°C for 130 min, then add 8 mL of 2 mol / L hydrochloric acid solution, and wash twice with deionized water to obtain mixture A; S6. 126g of mixture A, 45g of diglycidyl ether, and 1.4g of N,N-dimethylbenzylamine were heated and refluxed at 90°C for 5h. After filtration, the mixture was washed with a mixture of petroleum ether and deionized water and dried at 50°C for 48h to obtain modified lignin. S7. Mix 9.3g of pentamethyldiethylenetriamine with 0.8g of N,N-dimethylcyclohexane to obtain a catalyst; mix 18g of ammonium polyphosphate, 3.7g of 4A molecular sieve and 2.7g of trichloroethyl phosphate to obtain a composite flame retardant; then mix 25.3g of polyoxypropylene glycerol ether and 7.6g of polyoxypropylene glycol to obtain a polyether polyol; and mix 5g of silanized nano-silica with 14g of cellulose nanocrystals to obtain an additive. S8. Add 237g of polyether polyol, 12.5g of foaming agent and 2.4g of catalyst to the reaction vessel in sequence, mix well, and heat at 55℃ for 3.5h to obtain polyether; S9. Add 32g of acetylated wood powder and 11g of modified lignin to polyether to obtain component A. Add 75g of component B to 84g of component A and immediately stir at high speed of 2700r / min for 10min. After curing at 36℃ for 20min, demold to obtain high-strength wood-imitation PU wood-plastic composite material.

[0021] Example 2: A method for preparing a high-strength wood-plastic composite material, comprising the following steps: S1. Poplar wood powder was placed in a vacuum drying oven and dried at 100℃ for 6.5h. Then, 23mL of glacial acetic acid and 2.5g of poplar wood powder were added to a three-necked flask and stirred at room temperature for 1.5h. Then, 11mL of acetylation solution was added dropwise, wherein the volume ratio of perchloric acid to acetic anhydride in the acetylation solution was 50:1.7. The mixture was heated at 50℃ for 2.5h. After the reaction was completed, 36mL of deionized water was added to the flask and allowed to stand for 25min. The mixture was then separated, filtered, and dried to obtain acetylated wood powder. S2. Add 56g of octadecyl alcohol to 92mL of xylene, stir well, then add 49g of isophorone diisocyanate, continue stirring for 25min, then add 3 drops of dibutyltin dilaurate, heat at 45℃ for 3.5h, after the reaction is complete, wash with toluene and distill to obtain the compatibilizer; S3. Disperse 5.3g of nano-silica in 24mL of toluene, add 0.35g of γ-aminopropyltriethoxysilane, stir and react at 70℃ for 3h, then centrifuge and dry to obtain silanized nano-silica; S4. Add 2.5g wood powder, 13.5mL deionized water and 33mL acetone to a high-pressure reactor, heat and reflux at 192℃ for 120min, extract with dichloromethane at 35℃ for 35min, collect the extract by rotary evaporation, and dry to obtain lignin powder. S5. Place 1 mol of lignin powder and 2.55 mol of dimethyl sulfate in a flask, heat under reflux at 75°C for 140 min, then add 11 mL of 2 mol / L hydrochloric acid solution, and wash twice with deionized water to obtain mixture A; S6. 135g of mixture A, 56g of diglycidyl ether, and 0.7g of N,N-dimethylbenzylamine were heated and refluxed at 95°C for 5.5h. After filtration, the mixture was washed with a petroleum ether-deionized water mixture and dried at 55°C for 52h to obtain modified lignin. S7. Mix 10.5g of pentamethyldiethylenetriamine and 0.9g of N,N-dimethylcyclohexane evenly to obtain a catalyst; mix 22g of ammonium polyphosphate, 4.3g of 4A molecular sieve and 3.9g of trichloroethyl phosphate to obtain a composite flame retardant; then mix 27.4g of polyoxypropylene glycerol ether and 8.4g of polyoxypropylene glycol to obtain a polyether polyol; and mix 6.5g of silanized nano-silica with 16.5g of cellulose nanocrystals to obtain an additive. S8. Add 243g of polyether polyol, 13.2g of foaming agent and 2.5g of catalyst to the reaction vessel in sequence, mix well and heat at 58℃ for 4h to obtain polyether; S9. Add 35g of acetylated wood powder and 13g of modified lignin to polyether to obtain component A. Add 83g of component B to 90g of component A and immediately stir at high speed at 2800r / min for 12min. After curing at 38℃ for 25min, demold to obtain a high-strength wood-plastic composite material.

[0022] Example 3: A method for preparing a high-strength wood-plastic composite material, comprising the following steps: S1. Poplar wood powder was placed in a vacuum drying oven and dried at 105℃ for 7 hours. Then, 26 mL of glacial acetic acid and 3 g of poplar wood powder were added to a three-necked flask and stirred at room temperature for 2 hours. Next, 13 mL of acetylation solution was added dropwise, wherein the volume ratio of perchloric acid to acetic anhydride in the acetylation solution was 65:2.3. The mixture was heated at 55℃ for 3 hours. After the reaction was completed, 42 mL of deionized water was added to the flask and allowed to stand for 30 minutes. The mixture was then separated, filtered, and dried to obtain acetylated wood powder. S2. Add 60.8g of octadecyl alcohol to 100mL of xylene, stir well, then add 50g of isophorone diisocyanate, continue stirring for 30min, then add 3 drops of dibutyltin dilaurate, heat at 48℃ for 4h, after the reaction is complete, wash with toluene and distill to obtain the compatibilizer. S3. Disperse 6g of nano-silica in 28mL of toluene, add 0.5g of γ-aminopropyltriethoxysilane, stir and react at 80℃ for 4h, then centrifuge and dry to obtain silanized nano-silica; S4. Add 3g of wood powder, 15mL of deionized water and 36mL of acetone to a high-pressure reactor, heat and reflux at 200℃ for 130min, extract with dichloromethane at 40℃ for 40min, collect the extract by rotary evaporation, and dry to obtain lignin powder. S5. Place 1 mol of lignin powder and 2.7 mol of dimethyl sulfate in a flask, heat under reflux at 78°C for 150 min, then add 13 mL of 2 mol / L hydrochloric acid solution, and then wash twice with deionized water to obtain mixture A; S6. 142g of mixture A, 68g of diglycidyl ether, and 2g of N,N-dimethylbenzylamine were heated and refluxed at 100℃ for 6h. After filtration, the mixture was washed with a petroleum ether-deionized water mixture and dried at 60℃ for 55h to obtain modified lignin. S7. Mix 12g of pentamethyldiethylenetriamine with 1g of N,N-dimethylcyclohexane to obtain a catalyst; mix 24.3g of ammonium polyphosphate, 5g of 4A molecular sieve and 5g of trichloroethyl phosphate to obtain a composite flame retardant; then mix 29g of polyoxypropylene glycerol ether and 9g of polyoxypropylene glycol to obtain a polyether polyol; and mix 8g of silanized nano-silica with 19.2g of cellulose nanocrystals to obtain an additive. S8. Add 260g of polyether polyol, 14.2g of foaming agent and 2.6g of catalyst to the reaction vessel in sequence, mix well, and heat at 62℃ for 4.5h to obtain polyether; S9. Add 38g of acetylated wood powder and 16.5g of modified lignin to polyether to obtain component A. Add 90g of component B to 97g of component A and immediately stir at high speed at 2900r / min for 15min. After curing at 40℃ for 30min, demold to obtain high-strength wood-imitation PU wood-plastic composite material.

[0023] Comparative Example 1: Compared with Example 1, no additives were added during the preparation of the composite material in this comparative example. All other steps and parameters were the same, and will not be repeated here. The final composite material was obtained.

[0024] Comparative Example 2: Compared with Example 1, this comparative example did not add silanized nano-silica during the preparation of the additives. All other steps and parameters were the same, and will not be repeated here. The final composite material was obtained.

[0025] Comparative Example 3: Compared with Example 1, this comparative example did not add cellulose nanocrystals during the preparation of the additives. All other steps and parameters were the same, and will not be repeated here. The final composite material was obtained.

[0026] Comparative Example 4: Compared with Example 1, this comparative example did not add modified lignin during the preparation of the composite material. All other steps and parameters were the same, and will not be repeated here. The final composite material was obtained.

[0027] Comparative Example 5: Compared with Example 1, this comparative example did not add polyoxypropylene glycerol ether during the preparation of polyether polyol. All other steps and parameters were the same, and will not be repeated here. The final composite material was obtained.

[0028] Comparative Example 6: Compared with Example 1, this comparative example did not add polyoxypropylene glycol in the preparation process of polyether polyol. All other steps and parameters were the same, and will not be repeated here. The final composite material was obtained.

[0029] Comparative Example 7: Compared with Example 1, no compatibilizer was added in the preparation process of the composite material in this comparative example. All other steps and parameters were the same, and will not be repeated in this comparative example. The final composite material was obtained.

[0030] Comparative Example 8: This comparative example differs from Example 1 only in that "modified lignin" is replaced with "lignin". All other steps and parameters are the same, and will not be repeated here. The final composite material is obtained.

[0031] Comparative Example 9: Compared with Example 1, this comparative example only replaces "25.3g polyoxypropylene glycerol ether and 7.6g polyoxypropylene glycol" with "7.6g polyoxypropylene glycerol ether and 25.3g polyoxypropylene glycol". All other steps and parameters are the same, and will not be repeated in this comparative example. The final composite material is obtained.

[0032] Comparative Example 10: Compared with Example 1, this comparative example only replaces "25.3g polyoxypropylene glycerol ether and 7.6g polyoxypropylene glycol" with "25.3g polyoxypropylene glycerol ether and 25.3g polyoxypropylene glycol". All other steps and parameters are the same, and will not be repeated in this comparative example. The final composite material is obtained.

[0033] Performance testing: The composite materials prepared in Examples 1-3 and Comparative Examples 1-10 were conditioned in an oven at (23±2)℃ and 45%-55% relative humidity for 48h and their relevant mechanical properties were tested. The compressive strength test shall be conducted in accordance with GB / T1041—92 "Test Method for Compression Properties of Plastics"; Bending strength testing shall be conducted in accordance with GB / T9341—2000 "Test Method for Bending Properties of Plastics"; Shore hardness testing shall be performed in accordance with GB / T2411-89 "Shore Hardness Test Method for Plastics".

[0034] Table 1

[0035] Data Analysis: As shown in Table 1, the composite material prepared by this invention exhibits higher mechanical properties. This may be due to the fact that silanized nano-silica in the additives can be well dispersed in the matrix, effectively dispersing external stress and thus improving the tensile strength and other mechanical properties of the composite material. Furthermore, the cellulose nanocrystal molecules contain a large number of hydroxyl groups, which can combine with the active groups in the polyurethane. In other words, the silanized nano-silica and cellulose nanocrystals in the additives effectively improve the interfacial compatibility and mechanical properties of the composite material through an organic-inorganic synergistic effect. High-viscosity polyoxypropylene glycerol ether in polyether polyols has higher functionality; the higher the hydroxyl value, the better the mechanical properties of the resulting composite material, but the poor flowability. Its flowability is improved after mixing with low-viscosity polyoxypropylene glycol. When there is too much low-viscosity polyether polyol, the number of active sites in the reaction system is too small, while when there is too much high-viscosity polyether polyol... Excessive amounts of lignin can lead to poor fluidity in the system, potentially causing uneven foaming or molding and material defects. Furthermore, lignin modified with dimethyl sulfate, N,N-dimethylbenzylamine, and diglycidyl ether exhibits reduced polarity, improving compatibility in composite materials and reducing stress concentration within the composite. The rigid aromatic ring structure within the molecule also provides heat resistance, further enhancing the system's stability when added as a filler. Unmodified lignin, with its high polarity and significant polarity difference with polyurethane materials, exhibits poor compatibility and weaker mechanical properties in the composite. The molecular sieve in the composite flame retardant, with its interleaved arrangement of silicon-oxygen tetrahedral and aluminum-oxygen tetrahedral units, possesses excellent flame-retardant properties, which are further enhanced after compounding. Additionally, the compatibilizer in this invention effectively reduces the polarity of acetylated wood flour, achieving a synergistic effect through blending with other raw materials.

[0036] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

[0037] This invention is intended to cover all such substitutions, modifications, and variations that fall within the broad scope of the appended claims. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A high-strength wood-imitation PU-wood composite material, characterized in that, Includes the following quantities of raw materials: Component A: 84-97 parts; Component B: 75-90 parts; Component A comprises the following parts by weight of raw materials: Acetylated wood flour 32-38 parts; modified lignin 11-16.5 parts; polyether polyol 237-260 parts; compatibilizer 3.8-6 parts; catalyst 2.4-2.6 parts; foaming agent 12.5-14.2 parts; composite flame retardant 4.9-7 parts; additives 4.9-7 parts; The acetylated wood powder was prepared from poplar wood powder, perchloric acid, and acetic anhydride. The poplar wood powder has a particle size of 0.08-0.1 mm; The modified lignin was prepared from wood flour, dimethyl sulfate, N,N-dimethylbenzylamine and diglycidyl ether; The compatibilizer was prepared from isophorone diisocyanate, octadecyl alcohol and dibutyltin dilaurate; The additive is obtained by mixing silanized nano-silica and cellulose nanocrystals in a mass ratio of 5-8:14-19.2; The polyether polyol is obtained by mixing polyoxypropylene glycerol ether and polyoxypropylene diol in a mass ratio of 25.3-29:7.6-9; The viscosity of the polyoxypropylene glycerol ether is 3000-3500 mPa·s; The viscosity of the polyoxypropylene glycol is 800-1100 mPa·s; Component B is polyphenyl polymethylene polyisocyanate.

2. The high-strength wood-imitation PU-wood composite material according to claim 1, characterized in that, The preparation method of the acetylated wood flour is as follows: Poplar wood powder was placed in a vacuum drying oven and dried at 95-105℃ for 6-7 hours. Then, glacial acetic acid and poplar wood powder were added to a three-necked flask and stirred at room temperature for 1.5-2 hours. An acetylation solution was then added dropwise and the mixture was heated to react. After the reaction was completed, deionized water was added to the flask and the mixture was allowed to stand for 20-30 minutes. The mixture was then separated, filtered, and dried to obtain acetylated wood powder.

3. The high-strength wood-imitation PU-wood composite material according to claim 2, characterized in that, The ratio of glacial acetic acid, poplar wood powder, acetylated solution and deionized water is 20-26 mL: 2-3 g: 9-13 mL: 30-42 mL; The volume ratio of perchloric acid to acetic anhydride in the acetylation solution is 40-65:1.3-2.3; The heating reaction is carried out at a temperature of 48-55℃ for 2-3 hours.

4. The high-strength wood-imitation PU-wood composite material according to claim 1, characterized in that, The compatibilizer is prepared as follows: Add octadecyl alcohol to xylene and stir until homogeneous. Then add isophorone diisocyanate and continue stirring for 20-30 minutes. Subsequently, add 3 drops of dibutyltin dilaurate and heat to react. After the reaction is complete, wash with toluene and distill to obtain the compatibilizer.

5. The high-strength wood-imitation PU-wood composite material according to claim 4, characterized in that, The ratio of octadecyl alcohol, xylene, and isophorone diisocyanate is 52-60.8g:85-100mL:48-50g; The heating reaction is carried out at a temperature of 42-48℃ for 3-4 hours.

6. The high-strength wood-imitation PU-wood composite material according to claim 1, characterized in that, The foaming agent is dichlorofluoroethane; The catalyst was obtained by mixing pentamethyldiethylenetriamine and N,N-dimethylcyclohexane in a mass ratio of 9.3-12:0.8-1; The composite flame retardant is obtained by mixing ammonium polyphosphate, 4A molecular sieve and trichloroethyl phosphate in a mass ratio of 18-24.3:3.7-5:2.7-5.

7. The high-strength wood-imitation PU-wood composite material according to claim 1, characterized in that, The preparation method of the silanized nano-silica is as follows: Nano-silica was dispersed in toluene, γ-aminopropyltriethoxysilane was added, and the mixture was stirred at 60-80℃ for 2-4 hours. After centrifugation and drying, silanized nano-silica was obtained. The ratio of nano-silica, toluene and γ-aminopropyltriethoxysilane is 4.5-6g:20-28mL:0.22-0.5g.

8. The high-strength wood-imitation PU-wood composite material according to claim 1, characterized in that, The modified lignin is prepared as follows: Step A1. Add wood flour, deionized water and acetone to a high-pressure reactor, heat and reflux at 185-200℃ for 110-130 min, extract with dichloromethane at 30-40℃ for 30-40 min, collect the extract by rotary evaporation, and dry to obtain lignin powder. Step A2. Place lignin powder and dimethyl sulfate in a flask, heat under reflux at 72-78℃ for 130-150 min, then add 2 mol / L hydrochloric acid solution, and wash twice with deionized water to obtain mixture A; Step A3. Mixture A is heated under reflux with diglycidyl ether and N,N-dimethylbenzylamine, filtered, washed with a mixture of petroleum ether and deionized water, and dried at 50-60℃ for 48-55h to obtain modified lignin.

9. The high-strength wood-imitation PU-wood composite material according to claim 8, characterized in that, The ratio of wood flour, deionized water and acetone used in step A1 is 2-3g: 12-15mL: 30-36mL; The ratio of lignin powder to dimethyl sulfate and hydrochloric acid solution in step A2 is 1 mol: 2.4-2.7 mol: 8-13 mL; The mass ratio of mixture A to diglycidyl ether and N,N-dimethylbenzylamine in step A3 is 126-142:45-68:1.4-2; The volume ratio of petroleum ether to deionized water in the petroleum ether-deionized water mixture is 1:1-1.2; The temperature during the heating and reflux process is 90-100℃, and the time is 5-6 hours.

10. The high-strength wood-imitation PU-wood composite material according to claim 1, characterized in that, The preparation method of the high-strength wood-imitation PU wood-plastic composite material is as follows: Step S1. Add polyether polyol, foaming agent and catalyst to the reaction vessel in sequence, mix evenly and then heat to react to obtain polyether; Step S2. Add acetylated wood powder and modified lignin to polyether to obtain component A. Then add component B and immediately stir at high speed. After casting and curing for 20-30 minutes, demold to obtain high-strength wood-imitation PU wood-plastic composite material. The heating reaction in step S1 is carried out at a temperature of 55-62°C for 3.5-4.5 hours. The high-speed stirring speed mentioned in step S2 is 2700-2900 r / min and the time is 10-15 min; The temperature during the curing of the injection film is 36-40℃.

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