Flame-retardant biomass fiber composite material and preparation method thereof

Abstract

The invention discloses a flame-retardant biomass fiber composite material and a preparation method thereof.The preparation method comprises the steps that firstly, Al (OH) 3 is grafted to biomass fibers, then part of Al (OH) 3 on the biomass fibers is converted into AlPO4 through H3PO4, aluminum phosphate-aluminum hydroxide modified fibers of a core-shell structure are generated, then curing forming is conducted through a curing agent and epoxy resin, and the flame-retardant biomass fiber composite material is obtained. The flame-retardant biomass fiber composite material is obtained. Furthermore, according to the preparation method disclosed by the invention, the aluminum phosphate-aluminum hydroxide modified fiber with a core-shell structure is subjected to surface modification by using a silane coupling agent, and then the silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber obtained after modification is cured and molded by using a curing agent and epoxy resin; the flame-retardant biomass fiber composite material with better flame-retardant property and mechanical strength is prepared. The flame-retardant biomass fiber composite material disclosed by the invention is prepared based on the preparation method disclosed by the invention, and has excellent flame retardance and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of fire-resistant building material manufacturing technology, and particularly relates to a flame-retardant biomass fiber composite material and its preparation method. Background Technology

[0002] Biomass fiber flame-retardant composites are green and fire-resistant composite materials made from biomass fibers such as wood, bamboo, and straw as reinforcing materials and adhesives such as epoxy resin, phenolic resin, or urea-formaldehyde resin as matrix materials. Through certain flame-retardant modification methods, they are manufactured using hot pressing technology and can be widely used in furniture, interior and exterior decoration, construction and other fields.

[0003] Biomass fibers and most polymers are inherently composed of flammable carbon chain molecules, resulting in poor fire safety of composites. Therefore, flame-retardant modification of composites is crucial for expanding their applications. Various surface modification methods have been used to improve the properties of biomass, and currently, physically incorporating flame-retardant fillers such as metal hydroxides and carbonates into composites is a widely used method to improve their fire safety. These fillers typically provide flame-retardant effects by absorbing heat, promoting the formation of a dense char layer, or reducing oxygen concentration. However, satisfactory flame retardancy of composites often requires a high loading of flame-retardant fillers, and most inorganic fillers have poor compatibility with the polymer matrix, leading to deterioration of the mechanical properties of the composites. Therefore, it is of great significance to improve the flame retardancy of biomass fiber composites while ensuring their good mechanical properties. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a wood fiber composite material with excellent flame retardant and mechanical properties and its preparation method, in order to address the shortcomings of the prior art.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: A method for preparing a flame-retardant biomass fiber composite material involves first grafting Al(OH)3 onto biomass fibers, then using H3PO4 to convert some of the Al(OH)3 on the biomass fibers into AlPO4, generating core-shell structured aluminum phosphate-aluminum hydroxide modified fibers, and finally curing them with a curing agent and epoxy resin to obtain the flame-retardant biomass fiber composite material.

[0006] The preferred method for preparing the above-mentioned flame-retardant biomass fiber composite material includes the following steps: (1) Add ammonia water to an ethanol aqueous solution to obtain a mixed solution. Add Al(OH)3 and biomass fiber to the mixed solution, heat and stir to carry out the first modification reaction, filter, wash and dry the product to obtain aluminum hydroxide modified fiber. (2) The aluminum hydroxide modified fiber was added to an ethanol solution of H3PO4, heated and stirred to carry out the second modification reaction, and the product was dried to obtain aluminum phosphate-aluminum hydroxide modified fiber. (3) The aluminum phosphate-aluminum hydroxide modified fiber is mixed with a curing agent, epoxy resin is added, and the mixture is stirred to obtain a mixture. The mixture is then hot-pressed and cured to obtain a flame-retardant biomass fiber composite material.

[0007] In the preferred method for preparing the above-mentioned flame-retardant biomass fiber composite material, in step (1), the mass ratio of anhydrous ethanol to water in the ethanol aqueous solution is 3-6:1-2, the mass ratio of ammonia to ethanol aqueous solution is 1-2:100, the mass ratio of Al(OH)3, biomass fiber and mixed solution is 15-18:40-50:180-240, the temperature of the first modification reaction is 60℃-70℃, the reaction time is 1 h-2 h, the drying temperature is 70℃-80℃, the drying time is 24 h-36 h, and the size of the biomass fiber is 60 mesh-100 mesh.

[0008] In the preferred method for preparing the above-mentioned flame-retardant biomass fiber composite material, in step (2), the ethanol solution of H3PO4 is obtained by mixing H3PO4 and anhydrous ethanol, and the mass-volume ratio of the aluminum hydroxide modified fiber, H3PO4 and anhydrous ethanol is 40 g~50 g∶1.5 g~2.5 g∶160 ml~170 ml; the temperature of the second modification reaction is 60℃~70℃, the reaction time is 1 h~2 h, the drying temperature is 70℃~80℃, and the drying time is 24 h~36 h.

[0009] In the preferred method for preparing the above-mentioned flame-retardant biomass fiber composite material, in step (3), the mass of the aluminum phosphate-aluminum hydroxide modified fiber in the mixture accounts for 40% to 60% of the total mass of the epoxy resin and curing agent; the curing agent is T31 curing agent or 650 curing agent, the epoxy resin is E51 epoxy resin or E44 epoxy resin, and the mass ratio of the curing agent to the epoxy resin is 1 to 2: 4 to 5; the hot pressing is to prepare a sample with a thickness of 4 mm to 5 mm by hot pressing at 80℃ to 120℃ and 8MPa to 9MPa for 5 min to 15 min; and the curing is to place the sample at room temperature for 48 h to 72 h.

[0010] In the preferred embodiment of the above-mentioned method for preparing flame-retardant biomass fiber composite material, the aluminum phosphate-aluminum hydroxide modified fiber is further surface-modified with a silane coupling agent, and then cured and molded with a curing agent and epoxy resin.

[0011] The preferred method for preparing the above-mentioned flame-retardant biomass fiber composite material includes the following specific steps for surface modification: mixing the aluminum phosphate-aluminum hydroxide modified fiber, silane coupling agent, and glacial acetic acid in an ethanol aqueous solution, carrying out a surface modification reaction, filtering, washing, and drying the product to obtain silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber.

[0012] In the preferred method for preparing the above-mentioned flame-retardant biomass fiber composite material, the mass ratio of the aluminum phosphate-aluminum hydroxide modified fiber, silane coupling agent, glacial acetic acid, and ethanol aqueous solution is 40-50:0.25-0.75:0.5-1.5:180-240; the mass ratio of anhydrous ethanol to water in the ethanol aqueous solution is 3-6:1-2; the surface modification reaction time is 1-2 hours; the drying temperature is 70-80°C; and the drying time is 24-36 hours. During curing, the mass percentage of the silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber in the mixture of silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber, curing agent, and epoxy resin is 40%-60%.

[0013] In the above-mentioned method for preparing flame-retardant biomass fiber composites, preferably, the silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

[0014] As a general inventive concept, the present invention also provides a flame-retardant biomass fiber composite material prepared by the above-described preparation method.

[0015] Compared with the prior art, the advantages of the present invention are as follows: (1) To address the problem of decreased mechanical properties of composite materials caused by commonly used physical flame retardants, the preparation method of this invention employs a self-sacrificing template strategy to manufacture biomass fiber composite materials with both excellent flame retardancy and mechanical strength. First, Al(OH)3 is grafted onto biomass fibers, and then H3PO4 is introduced, causing some of the Al(OH)3 on the biomass fibers to self-sacrifice and transform into AlPO4, generating core-shell structured aluminum phosphate-aluminum hydroxide modified fibers. Then, the fibers are cured with a curing agent and epoxy resin to obtain a flame-retardant biomass fiber composite material with good flame retardancy and high mechanical strength.

[0016] (2) The preparation method of the present invention involves surface modification of core-shell structured aluminum phosphate-aluminum hydroxide modified fibers with silane coupling agent, followed by curing of the modified silane coupling agent-aluminum phosphate-aluminum hydroxide modified fibers with curing agent and epoxy resin to obtain flame-retardant biomass fiber composite material with better flame retardant performance and mechanical strength.

[0017] (3) The reason why the flame-retardant biomass fiber composite material prepared by the method of the present invention has high mechanical strength is that the flame retardant incorporated into the composite material is very small (less than 4%). For example, thermogravimetric analysis shows that the content of flame retardant AlPO4-Al(OH)3 in the silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber is as low as about 3.01%, and the loading of flame retardant filler is low, which can maintain good mechanical strength of the biomass fiber composite material. The key to the excellent flame retardant performance with low flame retardant content is that the flame retardant is chemically modified to stably combine with biomass fiber in a specific way. For example, the core-shell structure in the aluminum phosphate-aluminum hydroxide modified fiber and the Al-P-Si fireproof network on the silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber can significantly improve the thermal stability, flame retardancy and smoke suppression performance of the composite material. In addition, the covalent interfacial bonding between the silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber and the epoxy matrix also helps to improve the mechanical strength of the composite material. The preparation method of this invention provides a new perspective for manufacturing fire-resistant, safe, and mechanically robust biomass / polymer composite materials by utilizing biomass fiber surface modification and low-content inorganic flame-retardant fillers.

[0018] (4) The flame-retardant biomass fiber composite material of the present invention is prepared based on the preparation method of the present invention and has excellent flame retardancy and mechanical properties. Attached Figure Description

[0019] Figure 1 The images show the microstructures of the wood fiber, aluminum hydroxide-modified wood fiber, and aluminum phosphate-aluminum hydroxide-modified wood fiber used in Example 1 of this invention; wherein, (a) is wood fiber without flame retardant treatment, (b) is wood fiber modified with Al(OH)3, and (c) is wood fiber modified with AlPO4-Al(OH)3. Detailed Implementation

[0020] The present invention will be further described below with reference to the accompanying drawings and specific preferred embodiments, but this does not limit the scope of protection of the present invention. In the following embodiments, unless otherwise specified, the raw materials and instruments used are commercially available, wherein the mass fraction of ammonia water is 10% and the mass fraction of H3PO4 is 85%; T31 curing agent was purchased from Wuxi Morui Electronic Technology Co., Ltd.; E51 epoxy resin was purchased from Nantong Xingchen Synthetic Materials Co., Ltd., WSR618; KH560 silane coupling agent (i.e., γ-glycidyl etheroxypropyltrimethoxysilane) was purchased from Kangjin New Materials Technology Co., Ltd., Chinese Academy of Sciences KH-560; the mesh size of wood fiber is 60-100 mesh.

[0021] Example 1 A method for preparing a flame-retardant biomass fiber composite material according to the present invention includes the following steps: (1) 150 g of anhydrous ethanol and 30 g of water were mixed, and 1 wt% ammonia was added to obtain a mixed solution. Then, 17.5 g of Al(OH)3 and 50 g of wood fiber were added to the mixed solution, and the mixture was stirred vigorously in a water bath at 60 °C for 2 h to carry out the first modification reaction. Then, excess Al(OH)3 was washed away by filtration, and the product was dried in an oven at 70 °C for 24 h to obtain aluminum hydroxide modified fiber, denoted as Al(OH)3@fiber.

[0022] (2) Mix 1.5 g H3PO4 and 160 ml anhydrous ethanol to obtain an ethanol solution of H3PO4. Add 50 g Al(OH)3@ fiber to the solution and stir vigorously in a water bath at 70 °C for 2 h to carry out the second modification reaction. Dry the product in an oven at 70 °C for 24 h to obtain aluminum phosphate-aluminum hydroxide modified fiber, denoted as AlPO4-Al(OH)3@ fiber.

[0023] (3) Mix 12.5g of AlPO4-Al(OH)3@ fiber with 5g of T31 curing agent, then add 20g of E51 epoxy resin and stir vigorously for 0.5 h to obtain a mixture. The mass of the modified AlPO4-Al(OH)3@ fiber in the mixture accounts for 50% of the total mass of epoxy resin and curing agent. Hot press the mixture at 100℃, 8 MPa, and 10 min to prepare a sample with a thickness of 5 mm. Place the prepared sample at room temperature for 48 h to ensure complete curing and obtain flame-retardant biomass fiber composite material, namely AlPO4-Al(OH)3@ fiber composite material.

[0024] In step (3), the flame-retardant biomass fiber composite material obtained by first mixing AlPO4-Al(OH)3@ fiber with curing agent and then adding epoxy resin has the best mechanical strength because the viscosity of curing agent is lower than that of epoxy resin, the fiber can be better dispersed in curing agent, the contact surface between fiber and curing agent is larger, the fiber can be better wrapped by curing agent, so the biomass fiber can be mixed evenly. If AlPO4-Al(OH)3@ fiber is mixed with epoxy resin first, the viscosity is too high, and it is easy to mix unevenly. The contact surface between fiber and epoxy resin is small, and part of it will be exposed. This will lead to low mechanical strength of the material. If AlPO4-Al(OH)3@ fiber, curing agent and epoxy resin are mixed together, the epoxy resin and curing agent are easy to pre-cured. Thus, the material is pre-cured before the modified fiber is evenly dispersed, which is not conducive to improving the mechanical strength of the final product, flame-retardant biomass fiber composite material.

[0025] The microstructure of the untreated wood fiber, aluminum hydroxide-modified fiber, and aluminum phosphate-aluminum hydroxide-modified fiber in this embodiment was characterized by scanning electron microscopy at magnifications of 20x, 100x, and 10x, respectively. The results are as follows: Figure 1 As shown, Figure 1 In Figure (a), wood fiber without flame retardant treatment is shown; in Figure (b), wood fiber modified with Al(OH)3, i.e., the product of step (1), is shown; and in Figure (c), wood fiber modified with AlPO4-Al(OH)3, i.e., the product of step (2). A cluster of white, flower-like material can be seen in Figure (b), indicating that Al(OH)3 has been successfully anchored to the wood fiber. A layer of white, flocculent material can be seen on the surface of the wood fiber in Figure (c), indicating that H3PO4 and Al(OH)3 have partially reacted successfully to form AlPO4.

[0026] Comparative Example 1 A method for preparing a biomass fiber composite material includes the following steps: (1) Mix 150 g of anhydrous ethanol with 30 g of water, add 1 wt% ammonia water to obtain a mixed solution. Then, add 17.5 g of Al(OH)3 and 50 g of wood fiber to the mixed solution and stir vigorously in a water bath at 60 °C for 2 h to carry out the first modification reaction. Then, wash away excess Al(OH)3 by filtration and dry the product in an oven at 70 °C for 24 h to obtain aluminum hydroxide modified fiber, denoted as Al(OH)3@fiber.

[0027] (2) Mix 12.5g of Al(OH)3@ fiber with 5g of T31 curing agent, then add 20g of E51 epoxy resin, stir vigorously for 0.5 h to obtain a mixture. The mass of the modified Al(OH)3@ fiber in the mixture accounts for 50% of the total mass of epoxy resin and curing agent. Hot press the mixture at a temperature of 100℃, a pressure of 8 MPa, and a time of 10 min to prepare a sample with a thickness of 5 mm. Place the prepared sample at room temperature for 48 h to ensure complete curing to obtain the Al(OH)3@ fiber composite material.

[0028] Comparative Example 2 A method for preparing a flame-retardant biomass fiber composite material includes the following steps: First, the curing agent is mixed with wood fiber, then the material containing Al(OH)3 and epoxy resin is added and thoroughly mixed to obtain a mixture. A 5 mm thick sample is prepared by hot-pressing at 100℃, 8 MPa, and 10 min. The prepared sample is then left at room temperature for 48 h to ensure complete curing, resulting in a fiber composite material with physically added Al(OH)3. Al(OH)3 is a physical additive, and its mass percentage in the mixture is 35%. The resulting composite material exhibits good flame retardant properties, achieving self-extinguishing flame retardancy and a flame retardant rating of V0.

[0029] Example 2 A method for preparing a flame-retardant biomass fiber composite material according to the present invention includes the following steps: (1) Mix 150 g of anhydrous ethanol with 30 g of water, add 1 wt% ammonia water to obtain a mixed solution. Then, add 17.5 g of Al(OH)3 and 50 g of wood fiber to the mixed solution and stir vigorously in a water bath at 60 °C for 2 h to carry out the first modification reaction. Then, wash away excess Al(OH)3 by filtration and dry the product in an oven at 70 °C for 24 h to obtain aluminum hydroxide modified fiber, denoted as Al(OH)3@fiber.

[0030] (2) Mix 1.5 g H3PO4 and 160 ml anhydrous ethanol to obtain an ethanol solution of H3PO4. Add 50 g Al(OH)3@ fiber to the solution and stir vigorously in a water bath at 70 °C for 2 h to carry out the second modification reaction. Dry the product in an oven at 70 °C for 24 h to obtain aluminum phosphate-aluminum hydroxide modified fiber, denoted as AlPO4-Al(OH)3@ fiber.

[0031] (3) Add 50 g of AlPO4-Al(OH)3@ fiber, 0.75 g of KH560 silane coupling agent and 1.5 g of glacial acetic acid to a mixed solvent of 180 g of anhydrous ethanol and water (mass ratio 5:1) and mix thoroughly. React for 2 h to perform surface modification. Filter the product and wash it with deionized water. Dry it at 70 °C for 24 h to obtain silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber, denoted as KH560-AlPO4-Al(OH)3@ fiber.

[0032] (4) Mix 12.5g of KH560-AlPO4-Al(OH)3@ fiber with 5g of T31 curing agent, then add 20g of E51 epoxy resin and stir vigorously for 0.5 h to obtain a mixture. The mass of the modified KH560-AlPO4-Al(OH)3@ fiber in the mixture accounts for 50% of the total mass of epoxy resin and curing agent. Hot press the mixture at 100℃, 8 MPa, and 10 min to prepare a sample with a thickness of 5 mm. Place the prepared sample at room temperature for 48 h to ensure complete curing and obtain flame-retardant biomass fiber composite material, namely KH560-AlPO4-Al(OH)3@ fiber composite material.

[0033] Comparative Example 3 A method for preparing a biomass fiber composite material includes the following steps: (1) Mix 150 g of anhydrous ethanol with 30 g of water, add 1 wt% ammonia water to obtain a mixed solution. Then, add 17.5 g of Al(OH)3 and 50 g of wood fiber to the mixed solution and stir vigorously in a water bath at 60 °C for 2 h to carry out the first modification reaction. Then, wash away excess Al(OH)3 by filtration and dry the product in an oven at 70 °C for 24 h to obtain aluminum hydroxide modified fiber, denoted as Al(OH)3@fiber.

[0034] (2) Add 50 g Al(OH)3@ fiber, 0.75 g KH560 and 1.5 g glacial acetic acid to a mixed solvent of 180 g anhydrous ethanol and water (mass ratio of 5:1) and mix thoroughly. React for 2 h to perform surface modification. Filter the product and wash it with deionized water. Dry it at 70 °C for 24 h to obtain Al(OH)3-KH560@ fiber.

[0035] (3) Mix 12.5g of Al(OH)3-KH560@ fiber with 5g of T31 curing agent, then add 20g of E51 epoxy resin and stir vigorously for 0.5 h to obtain a mixture. The mass of the modified Al(OH)3-KH560@ fiber in the mixture accounts for 50% of the total mass of epoxy resin and curing agent. Hot press the mixture at a temperature of 100℃, a pressure of 8 MPa, and a time of 10 min to prepare a sample with a thickness of 5 mm. Place the prepared sample at room temperature for 48 h to ensure complete curing to obtain Al(OH)3-KH560@ fiber composite material.

[0036] The tensile strength, flexural strength, and flammability of the composite materials obtained in Examples 1-4 and Comparative Example 1 were tested according to GB / T 1040.2-2006 and GB / T 9341-2008. The material grades (tensile strength Class I ≥18 MPa, Class II ≥24 MPa, Class III ≥35 MPa) were evaluated according to GB / T 29500-2013. The content of flame retardant in the composite materials of Examples 1-2 and Comparative Examples 1 and 3 was calculated by thermogravimetric analysis. The content of flame retardant in Comparative Example 2 was calculated based on the amount added. The results are shown in Table 1.

[0037] Table 1 Performance test results of wood fiber flame-retardant composite materials

[0038] Based on the examples, comparative examples, and the data in Table 1, it can be seen that the flame-retardant biomass fiber composite material prepared by co-modification with aluminum phosphate and aluminum hydroxide in Example 1 exhibits significantly higher flame-retardant properties and mechanical strengths, including tensile strength and flexural strength, than the composite material prepared by modification with aluminum hydroxide alone in Comparative Example 1, and is even significantly superior to the flame-retardant material prepared by physically adding aluminum hydroxide in Comparative Example 1. A comparison of Examples 1 and 2 shows that the flame-retardant biomass fiber composite material prepared by triple modification in Example 2—namely, surface modification with a silane coupling agent on the basis of aluminum phosphate and aluminum hydroxide modification—has superior flame-retardant properties and mechanical strength compared to the dual modification in Example 1. A comparison of Examples 1 and Comparative Example 3 shows that although Comparative Example 3 also underwent surface modification with a silane coupling agent, it did not undergo phosphate modification; therefore, while its mechanical properties were good, its flame-retardant properties were poor.

[0039] While the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the invention. Any person skilled in the art can make many possible variations and modifications to the technical solutions of the present invention, or modify them into equivalent embodiments, without departing from the spirit and technical essence of the invention. Therefore, any simple modifications, equivalent substitutions, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A method for preparing a flame-retardant biomass fiber composite material, characterized in that, First, Al(OH)3 is grafted onto biomass fibers. Then, H3PO4 is used to convert some of the Al(OH)3 on the biomass fibers into AlPO4, generating core-shell structured aluminum phosphate-aluminum hydroxide modified fibers. Finally, a curing agent and epoxy resin are used to cure and mold the fibers, resulting in flame-retardant biomass fiber composites.

2. A method for preparing a flame-retardant biomass fiber composite material, characterized in that, Includes the following steps: (1) Add ammonia water to an ethanol aqueous solution to obtain a mixed solution. Add Al(OH)3 and biomass fiber to the mixed solution, heat and stir to carry out the first modification reaction, filter, wash and dry the product to obtain aluminum hydroxide modified fiber. (2) The aluminum hydroxide modified fiber was added to an ethanol solution of H3PO4, heated and stirred to carry out the second modification reaction, and the product was dried to obtain aluminum phosphate-aluminum hydroxide modified fiber. (3) The aluminum phosphate-aluminum hydroxide modified fiber is mixed with a curing agent, epoxy resin is added, and the mixture is stirred to obtain a mixture. The mixture is then hot-pressed and cured to obtain a flame-retardant biomass fiber composite material.

3. The method for preparing the flame-retardant biomass fiber composite material according to claim 2, characterized in that, In step (1), the mass ratio of anhydrous ethanol to water in the ethanol-water solution is 3-6:1-2, and the mass ratio of ammonia to ethanol-water solution is 1-2:100; the mass ratio of Al(OH)3, biomass fiber, and mixed solution is 15-18:40-50:180-240; the temperature of the first modification reaction is 60℃-70℃, and the reaction time is 1-2 h; the drying temperature is 70℃-80℃, and the drying time is 24-36 h; the size of the biomass fiber is 60 mesh-100 mesh.

4. The method for preparing the flame-retardant biomass fiber composite material according to claim 2, characterized in that, In step (2), the ethanol solution of H3PO4 is obtained by mixing H3PO4 and anhydrous ethanol. The mass-volume ratio of the aluminum hydroxide modified fiber, H3PO4 and anhydrous ethanol is 40 g~50 g ∶ 1.5 g~2.5 g ∶ 160 ml~170 ml. The temperature of the second modification reaction is 60℃~70℃ and the reaction time is 1 h~2 h. The drying temperature is 70℃~80℃ and the drying time is 24 h~36 h.

5. The method for preparing the flame-retardant biomass fiber composite material according to claim 2, characterized in that, In step (3), the mass of aluminum phosphate-aluminum hydroxide modified fiber in the mixture accounts for 40% to 60% of the total mass of epoxy resin and curing agent; the curing agent is T31 curing agent or 650 curing agent, the epoxy resin is E51 epoxy resin or E44 epoxy resin, and the mass ratio of curing agent to epoxy resin is 1 to 2: 4 to 5; the hot pressing is to prepare a sample with a thickness of 4 mm to 5 mm by hot pressing at 80℃ to 120℃ and 8MPa to 9MPa for 5 min to 15 min; the curing is to place the sample at room temperature for 48 h to 72 h.

6. The method for preparing the flame-retardant biomass fiber composite material according to any one of claims 1 to 5, characterized in that, The aluminum phosphate-aluminum hydroxide modified fiber was further surface modified with a silane coupling agent, and then cured and molded with a curing agent and epoxy resin.

7. The method for preparing the flame-retardant biomass fiber composite material according to claim 6, characterized in that, The specific steps of the surface modification include: adding the aluminum phosphate-aluminum hydroxide modified fiber, silane coupling agent and glacial acetic acid to an ethanol aqueous solution for mixing, carrying out a surface modification reaction, filtering, washing and drying the product to obtain silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber.

8. The method for preparing the flame-retardant biomass fiber composite material according to claim 7, characterized in that, The mass ratio of the aluminum phosphate-aluminum hydroxide modified fiber, silane coupling agent, glacial acetic acid, and ethanol aqueous solution is 40-50:0.25-0.75:0.5-1.5:180-240. The mass ratio of anhydrous ethanol to water in the ethanol aqueous solution is 3-6:1-2. The surface modification reaction time is 1-2 hours. The drying temperature is 70-80°C, and the drying time is 24-36 hours. During curing, the mass percentage of the silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber in the mixture of silane coupling agent-aluminum phosphate-aluminum hydroxide modified fiber, curing agent, and epoxy resin is 40%-60%.

9. The method for preparing the flame-retardant biomass fiber composite material according to claim 8, characterized in that, The silane coupling agent is γ-glycidoxypropyltrimethoxysilane.

10. A flame-retardant biomass fiber composite material prepared by the preparation method according to any one of claims 1 to 9.

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