Thermosetting composite material with high impact strength and preparation method thereof

Abstract

The invention discloses a thermosetting composite material with high impact strength and a preparation method thereof, and belongs to the technical field of thermosetting composites.The preparation method comprises the steps that enzymatic hydrolysis lignin is subjected to dialysis self-assembly treatment to obtain rigid nano lignin microspheres, then activated carbon-carbon double bonds are introduced to the nano lignin microspheres through a silane coupling agent, and the nano lignin microspheres are subjected to self-assembly treatment to obtain the high-impact-strength thermosetting composite material. The preparation method comprises the following steps: forming a flexible polyacrylate buffer layer on nano lignin microspheres through in-situ copolymerization to obtain modified nano lignin microspheres, further uniformly dispersing the modified nano lignin microspheres in an epoxy resin system, and carrying out vacuum defoaming and heating curing to obtain the thermosetting composite material. Through the energy absorption buffer effect of the flexible layer and the covalent chemical anchoring effect between the modified microspheres and the resin matrix, the composite material can still keep good impact strength and intrinsic structure rigidity in a high-temperature state, and is suitable for scenes such as a new energy automobile battery pack bottom shell and the like with harsh anti-impact and heat-resistant protection requirements.

Description

Technical Field

[0001] This invention belongs to the field of thermosetting composite materials technology, specifically a thermosetting composite material with high impact strength and its preparation method. Background Technology

[0002] The battery pack bottom shell of a new energy vehicle is a core structural component that serves the dual functions of physical protection and load-bearing of the battery pack. In complex actual driving conditions, the bottom shell is constantly exposed to transient high-energy damage scenarios such as high-frequency flying of road debris and collisions with road obstacles and potholes. Therefore, the protective material must have extremely high impact resistance to prevent catastrophic breakage. Thermosetting composite materials, represented by epoxy resin, are gradually replacing traditional metals and becoming the ideal matrix material for manufacturing such chassis protection components due to the high strength and lightweight advantages brought by the dense three-dimensional cross-linked network after curing.

[0003] However, epoxy resin has a very high crosslinking density and is inherently brittle. In order to make it have the extremely high impact resistance required for the bottom shell, industrial manufacturers usually need to introduce a large amount of toughening modifiers such as elastomers or flexible polymers. However, this traditional toughening method often comes at the cost of sacrificing the original dense crosslinking network of the matrix, which weakens the overall heat resistance and rigidity of the material. In actual service scenarios, the bottom shell not only has to cope with sudden physical collisions, but also has to be in the high-temperature environment where the battery releases a lot of heat during high-rate charging and discharging for a long time. Under high-temperature conditions, because the traditional toughening system destroys the high-temperature resistant skeleton of the epoxy resin itself, the free volume inside the polymer system will expand rapidly, and the molecular chain segments will undergo violent desorption and slip softening when heated. This makes the composite material unable to effectively transfer stress when subjected to external high-energy impacts, which makes the bottom shell prone to cracking and failure when it is hit.

[0004] Therefore, how to construct a thermosetting composite material with high impact strength that can maintain a rigid skeleton support in high-temperature environments, thereby effectively resisting high-energy physical collisions and ensuring the integrity of the overall structure, has become a key technical problem that urgently needs to be solved in the field of composite materials for new energy vehicles. Summary of the Invention

[0005] The purpose of this invention is to provide a thermosetting composite material with high impact strength and its preparation method. By constructing an efficient chemical anchoring network between modified lignin nanospheres and an epoxy resin matrix, the composite system can maintain stable rigid skeleton support and efficient impact energy dissipation under high temperature environment, so as to meet the actual needs of core protective components such as the bottom shell of new energy vehicle battery packs for high impact strength and structural safety in complex driving environments.

[0006] The objective of this invention can be achieved through the following technical solutions: This invention provides a thermosetting composite material with high impact strength, comprising the following raw materials by weight: 100-300 parts epoxy resin, 90-270 parts methyltetrahydrophthalic anhydride, 5-15 parts modified nano-lignin microspheres, and 2-6 parts N,N-dimethylbenzylamine.

[0007] This invention also provides a method for preparing a thermosetting composite material with high impact strength, comprising the following steps: Epoxy resin and methyltetrahydrophthalic anhydride (curing agent) are placed in a reaction vessel and stirred at 50-70℃ for 1-2 hours. Modified nano-lignin microspheres are added and ultrasonically dispersed for 1-2 hours. After cooling to 25-35℃, N,N-dimethylbenzylamine (accelerator) is added and stirred for 20-40 minutes. The mixture is then vacuum degassed at 25-35℃ for 20-40 minutes. The degassed mixture is then added to a mold, transferred to a forced-air drying oven, pre-cured for 1-2 hours, cured for 2-4 hours, cooled, and demolded to obtain a thermosetting composite material with high impact strength.

[0008] Furthermore, the pre-curing temperature is 80-100℃, and the curing temperature is 130-150℃. Furthermore, the preparation process of the modified lignin nanospheres is as follows: Double-bonded lignin nanospheres, butyl acrylate, acrylic acid, azobisisobutyronitrile, and N,N-dimethylformamide were placed in a reaction vessel under nitrogen atmosphere and reacted at 60-80℃ for 1-2 hours. The reaction solution was then added to a mixed solution of methanol and deionized water in a volume ratio of 1:1 to precipitate the precipitate. The precipitate was filtered and vacuum dried to constant weight to obtain modified lignin nanospheres.

[0009] Furthermore, the ratio of the amount of double-bonded lignin nanospheres, butyl acrylate, acrylic acid, azobisisobutyronitrile and N,N-dimethylformamide is 20-40g: 20-40g: 2-4g: 0.2-0.4g: 200-400mL.

[0010] Furthermore, the preparation process of the double-bond lignin nanospheres is as follows: γ-methacryloxypropyltrimethoxysilane and anhydrous ethanol were placed in a reaction vessel, and 0.5 mol / L aqueous acetic acid solution was added to adjust the pH of the reaction solution to 4-6. After stirring at 25-35℃ for 1-2 h, rigid nano-lignin microspheres were added, and the reaction was carried out at 50-60℃ for 1-2 h. The mixture was then filtered, washed, and vacuum dried to constant weight to obtain nano-lignin microspheres containing double bonds.

[0011] Furthermore, the ratio of γ-methacryloyloxypropyltrimethoxysilane, anhydrous ethanol, and rigid nano-lignin microspheres is 4-6g: 200-400mL: 30-50g.

[0012] Furthermore, the preparation process of rigid lignin nanospheres is as follows: Enzymatically hydrolyzed lignin, γ-valerolactone, and ultrapure water were placed in a reaction vessel and stirred at 25-35℃ for 20-40 min to obtain a lignin solution. The lignin solution was then added to 4-6 times its volume of ultrapure water, and the mixture was stirred at the same temperature for another 20-40 min. After dialyzing, the solution in the bag was transferred to the reaction vessel and reacted at 150-170℃ for 12-14 h. The mixture was then centrifuged and freeze-dried to constant weight to obtain rigid nano-lignin microspheres.

[0013] Furthermore, the ratio of enzymatic hydrolysis of lignin, γ-valerolactone, and ultrapure water is 40-60: 200-300 mL: 20-40 mL.

[0014] The beneficial effects of this invention are: 1. The thermosetting composite material with high impact strength prepared by the present invention is made by preparing rigid nano-lignin microspheres and forming a flexible polyacrylate buffer layer on the microspheres. When the material is impacted, the flexible buffer layer provided by the modified nano-lignin microspheres can absorb and consume the impact energy. At the same time, the thermally stable rigid lignin microspheres can still serve as a strong force fulcrum to maintain rigid support, thereby improving the mechanical strength of the epoxy resin matrix. Furthermore, the epoxy resin matrix, with its inherently dense cross-linked network, effectively improves the interfacial debonding or separation of the microspheres under severe stress, and further ensures that the external impact stress can be accurately and efficiently transferred to the microspheres. This allows the composite material to obtain extremely high impact strength while retaining the inherent high structural rigidity and physical load-bearing capacity of the epoxy resin system.

[0015] 2. The thermosetting composite material with high impact strength prepared by this invention has a strong covalent bond between the modified lignin nanospheres and the epoxy resin matrix during the cross-linking and curing process, which improves the uniform dispersion of the modified lignin nanospheres in the resin matrix. Under high-temperature service conditions, this strong interfacial chemical anchoring effect, combined with the steric hindrance effect of rigid lignin, restricts the thermal movement of the matrix molecular chain segments, effectively suppressing the expansion of the internal volume of the system and the slippage of the chain segments. This allows the composite material to efficiently transfer and dissipate stress through the chemical bond network when subjected to external high-energy physical collisions at high temperatures, ensuring the high impact resistance and structural safety of the composite material in a wide temperature range environment. Detailed Implementation

[0016] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0017] Example 1: This example provides a thermosetting composite material with high impact strength, prepared through the following steps: S1: 40g of enzymatically hydrolyzed lignin, 200mL of γ-valerolactone and 20mL of ultrapure water were placed in a reaction vessel and stirred at 200r / min for 20min at 25℃ to obtain a lignin solution. The lignin solution was added to 4 times its volume of ultrapure water and stirred at the same temperature and stirring rate for another 20min. After dialyzing through an 8 kDa dialysis bag, the solution in the dialysis bag was transferred to the reaction vessel and reacted at 150℃ with the same stirring rate for 12h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, and the solid was freeze-dried to constant weight to obtain rigid nano-lignin microspheres.

[0018] S2: 4g of γ-methacryloxypropyltrimethoxysilane and 200mL of anhydrous ethanol were placed in a reaction vessel. The pH of the reaction solution was adjusted to 4 by adding 0.5mol / L acetic acid aqueous solution. After stirring at 200r / min for 1h at 25℃, 30g of rigid nano-lignin microspheres were added. The reaction was stirred at 1000r / min for 1h at 50℃. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed twice with deionized water and anhydrous ethanol. The mixture was then vacuum dried at 40℃ to constant weight to obtain nano-lignin microspheres containing double bonds.

[0019] S3: 20g of double-bonded lignin nanospheres, 20g of butyl acrylate, 2g of acrylic acid, 0.2g of azobisisobutyronitrile and 200mL of N,N-dimethylformamide were placed in a reaction vessel under nitrogen atmosphere protection and reacted at 60℃ and 200r / min for 1h. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was added to a mixed solution of methanol and deionized water in a volume ratio of 1:1 to precipitate the mixture. The mixture was filtered, and the filter cake was vacuum dried at 40℃ to constant weight to obtain modified lignin nanospheres.

[0020] S4: Place 100g of epoxy resin and 90g of methyltetrahydrophthalic anhydride (curing agent) in a reactor and stir at 800r / min for 1h at 50℃. Add 5g of modified nano-lignin microspheres and ultrasonically disperse for 1h. After the reaction solution is cooled to 25℃, add 2g of N,N-dimethylbenzylamine (accelerator) and stir at 400r / min for 20min. Place the mixture in a vacuum degassing box and degas at 25℃ for 20min. Add the degassed mixture to a mold and transfer it to a forced-air drying oven for pre-curing at 80℃ for 1h. Then raise the temperature to 130℃ and cure for 2h. Cool to room temperature and demold to obtain a thermosetting composite material with high impact strength.

[0021] Example 2: This example provides a thermosetting composite material with high impact strength, prepared through the following steps: S1: 50g of enzymatically hydrolyzed lignin, 250mL of γ-valerolactone and 30mL of ultrapure water were placed in a reaction vessel and stirred at 250r / min for 30min at 30℃ to obtain a lignin solution. The lignin solution was added to 5 times its volume of ultrapure water and stirred at the same temperature and stirring rate for another 30min. After dialyzing through an 11 kDa dialysis bag, the solution in the dialysis bag was transferred to the reaction vessel and reacted at 160℃ with the same stirring rate for 13h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, and the solid was freeze-dried to constant weight to obtain rigid nano-lignin microspheres.

[0022] S2: 5g of γ-methacryloxypropyltrimethoxysilane and 300mL of anhydrous ethanol were placed in a reaction vessel. The pH of the reaction solution was adjusted to 5 by adding 0.5mol / L acetic acid aqueous solution. After stirring at 250r / min for 1.5h at 30℃, 40g of rigid nano-lignin microspheres were added. The reaction was stirred at 1500r / min for 1.5h at 55℃. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed three times with deionized water and anhydrous ethanol. The mixture was then vacuum dried at 45℃ to constant weight to obtain nano-lignin microspheres containing double bonds.

[0023] S3: 30g of double-bonded lignin nanospheres, 30g of butyl acrylate, 3g of acrylic acid, 0.3g of azobisisobutyronitrile, and 300mL of N,N-dimethylformamide were placed in a reaction vessel under nitrogen atmosphere protection and reacted at 70℃ and 250r / min for 1.5h. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was added to a mixed solution of methanol and deionized water in a volume ratio of 1:1 to precipitate the mixture. The mixture was filtered, and the filter cake was vacuum dried at 50℃ to constant weight to obtain modified lignin nanospheres.

[0024] S4: Place 200g of epoxy resin and 180g of methyltetrahydrophthalic anhydride (curing agent) in a reactor and stir at 900r / min for 1.5h at 60℃. Add 10g of modified nano-lignin microspheres and ultrasonically disperse for 1.5h. After the reaction solution cools to 30℃, add 4g of N,N-dimethylbenzylamine (accelerator) and stir at 500r / min for 30min. Place the mixture in a vacuum degassing chamber and degas at 30℃ for 30min. Add the degassed mixture to a mold and transfer it to a forced-air drying oven for pre-curing at 90℃ for 1.5h. Then raise the temperature to 140℃ and cure for 3h. Cool to room temperature and demold to obtain a thermosetting composite material with high impact strength.

[0025] Example 3: This example provides a thermosetting composite material with high impact strength, prepared through the following steps: S1: 60g of enzymatically hydrolyzed lignin, 300mL of γ-valerolactone and 40mL of ultrapure water were placed in a reaction vessel and stirred at 300r / min for 40min at 35℃ to obtain a lignin solution. The lignin solution was added to 6 times its volume of ultrapure water and stirred at the same temperature and stirring rate for another 40min. After dialyzing through a 14 kDa dialysis bag, the solution in the dialysis bag was transferred to the reaction vessel and reacted at 170℃ with the same stirring rate for another 14h. After the reaction was completed, the mixture was cooled to room temperature, centrifuged, and the solid was freeze-dried to constant weight to obtain rigid nano-lignin microspheres.

[0026] S2: 6g of γ-methacryloxypropyltrimethoxysilane and 400mL of anhydrous ethanol were placed in a reaction vessel. The pH of the reaction solution was adjusted to 6 by adding 0.5mol / L acetic acid aqueous solution. After stirring at 300r / min for 2h at 35℃, 50g of rigid nano-lignin microspheres were added. The reaction was stirred at 2000r / min for 2h at 60℃. After the reaction was completed, the mixture was cooled to room temperature, filtered, and the filter cake was washed 4 times with deionized water and anhydrous ethanol. The mixture was then vacuum dried at 50℃ to constant weight to obtain nano-lignin microspheres containing double bonds.

[0027] S3: 40g of double-bonded lignin nanospheres, 40g of butyl acrylate, 4g of acrylic acid, 0.4g of azobisisobutyronitrile and 400mL of N,N-dimethylformamide were placed in a reaction vessel under nitrogen atmosphere protection and reacted at 80℃ and 300r / min for 2h. After the reaction was completed, the mixture was cooled to room temperature. The reaction solution was added to a mixed solution of methanol and deionized water in a volume ratio of 1:1 to precipitate the mixture. The mixture was filtered, and the filter cake was vacuum dried at 60℃ to constant weight to obtain modified lignin nanospheres.

[0028] S4: Place 300g of epoxy resin and 270g of methyltetrahydrophthalic anhydride (curing agent) in a reactor and stir at 1000r / min for 2h at 70℃. Add 15g of modified nano-lignin microspheres and ultrasonically disperse for 2h. After the reaction solution is cooled to 35℃, add 6g of N,N-dimethylbenzylamine (accelerator) and stir at 600r / min for 40min. Place the mixture in a vacuum degassing box and vacuum degas for 40min at 35℃. Add the degassed mixture to a mold and transfer it to a forced-air drying oven for pre-curing at 100℃ for 2h. Then raise the temperature to 150℃ and cure for 4h. Cool to room temperature and demold to obtain a thermosetting composite material with high impact strength.

[0029] The thermosetting composite material with high impact strength prepared in the above-described comparative examples first utilizes the difference in solubility of enzymatically hydrolyzed lignin in a good solvent of γ-valerolactone and an antisolvent system of ultrapure water to promote the self-assembly of lignin molecular chains, forming nanosphere micelles. Subsequently, under high-temperature hydrothermal conditions, dehydration condensation and deep cross-linking occur to obtain rigid lignin nanospheres. Then, through a hydrolysis condensation reaction, the hydrolysis product of γ-methacryloyloxypropyltrimethoxysilane reacts with the hydroxyl groups on the surface of the rigid lignin nanospheres to form covalent bonds, thereby successfully introducing active double bonds on the surface of the microspheres, resulting in a double-bonded composite material. Modified lignin nanospheres were first formed. Then, using azobisisobutyronitrile (AIBN) as an initiator, a free radical graft copolymerization reaction was initiated between butyl acrylate and acrylic monomers and the active double bonds on the surface of the microspheres. A flexible buffer layer of polyacrylate with carboxyl groups was formed on the rigid lignin, resulting in modified lignin nanospheres. Finally, using epoxy resin and methyltetrahydrophthalic anhydride as the matrix system, the epoxy groups and the anhydride under high-temperature curing conditions underwent a crosslinking reaction. At the same time, the carboxyl groups on the modified lignin nanospheres underwent an in-situ ring-opening bonding reaction with the epoxy groups in the resin, constructing a micro-crosslinked network, and obtaining a thermosetting composite material with high impact strength.

[0030] Comparative Example 1: The difference from Example 2 is that commercially available nano-lignin was used instead of the modified nano-lignin microspheres prepared in step S3 in step S4, while the other steps remained unchanged, and a thermosetting composite material with high impact strength was prepared.

[0031] Comparative Example 2: The difference from Example 2 is that in step S4, the rigid nano-lignin microspheres prepared in step S1 are used instead of the modified nano-lignin microspheres prepared in step S3, while the other steps remain unchanged, and a thermosetting composite material with high impact strength is prepared.

[0032] Comparative Example 3: The difference from Example 2 is that the modified nano-lignin microspheres prepared in step S3 are removed in step S4, while the other steps remain unchanged, and a thermosetting composite material with high impact strength is prepared.

[0033] The nano-lignin purchased in the above examples and comparative examples was produced by Shanghai Maclean Biochemical Technology Co., Ltd., with an average particle size of 50-150 nm; the enzymatically hydrolyzed lignin was produced by Shanghai Aladdin Biochemical Technology Co., Ltd., with a purity ≥95% and a weight-average molecular weight of 2000 Da; the ultrapure water was produced by Sinopharm Chemical Reagent Co., Ltd., with a resistivity ≥18.2 MΩ·cm; and the epoxy resin was produced by Nantong Xingchen Synthetic Materials Co., Ltd., with the grade E-51 (bisphenol A type) and an epoxy value of 0.51 mol / 100g. The thermosetting composite materials with high impact strength prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to performance tests, and the test results are shown in Table 1: Sample preparation: The thermosetting composite materials with high impact strength prepared in the above examples and comparative examples were prepared into samples for performance testing.

[0034] Glass transition temperature test: Differential scanning calorimetry was used to test the sample. Under nitrogen atmosphere, the temperature was scanned at a heating rate of 10℃ / min, and the glass transition temperature of the material was recorded. The higher the glass transition temperature, the better the high temperature resistance of the material.

[0035] Tensile strength: Referring to standard GB / T 2567-2021, place the specimen on a universal testing machine and perform a tensile test at a constant tensile speed. Record the tensile strength of the material. The higher the tensile strength value, the better the mechanical properties of the material.

[0036] Notched impact strength test: Referring to standard GB / T 1843-2008, the specimen was placed on a pendulum impact testing machine for cantilever beam notched impact testing. The notched impact strength (kJ / m²) of the specimen at room temperature was recorded. 2 To simulate high-temperature conditions, the sample was placed in a constant-temperature environment chamber at 100℃ and kept at that temperature for 1 hour. The sample was then subjected to a notched impact strength test again, and the notched impact strength of the sample at high temperature was recorded. The higher the impact strength, the better the impact resistance of the material.

[0037] Table 1 Performance Test Table of Thermosetting Composite Materials with High Impact Strength As shown in Table 1, the thermosetting composite material with high impact strength prepared in the above embodiments has better performance than the comparative example in all aspects, and maintains good impact strength under high temperature environment. This indicates that the composite material prepared by the present invention utilizes thermally stable rigid lignin microspheres as strong force fulcrums to provide rigid physical support in the epoxy resin matrix, while being firmly anchored in the resin network by covalent bonds, so that the composite material still maintains good high impact resistance and structural integrity under high temperature environment.

[0038] In Comparative Example 1, the tensile strength and notched impact strength of the composite material at both room temperature and high temperature decreased significantly. This may be because commercially available nano-lignin tends to agglomerate within epoxy resin, easily forming macroscopic defects and stress concentration sources within the resin, and cannot effectively resist the impact stress generated by external physical collisions. This indicates that the modified nanospheres synthesized in this invention may have good dispersibility and interfacial compatibility, and can maintain the mechanical network strength of the composite matrix well under complex stress conditions.

[0039] In Comparative Example 2, the tensile strength and impact strength of the composite material both decreased significantly. This may be because the system used unmodified rigid nano-lignin microspheres, which resulted in the absence of flexible segments and reactive double bonds provided by acrylate and silane coupling agents in the material network. As a result, the material could not form strong chemical bonds with the epoxy resin, making it very easy for the interface to debond when subjected to tensile stress, leading to material cracking and failure.

[0040] In Comparative Example 3, the notched impact strength of the composite material was significantly reduced under both room temperature and high temperature conditions. This may be because the modified nano-lignin microspheres were removed. The epoxy resin matrix has a very high crosslinking density after curing and is relatively brittle. When subjected to external physical impact, it lacks an energy dissipation mechanism, which causes microcracks to propagate rapidly once they are generated inside the material, ultimately leading to a sharp decline in the impact resistance of the composite material.

[0041] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention.

Claims

1. A thermosetting composite material with high impact strength, characterized in that, By weight, it includes the following raw materials: 100-300 parts epoxy resin, 90-270 parts methyltetrahydrophthalic anhydride, 5-15 parts modified nano-lignin microspheres, and 2-6 parts N,N-dimethylbenzylamine. The modified lignin nanospheres were prepared through the following steps: Double-bonded lignin nanospheres, butyl acrylate, acrylic acid, azobisisobutyronitrile, and N,N-dimethylformamide were placed in a reaction vessel under nitrogen atmosphere and reacted at 60-80℃ for 1-2 hours. The reaction solution was then added to a mixed solution of methanol and deionized water in a volume ratio of 1:1 to precipitate the precipitate. The precipitate was filtered and vacuum dried to constant weight to obtain modified lignin nanospheres.

2. The thermosetting composite material with high impact strength according to claim 1, characterized in that, The ratio of the double-bond lignin nanospheres, butyl acrylate, acrylic acid, azobisisobutyronitrile, and N,N-dimethylformamide is 20-40g: 20-40g: 2-4g: 0.2-0.4g: 200-400mL.

3. The thermosetting composite material with high impact strength according to claim 2, characterized in that, The double-bond-containing lignin nanospheres were prepared by the following steps: γ-methacryloxypropyltrimethoxysilane and anhydrous ethanol were placed in a reaction vessel, and 0.5 mol / L aqueous acetic acid solution was added to adjust the pH of the reaction solution to 4-6. After stirring at 25-35℃ for 1-2 h, rigid nano-lignin microspheres were added, and the reaction was carried out at 50-60℃ for 1-2 h. The mixture was then filtered, washed, and vacuum dried to constant weight to obtain nano-lignin microspheres containing double bonds.

4. A thermosetting composite material with high impact strength according to claim 3, characterized in that, The ratio of γ-methacryloxypropyltrimethoxysilane, anhydrous ethanol, and rigid nano-lignin microspheres is 4-6g: 200-400mL: 30-50g.

5. A thermosetting composite material with high impact strength according to claim 4, characterized in that, The rigid lignin nanospheres are prepared by the following steps: Enzymatically hydrolyzed lignin, γ-valerolactone, and ultrapure water were placed in a reaction vessel and stirred at 25-35℃ for 20-40 min to obtain a lignin solution. The lignin solution was then added to 4-6 times its volume of ultrapure water, and the mixture was stirred at the same temperature for another 20-40 min. After dialyzing, the solution in the bag was transferred to the reaction vessel and reacted at 150-170℃ for 12-14 h. The mixture was then centrifuged and freeze-dried to constant weight to obtain rigid nano-lignin microspheres.

6. A thermosetting composite material with high impact strength according to claim 5, characterized in that, The ratio of enzymatic hydrolysis of lignin, γ-valerolactone, and ultrapure water is 40-60: 200-300 mL: 20-40 mL.

7. The method for preparing a thermosetting composite material with high impact strength according to claim 1, characterized in that, Includes the following steps: Epoxy resin and methyltetrahydrophthalic anhydride were placed in a reaction vessel and stirred at 50-70℃ for 1-2 hours. Modified nano-lignin microspheres were added and ultrasonically dispersed for 1-2 hours. After cooling to 25-35℃, N,N-dimethylbenzylamine was added and stirred for 20-40 minutes. The mixture was then vacuum degassed at 25-35℃ for 20-40 minutes. The degassed mixture was then poured into a mold, transferred to a forced-air drying oven, pre-cured for 1-2 hours, cured for 2-4 hours, cooled, and demolded to obtain a thermosetting composite material with high impact strength.

8. A method for preparing a thermosetting composite material with high impact strength according to claim 7, characterized in that, The pre-curing temperature is 80-100℃, and the curing temperature is 130-150℃.

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