Rice hull fiber composite material and method of making same

Abstract

This invention relates to a rice husk fiber composite material and its preparation method, belonging to the field of composite material technology. It includes the following raw materials: 65-75 parts polylactic acid, 10-20 parts modified rice husk fiber reinforcing material, 0.3-0.5 parts silane coupling agent, 0.2-0.5 parts antioxidant, 0.5-1.5 parts lubricant, and 5-8 parts reinforcing filler. In this invention, modified rice husk fiber is combined with an epoxy compound to obtain reinforcing material A; L-lactic acid is combined with a reactive oligomer, and then with 2-carboxyethyl acrylate to obtain reinforcing material B; reinforcing material A and reinforcing material B are combined to obtain the modified rice husk fiber reinforcing material; polylactic acid, modified rice husk fiber reinforcing material, silane coupling agent, antioxidant, lubricant, and reinforcing filler are mixed and melt-blended and extruded to obtain the rice husk fiber composite material; overall, the mechanical properties, flame retardant properties, and heat resistance of the rice husk fiber composite material are improved.

Description

Technical Field

[0001] This invention belongs to the field of composite material technology, specifically relating to a rice husk fiber composite material and its preparation method. Background Technology

[0002] With the rapid development of bio-based biodegradable materials, polylactic acid (PLA), a typical polyester biodegradable plastic, has been widely used in packaging materials, textiles, and disposable daily necessities due to its good biocompatibility, processability, and biodegradability. However, PLA itself has drawbacks such as high cost, brittleness, and poor heat resistance, which limit its wider application. Rice husk is one of my country's important agricultural wastes, with a huge annual output. Its fiber components have advantages such as high specific strength and specific modulus, biodegradability, low cost, and environmental friendliness. Composites of rice husk fiber as a reinforcing phase with PLA not only help to achieve high-value utilization of agricultural waste and reduce the overall cost of PLA-based composites, but also endow the composites with special properties, expand their application range, and conform to the concept of green and sustainable development.

[0003] In existing technologies, the practical application of rice husk fiber composites still has many shortcomings: 1) Rice husk fiber surfaces are rich in polar hydroxyl groups, exhibiting strong hydrophilicity, while polylactic acid (PLA) is a weakly polar polymer. The poor compatibility between the two leads to weak interfacial bonding, severely affecting the mechanical properties and long-term stability of the composite material; 2) PLA itself is a flammable material, dripping and releasing a large amount of heat when burning, and rice husk fiber is also flammable, resulting in a high fire risk in the composite system; 3) The heat distortion temperature of PLA is typically below 60℃, limiting its application in high-temperature environments, and its heat resistance needs further improvement. Therefore, preparing a rice husk fiber composite material with excellent comprehensive properties such as mechanical properties, flame retardancy, and heat resistance is a pressing technical challenge in this field. Summary of the Invention

[0004] The purpose of this invention is to provide a rice husk fiber composite material and its preparation method. The method involves modifying rice husk fibers and combining them with an epoxy compound to obtain reinforcing material A; combining L-lactic acid with a reactive oligomer and then with 2-carboxyethyl acrylate to obtain reinforcing material B; combining reinforcing material A from step S1 with reinforcing material B from step S2 to obtain a modified rice husk fiber reinforcing material; mixing polylactic acid, the modified rice husk fiber reinforcing material, a silane coupling agent, an antioxidant, a lubricant, and reinforcing fillers, followed by melt blending and extrusion to finally obtain the rice husk fiber composite material. The modified rice husk fiber reinforcing material effectively improves the mechanical properties, flame retardant properties, and heat resistance of the rice husk fiber composite material, and extends its service life, thus improving the overall performance of the rice husk fiber composite material.

[0005] The technical problem to be solved by this invention is as follows: In the existing technology, there are still many shortcomings in the practical application of rice husk fiber composite materials: 1) The surface of rice husk fiber is rich in polar hydroxyl groups and has strong hydrophilicity, while polylactic acid is a weakly polar polymer. The two have poor compatibility, resulting in weak interfacial bonding force, which seriously affects the mechanical properties and long-term stability of the composite material; 2) PLA itself is a flammable material. When burning, it drips and releases a lot of heat. Rice husk fiber is also flammable. The composite system composed of the two has a high fire risk; 3) The heat distortion temperature of PLA is usually below 60°C, which limits its application in high-temperature environments. Its heat resistance needs to be further improved.

[0006] The objective of this invention can be achieved through the following technical solutions:

[0007] A rice husk fiber composite material comprises the following raw materials in parts by weight: 65-75 parts of polylactic acid, 10-20 parts of modified rice husk fiber reinforcing material, 0.3-0.5 parts of silane coupling agent, 0.2-0.5 parts of antioxidant, 0.5-1.5 parts of lubricant, and 5-8 parts of reinforcing filler;

[0008] The preparation method of the modified rice husk fiber reinforced material includes the following steps:

[0009] S1: Reinforcing material A is obtained by combining modified rice husk fiber with epoxy compounds;

[0010] S2: By combining L-lactic acid with reactive oligomers and then with 2-carboxyethyl acrylate, reinforcing material B is obtained;

[0011] S3: Combine the reinforcing material A from step S1 with the reinforcing material B from step S2 to obtain the modified rice husk fiber reinforced material.

[0012] Furthermore, step S1 specifically includes:

[0013] Modified rice husk fiber was added to an epoxy compound and stirred under nitrogen protection. Then triethylamine was added and stirred until homogeneous. Next, a polymerization inhibitor was added and stirred until homogeneous. The system was heated to 85-95℃ and stirred to react. After the reaction was completed, the mixture was filtered, washed, and then subjected to Soxhlet extraction. Finally, it was vacuum dried to obtain reinforced material A.

[0014] In the above reaction process, the modified rice husk fiber surface has hydroxyl groups, and the epoxy compound has epoxy groups. The hydroxyl groups on the modified rice husk fiber can combine with the epoxy groups in the epoxy compound through a ring-opening reaction, thus combining the epoxy compound with the modified rice husk fiber to finally obtain reinforcing material A.

[0015] Furthermore, the mass ratio of the modified rice husk fiber, epoxy compound, triethylamine, and polymerization inhibitor is 0.9-1.1:4.9-5.1:1.9-2.1:0.08-0.12.

[0016] Furthermore, the epoxy compound is composed of glycidyl methacrylate and cashew phenol glycidyl ether in a mass ratio of 0.7-0.8:0.6-0.7.

[0017] Furthermore, the polymerization inhibitor is hydroquinone.

[0018] Furthermore, the stirring time is 15-20 minutes.

[0019] Furthermore, the stirring reaction time is 3-4 hours.

[0020] Furthermore, the vacuum drying time is 4-6 hours, and the temperature is 55-65℃.

[0021] Furthermore, the method for preparing the modified rice husk fiber includes the following steps:

[0022] A1: Alkali-treated rice husk fibers were added to deionized water and ultrasonically dispersed. Then, Tris-HCl buffer solution was added and stirred evenly. Dopamine hydrochloride was then added and stirred to react. After the reaction was completed, the mixture was filtered, washed, and finally vacuum dried to obtain the composite material.

[0023] A2: Add the composite material from step A1 to deionized water and ultrasonically disperse it to obtain a suspension. Add nano-silica to deionized water and ultrasonically disperse it to obtain a dispersion. Add the dispersion to the suspension and stir to obtain a mixture. Add magnesium chloride hexahydrate and aluminum nitrate nonahydrate to deionized water and mix evenly to obtain a metal salt solution. Add the metal salt solution to the mixture and continue stirring. Adjust the pH value of the system and then carry out the stirring reaction in an oil bath. After the reaction is completed, cool to room temperature, centrifuge, wash, and finally vacuum dry to obtain modified rice husk fiber.

[0024] In the above reaction process, in step A1, dopamine hydrochloride undergoes an oxidative self-polymerization reaction to generate polydopamine, which can coat the surface of alkali-treated rice husk fibers to obtain a composite material; in step A2, the surface of the composite material has hydroxyl and amino groups, and the surface of nano-silica has hydroxyl groups, which can be combined with the composite material through hydrogen bonding interaction. Then, layered double hydroxides are grown in situ on the surface of the composite material by co-precipitation method, and finally modified rice husk fibers are obtained.

[0025] Further, in step A1, the mass ratio of the alkali-treated rice husk fiber, deionized water, Tris-HCl buffer solution, and dopamine hydrochloride is 0.4-0.6:90-110:90-110:0.05-0.07.

[0026] Further, in step A1, the specific process of alkali treatment of rice husk fiber is as follows: rice husk powder is soaked in a 2wt% sodium hydroxide solution at a liquid-to-solid ratio of 20:1 and treated at 60°C for 2 hours. After treatment, it is washed with deionized water until neutral and then vacuum dried at 60°C for 24 hours to obtain alkali-treated rice husk fiber.

[0027] Furthermore, in step A1, the ultrasonic dispersion time is 25-35 minutes.

[0028] Furthermore, in step A1, the stirring reaction takes 22-24 hours and is carried out at room temperature.

[0029] Further, in step A2, the mass ratio of the composite material to deionized water is 0.4-0.6:90-110.

[0030] Further, in step A2, the mass ratio of the nano-silica to deionized water is 0.1-0.3:90-110.

[0031] Furthermore, in step A2, the mass ratio of the dispersion to the suspension is 1:1.

[0032] Further, in step A2, the mass ratio of magnesium chloride hexahydrate, aluminum nitrate nonahydrate, and deionized water is 0.4-0.6:0.2-0.4:90-110.

[0033] Furthermore, in step A2, the mass ratio of the mixture to the metal salt solution is 2:1.

[0034] Furthermore, in step A2, the temperature of the stirring reaction is 85-95℃, and the time is 11-12h.

[0035] Furthermore, step S2 specifically includes:

[0036] B1: Mix L-lactic acid, reactive oligomer and toluene and stir until homogeneous. Add catalyst and continue stirring until homogeneous. Then heat and stir under nitrogen protection and reflux. After the reaction is complete, cool, wash, dry and filter. Obtain intermediate product by rotary evaporation.

[0037] B2: Mix the intermediate product from step B1, ethyl 2-carboxyacrylate, and toluene, and stir until homogeneous. Then add the catalyst and polymerization inhibitor, and stir until homogeneous. Under nitrogen protection, heat and stir under reflux to react. After the reaction is complete, cool, wash, dry, filter, and obtain the reinforcing material B by rotary evaporation.

[0038] In the above reaction process, in step B1, L-lactic acid has hydroxyl and carboxyl groups, and the reactive oligomer has hydroxyl groups. The carboxyl groups in L-lactic acid can react and combine with the hydroxyl groups in the reactive oligomer, thus combining the reactive oligomer with L-lactic acid to obtain an intermediate product. In step B2, 2-carboxyethyl acrylate has carboxyl groups, and the intermediate product has remaining hydroxyl groups. The carboxyl groups in 2-carboxyethyl acrylate can react and combine with the hydroxyl groups in the intermediate product, thus combining 2-carboxyethyl acrylate with the intermediate product to finally obtain reinforcing material B.

[0039] Further, in step B1, the mass ratio of L-lactic acid, reactive oligomer, toluene, and catalyst is 1.75-1.85: 0.8-0.9: 0.9-1.1: 0.02-0.03.

[0040] Furthermore, in step B1, the catalyst is p-toluenesulfonic acid.

[0041] Furthermore, in step B1, the temperature of the stirring reflux reaction is 125-135℃, and the time is 5-6 hours.

[0042] Further, in step B2, the mass ratio of the intermediate product, 2-carboxyethyl acrylate, toluene, catalyst, and polymerization inhibitor is 2.25-2.35:1.9-2:0.8-1:0.02-0.03:0.1-0.2.

[0043] Furthermore, in step B2, the catalyst is p-toluenesulfonic acid.

[0044] Furthermore, in step B2, the polymerization inhibitor is hydroquinone.

[0045] Furthermore, in step B2, the temperature of the stirring reflux reaction is 125-135℃, and the time is 5.5-6.5h.

[0046] Further, in step B1, the method for preparing the reactive oligomer includes the following steps:

[0047] Polymethylhydrosiloxane, 9-decenol, vinyl phosphate and toluene were mixed and stirred under nitrogen protection, then heated and stirred, and Karstedt catalyst was added. The reaction was continued with stirring. After the reaction was completed, the mixture was cooled to room temperature, distilled under reduced pressure, and finally dried under vacuum to obtain the reactive oligomer.

[0048] In the above reaction process, polymethylhydrosiloxane has silane-hydrogen bonds, and 9-decenol and vinyl phosphate both have carbon-carbon double bonds. The silane-hydrogen bonds in polymethylhydrosiloxane can combine with the carbon-carbon double bonds in 9-decenol and vinyl phosphate through a hydrosilylation reaction, thus combining polymethylhydrosiloxane with 9-decenol and vinyl phosphate to finally obtain reactive oligomers.

[0049] Furthermore, the mass ratio of polymethylhydrosiloxane, 9-decenol, vinyl phosphate, and toluene is 9.8-10.2:3.8-4.2:2.8-3.2:19.9-20.1.

[0050] Furthermore, the stirring reaction is carried out at a temperature of 75-85°C for a time of 1.5-2.5 hours.

[0051] Furthermore, the vacuum drying temperature is 55-65℃, and the time is 4-6 hours.

[0052] Furthermore, step S3 specifically includes:

[0053] The reinforcing material A from step S1, the reinforcing material B from step S2, and the initiator are mixed and stirred under nitrogen protection. Then, the mixture is stirred and reacted in an oil bath. After the reaction is complete, the mixture is poured into a mold and subjected to gradient curing. After the reaction is complete, the mixture is cooled to room temperature and demolded to obtain the modified rice husk fiber reinforced material.

[0054] In the above reaction process, both reinforcing material A and reinforcing material B have carbon-carbon double bonds. Under the action of the initiator, the carbon-carbon double bonds in reinforcing material A and reinforcing material B can be combined through free radical polymerization reaction, thus combining reinforcing material A and reinforcing material B together, and finally obtaining modified rice husk fiber reinforcing material.

[0055] Furthermore, the mass ratio of the reinforcing material A, the reinforcing material B, and the initiator is 0.9-1.1:4.9-5.1:0.004-0.006.

[0056] Furthermore, the initiator is azobisisobutyronitrile.

[0057] Furthermore, the stirring time is 20-30 minutes.

[0058] Furthermore, the temperature of the stirring reaction is 80-90℃, and the time is 0.5-1h.

[0059] Furthermore, the specific process of gradient curing is as follows: maintaining at 35-45℃ for 22-24h, maintaining at 55-65℃ for 10-12h, maintaining at 75-85℃ for 10-12h, and maintaining at 105-115℃ for 2-4h.

[0060] A method for preparing a rice husk fiber composite material includes the following steps:

[0061] Weigh out the raw materials by mass, grind and sieve the modified rice husk fiber reinforced material to obtain powder, then mix polylactic acid, powder, silane coupling agent, antioxidant, lubricant and reinforcing filler evenly, stir at 400-500 rpm for 10-15 minutes, then add to a twin-screw extruder for melt blending extrusion, and finally obtain rice husk fiber composite material.

[0062] Furthermore, the powder particle size is 50-100 μm.

[0063] Furthermore, the silane coupling agent is 3-aminopropyltriethoxysilane.

[0064] Furthermore, the antioxidant is at least one of antioxidant 1076, antioxidant 1010, and antioxidant 168.

[0065] Furthermore, the lubricant is composed of calcium stearate and ethylene bis-stearamide mixed in a mass ratio of 1:1.

[0066] Furthermore, the reinforcing filler is nano-calcium carbonate.

[0067] Furthermore, the operating temperature of the twin-screw extruder is 160-170℃, and the main machine speed is 300-400rpm.

[0068] A rice husk fiber composite material is prepared by the above-described method for preparing rice husk fiber composite materials.

[0069] The beneficial effects of this invention are:

[0070] (1) In the technical solution of this invention, reinforcing material A is obtained by combining modified rice husk fiber with epoxy compound; wherein, epoxy compound is composed of glycidyl methacrylate and cashew phenol glycidyl ether, which play a synergistic role, not only having a good binding force with modified rice husk fiber, but also providing reaction sites for subsequent reactions, further improving the mechanical properties and thermal stability of rice husk fiber composite material; modified rice husk fiber is obtained by treating rice husk fiber with polydopamine-coated alkali, and then combining it with nano silica and layered double hydroxide; nano silica and layered double hydroxide can play a synergistic role, effectively improving the mechanical properties, flame retardant properties and heat resistance of rice husk composite material, and polydopamine-coated alkali treatment of rice husk fiber can improve its dispersibility, prevent its agglomeration, increase the binding force between rice husk fiber and nano silica and layered double hydroxide, and modify rice husk fiber Combining with epoxy compounds can enhance the bonding force between the two, further improving the mechanical properties, thermal stability, flame retardancy, and heat resistance of rice husk fibers. Reinforcing material B is obtained by combining L-lactic acid with reactive oligomers, followed by combination with 2-carboxyethyl acrylate. The reactive oligomers are prepared by combining polymethylhydrosiloxane, 9-decenol, and vinyl phosphate, which not only improves the bonding force between the reactive oligomers and L-lactic acid but also provides reaction sites for subsequent reactions. Furthermore, the silicon in polymethylhydrosiloxane and the phosphorus in vinyl phosphate synergistically enhance the flame retardancy of the rice husk fiber composite material, further improving its thermal stability, flame retardancy, and heat resistance. Combining L-lactic acid with reactive oligomers, followed by combination with 2-carboxyethyl acrylate, further improves the mechanical properties, toughness, flame retardancy, and heat resistance of the rice husk composite material.

[0071] (2) In the technical solution of the present invention, the reinforcing material A in step S1 is combined with the reinforcing material B in step S2 to obtain the modified rice husk fiber reinforcing material; the reinforcing material A and the reinforcing material B are combined by free radical polymerization, which not only enhances the bonding force between the two, but also increases the compatibility between the modified rice husk fiber reinforcing material and polylactic acid, improves its interfacial bonding force, and further enhances the mechanical properties, thermal stability, flame retardant properties and heat resistance of the rice husk fiber composite material; the polylactic acid, the modified rice husk fiber reinforcing material, the silane coupling agent, the antioxidant, the lubricant and the reinforcing filler are mixed and melt-blended and extruded to finally obtain the rice husk fiber composite material. The modified rice husk fiber reinforcing material improves the overall performance of the rice husk fiber composite material.

[0072] (3) In the technical solution of the present invention, reinforcing material A is obtained by combining modified rice husk fiber with epoxy compound. Reinforcing material B is obtained by combining L-lactic acid with reactive oligomer and then with 2-carboxyethyl acrylate. Reinforcing material A and reinforcing material B are combined to obtain modified rice husk fiber reinforcing material. Polylactic acid, modified rice husk fiber reinforcing material, silane coupling agent, antioxidant, lubricant and reinforcing filler are mixed and melt-blended and extruded to obtain rice husk fiber composite material. Overall, the mechanical properties, flame retardant properties and heat resistance properties of rice husk fiber composite material are improved, and its service life is extended. Its comprehensive performance is good. Detailed Implementation

[0073] 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.

[0074] The specific parameters of the raw materials used in this invention are as follows:

[0075] Polylactic acid (PLA), CAS No.: 26100-51-6, Product No.: P890263, provided by Shanghai Maclean Biochemical Technology Co., Ltd.; Nano calcium carbonate, CAS No.: 471-34-1, provided by Guangdong Yuanlei Powder Co., Ltd.; Rice husk powder, provided by Lingshou County Hongsheng New Material Co., Ltd.; Nano silica, specification: 20nm, specific surface area: 200m². 2 / g, provided by Nanjing Boket New Materials Co., Ltd.; L-lactic acid, provided by Jinan Jiayang Chemical Co., Ltd.; polymethylhydrosiloxane, CAS No.: 63148-57-2, trade number: P832168, provided by Shanghai Maclean Biochemical Technology Co., Ltd.; Karstedt catalyst, CAS No.: 81032-58-8, trade number: K855033, provided by Shanghai Maclean Biochemical Technology Co., Ltd.; glycidyl methacrylate, CAS No.: 106-91-2, trade number: G810426, provided by Shanghai Maclean Biochemical Technology Co., Ltd.; cashew phenol glycidyl ether, CAS No.: 171263-25-5, trade number: C992604, provided by Shanghai Maclean Biochemical Technology Co., Ltd.

[0076] Example 1

[0077] The specific steps for preparing modified rice husk fiber reinforced materials are as follows:

[0078] S1: According to the mass ratio of modified rice husk fiber, epoxy compound, triethylamine, and hydroquinone of 0.9:4.9:1.9:0.08, the modified rice husk fiber was added to the epoxy compound and stirred for 15 min under nitrogen protection. Then, triethylamine was added and stirred evenly. Then, hydroquinone was added and stirred evenly. The system was heated to 85℃ and stirred for 4 h. After the reaction was completed, the mixture was filtered and washed three times with acetone (each time the mass of acetone was 10 times the mass of triethylamine). Then, Soxhlet extraction was performed with acetone as the extraction solvent for 6 h. Finally, the mixture was vacuum dried at 55℃ for 6 h to obtain reinforcing material A. The epoxy compound is composed of glycidyl methacrylate and cashew phenol glycidyl ether mixed in a mass ratio of 0.7:0.6.

[0079] The preparation method of modified rice husk fiber includes the following steps:

[0080] A1: According to the mass ratio of alkali-treated rice husk fiber, deionized water, Tris-HCl buffer solution, and dopamine hydrochloride of 0.4:90:90:0.05, the alkali-treated rice husk fiber was added to deionized water and ultrasonically dispersed for 25 min (ultrasonic power of 100W, ultrasonic frequency of 40kHz). Then, 10mM Tris-HCl buffer solution (pH=8.5) was added and stirred evenly. Then, dopamine hydrochloride was added and stirred at room temperature for 22 h. After the reaction was completed, the mixture was filtered and washed three times with deionized water (each time the mass of deionized water was 30% of the mass of Tris-HCl buffer solution). Finally, it was vacuum dried at 55℃ for 12 h to obtain the composite material. The specific process of alkali treatment of rice husk fiber is as follows: according to the liquid-solid ratio of 20:1, rice husk powder was soaked in 2wt% sodium hydroxide solution and treated at 60℃ for 2 h. After the treatment, it was washed with deionized water until neutral and vacuum dried at 60℃ for 24 h to obtain alkali-treated rice husk fiber.

[0081] A2: Following a mass ratio of composite material to deionized water of 0.4:90, add the composite material from step A1 to deionized water and ultrasonically disperse for 10 minutes (ultrasonic power 100W, ultrasonic frequency 40kHz) to obtain a suspension. Following a mass ratio of nano-silica to deionized water of 0.1:90, add nano-silica to deionized water and ultrasonically disperse for 25 minutes (ultrasonic power 100W, ultrasonic frequency 40kHz) to obtain a dispersion. Following a mass ratio of dispersion to suspension of 1:1, add the dispersion to the suspension and stir for 20 minutes to obtain a mixture. Following a mass ratio of magnesium chloride hexahydrate, aluminum nitrate nonahydrate, and deionized water... The mass ratio of magnesium chloride hexahydrate and aluminum nitrate nonahydrate was 0.4:0.2:90. Magnesium chloride hexahydrate and aluminum nitrate nonahydrate were added to deionized water and mixed evenly to obtain a metal salt solution. The metal salt solution was added to the mixture at a mass ratio of 2:1 and stirred for 20 min. Then, 1 M sodium hydroxide solution was added to adjust the pH of the system to 9. The mixture was then stirred at 300 rpm in an oil bath at 85 °C for 12 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 8000 rpm for 5 min. The mixture was washed three times with anhydrous ethanol (each time the mass of anhydrous ethanol was 3 times the mass of the mixture). Finally, the mixture was vacuum dried at 55 °C for 12 h to obtain modified rice husk fiber.

[0082] S2: Preparation of reinforcing material B, specifically:

[0083] B1: The L-lactic acid, reactive oligomer, toluene, and p-toluenesulfonic acid were mixed and stirred until homogeneous according to a mass ratio of 1.75:0.8:0.9:0.02. Then, p-toluenesulfonic acid was added, and the mixture was stirred until homogeneous again. The mixture was then heated to 125°C under nitrogen protection and refluxed for 6 hours. After the reaction was complete, the mixture was cooled and washed three times each with 8.5 wt% saturated sodium bicarbonate solution and deionized water (each time the mass of the saturated sodium bicarbonate solution was twice the mass of toluene, and each time the mass of the deionized water was twice the mass of toluene). Anhydrous sodium sulfate was added and the mixture was dried for 30 minutes. After filtration, residual water and toluene were removed by rotary evaporation at 40°C to obtain the intermediate product.

[0084] B2: According to the mass ratio of intermediate product, 2-carboxyethyl acrylate, toluene, p-toluenesulfonic acid, and hydroquinone of step B1, the intermediate product, 2-carboxyethyl acrylate, and toluene are mixed and stirred evenly. Then, p-toluenesulfonic acid and hydroquinone are added and stirred evenly. The mixture is then heated to 125°C under nitrogen protection and stirred under reflux for 6.5 hours. After the reaction is completed, the mixture is cooled and washed three times each with 8.5wt% saturated sodium bicarbonate solution and deionized water (each time the mass of saturated sodium bicarbonate solution is 3 times the mass of toluene, and each time the mass of deionized water is 3 times the mass of toluene). Anhydrous sodium sulfate is added and dried for 30 minutes. After filtration, residual water and toluene are removed by rotary evaporation at 40°C to obtain reinforcing material B.

[0085] The preparation method of reactive oligomers includes the following steps:

[0086] The polymethylhydrosiloxane, 9-decenol, vinyl phosphate, and toluene were mixed in a mass ratio of 9.8:3.8:2.8:19.9 and stirred for 25 min under nitrogen protection. The mixture was then heated to 75 °C and stirred for 10 min. Karstedt catalyst (0.3% of the mass of toluene) was added, and the reaction was continued at 75 °C for 2.5 h. After the reaction was completed, the mixture was cooled to room temperature, distilled under reduced pressure at 60 °C, and finally dried under vacuum at 55 °C for 6 h to obtain the reactive oligomer.

[0087] S3: According to the mass ratio of reinforcing material A, reinforcing material B, and azobisisobutyronitrile (AIBN) of 0.9:4.9:0.004, reinforcing material A from step S1, reinforcing material B from step S2, and AIBN are mixed and stirred for 20 minutes under nitrogen protection. Then, the mixture is stirred and reacted in an oil bath at 80°C for 1 hour. After the reaction is completed, the mixture is poured into a silicone rubber mold and then subjected to gradient curing. The specific process is as follows: maintain at 35°C for 24 hours, maintain at 55°C for 12 hours, maintain at 75°C for 12 hours, and maintain at 105°C for 4 hours. After the process is completed, the mixture is cooled to room temperature and demolded to obtain the modified rice husk fiber reinforced material.

[0088] A rice husk fiber composite material comprises the following raw materials in parts by weight: 65 parts polylactic acid, 10 parts modified rice husk fiber reinforcing material, 0.3 parts 3-aminopropyltriethoxysilane, 0.2 parts antioxidant 1076, 0.5 parts lubricant, and 5 parts nano-calcium carbonate;

[0089] The lubricant is composed of calcium stearate and ethylene bis-stearamide mixed in a mass ratio of 1:1.

[0090] The preparation method includes the following steps:

[0091] Weigh out the raw materials by mass, grind and sieve the modified rice husk fiber reinforced material to obtain powder with a particle size of 50 μm, then mix polylactic acid, powder, 3-aminopropyltriethoxysilane, antioxidant 1076, lubricant and nano calcium carbonate evenly, stir at 400 rpm for 15 min, then add to a twin-screw extruder for melt blending extrusion. The working temperature of the twin-screw extruder is 160℃ and the main machine speed is 300 rpm. Finally, rice husk fiber composite material is obtained.

[0092] Example 2

[0093] The specific steps for preparing modified rice husk fiber reinforced materials are as follows:

[0094] S1: According to the mass ratio of modified rice husk fiber, epoxy compound, triethylamine, and hydroquinone of 1:5:2:0.1, the modified rice husk fiber was added to the epoxy compound and stirred for 18 min under nitrogen protection. Then, triethylamine was added and stirred evenly. Then, hydroquinone was added and stirred evenly. The system was heated to 90℃ and stirred for 3.5 h. After the reaction was completed, the mixture was filtered and washed three times with acetone (each time the mass of acetone was 10 times the mass of triethylamine). Then, Soxhlet extraction was performed with acetone as the extraction solvent for 7 h. Finally, the mixture was vacuum dried at 60℃ for 5 h to obtain reinforcing material A. The epoxy compound is composed of glycidyl methacrylate and cashew phenol glycidyl ether mixed in a mass ratio of 0.75:0.65.

[0095] The preparation method of modified rice husk fiber includes the following steps:

[0096] A1: According to the mass ratio of alkali-treated rice husk fiber, deionized water, Tris-HCl buffer solution, and dopamine hydrochloride of 0.5:100:100:0.06, the alkali-treated rice husk fiber was added to deionized water and ultrasonically dispersed for 30 min (ultrasonic power of 100W, ultrasonic frequency of 40kHz). Then, 10mM Tris-HCl buffer solution (pH=8.5) was added and stirred evenly. Then, dopamine hydrochloride was added and stirred at room temperature for 23 h. After the reaction was completed, the mixture was filtered and washed three times with deionized water (each time the mass of deionized water was 30% of the mass of Tris-HCl buffer solution). Finally, it was vacuum dried at 60℃ for 12 h to obtain the composite material. The specific process of alkali treatment of rice husk fiber is as follows: according to the liquid-solid ratio of 20:1, rice husk powder was soaked in 2wt% sodium hydroxide solution and treated at 60℃ for 2 h. After the treatment, it was washed with deionized water until neutral and vacuum dried at 60℃ for 24 h to obtain alkali-treated rice husk fiber.

[0097] A2: Following a mass ratio of composite material to deionized water of 0.5:100, add the composite material from step A1 to deionized water and ultrasonically disperse for 15 minutes (ultrasonic power 100W, ultrasonic frequency 40kHz) to obtain a suspension. Following a mass ratio of nano-silica to deionized water of 0.2:100, add nano-silica to deionized water and ultrasonically disperse for 30 minutes (ultrasonic power 100W, ultrasonic frequency 40kHz) to obtain a dispersion. Following a mass ratio of dispersion to suspension of 1:1, add the dispersion to the suspension and stir for 25 minutes to obtain a mixed solution. Following a mass ratio of magnesium chloride hexahydrate, aluminum nitrate nonahydrate, and deionized water... Magnesium chloride hexahydrate and aluminum nitrate nonahydrate were added to deionized water at a mass ratio of 0.5:0.3:100 and mixed thoroughly to obtain a metal salt solution. The metal salt solution was added to the mixture at a mass ratio of 2:1, and the mixture was stirred for 25 min. Then, 1 M sodium hydroxide solution was added to adjust the pH of the system to 9.5. The mixture was then stirred at 400 rpm in an oil bath at 90 °C for 11.5 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 8000 rpm for 8 min. The mixture was washed three times with anhydrous ethanol (each time the mass of anhydrous ethanol was 3 times the mass of the mixture). Finally, the mixture was vacuum dried at 60 °C for 12 h to obtain modified rice husk fiber.

[0098] S2: Preparation of reinforcing material B, specifically:

[0099] B1: The L-lactic acid, reactive oligomer, toluene, and p-toluenesulfonic acid were mixed and stirred until homogeneous according to a mass ratio of 1.8:0.85:1:0.025. Then, p-toluenesulfonic acid was added, and the mixture was stirred until homogeneous again. The mixture was then heated to 130°C under nitrogen protection and refluxed with stirring for 5.5 hours. After the reaction was complete, the mixture was cooled and washed three times each with 8.5 wt% saturated sodium bicarbonate solution and deionized water (each time the mass of saturated sodium bicarbonate solution was twice the mass of toluene, and each time the mass of deionized water was twice the mass of toluene). Anhydrous sodium sulfate was added and the mixture was dried for 30 minutes. After filtration, residual water and toluene were removed by rotary evaporation at 45°C to obtain the intermediate product.

[0100] B2: According to the mass ratio of intermediate product, 2-carboxyethyl acrylate, toluene, p-toluenesulfonic acid, and hydroquinone of 2.3:1.95:0.9:0.025:0.15, the intermediate product from step B1, 2-carboxyethyl acrylate, and toluene were mixed and stirred evenly. Then, p-toluenesulfonic acid and hydroquinone were added and stirred evenly. The mixture was then heated to 130°C under nitrogen protection and stirred under reflux for 6 hours. After the reaction was completed, the mixture was cooled and washed three times each with 8.5wt% saturated sodium bicarbonate solution and deionized water (each time the mass of saturated sodium bicarbonate solution was 3 times the mass of toluene, and each time the mass of deionized water was 3 times the mass of toluene). Anhydrous sodium sulfate was added and dried for 30 minutes. After filtration, residual water and toluene were removed by rotary evaporation at 45°C to obtain reinforcing material B.

[0101] The preparation method of reactive oligomers includes the following steps:

[0102] The polymethylhydrosiloxane, 9-decenol, vinyl phosphate, and toluene were mixed in a mass ratio of 10:4:3:20 and stirred for 30 min under nitrogen protection. Then, the mixture was heated to 80 °C and stirred for 8 min. The Karstedt catalyst (0.3% of the mass of toluene) was then added, and the mixture was stirred at 80 °C for 2 h. After the reaction was completed, the mixture was cooled to room temperature and distilled under reduced pressure at 65 °C. Finally, the mixture was dried under vacuum at 60 °C for 5 h to obtain the reactive oligomer.

[0103] S3: According to the mass ratio of reinforcing material A, reinforcing material B, and azobisisobutyronitrile (AIBN) of 1:5:0.005, the reinforcing material A from step S1, the reinforcing material B from step S2, and AIBN are mixed and stirred for 25 minutes under nitrogen protection. Then, the mixture is stirred and reacted in an oil bath at 85°C for 0.7 hours. After the reaction is completed, the mixture is poured into a silicone rubber mold and then subjected to gradient curing. The specific process is as follows: maintain at 40°C for 23 hours, maintain at 60°C for 11 hours, maintain at 80°C for 11 hours, and maintain at 110°C for 3 hours. After the process is completed, the mixture is cooled to room temperature and demolded to obtain the modified rice husk fiber reinforced material.

[0104] A rice husk fiber composite material comprises the following raw materials in parts by weight: 70 parts polylactic acid, 15 parts modified rice husk fiber reinforcing material, 0.4 parts 3-aminopropyltriethoxysilane, 0.35 parts antioxidant 1010, 1 part lubricant, and 7 parts nano calcium carbonate;

[0105] The lubricant is composed of calcium stearate and ethylene bis-stearamide mixed in a mass ratio of 1:1.

[0106] The preparation method includes the following steps:

[0107] Weigh out the raw materials by mass, grind and sieve the modified rice husk fiber reinforced material to obtain powder with a particle size of 75μm, then mix polylactic acid, powder, 3-aminopropyltriethoxysilane, antioxidant 1010, lubricant and nano calcium carbonate evenly, stir at 450rpm for 12min, then add to a twin-screw extruder for melt blending extrusion. The working temperature of the twin-screw extruder is 165℃ and the main machine speed is 350rpm, finally obtaining rice husk fiber composite material.

[0108] Example 3

[0109] The specific steps for preparing modified rice husk fiber reinforced materials are as follows:

[0110] S1: According to the mass ratio of modified rice husk fiber, epoxy compound, triethylamine, and hydroquinone of 1.1:5.1:2.1:0.12, the modified rice husk fiber was added to the epoxy compound and stirred for 20 min under nitrogen protection. Then, triethylamine was added and stirred evenly. Then, hydroquinone was added and stirred evenly. The system was heated to 95℃ and stirred for 3 h. After the reaction was completed, the mixture was filtered and washed three times with acetone (each time the mass of acetone was 10 times the mass of triethylamine). Then, Soxhlet extraction was performed with acetone as the extraction solvent for 8 h. Finally, the mixture was vacuum dried at 65℃ for 4 h to obtain reinforcing material A. The epoxy compound is composed of glycidyl methacrylate and cashew phenol glycidyl ether mixed in a mass ratio of 0.8:0.7.

[0111] The preparation method of modified rice husk fiber includes the following steps:

[0112] A1: According to the mass ratio of alkali-treated rice husk fiber, deionized water, Tris-HCl buffer solution, and dopamine hydrochloride of 0.6:110:110:0.07, the alkali-treated rice husk fiber was added to deionized water and ultrasonically dispersed for 35 min (ultrasonic power of 100W, ultrasonic frequency of 40kHz). Then, 10mM Tris-HCl buffer solution (pH=8.5) was added and stirred evenly. Then, dopamine hydrochloride was added and stirred at room temperature for 24 h. After the reaction was completed, the mixture was filtered and washed three times with deionized water (each time the mass of deionized water was 30% of the mass of Tris-HCl buffer solution). Finally, it was vacuum dried at 65℃ for 12 h to obtain the composite material. The specific process of alkali treatment of rice husk fiber is as follows: according to the liquid-solid ratio of 20:1, rice husk powder was soaked in 2wt% sodium hydroxide solution and treated at 60℃ for 2 h. After the treatment, it was washed with deionized water until neutral and vacuum dried at 60℃ for 24 h to obtain alkali-treated rice husk fiber.

[0113] A2: Following a mass ratio of composite material to deionized water of 0.6:110, add the composite material from step A1 to deionized water and ultrasonically disperse for 20 minutes (ultrasonic power 100W, ultrasonic frequency 40kHz) to obtain a suspension. Following a mass ratio of nano-silica to deionized water of 0.3:110, add nano-silica to deionized water and ultrasonically disperse for 35 minutes (ultrasonic power 100W, ultrasonic frequency 40kHz) to obtain a dispersion. Following a mass ratio of dispersion to suspension of 1:1, add the dispersion to the suspension and stir for 30 minutes to obtain a mixed solution. Following a mass ratio of magnesium chloride hexahydrate, aluminum nitrate nonahydrate, and deionized water... The mass ratio of magnesium chloride hexahydrate and aluminum nitrate nonahydrate was 0.6:0.4:110. Magnesium chloride hexahydrate and aluminum nitrate nonahydrate were added to deionized water and mixed evenly to obtain a metal salt solution. The metal salt solution was added to the mixture at a mass ratio of 2:1. The mixture was stirred for 30 min, and then 1 M sodium hydroxide solution was added to adjust the pH of the system to 10. The mixture was then stirred at 500 rpm in an oil bath at 95 °C for 11 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 8000 rpm for 10 min. The mixture was washed three times with anhydrous ethanol (each time the mass of anhydrous ethanol was 3 times the mass of the mixture). Finally, the mixture was vacuum dried at 65 °C for 12 h to obtain modified rice husk fiber.

[0114] S2: Preparation of reinforcing material B, specifically:

[0115] B1: The L-lactic acid, reactive oligomer, toluene, and p-toluenesulfonic acid were mixed and stirred until homogeneous according to a mass ratio of 1.85:0.9:1.1:0.03. Then, p-toluenesulfonic acid was added, and the mixture was stirred until homogeneous again. The mixture was then heated to 135°C under nitrogen protection and refluxed for 5 hours. After the reaction was complete, the mixture was cooled and washed three times each with 8.5 wt% saturated sodium bicarbonate solution and deionized water (each time the mass of the saturated sodium bicarbonate solution was twice the mass of toluene, and each time the mass of the deionized water was twice the mass of toluene). Anhydrous sodium sulfate was added and the mixture was dried for 30 minutes. After filtration, residual water and toluene were removed by rotary evaporation at 50°C to obtain the intermediate product.

[0116] B2: According to the mass ratio of intermediate product, 2-carboxyethyl acrylate, toluene, p-toluenesulfonic acid, and hydroquinone of step B1, the intermediate product, 2-carboxyethyl acrylate, and toluene are mixed and stirred evenly. Then, p-toluenesulfonic acid and hydroquinone are added and stirred evenly. The mixture is then heated to 135°C under nitrogen protection and stirred under reflux for 5.5 hours. After the reaction is completed, the mixture is cooled and washed three times each with 8.5wt% saturated sodium bicarbonate solution and deionized water (each time the mass of saturated sodium bicarbonate solution is 3 times the mass of toluene, and each time the mass of deionized water is 3 times the mass of toluene). Anhydrous sodium sulfate is added and dried for 30 minutes. After filtration, residual water and toluene are removed by rotary evaporation at 50°C to obtain reinforcing material B.

[0117] The preparation method of reactive oligomers includes the following steps:

[0118] The polymethylhydrosiloxane, 9-decenol, vinyl phosphate, and toluene were mixed in a mass ratio of 10.2:4.2:3.2:20.1 and stirred under nitrogen protection for 35 min. Then the mixture was heated to 85 °C and stirred for 5 min. Karstedt catalyst (0.3% of the mass of toluene) was added, and the reaction was continued at 85 °C for 1.5 h. After the reaction was completed, the mixture was cooled to room temperature, distilled under reduced pressure at 70 °C, and finally dried under vacuum at 65 °C for 4 h to obtain the reactive oligomer.

[0119] S3: According to the mass ratio of reinforcing material A, reinforcing material B, and azobisisobutyronitrile (AIBN) of 1.1:5.1:0.006, the reinforcing material A from step S1, the reinforcing material B from step S2, and AIBN are mixed and stirred for 30 min under nitrogen protection. Then, the mixture is stirred and reacted in an oil bath at 90°C for 0.5 h. After the reaction is completed, the mixture is poured into a silicone rubber mold and then subjected to gradient curing. The specific process is as follows: maintain at 45°C for 22 h, maintain at 65°C for 10 h, maintain at 85°C for 10 h, and maintain at 115°C for 2 h. After the process is completed, the mixture is cooled to room temperature and demolded to obtain the modified rice husk fiber reinforced material.

[0120] A rice husk fiber composite material comprises the following raw materials in parts by weight: 75 parts polylactic acid, 20 parts modified rice husk fiber reinforcing material, 0.5 parts 3-aminopropyltriethoxysilane, 0.5 parts antioxidant 168, 1.5 parts lubricant, and 8 parts nano-calcium carbonate;

[0121] The lubricant is composed of calcium stearate and ethylene bis-stearamide mixed in a mass ratio of 1:1.

[0122] The preparation method includes the following steps:

[0123] Weigh out the raw materials by mass, grind and sieve the modified rice husk fiber reinforced material to obtain powder with a particle size of 100μm, then mix polylactic acid, powder, 3-aminopropyltriethoxysilane, antioxidant 168, lubricant and nano calcium carbonate evenly, stir at 500rpm for 10min, then add to a twin-screw extruder for melt blending extrusion. The working temperature of the twin-screw extruder is 170℃ and the main machine speed is 400rpm, finally obtaining rice husk fiber composite material.

[0124] Comparative Example 1

[0125] The difference between this comparative example and Example 3 is that, in the preparation of the modified rice husk fiber reinforced material, in step S1, the epoxy compound is replaced by glycidyl methacrylate in equal mass, while the remaining steps and raw materials are the same as in Example 3.

[0126] S1: According to the mass ratio of modified rice husk fiber, glycidyl methacrylate, triethylamine, and hydroquinone of 1.1:5.1:2.1:0.12, the modified rice husk fiber was added to glycidyl methacrylate and stirred for 20 min under nitrogen protection. Then, triethylamine was added and stirred evenly. Hydroquinone was then added and stirred evenly. The system was heated to 95℃ and stirred for 3 h. After the reaction was completed, the mixture was filtered and washed three times with acetone (each time the mass of acetone was 10 times the mass of triethylamine). Then, Soxhlet extraction was performed using acetone as the extraction solvent for 8 h. Finally, the mixture was vacuum dried at 65℃ for 4 h to obtain reinforcing material A.

[0127] Comparative Example 2

[0128] The difference between this comparative example and Example 3 is that, in the preparation of the modified rice husk fiber reinforced material, in step S1, the epoxy compound is replaced by cashew phenol glycidyl ether in equal mass, while the remaining steps and raw materials are the same as in Example 3.

[0129] S1: According to the mass ratio of modified rice husk fiber, cashew phenol glycidyl ether, triethylamine, and hydroquinone of 1.1:5.1:2.1:0.12, the modified rice husk fiber was added to cashew phenol glycidyl ether and stirred for 20 min under nitrogen protection. Then, triethylamine was added and stirred evenly. Then, hydroquinone was added and stirred evenly. The system was heated to 95℃ and stirred for 3 h. After the reaction was completed, the mixture was filtered and washed three times with acetone (each time the mass of acetone was 10 times the mass of triethylamine). Then, Soxhlet extraction was performed with acetone as the extraction solvent for 8 h. Finally, the mixture was vacuum dried at 65℃ for 4 h to obtain reinforcing material A.

[0130] Comparative Example 3

[0131] The difference between this comparative example and Example 3 is that the preparation method of the modified rice husk fiber in step S1 is different when preparing the modified rice husk fiber reinforced material, while the other steps and raw materials are the same as in Example 3.

[0132] The preparation method of modified rice husk fiber includes the following steps:

[0133] A1: According to the mass ratio of alkali-treated rice husk fiber, deionized water, Tris-HCl buffer solution, and dopamine hydrochloride of 0.6:110:110:0.07, the alkali-treated rice husk fiber was added to deionized water and ultrasonically dispersed for 35 min (ultrasonic power of 100W, ultrasonic frequency of 40kHz). Then, 10mM Tris-HCl buffer solution (pH=8.5) was added and stirred evenly. Then, dopamine hydrochloride was added and stirred at room temperature for 24 h. After the reaction was completed, the mixture was filtered and washed three times with deionized water (each time the mass of deionized water was 30% of the mass of Tris-HCl buffer solution). Finally, it was vacuum dried at 65℃ for 12 h to obtain the composite material. The specific process of alkali treatment of rice husk fiber is as follows: according to the liquid-solid ratio of 20:1, rice husk powder was soaked in 2wt% sodium hydroxide solution and treated at 60℃ for 2 h. After the treatment, it was washed with deionized water until neutral and vacuum dried at 60℃ for 24 h to obtain alkali-treated rice husk fiber.

[0134] A2: According to the mass ratio of composite material to deionized water of 0.6:110, the composite material from step A1 was added to deionized water and ultrasonically dispersed for 20 min (ultrasonic power of 100W, ultrasonic frequency of 40kHz) to obtain a suspension. According to the mass ratio of magnesium chloride hexahydrate, aluminum nitrate nonahydrate, and deionized water of 0.6:0.4:110, magnesium chloride hexahydrate and aluminum nitrate nonahydrate were added to deionized water and mixed evenly to obtain a metal salt solution. According to the mass ratio of suspension to metal salt solution of 2:1, the metal salt solution was added to the suspension and stirred for 30 min. Then, 1M sodium hydroxide solution was added to adjust the pH of the system to 10. The reaction was then carried out in an oil bath at 95℃ with stirring at 500 rpm for 11 h. After the reaction was completed, the mixture was cooled to room temperature and centrifuged at 8000 rpm for 10 min. The mixture was washed three times with anhydrous ethanol (each time the mass of anhydrous ethanol was 3 times the mass of the suspension). Finally, the mixture was vacuum dried at 65℃ for 12 h to obtain modified rice husk fiber.

[0135] Comparative Example 4

[0136] The difference between this comparative example and Example 3 is that, in the preparation of the modified rice husk fiber reinforced material, in step S1, the modified rice husk fiber is replaced by an equal mass of composite material, and the original step A2 is deleted. The remaining steps and raw materials are the same as in Example 3.

[0137] S1: The composite material, epoxy compound, triethylamine, and hydroquinone were mixed in a mass ratio of 1.1:5.1:2.1:0.12. The composite material was added to the epoxy compound and stirred for 20 min under nitrogen protection. Then, triethylamine was added and stirred until homogeneous. Hydroquinone was then added and stirred until homogeneous. The system was heated to 95°C and stirred for 3 h. After the reaction was completed, the mixture was filtered and washed three times with acetone (each time the mass of acetone was 10 times the mass of triethylamine). Then, Soxhlet extraction was performed using acetone as the extraction solvent for 8 h. Finally, the mixture was vacuum dried at 65°C for 4 h to obtain reinforcing material A. The epoxy compound was composed of glycidyl methacrylate and cashew phenol glycidyl ether in a mass ratio of 0.8:0.7.

[0138] Comparative Example 5

[0139] The difference between this comparative example and Example 3 is that the preparation method of the reactive oligomer in step S2 is different when preparing the modified rice husk fiber reinforced material, while the other steps and raw materials are the same as in Example 3.

[0140] The preparation method of reactive oligomers includes the following steps:

[0141] The polymethylhydrosiloxane, 9-decenol, and toluene were mixed in a mass ratio of 10.2:7.4:20.1 and stirred under nitrogen protection for 35 min. Then the mixture was heated to 85 °C and stirred for 5 min. The Karstedt catalyst (0.3% of the mass of toluene) was then added, and the mixture was stirred at 85 °C for 1.5 h. After the reaction was completed, the mixture was cooled to room temperature and distilled under reduced pressure at 70 °C. Finally, it was dried under vacuum at 65 °C for 4 h to obtain the reactive oligomer.

[0142] Comparative Example 6

[0143] The difference between this comparative example and Example 3 is that, in the preparation of the modified rice husk fiber reinforced material, in step S2, the reactive oligomer is replaced by 9-decenol in equal mass, while the remaining steps and raw materials are the same as in Example 3.

[0144] B1: L-lactic acid, 9-decenol, toluene, and p-toluenesulfonic acid were mixed and stirred until homogeneous according to a mass ratio of 1.85:0.9:1.1:0.03. Then, p-toluenesulfonic acid was added, and the mixture was stirred until homogeneous again. The mixture was then heated to 135°C under nitrogen protection and refluxed with stirring for 5 hours. After the reaction was complete, the mixture was cooled and washed three times each with 8.5 wt% saturated sodium bicarbonate solution and deionized water (each time the mass of saturated sodium bicarbonate solution was twice the mass of toluene, and each time the mass of deionized water was twice the mass of toluene). The mixture was dried with anhydrous sodium sulfate for 30 minutes, filtered, and the residual water and toluene were removed by rotary evaporation at 50°C to obtain the intermediate product.

[0145] Comparative Example 7

[0146] The difference between this comparative example and Example 3 is that, in the preparation of the modified rice husk fiber reinforced material, in step S3, the reinforcing material B is replaced with an intermediate product of equal mass, and the original step B2 is deleted. The remaining steps and raw materials are the same as in Example 3.

[0147] S3: According to the mass ratio of reinforcing material A, intermediate product and azobisisobutyronitrile (AIBN) of 1.1:5.1:0.006, the reinforcing material A from step S1, the intermediate product from step S2 and AIBN are mixed and stirred for 30 min under nitrogen protection. Then, the mixture is stirred and reacted in an oil bath at 90℃ for 0.5 h. After the reaction is completed, the mixture is poured into a silicone rubber mold and then subjected to gradient curing. The specific process is as follows: keep at 45℃ for 22 h, keep at 65℃ for 10 h, keep at 85℃ for 10 h, keep at 115℃ for 2 h. After the process is completed, cool to room temperature and demold to obtain the modified rice husk fiber reinforced material.

[0148] Comparative Example 8

[0149] The difference between this comparative example and Example 3 is that, in the preparation of the modified rice husk fiber reinforced material, in step S3, reinforcing material A and reinforcing material B are directly mixed, while the remaining steps and raw materials are the same as in Example 3.

[0150] S3: Mix reinforcing material A from step S1 and reinforcing material B from step S2 according to a mass ratio of 1.1:5.1, and stir at room temperature for 30 minutes. After stirring, vacuum dry at 60°C for 24 hours to obtain modified rice husk fiber reinforced material.

[0151] The rice husk fiber composite materials prepared in Examples 1-3 and Comparative Examples 1-8 were tested for tensile strength, elongation at break, flame retardancy, and heat resistance. Tensile strength and elongation at break were tested according to GB / T 1040-2006 at a tensile rate of 2 mm / min. The UL-94 flame retardancy rating was tested according to GB / T 2406-2009. The heat distortion temperature was tested according to GB / T 1634.2-2019 at a heating rate of 120℃ / h. The test results are shown in Table 1 below.

[0152] Table 1 Performance parameters of rice husk fiber composite materials

[0153]

[0154] As shown in Table 1 above, a comparison between Comparative Examples 1-4 and Example 3 reveals that replacing the epoxy compound with glycidyl methacrylate or cashew phenol glycidyl ether, using different preparation methods for the modified rice husk fiber, or replacing the modified rice husk fiber with a composite material, ultimately resulted in a rice husk fiber composite material with poorer test results compared to Example 3. This indicates that the epoxy compound composed of glycidyl methacrylate and cashew phenol glycidyl ether can play a synergistic role, further improving the mechanical properties, heat resistance, and flame retardant properties of the rice husk fiber composite material. Furthermore, coating the rice husk fiber with polydopamine and then combining it with nano-silica and layered double hydroxides to obtain modified rice husk fiber not only enhances its dispersibility but also further improves the mechanical properties, heat resistance, and flame retardant properties of the rice husk fiber composite material.

[0155] Comparing Comparative Examples 5-8 and Example 3, it can be seen that in step S2, the preparation methods of the reactive oligomers are different. For example, the reactive oligomers are replaced by an equal mass of 9-decenol, or the reinforcing material B is replaced by an equal mass of the intermediate product, or reinforcing material A and reinforcing material B are directly mixed. Finally, the rice husk fiber composite material is prepared. The test results are worse than those of Example 3. This indicates that combining polymethylhydrosiloxane, 9-decenol, and vinyl phosphate to prepare reactive oligomers, and then combining them with L-lactic acid, not only increases the bonding force between the two but also effectively improves the flame retardant and heat resistance properties of the rice husk fiber composite material. Combining L-lactic acid first with the reactive oligomers and then with 2-carboxyethyl acrylate results in better bonding force among the three, which can further improve the heat resistance and flame retardant properties of the rice husk fiber composite material. Combining reinforcing material A and reinforcing material B through free radical polymerization can improve the bonding force between the two, thus significantly improving the mechanical properties, flame retardant properties, and heat resistance properties of the rice husk fiber composite material.

[0156] As shown in Table 1 above, the rice husk fiber composite materials prepared in Examples 1-3, compared to those prepared in Comparative Examples 1-8, achieved better performance. Examples 1-3 involved combining modified rice husk fibers with epoxy compounds to obtain reinforcing material A, combining L-lactic acid with reactive oligomers, and then combining it with 2-carboxyethyl acrylate to obtain reinforcing material B. Combining reinforcing material A with reinforcing material B yielded modified rice husk fiber reinforcing material. Mixing polylactic acid, modified rice husk fiber reinforcing material, silane coupling agent, antioxidant, lubricant, and reinforcing filler, followed by melt blending and extrusion, yielded the rice husk fiber composite material. The rice husk fiber composite materials prepared in Examples 1-8 did not meet the performance requirements. This indicates that the rice husk fiber composite material prepared in this invention not only possesses better mechanical properties, thermal stability, flame retardant properties, and heat resistance, but also has a longer service life, demonstrating excellent overall performance.

[0157] In the description of this specification, the references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0158] The above description is merely an example and illustration of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the invention or exceed the scope defined by the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A rice husk fiber composite material, characterized in that, The raw materials include the following parts by weight: 65-75 parts polylactic acid, 10-20 parts modified rice husk fiber reinforcing material, 0.3-0.5 parts silane coupling agent, 0.2-0.5 parts antioxidant, 0.5-1.5 parts lubricant, and 5-8 parts reinforcing filler; The preparation method of the modified rice husk fiber reinforced material includes the following steps: S1: Reinforcing material A is obtained by combining modified rice husk fiber with epoxy compounds; S2: By combining L-lactic acid with reactive oligomers and then with 2-carboxyethyl acrylate, reinforcing material B is obtained; S3: Combine the reinforcing material A from step S1 with the reinforcing material B from step S2 to obtain the modified rice husk fiber reinforcing material. The epoxy compound is composed of glycidyl methacrylate and cashew phenol glycidyl ether in a mass ratio of 0.7-0.8:0.6-0.7; The method for preparing the reactive oligomer includes the following steps: Polymethylhydrosiloxane, 9-decenol, vinyl phosphate and toluene were mixed and stirred under nitrogen protection, then heated and stirred, and Karstedt catalyst was added. The reaction was continued with stirring. After the reaction was completed, the mixture was cooled to room temperature, distilled under reduced pressure, and finally dried under vacuum to obtain the reactive oligomer.

2. The rice husk fiber composite material according to claim 1, characterized in that, Step S1 is as follows: Modified rice husk fiber was added to an epoxy compound and stirred under nitrogen protection. Then triethylamine was added and stirred until homogeneous. Next, a polymerization inhibitor was added and stirred until homogeneous. The system was heated to 85-95℃ and stirred to react. After the reaction was completed, the mixture was filtered, washed, and then subjected to Soxhlet extraction. Finally, it was vacuum dried to obtain reinforced material A.

3. The rice husk fiber composite material according to claim 2, characterized in that, The method for preparing the modified rice husk fiber includes the following steps: A1: Alkali-treated rice husk fibers were added to deionized water and ultrasonically dispersed. Then, Tris-HCl buffer solution was added and stirred evenly. Dopamine hydrochloride was then added and stirred to react. After the reaction was completed, the mixture was filtered, washed, and finally vacuum dried to obtain the composite material. A2: Add the composite material from step A1 to deionized water and ultrasonically disperse it to obtain a suspension. Add nano-silica to deionized water and ultrasonically disperse it to obtain a dispersion. Add the dispersion to the suspension and stir to obtain a mixture. Add magnesium chloride hexahydrate and aluminum nitrate nonahydrate to deionized water and mix evenly to obtain a metal salt solution. Add the metal salt solution to the mixture and continue stirring. Adjust the pH value of the system and then carry out the stirring reaction in an oil bath. After the reaction is completed, cool to room temperature, centrifuge, wash, and finally vacuum dry to obtain modified rice husk fiber.

4. The rice husk fiber composite material according to claim 1, characterized in that, Step S2 is as follows: B1: Mix L-lactic acid, reactive oligomer and toluene and stir until homogeneous. Add catalyst and continue stirring until homogeneous. Then heat and stir under nitrogen protection and reflux. After the reaction is complete, cool, wash, dry and filter. Obtain intermediate product by rotary evaporation. B2: Mix the intermediate product from step B1, ethyl 2-carboxyacrylate, and toluene, and stir until homogeneous. Then add the catalyst and polymerization inhibitor, and stir until homogeneous. Under nitrogen protection, heat and stir under reflux to react. After the reaction is complete, cool, wash, dry, filter, and obtain the reinforcing material B by rotary evaporation.

5. The rice husk fiber composite material according to claim 4, characterized in that, In step B1, the mass ratio of L-lactic acid, reactive oligomer, toluene, and catalyst is 1.75-1.85: 0.8-0.9: 0.9-1.1: 0.02-0.03; in step B2, the mass ratio of intermediate product, 2-carboxyethyl acrylate, toluene, catalyst, and polymerization inhibitor is 2.25-2.35: 1.9-2: 0.8-1: 0.02-0.03: 0.1-0.

2.

6. The rice husk fiber composite material according to claim 1, characterized in that, The mass ratio of polymethylhydrosiloxane, 9-decenol, vinyl phosphate, and toluene is 9.8-10.2: 3.8-4.2: 2.8-3.2: 19.9-20.

1.

7. The rice husk fiber composite material according to claim 1, characterized in that, Step S3 is as follows: The reinforcing material A from step S1, the reinforcing material B from step S2, and the initiator are mixed and stirred under nitrogen protection. Then, the mixture is stirred and reacted in an oil bath. After the reaction is complete, the mixture is poured into a mold and subjected to gradient curing. After the reaction is complete, the mixture is cooled to room temperature and demolded to obtain the modified rice husk fiber reinforced material.

8. A method for preparing a rice husk fiber composite material as described in any one of claims 1-7, characterized in that, Includes the following steps: Weigh out the raw materials by mass, grind and sieve the modified rice husk fiber reinforced material to obtain powder, then mix polylactic acid, powder, silane coupling agent, antioxidant, lubricant and reinforcing filler evenly, stir at 400-500 rpm for 10-15 minutes, then add to a twin-screw extruder for melt blending extrusion, and finally obtain rice husk fiber composite material.

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