Preparation method of high-strength and high-heat-insulation peanut shell-based polypropylene composite material

Abstract

The invention provides a preparation method of a high-strength and high-heat-insulation peanut shell-based polypropylene composite material, and belongs to the technical field of polymer composites.The preparation method comprises the following steps that S1, alkali liquor etching pretreatment is conducted on peanut shell fibers; s2, local grafting modification of a coupling agent; s3, carrying out secondary activation anchoring on the rigid particles; s4, carrying out multi-component melt blending and interface regulation and control; and S5, carrying out post-treatment. According to the method, waste peanut shell resources are used as raw materials, and the problems that rigid particles are prone to agglomeration, the binding force of the rigid particles on the fiber surface is weak, and stress is concentrated are solved through a multi-step process including alkaline pretreatment, coupling agent local grafting modification, nano rigid particle hybridization, plasma secondary activation and EAA interface regulation and control; the mechanical property of the prepared composite material is obviously improved; meanwhile, the micron-sized pore structure of the peanut shells retains a nano coarse structure and an interface thermal resistance network constructed by the nano particles to form a three-stage thermal insulation mechanism, so that the heat conductivity coefficient is obviously reduced.

Description

Technical Field

[0001] This invention relates to the field of polymer composite materials technology, specifically to a method for preparing a high-strength, high-heat-insulating peanut shell-based polypropylene composite material. Background Technology

[0002] As is well known, polypropylene (PP), a widely used general-purpose plastic, has advantages such as being lightweight, non-toxic, and easy to process, but its mechanical and thermal insulation properties are limited. Peanut shells, as agricultural waste, can be used as fillers in composites with polypropylene, representing an effective way to turn waste into treasure and reduce material costs. However, due to the poor interfacial compatibility between peanut shells and the polypropylene matrix, traditional peanut shell / polypropylene composites generally suffer from insufficient strength, poor toughness, and low thermal insulation performance, limiting their application in high-end fields.

[0003] Existing technologies include numerous modification treatments for plant-based fibers to address the aforementioned problems when combined with polypropylene. Chinese patent CN107033567A discloses a peanut shell powder-filled polypropylene / polylactic acid composite material, which improves mechanical properties to some extent, but its strength and thermal insulation performance still need improvement. Furthermore, Chinese patent CN113603972B employs simultaneous hydrolysis grafting of coupling agents and rigid particles, while CN114589995A uses a secondary modification method of first coupling and then coating with resin. Although these methods can improve the interface, they suffer from problems such as uneven distribution of rigid particles, easy agglomeration, and limited interfacial bonding strength, making it difficult to achieve a simultaneous and significant improvement in both mechanical and thermal insulation performance. This is especially problematic in applications requiring lightweight, high strength, and excellent thermal insulation performance, such as in construction, automotive, and home appliance industries. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing a high-strength, high-heat-insulating peanut shell-based polypropylene composite material, so as to solve the problems mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A method for preparing a high-strength, high-heat-insulating peanut shell-based polypropylene composite material includes the following steps:

[0007] S1. Alkali etching pretreatment of peanut shell fiber: Dry peanut shells are crushed to 60~140 mesh, immersed in alkaline solution, washed until neutral, and dried to obtain pretreated fiber;

[0008] S2. Local grafting modification of coupling agent: The pretreated fiber in step S1 is immersed in the hydrolyzed silane coupling agent alcohol-water solution and stirred in an enamel reactor equipped with a reflux condenser. After the reaction is completed, the fiber is obtained by filtration, washing and drying.

[0009] S3. Secondary activation and anchoring of rigid particles: After premixing the locally grafted fibers from step S2 with nano-rigid particles in a high-speed mixer, they are immediately subjected to low-temperature plasma treatment to obtain hybrid modified fibers.

[0010] S4. Multi-component melt blending and interface control: The hybrid modified fiber from step S3 is mixed evenly with polypropylene resin, toughening agent, compatibilizer, antioxidant, lubricant and interface control agent in proportion to obtain a premix.

[0011] S5. Post-processing: The premix from step S4 is added to a twin-screw extruder for melt extrusion granulation. After the granules are dried, peanut shell-based polypropylene composite material is obtained.

[0012] Preferably, in step S1, the alkaline solution is a sodium hydroxide solution with a mass fraction of 5-10%, the soaking time is 2-4 hours, the soaking temperature is 50-70℃, the drying temperature is 80-100℃, and the moisture content of the obtained pretreated fiber is <1%.

[0013] Preferably, in step S2, the mass fraction of silane coupling agent in the silane coupling agent alcohol aqueous solution is 2-4%, the solvent is anhydrous ethanol:water with a volume ratio of 9:1, and the mass ratio of pretreated fiber to silane coupling agent alcohol aqueous solution is (10-100):1.

[0014] Preferably, in step S2, the hydrolysis time of the silane coupling agent alcohol-water solution is 30-60 minutes, and the reaction conditions in the reactor are: pH 4-5, reaction temperature 70-80℃, stirring speed 200-500 rpm, reaction time 1.5-3.5 hours, drying temperature 85-95℃, and drying time 4-6 hours.

[0015] Preferably, in step S3, the nano-rigid particles are nano-calcium carbonate or nano-silica, the average particle size of the nano-rigid particles is 30~80nm, and the amount of nano-rigid particles added is 8~12% of the mass of the locally grafted fibers.

[0016] Preferably, in step S3, the plasma atmosphere is air or argon, the pressure is maintained at 30~50Pa, the low-temperature plasma processing power is 200~400W, and the processing time is 3~8 minutes.

[0017] Preferably, in step S4, the proportions, by weight, are: 50-65 parts polypropylene resin, 20-30 parts hybrid modified fiber, 5-10 parts toughening agent, 4-6 parts compatibilizer, 0.2-1 part antioxidant, 0.5-2 parts lubricant, and 1-3 parts interface modifier.

[0018] Preferably, in step S4, the toughening agent is a polyolefin elastomer (POE), the compatibilizer is polypropylene grafted maleic anhydride (PP-g-MAH), the antioxidant is antioxidant 1010, the lubricant is calcium stearate, and the interface regulator is ethylene-acrylic acid copolymer (EAA).

[0019] Preferably, in step S5, the melt extrusion granulation temperature of the twin-screw extruder is set as follows: Zone I 180~200℃, Zone II 190~210℃, Zone III 200~220℃, Zone IV 205~225℃, Zone V 195~215℃, the screw speed is 250~350rpm, the drying temperature is 90~100℃, and the drying time is 4~5 hours.

[0020] Another aspect of the present invention discloses a method for preparing high-strength, high-heat-insulating peanut shell-based polypropylene composite materials according to any of the above technical solutions, resulting in peanut shell-based polypropylene composite materials.

[0021] The beneficial effects of the above-described technical solution of the present invention are as follows:

[0022] (1) This invention provides a method for preparing high-strength and high-heat-insulating peanut shell-based polypropylene composite material. The steps are clear, the process parameters are controllable, and it is easy to realize industrial production.

[0023] (2) This invention significantly improves the interfacial bonding strength between peanut shell fiber and polypropylene matrix through a multi-step process of alkaline pretreatment, coupling agent modification and rigid particle hybridization. The introduction of rigid particles not only plays an anchoring role similar to "rivets", but also bears part of the load when the material is under stress, effectively transferring stress, thereby greatly improving the tensile strength, flexural strength and impact toughness of the composite material;

[0024] (3) Peanut shells are a porous natural material with good thermal insulation potential. This invention removes some components with high thermal conductivity through pretreatment and constructs a nanoscale rough structure on the fiber surface through hybridization modification. These structures form a large number of interfacial thermal resistances and micro-nano scale cavities in the composite material, effectively extending the heat conduction path, significantly reducing the thermal conductivity of the material, and endowing it with excellent thermal insulation performance;

[0025] (4) This invention makes full use of waste peanut shell resources, reduces environmental pollution, and conforms to the concept of sustainable development.

[0026] The key to this invention's breakthrough over existing technologies lies in:

[0027] Local anchoring structure: The coverage of the coupling agent on the fiber surface is determined by regulating the hydrolysis time of the coupling agent and the grafting reaction time. The two work together to control the degree of hydrolysis and grafting density of the coupling agent, so that the fiber surface is partially covered by the coupling agent, and some free hydroxyl groups are retained for subsequent plasma activation. The incomplete coverage of the coupling agent provides selective attachment sites for rigid particles, avoiding stress concentration caused by dense particle coating, and realizing efficient stress transfer and dispersion.

[0028] Secondary activation mechanism: Low-temperature plasma treatment solves the problems of particle aggregation in "simultaneous modification" of coupling agents and rigid nanoparticles and weak binding force in "stepwise modification". Through the synergy of physical bombardment and chemical activation, rigid particles and fibers form a strong "rivet effect".

[0029] Interface gradient regulation: EAA, as the third component, migrates to the interface during melt blending and forms a hydrogen bond network with the surface of the hybrid fiber, constructing a "rigid-flexible-rigid" gradient modulus interface layer, which significantly improves impact toughness.

[0030] Multi-scale thermal insulation: The micron-scale pore structure of peanut shells is preserved, and the nano-rough structure and interfacial thermal resistance network constructed by nanoparticles form a three-level thermal insulation mechanism, resulting in a significant reduction in thermal conductivity. Attached Figure Description

[0031] The above and other objects, features, and advantages of exemplary embodiments of the present invention will become readily understood by reading the following detailed description with reference to the accompanying drawings. Wherein:

[0032] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0033] The preferred embodiments of the present invention are described below. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0034] For experiments not specified in this protocol, the procedures and conditions described in the literature in this field should be followed. Reagents or instruments whose manufacturers are not specified are all commercially available products.

[0035] Example

[0036] A method for preparing a high-strength, high-heat-insulating peanut shell-based polypropylene composite material includes the following steps:

[0037] S1. Alkaline etching pretreatment of peanut shell fiber: Dry peanut shells are crushed to 60~140 mesh, immersed in 5~10% sodium hydroxide solution for 2~4 hours at 50~70℃, washed until neutral after immersion, and dried at 80~100℃ to obtain pretreated fiber.

[0038] S2. Local grafting modification of coupling agent: The pretreated fiber from step S1 is immersed in a silane coupling agent alcohol-water solution hydrolyzed at room temperature (25°C) for 30-60 minutes. The reaction is carried out in an enamel-lined reactor equipped with a reflux condenser with stirring. The reaction pH is 4-5, the reaction temperature is 70-80°C, the stirring rate is 200-500 rpm, and the reaction time is 1.5-3.5 hours. After the reaction, the fiber is vacuum filtered, washed, and vacuum dried at 85-95°C for 4-6 hours to obtain the locally grafted fiber. In the silane coupling agent alcohol-water solution, the mass fraction of silane coupling agent is 2-4%, the solvent is anhydrous ethanol:water with a volume ratio of 9:1, and the mass ratio of pretreated fiber to silane coupling agent alcohol-water solution is (10-100):1.

[0039] S3. Secondary activation and anchoring of rigid particles: After premixing the locally grafted fibers from step S2 with nano-rigid particles in a high-speed mixer, the fibers are immediately subjected to low-temperature plasma treatment to obtain hybrid modified fibers; wherein, the nano-rigid particles are nano-calcium carbonate or nano-silica, the average particle size of the nano-rigid particles is 30~80nm, the amount of nano-rigid particles added is 8~12% of the mass of the locally grafted fibers, the plasma atmosphere is air or argon, the pressure is maintained at 30~50Pa, the low-temperature plasma treatment power is 200~400W, and the treatment time is 3~8 minutes;

[0040] S4. Multi-component melt blending and interface control: The hybrid modified fiber from step S3 is mixed evenly with polypropylene resin, POE, PP-g-MAH, antioxidant 1010, calcium stearate and EAA in the following proportions by weight: 50-65 parts polypropylene resin, 20-30 parts hybrid modified fiber, 5-10 parts POE, 4-6 parts PP-g-MAH, 0.2-1 parts antioxidant 1010, 0.5-2 parts calcium stearate and 1-3 parts EAA to obtain a premix.

[0041] S5. Post-processing: Add the premixed material from step S4 to a twin-screw extruder. Set the melt extrusion granulation temperature of the twin-screw extruder to: Zone I 180~200℃, Zone II 190~210℃, Zone III 200~220℃, Zone IV 205~225℃, Zone V 195~215℃, and the screw speed to 250~350 rpm. After drying the granules at 90~100℃ for 4~5 hours, peanut shell-based polypropylene composite material is obtained.

[0042] Example 1

[0043] A method for preparing a high-strength, high-heat-insulating peanut shell-based polypropylene composite material includes the following steps:

[0044] S1. Crush peanut shells to 100 mesh, soak them in 8% NaOH solution at 60°C for 3 hours, wash until neutral, and dry at 90°C to obtain pretreated fibers;

[0045] S2. 100 parts of pretreated fiber and 2 parts of KH-550 coupling agent alcohol-water solution (coupling agent mass fraction 2wt%, alcohol-water volume ratio in alcohol-water solution 9:1, hydrolysis for 50 minutes) were reacted at 70℃ and 300rpm for 2 hours, and dried at 90℃ for 5 hours to obtain partially grafted fiber.

[0046] S3. Mix 100 parts of the above locally grafted fibers with 10 parts of nano-calcium carbonate in a high-speed mixer for 10 minutes, and then immediately perform argon plasma treatment (power 300W, pressure 40Pa, time 5 minutes) to obtain hybrid modified fibers.

[0047] S4. Premix 60 parts polypropylene, 30 parts hybrid modified fiber, 8 parts POE, 5 parts PP-g-MAH, 0.5 parts antioxidant 1010, 1 part calcium stearate, and 2 parts EAA in a high-speed mixer to obtain a premix.

[0048] S5. Add the premixed material from step S4 to a twin-screw extruder. Set the melt extrusion granulation temperature of the twin-screw extruder to: Zone I 190℃, Zone II 200℃, Zone III 210℃, Zone IV 215℃, Zone V 205℃, screw speed 300 rpm, and dry the granules at 90℃ for 5 hours to obtain peanut shell-based polypropylene composite material.

[0049] Example 2

[0050] S1. Crush peanut shells to 80 mesh, soak them in 10% NaOH solution at 60°C for 3 hours, wash until neutral, and dry at 80°C to obtain pretreated fibers;

[0051] S2. 100 parts of pretreated fiber and 2 parts of KH-550 coupling agent alcohol-water solution (coupling agent mass fraction 3wt%, alcohol:water volume ratio in alcohol-water solution 9:1, hydrolysis for 45 minutes) were reacted at 80℃ and 200rpm for 2.5 hours and dried at 85℃ for 6 hours to obtain locally grafted fiber.

[0052] S3. Mix 100 parts of the above locally grafted fibers with 12 parts of nano-calcium carbonate in a high-speed mixer for 10 minutes, and then immediately perform argon plasma treatment (power 400W, pressure 40Pa, time 8 minutes) to obtain hybrid modified fibers.

[0053] S4. Premix 65 parts polypropylene, 30 parts hybrid modified fiber, 10 parts POE, 6 parts PP-g-MAH, 1 part antioxidant 1010, 2 parts calcium stearate, and 3 parts EAA in a high-speed mixer to obtain a premix.

[0054] S5. Add the premixed material from step S4 to a twin-screw extruder. Set the melt extrusion granulation temperature of the twin-screw extruder to: Zone I 200℃, Zone II 210℃, Zone III 220℃, Zone IV 225℃, Zone V 215℃, screw speed 350 rpm, and dry the granules at 100℃ for 4 hours to obtain peanut shell-based polypropylene composite material.

[0055] Example 3

[0056] S1. Crush peanut shells to 60 mesh, soak them in 10% NaOH solution at 70°C for 2 hours, wash until neutral, and dry at 100°C to obtain pretreated fibers;

[0057] S2. 100 parts of pretreated fiber and 1 part of KH-550 coupling agent alcohol-water solution (coupling agent mass fraction 4wt%, alcohol-water volume ratio in alcohol-water solution 9:1, hydrolysis for 60 minutes) were reacted at 80℃ and 300rpm for 1.5 hours and dried at 95℃ for 4 hours to obtain locally grafted fiber.

[0058] S3. Mix 100 parts of the above locally grafted fibers with 8 parts of nano-calcium carbonate in a high-speed mixer for 10 minutes, and then immediately perform argon plasma treatment (power 200W, pressure 50Pa, time 3 minutes) to obtain hybrid modified fibers.

[0059] S4. Premix 50 parts polypropylene, 20 parts hybrid modified fiber, 5 parts POE, 4 parts PP-g-MAH, 0.2 parts antioxidant 1010, 0.5 parts calcium stearate, and 1 part EAA in a high-speed mixer to obtain a premix.

[0060] S5. Zone I: 180℃, Zone II: 190℃, Zone III: 210℃, Zone IV: 205℃, Zone V: 195℃, screw speed: 250 rpm, granules dried at 90℃ for 5 hours to obtain peanut shell-based polypropylene composite material.

[0061] Example 4

[0062] S1. Crush peanut shells to 120 mesh, soak them in 10% NaOH solution at 50°C for 4 hours, wash until neutral, and dry at 90°C to obtain pretreated fibers;

[0063] S2. 100 parts of pretreated fiber and 5 parts of KH-550 coupling agent alcohol-water solution (coupling agent mass fraction 2wt%, alcohol:water volume ratio in alcohol-water solution 9:1, hydrolysis for 40 minutes) were reacted at 70℃ and 400rpm for 3 hours and dried at 90℃ for 5 hours to obtain locally grafted fiber.

[0064] S3. Mix 100 parts of the above locally grafted fibers with 10 parts of nano-calcium carbonate in a high-speed mixer for 10 minutes, and then immediately perform argon plasma treatment (power 300W, pressure 30Pa, time 5 minutes) to obtain hybrid modified fibers.

[0065] S4. Premix 65 parts polypropylene, 25 parts hybrid modified fiber, 8 parts POE, 5 parts PP-g-MAH, 0.5 parts antioxidant 1010, 1.5 parts calcium stearate, and 2 parts EAA in a high-speed mixer to obtain a premix.

[0066] S5. Add the premixed material from step S4 to a twin-screw extruder. Set the melt extrusion granulation temperature of the twin-screw extruder to: Zone I 190℃, Zone II 200℃, Zone III 210℃, Zone IV 215℃, Zone V 205℃, screw speed 300 rpm, and dry the granules at 90℃ for 5 hours to obtain peanut shell-based polypropylene composite material.

[0067] Example 5

[0068] S1. Crush peanut shells to 140 mesh, soak them in 5% NaOH solution at 70°C for 4 hours, wash until neutral, and dry at 90°C to obtain pretreated fibers;

[0069] S2. 100 parts of pretreated fiber and 10 parts of KH-550 coupling agent alcohol-water solution (coupling agent mass fraction 2wt%, alcohol:water volume ratio in alcohol-water solution 9:1, hydrolysis for 30 minutes) were reacted at 70℃ and 500rpm for 3.5 hours and dried at 90℃ for 5 hours to obtain locally grafted fiber.

[0070] S3. Mix 100 parts of the above locally grafted fibers with 10 parts of nano-calcium carbonate in a high-speed mixer for 10 minutes, and then immediately perform argon plasma treatment (power 300W, pressure 40Pa, time 5 minutes) to obtain hybrid modified fibers.

[0071] S4. Premix 60 parts polypropylene, 30 parts hybrid modified fiber, 8 parts POE, 5 parts PP-g-MAH, 0.5 parts antioxidant 1010, 1 part calcium stearate, and 2 parts EAA in a high-speed mixer to obtain a premix.

[0072] S5. Add the premixed material from step S4 to a twin-screw extruder. Set the melt extrusion granulation temperature of the twin-screw extruder to: Zone I 190℃, Zone II 200℃, Zone III 210℃, Zone IV 215℃, Zone V 205℃, screw speed 300 rpm, and dry the granules at 90℃ for 5 hours to obtain peanut shell-based polypropylene composite material.

[0073] Comparative Example 1

[0074] The difference between this and Example 1 is that steps S2 and S3 are omitted, and 60 parts of polypropylene, 30 parts of unmodified peanut shell fiber, 8 parts of POE, 5 parts of PP-g-MAH, 0.5 parts of antioxidant 1010, and 1 part of calcium stearate are directly premixed in a high-speed mixer.

[0075] Comparative Example 2

[0076] The difference between this and Example 1 is that low-temperature plasma treatment is not performed, and step S3 is changed to: mixing the above-mentioned locally grafted fibers with 10 parts of nano-calcium carbonate in a high-speed mixer for 10 minutes to obtain untreated hybrid modified fibers.

[0077] Comparative Example 3

[0078] The difference between this and Example 1 is that step S2 is omitted, and the pretreated fibers obtained in step S1 are directly used in step S3.

[0079] Comparative Example 4

[0080] The difference between this and Example 1 is that EAA is removed in step S4.

[0081] The performance of the composite materials prepared in Examples 1-5 and Comparative Examples 1-4 was tested, and the results are shown in the table below:

[0082]

[0083] The data in the table shows that:

[0084] The composite material prepared in Example 1 exhibited the best performance, with tensile strength (39.6 MPa), flexural strength (52.1 MPa), and impact strength (9.2 kJ / m²) significantly higher than the comparative example, and thermal conductivity (0.16 W / (m·K)) significantly lower than the comparative example, thus confirming the effectiveness of the technical solution of the present invention.

[0085] Comparative Example 1 did not undergo local grafting modification with coupling agent, plasma activation, or EAA regulation. Due to poor interfacial compatibility, the peanut shell fiber and polypropylene matrix were weakly bonded, resulting in low stress transfer efficiency and the worst mechanical properties. Furthermore, due to numerous interfacial defects, its thermal insulation performance was also the worst.

[0086] Comparative Example 2 was not activated by plasma, and the interface bonding was improved only by local grafting modification with coupling agent. As a result, the bonding between the nano-rigid particles and the fiber was not as strong as in Example 1, the improvement in mechanical properties was limited, and the micro-nano scale thermal insulation structure was not effectively constructed. The thermal conductivity was higher than that of the other examples.

[0087] Comparative Example 3 did not undergo coupling agent treatment to achieve local grafting, resulting in a relatively small number of active groups on the material surface even after plasma activation, thus its performance was significantly different from that of Example 1.

[0088] Although Comparative Example 4 added nano-rigid particles, it lacked the interfacial regulation effect of EAA and failed to form a hydrogen bond network on the surface of the hybrid fiber. As a result, the anchoring effect of the rigid particles on the peanut shell fiber surface was worse than that of the Example, and the performance improvement effect was not good.

[0089] In summary, the multi-step process of local coupling grafting, plasma secondary activation, and EAA interface gradient control described in this invention is crucial for achieving high strength and high thermal insulation performance of materials, and none of these steps can be omitted.

[0090] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Any other modifications or equivalent substitutions made by those skilled in the art to the technical solutions of the present invention, as long as they do not depart from the spirit and scope of the technical solutions of the present invention, should be covered within the scope of the claims of the present invention.

Claims

1. A method for preparing high-strength high-insulation peanut shell-based polypropylene composite material, characterized in that, Comprise the following steps: S1. Alkaline etching pretreatment of peanut shell fiber: dry peanut shell is crushed to 60-140 mesh, soaked in alkaline solution, washed to neutral, dried, and pretreated fiber is obtained; S2. Local graft modification of coupling agent: the pretreated fiber of step S1 is immersed in the hydrolyzed silane coupling agent alcohol aqueous solution, and the stirring reaction is carried out in the enamel reaction kettle equipped with reflux condenser, after the reaction, the local graft fiber is obtained by suction filtration, washing and drying; S3. Secondary activation anchoring of rigid particles: the local graft fiber of step S2 is premixed with nano rigid particles in a high-speed mixer, and then low-temperature plasma treatment is carried out immediately to obtain hybrid modified fiber; S4. Multi-component melt blending and interface regulation: the hybrid modified fiber of step S3 is mixed with polypropylene resin, toughening agent, compatibilizer, antioxidant, lubricant and interface regulator in proportion to obtain premix; S5. Post-treatment: the premix of step S4 is added into a twin-screw extruder for melt extrusion and granulation, and the granules are dried to obtain peanut shell-based polypropylene composite material.

2. The method for preparing the high-strength, high-heat-insulating peanut shell-based polypropylene composite material according to claim 1, characterized in that, In step S1, the alkaline solution is sodium hydroxide solution with mass fraction of 5-10%, the soaking treatment time is 2-4 hours, the soaking treatment temperature is 50-70℃, the drying temperature is 80-100℃, and the moisture content of the obtained pretreated fiber is less than 1%.

3. The method for preparing the high-strength, high-heat-insulating peanut shell-based polypropylene composite material according to claim 1, characterized in that, In step S2, the mass fraction of silane coupling agent in the silane coupling agent alcohol aqueous solution is 2-4%, the solvent is anhydrous ethanol: water with volume ratio of 9:1, and the mass ratio of pretreated fiber to silane coupling agent alcohol aqueous solution is (10-100):

1.

4. The process for preparing high strength high thermal insulation peanut hull based polypropylene composites as claimed in claim 1, wherein, In step S2, the hydrolysis time of the silane coupling agent alcohol aqueous solution is 30-60 minutes, and the reaction conditions in the reaction kettle are as follows: pH is 4-5, reaction temperature is 70-80℃, stirring rate is 200-500 rpm, reaction time is 1.5-3.5 hours, drying temperature is 85-95℃, and drying time is 4-6 hours.

5. The process for preparing high strength high thermal insulation peanut hull based polypropylene composites as claimed in claim 1, wherein, In step S3, the nano rigid particles are nano calcium carbonate or nano silicon dioxide, the average particle size of the nano rigid particles is 30-80 nm, and the addition amount of the nano rigid particles is 8-12% of the mass of the local graft fiber.

6. The process for preparing high strength high thermal insulation peanut hull based polypropylene composites as claimed in claim 1, wherein, In step S3, the plasma atmosphere is air or argon, the gas pressure is maintained at 30-50 Pa, the low-temperature plasma treatment power is 200-400 W, and the treatment time is 3-8 minutes.

7. The process for preparing high strength high thermal insulation peanut hull based polypropylene composites as claimed in claim 1, wherein, In step S4, the proportion is as follows: polypropylene resin 50-65 parts, hybrid modified fiber 20-30 parts, toughening agent 5-10 parts, compatibilizer 4-6 parts, antioxidant 0.2-1 part, lubricant 0.5-2 parts, and interface regulator 1-3 parts.

8. The method for preparing the high-strength, high-heat-insulating peanut shell-based polypropylene composite material according to claim 7, characterized in that, In step S4, the toughening agent is polyolefin elastomer, the compatibilizer is polypropylene grafted maleic anhydride, the antioxidant is antioxidant 1010, the lubricant is calcium stearate, and the interface regulator is ethylene-acrylic acid copolymer.

9. The process for preparing high strength high thermal insulation peanut hull based polypropylene composites as claimed in claim 1, wherein, In step S5, the temperature of the twin-screw extruder melt extrusion granulation is set as: 180-200℃ in region I, 190-210℃ in region II, 200-220℃ in region III, 205-225℃ in region IV, and 195-215℃ in region V, the screw rotation speed is 250-350 rpm, the drying temperature is 90-100℃, and the drying time is 4-5 hours.

10. The peanut shell-based polypropylene composite material prepared by the method according to any one of claims 1-9.

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