High-temperature-resistant polypropylene composite material and preparation method thereof

Abstract

The invention relates to the technical field of high polymer material modification, and discloses a high-temperature-resistant polypropylene composite material and a preparation method thereof.The high-temperature-resistant polypropylene composite material is prepared from, by weight, 100 parts of polypropylene, 40-50 parts of maleic anhydride grafted ethylene-octylene copolymer and 5-25 parts of functionalized nano Al2O3 material through melt grafting, vulcanization and hot pressing, wherein the functionalized nano Al2O3 material is obtained by grafting a silane coupling agent containing an imide structure, nano Al2O3 and a hindered phenol antioxidant, a nano filler with an antioxidant function and an interfacial compatibilization effect is formed, the grafted nano Al2O3 can be used as a heterogeneous nucleating agent to improve the crystallinity of polypropylene, free radicals can be directionally captured through surface antioxidant molecules, and the mechanical property of polypropylene is improved. The compatibility of nanoparticles and a polypropylene matrix is remarkably improved, agglomeration is avoided, a continuous heat-conducting network is constructed to uniformly disperse high-temperature stress, meanwhile, antioxidant migration is reduced, and long-acting high-temperature resistance is achieved.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, specifically to a high-temperature resistant polypropylene composite material and its preparation method. Background Technology

[0002] Polypropylene (PP), as a lightweight, high-strength, chemically resistant, and low-cost engineering plastic, is widely used in automobiles, home appliances, electronics, medical devices, and packaging. However, the presence of a large number of unstable tertiary carbon atoms in the PP molecular chain makes it prone to thermo-oxidative degradation at high temperatures. The heat distortion temperature of ordinary PP is typically around 100°C, which is insufficient to meet the requirements of high-temperature applications such as automotive engine compartments and electronic component housings. Traditional pure PP materials also suffer from low heat distortion temperature, decreased mechanical properties, and additive migration and precipitation at high temperatures. In particular, under high temperature and humidity conditions, it is prone to stickiness, discoloration, and bulging, limiting its application in high-performance fields and hindering the development of lightweight materials and plastic-to-steel replacement processes. With the increasing demands of industrial technology on material performance, the development of PP composite materials that combine high-temperature resistance and mechanical stability has become an urgent technical challenge.

[0003] To improve the high-temperature resistance of polypropylene, existing technologies mainly involve adding high-temperature resistant fillers, such as glass fiber, talc, or copolymer modification. Although these methods can increase the heat distortion temperature of polypropylene materials to 130-150℃, the mechanical properties still decrease significantly at high temperatures, such as tensile strength and impact strength, leading to material failure under high-temperature impact or long-term heat load. Patent number CN111793277B discloses a high-strength transparent polypropylene and its preparation method. After premixing polypropylene imide-modified nano-silica, polypropylene grafted maleic anhydride, and polypropylene resin, modified polypropylene is obtained by extrusion granulation. This polypropylene resin has good transparency, tensile strength, and impact strength, but the improvement in heat resistance is limited, and the added components are numerous, making it unsuitable for industrial production.

[0004] Existing patents involve preparing composite materials by blending traditional hindered phenolic antioxidants with inorganic fillers. This is achieved by adding antioxidants such as phenols and phosphites for co-extrusion to inhibit the oxidative degradation of the polymer. However, traditional antioxidants have poor compatibility with the polypropylene matrix and are prone to migrating to the material surface during high-temperature processing or long-term use, leading to a decrease in antioxidant efficiency and an inability to continuously inhibit thermo-oxidative degradation reactions. In addition, inorganic fillers such as talc have weak interfacial bonding with polypropylene and are prone to forming agglomerates, which become stress concentration points under high-temperature conditions, thus accelerating the deterioration of material properties.

[0005] To address the aforementioned shortcomings, this invention prepares a modified silane coupling agent to chemically graft hindered phenolic antioxidants onto the surface hydroxyl groups of nano-Al2O3, forming a nanofiller that combines antioxidant function with interfacial compatibilization. This constructs a continuous thermally conductive network to uniformly disperse high-temperature stress while reducing antioxidant migration, thus achieving long-lasting high-temperature resistance. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of the existing technology and provide a high-temperature resistant polypropylene composite material and its preparation method, which solves the problems of low heat distortion temperature, mechanical property decay, and additive migration and precipitation of traditional pure polypropylene materials under high temperature environment.

[0007] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing a high-temperature resistant polypropylene composite material is carried out according to the following steps: Step (1): Under a nitrogen atmosphere, add 100 parts by weight of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride and toluene to a reaction flask. After stirring and dissolving, add 90-105 parts of aminoimide-modified nano-Al2O3 and 310-350 parts of triethylamine. Stir the reaction. After the reaction is completed, cool to room temperature, filter to remove toluene, wash with ethanol, and dry to obtain functionalized nano-Al2O3 material.

[0008] Step (2): Polypropylene, maleic anhydride-grafted ethylene-octene copolymer, functionalized nano-Al2O3 material and dicumyl peroxide are first added to a twin-screw extruder for melt grafting, and then placed in a flat vulcanizing machine and hot-pressed at 200-210℃ and 30-40MPa for 10-20s. After cooling and drying, a high-temperature resistant polypropylene composite material is obtained.

[0009] Furthermore, in step (1), the reaction temperature is 80-100℃ and the reaction time is 24-48h.

[0010] Furthermore, in step (2), the mass ratio of polypropylene, maleic anhydride-grafted ethylene-octene copolymer, functionalized nano-Al2O3 material, and dicumyl peroxide is 100:40-50:5-25:2-4.

[0011] Furthermore, in step (2), the temperatures of the extruder zones 1 to 5 are 170-180℃, 180-190℃, 190-200℃, 195-205℃, and 190-200℃, respectively, the melt grafting time is 5-10 min, and the main screw speed is 140-160 r / min.

[0012] Furthermore, the preparation method of aminoimide-modified nano-Al2O3 in step (1) is carried out according to the following steps: Step S1: Under a nitrogen atmosphere, N-[3-(trimethoxysilyl)propyl]ethylenediamine and isopropanol are added to a reaction flask and stirred until homogeneous. Then, methyl 4-maleimide benzoate and catalyst are added, and the mixture is heated to 70-85℃ and reacted for 8-16 hours. The mixture is then distilled under reduced pressure and cooled to obtain an imide-modified aminosilane coupling agent.

[0013] Step S2: Under a nitrogen atmosphere, nano-Al2O3 and ethanol are added to a reaction flask and dispersed evenly. Acetic acid is added to adjust the pH to 5-7, and imide-modified aminosilane coupling agent is added. The mixture is ultrasonically dispersed evenly at 500-600 r / min, and then the reaction is carried out. After the reaction is completed, the mixture is cooled, centrifuged, and dried to obtain aminoimide-modified nano-Al2O3.

[0014] Furthermore, the catalyst in step S1 is any one of sodium methoxide, DBU, or sodium isooctanoate.

[0015] Furthermore, in step S1, the molar ratio of N-[3-(trimethoxysilyl)propyl]ethylenediamine, methyl 4-maleimide benzoate, and catalyst is 1:1.05-1.2:0.08-0.12.

[0016] Furthermore, in step S2, the mass ratio of nano-Al2O3 to imide-modified aminosilane coupling agent is 100:5-8.

[0017] Furthermore, in step S2, the reaction temperature is 65-80℃ and the reaction time is 5-12h.

[0018] By adopting the above technical solution, the beneficial effects of the present invention are as follows: (1) It has good free radical scavenging ability: By using modified silane coupling agent as a "bridge" for covalent connection, hindered phenol antioxidant molecules with antioxidant ability are grafted onto the surface of nano Al2O3. During the thermo-oxidative degradation of polypropylene, the nano Al2O3 skeleton with free radical scavenging ability can combine with the free radicals generated in the early stage of polypropylene oxidation, so that they no longer participate in the oxidation reaction, thereby improving the overall free radical scavenging ability and greatly enhancing the thermo-oxidative stability of polypropylene composites.

[0019] (2) Excellent high temperature resistance: The thermal stability of nano Al2O3 is much higher than that of pure polypropylene, and chemical bonds are formed between it and the polypropylene matrix. After the surface modification of nano Al2O3 with modified silane coupling agent, the interaction between it and the polypropylene molecular chain is enhanced, forming a phase interface that restricts the movement of molecular chains, hindering the transfer of external heat to polypropylene molecules, slowing down the diffusion of gas generated by thermal decomposition from the matrix to the outside, thus reducing the thermal decomposition rate and making it more conducive to uniform thermal diffusion and heat conduction. At the same time, the highly symmetric imide five-membered ring structure has rigidity and three-dimensional dimensional stability, and excellent high temperature resistance. During the heating process, it will hinder the rotation of polypropylene chains, making the movement of the material difficult, thus giving the polypropylene material good high temperature resistance.

[0020] (3) Good interfacial compatibility: The double bonds of the imide groups in the functionalized nano-Al2O3 material can initiate polymerization with polypropylene. The amino groups in its structure form chemical bonds with the acyl chlorides on the surface of the antioxidant, which can inhibit the aggregation and bridging of nanoparticles and increase its compatibility with polypropylene. This is conducive to the full adsorption and bonding of nano-Al2O3 and polypropylene, enhancing the interaction between the two and thus bearing a greater load. At the same time, maleic anhydride-grafted ethylene-octene copolymer and polypropylene are very similar in structure and properties. During the impact process, it can inhibit the crystallization of polypropylene and can more effectively resist crack propagation, further improving the mechanical strength of the composite material. Detailed Implementation

[0021] The following provides a detailed description of preferred embodiments of the invention. These examples are provided to better illustrate the invention and are not intended to limit the invention to these examples. Non-essential improvements and adjustments to the embodiments based on the invention's description still fall within the scope of the invention. Unless otherwise stated, all raw materials and reagents used in this application are commercially available or can be prepared by known methods.

[0022] Preparation of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride: Under a nitrogen atmosphere, 0.35 g of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid and 50 mL of dichloromethane were added to a reaction flask. After stirring until homogeneous, 1 mL of sulfoxide was added, and the reaction was carried out at 80 °C for 5 h. Dichloromethane and excess sulfoxide were removed by vacuum distillation to obtain 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride. The preparation reaction formula is as follows:

[0023] Preparation of maleic anhydride-grafted ethylene-octene copolymer: 5g maleic anhydride and 0.75g dicumyl peroxide were ultrasonically dissolved in 80mL acetone. After complete dissolution, they were mixed with 500g ethylene-octene copolymer, dried, and then melt-grafted on a twin-screw extruder to obtain maleic anhydride-grafted ethylene-octene copolymer.

[0024] N-[3-(trimethoxysilyl)propyl]ethylenediamine, CAS number 1760-24-3.

[0025] Methyl 4-maleimide benzoate, CAS number 40349-49-3.

[0026] DBU, 1,8-diazabicyclo[5.4.0]undec-7-ene, CAS No. 6674-22-2.

[0027] Example 1 (1) Under a nitrogen atmosphere, 35 mmol of N-[3-(trimethoxysilyl)propyl]ethylenediamine and 210 mL of isopropanol were added to a reaction flask. After stirring evenly, 3.78 mmol of methyl 4-maleimide benzoate and 3.5 mmol of sodium methoxide were added. The mixture was heated to 80 °C and reacted for 12 h. The mixture was then distilled under reduced pressure and cooled to obtain an imide-modified aminosilane coupling agent. The preparation reaction formula is as follows:

[0028] (2) Under a nitrogen atmosphere, 10g of nano Al2O3 and 320mL of ethanol were added to the reaction flask. After the mixture was dispersed evenly, acetic acid was added to adjust the pH to 6. 0.5g of imide-modified aminosilane coupling agent was added and ultrasonically dispersed evenly at 550r / min. The mixture was reacted at 70℃ for 8h. After the reaction was completed, the mixture was cooled, centrifuged, and dried to obtain aminoimide-modified nano Al2O3.

[0029] (3) Under a nitrogen atmosphere, 5g of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride and 125mL of toluene were added to the reaction flask. After stirring and dissolving, 5.1g of aminoimide-modified nano-Al2O3 and 16g of triethylamine were added. The reaction was carried out at 90℃ for 32h. After cooling to room temperature, toluene was removed by filtration, washed with ethanol, and dried to obtain functionalized nano-Al2O3 material.

[0030] (4) 100g of polypropylene, 50g of maleic anhydride-grafted ethylene-octene copolymer, 5g of functionalized nano-Al2O3 material and 3g of dicumyl peroxide were first added to a twin-screw extruder for melt grafting. The temperatures of the first to fifth zones of the extruder were 175℃, 185℃, 195℃, 200℃ and 195℃, respectively. The melt grafting time was 6min and the main screw speed was 150r / min. Then it was placed in a flat vulcanizing machine and hot-pressed at 205℃ and 35MPa for 15s. After cooling and drying, a high-temperature resistant polypropylene composite material was obtained.

[0031] Example 2 (1) Under a nitrogen atmosphere, 120 mmol of N-[3-(trimethoxysilyl)propyl]ethylenediamine and 600 mL of isopropanol were added to a reaction flask. After stirring evenly, 126 mmol of methyl 4-maleimide benzoate and 9.6 mmol of DBU were added. The mixture was heated to 85 °C and reacted for 8 h. The mixture was then distilled under reduced pressure and cooled to obtain an imide-modified aminosilane coupling agent.

[0032] (2) Under a nitrogen atmosphere, 25g of nano Al2O3 and 625mL of ethanol were added to the reaction flask. After being dispersed evenly, acetic acid was added to adjust the pH to 7, and 1.25g of imide-modified aminosilane coupling agent was added. The mixture was ultrasonically dispersed evenly at 600r / min and reacted at 80℃ for 5h. After the reaction was completed, the mixture was cooled, centrifuged, and dried to obtain aminoimide-modified nano Al2O3.

[0033] (3) Under a nitrogen atmosphere, 20g of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride and 400mL of toluene were added to the reaction flask. After stirring and dissolving, 18g of aminoimide-modified nano-Al2O3 and 62g of triethylamine were added. The reaction was carried out at 100℃ for 24h. After cooling to room temperature, toluene was removed by filtration, washed with ethanol, and dried to obtain functionalized nano-Al2O3 material.

[0034] (4) 100g of polypropylene, 48g of maleic anhydride-grafted ethylene-octene copolymer, 10g of functionalized nano-Al2O3 material and 2g of dicumyl peroxide were first added to a twin-screw extruder for melt grafting. The temperatures of the first to fifth zones of the extruder were 180℃, 190℃, 200℃, 205℃ and 200℃, respectively. The melt grafting time was 5min and the main screw speed was 160r / min. Then it was placed in a flat vulcanizing machine and hot-pressed at 210℃ and 40MPa for 10s. After cooling and drying, a high-temperature resistant polypropylene composite material was obtained.

[0035] Example 3 (1) Under a nitrogen atmosphere, 80 mmol of N-[3-(trimethoxysilyl)propyl]ethylenediamine and 640 mL of isopropanol were added to a reaction flask. After stirring evenly, 96 mmol of methyl 4-maleimide benzoate and 9.6 mmol of sodium isooctanoate were added. The mixture was heated to 70 °C and reacted for 16 h. The mixture was then distilled under reduced pressure and cooled to obtain an imide-modified aminosilane coupling agent.

[0036] (2) Under a nitrogen atmosphere, 15g of nano Al2O3 and 600mL of ethanol were added to the reaction flask. After the mixture was evenly dispersed, acetic acid was added to adjust the pH to 5. 1.2g of imide-modified aminosilane coupling agent was added and ultrasonically dispersed evenly at 500r / min. The mixture was reacted at 65℃ for 12h. After the reaction was completed, the mixture was cooled, centrifuged, and dried to obtain aminoimide-modified nano Al2O3.

[0037] (3) Under a nitrogen atmosphere, 30g of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride and 900mL of toluene were added to the reaction flask. After stirring and dissolving, 31.5g of aminoimide-modified nano-Al2O3 and 105g of triethylamine were added. The reaction was carried out at 80℃ for 48h. After cooling to room temperature, toluene was removed by filtration, washed with ethanol, and dried to obtain functionalized nano-Al2O3 material.

[0038] (4) 100g of polypropylene, 45g of maleic anhydride-grafted ethylene-octene copolymer, 15g of functionalized nano-Al2O3 material and 4g of dicumyl peroxide were first added to a twin-screw extruder for melt grafting. The temperatures of the first to fifth zones of the extruder were 170℃, 180℃, 190℃, 195℃ and 190℃, respectively. The melt grafting time was 10min and the main screw speed was 140r / min. Then it was placed in a flat vulcanizing machine and hot-pressed at 200℃ and 30MPa for 20s. After cooling and drying, a high-temperature resistant polypropylene composite material was obtained.

[0039] Example 4 (1) Under a nitrogen atmosphere, 50 mmol of N-[3-(trimethoxysilyl)propyl]ethylenediamine and 360 mL of isopropanol were added to a reaction flask. After stirring evenly, 58 mmol of methyl 4-maleimide benzoate and 5.1 mmol of sodium methoxide were added. The mixture was heated to 75 °C and reacted for 15 h. The mixture was then distilled under reduced pressure and cooled to obtain an imide-modified aminosilane coupling agent.

[0040] (2) Under a nitrogen atmosphere, 40g of nano Al2O3 and 1200mL of ethanol were added to the reaction flask. After the mixture was evenly dispersed, acetic acid was added to adjust the pH to 6. 2.8g of imide-modified aminosilane coupling agent was added and ultrasonically dispersed evenly at 580r / min. The mixture was reacted at 70℃ for 10h. After the reaction was completed, the mixture was cooled, centrifuged, and dried to obtain aminoimide-modified nano Al2O3.

[0041] (3) Under a nitrogen atmosphere, 35g of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride and 980mL of toluene were added to the reaction flask. After stirring and dissolving, 36.4g of aminoimide-modified nano-Al2O3 and 85g of triethylamine were added. The reaction was carried out at 95℃ for 45h. After cooling to room temperature, toluene was removed by filtration, washed with ethanol, and dried to obtain functionalized nano-Al2O3 material.

[0042] (4) 100g of polypropylene, 42g of maleic anhydride-grafted ethylene-octene copolymer, 20g of functionalized nano-Al2O3 material and 2.5g of dicumyl peroxide were first added to a twin-screw extruder for melt grafting. The temperatures of the first to fifth zones of the extruder were 180℃, 180℃, 200℃, 200℃ and 195℃, respectively. The melt grafting time was 7min and the main screw speed was 155r / min. Then it was placed in a flat vulcanizing machine and hot-pressed at 205℃ and 36MPa for 12s. After cooling and drying, a high-temperature resistant polypropylene composite material was obtained.

[0043] Example 5 (1) Under a nitrogen atmosphere, 40 mmol of N-[3-(trimethoxysilyl)propyl]ethylenediamine and 210 mL of isopropanol were added to a reaction flask. After stirring evenly, 42.5 mmol of methyl 4-maleimide benzoate and 3.8 mmol of DBU were added. The mixture was heated to 85 °C and reacted for 16 h. The mixture was then distilled under reduced pressure and cooled to obtain an imide-modified aminosilane coupling agent.

[0044] (2) Under a nitrogen atmosphere, 50g of nano Al2O3 and 1500mL of ethanol were added to the reaction flask. After the mixture was evenly dispersed, acetic acid was added to adjust the pH to 5. 3.9g of imide-modified aminosilane coupling agent was added and ultrasonically dispersed evenly at 550r / min. The mixture was reacted at 75℃ for 8h. After the reaction was completed, the mixture was cooled, centrifuged, and dried to obtain aminoimide-modified nano Al2O3.

[0045] (3) Under a nitrogen atmosphere, 40 g of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride and 1100 mL of toluene were added to the reaction flask. After stirring and dissolving, 38.5 g of aminoimide-modified nano-Al2O3 and 130 g of triethylamine were added. The reaction was carried out at 95 °C for 35 h. After cooling to room temperature, toluene was removed by filtration, washed with ethanol, and dried to obtain functionalized nano-Al2O3 material.

[0046] (4) 100g of polypropylene, 40g of maleic anhydride-grafted ethylene-octene copolymer, 25g of functionalized nano-Al2O3 material and 3.5g of dicumyl peroxide were first added to a twin-screw extruder for melt grafting. The temperatures of the first to fifth zones of the extruder were 175℃, 185℃, 190℃, 200℃ and 200℃, respectively. The melt grafting time was 10min and the main screw speed was 160r / min. Then it was placed in a flat vulcanizing machine and hot-pressed at 210℃ and 35MPa for 20s. After cooling and drying, a high-temperature resistant polypropylene composite material was obtained.

[0047] Comparative Example 1 (1) Under a nitrogen atmosphere, 10g of nano Al2O3 and 320mL of ethanol were added to the reaction flask and dispersed evenly. Acetic acid was added to adjust the pH to 6, and 0.5g of N-[3-(trimethoxysilyl)propyl]ethylenediamine was added. The mixture was ultrasonically dispersed evenly at 550r / min and reacted at 70℃ for 8h. After the reaction was completed, the mixture was cooled, centrifuged, and dried to obtain amino-modified nano Al2O3.

[0048] (2) Under a nitrogen atmosphere, 5g of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride and 125mL of toluene were added to the reaction flask. After stirring and dissolving, 5.1g of amino-modified nano-Al2O3 and 16g of triethylamine were added. The reaction was carried out at 90℃ for 32h. After cooling to room temperature, toluene was removed by filtration, washed with ethanol, and dried to obtain modified nano-Al2O3 material.

[0049] (3) 100g of polypropylene, 50g of maleic anhydride-grafted ethylene-octene copolymer, 5g of modified nano-Al2O3 material and 3g of dicumyl peroxide were first added to a twin-screw extruder for melt grafting. The temperatures of the first to fifth zones of the extruder were 175℃, 185℃, 195℃, 200℃ and 195℃, respectively. The melt grafting time was 6min and the main screw speed was 150r / min. Then it was placed in a flat vulcanizing machine and hot-pressed at 205℃ and 35MPa for 15s. After cooling and drying, the polypropylene composite material was obtained.

[0050] Comparative Example 2 (1) Under a nitrogen atmosphere, 10g of nano Al2O3 and 320mL of ethanol were added to the reaction flask and dispersed evenly. Acetic acid was added to adjust the pH to 6, and 0.5g of N-[3-(trimethoxysilyl)propyl]ethylenediamine was added. The mixture was ultrasonically dispersed evenly at 550r / min and reacted at 70℃ for 8h. After the reaction was completed, the mixture was cooled, centrifuged, and dried to obtain amino-modified nano Al2O3.

[0051] (2) 100g of polypropylene, 50g of maleic anhydride-grafted ethylene-octene copolymer, 5g of amino-modified nano-Al2O3 and 3g of dicumyl peroxide were first added to a twin-screw extruder for melt grafting. The temperatures of the first to fifth zones of the extruder were 175℃, 185℃, 195℃, 200℃ and 195℃, respectively. The melt grafting time was 6min and the main screw speed was 150r / min. Then it was placed in a flat vulcanizing machine and hot-pressed at 205℃ and 35MPa for 15s. After cooling and drying, a polypropylene composite material was obtained.

[0052] Comparative Example 3 100g of polypropylene, 50g of maleic anhydride-grafted ethylene-octene copolymer, 5g of nano-Al2O3, and 3g of dicumyl peroxide were first added to a twin-screw extruder for melt grafting. The temperatures of zones one to five of the extruder were 175℃, 185℃, 195℃, 200℃, and 195℃, respectively. The melt grafting time was 6 minutes, and the main screw speed was 150 r / min. Then, the mixture was placed in a flat vulcanizing machine and hot-pressed at 205℃ and 35MPa for 15 seconds. After cooling and drying, the polypropylene composite material was obtained.

[0053] Tensile property test: The tensile strength of polypropylene composite was tested using an electronic universal testing machine in accordance with GB / T 1040.1-2006 standard, with a tensile rate of 10 mm / min.

[0054] Impact strength test: In accordance with GB / T 1043.1 2008 standard, the impact performance of polypropylene composite materials was tested using a pendulum impact testing machine. The sample size was 10mm×10mm×1.5mm, and the width of the V-notch was 2mm.

[0055] The test results in the table above show that the mechanical properties of the polypropylene composite material gradually increase with the increase of the content of functionalized nano-Al2O3 material. Among them, the tensile strength in Example 4 reaches 62.0 MPa and the impact strength is 38.2 kJ / m. 2 This is because, on the one hand, nano-Al2O3 itself has high mechanical strength. After modification with silane coupling agents, the surface defects of nano-Al2O3 are reduced and its hydrophobicity is enhanced, which is conducive to its uniform dispersion in composite materials. At the same time, the presence of a small number of alkyl segments on its surface can enhance the interaction between Al2O3 and polypropylene molecular chains, which is conducive to the transfer of external stress, thereby bearing a greater load and improving the mechanical properties of polypropylene composite materials. On the other hand, the double bonds of the imide groups in functionalized nano-Al2O3 materials can initiate polymerization with polypropylene, and the amino groups in its structure can form chemical bonds with the acyl chlorides on the surface of antioxidants, which can inhibit the aggregation and bridging of nanoparticles and increase its compatibility with polypropylene. This allows nano-Al2O3 to form a complete three-dimensional network structure in the polypropylene matrix, which is conducive to its full adsorption and bonding with polypropylene and enhances the interaction between the two. Meanwhile, maleic anhydride-grafted ethylene-octene copolymer and polypropylene are very similar in structure and properties. During impact, it can inhibit the crystallization of polypropylene and can more effectively resist crack propagation, further improving the mechanical strength of composite materials.

[0056] The silane coupling agent in Comparative Example 1 was unmodified and did not contain an imide structure, resulting in poor compatibility with polypropylene. The nano-Al2O3 in Comparative Example 3 was unmodified, leading to poor dispersibility in the matrix and easy agglomeration, resulting in the worst mechanical properties.

[0057] Thermal performance testing: Under a nitrogen atmosphere, the maximum thermal weight loss temperature of the composite material was tested using a thermogravimetric analyzer at a heating rate of 10℃ / min and a test temperature range of 25-700℃.

[0058] High temperature resistance test: The prepared composite material was placed at 120℃ for 28 days, and then the tensile strength of the polypropylene composite was tested using an electronic universal testing machine according to GB / T 1040.1-2006 standard, with a tensile rate of 10 mm / min.

[0059] As shown in the test results above, the high-temperature resistance of polypropylene composites gradually increases with the increase of functionalized nano-Al2O3 material content. The maximum thermogravimetric temperature in Example 5 is 462.0℃, and the tensile strength after aging at 120℃ for 28 days does not change much, still reaching 62.2MPa. This indicates that the addition of functionalized nano-Al2O3 material significantly improves the thermal stability of polypropylene. This is because, on the one hand, by using a modified silane coupling agent as a "bridge" for covalent connection, hindered phenolic antioxidant molecules with antioxidant capabilities are grafted onto the surface of nano-Al2O3. During the thermo-oxidative degradation of polypropylene, the nano-Al2O3 skeleton with free radical scavenging ability can bind to the free radicals generated in the early stage of polypropylene oxidation, preventing them from participating in the oxidation reaction, improving the overall free radical scavenging ability, and greatly enhancing the thermo-oxidative stability of polypropylene composites. On the other hand, the thermal stability of nano-Al2O3 is much higher than that of pure polypropylene, and it forms chemical bonds with the polypropylene matrix. After surface modification with modified silane coupling agent, the interaction between nano-Al2O3 and polypropylene molecular chains is enhanced, forming a phase interface that restricts the movement of molecular chains, hindering the transfer of external heat to polypropylene molecules, slowing down the diffusion of gases generated by thermal decomposition from the matrix, thus reducing the thermal decomposition rate and making it more conducive to uniform heat diffusion and heat conduction. This hinders the transfer of heat flow during pyrolysis and further improves thermal stability. At the same time, the highly symmetric imide five-membered ring structure has rigidity and three-dimensional dimensional stability, and excellent high-temperature resistance. During heating, it hinders the rotation of polypropylene chains, making the movement of the material difficult, thus giving the polypropylene material good high-temperature resistance. In contrast, Comparative Example 2 did not have the hindered phenol antioxidant grafted and did not contain the heat-resistant imide structure, resulting in poor interfacial compatibility with polypropylene and poor high-temperature resistance.

[0060] The foregoing has shown and described the basic principles and main features of the present invention, as well as its advantages. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A method for preparing a high-temperature resistant polypropylene composite material, characterized in that, The preparation method is carried out according to the following steps: Step (1): Under a nitrogen atmosphere, add 100 parts by weight of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionyl chloride and toluene to a reaction flask, stir to dissolve, then add 90-105 parts of aminoimide-modified nano-Al2O3 and 310-350 parts of triethylamine, stir to react, after the reaction is completed, cool to room temperature, filter to remove toluene, wash with ethanol, and dry to obtain functionalized nano-Al2O3 material; Step (2): Polypropylene, maleic anhydride-grafted ethylene-octene copolymer, functionalized nano-Al2O3 material and dicumyl peroxide are first added to a twin-screw extruder for melt grafting, and then placed in a flat vulcanizing machine and hot-pressed at 200-210℃ and 30-40MPa for 10-20s. After cooling and drying, a high-temperature resistant polypropylene composite material is obtained.

2. The method for preparing the high-temperature resistant polypropylene composite material according to claim 1, characterized in that, The reaction temperature in step (1) is 80-100℃ and the reaction time is 24-48h.

3. The method for preparing the high-temperature resistant polypropylene composite material according to claim 1, characterized in that, In step (2), the mass ratio of polypropylene, maleic anhydride-grafted ethylene-octene copolymer, functionalized nano-Al2O3 material, and dicumyl peroxide is 100:40-50:5-25:2-4.

4. The method for preparing the high-temperature resistant polypropylene composite material according to claim 1, characterized in that, In step (2), the temperatures of zones one to five of the extruder are 170-180℃, 180-190℃, 190-200℃, 195-205℃, and 190-200℃, respectively. The melt grafting time is 5-10 min, and the main screw speed is 140-160 r / min.

5. The method for preparing the high-temperature resistant polypropylene composite material according to claim 1, characterized in that, The preparation method of aminoimide-modified nano-Al2O3 in step (1) is carried out according to the following steps: Step S1: Under a nitrogen atmosphere, N-[3-(trimethoxysilyl)propyl]ethylenediamine and isopropanol are added to a reaction flask. After stirring evenly, methyl 4-maleimide benzoate and catalyst are added. The mixture is heated to 70-85℃ and reacted for 8-16 hours. The mixture is then distilled under reduced pressure and cooled to obtain an imide-modified aminosilane coupling agent. Step S2: Under a nitrogen atmosphere, nano-Al2O3 and ethanol are added to a reaction flask and dispersed evenly. Acetic acid is added to adjust the pH to 5-7, and imide-modified aminosilane coupling agent is added. The mixture is ultrasonically dispersed evenly at 500-600 r / min, and then the reaction is carried out. After the reaction is completed, the mixture is cooled, centrifuged, and dried to obtain aminoimide-modified nano-Al2O3.

6. The method for preparing the high-temperature resistant polypropylene composite material according to claim 5, characterized in that, The catalyst in step S1 is any one of sodium methoxide, DBU, or sodium isooctanoate.

7. The method for preparing the high-temperature resistant polypropylene composite material according to claim 5, characterized in that, In step S1, the molar ratio of N-[3-(trimethoxysilyl)propyl]ethylenediamine, methyl 4-maleimide benzoate, and catalyst is 1:1.05-1.2:0.08-0.

12.

8. The method for preparing the high-temperature resistant polypropylene composite material according to claim 5, characterized in that, In step S2, the mass ratio of nano-Al2O3 to imide-modified aminosilane coupling agent is 100:5-8.

9. The method for preparing the high-temperature resistant polypropylene composite material according to claim 5, characterized in that, In step S2, the reaction temperature is 65-80℃ and the reaction time is 5-12h.

10. A high-temperature resistant polypropylene composite material, characterized in that, It is obtained by the preparation method according to any one of claims 1-9.

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