A synergistically modified light-heat aging resistant polypropylene composite material and a preparation method thereof

Abstract

The application belongs to the technical field of polypropylene modified materials, and particularly relates to a synergistically modified light and heat aging resistant polypropylene composite material and a preparation method thereof; aiming at the problem of poor dispersibility and interface compatibility of nanoparticles in the current polypropylene composite material; the application realizes the uniform dispersion of nano-silicon dioxide in the polypropylene matrix, the enhancement of interface combination and the improvement of light and heat aging resistance of the nano-silicon dioxide by organic modification of the surface of the nano-silicon dioxide, immobilization of the hindered amine light stabilizing structure and melt grafting reaction initiated by peroxide.

Description

Technical Field

[0001] This invention belongs to the field of polypropylene modified materials technology, specifically relating to a synergistically modified photothermal aging resistant polypropylene composite material and its preparation method. Background Technology

[0002] Polypropylene (PP), as a general-purpose plastic, has advantages such as low density, excellent mechanical properties, good processability, and low price, and is widely used in automobiles, home appliances, construction, packaging, and other fields. However, the polypropylene molecular chain contains tertiary carbon atoms, which are prone to oxidative degradation under the influence of external factors such as light, heat, and oxygen. This leads to a decrease in the material's mechanical properties, deterioration in appearance, and a shortened service life, which limits the application of polypropylene in outdoor heat-exposed environments.

[0003] Composites of nano-silica and polypropylene are an effective way to improve the thermal stability and mechanical properties of polypropylene. However, nano-silica is hydrophilic with a large specific surface area and high surface energy, making it prone to aggregation; while polypropylene molecular chains are hydrophobic, resulting in poor interfacial compatibility between the two. Existing patent CN1286278A discloses an outdoor-specific photo- and heat-resistant polypropylene composite, whose components include polypropylene resin, toughening modifier, mineral reinforcing agent, coupling agent, processing aid, composite light stabilizer, and colorant; wherein the mineral reinforcing agent may include silica, and the coupling agent may include silane coupling agent. This approach uses a combination of mineral reinforcing agent, common coupling agent, and composite light stabilizer, but conventional coupling agent modification can only solve the dispersion problem and cannot simultaneously provide light-stabilizing functionality to the composite material.

[0004] In summary, there is an urgent need for a technical solution to maintain good dispersion of nano-silica in polypropylene, while reducing the migration of photo-stable structures and improving the material's resistance to photothermal aging in outdoor heated environments. Summary of the Invention

[0005] This invention provides a synergistically modified photo-thermal aging resistant polypropylene composite material and its preparation method. By using polypropylene resin as the matrix and alkenyl-hindered amine co-modified nano-silica as a functional inorganic filler, the uniform dispersion of nano-silica in the polypropylene matrix, enhanced interfacial bonding, and improved photo-thermal aging resistance are achieved through organic modification of the nano-silica surface, immobilization of the hindered amine photo-stable structure, and melt grafting reaction initiated by peroxide.

[0006] The specific technical solution is as follows: A method for preparing a synergistically modified polypropylene composite material resistant to photothermal aging is as follows: S1: Preparation of hindered amine silane coupling agent: 1,2,2,6,6-pentamethyl-4-piperidinol and 3-isocyanate propyltriethoxysilane were added to anhydrous toluene and stirred. Then, dibutyltin dilaurate was added, and the reaction was carried out under nitrogen protection. After cooling to room temperature, the mixture was rotary evaporated to obtain the hindered amine silane coupling agent (HS-1).

[0007] S2: Modified with nano-silica.

[0008] S21: Dry the nano-silica, cool it, add it to an ethanol-water mixture with a volume ratio of 95:5, adjust the pH to 4.5, and disperse it by ultrasonication to obtain a nano-silica dispersion.

[0009] S22: Add the hindered amine silane coupling agent prepared by KH-570 and S1 to the ethanol-water mixture (pH 4.5), stir, and obtain the silane pre-hydrolyzed solution.

[0010] S23: The silane pre-hydrolyzed solution prepared in S22 is added to the nano silica dispersion prepared in S21, the mixture is heated and reacted, filtered, washed, dried, ground and sieved to obtain alkenyl-hindered amine co-modified nano silica (MHS-SiO2-1).

[0011] S3: Preparation of polypropylene composite materials.

[0012] S31: The polypropylene resin is dried, and the alkenyl-hindered amine co-modified nano silica prepared in S23 is dried at 80°C for 2 hours to obtain the dried polypropylene resin and alkenyl-hindered amine co-modified nano silica, respectively.

[0013] S32: The dried polypropylene resin prepared in S31, alkenyl-hindered amine co-modified nano silica, dicumyl peroxide, antioxidant 1010 and antioxidant 168 are premixed, melt-extruded, cooled, pelletized and dried to obtain a photo- and heat-resistant polypropylene composite material.

[0014] Furthermore, the heating reaction described in S1 has the following parameter settings: temperature 70-80℃, duration 3-7h.

[0015] The rotary evaporator described in S1 has the following parameters: temperature 60-70℃.

[0016] The hindered amine silane coupling agent described in S1, wherein the molar ratio between 1,2,2,6,6-pentamethyl-4-piperidinol and 3-isocyanate propyltriethoxysilane is 1:1, and the amount of dibutyltin dilaurate added is 0.1 wt% of the total mass of 1,2,2,6,6-pentamethyl-4-piperidinol and 3-isocyanate propyltriethoxysilane.

[0017] Furthermore, the drying process described in S21 has the following parameter settings: temperature 110-130℃, duration 2-6h.

[0018] The nano-silica dispersion described in S21 has a mass fraction of 5-8 wt%.

[0019] The mass ratio of KH-570 described in S22 to the hindered amine silane coupling agent is 1:1.5.

[0020] The heating reaction described in S23 has the following parameters: temperature 60-70℃, duration 3-5h.

[0021] The drying process described in S23 has the following parameters: temperature 70–90°C, duration 8–16 hours.

[0022] Furthermore, the drying process described in S31 has the following parameter settings: temperature 90°C, duration 3 hours.

[0023] The premixing described in S32 has the following parameter settings: rotation speed 500-1500 rpm, duration 3-10 min.

[0024] The melt extrusion described in S32 has the following parameter settings: feeding section temperature 170-180℃, melting section temperature 185-195℃, mixing section temperature 200-210℃, die head temperature 200-210℃, and screw speed 100-300rpm.

[0025] The drying process described in S32 has the following parameters: temperature 70-90℃, duration 3-5h.

[0026] The photo- and heat-resistant polypropylene composite material described in S32 has the following composition of raw materials by weight: based on 100 parts of polypropylene resin, 1 to 12 parts of alkenyl-hindered amine co-modified nano silica, 0.03 to 0.3 parts of dicumyl peroxide, and 0.1 to 0.8 parts of antioxidant.

[0027] Compared with the prior art, the present invention has the following beneficial effects: 1. This invention achieves photostability by utilizing the addition reaction between hindered amine alcohols or hindered amines and reactive silanes.

[0028] 2. This invention improves the interfacial bonding strength between nano-silica and polypropylene matrix by modifying nano-silica, thereby reducing interfacial defects in the material during the aging process. Attached Figure Description

[0029] Figure 1This is an FTIR comparison of nano-silica from Example 1, alkenyl-hindered amine co-modified nano-silica, alkenyl silica modified only by KH-570 prepared in Comparative Example 1, and silica modified only by hindered amine silane prepared in Comparative Example 2. In this comparison, H1 is alkenyl-hindered amine co-modified nano-silica prepared in Example 1, C1 is alkenyl silica modified only by KH-570 prepared in Comparative Example 1, C2 is silica modified only by hindered amine silane prepared in Comparative Example 2, and SiO2 is nano-silica.

[0030] Figure 2 This is a thermogravimetric comparison diagram of nano-silica in Example 1, alkenyl-hindered amine co-modified nano-silica, and silica modified only by hindered amine silane prepared in Comparative Example 2. In this diagram, H1 is the alkenyl-hindered amine co-modified nano-silica prepared in Example 1, C2 is the silica modified only by hindered amine silane prepared in Comparative Example 2, and SiO2 is nano-silica. Detailed Implementation

[0031] The following embodiments further explain and illustrate the technical solutions of the present invention. It should be specifically noted that each specific embodiment is a concretization and explanation of the technical solution and should not be considered as a limitation on the scope of protection of the present invention. Those skilled in the art still have the right to modify the technical solutions of these embodiments and make equivalent substitutions for some or all of the technical features, and these modifications or substitutions do not change the essence of the corresponding technical solutions, nor do they cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions described in the present invention.

[0032] This invention proposes a synergistically modified photo- and heat-resistant polypropylene composite material and its preparation method, the detailed technical solution of which is as follows: First, a hindered amine silane coupling agent is prepared. Hindered amine structures inherently possess good photostability; however, common small-molecule hindered amine photostability agents are prone to migration, precipitation, or extraction during long-term use of polypropylene, leading to a decrease in photostability. To address this issue, this invention utilizes an addition reaction between hindered amine alcohols or hindered amine amines and reactive silanes to transform the hindered amine structure into a silanoxy-containing coupling agent structure. This hindered amine silane coupling agent retains the photostability of the hindered amine structure and also possesses hydrolyzable condensable silanoxy groups, which can further form chemical bonds with the silanol groups on the surface of nano-silica.

[0033] Secondly, alkenyl-hindered amine co-modified nano-silica was prepared. Nano-silica contains a large number of silanol groups on its surface, has a small particle size, large specific surface area, and high surface energy, making it prone to agglomeration in polypropylene and exhibiting poor compatibility with the non-polar polypropylene matrix. This invention uses KH-570 and a hindered amine silane coupling agent together for surface modification of nano-silica. In an alcohol-water system, the alkoxysilane structure in KH-570 and the hindered amine silane coupling agent first undergoes hydrolysis to generate a silanol structure; subsequently, the silanol structure undergoes a condensation reaction with the silanol groups on the nano-silica surface to form Si-O-Si chemical bonds. After this surface modification, a coating structure containing an organosilane layer is formed on the surface of the nano-silica. This coating structure simultaneously contains the methacryloyloxy double bond introduced by KH-570 and the hindered amine structure introduced by the hindered amine silane coupling agent.

[0034] In this step, KH-570 does not directly participate in the addition reaction with hindered amines, but rather acts as an alkenyl silane coupling agent grafted onto the surface of nano-silica. In this way, the methacryloyloxy double bond in KH-570 is preserved and used for grafting reactions with polypropylene macromolecular free radicals during subsequent melt processing. The hindered amine structure is independently introduced through the hindered amine silane coupling agent without consuming the carbon-carbon double bond of KH-570, thus ensuring that both the functions of "hindered amine immobilization" and "alkenyl grafting reactivity" can coexist.

[0035] Finally, melt grafting of polypropylene composites was performed. Polypropylene resin, alkenyl-hindered amine co-modified nano-silica, organic peroxide, and antioxidant were premixed and then melt-extruded. At the extrusion temperature, the organic peroxide decomposed to generate free radicals, which could abstract hydrogen atoms from the polypropylene molecular chain to generate polypropylene macromolecular free radicals. These polypropylene macromolecular free radicals further underwent free radical addition or grafting reactions with the methacryloyloxy double bonds on the surface of the co-modified nano-silica, resulting in a chemical bond or strong interfacial anchoring between the organic modified layer on the nano-silica surface and the polypropylene molecular chain. This structure significantly improves the interfacial bonding strength between the nano-silica and the polypropylene matrix, improves the dispersion state of the nanoparticles, and reduces interfacial defects during stress or aging.

[0036] Meanwhile, the hindered amine structure, once fixed on the surface of nano-silica, can play a role in free radical capture and peroxide free radical inhibition during the photothermal oxidation of polypropylene, thus delaying polypropylene molecular chain breakage, carbonyl group formation, and material embrittlement. Because the hindered amine structure is fixed to the nano-silica surface through Si-O-Si bonds, its migration in the polypropylene system is restricted, exhibiting better migration resistance and long-term stability compared to directly adding small-molecule hindered amine light stabilizers.

[0037] Thus, this invention establishes a synergistic modification system of "nano-silica reinforcement - hindered amine immobilization for anti-aging - alkenyl grafting interface reinforcement". Specifically, nano-silica provides reinforcement and thermal stability; the hindered amine structure provides resistance to photothermal aging; and the alkenyl structure introduced by KH-570 improves the interfacial bonding between nano-silica and the polypropylene matrix under the initiation of organic peroxides. The synergistic effect of these three components results in a polypropylene composite material with high mechanical properties, good processing stability, and excellent photothermal aging retention.

[0038] Example 1 A method for preparing a synergistically modified polypropylene composite material resistant to photothermal aging is as follows: Table 1 Main Raw Materials

[0039] ; S1: Preparation of hindered amine silane coupling agent: 8.56 g of 1,2,2,6,6-pentamethyl-4-piperidinol, 12.37 g of 3-isocyanate propyltriethoxysilane, and 100 mL of anhydrous toluene were added to a reaction flask equipped with a mechanical stirrer, a reflux condenser, and a nitrogen protection device. After stirring evenly, 0.02 g of dibutyltin dilaurate was added. The mixture was heated to 75 °C and reacted for 5 h under nitrogen protection. After cooling to room temperature, the mixture was rotary evaporated to obtain the hindered amine silane coupling agent HS-1.

[0040] S2: Modified with nano-silica.

[0041] S21: Place 10.0g of nano-silica in a 120℃ drying oven and dry for 4h. After cooling, add it to 180mL of ethanol-water mixture (ethanol to water volume ratio of 95:5), adjust the pH to 4.5, and ultrasonically disperse for 30min to obtain nano-silica dispersion.

[0042] S22: Add 0.80g KH-570 and 1.20g S1 of the hindered amine silane coupling agent HS-1 to 40mL of ethanol-water mixture (pH4.5), stir at room temperature for 30min to pre-hydrolyze, and obtain silane pre-hydrolyzed solution.

[0043] S23: The silane pre-hydrolyzed solution prepared in S22 was added dropwise to the nano-silica dispersion prepared in S21, and the reaction was carried out at a high temperature (65℃ for 4 hours). After filtration, the mixture was washed three times with anhydrous ethanol, dried (80℃ for 12 hours), ground and sieved to obtain alkenyl-hindered amine co-modified nano-silica (MHS-SiO2-1).

[0044] S3: Preparation of polypropylene composite materials.

[0045] S31: The polypropylene resin was dried in a 90℃ forced-air drying oven for 3 hours, and the alkenyl-hindered amine co-modified nano silica prepared in S23 was vacuum dried at 80℃ for 2 hours to obtain the dried polypropylene resin and alkenyl-hindered amine co-modified nano silica, respectively.

[0046] S32: The dried polypropylene resin (100g) prepared in S31, the alkenyl-hindered amine co-modified nano silica (5g), and 0.12g dicumyl peroxide, 0.20g antioxidant 1010 and 0.10g antioxidant 168 were premixed (1000rpm, 5min), melt-extruded, cooled, pelletized and dried at 80℃ for 4h to obtain a photo- and heat-resistant polypropylene composite material.

[0047] Example 2 The composition and preparation process are the same as in Example 1, except that: In step S1 of the preparation process, the temperature and reaction parameters are set as follows: temperature 70℃, duration 3h; the rotary evaporation parameters are set as follows: temperature 60℃; and other steps are the same.

[0048] The drying parameters in step S21 of the preparation process are set as follows: temperature 110℃, duration 2h, and other steps are the same.

[0049] In the preparation process S21, the mass fraction of the nano-silica dispersion is 5 wt%, and the other components are the same.

[0050] Example 3 The composition and preparation process are the same as in Example 1, except that: In step S1 of the preparation process, the temperature and reaction parameters are set as follows: temperature 80℃, duration 7h; the rotary evaporation parameters are set as follows: temperature 70℃; and other steps are the same.

[0051] The drying parameters in step S21 of the preparation process are set as follows: temperature 130℃, duration 6h, and other steps are the same.

[0052] In the preparation process S21, the mass fraction of the nano-silica dispersion is 8 wt%, and the other components are the same.

[0053] Example 4 The composition and preparation process are the same as in Example 1, except that: In the preparation process S23, the heating reaction parameters were set as follows: temperature 60℃, duration 3h; the drying parameters were set as follows: temperature 70℃, duration 8h; and other steps were the same.

[0054] In the preparation process S32, the premixing parameters are set as follows: rotation speed 500 rpm, duration 3 min; the melt extrusion parameters are set as follows: feeding section temperature 170℃, melting section temperature 185℃, mixing section temperature 200℃, die head temperature 200℃, screw speed 100 rpm; and the drying parameters are set as follows: temperature 70℃, duration 3 h. Other steps are the same.

[0055] Example 5 The composition and preparation process are the same as in Example 1, except that: In the preparation process S23, the heating reaction parameters were set as follows: temperature 70℃, duration 5h; the drying parameters were set as follows: temperature 90℃, duration 16h; and other steps were the same.

[0056] In the preparation process S32, the premixing parameters are set as follows: rotation speed 1500 rpm, duration 10 min; the melt extrusion parameters are set as follows: feeding section temperature 180℃, melting section temperature 195℃, mixing section temperature 210℃, die head temperature 210℃, screw speed 300 rpm; and the drying parameters are set as follows: temperature 90℃, duration 5 h. Other steps are the same.

[0057] Example 6 The composition and preparation process are the same as in Example 1, except that: In the preparation process S32, based on 100 parts of polypropylene resin, 1 part of alkenyl-hindered amine co-modified nano silica, 0.03 parts of dicumyl peroxide, 0.1 parts of antioxidant, and other components are the same.

[0058] Example 7 The composition and preparation process are the same as in Example 1, except that: In the preparation process S32, based on 100 parts of polypropylene resin, there are 12 parts of alkenyl-hindered amine co-modified nano silica, 0.3 parts of dicumyl peroxide, 0.8 parts of antioxidant, and other components are the same.

[0059] Comparative Example 1 The composition and preparation process are the same as in Example 1, except that: In step S3 of the preparation process, no hindered amine silane coupling agent is added; the other steps are the same.

[0060] Comparative Example 2 The composition and preparation process are the same as in Example 1, except that: In step S3 of the preparation process, alkenyl-hindered amine co-modified nano-silica is not added, while the other steps are the same.

[0061] Comparative Example 3 The composition and preparation process are the same as in Example 1, except that: DCP is not added in step S3 of the preparation process; the other steps are the same.

[0062] Samples were taken from the unmodified nano-silica in Example 1, the prepared alkenyl-hindered amine co-modified nano-silica, the alkenyl silica modified only by KH-570 prepared in Comparative Example 1, and the silica modified only by hindered amine silane prepared in Comparative Example 2. The samples were washed, dried (unmodified silica was dried at 115℃ for 3 hours, and organically modified samples were dried at 75℃ for 10 hours), cooled to room temperature, ground, passed through a 200-mesh sieve, and subjected to FTIR testing (scanning range 4000–500 cm⁻¹). -1 (32 scans) Figure 1 As shown, H1 is the alkenyl-hindered amine co-modified nano-silica prepared in Example 1, C1 is the alkenyl silica modified only by KH-570 prepared in Comparative Example 1, C2 is the silica modified only by hindered amine silane prepared in Comparative Example 2, SiO2 is nano-silica, and H1 retains the Si-O-Si framework absorption while exhibiting high absorption at 2930–2860 cm⁻¹. -1 Organic CH absorption was observed nearby at 1720 cm⁻¹ -1 Nearby carbonyl absorption and 1635 cm⁻¹ -1 Nearby weak alkenyl-related absorption, and at 950 cm⁻¹ -1 The relatively weakened Si-OH features in the vicinity indicate that KH-570 and the hindered amine silane structure have been fixed to the silica surface through silanization / condensation.

[0063] Samples were taken from the unmodified nano-silica in Example 1, the prepared alkenyl-hindered amine co-modified nano-silica, and the hindered amine silane-modified silica prepared in Comparative Example 2. The samples were washed and dried (unmodified silica was dried at 115℃ for 3 hours, and the organically modified sample was dried at 75℃ for 10 hours). 6 mg of powder was weighed and subjected to thermogravimetric analysis (temperature 30–800℃, heating rate 10℃ / min). To avoid the influence of low-temperature adsorbed water, the mass after 150℃ was used as the dry basis mass for calculation. Figure 2 As shown, H1 is the alkenyl-hindered amine co-modified nano silica prepared in Example 1, C2 is the silica prepared in Comparative Example 2 with only hindered amine silane modification, and SiO2 is nano silica. Unmodified silica only exhibits low-temperature water adsorption and a small amount of high-temperature dehydroxylation weight loss, while C2 shows a moderate degree of organic layer decomposition weight loss. H1 has the most significant mass decrease at 250–450 °C and the lowest final mass retention rate, indicating that more organosilanes / hindered amine structures are introduced onto the surface of H1.

[0064] Based on Examples 1-7 and Comparative Examples 1-3, samples of the finally prepared photo- and heat-resistant polypropylene composite material were taken for tensile strength and photo- and heat-resistant aging retention rate tests. The photo- and heat-resistant polypropylene composite material was prepared into dumbbell-shaped specimens (150 mm long, 60 mm parallel section length, 10 mm parallel section width, 20 mm end width, and 4 mm thickness), and placed in an environment of 23°C and 50% relative humidity for 96 hours. The specimens were divided into an initial group and an aging group. The initial group was tested using a universal tensile testing machine (tensile speed 50 mm / min), and the maximum force value was recorded. Five groups were measured, and the average value was taken. The aging group was placed in an aging test chamber for aging (light source: xenon arc lamp, irradiance 0.35 W / m²). 2 The wavelength was 340nm, the blackboard temperature was 65℃, the relative humidity was 50%, the spraying time was 18min, the drying time was 102min, and the aging time was 1000h. Then, it was placed in an environment of 23℃ and 50% relative humidity for 24h for conditioning. The subsequent test steps were the same as the initial group.

[0065] Based on Examples 1-7 and Comparative Examples 1-3, samples of the finally prepared photo- and heat-resistant polypropylene composite material were taken for impact strength and impact strength retention rate after photo- and heat aging tests. The photo- and heat-resistant polypropylene composite material was prepared into Type 1A specimens with a V-notch (80mm long, 10mm wide, 4mm thick, notch depth 2mm, bottom radius 0.25mm). These specimens were conditioned at 23℃ and 50% relative humidity for 96 hours and divided into an initial group and an aging group. For the initial group, the specimens were vertically clamped on the testing machine base with the notch facing away from the impact direction. The pendulum was released, and the impact energy absorbed when the specimen broke was recorded. Five groups were measured, and the average value was taken. The aging group was placed in an aging test chamber for aging (light source: xenon arc lamp, irradiance 0.35W / m²). 2 The wavelength was 340nm, the blackboard temperature was 65℃, the relative humidity was 50%, the spraying time was 18min, the drying time was 102min, and the aging time was 1000h. Then, it was placed in an environment of 23℃ and 50% relative humidity for 24h for conditioning. The subsequent test steps were the same as the initial group.

[0066] The specific test results are shown in Table 2. Figure 1 , Figure 2 As shown: Table 2 Comparison of core performance of Examples 1-7 and Comparative Examples 1-3 ; The comparison results above show that Example 1 exhibits the best overall performance. The synergistic effect of the hindered amine silane coupling agent modification conditions, nano-silica dispersion process, DCP crosslinking, and antioxidant system effectively improves the dispersibility and interfacial compatibility of nanoparticles, indicating that Example 1 successfully endows the composite material with excellent photothermal aging resistance. The overall performance of Examples 2 to 7 is slightly lower than that of Example 1 but still maintains a high level, indicating that excellent photothermal aging resistance was still achieved under a wide range of parameter variations. Comparative Example 1, lacking the hindered amine silane coupling agent, has poor nanoparticle dispersibility and weak interfacial bonding, resulting in a sharp decline in performance after aging. Comparative Example 2, without the addition of modified nano-silica, lacks reinforcement and interfacial modification effects, resulting in the lowest mechanical properties. Comparative Example 3, lacking DCP, has insufficient crosslinking and interfacial bonding, resulting in a significant decrease in performance retention rate after photothermal aging.

[0067] In summary, it can be clearly seen from the above embodiments and comparative examples that the synergistically modified photothermal aging resistant polypropylene composite material provided by the present invention has a significant improvement in photothermal aging resistance. This is attributed to the construction of a bifunctional-double grafting technology scheme, which endows the composite material with excellent photothermal aging resistance.

Claims

1. A synergistically modified polypropylene composite material resistant to photothermal aging, characterized in that: The photo- and heat-resistant polypropylene composite material is prepared by melt grafting extrusion of the following raw materials in parts by weight: based on 100 parts of polypropylene resin, 1 to 12 parts of alkenyl-hindered amine co-modified nano silica, 0.03 to 0.3 parts of dicumyl peroxide, and 0.1 to 0.8 parts of antioxidant; wherein, the alkenyl-hindered amine co-modified nano silica is a surface modifier of nano silica with methacryloyloxysilane structural units and hindered amine silane structural units grafted onto the surface of nano silica through silicon-oxygen bonds.

2. The photo- and heat-resistant modified polypropylene composite material according to claim 1, characterized in that: The antioxidant is a compound of antioxidant 1010 and antioxidant 168, with a mass ratio of 2:

1.

3. The photo- and heat-resistant modified polypropylene composite material according to claim 1, characterized in that: The nano-silica has a particle size of 20–60 nm.

4. The photo- and heat-resistant modified polypropylene composite material according to claim 1, characterized in that: The methacryloyloxysilane structural unit contains a carbon-carbon double bond that can react with polypropylene radicals in the presence of organic peroxides; the hindered amine silane structural unit contains a 2,2,6,6-tetramethylpiperidine structure or a 1,2,2,6,6-pentamethylpiperidine structure.

5. A method for preparing a synergistically modified photo- and heat-resistant polypropylene composite material according to any one of claims 1-4, characterized in that, Includes the following steps: S1: Preparation of hindered amine silane coupling agent: 1,2,2,6,6-pentamethyl-4-piperidinol and 3-isocyanate propyltriethoxysilane were added to anhydrous toluene and stirred. Then, dibutyltin dilaurate was added, and the reaction was carried out under nitrogen protection. After cooling to room temperature, the mixture was rotary evaporated to obtain the hindered amine silane coupling agent. S2: Modified with nano-silica; S21: Dry the nano-silica, cool it, add it to an ethanol-water mixture with a volume ratio of 95:5, adjust the pH to 4.5, and disperse it by ultrasonication to obtain a nano-silica dispersion. S22: Add the hindered amine silane coupling agent prepared by KH-570 and S1 to an ethanol-water mixture at pH 4.5 and stir to obtain a silane pre-hydrolyzed solution. S23: The silane pre-hydrolyzed solution prepared in S22 is added to the nano silica dispersion prepared in S21, the reaction is heated, filtered, washed, dried, ground and sieved to obtain alkenyl-hindered amine co-modified nano silica. S3: Preparation of polypropylene composite materials; S31: The polypropylene resin is dried, and the alkenyl-hindered amine co-modified nano silica prepared in S23 is dried at 80℃ for 2h to obtain the dried polypropylene resin and alkenyl-hindered amine co-modified nano silica, respectively. S32: The dried polypropylene resin prepared in S31, alkenyl-hindered amine co-modified nano silica, dicumyl peroxide, antioxidant 1010 and antioxidant 168 are premixed, melt-extruded, cooled, pelletized and dried to obtain a photo- and heat-resistant polypropylene composite material.

6. The method for preparing a synergistically modified photo-thermal aging resistant polypropylene composite material according to claim 5, characterized in that: The heating reaction described in S1 has the following parameter settings: temperature 70-80℃, duration 3-7h; The rotary evaporator described in S1 has the following parameter settings: temperature 60-70℃; The hindered amine silane coupling agent described in S1, wherein the molar ratio between 1,2,2,6,6-pentamethyl-4-piperidinol and 3-isocyanate propyltriethoxysilane is 1:1, and the amount of dibutyltin dilaurate added is 0.1 wt% of the total mass of 1,2,2,6,6-pentamethyl-4-piperidinol and 3-isocyanate propyltriethoxysilane.

7. The method for preparing a synergistically modified photo-thermal aging resistant polypropylene composite material according to claim 5, characterized in that: The drying process described in S21 has the following parameter settings: temperature 110~130℃, duration 2~6h; The nano-silica dispersion described in S21 has a mass fraction of 5-8 wt%. The mass ratio of KH-570 described in S22 to the hindered amine silane coupling agent is 1:1.

5.

8. The method for preparing a synergistically modified photo-thermal aging resistant polypropylene composite material according to claim 5, characterized in that: The heating reaction described in S23 has the following parameter settings: temperature 60-70℃, duration 3-5h; The drying process described in S23 has the following parameters: temperature 70–90°C, duration 8–16 hours.

9. The method for preparing a synergistically modified photo-thermal aging resistant polypropylene composite material according to claim 5, characterized in that: The drying process described in S31 has the following parameters: temperature 90℃, duration 3h.

10. The method for preparing a synergistically modified photo-thermal aging resistant polypropylene composite material according to claim 5, characterized in that: The premixing described in S32 has the following parameter settings: rotation speed 500-1500 rpm, duration 3-10 min; The melt extrusion described in S32 has the following parameter settings: feeding section temperature 170-180℃, melting section temperature 185-195℃, mixing section temperature 200-210℃, die head temperature 200-210℃, and screw speed 100-300 rpm. The drying process described in S32 has the following parameters: temperature 70-90℃, duration 3-5h.

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