A UV-resistant modified PP plastic and its molding process

Abstract

This invention discloses a UV-resistant modified PP plastic and its molding process. The modified PP plastic comprises 95-99 parts isotactic polypropylene, 4-6 parts organic-inorganic hybrid silica sol-modified ZnO nanoparticles, and 0.3-0.5 parts antioxidant. The modified ZnO has a core-shell structure, with an 8-18 nm ultrafine ZnO core and an organic-inorganic hybrid layer formed by co-hydrolysis of tetraethyl orthosilicate and N-[3-(trimethoxysilyl)propyl]ethylenediamine. This invention first prepares ultrafine ZnO nanoparticles, then constructs a resistant hybrid coating layer in situ through co-hydrolysis of the two silica sources. The composite material is obtained after drying, mixing, and pressing. This invention solves the problem of easy agglomeration of 8-18 nm ultrafine ZnO, ensuring uniform dispersion of the hybrid ZnO in the PP matrix, efficient absorption and scattering of ultraviolet light, and significantly improving the UV aging resistance and mechanical stability of polypropylene.

Description

Technical Field

[0001] This invention belongs to the technical field of modified polypropylene plastic materials, specifically relating to a UV-resistant modified PP plastic and its molding process. Background Technology

[0002] In recent years, the application scale of general-purpose modified polypropylene (PP) plastics in outdoor engineering plastic products, home building materials, automotive exteriors, agricultural plastics, and outdoor protective components has continued to expand. Various industries have placed increasingly stringent requirements on the UV aging resistance, weather stability, long-term mechanical properties, and environmental adaptability of PP plastic products. Ordinary unmodified PP plastic products have poor weather resistance and are prone to aging, powdering, cracking, fading, and mechanical degradation during long-term outdoor service, resulting in a short service life. This makes it difficult to meet the long-term service requirements of high-end outdoor plastic components and long-term exposed plastic products. Therefore, the industry urgently needs new modified PP materials with high weather resistance and high stability.

[0003] Polypropylene (PP), as the most produced and widely used general-purpose thermoplastic, boasts outstanding advantages such as low density, high cost-effectiveness, good processability, excellent toughness, good chemical stability, and recyclability. It is currently one of the most widely used base materials in the fields of general-purpose plastics and engineering modified plastics. However, the pure polypropylene molecular chain contains a large number of low-bond-energy α-hydrogen bonds and highly reactive tertiary hydrocarbons. Under the coupled effects of outdoor ultraviolet radiation, high-temperature thermo-oxidation, and alternating wet and dry environments, it is highly susceptible to free radical chain oxidation reactions, causing molecular chain breakage, degradation, and cross-linking. This leads to aging failures such as fading, powdering, cracking, and a significant decrease in strength, severely limiting the high-end and large-scale application of pure PP materials in various outdoor weather-resistant plastic products and long-term service plastic components.

[0004] Significant progress has been made in the research of nanoparticle-doped modified polypropylene. Modification with nanofillers such as MgO, ZnO, SiO2, and TiO2 can improve the electrical and tensile mechanical properties of PP materials, increase DC breakdown strength and volume resistivity, and suppress the accumulation of space charge within the material. Among these, the nano-ZnO modification system can also enhance the UV aging resistance of polypropylene.

[0005] Existing technologies mostly use ZnO fillers in the micrometer or hundreds of nanometer range, resulting in small particle surface areas, weak UV absorption, and excessively large particle sizes that can damage the mechanical properties of the original PP matrix. While directly using 8-18nm ultrafine ZnO offers significant performance potential, particles at this size have extremely high surface energy, making them highly prone to severe agglomeration. Current industry-standard modification methods involve surface grafting of ZnO with surfactants or silane coupling agents, resulting in weak molecular adsorption or single-bond grafting with weak binding forces, making them highly susceptible to detachment and failure during melt processing and solvent cleaning. Currently, there is no mature solution in the industry that can stably disperse 8-18nm ultrafine ZnO while constructing a high-strength, detachment-resistant coating structure, ensuring long-term UV shielding and anti-aging effects while maintaining uniform particle dispersion. The industry urgently needs a highly stable, detachment-resistant ultrafine ZnO-modified PP solution. Summary of the Invention

[0006] The purpose of this invention is to address the issues of poor UV aging resistance of existing pure PP plastics, the fact that conventional ZnO particles are mostly micrometers or hundreds of nanometers in size, the tendency of 8-18nm ZnO nanoparticles to agglomerate, and the poor effectiveness of conventional surface modification. This invention provides a UV-resistant modified PP plastic and its molding process.

[0007] This invention synthesizes ultra-small ZnO nanoparticles with a particle size of 8-18 nm, which differs from micron-sized and hundreds of nanometer-sized ZnO fillers. This particle size range has a larger specific surface area and stronger ultraviolet broad-spectrum absorption and free radical scavenging capabilities.

[0008] More importantly, this invention abandons the traditional simple grafting and easily detachable modification methods using silane coupling agents and surfactants. Instead, it employs a two-component co-hydrolysis synergistic modification technique using tetraethyl orthosilicate and N-[3-(trimethoxysilyl)propyl]ethylenediamine to deposit and grow a dense organic-inorganic hybrid coating shell on the surface of 8-18nm ZnO particles. The inorganic SiO2 network forms a rigid framework, while the organosilicon functional groups provide interfacially compatible segments, forming a rigid, locked core-shell structure with stable coating structure. The hybrid-modified ZnO particles can be uniformly dispersed in the PP matrix, providing long-lasting and efficient UV blocking, significantly improving the material's UV aging resistance and mechanical stability.

[0009] To achieve the above technical objectives, the present invention adopts the following technical solution: A UV-resistant modified PP plastic comprises the following raw materials in parts by weight: 95-99 parts of isotactic polypropylene (PP) resin, 4-6 parts of organic-inorganic hybrid silica sol modified ZnO nanoparticles, and 0.3-0.5 parts of antioxidant. The organic-inorganic hybrid silica sol-modified ZnO nanoparticles are prepared by co-hydrolysis modification of ZnO nanoparticles with a particle size of 8-18 nm using dual silicon sources. The dual silicon source is tetraethyl orthosilicate and N-[3-(trimethoxysilyl)propyl]ethylenediamine; The organic-inorganic hybrid silica sol-modified ZnO nanoparticles have a dense core-shell structure. The core layer consists of 8-18 nm ultrafine ZnO particles, and the shell layer is an organic-inorganic hybrid coating layer formed by the combination of an inorganic SiO2 rigid network formed by the hydrolysis of tetraethyl orthosilicate and N-[3-(trimethoxysilyl)propyl]ethylenediamine organic functional segments.

[0010] Furthermore, the isotactic polypropylene is F401 type isotactic polypropylene; The antioxidant is antioxidant 1010, chemically named pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid].

[0011] This invention also provides a molding process for the above-mentioned UV-resistant modified PP plastic, comprising the following steps: S1, ZnO nanoparticle synthesis: Zinc salt was dissolved in anhydrous ethanol, alkali was dissolved in anhydrous ethanol, the alkali solution was added dropwise to the zinc salt solution and stirred to react, n-hexane was added, and after standing, the mixture was centrifuged, washed and vacuum dried to obtain ultrafine ZnO nanoparticles with a particle size of 8-18 nm. S2. Modification of organic-inorganic hybrid silica sol: Anhydrous ethanol, deionized water, and ammonia were mixed evenly, and the ultrafine ZnO nanoparticles prepared in step S1 were added and ultrasonically dispersed; then tetraethyl orthosilicate and N-[3-(trimethoxysilyl)propyl]ethylenediamine were added dropwise, and the mixture was stirred at a constant temperature to complete the modification; after the reaction was completed, the mixture was centrifuged, washed, and vacuum dried to obtain organic-inorganic hybrid silica sol modified ZnO nanoparticles; S3. Raw material pretreatment: Place isotactic polypropylene resin, antioxidant, and modified ZnO nanoparticles in a vacuum drying oven for drying. S4. Melt blending: The pretreated raw materials are fed into an internal mixer for internal blending to obtain modified PP composite melt material; S5. Compressed sheet molding: The modified PP composite molten material is placed in a mold, preheated, and then pressed into sheets under pressure. After cooling and demolding, the UV-resistant modified PP plastic finished product is obtained.

[0012] Further, in step S1, the zinc salt is zinc chloride or zinc acetate, and the alkali is sodium hydroxide or potassium hydroxide.

[0013] Further, in step S1, the amount of zinc salt used is 8-10 mmol, and the volume of anhydrous ethanol used to dissolve the zinc salt is 40-60 mL; the amount of alkali used is 16-20 mmol, and the volume of anhydrous ethanol used to dissolve the alkali is 8-18 mL; the reaction temperature is 60-80℃; and hexane with a volume of 3 times that of the original solution is added.

[0014] Further, in step S2, the ammonia water is analytical grade ammonia water with a mass fraction of 25%-28%; the amount of anhydrous ethanol is 60-80 mL, the amount of deionized water is 2-3 mL, and the amount of ammonia water is 0.5-0.8 mL; the amount of ZnO nanoparticles is 0.4-0.6 g; the amount of tetraethyl orthosilicate is 2-3 mL, and the amount of N-[3-(trimethoxysilyl)propyl]ethylenediamine is 0.5-1 mL; the constant temperature stirring temperature is 40-60℃, and the stirring time is 5-6 h; the vacuum drying temperature is 60-70℃, and the drying time is 5-7 h.

[0015] Furthermore, in step S2, the ultrasonic dispersion power is 200-300W, and the ultrasonic dispersion time is 30-60min.

[0016] Furthermore, in step S3, the drying temperature is 60℃ and the drying time is 10-14h.

[0017] Furthermore, in step S4, the mixing temperature is 185-195℃, the rotor speed is 25-35rpm, and the mixing time is 2-4min.

[0018] Furthermore, in step S5, the preheating temperature is 185-195℃, the preheating time is 4-6 min; the tableting pressure is 10t, the tableting time is 4-6 min; and the constant temperature cooling is 20℃ for 8-12 min.

[0019] Explanation of the invention mechanism First, small-diameter ZnO particles of 8-18nm are synthesized. Compared with commercially available large-diameter ZnO, they have a larger specific surface area and stronger ultraviolet broad-spectrum blocking ability, which can efficiently absorb ultraviolet light in the environment and reduce the irradiation damage of ultraviolet light to the PP matrix.

[0020] Secondly, traditional modification techniques rely solely on surfactants or silane coupling agents for monolayer physical adsorption or weak chemical bond grafting. The grafted layer is thin and lacks skeletal support, making it extremely prone to desorption, peeling, and failure during cleaning and processing. This leads to the agglomeration of ultrafine ZnO and a significant degradation in material properties.

[0021] This invention utilizes a two-component co-hydrolysis reaction of tetraethyl orthosilicate and N-[3-(trimethoxysilyl)propyl]ethylenediamine to form an organic-inorganic coating layer. The tetraethyl orthosilicate hydrolyzes and cross-links to form a three-dimensional rigid inorganic SiO2 network framework, firmly coating the ZnO grain surface and playing a crucial role in physical locking, erosion resistance, and preventing detachment. Simultaneously, the N-[3-(trimethoxysilyl)propyl]ethylenediamine component introduces flexible organic functional segments, significantly improving the interfacial compatibility between the inorganic particles and the PP organic matrix. The uniformly dispersed ultrafine hybrid modified ZnO achieves ultra-high UV aging resistance while simultaneously enhancing the mechanical strength and structural stability of the composite material.

[0022] The beneficial effects of this invention are as follows: (1) This invention uses 8-18nm ZnO nanoparticles combined with organic-inorganic hybrid silica sol for modification, which breaks through the limitations of existing technologies that generally use micron-level or hundreds of nanometer-level ZnO fillers, and makes full use of the high specific surface area advantage of ultrafine particles; at the same time, it solves the problem of high surface energy and easy agglomeration of 8-18nm ZnO. The nanoparticles are uniformly dispersed in the PP matrix without local agglomeration defects, ensuring the uniformity of material properties.

[0023] (2) Abandoning the traditional silane coupling agent and surfactant grafting techniques that are prone to detachment, an organic-inorganic skeleton hybrid coating layer is constructed by co-hydrolysis of dual silicon sources. The organic-inorganic hybrid shell layer takes into account both rigid support and organic compatibility. Ultrafine ZnO can still be uniformly dispersed at high filling ratios without agglomeration defects, ensuring the overall uniformity of the PP composite material performance.

[0024] (3) It has both anti-UV aging and mechanical enhancement effects: The stable and dispersed 8-18nm hybrid ZnO not only effectively blocks UV rays, but also achieves dual gains of anti-aging and high strength. Attached Figure Description

[0025] Figure 1 This is a TEM image of the ZnO nanoparticles before modification in this invention; Figure 2 This is a particle size distribution chart of the ZnO nanoparticles of this invention. Figure 3 This is a TEM image of the modified ZnO nanoparticles in this invention. Figure 4 SEM image of the original PP plastic material; Figure 5 This is a SEM image of the modified PP plastic material prepared in Example 1 of the present invention; Figure 6 This is a SEM image of the PP plastic material prepared in Comparative Example 1 of this invention; Figure 7 This is a SEM image of the modified PP plastic material prepared in Comparative Example 2 of this invention; Figure 8 UV absorption curves of materials with different ZnO addition amounts; Figure 9 Photographs of the PP+ZnO-1 prepared in Example 1 and the original PP plastic material before and after 100 hours of ultraviolet light irradiation; Figure 10 The curves show the comparison of tensile strength retention rates after UV aging between the example and comparative samples. Detailed Implementation

[0026] To make the above-mentioned objectives, features, and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to examples. The following content is merely illustrative and explanatory of the concept of the present invention. Those skilled in the art can make various modifications or additions to the described specific embodiments or use similar methods to replace them, as long as they do not deviate from the inventive concept, all of which should fall within the protection scope of the present invention. The preparation method of the present invention will be described below through specific embodiments.

[0027] Example 1

[0028] A UV-resistant modified PP plastic comprises the following raw materials in parts by weight: 95 parts of isotactic polypropylene F401, 5 parts of organic-inorganic hybrid silica sol modified 8-18nm ultrafine ZnO, and 0.4 parts of antioxidant 1010.

[0029] The molding process includes the following steps: Synthesis of S1 and ZnO nanoparticles: 9 mmol of zinc acetate dihydrate was dissolved in 50 mL of anhydrous ethanol, and 18 mmol of KOH was dissolved in 15 mL of anhydrous ethanol. The KOH ethanol solution was slowly added dropwise to the zinc acetate ethanol solution, and stirred at 70 °C for 25 min. Then, three times the volume of n-hexane was added to the mixture, and stirring was continued for 8 min. The mixture was then allowed to stand at room temperature for 15 min. After centrifugation, the nanoparticles were washed alternately with ethanol and deionized water and dried under vacuum to obtain ultrafine ZnO nanoparticles with uniform particle size of 8-18 nm.

[0030] S2. Organic-inorganic hybrid silica sol two-component co-hydrolysis modification: 70 mL of anhydrous ethanol, 2.5 mL of deionized water, and 0.6 mL of 25%-28% concentrated ammonia were mixed and stirred evenly to obtain a transparent homogeneous solvent system; 0.5 g of the 8-18 nm ultrafine ZnO prepared above was added and ultrasonically dispersed at 250 W for 45 min; then 2.5 mL of tetraethyl orthosilicate and 0.8 mL of N-[3-(trimethoxysilyl)propyl]ethylenediamine were slowly added dropwise, and the mixture was stirred at 50 °C for 5.5 h to complete the two-component co-hydrolysis in-situ coating reaction; after the reaction, the mixture was centrifuged, washed three times with ethanol, and vacuum dried at 65 °C for 6 h to obtain inorganic rigid framework resistant to shedding organic-inorganic hybrid modified ultrafine ZnO.

[0031] S3. Raw material pretreatment: F401 isotactic polypropylene, antioxidant 1010, and hybrid modified ultrafine ZnO are placed together in a 60℃ vacuum drying oven and dried at a constant temperature for 12 hours to completely remove the adsorbed moisture from the raw materials.

[0032] S4. Melt blending: The dried raw materials are fed into the internal mixer according to the proportion. The mixing temperature is set to 190℃ and the rotor speed is 30rpm. The mixture is mixed for 3 minutes to obtain a uniformly dispersed modified PP melt composite material.

[0033] S5. Compressed sheet molding: The modified PP molten material is placed in the mold of a flat vulcanizing machine, preheated at 190℃ for 5 minutes, held at 10t pressure for 5 minutes, and then cooled at 20℃ for 10 minutes. The modified PP plastic product is obtained by demolding and is denoted as PP+ZnO-1.

[0034] Example 2

[0035] A UV-resistant modified PP plastic comprises the following raw materials in parts by weight: 96 parts of isotactic polypropylene F401, 4 parts of organic-inorganic hybrid silica sol modified 8-18nm ultrafine ZnO, and 0.3 parts of antioxidant 1010.

[0036] The preparation process and parameters were completely consistent with those in Example 1, and the modified PP plastic product was obtained, denoted as PP+ZnO-2.

[0037] Example 3

[0038] A UV-resistant modified PP plastic comprises the following raw materials in parts by weight: 94 parts of isotactic polypropylene F401, 6 parts of organic-inorganic hybrid silica sol modified 8-18nm ultrafine ZnO, and 0.5 parts of antioxidant 1010.

[0039] The preparation process and parameters were completely consistent with those in Example 1, and the modified PP plastic product was obtained, denoted as PP+ZnO-3.

[0040] Comparative Example 1 Unmodified pure 8-18nm ultrafine ZnO direct filling The raw material ratios and all molding process parameters are completely consistent with those of Example 1, the only difference being that the self-made 8-18nm ultrafine ZnO of this invention is directly added without any surface modification treatment. The resulting product is denoted as PP+ZnO-4.

[0041] Comparative Example 2 Silane coupling agent KH550 modified 8-18nm ZnO The raw material ratio is exactly the same as in Example 1. The only difference is that the two-component organic-inorganic hybrid co-hydrolysis modification process of the present invention is replaced with the traditional single KH550 silane coupling agent surface grafting modification. The rest of the synthesis and processing processes are the same.

[0042] Modification method: Equal masses of 8-18 nm ZnO nanoparticles were placed in an ethanol-water system, and an equal amount of KH550 silane coupling agent was added. The grafting reaction was carried out with conventional stirring for 3 hours, achieving only weak surface grafting modification of the monolayer without the construction of a rigid inorganic SiO2 framework. The nanoparticles were then dried for later use. The resulting product was denoted as PP+ZnO-5.

[0043] The performance test conditions for this experiment are as follows: (1) Ultraviolet-visible absorption spectrum: The ultraviolet-visible spectrophotometer was used to test the sample. The sample was cut into a film and the test wavelength range was 300-500nm. Pure PP film was used as a blank reference. The light absorption signal in the ultraviolet band of 300-500nm was recorded to obtain the ultraviolet absorption curves of samples with different filler addition amounts.

[0044] (2) Macroscopic morphology photos of UV aging: UVB-313 UV lamp tubes were used, with UV irradiance of 0.76W / (m²) and blackboard temperature of 60℃, and continuous irradiation for 100h. Pure PP and PP+ZnO-1 samples were photographed before aging and after 100h of aging, and the color and appearance changes of the samples were recorded.

[0045] (3) Tensile mechanical properties and strength retention rate after aging: The tensile mechanical properties were tested in accordance with GB / T 1040.3-2006 "Determination of tensile properties of plastics - Part 3: Test conditions for films and sheets". 100μm thick pressed film samples were used. The sample type was II. The tensile rate was 50mm / min. The test environment temperature was 25℃ and the relative humidity was 50%. Five samples were tested in parallel for each group of samples. The arithmetic mean was taken as the test result.

[0046] The UV aging conditions were the same as above. The tensile strength of the samples before and after aging was tested respectively. The tensile strength retention rate was calculated as (tensile strength after aging ÷ tensile strength before aging) × 100%. A comparison curve was plotted based on the tensile strength retention rate.

[0047] Figure 1 The image shows the TEM morphology of the ZnO nanoparticles before modification. As can be seen from the image, the unmodified ZnO nanoparticles have clear boundaries, but the particles are in contact with each other, showing a clear tendency for primary aggregation.

[0048] Figure 2 The diagram shows the particle size distribution of the ZnO nanoparticles of this invention. The statistical results indicate that the particle size of the prepared ZnO nanoparticles is mainly distributed in the range of 8-18 nm, with a narrow particle size distribution and relatively uniform particle size.

[0049] Figure 3 The image shows the TEM morphology of the modified ZnO nanoparticles in this invention. It can be seen that the ZnO nanoparticles are coated with a shell, forming a core-shell structure, and the particle dispersibility becomes more excellent.

[0050] Figure 4 The image shows a SEM image of the original pure PP plastic material. The cross-section of the pure PP matrix is ​​relatively smooth. Figure 5 The image shows a cross-sectional SEM image of the modified PP plastic material prepared in Example 1 of this invention. The 8-18nm ZnO nanoparticles after organic-inorganic hybrid modification are uniformly dispersed in the PP matrix, without large-sized agglomerates, and the particles have good interfacial bonding with the matrix. Figure 6 This is a SEM image of the PP plastic material prepared in Comparative Example 1 of the present invention (direct filling with unmodified ZnO). Unmodified ultrafine ZnO forms a large number of aggregates in the matrix. Figure 7 This is a SEM image of the PP plastic material prepared by Comparative Example 2 (KH550 monosilane modified ZnO) of the present invention. Local particle agglomeration can still be seen in the sample.

[0051] Figure 8 The ultraviolet absorption curves of PP materials modified with different ZnO addition amounts are shown. As the content of hybrid modified ZnO filler increases, the light absorption capacity of the material in the 200-400nm ultraviolet band gradually increases.

[0052] Figure 9 Macroscopic photographs of PP+ZnO-1 prepared in Example 1 and the original PP plastic material before and after 100 hours of ultraviolet light irradiation; the original PP showed obvious yellowing after ultraviolet irradiation, while the PP+ZnO-1 sample did not show significant color change, which directly demonstrates the excellent anti-ultraviolet aging effect.

[0053] Figure 10 This is a comparison curve showing the retention rate of tensile strength of pure PP, samples from Examples 1-3, and Comparative Examples 1-2 after 100 hours of UV aging; used to compare the differences in UV aging resistance of composite materials under different modification schemes. Figure 10 It can be seen that the tensile strength retention rate of pure PP without filler after 100 hours of UV aging is only 61%, indicating severe UV aging damage. Examples 1-3 of this invention use organic-inorganic hybrid silica sol-modified 8-18nm ZnO as filler, achieving tensile strength retention rates of 90% and above. Comparative Example 1, directly filled with unmodified ultrafine ZnO, suffers from severe particle agglomeration, offering almost no long-term UV protection, with a strength retention rate of only 66% after aging. Comparative Example 2 uses traditional KH550 monosilane graft modification, but the modified layer is prone to detachment and failure during high-temperature processing, resulting in a tensile strength retention rate of 75% after aging, significantly lower than the technical solution of this invention. These results demonstrate that this invention, through two-component co-hydrolysis to construct an organic-inorganic hybrid coating shell with an inorganic rigid framework, can significantly improve the dispersion stability and long-term UV aging resistance of ultrafine ZnO in the PP matrix.

Claims

1. A UV-resistant modified PP plastic, characterized in that, The raw materials include the following parts by weight: 95-99 parts of isotactic polypropylene resin, 4-6 parts of organic-inorganic hybrid silica sol modified ZnO nanoparticles, and 0.3-0.5 parts of antioxidant. The organic-inorganic hybrid silica sol-modified ZnO nanoparticles are prepared by co-hydrolysis modification of ZnO nanoparticles with a particle size of 8-18 nm using dual silicon sources. The dual silicon source is tetraethyl orthosilicate and N-[3-(trimethoxysilyl)propyl]ethylenediamine; The organic-inorganic hybrid silica sol-modified ZnO nanoparticles have a dense core-shell structure. The core layer consists of 8-18 nm ultrafine ZnO particles, and the shell layer is an organic-inorganic hybrid coating layer formed by the combination of an inorganic SiO2 rigid network formed by the hydrolysis of tetraethyl orthosilicate and N-[3-(trimethoxysilyl)propyl]ethylenediamine organic functional segments.

2. The UV-resistant modified PP plastic according to claim 1, characterized in that, The isotactic polypropylene is F401 type isotactic polypropylene; the antioxidant is antioxidant 1010.

3. A molding process for the UV-resistant modified PP plastic as described in claim 1 or 2, characterized in that, Includes the following steps: S1, ZnO nanoparticle synthesis: Zinc salt was dissolved in anhydrous ethanol, alkali was dissolved in anhydrous ethanol, the alkali solution was added dropwise to the zinc salt solution and stirred to react, n-hexane was added, and after standing, the mixture was centrifuged, washed and vacuum dried to obtain ZnO nanoparticles with a particle size of 8-18 nm. S2. Modification of organic-inorganic hybrid silica sol: Anhydrous ethanol, deionized water, and ammonia were mixed evenly, and the ZnO nanoparticles prepared in step S1 were added and ultrasonically dispersed; then tetraethyl orthosilicate and N-[3-(trimethoxysilyl)propyl]ethylenediamine were added dropwise, and the mixture was stirred at a constant temperature to complete the modification; after the reaction was completed, the mixture was centrifuged, washed, and vacuum dried to obtain organic-inorganic hybrid silica sol-modified ZnO nanoparticles; S3. Raw material pretreatment: Place isotactic polypropylene resin, antioxidant, and modified ZnO nanoparticles in a vacuum drying oven for drying. S4. Melt blending: The pretreated raw materials are fed into an internal mixer for internal blending to obtain modified PP composite melt material; S5. Compressed sheet molding: The modified PP composite molten material is placed in a mold, preheated, and then pressed into sheets under pressure. After cooling and demolding, the UV-resistant modified PP plastic finished product is obtained.

4. The molding process according to claim 3, characterized in that, In step S1, the zinc salt is zinc chloride or zinc acetate, and the alkali is sodium hydroxide or potassium hydroxide.

5. The molding process according to claim 3, characterized in that, In step S1, the amount of zinc salt used is 8-10 mmol, and the volume of anhydrous ethanol used to dissolve the zinc salt is 40-60 mL; the amount of alkali used is 16-20 mmol, and the volume of anhydrous ethanol used to dissolve the alkali is 8-18 mL; the reaction temperature is 60-80℃; and hexane with a volume of 3 times that of the original solution is added.

6. The molding process according to claim 3, characterized in that, In step S2, the ammonia water is analytical grade ammonia water with a mass fraction of 25%-28%; the amount of anhydrous ethanol is 60-80 mL, the amount of deionized water is 2-3 mL, and the amount of ammonia water is 0.5-0.8 mL; the amount of ZnO nanoparticles is 0.4-0.6 g; the amount of tetraethyl orthosilicate is 2-3 mL, and the amount of N-[3-(trimethoxysilyl)propyl]ethylenediamine is 0.5-1 mL; the constant temperature stirring temperature is 40-60℃, and the stirring time is 5-6 h; the vacuum drying temperature is 60-70℃, and the drying time is 5-7 h.

7. The molding process according to claim 6, characterized in that, In step S2, the ultrasonic dispersion power is 200-300W, and the ultrasonic dispersion time is 30-60min.

8. The molding process according to claim 3, characterized in that, In step S3, the drying temperature is 60℃ and the drying time is 10-14h.

9. The molding process according to claim 3, characterized in that, In step S4, the mixing temperature is 185-195℃, the rotor speed is 25-35rpm, and the mixing time is 2-4min.

10. The molding process according to claim 3, characterized in that, In step S5, the preheating temperature is 185-195℃ and the preheating time is 4-6 min; the tableting pressure is 10t and the tableting time is 4-6 min.

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