A multi-scale filler synergistically reinforced polypropylene composite material and a preparation method thereof

Abstract

The application discloses a kind of multi-scale filler synergistic reinforced polypropylene composite material and preparation method thereof, the polypropylene composite material includes: polypropylene resin, chopped glass fiber, carbon nanotube, boron nitride nanosheet, hyperbranched polysiloxane, styrene-ethylene-propylene-styrene copolymer, maleic anhydride grafting polyolefin elastomer, maleic anhydride grafting polypropylene, antioxidant, lubricant, color mother.The polypropylene composite material provided by the application has high rigidity, high toughness and high heat distortion temperature, and has excellent comprehensive performance.The polypropylene resin used can be virgin polypropylene or recycled polypropylene, enabling the high-value use of recycled polypropylene.Further, during the preparation of the polypropylene composite material, the fillers do not need to be pre-modified, and various different scale fillers can be dynamically modified simultaneously online during the raw material blending and granulation process, resulting in a simple process flow and low cost.

Description

Technical Field

[0001] This invention relates to a multi-scale filler synergistic reinforcement polypropylene composite material and its preparation method, belonging to the field of polypropylene composite material technology. Background Technology

[0002] Polypropylene (PP), as a general-purpose thermoplastic, has advantages such as low density, chemical resistance, easy processing and molding, and low price, and is widely used in the automotive industry, home appliances, electronics, packaging materials and other fields. However, PP itself has inherent defects such as low strength, low modulus, poor heat resistance and insufficient impact toughness, which limit its use in structural components and high-end applications. Therefore, it is necessary to enhance and modify its properties.

[0003] Currently, the main method for modifying polypropylene (PP) is by introducing fillers. Using glass fiber as a filler is one of the most effective ways to improve the mechanical properties of PP. However, traditional glass fiber reinforced PP materials face two major technical bottlenecks: firstly, the interfacial bond between the glass fiber and the PP matrix is ​​weak; secondly, there is a contradiction of "increasing stiffness while decreasing toughness," meaning that as the glass fiber content increases, the rigidity and strength of the material increase, but the impact toughness decreases sharply. Existing technologies include methods that use silane coupling agents to treat the glass fiber surface, but traditional silane coupling agents are small molecule compounds, and the interfacial layer formed on the glass fiber surface is too thin to effectively buffer stress concentration.

[0004] In recent years, the high-value utilization of recycled polypropylene (rPP) has become a hot topic in the industry. With the increasingly severe global plastic pollution problem, various countries have successively introduced regulations mandating the use of recycled materials. For example, the EU's Packaging and Packaging Waste Regulation requires that the proportion of recycled materials in plastic packaging reach 30% by 2030, and the ELV Directive for the automotive industry also sets clear requirements for the proportion of recycled materials used. However, rPP undergoes multiple thermal histories during its initial use and recycling processes, resulting in molecular chain breakage and degradation, leading to a decrease in molecular weight, a wider molecular weight distribution, increased and fluctuating melt flow rate, and a significant decrease in impact toughness and thermal stability. These performance defects make it difficult to apply rPP in high proportions and with high performance in glass fiber reinforced composites. Although there are reports of blending rPP with glass fiber in existing technologies, due to weak interfacial bonding and severe fiber length loss during processing, the problem of "increased fiber length without increased toughness" or even a comprehensive decline in performance often occurs, limiting the application of rPP in high-end structural components.

[0005] Since glass fiber reinforcement alone is insufficient to achieve all the desired properties of polypropylene resin, composite fillers are typically used for synergistic modification. However, different fillers have different properties, making it difficult to disperse them uniformly in polypropylene resin. More importantly, existing technologies usually require separate offline pretreatment for each filler (such as acidification, coupling agent grafting, drying, etc.), resulting in cumbersome processes, high energy consumption, poor batch-to-batch stability, and different molecular layers grafted onto the surfaces of different fillers, making it difficult to form a uniform interfacial chemical environment and thus failing to achieve synergistic reinforcement between fillers.

[0006] Therefore, developing a polypropylene composite material and its preparation method that can simplify the process flow, unify the interfacial chemical environment, realize the high-value utilization of recycled PP, and achieve multi-scale filler synergistic reinforcement has important industrial value and environmental significance. Summary of the Invention

[0007] To address the aforementioned problems in the existing technology, the purpose of this invention is to provide a multi-scale filler synergistic reinforcement polypropylene composite material and its preparation method.

[0008] To achieve the above objectives, the present invention adopts the following technical solution: A multi-scale filler synergistic reinforcement polypropylene composite material has the following composition and proportions: Polypropylene resin: 100 parts by weight; Chopped glass fiber: 25-30 parts by weight; Carbon nanotubes: 2-3 parts by weight; Boron nitride nanosheets: 2-3 parts by weight; Hyperbranched polysiloxane: 3.0-4.0 parts by weight; Styrene-ethylene-propylene-styrene copolymer: 4-6 parts by weight; Maleic anhydride-grafted polyolefin elastomer: 4-6 parts by weight; Maleic anhydride-grafted polypropylene: 0.5-1.5 parts by weight; Antioxidant: 0.3-0.6 parts by weight; Lubricant: 0.1-0.2 parts by weight; Color masterbatch: 0-2 parts by weight (0 parts by weight means that the polypropylene composite material is not colored. If a polypropylene composite material with a specific color needs to be prepared, the corresponding color masterbatch can be added. Commercially available polypropylene resin color masterbatch can be used. For example, when it is necessary to prepare a black polypropylene composite material, 1 part by weight of black masterbatch can be added. The black masterbatch can be Cabot's black masterbatch MBB3041A). The hyperbranched polysiloxane is obtained by the hydrolysis and condensation reaction of hyperbranched polysiloxane with γ-glycidoxypropyltrimethoxysilane (KH-560), C12-C18 alkyltrimethoxysilane, phenyltrimethoxysilane (PTMS) and aminopropyltriethoxysilane (KH-550).

[0009] In one embodiment, the polypropylene resin is virgin polypropylene or recycled polypropylene (rPP).

[0010] In one embodiment, the C12-C18 alkyltrimethoxysilane is one or more of dodecyltrimethoxysilane, hexadecyltrimethoxysilane, and octadecyltrimethoxysilane.

[0011] In one embodiment, the molar ratio of γ-glycidoxypropyltrimethoxysilane:C12-C18 alkyltrimethoxysilane:phenyltrimethoxysilane:aminopropyltriethoxysilane in the hyperbranched polysiloxane is (5.0-5.5):(1.5-2.0):(1.5-2.0):(0.5-0.8), preferably 5.5:2.0:2.0:0.6.

[0012] In one embodiment, the chopped glass fiber has a diameter of 10-13 μm and a length of 3-4.5 mm; the carbon nanotube is a multi-walled carbon nanotube with an outer diameter of 8-15 nm and a length of 10-20 μm; and the boron nitride nanosheet has a diameter of 1-5 μm and a thickness of less than 5 nm.

[0013] In one embodiment, the antioxidant is a composite system of antioxidant 1010, antioxidant 168, and antioxidant DSTP, wherein the mass ratio of antioxidant 1010: antioxidant 168: antioxidant DSTP is 2:2:1.

[0014] In one embodiment, the lubricant is a composite system of a fluoropolymer processing aid and erucamide, wherein the mass ratio of the fluoropolymer processing aid to erucamide is 1:1.

[0015] One embodiment of the preparation of the hyperbranched polysiloxane includes the following steps: 1) Add γ-glycidoxypropyltrimethoxysilane, phenyltrimethoxysilane and organic solvent to the reactor, and stir and mix them evenly at 50-60℃ under nitrogen protection; dissolve glacial acetic acid in deionized water to obtain an acetic acid aqueous solution with pH=4-5; slowly add the acetic acid aqueous solution dropwise to the reactor, and after the addition is complete, keep the mixture at 70-75℃ and stir for 2.5-3.5 hours. 2) Slowly add C12-C18 alkyltrimethoxysilane and aminopropyltriethoxysilane to the reactor, stir and mix evenly, then add the catalyst. After the addition is complete, continue to stir and react at 70-75℃ for 2.5-3.5 hours to obtain hyperbranched polysiloxane.

[0016] In a preferred embodiment, during the preparation of hyperbranched polysiloxane, the mass ratio of total monomers (i.e., γ-glycidoxypropyltrimethoxysilane + C12-C18 alkyltrimethoxysilane + phenyltrimethoxysilane + aminopropyltriethoxysilane) to deionized water is 1:(0.15-0.25); the amount of glacial acetic acid used is 3-8% of the amount of deionized water used; and the mass ratio of total monomers to organic solvents is 1:(1.5-3).

[0017] In a preferred embodiment, during the preparation of hyperbranched polysiloxanes, the organic solvent is a mixed solvent of ethanol and ethyl acetate in a volume ratio of 1:2; and the catalyst is an organobismuth catalyst, such as Borchi Kat 22.

[0018] In a preferred embodiment, during the preparation of hyperbranched polysiloxane, after the reaction is completed, the temperature is lowered to 50-60℃, activated carbon is added to the obtained reactants, the mixture is kept warm and stirred for 20-40 minutes, filtered, and the filtrate is distilled under reduced pressure to obtain hyperbranched polysiloxane.

[0019] The preparation of a multi-scale filler synergistic reinforcement polypropylene composite material includes the following steps: a) Mix polypropylene resin, styrene-ethylene-propylene-styrene copolymer, maleic anhydride-grafted polyolefin elastomer, maleic anhydride-grafted polypropylene, antioxidant, lubricant, and color masterbatch evenly, and feed them into the twin-screw extruder through the main feed port. b) After the material is melted and plasticized in the twin-screw extruder, hyperbranched polysiloxane is injected into the melt through the liquid injection port and pre-dispersed in the dispersion and mixing section; at the same time, chopped glass fibers are added through the first side feed port, and carbon nanotubes and boron nitride nanosheets are added through the second side feed port, so that the three fillers of chopped glass fibers, carbon nanotubes and boron nitride nanosheets are in synchronous contact with hyperbranched polysiloxane in the melt. Under the action of high temperature and high shear, hyperbranched polysiloxane simultaneously performs online dynamic surface modification on chopped glass fibers, carbon nanotubes and boron nitride nanosheets; c) The material is melt-blended, extruded, cooled, and granulated to obtain a polypropylene composite material.

[0020] In one embodiment, the process parameters of the twin-screw extruder are as follows: barrel zone 1 temperature: 200-220℃, barrel zones 2-5 temperature: 210-230℃, barrel zone 6 temperature: 190-210℃, barrel zone 7 temperature: 200-220℃, barrel zone 8 temperature: 190-210℃, barrel zone 9 temperature: 180-200℃, barrel zone 10 temperature: 190-210℃, die head temperature: 190-210℃, and screw speed: 300-450 rpm.

[0021] In a preferred embodiment, polypropylene resin, styrene-ethylene-propylene-styrene copolymer, maleic anhydride-grafted polyolefin elastomer, maleic anhydride-grafted polypropylene, antioxidant, lubricant, and color masterbatch are added from the main feed port in zone 1 of the barrel; hyperbranched polysiloxane is injected from the liquid injection port in zone 4 of the barrel; chopped glass fiber is added from the first side feed port in zone 6 of the barrel; and carbon nanotubes and boron nitride nanosheets are premixed and added from the second side feed port in zone 8 of the barrel.

[0022] In one embodiment, the hyperbranched polysiloxane is preheated to 50-60°C before injection and injected using a gear metering pump at an injection pressure of 5-10 MPa.

[0023] Compared with the prior art, the present invention has the following significant advantages: 1) The polypropylene composite material provided by this invention uses glass fiber, carbon nanotubes, and boron nitride nanosheets as fillers, hyperbranched polyoxysilane as a filler modifier, and adds styrene-ethylene-propylene-styrene copolymer, maleic anhydride-grafted polyolefin elastomer, maleic anhydride-grafted polypropylene, antioxidants, lubricants, and other additives. It has high rigidity, high toughness, and high heat distortion temperature, and excellent comprehensive performance, which can meet the requirements of structural components and high-end application fields, and has extremely strong industrial application value. In addition, due to the good synergistic effect between the components in the polypropylene composite material, the polypropylene resin used can be not only virgin polypropylene but also recycled polypropylene, thereby realizing the high-value utilization of recycled polypropylene, which has important environmental significance. 2) The hyperbranched polysiloxane used in this invention is a multifunctional hyperbranched polymer containing multiple functional groups such as epoxy groups, C12-18 long alkyl chains, benzene rings, and amino groups. It can simultaneously modify glass fibers, carbon nanotubes, and boron nitride nanosheets. This not only enables the filler to be uniformly dispersed in polypropylene resin, significantly improving the interfacial compatibility between the filler and polypropylene resin, but also eliminates the interfacial incompatibility between different fillers. It establishes direct chemical bond connections between glass fibers, carbon nanotubes, and boron nitride nanosheets, forming an integrated multi-level reinforcing network, and realizing the multi-scale synergistic effect of glass fibers, carbon nanotubes, and boron nitride nanosheets. 3) This invention uses hyperbranched polysiloxane to simultaneously modify glass fiber, carbon nanotubes and boron nitride nanosheets, so that there is no need to pre-modify the fillers during the preparation of polypropylene composite materials. Multiple fillers of different sizes can be dynamically modified online simultaneously during the raw material blending and granulation process. Compared with the traditional two-step process of "pre-treating the fillers first and then blending and granulating with the raw materials", the one-step process of this invention is extremely simple and low cost. Detailed Implementation

[0024] The technical solution of the present invention will be further described in detail and completely below with reference to the embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Example 1

[0025] 1) Preparation of hyperbranched polysiloxanes 1) Add γ-glycidoxypropyltrimethoxysilane (5.5 mol, 1360 g, Nanjing Nengde New Material Technology Co., Ltd.), phenyltrimethoxysilane (2.0 mol, 396 g, Zhejiang Boiling Point Chemical Co., Ltd.), and a mixed solvent of ethanol / ethyl acetate (1:2, v / v) (total monomer to solvent mass ratio 1:2) to the reactor. Stir and mix at 55°C for 30 minutes under nitrogen protection to ensure homogeneity. Dissolve glacial acetic acid (5% of the amount of deionized water) in deionized water (total monomer to deionized water mass ratio 1:0.2) to obtain an acetic acid aqueous solution with pH=4.5. Slowly add this acetic acid aqueous solution dropwise to the reactor over 1 hour. After the addition is complete, keep the mixture at 72°C and stir for 3 hours. 2) Slowly add dodecyltrimethoxysilane (C12, 2.0 mol, 580 g, Qufu Chenguang Chemical Co., Ltd.) and aminopropyltriethoxysilane (0.6 mol, 133 g, Nanjing Nengde New Material Technology Co., Ltd.) to the reactor and stir for 15 minutes to mix them evenly. Then add (Borchi Kat 22, 0.1% of the total monomer mass). After the addition is complete, continue to stir and react at 72℃ for 3 hours. After the reaction is completed, cool down to 55℃, add activated carbon (2% of the total monomer mass), stir for 30 minutes, filter, and distill the filtrate under reduced pressure at -0.095 MPa and 80℃ for 1 hour to obtain a light yellow viscous liquid hyperbranched polysiloxane.

[0026] (ii) Preparation of polypropylene composites with synergistic reinforcement by multi-scale fillers The preparation was carried out using a twin-screw extruder (Nanjing Coperlon, ZSK-26Mc, L / D ratio 48:1). The temperature and process parameters for each zone are as follows: Barrel Zone 1: 210℃, Barrel Zones 2-5: 220℃, Barrel Zone 6: 200℃, Barrel Zone 7: 210℃, Barrel Zone 8: 200℃, Barrel Zone 9: 190℃, Barrel Zone 10: 200℃, Die Head: 200℃, Screw Speed: 350 rpm; The specific preparation steps are as follows: a) Mix 100 parts by weight of polypropylene resin (Sinopec K8003), 5 parts by weight of styrene-ethylene-propylene-styrene copolymer (Kertene G1730), 5 parts by weight of maleic anhydride-grafted polyolefin elastomer (Dow GR216), 1.0 part by weight of maleic anhydride-grafted polypropylene (Arkema CA100), 0.2 parts by weight of antioxidant 1010 (BASF Irganox 1010), 0.2 parts by weight of antioxidant 168 (BASF Irganox 168), 0.1 parts by weight of antioxidant DSTP (Nonox DSTP), 0.075 parts by weight of lubricant fluoropolymer processing aid (PPA, 3M, Dynamar FX-5911), and 0.075 parts by weight of lubricant erucamide (Crodamide). ER), 1 part by weight of black masterbatch (Cabote MBB3041A) are mixed evenly in a high-speed mixer and fed into a twin-screw extruder through the main feed port (barrel zone 1); b) After the material is melted and plasticized in the twin-screw extruder, 3.5 parts by mass of hyperbranched polysiloxane are injected into the melt through the liquid injection port in zone 4 of the barrel (the hyperbranched polysiloxane is preheated to 55°C before injection and injected through a gear metering pump at an injection pressure of 8MPa) and pre-dispersed in the dispersion and mixing section; at the same time, 28 parts by mass of chopped glass fiber (Taishan T435TM) are added from the first side feed port in zone 6 of the barrel, and 2.5 parts by mass of carbon nanotubes (Chengdu Organic TNM5, Chinese Academy of Sciences) and 2.5 parts by mass of boron nitride nanosheets (Xianfeng XFBN-01) are premixed and added from the second side feed port in zone 8 of the barrel, so that the three fillers of chopped glass fiber, carbon nanotubes and boron nitride nanosheets are in simultaneous contact with the hyperbranched polysiloxane in the melt. Under the action of high temperature and high shear, the hyperbranched polysiloxane simultaneously performs online dynamic surface modification on the chopped glass fiber, carbon nanotubes and boron nitride nanosheets; c) The material is melt-blended, extruded, cooled, and granulated to obtain a polypropylene composite material. Example 2

[0027] The difference between this embodiment and Embodiment 1 is that the virgin polypropylene resin in the polypropylene composite material is replaced with recycled polypropylene resin (rPP, Anhui Guanhong GH-PPR-01), and it does not contain black masterbatch. The rest is the same as in Embodiment 1. Example 3

[0028] The difference between this embodiment and Example 1 is that the alkyltrimethoxysilane used in the preparation process of the hyperbranched polysiloxane in the polypropylene composite material is a compound of C12 alkyltrimethoxysilane and C16 alkyltrimethoxysilane in a molar ratio of 1:1, while the rest is the same as in Example 1.

[0029] Comparative Example 1 The difference between this comparative example and Example 1 is that the polypropylene composite material does not contain hyperbranched polysiloxane, while the rest is the same as in Example 1.

[0030] Comparative Example 2 The difference between this comparative example and Example 1 is that the polypropylene composite material does not contain carbon nanotubes and boron nitride nanosheets, while the rest is the same as in Example 1.

[0031] Comparative Example 3 The difference between this comparative example and Example 1 is that the self-made hyperbranched polysiloxane is replaced with the traditional small molecule silane coupling agent KH-560 in the polypropylene composite material, while the rest is the same as in Example 1.

[0032] Comparative Example 4 The difference between this comparative example and Example 1 is that the monomers used in the preparation process of the hyperbranched polysiloxane in the polypropylene composite material do not contain C12 alkyltrimethoxysilane and phenyltrimethoxysilane, while the rest are the same as in Example 1.

[0033] Comparative Example 5 The difference between this comparative example and Example 1 is that the monomer used in the preparation process of the hyperbranched polysiloxane in the polypropylene composite material does not contain aminopropyltriethoxysilane, while the rest is the same as in Example 1.

[0034] The performance of the polypropylene composite materials prepared in Examples 1-3 and Comparative Examples 1-5 was tested according to relevant standards, specifically as follows: Tensile breaking strength: Tested according to ISO 527-2, with specimen size of ISO 3167 IA type dumbbell shape, and tensile test speed of 50 mm / min; Bending strength: conducted according to ISO 178, with specimen size of 80×10×4mm, span of 64mm, and test speed of 2mm / min; Flexural modulus: calculated according to ISO 178 using stress-strain curves; Impact strength (unnotched): tested according to ISO 179-1 / 1eU, with specimen size of 80×10×4mm and span of 62mm; Notched impact strength: conducted according to ISO 179-1 / 1eA, with specimen size of 80×10×4mm, the specimen having a Type A notch machined on the wide side, and a 4J pendulum. Heat distortion temperature (HDT): According to ISO 75-2, the specimen size is 80×10×4mm, laid flat, with a load of 1.80MPa (T1.8) and a span of 64mm; Density: determined according to ISO 1183-1 (Method A), by impregnation method; Ash content: Calcinated according to ISO 3451-1 (Method A), calcined at 800℃ for 2 hours; The test results are shown in Table 1.

[0035] Table 1. Performance test data of polypropylene composite materials prepared in Examples 1-3 and Comparative Examples 1-5

[0036] As shown in Table 1, the polypropylene composite materials prepared in Examples 1-3 exhibit tensile fracture strengths of 96.8-106.5 MPa, indicating strong tensile load-bearing capacity and suggesting high safety margins and lightweight potential in structural load-bearing components (such as supports and shells); flexural strengths of 121.0-133.8 MPa indicate high resistance to flexural deformation, making the products less prone to deformation or fracture under stress, suitable for applications requiring high rigidity and shape stability (such as large thin-walled parts); flexural modulus of 6210-6650 MPa indicates high rigidity (resistance to elastic deformation), resulting in good dimensional accuracy and service stability, suitable for precision structural components; and impact strength (unnotched) of 54.5-63.5 kJ / m² indicates high toughness, demonstrating a strong ability to absorb impact energy and effectively preventing brittle fracture under sudden impact, ensuring safe use. The material exhibits excellent structural integrity; its notched impact strength ranges from 8.80 to 10.52 kJ / m², indicating that it maintains excellent impact resistance even under harsh conditions with stress concentration, reflecting its superior resistance to crack propagation; its heat distortion temperature ranges from 137 to 143°C, demonstrating strong shape retention at high temperatures, thus broadening its application limits in high-temperature environments (such as near automotive engine compartments and high-temperature electrical appliances); its density ranges from 1.122 to 1.126 g / cm³, indicating that the material can be lightweight; and its ash content ranges from 31.2% to 31.5%, indicating that the filler content and distribution are reasonable, and its excellent performance is not simply achieved by increasing the filler content, verifying the effectiveness of interface modification and dispersion technology. Therefore, the polypropylene composite material prepared in the examples possesses high rigidity, high toughness, and high heat distortion temperature, exhibiting excellent comprehensive performance and meeting the requirements for polypropylene composite materials in structural components and high-end applications. Furthermore, although the data of the composite material prepared by recycled PP in Example 2 is slightly inferior to that of the composite materials prepared by virgin PP in Examples 1 and 3, it is still excellent. This shows that the formulation used in this invention can effectively compensate for the degradation defects of rPP and suppress the stress concentration caused by impurities and low molecular weight components in rPP. This demonstrates that it is feasible to prepare high-performance polypropylene composite materials using recycled polypropylene resin. Furthermore, the performance test data of Example 3 is the best, indicating that in hyperbranched polysiloxanes, the alkyltrimethoxysilane system composed of C12 alkyltrimethoxysilane and C16 alkyltrimethoxysilane has a good synergistic effect. Among them, C12 alkyltrimethoxysilane can ensure processing fluidity and interface wetting, ensuring that the modifier migrates quickly to the filler surface, while C16 alkyltrimethoxysilane can enhance the interfacial bonding strength and stress dissipation. The long chain can effectively slide and extend to absorb impact energy. The combination of the two can achieve a synergistic interface layer of long and short chains, thereby improving the impact strength of the composite material. Furthermore, as can be seen from the table, the overall performance of the polypropylene composites prepared in Examples 1-3 is significantly better than that of the polypropylene composites prepared in Comparative Examples 1-5. This may be because: 1) Compared with Comparative Example 1: Comparative Example 1 does not contain hyperbranched polysiloxane. The glass fiber and PP matrix are only physically interlocked, and the interfacial bonding is extremely weak. At the same time, carbon nanotubes and boron nitride nanosheets are severely aggregated due to their high surface energy, becoming defects and stress concentration points inside the composite material, which leads to easy interfacial debonding and cracking when the material is under stress. In contrast, Example 1 uses self-made hyperbranched polysiloxane. The dense epoxy groups on its molecular chain can chemically bond with the hydroxyl groups on the surface of the glass fiber, and the long alkyl chains form physical entanglement with the PP matrix. At the same time, the amino and epoxy groups on its hyperbranched structure can also interact with the defect sites on the surface of carbon nanotubes and boron nitride nanosheets, like molecular bridges, which can connect the three fillers into a unified multi-scale reinforcing network, realizing efficient stress transfer and thus greatly improving the mechanical properties of the material. 2) Comparison of Example 1 and Comparative Example 2: Comparative Example 2 does not contain carbon nanotubes and boron nitride nanosheets, and uses a single glass fiber to reinforce the PP matrix. Although glass fiber can significantly improve rigidity and strength, stress concentration is easily caused at the ends of glass fibers, leading to rapid crack propagation and poor toughness. In contrast, Example 1 uses a composite filler of glass fiber, carbon nanotubes and boron nitride nanosheets. The nanoscale effect of carbon nanotubes and boron nitride nanosheets allows them to be uniformly dispersed in the PP matrix and around the glass fiber. When the material is impacted, the nanofiller can prevent the propagation of microcracks through the pinning effect. At the same time, the cracks will be deflected when they encounter the nanofiller during the propagation process, consuming more energy. The high aspect ratio of carbon nanotubes can also play a role in "bridging" the cracks. This multi-level energy dissipation mechanism from macroscopic (glass fiber) to micro / nano (nanofiller) achieves synergistic reinforcement of high rigidity and high toughness of the material. 3) Compared with Comparative Example 3: The modifier used in Comparative Example 3 is the traditional small molecule silane coupling agent KH-560. KH-560 can only form a monolayer on the glass fiber surface. The interface layer is too thin and cannot effectively buffer stress, let alone connect carbon nanotubes and boron nitride nanosheets at the same time. In contrast, the self-made hyperbranched polysiloxane in Example 1 is a hyperbranched macromolecule that can form a three-dimensional network-like flexible interface layer with controllable thickness on the filler surface. This interface layer can achieve strong bonding through chemical bonds and physical entanglement, and can also dissipate energy through conformational changes of flexible molecular chains, playing a role of both rigidity and flexibility. At the same time, the multiple functional groups of hyperbranched polysiloxane make it a universal connector for multi-scale fillers, which is something that a single small molecule coupling agent cannot achieve. In addition, the epoxy and amino groups of hyperbranched polysiloxane can react with the anhydride groups in the maleic anhydride-grafted polyolefin elastomer and maleic anhydride-grafted polypropylene in the formulation, further enhancing the interface. 4) Compared with Comparative Example 4: In the preparation process of hyperbranched polysiloxane in Comparative Example 4, the monomers used do not contain C12 alkyltrimethoxysilane and phenyltrimethoxysilane. As a result, the hyperbranched polysiloxane prepared in Comparative Example 4 lacks long-chain alkyl and phenyl groups compared with that in Example 1. Long alkyl chains can form dense physical entanglements with the PP matrix. When subjected to impact, they can dissipate energy through chain segment sliding / extension. Benzene rings can improve the rigidity and thermal stability of the interface layer. As a result, after the long-chain alkyl and phenyl groups are missing in Comparative Example 4, the compatibility between the modifier and the PP matrix deteriorates, the material interface layer becomes brittle, and the toughness decreases. Compared with Comparative Example 5, in the preparation of the hyperbranched polysiloxane in Comparative Example 5, the monomer used did not contain aminopropyltriethoxysilane. As a result, the hyperbranched polysiloxane prepared in Comparative Example 5 lacked amino groups compared with that in Example 1. Amino groups can form strong interactions with the defect sites on the surface of carbon nanotubes and boron nitride nanosheets in the formulation, ensuring the uniform dispersion of the nanofiller. They can also react with the anhydride groups of maleic anhydride grafts (maleic anhydride grafted polyolefin elastomer, maleic anhydride grafted polypropylene) in the formulation, establishing additional chemical bridges between the filler and the matrix. As a result, after the amino groups were missing in Comparative Example 5, the dispersion stability of carbon nanotubes and boron nitride nanosheets decreased, and some agglomerated into defects, which in turn led to a decrease in the notched impact strength of the material. As can be seen from Comparative Examples 4 and 5 and Example 1, the superior performance of the hyperbranched polysiloxane in the embodiments of the present invention comes from the synergistic effect of four monomers: γ-glycidoxypropyltrimethoxysilane, C12-C18 alkyltrimethoxysilane, phenyltrimethoxysilane and aminopropyltriethoxysilane. The absence of any monomer will lead to the deterioration of specific properties.

[0037] Finally, it should be noted that the above are only some preferred embodiments of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention shall fall within the scope of protection of the present invention.

Claims

1. A multi-scale filler synergistic reinforcement polypropylene composite material, characterized in that, It has the following composition and proportions: Polypropylene resin: 100 parts by weight; Chopped glass fiber: 25-30 parts by weight; Carbon nanotubes: 2-3 parts by weight; Boron nitride nanosheets: 2-3 parts by weight; Hyperbranched polysiloxane: 3.0-4.0 parts by weight; Styrene-ethylene-propylene-styrene copolymer: 4-6 parts by weight; Maleic anhydride-grafted polyolefin elastomer: 4-6 parts by weight; Maleic anhydride-grafted polypropylene: 0.5-1.5 parts by weight; Antioxidant: 0.3-0.6 parts by weight; Lubricant: 0.1-0.2 parts by weight; Color masterbatch: 0-2 parts by weight; The hyperbranched polysiloxane is obtained by the hydrolysis and condensation reaction of hyperbranched polysiloxane from γ-glycidoxypropyltrimethoxysilane, C12-C18 alkyltrimethoxysilane, phenyltrimethoxysilane and aminopropyltriethoxysilane.

2. The multi-scale filler synergistic reinforcement polypropylene composite material according to claim 1, characterized in that: The polypropylene resin is virgin polypropylene or recycled polypropylene.

3. The multi-scale filler synergistic reinforcement polypropylene composite material according to claim 1, characterized in that: The C12-C18 alkyltrimethoxysilane is one or more of dodecyltrimethoxysilane, hexadecyltrimethoxysilane, and octadecyltrimethoxysilane.

4. The multi-scale filler synergistic reinforcement polypropylene composite material according to claim 1, characterized in that, In hyperbranched polysiloxanes, the molar ratio of γ-glycidoxypropyltrimethoxysilane:C12-C18 alkyltrimethoxysilane:phenyltrimethoxysilane:aminopropyltriethoxysilane is (5.0-5.5):(1.5-2.0):(1.5-2.0):(0.5-0.8).

5. The multi-scale filler synergistic reinforcement polypropylene composite material according to claim 1, characterized in that, The antioxidant is a composite system of antioxidant 1010, antioxidant 168 and antioxidant DSTP, wherein the mass ratio of antioxidant 1010: antioxidant 168: antioxidant DSTP is 2:2:

1.

6. The multi-scale filler synergistic reinforcement polypropylene composite material according to claim 1, characterized in that, The lubricant is a composite system of fluoropolymer processing aid and erucamide, wherein the mass ratio of fluoropolymer processing aid to erucamide is 1:

1.

7. The multi-scale filler synergistic reinforcement polypropylene composite material according to claim 1, characterized in that: The preparation of the hyperbranched polysiloxane includes the following steps: 1) Add γ-glycidoxypropyltrimethoxysilane, phenyltrimethoxysilane and organic solvent to the reactor, and stir and mix them evenly at 50-60℃ under nitrogen protection; dissolve glacial acetic acid in deionized water to obtain an acetic acid aqueous solution with pH=4-5; slowly add the acetic acid aqueous solution dropwise to the reactor, and after the addition is complete, keep the mixture at 70-75℃ and stir for 2.5-3.5 hours. 2) Slowly add C12-C18 alkyltrimethoxysilane and aminopropyltriethoxysilane to the reactor, stir and mix evenly, then add the catalyst. After the addition is complete, continue to stir and react at 70-75℃ for 2.5-3.5 hours to obtain hyperbranched polysiloxane.

8. The multi-scale filler synergistic reinforcement polypropylene composite material according to claim 7, characterized in that: In the preparation process of hyperbranched polysiloxane, the mass ratio of total monomer to deionized water is 1:(0.15-0.25); the amount of glacial acetic acid used is 3-8% of the amount of deionized water used; the mass ratio of total monomer to organic solvent is 1:(1.5-3); the organic solvent is a mixed solvent of ethanol and ethyl acetate in a volume ratio of 1:2; and the catalyst is an organic bismuth catalyst.

9. A method for preparing a multi-scale filler synergistic reinforced polypropylene composite material as described in claim 1, characterized in that, Includes the following steps: a) Mix polypropylene resin, styrene-ethylene-propylene-styrene copolymer, maleic anhydride-grafted polyolefin elastomer, maleic anhydride-grafted polypropylene, antioxidant, lubricant, and color masterbatch evenly, and feed them into the twin-screw extruder through the main feed port. b) After the material is melted and plasticized in the twin-screw extruder, hyperbranched polysiloxane is injected into the melt through the liquid injection port and pre-dispersed in the dispersion and mixing section; at the same time, chopped glass fibers are added through the first side feed port, and carbon nanotubes and boron nitride nanosheets are added through the second side feed port, so that the three fillers of chopped glass fibers, carbon nanotubes and boron nitride nanosheets are in synchronous contact with hyperbranched polysiloxane in the melt. Under the action of high temperature and high shear, hyperbranched polysiloxane simultaneously performs online dynamic surface modification on chopped glass fibers, carbon nanotubes and boron nitride nanosheets; c) The material is melt-blended, extruded, cooled, and granulated to obtain a polypropylene composite material.

10. The method for preparing the multi-scale filler synergistic reinforcement polypropylene composite material according to claim 9, characterized in that, The process parameters of the twin-screw extruder are as follows: barrel zone 1 temperature: 200-220℃, barrel zones 2-5 temperature: 210-230℃, barrel zone 6 temperature: 190-210℃, barrel zone 7 temperature: 200-220℃, barrel zone 8 temperature: 190-210℃, barrel zone 9 temperature: 180-200℃, barrel zone 10 temperature: 190-210℃, die head temperature: 190-210℃, screw speed: 300-450 rpm.

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