Polypropylene composite material for automotive trim and preparation method of polypropylene composite material

Abstract

The invention relates to the technical field of high-performance polypropylene, in particular to a polypropylene composite material for automotive trim and a preparation method of the polypropylene composite material. The problems that the mechanical property of the polypropylene composite material is difficult to comprehensively improve and the thermo-oxidative aging resistance is poor are solved. The talc powder is grafted and modified through maleic anhydride grafted polypropylene, so that the interface bonding between the filler and a matrix is enhanced; through double toughening and stiffening of the cross-linked modified POE and the pretreated mixed fiber, a composite structure of a rigid framework and a flexible network is formed in the material; through a microcapsule packaging technology and a sectional type feeding process, a heat-sensitive antioxidant and fibers are added in a downstream area of an extrusion process, so that the long-acting slow-release effect of the antioxidant and the complete length of the fibers are ensured; the process is matched with the components, so that the prepared composite material not only has excellent comprehensive mechanical properties, but also has lasting and stable thermo-oxidative aging resistance, and the service life of the product is prolonged.

Description

Technical Field

[0001] This invention relates to the field of high-performance polypropylene technology, specifically to a polypropylene composite material for automotive interiors and its preparation method. Background Technology

[0002] Polypropylene (PP) is widely used in automotive interior parts due to its excellent cost-effectiveness, low density, ease of processing, and pleasant feel, such as door panels, dashboards, pillars, and storage compartments. However, as consumers increasingly demand higher quality, safety, and longer lifespan for automotive interior components, existing PP materials still face numerous challenges in practical applications.

[0003] First, the mechanical properties of traditional polypropylene materials, especially low-temperature impact strength and high-temperature rigidity, often fail to meet the requirements of complex stresses and extreme environments in automotive interior components. For example, insufficient impact toughness of the material may lead to brittle cracking of components during a vehicle collision; while in high summer temperatures or under engine heat radiation, decreased rigidity may cause dimensional stability problems or appearance deformation.

[0004] Secondly, automotive interior parts are constantly exposed to sunlight, high temperatures, and the enclosed space of the vehicle, making them highly susceptible to thermo-oxidative aging. This aging process causes the polypropylene molecular chains to break and cross-link, resulting in yellowing, powdering, surface cracking, and decreased gloss, accompanied by a significant decline in mechanical properties. This severely affects the lifespan and aesthetics of the interior parts and may even produce odors or release harmful substances, posing a potential threat to the health of occupants.

[0005] Existing technologies typically improve rigidity by adding inorganic fillers or toughness by adding elastomers. However, these methods often compromise on one aspect while failing to achieve a comprehensive improvement in mechanical properties, and their improvement in resistance to thermo-oxidative aging is limited. Traditional antioxidant systems also suffer from problems such as easy migration and insufficient long-term stability. Therefore, there is an urgent need to develop a novel polypropylene composite material that can significantly improve its mechanical properties while endowing it with excellent long-term resistance to thermo-oxidative aging, in order to meet the increasingly stringent environmental requirements of automotive interior components.

[0006] To this end, a polypropylene composite material for automotive interiors and its preparation method are proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a polypropylene composite material for automotive interiors and its preparation method.

[0008] To achieve the above objectives, the present invention provides the following technical solution: It should be noted that, unless otherwise specified, all parts in this invention are parts by weight.

[0009] This invention provides a method for preparing a polypropylene composite material for automotive interiors, the method being as follows: Add 65-75 parts of polypropylene, 4-8 parts of modified talc, 0.8-1.5 parts of nucleating agent, 6-9 parts of crosslinked modified POE, 0.5 parts of calcium stearate, and 0.3 parts of polyethylene wax to a mixer. Stir and mix at 1000 rpm for 15 minutes at 85℃, stopping once during the process. Manually turn the bottom material to ensure there are no dead corners. Turn off the heating and continue stirring until the temperature drops below 40℃ to obtain a premix. Add the premix to the main feed port at a feeding rate of 20-22 kg / h. Add 12-18 parts of mixed fiber to side feed port one (3-section barrel) at a feeding rate of 3-4.5 kg / h. Add 1.5-2.5 parts of microencapsulated antioxidant to side feed port two (5-section barrel) at a feeding rate of 0.1 kg / h. Extrude the mixture using an extruder, then water-cool and pelletize it. Dry it in an 80℃ forced-air oven for 2 hours to obtain a polypropylene composite material for automotive interiors. Modified talc is obtained by grafting maleic anhydride-grafted polypropylene onto flake talc; the maleic anhydride-grafted polypropylene is designated as PA95504. Crosslinked modified POE was obtained by reacting POE with dicumyl peroxide; the melt index of POE was 1.5-2 g / 10 min. The hybrid fiber is obtained by mixing glass fiber and carbon fiber after separate pretreatment; the glass fiber is alkali-free glass fiber, purchased from Taian Haili New Material Co., Ltd.; the carbon fiber is PAN-based carbon fiber, grade MR7012P. The microencapsulated antioxidant is prepared by mixing antioxidant 1010 and antioxidant 168.

[0010] Preferred method for preparing modified talc powder is as follows: 6 parts of flake talc powder (average particle size 0.8-1.5μm) are added to a high-speed mixer, heated to 150-180℃, preheated at 1200rpm for 5min, 0.4 parts of maleic anhydride-grafted polypropylene and 0.012 parts of dicumyl peroxide are added, melt-blended for 20-30min, heating is turned off, stirring is continued until the temperature drops below 60℃, the material is discharged, pulverized and passed through a 200-mesh sieve to obtain modified talc powder.

[0011] Preferably, the nucleating agent is prepared as follows: 0.64-1.2 parts of nucleating agent 3988 (CAS: 135861-56-2) and 0.16-0.3 parts of polyethylene wax are mixed and added to a twin-screw extruder for extrusion. The extrusion parameters are set as follows: feeding section 180°C, melting section 210°C, homogenization section 200°C, die head 210°C, screw speed 250 rpm. After water cooling and pelletizing, the mixture is pulverized into powder of 0.5-1 mm to obtain the nucleating agent.

[0012] Preferred method for preparing crosslinked modified POE is as follows: Preheat the internal mixer to 160-170℃, add 8 parts of POE, and internally mix and melt at 60 rpm for 5 min. Add 0.024 parts of dicumyl peroxide, adjust the speed to 80 rpm, and internally mix for 10-15 min. Cool to room temperature and pulverize into 2-3 mm particles to obtain crosslinked modified POE.

[0013] Preferably, the method for preparing the mixed fiber is as follows: KH560 is added to deionized water, the pH value is adjusted to 4-5 with dilute hydrochloric acid, and the mixture is stirred and hydrolyzed for 30 min to obtain a 3wt% KH560 aqueous solution; alkali-free glass fiber (4-6 mm in length) and PAN-based carbon fiber are respectively immersed in the 3wt% KH560 aqueous solution (20 times the total mass of the fiber) and pretreated by soaking at room temperature for 2 h, with stirring once every 30 min during the process; after soaking, the fiber is taken out and placed in a 100℃ forced-air oven to dry for 3 h, then cooled to room temperature, and the pretreated glass fiber and carbon fiber are mixed at a mass ratio of 2-5:1 to obtain the mixed fiber.

[0014] Preferably, the preparation method of microcapsule antioxidant is as follows: Antioxidant 1010 and antioxidant 168 are added to a mixer at a mass ratio of 2:1 and mixed at 1000 rpm for 10-20 min to obtain a composite antioxidant; deionized water (5 times the total mass of antioxidant) is added to the composite antioxidant and stirred to form a suspension; polyvinyl alcohol (shell material, 25%-35% of the total mass of antioxidant) is added, the temperature is raised to 65℃, and the mixture is stirred at 500 rpm. The pH is adjusted to 3-4 with 10wt% hydrochloric acid, and formaldehyde (10% of the mass of polyvinyl alcohol) is added dropwise at a rate of 1 drop / s. The mixture is stirred at a constant temperature for 2 h, centrifuged at 8000 rpm for 15 min, and the resulting precipitate is placed in a vacuum drying oven and dried at 70℃ and -0.08 MPa for 6 h. After pulverizing, the precipitate is passed through a 100-mesh sieve to obtain the microcapsule antioxidant.

[0015] Preferably, the extrusion parameters are set as follows: screw speed: 250 rpm; feeding section 170℃ → barrel section 1 180℃ → barrel section 2 185℃ → barrel section 3 190℃ (side feed port 1) → barrel section 4 195℃ → barrel section 5 195℃ (side feed port 2) → barrel section 6 190℃ → die head 185℃.

[0016] Another aspect of the present invention provides a polypropylene composite material for automotive interiors, which is prepared by any of the above preparation methods; the raw materials for preparing the polypropylene composite material for automotive interiors include polypropylene, modified talc, nucleating agent, crosslinked modified POE, microencapsulated antioxidant and mixed fiber.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention employs in-situ grafting modification technology to graft maleic anhydride onto the surface of ultrafine flake talc powder, significantly improving the dispersibility of talc powder in a polypropylene matrix. The modified talc powder and the polypropylene matrix form a strong interfacial bond through chemical bonds, effectively avoiding the decline in material mechanical properties caused by poor interfacial bonding in traditional inorganic fillers. This tight interfacial bond allows stress to be transferred more effectively from the polypropylene matrix to the talc particles, thereby significantly improving the tensile and flexural strength of the material and endowing it with excellent rigidity. Simultaneously, the uniform dispersion of talc powder and the enhanced interfacial bond prevent the formation of stress concentration points, making the material less prone to brittle fracture under impact. Thus, while significantly improving rigidity, it also maintains good impact toughness, achieving synergistic optimization of rigidity and toughness.

[0018] 2. This invention employs a dual modification strategy of cross-linked modified POE and mixed fibers to further enhance the mechanical properties of the material. Cross-linked modified POE, through chemical cross-linking between molecular chains, maintains its original toughening effect while exhibiting stronger resistance to deformation, thus effectively improving the impact toughness of the material without significantly sacrificing its rigidity. Simultaneously, the introduced glass fiber and carbon fiber mixture, after pretreatment, exhibits good interfacial compatibility with the polypropylene matrix, forming a three-dimensional network skeleton structure within the material, greatly enhancing its tensile strength and flexural modulus. These two components form a synergistic system of a rigid skeleton and a flexible network within the material. The rigid fiber skeleton provides the main load-bearing capacity, while the cross-linked POE network absorbs energy upon impact, jointly endowing the composite material with high rigidity and high toughness.

[0019] 3. The nucleating agent of this invention is a compound of sorbitol-based nucleating agents and polyethylene wax, and is prepared into a uniform powder by single-screw extrusion granulation. This nucleating agent can significantly improve the crystallization rate and crystallinity of polypropylene. The nucleating agent is uniformly dispersed in the polypropylene matrix, providing a large number of crystal nuclei, which allows the polypropylene to form a finer and more uniform spherulite structure during cooling. The small spherulite size and uniform distribution can effectively reduce stress concentration points in the material and better transfer and disperse external stress. This not only helps to improve the tensile strength of the material, but more importantly, it can significantly improve the impact toughness of the material; at the same time, the high crystallinity also endows the material with a higher heat distortion temperature and better dimensional stability.

[0020] 4. This invention employs a microencapsulated antioxidant system composed of antioxidant 1010 and antioxidant 168, thereby significantly improving the material's resistance to thermo-oxidative aging. By encapsulating the antioxidant in polyvinyl alcohol microcapsules, the microcapsule shell protects the internal antioxidant, making it less prone to decomposition under the high-temperature, high-shear environment of extrusion granulation, thus maximizing the preservation of the antioxidant's activity. During long-term use in automotive interiors, the microcapsules slowly release the antioxidant. The hindered phenolic antioxidant captures peroxide free radicals generated by thermo-oxidative aging, while the phosphate ester antioxidant decomposes hydrogen peroxide. Together, they construct a complete antioxidant chain of "free radical capture - hydrogen peroxide decomposition." This slow-release mechanism ensures that the material maintains its excellent mechanical properties and appearance even under long-term high-temperature and air-exposed environments, greatly extending the product's service life.

[0021] 5. This invention employs a segmented feeding extrusion process, effectively protecting each functional component and maximizing their synergistic effects. In the first stage, components such as polypropylene and modified talc are added through the main feed port and fully melt-blended under high shear and high temperature conditions, ensuring uniform dispersion of talc and nucleating agents in the matrix. Subsequently, microencapsulated antioxidants and mixed fibers are added through downstream side feed ports. This segmented feeding effectively avoids damage to microcapsules and fibers in the initial stage, preserving the slow-release function of antioxidants and the integrity of fiber length. Intact fibers can more effectively form an internal skeleton, providing higher strength; while intact microcapsules can better exert their long-term anti-aging effects. This perfect match between the process and component characteristics ensures that the final composite material achieves optimal balance of various properties, realizing synergistic performance enhancement. Attached Figure Description

[0022] Figure 1 The figures show the tensile strength and bending strength test results of Examples 1-3 and Comparative Examples 1-4 of the present invention. Detailed Implementation

[0023] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0024] Please see Figure 1 This invention provides a polypropylene composite material for automotive interiors and its preparation method, the technical solution of which is as follows: Example 1

[0025] Add 6 parts of flake talc powder to a high-speed mixer, heat to 150℃, preheat at 1200 rpm for 5 minutes, add 0.4 parts of maleic anhydride-grafted polypropylene and 0.012 parts of dicumyl peroxide, melt and blend for 20 minutes, turn off the heating, continue stirring until the temperature drops below 60℃, discharge the material, pulverize and pass through a 200-mesh sieve to obtain modified talc powder.

[0026] The nucleating agent is prepared as follows: 0.64 parts of nucleating agent 3988 and 0.16 parts of polyethylene wax are mixed and added to a twin-screw extruder for extrusion. The extrusion parameters are set as follows: feeding section 180℃, melting section 210℃, homogenization section 200℃, die head 210℃, screw speed 250rpm. After water cooling and pelletizing, the mixture is pulverized into powder to obtain the nucleating agent.

[0027] The preparation method of crosslinked modified POE is as follows: Preheat the internal mixer to 160℃, add 8 parts of POE, and internally mix and melt at 60 rpm for 5 min. Add 0.024 parts of dicumyl peroxide, adjust the speed to 80 rpm and internally mix for 10 min. Cool to room temperature, pulverize into granules, and obtain crosslinked modified POE.

[0028] The method for preparing the mixed fiber is as follows: KH560 is added to deionized water, the pH value is adjusted to 4-5 with dilute hydrochloric acid, and the mixture is stirred and hydrolyzed for 30 min to obtain a 3wt% KH560 aqueous solution; alkali-free glass fiber and PAN-based carbon fiber are respectively immersed in the KH560 aqueous solution (20 times the total mass of the fiber) and pretreated by soaking at room temperature for 2 h, with stirring once every 30 min during the process; after soaking, the fiber is taken out and placed in a 100℃ forced-air oven to dry for 3 h, then removed and cooled to room temperature, and the pretreated glass fiber and carbon fiber are mixed at a mass ratio of 2:1 to obtain the mixed fiber.

[0029] Antioxidant 1010 and antioxidant 168 were added to a mixer at a mass ratio of 2:1 and mixed at 1000 rpm for 10 min to obtain a composite antioxidant. Deionized water (5 times the total mass of antioxidants) was added to the composite antioxidant and stirred to form a suspension. Polyvinyl alcohol (shell material, 25% of the total mass of antioxidants) was added, the temperature was raised to 65℃, and the mixture was stirred at 500 rpm. The pH was adjusted to 3-4 with 10 wt% hydrochloric acid, and formaldehyde (10% of the mass of polyvinyl alcohol) was added dropwise at a rate of 1 drop / s. The mixture was stirred at a constant temperature for 2 h, centrifuged at 8000 rpm for 15 min, and the resulting precipitate was placed in a vacuum drying oven and dried at 70℃ and -0.08 MPa for 6 h. After pulverizing, the precipitate was passed through a 100-mesh sieve to obtain the microcapsule antioxidant.

[0030] Add 65 parts polypropylene, 4 parts modified talc, 0.8 parts nucleating agent, 6 parts crosslinked modified POE, 0.5 parts calcium stearate, and 0.3 parts polyethylene wax to a mixer. Mix at 1000 rpm for 15 minutes at 85°C, stopping once during the mixing process. Manually agitate the bottom material to ensure no dead zones. Turn off the heating and continue mixing until the temperature drops below 40°C to obtain a premix. Add the premix to the main feed inlet at a feed rate of 20 kg / h, and add 12 parts of mixed fiber to the side feed inlet (section 3) at a feed rate of 3 kg / h. 1.5 parts of microencapsulated antioxidant were added to the side feed port 2 (5-section barrel) at a feed rate of 0.1 kg / h. After extrusion, the extruder was turned on and water-cooled into pellets. The pellets were then dried in an 80℃ forced-air oven for 2 hours to obtain polypropylene composite material for automotive interiors. Extrusion parameters were set as follows: screw speed: 250 rpm; feed section 170℃ → 1st barrel section 180℃ → 2nd barrel section 185℃ → 3rd barrel section 190℃ (side feed port 1) → 4th barrel section 195℃ → 5th barrel section 195℃ (side feed port 2) → 6th barrel section 190℃ → die head 185℃. Example 2

[0031] Referring to the preparation method and parameters of Example 1, the difference is that when preparing modified talc, the talc is added to a high-speed mixer and then heated to 165°C, and the melt blending time is 25 min; when preparing the nucleating agent, the amount of nucleating agent 3988 is 1 part and the amount of polyethylene wax is 0.23 parts; when preparing polypropylene composite material, the amount of polypropylene is 70 parts, the amount of modified talc is 6 parts, and the amount of nucleating agent is 1.2 parts. Example 3

[0032] Referring to the preparation method and parameters of Example 1, the difference is that when preparing modified talc, the talc is added to a high-speed mixer and then heated to 180°C, and the melt blending time is 30 min; when preparing the nucleating agent, the amount of nucleating agent 3988 is 1.2 parts and the amount of polyethylene wax is 0.3 parts; when preparing polypropylene composite material, the amount of polypropylene is 75 parts, the amount of modified talc is 8 parts, and the amount of nucleating agent is 1.5 parts.

[0033] Comparative Example 1 The preparation method and parameters were the same as in Example 1, except that the talc powder was not modified.

[0034] Comparative Example 2 The preparation method and parameters were the same as in Example 1, except that no modified talc was added.

[0035] Comparative Example 3 The preparation method and parameters of Example 1 are the same, except that only sorbitol-based nucleating agent 3988 is used as the nucleating agent.

[0036] Comparative Example 4 The preparation method and parameters were the same as in Example 1, except that no nucleating agent was added.

[0037] Experimental Example 1: Mechanical Properties and Aging Resistance Testing Tensile strength was tested according to ISO 527; flexural strength was tested according to ISO 178; notched impact strength was tested according to ISO 180; thermal aging was tested according to GB / T 3512, and the tensile strength before and after aging was tested and the retention rate was calculated; the results are shown in Table 1 and... Figure 1 As shown.

[0038] Table 1 Mechanical properties and aging resistance tests of Examples 1-3 and Comparative Examples 1-4

[0039] From Table 1 and Figure 1 As can be seen from Examples 1-3, the modified talc binds to the PP matrix through chemical bonds, and the uniformly dispersed lamellar structure enhances rigidity while avoiding the decrease in toughness caused by traditional talc. The modified nucleating agent induces the formation of fine grains in PP, which not only enhances tensile strength and heat distortion temperature but also hinders the diffusion of aging molecular chains through dense crystals. When the two work synergistically, the increased rigidity of talc and the crystallization strengthening of the nucleating agent are superimposed, further optimizing the mechanical properties of the material. At the same time, the interface between the refined grains of the nucleating agent and talc forms a "structural barrier," delaying the thermo-oxidative aging process and achieving a simultaneous breakthrough in "rigidity-toughness balance" and "anti-aging enhancement." This allows the material to maintain structural stability while extending the anti-aging period, resulting in a composite material with a tensile strength of up to 28.2 MPa, a flexural strength of up to 34.5 MPa, and a notched impact strength of up to 24.6 KJ / m. 2The tensile strength retention rate before and after aging can reach 94.4%. In Comparative Example 1, without modification of talc, the talc surface lacks chemical bonds, forming stress concentration points in the matrix. Under external force, this easily leads to crack propagation, resulting in decreased strength and toughness. Simultaneously, the agglomerated talc cannot form a uniform "structural barrier," accelerating the diffusion rate of molecular chains during thermo-oxidative aging and weakening anti-aging performance. The lamellar structure of modified talc can hinder the movement of PP molecular chains. In Comparative Example 2, without the addition of modified talc, the material loses its rigid core support, but the toughness is slightly improved. Furthermore, the chemical bond between modified talc and the matrix enhances structural density; its absence makes thermo-oxidative aging more likely to penetrate, leading to a decline in anti-aging performance. In Comparative Example 3, only sorbitol-based nucleating agent 3988 was used as the nucleating agent, without polyethylene wax coating. Uncoated nucleating agents are prone to agglomeration, only locally inducing PP crystallization, resulting in uneven grain size and diminished mechanical property improvement. Simultaneously, the uneven grains cannot form a dense "physical barrier," hindering and weakening molecular chain diffusion during thermo-oxidative aging, thus reducing anti-aging performance. In Comparative Example 4, without the addition of a nucleating agent, the coarse grains formed by natural PP crystallization are prone to stress concentration, making cracks easily propagate under external force, leading to a sharp drop in strength and toughness. Furthermore, the gaps between the coarse grains provide channels for thermo-oxidative aging, accelerating molecular chain degradation and diffusion, and severely reducing anti-aging performance. Example 4

[0040] The preparation method and parameters of Example 2 are the same, except that when preparing crosslinked modified POE, the preheating temperature of the internal mixer is 165°C, and after adding dicumyl peroxide, the internal mixer is mixed for 12 minutes; the mass ratio of pretreated glass fiber to carbon fiber in the mixed fiber is 3.5:1; the amount of crosslinked modified POE is 7.5 parts; and the amount of mixed fiber is 15 parts. Example 5

[0041] The preparation method and parameters of Example 2 are the same, except that when preparing crosslinked modified POE, the preheating temperature of the internal mixer is 170°C, and after adding dicumyl peroxide, the internal mixer is mixed for 15 min; the mass ratio of pretreated glass fiber to carbon fiber in the mixed fiber is 5:1; the amount of crosslinked modified POE is 9 parts; and the amount of mixed fiber is 18 parts.

[0042] Comparative Example 5 The preparation method and parameters were the same as in Example 2, except that POE was not crosslinked.

[0043] Comparative Example 6 The preparation method and parameters were the same as in Example 2, except that no cross-linked modified POE was added.

[0044] Comparative Example 7 The preparation method and parameters are the same as in Example 2, except that the glass fiber and carbon fiber were not pretreated.

[0045] Comparative Example 8 The preparation method and parameters of Example 2 are the same, except that only 12 parts of pretreated glass fiber are added to the composite material (the pretreatment method remains the same).

[0046] Comparative Example 9 The preparation method and parameters of Example 2 are the same, except that only 12 parts of pretreated carbon fiber are added to the composite material (the pretreatment method remains the same).

[0047] Experiment Example 2: Mechanical Property Testing Tensile strength was tested according to ISO 527 standard; flexural modulus was tested according to ISO 178 standard; notched impact strength was tested according to ISO 180 standard; the results are shown in Table 2.

[0048] Table 2 Mechanical property tests of Examples 2, 4-5 and Comparative Examples 5-9

[0049] As shown in Table 2, in Examples 2 and 4-5, the hybrid fibers pretreated with KH560 intertwine to form a network structure in the matrix. Glass fibers enhance rigidity, while carbon fibers supplement toughness, providing basic mechanical support for the material. Crosslinked modified POE is uniformly distributed as an elastic dispersed phase, absorbing energy and alleviating stress concentration upon impact. Through their synergistic effect, the fiber network strengthens the material's structural strength, preventing deformation under stress, while the elastic deformation of POE enhances impact resistance. Simultaneously, the three-dimensional network structure of crosslinked POE prevents strength loss due to toughening, solving the problem of "difficulty in balancing rigidity and toughness, and inevitable strength reduction with toughening." This results in a composite material with both excellent structural strength and impact resistance, suitable for the diverse mechanical requirements of automotive interior parts. The resulting composite material exhibits a tensile strength of 28.8 MPa, a flexural modulus of 1995 MPa, and a notched impact strength of 25.1 KJ / m². 2In Comparative Example 5, POE was not cross-linked modified, resulting in highly mobile molecular chains and weak interfacial bonding with PP. Under impact, it could not effectively absorb energy and instead became stress concentration points due to uneven dispersion, leading to a sharp drop in impact strength. Simultaneously, the flexible chains of uncross-linked POE easily disrupted the structural integrity of the PP matrix, causing a decline in tensile strength and flexural modulus. In Comparative Example 6, the absence of cross-linked modified POE resulted in the lack of an elastic dispersed phase to absorb energy under impact, making the material prone to brittle fracture. The PP matrix, unaffected by the flexible chains of POE, had a more compact molecular chain arrangement, thus slightly increasing tensile strength and flexural modulus. In Comparative Example 7, glass fibers and carbon fibers were not pretreated, resulting in a lack of coupling agent bridging the fiber surface and weak interfacial bonding with the PP matrix. They easily aggregated within the matrix and were prone to peeling off. Under stress, the fibers could not effectively bear the load, and instead, internal defects formed due to aggregation led to a significant decrease in tensile strength and flexural modulus. Furthermore, the weak interfacial bonding between the fiber and the matrix prevented the transfer of impact energy to the fiber, significantly weakening its impact resistance. In Comparative Example 8, only 12 parts of pretreated glass fiber were added to the composite material. Although this improved rigidity, the toughness was poor, and it was impossible to achieve both strength and toughness when used alone. In Comparative Example 9, only 12 parts of pretreated carbon fiber were added to the composite material. The tensile modulus of carbon fiber is lower than that of glass fiber. When used alone, it cannot provide sufficient rigidity for the material, so the tensile strength and flexural modulus decreased significantly. Example 6

[0050] The preparation method and parameters of Example 4 are the same, except that when preparing the microcapsule antioxidant, the mixing time of the composite antioxidant is 15 min, the amount of polyvinyl alcohol is 30% of the total mass of the antioxidant, the amount of microcapsule antioxidant is 2 parts, the feeding rate of the premix is ​​21 kg / h, and the feeding rate of the mixed fiber is 4 kg / h. Example 7

[0051] Referring to the preparation method and parameters of Example 4, the difference is that when preparing the microcapsule antioxidant, the mixing time of the composite antioxidant is 20 min, the amount of polyvinyl alcohol is 35% of the total mass of the antioxidant, the amount of microcapsule antioxidant is 2.5 parts, the feeding rate of the premix is ​​22 kg / h, and the feeding rate of the mixed fiber is 4.5 kg / h.

[0052] Comparative Example 10 The preparation method and parameters were the same as in Example 4, except that no microcapsule antioxidant was added.

[0053] Comparative Example 11 The preparation method and parameters of Example 4 are the same, except that the antioxidants are not made into microcapsules, but antioxidants 1010 and antioxidant 168 are directly added to the composite material in a mass ratio of 2:1.

[0054] Comparative Example 12 The preparation method and parameters of Example 4 are the same, except that only 1.5 parts of antioxidant 1010 are added to the composite material.

[0055] Comparative Example 13 The preparation method and parameters of Example 4 are the same, except that only 1.5 parts of antioxidant 168 are added to the composite material.

[0056] Comparative Example 14 The preparation method and parameters of Example 4 are the same, except that the segmented feeding extrusion process is not used. Instead, the premix, mixed fiber and microcapsule antioxidant are added together to the main feed port.

[0057] Experiment Example 3: Aging Resistance Test The aging resistance was tested according to the method in Experiment Example 1; the results are shown in Table 3.

[0058] Table 3. Aging resistance test results of Examples 4, 6-7, and Comparative Examples 10-14

[0059] As shown in Table 3, in Examples 4 and 6-7, the synergistic strategy of microencapsulated antioxidants and segmented feeding processes achieved a breakthrough in the long-term thermo-oxidative aging resistance of the composite material. Traditional antioxidants are prone to volatilization and decomposition during high-temperature extrusion, resulting in a significant reduction in their effectiveness in the final product. This invention, through microencapsulation technology, encapsulates antioxidants 1010 and 168, effectively protecting them during high-temperature processing and maximizing their activity. Furthermore, with the segmented feeding process, the heat-sensitive microencapsulated antioxidants are added downstream, further preventing degradation and ensuring the microcapsules remain intact in the product. The antioxidants are continuously and slowly released during long-term use, providing durable and stable antioxidant protection at high temperatures and greatly extending the material's service life. The tensile strength retention rate of the resulting composite material before and after aging reaches 95.0%. In Comparative Example 10, without the addition of microencapsulated antioxidants, the PP matrix was prone to molecular chain breakage under high-temperature conditions, generating a large number of peroxide free radicals and hydroperoxides, triggering a chain degradation reaction. Simultaneously, the material's own structural barriers (such as refined grains and fiber networks) could only delay aging but could not prevent free radical diffusion, leading to a rapid acceleration of the aging rate and a significant loss of tensile strength after aging. In Comparative Example 11, the antioxidants were not microencapsulated; instead, antioxidants 1010 and 168 were directly added to the composite material at a 2:1 mass ratio. Without shell protection, the antioxidants were prone to volatilization and migration under the high temperatures of extrusion processing. Furthermore, during the aging process, the antioxidants were directly exposed to the environment, rapidly capturing free radicals and being consumed, thus failing to continuously inhibit subsequent aging reactions. In Comparative Example 12, only 1.5 parts of antioxidant 1010 were added to the composite material. It could only react with peroxide free radicals through its own hydroxyl groups, terminating the free radical chain reaction. However, it could not treat the hydroperoxides generated during thermo-oxidative aging. The hydroperoxides would further decompose into new free radicals, triggering molecular chain degradation again, resulting in incomplete antioxidant effect and a lower tensile strength retention rate than in the examples. In Comparative Example 13, only 1.5 parts of antioxidant 168 were added to the composite material. It could only react with hydroperoxides through phosphorus atoms, converting them into stable compounds. However, it could not combine with peroxide free radicals. The generated peroxide free radicals would continuously attack the PP molecular chain, triggering chain degradation and leading to a rapid aging rate of the material. In Comparative Example 14, a segmented feeding extrusion process was not used. Instead, the premix, mixed fibers, and microcapsule antioxidants were added together to the main feed port. Under the high temperature and high shear of the main feed section to the melting section, the shell of the microcapsule antioxidants was prone to rupture, causing premature release and loss of the antioxidants, resulting in decreased aging resistance.

[0060] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a polypropylene composite material for automotive interiors, characterized in that: The preparation method is as follows: Polypropylene, modified talc, nucleating agent, crosslinked modified POE, calcium stearate and polyethylene wax are added to a mixer and stirred to obtain a premix; the premix is ​​added to the main feed port, the mixed fiber is added to the first side feed port, the microcapsule antioxidant is added to the second side feed port, and after extrusion, it is water-cooled and pelletized, and then dried to obtain the polypropylene composite material for automotive interiors. The modified talc powder is obtained by grafting maleic anhydride-grafted polypropylene onto flake talc powder. The crosslinked modified POE is obtained by reacting POE with dicumyl peroxide; The hybrid fiber is obtained by mixing glass fiber and carbon fiber after pretreatment respectively; The microcapsule antioxidant is prepared by mixing antioxidant 1010 and antioxidant 168.

2. The method for preparing a polypropylene composite material for automotive interiors according to claim 1, characterized in that: The modified talc powder preparation method is as follows: add flake talc powder to a high-speed mixer, preheat the temperature, add the maleic anhydride-grafted polypropylene and the dicumyl peroxide for melt mixing, turn off the heating, continue stirring until the temperature drops below 60°C and discharge the material, pulverize and sieve to obtain the modified talc powder.

3. The method for preparing a polypropylene composite material for automotive interiors according to claim 1, characterized in that: The nucleating agent is prepared as follows: sorbitol-based nucleating agent and polyethylene wax are mixed, added to a twin-screw extruder for extrusion, water-cooled, pelletized, and then pulverized to obtain the nucleating agent.

4. The method for preparing a polypropylene composite material for automotive interiors according to claim 1, characterized in that: The preparation method of the crosslinked modified POE is as follows: preheat the internal mixer, add the POE and melt it, add the dicumyl peroxide and melt it, cool it to room temperature, and pulverize it to obtain the crosslinked modified POE.

5. The method for preparing a polypropylene composite material for automotive interiors according to claim 1, characterized in that: The method for preparing the hybrid fiber is as follows: alkali-free glass fiber and PAN-based carbon fiber are respectively immersed in KH560 aqueous solution and pretreated by soaking at room temperature; after soaking, they are taken out, dried, cooled to room temperature, and mixed to obtain the hybrid fiber.

6. The method for preparing a polypropylene composite material for automotive interiors according to claim 1, characterized in that: The preparation method of the microcapsule antioxidant is as follows: antioxidant 1010 and antioxidant 168 are added to a mixer and mixed to obtain a composite antioxidant; deionized water is added to the composite antioxidant and stirred to form a suspension; polyvinyl alcohol is added, heated and stirred, pH is adjusted with hydrochloric acid, formaldehyde is added dropwise and stirred at a constant temperature, centrifuged, the obtained precipitate is dried, pulverized and sieved to obtain the microcapsule antioxidant.

7. The method for preparing a polypropylene composite material for automotive interiors according to claim 1, characterized in that: The feeding rate of the premix is ​​20-22 kg / h; the feeding rate of the mixed fiber is 3-4.5 kg / h.

8. A polypropylene composite material for automotive interiors, characterized in that: The polypropylene composite material for automotive interiors is prepared by any one of the preparation methods of claims 1-7; the raw materials for preparing the polypropylene composite material for automotive interiors include polypropylene, modified talc, nucleating agent, crosslinked modified POE, microencapsulated antioxidant and mixed fiber.

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