Top whitening resistant polypropylene composite material as well as preparation method and application thereof

Abstract

The invention relates to the technical field of high polymer material modification, in particular to a top whitening resistant polypropylene composite material as well as a preparation method and application thereof. The top whitening resistant polypropylene composite material is prepared from the following components in parts by weight: 60 to 80 parts of polypropylene resin, 20 to 30 parts of talcum powder, 5 to 15 parts of hydrogenated styrene-butadiene-styrene block copolymer, 0.1 to 0.5 part of beta crystal form nucleating agent, 3 to 8 parts of maleic anhydride grafted polypropylene, 0.3 to 1 part of composite antioxidant and 0.5 to 2 parts of zinc stearate. Through the synergistic effect of the hydrogenated styrene-butadiene-styrene block copolymer toughening system and the beta crystal form nucleating agent in a specific formula, high rigidity (the filling amount of talcum powder reaches 20-30 parts) is kept, and meanwhile, the top whitening resistance of the composite material is remarkably improved; the method is suitable for parts such as automobile dashboards and door plates which have strict requirements on surface quality.

Description

Technical Field

[0001] This invention relates to the field of polymer material modification technology, specifically to an anti-whitening polypropylene composite material, its preparation method, and its application. Background Technology

[0002] Polypropylene (PP) has become one of the most widely used plastics in the automotive industry due to its significant advantages such as low cost, low density, excellent comprehensive mechanical properties, and ease of processing. In practical applications, inorganic fillers are often introduced for modification to further improve the rigidity, heat resistance, and dimensional stability of polypropylene. Talc, with its layered structure, high whiteness, and economical price, has become the most commonly used inorganic filler in the modification of polypropylene.

[0003] However, while high-filled talc significantly improves material rigidity, it also causes a series of negative problems. On the one hand, the material's toughness decreases significantly, its resistance to whitening deteriorates sharply, and its processing fluidity worsens; these problems become more severe with higher talc filler content. On the other hand, high solid filler content increases melt viscosity and reduces material fluidity, making it extremely difficult to mold and fill complex structural products.

[0004] Currently, the conventional method to improve the toughness of filled polypropylene is to add elastomers, such as polyolefin elastomers (POE) and ethylene propylene diene monomer (EPDM). However, in the process of improving toughness, these traditional elastomers lead to a significant loss in the material's rigidity, heat resistance, and surface hardness, making it difficult to achieve a balance in the material's overall performance. Therefore, developing a polypropylene composite material that can maintain high rigidity (i.e., high talc filler content) while also possessing excellent anti-whitening properties and good toughness to meet the stringent requirements for appearance and performance in high-end interior components such as automotive dashboards and door panels has become a pressing technical challenge in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the objective of this invention can be achieved through the following technical solutions: A talc-filled polypropylene composite material resistant to top whitening is made from the following components in parts by weight: 60-80 parts of polypropylene 20-30 parts talcum powder 5-15 parts of styrene-butadiene-styrene block copolymer (SEBS) 0.1-0.5 parts of β-crystal nucleating agent. 3-8 parts of maleic anhydride-grafted polypropylene (PP-g-MAH). 0.3-1 part of compound antioxidant, 0.5 to 5 parts of zinc stearate.

[0006] Furthermore, the polypropylene described above has a melt flow rate of 20-60 g / 10 min at 230°C and 2.16 kg.

[0007] Furthermore, the talc powder is a high aspect ratio flake talc powder that has undergone surface modification treatment with a silane coupling agent, and its particle size D97≤10μm.

[0008] Furthermore, in the hydrogenated styrene-butadiene-styrene block copolymer, the degree of hydrogenation of the ethylene-butadiene block is greater than 95%, and the styrene content is 20-35%.

[0009] Selection of SEBS Toughening System: Compared with traditional POE and EPDM, SEBS has a saturated molecular chain structure, and its resistance to heat and oxygen aging is far superior to the former, avoiding performance degradation caused by degradation during processing and use. Its unique "island" structure (rubber segments as the sea, plastic segments as islands) can more effectively initiate, terminate, and absorb impact energy, thus achieving high-efficiency toughening with a small addition amount and minimal loss of rigidity. Furthermore, the β-crystal nucleating agent is an aromatic amide compound.

[0010] The core function of β-crystal nucleating agents: β-crystalline polypropylene exhibits significantly higher impact toughness and ductility than the common α-crystalline form. The addition of β-crystal nucleating agents induces the formation of a high content of β-crystals in the polypropylene matrix, fundamentally enhancing the matrix's impact resistance and stress deformation resistance, which is crucial for improving its resistance to whitening.

[0011] Furthermore, the grafting rate of the maleic anhydride-grafted polypropylene is 0.8-1.5%, and the melt flow rate of its matrix resin is not less than 50 g / 10 min at 230℃ / 2.16 kg.

[0012] Synergistic bridging of PP-g-MAH: Maleic anhydride-grafted polypropylene (PP-g-MAH) plays multiple roles in this system. Its maleic anhydride groups can chemically react with the SEBS molecular chains and the hydroxyl groups on the surface of talc, forming a strong interfacial bond; its polypropylene segments are completely compatible with the matrix PP resin. This constructs a robust "bridge" between the SEBS elastomer, talc filler, and PP matrix, greatly improving interfacial compatibility, effectively transferring and dispersing stress, preventing interfacial debonding, and thus significantly suppressing the occurrence of top whitening.

[0013] The antioxidant is at least one of hindered phenolic, thioester, and phosphite antioxidants. Preferably, the hindered phenolic antioxidant is antioxidant 1010, the thioester antioxidant is antioxidant DLTP, and the phosphite antioxidant is antioxidant 168.

[0014] A method for preparing a talc-filled polypropylene composite material resistant to top whitening, characterized by comprising the following steps: S1. Weigh each component according to the stated weight ratio; S2. Add polypropylene resin, β-crystal nucleating agent, composite antioxidant and zinc stearate into a high-speed mixer to obtain a premix; S3. The premix obtained in step S2 is added from the main feed port of the twin-screw extruder; the hydrogenated styrene-butadiene-styrene block copolymer and maleic anhydride grafted polypropylene are premixed and added from the first side feed port; talc is added from the second side feed port. S4. After melt extrusion, cooling, traction, and pelletizing, the talc-filled polypropylene composite material with anti-whitening properties is obtained. The processing temperature of the twin-screw extruder is set to 180-200℃, and the screw speed is 300-500rpm.

[0015] Furthermore, in step S2, the mixing conditions of the high-speed mixer are: mixing for 3-5 minutes at a speed of 800-1200 rpm. In step S3, the first side feed port is located in the early stage of the melting section, and the second side feed port is located in the middle and late stages of the melting section.

[0016] The above-mentioned talc-filled polypropylene composite material with a white top coating is used in the preparation of automotive interior parts, which include automotive dashboards, door panels, pillar guards, or sub-dashboards.

[0017] The beneficial effects of this invention are: 1. By improving the polypropylene matrix structure through β-crystal nucleating agents and optimizing the interfacial compatibility of PP-g-MAH, the possibility of whitening under external force is significantly suppressed, thus meeting the high requirements of automotive interior parts for appearance quality.

[0018] 2. The SEBS toughening system improves the toughness of materials while minimizing the loss of rigidity. Combined with the high rigidity brought by high-filled talc, the composite material can simultaneously possess high flexural modulus and notched impact strength, achieving a good balance between rigidity and toughness. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0020] Example 1 Take 70 parts of copolymer polypropylene, 0.3 parts of β-crystal nucleating agent, 0.5 parts of composite antioxidant, and 1 part of zinc stearate, mix them evenly, and add them to the twin-screw extruder through the main feed port. Add 10 parts of SEBS and 5 parts of maleic anhydride grafted polypropylene premix through the first side feed port, and then add 25 parts of talc powder through the second side feed port. After melting, mixing, dispersing, extruding, water cooling, and pelletizing, polypropylene composite material is obtained. The twin-screw extruder has a screw length-to-diameter ratio of 40:1, an extrusion temperature of 180-200℃, and a screw speed of 400 r / min.

[0021] Composite material particles are obtained through melt extrusion, water cooling, air drying, and pelletizing.

[0022] After drying the granules at 80°C for 4 hours, they were injection molded into standard test strips for performance testing.

[0023] Example 2 Take 65 parts of copolymer polypropylene, 0.5 parts of β-crystal nucleating agent, 0.8 parts of composite antioxidant, and 1.5 parts of zinc stearate, mix them evenly, and add them to the twin-screw extruder through the main feed port. Add 15 parts of SEBS and 8 parts of maleic anhydride grafted polypropylene premix through the first side feed port, and then add 30 parts of talc powder through the second side feed port. After melting, mixing, dispersing, extruding, water cooling, and pelletizing, polypropylene composite material is obtained. The twin-screw extruder has a screw length-to-diameter ratio of 40:1, an extrusion temperature of 180-200℃, and a screw speed of 400 r / min.

[0024] Comparative Example 1 Compared to Example 1, SEBS and PP-g-MAH were not added, and their weight parts were made up with an equal amount of PP resin. The remaining components and preparation method remained unchanged.

[0025] Comparative Example 2 Compared to Example 1, no β-crystal nucleating agent was added, and its weight was made up with an equal amount of PP resin. The remaining components and preparation method remained unchanged.

[0026] Comparative Example 3 Compared to Example 1, SEBS was replaced with an equal amount of POE (Engage8150, Dow Chemical). The remaining components and preparation methods remained unchanged.

[0027] Comparative Example 4 Compared to Example 1, the copolymer polypropylene with a melt flow rate (230℃ / 2.16kg) of 20-60 g / 10 min was replaced with an equal amount of low-flow polypropylene with a melt flow rate (230℃ / 2.16kg) of 15 g / 10 min. The remaining components and preparation method remained unchanged.

[0028] Objective: To verify the effect of matrix resin flowability on processability and final properties.

[0029] Comparative Example 5 Compared to Example 1, the high aspect ratio flaky talc powder with a particle size D97 ≤ 10 μm was replaced with an equal amount of ordinary talc powder with a D97 of approximately 20 μm. The remaining components and preparation method remained unchanged.

[0030] Objective: To verify the key effects of talc particle size and morphology on rigidity, toughness and surface properties (resistance to top whitening).

[0031] Comparative Example 6 Compared to Example 1, SEBS (YH-503) with a hydrogenation degree greater than 95% and a styrene content of 20-35% was replaced with an equal amount of SEBS with a hydrogenation degree of 90% and a styrene content of 15%. The remaining components and preparation method remained unchanged.

[0032] Objective: To verify the effects of key SEBS parameters (degree of hydrogenation, styrene content) on the thermal stability, stiffness-toughness balance, and resistance to top whitening of the material.

[0033] The performance of the materials in the above embodiments and comparative examples was tested, and the results are shown in the table below: Table 1: Performance of each sample in Examples 1-2 and Comparative Examples 1-6 As can be seen from the test data in Table 1, the table above shows that: 1. The notched impact strength of Comparative Example 1 was only 24.3% (4.5 / 18.5) of that of Example 1, and the material was extremely brittle. This proves that the "island" structure of SEBS (rubber segments absorb impact energy) is the core of improving toughness. Without SEBS, the rigidity advantage (higher flexural modulus) brought by high-filled talc is completely offset by the sharp decrease in toughness, failing to meet the impact resistance requirements of automotive interior parts. Comparative Example 1 exhibited severe whitening, essentially due to poor interfacial compatibility between the PP matrix and talc. The lack of the "bridging effect" of PP-g-MAH (maleic anhydride groups combine with talc hydroxyl groups, PP segments are compatible with the matrix) makes the interface prone to debonding and generating microcracks under external force, manifesting as surface whitening. In contrast, Example 1, due to its strong interfacial bonding, allows for uniform stress transmission and exhibits no whitening. Since only SEBS and PP-g-MAH were removed while the other components remained unchanged, the difference in test results can be directly attributed to these two components, proving that they are necessary conditions for achieving "rigidity-toughness balance + resistance to whitening".

[0034] 2. The impact toughness of β-crystalline PP is significantly higher than that of ordinary α-crystalline PP. In Comparative Example 2, due to the absence of a β-crystalline nucleating agent, the matrix is ​​predominantly α-crystalline, resulting in a 19% decrease in notched impact strength ((18.5-15.0) / 18.5). This demonstrates that the β-crystalline nucleating agent, by inducing a high content of β-crystals, enhances impact resistance at the matrix structure level, serving as an important supplement to the SEBS toughening system. Comparative Example 2 exhibits significant whitening at the top, likely due to the poor stress deformation resistance of α-crystalline PP. Under external force, the matrix is ​​prone to plastic deformation, and even with SEBS and PP-g-MAH interface optimization, the matrix's own deformation still leads to surface whitening. In contrast, the β-crystalline matrix in Example 1 can disperse stress and suppress deformation, achieving "no whitening" in synergy with interface optimization. The melt flow rates of both are similar (25 vs 26), proving that the performance difference is unrelated to processing fluidity and is solely due to crystal structure regulation.

[0035] 3. POE is an amorphous elastomer, and toughening it significantly reduces material rigidity—the flexural modulus of Comparative Example 3 is 10.6% lower than that of Example 1 (2350-2100), proving that the "plastic segment (styrene)" of SEBS can synergistically maintain rigidity with the PP matrix, solving the problem of "toughening inevitably reduces rigidity" in traditional elastomers. Although POE has good compatibility with PP, its molecular chains lack rigid segments for support, making it prone to localized deformation under external forces, resulting in noticeable whitening. In contrast, the "island" structure of SEBS provides support through the plastic segments, while the rubber segments absorb impact, balancing toughness and resistance to deformation. Therefore, Example 1 showed no whitening. The comparison shows that SEBS is superior to POE in terms of "rigidity-toughness balance + resistance to whitening," proving the rationality of choosing SEBS instead of traditional elastomers in this invention.

[0036] 4. The MFR of Comparative Example 4 was only 32% (8 / 25) of that of Example 1, indicating that low-flow PP leads to a significant increase in melt viscosity - uneven dispersion of components during processing (such as SEBS and talc powder cannot be evenly distributed), which directly affects the final performance.

[0037] The main reason is that: Deterioration in resistance to whitening: Uneven dispersion leads to weak adhesion at local interfaces, making it prone to detachment and whitening under external force; Decreased toughness: Uneven dispersion of SEBS prevents the formation of a continuous toughening network, thus the impact energy cannot be effectively absorbed, resulting in a 19% decrease in notched impact strength.

[0038] The present invention specifies the MFR of PP as 20-60 g / 10 min, which is not set arbitrarily, but is a key parameter to ensure uniform dispersion of components and smooth processing.

[0039] 5. High aspect ratio flaky talc can form a "lamellar overlapping structure" in the PP matrix, which significantly enhances rigidity; while ordinary coarse-grained talc does not have this structure. Therefore, the flexural modulus of Comparative Example 4 is 17% lower than that of Example 1 (2350-1950), proving that the "high aspect ratio + fine particle size" of talc is the core to achieve high rigidity.

[0040] Coarse-grained talc has a small specific surface area, resulting in less contact area with the PP matrix and weak interfacial adhesion. Under external force, it is prone to interfacial cracks, which reduces impact strength (by 32.4%) and causes severe whitening. In contrast, fine-grained talc interacts more fully with PP-g-MAH, resulting in a stronger interface and better performance.

[0041] The present invention specifies that the talc powder with "D97≤10μm+high aspect ratio+silane modification" is a necessary condition that balances rigidity, toughness and resistance to top whitening, and cannot be replaced by ordinary talc powder.

[0042] 6. When the hydrogenation degree of SEBS is >95%, the molecular chain is highly saturated, has good resistance to heat and oxygen aging, and the rubber segment (ethylene-butadiene) is elastically stable; while SEBS with a hydrogenation degree of 90% contains unsaturated double bonds, which are easily degraded or cross-linked, resulting in a decrease in the elasticity of the rubber segment, thus reducing the impact strength by 13.5% (18.5-16.0).

[0043] When the styrene content is 20-35%, the plastic segments of SEBS can work together with the PP matrix to maintain rigidity; however, when the styrene content is 15%, the proportion of plastic segments is insufficient, the supporting effect is weakened, and the flexural modulus decreases by 6.4% (2350-2200).

[0044] Low hydrogenation leads to insufficient elasticity of SEBS, and low styrene content results in weak support. The combined effect of these two factors reduces the material's resistance to deformation, thus causing noticeable whitening at the top. In contrast, the optimized SEBS parameters in Example 1 balance elasticity and support, eliminating the whitening phenomenon.

[0045] This invention specifies that SEBS with "hydrogenation degree > 95% + styrene content 20-35%" is the key to ensuring stable performance and achieving a balance between rigidity and toughness, and not just any SEBS can be used.

[0046] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0047] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A talc-filled polypropylene composite material resistant to top whitening, characterized in that, By weight, it includes the following components 60-80 parts of polypropylene 20-30 parts talcum powder 5-15 parts of styrene-butadiene-styrene block copolymer, 0.1-0.5 parts of β-crystal nucleating agent. 3-8 parts of maleic anhydride-grafted polypropylene 0.3-1 part of compound antioxidant, 0.5 to 5 parts of zinc stearate.

2. The talc-filled polypropylene composite material with tocopherol resistance according to claim 1, characterized in that: The polypropylene resin is a copolymer polypropylene, and its melt flow rate is 20-60 g / 10 min at 230℃ / 2.16 kg.

3. The talc-filled polypropylene composite material with tocopherol resistance according to claim 1, characterized in that: The talc powder is a high aspect ratio flake talc powder that has undergone surface modification treatment with a silane coupling agent, and its particle size D97≤10μm.

4. The talc-filled polypropylene composite material with tocopherol resistance according to claim 1, characterized in that: In the hydrogenated styrene-butadiene-styrene block copolymer, the degree of hydrogenation of the ethylene-butadiene block is greater than 95%, and the styrene content is 20-35%.

5. The talc-filled polypropylene composite material with tocopherol resistance according to claim 1, characterized in that: The β-crystal nucleating agent is an aromatic amide compound.

6. The talc-filled polypropylene composite material with tocopherol resistance according to claim 1, characterized in that: The grafting rate of the maleic anhydride-grafted polypropylene is 0.8-1.5%, and the melt flow rate of its matrix resin is not less than 50 g / 10 min at 230℃ / 2.16 kg.

7. The talc-filled polypropylene composite material with tocopherol resistance according to claim 1, characterized in that: The composite antioxidant is composed of pentaerythritol tetrakis[β-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate] as the primary antioxidant and tris(2,4-di-tert-butylphenyl)phosphite as the secondary antioxidant in a mass ratio of 1:1 to 1:

2.

8. A method for preparing the talc-filled polypropylene composite material as described in any one of claims 1-7, characterized in that, Includes the following steps: S1. Weigh each component according to the stated weight ratio; S2. Add polypropylene resin, β-crystal nucleating agent, composite antioxidant and zinc stearate into a high-speed mixer to obtain a premix; S3. The premix obtained in step S2 is added from the main feed port of the twin-screw extruder; the hydrogenated styrene-butadiene-styrene block copolymer and maleic anhydride grafted polypropylene are premixed and added from the first side feed port; talc is added from the second side feed port. S4. After melt extrusion, cooling, traction, and pelletizing, the talc-filled polypropylene composite material with anti-whitening properties is obtained. The processing temperature of the twin-screw extruder is set to 180-200℃, and the screw speed is 300-500rpm.

9. The method according to claim 8, characterized in that: In step S2, the mixing conditions of the high-speed mixer are: mixing for 3-5 minutes at a speed of 800-1200 rpm. In step S3, the first side feed port is located in the early stage of the melting section, and the second side feed port is located in the middle and late stages of the melting section.

10. The application of the talc-filled polypropylene composite material according to any one of claims 1-7 in the preparation of automotive interior parts, wherein the automotive interior parts include automotive dashboards, door panels, pillar guards, or sub-dashboards.

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