High-rigidity low-warpage polypropylene material for automobile structural member and preparation method of high-rigidity low-warpage polypropylene material

Abstract

The invention relates to the field of polypropylene materials, in particular to a high-rigidity low-warpage polypropylene material for automobile structural parts and a preparation method of the high-rigidity low-warpage polypropylene material. The polypropylene material comprises the following components in parts by mass: 50-65 parts of polypropylene resin; 10 to 15 parts of talcum powder; 2 to 5 parts of compatilizer; 0.2 part to 0.6 part of an antioxidant; 0.5 to 1.5 parts of a lubricant; 15 to 30 parts of modified glass fiber; wherein the modified glass fiber is alkali-free chopped glass fiber grafted with a beta nucleating agent, and the beta nucleating agent comprises one or more of glutaric acid metal salt, pimelic acid metal salt, adipic acid metal salt, terephthalic acid metal salt and phthalic acid metal salt. By adding the modified glass fiber with the surface grafted with the beta nucleating agent, buckling deformation, caused by anisotropic distribution of the glass fiber, of the polypropylene material is improved, the assembly precision of automobile structural parts is met, and meanwhile the excellent rigidity is achieved.

Description

Technical Field

[0001] The present application relates to the field of polypropylene materials, and in particular to a high-rigidity, low-warpage polypropylene material for automotive structural parts and a preparation method thereof. Background Art

[0002] Polypropylene (PP), with its abundant resources, low price, and lightweight properties, is widely used in the automotive industry, becoming the most widely used and fastest-growing automotive plastic. In recent years, with the rapid development of the automotive industry, the performance requirements for automotive structural components have become increasingly stringent. To improve the mechanical properties of polypropylene used in automotive structural components, adding glass fiber to the polypropylene matrix is ​​an effective method. Glass fiber includes both long and short chopped glass fibers.

[0003] Chopped glass fiber can significantly improve the mechanical properties of polypropylene. However, it has disadvantages such as high shear sensitivity, poor fluidity, high cost, difficulty in processing, high equipment requirements, and prone to fiber floating, making it unsuitable for industrial application. Compared to chopped glass fiber, short-cut glass fiber has low cost, strong processing adaptability, and is not prone to fiber floating. Its improvement in mechanical properties can meet most requirements. Therefore, short-cut glass fiber is widely used to reinforce polypropylene materials. However, due to the dimensional characteristics of short-cut glass fiber and the molding process, short-cut glass fiber reinforced polypropylene materials are prone to warping and deformation, affecting the assembly accuracy and use of automotive structural parts.

[0004] Therefore, developing a high-rigidity, low-warping polypropylene material for automotive structural parts has become a research hotspot in the field of polypropylene materials. Summary of the Invention

[0005] In order to solve the above problems, the present application provides a high-rigidity, low-warpage polypropylene material for automotive structural parts and a preparation method thereof. By adding modified glass fiber grafted with a β-nucleating agent, the polypropylene material has both excellent rigidity and low warpage.

[0006] The first aspect of the present application provides a high-rigidity, low-warpage polypropylene material for automotive structural parts, the polypropylene material comprising the following components calculated in parts by mass: 50-65 parts of polypropylene resin; 10-15 parts of talc; 2-5 parts of a compatibilizer; 0.2-0.6 parts of an antioxidant; 0.5-1.5 parts of a lubricant; and 15-30 parts of modified glass fiber; wherein the modified glass fiber is an alkali-free chopped glass fiber grafted with a β-nucleating agent, and the β-nucleating agent comprises one or more of a metal salt of glutaric acid, a metal salt of pimelic acid, a metal salt of adipate, a metal salt of terephthalic acid, and a metal salt of phthalic acid.

[0007] Through research, the applicant discovered that warping in glass fiber-reinforced polypropylene (PP) materials occurs because the chopped glass fibers have a specific aspect ratio. During the injection molding process, they are prone to rotation under shear, leading to orientation along the flow direction. Talc, commonly used to improve the mechanical properties of PP materials, is an inorganic α-nucleating agent that promotes the formation of spherical α-spherulites in PP. These tightly packed α-spherulite molecular chains form regular segments upon cooling, resulting in high volumetric shrinkage. However, because glass fibers maintain minimal dimensional change at high temperatures and exhibit a rigid structure, the anisotropic orientation of the chopped glass fibers inhibits shrinkage of the PP material along the glass fiber orientation direction (i.e., the injection molding flow direction) during the cooling and crystallization phase. This shrinkage difference causes warping in the PP material and generates tensile stress at the interface, inducing debonding between the PP and the filler. The shrinkage of the PP material in the debonded areas increases further, creating a larger shrinkage gradient compared to the non-debonded areas. This further differential shrinkage leads to a vicious cycle, exacerbating the warping phenomenon.

[0008] The applicants further discovered through research that grafting a β-nucleating compound onto the surface of chopped glass fibers can improve the warpage of polypropylene materials. Analysis suggests that this may be due to the formation of β-lamellae around the glass fibers during cooling, as the β-nucleating agent on the glass fiber surface often induces these β-lamellae to be distributed perpendicular to the glass fiber orientation. Compared to the high shrinkage of α-spherulites, β-lamellae have lower shrinkage characteristics. The β-lamellae distributed perpendicular to the glass fiber orientation balance the high shrinkage caused by the α-spherulites in that direction, thereby reducing the shrinkage of the polypropylene material perpendicular to the fiber orientation and parallel to the fiber orientation, thus alleviating the warpage. Furthermore, the β-lamellae structure possesses excellent toughness, absorbing tensile stress through plastic deformation, ensuring uniform stress transfer and reducing the risk of interfacial debonding. This further avoids further differential shrinkage caused by debonding, further improving the warpage of the polypropylene material. Furthermore, the β-lamellae structure combines with the three-dimensional network of surrounding α-spherulites to form a tightly packed crystal structure. This coexistence of α / β crystals around the glass fibers further enhances the impact resistance of the polypropylene. Compared with other methods of adding β-nucleating agents, such as physical mixing or loading the β-nucleating agent on the glass fiber through crystallization, the grafting method can achieve uniform and stable distribution of the β-nucleating agent on the surface of the glass fiber, and exert an excellent nucleating effect to form specifically oriented β-platelets in specific areas, thereby effectively reducing the shrinkage rate difference and improving the warpage of the chopped glass fiber reinforced polypropylene material. When the mass fraction of the modified glass fiber is within the above range, the polypropylene material has both excellent flexural modulus and low warpage.

[0009] In any embodiment, the preparation method of the modified glass fiber comprises the following steps: (1) dispersing the alkali-free short glass fiber in a mixed solvent of ethanol and deionized water, adding aminopropyl triethoxysilane, stirring and reacting at 60°C-80°C for 10 hours-14 hours, and centrifuging and drying to obtain the surface amino-modified alkali-free short glass fiber; (2) dispersing the dicarboxylic acid compound in dichloromethane, adding dichlorothionyl and catalyst N,N-dimethylformamide, stirring and reacting at 22°C-28°C for 1 hour-3 hours, and removing dichloromethane to obtain the first intermediate product, wherein the dicarboxylic acid compound includes glutaric acid, pimelic acid, adipic acid, , one or more of terephthalic acid and phthalic acid, the molar ratio of the dicarboxylic acid compound to dithionyl chloride is 1:1; (3) dispersing the first intermediate product in dichloromethane, adding the surface amino-modified alkali-free glass fiber, stirring and reacting at 0°C-10°C for 10 hours-14 hours, centrifuging to obtain a solid, and drying to obtain a second intermediate product; (3) dispersing the second intermediate product and a metal hydroxide in methanol, stirring and reacting at 22°C-28°C for 20 hours-28 hours, centrifuging and drying to obtain a modified glass fiber, wherein the metal hydroxide includes at least one of an alkali metal hydroxide and an alkaline earth metal hydroxide.

[0010] After hydrolysis, the siloxy groups in the aminopropyltriethoxysilane molecules generate silanol groups, which can undergo a condensation reaction with a large number of hydroxyl groups on the surface of the glass fiber to form stable chemical bonds, so that the aminopropyltriethoxysilane molecules are firmly connected to the surface of the glass fiber, providing amino active sites for the glass fiber, and obtaining amino-modified chopped glass fibers. Furthermore, by controlling the molar ratio of the dicarboxylic acid compound to thionyl chloride to be 1:1, the unilateral carboxylic acid of the dicarboxylic acid compound is chlorinated, and the obtained first intermediate product and the amino-modified glass fiber undergo an acylation reaction between the amino group and the acyl chloride group under the condition of 0°C-10°C. This reaction has higher activity and the reaction product is easier to purify. The dicarboxylic acid compound is grafted onto the glass fiber to obtain a second intermediate product. Further, the free carboxyl groups of the dicarboxylic acid compound grafted onto the glass fiber are reacted with a metal hydroxide to obtain a glass fiber grafted with a dicarboxylic acid metal salt (such as at least one of glutaric acid metal salt, pimelic acid metal salt, adipate metal salt, terephthalic acid metal salt and phthalic acid metal salt). The special lattice structure formed by the fatty chain or benzene ring and metal ion (such as at least one of alkali metal ion and alkaline earth metal ion) in the dicarboxylic acid compound and the carboxylate group matches the hexagonal crystal parameters of the polypropylene β lamellae, thereby inducing the growth of the β lamellae and achieving improvement in warpage.

[0011] In any embodiment, the dicarboxylic acid compound in step (2) comprises glutaric acid and phthalic acid, and the molar ratio of glutaric acid to phthalic acid is 1:1-3:1.

[0012] Through experimental research, the present application found that the dicarboxylic acid compound includes glutaric acid and phthalic acid, and the molar ratio of glutaric acid to phthalic acid is 1:1-3:1. As a result, when the dicarboxylic acid metal salt grafted on the glass fiber includes a suitable ratio of glutaric acid metal salt and phthalic acid metal salt, the warpage of the polypropylene material is further improved, while having better rigidity. After analysis, this may be because the main body of the glutaric acid metal salt is a flexible fatty chain, and the main body of the phthalic acid metal salt is a rigid benzene ring. The two β-nucleating agents have different nucleation induction temperatures and the size of the final β-spherulites formed. At the appropriate ratio, the synergistic effect makes the temperature range of β-platelets generated during cooling wider, the content of β-platelets generated perpendicular to the orientation direction of the glass fiber higher, and finally includes larger β-spherulites with better toughness and smaller β-spherulites with better strength, thereby achieving further improvement in warpage and better strength.

[0013] In any embodiment, the metal hydroxide in step (4) includes at least one of barium hydroxide and potassium hydroxide.

[0014] Through experimental research, the present application has found that the metal hydroxide includes at least one of barium hydroxide and potassium hydroxide, and the modified glass fiber has an excellent improvement effect on the warpage of the polypropylene material. Through experimental research, the present application has further found that the metal hydroxide is barium hydroxide. The divalent metal ions make the β-nucleating agent formed on the glass fiber have a chelated carboxylate structure, and the strong polarization ability of the barium ions makes the β-nucleating agent more efficient in inducing the formation of β-platelets in the polypropylene matrix, which is conducive to further increasing the content of β-platelets generated perpendicular to the orientation direction of the glass fiber, thereby further improving the warpage of the polypropylene material while also having excellent strength.

[0015] In any embodiment, the mass ratio of the alkali-free chopped glass fibers to the aminopropyltriethoxysilane in step (1) is 4:1-10:1.

[0016] Through experimental research, the present application further found that by controlling the mass ratio of glass fiber to aminopropyltriethoxysilane in step (1) within the above range, the glass fiber has a suitable amino grafting rate and then a suitable β-nucleating agent grafting rate, so that the prepared polypropylene material has both excellent warpage and rigidity.

[0017] In any embodiment, the length of the alkali-free chopped glass fibers in step (1) is 3 mm to 5 mm, and the diameter is 12 μm to 15 μm.

[0018] The length and diameter of the chopped glass fibers are within the above ranges, and have excellent processing capabilities and mechanical property enhancement effects.

[0019] In any embodiment, the polypropylene resin includes a high-impact polypropylene resin and a high-flow polypropylene resin, the high-impact polypropylene resin having a melt index of 0.5 g / 10 min to 20 g / 10 min at 230° C. and 2.16 kg, and the high-flow polypropylene resin having a melt index of 25 g / 10 min to 30 g / 10 min at 230° C. and 2.16 kg.

[0020] High-impact polypropylene resin can provide excellent rigidity, but has poor fluidity and is difficult to injection mold. High-flow polypropylene has good fluidity and can meet the structural requirements of automotive structural parts such as bumper materials during injection molding. It is also beneficial to reduce the shear-induced anisotropic orientation of glass fiber, but has poor rigidity. The compound use of impact-resistant polypropylene resin and high-flow polypropylene resin is beneficial to meet the dual requirements of mechanical properties and processing performance.

[0021] In any embodiment, the antioxidant includes a hindered phenol primary antioxidant 1010 and a phosphite secondary antioxidant 168 .

[0022] The combined use of antioxidants 1010 and 168 is beneficial to improving the thermal stability and antioxidant properties of polypropylene materials.

[0023] In any embodiment, the compatibilizer comprises maleic anhydride grafted polypropylene.

[0024] The maleic anhydride groups in the molecular structure of maleic anhydride grafted polypropylene can form covalent bonds with the surface hydroxyl groups of fillers such as glass fiber and talc, thereby achieving compatibility between the filler and the polypropylene matrix, reducing interfacial debonding, alleviating the deterioration of the warpage of the polypropylene material, and further improving the mechanical properties.

[0025] In any embodiment, the lubricant includes one or more of polyethylene wax, ethylene bis fatty acid amide, silicone masterbatch, and pentaerythritol stearate.

[0026] Lubricants help reduce the internal friction between polypropylene molecular chains, increase the melt flow rate, and also help reduce the friction coefficient between the melt and the mold, making injection molding, extrusion and other processes smoother. It also helps to reduce the anisotropic orientation of glass fibers, thereby further improving the warpage of polypropylene materials.

[0027] The present application also provides a method for preparing a high-rigidity, low-warpage polypropylene material for automotive structural parts, comprising the following steps: mixing polypropylene resin, talcum powder, a compatibilizer, an antioxidant, and a lubricant in proportion by mass and adding the mixture to the main feed port of a twin-screw extruder; adding modified glass fiber to the side feed port of the twin-screw extruder; the temperature of each zone of the twin-screw extruder is 180°C-220°C; and extruding and drying to obtain a high-rigidity, low-warpage polypropylene material for automotive structural parts.

[0028] In the present application, the modified glass fiber is added through the side feed port, which helps to retain the β-nucleating agent grafted on the glass fiber and is beneficial to further improve the warpage of the polypropylene material.

[0029] In summary, this application has the following beneficial effects: The use of glass fibers grafted with β-nucleating agents is beneficial for inducing the formation of β-lamellae structures oriented perpendicular to the glass fibers near the glass fibers. The low shrinkage characteristics of the β-lamellae reduce the difference between the shrinkage of the polypropylene material along the glass fiber orientation direction and the shrinkage of the polypropylene material perpendicular to the glass fiber orientation direction, thereby improving the warpage of the polypropylene material. By selecting the appropriate preparation process and the grafting rate and the type of grafted β-nucleating agent, the warpage of the polypropylene material can be further improved while also having better rigidity. Adding modified glass fiber through the side feed port is beneficial to retaining the grafted β-nucleating agent, thereby further improving the warpage of the polypropylene material. DETAILED DESCRIPTION

[0030] In order to make the above-mentioned purpose, characteristics and advantages of the present invention more obvious and easy to understand, the specific embodiment of the present invention is described in detail below. In the following description, a lot of specific details are set forth so that a full understanding of the present invention is achieved. But the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below. Unless otherwise stated, the raw materials and reagents used in the embodiments of the present invention are conventional raw materials and reagents purchased. Below in conjunction with Examples and Comparative Examples, the application is described in further detail.

[0031] Preparation Example 1 (1) Take 8g of chopped glass fiber (alkali-free chopped glass fiber ECS13-4.5-T538D, Taishan Glass Fiber, length 4.5mm, diameter 13μm) and disperse it in 300mL of ethanol aqueous solution (mixed with anhydrous ethanol and deionized water in a volume ratio of 3:1), add 1g of aminopropyltriethoxysilane, place the mixed system at 70℃ and stir at a speed of 100rpm for 12 hours, after the reaction is completed, centrifuge the mixed solution 3 times, and vacuum dry the solid material at a drying temperature of 100℃ for 4 hours to obtain surface amino-modified glass fiber; (2) Take 1 mol of the dicarboxylic acid compound phthalic acid and disperse it in 200 mL of dichloromethane, add 1 mol of dichlorothionyl and 1 mL of N,N-dimethylformamide dropwise, and stir at 25°C at a speed of 200 rpm for 2 hours. After the reaction is completed, use a rotary evaporator to remove dichloromethane to obtain the first intermediate product.

[0032] (3) 1 g of the first intermediate product prepared in step (2) was dispersed in 100 mL of dichloromethane and ultrasonically dispersed to obtain a dispersion of the first intermediate product. 4 g of the surface amino-modified glass fiber prepared in step (1) was added dropwise to the dispersion at 0°C and stirred at 100 rpm for 12 hours. The resulting mixture was centrifuged three times to obtain a solid, which was then washed three times with anhydrous ethanol to obtain a second intermediate product.

[0033] (4) 4 g of the second intermediate product prepared in step (3) and 2 g of barium hydroxide were added to 200 mL of methanol, stirred and mixed thoroughly, and stirred at 25° C. and 200 rpm for 24 hours. The reaction mixture was centrifuged three times, and the solid was vacuum dried at a drying temperature of 100° C. for 4 hours to obtain glass fiber grafted with barium phthalate.

[0034] Preparation Example 2-7 The preparation method of Preparation Example 2-7 is basically the same as that of Preparation Example 1, except that the dicarboxylic acid compound added in step (2) of Preparation Example 2-7 is different, and the other steps are the same as those of Preparation Example 1, as follows: Preparation Example 2: Using an equal molar amount of terephthalic acid to replace phthalic acid.

[0035] Preparation Example 3: Using an equal molar amount of pimelic acid to replace phthalic acid.

[0036] Preparation Example 4: An equal molar amount of glutaric acid was used to replace phthalic acid.

[0037] Preparation Example 5: Glutaric acid and phthalic acid are used instead of phthalic acid. The total molar amount of glutaric acid and phthalic acid is the same as the molar amount of phthalic acid, and the molar ratio of glutaric acid to phthalic acid is 1:1.

[0038] Preparation Example 6: Glutaric acid and phthalic acid are used instead of phthalic acid. The total molar amount of glutaric acid and phthalic acid is the same as the molar amount of phthalic acid, and the molar ratio of glutaric acid to phthalic acid is 2:1.

[0039] Preparation Example 7: Glutaric acid and phthalic acid are used instead of phthalic acid. The total molar amount of glutaric acid and phthalic acid is the same as the molar amount of phthalic acid, and the molar ratio of glutaric acid to phthalic acid is 3:1.

[0040] Preparation Example 8 The preparation method of Preparation Example 8 is basically the same as that of Preparation Example 6, except that in step (4) of Preparation Example 8, an equal mass of potassium hydroxide is used to replace barium hydroxide, and the rest remains the same as Preparation Example 6.

[0041] Preparation Examples 9-10 The preparation methods of Preparation Examples 9-10 are basically the same as those of Preparation Example 6, except that the mass ratio of chopped glass fiber to aminopropyltriethoxysilane in step (1) of Preparation Examples 9-10 is different. The other methods remain the same as those of Preparation Example 6, as follows: Preparation Example 9: The mass of the chopped glass fibers is 7.2 g, the mass of aminopropyltriethoxysilane is 1.8 g, and the mass ratio of the chopped glass fibers to aminopropyltriethoxysilane is 4:1.

[0042] Preparation Example 10: The mass of the chopped glass fibers is 8.2 g, the mass of aminopropyltriethoxysilane is 0.8 g, and the mass ratio of the chopped glass fibers to aminopropyltriethoxysilane is 10.25:1.

[0043] Preparation Example 11 The preparation method of the modified glass fiber of Preparation Example 11 is as follows: 1 g of barium phthalate was dissolved in xylene at 80°C, and 4 g of chopped glass fiber (alkali-free chopped glass fiber ECS13-4.5-T538D, Taishan Fiberglass, length 4.5 mm, diameter 13 μm) was added. The mixture was refluxed at 100°C for 1 hour, cooled to room temperature (25°C) to allow barium phthalate to crystallize on the surface of the glass fiber, and then centrifuged and dried at a drying temperature of 100°C for 4 hours to obtain modified glass fiber.

[0044] Preparation Example 12 The preparation method of Preparation Example 12 is basically the same as that of Preparation Example 1, except that an equal molar amount of benzoic acid is used to replace phthalic acid in step (2). Other steps remain the same as those of Preparation Example 1. Example 1

[0045] Weigh 42 parts by mass of high-impact polypropylene resin (copolymer polypropylene resin K8303, purchased from Yanshan Petrochemical, with a melt index of 2 g / 10 min at 230°C and 2.16 kg), 18 parts of high-flow polypropylene resin (copolymer polypropylene resin EP548R, purchased from CNOOC Shell, with a melt index of 28 g / 10 min at 230°C and 2.16 kg), 14 parts of talc (purchased from Tianyuan Company, model TYT-8875B, mesh size 2000 mesh), 3 parts of maleic anhydride grafted polypropylene (grade CA100, maleic anhydride grafting rate 1%, Arkema), 0.25 parts of antioxidant 1010 (Tianjin Li An Chemical Co., Ltd.), and 10 parts of talc powder. The following preparation methods were used: preparation method of the polypropylene glycol monoacrylate (PEG-100) was prepared by mixing 0.25 parts of antioxidant 168 (Tianjin Li'an Long RIANOX), 0.25 parts of antioxidant 168 (Tianjin Li'an Long RIANOX), and 1 part of ethylene bis fatty acid amide in a high-speed mixer. The mixture was fed into a twin-screw extruder through the main feeding port, and 22 parts of modified glass fiber prepared in Preparation Example 1 were fed into the twin-screw extruder through the side feeding port. The temperatures of each section of the barrel from the feeding port to the die were controlled to be 180°C, 210°C, 210°C, 220°C, 220°C, 210°C, 210°C, 210°C, 205°C, and 205°C in sequence. At a twin-screw speed of 500rpm, the material was melt-extruded and granulated to obtain a high-rigidity and low-warpage polypropylene material for automotive structural parts.

[0046] Example 2-3 The preparation method of Example 2-3 is basically similar to that of Example 1, except that the mass fraction of the modified glass fiber is different, the total mass fraction of the raw materials has changed accordingly, and the rest remains the same as Example 1.

[0047] Example 2: The mass fraction of the modified glass fiber is 15 parts.

[0048] Example 3: The mass fraction of the modified glass fiber is 30 parts. Example 4

[0049] The preparation method of Example 4 is basically similar to that of Example 1, except that in Example 4, the modified glass fiber prepared in Preparation Example 2 is used in equal parts by mass to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as in Example 1. Example 5

[0050] The preparation method of Example 5 is basically similar to that of Example 1, except that in Example 5, the modified glass fiber prepared in Preparation Example 3 is used in equal parts by mass to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as in Example 1. Example 6

[0051] The preparation method of Example 6 is basically similar to that of Example 1, except that in Example 6, the modified glass fiber prepared in Preparation Example 4 is used in equal parts by mass to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as in Example 1. Example 7

[0052] The preparation method of Example 7 is basically similar to that of Example 1, except that in Example 7, the modified glass fiber prepared in Preparation Example 5 is used in equal parts by mass to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as Example 1. Example 8

[0053] The preparation method of Example 8 is basically similar to that of Example 1, except that in Example 8, the modified glass fiber prepared in Preparation Example 6 is used in equal parts by mass to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as Example 1. Example 9

[0054] The preparation method of Example 9 is basically similar to that of Example 1, except that in Example 9, the modified glass fiber prepared in Preparation Example 7 is used in equal parts by mass to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as in Example 1. Example 10

[0055] The preparation method of Example 10 is basically similar to that of Example 1, except that in Example 10, the modified glass fiber prepared in Preparation Example 8 is used in equal parts by mass to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as in Example 1. Example 11

[0056] The preparation method of Example 11 is basically similar to that of Example 1, except that in Example 11, the modified glass fiber prepared in Preparation Example 9 is used in equal parts by mass to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as in Example 1. Example 12

[0057] The preparation method of Example 12 is basically similar to that of Example 1, except that in Example 12, the modified glass fiber prepared in Preparation Example 10 is used in equal parts by mass to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as in Example 1.

[0058] Comparative Example 1 The preparation method of Comparative Example 1 is basically similar to that of Example 1, except that equal parts by mass of chopped glass fibers (alkali-free chopped glass fibers ECS13-4.5-T538D, Taishan Fiberglass, 4.5 mm in length and 13 μm in diameter) are used to replace the modified glass fibers prepared in Preparation Example 1.

[0059] Comparative Example 2 The preparation method of Comparative Example 2 is basically similar to that of Example 1, except that a mixture of 18 parts by mass of chopped glass fiber (alkali-free chopped glass fiber ECS13-4.5-T538D, Taishan Fiberglass, with a length of 4.5 mm and a diameter of 13 μm) and 4 parts by mass of barium phthalate (purchased from Alpha Company) is used to replace the modified glass fiber prepared in Preparation Example 1.

[0060] Comparative Example 3 The preparation method of Comparative Example 3 is basically similar to that of Example 1, except that in Comparative Example 3, the modified glass fiber prepared in Preparation Example 11 is used in equal parts by mass to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as Example 1.

[0061] Comparative Example 4 The preparation method of Comparative Example 4 is basically similar to that of Example 1, except that in Comparative Example 4, the modified glass fiber prepared in Preparation Example 12 in equal parts by mass is used to replace the modified glass fiber prepared in Preparation Example 1, and the rest remains the same as Example 1. Performance testing

[0062] 1. Warpage The polypropylene composition was injection molded into specimens measuring 100 mm in length, 100 mm in width, and 2 mm in thickness. One corner of the specimen was fixed against a horizontal table and allowed to stand at room temperature for 72 hours to achieve full shrinkage. The height of the warpage at the opposite corner was measured using a vernier caliper and recorded as the warpage. To ensure the reliability of the test results, five specimens were randomly selected for measurement in each test, and the average value was used as the warpage test result.

[0063] 2. Flexural modulus Flexural modulus: tested in accordance with ISO178-2019, the length × width × thickness of the spline is 80 mm × 10 mm × 4 mm, the span is 64 mm, and the speed is 2 mm / min.

[0064] The polypropylene test strips prepared in Examples 1-12 and Comparative Examples 1-4 were tested, and the test results are shown in Table 1.

[0065] Table 1 Performance test table of polypropylene of Examples 1-12 and Comparative Examples 1-4 Experimental group Warpage (mm) Flexural modulus (MPa) Example 1 0.52 1750 Example 2 0.44 1590 Example 3 0.73 1800 Example 4 0.66 1770 Example 5 0.50 1680 Example 6 0.46 1620 Example 7 0.41 1690 Example 8 0.36 1670 Example 9 0.39 1680 Example 10 0.45 1710 Example 11 0.29 1580 Example 12 0.49 1720 Comparative Example 1 2.83 1890 Comparative Example 2 2.77 1760 Comparative Example 3 2.64 1570 Comparative Example 4 3.35 1640 In conjunction with Table 1 above, a comparison of the test results of Examples 1-12 of the present application with Comparative Examples 1-4 reveals that, compared to Comparative Example 1, which incorporates unmodified glass fibers; Comparative Example 2, which incorporates a physical mixture of glass fibers and a β-nucleating agent; Comparative Example 3, which incorporates glass fibers loaded with a β-nucleating agent via crystallization; and Comparative Example 4, which incorporates glass fibers grafted with an α-nucleating agent, the modified glass fibers grafted with a β-nucleating agent in the Examples of the present application effectively promote the formation of β-lamellae perpendicular to the glass fiber orientation direction around the glass fibers during the cooling and crystallization process of the polypropylene material. The low shrinkage of the β-lamellae compensates for the high shrinkage of the α-spherulites perpendicular to the glass fiber orientation direction, narrowing the difference in shrinkage relative to the glass fiber orientation direction, thereby reducing the warpage of the polypropylene material while maintaining an excellent flexural modulus. Comparative Example 1, in which unmodified glass fibers are added, exhibits an excellent flexural modulus, but exhibits a high degree of warpage, which is unfavorable for its application in automotive structural parts. In Comparative Example 2, a physical mixture of glass fiber and β-nucleating agent was added. During the polypropylene preparation process, the β-nucleating agent was uniformly dispersed in the polypropylene, resulting in an isotropic distribution of β-platelets. This had little effect on improving the material's warpage, and the introduced β-crystals actually reduced the flexural modulus of the polypropylene. In Comparative Example 3, the β-nucleating agent was loaded onto the glass fiber by crystallization. However, due to differences in fiber surface properties and limitations in crystallization dynamics, the β-nucleating agent on the glass fiber exhibited a non-uniform or bulk distribution, which was detrimental to the β-nucleating agent's nucleation effect. The resulting β-platelets were low in content and unevenly distributed, resulting in minimal improvement in the polypropylene's warpage and, in fact, a significant deterioration in its flexural modulus. In Comparative Example 4, benzoic acid was grafted onto the glass fiber. Benzoic acid has an α-nucleating effect, and the resulting α-spherulites did not help reduce the shrinkage of the polypropylene material in the direction perpendicular to the glass fiber orientation. Furthermore, the formation of transverse crystals further deteriorated the warpage and the flexural modulus of the polypropylene material.

[0066] It can be seen from Examples 1-3 that when the addition amount of the modified glass fiber is 15 to 30 parts, the polypropylene material has both low warpage and excellent flexural modulus.

[0067] As can be seen from the comparison between Examples 1, 4-6 and Examples 7-9, the dicarboxylic acid compound includes glutaric acid and phthalic acid, and the molar ratio of glutaric acid to phthalic acid is 1:1-3:1, so that a certain proportion of phthalic acid metal salt and glutaric acid metal salt are grafted onto the glass fiber, which is beneficial for further reducing warpage while also having excellent flexural modulus.

[0068] As shown in Examples 8 and 10, when the metal hydroxide is at least one of barium hydroxide and potassium hydroxide, the modified glass fiber produced results in a polypropylene material with low warpage. A comparison of Examples 8 and 10 shows that when the metal hydroxide is barium hydroxide, the polypropylene material further reduces warpage while also maintaining excellent flexural modulus.

[0069] It can be seen from Examples 8, 11, and 12 that the mass ratio of glass fiber to silane coupling agent is 2:1-10:1, and the modified glass fiber finally prepared enables the polypropylene material to have both low warpage and excellent flexural modulus.

[0070] This specific embodiment is merely an explanation of the present application and is not a limitation of the present application. After reading this specification, those skilled in the art may make non-creative modifications to the present embodiment as needed, but as long as they are within the scope of the claims of the present application, they are protected by the patent law.

Claims

1. A high-rigidity, low-warpage polypropylene material for automotive structural parts, characterized in that: The polypropylene material includes the following components calculated in parts by mass: 50-65 parts of polypropylene resin; 10-15 parts of talc; 2-5 parts of compatibilizer; 0.2-0.6 parts of antioxidant; 0.5-1.5 parts of lubricant; 15-30 parts of modified glass fiber; The modified glass fiber is an alkali-free chopped glass fiber grafted with a β-nucleating agent, and the β-nucleating agent includes one or more of metal salts of glutaric acid, metal salts of pimelic acid, metal salts of adipate, metal salts of terephthalic acid and metal salts of phthalic acid.

2. The high rigidity and low warpage polypropylene material for automotive structural parts according to claim 1, characterized in that: The preparation method of the modified glass fiber comprises the following steps: (1) Dispersing alkali-free short glass fibers in a mixed solvent of ethanol and deionized water, adding aminopropyltriethoxysilane, stirring and reacting at 60°C-80°C for 10 hours-14 hours, and centrifugally drying to obtain surface amino-modified alkali-free short glass fibers; (2) dispersing a dicarboxylic acid compound in dichloromethane, adding thionyl chloride and a catalyst N,N-dimethylformamide, stirring and reacting at 22° C.-28° C. for 1 hour-3 hours, and removing the dichloromethane to obtain a first intermediate product, wherein the dicarboxylic acid compound includes one or more of glutaric acid, pimelic acid, adipic acid, terephthalic acid and phthalic acid, and the molar ratio of the dicarboxylic acid compound to the thionyl chloride is 1:1; (3) dispersing the first intermediate product in dichloromethane, adding the surface amino-modified alkali-free chopped glass fiber, stirring and reacting at 0°C-10°C for 10 hours-14 hours, centrifuging to obtain a solid, and drying to obtain a second intermediate product; (4) dispersing the second intermediate product and a metal hydroxide in methanol, stirring and reacting at 22° C. to 28° C. for 20 to 28 hours, and centrifugally drying to obtain the modified glass fiber, wherein the metal hydroxide includes at least one of an alkali metal hydroxide and an alkaline earth metal hydroxide.

3. The high rigidity and low warpage polypropylene material for automotive structural parts according to claim 2, characterized in that: The dicarboxylic acid compound in step (2) includes glutaric acid and phthalic acid, and the molar ratio of the glutaric acid to the phthalic acid is 1:1-3:

1.

4. The high rigidity and low warpage polypropylene material for automotive structural parts according to claim 2, characterized in that: The metal hydroxide in step (4) includes at least one of barium hydroxide and potassium hydroxide.

5. The high rigidity and low warpage polypropylene material for automotive structural parts according to claim 2, characterized in that: The mass ratio of the alkali-free chopped glass fibers to the aminopropyltriethoxysilane in step (1) is 4:1-10:

1.

6. The high rigidity and low warpage polypropylene material for automotive structural parts according to claim 2, characterized in that: The length of the alkali-free chopped glass fibers in step (1) is 3 mm to 5 mm, and the diameter is 12 μm to 15 μm.

7. The high rigidity and low warpage polypropylene material for automotive structural parts according to claim 1, characterized in that: The polypropylene resin includes high-impact polypropylene resin and high-flow polypropylene resin. The high-impact polypropylene resin has a melt index of 0.5g / 10min-20g / 10min at 230°C and 2.16kg, and the high-flow polypropylene resin has a melt index of 25g / 10min-30g / 10min at 230°C and 2.16kg.

8. The high rigidity and low warpage polypropylene material for automotive structural parts according to claim 1, characterized in that: The antioxidant includes a hindered phenol primary antioxidant 1010 and a phosphite secondary antioxidant 168; and / or, The compatibilizer includes maleic anhydride grafted polypropylene.

9. The high rigidity and low warpage polypropylene material for automotive structural parts according to claim 1, characterized in that: The lubricant includes one or more of polyethylene wax, ethylene bis fatty acid amide, silicone masterbatch and pentaerythritol stearate.

10. A method for preparing a high-rigidity, low-warpage polypropylene material for automotive structural parts according to any one of claims 1 to 9, characterized in that: The following steps are involved: Polypropylene resin, talc, compatibilizer, antioxidant, and lubricant are mixed according to a mass ratio and added to the main feed port of a twin-screw extruder. The modified glass fiber is added to the side feed port of the twin-screw extruder. The temperature of each zone of the twin-screw extruder is 180°C-220°C. After extrusion and drying, a high-rigidity, low-warpage polypropylene material for automotive structural parts is obtained.