A glass fiber reinforced nylon composite and a method for making the same

Abstract

The application belongs to the technical field of polymer composites, and provides a glass fiber reinforced nylon composite material and a preparation method thereof.The nylon composite material comprises nylon 6 resin, flat cross-section glass fiber, epoxy functionalized styrene-acrylate polymer chain extender, antioxidant and lubricant; the flat cross-section glass fiber is treated by amino silane, and is coated with a maleic anhydride grafted nylon 6 oligomer coating layer.In the preparation, first, nylon 6 oligomer is prepared from caprolactam, 6-aminohexanoic acid and adipic acid, and then the interface coating component is obtained by grafting maleic anhydride; then, the glass fiber is coated by silane treatment and formic acid impregnation, and is melt extruded and granulated with the nylon 6 resin, the polymer chain extender and the additive.The application reduces the shrinkage difference and residual stress concentration in the forming process by the cooperation of the glass fiber interface layer and the nylon matrix, so that the material has good size stability, low warping and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, and relates to a glass fiber reinforced nylon composite material and its preparation method. Background Technology

[0002] Glass fiber reinforced nylon composites are commonly used structural materials in the field of engineering plastics. During injection molding, glass fibers tend to orient themselves along the melt flow direction, causing differences in shrinkage behavior between the flow direction and the direction perpendicular to the flow. While flat-section glass fibers can improve the localized orientation problem caused by ordinary round glass fibers to some extent, their constraint on the shrinkage of the nylon matrix remains directional. During cooling, the nylon matrix undergoes crystallization and volume shrinkage, while the glass fibers themselves shrink less. These differences in shrinkage response at the interface result in uneven distribution of residual stress within the product, which can easily lead to warping, edge curling, or assembly dimensional deviations after demolding.

[0003] In existing technologies, methods such as adjusting the cross-sectional morphology of glass fibers, adding mineral fillers, changing the nucleation system, or optimizing the injection molding process are commonly used to reduce warpage in glass fiber reinforced nylon products. These methods mainly focus on the influence of overall shrinkage rate or glass fiber orientation on warpage, but pay insufficient attention to the shrinkage coordination between the glass fiber interface region and the nylon bulk phase region during cooling and molding. Especially in conventional silane treatment systems, the silane coupling layer is mainly used to improve the adhesion between the glass fiber and the nylon matrix, but there is a lack of transitional structures between the interface layer and the nylon bulk phase that can participate in matrix reaction and shrinkage transfer, resulting in the shrinkage difference between the interface region and the bulk phase region easily accumulating into residual stress.

[0004] The technical problem addressed by this invention is that in existing glass fiber reinforced nylon composite materials, the shrinkage behavior of the glass fiber interface region and the nylon bulk region is not coordinated during the cooling and molding process, resulting in uneven distribution of residual stress, which makes the injection molded products prone to warping and deformation after molding. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a glass fiber reinforced nylon composite material and its preparation method. The composite material is made from nylon 6 resin, flat-section glass fiber treated with aminosilane and coated with maleic anhydride-grafted nylon 6 oligomer coating, epoxy-functionalized styrene-acrylate polymer chain extender and additives, through oligomer preparation, grafting, glass fiber treatment and melt extrusion, and is used to reduce molding warpage and maintain the mechanical properties of the material.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a glass fiber reinforced nylon composite material, the nylon composite material comprising nylon 6 resin, flat cross-section glass fiber, epoxy-functionalized styrene-acrylate polymer chain extender, antioxidant, and lubricant, wherein the mass ratio is (58-73):(25-40):(0.3-1.2):(0.2-0.6):(0.2-0.8). The flat-section glass fiber is treated with aminosilane and coated with a maleic anhydride-grafted nylon 6 oligomer coating.

[0007] Preferably, the aspect ratio of the flat cross-section glass fiber is (2.5-5):1.

[0008] Preferably, the maleic anhydride-grafted nylon 6 oligomer is prepared by melt grafting of nylon 6 oligomer, maleic anhydride and initiator, wherein the nylon 6 oligomer is prepared by reacting caprolactam, 6-aminohexanoic acid and adipic acid.

[0009] Preferably, the number-average molecular weight of the nylon 6 oligomer is 3000-8000 g / mol.

[0010] Preferably, the mass ratio of the maleic anhydride-grafted nylon 6 oligomer coating to the flat cross-section glass fiber is (0.5-3.0):100.

[0011] Preferably, the epoxy-functionalized styrene-acrylate polymer chain extender has an epoxy equivalent of 250-600 g / eq and a weight-average molecular weight of 3000-10000 g / mol.

[0012] Preferably, the epoxy-functionalized styrene-acrylate polymer chain extender is a copolymer of styrene, methacrylate, and glycidyl methacrylate; the aminosilane is 3-aminopropyltriethoxysilane or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; the antioxidant includes hindered phenolic antioxidants and phosphite antioxidants; and the lubricant is one of pentaerythritol stearate, ethylene bis-stearamide, and silicone masterbatch.

[0013] In a second aspect, the present invention provides a method for preparing a glass fiber reinforced nylon composite material as described in the first aspect, the method comprising: S1, caprolactam, 6-aminohexanoic acid and adipic acid are mixed and reacted under nitrogen protection and reflux conditions, and then unreacted monomers and volatile components are removed under reduced pressure to obtain nylon 6 oligomers; S2, nylon 6 oligomer, maleic anhydride and initiator are melt-grafted to obtain maleic anhydride-grafted nylon 6 oligomer; S3, glass fiber is placed in aminosilane hydrolysate for treatment and dried to obtain first glass fiber, then maleic anhydride grafted nylon 6 oligomer is dissolved in formic acid, the first glass fiber is added for impregnation, taken out and dried to obtain second glass fiber, the glass fiber is a flat cross section glass fiber; S4. Nylon 6 resin, epoxy-functionalized styrene-acrylate polymer chain extender, antioxidant and lubricant are added to the main feed port of a twin-screw extruder, and the second glass fiber is added to the side feed port of the twin-screw extruder. The mixture is melt-extruded, cooled and pelletized to obtain a glass fiber reinforced nylon composite material.

[0014] Preferably, in S1, the mass ratio of caprolactam, 6-aminohexanoic acid and adipic acid is 100:(5-15):(0.5-2), the reaction temperature is 220-245℃, the reaction time is 2-5h, and the temperature for removing unreacted monomers and volatile components under reduced pressure is 220-245℃, and the time is 0.5-2h.

[0015] Preferably, in S2, the mass ratio of the nylon 6 oligomer, maleic anhydride and initiator is 100:(2-8):(0.05-0.5), the initiator is di-tert-butyl peroxide, the melt grafting temperature is 220-235℃, and the melt grafting time is 2-6 min.

[0016] Preferably, in step S3, the mass concentration of aminosilane in the aminosilane hydrolysate is 0.5%-3.0%, and the pH of the aminosilane hydrolysate is 4-6; the drying temperature after aminosilane treatment is 90-120℃, and the drying time is 0.5-2h; the mass concentration of maleic anhydride-grafted nylon 6 oligomer in formic acid is 3%-10%, the impregnation time is 5-20min, the drying temperature after impregnation is 70-110℃, and the drying time is 0.5-2h.

[0017] Preferably, in S4, the temperature from zone one to the die head of the twin-screw extruder is 220-260℃, and the screw speed is 250-450rpm.

[0018] Caprolactam undergoes ring-opening polymerization with the participation of 6-aminohexanoic acid. The amino and carboxyl groups in 6-aminohexanoic acid can participate in amide bond formation, allowing the aminohexanoyl segments of the caprolactam ring-opening chain to continue condensing to form nylon 6 oligomers. Adipic acid provides a dicarboxyl group structure, which can undergo condensation with the aminohexanoyl segments and adjust the oligomer segment length, ensuring that the resulting nylon 6 oligomer retains carboxyl end groups capable of participating in subsequent reactions. After the reaction, unreacted caprolactam and volatile components are removed under reduced pressure to minimize the migration of low-molecular-weight components during subsequent melt grafting and extrusion processes.

[0019] Di-tert-butyl peroxide decomposes at the melt grafting temperature to form alkoxy radicals. These alkoxy radicals can abstract hydrogen atoms from the methylene positions of the nylon 6 oligomer backbone, generating polyamide chain radicals. These polyamide chain radicals undergo addition reactions with the carbon-carbon double bonds in maleic anhydride, grafting the maleic anhydride structure onto the nylon 6 oligomer segments to form maleic anhydride-grafted nylon 6 oligomers containing anhydride groups and carboxyl conversion sites. This grafted product retains polyamide segments, enabling it to form segmental entanglement and hydrogen bonding between amide groups with the nylon 6 matrix. Simultaneously, its anhydride or carboxyl structure can participate in the interfacial reactions of the amino layer on the glass fiber surface and subsequent epoxy chain extenders.

[0020] Aminosilanes undergo alkoxy-hydroxyl hydrolysis in the hydrolysis solution to generate silanol groups. These silanol groups condense with the silanol groups on the glass fiber surface, forming Si-O-Si bonds and Si-O-glass bonds. Uncondensed silanol groups can also condense with each other, forming a silane layer attached to the glass fiber surface. The amino group in the aminosilane molecule remains on the outer side of the interfacial layer, providing reaction sites and polar interaction sites for interaction with the anhydride groups and carboxyl groups in the maleic anhydride-grafted nylon 6 oligomer.

[0021] Maleic anhydride-grafted nylon 6 oligomers dissolve in formic acid to form a coating solution containing polyamide segments. During impregnation, this grafted material is distributed on the surface of glass fibers treated with aminosilane. After the formic acid evaporates, the maleic anhydride-grafted nylon 6 oligomers deposit and coat the glass fiber surface. Its polyamide segments have the same amide structure as the subsequent nylon 6 matrix, enabling entanglement with the matrix segments during melt extrusion. Its anhydride and carboxyl groups can form salt bonds and hydrogen bonds with the amino groups in the aminosilane layer, and undergo anhydride ring-opening amidation reactions during drying or melt processing. Thus, an interface layer with both chemical and polar interactions is formed between the silane layer on the glass fiber surface and the polyamide-compatible coating.

[0022] During melt extrusion, nylon 6 resin melts to form a continuous phase, and the second glass fiber enters the melt via side feeding. After the maleic anhydride-grafted nylon 6 oligomer coating on the glass fiber surface comes into contact with the nylon 6 melt, its polyamide segments enter the nylon 6 continuous phase and undergo chain entanglement. Anhydride or carboxyl groups are distributed near the glass fiber interface. The epoxy groups in the epoxy-functionalized styrene-acrylate polymer chain extender can undergo ring-opening esterification with the terminal carboxyl groups of nylon 6, and also ring-opening addition with the terminal amino groups. Simultaneously, the epoxy groups can also react with the carboxyl groups in the maleic anhydride-grafted nylon 6 oligomer or the carboxyl groups after ring-opening of the anhydride. The chain extender molecule contains multiple epoxy reaction sites, which, under melt shear conditions, can connect the nylon 6 matrix segments and the interface coating segments, allowing the polyamide coating near the glass fiber interface to participate in the chain growth, branching, and interfacial bonding processes of the nylon 6 bulk phase.

[0023] Flat-section glass fibers are subjected to melt shear during injection molding, and their long axis tends to align with the flow field. The shrinkage of the glass fiber itself is less than that of the nylon 6 matrix, and the area near the glass fiber constrains the shrinkage of the matrix during cooling. After treatment with aminosilane and coating with maleic anhydride-grafted nylon 6 oligomers, the glass fiber surface no longer directly contacts the nylon 6 bulk phase. Instead, a transition interface is formed through a silane layer, a grafted polyamide coating, and an epoxy chain extension reaction. This transition interface contains Si-O-glass bonds and siloxane condensation structures, as well as polyamide segment entanglements, amide hydrogen bonds, anhydride ring-opening reaction products, and epoxy ring-opening reaction products, creating continuous segmental connections and polar interactions between the glass fiber surface area and the nylon 6 bulk phase.

[0024] During the cooling and crystallization of nylon 6, the bulk phase segments undergo regular arrangement and volume shrinkage. Without a polyamide compatibility coating, the shrinkage response between the glass fiber surface and the nylon 6 bulk phase is mainly transmitted through the ordinary coupling layer. The segment movement patterns in the interface region and the bulk phase region differ, and shrinkage stress tends to concentrate on the glass fiber surface and ends. The maleic anhydride-grafted nylon 6 oligomer coating contains the same polyamide segments as the matrix, which can participate in the segment rearrangement during the cooling process along with the nylon 6 bulk phase. The bonding structure formed by the epoxy chain extender near the interface restricts the relative slippage between the coating segments and the bulk phase segments. During cooling, the glass fiber surface constraint, polyamide coating segment rearrangement, and bulk nylon 6 crystallization shrinkage are transmitted through the interface layer, and the shrinkage difference between the interface region and the bulk phase region is dispersed into the coating segments and the branched bonding structure.

[0025] Flat-section glass fibers exhibit different shrinkage constraints in the flow direction and perpendicular to the flow direction. After the glass fiber surface coating and bulk chain extension structure are formed, the nylon 6 segments surrounding the glass fiber no longer rely solely on physical adhesion to bear shrinkage stress, but participate in stress transfer through grafted polyamide segments and epoxy ring-opening connection points. The branched segments formed by melt extrusion increase the chain entanglement density of the nylon 6 continuous phase during cooling, enabling the transfer of local shrinkage stress between the glass fiber interface, coating, and bulk phase. After demolding, the residual stress generated by glass fiber orientation and nylon 6 crystallization shrinkage in the product is no longer concentrated at a single interface boundary, but is released and redistributed in the region where the glass fiber surface coating and nylon 6 bulk phase connect, thus corresponding to lower warpage and better dimensional stability.

[0026] Compared with existing technologies, the beneficial effects of this invention are as follows: This invention treats flat cross-section glass fibers with aminosilane and coats their surface with a maleic anhydride-grafted nylon 6 oligomer coating, forming a polyamide-compatible interface between the glass fiber surface and the nylon matrix. This reduces shrinkage separation between the glass fiber interface region and the nylon bulk phase region during cooling and molding. The epoxy-functionalized styrene-acrylate polymer chain extender can react with the active groups in the nylon end groups and interface coating during melt extrusion, allowing the interface coating to participate in the chain segment connection and stress transfer of the nylon continuous phase. This structure can mitigate the shrinkage differences caused by glass fiber orientation, reduce warpage after injection molding, and maintain the reinforcing effect of glass fiber on the nylon material, resulting in a composite material that possesses dimensional stability, mechanical properties, and processing adaptability. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below with reference to specific embodiments. The embodiments described herein are specific implementations of the present invention and are used to illustrate the concept of the present invention; these descriptions are explanatory and exemplary and should not be construed as limiting the implementation of the present invention or the scope of protection of the present invention. In addition to the embodiments described herein, those skilled in the art can also adopt other obvious technical solutions based on the content disclosed in the claims and the specification of this application. These technical solutions include those that make any obvious substitutions and modifications to the embodiments described herein.

[0028] The chemical reagents used in the embodiments and comparative examples of this invention are all commercially available products and have not undergone any further purification treatment.

[0029] The epoxy-functionalized styrene-acrylate polymer chain extender selected is ADR-4368-S type polymer chain extender, which has an epoxy equivalent of 285 g / eq, a weight-average molecular weight of 6800 g / mol, and a Tg (glass transition temperature) of 54℃.

[0030] The relative viscosity of nylon 6 resin is 2.4-2.7, the melting point is 220-225℃, and it is vacuum dried at 80℃ for 6 hours before use. The moisture content after drying is not higher than 0.12%.

[0031] Example 1 This embodiment provides a glass fiber reinforced nylon composite material and its preparation method, the preparation method specifically including the following steps: S1, caprolactam, 6-aminohexanoic acid and adipic acid were mixed in a mass ratio of 100:5:1.5 and reacted at 230°C for 3 hours under nitrogen protection and reflux. Then, unreacted monomers and volatile components were removed under reduced pressure at 245°C for 0.5 hours to obtain nylon 6 oligomer with a number average molecular weight of 4200 g / mol. S2, Nylon 6 oligomer, maleic anhydride and di-tert-butyl peroxide were melt-grafted at a mass ratio of 100:8:0.2, the melt-grafting temperature was 220℃ and the melt-grafting time was 6min, to obtain maleic anhydride-grafted nylon 6 oligomer; S3, glass fibers are treated and dried in an aminosilane hydrolysate to obtain a first glass fiber; the glass fiber is a flat cross-section glass fiber with a length-to-short axis ratio of 5:1; the aminosilane is 3-aminopropyltriethoxysilane, the mass concentration of aminosilane in the aminosilane hydrolysate is 3.0%, the pH of the aminosilane hydrolysate is 5, the drying temperature after aminosilane treatment is 90℃, and the drying time is 1.5h; then, maleic anhydride-grafted nylon 6 oligomer is dissolved in formic acid, the mass concentration of maleic anhydride-grafted nylon 6 oligomer in formic acid is controlled at 3%, the first glass fiber is added and impregnated for 20min, then removed and dried at 110℃ for 0.5h to obtain a second glass fiber; the mass ratio of the maleic anhydride-grafted nylon 6 oligomer coating to the flat cross-section glass fiber is 3.0:100; S4, Nylon 6 resin, epoxy-functionalized styrene-acrylate polymer chain extender, antioxidant, and lubricant are added to the main feed port of a twin-screw extruder, and second glass fiber is added to the side feed port of the twin-screw extruder. The mixture is melt-extruded, cooled, and pelletized to obtain a glass fiber reinforced nylon composite material. The mass ratio of the nylon 6 resin, the flat-section glass fiber in the second glass fiber, the epoxy-functionalized styrene-acrylate polymer chain extender, the antioxidant, and the lubricant is 64:40:0.3:0.4:0.8. The antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The lubricant is pentaerythritol stearate. The temperatures from zone one to the die head of the twin-screw extruder are 220℃, 230℃, 240℃, 250℃, 255℃, and 260℃, respectively, and the screw speed is 250 rpm.

[0032] Example 2 This embodiment provides a glass fiber reinforced nylon composite material and its preparation method, the preparation method specifically including the following steps: S1, caprolactam, 6-aminohexanoic acid and adipic acid were mixed in a mass ratio of 100:12:0.5 and reacted at 220°C for 5 h under nitrogen protection and reflux. Then, unreacted monomers and volatile components were removed at 230°C under reduced pressure for 2 h to obtain nylon 6 oligomer with a number average molecular weight of 8000 g / mol. S2, Nylon 6 oligomer, maleic anhydride and di-tert-butyl peroxide were melt-grafted at a mass ratio of 100:2:0.5, the melt-grafting temperature was 235℃ and the melt-grafting time was 2min, to obtain maleic anhydride-grafted nylon 6 oligomer; S3, glass fibers are treated in an aminosilane hydrolysate and dried to obtain a first glass fiber; the glass fiber is a flat cross-section glass fiber with a length-to-minor axis ratio of 3.4:1; the aminosilane is 3-aminopropyltriethoxysilane, the mass concentration of aminosilane in the aminosilane hydrolysate is 0.5%, the pH of the aminosilane hydrolysate is 4, the drying temperature after aminosilane treatment is 110℃, and the drying time is 0.5h; then, maleic anhydride-grafted nylon 6 oligomer is dissolved in formic acid, the mass concentration of maleic anhydride-grafted nylon 6 oligomer in formic acid is controlled at 10%, the first glass fiber is added and impregnated for 5min, then removed and dried at 70℃ for 2h to obtain a second glass fiber; the mass ratio of the maleic anhydride-grafted nylon 6 oligomer coating to the flat cross-section glass fiber is 0.5:100; S4, Nylon 6 resin, epoxy-functionalized styrene-acrylate polymer chain extender, antioxidant, and lubricant are added to the main feed port of a twin-screw extruder, and second glass fiber is added to the side feed port of the twin-screw extruder. The mixture is melt-extruded, cooled, and pelletized to obtain a glass fiber reinforced nylon composite material. The mass ratio of the nylon 6 resin, the flat-section glass fiber in the second glass fiber, the epoxy-functionalized styrene-acrylate polymer chain extender, the antioxidant, and the lubricant is 73:33:0.9:0.2:0.4. The antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The lubricant is pentaerythritol stearate. The temperatures from zone one to the die head of the twin-screw extruder are 225℃, 235℃, 245℃, 250℃, 255℃, and 258℃, respectively, and the screw speed is 450 rpm.

[0033] Example 3 This embodiment provides a glass fiber reinforced nylon composite material and its preparation method, the preparation method specifically including the following steps: S1, caprolactam, 6-aminohexanoic acid and adipic acid were mixed in a mass ratio of 100:15:2 and reacted at 245℃ for 2 hours under nitrogen protection and reflux. Then, unreacted monomers and volatile components were removed at 220℃ under reduced pressure for 1 hour to obtain nylon 6 oligomer with a number average molecular weight of 3000 g / mol. S2, Nylon 6 oligomer, maleic anhydride and di-tert-butyl peroxide were melt-grafted at a mass ratio of 100:5:0.05, the melt-grafting temperature was 228℃ and the melt-grafting time was 4min, to obtain maleic anhydride-grafted nylon 6 oligomer. S3, glass fibers are treated and dried in an aminosilane hydrolysate to obtain a first glass fiber; the glass fiber is a flat cross-section glass fiber with a length-to-short axis ratio of 2.5:1; the aminosilane is 3-aminopropyltriethoxysilane, the mass concentration of aminosilane in the aminosilane hydrolysate is 1.8%, the pH of the aminosilane hydrolysate is 6, the drying temperature after aminosilane treatment is 120℃, and the drying time is 2h; then, maleic anhydride-grafted nylon 6 oligomer is dissolved in formic acid, the mass concentration of maleic anhydride-grafted nylon 6 oligomer in formic acid is controlled at 6%, the first glass fiber is added and impregnated for 12min, then removed and dried at 90℃ for 1.2h to obtain a second glass fiber; the mass ratio of the maleic anhydride-grafted nylon 6 oligomer coating to the flat cross-section glass fiber is 1.6:100; S4, Nylon 6 resin, epoxy-functionalized styrene-acrylate polymer chain extender, antioxidant, and lubricant are added to the main feed port of a twin-screw extruder, and second glass fiber is added to the side feed port of the twin-screw extruder. The mixture is melt-extruded, cooled, and pelletized to obtain a glass fiber reinforced nylon composite material. The mass ratio of the nylon 6 resin, the flat-section glass fiber in the second glass fiber, the epoxy-functionalized styrene-acrylate polymer chain extender, the antioxidant, and the lubricant is 58:36:1.2:0.6:0.2. The antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The lubricant is pentaerythritol stearate. The temperatures from zone one to the die head of the twin-screw extruder are 220℃, 225℃, 235℃, 245℃, 250℃, and 255℃, respectively, and the screw speed is 320 rpm.

[0034] Example 4 This embodiment provides a glass fiber reinforced nylon composite material and its preparation method, the preparation method specifically including the following steps: S1, caprolactam, 6-aminohexanoic acid and adipic acid were mixed in a mass ratio of 100:8:1 and reacted at 238℃ for 4 hours under nitrogen protection and reflux. Then, unreacted monomers and volatile components were removed under reduced pressure at 235℃ for 1.5 hours to obtain nylon 6 oligomer with a number average molecular weight of 5800 g / mol. S2, Nylon 6 oligomer, maleic anhydride and di-tert-butyl peroxide were melt-grafted at a mass ratio of 100:6.5:0.35, the melt-grafting temperature was 232℃ and the melt-grafting time was 5min, to obtain maleic anhydride-grafted nylon 6 oligomer; S3, glass fibers are treated in an aminosilane hydrolysate and dried to obtain a first glass fiber; the glass fiber is a flat cross-section glass fiber with a length-to-short axis ratio of 4.2:1; the aminosilane is 3-aminopropyltriethoxysilane, the mass concentration of aminosilane in the aminosilane hydrolysate is 2.4%, the pH of the aminosilane hydrolysate is 4.8, the drying temperature after aminosilane treatment is 100℃, and the drying time is 1h; then, maleic anhydride-grafted nylon 6 oligomer is dissolved in formic acid, the mass concentration of maleic anhydride-grafted nylon 6 oligomer in formic acid is controlled at 8%, the first glass fiber is added and impregnated for 16min, then removed and dried at 100℃ for 1.6h to obtain a second glass fiber; the mass ratio of the maleic anhydride-grafted nylon 6 oligomer coating to the flat cross-section glass fiber is 2.3:100; S4, Nylon 6 resin, epoxy-functionalized styrene-acrylate polymer chain extender, antioxidant, and lubricant are added to the main feed port of a twin-screw extruder, and second glass fiber is added to the side feed port of the twin-screw extruder. The mixture is melt-extruded, cooled, and pelletized to obtain a glass fiber reinforced nylon composite material. The mass ratio of the nylon 6 resin, the flat-section glass fiber in the second glass fiber, the epoxy-functionalized styrene-acrylate polymer chain extender, the antioxidant, and the lubricant is 69:25:0.6:0.5:0.6. The antioxidant is composed of antioxidant 1010 and antioxidant 168 in a mass ratio of 1:1. The lubricant is pentaerythritol stearate. The temperatures from zone one to the die head of the twin-screw extruder are 222℃, 232℃, 242℃, 248℃, 253℃, and 258℃, respectively, and the screw speed is 380 rpm.

[0035] Comparative Example 1 This comparative example provides a glass fiber reinforced nylon composite material and its preparation method. The difference between this example and Example 1 is that in S3, the glass fiber is not treated in an aminosilane hydrolysate, nor is it impregnated with maleic anhydride-grafted nylon 6 oligomer. Instead, it is directly added as the second glass fiber to the side feed port of the twin-screw extruder. Other process parameters and operating conditions are exactly the same as in Example 1.

[0036] Comparative Example 2 This comparative example provides a glass fiber reinforced nylon composite material and its preparation method. The difference between this example and Example 1 is that in S3, the glass fiber is treated in an aminosilane hydrolysate and dried, and then directly added as the second glass fiber to the side feed port of the twin-screw extruder. Maleic anhydride-grafted nylon 6 oligomer is no longer used for impregnation treatment. Other process parameters and operating conditions are exactly the same as in Example 1.

[0037] Comparative Example 3 This comparative example provides a glass fiber reinforced nylon composite material and its preparation method. The difference between this example and Example 1 is that no epoxy-functionalized styrene-acrylate polymer chain extender is added in S4, and an equal mass of nylon 6 resin is used to replace the epoxy-functionalized styrene-acrylate polymer chain extender in Example 1. Other process parameters and operating conditions are exactly the same as in Example 1.

[0038] Test method: The obtained glass fiber reinforced nylon composite granules were vacuum dried at 80℃ for 6 hours, and test samples were prepared using the same injection molding machine. The barrel temperature of the injection molding machine was 240℃, 250℃, 260℃, and 260℃ sequentially from the feeding section to the nozzle; the mold temperature was 80℃; the injection pressure was 80MPa; the holding pressure was 50MPa; the holding time was 10s; and the cooling time was 25s. After injection molding, the samples were placed in an environment with a temperature of 23℃ and a relative humidity of 50% for 24 hours before testing.

[0039] Warpage deformation test: Each group of materials was injection molded into flat specimens measuring 120mm × 120mm × 2mm. The gate was located in the middle of one side of the flat plate, allowing the melt to flow along the length of the plate. After demolding, the specimens were placed in an environment of 23℃ and 50% relative humidity for 24 hours. During testing, the specimens were placed naturally on a horizontal marble platform without applying any external force to flatten them, allowing the specimens to contact the platform in their natural state. The maximum vertical distance between the warped part of the specimen and the platform was measured using a height gauge or laser displacement meter and recorded as the warping deformation in mm. Measurements were taken at the four corners and the midpoints of the four sides of each specimen, and the maximum value was recorded as the warping deformation of that specimen.

[0040] Test of the difference in molding shrinkage rate between the flow direction and the perpendicular flow direction: The same injection-molded flat specimens as those used in the warpage deformation test were used. The dimensions of the mold cavity in the flow direction and perpendicular to the flow direction were recorded. After demolding and acclimatizing for 24 hours, the actual dimensions of the specimen in the flow direction and perpendicular to the flow direction were measured using vernier calipers. The molding shrinkage rate in the flow direction was calculated as "mold cavity flow direction dimension minus specimen flow direction dimension, then divided by mold cavity flow direction dimension"; the molding shrinkage rate perpendicular to the flow direction was calculated as "mold cavity perpendicular to the flow direction dimension minus specimen perpendicular to the flow direction dimension, then divided by mold cavity perpendicular to the flow direction dimension". The absolute value of the difference between the molding shrinkage rate in the flow direction and the molding shrinkage rate perpendicular to the flow direction was recorded as the molding shrinkage rate difference, expressed as a percentage (%). This value is used to evaluate the magnitude of the material's molding shrinkage anisotropy.

[0041] Bending strength test: Each group of materials was injection molded into standard bending specimens with dimensions of 80mm × 10mm × 4mm. After the specimens were conditioned for 24 hours, a three-point bending test was performed on a universal testing machine. The test span was set to 64mm, the loading speed was set to 2mm / min, and the loading head was located at the center of the specimen. The load values ​​at which the specimen broke or reached the maximum load were recorded, and the bending strength was calculated according to the three-point bending formula, in MPa.

[0042] Notched impact strength test: Each group of materials was injection molded into impact specimens with dimensions of 80mm × 10mm × 4mm. A V-shaped notch was machined in the middle of the specimen, with a notch depth of 2mm and a bottom radius of 0.25mm. After the specimens were conditioned for 24 hours, they were tested using a simply supported beam impact testing machine with a support span of 62mm, a pendulum energy of 2J, and an impact velocity of 2.9m / s. The energy absorbed by the specimen upon fracture was recorded, and the notched impact strength was calculated based on the remaining cross-sectional area at the notch, in kJ / m². 2 .

[0043] The test results are shown in Table 1.

[0044] Table 1. Test results of glass fiber reinforced nylon composite materials in Examples 1-4 and Comparative Examples 1-3

[0045] As shown in Table 1, compared with Example 1, Comparative Example 1 has increased warpage deformation, increased difference in molding shrinkage rate, decreased bending strength, and decreased notched impact strength; Comparative Example 2 has increased warpage deformation, increased difference in molding shrinkage rate, decreased bending strength, and decreased notched impact strength; Comparative Example 3 has increased warpage deformation, increased difference in molding shrinkage rate, decreased bending strength, and decreased notched impact strength.

[0046] This is because Comparative Example 1 did not undergo aminosilane treatment or a maleic anhydride-grafted nylon 6 oligomer coating. The glass fiber and nylon 6 matrix primarily relied on physical contact. During cooling and molding, the shrinkage transfer between the glass fiber interface and the nylon bulk phase was discontinuous, resulting in residual stress concentration. This led to an increase in the difference between warpage and molding shrinkage, and a decrease in flexural strength and notched impact strength. Comparative Example 2 only used aminosilane treatment on the glass fiber. Lacking a maleic anhydride-grafted nylon 6 oligomer coating as a polyamide compatibility interface between the glass fiber surface and the nylon 6 matrix, the chain segment transition between the interface and the nylon bulk phase was insufficient. The difference in cooling shrinkage was still significant, therefore the difference in warpage and shrinkage was higher than in Example 1. In Comparative Example 3, no epoxy-functionalized styrene-acrylate polymer chain extender was added. Although the glass fiber surface coating could form a compatible interface with the nylon 6 matrix, there was a lack of further chain segment connections between the interface coating and the nylon bulk phase. During the cooling process, the interfacial stress transfer and shrinkage coordination were insufficient, resulting in an increase in the warpage deformation, the difference in molding shrinkage rate, and a decrease in notched impact strength.

[0047] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A glass fiber reinforced nylon composite material, characterized in that, The nylon composite material comprises nylon 6 resin, flat cross-section glass fiber, epoxy-functionalized styrene-acrylate polymer chain extender, antioxidant, and lubricant, with a mass ratio of (58-73):(25-40):(0.3-1.2):(0.2-0.6):(0.2-0.8). The flat cross-section glass fiber is treated with aminosilane and coated with a maleic anhydride-grafted nylon 6 oligomer coating. The preparation method of the glass fiber reinforced nylon composite material includes: S1, caprolactam, 6-aminohexanoic acid and adipic acid are mixed and reacted under nitrogen protection and reflux conditions, and then unreacted monomers and volatile components are removed under reduced pressure to obtain nylon 6 oligomers; S2, nylon 6 oligomer, maleic anhydride and initiator are melt-grafted to obtain maleic anhydride-grafted nylon 6 oligomer; S3, glass fiber is placed in aminosilane hydrolysate for treatment and dried to obtain first glass fiber, then maleic anhydride grafted nylon 6 oligomer is dissolved in formic acid, the first glass fiber is added for impregnation, taken out and dried to obtain second glass fiber, the glass fiber is a flat cross section glass fiber; S4. Nylon 6 resin, epoxy-functionalized styrene-acrylate polymer chain extender, antioxidant and lubricant are added to the main feed port of a twin-screw extruder, and the second glass fiber is added to the side feed port of the twin-screw extruder. The mixture is melt-extruded, cooled and pelletized to obtain a glass fiber reinforced nylon composite material.

2. The glass fiber reinforced nylon composite material according to claim 1, characterized in that, The aspect ratio of the flat cross-section glass fiber is (2.5-5):

1.

3. The glass fiber reinforced nylon composite material according to claim 1, characterized in that, The maleic anhydride-grafted nylon 6 oligomer is prepared by melt grafting of nylon 6 oligomer, maleic anhydride and initiator, and the nylon 6 oligomer is prepared by reacting caprolactam, 6-aminohexanoic acid and adipic acid.

4. The glass fiber reinforced nylon composite material according to claim 3, characterized in that, The number-average molecular weight of the nylon 6 oligomer is 3000-8000 g / mol.

5. The glass fiber reinforced nylon composite material according to claim 1, characterized in that, The mass ratio of the maleic anhydride-grafted nylon 6 oligomer coating to the flat cross-section glass fiber is (0.5-3.0):

100.

6. The glass fiber reinforced nylon composite material according to claim 1, characterized in that, The epoxy-functionalized styrene-acrylate polymer chain extender has an epoxy equivalent of 250-600 g / eq and a weight-average molecular weight of 3000-10000 g / mol.

7. The glass fiber reinforced nylon composite material according to claim 1, characterized in that, The epoxy-functionalized styrene-acrylate polymer chain extender is a copolymer of styrene, methacrylate, and glycidyl methacrylate; the aminosilane is 3-aminopropyltriethoxysilane or N-(2-aminoethyl)-3-aminopropyltrimethoxysilane; the antioxidant includes hindered phenolic antioxidants and phosphite antioxidants; and the lubricant is one of pentaerythritol stearate, ethylene bis-stearamide, and silicone masterbatch.

8. The glass fiber reinforced nylon composite material according to claim 1, characterized in that, In S1, the mass ratio of caprolactam, 6-aminohexanoic acid and adipic acid is 100:(5-15):(0.5-2), the reaction temperature is 220-245℃, the reaction time is 2-5h, and the temperature and time for removing unreacted monomers and volatile components under reduced pressure are 220-245℃ and 0.5-2h. In S2, the mass ratio of the nylon 6 oligomer, maleic anhydride and initiator is 100:(2-8):(0.05-0.5), the initiator is di-tert-butyl peroxide, the melt grafting temperature is 220-235℃, and the melt grafting time is 2-6 min.

9. The glass fiber reinforced nylon composite material according to claim 1, characterized in that, In S3, the mass concentration of aminosilane in the aminosilane hydrolysate is 0.5%-3.0%, and the pH of the aminosilane hydrolysate is 4-6; the drying temperature after aminosilane treatment is 90-120℃, and the drying time is 0.5-2h; the mass concentration of maleic anhydride-grafted nylon 6 oligomer in formic acid is 3%-10%, the impregnation time is 5-20min, the drying temperature after impregnation is 70-110℃, and the drying time is 0.5-2h. In S4, the temperature from zone 1 to the die head of the twin-screw extruder is 220-260℃, and the screw speed is 250-450rpm.

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