A high-strength polyamide resin composition and a method for producing the same

Abstract

This invention relates to the field of polyamide resin technology, specifically to a high-strength polyamide resin composition and its preparation method. This invention overcomes the problem of poor mechanical properties caused by poor interfacial compatibility in existing polyamide resins. The composition of this invention consists of PA6 resin, carboxyl-terminated modified PA6 resin, furan-grafted polyamide, maleimide-grafted polyolefin elastomer, and bifunctional stepwise modified glass fiber. It utilizes the dynamic covalent bond mechanism between furan and maleimide to eliminate surface fiber floating in the product; spontaneous cross-linking occurs during cooling and setting, combining the in-situ anchoring of epoxy and amino groups on the surface to construct a three-dimensional interpenetrating locked network. This invention solves the problem of poor interfacial compatibility in polyamide materials, improves the overall mechanical strength of polyamide materials, and can be applied to the manufacture of paint-free high-strength automotive structural components and precision electronic casings.

Description

Technical Field

[0001] This invention relates to the field of polyamide resin technology, specifically to a high-strength polyamide resin composition and its preparation method. Background Technology

[0002] Polyamide composites are a core category in the field of polymer material modification due to their excellent mechanical properties and heat resistance. These materials are widely used in harsh scenarios such as lightweight structural components for new energy vehicles (such as battery brackets and front-end modules) and housings for high-end power tools. However, these high-end applications require materials to have good mechanical strength to meet the structural load-bearing and drop impact resistance requirements, and also require the material surface to have a flawless, paint-free, high-gloss or matte texture.

[0003] In the prior art, in order to improve the rigidity of polyamide compositions, a high proportion of inorganic fillers is usually added to the polyamide resin for reinforcement. However, in practical applications, there is a serious problem of poor interfacial compatibility between the polyamide matrix and inorganic materials. In the high shear flow field of injection molding, due to the mismatch of surface tension between the resin melt and the inorganic material, and the fast crystallization speed of polyamide, the resin often cannot coat the inorganic system in time, resulting in a large amount of filler accumulating and being exposed on the surface of the product, forming a serious fiber floating phenomenon and damaging the surface appearance of the product.

[0004] In order to cover up the floating fibers, traditional modification processes often rely on adding low molecular weight lubricants or using high-flow matrix to forcibly reduce the melt viscosity. However, the introduction of a large number of small molecules further weakens the already fragile resin-glass fiber interface bond. When automotive structural parts or power tools are subjected to alternating stress, vibration and external impact for a long time, stress concentration and debonding are likely to occur at the micro interface, which directly leads to a significant decrease in the notched impact strength, creep resistance and bending fatigue life of the material, causing brittle fracture failure of the structural parts and failing to meet industrial-grade safety standards.

[0005] In summary, existing technologies improve overall interfacial compatibility by introducing inorganic materials and adding small-molecule lubricants, thus addressing the problem of poor compatibility in polyamide resin compositions. However, existing technologies still present the technical challenge of balancing high processing fluidity and high interfacial bonding strength in polyamide material compositions.

[0006] Therefore, a high-strength polyamide resin composition and its preparation method are proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a high-strength polyamide resin composition and its preparation method. This invention overcomes the problem of poor mechanical properties caused by poor interfacial compatibility in existing polyamide resins. The composition of this invention consists of PA6 resin, carboxyl-terminated modified PA6 resin, furan-grafted polyamide, maleimide-grafted polyolefin elastomer, and bifunctional stepwise modified glass fiber. It utilizes the dynamic covalent bond mechanism between furan and maleimide to eliminate surface fiber floating in the product; spontaneous cross-linking occurs during cooling and setting, combined with the in-situ anchoring of epoxy and amino groups on the modified glass fiber surface, constructing a three-dimensional interpenetrating network of polyamide matrix, covalently cross-linked elastomer, and glass fiber. This invention solves the problem of poor interfacial compatibility in glass fiber reinforced polyamide, improves the overall mechanical strength of polyamide materials, and can be applied to the manufacture of paint-free high-strength automotive structural components and precision electronic housings.

[0008] To achieve the above objectives, the present invention provides the following technical solution: the number of parts in the present invention is the number of parts by weight; This invention provides a method for preparing a high-strength polyamide resin composition, comprising the following preparation process: 15-25 parts of PA6 resin, 20-30 parts of modified PA6 resin, 6-10 parts of furan-grafted polyamide, 7-11 parts of maleimide-grafted polyolefin, 0.4-0.8 parts of composite antioxidant, and 0.3-0.5 parts of pentaerythritol stearate are added to a high-speed mixer and mixed at room temperature for 300-500 rpm for 3-5 minutes to obtain a premix. First, the premix is ​​added to the main feed port of a co-rotating twin-screw extruder with a length-to-diameter ratio of 48:1. The extruder is then connected to the main feed port of the first extruder section... The temperature in zone five is set at 255-265℃, and the screw speed is set at 400-550 rpm. Next, in zones six to eight of the extruder, 40-50 parts of modified inorganic filler are added through the side feed port. The temperature in this zone is set at 250-260℃, and a weak shear distribution mixed screw block combination is adopted. Under the full wetting of the ultra-low viscosity melt, the epoxy groups on the surface of the modified inorganic filler undergo a ring-opening reaction with the terminal carboxyl groups of the modified PA6 resin, and the amino groups undergo micro-crosslinking and anchoring with a small amount of maleimide groups. Finally, the melt is subjected to vacuum evacuation and degassing at a vacuum degree of -0.08 MPa in zones 9 to 11 with a temperature set at 245-255℃. Then, it is extruded from the die head with a temperature set at 235-245℃ to obtain the molten extrudate. The extrudate is then cooled to 60-80℃ in a water bath and allowed to cool naturally to allow the furan groups and maleimide groups to undergo a Diels-Alder cycloaddition reaction. During the cooling and shaping process, a three-dimensional cross-linked interpenetrating network is formed. The extrudate is then pelletized and vacuum dried at 80-90℃ for 4-6 hours to obtain the polyamide resin composition.

[0009] The composite antioxidant is composed of antioxidant 1098 and antioxidant 168 in a 1:1 mass ratio. To compensate for the side reaction consumption of maleimide groups by the residual terminal amino groups of conventional PA6 resin and the amino groups on the surface of modified inorganic fillers, the amount of maleimide-grafted polyolefin elastomer added is higher than that of furan-grafted polyamide. This ensures that after the system is processed at high temperature and undergoes some Michael addition side reactions, the molar ratio of the remaining maleimide groups to furan groups is controlled at 1:1.

[0010] Conventional PA6 resin, due to the presence of dual-terminal groups (amino and carboxyl groups), is prone to irreversible crosslinking with modified components at high temperatures. Therefore, isophthalic acid-terminated modified PA6 resin was designed as the main matrix. Its enriched terminal carboxyl groups not only cut off the side reaction pathways that consume BMI groups, but also undergo ring-opening reactions with the epoxy groups on the surface of the modified inorganic filler during the mixing stage, providing basic interfacial locking force. Furan-grafted polyamide, as a diene of the Diels-Alder ring reaction, has a polyamide main chain, ensuring good thermodynamic compatibility with the matrix resin. In the high-temperature depolymerization state, it exhibits low melt viscosity, becoming a flow carrier for encapsulating glass fibers and migrating to the product surface, inhibiting the formation of floating fibers. Maleimide-grafted polyolefin elastomer, as... The dienophile and toughening phase of the Diels-Alder ring reaction has a flexible polyolefin backbone that can effectively absorb external impacts. At the same time, to compensate for the irreversible consumption of BMI groups by a small amount of free amino groups in the conventional system, this component is added in slightly excess in the overall formulation to ensure that the remaining BMI groups can match with furan groups during the cooling stage to form a dense dynamic covalent cross-linked network. The modified inorganic filler surface is treated with a specific low-amino / high-epoxy mixed silane. A small amount of amino groups are used to slightly anchor the BMI on the elastomer phase during the side-feeding wetting stage, while a large amount of epoxy groups combine with the terminal carboxyl groups of the modified PA6, reacting with each other at the microscale to construct a three-dimensional interpenetrating locked network of polyamide matrix-covalently cross-linked elastomer-glass fiber.

[0011] Preferably, the preparation of modified PA6 resin includes the following steps: 100 parts of caprolactam monomer, 2-4 parts of deionized water, and 0.5-1.5 parts of isophthalic acid are added sequentially to a polymerization reactor, along with 0.05-0.15 parts of sodium hypophosphite as a catalyst. Under the protection of high-purity nitrogen, the temperature is raised to 250-260℃, and a ring-opening polymerization reaction is carried out at a pressure of 0.5-1.0 MPa for 4-6 hours. Subsequently, the pressure is slowly reduced to less than 5 kPa, and a vacuum polycondensation reaction is continued for 1-2 hours. The material is discharged, pelletized, and subjected to boiling water extraction and drying to obtain modified PA6 resin. The relative viscosity of the modified PA6 resin is controlled at 2.4-2.6, the weight-average molecular weight is 18000-21000, and the concentration of terminal carboxyl groups is greater than 70 μmol / g, while the concentration of terminal amino groups is less than 15 μmol / g. This is to avoid interference from terminal amino groups in subsequent reactions by using excess carboxyl groups for end-capping.

[0012] Preferably, the preparation of furan-grafted polyamide includes the following steps: 100 parts of maleic anhydride-grafted polyamide, 1.5-2.0 parts of furfurylamine, and 0.2 parts of antioxidant were added to a twin-screw extruder for melt grafting reaction. The temperature of each zone of the extruder was set to 220-240℃. During the melt grafting process in the twin-screw extruder, vacuum exhaust (vacuum degree ≤ -0.09MPa) was turned on in the rear section of the extruder to remove the moisture generated by the imidization reaction. The primary amino group of furfurylamine and the anhydride ring of maleic anhydride under high temperature shearing undergo an imidization ring-closure reaction. After the extruded strands were water-cooled and pelletized, they were dried in a vacuum oven at 100℃ for 10-12h to obtain furan-grafted polyamide with a grafting rate of 1-1.5%.

[0013] Preferably, the preparation of maleimide-grafted polyolefins includes the following steps: 100 parts of maleic anhydride-grafted elastomer and 1.2-1.8 parts of p-aminophenyl maleimide were mixed evenly and then reacted and extruded through a twin-screw extruder. To prevent the elastomer from undergoing cross-linking degradation at high temperatures, the reaction temperature was strictly controlled at 180-210℃. After extrusion granulation, the product was vacuum dried to obtain maleimide-grafted polyolefin with a grafting rate of 0.8-1.2%.

[0014] Preferably, the preparation of the modified inorganic filler includes the following steps: mixing 45-80 parts of anhydrous ethanol with 5-10 parts of deionized water to prepare a mixed solvent; adding 0.8-0.85 parts of KH-560 to obtain the treated fiber, and ultrasonically oscillating at a frequency of 40 kHz and an ultrasonic power of 300 W; so that the epoxy silane preferentially undergoes a condensation reaction with the hydroxyl groups on the surface of the glass fiber; then adding 0.15-0.2 parts of KH-550 to the mixed solvent for pre-hydrolysis, impregnating the treated fiber surface, continuing ultrasonic vibration for 5-10 min, centrifuging to remove excess liquid, and placing it in a vacuum drying oven at 110-120℃ for cross-linking and curing for 1.5-2.5 h to obtain the modified inorganic filler.

[0015] The present invention also provides a high-strength polyamide resin composition, characterized in that the raw materials for preparation include PA6 resin, modified PA6 resin, furan-grafted polyamide, maleimide-grafted polyolefin, composite antioxidant, pentaerythritol stearate and modified inorganic filler.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. Existing glass fiber reinforced polyamide technology often leads to a decrease in tensile strength and modulus when introducing elastomers for toughening. This invention introduces maleimide-grafted polyolefin elastomer as a dienophile. At the solid-phase interface after cooling and shaping, it undergoes reversible covalent bonding with furan-grafted polyamide through the Diels-Alder ring reaction, forming a cross-interface molecular stitching effect. This cross-links the high-rigidity polyamide matrix with the high-flexibility elastomer, enabling the elastomer to not only effectively absorb external impacts but also avoid interfacial slippage, thus maintaining the overall mechanical properties.

[0017] 2. Traditional glass fiber modification often uses a single silane coupling agent, resulting in weak interfacial locking force. This invention uses a mixture of low-amino and high-epoxy silanes to process glass fiber in stages. During extrusion, the epoxy groups on the surface of the modified glass fiber combine with the terminal carboxyl groups of the modified PA6, providing basic interfacial locking force. Meanwhile, the amino groups are slightly anchored to the BMI on the elastomer phase during the side-feeding wetting stage. This three-dimensional interpenetrating network at the microscale effectively transfers the stress on the glass fiber surface to the elastomer for dissipation, thereby improving the shear strength of the micro-debonding interface.

[0018] 3. Existing technologies mainly rely on viscosity reducers to solve the problem of fiber floating, which sacrifices the intrinsic bonding strength of the material. In this invention, the furan-grafted polyamide backbone is thermodynamically compatible with the matrix. In the high-temperature processing section of 255-265℃, the furan groups and maleimide groups are in the reverse Diels-Alder state, and the system instantly exhibits a lower melt viscosity. The furan-modified phase becomes a flow carrier that encapsulates the glass fiber and migrates to the surface of the product, thus inhibiting the generation of fiber floating.

[0019] 4. Traditional engineering plastics are prone to molecular chain slippage and microcrack propagation under long-term alternating loads. In this invention, isophthalic acid is used to end-cap PA6 to avoid irreversible consumption of the dynamic network precursor by the terminal amino groups. The three-dimensional dynamic cross-linked network formed inside the system not only ensures good cross-linking density, but also endows the material with good self-healing rate of microcracks after friction and impact, extends bending fatigue life, and improves the overall stability of the material. Attached Figure Description

[0020] Figure 1 The X-ray photoelectron spectroscopy (XPS) spectrum of the modified inorganic filler prepared in Example 1 is shown below. Figure 2 The graph shows the changes in the mechanical properties of the polyamide resin compositions obtained in Example 1 and Comparative Examples 2-8. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] The conventional PA6 resin used in this invention has a relative viscosity of 2.4-2.8 and is of conventional injection molding grade; the maleic anhydride grafting rate of the maleic anhydride-grafted polyamide is 1.0-1.5%, and the melt flow rate is 5-10 g / 10 min (230℃ / 2.16 kg); the maleic anhydride grafting rate of the maleic anhydride-grafted elastomer is 0.8-1.2%, and the melt flow rate is 1.5-3.0 g / 10 min (190℃ / 2.16 kg); the alkali-free glass fiber is alkali-free chopped glass fiber that has undergone 400℃ heat annealing to remove the surface wetting agent, with a single filament diameter of 10-13 μm and an initial length of 3-4 mm, all of which are commercially available raw materials.

[0023] Please see Figures 1 to 2 This invention provides a high-strength polyamide resin composition and its preparation method, the technical solution of which is as follows:

[0024] Example 1 100 parts of caprolactam monomer, 3 parts of deionized water, and 1 part of isophthalic acid were added sequentially to a polymerization reactor. 0.1 parts of sodium hypophosphite were added as a catalyst. Under the protection of high-purity nitrogen, the temperature was raised to 255°C and the ring-opening polymerization reaction was carried out at a pressure of 0.8 MPa for 5 hours. Then, the pressure was slowly reduced to less than 5 kPa, and the vacuum polycondensation reaction was continued for 2 hours. The material was discharged, granulated, and subjected to boiling water extraction and drying to obtain modified PA6 resin. 100 parts of maleic anhydride-grafted polyamide, 1.8 parts of furfurylamine, and 0.2 parts of antioxidant 1010 were added to a twin-screw extruder for melt grafting reaction. The temperature of each zone of the extruder was set to 220-240℃. After the extruded strands were water-cooled and pelletized, they were dried in a vacuum oven at 100℃ for 10 hours to obtain furan-grafted polyamide.

[0025] 100 parts of maleic anhydride-grafted elastomer and 1.5 parts of p-aminophenyl maleimide were mixed evenly and then reacted and extruded through a twin-screw extruder. To prevent the elastomer from undergoing cross-linking degradation at high temperatures, the reaction temperature was strictly controlled at 180-210℃. After extrusion granulation, the product was vacuum dried to obtain maleimide-grafted polyolefin. First, 60 parts of anhydrous ethanol and 6 parts of deionized water were mixed to prepare a mixed solvent. 0.82 parts of KH-560 were added to one part of the mixed solvent for pre-hydrolysis, and then impregnated onto the surface of 100 parts of alkali-free glass fiber. The fiber was ultrasonically vibrated at room temperature for 10 minutes to obtain the treated fiber. The ultrasonic frequency was 40 kHz and the ultrasonic power was 300 W. Then, 0.18 parts of KH-550 were added to another part of the mixed solvent for pre-hydrolysis, and then impregnated onto the surface of the treated fiber. The fiber was ultrasonically vibrated for another 10 minutes. After centrifugation to remove excess liquid, the fiber was placed in a vacuum drying oven at 115 ℃ for cross-linking and curing for 2 hours to obtain the modified inorganic filler. 20 parts of PA6 resin, 25 parts of modified PA6 resin, 8 parts of furan-grafted polyamide, 9 parts of maleimide-grafted polyolefin, 0.6 parts of composite antioxidant, and 0.4 parts of pentaerythritol stearate were added to a high-speed mixer and mixed at room temperature for 5 minutes at 400 rpm to obtain a premix. First, the premix was added to the main feed port of a co-rotating twin-screw extruder with a length-to-diameter ratio of 48:1. The temperature of zones one to five of the extruder was set to 260℃, and the screw speed was set to 480 rpm. Then, the extruder... From zone 6 to zone 8, 45 parts of modified inorganic filler are added through the side feed port. The temperature in this zone is set at 255℃, and a weak shear distribution mixing screw block combination is used. Finally, the melt is evacuated and degassed in zone 9 to zone 11 at a temperature set at 250℃ with a vacuum degree of -0.08MPa. Then, it is extruded from the die head at a temperature set at 240℃ to obtain the molten extrudate. The molten extrudate is then cooled to below 70℃ in a water bath, pelletized, and vacuum dried at 90℃ for 5 hours to obtain the polyamide resin composition.

[0026] Examples 2-4 follow the same preparation method and parameter conditions as Example 1, with differences shown in Table 1.

[0027] Table 1. Parameter changes in Examples 1-4 Key process parameters Example 1 Example 2 Example 3 Example 4 Mass of isophthalic acid (parts) 1.0 0.5 1.5 1.2 Modified PA6 resin reaction temperature / ℃ 255 250 260 258 Mass dosage of furfurylamine / part 1.8 1.5 2.0 1.6 furan-grafted polyamide grafting rate / % 1.2 1.0 1.5 1.3 p-Aminophenylmaleimide dosage (parts) 1.5 1.2 1.8 1.4 Maleimide-grafted polyolefin grafting rate / % 1.0 0.8 1.2 0.9 KH560 dosage (per serving) 0.82 0.80 0.85 0.83 KH550 dosage (per serving) 0.18 0.15 0.20 0.16 Crosslinking curing temperature of modified inorganic fillers / ℃ 115 110 120 118 Modified inorganic filler crosslinking and curing time / h 2.0 1.5 2.5 2.2 Standard PA6 resin usage per part 20 15 25 22 Modified PA6 resin mass dosage / part 25 20 30 28 Furan-grafted polyamide mass dosage / part 8 6 10 7 Maleimide-grafted polyolefin dosage (parts) 9 7 11 10 Modified inorganic filler mass dosage / part 45 40 50 48 Reaction temperatures in zones 1 to 5 / °C 260 255 265 262 Melting temperatures in zones 6 to 8 / °C 255 250 260 258 Twin-screw extruder speed / rpm 480 400 550 500 Comparative Example 1 is the same as Example 1, except that the temperature of the high-temperature reaction section in zones one to five of the twin-screw extruder is reduced from 260°C to 235°C, while the rest of the process remains unchanged.

[0028] Comparative Example 2 is the same as Example 1, except that the modified PA6 resin is replaced with an equal amount of PA6 resin, while the rest of the process remains unchanged.

[0029] Comparative Example 3 is the same as Example 1, except that furan-grafted polyamide is not added and is replaced with conventional PA6 resin in equal amounts, while the rest of the process remains unchanged.

[0030] Comparative Example 4 is the same as Example 1, except that in the preparation of the modified inorganic filler, KH560 is not used, but KH-550 in equal parts by mass is used to modify the surface of alkali-free glass fiber, while the rest of the process remains unchanged.

[0031] Comparative Example 5 is the same as Example 1, except that maleimide-grafted polyolefin elastomer is not added, and it is replaced with an equal amount of ordinary polyolefin elastomer, while the rest of the process remains unchanged.

[0032] Comparative Example 6 is the same as Example 1, except that in the preparation of the modified inorganic filler, KH550 is not used, but an equal mass fraction of KH-560 is used to modify the surface of the alkali-free glass fiber, while the rest of the process remains unchanged.

[0033] Comparative Example 7 is the same as Example 1, except that in the preparation of the modified inorganic filler, the stepwise hydrolysis and stepwise impregnation ultrasonic process is not used. Instead, KH-550 and KH-560 are mixed together in a mixed solvent for one-step hydrolysis and impregnation treatment. The rest of the process remains unchanged.

[0034] Comparative Example 8 is the same as Example 1, except that the modified inorganic filler is added together with the resin premix from the main feed port of Zone 1 of the twin-screw extruder instead of the side feed port, while the rest of the process remains the same.

[0035] Experiment Example 1: Interface Compatibility Test The polyamide resin compositions prepared in Examples 1-4 and Comparative Examples 1-4 were subjected to interfacial compatibility tests. The degree of fiber floating was quantitatively characterized using a specular gloss meter with an incident angle of 60°, according to GB / T 8807-1988, reflecting the pass rate of appearance. Specifically, each group of resin compositions was injection molded into black standard square plates with dimensions of 100mm × 100mm × 3mm in an injection molding machine (injection temperature 260℃, mold temperature 80℃). After the samples were conditioned for 24 hours in a standard environment (23℃, 50%RH), the reflected light flux on the surface of the square plates was measured using a gloss meter at a geometric angle of 60°. Five points were measured at different locations for each sample. The arithmetic mean was taken; using a melt indexer, the barrel temperature was set to 260℃, and dried sample particles were added to the barrel and preheated at a constant temperature for 5 minutes; a standard load of 2.16 kg was applied, and extruded strips were cut at each time interval (every 10 seconds), the mass of the cut strips was weighed, and the mass of the extruded melt per 10 minutes was calculated; a single modified inorganic filler was extracted, and its two ends were fixed to a special metal frame. A small amount of premixed resin from each group was placed on the fiber, and melted at 260℃ to form microdroplets (diameter...) coating the fiber. (Approximately 5-10 times the fiber diameter), after cooling to room temperature, the sample was mounted on a tensile testing machine with micron-level displacement control. A microblade was used to clamp the resin droplet, and the fiber was pulled out of the droplet at a speed of 1 mm / min. The maximum pull-out force was recorded and the shear strength was calculated. The prepared polyamide fiber was hot-pressed into a flat sheet with a thickness of 2 mm in the molten state and conditioned under standard conditions. A special micro / nano scratch tester was used, equipped with a diamond indenter with a tip radius of 20 microns, and a constant load of 200 mN was applied. After the scratch was generated, the three-dimensional morphology of the scratch area was immediately scanned using a laser confocal scanning microscope. The initial maximum scratch depth was accurately measured and recorded as (D1). The sample was placed in a vacuum oven at 120°C for 2 hours to induce the DA cycloaddition reaction between the free furan groups and BMI groups at the interface. Comparative Example 4 without crosslinking agent was selected and subjected to the same scratch and vacuum oven treatment as the example. The physical relaxation recovery rate R caused by the thermal relaxation and thermal expansion of the polymer chain segments was measured. 基体 After removing the heat-treated sample and cooling it to room temperature, measure the repaired scratch depth (D2) at the same location. Calculate the total self-repair rate R based on the formula: self-repair rate = (D1-D2) / D1 × 100%. 总 After deducting matrix thermal relaxation recovery, the net scratch self-healing rate driven by the dynamic covalent network = R 总 -R 基体The dried sample strip was crushed, and about 0.5 g of the sample was weighed and placed in a 120-mesh stainless steel wire mesh bag of known mass. The mesh bag was placed in a Soxhlet extractor and continuously refluxed for 24 h with a mixed solvent of formic acid and trifluoroacetic acid at a volume ratio of 8:2 (which can dissolve uncrosslinked pure PA6 and elastomer). The mesh bag was removed and dried in a vacuum oven at 80℃ to constant weight. The mass of the residual insoluble matter was weighed, and the gel content of the pure resin part was calculated after deducting the mass ratio of glass fiber. The test results are shown in Table 2.

[0036] Table 2 Test results of the examples and comparative examples Example Surface gloss High-temperature melt flow rate (g / 10min) Micro-debonding interface shear strength / MPa Scratch self-healing rate / % Gel content test / % Example 1 88.5 36.4 48.7 92.1 78.6 Example 2 82.1 31.8 44.3 86.5 74.2 Example 3 86.7 39.2 47.9 89.4 77.3 Example 4 84.9 35.6 46.1 87.8 76.9 Comparative Example 1 41.2 12.3 32.5 81.6 73.4 Comparative Example 2 77.4 28.7 25.8 18.2 35.7 Comparative Example 3 59.8 17.5 34.2 38.3 46.9 Comparative Example 4 36.3 6.1 21.6 45.9 84.8 As shown in Table 2, the comparative example, through adjustments to the components and process, exhibits significantly different interfacial compatibility and processing performance compared to the examples. In the examples, the introduction of specific active groups into furan-grafted polyamide and maleimide-grafted polyolefin enables reversible reactions via Diels-Alder addition and reverse decoupling, forming a cross-phase molecular stitching effect at the cooled and shaped interface, tightly bonding the matrix and toughening phase. Furthermore, the stepwise modified inorganic filler undergoes a ring-opening reaction with the terminal carboxyl groups of modified PA6 during extrusion. The grafted polar segments not only impart basic interfacial locking force, but the small amount of amino groups in their molecular structure also enhances the free energy for micro-crosslinking and anchoring of the system with BMI, which is beneficial for suppressing fiber floating and constructing a three-dimensional network.

[0037] In Comparative Example 1, lacking the high-temperature reverse Diels-Alder reaction, furan-grafted polyamide and maleimide-grafted polyolefin rely solely on physical molecular chain peristalsis for bonding during blending and melting. Due to the incomplete depolymerization and viscosity reduction, increased melt flow resistance occurs, and physical flow is insufficient to maintain the structural integrity of the fiberglass as a flow carrier, resulting in low surface gloss and significant fiber exposure. In Comparative Example 2, within the reactive extrusion channel, the conventional PA6 material contains a large number of free terminal amino groups, making irreversible cross-linking likely. These numerous terminal amino groups generate complex side reactions and consume the dynamic network precursor during high-temperature confluence. Furthermore, during subsequent cooling and molding, the reduced number of effective dynamic covalent bonds leads to insufficient deformation resistance due to the reduced cross-link density, resulting in severe stress concentration at the interface and weakening the overall scratch self-healing rate and gel content. In Comparative Example 3, although the main function of conventional PA6 is to provide rigid support, its equivalent substitution of furan... The presence of furan-grafted polyamide in the system, with the absence of dienes, indicates a higher proportion of pure non-dynamic components in the matrix. This alters the matrix's crystallization rate and high-temperature melt viscosity, resulting in a difference in the molecular chain wetting and diffusion depth when in contact with modified glass fiber compared to when furan-grafted polyamide is present. This affects the initial micro-debonding interface shear strength. Furthermore, the system's scratch self-healing performance is significantly reduced in the later stages due to the loss of the dynamic covalent bond network. In Comparative Example 4, when modified with a single KH-550, the proportion of amino groups increases significantly. In the side-feed confluence extrusion channel, the modified glass fiber surface contains a large number of highly active amino components, whose rheological and reaction characteristics do not perfectly match the system. The denser amino groups generate complex and intense irreversible cross-linking flows when in contact with the melt. Moreover, during subsequent processing and molding, the rigid cross-linked dead material formed at high temperatures exhibits high deformation resistance, leading to severe flow obstruction at the melt interface and weakening the overall high-temperature melt flow rate and surface gloss.

[0038] like Figure 1 As shown in the full spectrum, in addition to the characteristic matrix elements silicon (Si 2p, binding energy about 103 eV) and oxygen (O 1s, binding energy about 532 eV) of the glass fiber itself, the modified inorganic filler surface also showed obvious carbon (C 1s, binding energy about 285 eV) and weak but clear nitrogen (N 1s, binding energy about 400 eV) characteristic peaks. Since the surface of the untreated alkali-free glass fiber contains almost no nitrogen, the appearance of the N 1s peak confirms that the pre-hydrolyzed KH550 in the system has been successfully introduced into the glass fiber surface, and the peak intensity of the O 1s peak also verifies the introduction of KH560 in the system.

[0039] Experiment Example 2: Mechanical Property Testing The polyamide resin compositions prepared in Examples 1-4 and Comparative Examples 2-8 were subjected to mechanical property tests. Following GB / T 1040.2-2022, a type 1A multi-purpose dumbbell-shaped standard specimen (total length 170 mm, narrow parallel section width 10 mm, thickness 4 mm) was molded using an injection molding machine. The specimens were conditioned at 23°C and 50%RH for 48 hours. A universal testing machine was used to perform tensile fracture tests at a tensile speed of 5 mm / min, automatically recording the yield strength, breaking force, and elongation within the gauge length. Following GB / T1043.1-2008, a strip specimen with dimensions of 80 mm × 10 mm × 4 mm was injection molded. A Type A notch (notch bottom radius 0.25 mm, remaining width 8 mm) was milled in the middle using a CNC notching machine. A pendulum impact tester was used to deliver a single rapid impact to the back of the notch at 23°C, recording the energy absorbed during fracture and converting it into notched impact strength. A rectangular standard specimen was mounted on an electro-hydraulic servo fatigue testing machine. A three-point bending loading mode was adopted, applying a sinusoidal alternating cyclic load with a stress ratio R=0.1. The maximum stress was set to 60% of the static bending strength of this group, and the test frequency was set to 5Hz (to avoid excessive hysteresis heat generation due to high frequency, which could lead to sample melting). The number of cycles experienced by the sample when macroscopic fracture occurred or the stiffness decreased to 50% of the initial value was recorded. The 1A standard sample was fixed on a dedicated high-temperature creep endurance testing machine, and the ambient temperature was kept constant at 80℃ (simulating the temperature around an automobile engine). A constant tensile stress of 30MPa was applied to the sample, and the deformation data was continuously recorded over 1000 hours using a non-contact optical extensometer. The ratio of the total elongation to the gauge length at 1000 hours was calculated, which is the long-term creep strain rate. The changes in the mechanical properties of the polyamide resin compositions obtained in Example 1 and Comparative Examples 2-8 are as follows. Figure 2 As shown in the figure; the test results are shown in Table 3.

[0040] Table 3. Test results of the examples and comparative examples Example Tensile strength / MPa Elongation at break / % Notched impact strength / kJ / m² Bending fatigue life / cycle Long-term creep resistance strain rate / % Example 1 235.1 3.4 28.7 58400 1.2 Example 2 228.4 3.1 26.3 52100 1.5 Example 3 231.8 3.5 27.6 55300 1.4 Example 4 233.2 3.2 26.9 54800 1.3 Comparative Example 2 205.6 2.7 18.2 28500 2.1 Comparative Example 3 210.3 2.4 15.8 24200 2.3 Comparative Example 4 195.9 1.8 12.5 18900 2.9 Comparative Example 5 190.5 2.1 10.4 15600 3.1 Comparative Example 6 215.7 2.9 17.1 31400 1.9 Comparative Example 7 201.0 2.5 19.3 27800 2.2 Comparative Example 8 145.2 1.6 8.6 11200 4.5 As shown in Table 3, the mechanical properties of the polyamide resin composition obtained in the comparative example, through adjustments to the components and process, are significantly different from those in the examples. In the examples, furan-grafted polyamide and maleimide-grafted polyolefin elastomers both introduce specific polar reactive groups, which can undergo reversible covalent bonding at the interface of the cooled and shaped solid phase through the Diels-Alder ring reaction, forming a cross-interface molecular stitching effect that tightly crosslinks the high-rigidity polyamide matrix with the high-flexibility elastomer phase. In addition, the mixed silane on the surface of the modified inorganic filler reacts during the extrusion process, and the epoxy groups combine with the terminal carboxyl groups of the modified PA6. Some amino groups are slightly anchored to the BMI on the elastomer phase during the side-feeding wetting stage, constructing a three-dimensional interpenetrating locked network at the microscale, which improves the overall mechanical properties of the resin composition.

[0041] In Comparative Example 2, when unclosed conventional PA6 resin was used, the free terminal amino groups underwent irreversible crosslinking with BMI groups at high temperatures, disrupting the integrity of the crosslinking network. This resulted in a decrease in the material's macroscopic resistance to stress cracking, and consequently, a decrease in flexural fatigue life and notched impact strength. In Comparative Example 3, the lack of furan-grafted polyamide as a diene in the Diels-Alder ring reaction led to the loss of the dynamic covalent bond network in the system, resulting in significant mechanical degradation. In Comparative Example 4, the use of KH-550 to treat glass fibers introduced excessive amino groups, causing significant high-temperature crosslinking dead zone rheological problems and disrupting the effective dispersion and length of the glass fibers in the matrix. The retention of this material leads to a significant decrease in mechanical properties. In Comparative Example 5, the lack of a maleimide-grafted polyolefin, a chemical bridge carrying a dienophile, means that ordinary polyolefins rely solely on physical molecular chain entanglement to bond with the matrix during blending. Due to interfacial shear stress generated under external impact, the physical entanglement is insufficient to maintain structural integrity, leading to easy slippage and voiding at the phase interface. The elastomer cannot effectively absorb external impact, resulting in a significant decrease in notched impact strength and elongation at break. In Comparative Example 6, when treated with pure KH-560, although the epoxy groups can still bind to the terminal carboxyl groups of the modified PA6, the mechanical properties are significantly reduced. While providing basic interfacial locking force, the lack of a small amount of amino groups provided by KH-550 prevents the glass fiber from achieving slight anchoring with the BMI on the elastomer phase during the wetting stage. This leads to a disconnect between the inorganic reinforcing phase and the flexible toughening phase. When the material is subjected to long-term static loads or alternating stress, the stress on the glass fiber surface cannot be effectively transferred to the elastomer network for dissipation, resulting in significant stress concentration at the interface and weakening the overall flexural fatigue life and long-term creep resistance. In Comparative Example 7, when the modified inorganic filler is prepared using a one-step mixed hydrolysis method instead of a stepwise process, KH550 and KH560 undergo reactions in the mixed solvent. The self-condensation reaction forms inactive oligomeric siloxanes with large steric hindrance, resulting in a reduction in the number of epoxy and amino groups that can be effectively grafted onto the surface of the glass fiber. This leads to a severe shortage of chemical bonding sites when in contact with the resin matrix in the co-extrusion channel, resulting in a decrease in tensile strength and impact strength. In Comparative Example 8, the feed position was adjusted to the main feed port in Zone 1. Under the high-temperature and strong shearing action of the entire screw's length-to-diameter ratio, the glass fiber was mechanically crushed due to the lack of weak shear protection from the side feed. The length of the glass fiber decreased to below the critical length for reinforcement, causing the loss of its length-to-diameter ratio effect when in contact with the resin, which significantly affected the load-bearing capacity of the material.

[0042] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-strength polyamide resin composition, characterized in that, The preparation process includes the following steps: PA6 resin, modified PA6 resin, furan-grafted polyamide, maleimide-grafted polyolefin, and additives are stirred and blended to obtain a premix; then the premix is ​​added to the main feed port of an extruder, with the melting temperature of zones one to five being 255-265℃; modified inorganic filler is added through the side feed port, vacuum degassing is performed, and the mixture is extruded into strands to obtain a melt extrudate; then the mixture is cooled in a water bath, pelletized, and dried to obtain the polyamide resin composition; the modified PA6 resin is obtained by polycondensation reaction of caprolactam monomer, isophthalic acid, and deionized water; the modified inorganic filler is obtained by stepwise impregnation and crosslinking curing of glass fiber, KH-550, and KH-560.

2. The method for preparing the high-strength polyamide resin composition according to claim 1, characterized in that, The preparation of the melt extrudate includes the following steps: 15-25 parts of the PA6 resin, 20-30 parts of the modified PA6 resin, 6-10 parts of the furan-grafted polyamide, 7-11 parts of the maleimide-grafted polyolefin, 0.6 parts of the composite antioxidant, and 0.4 parts of pentaerythritol stearate are added to a high-speed mixer and stirred to obtain the premix; then 40-50 parts of the modified inorganic filler are added to the side feed port of zones six to eight; and after vacuum degassing, the melt extrudate is obtained by extrusion into strips.

3. The method for preparing the high-strength polyamide resin composition according to claim 2, characterized in that, The preparation of the modified PA6 resin includes the following steps: 100 parts of caprolactam monomer, 0.5-1.5 parts of deionized water and isophthalic acid are added sequentially to a polymerization reactor, and the temperature is raised to 250-260°C under nitrogen protection for ring-opening polymerization; then vacuum polycondensation reaction is carried out, and the material is discharged and granulated to obtain the modified PA6 resin.

4. The method for preparing the high-strength polyamide resin composition according to claim 2, characterized in that, The preparation of the furan-grafted polyamide includes the following steps: adding 100 parts of maleic anhydride-grafted polyamide, 1.5-2.0 parts of furfurylamine and antioxidant 1010 to a twin-screw extruder for melt grafting reaction, extruding the strands, water-cooling and pelletizing, and vacuum drying to obtain the furan-grafted polyamide with a grafting rate of 1.0-1.5%.

5. The method for preparing the high-strength polyamide resin composition according to claim 2, characterized in that, The preparation of the maleimide-grafted polyolefin includes the following steps: 100 parts of maleic anhydride-grafted elastomer and 1.2-1.8 parts of p-aminophenyl maleimide are mixed evenly and then subjected to reactive extrusion through a twin-screw extruder. After extrusion granulation, the mixture is vacuum dried to obtain the maleimide-grafted polyolefin with a grafting rate of 0.8-1.2%.

6. The method for preparing the high-strength polyamide resin composition according to claim 2, characterized in that, The preparation of the modified inorganic filler includes the following steps: mixing anhydrous ethanol and deionized water to obtain a mixed solvent; adding 0.8-0.85 parts of KH-560 to the mixed solvent for pre-hydrolysis, impregnating 100 parts of glass fiber, and ultrasonically treating to obtain treated fiber; subsequently adding 0.15-0.2 parts of KH-550 to the mixed solvent for pre-hydrolysis, impregnating the surface of the treated fiber, ultrasonically vibrating, centrifuging, and then placing it in a vacuum drying oven for cross-linking and curing to obtain the modified inorganic filler.

7. A high-strength polyamide resin composition, characterized in that, The raw materials include PA6 resin, modified PA6 resin, furan-grafted polyamide, maleimide-grafted polyolefin, composite antioxidant, pentaerythritol stearate, and modified inorganic filler; the high-strength polyamide resin composition is prepared by any one of the preparation methods of claims 1-6.

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