Impact-resistant plastic particles and method for making same

Abstract

This invention discloses an impact-resistant plastic granule and its preparation method, belonging to the technical field of polyamide modified materials. The preparation method includes the following steps: raw material drying pretreatment, premixing and activation treatment, overall material blending, twin-screw oriented melt extrusion, cooling granulation, and post-treatment sieving. A twin-screw extruder, combined with a stretching die, induces hydroxyapatite (HAP) nanowires to orient orderly along the melt flow direction, forming a biomimetic enamel-like framework structure. Simultaneously, utilizing the B-N coordination between the terminal amino groups of polyamide and boric acid, and the dehydration esterification reaction of the terminal hydroxyl groups introduced by the hydroxylated graft compatibilizer with boric acid and HAP surface hydroxyl groups, dynamic borate ester covalent bonds and B-N coordination bonds are generated in situ, supplemented by Ca coordination bonds and hydrogen bonds to construct a multi-interface bonding system. This invention completely eliminates the use of elastomer toughening agents, increasing the notched impact strength of the cantilever beam from 5 kJ / m of pure PA6 to 12–15 kJ / m, and the flexural modulus from 2.5 GPa to 3.2–3.8 GPa, achieving a simultaneous improvement in rigidity and toughness.

Description

Technical Field

[0001] This invention belongs to the field of polyamide modified materials technology, and more specifically, relates to an impact-resistant plastic granule and its preparation method. Background Technology

[0002] Polyamide (nylon, PA) is a widely used engineering plastic with advantages such as high strength, wear resistance, and chemical corrosion resistance, but it still has the following core defects: (1) High notch sensitivity and prominent low-temperature brittleness: The notched impact strength of pure PA6 / PA66 cantilever beams is only 4-6 kJ / m. 2 Its toughness decreases sharply at low temperatures, making it prone to brittle fracture, which limits its application under impact load conditions.

[0003] (2) It is difficult to improve rigidity and toughness in a coordinated manner: Traditional impact modification often uses elastomers (such as POE-g-MAH) blends, which can improve impact strength, but will significantly reduce the flexural modulus, tensile strength and heat resistance of the material, resulting in the technical bottleneck of "increasing toughness inevitably reduces rigidity".

[0004] (3) Inorganic filler modification is prone to stress concentration: When inorganic fillers such as calcium carbonate and ordinary HAP powder are used for modification, the fillers are randomly dispersed and tend to form stress concentration points in the matrix. When subjected to impact, the cracks will spread rapidly, which will reduce the impact resistance of the material.

[0005] (4) Weak interface bonding and rapid performance degradation under humid heat aging: The inorganic filler and the PA matrix are only physically coated or weakly bonded. The interface is prone to debonding under humid heat. After long-term use, the impact resistance retention rate is less than 60%, and the service life is greatly shortened.

[0006] (5) No self-healing ability of microcracks: Traditional modified PA cannot repair itself after microcracks are generated by impact. The microcracks gradually expand under cyclic load, leading to material failure.

[0007] In existing technologies, the preparation of biomimetic enamel structural materials mostly adopts a two-way cryogenic casting process. Although this method can prepare bulk materials with highly oriented structures, it is only suitable for bulk materials and cannot be adapted to the industrial production of continuous granulation by twin-screw extrusion. Furthermore, it does not design an interfacial bonding system for the molecular structure of polyamide, resulting in problems such as strong notch sensitivity, difficulty in synergistically improving rigidity and toughness, weak interfacial bonding of inorganic fillers, rapid degradation of wet heat aging performance, and lack of self-healing ability for microcracks. Summary of the Invention

[0008] 1. The problem to be solved To address the problems of existing polyamide materials, such as high notch sensitivity, difficulty in synergistically improving rigidity and toughness, weak interfacial bonding of inorganic fillers, rapid degradation of damp heat aging performance, and lack of microcrack self-healing ability, this invention provides an impact-resistant plastic particle and its preparation method.

[0009] 2. Technical Solution To solve the above problems, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing impact-resistant plastic granules, characterized by comprising the following steps: Step S1: Raw material drying pretreatment The polyamide matrix resin was placed in a hot air drying oven and dried at 100-120℃ for 4-8 hours, with the moisture content controlled to be ≤0.05%; the hydroxyapatite (HAP) nanowires were placed in a vacuum drying oven at 60-80℃ for 2-4 hours to remove surface adsorbed moisture. Step S2: Premixed activation treatment According to the weight ratio, 5-18 parts of dried HAP nanowires, 0.3-2.5 parts of boric acid, and 2-8 parts of hydroxylation graft compatibilizer are added to a high-speed mixer and mixed at 800-2000 rpm at room temperature for 3-6 minutes to achieve pre-activation of hydroxyl groups on the HAP surface and initially form an interfacial reaction precursor. Step S3: Blending of the entire material Add 70-90 parts of dried polyamide matrix resin and 0.4-3.0 parts of composite additive to a high-speed mixer, and continue stirring at 800-2000 rpm for 5-10 minutes to obtain a uniform composite premix. Step S4: Twin-screw orientation melt extrusion A high-shear twin-screw extruder with an aspect ratio (L / D) of 36–40, equipped with a stretching die, was used. The screw speed was set at 200–500 rpm and the feed rate at 15–45 kg / h to melt-extrude the composite premix. Under the synergistic effect of the twin-screw shear field and the die stretching flow field, the melt induced the ordered orientation of HAP nanowires along the extrusion direction. Simultaneously, an in-situ interfacial reaction occurred during extrusion. The terminal hydroxyl groups on the hydroxylated graft compatibilizer reacted with boric acid and the hydroxyl groups on the HAP nanowire surface to form dynamic borate covalent bonds. The terminal amino groups of the polyamide matrix formed BN coordination bonds with boric acid. The CaO on the surface of the HAP nanowires... 2+ Ca forms with the oxygen atoms of the amide bond in the polyamide molecular chain. 2+ Coordination bonds are formed between the amide bonds of the polyamide molecular chain, the hydroxyl groups of the HAP nanowires, and the hydroxyl groups of the boric acid, thus constructing a multi-interface bonding system. Step S5: Cooling and granulation Water bath strip cooling is used, with cooling water temperature of 20-35℃. After the melt strip is cooled and shaped, it is fed into a pelletizer to prepare cylindrical plastic granules with a particle size of 2-4mm and a length of 2-5mm. Step S6: Post-processing screening The granules are dried in hot air at 40-60℃ for 1-3 hours, and then sieved through a vibrating screen to remove fine powder and oversized particles, thus obtaining the finished high-impact polyamide plastic granules.

[0010] Preferably, the weight parts and material selection of each raw material in this invention are shown in Table 1 below: Table 1. Composition of each raw material by weight and selection of materials

[0011] Preferably, the polyamide matrix resin is selected from any one of PA6, PA66, copolynylon (PA6 / 66 copolymer), and PA46.

[0012] Preferably, the polyamide matrix resin accounts for 78 to 85 parts of the total mass of the plastic particles.

[0013] Preferably, the HAP nanowires are high aspect ratio one-dimensional nanostructures with an aspect ratio of 20-50, a diameter of 20-50 nm, a length of 1-3 μm, and a surface rich in hydroxyl active groups; the HAP nanowires account for 8-15 parts of the total mass of the plastic particles; the high aspect ratio one-dimensional nanostructure can form an ordered oriented skeleton under the action of melt shear and tensile flow field, replace traditional disordered fillers, eliminate stress concentration points, and dissipate impact energy through nanowire bridging and pull-out effects.

[0014] Preferably, the boric acid accounts for 0.5 to 1.8 parts of the total mass of the plastic particles; the hydroxylated graft compatibilizer is selected from one or more of hydroxylated PA6, hydroxylated PA66, and hydroxylated copolynylon, corresponding to the type of polyamide matrix resin, and accounts for 3 to 6 parts of the total mass of the plastic particles.

[0015] Preferably, the composite additive is composed of antioxidant 1010, antioxidant 168, and lubricant in a mass ratio of 2:1:1; the lubricant is selected from zinc stearate or EBS (ethylene bis-stearamide); the composite additive accounts for 0.6 to 2.0 parts of the total mass of the plastic particles.

[0016] Preferably, when the polyamide matrix resin is PA66 or PA46, the antioxidant 1010 is replaced with antioxidant 1098.

[0017] Preferably, in step S4, the stretching die forms an axial stretching flow field at the melt outlet, causing the HAP nanowires to be further arranged in an orderly manner along the extrusion direction based on shear orientation, with an orientation degree of over 60%. The orientation degree is defined as the percentage of nanowires whose long axis direction is less than 30° from the extrusion direction to the total number of nanowires. Compared with conventional straight dies, the stretching die can increase the cantilever beam notched impact strength by 30% to 50%.

[0018] Preferably, in step S4, the extrusion temperature is adjusted according to the type of polyamide matrix resin: 210-250℃ for PA6, 240-280℃ for PA66, 220-260℃ for copolynylon, and 280-320℃ for PA46.

[0019] More preferably, the above extrusion temperature control is as shown in Table 2 below: Table 2 Extrusion Temperature Control

[0020] The present invention also provides impact-resistant plastic granules, which are prepared by any of the above-described preparation methods.

[0021] The working principle diagram of this invention can be referred to. Figure 1 The specific principles are as follows: (I) Biomimetic oriented skeleton toughening principle HAP nanowires have a high aspect ratio, forming an enamel-like ordered orientation structure under the shearing action of a twin-screw extruder and the stretching action of a die, replacing traditional disordered fillers. Under external impact, the ordered nanowires can efficiently bear stress, induce crack deflection and branching, dissipate impact energy through nanowire bridging and pull-out effects, prevent cracks from penetrating the matrix in a straight line, and eliminate stress concentration points.

[0022] (II) Principle of Multiple Interface Bonding (Triple Effect) 1. Dynamic borate ester covalent bonds and BN coordination bonds: The terminal hydroxyl groups on the hydroxylated graft compatibilizer react with boric acid and the hydroxyl groups on the surface of HAP nanowires through dehydration at high temperature, generating dynamic borate ester covalent bonds in situ; at the same time, the terminal amino groups of the PA matrix form BN coordination bonds with boric acid, further enhancing the interfacial bonding strength and dynamic reversibility.

[0023] 2. Coordinate bonds (including BN coordination and Ca coordination) 2+ (Coordination): The terminal amino group of the PA matrix forms a BN coordination bond with boric acid, and the Ca on the HAP surface... 2+ It forms Ca with the amide bond oxygen atom in the PA molecular chain. 2+ Coordination bonds, with two coordination functions working together to enhance interface integration.

[0024] 3. Hydrogen bonds: A large number of hydrogen bonds are formed between the amide bonds of the PA molecular chain, the hydroxyl groups of the HAP nanowires, and the hydroxyl groups of boric acid, constructing a multi-interface interaction system and completely solving the problem of interfacial debonding between inorganic fillers and PA matrix.

[0025] (III) Dynamic Bond Self-Healing Principle Both boronic acid ester bonds and BN coordination bonds exhibit reversible fracture-recombination characteristics under humid and hot conditions: when the material is subjected to impact and microcracks are generated, the dynamic bonds break and dissipate energy; under warm conditions (60℃ / 80%RH), the broken dynamic bonds can be rebonded through water molecule mediation, repairing the microcracks and restoring the material's mechanical and impact resistance properties. After humid and hot aging at 85℃ / 85%RH for 500 hours, the impact resistance retention rate is ≥85%.

[0026] (iv) The principle of synergistic improvement of rigidity and toughness Ordered HAP nanowire frameworks can significantly improve the rigidity of materials, such as flexural modulus and tensile strength; dynamic bond fracture energy dissipation, nanowire pull-out / crack deflection and other multi-scale toughening mechanisms can greatly improve notched impact strength, breaking the technical bottleneck of "toughening inevitably reduces rigidity" in traditional elastomer toughening.

[0027] 3. Beneficial effects Compared with the prior art, the beneficial effects of the present invention are as follows: (1) Significantly improved mechanical properties: Taking the PA6 matrix as an example, the notched impact strength of the cantilever beam is significantly improved from 5 kJ / m² of pure PA6. 2 Increased to 12-15 kJ / m 2 The improvement ranges from 140% to 200%; the flexural modulus increases from 2.5 GPa to 3.2 to 3.8 GPa, an increase of 28% to 52%; and the tensile strength increases by 20% to 35%.

[0028] (2) Excellent interface stability: After 500h of damp heat aging at 85℃ / 85%RH, the impact resistance retention rate is ≥85%, which is much higher than the ≤60% of traditional elastomer modified PA.

[0029] (3) Outstanding self-healing performance: After the material develops microcracks, it can achieve a self-healing efficiency of more than 80% when placed in a warm environment of 60℃ / 80%RH for 48 hours.

[0030] (4) Strong process adaptability: The entire process adopts conventional twin-screw extrusion granulation process, without the need for special equipment such as cryogenic casting, and can be directly adapted to existing industrial production lines, with controllable production costs.

[0031] (5) Good dimensional stability: The filler is oriented in an orderly manner with no stress concentration points, resulting in small warping deformation after injection molding and excellent dimensional stability. Attached Figure Description

[0032] Figure 1 This is a schematic diagram illustrating the structural principle of the high-impact polyamide plastic particles of the present invention; Figure 2 Scanning electron microscope (SEM) image of the cross-section of high-impact polyamide plastic granules; Figure 3 High-magnification SEM images of cross-sections of high-impact polyamide plastic particles reveal the multilayer structure and the interfacial bonding structure between HAP nanowires and the PA matrix. Detailed Implementation

[0033] The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and does not limit the description of the features and characteristics of the invention, in order to suggest the best mode for carrying out the invention and to enable those skilled in the art to practice the invention. However, it should be understood that various modifications and variations can be made without departing from the scope of the invention as defined by the appended claims. The detailed description should be considered illustrative only and not restrictive, and any such modifications and variations shall fall within the scope of the invention described herein. Furthermore, the background art is intended to illustrate the current state of research and development and significance of the technology, and is not intended to limit the invention or the scope of application of this application.

[0034] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains; the terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to limit the invention.

[0035] The present invention will be further described below with reference to specific embodiments.

[0036] Example Example 1 (PA6-based high-impact plastic granules): Step S1: Raw material drying pretreatment PA6 resin was placed in a hot air drying oven and dried at 105℃ for 5 hours, with the moisture content controlled to be ≤0.05%; HAP nanowires (aspect ratio 35, diameter 35nm, length 2μm) were placed in a vacuum drying oven at 70℃ for 3 hours to remove surface adsorbed moisture.

[0037] Step S2: Premixed activation treatment 12 parts by weight of dried HAP nanowires, 1.2 parts by weight of boric acid and 4.5 parts by weight of hydroxylated PA6 were added to a high-speed mixer and mixed at 1500 rpm at room temperature for 5 min to achieve pre-activation of hydroxyl groups on the HAP surface and to initially form an interfacial reaction precursor.

[0038] Step S3: Blending of the entire material Add 82 parts of dried PA6 resin and 1.1 parts of composite additive (composed of antioxidant 1010, antioxidant 168 and zinc stearate in a mass ratio of 2:1:1) to a high-speed mixer, and continue stirring at 1500 rpm for 8 minutes to obtain a uniform composite premix.

[0039] Step S4: Twin-screw orientation melt extrusion A high-shear twin-screw extruder with an aspect ratio (L / D) of 38 was used, paired with a stretching die. The screw speed was set at 350 rpm and the feed rate at 25 kg / h. Extrusion temperatures were set as follows: Zone 1 215℃, Zone 2 230℃, Zone 3 240℃, Zone 4 245℃, and the die temperature at 250℃. Under the synergistic effect of the twin-screw shear field and the die stretching flow field, the melt induced ordered orientation of HAP nanowires along the extrusion direction, achieving an orientation degree of 68%. Simultaneously, in-situ interfacial reactions occurred during extrusion. Dynamic borate ester covalent bonds were formed by the dehydration reaction of terminal hydroxyl groups on hydroxylated PA6 with boric acid and hydroxyl groups on the HAP nanowire surface. BN coordination bonds were formed by the terminal amino groups of the PA6 matrix with boric acid. Furthermore, CaO on the surface of the HAP nanowires... 2+ It forms Ca with the amide bond oxygen atom in the PA6 molecular chain. 2+ Coordination bonds are formed between the amide bonds of the PA6 molecular chain, the hydroxyl groups of the HAP nanowires, and the hydroxyl groups of boric acid, thus constructing a multi-interface bonding system.

[0040] Step S5: Cooling and granulation Water bath strip cooling is used, with the cooling water temperature at 25℃. After the melt strip is cooled and shaped, it is fed into a pelletizer to produce cylindrical plastic pellets with a particle size of 3mm and a length of 3mm.

[0041] Step S6: Post-processing screening The granules were dried in hot air at 50°C for 2 hours, and then sieved through a vibrating screen to remove fine powder and oversized particles, resulting in high-impact polyamide plastic granules.

[0042] The SEM images of the fracture surfaces of the finished high-impact polyamide plastic granules after liquid nitrogen brittle fracture are shown below. Figure 2 and Figure 3 As shown, the multilayer structure of the finished high-impact polyamide plastic particles and the interfacial bonding structure between the HAP nanowires and the PA matrix are displayed, which forms the structural basis for the excellent performance of the high-impact polyamide plastic particles of this invention.

[0043] Performance test results: Notched impact strength of the cantilever beam is 13.2 kJ / m. 2 The flexural modulus is 3.5 GPa, the tensile strength is 68 MPa, and the impact strength retention rate is 88% after 500 hours of humid heat aging at 85℃ / 85%RH. The self-healing efficiency of microcracks (60℃ / 80%RH / 48h) is 96%.

[0044] Example 2 (PA66-based high-impact plastic granules): Step S1: Raw material drying pretreatment PA66 resin was placed in a hot air drying oven and dried at 115℃ for 6 hours, with the moisture content controlled to be ≤0.05%; HAP nanowires (aspect ratio 40, diameter 40nm, length 2.5μm) were placed in a vacuum drying oven at 75℃ for 3 hours to remove surface adsorbed moisture.

[0045] Step S2: Premixed activation treatment According to the weight ratio, 13 parts of dried HAP nanowires, 1.0 part of boric acid, and 5.0 parts of hydroxylated PA66 were added to a high-speed mixer and mixed at 1600 rpm at room temperature for 5 minutes to achieve pre-activation of hydroxyl groups on the HAP surface and initially form an interfacial reaction precursor.

[0046] Step S3: Blending of the entire material Add 80 parts of dried PA66 resin and 1.0 part of composite additive (composed of antioxidant 1098, antioxidant 168 and zinc stearate in a mass ratio of 2:1:1) to a high-speed mixer, and continue stirring at 1600 rpm for 8 minutes to obtain a uniform composite premix.

[0047] Step S4: Twin-screw orientation melt extrusion A high-shear twin-screw extruder with an aspect ratio (L / D) of 38 was used, paired with a stretching die. The screw speed was set at 400 rpm and the feed rate at 22 kg / h. Extrusion temperatures were set as follows: Zone 1 245℃, Zone 2 260℃, Zone 3 270℃, Zone 4 275℃, and the die temperature at 280℃. Under the synergistic effect of the twin-screw shear field and the die stretching flow field, the melt induced ordered orientation of HAP nanowires along the extrusion direction, achieving an orientation degree of 65%. Simultaneously, in-situ interfacial reactions occurred during extrusion. Dynamic borate ester covalent bonds were formed by the dehydration reaction of terminal hydroxyl groups on hydroxylated PA66 with boric acid and hydroxyl groups on the HAP nanowire surface. BN coordination bonds were formed by the terminal amino groups of the PA66 matrix with boric acid. Furthermore, CaO on the surface of the HAP nanowires... 2+ It forms Ca with the amide bond oxygen atoms in the PA66 molecular chain. 2+ Coordination bonds are formed, and hydrogen bonds are formed between the amide bonds of the PA66 molecular chain, the hydroxyl groups of the HAP nanowires, and the hydroxyl groups of boric acid, thus constructing a multi-interface bonding system.

[0048] Step S5: Cooling and granulation Water bath strip cooling is used, with the cooling water temperature at 28℃. After the melt strip is cooled and shaped, it is fed into a pelletizer to produce cylindrical plastic pellets with a diameter of 3mm and a length of 3mm.

[0049] Step S6: Post-processing screening The granules were dried in hot air at 55℃ for 2 hours, and then sieved through a vibrating screen to remove fine powder and oversized particles, resulting in high-impact polyamide plastic granules.

[0050] Performance test results: Notched impact strength of the cantilever beam is 10.8 kJ / m. 2 The flexural modulus is 4.1 GPa, the tensile strength is 78 MPa, and the impact strength retention rate is 86% after 500 hours of humid heat aging at 85℃ / 85%RH. The self-healing efficiency of microcracks (60℃ / 80%RH / 48h) is 94%.

[0051] Example 3 (Copolymer Nylon (PA6 / 66) Based High Impact Plastic Granules): Step S1: Raw material drying pretreatment PA6 / 66 copolymer was placed in a hot air drying oven and dried at 110℃ for 5 hours, with the moisture content controlled to be ≤0.05%; HAP nanowires (aspect ratio 30, diameter 30nm, length 1.5μm) were placed in a vacuum drying oven at 70℃ for 3 hours to remove surface adsorbed moisture.

[0052] Step S2: Premixed activation treatment According to the weight ratio, 10 parts of dried HAP nanowires, 0.8 parts of boric acid, and 3.8 parts of hydroxylated copolymer nylon were added to a high-speed mixer and mixed at 1400 rpm at room temperature for 5 minutes to achieve pre-activation of hydroxyl groups on the HAP surface and initially form an interfacial reaction precursor.

[0053] Step S3: Blending of the entire material Add 84 parts of dried PA6 / 66 copolymer and 1.4 parts of composite additive (composed of antioxidant 1010, antioxidant 168 and EBS in a mass ratio of 2:1:1) to a high-speed mixer, and continue stirring at 1400 rpm for 8 minutes to obtain a uniform composite premix.

[0054] Step S4: Twin-screw orientation melt extrusion A high-shear twin-screw extruder with an aspect ratio (L / D) of 38 was used, equipped with a stretching die. The screw speed was set at 300 rpm and the feed rate at 30 kg / h. Extrusion temperatures were set as follows: Zone 1 225℃, Zone 2 240℃, Zone 3 250℃, Zone 4 255℃, and die temperature 260℃. Under the synergistic effect of the twin-screw shear field and the die stretching flow field, the melt induced ordered orientation of HAP nanowires along the extrusion direction, achieving an orientation degree of 72%. Simultaneously, in-situ interfacial reactions occurred during extrusion. The terminal hydroxyl groups on the hydroxylated copolymer nylon reacted with boric acid and the hydroxyl groups on the HAP nanowire surface to form dynamic borate ester covalent bonds. The terminal amino groups on the copolymer nylon matrix formed BN coordination bonds with boric acid. The CaO on the surface of the HAP nanowires... 2+ Ca forms with the amide bond oxygen atoms in the copolymer nylon molecular chain.2+ Coordination bonds are formed, and hydrogen bonds are formed between the amide bonds of the copolymer nylon molecular chain, the hydroxyl groups of the HAP nanowires, and the hydroxyl groups of boric acid, thus constructing a multi-interface bonding system.

[0055] Step S5: Cooling and granulation Water bath strip cooling is used, with the cooling water temperature at 25℃. After the melt strip is cooled and shaped, it is fed into a pelletizer to produce cylindrical plastic pellets with a particle size of 3mm and a length of 3mm.

[0056] Step S6: Post-processing screening The granules were dried in hot air at 50°C for 2 hours, and then sieved through a vibrating screen to remove fine powder and oversized particles, resulting in high-impact polyamide plastic granules.

[0057] Performance test results: Notched impact strength of the cantilever beam is 14.5 kJ / m. 2 The flexural modulus is 3.1 GPa, the tensile strength is 62MPa, and the impact strength retention rate is 90% after 500h of humid heat aging at 85℃ / 85%RH. The self-healing efficiency of microcracks (60℃ / 80%RH / 48h) is 97%.

[0058] Comparative Example The following comparative examples all use the PA6 resin of Example 1, with only the specified characteristics changed, and the rest of the formulation and process are completely consistent with Example 1.

[0059] Comparative Example 1: This comparative example also provides a plastic particle, the main difference between its preparation method and the examples being that it lacks HAP nanowires (no biomimetic orientation framework). Its specific preparation method is as follows: Step S1: Raw material drying pretreatment PA6 resin was placed in a hot air drying oven and dried at 105℃ for 5 hours, with the moisture content controlled to be ≤0.05%.

[0060] Step S2: Premixed activation treatment Add 1.2 parts by weight of boric acid and 4.5 parts by weight of hydroxylated PA6 into a high-speed mixer and mix at 1500 rpm at room temperature for 5 minutes.

[0061] Step S3: Blending of the entire material Add 94 parts of dried PA6 resin and 1.1 parts of composite additive to a high-speed mixer, and continue stirring at 1500 rpm for 8 minutes to obtain a uniform composite premix.

[0062] Step S4: Twin-screw orientation melt extrusion A high-shear twin-screw extruder with an L / D ratio of 38 was used, equipped with a stretching die, with a screw speed of 350 rpm and a feed rate of 25 kg / h. Extrusion temperatures were set as follows: Zone 1 215℃, Zone 2 230℃, Zone 3 240℃, Zone 4 245℃, and die temperature 250℃. Due to the absence of HAP nanowires, an oriented framework structure could not be formed.

[0063] Step S5: Cooling and granulation The molten strip is cooled by a water bath at a temperature of 25°C. After cooling and solidification, it is fed into a pelletizer to produce plastic pellets.

[0064] Step S6: Post-processing screening The granules were dried in hot air at 50°C for 2 hours and then sieved through a vibrating screen to obtain plastic granules.

[0065] Performance limitations: The non-oriented nanowire framework cannot dissipate energy through crack deflection / pull-out, relying solely on the resin's inherent toughness; the cantilever beam notched impact strength is only 4.6 kJ / m. 2 Compared to Example 1, the strength decreased by 65%; the flexural modulus was 2.1 GPa, a decrease of 40%; it had no self-healing ability, and after 500 hours of damp heat aging at 85℃ / 85%RH, the impact strength retention rate was only 52%.

[0066] Comparative Example 2: This comparative example also provides a plastic granule, the main difference between its preparation method and the previous example being that HAP nanowires are replaced with ordinary micron-sized HAP powder. The specific preparation method is as follows: Step S1: Raw material drying pretreatment PA6 resin was placed in a hot air drying oven and dried at 105℃ for 5 hours, with the moisture content controlled to be ≤0.05%; ordinary micron-sized HAP powder (particle size 1~5μm, no aspect ratio) was placed in a vacuum drying oven at 70℃ for 3 hours to remove surface adsorbed moisture.

[0067] Step S2: Premixed activation treatment According to the weight ratio, 12 parts of dried ordinary micron-sized HAP powder, 1.2 parts of boric acid, and 4.5 parts of hydroxylated PA6 were added into a high-speed mixer and mixed at 1500 rpm at room temperature for 5 minutes.

[0068] Step S3: Blending of the entire material Add 82 parts of dried PA6 resin and 1.1 parts of composite additive to a high-speed mixer, and continue stirring at 1500 rpm for 8 minutes to obtain a uniform composite premix.

[0069] Step S4: Twin-screw orientation melt extrusion A high-shear twin-screw extruder with an L / D ratio of 38 was used, equipped with a stretching die. The screw speed was set at 350 rpm and the feed rate at 25 kg / h. Extrusion temperatures were set as follows: Zone 1 215℃, Zone 2 230℃, Zone 3 240℃, Zone 4 245℃, and the die temperature was 250℃. Because HAP powder has no L / D ratio, it cannot form an oriented structure, resulting in numerous stress concentration points randomly distributed within the matrix.

[0070] Step S5: Cooling and granulation The molten strip is cooled by a water bath at a temperature of 25°C. After cooling and solidification, it is fed into a pelletizer to produce plastic pellets.

[0071] Step S6: Post-processing screening The granules were dried in hot air at 50°C for 2 hours and then sieved through a vibrating screen to obtain plastic granules.

[0072] Performance defects: The powder has no aspect ratio and cannot form an oriented structure, resulting in numerous stress concentration points randomly distributed within the matrix; it is prone to rapid crack propagation upon impact, and its notched impact strength is only 7.6 kJ / m. 2 Compared to Example 1, the strength decreased by 42%; after damp heat aging, the interface debonding was severe, and the impact strength retention rate was only 55% after 500 hours of damp heat aging at 85℃ / 85%RH. This proves that the high aspect ratio one-dimensional nanostructure of HAP nanowires is the key to the formation of the orientation framework.

[0073] Comparative Example 3: This comparative example also provides a plastic granule, the main difference between its preparation method and the examples being that it does not contain boric acid. The specific preparation method is as follows: Step S1: Raw material drying pretreatment PA6 resin was placed in a hot air drying oven and dried at 105℃ for 5 hours, with the moisture content controlled to be ≤0.05%; HAP nanowires (aspect ratio 35, diameter 35nm, length 2μm) were placed in a vacuum drying oven at 70℃ for 3 hours.

[0074] Step S2: Premixed activation treatment According to the weight ratio, 12 parts of dried HAP nanowires and 4.5 parts of hydroxylated PA6 were added to a high-speed mixer and mixed at 1500 rpm at room temperature for 5 minutes.

[0075] Step S3: Blending of the entire material Add 83.2 parts of dried PA6 resin and 1.1 parts of composite additive to a high-speed mixer, and continue stirring at 1500 rpm for 8 minutes to obtain a uniform composite premix.

[0076] Step S4: Twin-screw orientation melt extrusion A high-shear twin-screw extruder with an L / D ratio of 38 was used, equipped with a stretching die. The screw speed was set at 350 rpm and the feed rate at 25 kg / h. Extrusion temperatures were set as follows: Zone 1 215℃, Zone 2 230℃, Zone 3 240℃, Zone 4 245℃, and the die temperature was 250℃. Due to the absence of boric acid, dynamic borate ester covalent bonds and BN coordination bonds could not be formed; bonding occurred solely through hydrogen bonds.

[0077] Step S5: Cooling and granulation The molten strip is cooled by a water bath at a temperature of 25°C. After cooling and solidification, it is fed into a pelletizer to produce plastic pellets.

[0078] Step S6: Post-processing screening The granules were dried in hot air at 50°C for 2 hours and then sieved through a vibrating screen to obtain plastic granules.

[0079] Performance defects: It relies solely on hydrogen bonding and physical adsorption to form dynamic covalent bonds, resulting in weak interfacial adhesion and easy packing material peeling; the notched impact strength of the cantilever beam is only 8.6 kJ / m². 2 Compared to Example 1, the strength decreased by 35%; it lacked self-healing ability for microcracks, and after 500 hours of damp heat aging at 85°C / 85%RH, the impact strength retention rate was only 58%. This demonstrates that the covalent bonds of the dynamic borate ester and the coordination bonds of BN are key to the self-healing ability and damp heat aging performance.

[0080] Comparative Example 4: This comparative example also provides a plastic granule, the main difference between its preparation method and the examples being that it does not involve stretching or orientation. The specific preparation method is as follows: Step S1: Raw material drying pretreatment PA6 resin was placed in a hot air drying oven and dried at 105℃ for 5 hours, with the moisture content controlled to be ≤0.05%; HAP nanowires (aspect ratio 35, diameter 35nm, length 2μm) were placed in a vacuum drying oven at 70℃ for 3 hours.

[0081] Step S2: Premixed activation treatment According to the weight ratio, 12 parts of dried HAP nanowires, 1.2 parts of boric acid, and 4.5 parts of hydroxylated PA6 were added to a high-speed mixer and mixed at 1500 rpm at room temperature for 5 minutes.

[0082] Step S3: Blending of the entire material Add 82 parts of dried PA6 resin and 1.1 parts of composite additive to a high-speed mixer, and continue stirring at 1500 rpm for 8 minutes to obtain a uniform composite premix.

[0083] Step S4: Twin-screw orientation melt extrusion A high-shear twin-screw extruder with an L / D ratio of 38 was used, replacing the stretching die with a conventional straight die, reducing the screw speed to 100 rpm, and the feed rate to 25 kg / h. Extrusion temperatures were set as follows: Zone 1 215℃, Zone 2 230℃, Zone 3 240℃, Zone 4 245℃, and die temperature 250℃. Due to the lack of melt stretching and orientation, the HAP nanowires were randomly dispersed within the matrix, unable to form an oriented framework structure.

[0084] Step S5: Cooling and granulation The molten strip is cooled by a water bath at a temperature of 25°C. After cooling and solidification, it is fed into a pelletizer to produce plastic pellets.

[0085] Step S6: Post-processing screening The granules were dried in hot air at 50°C for 2 hours and then sieved through a vibrating screen to obtain plastic granules.

[0086] Performance defects: Without melt stretching and orientation, HAP nanowires are randomly dispersed within the matrix, failing to form an oriented framework structure, resulting in a significant decrease in toughening effect; the cantilever beam notched impact strength is only 8.9 kJ / m. 2 The concentration decreased by 33% compared to Example 1. This demonstrates that the axial stretching flow field formed by the stretching die is key to the ordered orientation of HAP nanowires.

[0087] Performance testing methods: 1. Cantilever beam notched impact strength: Tested according to GB / T 1843-2008 "Determination of impact strength of plastic cantilever beam", with a sample size of 80mm×10mm×4mm and notch type A.

[0088] 2. Flexural modulus: Tested in accordance with GB / T 9341-2008 "Determination of Flexural Properties of Plastics", with a span of 64 mm and a test speed of 2 mm / min.

[0089] 3. Tensile strength: Tested in accordance with GB / T 1040.2-2006 "Determination of tensile properties of plastics", with specimen type 1A and test speed of 5 mm / min.

[0090] 4. Damp heat aging test: The test shall be conducted in accordance with GB / T 12000-2003 "Determination of the effects of exposure of plastics to damp heat, water spray and salt spray", under the conditions of 85℃ / 85%RH and an aging time of 500h.

[0091] 5. Microcrack self-healing efficiency test: After pre-forming microcracks in the sample, place it in a 60℃ / 80%RH environment for 48 hours. Test the impact strength of the cantilever beam notch before and after repair, and calculate the self-healing efficiency = (impact strength after repair / original impact strength) × 100%. (- indicates no relevant capability or inability to test) Table 3 Mechanical Performance Test Results

[0092] Table 4 Results of damp heat aging and self-healing performance tests

[0093] The performance data of each embodiment and comparative example are summarized in Tables 3 and 4. In summary, the comparison shows that all three embodiments achieved a significant synergistic improvement in rigidity and toughness. Taking Example 1, based on PA6, as an example, the notched impact strength increased from 5 kJ / m² of pure PA6. 2 It jumped to 13.2 kJ / m 2 (164% improvement), flexural modulus increased from 2.5 GPa to 3.5 GPa (40% improvement), completely breaking the technical bottleneck of "toughening inevitably reduces stiffness" in traditional elastomer toughening. Among them, Example 3 with copolymer nylon base showed the most outstanding toughness (14.5 kJ / m). 2 The PA66-based Example 2 exhibits the best rigidity (flexural modulus 4.1 GPa, tensile strength 78 MPa), while the PA6-based Example 1 demonstrates the most balanced overall performance, lowest cost, and highest industrialization potential. The item-by-item comparison of the four comparative examples further validates the indivisibility and synergy of the technical solutions: the impact strength drops sharply to 4.6 kJ / m² when the HAP nanowire framework is missing (Comparative Example 1). 2 (Reduction of 65%), and the retention rate after damp heat aging was only 52%; when the nanowires were replaced with ordinary micron powder (Comparative Example 2), the impact strength was only 7.6 kJ / m because the orientation could not guide the crack deflection. 2 (42% reduction); the impact strength of the boric acid dynamic bonding system (Comparative Example 3) with only weak hydrogen bonds at the interface is 8.6 kJ / m. 2 (Reduced by 35%) and completely lost its self-healing ability; using a conventional straight die head to replace the stretching die head (Comparative Example 4), the HAP nanowires were randomly dispersed, and the impact strength decreased to 8.9 kJ / m. 2 (Reduced by 33%). The above fully demonstrates that the HAP nanowire biomimetic orientation framework, the dynamic borate ester / BN coordination bonding system, and the stretching die orientation process are all indispensable. Their synergistic effect constitutes the technical foundation for the three core advantages of this invention: simultaneous improvement of rigidity and toughness, excellent damp heat aging performance, and self-healing ability of microcracks.

[0094] The present invention has been described in detail above with reference to specific exemplary embodiments. However, it should be understood that various modifications and variations can be made without departing from the scope of the invention as defined by the appended claims. The detailed description should be considered illustrative only and not restrictive, and any such modifications and variations shall fall within the scope of the invention described herein. Furthermore, the background art is intended to illustrate the current state of development and significance of the technology and is not intended to limit the present invention or the scope of application of the present application.

[0095] More specifically, although exemplary embodiments of the invention have been described herein, the invention is not limited to these embodiments, but includes any and all embodiments modified, omitted, such as combinations between various embodiments, adaptive changes, and / or substitutions, as would be apparent to those skilled in the art from the foregoing detailed description. The limitations in the claims are to be interpreted broadly as used in the language of the claims and are not limited to the examples described in the foregoing detailed description or during the implementation of this application, which should be considered non-exclusive. Any step listed in any method or process claim may be performed in any order and is not limited to the order set forth in the claims. Therefore, the scope of the invention should be determined solely by the appended claims and their legal equivalents, and not by the description and examples given above.

[0096] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. In case of conflict, the definitions in this specification shall prevail. When flow rate, power, refractive index, time, or other values ​​or parameters are expressed as ranges, preferred ranges, or a series of upper and lower preferred values, this should be understood as specifically disclosing all ranges formed by any pair of any upper or preferred value with any lower or preferred value, regardless of whether such range is disclosed individually. For example, the range 1-50 should be understood to include any number, combination of numbers, or subrange selected from 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, or 50, as well as all decimal values ​​between the integers mentioned above, such as 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, and 1.9. Regarding subranges, specifically consider "nested subranges" extending from any endpoint of the range. For example, nested sub-ranges of the exemplary range 1-50 may include 1-10, 1-20, 1-30 and 1-40 in one direction, or 50-40, 50-30, 50-20 and 50-10 in another direction.

Claims

1. A method for preparing impact-resistant plastic granules, characterized in that, Includes the following steps: Step S1: Raw material drying pretreatment The polyamide matrix resin was placed in a hot air drying oven and dried at 100-120℃ for 4-8 hours, with the moisture content controlled to be ≤0.05%; the hydroxyapatite nanowires were placed in a vacuum drying oven at 60-80℃ for 2-4 hours to remove surface adsorbed moisture. Step S2: Premixed activation treatment According to the weight ratio, 5-18 parts of dried hydroxyapatite nanowires, 0.3-2.5 parts of boric acid, and 2-8 parts of hydroxylation graft compatibilizer are added to a high-speed mixer and mixed at room temperature at 800-2000 rpm for 3-6 minutes to achieve pre-activation of hydroxyl groups on the surface of hydroxyapatite nanowires and initially form an interfacial reaction precursor. Step S3: Blending of the entire material Add 70-90 parts of dried polyamide matrix resin and 0.4-3.0 parts of composite additive to a high-speed mixer, and continue stirring at 800-2000 rpm for 5-10 minutes to obtain a uniform composite premix. Step S4: Twin-screw orientation melt extrusion A high-shear twin-screw extruder with an aspect ratio (L / D) of 36–40, equipped with a stretching die, is used. The screw speed is set at 200–500 rpm and the feed rate at 15–45 kg / h to melt-extrude the composite premix. Under the synergistic effect of the twin-screw shear field and the die stretching flow field, the melt induces the ordered orientation of hydroxyapatite nanowires along the extrusion direction. Simultaneously, an in-situ interfacial reaction occurs in the melt during extrusion. The terminal hydroxyl groups on the hydroxylated graft compatibilizer react with boric acid and the hydroxyl groups on the surface of the hydroxyapatite nanowires to form dynamic borate ester covalent bonds. The terminal amino groups of the polyamide matrix form BN coordination bonds with boric acid. The Ca on the surface of the hydroxyapatite nanowires... 2+ Ca forms with the oxygen atoms of the amide bond in the polyamide molecular chain. 2+ Coordination bonds are formed, and hydrogen bonds are formed between the amide bonds of the polyamide molecular chain, the hydroxyl groups of the hydroxyapatite nanowires, and the hydroxyl groups of boric acid, thus constructing a multi-interface bonding system. Step S5: Cooling and granulation Water bath strip cooling is used, with cooling water temperature of 20-35℃. After the melt strip is cooled and shaped, it is fed into a pelletizer to prepare cylindrical plastic granules with a particle size of 2-4mm and a length of 2-5mm. Step S6: Post-processing screening The granules are dried in hot air at 40-60℃ for 1-3 hours, and then sieved through a vibrating screen to remove fine powder and oversized particles, thus obtaining the finished high-impact polyamide plastic granules.

2. The preparation method according to claim 1, characterized in that, The polyamide matrix resin is selected from any one of PA6, PA66, copolynylon, and PA46.

3. The preparation method according to claim 1 or 2, characterized in that, The polyamide matrix resin accounts for 78 to 85 parts of the total mass of the plastic particles.

4. The preparation method according to claim 1, characterized in that, The hydroxyapatite nanowires are high aspect ratio one-dimensional nanostructures with an aspect ratio of 20-50, a diameter of 20-50 nm, and a length of 1-3 μm. The surface is rich in hydroxyl active groups. The hydroxyapatite nanowires account for 8-15 parts of the total mass of the plastic particles. The high aspect ratio one-dimensional nanostructure can form an ordered orientation framework under the action of melt shear and stretching flow field.

5. The preparation method according to claim 1, characterized in that, The boric acid accounts for 0.5 to 1.8 parts of the total mass of the plastic particles; the hydroxylated graft compatibilizer is selected from one or more of hydroxylated PA6, hydroxylated PA66, and hydroxylated copolynylon, corresponding to the type of polyamide matrix resin, and accounts for 3 to 6 parts of the total mass of the plastic particles.

6. The preparation method according to claim 1, characterized in that, The composite additive is composed of antioxidant 1010, antioxidant 168, and lubricant in a mass ratio of 2:1:1; the lubricant is selected from zinc stearate or EBS; the composite additive accounts for 0.6 to 2.0 parts of the total mass of the plastic granules.

7. The preparation method according to claim 5, characterized in that, When the polyamide matrix resin is PA66 or PA46, antioxidant 1010 is replaced with antioxidant 1098.

8. The preparation method according to claim 1, characterized in that, In step S4, the stretching die forms an axial stretching flow field at the melt outlet, which further arranges the hydroxyapatite nanowires in an orderly manner along the extrusion direction on the basis of shear orientation, with an orientation degree of more than 60%. The orientation degree is defined as the percentage of nanowires whose long axis direction is less than 30° from the extrusion direction to the total number of nanowires.

9. The preparation method according to claim 1, characterized in that, In step S4, the extrusion temperature is adjusted according to the type of polyamide matrix resin: 210-250℃ for PA6, 240-280℃ for PA66, 220-260℃ for copolynylon, and 280-320℃ for PA46.

10. An impact-resistant plastic granule, characterized in that, The impact-resistant plastic granules are prepared by the preparation method according to any one of claims 1 to 9.

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