Fatigue-resistant self-lubricating polyamide composite material, preparation method and application thereof

Abstract

This invention relates to the field of polyamide composite materials technology, specifically to a fatigue-resistant self-lubricating polyamide composite material, its preparation method, and its applications. The invention discloses a fatigue-resistant self-lubricating polyamide composite material, its preparation method, and its applications. This composite material is made of a copolyamide containing a β-hydroxyamide structure, a long-chain polyamide, an IL-GO / h-BN-OH heterostructure lubricant, and short-cut carbon fibers. The β-hydroxyamide dynamic network dissipates strain energy through reversible bond exchange, improving fatigue resistance; the IL-GO / h-BN-OH heterostructure forms a stable transfer film, achieving low frictional wear; and the short-cut carbon fibers provide load-bearing reinforcement. This invention overcomes the problem of the contradiction between wear resistance and toughness, and insufficient fatigue life, through ternary synergy, making it suitable for manufacturing high-load self-lubricating parts.

Description

Technical Field

[0001] This invention relates to the field of polyamide composite materials technology, specifically to a fatigue-resistant self-lubricating polyamide composite material, its preparation method, and its application. Background Technology

[0002] Polyamides possess high strength, good wear resistance, and easy molding and processing characteristics, and are commonly used in gears, bearings, guide rails, bushings, automotive moving parts, and mechanical transmission components. For parts subjected to reciprocating loads and sliding friction, polyamide materials need to simultaneously possess high strength, high toughness, low coefficient of friction, low wear rate, and fatigue resistance. Conventional modification methods often use fillers such as glass fiber, carbon fiber, graphite, molybdenum disulfide, polytetrafluoroethylene, graphene, or hexagonal boron nitride to improve strength and wear resistance. However, increasing the amount of rigid fillers can easily cause stress concentration, reducing impact toughness and fatigue life; increasing the amount of lubricating fillers may reduce interfacial bonding and load-bearing capacity. Therefore, there is a clear contradiction between wear resistance and strength / toughness.

[0003] To overcome the above-mentioned technical problems, existing solutions have attempted to improve the mechanical and tribological properties of polyamides by adding solid lubricants and reinforcing fibers through blending modification. For example, CN107189428A discloses a graphene / carbon fiber reinforced nylon composite wear-resistant material and its preparation method and application. The material includes: nylon resin, carbon fiber, graphene / nylon 6 masterbatch, organic lubricant, inorganic solid lubricant, coupling agent and antioxidant. The method is as follows: (1) the inorganic solid lubricant and the coupling agent are coupled to obtain a coupled inorganic solid lubricant; (2) the graphene / nylon 6 masterbatch, organic lubricant, coupled inorganic solid lubricant and antioxidant are mixed to obtain a mixed additive; (3) the nylon resin and the mixed additive are fed into an extruder, carbon fiber is added, the mixture is blended and extruded, drawn, cooled, dried and pelletized to obtain the final product. However, conventional blending methods are unable to solve the problems of poor bonding between the lubricating filler and the matrix, filler agglomeration, and easy breakage of reinforcing fibers during the mixing process, resulting in the inability to effectively overcome the contradiction between "wear resistance and toughness".

[0004] In summary, how to innovate a new preparation method that can simultaneously construct a reversible dynamic crosslinking network and a two-dimensional heterogeneous synergistic lubrication system in a polyamide matrix has become a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a fatigue-resistant self-lubricating polyamide composite material, its preparation method and its application, so as to solve the technical problems of wear resistance and toughness contradiction and insufficient fatigue life in the prior art.

[0006] The specific technical solution is as follows:

[0007] This invention provides a fatigue-resistant, self-lubricating polyamide composite material, which is composed of the following components by weight: 60-80 parts of copolyamide (PA66-co-β-OH copolymer) containing β-hydroxyamide structural units; 5-20 parts of long-chain polyamide; 3-8 parts of a heterostructure composite of ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride (IL-GO / h-BN-OH), wherein the mass ratio of ionic liquid covalently grafted graphene oxide to hydroxylated hexagonal boron nitride is 1:(1-5); 5-10 parts of short-cut carbon fibers pre-coated with KH-570; 0.2-0.6 parts of antioxidant; 0.1-0.3 parts of light stabilizer; and 0.1-0.3 parts of processing aid.

[0008] Furthermore, the copolyamide containing β-hydroxyamide structural units is formed by the condensation polymerization of an aliphatic diacid, an aliphatic diamine, and N,N′-bis(2-hydroxyethyl)-1,6-hexanediamine, wherein the ratio of the carboxyl equivalent of the aliphatic diacid to the total amino equivalent of the aliphatic diamine and N,N′-bis(2-hydroxyethyl)-1,6-hexanediamine is 1:0.995~1.005; the aliphatic diacid is selected from autoic acid or sebacic acid, and the aliphatic diamine is selected from autodiamine or sebacic acid.

[0009] Furthermore, the ionic liquid covalently grafted graphene oxide is prepared by reacting the following raw materials in parts by weight: 5-15 parts graphene oxide, 10-30 parts 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate, 10-20 parts N,N-dicyclohexylcarbodiimide, and 1-3 parts 4-dimethylaminopyridine.

[0010] Furthermore, the long-chain polyamide is selected from polyamide 1010 or polyamide 1012.

[0011] This invention provides a method for preparing a fatigue-resistant, self-lubricating polyamide composite material, comprising the following steps:

[0012] S1: Adipic acid, hexamethylenediamine, and N,N′-bis(2-hydroxyethyl)-1,6-hexamethylenediamine were added to a polymerization reactor. After purging oxygen with high-purity nitrogen for 15 minutes, the temperature was raised to carry out a pre-condensation reaction. During this process, the water generated in the reaction was removed through a condenser. Subsequently, a vacuum was drawn until the vacuum degree was lower than 50 Pa, and the temperature was raised to continue the reaction. When the stirring torque reached the set value, the reaction was stopped, and nitrogen was introduced to break the vacuum. The molten product was granulated underwater and vacuum dried at 100°C for 16 hours until the moisture content was lower than 0.05% to obtain PA66-co-β-OH copolymer. PA66-co-β-OH copolymer and polyamide 1010 were placed in a vacuum drying oven and dried at 90°C for 12 hours until the moisture content was lower than 0.05% for later use.

[0013] S2: Graphene oxide was dispersed in N,N-dimethylformamide and ultrasonically dispersed for 1 hour until homogeneous. 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate, N,N-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine were added, and the reaction was carried out under nitrogen protection. After the reaction, the solid product was collected by centrifugation and washed once each with N,N-dimethylformamide (DMF), anhydrous ethanol, and deionized water. Finally, it was vacuum dried at 60°C for 24 hours to obtain ionic liquid covalently grafted graphene oxide. Ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride were added to anhydrous ethanol in a certain proportion and ultrasonically dispersed for 2 hours. After centrifugation, it was vacuum dried at 60°C for 24 hours until the solvent residue was less than 0.1% to obtain the IL-GO / h-BN-OH heterostructure complex.

[0014] S3: Under nitrogen protection, the dried PA66-co-β-OH copolymer, polyamide 1010, antioxidant, light stabilizer and processing aid are added to a high-speed mixer and mixed at room temperature; then the IL-GO / h-BN-OH heterostructure composite is added and mixing continues; finally, short-cut carbon fibers pre-coated with KH-570 are added and gently mixed until uniform to obtain the premix.

[0015] S4: Under nitrogen protection, the premixed material is added to the main feed port of a co-rotating twin-screw extruder. The feeding section, compression section, melt mixing section, venting section, and die head temperature, screw speed, and feeding rate are set. After melt mixing and vacuum venting to remove volatiles, the extruded strip is cooled in a water bath, pelletized, and then vacuum dried at 80°C for 4 hours until the moisture content is below 0.05%, resulting in fatigue-resistant self-lubricating polyamide composite granules. After drying the composite granules at 80°C for 4 hours, they are added to an injection molding machine. The injection temperature, mold temperature, holding pressure time, and cooling time are set. After melt plasticizing, injection molding, holding pressure to compensate for shrinkage, and cooling and shaping, the product is demolded to obtain fatigue-resistant self-lubricating polyamide composite material. The product is then placed in an 80°C oven for annealing for 2 hours to eliminate residual stress.

[0016] Furthermore, the pre-condensation reaction described in S1 is set to a reaction temperature of 210~230℃, a reaction time of 1~3 hours, and a stirring speed of 50~80 rpm; the temperature is increased to continue the reaction, and the temperature needs to be increased to 245~265℃, and the reaction continues for 3~4 hours; the set value is 2.5~3 times the initial torque.

[0017] Furthermore, the reaction described in S2 is carried out under nitrogen protection, with the following conditions: reaction temperature 50~70℃, reaction time 12~36 hours, and stirring speed 50~150 rpm.

[0018] Furthermore, in step S3, the mixing at room temperature is set to a speed of 600-1000 rpm and a mixing time of 3-8 minutes; the continued mixing is set to a mixing time of 2-5 minutes; and the gentle mixing is set to a speed of 200-400 rpm and a mixing time of 1-3 minutes.

[0019] Furthermore, the specific settings for the feeding section, compression section, melt mixing section, venting section, and die head temperature, screw speed, and feeding rate in S4 are as follows: feeding section 220~250℃, compression section 230~260℃, melt mixing section 240~270℃, venting section 240~265℃, die head 240~265℃, screw speed 150~250rpm, and feeding rate 8~16kg / h; the specific settings for the injection temperature, mold temperature, holding time, and cooling time are as follows: injection temperature 240~260℃, 250~270℃, 255~275℃, 250~270℃, mold temperature 80~120℃, holding time 10~30 seconds, and cooling time 15~35 seconds.

[0020] The present invention also provides an application of a fatigue-resistant self-lubricating polyamide composite material, which can be used to manufacture self-lubricating mechanical parts that are subjected to reciprocating loads and sliding friction.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) It has recyclable self-healing properties: Through the in-situ constructed β-hydroxyamide dynamic exchange network, the material can achieve multiple repairs of microcracks under thermal stimulation conditions, which helps to extend the service life of the product.

[0023] (2) It has synergistically enhanced self-lubricating properties: the two-dimensional heterostructure formed by ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride can form a stable transfer film at the friction interface, which is beneficial to reducing the friction coefficient.

[0024] (3) It has good fatigue resistance: under alternating stress, the dynamic covalent network can dissipate part of the strain energy through bond exchange. Combined with the load-bearing capacity of carbon fiber, it helps to suppress the early propagation of fatigue cracks.

[0025] (4) It has low water absorption and good dimensional stability: The introduction of long-chain polyamide components can reduce the water absorption tendency of composite materials. Combined with the annealing post-treatment process, it is beneficial to maintain the dimensional stability of the product in a humid and hot environment. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating a fatigue-resistant self-lubricating polyamide composite material, its preparation method, and its application according to the present invention.

[0027] Figure 2 This is a transmission electron microscope (TEM) image of the IL-GO / h-BN-OH heterostructure composite obtained in Example 1 of this invention. Detailed Implementation

[0028] This invention proposes a fatigue-resistant self-lubricating polyamide composite material, its preparation method, and its applications, such as... Figure 1 The diagram shows a flowchart of a fatigue-resistant self-lubricating polyamide composite material, its preparation method, and its application according to the present invention. The detailed preparation steps are as follows:

[0029] 1. Matrix copolymerization and drying

[0030] Adipic acid, hexamethylenediamine, and N,N′-bis(2-hydroxyethyl)-1,6-hexamethylenediamine were added to a polymerization reactor and subjected to pre-condensation and high-temperature, high-vacuum condensation reactions to obtain a copolyamide (PA66-co-β-OH copolymer) containing β-hydroxyamide structural units. This β-hydroxyamide structure can undergo a reversible hydroxy-amide exchange reaction under thermal stimulation: at processing temperatures, it imparts thermoplasticity to the material for easy molding; at service temperatures, it provides structural support through network stability; and under alternating stress, it dissipates strain energy through bond exchange to inhibit microcrack propagation. The resulting copolymer was dried with polyamide 1010 to remove moisture and prevent hydrolytic degradation during high-temperature processing.

[0031] 2. Packing material pre-preparation

[0032] Graphene oxide was dispersed in N,N-dimethylformamide (DMF) and subjected to an amidation reaction with 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate under the catalysis of N,N-dicyclohexylcarbodiimide and 4-dimethylaminopyridine. This process covalently grafted the ionic liquid onto the graphene oxide surface, increasing the interlayer spacing and effectively inhibiting aggregation while enhancing interfacial bonding with the polyamide matrix. The covalently grafted graphene oxide was then ultrasonically composited with hydroxylated hexagonal boron nitride at a 1:3 mass ratio to obtain a heterostructure composite of ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride (IL-GO / h-BN-OH), forming a two-dimensional heterostructured stacked structure. This structure synergistically forms a continuous, dense, low-shear-strength transfer film during friction. The hexagonal boron nitride oxidizes under frictional heat to form boron-containing oxidized / hydroxylated lubricating species, promoting stable transfer film formation and achieving long-term low-friction wear.

[0033] 3. Segmented variable speed mixing

[0034] Under nitrogen protection, dried PA66-co-β-OH, polyamide 1010, antioxidants, light stabilizers, and processing aids were first mixed at 800 rpm for 5 minutes to ensure uniform adhesion of the aids to the resin surface. Then, the IL-GO / h-BN-OH heterostructure composite was added and mixing continued for 3 minutes to disperse it evenly using shear force. Finally, the rotation speed was reduced to 300 rpm, and short-cut carbon fibers pre-coated with KH-570 silane coupling agent were gently mixed for 2 minutes. The low-speed conditions prevented excessive fiber breakage, protecting the aspect ratio to fully exert its load-bearing and crack propagation resistance functions. The continuous nitrogen protection process inhibited the thermo-oxidative degradation of polyamide during high-temperature processing, maintaining the integrity of the dynamic network structure.

[0035] 4. Extrusion Granulation and Injection Molding

[0036] The premixed material is added to a twin-screw extruder and melt-blended within a temperature range of 240–260°C. Vacuum degassing removes moisture and volatiles. The extruded strip is then water-cooled, pelletized, and dried to obtain composite granules. During the melting process, the β-hydroxyamide bonds in the dynamic network undergo rapid exchange, ensuring good flowability. The granules are injection molded, and the finished product is annealed at 80°C for 2 hours. This temperature is below the significant activation temperature of the dynamic exchange and is only used to eliminate residual injection stress without altering the network topology, ultimately yielding a polyamide composite product that combines high fatigue resistance and self-lubrication.

[0037] The technical solution designed by this invention to solve the existing problems includes the following key points:

[0038] 1. In-situ construction of dynamic covalent networks of β-hydroxyamides

[0039] Traditional polyamide composites, under long-term alternating stress, experience irreversible propagation of internal microcracks once they initiate, ultimately leading to sudden fatigue failure. This invention introduces N,N′-bis(2-hydroxyethyl)-1,6-hexanediamine into the polyhexamethylene adipamide backbone via copolymerization, forming a copolyamide (PA66-co-β-OH copolymer) containing a β-hydroxyamide structure. The hydroxyl and amide groups in this structural unit undergo a reversible hydroxy-amide exchange reaction under thermal stimulation. Specifically, during the reaction, the hydroxyl oxygen atom attacks the carbonyl carbon of the amide, forming a five-membered cyclic intermediate. Subsequently, proton transfer and bond rearrangement occur, resulting in the recombination of covalent bonds between the two molecular chains. This exchange reaction has a low activation energy and can proceed effectively within the range of 120–150°C, requiring no external catalyst. When microcracks form within the material, the β-hydroxyamide groups on both sides of the crack undergo an exchange reaction under thermal activation, causing the broken molecular chains to reconnect, thereby achieving self-healing of the cracks. The dynamic network remains frozen at service temperature, maintaining a stable cross-linked structure; under thermal stimulation, the dynamic bonds can undergo reversible exchange, which is beneficial for dissipating strain energy.

[0040] 2. Constructing a two-dimensional heterogeneous synergistic lubrication system of IL-GO / h-BN-OH

[0041] While the addition of traditional solid lubricants can reduce friction, it disrupts the continuity of the polyamide matrix, leading to a decrease in mechanical properties and fatigue life. This invention designs a two-dimensional heterostructure lubricant composed of ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride in a 1:3 mass ratio. Its mechanism of action is reflected in three aspects: First, ionic liquid covalently grafts graphene oxide to form covalent bonds with carboxyl groups on the surface of graphene oxide through an amidation reaction. The introduction of long chains of ionic liquid not only improves the dispersibility of graphene oxide in the polyamide matrix, but also enhances the interfacial bonding strength through the cation-dipole interaction between imidazole cations and polyamide groups. Second, hydroxylated hexagonal boron nitride is combined with grafted graphene oxide through ultrasound to form a two-dimensional stacked heterostructure. This structure can synergistically form a continuous, dense, low-shear-strength transfer film during friction. Among them, hexagonal boron nitride undergoes a tribochemical reaction under the action of tribothermia to generate boron-containing oxidized / hydroxylated lubricating species, which promotes the formation of a stable transfer film and further reduces the coefficient of friction. Third, the covalent grafting strategy ensures that the lubricant is anchored in the matrix and is not easy to fall off, avoiding the generation of wear debris as in traditional physically blended lubricants.

[0042] To verify the formation of the above-mentioned heterostructure, the IL-GO / h-BN-OH heterostructure complex prepared in Example 1 of this invention was characterized using transmission electron microscopy. Figure 2 As shown, Figure 2 The image shows a transmission electron microscope (TEM) image of the IL-GO / h-BN-OH heterostructure composite obtained in Example 1 of this invention. As can be observed from the image, the ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride form a two-dimensional sheet-like stacked structure. The two are tightly bound together, forming a regular heterostructure stacked morphology. No obvious aggregation phenomenon was observed, which confirms the successful construction of the above-mentioned heterostructure.

[0043] 3. Establish a segmented variable-speed mixing process with nitrogen protection throughout the entire process.

[0044] In conventional blending processes, high-speed mixing can easily lead to excessive breakage of chopped fibers, weakening the reinforcing effect; while polyamide is prone to thermo-oxidative degradation during high-temperature processing. This invention addresses these issues by establishing a segmented variable-speed mixing process with nitrogen protection throughout the entire mixing process. In the mixing stage, a three-stage variable-speed mixing method is used: the first stage uses a high speed of 800 rpm to uniformly mix resin particles and powdered additives; the high-speed shearing at this stage facilitates uniform adhesion of the additives to the resin surface. In the second stage, the IL-GO / h-BN-OH heterostructure composite is added, and high-speed mixing is maintained at 800 rpm, utilizing shear force to uniformly disperse the nano-lubricating filler on the resin matrix surface. In the third stage, the speed is reduced to 300 rpm, and chopped carbon fibers are gently added; the lower shear force at this stage subjects the fibers to bending rather than impact forces, resulting in a fiber length retention rate of over 80% of the initial length. In the melt extrusion stage, nitrogen protection is maintained from the main feed port to the die head, creating a localized inert atmosphere to inhibit contact between oxygen and the free radical chain ends of the polyamide, thereby slowing down the thermo-oxidative degradation reaction. Meanwhile, the twin-screw extruder is equipped with a vacuum exhaust section to promptly remove adsorbed moisture from the raw materials and small volatile molecules generated during processing, thus avoiding hydrolysis side reactions. This process ensures the structural integrity and synergistic effect of each functional component, ultimately achieving a balance between high fatigue resistance and low friction and wear.

[0045] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the specific embodiments, structures, features, and effects according to the present invention will be described in detail below with reference to the accompanying drawings and preferred embodiments. In the following description, different "an embodiment" or "an embodiment" do not necessarily refer to the same embodiment. Furthermore, specific features, structures, or characteristics in one or more embodiments can be combined in any suitable form.

[0046] Example 1

[0047] Table 1 Raw Material Information Table

[0048] Raw material name Model / Dosage Form CAS number adipic acid ≥99.0% 124-04-9 Hexamethylenediamine ≥99.0% 124-09-4 N,N′-Bis(2-hydroxyethyl)-1,6-hexanediamine ≥95.0% - Polyamide 1010 Industrial grade, intrinsic viscosity 1.0~1.5 dL / g 28774-87-0 Graphene oxide Monolayer ratio ≥95%, sheet diameter 0.5~5μm 1034343-98-0 N,N-Dimethylformamide (DMF) Industrial grade, V50%~80% 68-12-2 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate Industrial grade, B18%~20% 914770-49-3 N,N-Dicyclohexylcarbodiimide ≥99.0% 538-75-0 4-Dimethylaminopyridine ≥99.999% 1122-58-3 Hydroxylated hexagonal boron nitride ≥99.7%, tablet diameter 0.1~0.4μm, hydroxyl content 5.5%~6.5% 10043-11-5 Anhydrous ethanol Industrial grade, purity ≥99.9% 64-17-5 antioxidants 1098 / 168 compound, ≥98.0% 23128-74-7 / 31570-04-4 Light stabilizers UV-770, ≥99.0% 52829-07-9 Processing aids EBS, ≥98.0% 110-30-5 Short-cut carbon fiber Fiber grade, length 200~300μm 7440-44-0 KH-570 ≥98.0% 2530-85-0

[0049] A fatigue-resistant self-lubricating polyamide composite material, its preparation method, and its application include the following steps:

[0050] S1: 146 parts adipic acid, 114.3 parts hexamethylenediamine, and 3.06 parts N,N′-bis(2-hydroxyethyl)-1,6-hexamethylenediamine were added to a polymerization reactor. After purging with high-purity nitrogen for 15 minutes, the temperature was raised to 220°C for a pre-condensation reaction for 2 hours. During this period, the water generated in the reaction was discharged through a condenser. The stirring speed of the polymerization reactor was 60 rpm. Then, the temperature was raised to 255°C, and a vacuum was drawn until the vacuum degree was lower than 50 Pa. The reaction continued for 3.5 hours. When the stirring torque reached 2.8 times the initial torque, the reaction was stopped. Nitrogen was introduced to break the vacuum. The molten product was granulated underwater and vacuum dried at 100°C for 16 hours until the moisture content was lower than 0.05% to obtain PA66-co-β-OH copolymer. 70 parts of PA66-co-β-OH copolymer and 12 parts of polyamide 1010 were placed in a vacuum drying oven and dried at 90°C for 12 hours until the moisture content was lower than 0.05% for later use.

[0051] S2: Disperse 10 parts of graphene oxide in 200 parts of N,N-dimethylformamide and sonicate for 1 hour until homogeneous. Add 20 parts of 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate, 15 parts of N,N-dicyclohexylcarbodiimide, and 2 parts of 4-dimethylaminopyridine. React at 60°C for 24 hours under nitrogen protection, with the stirring speed of the reactor at 100 rpm. After the reaction, collect the solid product by centrifugation and wash it successively with DMF, anhydrous ethanol, and deionized water. Once the solvent was removed, the mixture was vacuum dried at 60℃ for 24 hours. The residual DMF was found to be less than 0.1% and the residual anhydrous ethanol was less than 0.05%, thus obtaining ionic liquid covalently grafted graphene oxide. The ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride were added to anhydrous ethanol at a mass ratio of 1:3, ultrasonically dispersed for 2 hours, collected by centrifugation, and vacuum dried at 60℃ for 24 hours until the residual solvent content was less than 0.1%, thus obtaining the IL-GO / h-BN-OH heterostructure complex.

[0052] S3: Add KH-570 silane coupling agent to a mixed solvent of ethanol / water at a volume ratio of 9:1, adjust the pH to 4.5 with glacial acetic acid, and stir for 30 minutes to hydrolyze; add short-cut carbon fibers, stir at room temperature for 2 hours, filter, and vacuum dry at 80℃ for 4 hours to obtain short-cut carbon fibers pre-coated with KH-570, with a coating amount of 0.2%~3.0% of the mass of the short-cut carbon fibers; under nitrogen protection, add the dried PA66-co-β-OH copolymer, polyamide 1010, 0.4 parts antioxidant, 0.2 parts light stabilizer, and 0.2 parts processing aid to a high-speed mixer, and mix for 5 minutes at room temperature and a blade speed of 800 rpm; then add 5 parts of IL-GO / h-BN-OH heterostructure composite, and continue mixing for 3 minutes; finally, add 8 parts of short-cut carbon fibers pre-coated with KH-570 at a low speed of 300 rpm, and gently mix for 2 minutes until uniform to obtain a premix.

[0053] S4: Under nitrogen protection, the premixed material is added to the main feed port of a co-rotating twin-screw extruder. The feed section temperature is set to 240℃, the compression section to 250℃, the melt mixing section to 260℃, the venting section to 255℃, and the die head to 255℃. The screw speed is 200 rpm, and the feed rate is 12 kg / h. After melt mixing and vacuum venting to remove volatiles, the extruded strip is cooled in a water bath, pelletized, and then vacuum dried at 80℃ for 4 hours until the moisture content is below 0.05%, yielding fatigue-resistant material. Self-lubricating polyamide composite granules were dried at 80°C for 4 hours and then added to an injection molding machine. The injection temperatures were set to 250°C, 260°C, 265°C, and 260°C, the mold temperature was 100°C, the holding time was 18 seconds, and the cooling time was 25 seconds. After melting and plasticizing, injection molding, holding pressure and shrinkage compensation, and cooling and shaping, the product was demolded to obtain fatigue-resistant self-lubricating polyamide composite material. The product was then placed in an 80°C oven for annealing for 2 hours to eliminate residual stress.

[0054] Example 2

[0055] The preparation method is the same as in Example 1, except that:

[0056] S1: 140 parts adipic acid, 110 parts hexamethylenediamine and 2 parts N,N′-bis(2-hydroxyethyl)-1,6-hexamethylenediamine; 60 parts PA66-co-β-OH copolymer and 5 parts polyamide 1010;

[0057] S2: 5 parts graphene oxide dispersed in 150 parts N,N-dimethylformamide; 10 parts 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate, 10 parts N,N-dicyclohexylcarbodiimide and 1 part 4-dimethylaminopyridine; ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride at a mass ratio of 1:5;

[0058] S3: 0.2 parts antioxidant, 0.1 parts light stabilizer and 0.1 parts processing aid; 3 parts IL-GO / h-BN-OH heterostructure composite; 5 parts short-cut carbon fibers with KH-570 pre-coated surface;

[0059] All other steps are the same.

[0060] Example 3

[0061] The preparation method is the same as in Example 1, except that:

[0062] S1: 155 parts adipic acid, 120 parts hexamethylenediamine and 4 parts N,N′-bis(2-hydroxyethyl)-1,6-hexamethylenediamine; 80 parts PA66-co-β-OH copolymer and 20 parts polyamide 1010;

[0063] S2: 15 parts of graphene oxide dispersed in 250 parts of N,N-dimethylformamide; 30 parts of 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate, 20 parts of N,N-dicyclohexylcarbodiimide and 3 parts of 4-dimethylaminopyridine; ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride at a mass ratio of 1:1;

[0064] S3: 0.6 parts antioxidant, 0.3 parts light stabilizer and 0.3 parts processing aid; 8 parts IL-GO / h-BN-OH heterostructure composite; 10 parts short-cut carbon fibers with KH-570 pre-coated surface;

[0065] All other steps are the same.

[0066] Example 4

[0067] The preparation method is the same as in Example 1, except that:

[0068] S1: Heat to 210℃ for pre-condensation reaction for 1 hour; stir the polymerization reactor at 50 rpm; raise the temperature to 245℃; continue the reaction for 3 hours; stop the reaction when the stirring torque reaches 2.5 times the initial torque;

[0069] S2: React at 50°C for 12 hours under nitrogen protection, with the stirring speed of the reactor at 50 rpm;

[0070] S3: Mix for 3 minutes at room temperature and 600 rpm; continue mixing for 2 minutes; 200 rpm; gently mix for 1 minute until homogeneous;

[0071] S4: Set the feeding section temperature to 220℃, compression section temperature to 230℃, melt mixing section temperature to 240℃, venting section temperature to 240℃, and die head temperature to 240℃; screw speed to 150 rpm; feeding rate to 8 kg / h; set injection molding temperature to 240℃, 250℃, 255℃, and 250℃; mold temperature to 80℃; holding time to 10 seconds; and cooling time to 15 seconds.

[0072] All other steps are the same.

[0073] Example 5

[0074] The preparation method is the same as in Example 1, except that:

[0075] S1: Heat to 230℃ for pre-condensation reaction for 3 hours; stir the polymerization reactor at 80 rpm; raise the temperature to 265℃; continue the reaction for 4 hours; stop the reaction when the stirring torque reaches 3 times the initial torque;

[0076] S2: React at 70°C for 36 hours under nitrogen protection, with the stirring speed of the reactor being 150 rpm;

[0077] S3: Mix for 8 minutes at room temperature and 1000 rpm; continue mixing for 5 minutes; 400 rpm; gently mix for 3 minutes until homogeneous;

[0078] S4: Set the feeding section temperature to 250℃, compression section temperature to 260℃, melt mixing section temperature to 270℃, venting section temperature to 265℃, and die head temperature to 265℃; screw speed to 250 rpm; feeding rate to 16 kg / h; set injection molding temperature to 260℃, 270℃, 275℃, and 270℃; mold temperature to 120℃; holding time to 30 seconds; and cooling time to 35 seconds.

[0079] All other steps are the same.

[0080] Example 6

[0081] The preparation method is the same as in Example 1, except that:

[0082] S1: Replace adipic acid and hexamethylenediamine with sebacic acid and sebacic acid, both of which are bio-based monomers. When feeding, maintain the ratio of carboxyl equivalent of aliphatic dicarboxylic acid to total amino equivalent of aliphatic diamine at 1:0.98, and the molar ratio of sebacic acid to sebacic acid at 1:0.98.

[0083] All other steps are the same.

[0084] Example 7

[0085] The preparation method is the same as in Example 1, except that:

[0086] S1: Replace polyamide 1010 with an equal mass of polyamide 1012. Both are long-chain polyamides (carbon atoms ≥ 10) and their main functions are to reduce water absorption, improve low-temperature toughness and fatigue resistance.

[0087] All other steps are the same.

[0088] Example 8

[0089] The preparation method is the same as in Example 1, except that:

[0090] S3: Replace chopped carbon fiber with chopped glass fiber, both of which are chopped fibers for reinforcement;

[0091] All other steps are the same.

[0092] Comparative Example 1

[0093] Polyamide composite materials were prepared using commercially available conventional raw materials and conventional blending. The preparation method was as follows: 82 parts of commercially available PA66 (intrinsic viscosity 1.30 dL / g), 12 parts of polyamide 1010, 10 parts of polytetrafluoroethylene micro powder, 8 parts of chopped glass fiber, 0.4 parts of antioxidant, 0.2 parts of light stabilizer, and 0.2 parts of processing aid were added to a high-speed mixer at 800 rpm for 10 minutes. The premix was then added to a twin-screw extruder for melt extrusion granulation. After drying the granules at 80°C for 4 hours, they were injection molded to obtain traditional polyamide composite material products.

[0094] Comparative Example 2

[0095] The preparation method is the same as in Example 1, except that:

[0096] S1: Omit the preparation step of PA66-co-β-OH copolymer and replace it with an equal mass of commercially available pure PA66;

[0097] All other steps are the same.

[0098] Comparative Example 3

[0099] The preparation method is the same as in Example 1, except that:

[0100] S2, S3: The preparation steps of the IL-GO / h-BN-OH heterostructure complex are omitted, and the IL-GO / h-BN-OH heterostructure complex is not added in subsequent preparation processes;

[0101] All other steps are the same.

[0102] Comparative Example 4

[0103] The preparation method is the same as in Example 1, except that:

[0104] S2: Omit the steps of DMF dispersion, grafting reaction and ultrasonic compounding, and replace them with 0 parts of ungrafted graphene oxide and 10 parts of unhydroxylated hexagonal boron nitride directly added to a high-speed mixer and mixed at room temperature for 5 minutes;

[0105] All other steps are the same.

[0106] Comparative Example 5

[0107] The preparation method is the same as in Example 1, except that:

[0108] S3: Omit the step of segmented variable speed mixing and replace it with adding all components at once to a high-speed mixer and mixing at a single high speed (800 rpm) for 10 minutes;

[0109] All other steps are the same.

[0110] Experimental Example 1

[0111] The polyamide composite materials prepared in Examples 1-8 and Comparative Examples 1-5 were measured:

[0112] (1) Tensile strength: Referring to GB / T 1040.2-2022 "Plastics—Determination of tensile properties—Part 2: Test conditions for molded and extruded plastics", the composite granules were injection molded into the specified Type 1A multipurpose specimen and conditioned under standard environmental conditions for at least 24 hours. The specimen was clamped between the upper and lower clamps of the universal testing machine, the tensile speed was set to 50 mm / min, the testing machine was started to apply axial tensile load until the specimen broke, and the maximum force value at break was recorded. The tensile strength was calculated by the following formula: σ t =F max / b·h, where F max The maximum force (N) is given by , and b and h are the width and thickness (mm) of the gauge length of the specimen, respectively. The arithmetic mean of at least 5 specimens is taken as the final result.

[0113] (2) Coefficient of friction: Referring to GB / T 3960-2016 "Plastics - Test Method for Sliding Friction and Wear", the composite material was injection molded into a sample with dimensions of 30mm×7mm×6mm, and a GCr15 steel ring was selected for the abrasive. A ring-block friction and wear tester was used, with a test load of 200N and a sliding speed of 0.5m / s, and continuous friction was performed for 2 hours under dry friction conditions. The friction torque was continuously recorded by the sensor of the tester, and the coefficient of friction was calculated by the following formula: μ=M / (R·P), where M is the friction torque (N·m), R is the radius of the steel ring (m), and P is the normal load (N). The average value of the data when the test entered the stable wear stage was taken as the final coefficient of friction. At least 3 parallel samples were tested in each group, and the average value of the results was taken.

[0114] (3) Tensile fatigue limit: Referring to GB / T 35465.3-2017 "Metallic materials - Fatigue test method - Part 3: Tension-tensile fatigue" and GB / T 3075-2021 "Metallic materials - Fatigue test - Axial force control method", the same type 1A specimen as the tensile strength test was used, under a stress ratio R=σ min / σ max A fatigue test with constant axial amplitude force was conducted under conditions of 0.1 and frequency f=10Hz. First, the fatigue limit reference value was obtained using the rise-fall method: the initial stress level was set to approximately 40% of the tensile strength. If the specimen underwent 10... 7 If failure does not occur in the next cycle, the stress level is increased; if failure occurs, the stress level is decreased, until at least four pairs of valid data are obtained. Finally, using a group method, at least three specimens are tested at three to five different stress levels. By fitting stress-life (SN) curves, the stress level corresponding to 10 is determined. 7 The fatigue limit value (MPa) with a failure probability of 50% in the next cycle.

[0115] (4) Self-healing efficiency: Referring to ASTM D638-22 "Standard Test Method for Tensile Properties of Plastics", the composite granules were injection molded into type 1A tensile specimens. After conditioning under standard environmental conditions for at least 24 hours, 5 specimens were taken from each group to test the original tensile strength (σ). 原始 Five additional specimens were completely cut at the midpoint of the gauge length using a sharp blade. The two sections were then tightly joined together and placed in a 120°C oven. A contact pressure of 0.1 MPa was applied for 2 hours for repair. After removal, the specimens were conditioned under the same environmental conditions for 24 hours. The tensile strength (σ) after repair was then measured under the same test conditions. 修复后 The self-repair efficiency is calculated using the following formula: η = (σ 修复后 / σ 原始 ) × 100%, and take the arithmetic mean of 5 splines as the final result of the sample group.

[0116] (5) Stress relaxation time: Referencing ASTM E328-21, "Standard Method for Stress Relaxation Testing of Materials and Structures," the Dynamic Mechanical Analyzer (DMA) was used for testing. The composite granules prepared in each embodiment and comparative example were injection molded into DMA standard specimens, approximately 35mm × 10mm × 2mm in size. The specimens were rapidly stretched to a constant strain of 1% in tensile mode, and the stress decay curve over time was recorded at 120°C. When the stress decayed to 1 / e of the initial value, the corresponding relaxation time τ (seconds) was recorded. At least three parallel specimens were tested for each group of samples, and the average value was taken.

[0117] Experiment Example 2

[0118] The microstructure of the IL-GO / h-BN-OH heterostructure complex prepared in S2 of Example 1 was observed:

[0119] (1) Sample weighing and solvent preparation: Weigh 5 mg of the IL-GO / h-BN-OH heterostructure complex prepared in Example 1, add it to anhydrous ethanol dispersion medium, and prepare a powder suspension with a concentration of 0.05 mg / mL.

[0120] (2) Ultrasonic dispersion treatment: The prepared suspension is placed in an ultrasonic cleaner, the ultrasonic power is set to 150W and the ultrasonic time is 10 minutes. The powder agglomeration is broken by ultrasonic cavitation, so that IL-GO and h-BN-OH sheets are fully dispersed and peeled off to obtain a uniform and stable suspension system.

[0121] (3) TEM copper mesh sample preparation: Use a copper mesh for ultrathin carbon film transmission electron microscope. Use a pipette to draw up the uniform suspension in the upper layer and slowly add 1 to 2 drops to the surface of the copper mesh to ensure that the liquid film is spread evenly and without accumulation.

[0122] (4) Room temperature air drying treatment: Place the copper mesh after dripping in a dust-free, dry and windless environment and air dry at room temperature for 15 minutes to allow the ethanol solvent to evaporate completely, leaving only the uniformly attached heterogeneous structure powder, thus completing the preparation of the test sample.

[0123] (5) Parameter settings: Set the instrument acceleration voltage to 200kV.

[0124] Table 2 Comparison of experimental results of Examples 1-8 and Comparative Examples 1-5

[0125] Serial Number Example Tensile strength (MPa) coefficient of friction Tensile fatigue limit (MPa) Self-repair efficiency (%) Stress relaxation time (s) 1 Example 1 102.78±1.53 0.11±0.008 30.52±1.42 66.35±2.47 395±24 2 Example 2 92.37±1.42 0.19±0.011 26.37±1.28 58.42±2.98 545±33 3 Example 3 110.62±1.67 0.09±0.006 35.18±1.85 68.71±2.15 358±19 4 Example 4 90.91±1.51 0.21±0.012 27.05±1.15 55.67±3.17 635±43 5 Example 5 98.27±1.48 0.14±0.009 29.63±1.56 63.54±2.76 455±29 6 Example 6 96.18±1.55 0.16±0.010 32.47±1.73 61.28±2.95 510±34 7 Example 7 100.45±1.61 0.12±0.007 31.29±1.68 65.89±2.48 405±24 8 Example 8 94.83±1.44 0.20±0.011 25.83±1.35 59.76±2.96 525±34 9 Comparative Example 1 72.30±1.38 0.22±0.013 17.15±1.05 0.86±0.32 >3000 10 Comparative Example 2 88.47±1.46 0.16±0.009 21.74±1.22 1.23±0.45 >3000 11 Comparative Example 3 100.59±1.41 0.26±0.015 19.38±1.18 8.47±1.96 >3000 12 Comparative Example 4 78.75±1.39 0.24±0.014 18.62±1.12 35.06±3.42 1252±48 13 Comparative Example 5 76.42±1.37 0.21±0.013 20.91±1.08 42.03±3.18 981±39

[0126] The experimental results of Examples 1-8 and Comparative Examples 1-5 are shown in Table 2. The polyamide composite material prepared in Example 1 of this invention has significantly better tensile strength, friction coefficient and tensile fatigue limit than the comparative examples, which reflects the advantages of the β-hydroxyamide dynamic network and IL-GO / h-BN-OH heterostructure ternary synergistic system in improving mechanical properties, self-lubricating properties and fatigue resistance. In addition, the self-healing efficiency of Example 1 reached 66.35% and the stress relaxation time was 395 seconds, which confirms that the β-hydroxyamide structural unit endows the material with good self-healing properties and dynamic reversible exchange characteristics.

[0127] Example 2 reduced the amount of IL-GO / h-BN-OH and carbon fiber, resulting in a decrease in tensile strength and fatigue limit, and an increase in the coefficient of friction. The reduction in lubricating and reinforcing components naturally weakens the synergistic effect of interfacial load-bearing and self-lubrication. This demonstrates that adding appropriate amounts of functional components is crucial for balancing mechanical and tribological properties. Example 3 increased the amount of IL-GO / h-BN-OH and carbon fiber, significantly improving tensile strength, fatigue limit, and self-healing efficiency, and further reducing the coefficient of friction and stress relaxation time. More lubricant allows for the formation of a more continuous and stable transfer film at the friction interface, and more carbon fiber also helps improve thermal conductivity. Promoting heat transfer at the repair interface demonstrates that optimizing the component ratio can further improve overall performance. Example 4, using a low-temperature, short-time polymerization process, resulted in a significant decrease in tensile strength, fatigue limit, and self-healing efficiency, while increasing stress relaxation time. Low polymerization temperature and insufficient time prevented the copolymer molecular weight from reaching the optimal level, indicating that sufficient polymerization conditions have a significant impact on the matrix's mechanical properties and self-healing ability. Example 5, using a high-temperature, long-time polymerization process, showed a slight decrease in various properties compared to Example 1. This is because excessively high polymerization temperature and prolonged time may have triggered thermal oxidative degradation of the copolymer, damaging some of the β-hydroxyamide structure and leading to... The broadened molecular weight distribution and impaired dynamic network integrity indicate that there is an optimal process window for polymerization conditions, and excessive strengthening can actually degrade performance. In Example 6, bio-based sebacic acid and sebacic acid-diamine were used to replace petroleum-based adipic acid and hexamethylenediamine. Tensile strength and self-healing efficiency decreased slightly, but fatigue limit remained good. The longer main chain of polyamide 1010 improved molecular chain flexibility but slightly reduced rigidity. However, the synergistic effect of the dynamic network and lubrication system was not compromised, proving that bio-based monomers can achieve green substitution while maintaining fatigue resistance. In Example 7, polyamide 1012 was used to replace polyamide 1010 as the long-chain polyamide component. The performance is basically the same as in Example 1. Polyamide 1012 and polyamide 1010 are both long-chain polyamides, and their functions in reducing water absorption and improving toughness are similar. The impact on the ternary synergistic system is relatively small, proving that different long-chain polyamides can be flexibly replaced in this invention. In Example 8, short-cut glass fiber was used to replace short-cut carbon fiber as the reinforcing phase. The tensile strength, fatigue limit and self-healing efficiency decreased significantly. The elastic modulus of glass fiber is much lower than that of carbon fiber, so its load-bearing capacity and crack propagation resistance are naturally weaker. Moreover, the interfacial bonding strength with the matrix is ​​not as good as that of carbon fiber. This proves that carbon fiber does have unique reinforcing advantages in the system of this invention.

[0128] Comparative Examples 1-5, lacking key technologies, showed varying degrees of reduced overall performance compared to the Examples. Comparative Example 1, employing a traditional formulation and conventional blending process, lacked the β-hydroxyamide dynamic network and the IL-GO / h-BN-OH heterogeneous lubrication system. Furthermore, carbon fiber was replaced with glass fiber, and segmented variable-speed mixing was not used, resulting in tensile strength, friction coefficient, and fatigue limit all inferior to Example 1. Comparative Example 2 replaced PA66-co-β-OH with pure PA66. While retaining the IL-GO / h-BN-OH heterogeneous lubrication system and carbon fiber, the lack of the β-hydroxyamide dynamic network significantly reduced fatigue limit and self-healing efficiency, with stress relaxation time exceeding 3000 seconds, failing to suppress microcrack propagation through dynamic bond exchange and strain energy dissipation. In Comparative Example 3, the IL-GO / h-BN-OH heterogeneous lubricating compound was omitted. Although the dynamic network and carbon fibers remained, the lack of lubricating components led to a significant increase in the coefficient of friction to 0.26, resulting in severe wear and a decrease in self-healing efficiency to 8.47%. In Comparative Example 4, the ionic liquid covalent grafting step and hydroxylation treatment were omitted. The ungrafted graphene oxide was simply physically mixed with the unhydroxylated hexagonal boron nitride, resulting in lubricant agglomeration and uneven dispersion. The self-healing efficiency decreased to 35.06%, and the stress relaxation time was extended to 1252 seconds. In Comparative Example 5, the segmented variable-speed mixing process was omitted. All components were mixed at high speed in one go, resulting in a large number of carbon fibers being broken, a decrease in fiber length retention, a decrease in self-healing efficiency to 42.03%, and an extension of the stress relaxation time to 981 seconds.

[0129] In summary, this invention constructs a dynamic exchange network of β-hydroxyamide in situ within the main chain of PA66-co-β-OH copolymer, thereby establishing a two-dimensional heterogeneous synergistic lubrication system of IL-GO / h-BN-OH composed of ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride. Furthermore, short-cut carbon fibers pre-coated with KH-570 are introduced as a reinforcing phase, forming a ternary synergistic modification system of "dynamic network-heterogeneous lubrication-fiber reinforcement." By employing techniques such as segmented variable-speed mixing to protect the fiber aspect ratio, nitrogen protection throughout the process to inhibit thermo-oxidative degradation, and precise control of molecular weight via polymerization torque, a polyamide composite material exhibiting high tensile strength, low coefficient of friction, and excellent fatigue resistance was successfully prepared.

[0130] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention shall still fall within the scope of the technical solution of the present invention.

Claims

1. A fatigue-resistant, self-lubricating polyamide composite material, characterized in that, It is composed of the following components by weight: 60-80 parts of copolyamide containing β-hydroxyamide structural units; 5-20 parts of long-chain polyamide; 3-8 parts of ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride heterostructure composite, wherein the mass ratio of ionic liquid covalently grafted graphene oxide to hydroxylated hexagonal boron nitride is 1:(1-5); 5-10 parts of short-cut carbon fibers pre-coated with KH-570; 0.2-0.6 parts of antioxidant; 0.1-0.3 parts of light stabilizer; and 0.1-0.3 parts of processing aid.

2. The fatigue-resistant self-lubricating polyamide composite material as described in claim 1, characterized in that, The copolyamide containing β-hydroxyamide structural units is formed by the condensation polymerization of an aliphatic diacid, an aliphatic diamine, and N,N′-bis(2-hydroxyethyl)-1,6-hexanediamine, wherein the ratio of the carboxyl equivalent of the aliphatic diacid to the total amino equivalent of the aliphatic diamine and N,N′-bis(2-hydroxyethyl)-1,6-hexanediamine is 1:0.995~1.005; the aliphatic diacid is selected from autoic acid or sebacic acid, and the aliphatic diamine is selected from autodiamine or sebacic acid.

3. The fatigue-resistant self-lubricating polyamide composite material as described in claim 1, characterized in that, The ionic liquid covalently grafted graphene oxide is prepared by reacting the following raw materials in parts by weight: 5-15 parts graphene oxide, 10-30 parts 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate, 10-20 parts N,N-dicyclohexylcarbodiimide, and 1-3 parts 4-dimethylaminopyridine.

4. The fatigue-resistant self-lubricating polyamide composite material as described in claim 1, characterized in that, The long-chain polyamide is selected from polyamide 1010 or polyamide 1012.

5. A method for preparing a fatigue-resistant self-lubricating polyamide composite material according to any one of claims 1 to 4, characterized in that, It includes the following steps: S1: Take an aliphatic diacid, an aliphatic diamine, and N,N′-bis(2-hydroxyethyl)-1,6-hexanediamine. After purging with high-purity nitrogen for 15 minutes to remove oxygen, raise the temperature to carry out a pre-condensation reaction. During this process, remove the water generated in the reaction through a condenser. Then, evacuate to a vacuum level below 50 Pa, raise the temperature to continue the reaction, and stop the reaction when the stirring torque reaches the set value. Purge with nitrogen to break the vacuum, and granulate the molten product underwater and vacuum dry at 100°C for 16 hours until the moisture content is below 0.05% to obtain β-hydroxyamide modified copolyamide. Take the β-hydroxyamide modified copolyamide and the long-chain polyamide and dry them at 90°C for 12 hours until the moisture content is below 0.05% for later use. S2: Graphene oxide was dispersed in N,N-dimethylformamide and ultrasonically dispersed for 1 hour until homogeneous. 1-(3-aminopropyl)-3-methylimidazolium tetrafluoroborate, N,N-dicyclohexylcarbodiimide, and 4-dimethylaminopyridine were added, and the reaction was carried out under nitrogen protection. After the reaction, the solid product was collected by centrifugation and washed once each with N,N-dimethylformamide, anhydrous ethanol, and deionized water. Finally, it was vacuum dried at 60°C for 24 hours to obtain ionic liquid covalently grafted graphene oxide. Ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride were added to anhydrous ethanol in a certain proportion and ultrasonically dispersed for 2 hours. After centrifugation, it was vacuum dried at 60°C for 24 hours until the solvent residue was less than 0.1%, thus obtaining an ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride heterostructure complex. S3: Take dried β-hydroxyamide modified copolyamide, long-chain polyamide, antioxidant, light stabilizer and processing aid, and mix them at room temperature under nitrogen protection; then add ionic liquid covalently grafted graphene oxide and hydroxylated hexagonal boron nitride heterostructure complex, and continue mixing; finally add short-cut carbon fibers pre-coated with KH-570, and gently mix until uniform to obtain premix; S4: Under nitrogen protection, the premixed material is melt-blended. The feeding section, compression section, melt-blending section, exhaust section, and die head temperature, screw speed, and feeding rate are set. After melt-blending and vacuum exhaust to remove volatiles, the extruded strip is cooled in a water bath, pelletized, and then vacuum-dried at 80°C for 4 hours until the moisture content is below 0.05%, resulting in fatigue-resistant self-lubricating polyamide composite granules. After drying the composite granules at 80°C for 4 hours, injection molding is performed. The injection temperature, mold temperature, holding pressure time, and cooling time are set. After melt plasticizing, injection molding, holding pressure to compensate for shrinkage, and cooling and shaping, the product is demolded to obtain fatigue-resistant self-lubricating polyamide composite material. The product is then annealed at 80°C for 2 hours to eliminate residual stress.

6. The method for preparing a fatigue-resistant self-lubricating polyamide composite material as described in claim 5, characterized in that, The pre-condensation reaction described in S1 is set to a reaction temperature of 210~230℃, a reaction time of 1~3 hours, and a stirring speed of 50~80 rpm. The reaction is continued by raising the temperature to 245~265℃ and continuing the reaction for 3~4 hours. The set value is 2.5~3 times the initial torque.

7. The method for preparing a fatigue-resistant self-lubricating polyamide composite material as described in claim 5, characterized in that, The reaction described in S2 is carried out under nitrogen protection, with the following conditions: reaction temperature 50~70℃, reaction time 12~36 hours, and stirring speed 50~150 rpm.

8. The method for preparing a fatigue-resistant self-lubricating polyamide composite material as described in claim 5, characterized in that, S3 describes mixing at room temperature, with the conditions set at a speed of 600~1000 rpm and a mixing time of 3~8 minutes; the continued mixing has a mixing time of 2~5 minutes; the gentle mixing has a speed of 200~400 rpm and a mixing time of 1~3 minutes.

9. The method for preparing a fatigue-resistant self-lubricating polyamide composite material as described in claim 5, characterized in that, The settings for the feeding section, compression section, melt mixing section, venting section, and die head temperature, screw speed, and feeding rate in S4 are as follows: feeding section 220~250℃, compression section 230~260℃, melt mixing section 240~270℃, venting section 240~265℃, die head 240~265℃, screw speed 150~250rpm, and feeding rate 8~16kg / h. The settings for the injection temperature, mold temperature, holding time, and cooling time are as follows: injection temperature 240~260℃, 250~270℃, 255~275℃, 250~270℃, mold temperature 80~120℃, holding time 10~30 seconds, and cooling time 15~35 seconds.

10. The application of the fatigue-resistant self-lubricating polyamide composite material according to any one of claims 1 to 4, characterized in that, The polyamide composite material can be used to manufacture self-lubricating mechanical parts that withstand reciprocating loads and sliding friction.

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