High-strength polyamide 66 material and method for producing same

Abstract

The application relates to the technical field of high polymer materials, in particular to a high-strength polyamide 66 material and a preparation method thereof. The application overcomes the technical problem of poor aging resistance of traditional polyamide 66 materials. Amino-graphene is first dispersed in liquid phase with modified nano-silicon dioxide through ultrasonic co-dispersion, then mixed with nylon 66 salt and neodymium stearate, and high-pressure in-situ polymerization is carried out to form covalent bond anchoring between the filler and the polyamide main chain; benzoic acid is added for high-vacuum polycondensation, and finally, the polyamide 66 material is prepared through double-screw reactive extrusion granulation. The application constructs a synergistic anti-aging system of two-dimensional physical barrier and zero-dimensional targeted capture, delays oxygen permeation by using the graphene labyrinth effect, combines with modified silicon dioxide to extinguish aging free radicals, and improves the long-acting aging resistance and mechanical strength of the material.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, specifically to a high-strength polyamide 66 material and its preparation method. Background Technology

[0002] Polyamide 66, as an important polymer engineering plastic, is widely used in core fields such as automotive manufacturing, electronics, aerospace, and machinery industries due to its excellent mechanical strength, wear resistance, self-lubricating properties, and good processing flow. With the continuous advancement of lightweighting trends, the replacement of steel with plastics has placed higher demands on the comprehensive mechanical properties of engineering plastics. Although traditional PA66 has high initial strength, it is still prone to yielding and creep under extreme mechanical stress, and it is notch-sensitive. Balancing toughness and strength has always been a key research direction in the field of polymer materials.

[0003] However, traditional PA66 materials face significant technical bottlenecks in practical applications, particularly their poor aging resistance. Due to the large number of amide bonds (-CONH-) and terminal amino groups in the PA66 molecular chain, long-term exposure to high temperatures, oxygen, ultraviolet radiation, or alternating humid and hot environments easily triggers free radical chain degradation reactions, leading to molecular chain breakage, cross-linking, or macromolecular degradation. This manifests macroscopically as yellowing and cracking of the material surface, as well as a precipitous drop in tensile strength and impact toughness. This aging problem caused by photothermal oxidation severely limits the high-end application of PA66 in long-term outdoor load-bearing components.

[0004] To this end, a high-strength polyamide 66 material and its preparation method are proposed. Summary of the Invention

[0005] The purpose of this invention is to design a high-strength polyamide 66 material and its preparation method. This invention involves liquid-phase ultrasonic co-dispersion of aminated graphene and modified nano-silica, followed by mixing with nylon 66 salt and neodymium stearate. High-pressure in-situ polymerization is then used to anchor the filler to the polyamide backbone through covalent bonds. Benzoic acid is then added for high-vacuum polycondensation, and finally, the polyamide 66 material is obtained by twin-screw reactive extrusion granulation. This invention constructs a synergistic anti-aging system combining two-dimensional physical barrier and zero-dimensional targeted capture. The graphene labyrinth effect is utilized to delay oxygen permeation, while modified silica eliminates aging free radicals, thereby improving the material's long-term aging resistance and mechanical strength.

[0006] To achieve the above objectives, the present invention provides the following technical solution: Unless otherwise specified, all the following parts are by weight.

[0007] This invention provides a method for preparing a high-strength polyamide 66 material, comprising the following steps: Aminated graphene and modified silica were added to a premixed tank containing 80 parts of deionized water in a reaction vessel. An ultrasonic generator (500W) was turned on, and the ambient temperature was controlled at 30℃ for 1.5 hours to form a nano-co-dispersion. The nano-co-dispersion was pumped into a high-pressure polymerization reactor, and 100 parts of hexamethylene adipate (nylon 66 salt), 0.2-0.5 parts of benzoic acid, and 0.1-0.3 parts of neodymium stearate were added. Nitrogen gas was introduced to replace the air three times. The high-pressure polymerization reactor was completely sealed, and heating and mechanical stirring were turned on (stirring speed set to 100 rpm). The temperature was raised to 215-225℃. The pressure inside the reactor was naturally increased and stabilized at about 1.75 MPa by utilizing the saturated vapor pressure generated by the vaporization of deionized water in the system. The reaction was carried out under constant temperature and pressure conditions for 2 hours. After the pressure holding reaction is completed, the exhaust valve is slowly opened within 60 minutes to release the pressure inside the reactor from high pressure to normal pressure (0.1 MPa). The reactor temperature is raised to 275°C, the vacuum system is turned on, and the vacuum degree is gradually increased to reduce the absolute pressure inside the reactor to below 100 Pa. Vacuum polycondensation is continued for 1.5-2 hours. The torque of the stirring motor is monitored, and the reactor is stopped after the target value is reached (when the relative viscosity reaches 2.6-3.0). Nitrogen is introduced to break the vacuum. The melt is granulated underwater and vacuum dried at 100°C to obtain prepolymer particles. Prepolymer particles are uniformly fed into the main feed port of a co-rotating twin-screw extruder (screw length-to-diameter ratio L / D greater than 40:1) via a loss-in-weight feeder. The temperature gradient is set as follows: Zone 1 260-270℃, Zones 2-4 270-280℃, Zones 5-8 280-290℃ (with vacuum exhaust activated in Zone 7 to maintain a vacuum degree ≤-0.08MPa), die head 275℃, and screw speed set to 280rpm. The molten material is extruded into strips through the die head, cooled and shaped in a circulating water tank, dried by an air knife, and pelletized to obtain polyamide 66 material.

[0008] Preferably, the preparation method of aminated graphene is as follows: 0.5-1.5 parts of graphene oxide (GO, aspect ratio of 1000-10000) are added to 200 parts of deionized water to obtain a suspension; the suspension is placed in an ice-water bath and ultrasonically treated at 800W power for 2 hours (during which the system temperature is controlled not to exceed 40℃), then 1-2 parts of ethylenediamine are added dropwise, the system is heated to 95℃, and the reaction is continuously stirred under reflux for 12 hours; after the reaction is completed, the system is cooled to room temperature, and washed three times by alternating centrifugation with deionized water and anhydrous ethanol until the pH of the supernatant after washing is neutral, then dried in a vacuum drying oven at 60℃ for 24 hours, and ground through a 200-mesh sieve to obtain aminated graphene.

[0009] Preferred method for preparing modified silica is as follows: 1-3 parts of fumed nano-silica (average particle size 15-20 nm) are ultrasonically dispersed (power 500 W, time 1.5 h) in 180 parts of anhydrous toluene. 0.2-0.5 parts of KH-550 are slowly added dropwise under nitrogen protection. The mixture is heated to 110 °C and refluxed for 6 h. The mixture is then washed three times by high-speed centrifugation with anhydrous ethanol (centrifugation speed 10000-15000 rpm, 10 min each time). The washed solid is then dispersed in 100 parts of N,N-dimethyl... A dispersion was obtained in formamide; 0.5-1.0 parts of antioxidant (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid) was dissolved in 25 parts of N,N-dimethylformamide, 0.6 parts of EDC and 0.3 parts of NHS were added, and the mixture was stirred and activated at room temperature for 1.5 h to obtain an activated solution; the activated solution was added to the dispersion, and the mixture was continuously stirred magnetically at 40 °C for 24 h; the product was centrifuged, washed three times alternately with acetone and ethanol, dried under vacuum at 80 °C for 12 h, ground and passed through a 250-mesh sieve to obtain modified silica.

[0010] Another aspect of the present invention provides a high-strength polyamide 66 material, the raw materials for which include hexamethylenediamine adipic acid salt, aminated graphene, modified silica, neodymium stearate and benzoic acid.

[0011] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention utilizes the microscopic labyrinth effect formed by aminated graphene within a nylon matrix to significantly extend the pathways for oxygen, moisture, and heat to penetrate the material, establishing a strong first physical barrier. Simultaneously, this invention chemically bonds hindered phenolic antioxidants to the surface of modified nano-silica via a carbodiimide condensation reaction, overcoming the shortcomings of traditional small-molecule antioxidants, such as easy volatilization, precipitation, and migration during high-temperature processing and long-term outdoor service. When trace amounts of oxygen penetrate the graphene barrier, the antioxidant groups loaded on the uniformly dispersed nano-silica can capture free aging free radicals. This combination of physical defense and chemical elimination solves the technical problem of poor aging resistance in traditional polyamide 66 materials.

[0012] In the liquid-phase pre-dispersion stage, this invention uses fumed silica as nanospheres inserted between two-dimensional graphene sheets, effectively blocking secondary agglomeration due to van der Waals forces and achieving uniform dispersion of the multi-scale hybrid network. More importantly, the active amino groups on the surfaces of the aminated graphene and modified silica directly participate in the dehydration condensation reaction of hexamethylenediamine adipic acid salt within the high-pressure polymerization reactor, forming strong covalent amide bonds between the inorganic hybrid network and the organic macromolecular chains. This in-situ chemical anchoring effect transforms the nanofiller from a free foreign object into a robust cross-linking node on the polyamide backbone, improving stress transfer efficiency under load and preventing slippage and debonding at the phase interface.

[0013] This invention introduces neodymium stearate as a rare-earth nucleating agent, which, together with a graphene template, induces the formation of numerous spherulite structures in the polyamide 66 matrix. This microcrystallization effect not only eliminates amorphous defects between large-sized spherulites but also further seals oxygen permeation channels. Simultaneously, this process perfectly integrates front-end liquid-phase ultrasonic in-situ dispersion, mid-stage high-vacuum polycondensation for precise viscosity control, and rear-end co-rotating twin-screw high-temperature, high-shear extrusion, eliminating microscopic pore defects within the material and yielding a high-strength, aging-resistant polyamide 66 material. Attached Figure Description

[0014] Figure 1 The tensile strength diagrams of Embodiment 1 and Comparative Examples 1-8 after aging are shown. Detailed Implementation

[0015] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0016] For details, please refer to [link / reference]. Figure 1 This invention provides a high-strength polyamide 66 material and its preparation method, the technical solution of which is as follows:

[0017] Example 1 One part of graphene oxide was added to 200 parts of deionized water to obtain a suspension. The suspension was placed in an ice-water bath and ultrasonically treated at 800W for 2 hours (during which the system temperature was controlled not to exceed 40℃). Then, 1-2 parts of ethylenediamine were added dropwise, and the system was heated to 95℃. The reaction was stirred continuously under reflux for 12 hours. After the reaction was completed, the system was cooled to room temperature and washed three times by alternating centrifugation with deionized water and anhydrous ethanol until the pH of the supernatant was neutral. The supernatant was then dried in a vacuum drying oven at 60℃ for 24 hours and ground through a 200-mesh sieve to obtain amino-based graphene.

[0018] Two parts of fumed silica nanoparticles were ultrasonically dispersed (500W power, 1.5h) in 180 parts of anhydrous toluene. 0.3 parts of KH-550 were slowly added dropwise under nitrogen protection, and the mixture was refluxed at 110℃ for 6h. The solid was washed three times by high-speed centrifugation with anhydrous ethanol. The washed solid was dispersed in 100 parts of N,N-dimethylformamide to obtain a dispersion. 0.8 parts of antioxidant (3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid) were dissolved in 25 parts of N,N-dimethylformamide, and 0.6 parts of EDC and 0.3 parts of NHS were added. The mixture was stirred and activated at room temperature for 1.5h to obtain an activated solution. The activated solution was added to the dispersion, and the mixture was continuously magnetically stirred at 40℃ for 24h. The product was centrifuged, washed three times alternately with acetone and ethanol, dried under vacuum at 80℃ for 12h, ground, and passed through a 250-mesh sieve to obtain modified silica.

[0019] Aminated graphene and modified silica were added to a premixed tank containing 80 parts of deionized water in a reaction vessel. An ultrasonic generator (500W) was turned on, and the ambient temperature was controlled at 30℃ for 1.5 hours to form a nano-co-dispersion. The nano-co-dispersion was pumped into a high-pressure polymerization reactor, and 100 parts of hexamethylene adipate salt, 0.2-0.5 parts of benzoic acid and 0.2 parts of neodymium stearate were added. Nitrogen gas was introduced to replace the air three times. The high-pressure polymerization reactor was completely sealed, and heating and mechanical stirring were turned on (stirring speed set to 100 rpm). The temperature was raised to 220℃. The pressure inside the reactor was naturally increased and stabilized at about 1.75 MPa by utilizing the saturated vapor pressure generated by the vaporization of deionized water in the system. The reaction was carried out under constant temperature and pressure conditions for 2 hours. After the pressure holding reaction is completed, the exhaust valve is slowly opened within 60 minutes to release the pressure inside the reactor from high pressure to normal pressure (0.1 MPa). The reactor temperature is raised to 275°C, the vacuum system is turned on, and the vacuum degree is gradually increased to reduce the absolute pressure inside the reactor to below 100 Pa. Vacuum polycondensation is continued for 1.5-2 hours. The torque of the stirring motor is monitored, and the reactor is stopped after the target value is reached (when the relative viscosity reaches 2.6-3.0). Nitrogen is introduced to break the vacuum. The melt is granulated underwater and vacuum dried at 100°C to obtain prepolymer particles. The dried prepolymer granules are evenly fed into the main feed port of a co-rotating twin-screw extruder via a loss-in-weight feeder. The temperature gradient is set as follows: Zone 1 265℃, Zones 2 to 4 275℃, Zones 5 to 8 285℃ (with vacuum exhaust activated in Zone 7 to maintain a vacuum of ≤-0.08MPa), the die head is set to 275℃, and the screw speed is set to 280rpm. The molten material is extruded into strips through the die head, cooled and shaped in a circulating water tank, dried by an air knife, and granulated to obtain polyamide 66 material.

[0020] Examples 2-5 refer to the parameter conditions in Example 1, with specific differences shown in Table 1.

[0021] Table 1 Parameters and conditions for Examples 1-5 Amount / parts of graphene oxide 1 0.5 0.8 1.2 1.5 Dosage of ethylenediamine / part 1.5 1 1 2 2 Dosage of nano silica (per part) 2 1 1.5 2.5 3 Dosage of KH-550 / serving 0.3 0.2 0.3 0.4 0.5 Antioxidant dosage / part 0.8 0.5 0.6 0.9 1 Dosage of neodymium stearate / part 0.2 0.1 0.3 0.1 0.3 Temperature of the heating reaction / °C 220 215 215 225 225 Benzoic acid dosage / part 0.3 0.2 0.3 0.4 0.5 Vacuum polycondensation time / h 1.8 1.5 1.6 1.9 2 Temperature in Zone 1 / °C 265 260 260 270 270 Temperature in zones two through four / °C 275 270 280 270 280 Temperature in zones 5 to 8 / °C 285 290 280 280 290 Comparative Example 1 follows the same parameters and conditions as in Example 1, except that amino-based graphene is not added.

[0022] Comparative Example 2 follows the same parameters and conditions as in Example 1, except that no modified silica is added.

[0023] Comparative Example 3 follows the same parameters and conditions as in Example 1, except that the high-pressure in-situ polymerization process was not used: after drying conventional pure polyamide 66 resin chips, they were directly mixed with aminated graphene, modified nano silica, and neodymium stearate in a high-speed mixer, and then directly fed into a co-rotating twin-screw extruder for melt extrusion granulation.

[0024] Comparative Example 4 follows the same parameters and conditions as in Example 1, except that untreated graphene oxide, fumed nano silica, and an equal amount of 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionic acid (antioxidant) are directly added to a premix tank for liquid-phase dispersion and subsequent polymerization.

[0025] Comparative Example 5 follows the same parameters and conditions as in Example 1, except that an equal amount of antioxidant 1098 is used instead of modified silica.

[0026] Comparative Example 6 follows the same parameters and conditions as in Example 1, except that neodymium stearate is not added.

[0027] Comparative Example 7 follows the same parameters and conditions as in Example 1, except that no modified silica is added, and the amount of aminated graphene added is increased to the sum of the weight parts of the two.

[0028] Comparative Example 8 follows the same parameters and conditions as in Example 1, except that the liquid-phase ultrasonic co-dispersion step is not performed.

[0029] Experimental Example 1: Mechanical Property Testing The tensile strength of Examples 1-5 and Comparative Examples 1-8 was tested according to ISO 527-2 standard; the notched impact strength of Examples 1-5 and Comparative Examples 1-8 was tested according to ISO 180 standard; the results are shown in Table 2.

[0030] Table 2 Mechanical properties of Examples 1-5 and Comparative Examples 1-8 Example 1 187 14.8 Example 2 179 14.1 Example 3 182 14.5 Example 4 186 14.6 Example 5 184 14.3 Comparative Example 1 135 11.2 Comparative Example 2 142 10.7 Comparative Example 3 106 6.5 Comparative Example 4 118 7.8 Comparative Example 5 144 11.4 Comparative Example 6 161 12.1 Comparative Example 7 129 8.3 Comparative Example 8 148 9.9 Table 2 shows that in Comparative Example 1, the tensile strength and notched impact strength of the material decreased significantly after omitting the aminated graphene. This indicates that the micron-sized, two-dimensional aminated graphene acts as the core rigid framework in the system. Without graphene, the material cannot efficiently transfer and disperse stress over a large area when subjected to external forces. Comparative Example 2, without modified silica, showed a significant decrease in both tensile strength and impact strength. This is due to the absence of zero-dimensional nano-silica particles. On the one hand, the system loses the toughening mechanism of rigid particles inducing microcracks and shear bands in the matrix to absorb energy under load; on the other hand, the lack of zero-dimensional particles leads to a significant reduction in the chemical crosslinking node density between the inorganic phase and the nylon backbone, weakening the interfacial adhesion. Comparative Example 3, using a traditional twin-screw physical melt blending process, showed a significant decrease in tensile and impact strength. The fundamental reason is that without a high-pressure in-situ polymerization process, the active amino groups on the surface of the nanofiller could not undergo amidation condensation with hexamethylenediamine adipic acid salt. The inorganic phase and organic macromolecular chains were maintained only by weak physical compatibility. Under van der Waals forces, graphene and silica experienced severe macroscopic agglomeration in the extruder, and these agglomerates became stress concentration defect areas in the matrix. Comparative Example 4, using pure graphene oxide and pure silica without any chemical modification, showed poor mechanical properties. This is because the unaminated filler surface lacks active functional groups that can react with nylon segments, resulting in poor interfacial compatibility. Simultaneously, free antioxidant molecules easily volatilized and were extracted during the high-vacuum condensation stage and the high-temperature shearing stage of the twin-screw extruder, failing to be immobilized.

[0031] Comparative Example 5 used an equal amount of antioxidant 1098 to replace the modified silica. Since antioxidant 1098 lacks the rigid physical center structure of inorganic nanoparticles, the tensile strength of the material was significantly lower than in Example 1. This indicates that the modified silica of the present invention, by immobilizing hindered phenolic groups on the surface of nano-silica, not only locks in anti-aging activity but also leverages the unique geometric morphology strengthening effect of zero-dimensional particles, achieving a synergistic integration of physical reinforcement and chemical anti-aging. Comparative Example 6 removed neodymium stearate during in-situ polymerization, resulting in a decrease in the tensile strength and impact strength of the material. This confirms that the introduction of neodymium stearate, combined with the heterogeneous nucleation effect of graphene's large specific surface area, enables the PA66 macromolecular chains to rapidly generate a dense and fine microcrystalline structure. Without rare earth nucleating agents, larger spherulites easily form inside the material, increasing amorphous defects at grain boundaries, making cracks more likely to propagate along large grain boundaries under load. Comparative Example 7, while maintaining the total filler content unchanged, completely removed silica and doubled the amount of graphene. However, its performance deteriorated significantly. This result confirms that when zero-dimensional silica is removed as nano-balls / spacers interspersed between graphene layers, the high-concentration graphene sheets undergo irreversible self-overlapping and tight aggregation under strong π-π stacking effects. This indicates that simply increasing the number of single components not only fails to enhance performance but also disrupts the matrix continuity due to severe stacking and aggregation of nanosheets. Comparative Example 8 eliminated the initial liquid-phase ultrasonic co-dispersion step, resulting in a significant decrease in its mechanical properties compared to Example 1. The cavitation effect of ultrasound is the key mechanical force for forcibly peeling off the graphene stacks and forming a microscopic pre-assembled co-dispersion state of nano-silica on its surface. Skipping this step and directly feeding the materials resulted in difficulty in achieving uniform molecular-level contact between the two nanomaterials in the reactor. The micron-sized aggregates generated locally were encapsulated in situ during subsequent reactions, reducing the uniformity of stress at the macroscopic interface.

[0032] Experiment Example 2: Aging Resistance Test After being placed at 230℃ for 1000 hours, the tensile strength and notched impact strength of Examples 1-5 and Comparative Examples 1-8 after aging were tested according to the method of Experimental Example 1. The results are shown in Table 3. The tensile strength of Examples 1 and Comparative Examples 1-8 after aging is as follows: Figure 1 As shown.

[0033] Table 3 Aging resistance of Examples 1-5 and Comparative Examples 1-8 Example 1 168 13.3 Example 2 156 12.3 Example 3 160 12.8 Example 4 165 13.0 Example 5 163 12.7 Comparative Example 1 81 6.2 Comparative Example 2 78 5.6 Comparative Example 3 47 2.8 Comparative Example 4 56 3.4 Comparative Example 5 94 6.7 Comparative Example 6 120 8.6 Comparative Example 7 83 4.9 Comparative Example 8 103 6.5 From Table 3 and Figure 1It can be observed that after aging at 230℃ for 1000 hours, the tensile strength and impact strength of Comparative Example 1 decreased significantly. This directly proves that without two-dimensional aminated graphene, the material loses its macroscopic maze-like physical barrier. At high temperatures, a large number of free oxygen molecules can penetrate unimpeded into the polyamide 66 matrix, causing thermo-oxidative degradation of the macromolecular backbone and breakage of amide bonds. Comparative Example 2 showed severe performance degradation in the aging test. This is because the system lacked zero-dimensional modified nano-silica grafted with antioxidants. Although graphene can delay oxygen entry, it will still inevitably generate aging free radicals at 230℃. Due to the lack of targeted capture and annihilation of hindered phenolic groups, these free radicals underwent an autocatalytic oxidation chain reaction in the matrix, leading to destructive cross-linking, brittleness, or degradation of the nylon molecular chains. Comparative Example 3 employed traditional physical melt blending. During long-term ultra-high temperature service, the difference in thermal expansion coefficients between the inorganic filler, which was not chemically bonded, and the organic nylon matrix led to macroscopic interfacial debonding. Oxygen and heat penetrated through these microscopic interfacial gaps, causing not only the anti-aging network to fail but also turning the phase interface into a major area for degradation reactions. Comparative Example 4 used unmodified graphene oxide and silica, supplemented with free small-molecule antioxidants. Its performance after aging remained extremely poor. Because the free hindered phenolic antioxidants were not chemically immobilized on the silica surface, a large amount of them had already volatilized and been extracted in the high-temperature vacuum exhaust section of the twin-screw extruder at 285°C in the early stage. The remaining trace antioxidants had also been completely precipitated or sublimated and consumed in the long-term thermo-oxidative environment of 230°C for 1000 hours.

[0034] Comparative Example 5 used antioxidant 1098 instead of the modified system of this invention. Although antioxidant 1098 provided some protection in the early stages of testing, during the long-term aging process at 230°C, the small molecule additive underwent thermal migration and volatilization loss to the material surface, resulting in a sharp decline in the material's anti-aging ability in the later stages. Comparative Example 6, due to the absence of neodymium stearate as a rare earth nucleating agent, showed a significant decrease in the strength retention rate of the material after aging. The lack of rare earth ion-induced nucleation led to the formation of large-sized spherulites in the nylon 66 matrix, increasing the proportion of amorphous regions at the grain boundaries. During high-temperature aging, oxygen molecules easily penetrated through these loose amorphous regions and triggered degradation. Comparative Example 7 used a single type of amino graphene, excluding the intercalation effect of nano-silica. After aging, its tensile strength and impact strength decreased significantly. This is because, without support, the excessive graphene sheets underwent severe π-π stacking and agglomeration, which not only disrupted the continuity of the matrix but also caused the original planar barrier network to shrink into blocky dead corners, exposing a large area of ​​the nylon matrix to the thermo-oxidative environment. Comparative Example 8 skipped the liquid-phase ultrasonic pre-dispersion step, resulting in the formation of numerous micron-sized agglomerates in the system. These agglomerates became defects that easily triggered stress concentration and microcrack initiation during high-temperature aging. When microcracks formed at 230°C, the fresh fracture surface was rapidly exposed to oxygen, leading to localized oxidative degradation within the material.

[0035] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a high-strength polyamide 66 material, characterized in that, Includes the following steps: Aminated graphene and modified silica were subjected to liquid-phase ultrasonication to obtain a nano-co-dispersion. Hexamethylenediamine adipic acid salt and neodymium stearate were added to the nano-co-dispersion, and prepolymer particles were obtained by in-situ prepolymerization and polycondensation end-capping treatment; the prepolymer particles were then subjected to twin-screw compounding and extrusion to obtain polyamide 66 material; the aminated graphene was obtained by ethylenediamine amination modification of graphene oxide; The modified silica is obtained by coupling nano-silica with KH-550 and chemical grafting with antioxidants.

2. The method for preparing a high-strength polyamide 66 material according to claim 1, characterized in that, The in-situ prepolymerization treatment and polycondensation end-capping treatment process is as follows: the nano-co-dispersion liquid is pumped into the polymerization reactor, the hexamethylenediamine adipic acid salt, benzoic acid and neodymium stearate are added, and the mixture is stirred and heated to 215-225℃ for reaction; after the reaction is completed, vacuum polycondensation is carried out for 1.5-2 hours, and the melt is granulated underwater and dried to obtain the prepolymer particles.

3. The method for preparing a high-strength polyamide 66 material according to claim 1, characterized in that, The twin-screw compounding and extrusion process is as follows: the prepolymer particles are fed into the main feed port of a co-rotating twin-screw extruder through a loss-in-weight feeder. The temperature gradient is set as follows: Zone 1 260-270℃, Zones 2 to 4 270-280℃, Zones 5 to 8 280-290℃. The molten material is extruded into strips through the die head, cooled and shaped in a circulating water tank, dried by an air knife, and granulated to obtain the polyamide 66 material.

4. The method for preparing a high-strength polyamide 66 material according to claim 1, characterized in that, The preparation method of the aminated graphene is as follows: the graphene oxide is added to deionized water to obtain a suspension; the suspension is placed in an ice-water bath, ultrasonically treated, and then the ethylenediamine is added dropwise. After stirring and reacting, the mixture is cooled to room temperature, washed, vacuum dried, ground, and sieved to obtain the aminated graphene.

5. The method for preparing a high-strength polyamide 66 material according to claim 1, characterized in that, The modified silica is prepared by: ultrasonically dispersing fumed nano-silica in anhydrous toluene, adding KH-550 dropwise under nitrogen protection, refluxing and washing, dispersing the washed solid in N,N-dimethylformamide to obtain a dispersion; dissolving the antioxidant in N,N-dimethylformamide, adding EDC and NHS, stirring and activating at room temperature to obtain an activated solution; adding the activated solution to the dispersion, stirring and washing, vacuum drying, and grinding to obtain the modified silica.

6. A high-strength polyamide 66 material, characterized in that, The raw materials for preparing polyamide 66 include hexamethylenediamine adipic acid salt, aminographene, modified silica, neodymium stearate, and benzoic acid; the polyamide 66 material is prepared by the preparation method according to any one of claims 1-6.

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