Modified pa6 material and method for producing the same

Abstract

The application belongs to the technical field of modified copolymer nylon and specifically relates to a modified PA6 material and a preparation method thereof. The application aims to solve the problem of high moisture absorption and lack of high insulation of the existing copolymer modified PA6 material. The application mixes caprolactam and lauryl lactam to obtain a PA6 / 12 random copolymer; pre-blends modified graphene oxide, boron nitride nanosheet and polyamide oligomer to obtain a composite suspension; coats the PA6 / 12 random copolymer on the surface, feeds the coated PA6 / 12 random copolymer into an extruder, adds the composite suspension after complete melting, uniformly mixes the composite suspension and the PA6 / 12 random copolymer, adds a flame retardant aid, and finally extrudes to obtain the modified PA6 material. The modified PA6 material prepared by the application has low water absorption and good insulation, and is not prone to electric leakage and tracking in a high-temperature working environment.

Description

Technical Field

[0001] This invention belongs to the field of modified copolymer nylon technology, specifically relating to a modified PA6 material and its preparation method. Background Technology

[0002] Nylon is one of the most widely used and produced engineering plastics, including various types such as PA6, PA66, and PA46. Due to its excellent tensile strength, wear resistance, chemical resistance, and relatively low cost, it has important application value in various fields.

[0003] PA6 (polycaprolactam) is a typical nylon material containing a large number of polar amide groups in its molecular chain. It readily absorbs water during use, causing its stiffness and strength to gradually decrease over time. Furthermore, PA6 easily swells after absorbing water, leading to dimensional changes in components, a fatal flaw for high-precision applications (such as electronic connectors and precision gears). Therefore, modified PA6 materials have gradually replaced basic PA6 and gained attention in industry, such as copolymerized and composite modified PA6, which offer improvements in both mechanical properties and functionality. Modified PA6 materials are now widely used in new energy vehicles, new infrastructure, and advanced manufacturing.

[0004] Although PA6 modification technology is quite mature, some key technical issues remain. While copolymerization modification can reduce water absorption, this usually comes at the cost of sacrificing heat resistance or increasing costs. In fiber-reinforced composites, even if the PA6 matrix has low hygroscopicity, poor interfaces between the fibers and the matrix can become capillary channels for moisture penetration, reintroducing the hygroscopicity problem. Furthermore, the addition of various fillers to improve the mechanical properties of modified PA6 limits its composite functionality; nanofillers or powdered additives are prone to agglomeration in the melt, forming stress concentration points and weakening material performance. Simultaneously, inorganic fillers are naturally incompatible with the organic PA6 matrix, necessitating efficient compatibilizer technology to construct a stable interfacial bond. Particularly in insulating component applications such as high-voltage battery modules and precision engineering instruments, existing modified PA6 materials, while possessing insulation properties, exhibit significant tracking and leakage under long-term high-temperature and high-voltage operation.

[0005] To address the issues of high hygroscopicity and lack of high insulation in existing copolymer-modified PA6 materials, a modified PA6 material and its preparation method are proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a modified PA6 material and its preparation method. This invention involves copolymerizing caprolactam and dodecylactam to obtain a PA6 / 12 random copolymer; pre-blending modified graphene oxide, boron nitride nanosheets, and polyamide oligomers to obtain a composite suspension; surface-coating the PA6 / 12 random copolymer and feeding it into an extruder, where it is completely melted and then added to the composite suspension. After uniform mixing, a flame retardant is added, and finally, the modified PA6 material is obtained by extrusion.

[0007] To achieve the above objectives, the present invention provides the following technical solution:

[0008] A method for preparing a modified PA6 material includes the following steps:

[0009] Unless otherwise specified, the parts in this invention refer to parts by mass.

[0010] Copolymerization: Under nitrogen protection, caprolactam and dodecanolactam were mixed in a molar ratio of 85:15, using oxalic acid as an initiator. The mixture was heated to 260-280℃ and reacted for 12 hours at an operating pressure of 1.5 MPa. The polymer melt was extruded into strips, cooled, and then extracted with hot water to remove unreacted monomers and oligomers. After drying, PA6 / 12 random copolymer was obtained.

[0011] Mix 100 parts of PA6 / 12 random copolymer with 2 parts of modified hydrotalcite at 1500 rpm for 5-10 min for surface coating treatment.

[0012] The modified hydrotalcite is prepared as follows: 100 parts of aluminum-magnesium hydrotalcite powder are dispersed in ethanol, sodium stearate solution is added dropwise, and the mixture is stirred at 70°C for 4 hours. The resulting solid product is washed with hot water and ethanol and then dried to obtain the modified hydrotalcite. The magnesium-to-aluminum ratio in the aluminum-magnesium hydrotalcite powder is 3:1 (molar ratio), and the amount of sodium stearate added is 3 parts.

[0013] Surface amination of graphene oxide yields modified graphene oxide.

[0014] Preferably, the surface amination process is as follows: 1 part of graphene oxide is dispersed in deionized water, ultrasonically treated for 20 min, then 50 parts of ethylenediamine are added, and the mixture is reacted in a water bath at 80°C for 8 hours under nitrogen protection. The resulting solid product is washed by centrifugation multiple times and dried to obtain modified graphene oxide. The thickness of the graphene oxide sheets used is less than 5 nm.

[0015] 0.2 parts of modified graphene oxide were ultrasonically dispersed in 20 parts of polyamide oligomer, and then 10-15 parts of boron nitride nanosheets were added to obtain a composite suspension.

[0016] Preferably, the ultrasonic dispersion process is as follows: the polyamide oligomer is heated to 180-200℃, then the NMP dispersion of modified graphene oxide is added, and after ultrasonic homogenization, boron nitride nanosheets are added. After mixing evenly, the mixture is vacuum-treated at an operating pressure of 0.1 atm to remove the organic solvent, resulting in a composite suspension. The polyamide oligomer is a hydroxyl-terminated PA6 oligomer with a number-average molecular weight of 1000-3000 g / mol; the boron nitride nanosheets have an average diameter of 10-20 μm and a sheet thickness of less than 200 nm.

[0017] A flame retardant additive is obtained by pre-mixing 10 parts of melamine phosphate and 4 parts of zinc borate.

[0018] 100 parts of PA6 / 12 random copolymer were fed into an extruder and melted at 260°C. Then, 25-35 parts of composite suspension were added. The operating temperature of the extrusion section was increased to 280°C, and 15 parts of flame retardant were added. After mixing, the mixture was extruded, cooled in a water bath, and dried to obtain the modified PA6 material product.

[0019] According to the extruder barrel operation sequence, the feeding sequence of this invention is as follows: the first barrel is the main feed port, with an operating temperature of 260°C, where PA6 / 12 random copolymer with surface coating treatment is added; the second to fourth barrels are the melting and plasticizing zones; in the fifth barrel zone, a composite suspension is added via a metering pump; the sixth barrel is the conventional stretching and shearing treatment section; the seventh barrel is the side feed port, where flame retardant additives are added and mixed, and the operating temperature is raised to 280°C; the eighth barrel is the conventional stretching and shearing treatment section; the ninth barrel is the venting zone, with an operating pressure of 0.1 atm; the tenth to twelfth barrels are the homogenization pressure zone, and finally, the melt is extruded through weak shear force.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] Introducing a certain proportion of long-chain lactam monomers during the ring-opening polymerization stage randomly inserts long alkyl chains into the PA6 molecular backbone, reducing the concentration of polar amide groups at the molecular level and forming a low-amide-density PA6 / 12 random copolymer. The in-situ copolymerization process ensures the uniform bonding of the two monomers, avoiding phase separation problems that may occur with physical blending. Structurally, the long-chain methylene segments are naturally hydrophobic groups, reducing the equilibrium and saturation water absorption rates of the PA6 matrix from the source. Functionally, it retains most of the excellent mechanical properties and cost advantages of PA6, while the reserved amide groups and end groups provide active sites for subsequent reactive bonding with other additives.

[0022] Boron nitride nanosheets were blended with polyamide oligomers and then injected into a twin-screw extruder after the random copolymer was completely melted. The pre-dispersed boron nitride nanosheets exhibited improved dispersibility in the thermoplastic nylon matrix. Simultaneously, the low hygroscopicity of the PA6 / 12 random copolymer matrix ensured the phonon transfer efficiency at the boron nitride-polymer interface, guaranteeing the good thermal conductivity of the final modified PA6 material. Furthermore, the introduction of boron nitride enhanced the insulation properties of the modified PA6 material. The well-dispersed boron nitride nanosheets gradually oriented during subsequent tensile shearing, forming partially parallel lamellar structures, thus improving the high-voltage resistance of the modified PA6 material.

[0023] A small amount of zinc borate and melamine phosphate were introduced as flame retardant additives in the later stage of extrusion. Modified graphene oxide was pre-blended with boron nitride nanosheets and polyamide oligomers and then added. Graphene oxide itself is an electrical insulator, and its surface amino groups can chemically bond with a large number of polar groups in the PA6 / 12 random copolymer matrix. Its two-dimensional sheet structure and excellent mechanical and thermal properties, combined with the uniformly dispersed boron nitride nanosheets, further enhance the thermal conductivity of the modified PA6 material, compensating for the negative impact of reduced thermal conductivity caused by the introduction of flame retardant additives. Simultaneously, melamine phosphate and zinc borate, as inorganic powders, have weak interfacial bonding with the PA6 / 12 random copolymer, leading to a decrease in material strength and toughness. Modified graphene oxide partially coats the surface of these particles, partially restoring the material's mechanical strength.

[0024] Before the PA6 / 12 random copolymer is fed into the twin-screw extruder, a small amount of modified hydrotalcite is coated onto it using a surface coating method. Modified hydrotalcite, as a heat stabilizer, exhibits typical functions as both an acid scavenger and an anion exchanger. Melamine phosphate flame retardants may undergo slight decomposition or hydrolysis under prolonged heating, producing conductive phosphoric acidic substances. The uniformly dispersed modified hydrotalcite actively captures and neutralizes these acidic substances, fixing them within its layered structure through a chemical reaction, transforming them into harmless stable salts. This fundamentally prevents the damage to electrical properties caused by acidic ions, ensuring the long-term safety of the flame-retardant system under high pressure. Furthermore, during the melt shearing process, the modified hydrotalcite partially inserts between the boron nitride nanosheets and the modified graphene oxide nanosheets, effectively inhibiting the aggregation of graphene oxide. At the same time, the modified hydrotalcite can neutralize the acidic functional groups remaining on the surface of graphene oxide, improve its interfacial compatibility with the matrix, and ensure the good insulation and heat resistance of the modified PA6 material. Attached Figure Description

[0025] Figure 1 This is a flowchart of the preparation method of the modified PA6 material in this invention. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below through some embodiments and experimental examples. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0027] Reference Figure 1 The process flow diagram shown illustrates that this invention provides a method for preparing modified PA6 material, the technical solution of which is as follows:

[0028] Example 1:

[0029] Under nitrogen protection, caprolactam and dodecanolactam were mixed at a molar ratio of 85:15, with oxalic acid as the initiator, and the mixture was heated to 260°C and reacted at an operating pressure of 1.5 MPa for 12 hours. The polymer melt was extruded into strips, cooled, and then extracted with hot water to remove unreacted monomers and oligomers. After drying, PA6 / 12 random copolymer was obtained. The number average molecular weight of the PA6 / 12 random copolymer obtained by this method was 30,000-35,000 g / mol.

[0030] 100 parts of PA6 / 12 random copolymer and 2 parts of modified hydrotalcite were mixed at 1500 rpm for 5 min for surface coating treatment.

[0031] The modified hydrotalcite is prepared as follows: 100 parts of aluminum-magnesium hydrotalcite powder are dispersed in ethanol, sodium stearate solution is added dropwise, and the mixture is stirred at 70°C for 4 hours. The resulting solid product is washed with hot water and ethanol and then dried to obtain the modified hydrotalcite. The amount of sodium stearate added is 3 parts.

[0032] One part of graphene oxide was dispersed in deionized water and ultrasonically treated for 20 min. Then, 50 parts of ethylenediamine were added, and the mixture was reacted in a water bath at 80°C for 8 hours under nitrogen protection. The solid product was obtained by centrifugation and washing multiple times and then dried to obtain modified graphene oxide.

[0033] Twenty parts of polyamide oligomer were heated to 180°C, and then 0.2 parts of NMP dispersion of modified graphene oxide were added. After ultrasonic homogenization, 10 parts of boron nitride nanosheets were added. After mixing evenly, the mixture was vacuum treated at an operating pressure of 0.1 atm to remove organic solvents, thus obtaining a composite suspension.

[0034] A flame retardant additive is obtained by pre-mixing 10 parts of melamine phosphate and 4 parts of zinc borate.

[0035] 100 parts of PA6 / 12 random copolymer were fed into an extruder and melted at 260°C. Then, 25 parts of composite suspension were added. The operating temperature of the extrusion section was increased to 280°C, and 15 parts of flame retardant were added. After mixing, the mixture was extruded, cooled in a water bath, and dried to obtain the modified PA6 material product.

[0036] Examples 2-16 differ from Example 1 in operating parameters, but the other process steps and the range of raw material selection are the same.

[0037] The specific changes in operating parameters are summarized in Table 1.

[0038] Table 1. Changes in operating parameters in Examples 1-16

[0039] Copolymerization reaction temperature (°C) Surface coating treatment time (min) Amount of boron nitride nanosheets added (parts) Ultrasonic dispersion heating temperature (°C) Amount of composite suspension added (parts) Example 1 260 5 10 180 25 Example 2 280 10 15 200 35 Example 3 271 8 12 191 30 Example 4 265 6 14 184 27 Example 5 278 9 11 198 34 Example 6 262 7 10 182 26 Example 7 275 5 15 195 35 Example 8 268 10 13 188 31 Example 9 273 8 11 193 29 Example 10 261 6 14 181 33 Example 11 279 9 12 199 28 Example 12 266 7 13 186 32 Example 13 276 5 10 196 25 Example 14 264 10 15 183 35 Example 15 270 8 11 190 29 Example 16 269 7 14 189 31

[0040] Comparative Example 1

[0041] Unlike Example 1, dodecyl lactam was replaced with an equimolar amount of caprolactam, while all other process parameters remained the same.

[0042] Comparative Example 2

[0043] Unlike Example 1, the molar ratio of dodecanoic acid added was changed from 15% to 5%, while other process parameters remained the same.

[0044] Comparative Example 3

[0045] Unlike Example 5, boron nitride nanosheets were not added, but all other process parameters remained the same.

[0046] Comparative Example 4

[0047] Unlike Example 5, boron nitride nanosheets were not pre-blended with polyamide oligomers, but were added separately to the extruder in steps, while other process parameters remained the same.

[0048] Comparative Example 5

[0049] Unlike Example 5, the composite suspension was added together with the flame retardant additive in the seventh cylinder, while all other process parameters remained the same.

[0050] Comparative Example 6

[0051] Unlike Example 9, the modified graphene oxide was replaced with an equal mass fraction of unaminated graphene oxide, while all other process parameters remained the same.

[0052] Comparative Example 7

[0053] Unlike Example 9, the amount of flame retardant additive added was increased to 30 parts, while other process parameters remained the same.

[0054] Comparative Example 8

[0055] Unlike Example 9, no polyamide oligomers were added. Instead, modified graphene oxide and boron nitride nanosheets were directly added and blended in solid form, while all other process parameters remained the same.

[0056] Comparative Example 9

[0057] Unlike Example 13, the modified hydrotalcite and modified graphene oxide were simultaneously dispersed in the polyamide oligomer and added to the system, rather than through surface coating. All other process parameters were the same.

[0058] Comparative Example 10

[0059] Unlike Example 13, no modified hydrotalcite was added, but all other process parameters remained the same.

[0060] Experimental Example 1

[0061] The water absorption rate, dimensional stability before and after moisture absorption, and dielectric properties of the modified PA6 material products prepared in Examples 1-4 and Comparative Examples 1-2 were tested. The relevant results are summarized in Table 2.

[0062] The test methods for water absorption and dimensional stability are as follows: Referring to ISO 62 standard, the sample is immersed in distilled water at 23°C. The sample size is 60mm × 1mm × 2mm. The rate of change in mass (%) before and after water absorption is recorded as the water absorption rate, and the rate of change in the major axis length (%) is recorded to represent the dimensional stability of the sample before and after moisture absorption.

[0063] The dielectric constant was tested and recorded according to the relevant test method of ASTM D150 standard. The test frequency was 1MHz.

[0064] Table 2. Water absorption rate and properties before and after moisture absorption of the modified PA6 materials prepared in Examples 1-4 and Comparative Examples 1-2.

[0065] Water absorption rate (%) Rate of change of major axis length (%) Dielectric constant before moisture absorption Dielectric constant after moisture absorption Example 1 2.7 0.6 4.5 7.2 Example 2 3.1 1.0 5.1 7.4 Example 3 3.2 0.8 4.8 7.1 Example 4 2.8 0.7 5.0 7.2 Comparative Example 1 5.7 1.2 4.6 13.6 Comparative Example 2 4.8 1.0 4.8 11.9

[0066] As shown in Table 2, the modified PA6 materials prepared in Examples 1-4 are significantly superior to Comparative Examples 1 and 2 in terms of water absorption and dimensional stability after moisture absorption. Furthermore, the dielectric constants of Examples 1-4 remain relatively stable after moisture absorption, while the dielectric properties of Comparative Examples 1 and 2 show a significant decrease after moisture absorption. This indicates that the copolymer matrix prepared by the complete technical solution of this application has a clear advantage in reducing material hygroscopicity and maintaining dimensional and electrical property stability under humid and hot conditions.

[0067] Comparative Example 1 used an equimolar amount of caprolactam instead of dodecanoic acid, resulting in a pure PA6 polymer matrix. This example exhibited the highest water absorption rate and the largest change in dielectric constant after moisture absorption, along with poorer dimensional stability. This indicates that the molecular backbone composed entirely of polar amide groups is the fundamental reason for the material's high hygroscopicity. Comparative Example 2 reduced the proportion of dodecanoic acid, leading to inferior water absorption rate and dielectric stability compared to the examples. This further demonstrates the necessity of introducing sufficient amounts of long-chain lactam monomers to suppress matrix water absorption.

[0068] In summary, this application introduces a specific proportion of long-chain dodecyl lactam monomers during the ring-opening polymerization stage, embedding hydrophobic long alkyl chain structures into the PA6 molecular backbone through in-situ random copolymerization. This design reduces the concentration of polar amide groups at the molecular level, weakening the ability of the matrix material to bind with water molecules from the source, thereby significantly reducing the equilibrium water absorption rate and saturation water absorption rate of the material. This process ensures the uniform bonding of the two monomers, avoids the phase separation problems that may occur in physical blending, and synergistically achieves a significant improvement in the dimensional stability and electrical performance stability under humid and hot environments while retaining most of the excellent mechanical properties of PA6.

[0069] Experiment Example 2

[0070] The thermal conductivity and electrical breakdown strength of the modified PA6 materials prepared in Examples 5-8 and Comparative Examples 3-5 were tested, and the relevant results are summarized in Table 3.

[0071] The thermal conductivity test method refers to the relevant test method of ASTM E1461 standard. The thermal conductivity (W / (m·K)) in the thickness direction of the specimen is tested and recorded. The specimen size is 12.7 mm in diameter and 2 mm in thickness.

[0072] The electrical breakdown strength test method refers to the test method of ASTM D149 standard. The breakdown test is carried out at a power frequency of 60Hz, and the maximum breakdown voltage of the sample (kV / mm) is recorded. The sample size is 100mm×100mm×2mm.

[0073] Table 3. Thermal conductivity and electrical breakdown strength of the modified PA6 materials prepared in Examples 5-8 and Comparative Examples 3-5.

[0074] Thermal conductivity (W / (m·K)) Maximum breakdown voltage (kV / mm) Example 5 1.7 45.0 Example 6 1.8 44.5 Example 7 1.7 44.5 Example 8 1.9 45.0 Comparative Example 3 0.6 25.5 Comparative Example 4 0.9 28.5 Comparative Example 5 1.3 39.5

[0075] As shown in Table 3, the modified PA6 materials prepared in Examples 5-8 are significantly better than those in Comparative Examples 3, 4 and 5 in terms of both thermal conductivity and maximum breakdown voltage, indicating that this technical solution has obvious advantages in improving the thermal conductivity and high-voltage insulation of the material.

[0076] Comparative Example 3, without the addition of boron nitride nanosheets, exhibited the worst thermal conductivity and voltage withstand capability among all samples, demonstrating that boron nitride is a core functional additive for achieving high thermal conductivity and high insulation performance. Comparative Example 4, where boron nitride nanosheets and the matrix resin were added separately to the extruder without pre-dispersion treatment, resulted in a final product with significantly lower thermal conductivity and electrical breakdown strength than the examples. This indicates that preparing the filler into a suspension is a crucial step in improving its dispersibility in the matrix. Comparative Example 5, where the composite suspension was added together with the flame retardant in the later stages of extrusion, also showed inferior material properties compared to the examples, further highlighting the importance of adding the thermally conductive filler as early as possible after the polymer is completely melted for forming a uniformly dispersed structure.

[0077] In summary, this application prepares a composite suspension by blending boron nitride nanosheets with polyamide oligomers, and injects it into a twin-screw extruder after the matrix resin is completely melted. This pre-dispersion treatment significantly improves the dispersibility of boron nitride nanosheets in a thermoplastic nylon matrix. The uniformly dispersed boron nitride not only constructs an efficient phonon transport network to ensure good thermal conductivity of the material, but also forms a partially parallel lamellar structure during subsequent tensile shearing, thereby simultaneously improving the insulation and high-voltage resistance of the modified PA6 material, achieving a synergistic enhancement of thermal conductivity and insulation performance.

[0078] Experimental Example 3

[0079] The thermal conductivity, tensile properties, and flame retardant properties of the modified PA6 materials prepared in Examples 9-12 and Comparative Examples 6-8 were tested. The relevant results are summarized in Table 4.

[0080] For the test method of thermal conductivity, refer to Experiment Example 2.

[0081] The tensile properties were tested according to the relevant test methods of ISO 527. The tensile strength (MPa) of the specimen was recorded. A dumbbell-shaped specimen was used with a total length of 170 mm, a gauge length of 80 mm, a gauge width of 10 mm, and a thickness of 4 mm.

[0082] The flame retardant performance test method refers to UL 94 standard. After the test, the flame retardant performance level of the sample is recorded. The sample size is 125mm×13mm×1.6mm.

[0083] Table 4. Thermal conductivity, tensile properties, and flame retardant properties of the modified PA6 materials prepared in Examples 9-12 and Comparative Examples 6-8.

[0084] Thermal conductivity (W / (m·K)) Tensile strength (MPa) Flame retardant rating Example 9 1.8 118.7 V-0 Example 10 1.9 121.9 V-0 Example 11 1.9 120.5 V-0 Example 12 1.8 119.4 V-0 Comparative Example 6 1.5 82.5 V-0 Comparative Example 7 1.2 62.8 V-0 Comparative Example 8 0.7 51.6 V-0

[0085] As shown in Table 4, the modified PA6 materials prepared in Examples 9-12 maintained high thermal conductivity and tensile strength while achieving a V-0 flame retardant rating. In contrast, Comparative Examples 6, 7, and 8, although also achieving the same flame retardant rating, showed a significant decrease in tensile strength and thermal conductivity. This indicates that the proposed technical solution can effectively compensate for the loss of mechanical and thermal properties caused by the introduction of flame retardant additives, achieving a good balance between flame retardancy, thermal conductivity, and mechanical properties.

[0086] Comparative Example 6 used unaminated graphene oxide, and its tensile strength was significantly lower than that of the examples, indicating that amination modification of the graphene oxide surface is crucial for enhancing the mechanical properties of the material. Comparative Example 7 increased the amount of flame retardant additive, leading to a significant deterioration in the tensile strength and thermal conductivity of the material, demonstrating that excessive inorganic powder fillers can severely damage the overall performance of the material due to weak interfacial bonding. Comparative Example 8 did not use polyamide oligomer pre-dispersion filler, directly blending in a solid state, resulting in the most severe loss of mechanical and thermal conductivity properties, highlighting the core role of the pre-dispersion process in ensuring filler functionality and maintaining the mechanical properties of the matrix.

[0087] In summary, this application synergistically utilizes the functions of multiple components. Melamine phosphate and zinc borate, as inorganic powder flame retardants, exhibit weak interfacial bonding with the polymer matrix, leading to a decrease in material strength and toughness. This solution introduces surface-aminated modified graphene oxide, whose surface amino groups can chemically bond with the polar groups in the PA6 / 12 random copolymer matrix. Simultaneously, its two-dimensional sheet-like structure partially coats the surface of the flame retardant particles, improving interfacial stress transfer and thus partially restoring the material's mechanical strength. Furthermore, the modified graphene oxide, in conjunction with the uniformly dispersed boron nitride nanosheets, further enhances the thermal conductivity of the modified PA6 material, effectively compensating for the negative impact of reduced thermal conductivity caused by the introduction of flame retardant additives.

[0088] Experiment Example 4

[0089] The comparative tracking index (CTI) and volume resistivity of the modified PA6 materials prepared in Examples 13-16 and Comparative Examples 9-10 were tested, and the results are summarized in Table 5.

[0090] Compared to the tracking index (CTI) test method, which refers to IEC 60112, the CTI values ​​of the sample were tested before and after aging in hot air at 150°C for 500 hours. The sample size was 60mm×60mm×3mm.

[0091] The volume resistivity test method refers to ASTM D257. The volume resistivity of the sample is tested before and after hot air aging. The sample size is 100 mm in diameter and 3 mm in thickness.

[0092] Table 5. CTI values ​​and volume resistivity of the modified PA6 materials prepared in Examples 13-16 and Comparative Examples 9-10

[0093] CTI value (V) before aging CTI value (V) after aging <![CDATA[Volume resistivity before aging (10 14 Ω·cm)]]> <![CDATA[Volume resistivity after aging (10 14 Ω·cm)]]> Example 13 645, PLC0 625, PLC0 22.4 8.9 Example 14 645, PLC0 630, PLC0 21.7 8.4 Example 15 650, PLC0 625, PLC0 21.9 8.5 Example 16 645, PLC0 620, PLC0 22.1 8.2 Comparative Example 9 630, PLC0 550, PLC1 20.9 4.2 Comparative Example 10 635, PLC0 450, PLC2 22.1 1.8

[0094] As shown in Table 5, the modified PA6 materials prepared in Examples 13-16 maintained high levels of comparative tracking index and volume resistivity before and after prolonged hot air aging, and their CTI values ​​remained at the highest performance level of PLC0 after aging. In contrast, the materials in Comparative Examples 9 and 10 showed significant degradation in electrical performance after aging, with a marked decrease in their CTI levels. This indicates that the present technical solution has a significant advantage in ensuring the electrical performance stability of materials during long-term service at high temperatures.

[0095] Comparative Example 10, without the addition of modified hydrotalcite, exhibited the most severe deterioration in its electrical properties after thermal aging. This directly demonstrates that modified hydrotalcite is a key additive for maintaining the long-term thermal stability and electrical insulation of the material. Comparative Example 9, which incorporated modified hydrotalcite in blends with other additives instead of surface coating the matrix resin, showed better performance after aging than Comparative Example 10, but still significantly inferior to the examples. This result underscores the importance of surface coating pretreatment for ensuring uniform dispersion of modified hydrotalcite and maximizing its functionality.

[0096] In summary, this application utilizes a surface coating method to pre-coat modified hydrotalcite onto PA6 / 12 random copolymer particles. As a heat stabilizer and acid trapping agent, the core function of modified hydrotalcite is to neutralize the conductive phosphoric acid-like acidic substances that may be generated by the decomposition or hydrolysis of the flame retardant melamine phosphate under prolonged heating. The uniformly dispersed modified hydrotalcite actively traps these acidic substances and fixes them within its layered structure, transforming them into harmless stable salts. This fundamentally prevents the destructive effects of acidic ions on electrical properties, ensuring the long-term safety of the flame-retardant system under high pressure. Simultaneously, the modified hydrotalcite also inhibits the aggregation of graphene oxide, improving its interfacial compatibility with the matrix, synergistically guaranteeing the final excellent insulation and heat resistance of the modified PA6 material.

[0097] 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 modified PA6 material, characterized in that: The preparation method is as follows: Caprolactam and dodecanolactam were mixed at a molar ratio of 85:15 and copolymerized to obtain a PA6 / 12 random copolymer. The PA6 / 12 random copolymer was surface-coated with modified hydrotalcite; The modified hydrotalcite is obtained by treating aluminum magnesium hydrotalcite powder with sodium stearate. 100 parts of the PA6 / 12 random copolymer were fed into an extruder, melted, and then a composite suspension was added. The temperature was increased and 15 parts of flame retardant were added in the later stage of extrusion. The modified PA6 material was obtained after extrusion. According to the extruder barrel operation sequence, the feeding sequence is as follows: the first barrel is the main feed port, with an operating temperature of 260℃, where the surface-coated PA6 / 12 random copolymer is added; the second to fourth barrels are the melting and plasticizing zones; in the fifth barrel zone, the composite suspension is added via a metering pump; the sixth barrel is the conventional stretching and shearing treatment section; the seventh barrel is the side feed port, where the flame retardant additive is added and mixed, and the operating temperature is raised to 280℃; the eighth barrel is the conventional stretching and shearing treatment section; the ninth barrel is the venting zone, with an operating pressure of 0.1 atm; the tenth to twelfth barrels are the homogenization pressure zone, and finally, the melt is extruded through weak shear force; The composite suspension comprises: polyamide oligomers, boron nitride nanosheets, and modified graphene oxide; The surface coating process is as follows: the PA6 / 12 random copolymer and the modified hydrotalcite are mixed under stirring for 5-10 minutes; The modified graphene oxide is prepared by dispersing graphene oxide in deionized water, adding ethylenediamine, reacting in a water bath, and washing and drying the resulting solid product to obtain the modified graphene oxide. The composite suspension is prepared by heating the polyamide oligomer, adding the modified graphene oxide dispersion, homogenizing by ultrasonication, adding the boron nitride nanosheets, mixing evenly, and then vacuum treating to obtain the composite suspension. The flame retardant additives include: melamine phosphate and zinc borate; the polyamide oligomer is a hydroxyl-terminated PA6 oligomer. The mass ratio of the PA6 / 12 random copolymer to the composite suspension is 100:25-35.

2. The method for preparing a modified PA6 material according to claim 1, characterized in that: In the copolymerization reaction, the reaction temperature is 260-280℃.

3. A modified PA6 material, characterized in that: The modified PA6 material is prepared by the preparation method described in any one of claims 1-2.

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