Graphene modified high-conductive PEI composite material and preparation process thereof

Abstract

This invention belongs to the field of polymer materials and discloses a graphene-modified high-conductivity PEI composite material and its preparation process. The composite material includes the following raw materials in parts by weight: 88-92 parts of PEI resin, 2-4 parts of modified graphene, 4-6 parts of modified carbon fiber, 0.5-1 parts of dispersant, and 1-2 parts of toughening agent. The modified graphene is prepared by grafting functionalized polyimide prepolymer onto the graphene surface, and hindered phenolic antioxidant groups are grafted onto the main chain or ends of the functionalized polyimide prepolymer. The modified carbon fiber is prepared by first modifying the surface of carbon fiber with a silane coupling agent, and then copolymerizing polythiophene monomer and flame retardant monomer in situ on the carbon fiber surface to form a composite conductive and flame-retardant layer. This invention uses low-viscosity PEI resin as the matrix, combined with modified graphene, modified carbon fiber, dispersant, and toughening agent to form a synergistic and complementary composite system, achieving comprehensive properties of high conductivity, high mechanical strength, high flame retardancy, high stability, and easy processing.

Description

Technical Field

[0001] This invention belongs to the field of polymer materials technology, specifically relating to a graphene-modified high-conductivity PEI composite material and its preparation process. Background Technology

[0002] Polyetherimide (PEI) is a type of thermoplastic high-performance engineering plastic obtained by introducing ether bonds (-O-) into the polyimide backbone. PEI combines the excellent high-temperature resistance of polyimide with the good processability of thermoplastic resins. It has a high glass transition temperature (approximately 210°C), outstanding dimensional stability, natural flame retardancy, good mechanical strength and modulus, as well as excellent acid and alkali resistance and chemical resistance. Therefore, it is widely used in aerospace, electronics, medical devices and other fields. However, PEI itself has poor electrical insulation properties (volume resistivity is typically above 10). 16 The high conductivity (above Ω·cm) severely restricts its application in fields with high requirements for conductivity, such as electromagnetic shielding, electrostatic discharge (ESD), and flexible electronics.

[0003] In existing technologies, PEI is usually modified by adding conductive fillers, such as graphite, carbon fiber, and carbon nanotubes. However, unmodified or conventionally modified conductive fillers have poor compatibility with the PEI matrix, are prone to agglomeration, and are difficult to form a dense conductive network. At the same time, additional coupling agents, antioxidants and other additives are required to improve compatibility and stability, resulting in complex formulations and increased production costs. Furthermore, it is difficult to balance conductivity, mechanical properties and flame retardancy. Modified materials are prone to performance degradation and increased processing difficulty. Summary of the Invention

[0004] To address the shortcomings mentioned in the background art, the present invention aims to provide a graphene-modified high-conductivity PEI composite material and its preparation process. The present invention uses low-viscosity PEI resin as the matrix, combined with modified graphene, modified carbon fiber, dispersant and toughening agent to form a synergistic and complementary composite system, achieving comprehensive performance of high conductivity, high mechanical properties, high flame retardancy, high stability and easy processing.

[0005] The objective of this invention can be achieved through the following technical solutions: A graphene-modified high-conductivity PEI composite material comprises the following raw materials in parts by weight: 88-92 parts of PEI resin, 2-4 parts of modified graphene, 4-6 parts of modified carbon fiber, 0.5-1 part of dispersant, and 1-2 parts of toughening agent. Modified graphene is achieved by grafting functionalized polyimide prepolymer onto the graphene surface, with hindered phenolic antioxidant groups grafted onto the main chain or ends of the functionalized polyimide prepolymer; modified carbon fiber is achieved by first modifying the surface of carbon fiber with a silane coupling agent, and then copolymerizing polythiophene monomer and flame retardant monomer in situ on the carbon fiber surface to form a composite conductive and flame-retardant layer.

[0006] Preferably, the PEI resin is a low-viscosity polyetherimide with a viscosity of 0.4~0.8 dL / g.

[0007] Preferably, the dispersant is one of stearamide, ethylene bis-stearamide, or polyglycerol fatty acid ester.

[0008] Preferably, the toughening agent is one of polyethersulfone, polycarbonate, or styrene-butadiene copolymer.

[0009] Preferably, the method for preparing modified graphene includes the following steps: (1) Add graphene powder to a mixed solution of deionized water and ethanol, then add sodium dodecylbenzenesulfonate, and ultrasonically disperse for 30-40 min to form a uniform graphene dispersion. Then add concentrated nitric acid, stir in a 60°C water bath for 1.5-2.5 h, filter, wash until neutral, and vacuum dry to obtain graphene oxide. (2) Take pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and 3,5-di-tert-butyl-4-hydroxystyrene, add N,N-dimethylformamide, and stir at 50°C for 1-2 hours under nitrogen protection to form a low molecular weight polyimide prepolymer solution. (3) Add the graphene oxide prepared in step (1) to the above polyimide prepolymer solution, add triethylamine, stir and react at 80°C for 3-5 hours under nitrogen protection. After the reaction is completed, add deionized water to precipitate, filter and wash with deionized water 3 times, and vacuum dry to obtain modified crude graphene. (4) The modified graphene crude product is placed in a tube furnace and calcined at 300°C for 1.5 to 2.5 hours under inert gas protection. After cooling to room temperature, it is crushed and passed through a 100-mesh sieve to obtain modified graphene.

[0010] Preferably, the mass ratio of graphene, pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, 3,5-di-tert-butyl-4-hydroxystyrene and triethylamine is 100:10:12.5:1.5:4.

[0011] Preferably, the method for preparing modified carbon fiber includes the following steps: A. Place the carbon fiber in an acetone solution and ultrasonically clean it for 15-25 minutes to remove surface oil and impurities. After vacuum drying, place it in a plasma treatment instrument, introduce argon gas, and plasma treat for 5-15 minutes to obtain activated carbon fiber. B. Take 3-glycidyl etheroxypropyltrimethoxysilane and 3-aminopropyltriethoxysilane, add ethanol and deionized water, stir evenly, then immerse the activated carbon fibers in the solution, stir in a water bath at 60°C for 0.5–1.5 h, remove the carbon fibers and vacuum dry to obtain carbon fibers with coupling agent surface modification. C. Take polythiophene monomer, add chloroform and N,N-dimethylformamide, stir to dissolve, add ferric chloride, and simultaneously add phosphate ester styrene. After stirring evenly, immerse the surface-modified carbon fiber in the solution, and stir and react at 40°C for 2-4 hours under nitrogen protection. After the reaction is complete, wash three times with chloroform, vacuum dry, and place in an oven for constant temperature treatment at 150°C for 2-4 hours. Cool to room temperature to obtain modified carbon fiber.

[0012] Preferably, the mass ratio of carbon fiber, 3-glycidoxypropyltrimethoxysilane, and 3-aminopropyltriethoxysilane is 50:1:1.

[0013] Preferably, the mass ratio of surface-modified carbon fiber impregnation, polythiophene monomer, and phosphate-based styrene is 20:1:0.075.

[0014] A preparation process for a graphene-modified highly conductive PEI composite material includes the following steps: S1. Weigh out the PEI resin, modified graphene, modified carbon fiber, dispersant, and toughening agent according to the formula content, put them into a high-speed mixer, adjust the speed to 2000 r / min, and mix at room temperature for 10-20 min to obtain a homogeneous mixture. S2. Feed the mixture into a twin-screw extruder, set the extrusion temperature to 320~340℃ and the screw speed to 180r / min, melt-blend and then extrude and granulate to obtain composite material particles; S3. Place the composite material particles into the injection molding machine, set the injection temperature to 330~350℃, the mold temperature to 120℃, the injection pressure to 80MPa, and the holding time to 10s, and perform injection molding. Place the molded product into an oven and treat it at a constant temperature of 120℃ for 1.5~2.5h. Allow it to cool naturally to room temperature to obtain the graphene-modified high-conductivity PEI composite material.

[0015] The beneficial effects of this invention are: This invention uses low-viscosity PEI resin as the matrix, combined with modified graphene, modified carbon fiber, dispersant and toughening agent to form a synergistic and complementary composite system. PEI resin ensures the heat resistance and molding processability of the material, while modified graphene and modified carbon fiber form a point-line synergistic conductive network, which significantly improves the conductivity of the material. At the same time, it endows the material with excellent flame retardancy and stability, achieving comprehensive performance of high conductivity, high mechanical properties, high flame retardancy, high stability and easy processing.

[0016] In this invention, the modified graphene is first pretreated by mild oxidation to introduce carboxyl (-COOH) and hydroxyl (-OH) active groups, providing sites for subsequent grafting reactions. Then, a low molecular weight PI prepolymer containing the antioxidant monomer 3,5-di-tert-butyl-4-hydroxystyrene is prepared. The amino (-NH2) at the end of the PI prepolymer reacts with the active groups on the surface of graphene oxide, and the PI fragments are grafted onto the graphene surface in situ through amide bonds (-CONH-). Finally, the PI fragments are activated by calcination to crosslink and solidify, forming a stable modified layer, while removing residual impurities. Modified graphene not only retains the high conductivity of original graphene but also achieves two core functional enhancements through grafted PI fragments: First, significantly improved interfacial compatibility. The PI fragments, structurally homologous to PEI resin, can replace coupling agents, effectively solving the technical challenges of uneven graphene dispersion and weak interfacial bonding in the PEI matrix, ensuring uniform graphene dispersion and a strong bond with the matrix. Second, it endows graphene with excellent antioxidant properties. The grafted 3,5-di-tert-butyl-4-hydroxystyrene effectively captures free radicals generated during material aging, inhibiting the oxidative degradation of the PEI matrix and the graphene itself. Simultaneously, the PI-modified layer isolates external oxygen and moisture, further enhancing the antioxidant effect and acting as an antioxidant. Furthermore, the sheet-like structure of modified graphene can form a physical barrier during combustion, helping to improve the flame retardant properties of the material. Together with modified carbon fibers, it constructs a dense conductive network, significantly reducing the material's volume resistivity, providing core support for the high conductivity and high stability of the composite material.

[0017] This invention modifies carbon fibers by first pretreating them: acetone cleaning removes surface oil, and plasma treatment introduces active free radicals and increases surface area, providing sites for subsequent anchoring layer bonding. Anchoring layers are then prepared using KH-560 and KH-550 coupling agents. The hydrolysis of the siloxane groups in the coupling agents combines with the active free radicals on the carbon fiber surface to form a robust silane anchoring layer. Finally, a conductive-flame-retardant composite layer is formed by in-situ copolymerization of polythiophene monomers and flame-retardant phosphate ester styrene monomers on the carbon fiber surface. Finally, synergistic activation ensures full cross-linking between the anchoring layer and the composite layer, guaranteeing strong adhesion of the composite layer and activating conductive sites to enhance interfacial anchoring. This invention modifies carbon fibers to possess high conductivity, flame retardancy, corrosion resistance, and excellent interfacial bonding performance. The bottom silane anchoring layer can replace the coupling agent, forming chemical bonds with the PEI matrix, effectively solving the problem of carbon fiber-PEI matrix interface delamination and improving the mechanical properties of the composite material. The top polythiophene layer has good conductivity, forming a point-to-line synergistic conductive network with modified graphene, filling the gaps between carbon fibers, and improving the density and continuity of the conductive network. The phosphate-based styrene in the top composite layer decomposes during combustion to produce phosphoric acid flame retardants, forming a char layer that covers the material surface, isolating oxygen and heat transfer, and inhibiting flame spread. The high-temperature resistance of the polythiophene layer further enhances the flame retardant effect. The dual-functional modified layer can isolate external corrosive media, protect the carbon fiber body, and extend the service life of the composite material.

[0018] Of course, any product implementing this invention does not necessarily need to achieve all of the advantages described above at the same time. Detailed Implementation

[0019] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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.

[0020] Example 1 A modified graphene, prepared by grafting a functionalized polyimide prepolymer onto the surface of graphene, wherein hindered phenolic antioxidant groups are grafted onto the main chain or ends of the functionalized polyimide prepolymer, includes the following steps: (1) Add 10g of graphene powder to a mixed solution of 50mL of deionized water and 50mL of ethanol (volume ratio 1:1), then add 0.15g of sodium dodecylbenzenesulfonate, and ultrasonically disperse for 35min to form a uniform graphene dispersion. Then add 0.75g of concentrated nitric acid (mass fraction 65%), stir in a 60℃ water bath for 2h, filter, wash until neutral, and vacuum dry to obtain graphene oxide. (2) Take 1.0 g of pyromellitic dianhydride, 1.25 g of 4,4'-diaminodiphenyl ether, and 0.15 g of 3,5-di-tert-butyl-4-hydroxystyrene, add 80 mL of N,N-dimethylformamide, and stir at 50 °C for 1.5 h under nitrogen protection to form a low molecular weight polyimide prepolymer solution (viscosity controlled at 0.1~0.2 dL / g). (3) Add the graphene oxide prepared in step (1) to the above polyimide prepolymer solution, add 0.4g of triethylamine, stir and react at 80°C for 4h under nitrogen protection. After the reaction is completed, add 200mL of deionized water for precipitation, filter and wash with deionized water 3 times, and vacuum dry to obtain crude modified graphene. (4) The modified graphene crude product is placed in a tube furnace and calcined at 300°C for 2 hours under inert gas protection. After cooling to room temperature, it is crushed and passed through a 100-mesh sieve to obtain the modified graphene.

[0021] Example 2 A modified carbon fiber is prepared by first modifying the surface of the carbon fiber with a silane coupling agent, and then copolymerizing polythiophene monomer and flame-retardant monomer in situ on the surface of the carbon fiber to form a composite conductive and flame-retardant layer. The preparation method includes the following steps: A. Take 20g of polyacrylonitrile-based carbon fiber with a length of 50~100μm, put it into 100mL of acetone solution, ultrasonically clean it for 20min to remove surface oil and impurities, vacuum dry it and put it into a plasma treatment instrument, introduce argon gas, and plasma treat it for 10min to obtain activated carbon fiber. B. Take 0.4 g of 3-glycidyl etheroxypropyltrimethoxysilane and 0.4 g of 3-aminopropyltriethoxysilane (mass ratio 1:1), add 38.4 mL of ethanol and 12.8 mL of deionized water (volume ratio 3:1), stir well, then immerse the activated carbon fibers in the solution, stir in a 60°C water bath for 1 h, remove the carbon fibers and vacuum dry to obtain carbon fibers with coupling agent surface modification. C. Take 1.0 g of polythiophene monomer, add 66.7 mL of chloroform and 33.3 mL of DMF, stir to dissolve, add 0.15 g of ferric chloride and 0.075 g of phosphate ester styrene, stir evenly, immerse the surface-modified carbon fiber in the solution, stir and react at 40 °C for 3 h under nitrogen protection. After the reaction is completed, wash with chloroform 3 times, vacuum dry and put into an oven, constant temperature treatment at 150 °C for 3 h, cool to room temperature to obtain modified carbon fiber.

[0022] Example 3 A graphene-modified high-conductivity PEI composite material comprises the following raw materials in parts by weight: 88 parts of PEI resin with a viscosity of 0.4 dL / g, 2 parts of modified graphene, 4 parts of modified carbon fiber, 0.5 parts of stearamide, and 1 part of styrene-butadiene copolymer; the modified graphene is prepared in Example 1, and the modified carbon fiber is prepared in Example 2.

[0023] The preparation method of the above-mentioned graphene-modified high-conductivity PEI composite material includes the following steps: S1. Weigh out PEI resin with a viscosity of 0.4 dL / g, modified graphene, modified carbon fiber, stearamide and styrene-butadiene copolymer according to the formula content, put them into a high-speed mixer, adjust the speed to 2000 r / min, mix at room temperature for 10 min to obtain a uniform mixture. S2. Feed the mixture into a twin-screw extruder, set the extrusion temperature to 320℃ and the screw speed to 180r / min, melt-blend and then extrude and granulate to obtain composite material particles; S3. Place the composite material particles into the injection molding machine, set the injection temperature to 330℃, the mold temperature to 120℃, the injection pressure to 80MPa, and the holding time to 10s, and perform injection molding. Place the molded product into an oven and treat it at a constant temperature of 120℃ for 1.5h. Allow it to cool naturally to room temperature to obtain the graphene-modified high-conductivity PEI composite material.

[0024] Example 4 A graphene-modified high-conductivity PEI composite material comprises the following raw materials in parts by weight: 92 parts of PEI resin with a viscosity of 0.8 dL / g, 4 parts of modified graphene, 6 parts of modified carbon fiber, 1 part of polyglycerol fatty acid ester, and 2 parts of polycarbonate; the modified graphene was prepared in Example 1, and the modified carbon fiber was prepared in Example 2.

[0025] The preparation method of the above-mentioned graphene-modified high-conductivity PEI composite material includes the following steps: S1. Weigh out PEI resin with a viscosity of 0.8 dL / g, modified graphene, modified carbon fiber, polyglycerol fatty acid ester, and polycarbonate according to the formula, put them into a high-speed mixer, adjust the speed to 2000 r / min, mix at room temperature for 20 min, and obtain a homogeneous mixture. S2. Feed the mixture into a twin-screw extruder, set the extrusion temperature to 340℃ and the screw speed to 180r / min, melt-blend and then extrude and granulate to obtain composite material particles; S3. Place the composite material particles into the injection molding machine, set the injection temperature to 350℃, the mold temperature to 120℃, the injection pressure to 80MPa, and the holding time to 10s, and perform injection molding. Place the molded product into an oven and treat it at a constant temperature of 120℃ for 2.5h. Allow it to cool naturally to room temperature to obtain the graphene-modified high-conductivity PEI composite material.

[0026] Example 5 A graphene-modified high-conductivity PEI composite material comprises the following raw materials in parts by weight: 90 parts of PEI resin with a viscosity of 0.6 dL / g, 3 parts of modified graphene, 5 parts of modified carbon fiber, 0.75 parts of ethylene bis-stearamide, and 1.5 parts of polyethersulfone; the modified graphene was prepared in Example 1, and the modified carbon fiber was prepared in Example 2.

[0027] The preparation method of the above-mentioned graphene-modified high-conductivity PEI composite material includes the following steps: S1. Weigh out PEI resin with a viscosity of 0.6 dL / g, modified graphene, modified carbon fiber, ethylene bis-stearamide, and polyethersulfone according to the formula, put them into a high-speed mixer, adjust the speed to 2000 r / min, mix at room temperature for 15 min, and obtain a homogeneous mixture. S2. Feed the mixture into a twin-screw extruder, set the extrusion temperature to 330℃ and the screw speed to 180r / min, melt-blend and then extrude and granulate to obtain composite material particles; S3. Place the composite material particles into the injection molding machine, set the injection temperature to 340℃, the mold temperature to 120℃, the injection pressure to 80MPa, and the holding time to 10s, and perform injection molding. Place the molded product into an oven and treat it at a constant temperature of 120℃ for 2 hours. Allow it to cool naturally to room temperature to obtain the graphene-modified high-conductivity PEI composite material.

[0028] Comparative Example 1 A graphene-modified highly conductive PEI composite material comprises the following raw materials in parts by weight: 90 parts of PEI resin with a viscosity of 0.6 dL / g, 5 parts of modified carbon fiber, 0.75 parts of ethylene bis-stearamide, and 1.5 parts of polyethersulfone; the modified carbon fiber is prepared in Example 2.

[0029] The preparation method of the above graphene-modified high-conductivity PEI composite material is the same as that in Example 5, except that no modified graphene is added in step S1.

[0030] Comparative Example 2 A graphene-modified high-conductivity PEI composite material comprises the following raw materials in parts by weight: 90 parts of PEI resin with a viscosity of 0.6 dL / g, 3 parts of modified graphene, 0.75 parts of ethylene bis-stearamide, and 1.5 parts of polyethersulfone; the modified graphene is prepared in Example 1.

[0031] The preparation method of the graphene-modified high-conductivity PEI composite material is the same as that in Example 5, except that modified carbon fiber is not added in step S1.

[0032] Performance testing (1) Conductivity: The volume resistivity (Ω·cm) of the sample was tested using a four-probe tester in accordance with GB / T15662-1995 standard. Five points were tested for each sample and the average value was taken. (2) Mechanical properties: ① Tensile strength: According to GB / T1040.1-2025 standard, the universal testing machine was used for testing, with a tensile speed of 5 mm / min; ② Impact strength: According to GB / T1843-2008 standard, the simple beam impact testing machine was used for testing, with 5 tests for each sample and the average value was taken; (3) Flame retardant performance: The vertical burning rating of the sample was tested according to UL94 standard, and the sample thickness was 3.2 mm; (4) Antioxidant stability: The sample was placed in a constant temperature oven at 100℃ for 1000h and the decay rate of volume resistivity and tensile strength after aging was tested. (5) Processing performance: The melt flow rate (MFR) under the condition of 230℃ / 5kg was tested using a melt flow rate meter in accordance with GB / T3682.1-2018 standard to evaluate melt flowability.

[0033] The results are shown in Table 1 below.

[0034] Table 1. Performance test results of graphene-modified high-conductivity PEI composite materials

[0035] As can be seen from the data in Table 1, the volume resistivity of Examples 3 to 5 is all around 10. -3 ~10 -4 Within the Ω·cm range, it exhibits excellent high conductivity. This is because modified graphene and modified carbon fibers form a point-to-line synergistic conductive network in the PEI matrix. The sheet-like graphene can fill the gaps between the linear carbon fibers, reducing the discontinuities in the conductive path. Both graphene and carbon fibers possess good conductivity and compatibility, allowing them to be uniformly dispersed in the matrix, ensuring the density and continuity of the conductive network. Comparative Examples 1 and 2 show a significant increase in volume resistivity. Comparative Example 1 lacks sheet-like modified graphene; relying solely on linear modified carbon fibers, it cannot form a dense conductive network. The gaps between the carbon fibers cannot be filled, resulting in discontinuous conductive paths and a significant increase in electron transport resistance, leading to a sharp decline in conductivity. Comparative Example 2 also lacks linear modified carbon fibers; relying solely on sheet-like modified graphene makes it difficult to construct a conductive path throughout the entire matrix. Graphene sheets are prone to aggregation or uneven dispersion, resulting in low electron transport efficiency and failing to achieve the desired conductivity.

[0036] The tensile strength and impact strength of Examples 3-5 are superior to those of the two comparative examples, and Example 4 has the best mechanical properties. This is because both modified graphene and modified carbon fiber have excellent mechanical strength, and both form a strong interfacial bond with the PEI matrix through their respective modified layers. The PI fragments on the surface of modified graphene are homologous to the structure of PEI resin, which improves interfacial compatibility. The silane anchoring layer on the surface of modified carbon fiber can form chemical bonds with the PEI matrix, which enhances the interfacial adhesion. The synergistic effect of the two can effectively disperse the stress and inhibit the generation and propagation of cracks. At the same time, the toughening agent further improves the toughness of the material, thereby comprehensively improving the mechanical properties of the composite material. Comparative Example 1 lacks modified graphene, relying solely on modified carbon fibers to bear the load. The stress between the carbon fibers cannot be dispersed through the graphene sheets, easily leading to stress concentration at the interface between the carbon fibers and the matrix, resulting in interfacial delamination and consequently reducing tensile and impact strength. Comparative Example 2 also lacks modified carbon fibers. Although modified graphene can improve strength to some extent, sheet-like graphene cannot provide the same skeletal support as linear carbon fibers, making it unable to effectively resist external impacts and tension. Furthermore, the graphene sheets are prone to slippage under stress, resulting in a significant decrease in material toughness. At the same time, the reduction in interfacial bonding sites further exacerbates the degradation of mechanical properties.

[0037] Examples 3-5 all achieved the UL94 V-0 flame retardant standard, demonstrating excellent flame retardant performance. In contrast, Comparative Examples 1 and 2 only achieved the UL94 V-1 standard, showing a significant decrease in flame retardant performance. This clearly demonstrates that the synergistic effect of modified graphene and modified carbon fiber is key to ensuring the high flame retardant performance of the material. In the polythiophene-flame retardant monomer copolymer layer on the surface of the modified carbon fiber, phosphate ester-based styrene decomposes during combustion to produce phosphoric acid-based flame retardant substances, forming a char layer that covers the material surface, isolating oxygen and heat transfer, and inhibiting flame spread. Simultaneously, the polythiophene layer possesses certain high-temperature resistance, which can further enhance the flame retardant effect. The sheet-like structure of modified graphene can form a physical barrier during combustion, hindering heat conduction and smoke diffusion, further strengthening the flame retardant performance. The synergistic effect of both makes the char layer denser and more stable, continuously exerting the flame retardant effect, thereby achieving the V-0 standard. Comparative Example 1 lacks modified graphene and relies solely on the flame-retardant effect of modified carbon fiber. Although a char layer can be formed through the decomposition of flame-retardant monomers, the lack of a physical barrier provided by graphene allows heat to easily be conducted through the PEI matrix into the material, causing the char layer to easily crack and fall off when heated. This results in an inability to continuously and effectively isolate oxygen and heat, accelerating the spread of flames and prolonging the burning time, thus reducing the flame-retardant rating to V-1. Comparative Example 2 also lacks modified carbon fiber. Although the physical barrier effect of modified graphene can help block the transfer of heat and smoke, the lack of chemical flame-retardant effect provided by flame-retardant monomers prevents the formation of a dense and stable char layer. During combustion, the material is prone to melting and dripping, and the flame cannot be quickly suppressed. It can only achieve the V-1 flame-retardant standard and cannot achieve the excellent flame-retardant effect of V-0.

[0038] The aging performance degradation rates of Examples 3-5 were all less than 10%, demonstrating excellent stability. This is because the PI fragments grafted onto the modified graphene surface contain 3,5-di-tert-butyl-4-hydroxystyrene antioxidant monomers, which can effectively capture free radicals generated during aging and inhibit the oxidative degradation of the PEI matrix and modified fillers. At the same time, the stable modified layers of modified graphene and modified carbon fibers can isolate external oxygen and moisture, reducing the occurrence of oxidation reactions and thus delaying the degradation of material performance. Comparative Example 1 lacks modified graphene, thus lacking the antioxidant monomer effect and unable to effectively capture free radicals. Furthermore, the absence of graphene's physical barrier allows oxygen and moisture to easily penetrate the material, accelerating the oxidative degradation of the PEI matrix. Simultaneously, the surface modification layer of the modified carbon fiber is prone to oxidation under long-term high-temperature conditions, leading to a significant decrease in conductivity and mechanical properties. Comparative Example 2 also lacks modified carbon fiber. Although modified graphene provides antioxidant protection, the internal conductive network and interfacial bonding are weak, making it prone to interfacial peeling and conductive network breakage during oxidation. The lack of carbon fiber support further accelerates the degradation of mechanical properties, resulting in a significant decrease in overall antioxidant stability.

[0039] Example 3 had the highest MFR, while Example 4 had the lowest. Both modified graphene and modified carbon fiber are solid fillers. Increasing their dosage would increase the friction of the material in the molten state, hindering melt flow. At the same time, the interfacial interaction between the filler and the PEI matrix would further reduce melt flowability. Comparative Example 1 lacked modified graphene, and Comparative Example 2 lacked modified carbon fiber. The total amount of filler was reduced, and the hindering effect on melt flow was weakened. Therefore, the melt flowability was slightly improved, but the improvement was not significant and remained within a reasonable processing range, which would not affect the feasibility of industrial production.

[0040] In the description of this specification, references to terms such as "an embodiment," "example," "specific example," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0041] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the claimed invention.

Claims

1. A graphene-modified high-conductivity PEI composite material, characterized in that, The raw materials include the following parts by weight: 88-92 parts of PEI resin, 2-4 parts of modified graphene, 4-6 parts of modified carbon fiber, 0.5-1 part of dispersant, and 1-2 parts of toughening agent; Modified graphene is prepared by grafting functionalized polyimide prepolymer onto the graphene surface, wherein hindered phenolic antioxidant groups are grafted onto the main chain or ends of the functionalized polyimide prepolymer; modified carbon fiber is prepared by first modifying the surface of carbon fiber with a silane coupling agent, and then copolymerizing polythiophene monomer and flame retardant monomer in situ on the carbon fiber surface to form a composite conductive and flame-retardant layer.

2. The graphene-modified high-conductivity PEI composite material according to claim 1, characterized in that, The PEI resin is a low-viscosity polyetherimide with a viscosity of 0.4~0.8 dL / g.

3. The graphene-modified high-conductivity PEI composite material according to claim 1, characterized in that, The dispersant is one of stearamide, ethylene bis-stearamide, or polyglycerol fatty acid ester.

4. The graphene-modified high-conductivity PEI composite material according to claim 1, characterized in that, The toughening agent is one of polyethersulfone, polycarbonate, or styrene-butadiene copolymer.

5. The graphene-modified high-conductivity PEI composite material according to claim 1, characterized in that, The method for preparing the modified graphene includes the following steps: (1) Add graphene powder to a mixed solution of deionized water and ethanol, then add sodium dodecylbenzenesulfonate, and ultrasonically disperse for 30-40 min to form a uniform graphene dispersion. Then add concentrated nitric acid, stir in a 60°C water bath for 1.5-2.5 h, filter, wash until neutral, and vacuum dry to obtain graphene oxide. (2) Take pyromellitic dianhydride, 4,4'-diaminodiphenyl ether and 3,5-di-tert-butyl-4-hydroxystyrene, add N,N-dimethylformamide, and stir at 50°C for 1-2 hours under nitrogen protection to form a low molecular weight polyimide prepolymer solution. (3) Add the graphene oxide prepared in step (1) to the above polyimide prepolymer solution, add triethylamine, stir and react at 80°C for 3-5 hours under nitrogen protection. After the reaction is completed, add deionized water to precipitate, filter and wash with deionized water 3 times, and vacuum dry to obtain modified crude graphene. (4) The modified graphene crude product is placed in a tube furnace and calcined at 300°C for 1.5 to 2.5 hours under inert gas protection. After cooling to room temperature, it is crushed and passed through a 100-mesh sieve to obtain the modified graphene.

6. The graphene-modified high-conductivity PEI composite material according to claim 5, characterized in that, The mass ratio of graphene, pyromellitic dianhydride, 4,4'-diaminodiphenyl ether, 3,5-di-tert-butyl-4-hydroxystyrene and triethylamine is 100:10:12.5:1.5:

4.

7. The graphene-modified high-conductivity PEI composite material according to claim 1, characterized in that, The method for preparing the modified carbon fiber includes the following steps: A. Place the carbon fiber in an acetone solution and ultrasonically clean it for 15-25 minutes to remove surface oil and impurities. After vacuum drying, place it in a plasma treatment instrument, introduce argon gas, and plasma treat for 5-15 minutes to obtain activated carbon fiber. B. Take 3-glycidyl etheroxypropyltrimethoxysilane and 3-aminopropyltriethoxysilane, add ethanol and deionized water, stir evenly, then immerse the activated carbon fibers in the solution, stir in a water bath at 60°C for 0.5–1.5 h, remove the carbon fibers and vacuum dry to obtain carbon fibers with coupling agent surface modification. C. Take polythiophene monomer, add chloroform and N,N-dimethylformamide, stir to dissolve, add ferric chloride, and simultaneously add phosphate ester styrene. After stirring evenly, immerse the surface-modified carbon fiber in the solution, and stir and react at 40°C for 2-4 hours under nitrogen protection. After the reaction is complete, wash three times with chloroform, vacuum dry, and place in an oven for constant temperature treatment at 150°C for 2-4 hours. Cool to room temperature to obtain modified carbon fiber.

8. The graphene-modified high-conductivity PEI composite material according to claim 7, characterized in that, The mass ratio of the carbon fiber, 3-glycidoxypropyltrimethoxysilane, and 3-aminopropyltriethoxysilane is 50:1:

1.

9. The graphene-modified high-conductivity PEI composite material according to claim 7, characterized in that, The mass ratio of the surface-modified carbon fiber impregnation, polythiophene monomer, and phosphate-based styrene is 20:1:0.

075.

10. The preparation process of the graphene-modified highly conductive PEI composite material according to any one of claims 1 to 9, characterized in that, Includes the following steps: S1. Weigh out the PEI resin, modified graphene, modified carbon fiber, dispersant, and toughening agent according to the formula content, put them into a high-speed mixer, adjust the speed to 2000 r / min, and mix at room temperature for 10-20 min to obtain a homogeneous mixture. S2. Feed the mixture into a twin-screw extruder, set the extrusion temperature to 320~340℃ and the screw speed to 180r / min, melt-blend and then extrude and granulate to obtain composite material particles; S3. Place the composite material particles into the injection molding machine, set the injection temperature to 330~350℃, the mold temperature to 120℃, the injection pressure to 80MPa, and the holding time to 10s, and perform injection molding. Place the molded product into an oven and treat it at a constant temperature of 120℃ for 1.5~2.5h. Allow it to cool naturally to room temperature to obtain the graphene-modified high-conductivity PEI composite material.

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