Modified carbon fiber preparation method and epoxy resin heat-conducting composite material preparation method

Abstract

The application provides a preparation of modified carbon fibers and a method for preparing an epoxy resin heat-conducting composite material by using the modified carbon fibers, wherein the modified carbon fibers are obtained by immersing carbon fibers in a mixed solution of hybrid modification of carbon nanotubes and a random copolymer containing benzene rings, and then performing a modification reaction; oxygen-containing functional groups of the random copolymer containing benzene rings and the carbon nanotubes on the surface of the fibers increase the surface activity and mechanical interlocking effect of the carbon fibers, improve the combination between the carbon fibers and the epoxy resin, reduce heat flow scattering and stress concentration at the interface; and the epoxy resin heat-conducting composite material is prepared by introducing a liquid crystal structure containing benzene rings into the modified carbon fibers, improving the structural order of the epoxy resin, improving the phonon transmission efficiency in the heat-conducting / dissipating process, and making the epoxy resin heat-conducting composite material have excellent heat-conducting performance and mechanical properties.

Description

Technical Field

[0001] This invention belongs to the field of thermally conductive polymer composite materials technology, specifically relating to a method for preparing modified carbon fiber and a method for preparing epoxy resin thermally conductive composite materials using the modified carbon fiber. Background Technology

[0002] Carbon fiber / epoxy resin composites possess numerous advantages, including lightweight, high specific strength, and high specific modulus, and are frequently used as substrates and housings for electronic systems in unmanned aerial vehicles and autonomous vehicles. With the rapid development of aerospace and transportation, electronic system components are becoming increasingly high-frequency, high-power, and high-density, inevitably leading to rapid heat accumulation and seriously threatening their operational stability and lifespan. This places higher demands on the thermal conductivity of carbon fiber / epoxy resin composites.

[0003] The low interfacial thermal conductivity of carbon fiber / epoxy resin composites limits the rapid conduction of heat within them, making their thermal conductivity unsatisfactory for application requirements. This is partly due to the low intrinsic thermal conductivity of epoxy resin (<0.2 W / (m·K)) and partly because the surface of carbon fiber is highly inert, making it difficult for epoxy resin to wet the carbon fiber. This results in voids or defects between the carbon fiber and epoxy resin, leading to poor interfacial bonding and blocking the thermal conduction pathways within the composite material.

[0004] Therefore, how to improve the intrinsic thermal conductivity of epoxy resin and enhance the bonding between carbon fiber and epoxy resin, thereby improving the thermal conductivity of carbon fiber / epoxy resin composites and preparing composites that integrate thermal conductivity and load-bearing capacity, has become a key issue that urgently needs to be addressed in the field of carbon fiber / epoxy resin composites. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing modified carbon fiber and a method for preparing epoxy resin thermally conductive composite materials. The modified carbon fiber provided by this invention can improve the bonding force between carbon fiber and epoxy resin, thereby enabling the epoxy resin thermally conductive composite material to possess both excellent mechanical and thermal conductivity properties.

[0006] This invention provides a method for preparing modified carbon fiber, comprising the following steps: Carbon fibers are immersed in a hybrid modified solution of carbon nanotubes and a random copolymer containing benzene rings to carry out a modification reaction, thereby obtaining the modified carbon fibers. The preparation method of the benzene ring-containing random copolymer is as follows: styrene, 4-vinylbenzocyclobutene, methyl methacrylate, reversible addition-fragmentation chain transfer polymerization (RAFT) reagent, initiator and reaction solvent are mixed and RAFT polymerization reaction is carried out under a protective atmosphere to obtain the benzene ring-containing random copolymer. The benzene ring-containing random copolymer has the structure shown in Formula 1: Formula 1 The ratio of x, y, z is (10~40): (1~4): (10~20).

[0007] In the above technical solution, the mass ratio of carbon nanotubes, benzene ring random copolymers, and dispersion medium in the hybrid modified mixture of carbon nanotubes and benzene ring random copolymers is (1~10):(10~50):10000. In the above technical solution, the temperature of the carbon fiber modification reaction is 200~250℃ and the time is 10~20 minutes.

[0008] In the above technical solution, the RAFT polymerization reaction is carried out at a temperature of 60~90℃ and for a time of 20~28 hours during the preparation of the benzene ring-containing random copolymer.

[0009] In the above technical solution, the molar ratio of each raw material for preparing the benzene ring random copolymer is: the molar ratio of styrene, 4-vinylbenzocyclobutene and methyl methacrylate is (20~50):(1~4):(10~20). This invention also provides a method for preparing an epoxy resin thermally conductive composite material, comprising the following steps: (1) The modified carbon fiber prepared in the above method is immersed in the first organic solvent solution of the modified epoxy resin prepolymer. After the first organic solvent evaporates, the modified carbon fiber prepreg is obtained. (2) The modified carbon fiber prepreg is cured at 150°C to obtain the epoxy resin thermally conductive composite material; The method for preparing the modified epoxy resin prepolymer is as follows: after heating the bisphenol A type epoxy resin monomer to 130~160℃, liquid crystal epoxy resin monomer and curing agent are added, mixed evenly, and then cooled to room temperature to obtain the modified epoxy resin prepolymer. The liquid crystal epoxy resin monomer has the structure shown in Formula 2: Formula 2.

[0010] In the above technical solution, in step (1), the weight parts of each raw material are: 50-70 parts of modified carbon fiber, 30-50 parts of modified epoxy resin prepolymer, and 30-50 parts of the first organic solvent.

[0011] In the above technical solution, in step (2), the molar amounts of each raw material used to prepare the modified epoxy resin prepolymer are: 20-30 parts of curing agent, 70-95 parts of bisphenol A type epoxy resin monomer, and 5-30 parts of liquid crystal epoxy resin monomer. The curing agent may be m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, or 4,4'-diaminodiphenyl sulfone.

[0012] In the above technical solution, the liquid crystal epoxy resin monomer comprises the following parts by weight of raw materials obtained through a substitution reaction: 9-11 parts of 4,4'-dihydroxybiphenyl, 40-50 parts of epichlorohydrin, 9-10 parts of deionized water, 20-30 parts of a second organic solvent, and 8-12 parts of sodium hydroxide deionized water solution.

[0013] 4,4'-dihydroxybiphenyl, deionized water, a second organic solvent, and epichlorohydrin were uniformly mixed at 80-100°C and subjected to a substitution reaction for 20-40 minutes. Then, sodium hydroxide deionized water solution was added dropwise over 30-90 minutes, and the substitution reaction was continued for another 30-90 minutes. The mixture was cooled to room temperature to obtain a precipitated solid, which was washed with deionized water and reacted at 50-80°C for 12-24 hours to obtain a liquid crystal epoxy resin monomer.

[0014] In the above technical solution, the first organic solvent is dichloromethane, acetone, or tetrahydrofuran, and the second organic solvent is dichloromethane, acetone, or tetrahydrofuran.

[0015] Compared with the prior art, the present invention can achieve the following beneficial effects: The modified carbon fiber provided by this invention is composed of a benzene ring-containing random copolymer and carbon nanotubes. Through ring-opening thermal crosslinking of the styrene-cyclobutene structure in the benzene ring-containing random copolymer, a crosslinked network is formed. Furthermore, the π-π interaction between the benzene ring and the carbon fiber fixes the thermally conductive carbon nanotubes to the carbon fiber surface. The oxygen-containing functional groups of the benzene ring-containing random copolymer and the nano-reinforcing effect of the carbon nanotubes improve the surface activity of the carbon fiber and the mechanical interlocking between the fiber and the epoxy resin, enhance the bonding between the carbon fiber and the epoxy resin, and construct thermally conductive pathways between the fibers. This reduces heat scattering and stress concentration at the interface, endowing the modified carbon fiber / epoxy resin composite material with excellent thermal conductivity and mechanical properties.

[0016] This invention also provides an epoxy resin thermally conductive composite material, in which a liquid crystal structure is introduced into the epoxy resin, giving it a more regular structure and improving the heat transfer efficiency within the epoxy resin. Furthermore, the use of modified carbon fibers ensures good bonding between the carbon fibers and the resin, and the construction of thermally conductive pathways between the carbon fibers through carbon nanotubes reduces phonon scattering at the interface and stress concentration at the interface during heat transfer, thus endowing the modified carbon fiber / epoxy resin thermally conductive composite material with excellent thermal conductivity and mechanical properties. The results of the embodiments show that the modified carbon fiber / epoxy resin thermally conductive composite material provided by this invention possesses both excellent thermal conductivity (in-plane thermal conductivity up to 10.07 W / (m·K), inter-plane thermal conductivity up to 0.58 W / (m·K)) and mechanical properties (interlaminar shear strength up to 31.4 MPa, flexural strength up to 369.1 MPa, and tensile strength up to 618.5 MPa). Attached Figure Description

[0017] Figure 1 Fourier transform infrared spectrum of random copolymer containing benzene rings; Figure 2 Fourier transform infrared spectra of liquid crystal epoxy resin monomers; Figure 3 Scanning electron microscope (SEM) images of carbon fibers and modified carbon fibers in Comparative Examples 1-2 and Examples 1-2; Figure 4 The interlaminar shear strength and flexural strength test results are for Comparative Examples 1-2 and Examples 1-2; Figure 5 These are scanning electron microscope (SEM) images of interlayer shear sections from Comparative Examples 1-2 and Examples 1-2; Figure 6 The tensile strength test results are for Comparative Examples 1-2 and Examples 1-2; Figure 7 The thermal conductivity test results are for Comparative Examples 1-2 and Examples 1-2. Detailed Implementation

[0018] This invention provides a method for preparing modified carbon fiber, comprising the following steps: Carbon fibers are immersed in a hybrid modified solution of carbon nanotubes and a random copolymer containing benzene rings to carry out a modification reaction, thereby obtaining the modified carbon fibers. In this invention, the preferred type of carbon fiber is Toray T-300, and the preferred type of filament bundle is 3000.

[0019] In this invention, the preferred mass ratio of carbon nanotubes, benzene ring random copolymers, and dispersion media is (1~10):(10~50):10000, and more preferably (1~4):(10~15):10000.

[0020] In this invention, the weight ratio of carbon fiber to hybrid modified mixture is 1:(1~10), and more preferably 1:(2~5).

[0021] In this invention, the temperature of the modification reaction is 200~250℃ and the time is 10~20 minutes.

[0022] The preparation method of the benzene ring-containing random copolymer is as follows: styrene, 4-vinylbenzocyclobutene, methyl methacrylate, reversible addition-fragmentation chain transfer polymerization (RAFT) reagent, initiator and reaction solvent are mixed and RAFT polymerization reaction is carried out under a protective atmosphere to obtain the benzene ring-containing random copolymer. The benzene ring-containing random copolymer has the structure shown in Formula 1: Formula 1 The ratio of x, y, z is (10~40):(1~4):(10~20), preferably (15~35):(1~2):(12~18). In this invention, the number-average molecular weight of the benzene-containing random copolymer is preferably 0.8 to 30,000, more preferably 0.9 to 15,000; the dispersion coefficient of the benzene-containing random copolymer is preferably 1.02 to 1.5, more preferably 1.05 to 1.25.

[0023] Unless otherwise specified, all raw materials used in this invention are commercially available products.

[0024] In this invention, the molar ratio of styrene, 4-vinylbenzocyclobutene and methyl methacrylate is (20~50):(1~4):(10~20), preferably (25~45):(1~2):(10~18).

[0025] In this invention, the RAFT reagent is preferably 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valerate; the molar ratio of styrene to RAFT reagent is preferably (30~50):(0.1~0.5), more preferably (25~45):(0.1~0.3).

[0026] In this invention, the initiator is preferably azobisisobutyronitrile, and the molar ratio of the initiator to the RAFT reagent is preferably 1:(3~10), more preferably 1:(4.5~5.5).

[0027] In this invention, the temperature of the RAFT polymerization reaction is 60~90℃, more preferably 90℃, and the reaction time is preferably 20~28 hours, more preferably 24 hours. In this invention, the RAFT polymerization reaction is preferably carried out under oil bath conditions.

[0028] After the RAFT polymerization reaction is completed, the present invention preferably further includes precipitating and drying the obtained RAFT polymerization reaction system with n-hexane to obtain a random copolymer containing benzene rings.

[0029] In this invention, the number of times the n-hexane is precipitated is preferably 4 to 8 times, more preferably 5 times; each time n-hexane is precipitated, the volume ratio of n-hexane to the RAFT polymerization reaction system is preferably (3 to 10):1, more preferably (4 to 6):1. This invention does not have specific limitations on the drying conditions, as long as a product of constant weight is obtained. In the embodiments of this invention, the drying temperature is preferably 40 to 80°C, more preferably 60°C, and the drying time is preferably 10 to 14 hours, more preferably 12 hours. This invention also provides a method for preparing an epoxy resin thermally conductive composite material, comprising the following steps: (1) The modified carbon fiber prepared in the above method is immersed in the first organic solvent solution of the modified epoxy resin prepolymer. After the first organic solvent evaporates, the modified carbon fiber prepreg is obtained. (2) The modified carbon fiber prepreg is cured at 150°C to obtain the epoxy resin thermally conductive composite material; In this invention, the preferred immersion time of the modified carbon fiber in the modified epoxy resin prepolymer is 5 to 10 minutes.

[0030] After the modified carbon fiber is impregnated into the modified epoxy resin prepolymer, the resulting material is allowed to air dry naturally.

[0031] In this invention, the curing process is preferably carried out on a vulcanizing machine, and the curing pressure is preferably 5-12 MPa, more preferably 9-11 MPa. After the curing process, the resulting cured material is allowed to cool naturally to room temperature.

[0032] The method for preparing the modified epoxy resin prepolymer is as follows: after heating the bisphenol A type epoxy resin monomer to 130~160℃, liquid crystal epoxy resin monomer and curing agent are added, mixed evenly, and then cooled to room temperature to obtain the modified epoxy resin prepolymer. The liquid crystal epoxy resin monomer has the structure shown in Formula 2: Formula 2.

[0033] In step (1), the weight parts of each raw material are as follows: the modified carbon fiber is preferably 50-70 parts, more preferably 55-65 parts; the modified epoxy resin prepolymer is preferably 30-50 parts, more preferably 35-45 parts; and the first organic solvent is 30-50 parts, more preferably 35-45 parts.

[0034] In this invention, in step (2), the molar amounts of each raw material used to prepare the modified epoxy resin prepolymer are as follows: the curing agent is preferably 20-30 parts, more preferably 20-25 parts, the bisphenol A type epoxy resin monomer is 70-95 parts, more preferably 70-80 parts, and the liquid crystal epoxy resin monomer is preferably 5-30 parts, more preferably 20-30 parts.

[0035] The curing agent may be m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, or 4,4'-diaminodiphenyl sulfone.

[0036] In this invention, the crystalline epoxy resin monomer comprises the following parts by weight of raw materials obtained through a substitution reaction: The preferred components of 4,4'-dihydroxybiphenyl are 9 to 11 parts, more preferably 10 parts; the preferred components of epichlorohydrin are 40 to 50 parts, more preferably 44 to 48 parts; the preferred components of deionized water are 9 to 10 parts; the preferred components of the second organic solvent are 20 to 30 parts, more preferably 25 to 28 parts; and the preferred components of sodium hydroxide deionized aqueous solution are 8 to 12 parts, more preferably 9 to 10 parts.

[0037] The first substitution reaction was carried out by uniformly mixing 4,4'-dihydroxybiphenyl, deionized water, a second organic solvent and epichlorohydrin. Then, sodium hydroxide deionized water solution was added dropwise to continue the substitution reaction. The mixture was cooled to room temperature to obtain a precipitated solid, which was washed with deionized water and dried to obtain a liquid crystal epoxy resin monomer.

[0038] In this invention, the preferred temperature for the first substitution reaction is 80-100°C, more preferably 90°C. The preferred time is 20-40 minutes, more preferably 25-35 minutes; the preferred time for adding sodium hydroxide is 30-90 minutes, more preferably 45-60 minutes; the preferred time for the second substitution reaction is 30-90 minutes, more preferably 50-70 minutes; the preferred drying temperature is 50-80°C, more preferably 60°C, and the preferred time is 12-24 hours, more preferably 18-22 hours. In this invention, the sodium hydroxide deionized aqueous solution contains 10 to 20 parts by weight of sodium hydroxide in the solution.

[0039] In this invention, the first organic solvent is preferably dichloromethane, acetone, or tetrahydrofuran, more preferably acetone. The second organic solvent is preferably dichloromethane, acetone, or tetrahydrofuran, more preferably dichloromethane.

[0040] The present invention will be further described in detail below with reference to specific embodiments, but the scope of protection of the present invention is not limited to the following embodiments. All raw materials used in the embodiments are commercially available analytical grade products, or synthesized according to methods known in the art.

[0041] Example 1 This embodiment provides a modified carbon fiber and a method for preparing epoxy resin thermally conductive composite materials using the modified carbon fiber, including: 26.1 mmol of styrene, 11.3 mmol of methacrylate, 1.4 mmol of 4-vinylbenzocyclobutene, 0.15 mmol of 4-cyano-4-[(dodecylthioalkylthiocarbonyl)thioalkyl]valeric acid, and 0.03 mmol of azobisisobutyronitrile were added to a round-bottom flask, stirred thoroughly, and reacted at 90 °C for 24 hours under a nitrogen atmosphere. The reaction mixture was precipitated five times with n-hexane to obtain a benzene-containing random copolymer. The number-average molecular weight of the obtained benzene-containing random copolymer was 10,500, and the dispersive index was 1.17, as measured by gel permeation chromatography (GPC).

[0042] A dichloromethane hybrid modification solution containing 0.1 wt% benzene ring random copolymer and 0.02 wt% carbon nanotubes was prepared. 100 parts by weight of carbon fiber were immersed in 200 parts by weight of the modification solution. After the dichloromethane evaporated, the mixture was placed in a tube furnace and heated for crosslinking at 250°C under nitrogen for 10 minutes to obtain modified carbon fiber, denoted as CF@(CNT / P)-1.

[0043] 4,4'-Dihydroxybiphenyl (10 g, 54 mmol), deionized water (9.5 mL), isopropanol (33 mL), and epichlorohydrin (42.5 mL, 64.2 mmol) were added to a three-necked flask equipped with a stir bar, and then refluxed in an oil bath at 90 °C for 30 minutes. After the system became clear and transparent, 9.5 mL of 15 wt% NaOH aqueous solution was added dropwise over 1 hour, and the reaction was continued for another hour. This process was repeated once more. After the reaction was complete, the mixture was cooled to room temperature. The precipitated solid was filtered and washed successively with deionized water. After drying in an oven at 60 °C for 20 hours, a white liquid crystal epoxy monomer was obtained.

[0044] A certain amount of bisphenol A epoxy resin monomer was preheated and stirred at 150℃ until it became clear and transparent. Then, an appropriate amount of liquid crystal epoxy monomer was added, dissolved, and stirred evenly to obtain a bisphenol A epoxy resin monomer / liquid crystal epoxy monomer mixture (mol:mol=9:1). Next, an appropriate amount of curing agent 4,4'-diaminodiphenylmethane was added to the above mixture (the ratio of the sum of the molar fractions of amino active hydrogens to the molar fraction of epoxy groups was 1:1) to prepolymerize to a gel state. After cooling to room temperature, acetone (vol:vol = 1:1) was added in proportion to prepare a prepreg. An appropriate amount of CF@(CNT / P)-1 was impregnated into the above prepreg to obtain CF@(CNT / P)-1 / epoxy resin prepreg (resin content 40 wt%). The prepreg was then laid up and cured at 150℃ for 6 hours under 10 MPa pressure. After cooling and demolding, an epoxy resin thermally conductive composite material was obtained, denoted as CF@(CNT / P)-1 / epoxy resin thermally conductive composite material.

[0045] Example 2 The difference between Example 2 and Example 1 is that the mass fraction of carbon nanotubes in the hybrid modified mixture is 0.03 wt%.

[0046] The modified carbon fiber prepared in Example 2 is denoted as CF@(CNT / P)-2; the prepared epoxy resin thermally conductive composite material is denoted as CF@(CNT / P)-2 / epoxy resin thermally conductive composite material.

[0047] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that the step of modifying the carbon fiber with a hybrid modification mixture is omitted, and the epoxy resin thermally conductive composite material is prepared according to the method of Example 1.

[0048] Carbon fiber is denoted as CF, and carbon fiber / epoxy resin thermally conductive composite material is denoted as CF / epoxy resin thermally conductive composite material.

[0049] Comparative Example 2 The difference between Comparative Example 2 and Example 1 is that the carbon nanotubes in the hybrid modification mixture are omitted, and the carbon fibers are directly modified with a solution of random copolymer containing benzene rings with a mass fraction of 0.1 wt%, and the epoxy resin thermally conductive composite material is prepared according to the method of Example 1.

[0050] The modified carbon fiber is denoted as CF@P, and the epoxy resin thermally conductive composite material is denoted as CF@P / epoxy resin thermally conductive composite material.

[0051] To verify the structure of the benzene-ring-containing random copolymers in Examples 1-2 and Comparative Example 2 of this application, Fourier transform infrared spectroscopy characterization was performed on the benzene-ring-containing random copolymers in the examples and Comparative Example 2. The results are as follows: Figure 1 As shown. It can be seen that 2930 / 2850 cm-1 and 1760 cm -1 The characteristic absorption peaks appearing at 1450–1600 cm⁻¹ correspond to the -CH₂- groups on the main chain and the ester groups on the side chains of the random copolymer containing benzene rings. -1 A skeletal vibration peak of the benzene ring was observed. These results indicate that the random copolymer containing the benzene ring has been successfully synthesized.

[0052] To verify the structure of the liquid crystal epoxy resin monomer in the epoxy resin thermally conductive composite materials of Examples 1-2 and Comparative Examples 1-2 of this application, Fourier transform infrared spectroscopy characterization was performed on the structure of the liquid crystal epoxy resin monomer in the examples and comparative examples. The results are as follows: Figure 2 As shown in the figure. It can be seen that the liquid crystal epoxy resin monomer is in the range of 2800~3000 cm⁻¹ -1 A stretching vibration peak of the methylene group appears; at 1500–1600 cm⁻¹. -1 A stretching vibration peak attributable to the benzene ring appears; in the range of 1030–1150 cm⁻¹. -1 Characteristic peaks attributable to ether bonds appear; at 910 cm⁻¹ -1 The presence of characteristic peaks belonging to epoxy groups nearby indicates that the liquid crystal epoxy resin monomer was successfully synthesized.

[0053] To verify the structure of the fibers in Comparative Examples 1-2 and Examples 1-2 of this application, the morphology of CF, CF@P, CF@(CNT / P)-1, and CF@(CNT / P)-2 was characterized using scanning electron microscopy. The results are as follows: Figure 3 As shown, the CF surface has a grooved structure with a diameter of approximately 6.65 μm. After modification with a benzene-containing random copolymer, the diameter of CF@P reaches 6.71 μm, and the grooved structure is uniformly covered by the benzene-containing random copolymer. Furthermore, in Examples 1-2, the carbon nanotube structure is uniformly distributed on the surfaces of CF@(CNT / P)-1 and CF@(CNT / P)-2, indicating that the modified carbon fiber was successfully obtained by using a hybrid modification mixture of benzene-containing random copolymer and carbon nanotubes.

[0054] The flexural strength and interlaminar shear strength of Comparative Examples 1-2 and Examples 1-2 provided in this application were tested using a CMT-7204 high-performance mechanical testing machine from Shenzhen Xin Sansi Co., Ltd., and the tensile strength of Comparative Examples 1-2 and Examples 1-2 provided in this application were tested using a CMT-5105 high-performance mechanical testing machine from Shenzhen Xin Sansi Co., Ltd., as shown in the results. Figure 4 and Figure 5 As shown. Furthermore, the interlaminar shear fracture surfaces of Comparative Examples 1-2 and Examples 1-2 were characterized by scanning electron microscopy, and their fracture mechanisms were analyzed. The results are as follows. Figure 5Examples 1-2 exhibited higher interlaminar shear strengths, at 30.1 MPa and 31.4 MPa respectively, significantly higher than Comparative Example 1 (23.7 MPa) and Comparative Example 2 (27.3 MPa). This is because the performance of ILSS primarily depends on the bonding between the reinforcing fiber and the epoxy resin. Carbon fibers have a grooved structure, are highly inert, and have low surface energy, making them difficult to wet with epoxy resin. This results in micro-voids between the fiber and resin, preventing effective stress transfer. During stress application, these voids become stress concentration points, leading to fiber-resin debonding and interlaminar slip failure, leaving almost no resin residue on the fiber surface. After the CF@P interlaminar shear test, the amount of epoxy resin adhering to the fiber surface increased, indicating that the introduction of the benzene ring-containing random copolymer enhances the π-π interactions and hydrogen bonding at the fiber-epoxy resin interface by introducing benzene rings and ester groups. This facilitates stress transfer between the fiber and epoxy resin. In the cross-sections of Examples 1-2, the resin completely covers the fibers, indicating good bonding between the fibers and resin. During fracture, the resin structure is the primary fracture component. This demonstrates that Examples 1-2 further enhance stress transfer at the interface through mechanical interlocking, resulting in the highest interlaminar shear strength. Furthermore, due to the improved interfacial bonding, Examples 1-2 also exhibit significantly increased flexural and tensile strengths, reaching 352.8 MPa and 610.3 MPa, and 369.1 MPa and 618.5 MPa, respectively, higher than Comparative Example 1 (252.5 MPa, 582.6 MPa) and Comparative Example 2 (327.1 MPa, 592.4 MPa). This also demonstrates that surface modification of carbon fibers does not compromise their excellent tensile properties.

[0055] The thermal conductivity of Comparative Examples 1-2 and Examples 1-2 provided in this application was tested using a Hot Disk TPS2200 thermal conductivity tester. The results are as follows: Figure 6 The in-plane thermal conductivity of the carbon fibers was 7.16 W / (m·K), 7.88 W / (m·K), 9.46 W / (m·K), and 10.07 W / (m·K), respectively. The inter-plane thermal conductivity was 0.31 W / (m·K), 0.40 W / (m·K), 0.54 W / (m·K), and 0.58 W / (m·K), respectively. This is attributed to the improved interfacial bonding between the carbon fibers and epoxy resin, as well as the increased thermal conductivity pathways created by the carbon nanotubes.

Claims

1. A method for preparing modified carbon fiber, characterized in that, Includes the following steps: Carbon fibers are immersed in a hybrid modified solution of carbon nanotubes and a random copolymer containing benzene rings to carry out a modification reaction, thereby obtaining the modified carbon fibers. The preparation method of the benzene ring-containing random copolymer is as follows: styrene, 4-vinylbenzocyclobutene, methyl methacrylate, reversible addition-fragmentation chain transfer polymerization (RAFT) reagent, initiator and reaction solvent are mixed and RAFT polymerization reaction is carried out under a protective atmosphere to obtain the benzene ring-containing random copolymer; The benzene ring-containing random copolymer has the structure shown in Formula 1: Formula 1 The ratio of x, y, z is (10~40): (1~4): (10~20).

2. The method for preparing modified carbon fiber according to claim 1, characterized in that, In the hybrid modified mixture of carbon nanotubes and benzene ring random copolymer, the mass ratio of carbon nanotubes, benzene ring random copolymer, and dispersion medium is (1~10):(10~50):10000.

3. The method for preparing modified carbon fiber according to claim 1, characterized in that, The carbon fiber modification reaction is carried out at a temperature of 200~250℃ for 10~20 minutes.

4. The method for preparing modified carbon fiber according to claim 1, characterized in that, In the preparation of the benzene ring-containing random copolymer, the RAFT polymerization reaction is carried out at a temperature of 60~90℃ for 20~28 hours.

5. The method for preparing modified carbon fiber according to claim 1, characterized in that, The molar ratio of each raw material used to prepare the benzene ring random copolymer is as follows: the molar ratio of styrene, 4-vinylbenzocyclobutene and methyl methacrylate is (20~50):(1~4):(10~20).

6. A method for preparing an epoxy resin thermally conductive composite material, characterized in that, Includes the following steps: (1) The modified carbon fiber of any one of claims 1 to 5 is immersed in a first organic solvent solution of the modified epoxy resin prepolymer, and after the first organic solvent evaporates, the modified carbon fiber prepreg is obtained. (2) The modified carbon fiber prepreg is cured at 150°C to obtain the epoxy resin thermally conductive composite material; The method for preparing the modified epoxy resin prepolymer is as follows: after heating the bisphenol A type epoxy resin monomer to 130~160℃, liquid crystal epoxy resin monomer and curing agent are added, mixed evenly, and then cooled to room temperature to obtain the modified epoxy resin prepolymer. The liquid crystal epoxy resin monomer has the structure shown in Formula 2: Equation 2.

7. The method for preparing an epoxy resin thermally conductive composite material according to claim 6, characterized in that, In step (1), the weight parts of each raw material are: 50-70 parts of modified carbon fiber, 30-50 parts of modified epoxy resin prepolymer, and 30-50 parts of the first organic solvent.

8. The method for preparing an epoxy resin thermally conductive composite material according to claim 6, characterized in that, In step (2), the molar amounts of each raw material used to prepare the modified epoxy resin prepolymer are: 20-30 parts of curing agent, 70-95 parts of bisphenol A type epoxy resin monomer, and 5-30 parts of liquid crystal epoxy resin monomer. The curing agent may be m-phenylenediamine, p-phenylenediamine, 4,4'-diaminodiphenylmethane, or 4,4'-diaminodiphenyl sulfone.

9. The method for preparing an epoxy resin thermally conductive composite material according to claim 8, characterized in that, The liquid crystal epoxy resin monomer is obtained by a substitution reaction from the following raw materials in parts by weight: 9-11 parts of 4,4'-dihydroxybiphenyl, 40-50 parts of epichlorohydrin, 9-10 parts of deionized water, 20-30 parts of a second organic solvent, and 8-12 parts of sodium hydroxide deionized water solution. 4,4'-dihydroxybiphenyl, deionized water, a second organic solvent, and epichlorohydrin were heated at 80-100 °C. ℃ After uniform mixing, a substitution reaction is carried out for 20-40 minutes. Then, sodium hydroxide deionized water solution is added dropwise over 30-90 minutes, and the substitution reaction continues for another 30-90 minutes. The mixture is cooled to room temperature to obtain a precipitated solid, which is washed with deionized water and reacted at 50-80°C for 12-24 hours to obtain a liquid crystal epoxy resin monomer.

10. The method for preparing an epoxy resin thermally conductive composite material according to claim 9, characterized in that, The first organic solvent is dichloromethane, acetone, or tetrahydrofuran, and the second organic solvent is dichloromethane, acetone, or tetrahydrofuran.

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