A method for covalently bonding graphene to the surface of carbon fibers and its application

Abstract

This invention discloses a method and its application for covalently linking graphene to the surface of carbon fibers, belonging to the field of carbon fiber modification technology. This invention addresses the problems of traditional carbon fiber modification methods, which often involve high equipment requirements, high energy consumption, long cycles, or easy oxidation of the carbon fiber surface during modification, leading to a significant decrease in its mechanical properties, or are unsuitable for large-scale production. This invention involves taking carbon fibers or carbon fibers coated with organic matter, mixing them with a carbon source and a reducing agent until homogeneous, performing a combustion synthesis reaction, and then purifying by acid washing. This invention has broad application prospects in the production of resin-based composite materials, metal-based composite materials, ceramic-based composite materials, and carbon-based composite materials.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber modification technology, specifically, it relates to a method and application of covalently linking graphene to the surface of carbon fibers. Background Technology

[0002] Carbon fiber is an ideal reinforcing phase in composite materials, possessing characteristics such as lightweight, high strength, high modulus, and high electrical conductivity. It is widely used in resin-based, cement-based, metal-based, and carbon-based composites. However, the graphite layer on the surface of carbon fiber exhibits chemical inertness, resulting in poor bonding with the composite matrix and hindering its reinforcing effect. Surface modification technology is widely used for carbon fibers; surface activation can enhance the bonding between carbon fibers and the matrix, thereby improving the overall performance of the material.

[0003] Existing methods for modifying carbon fiber surfaces mainly include oxidation, plasma treatment, electrophoretic deposition, and grafting.

[0004] Oxidation methods involve treating carbon fibers with gases (such as air, oxygen, or ozone) or liquids (such as acids, alkalis, hydrogen peroxide, or potassium permanganate solution), and adjusting the degree of oxidation by controlling parameters such as temperature, time, and concentration. Huang et al. (Applied Surface Science, 2019, 497, 143765) achieved surface modification of carbon fibers through ethanol plasma polymerization, obtaining enhanced mechanical properties of carbon fiber-reinforced lightweight oil well cement. Compared with the untreated material, the flexural strength and tensile strength increased by 27.25% and 70.56%, respectively.

[0005] Plasma-modified carbon fiber surfaces utilize the physical and chemical interactions between active particles in plasma and the carbon fiber surface to increase surface roughness and functional groups, thereby improving the adhesion between carbon fiber and the resin matrix and the overall mechanical properties of the composite material. Baghery et al. (Composites Science and Technology, 2016, 128, 215-221) optimized plasma treatment parameters using response surface methodology (RSM) and Box Behnken design, achieving improved performance of carbon fiber / epoxy composites and obtaining higher interlaminar shear strength (ILSS), approximately 32.6% higher than the untreated carbon fiber composite. Electrophoretic deposition is a method that deposits charged particles onto the carbon fiber surface under an electric field. It is characterized by its simplicity, low cost, uniform coating, and high controllability, and is used to improve the bonding between carbon fiber and the matrix material, thereby enhancing the mechanical properties and interfacial adhesion of the composite material. Lu et al. (Cement and Concrete Composites, 2018, 8, 220-238) improved the surface properties of carbon fibers (CF) by depositing graphene oxide (GO) onto the CF surface via electrophoretic deposition (EPD), including increased surface roughness, wettability, and chemical activity, resulting in enhanced mechanical properties. Compared to untreated CF-reinforced cementitious materials, the flexural strength of GO / CF composite fiber-reinforced cementitious composites increased by 14.58%, and this property could be further improved by 10.53% when the GO / CF composite fibers were pre-dispersed in a GO solution and mixed with cement powder.

[0006] Grafting is a method of surface modification of carbon fibers by introducing functional molecules or nanostructures, such as carbon nanotubes, graphene oxides, or nano-silica, onto the surface through covalent bonding. This method not only enhances the surface roughness and chemical activity of carbon fibers and improves their physical and chemical bonding with the matrix material, but also significantly improves the mechanical strength and durability of composite materials by improving dispersibility and interfacial adhesion. Cui et al. (Construction and Building Materials, 2018, 181, 713-720) prepared CF-CNTs composite cementitious materials by grafting carbon nanotubes (CNTs) onto the surface of carbon fiber (CF) using (3-Aminopropyl)triethoxysilane (KH550) as a chemical bridging agent, achieving a flexural strength increase of more than 40% compared to pure cement slurry.

[0007] The aforementioned methods for modifying carbon fibers either require sophisticated equipment, consume large amounts of energy, and have long production cycles, or the carbon fiber surface is prone to oxidation during the modification process, leading to a significant decrease in its mechanical properties, or they are not suitable for large-scale production. Therefore, there is a need to develop simple, efficient, low-energy-consumption, and high-performance methods for modifying carbon fiber surfaces. Summary of the Invention

[0008] This invention addresses the technical problems of carbon fiber modification methods that either require high-end equipment, consume large amounts of energy, have long cycles, or are prone to oxidation of the carbon fiber surface during the modification process, resulting in a significant decrease in its mechanical properties, or are unsuitable for large-scale production. Instead, it provides a carbon fiber surface modification method with uniform surface morphology, good graphene grafting morphology, and applicability to carbon-based composite materials.

[0009] To address the aforementioned technical problems, the present invention adopts the following technical solution:

[0010] The purpose of this invention is to provide a method for covalently bonding graphene to the surface of carbon fibers, comprising the following steps:

[0011] Take carbon fiber or organic material coated on its surface. carbon fiber, Mix with carbon source and reducing agent until homogeneous, and then undergo combustion synthesis reaction, i.e., covalently attach graphene to the surface of carbon fiber;

[0012] In this process, a carbon source is added at a mass ratio of 1:(0.2-200) for carbon fiber and graphene to be generated by the combustion synthesis reaction, and a reducing agent is added at a mass ratio of 1:(1.5-3) for the organic matter coating the carbon fiber surface and the total oxygen atoms in the carbon source and the reducing agent.

[0013] Based on the above technical solution, the product of the combustion synthesis reaction of the present invention is acid washed and dried to obtain carbon fibers with graphene covalently connected on the surface.

[0014] Further specifying, the combustion synthesis reaction is either a high-pressure combustion synthesis reaction or an atmospheric-pressure combustion synthesis reaction.

[0015] To further specify, the high-pressure combustion synthesis reaction can be carried out according to the following steps:

[0016] Step a: Place the mixed powder in a general-purpose combustion synthesis reaction device with a pressure resistance of 1MPa to 30MPa, and then add an igniter above the mixed powder; wherein, the igniter is Fe3O4+Mg or MnO2+Mg or CaCO3+Mg of the magnesian reaction or Fe3O4+Al or Cr2O3+Al of the aluminothermic reaction.

[0017] Step b: Evacuate the inside of the combustion synthesis reaction apparatus, then introduce carbon dioxide, nitrogen or argon gas at 0.1 MPa into the combustion synthesis reaction apparatus, and then seal the reaction apparatus.

[0018] Step c: Ignite the igniter in step a using localized electric ignition or localized high-frequency induction heating to cause the mixed powder to undergo a combustion reaction; wherein, localized electric ignition is achieved by passing a 10A to 30A DC current through a spiral tungsten wire coil to heat the localized reactants and initiate a combustion synthesis reaction; localized high-frequency induction heating is achieved by using a high-frequency induction coil to heat the localized reactants and initiate a combustion synthesis reaction.

[0019] To further specify, the atmospheric pressure combustion synthesis reaction can be carried out according to the following steps:

[0020] Step a: Place the mixed powder in a crucible and add an ignition agent above the mixed powder; wherein the ignition agent is Fe3O4+Mg or MnO2+Mg or CaCO3+Mg from the magnesian reaction or Fe3O4+Al or Cr2O3+Al from the aluminothermic reaction.

[0021] Step b: Then place the crucible at the bottom of the top-opening container; wherein the volume of the top-opening container is 5 to 500 times the volume of the crucible, and the height of the container is 2 to 50 times the height of the crucible.

[0022] Step c: Introduce carbon dioxide, nitrogen, or argon into the bottom of the upper open container to fill the crucible and the interior of the upper open container with gas.

[0023] Step d: Ignite the igniter using local electric ignition or local high-frequency induction heating to induce a combustion reaction in the mixed powder. During the reaction, carbon dioxide (or nitrogen or argon) is continuously introduced at a rate of 1–1000 L / min. Local electric ignition involves passing a 10A–30A DC current through a spiral tungsten wire coil to heat the local reactants and initiate a combustion synthesis reaction. Local high-frequency induction heating uses a high-frequency induction coil to heat the local reactants and initiate a combustion synthesis reaction.

[0024] Further specifying, carbon fiber can be one or a mixture of several of the following in any proportion: chopped carbon fiber, long carbon fiber, carbon fiber cloth, carbon fiber prepreg, and carbon fiber reinforced polymer composite material.

[0025] Further specifying, the carbon fiber can be one or a mixture of several of PAN-based carbon fiber, pitch-based carbon fiber, and biomass carbon fiber in any proportion.

[0026] Furthermore, the diameter of the carbon fiber is 0.05μm-50μm, and the length is 0.05mm-2000mm.

[0027] Further specified, the organic resin is epoxy resin, phenolic resin, thermoplastic plastic, or polycarbonate; the mass ratio of organic resin to carbon fiber is (0.001-0.67):1, and the carbon fiber surface is coated by sizing or pre-impregnation.

[0028] Further specifying, the organic sizing agent or prepreg coating the carbon fiber surface can be bisphenol A diglycidyl ether epoxy resin and its derivatives.

[0029] Furthermore, the carbon source can be one or a mixture of several of the following in any proportion: carbon dioxide, carbonate, oxalate, and organic glycogen.

[0030] Furthermore, the reducing agent can react with the reducing atmosphere, carbon source, sizing agent or prepreg on the carbon fiber surface in the system; for example, magnesium or aluminum.

[0031] Further specifying, the combustion atmosphere can be vacuum, nitrogen, argon, a mixture of hydrogen and argon, or CO2.

[0032] Further specifying, the mixture is made using one or more of the following methods: ball milling, homogenous dispersion, mechanical stirring, ultrasonic stirring, and mechanical grinding.

[0033] Carbon fibers with surface covalently linked graphene prepared by any of the above methods can be used to prepare carbon-based, resin-based, metal-based, and ceramic-based composite materials.

[0034] Further specified, the characteristic is that the metal base is one of copper, aluminum, and magnesium.

[0035] This invention introduces carbon fiber into a combustion synthesis reaction, allowing wrinkled graphene to grow on the carbon fiber surface, resulting in carbon fiber with covalently linked graphene surface modification. The combustion synthesis process, with its ultra-high temperature reaction, reducing atmosphere, and ultra-rapid heating and cooling non-equilibrium process, generates a large number of highly reactive carbon atoms. These carbon atoms nucleate and grow on the carbon fiber surface, covalently linking and growing wrinkled graphene.

[0036] Compared with the prior art, the present invention has the following beneficial effects:

[0037] This invention provides a simple and rapid method for the mass production of carbon fibers with covalently linked graphene surface modification. Compared with existing carbon fiber modification methods, the carbon fiber modification method proposed in this patent is simple and highly operable.

[0038] The graphene-modified carbon fiber of this invention, due to the three-dimensional wrinkles of graphene and the high covalent bonding strength between graphene and carbon fiber structure, is very beneficial for providing various carbon fiber composite materials with mechanical, thermal and electrical properties. It can be used to produce resin-based composite materials, metal-based composite materials, ceramic-based composite materials and carbon-based composite materials, etc., and has broad application prospects.

[0039] To further understand the features and technical content of this invention, please refer to the following detailed description and accompanying drawings. However, the accompanying drawings are for reference and illustration only and are not intended to limit the invention. Attached Figure Description

[0040] Figure 1 This diagram illustrates and shows the effects of a combustion synthesis method for preparing graphene-covalently linked carbon fibers. Figure 1 (a) Schematic diagram of the preparation method of graphene covalently linked carbon fibers by combustion synthesis. The process shown in the diagram is as follows: magnesium, calcium carbonate and carbon fibers are mixed and placed in a combustion synthesis reactor under vacuum. SHS (Self-propagating high-temperature synthesis) is the combustion synthesis method. Subsequently, the composite powder is locally heated and ignited by passing current through a resistance wire. The characteristic of combustion synthesis is self-propagating combustion. The temperature curves of the outer flame and the reactor body temperature-time curve are shown in the figure. After the reaction, the carbon fibers are washed with hydrochloric acid, filtered and dried to obtain graphene covalently linked carbon fibers and graphene powder. (b) Carbon fiber scraps containing 2.7% by mass of DGEBA epoxy resin sizing agent are subjected to combustion synthesis reaction to obtain graphene covalently linked carbon fibers. The top two figures are photographs of the actual product, and the bottom two figures are corresponding scans. (c) A carbon fiber prepreg containing 38.6% by mass of DGEBA epoxy resin was subjected to a combustion synthesis reaction to obtain graphene covalently linked carbon fibers; the top two images are photographs of the actual object, and the bottom two images are corresponding scanning electron microscope images; the scale bar is 5 micrometers; (d) A carbon fiber composite material containing 35.2% by mass of cured DGEBA epoxy resin was ground and then subjected to a combustion synthesis reaction to obtain graphene covalently linked carbon fibers; the top two images are photographs of the actual object, and the bottom two images are corresponding scanning electron microscope images; the scale bar is 10 micrometers.

[0041] Figure 2 The graphene covalently linked carbon fibers obtained by combustion synthesis of T800S type containing epoxy resin sizing agent in Example 1 were characterized by scanning electron microscopy, Raman surface scanning, and transmission electron microscopy. Figure 2 (a) Surface characterization of raw T800S carbon fiber. The left image is a scanning electron microscope image of raw T800S carbon fiber, scale bar 2 μm; the two images on the right are the I-shaped areas within the orange box shown in the left image. D / I Gand I 2D / I G Raman spectrum surface scan; I-wave pattern of the original carbon fiber surface Raman spectrum of T800S model. D / I G Generally between 0.3 and 0.6 and I 2D / I G The values ​​are generally less than 0.3, indicating that the surface of the carbon fiber is not graphene, but amorphous carbon and graphite microcrystals formed by pyrolysis; (b) Surface characterization of T800S model graphene covalently bonded carbon fiber, the left image is a scanning electron microscope image of T800S model graphene covalently bonded carbon fiber, scale bar 2 micrometers; the two images on the right are respectively the I in the orange box shown in the left image. D / I G and I 2D / I G Raman spectral surface scan; I-wavelength Raman spectrum of T800S model graphene covalently bonded carbon fiber surface. D / I G Generally less than 0.3 and I 2D / I G The thickness is generally between 0.6 and 1.3, indicating that high-quality, few-layer graphene has grown on the carbon fiber surface; (c) A cross-sectional sample of T800S type graphene covalently linked to carbon fiber was prepared using focused ion beam thinning (FIB) technology. The figure shows a transmission electron microscope (TEM) image of the FIB sample, scale bar 2 μm; (d) magnified TEM image of the area within the red box. The surface of the FIB sample can be divided into three parts: platinum organometallic adhesive, surface covalently linked graphene, and carbon fiber matrix, scale bar 200 nm; (e) TEM image of the interface between surface covalently linked graphene and carbon fiber matrix, scale bar 10 nm; (f) magnified TEM image of the area within the orange box. An approximately 8-layer few-layer graphene sheet is covalently linked to the graphite layer on the carbon fiber surface through surface grafting points, scale bar 5 nm.

[0042] Figure 3 The mechanism of surface covalently linked graphene carbon fibers obtained by combustion synthesis of T800S type containing epoxy resin sizing agent; Figure 3(a) A radial cross-sectional sample of T800S graphene covalently linked carbon fibers was prepared using focused ion beam thinning (FIB) technology. The image shows a transmission electron microscope (TEM) image of this FIB sample, scale bar 100 nm. (b) A magnified TEM image of the area within the red box, scale bar 20 nm. (c) A high-resolution TEM image of the area within the blue box. The image clearly shows the graphene sheet, carbon fiber, and magnesium oxide, with magnesium oxide embedded between the graphene sheet and the carbon fiber surface, indicating that magnesium oxide plays a role in the formation of the graphene sheet, scale bar 10 nm. (d) The EDS surface scan result of the area shown, scale bar 20 nm; a high-resolution TEM image of the interface between the graphene sheet and the carbon fiber surface. The dotted line in the diagram represents the interface. Some graphite edge structures (indicated by the red arrows) can be clearly observed on the carbon fiber surface. These are surface defects caused during the carbon fiber production process, providing nucleation and growth points for graphene covalent bonding. (Scale bar: 5 nm). The reaction process of T800S carbon fiber containing epoxy resin sizing agent during combustion synthesis was simulated using reactive force field molecular dynamics. The black atoms represent carbon atoms in the graphite layer on the carbon fiber surface, and the flesh-colored atoms represent carbon atoms in the epoxy resin. At 155 ps of reaction, a covalent bond between these two types of carbon atoms is clearly visible, which is the basis for graphene covalent bonding. (e) shows the graphite defects on the carbon fiber surface. (f) demonstrates the covalent bonding through molecular dynamics simulation.

[0043] Figure 4a This comparison shows the tensile strength and modulus of carbon fiber monofilaments covalently bonded to graphene on their surface after combustion synthesis, compared to the original carbon fibers. VCF represents the original carbon fibers, while SHSCF represents the carbon fibers covalently bonded to graphene on their surface after combustion synthesis.

[0044] Figure 4b This is a density histogram showing the density of carbon-based composite materials reinforced with carbon fibers containing 0–50% by mass of surface-covalently linked graphene. The composite material exhibits the highest density (1.79 g / cm³) when the added graphene content is 10%. 3 The illustration shows the small-angle X-ray scattering characterization results of a carbon-based composite material (denoted as SHSCF / C) reinforced with carbon fibers containing 10% surface covalently linked graphene.

[0045] Figure 4c These are the bending stress-strain curves of pure carbon-based materials and SHSCF / C. After adding carbon fibers with surface covalently linked graphene, the fracture process of the composite material exhibits pseudo-plastic fracture characteristics, indicating that the carbon fibers with surface covalently linked graphene form a high-strength interface with the carbon matrix;

[0046] Figure 4dThese are scanning electron microscope (SEM) images of cracks in SHSCF / C. (d1) is a macroscopic image of the crack, with a scale bar of 500 micrometers; (d2) is a magnified SEM image of the area within the magenta box in (d1). The red area represents the fiber fracture morphology, and the yellow area represents the fiber bridging morphology. This is a typical sample of fiber-reinforced composite material fracture, with a scale bar of 100 micrometers.

[0047] Figure 4e These are scanning electron microscope (SEM) images of the fracture surface of the original carbon fiber-reinforced carbon-based composite material. Significant debonding is visible at the interface, indicating poor reinforcement from the original carbon fiber. Scale bars are 5 μm and 2 μm, respectively.

[0048] Figure 4f These are scanning electron microscope (SEM) images of the fracture surface of SHSCF / C. Strong bonds remain at the fiber-matrix interface after the composite material fractures, indicating good reinforcement from the original carbon fibers. The scale bars are 5 μm and 2 μm, respectively. Detailed Implementation

[0049] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, while not limiting the invention in any way. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention.

[0050] Example 1: The carbon fiber surface modification method in this example, which exhibits uniform surface modification morphology, good graphene grafting morphology, and is suitable for carbon-based composite materials, is carried out according to the following steps:

[0051] Weigh 1 part of chopped carbon fiber, 30.5 parts of magnesium powder, and 59.5 parts of calcium carbonate, and mix them evenly.

[0052] CO2 is introduced into the combustion synthesis reactor, with the inlet valve kept open. The resistance wire is heated using a DC power supply to ignite the reactants. The power is then cut off to begin the combustion synthesis reaction. After the reaction is complete, the inlet valve is closed after 5 minutes. The product is collected after cooling for 30 minutes.

[0053] The resistance wire was removed using a magnet. 20% hydrochloric acid was added to a beaker containing the reaction product while stirring to obtain the acid-leached reaction product. The beaker was sealed, sonicated for 3 hours, magnetically stirred for 12 hours, and then dried at 120°C for 12 hours to obtain a composite powder containing graphene and surface-covalently linked graphene carbon fibers.

[0054] Graphene-covalently linked carbon fibers can be used as a reinforcing phase in matrices such as high-performance carbon-based composites. The carbon-based composite material reinforced with graphene-covalently linked carbon fibers prepared according to this invention achieves a density of 1.79 g / cm³. 3 The bending strength can reach up to 120 MPa, and the electrical conductivity can reach up to 4.2*10. 4 S / m. Among them, the matrix of the carbon-based composite material is a bulk material assembled from graphene synthesized by combustion, and the mass ratio of the carbon fibers covalently bonded with graphene to the matrix is ​​1:10.

[0055] Typical morphology of carbon fibers with surface covalently linked graphene rapidly prepared by combustion synthesis: SEM surface morphology characterization as follows Figure 2 As shown, by Figure 2 It can be seen that the diameter of the carbon fiber increased from 5μm to 5.2μm. This is because the surface covalently linked graphene was generated during the combustion synthesis process, and the carbon fiber surface morphology was rough and uniformly distributed.

[0056] Typical morphology of carbon fibers with surface covalently linked graphene rapidly prepared by combustion synthesis; TEM characterization of carbon fiber surface structure cross-section, as shown in... Figure 3 As shown, by Figure 3 It can be seen that the covalently bonded graphene on the carbon fiber surface exhibits an inclined growth morphology.

[0057] Properties of graphene-covalently linked carbon fiber reinforced carbon-based composites, such as Figure 4a -f indicates that, by Figure 4a As can be seen from -f, carbon fibers with surface covalently linked graphene are beneficial for achieving densification of carbon-based composite materials and improving their mechanical and electrical properties.

[0058] Example 2: The method for covalently bonding graphene to the surface of carbon fibers in this example is carried out according to the following steps:

[0059] The sizing agent applied to the surface of the short-cut carbon fibers is bisphenol A diglycidyl ether epoxy resin with an average thickness of 1 μm.

[0060] Then weigh 1 part of sized short-cut carbon fiber, 30.5 parts of magnesium powder, and 59.5 parts of calcium carbonate, mix them evenly, and place them in a combustion synthesis reactor.

[0061] Introduce CO2 into the combustion synthesis reactor while keeping the inlet valve open.

[0062] The resistance wire was heated by a DC power supply to ignite the reactants. The power was then cut off to start the combustion synthesis reaction. After the reaction was completed, the inlet valve was closed after 5 minutes. The combustion synthesis products were collected after cooling for 30 minutes.

[0063] The resistance wire was removed using a magnet. 20% hydrochloric acid was added to a beaker containing the reaction product while stirring to obtain the acid-leached reaction product. The beaker was sealed, sonicated for 3 hours, magnetically stirred for 12 hours, and then dried at 120°C for 12 hours to obtain a composite powder containing graphene and surface-covalently linked graphene carbon fibers.

[0064] The composite powder was sieved using a 150-mesh sieve to separate the graphene-modified carbon fibers and graphene powder, resulting in carbon fibers with covalently bonded graphene on the surface and combustion-synthesized graphene powder.

[0065] Example 3:

[0066] The sizing agent applied to the surface of the short-cut carbon fibers is bisphenol A diglycidyl ether epoxy resin with an average thickness of 1 μm.

[0067] Then weigh 1 part of sized short-cut carbon fiber, 30.5 parts of magnesium powder, and 59.5 parts of calcium carbonate, and mix them evenly.

[0068] The mixed powder is placed in a crucible, and an ignition agent is added above the mixed powder; wherein, the ignition agent is Fe3O4+Mg or MnO2+Mg from the magnesian reaction or Fe3O4+Al or Cr2O3+Al from the aluminothermic reaction;

[0069] Then the crucible is placed at the bottom of the top-opening container; wherein the volume of the top-opening container is 5 to 500 times the volume of the crucible, and the height of the container is 2 to 50 times the height of the crucible.

[0070] Carbon dioxide is introduced into the bottom of the top-opening container to fill the crucible and the inside of the top-opening container with gas;

[0071] The igniter is ignited by local electric ignition or local high-frequency induction heating to induce a combustion reaction in the mixed powder. Carbon dioxide is continuously introduced during the reaction at a rate of 5 L / min. Local electric ignition involves passing a 20 A DC current through a spiral tungsten wire coil to heat the local reactants and initiate a combustion synthesis reaction. Local high-frequency induction heating uses a high-frequency induction coil to heat the local reactants and initiate a combustion synthesis reaction.

[0072] Example 4: This example uses the preparation of carbon-based composite materials as an example, and the specific steps are as follows:

[0073] The carbon fibers with surface covalently linked graphene prepared in Example 2 were mixed with graphene powder at a mass ratio of 1:10. High-strength, high-conductivity carbon fiber-reinforced carbon-based composite material was prepared by SPS sintering under vacuum. The sintering temperature was 2300℃, the sintering pressure was 100MPa, and the holding time was 5 min.

[0074] The density of the high-strength, high-conductivity carbon fiber reinforced carbon-based composite material is 1.79 g / cm³. 3 The flexural strength of the composite material was 99-120 MPa in the three-point bending test, and the electrical conductivity of the composite material was 33249-41753 S / m in the four-probe method. These results exceed those of common commercially available high-strength graphite and reach the strength of some carbon-carbon composite materials with shorter densification processes.

[0075] The specific embodiments of the present invention have been described above. It should be noted that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for covalently bonding graphene to the surface of carbon fibers, characterized in that, The main steps include: Take raw carbon fibers or carbon fibers with organic coatings on their surface, mix them with a carbon source and a reducing agent until homogeneous, and then burn them to synthesize the reaction, that is, covalently attach graphene to the surface of the carbon fibers. Among them, carbon source is added in a mass ratio of 1:(0.2-200) of carbon fiber and graphene to be generated by combustion synthesis reaction, and reducing agent is added in a mass ratio of 1:(1.5-3) of organic matter coated on carbon fiber surface and total oxygen atoms in carbon source and reducing agent. The carbon source is one or a mixture of several of the following: carbon dioxide, carbonate, oxalate, and organic glycogen; the reducing agent is magnesium or aluminum.

2. The method according to claim 1, characterized in that, After the combustion synthesis reaction, the product is acid-washed and dried to obtain carbon fibers with graphene covalently bonded to the surface.

3. The method according to claim 1 or 2, characterized in that, The combustion synthesis reaction can be either a high-pressure combustion synthesis reaction or an atmospheric-pressure combustion synthesis reaction.

4. The method according to claim 1 or 2, characterized in that, The carbon fiber forms include chopped carbon fiber, long carbon fiber, carbon fiber felt, and carbon fiber braid; the carbon fiber raw materials are pure carbon fiber without surface coating, carbon fiber prepreg, carbon fiber with sizing agent, and any kind of carbon fiber reinforced resin matrix composite material; the carbon fiber type is one or a mixture of several of PAN-based carbon fiber, pitch-based carbon fiber, and biomass carbon fiber in any proportion.

5. The method according to claim 1 or 2, characterized in that, The organic materials are epoxy resin, phenolic resin, thermoplastic plastic, polycarbonate, bisphenol A diglycidyl ether epoxy resin and its derivatives; the carbon fiber surface is coated by sizing or pre-impregnation.

6. The method according to claim 1 or 2, characterized in that, The mass ratio of organic matter to carbon fiber is (0.001-0.67):

1.

7. The method according to claim 1 or 2, characterized in that, The diameter of carbon fiber ranges from 0.05μm to 50μm, and the length ranges from 0.05mm to 2000mm.

8. The method according to claim 1 or 2, characterized in that, The combustion atmosphere is vacuum, nitrogen, argon, a mixture of hydrogen and argon, or CO2; the mixing is carried out by one or any combination of ball milling, homogenization, mechanical stirring, ultrasonic stirring, or mechanical grinding.

9. The application of carbon fibers with surface covalently linked graphene prepared by any one of claims 1-8 in the preparation of carbon-based, resin-based, metal-based, and ceramic-based composite materials.

10. The application according to claim 9, characterized in that... The metal base is one of copper, aluminum, or magnesium.

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