Preparation method of modified carbon fiber / epoxy resin composite material

Abstract

The invention relates to a preparation method of a modified carbon fiber / epoxy resin composite material, which is characterized in that polyethyleneimine functionalization treatment of graphene oxide is utilized in surface modification of carbon fibers, and after the graphene oxide is grafted to the surfaces of the carbon fibers, the surface roughness of the carbon fibers can be improved; the surface activity of the functionalized graphene oxide is increased, so that the surface activity of the grafted carbon fiber is remarkably increased, and the bonding capacity between the fiber and the resin is greatly enhanced through the physical and chemical dual effects. Compared with direct grafting of the graphene oxide, the surface functionalization of the graphene oxide can obviously improve the characteristic that the graphene oxide is easy to agglomerate. Compared with an unmodified composite material, the tensile property of the composite material disclosed by the invention is improved by 49.82%.

Description

Technical Field

[0001] The invention belongs to the technical field of carbon fiber reinforced composite materials, and particularly relates to a method for preparing a modified carbon fiber / epoxy resin composite material. Background Art

[0002] Carbon fiber reinforced composite materials have broad application prospects in aerospace, military, wind power equipment and high-end civilian products due to their high specific strength, high specific modulus, design strength, high temperature resistance and other performance characteristics. However, since the surface of carbon fiber is smooth and chemically inert, and at the same time its own surface energy is low, this will lead to poor interface bonding between carbon fiber reinforcement and matrix. There is still a large gap between the actual strength of carbon fiber composites and the theoretical calculated value, and the application of carbon fiber composites is also greatly affected. Therefore, modifying the surface of carbon fiber to improve the interface performance of composite materials has always been a hot research topic in academia. Currently common modification methods include oxidation, deposition, coating, plasma treatment and other methods.

[0003] CN116356553A discloses a green and efficient surface modification method of carbon fiber fabric by ozone oxidation and its resin composite material, which improves the interface bonding ability of carbon fiber composite materials without damaging the performance of carbon fiber itself, but the single modification strengthening effect is not obvious, so the strengthening effect is also relatively limited.

[0004] CN118110027A "A treatment method for carbon fiber surface modification" discloses a method of modifying carbon nanotubes on the surface of carbon fiber by vapor deposition and in-situ growth, which successfully enhances the performance of carbon fiber composite materials. However, since vapor deposition will cause great damage to the carbon fiber itself, this will have a great impact on the mechanical properties of the composite material obtained later after the carbon fiber itself is damaged, such as a certain impact on the tensile mechanical properties.

[0005] The present invention performs KH560 silane coupling agent treatment on the basis of oxidation treatment of carbon fiber, and at the same time performs polyethyleneimine functionalization treatment on graphene oxide, and grafts the carbon fiber treated with the coupling agent and the graphene oxide functionalized with polyethyleneimine to form "flexible and rigid" reinforcement layers with different moduli, and completes the modification treatment of the carbon fiber to improve the mechanical properties of the composite material. The method has strong designability, controllable reaction conditions, cleanness and environmental protection, chemical bonding between grafted materials and the formed reinforcement layers with different moduli, so that the modification effect of the composite material is better. Summary of the invention

[0006] In view of the defects of the prior art, the object of the present invention is to provide a method for preparing a modified carbon fiber / epoxy resin composite material, which can enhance the bonding between the carbon fiber and the resin matrix to obtain a composite material with excellent performance.

[0007] To achieve the above object, the technical solution of the present invention is:

[0008] A method for preparing a modified carbon fiber / epoxy resin composite material, the preparation method comprising the following steps:

[0009] 1) Desizing the carbon fiber surface: Place the carbon fiber in an acetone solution and let it stand, then clean it with deionized water and vacuum dry it for later use;

[0010] 2) Surface oxidation treatment of carbon fiber: placing the desizing carbon fiber in a nitric acid solution, heating it in a water bath, then washing it with deionized water several times and vacuum drying it for later use to obtain an oxidized carbon fiber cloth;

[0011] 3) adding KH560 silane coupling agent to anhydrous ethanol, wherein the mass ratio of KH560 silane coupling agent to anhydrous ethanol is 1:10-20, adding acetic acid until the pH value of the system is 3-5, and ultrasonicating for 30-60 minutes to obtain a dispersion;

[0012] The oxidized carbon fiber is placed in a dispersion liquid and reacted at 50-80° C. for 10-15 hours, then washed with alcohol and vacuum dried for standby use to obtain a carbon fiber cloth treated with a KH560 silane coupling agent;

[0013] 4) functionalizing the graphene oxide with polyethyleneimine: preparing a 1wt% potassium hydroxide aqueous solution, mixing polyethyleneimine and anhydrous ethanol in a volume ratio of 1:2-3 to obtain a polyethyleneimine solution; mixing the potassium hydroxide aqueous solution and the polyethyleneimine solution in a volume ratio of 5:(3-6), placing the graphene oxide in the mixed solution, stirring magnetically at 75-80°C for 16-20h, adding a sodium borohydride solution, and continuing to treat for 4-5h, washing with deionized water several times and using a centrifuge to obtain the polyethyleneimine-functionalized graphene oxide, and vacuum drying and setting aside;

[0014] The mass ratio of graphene oxide to the volume of polyethyleneimine is (0.5-1) g:10-20 mL; the mass ratio of sodium borohydride to the mass of graphene oxide in the sodium borohydride solution is (0.6-1):1;

[0015] 5) Surface modification of carbon fiber: adding the polyethyleneimine functionalized graphene oxide obtained in step 4) into deionized water, wherein the mass fraction of the polyethyleneimine functionalized graphene oxide is 0.5-2%, preferably 1-2%, and performing ultrasonic treatment to make it uniformly dispersed, and then adding the carbon fiber cloth treated with KH560 silane coupling agent obtained in step 3), mixing evenly under magnetic stirring at 50-80° C., and then washing with deionized water and vacuum drying to obtain the modified carbon fiber cloth;

[0016] 6) Preparation of composite materials; Degassing E51 epoxy resin and mixing it with T31 ​​curing agent at a mass ratio of 4:1, and stirring continuously to obtain epoxy resin glue; laying the carbon fiber cloth obtained in step 5) on the mold layer by layer, and evenly applying epoxy resin glue on the surface of the carbon fiber cloth, spraying a release agent on the surface of the mold, and evenly applying epoxy resin glue on each layer of carbon fiber cloth, sending the mold to a flat vulcanizer, and hot pressing for 30-60 minutes at 80-120°C and 1-2MPa to obtain a modified carbon fiber / epoxy resin composite material, i.e., a carbon fiber plate.

[0017] Furthermore, in the step 1), the carbon fiber cloth is placed in the acetone solution for 24-48 hours, and the vacuum drying temperature is 50-80° C. and the drying time is 4-6 hours.

[0018] Furthermore, in the step 2), the water bath heating temperature is 78° C., and the product is washed with deionized water until the pH is neutral and then placed in a vacuum oven for drying.

[0019] Furthermore, in the step 4), the volume of the 1% KOH aqueous solution is 50-100 ml, 10-20 ml of polyethyleneimine is placed in 20-40 ml of anhydrous ethanol to prepare a polyethyleneimine solution; the mass of graphene oxide is 0.5-1 g; the magnetic stirring speed is 200-600 rpm / min; the sodium borohydride solution is prepared by placing 0.5-1 g of sodium borohydride in 10-20 ml of deionized water; the centrifuge speed is 7000-10000 rpm / min, the centrifugation is repeated 4-6 times, the vacuum drying temperature is 60-80°C, and the drying time is 12-24 h.

[0020] Furthermore, in the step 5), the mass fraction of graphene oxide functionalized with polyethyleneimine is 1-2%, and the ultrasonic treatment time is 30-60 min.

[0021] Furthermore, in the step 6), the degassing process is as follows: the epoxy resin degassing treatment is to ultrasonically treat the epoxy resin at 50° C. for 30 minutes;

[0022] Epoxy resin glue was prepared by using epoxy resin and curing agent, and the mass ratio of carbon fiber cloth to epoxy resin glue was 1:1.

[0023] The present invention also protects a modified carbon fiber / epoxy resin composite material obtained by the preparation method, wherein the modified carbon fiber / epoxy resin composite material has a tensile strength of more than 600 MPa, preferably 620-670 MPa.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] The present invention adopts a chemical grafting method to construct a reinforcing interface layer of different moduli such as silane coupling agent, polyethyleneimine, graphene oxide, etc. on the surface of carbon fiber, which greatly increases the surface roughness and active functional groups of the carbon fiber. The present invention has strong designability, controllable reaction conditions, cleanness and environmental protection, and obvious strengthening effect.

[0026] The present invention utilizes the polyethyleneimine functionalization treatment of graphene oxide in the surface modification of carbon fiber. After being grafted to the surface of carbon fiber, not only can the surface roughness of carbon fiber be improved, but the increase in the surface activity of functionalized graphene oxide will also significantly increase the surface activity of grafted carbon fiber. The dual effects of physics and chemistry greatly enhance the bonding ability between fiber and resin. Compared with directly grafting graphene oxide, surface functionalization of graphene oxide can significantly improve the characteristic of easy aggregation of graphene oxide.

[0027] In order to increase the bonding ability between carbon fiber and functionalized graphene oxide, the present application uses KH560 as a bridging agent, and uses its own easy hydrolysis property to increase the adhesion rate of KH560, and the epoxy group of KH560 itself can also form a tight bond with the amino group in the epoxy curing agent. The tensile properties of the composite material grafted with 1 mg / ml polyethyleneimine functionalized graphene oxide are improved by 49.82% compared with the unmodified composite material. The present application uses the KH560 coupling agent with milder reaction conditions. KH560 itself has a low cost and mild reaction conditions. It can undergo a condensation reaction with the hydroxyl groups on the surface of CF itself, and it contains epoxy groups, which can form a tight chemical bond with amine-containing molecules. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is an electron microscope image of the surface morphology of graphene oxide after polyethyleneimine functionalization.

[0029] Figure 2 This is an electron microscope image of the surface morphology of carbon fiber after desizing.

[0030] Figure 3 This is an electron microscope image of the surface morphology of the modified carbon fiber.

[0031] Figure 4 This is the XPS wide scan spectrum of the carbon fiber surface after desizing.

[0032] Figure 5 This is the XPS wide scan spectrum of the carbon fiber surface after treatment with KH560 silane coupling agent.

[0033] Figure 6 This is the XPS wide scan spectrum of the carbon fiber surface after modification.

[0034] Figure 7 This is an electron microscope image of the tensile fracture morphology of a composite material made directly from desized carbon fiber.

[0035] Figure 8 It is an electron microscope image of the tensile fracture morphology of the modified carbon fiber / epoxy resin composite material of the present invention. DETAILED DESCRIPTION

[0036] In order to understand the present invention more clearly, the present invention is further described in detail below with reference to the accompanying drawings and embodiments.

[0037] The raw materials and equipment used in the present invention are all known products and can be obtained by purchasing commercially available products.

[0038] In the present invention, the three reinforcing layers of KH560 silane coupling agent layer, polyethyleneimine layer and graphene oxide layer have different moduli and play different reinforcing roles. KH560 mainly plays the role of a bridge. After being grafted to the carbon fiber, the epoxy group on its surface can react with the graphene oxide after subsequent amino treatment to form a tight chemical bond. At the same time, KH560 can also react chemically with the amino group in the epoxy curing agent, which has a certain promoting effect on the performance of the carbon fiber composite material. The amino group rich on the surface of polyethyleneimine can be chemically bonded with the epoxy group on the surface of the carbon fiber after the coupling agent treatment, and the surface of polyethyleneimine has water-based vinyl and polar hydrophilic group amine groups, so it has high adsorption and adhesion. This characteristic of polyethyleneimine also plays a certain physical role when grafted with the carbon fiber surface. The structure of graphene oxide itself makes it have a large specific surface area, and at the same time has excellent mechanical properties. It has good dispersibility after functionalization treatment, and graphene oxide can significantly improve the surface roughness of carbon fiber, thereby improving the mechanical locking effect between carbon fiber and matrix. This application mainly provides excellent modification effects through the interaction of chemical bonds between these different reinforcement layers and the promotion of different reinforcement layers on the combination of carbon fiber and composite materials. The hydroxyl groups on the surface of the oxidized carbon fiber undergo condensation reaction with the silanol groups after the coupling agent hydrolysis to form chemical bonds. This step introduces epoxy groups on the surface of the carbon fiber. The epoxy groups can form tight chemical bonds with the amino groups at a certain temperature. The surface of the graphene oxide functionalized with polyethyleneimine has more amino groups, so it can form chemical bonds with the carbon fiber treated with the coupling agent.

[0039] The preparation method of the modified carbon fiber / epoxy resin composite material of the present invention comprises the following steps:

[0040] 1) Desizing treatment of carbon fiber surface: Place the carbon fiber in an acetone solution and let it stand, then clean it with deionized water and vacuum dry it for later use; this process removes the slurry that the carbon fiber carries when it leaves the factory, exposing the functional groups of the carbon fiber itself, which is convenient for subsequent modification.

[0041] 2) Surface oxidation treatment of carbon fiber: the desizing carbon fiber is placed in a nitric acid solution, heated in a water bath, then washed several times with deionized water and vacuum dried for use to obtain oxidized carbon fiber cloth. This process increases the content of active functional groups on the carbon fiber surface.

[0042] The preferred technical solution is that in step 2), 97% concentrated nitric acid is used for oxidation, the oxidation time is controlled at 2.5-3.5h, and the temperature is maintained at 78°C.

[0043] 3) adding KH560 silane coupling agent to anhydrous ethanol, wherein the mass ratio of KH560 silane coupling agent to anhydrous ethanol is 1:10-20, adding acetic acid until the pH value of the system is 3-5, and ultrasonicating for 30-60 minutes to obtain a dispersion;

[0044] This process utilizes the property of the silane coupling agent itself to be easily hydrolyzed in an acidic environment to introduce the epoxy functional groups on the surface of the silane coupling agent into the surface of the carbon fiber.

[0045] The oxidized carbon fiber is placed in a dispersion and reacted at 50-80° C. for 10-15 hours, then washed with alcohol and vacuum dried for later use to obtain a carbon fiber cloth treated with a KH560 silane coupling agent.

[0046] 4) functionalizing the graphene oxide with polyethyleneimine: preparing a 1wt% potassium hydroxide aqueous solution, mixing polyethyleneimine and anhydrous ethanol in a volume ratio of 1:2-3 to obtain a polyethyleneimine solution; mixing the potassium hydroxide aqueous solution and the polyethyleneimine solution in a volume ratio of 5:(3-6), placing the graphene oxide in the mixed solution, stirring magnetically at 75-80°C for 16-20h, adding a sodium borohydride solution, and continuing to treat for 4-5h, washing with deionized water several times, and obtaining the polyethyleneimine-functionalized graphene oxide by a centrifuge, and vacuum drying and setting aside;

[0047] The mass ratio of graphene oxide to the volume of polyethyleneimine is (0.5-1) g:10-20 ml; the mass ratio of sodium borohydride to the mass of graphene oxide in the sodium borohydride solution is (0.6-1):1;

[0048] In this process, graphene oxide is reduced and functionalized with polyethyleneimine. Compared with graphene, graphene oxide contains more active functional groups, but its mechanical properties are weaker than graphene. The reduced graphene oxide has the excellent properties of graphene and also contains sufficient functional groups on its surface. Polyethyleneimine introduces amino groups to the surface of graphene oxide, which can react with the epoxy functional groups on the surface of KH560 silane coupling agent on the one hand, and also have a good chemical bond with epoxy resin on the other hand.

[0049] The preferred technical solution is that the graphene oxide selected in step 4) is multilayer graphene oxide. A KOH aqueous solution with a mass fraction of 1% is prepared, and the volume ratio of polyethyleneimine to anhydrous ethanol in the polyethyleneimine solution is 1:2. The KOH aqueous solution and the polyethyleneimine solution are mixed in a volume ratio of 1:1. The graphene oxide is placed in the mixed solution and magnetically stirred at a speed of 200-600rpm for 18h at 78°C. A sodium borohydride deionized water solution with a mass fraction of 5% is prepared, added thereto, and the treatment is continued for 4h under the same conditions. When the graphene oxide after polyethylene functionalization is extracted by a centrifuge, it is centrifuged at a speed of 7000-10000rpm for 10min, washed with deionized water, and then centrifuged repeatedly 3-5 times before being taken out and dried.

[0050] 5) Surface modification of carbon fiber: adding the polyethyleneimine functionalized graphene oxide obtained in step 4) into deionized water, wherein the mass fraction of the polyethyleneimine functionalized graphene oxide is 0.5-2%, preferably 1-2%, and performing ultrasonic treatment to make it uniformly dispersed, and then adding the carbon fiber cloth treated with KH560 silane coupling agent obtained in step 3), mixing evenly under magnetic stirring at 50-80° C., and then washing with deionized water and vacuum drying to obtain the modified carbon fiber cloth;

[0051] In this process, KH560 silane coupling agent acts as a bridge, and the epoxy groups on the surface can form a tight bond with the amino groups on the surface of graphene oxide functionalized with polyethyleneimine.

[0052] The preferred technical solution is that in step 5), magnetic stirring is performed at 60° C. with a magnetic stirring speed of 200-600 rpm / min and a stirring time of 2 h to achieve surface modification of the carbon fiber.

[0053] 6) Preparation of composite materials; Degassing E51 epoxy resin and mixing it with T31 ​​curing agent in a ratio of 4:1, and stirring continuously to obtain epoxy resin glue; laying the carbon fiber cloth obtained in step 5) on the mold layer by layer, and evenly applying epoxy resin glue on the surface of the carbon fiber cloth, spraying a release agent on the surface of the mold, and evenly applying epoxy resin glue on each layer of carbon fiber cloth, sending the mold to a flat vulcanizer, and hot pressing for 30-60 minutes at 80-100°C and 1-2MPa to obtain a modified carbon fiber / epoxy resin composite material, i.e., a carbon fiber plate.

[0054] In this process, the modified carbon fiber cloth is mainly made into a composite material by hot pressing. The hot pressing process is mainly divided into three parts: the configuration of epoxy glue, the laying of carbon fiber cloth and hot pressing molding.

[0055] The preferred technical solution is that in step 6), the carbon fiber cloth is a cross-grained carbon fiber cloth, and the E51 epoxy resin is ultrasonically treated for 30 minutes at 50°C to achieve degassing. The mass ratio of epoxy resin glue to carbon fiber cloth is 1:1, and the epoxy resin glue is evenly applied to the surface of the carbon fiber cloth by spot coating.

[0056] Embodiment 1:

[0057] The preparation method of the modified carbon fiber / epoxy resin composite material of this embodiment specifically comprises the following steps:

[0058] 1) Desizing the surface of the carbon fiber cloth: put the carbon fiber cloth into an acetone solution and let it stand for 24 hours. After taking it out, wash it repeatedly with deionized water and put it into an oven to dry it at 60° C. for 6 hours.

[0059] 2) The desized carbon fiber cloth was placed in a nitric acid solution and heated in a water bath at 78°C for 3 h. After being taken out, it was repeatedly washed with deionized water until the pH of the fiber surface was neutral and then placed in an oven for drying at 60°C for 6 h.

[0060] 3) KH560 silane coupling agent and anhydrous ethanol were prepared into KH560 solution in a mass ratio of 5:100, acetic acid was added to adjust the pH of the solution to 5, and a dispersion was obtained after ultrasonic treatment for 30 minutes. The carbon fibers were arranged in the dispersion and heated in a water bath at 50°C for 12 hours. After washing with ethanol, the dispersion was placed in an oven at 60°C and dried for 6 hours.

[0061] 4) Add KOH to deionized water to prepare 50 ml of 1% KOH aqueous solution, place 10 ml of polyethyleneimine in 20 ml of anhydrous ethanol to prepare polyethyleneimine solution, mix the two solutions, place 500 mg of graphene oxide in the mixed solution, and stir magnetically at 78°C at 500 rpm / min for 18 hours, then keep the treatment conditions unchanged and add 10 ml of 1M sodium borohydride solution and continue stirring for 4 hours. Place in a centrifuge and centrifuge at 9000 rpm / min for 9 minutes, wash repeatedly with deionized water and centrifuge again 5 times, place in an oven and dry at 70°C for 12 hours to obtain graphene oxide functionalized with polyethyleneimine. The surface morphology of graphene oxide functionalized with polyethyleneimine is as follows: Figure 1 As shown in the figure, it can be seen that some polyethyleneimine slurry is attached to the surface of graphene oxide after polyethyleneimine treatment, and the presence of these slurries will greatly increase the adhesion of graphene oxide.

[0062] 5) The graphene oxide functionalized with polyethyleneimine was prepared into a 1 mg / ml graphene oxide solution, and the carbon fiber treated with the silane coupling agent was placed in the graphene oxide solution, stirred at 500 rpm / min for 3 h at 50 ° C, washed with deionized water, and then placed in an oven at 60 ° C for 6 h to obtain a modified carbon fiber cloth. The surface morphology of the carbon fiber after desizing is as follows: Figure 2 As shown in the figure, there are obvious grooves on the surface, which increase the surface roughness of the carbon fiber to a certain extent. The surface morphology of the modified carbon fiber is as follows Figure 3 As shown, it can be seen from the figure that there is lamellar functionalized graphene oxide on the surface of the modified carbon fiber, which greatly improves the surface roughness and surface activity of the carbon fiber. Figure 4 This is the XPS wide scan spectrum of the carbon fiber surface after desizing. It can be seen from the figure that the main components of the carbon fiber surface are carbon and oxygen, among which carbon is the main component, accounting for 81.31%. After being treated with KH560 silane coupling agent, the oxygen content on the carbon fiber surface has been significantly improved, such as Figure 5 As shown in the figure, the increase of oxygen elements indicates the increase of active functional groups on the surface of carbon fiber. The coupling agent treatment can greatly improve the activity of the carbon fiber surface. Figure 6 It shows that after the final grafting of graphene oxide functionalized with polyethyleneimine, the content of oxygen elements on the surface of carbon fiber has been reduced to a certain extent. At the same time, the appearance of nitrogen elements proves the access of polyethyleneimine. The access of functionalized graphene oxide introduces amino groups to the surface of carbon fiber and increases the surface roughness of carbon fiber, which will greatly improve the bonding ability between fiber and resin.

[0063] 6) E51 epoxy resin was ultrasonically treated at 50°C for 30 minutes to remove internal bubbles, and then E51 epoxy resin and T31 curing agent were mixed in a mass ratio of 4:1, and stirred with a glass rod to prepare epoxy resin glue with a mass ratio of 1:1 to carbon fiber cloth. After spraying the mold with a release agent, the carbon fiber cloth was placed on the mold layer by layer, and each layer was evenly applied to the surface of the fiber cloth with a brush. After completion, the mold was sent to a flat vulcanizer and hot-pressed at a temperature of 80°C and a pressure of 1MPa for 30 minutes. The mold was taken out for demoulding, and the required carbon fiber plate was obtained after correcting the edges and corners, and sent for cutting for subsequent mechanical property testing.

[0064] The tensile fracture morphology of the composite material made directly from desizing carbon fiber is as follows: Figure 7 As shown in the figure, there is a large gap between the fibers, and the fiber surface is relatively smooth, with less residual resin, indicating that the resin impregnation is insufficient.

[0065] The tensile fracture morphology of modified carbon fiber / epoxy resin composites is shown in Figure 8 As shown in the figure, the holes on the tensile fracture completely disappear, and the presence of resin can be clearly seen on the exposed fiber surface. The grafting of functionalized graphene oxide provides more active functional groups for carbon fiber and increases the surface roughness of carbon fiber. The dual effects of chemical condensation and mechanical condensation between the fiber and the resin matrix form a good infiltration between the fiber and the resin matrix.

[0066] Example 2: The preparation process of this example is the same as that of Example 1, except that in step 3), the mass ratio of the silane coupling agent to anhydrous ethanol is 1:100.

[0067] Example 3: The preparation process of this example is the same as that of Example 1, except that in step 3), the mass ratio of the silane coupling agent to anhydrous ethanol is 1:10.

[0068] Example 4: The preparation process of this example is the same as that of Example 1, except that the concentration of the polyethyleneimine functionalized graphene oxide solution in step 5) is 0.5 mg / ml.

[0069] Example 5: The preparation process of this example is the same as that of Example 1, except that the concentration of the polyethyleneimine functionalized graphene oxide solution in step 5) is 2 mg / ml.

[0070] Example 6: The preparation process of this example is the same as that of Example 1, except that in step 6), the plate vulcanizing machine parameters are hot-pressed at 110°C and 2MPa.

[0071] Example 7: The preparation process of this example is the same as that of Example 1, except that in step 6), the plate vulcanizing machine parameters are hot pressed at 100°C and 3MPa.

[0072] Embodiment 8: The preparation process of this embodiment is the same as that of embodiment 1, except that in step 6), the parameters of the flat plate vulcanizing machine are hot pressed under the conditions of 120℃ and 2MPa.

[0073] The test results of the composite material properties of the above embodiments are shown in Table 1:

[0074] Table 1 Statistics of tensile strength of composite materials

[0075] sample Tensile strength(MPa) Initial sample 446.8 Example 1 669.4 Example 2 565.9 Example 3 646.95 Example 4 593 Example 5 629.7 Example 6 570.6 Example 7 546 Example 8 512

[0076] Referring to Table 1, it can be seen from Examples 1-6 and the comparison with the initial sample (the initial sample refers to the composite material directly obtained by desizing the carbon fiber without modification treatment), that the concentration of KH560 silane coupling agent and the concentration of polyethyleneimine functionalized graphene oxide have a significant effect on the tensile strength of the composite material. When the concentration of KH560 is low, the attachment rate of the coupling agent on the carbon fiber surface is low, so the grafting rate of polyethyleneimine functionalized graphene oxide is greatly affected, resulting in low tensile properties of the composite material. At the same time, too low or too high concentrations of polyethyleneimine functionalized graphene oxide will cause the tensile properties of the composite material to decrease. Too low concentrations lead to unclear grafting effects, and too high concentrations will cause mechanical properties to decrease due to the agglomeration of graphene oxide. Different hot pressing molding conditions will also have a significant impact on the composite material. When the mass fraction of the silane coupling agent is controlled between 5% and 10%, the concentration of functionalized graphene oxide is controlled between 1 mg / ml and 2 mg / ml, the temperature of the flat vulcanizer is controlled between 80°C and 100°C, and the pressure is controlled between 1MPa and 2MPa, the requirement of significantly enhancing the tensile properties of the composite material can be achieved.

[0077] Within the parameter range given by the present invention, the tensile strength is above 600 MPa. Compared with the composite material that has not been modified, the tensile performance is improved by more than 30%. The molding temperature is controlled at about 80°C, the pressure is about 1 MPa, and the graphene oxide concentration is 1 mg / ml-2 mg / ml, which has a better effect.

[0078] The surface of the KH560 silane coupling agent with a suitable amount of addition has abundant epoxy groups, which can have a close chemical bond with the amino groups on the surface of the graphene oxide functionalized with polyethyleneimine, and at the same time, it can also react with the amino groups in the epoxy curing agent. The abundant amino groups on the surface of polyethyleneimine and the epoxy resin have a good promoting effect. At the same time, the large specific surface area and unique structure of the graphene oxide itself increase the roughness of the carbon fiber, thereby further increasing the contact area between the carbon fiber and the resin matrix. This reinforced interface layer with different moduli is conducive to the transmission of interfacial stress. The synergistic effect of each component and process enables the present invention to form a multi-scale surface morphology, effectively improve the bonding ability between the fiber and the resin, and finally achieve the purpose of improving the comprehensive performance of the fiber / epoxy resin.

[0079] The embodiments described above are only part of the embodiments of the present application, but not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0080] Any matters not described in the present invention are applicable to the prior art.

Claims

1. A method for preparing a modified carbon fiber / epoxy resin composite material, characterized in that: The preparation method comprises the following steps: 1) Desizing the carbon fiber surface: Place the carbon fiber in an acetone solution and let it stand, then clean it with deionized water and vacuum dry it for later use; 2) Surface oxidation treatment of carbon fiber: placing the desizing carbon fiber in a nitric acid solution, heating it in a water bath, then washing it with deionized water several times and vacuum drying it for later use to obtain an oxidized carbon fiber cloth; 3) adding KH560 silane coupling agent to anhydrous ethanol, wherein the mass ratio of KH560 silane coupling agent to anhydrous ethanol is 1:10-20, adding acetic acid until the pH value of the system is 3-5, and ultrasonicating for 30-60 minutes to obtain a dispersion; The oxidized carbon fiber is placed in a dispersion and reacted at 50-80°C for 10-15 hours, then washed with alcohol and vacuum dried for standby use to obtain a carbon fiber cloth treated with a KH560 silane coupling agent; 4) functionalizing the graphene oxide with polyethyleneimine: preparing a 1wt% potassium hydroxide aqueous solution, mixing polyethyleneimine and anhydrous ethanol in a volume ratio of 1:2-3 to obtain a polyethyleneimine solution; mixing the potassium hydroxide aqueous solution and the polyethyleneimine solution in a volume ratio of 5:(3-6), placing the graphene oxide in the mixed solution, stirring magnetically at 75-80°C for 16-20h, adding a sodium borohydride solution, and continuing to treat for 4-5h, washing with deionized water several times and using a centrifuge to obtain the polyethyleneimine-functionalized graphene oxide, and vacuum drying and setting aside; The mass ratio of graphene oxide to the volume of polyethyleneimine is (0.5-1) g:10-20 mL; the mass ratio of sodium borohydride to the mass of graphene oxide in the sodium borohydride solution is (0.6-1):1; 5) Surface modification of carbon fiber: adding the polyethyleneimine functionalized graphene oxide obtained in step 4) into deionized water, wherein the mass fraction of the polyethyleneimine functionalized graphene oxide is 0.5-2%, preferably 1-2%, and performing ultrasonic treatment to make it uniformly dispersed, and then adding the carbon fiber cloth treated with KH560 silane coupling agent obtained in step 3), mixing evenly under magnetic stirring at 50-80° C., and then washing with deionized water and vacuum drying to obtain the modified carbon fiber cloth; 6) Preparation of composite materials; Degassing E51 epoxy resin and mixing it with T31 ​​curing agent at a mass ratio of 4:1, and stirring continuously to obtain epoxy resin glue; laying the carbon fiber cloth obtained in step 5) on the mold layer by layer, and evenly applying epoxy resin glue on the surface of the carbon fiber cloth, spraying a release agent on the surface of the mold, and evenly applying epoxy resin glue on each layer of carbon fiber cloth, sending the mold to a flat vulcanizer, and hot pressing for 30-60 minutes at 80-120°C and 1-2MPa to obtain a modified carbon fiber / epoxy resin composite material, i.e., a carbon fiber plate.

2. The preparation method according to claim 1, characterized in that: In the step 1), the carbon fiber cloth is placed in the acetone solution for 24-48 hours, and the vacuum drying temperature is 50-80° C. and the drying time is 4-6 hours.

3. The preparation method according to claim 1, characterized in that: In the step 2), the water bath is heated at 78° C., and the product is washed with deionized water until the pH is neutral and then placed in a vacuum oven for drying.

4. The preparation method according to claim 1, characterized in that: In the step 4), the volume of the 1% KOH aqueous solution is 50-100 ml, 10-20 ml of polyethyleneimine is placed in 20-40 ml of anhydrous ethanol to prepare a polyethyleneimine solution; the mass of graphene oxide is 0.5-1 g; the magnetic stirring speed is 200-600 rpm / min; the sodium borohydride solution is prepared by placing 0.5-1 g of sodium borohydride in 10-20 ml of deionized water; the centrifuge speed is 7000-10000 rpm / min, the centrifugation is repeated 4-6 times, the vacuum drying temperature is 60-80°C, and the drying time is 12-24 hours.

5. The preparation method according to claim 1, characterized in that: In the step 5), the mass fraction of graphene oxide functionalized with polyethyleneimine is 1-2%, and the ultrasonic treatment time is 30-60 min.

6. The preparation method according to claim 1, characterized in that: In the step 6), the degassing process is as follows: the epoxy resin degassing process is to ultrasonically treat the epoxy resin at 50° C. for 30 minutes; Epoxy resin glue was prepared by using epoxy resin and curing agent, and the mass ratio of carbon fiber cloth to epoxy resin glue was 1:

1.

7. A modified carbon fiber / epoxy resin composite material obtained by the preparation method according to any one of claims 1 to 6, characterized in that: The tensile strength of the modified carbon fiber / epoxy resin composite material is above 600 MPa.

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