Carbon fiber prepreg, preparation method thereof and carbon fiber composite material

Abstract

The invention relates to a carbon fiber prepreg, a preparation method thereof and a carbon fiber composite material, and relates to the technical field of composite materials. The preparation method of the carbon fiber prepreg comprises the following steps: sequentially carrying out primary electrochemical surface treatment and secondary electrochemical surface treatment on carbon fibers to obtain surface modified carbon fibers; wherein the first-stage electrochemical surface treatment adopts an acidic electrolyte comprising inorganic acid ammonium salt, and the second-stage electrochemical surface treatment adopts a compound electrolyte comprising inorganic alkaline ammonium salt and an amino-containing compound; carrying out hot melting on the epoxy resin composition and cooling to form a film to obtain a resin adhesive film; and carrying out impregnation compounding on the surface modified carbon fiber and a resin adhesive film to obtain the carbon fiber prepreg. The carbon fibers are subjected to specific two-stage electrochemical surface treatment, so that the interface performance of the carbon fiber composite material can be effectively improved, and the mechanical property is further effectively improved.

Description

Technical Field

[0001] This application relates to the field of composite materials technology, and in particular to a carbon fiber prepreg and its preparation method, and carbon fiber composite materials. Background Technology

[0002] High-strength, high-modulus carbon fiber composites can achieve a combination of lightweight and high-strength properties, making them widely used in aerospace and military fields. However, high-strength, high-modulus carbon fibers (tensile strength ≥ 5000 MPa, elastic modulus ≥ 436 GPa) produced by dry-jet wet spinning have very smooth microscopic surfaces, resulting in unsatisfactory chemical activity and physical roughness. This leads to a significant reduction in interfacial properties. Compared with tensile properties, the bending, lamellar shear, and compressive properties of carbon fiber composites are more significantly affected by the interface. Poor interfacial properties result in poor mechanical performance of the composite material, affecting the overall performance of the component and thus limiting its widespread application. Summary of the Invention

[0003] To address the problems existing in related technologies, this application provides a carbon fiber prepreg and its preparation method, as well as a carbon fiber composite material, to improve the interfacial properties of the carbon fiber composite material.

[0004] In a first aspect, embodiments of this application provide a method for preparing carbon fiber prepreg, comprising the following steps: S1: Carbon fibers are subjected to a first-stage electrochemical surface treatment and a second-stage electrochemical surface treatment in sequence to obtain surface-modified carbon fibers; wherein, the first-stage electrochemical surface treatment uses an acidic electrolyte including inorganic acidic ammonium salts, and the second-stage electrochemical surface treatment uses a compound electrolyte including inorganic alkaline ammonium salts and amino compounds. S2: The epoxy resin composition is hot-melted and cooled to form a film to obtain a resin film; the surface-modified carbon fiber is impregnated and compounded with the resin film to obtain a carbon fiber prepreg. In the above technical solution, by modifying the surface of carbon fibers, the first-stage electrochemical surface treatment uses inorganic acidic ammonium salts for electrochemical activation, which removes the inert graphite layer on the carbon fiber surface, forming a rough microstructure (increasing specific surface area). Simultaneously, oxygen-containing active groups such as hydroxyl (-OH) and carboxyl (-COOH) groups are introduced, providing anchoring sites for the functionalization reactions in the subsequent second-stage treatment. In the second-stage electrochemical surface treatment, inorganic alkaline ammonium salts and amino-containing compounds are used for electrochemical polymerization, grafting and activating the fiber surface. Amino groups are covalently grafted onto the carboxyl groups on the fiber surface, forming stable chemical bonds. In the subsequent impregnation and composite process, the amino groups grafted onto the fiber surface will undergo a cross-linking reaction with the epoxy resin, thereby effectively improving the interfacial properties. This preparation method, by modifying the surface of carbon fibers and using a hot-melt impregnation and composite method, can effectively improve the interfacial properties of carbon fiber composites, thereby effectively enhancing their mechanical properties. In some embodiments, the acidic electrolyte is an aqueous solution of ammonium sulfate, and the compound electrolyte is an aqueous solution of a mixture of ammonium bicarbonate and diethylenetriamine.

[0005] In the above technical solution, the ammonium sulfate aqueous solution is weakly acidic (pH about 4-6), which can gently etch the carbon fiber surface, reducing the impact on the strength of the carbon fiber body while introducing active groups. Furthermore, during the electrochemical oxidation process, sulfate ions can act as an oxidizing agent, reacting with carbon atoms on the carbon fiber surface to efficiently generate oxygen-containing active groups such as hydroxyl and carboxyl groups, forming more dense and more uniformly distributed active sites on the carbon fiber surface, providing sufficient anchor points for amino grafting in the secondary electrochemical treatment.

[0006] In the compound electrolyte, the ammonium bicarbonate aqueous solution is weakly alkaline (pH approximately 8-10), which can neutralize the residual acidic groups on the carbon fiber surface, adjust the surface charge state to facilitate the adsorption of amino compounds, and further protect the fiber strength. Diethylenetriamine (DETA) contains three amino groups, which can efficiently covalently bind to the carboxyl groups on the carbon fiber surface. Furthermore, the unreacted amino groups can undergo cross-linking reactions with the epoxy resin during subsequent impregnation and compounding processes, thereby effectively improving interfacial properties. Moreover, the weakly alkaline environment of ammonium bicarbonate can promote the protonation of the amino groups in DETA, enhancing its adsorption capacity on the negatively charged carbon fiber surface.

[0007] By using a combination of specific acidic electrolytes and compound electrolytes, the interfacial bonding performance of carbon fibers can be effectively improved, while the bulk strength of the carbon fibers is not significantly reduced.

[0008] In some embodiments, the concentration of inorganic acidic ammonium salt in the acidic electrolyte is 0.1 mol / L to 0.15 mol / L; in the compound electrolyte, the concentration of inorganic alkaline ammonium salt is 0.2 mol / L to 0.4 mol / L, and the concentration of amino-containing compound is 0.1 mol / L to 0.2 mol / L. In the above technical solutions, the concentration of inorganic acidic ammonium salts within a suitable range is beneficial for providing a weakly acidic environment and sufficient active sulfate ions, thereby reducing the impact on the mechanical properties of the carbon fiber while simultaneously activating it electrochemically. The concentration of inorganic basic ammonium salts within a suitable range is beneficial for providing a weakly alkaline environment, which can effectively neutralize residual acidic groups on the carbon fiber surface and effectively promote the protonation of diethylenetriamine. The concentration of amino-containing compounds within a suitable range can provide sufficient amino groups to fully react and combine with the carboxyl groups on the carbon fiber surface.

[0009] In some embodiments, the current density of the primary electrochemical surface treatment is 20 A / m. 2 ~23A / m 2The processing time is 3-5 minutes; the current density for secondary electrochemical surface treatment is 5 A / m. 2 ~8A / m 2 The processing time is 10 to 15 minutes. In the above technical solutions, performing primary electrochemical surface treatment at a higher current density and within a shorter time range is beneficial for achieving efficient etching, controlling the etching depth, and reducing the impact on the mechanical properties of the carbon fiber itself; while performing secondary electrochemical surface treatment at a lower current density and within a longer time range is beneficial for the stable adsorption of amino compounds on the carbon fiber surface and for a full grafting reaction.

[0010] In some embodiments, the carbon fiber is prepared by a dry-jet wet spinning process, and the carbon fiber has a tensile strength ≥5000MPa and a tensile modulus ≥436GPa. In the above technical solution, the carbon fiber is a high-strength, high-modulus carbon fiber with a smooth microscopic surface, strong inertness, and high interfacial bonding difficulty. By employing the above two-stage electrochemical surface treatment modification and graphene oxide resin composite, precise modification can be achieved, effectively improving interfacial properties while retaining high strength and high modulus, thereby preparing carbon fiber composite materials with excellent mechanical properties.

[0011] In some embodiments, step S2 includes: mixing an epoxy resin composition and graphene oxide, hot-melting and cooling to form a film to obtain a resin film; and impregnating and compounding surface-modified carbon fibers with the resin film to obtain a carbon fiber prepreg.

[0012] In the above technical solution, by adding graphene oxide to the resin film, the graphene oxide has a sheet-like structure and abundant oxygen-containing groups. When mixed with epoxy resin, it can not only enhance the mechanical properties of the resin itself through the group effect, but also form a bridge at the carbon fiber-resin interface, fill the micro-voids at the interface, reduce stress concentration, and further optimize the interface transfer efficiency.

[0013] In some embodiments, the mass ratio of the graphene oxide and epoxy resin composition is (1~8):100.

[0014] In the above technical solution, the appropriate amount of graphene oxide can achieve efficient reinforcement and toughening while reducing agglomeration. Especially when applied to high-strength, high-modulus carbon fibers, it can effectively toughen the fibers and reduce interfacial debonding caused by stress concentration. Furthermore, it helps maintain good flexibility and melt viscosity of the resin film, enabling rapid composite with carbon fibers during impregnation.

[0015] In some embodiments, the epoxy resin composition includes a matrix resin, a curing agent, and a toughening agent. In the above technical solution, the matrix resin provides matrix rigidity and strength, ensuring the load-bearing capacity of the epoxy resin composition; the curing agent forms a dense network through cross-linking, maintaining the thermal stability and mechanical strength of the epoxy resin composition; and the toughening agent can disperse stress concentration, inhibit crack propagation, and improve impact resistance.

[0016] In some implementations, step S2 includes: The first epoxy resin composition is hot-melted and cooled to form a film to obtain a first resin film; the second epoxy resin composition and graphene oxide are mixed, hot-melted and cooled to form a film to obtain a second resin film. Surface-modified carbon fibers are impregnated and laminated with two first resin films to obtain an intermediate; the intermediate is then impregnated and laminated with two second resin films to obtain carbon fiber prepreg. In the above technical solution, a two-step hot melt method (four-film method) is used for impregnation, and a resin film containing graphene oxide is placed on the outer layer. The first resin film in the inner layer can be combined with the surface-modified carbon fiber and the reverse efficient impregnation and interface. The second resin film containing graphene oxide in the outer layer can effectively strengthen and toughen the composite material, and can reduce the impact of rigid graphene oxide particles on the carbon fiber structure. In some embodiments, the areal density of the first resin film is 18 g / m³. 2 ~22g / m 2 The areal density of the second resin film is 25 g / m³. 2 ~35g / m 2 . In the above technical solution, the thinner first resin film is located in the inner layer, which is conducive to fully impregnating the carbon fiber and improving the interfacial bonding density; while the thicker second resin film is located in the outer layer, which is conducive to providing sufficient resin carrier for graphene oxide, reducing agglomeration, and can be tightly bonded to the inner layer to ensure the reinforcement and toughening effect.

[0017] In some embodiments, the impregnation and compounding step is carried out at a temperature of 105°C to 110°C and a pressure of 4.5 kg·cm². -1 ~9.0kg·cm -1 .

[0018] In the above technical solution, the temperature and pressure of the impregnation step are within a suitable range, which is beneficial to improving the resin fluidity and penetration density, and further improving the interfacial bonding force between the fiber and the resin.

[0019] Secondly, embodiments of this application provide a carbon fiber prepreg, which is prepared using the preparation method provided in the first aspect of this application.

[0020] Thirdly, embodiments of this application provide a carbon fiber composite material, which is obtained by curing the carbon fiber prepreg provided in the second aspect of embodiments of this application.

[0021] In the above technical solution, the carbon fiber composite material has excellent mechanical properties, with interlaminar shear strength ≥80MPa, 0° compressive strength ≥1300MPa, 0° flexural strength ≥1450MPa, and open-cell compressive strength ≥230MPa. Attached Figure Description To more clearly illustrate the technical solutions of the embodiments of this application, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of this application and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 This is a process flow diagram of a method for preparing carbon fiber prepreg provided in an embodiment of this application.

[0023] Figure 2 This is a structural schematic diagram of a carbon fiber prepreg provided in an embodiment of this application.

[0024] Figure 3 This is a structural schematic diagram of a carbon fiber prepreg provided for another embodiment of this application.

[0025] Explanation of reference numerals in the attached drawings: 100, 200 - carbon fiber prepreg; 10 - surface-modified carbon fiber; 20 - first resin film; 30 - second resin film. Detailed Implementation

[0026] The following detailed description, with appropriate reference to the accompanying drawings, discloses the preparation method of the carbon fiber prepreg, the carbon fiber prepreg, and embodiments of the carbon fiber composite material of this application. However, unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of actually identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0027] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60~120 and 80~110 are listed for a specific parameter, it is also expected that ranges of 60~110 and 80~120 are also included. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1~3, 1~4, 1~5, 2~3, 2~4, and 2~5. In this application, unless otherwise stated, the numerical range "a~b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0028] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0029] High-strength, high-modulus carbon fibers (tensile strength ≥ 5000 MPa, elastic modulus ≥ 436 GPa) are usually made by dry-jet wet spinning process. The microscopic surface is very smooth and the surface is relatively inert. The interfacial bonding ability with the resin matrix is ​​poor, which leads to poor mechanical properties of carbon fiber composites, especially poor bending, lamination shear and compression properties.

[0030] In recent years, research has focused on surface modification of carbon fibers using electrochemical surface treatment. However, as fiber strength and modulus increase, the difficulty of improving the fiber-resin interface also increases. When the surface treatment is weak, it does not improve the fiber interface performance; when the surface treatment is strong, the fiber bulk strength decreases significantly, and it is prone to fuzzing and breakage. Based on this, this application provides a method for preparing carbon fiber prepreg. Figure 1 For a process flow diagram of a method for preparing carbon fiber prepreg provided in this application embodiment, please refer to [link / reference]. Figure 1 The preparation method includes the following steps: S1: Carbon fibers are subjected to a first-stage electrochemical surface treatment and a second-stage electrochemical surface treatment in sequence to obtain surface-modified carbon fibers; wherein, the first-stage electrochemical surface treatment uses an acidic electrolyte including inorganic acidic ammonium salts, and the second-stage electrochemical surface treatment uses a compound electrolyte including inorganic alkaline ammonium salts and amino compounds.

[0031] In some embodiments, the acidic electrolyte is an aqueous solution of ammonium sulfate, and the compound electrolyte is an aqueous solution of a mixture of ammonium bicarbonate and diethylenetriamine.

[0032] In some embodiments, the concentration of inorganic acidic ammonium salt in the acidic electrolyte is 0.1 mol / L to 0.15 mol / L; in the compound electrolyte, the concentration of inorganic alkaline ammonium salt is 0.2 mol / L to 0.4 mol / L, and the concentration of amino-containing compounds is 0.1 mol / L to 0.2 mol / L.

[0033] As an example, the concentration of inorganic acidic ammonium salt in the acidic electrolyte is any one of 0.1 mol / L, 0.11 mol / L, 0.12 mol / L, 0.13 mol / L, 0.14 mol / L, or 0.15 mol / L, or a range between any two; in the compound electrolyte, the concentration of inorganic basic ammonium salt is any one of 0.2 mol / L, 0.25 mol / L, 0.30 mol / L, 0.35 mol / L, or 0.4 mol / L, or a range between any two; and the concentration of amino-containing compounds is any one of 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.18 mol / L, or 0.2 mol / L, or a range between any two.

[0034] In some embodiments, the current density of the primary electrochemical surface treatment is 20 A / m. 2 ~23A / m 2 The voltage is 32V, and the treatment time is 3-5 minutes. As an example, the current density for primary electrochemical surface treatment is 20A / m². 2 21A / m 2 22A / m 2 23A / m 2 The value of any one of the points or the range between any two; the value of any one of the processing times of 3 min, 4 min, and 5 min or the range between any two.

[0035] In some embodiments, the current density for secondary electrochemical surface treatment is 5 A / m. 2 ~8A / m 2 The voltage was 32V, and the treatment time was 10-15 minutes. As an example, the current density for the secondary electrochemical surface treatment was 5 A / m². 2 6A / m 2 7A / m 2 8A / m 2The value of any one of the points or the range between any two; the value of any one of the processing times of 10 min, 11 min, 12 min, 13 min, 14 min, and 15 min or the range between any two.

[0036] In some embodiments, the carbon fiber is prepared by a dry-jet wet spinning process, and the carbon fiber has a tensile strength ≥5000MPa and a tensile modulus ≥436GPa.

[0037] Furthermore, the tensile strength of carbon fiber can be 5000MPa~7000MPa, such as 5250MPa, 5300MPa, 5350MPa, 6000MPa, etc.; the tensile modulus can be 436GPa~500GPa, such as 436GPa, 439GPa, 445GPa, 450GPa, etc.

[0038] Furthermore, the carbon fiber can be a high-strength, high-modulus 12K polyacrylonitrile-based carbon fiber tow with a length greater than 500m.

[0039] Understandably, the "GB / T 26752-2011" standard for polyacrylonitrile-based carbon fiber classifies high-strength, high-strength medium-modulus, high-modulus, high-strength high-modulus, and tow specifications. The carbon fiber used in this application can be prepared by conventional dry-jet wet spinning process or can be purchased directly. This application does not limit the specific type of carbon fiber used.

[0040] S2: The epoxy resin composition is hot-melted and cooled to form a film to obtain a resin film; the surface-modified carbon fiber is impregnated and compounded with the resin film to obtain a carbon fiber prepreg.

[0041] In some embodiments, the epoxy resin composition includes a matrix resin, a curing agent, and a toughening agent.

[0042] Furthermore, the matrix resin may include tetraglycidylamine type epoxy resin and / or bisphenol A type epoxy resin. For example, the tetraglycidylamine type epoxy resin may be AG-80 epoxy resin, and the bisphenol A type epoxy resin may include at least one of E44 epoxy resin and E51 epoxy resin.

[0043] Furthermore, the toughening agent can be polyamide particles, which can improve the impact resistance and fracture toughness of carbon fiber prepreg. The polyamide particles can be 300-400 mesh particles.

[0044] Furthermore, the curing agent includes 4,4' Diaminodiphenylmethane and 4,4' At least one of the following: 4,4'-diaminodiphenylmethane (DDM) curing agent. 4,4'-diaminodiphenylmethane (DDS) curing agent exhibits excellent mechanical properties after curing, while 4,4'-diaminodiphenylmethane (DDS) curing agent demonstrates excellent heat resistance and strong chemical stability. Depending on different product or process requirements, either 4,4'-diaminodiphenylmethane or 4,4'-diaminodiphenyl sulfone can be selected as a curing agent, or both can be used simultaneously, so that the epoxy resin composition possesses both excellent mechanical properties and excellent heat resistance and chemical stability.

[0045] Furthermore, the mass ratio of the matrix resin, curing agent, and toughening agent can be (2.5-3.5):(1-1.5):(2-2.5), for example, 3:1:2, 2.5:1:2, or 3:1.2:2.3, etc.

[0046] In some embodiments, step S2 includes: mixing an epoxy resin composition and graphene oxide, hot-melting and cooling to form a film to obtain a resin film; and impregnating and compounding surface-modified carbon fibers with the resin film to obtain a carbon fiber prepreg.

[0047] Further, the mass ratio of graphene oxide to epoxy resin composition is (1~8):100. As an example, the mass ratio of graphene oxide to epoxy resin composition is any one of 1:100, 2:100, 4:100, 6:100, 8:100 or any range between the two.

[0048] In some embodiments, step S2 includes: Step S21: The first epoxy resin composition is hot-melted and cooled to form a film to obtain a first resin film; the second epoxy resin composition and graphene oxide are mixed, hot-melted and cooled to form a film to obtain a second resin film; Step S22: Impregnate and composite the surface-modified carbon fiber with the first resin film on both sides to obtain an intermediate; impregnate and composite the intermediate with the second resin film on both sides to obtain carbon fiber prepreg.

[0049] Further, step S21 may include: hot-melting the first epoxy resin composition and the second epoxy resin composition into the glue tank of the film-making machine, adjusting the coating temperature to 70℃~90℃, coating the resin onto the release paper, cooling, laminating and winding for later use.

[0050] In some embodiments, the areal density of the first resin film is 18 g / m³. 2 ~22g / m 2 The areal density of the second resin film is 25 g / m³. 2 ~35g / m 2 As an example, the areal density of the first resin film can be 18 g / m³. 2 19g / m2 20g / m 2 21g / m 2 22g / m 2 The value of any one of the points or the range between any two; the areal density of the second resin film can be 25 g / m³. 2 28g / m 2 30g / m 2 32g / m 2 35g / m 2 The value of any one of the points or the range between any two.

[0051] Step S22 may include: installing a certain number of surface-modified carbon fibers on a yarn frame and yarn shaft, pulling them through the yarn guide hole, opening the yarn with a yarn spreader, and impregnating and bonding them with a prepared first resin film under a certain temperature and pressure, so that the resin film adheres to the upper and lower surfaces of the fiber. Then, heating the fiber and resin layer as a whole, controlling the impregnation temperature and impregnation pressure, to produce a 2-film prepreg intermediate; then using a second resin film, after peeling off the surface release paper, bonding the second resin film to the upper and lower surfaces of the 2-film prepreg intermediate, then heating the fiber and resin layer as a whole, controlling the impregnation temperature and impregnation pressure, to produce a 4-film carbon fiber prepreg, covering it with a release film, and winding it onto a paper tube to obtain the prepreg.

[0052] Understandably, in other embodiments, the impregnation and composite step may further include: applying a first resin film and a second resin film to the opposite surfaces of the surface-modified carbon fiber, controlling the impregnation temperature and impregnation pressure, and preparing a two-film carbon fiber prepreg.

[0053] In some embodiments, the impregnation and composite step is performed at a temperature of 105°C to 110°C and a pressure of 4.5 kg·cm². -1 ~9.0kg·cm -1 As an example, the temperature for the impregnation and compounding step is any one of 105°C, 106°C, 108°C, 109°C, or 110°C, or a range between any two; the pressure is 4.5 kg·cm². -1 5.0 kg·cm -1 6.0 kg·cm -1 7.0 kg·cm -1 8.0 kg·cm -1 9.0 kg·cm -1 The value of any one of the points or the range between any two.

[0054] In addition, this application also provides a carbon fiber prepreg prepared by the above preparation method.

[0055] In some embodiments, the fiber areal density of the carbon fiber prepreg is 120 g / m³.2 ~150g / m 2 The resin content is 30% to 40%. As an example, the fiber areal density of the carbon fiber prepreg is 120 g / m². 2 130g / m 2 140g / m 2 150g / m 2 The value of any one of the points or the range between any two; the value of any one of the resin contents of 30%, 32%, 35%, 38%, and 40% or the range between any two.

[0056] Please see Figure 2 In some embodiments, the carbon fiber prepreg 100 includes surface-modified carbon fiber 10, a first resin film 20 disposed on two opposing surfaces of the surface-modified carbon fiber 10, and a second resin film 30 disposed on the surface of the first resin film 20 away from the surface-modified carbon fiber 10.

[0057] Please see Figure 3 In other embodiments, the carbon fiber prepreg 200 includes surface-modified carbon fiber 10 and a first resin film 20 and a second resin film 30 respectively disposed on opposite surfaces of the surface-modified carbon fiber 10.

[0058] In addition, this application embodiment also provides a carbon fiber composite material, which is obtained by curing the above-mentioned carbon fiber prepreg.

[0059] In some embodiments, the method for preparing carbon fiber composite materials includes: sequentially cutting, laying, sealing, and autoclaving carbon fiber prepreg.

[0060] Furthermore, the autoclave curing process includes: vacuuming at room temperature, with the vacuum bag having a vacuum level of -0.090 to -0.098 MPa; initially pressurizing at room temperature, increasing the pressure to 0.6 MPa at a rate of 0.02 MPa / min; then raising the temperature to 180°C at a rate of 1.5°C / min and holding the temperature and pressure for 120 min; finally, holding the pressure and cooling down to below 60°C at a rate of 2.0°C / min, and then releasing the pressure and removing the product from the autoclave.

[0061] This carbon fiber composite material has excellent mechanical properties, with interlaminar shear strength ≥80MPa, 0° compressive strength ≥1300MPa, 0° flexural strength ≥1450MPa, and open-cell compressive strength ≥230MPa. To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0062] Example 1 This embodiment provides a carbon fiber composite material, the preparation method of which includes the following steps: (1) Unsized carbon fiber (tensile strength at the center of the hole is 5250 MPa, elastic modulus at the center of the hole is 439 GPa) tow was placed on the activation surface of the surface modification device. The carbon fiber was used as the anode, the graphite electrode as the cathode, and a 0.1 mol / L ammonium sulfate aqueous solution was used as the electrolyte. The fiber tow was immersed in the electrolyte solution and the current density was set to 20 A / m. 2 The voltage was 32V, the processing time was 3 minutes, and after processing, the carbon fibers were taken out, shaped, and the residual electrolyte on the surface was washed to obtain activated carbon fibers.

[0063] (2) The activated carbon fiber bundle was placed on the activation surface of the surface modification device, with the activated carbon fiber as the anode, the graphite electrode as the cathode, and a mixed aqueous solution of ammonium bicarbonate and DETA as the electrolyte. The concentration of ammonium bicarbonate was 0.2 mol / L, and the concentration of DETA was 0.2 mol / L. The bundle was immersed in the electrolyte solution, and the current density was set to 7 A / m. 2 The voltage was 32V, the processing time was 15min, and after processing, the fiber was taken out and shaped. The residual electrolyte on the surface was washed to ensure that the conductivity of the fiber leachate after washing was controlled at 20μS / m, thus obtaining surface-modified carbon fibers. 200 axial lengths of continuous modified carbon fibers with a length of >200m per axial length were prepared according to the process of steps (1) and (2).

[0064] (3) Prepare 5 kg of matrix resin according to the mixing ratio of AG-80:E51:E44 = 4:1:0.5. Stir thoroughly and evenly for 30 min at a stirring speed of 30 r / min and a temperature of 80℃. Then lower the temperature to 70℃ and add curing agent DDS. The mass ratio of curing agent to matrix resin is 1:3. Add in small amounts several times, and stir thoroughly until uniform after each addition. Then add 300 mesh polyamide (PES) toughening agent particles at the same temperature. The mass ratio of toughening agent to matrix resin is 1:1.5. Add in small amounts several times, and stir thoroughly at 50 r / min for 6 h after the addition is complete. At this time, the mixing ratio of toughening agent, curing agent and resin is toughening agent:DDS:resin = 2:1:3, and the first epoxy resin composition is obtained.

[0065] (4) Prepare 5 kg of matrix resin according to the mixing ratio of AG-80:E51:E44 = 4:1:1. Stir thoroughly and evenly for 30 min at a stirring speed of 30 r / min and a temperature of 80℃. Then lower the temperature to 70℃ and add curing agent DDS. The mass ratio of curing agent to matrix resin is 1:3. Add in small amounts several times, and stir thoroughly until uniform after each addition. Then add 300 mesh polyamide (PES) toughening agent particles at the same temperature. The mass ratio of toughening agent to matrix resin is 1:2. Add in small amounts several times, and stir thoroughly at 50 r / min for 6 h after the addition is complete. At this time, the mixing ratio of toughening agent, curing agent and resin is toughening agent:DDS:resin = 1.5:1:3, and obtain the second epoxy resin composition. Based on this, graphene oxide particles were added to the second epoxy resin composition at a ratio of 3g (graphene oxide) / 100g (second epoxy resin composition), added in small amounts multiple times. After complete addition, the mixture was stirred thoroughly at 50r / min for 12h to obtain a mixture of the second epoxy resin composition and graphene oxide.

[0066] (5) The hot-melted first epoxy resin composition and the mixture of the second epoxy resin composition and graphene oxide are poured into the glue tank of the film-making machine, coated onto release paper, cooled, laminated, and rolled up for later use, thus preparing the first resin film and the second resin film. The coating temperature of the first resin film is (80±1.0)℃, and the areal density is (20±1) g / m³. 2 The coating temperature of the second resin film is (85±1.0)℃, and the areal density is (30±1) g / m³. 2 .

[0067] (6) A certain amount of surface-modified carbon fibers are installed on the yarn frame and yarn beam, pulled through the yarn guide hole, and opened by the yarn unfolding machine. Under a certain temperature and pressure, the fibers are impregnated and compounded with the prepared first resin film, so that the resin film adheres to the upper and lower surfaces of the fibers. Then, the fibers and resin layers are heated as a whole, and the impregnation temperature and impregnation pressure are controlled to produce a 2-film prepreg intermediate. Then, the second resin film is used. After peeling off the surface release paper, the second resin film is adhered to the upper and lower surfaces of the 2-film prepreg intermediate. Then, the fibers and resin layers are heated as a whole, and the impregnation temperature and impregnation pressure are controlled to produce a 4-film carbon fiber prepreg. After covering with the release film, it is wound onto a paper tube to obtain the carbon fiber prepreg. The impregnation temperature of the first resin film and the second resin film is 110℃, and the pressure is 9kg / cm. -1 The prepreg has a resin content of 34% and a fiber areal density of 133 g / m³. 2 .

[0068] (7) Clean the mold with soft material, then apply release agent to the mold, cut an appropriate number of pieces with a prepreg cutting machine, and then lay up and stack them according to the corresponding test standards to form a preform; after the composite material blank is assembled and bagged, it is cured by heating and pressurizing with the resin system curing process. The curing process is to vacuum at room temperature, and the vacuum in the vacuum bag is -0.090~-0.098MPa; pressurize at room temperature, pressurize to 0.6MPa at a rate of 0.02MPa / min; then heat to 180℃ at 1.5℃ / min and keep it at 120min; finally, keep it at 2.0℃ / min and cool it down to below 60℃, depressurize and remove it from the can to obtain carbon fiber composite laminate.

[0069] Example 2 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: In step (1), the tensile strength of the carbon fiber is 5341 MPa, and the elastic modulus is 443 GPa; the concentration of ammonium sulfate in the electrolyte is 0.15 mol / L, and the current density is 23 A / m. 2 .

[0070] Example 3 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: In step (1), the tensile strength of the carbon fiber is 5341 MPa and the elastic modulus is 443 GPa; the concentration of ammonium sulfate in the electrolyte is 0.15 mol / L and the treatment time is 5 min.

[0071] Example 4 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: In step (1), an aqueous solution of ammonium bisulfate with a concentration of 0.05 mol / L is used as the electrolyte, and the treatment time is 2 min.

[0072] Example 5 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: In step (2), the concentration of ammonium bicarbonate is 0.3 mol / L, and the current density is 5 A / m. 2 The processing time is 12 minutes.

[0073] Example 6 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: In step (2), the concentration of ammonium bicarbonate is 0.4 mol / L, and the current density is 8 A / m. 2 The processing time is 10 minutes.

[0074] Example 7 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: In step (3), AG-80:E51:E44 =4:1.5:0.5.

[0075] Example 8 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: In step (3), the matrix resin does not contain E44, and the ratio of AG-80 to E51 is 4:1.5; in step (4), the matrix resin does not contain E44, and the ratio of AG-80 to E51 is 4:2.

[0076] Example 9 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Embodiment 1 in that: in step (3), the toughening agent: DDS: resin = 2.5: 1: 3; in step (4), the toughening agent: DDS: resin = 2.5: 1: 3.

[0077] Example 10 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: in step (4), the addition ratio of graphene oxide particles is 1g (graphene oxide) / 100g (second epoxy resin composition).

[0078] Example 11 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: in step (4), the addition ratio of graphene oxide particles is 8g (graphene oxide) / 100g (second epoxy resin composition).

[0079] Example 12 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: In step (4), silica particles are used instead of graphene oxide particles.

[0080] Example 13 This embodiment provides a carbon fiber composite material, the preparation method of which differs from that of Example 1 in that: Step (6) includes: installing a certain number of surface-modified carbon fibers on the yarn frame and yarn shaft, pulling them through the yarn guide hole, opening the yarn with the yarn spreader, and impregnating and compounding them with the prepared first resin film and second resin film under a certain temperature and pressure, so that the first resin film and second resin film are respectively attached to the upper and lower surfaces of the fiber, and then heating the fiber and resin layer as a whole, controlling the impregnation temperature and impregnation pressure to produce 2-film carbon fiber prepreg.

[0081] Comparative Example 1 This comparative example provides a carbon fiber composite material whose preparation method differs from that of Example 1 in that it does not include steps (1) and (2), i.e., surface modification of the carbon fiber.

[0082] Comparative Example 2 This comparative example provides a carbon fiber composite material whose preparation method differs from that of Example 1 in that it does not include step (1).

[0083] Performance testing and results analysis The mechanical properties of the carbon fiber composite laminates prepared in the above embodiments and comparative examples were tested, and the test results are shown in Table 1. The specific test methods are as follows: (1) Interlaminar shear strength According to the ASTM D2344 test standard, ten carbon fiber composite laminates were cut into specimens with a length × width × thickness of 12 mm × 4 mm × 2 mm. The interlaminar shear strength was then tested according to the test rate (1 mm / min) and the lower span (8 mm) parameters.

[0084] (2) 0° compressive strength According to the ASTM D6641 testing standard, ten carbon fiber composite laminates were engraved into specimens with dimensions of 140mm × 13mm × 2mm (length × width × thickness) using a precision milling machine. Reinforcing plates were attached to both ends of the specimens to ensure that the working section length was 13mm. The 0° compressive strength of the carbon fiber composite was tested according to the required combined loading clamping method, strain gauge connection method, loading speed, and other parameters.

[0085] (3) 0° bending strength According to the ASTM D7264 test standard, carbon fiber composite laminates were engraved to dimensions of length × width × thickness = 77mm × 13mm × 2mm using a precision engraving milling machine. The 0° bending strength of the carbon fiber composite was then tested according to the required parameters such as support span, loading head radius, and loading speed.

[0086] (4) Opening compressive strength According to the ASTM D6484 test standard, carbon fiber composite laminates are engraved to dimensions of 300mm × 36mm × 1mm using a precision milling machine. A hole with a diameter of 6mm is made in the center of the sample, and the open-cell compressive strength of the carbon fiber composite is tested.

[0087] Table 1 Performance test results of carbon fiber composites

[0088] As can be seen from Table 1, the carbon fiber composite materials prepared in Examples 1 to 12 of this application have good mechanical properties, with interlaminar shear strength ≥80MPa, 0° compressive strength ≥1300MPa, 0° flexural strength ≥1450MPa, and open-cell compressive strength ≥230MPa.

[0089] The performance test results of Examples 1 and 4 show that using weakly acidic ammonium sulfate as an electrolyte can reduce fiber surface damage and improve interfacial properties, while further improving the interlaminar shear strength, 0° compressive strength, 0° flexural strength and open-pore compressive strength of the composite material.

[0090] The performance test results of Examples 1 and 12 show that the use of graphene oxide particles for reinforcement and toughening has higher surface activity and better compatibility with resins and fibers compared to silicon dioxide.

[0091] A comparison of the performance test results of Examples 1 and 13 shows that, compared with the 2-film carbon fiber prepreg, the 4-film carbon fiber prepreg used in Example 1 can effectively improve the mechanical properties of the carbon fiber composite material. This may be because the graphene oxide particles in the second resin film will inevitably be pressed into the fiber layer during the impregnation process, which will damage the structural integrity and reduce the strength and toughness.

[0092] The performance test results of Example 1 and Comparative Examples 1 and 2 show that both primary and secondary electrochemical surface treatments are indispensable in this application. Only through two-stage electrochemical surface treatment can carbon fibers be effectively modified, thereby improving the interfacial properties of carbon fiber composite materials.

[0093] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A method for preparing carbon fiber prepreg, characterized in that, Includes the following steps: S1: Carbon fibers are subjected to a first-stage electrochemical surface treatment and a second-stage electrochemical surface treatment in sequence to obtain surface-modified carbon fibers; wherein, the first-stage electrochemical surface treatment uses an acidic electrolyte including an inorganic acidic ammonium salt, and the second-stage electrochemical surface treatment uses a compound electrolyte including an inorganic alkaline ammonium salt and an amino compound. S2: The epoxy resin composition is hot-melted and cooled to form a film to obtain a resin film; the surface-modified carbon fiber is impregnated and compounded with the resin film to obtain a carbon fiber prepreg.

2. The preparation method according to claim 1, characterized in that, The acidic electrolyte is an aqueous solution of ammonium sulfate, and the compound electrolyte is an aqueous solution of a mixture of ammonium bicarbonate and diethylenetriamine.

3. The preparation method according to claim 1, characterized in that, The concentration of the inorganic acidic ammonium salt in the acidic electrolyte is 0.1 mol / L to 0.15 mol / L; In the compound electrolyte, the concentration of the inorganic alkaline ammonium salt is 0.2 mol / L to 0.4 mol / L, and the concentration of the amino-containing compound is 0.1 mol / L to 0.2 mol / L.

4. The preparation method according to claim 1, characterized in that, The current density of the primary electrochemical surface treatment is 20 A / m. 2 ~23A / m 2 Processing time: 3-5 minutes; And / or, the current density of the secondary electrochemical surface treatment is 5 A / m 2 ~8A / m 2 The processing time is 10 to 15 minutes.

5. The preparation method according to claim 1, characterized in that, The carbon fiber is prepared by dry-jet wet spinning process, and the tensile strength of the carbon fiber is ≥5000MPa and the tensile modulus is ≥436GPa.

6. The preparation method according to claim 1, characterized in that, Step S2 includes: mixing the epoxy resin composition and graphene oxide, hot-melting and cooling to form a film to obtain a resin film; impregnating and compounding the surface-modified carbon fiber with the resin film to obtain the carbon fiber prepreg. Preferably, the mass ratio of the graphene oxide to the epoxy resin composition is (1~8):100; Preferably, the epoxy resin composition comprises a matrix resin, a curing agent, and a toughening agent.

7. The preparation method according to claim 1 or 6, characterized in that, Step S2 includes: The first epoxy resin composition is hot-melted and cooled to form a film to obtain a first resin film; the second epoxy resin composition and graphene oxide are mixed, hot-melted and cooled to form a film to obtain a second resin film. The surface-modified carbon fiber is impregnated and compounded with the first resin film on both sides to obtain an intermediate; the intermediate is then impregnated and compounded with the second resin film on both sides to obtain a carbon fiber prepreg.

8. The preparation method according to claim 7, characterized in that, The areal density of the first resin film is 18 g / m³. 2 ~22g / m 2 The areal density of the second resin film is 25 g / m³. 2 ~35g / m 2 ; And / or, the temperature of the impregnation and composite step is 105℃~110℃, and the pressure is 4.5 kg·cm. -1 ~9.0kg·cm -1 .

9. A carbon fiber prepreg, characterized in that, It is prepared by the preparation method according to any one of claims 1 to 8.

10. A carbon fiber composite material, characterized in that, It is obtained by curing the carbon fiber prepreg as described in claim 9.

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