Preparation method of carbon fiber sizing agent containing multi-walled carbon nanotubes and carbon fiber

Abstract

The invention provides a preparation method of a carbon fiber sizing agent containing multi-walled carbon nanotubes and carbon fibers, and belongs to the technical field of carbon fiber manufacturing. The preparation method of the carbon fiber sizing agent containing the multi-walled carbon nanotubes comprises the following steps that the multi-walled carbon nanotubes are placed in an inert atmosphere to be subjected to heat treatment, the heat treatment temperature ranges from 2000 DEG C to 3000 DEG C, and the treatment time ranges from 1 h to 6 h; the multi-walled carbon nanotubes subjected to heat treatment, a sizing agent resin matrix and a surfactant solution are subjected to mixing treatment, the steps of mixing treatment are sequentially carried out under ultrasonic and mechanical stirring conditions, and the carbon fiber sizing agent containing the multi-walled carbon nanotubes is obtained. According to the preparation method, the problem that the multi-walled carbon nanotubes are easy to agglomerate in the carbon fiber sizing agent can be improved to a certain extent.

Description

Technical Field

[0001] The present application relates to the technical field of carbon fiber manufacturing, and in particular to a method for preparing a carbon fiber sizing agent containing multi-walled carbon nanotubes and carbon fibers. Background Art

[0002] Carbon fiber, with its excellent properties such as high strength, high modulus, and low density, is widely used in aerospace, sports equipment, and automotive manufacturing. Sizing agents are key additives in the carbon fiber production process, protecting the carbon fiber surface and improving the interfacial bonding between the carbon fiber and the matrix resin.

[0003] On this basis, multi-walled carbon nanotubes have a unique one-dimensional nanostructure, excellent mechanical properties, electrical properties and thermal properties. Technicians have found that adding multi-walled carbon nanotubes to carbon fiber sizing agents to modify carbon fibers, after the corresponding carbon fibers are combined with the resin matrix, is expected to further improve the mechanical properties, electrical properties and thermal properties of carbon fiber resin composites.

[0004] However, multi-walled carbon nanotubes are prone to agglomeration in carbon fiber sizing agents. Not only can the unevenly dispersed multi-walled carbon nanotubes fail to perform their modification function, but they may also form defects in carbon fiber resin composites (for example, reducing the interfacial bonding strength between the carbon fiber and the resin matrix), resulting in poor performance of the composite material. Summary of the Invention

[0005] The purpose of the present application is to provide a method for preparing a carbon fiber sizing agent containing multi-walled carbon nanotubes and carbon fibers, which can improve the problem of easy agglomeration of multi-walled carbon nanotubes in the carbon fiber sizing agent to a certain extent.

[0006] The embodiment of the present application is implemented as follows:

[0007] In the first aspect, an embodiment of the present application provides a method for preparing a carbon fiber sizing agent containing multi-walled carbon nanotubes, comprising the following steps: placing the multi-walled carbon nanotubes under an inert atmosphere for heat treatment, wherein the heat treatment temperature is 2000-3000°C and the treatment time is 1-6 hours; mixing the heat-treated multi-walled carbon nanotubes, a sizing agent resin matrix and a surfactant solution, wherein the mixing step is carried out in sequence under ultrasonic and mechanical stirring conditions to obtain a carbon fiber sizing agent containing multi-walled carbon nanotubes.

[0008] In the prior art, it is currently believed that the main reason why multi-walled carbon nanotubes (MWCNTs) easily agglomerate in carbon fiber sizing agents is that MWCNTs themselves have a high specific surface area and there are strong van der Waals forces between MWCNTs. A common improvement method is to use ultrasound and mechanical stirring in a surfactant solution to assist dispersion; however, actual results have shown that this dispersion method also makes it difficult to achieve uniform dispersion of MWCNTs. After research, the inventors found that the presence of some impurities in MWCNTs, including but not limited to metal catalysts introduced during the preparation of MWCNTs, moisture, and incompletely converted single-walled components, is one of the reasons that induce MWCNTs to easily agglomerate in carbon fiber sizing agents. Based on this, in the present application, before the multi-walled carbon nanotubes, the sizing agent resin matrix and the surfactant solution are mixed, the multi-walled carbon nanotubes are first heat-treated in an inert atmosphere at 2000-3000°C for 1-6 hours. On the one hand, the high-temperature treatment can remove impurities such as metal catalysts and moisture remaining in the multi-walled carbon nanotubes, thereby improving the purity of the multi-walled carbon nanotubes; on the other hand, the high-temperature treatment can deeply repair the lattice defects in the multi-walled carbon nanotubes (such as defects such as five-membered ring or seven-membered ring distortion), thereby promoting the reconstruction of multi-layer tube walls and inducing single-layer tube walls to form a multi-layer structure through carbon atom rearrangement (that is, the single-wall structure remaining in the multi-walled carbon nanotubes is also converted into a multi-wall structure, which is equivalent to improving the purity of the multi-walled carbon nanotubes); through the combined action of these two aspects, the purity of the multi-walled carbon nanotubes can be improved, thereby effectively improving the problem that the multi-walled carbon nanotubes are easily agglomerated due to the presence of impurities. At the same time, ultrasonic and mechanical stirring are sequentially used in the surfactant solution to perform mixing treatment, so that a carbon fiber sizing agent with relatively uniform dispersion of multi-walled carbon nanotubes can be finally prepared.

[0009] In some optional embodiments, the temperature of the heat treatment is 2550-3000°C; the heat treatment step is carried out in a graphite furnace, the real-time temperature of the graphite furnace is T, and during the heating process, when T≤1500°C, the heating rate is C1, when 1500°C<T≤2500°C, the heating rate is C2, and when 2500°C<T≤3000°C, the heating rate is C3, wherein C1>C2>C3.

[0010] In the above technical solution, when the temperature range of the heat treatment is within the range of 2550-3000°C, the heating rate is set according to different temperature ranges. Specifically, the higher the temperature, the smaller the heating rate, which helps to better balance the structural stability of multi-walled carbon nanotubes at high temperatures and the impurity removal effect.

[0011] In some optional embodiments, the difference in heating rate between any two adjacent ones of C1, C2 and C3 is 5-6°C / min; optionally, C1 is 15-18°C / min.

[0012] In the above technical solution, the difference in the heating rate between any two adjacent ones of C1, C2 and C3 is limited to the above range, and C1 is limited to the above range, so that each stage of heating has a more appropriate heating rate, thereby being able to better take into account the structural stability of multi-walled carbon nanotubes at high temperature and the impurity removal effect.

[0013] In some optional embodiments, the step of mixing the heat-treated multi-walled carbon nanotubes, the sizing agent resin matrix and the surfactant solution includes: first mixing the heat-treated multi-walled carbon nanotubes and the surfactant solution for a first time, wherein the first mixing step is carried out in sequence under conditions of ultrasound and mechanical stirring to obtain a dispersion; and then mixing the dispersion and the sizing agent resin matrix for a second time.

[0014] In the above technical solution, in the step of mixing the multi-walled carbon nanotubes, the sizing agent resin matrix and the surfactant solution, a step-by-step mixing method is adopted, which can make the multi-walled carbon nanotubes in the prepared carbon fiber sizing agent more evenly distributed.

[0015] In some optional embodiments, in the first mixing step, the ultrasonic power is 200-600 W, and the ultrasonic treatment time is 30-60 min.

[0016] In the above technical solution, limiting the ultrasonic power and treatment time to the above ranges respectively helps to better disperse the multi-walled carbon nanotubes in the surfactant solution.

[0017] In some optional embodiments, in the first mixing step, the rotation speed of the mechanical stirring is 500 to 1500 rpm, and the treatment time of the mechanical stirring is 2 to 4 hours.

[0018] In the above technical solution, limiting the rotation speed of the mechanical stirring and the processing time to the above ranges respectively helps to better disperse the multi-walled carbon nanotubes in the surfactant solution.

[0019] In some optional embodiments, in the step of mixing the heat-treated multi-walled carbon nanotubes, the sizing agent resin matrix, and the surfactant solution:

[0020] Calculated by weight, the added amount of multi-walled carbon nanotubes is 0.1 to 5 parts, the added amount of sizing agent resin matrix is 10 to 40 parts, and the added amount of surfactant solution is 50.5 to 100 parts.

[0021] In the above technical solution, the multi-walled carbon nanotubes, the sizing agent resin matrix and the surfactant solution are mixed according to the above mass fractions, which can take into account both the dispersion effect of each component and the modification effect on the carbon fibers.

[0022] In some optional embodiments, the surfactant solution comprises: 0.5 to 10 parts of a surfactant and 50 to 90 parts of a solvent.

[0023] In the above technical solution, the surfactant and solvent in the surface modifier solution are mixed according to the above mass fractions, so that the surfactant solution has a relatively suitable mass proportion of surfactant, which helps to better disperse the various components.

[0024] In some optional embodiments, the preparation method satisfies at least one of the following conditions A to C:

[0025] The sizing agent resin matrix A is selected from at least one of epoxy resin and polyurethane.

[0026] The surfactant B is selected from at least one of sodium dodecylbenzenesulfonate and Tween-80.

[0027] Solvent C is selected from at least one of deionized water and ethanol.

[0028] In the above technical solution, the types of the sizing agent matrix, surfactant and solvent are respectively limited to the above ranges so that each component can be well dispersed.

[0029] In a second aspect, an embodiment of the present application provides a carbon fiber, comprising a carbon fiber matrix and a modified coating located on the surface of the carbon fiber matrix, wherein the modified coating is formed by curing after coating with the carbon fiber sizing agent provided in the embodiment of the first aspect.

[0030] In the above technical solution, the surface of the carbon fiber has a modified coating formed by curing after applying the carbon fiber sizing agent provided in the first aspect embodiment. Since the multi-walled carbon nanotubes in the modified coating are evenly distributed on the surface of the carbon fiber, when the corresponding carbon fiber is combined with the resin matrix, the mechanical properties, electrical properties and thermal properties of the carbon fiber resin composite material can be improved, and the interface bonding strength between the carbon fiber and the resin matrix can also be relatively excellent. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following is a brief introduction to the drawings required for use in the embodiments. It should be understood that the following drawings only show certain embodiments of the present application and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without creative work.

[0032] Figure 1 A process flow chart of a method for preparing a carbon fiber sizing agent containing multi-walled carbon nanotubes provided in an embodiment of the present application;

[0033] Figure 2 This is a distribution diagram of multi-walled carbon nanotubes on the carbon fiber surface in Example 1 of the present application;

[0034] Figure 3 This is a distribution diagram of multi-walled carbon nanotubes on the carbon fiber surface in Example 2 of the present application;

[0035] Figure 4 This is a distribution diagram of multi-walled carbon nanotubes on the carbon fiber surface in Comparative Example 1 of this application;

[0036] Figure 5 This is a distribution diagram of multi-walled carbon nanotubes on the carbon fiber surface in Comparative Example 3 of this application. DETAILED DESCRIPTION

[0037] To make the purpose, technical solutions and advantages of the examples of the present application clearer, the technical solutions in the examples of the present application will be described clearly and completely below. Where specific conditions are not specified in the examples, conventional conditions or conditions recommended by the manufacturer are used. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0038] It should be noted that “and / or” in this application, such as “Feature 1 and / or Feature 2”, refers to three situations: “Feature 1” alone, “Feature 2” alone, or “Feature 1” plus “Feature 2”.

[0039] In addition, in the description of this application, unless otherwise specified, the meaning of "multiple" in "one or more" refers to two or more; the range of "value a to value b" includes the two end values "a" and "b", and the "unit of measurement" in "value a to value b+unit of measurement" represents the "unit of measurement" of both "value a" and "value b".

[0040] The current state of the art believes that the primary reason multi-walled carbon nanotubes (MWCNTs) tend to agglomerate in carbon fiber sizing agents is due to their high surface area and the strong van der Waals forces between them. A common approach to improve this is to sequentially employ ultrasound and mechanical stirring in a surfactant solution to aid dispersion. However, actual results demonstrate that even this method of dispersion struggles to achieve uniform dispersion of the MWCNTs.

[0041] After research, the inventors found that there are some impurities in multi-walled carbon nanotubes, including but not limited to metal catalysts, moisture, and incompletely converted single-walled components introduced during the preparation process of multi-walled carbon nanotubes. The presence of these impurities is also one of the reasons why multi-walled carbon nanotubes are easily agglomerated in carbon fiber sizing agents.

[0042] Based on this, the inventors further heat-treated the multi-walled carbon nanotubes before the mixing treatment on the basis of the existing mixing treatment, and found that this could effectively improve the problem of multi-walled carbon nanotubes being easily agglomerated due to the presence of impurities; at the same time, the subsequent mixing treatment was carried out in the form of ultrasound and mechanical stirring in a surfactant solution, and it was found that a carbon fiber sizing agent with more uniform dispersion of multi-walled carbon nanotubes could be prepared.

[0043] The preparation method of the carbon fiber sizing agent containing multi-walled carbon nanotubes and the carbon fiber according to the embodiments of the present application are described in detail below.

[0044] In a first aspect, the embodiment of the present application provides a method for preparing a carbon fiber sizing agent containing multi-walled carbon nanotubes, comprising the following steps: placing the multi-walled carbon nanotubes in an inert atmosphere for heat treatment, wherein the heat treatment temperature is 2000-3000°C (for example, but not limited to, the treatment temperature is any one of 2000°C, 2100°C, 2200°C, 2300°C, 2400°C, 2500°C, 2600°C, 2700°C, 2800°C, 2900°C and 3000°C or any two thereof). ), the treatment time is 1 to 6 hours (for example, but not limited to, the treatment time is any one of 1 hour, 2 hours, 3 hours, 4 hours, 5 hours and 6 hours, or a range of values between any two of them); the multi-walled carbon nanotubes after heat treatment, the sizing agent resin matrix and the surfactant solution are mixed, wherein the mixing steps are sequentially carried out under the conditions of ultrasound and mechanical stirring (i.e., ultrasound is first used for mixing, and then mechanical stirring is used for mixing), to obtain a carbon fiber sizing agent containing multi-walled carbon nanotubes.

[0045] In the present application, before multi-walled carbon nanotubes, sizing agent resin matrix and surfactant solution are mixed, multi-walled carbon nanotubes are first heat-treated in an inert atmosphere at 2000-3000 ° C for 1-6 hours. On the one hand, high temperature treatment can remove impurities such as metal catalysts and moisture remaining in multi-walled carbon nanotubes, thereby improving the purity of multi-walled carbon nanotubes. On the other hand, high temperature treatment can deeply repair lattice defects (such as defects such as five-membered ring or seven-membered ring distortion) in multi-walled carbon nanotubes, thereby promoting multi-layer tube wall reconstruction and inducing single-layer tube wall to form a multi-layer structure by carbon atom rearrangement (even if the single-wall structure remaining in the multi-walled carbon nanotubes is also converted into a multi-wall structure, which is equivalent to improving the purity of multi-walled carbon nanotubes). Through the combined effect of the two aspects, the purity of multi-walled carbon nanotubes can be improved, thereby effectively improving the problem that multi-walled carbon nanotubes are easily agglomerated due to the presence of impurities. At the same time, subsequent mixing is carried out in the surfactant solution in the form of ultrasound combined with mechanical stirring, so that a carbon fiber sizing agent with a relatively uniform dispersion of multi-walled carbon nanotubes can be finally prepared.

[0046] It should be noted that the type of inert atmosphere is not limited, and for example, it can be at least one of nitrogen and argon.

[0047] As an example, the temperature of the heat treatment is 2550-3000°C; the heat treatment step is carried out in a graphite furnace, the real-time temperature of the graphite furnace is T, and during the heating process, when T≤1500°C, the heating rate is C1, when 1500°C<T≤2500°C, the heating rate is C2, and when 2500°C<T≤3000°C, the heating rate is C3, wherein C1>C2>C3.

[0048] In this embodiment, when the temperature range of the heat treatment is within the range of 2550-3000°C, the heating rate is set according to different temperature ranges. Specifically, the higher the temperature, the smaller the heating rate. This helps to better balance the structural stability of the multi-walled carbon nanotubes at high temperatures and the impurity removal effect.

[0049] As an example, among C1, C2 and C3, the difference in heating rate between any two adjacent ones is 5-6°C / min, for example, but not limited to, the difference is any point value of 56°C / min, 5.1°C / min, 5.2°C / min, 5.3°C / min, 5.4°C / min, 5.5°C / min, 5.6°C / min, 5.7°C / min, 5.8°C / min, 5.9°C / min and 6°C / min, or a range value between any two of them; and C1 is 15-18°C / min, for example, but not limited to, C1 is any point value of 15°C / min, 16°C / min, 17°C / min and 18°C / min, or a range value between any two of them.

[0050] In this embodiment, the difference in the heating rate between any two adjacent ones of C1, C2 and C3 is limited to the above range, and C1 is limited to the above range, so that each stage of heating has a more appropriate heating rate, thereby being able to better take into account the structural stability of multi-walled carbon nanotubes at high temperature and the impurity removal effect.

[0051] In other possible implementations, the same heating rate may be used in all heating stages.

[0052] As an example, the step of mixing the heat-treated multi-walled carbon nanotubes, the sizing agent resin matrix and the surfactant solution includes: first mixing the heat-treated multi-walled carbon nanotubes and the surfactant solution for a first time, wherein the first mixing step is carried out in sequence under ultrasonic and mechanical stirring conditions to obtain a dispersion; and then mixing the dispersion and the sizing agent resin matrix for a second time.

[0053] In this embodiment, in the step of mixing the multi-walled carbon nanotubes, the sizing agent resin matrix and the surfactant solution, a step-by-step mixing method is adopted, which can make the multi-walled carbon nanotubes in the prepared carbon fiber sizing agent more evenly distributed.

[0054] In other possible implementations, a one-step mixing process may also be adopted.

[0055] As an example, in the first mixing treatment step, the ultrasonic power is 200-600 W, for example but not limited to the ultrasonic power being any one of 200 W, 300 W, 400 W, 500 W and 600 W or a range between any two of them; the ultrasonic treatment time is 30-60 min, for example but not limited to the time being any one of 30 min, 40 min, 50 min and 60 min or a range between any two of them.

[0056] In this embodiment, limiting the ultrasonic power and treatment time to the above ranges respectively helps to better disperse the multi-walled carbon nanotubes in the surfactant solution.

[0057] As an example, in the first mixing treatment step, the mechanical stirring speed is 500-1500 rpm, for example but not limited to the stirring speed of any one of 500 rpm, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm or a range between any two of them; the mechanical stirring treatment time is 2-4 h, for example but not limited to the treatment time of any one of 2 h, 2.5 h, 3 h, 3.5 h and 4 h or a range between any two of them.

[0058] In this embodiment, limiting the rotation speed of the mechanical stirring and the processing time to the above ranges respectively helps to better disperse the multi-walled carbon nanotubes in the surfactant solution.

[0059] It should be noted that the second mixing step can be performed by mechanical stirring only (since the multi-walled carbon nanotubes are already uniformly dispersed, the second mixing step does not require ultrasonication), or can be performed with reference to the first mixing step.

[0060] As an example, in the step of mixing the heat-treated multi-walled carbon nanotubes, the sizing agent resin matrix and the surfactant solution: in terms of weight, the amount of multi-walled carbon nanotubes added is 0.1 to 5 parts, the amount of sizing agent resin matrix added is 10 to 40 parts, and the amount of surfactant solution added is 50.5 to 100 parts.

[0061] In this embodiment, the multi-walled carbon nanotubes, the sizing agent resin matrix and the surfactant solution are mixed according to the above-mentioned mass fractions, which can take into account both the dispersion effect of each component and the modification effect on the carbon fibers.

[0062] As an example, the surfactant solution includes 0.5 to 10 parts of a surfactant and 50 to 90 parts of a solvent.

[0063] In this embodiment, the surfactant and the solvent in the surface modifier solution are mixed according to the above-mentioned mass fractions, so that the surfactant solution has a relatively suitable mass fraction of the surfactant, thereby facilitating better dispersion of the various components.

[0064] As an example, the preparation method satisfies at least one of the following conditions A to C:

[0065] The sizing agent resin matrix A is selected from at least one of epoxy resin and polyurethane.

[0066] The surfactant B is selected from at least one of sodium dodecylbenzenesulfonate and Tween-80.

[0067] Solvent C is selected from at least one of deionized water and ethanol.

[0068] In this embodiment, the types of the sizing agent base, the surfactant, and the solvent are respectively limited to the above ranges so that each component can be well dispersed.

[0069] It should be noted that, in the preparation process of the carbon fiber sizing agent containing multi-walled carbon nanotubes, any process or step not specifically described or limited can be arranged according to conventional selection in the art.

[0070] As an example, after the step of mixing the dispersion liquid and the sizing agent resin matrix for the second time is completed, the method further includes a step of filtering the mixed system using a 0.4 μm microporous filter membrane.

[0071] As an example, the process flow chart of the preparation method of the carbon fiber sizing agent containing multi-walled carbon nanotubes is shown in FIG. Figure 1 .

[0072] In a second aspect, an embodiment of the present application provides a carbon fiber, comprising a carbon fiber matrix and a modified coating located on the surface of the carbon fiber matrix, wherein the modified coating is formed by curing after coating with the carbon fiber sizing agent provided in the embodiment of the first aspect.

[0073] In the present application, the surface of the carbon fiber has a modified coating formed by curing after applying the carbon fiber sizing agent provided in the first aspect embodiment. Since the multi-walled carbon nanotubes in the modified coating are evenly distributed on the surface of the carbon fiber, when the corresponding carbon fiber is combined with the resin matrix, the mechanical properties, electrical properties and thermal properties of the carbon fiber resin composite material can be improved, and the interface bonding strength between the carbon fiber and the resin matrix can also be relatively excellent.

[0074] It should be noted that the preparation process of carbon fiber can be carried out according to conventional processes in the art and will not be described in detail in this application.

[0075] The features and performance of the present application are further described in detail below with reference to the embodiments.

[0076] Example 1

[0077] The present invention provides a method for preparing carbon fiber, comprising the following steps:

[0078] S1 Preparation of carbon fiber sizing agent containing multi-walled carbon nanotubes:

[0079] The multi-walled carbon nanotubes were placed in a graphite furnace with a nitrogen atmosphere and heat treated at 2400°C for 4 hours, wherein the heating program was: room temperature to 1500°C at 15°C / min, and 1500°C to 2400°C at 10°C / min.

[0080] 0.5 parts of heat-treated multi-walled carbon nanotubes were added to 72 parts of a surface modifier solvent (prepared by stirring 2 parts of sodium dodecylbenzenesulfonate in 70 parts of deionized water), and then ultrasonically dispersed at an ultrasonic power of 300 W for 0.75 h, and then mechanically stirred and dispersed at a stirring speed of 800 rpm for 3 h to obtain a dispersion.

[0081] 72.5 parts of the above dispersion and 27.5 parts of epoxy resin (sizing agent resin matrix) were mechanically stirred and dispersed at a stirring speed of 800 rpm for 3 hours; then the mixed system was filtered using a 0.4 μm microporous filter membrane, and the filtrate was collected to obtain a carbon fiber sizing agent containing multi-walled carbon nanotubes.

[0082] Preparation of S2 carbon fiber

[0083] The sizing agent in step S1 is applied to the surface of the carbon fiber substrate (polyacrylonitrile carbon fiber substrate), and then dried at 80° C. for 1 hour to obtain a carbon fiber with a modified coating.

[0084] Example 2

[0085] The present invention provides a method for preparing carbon fiber, comprising the following steps:

[0086] S1 Preparation of carbon fiber sizing agent containing multi-walled carbon nanotubes:

[0087] The multi-walled carbon nanotubes were placed in a graphite furnace with a nitrogen atmosphere and heat treated at 2800°C for 2 hours, wherein the heating program was: room temperature to 1500°C at 15°C / min, 1500°C to 2500°C at 10°C / min, and 2500°C to 2800°C at 5°C / min.

[0088] One part of heat-treated multi-walled carbon nanotubes was added to 63 parts of a surface modifier solvent (obtained by adding 3 parts of Tween-80 to 60 parts of ethanol and stirring), and then ultrasonically dispersed at an ultrasonic power of 400 W for 50 minutes, and then mechanically stirred and dispersed at a stirring speed of 1000 rpm for 2.5 hours to obtain a dispersion.

[0089] 64 parts of the above dispersion and 36 parts of polyurethane (sizing agent resin matrix) were mechanically stirred and dispersed at a stirring speed of 800 rpm for 3 hours; then the mixed system was filtered using a 0.4 μm microporous filter membrane, and the filtrate was collected to obtain a carbon fiber sizing agent containing multi-walled carbon nanotubes.

[0090] Preparation of S2 carbon fiber

[0091] The sizing agent in step S1 is applied to the surface of the carbon fiber substrate (polyacrylonitrile carbon fiber substrate), and then dried at 80° C. for 1 hour to obtain a carbon fiber with a modified coating.

[0092] Comparative Example 1

[0093] The comparative example of the present application provides a method for preparing carbon fiber, which differs from Example 1 only in that no heat treatment is performed in step S1.

[0094] Comparative Example 2

[0095] The comparative example of the present application provides a method for preparing carbon fiber, which differs from Example 1 only in that: in step S1, the heat treatment temperature is 1500°C.

[0096] Comparative Example 3

[0097] The comparative example of the present application provides a method for preparing carbon fiber, which differs from Example 1 only in that: in step S1, 0.5 parts of heat-treated multi-walled carbon nanotubes are added to 72 parts of surface modifier solvent (obtained by adding 2 parts of sodium dodecylbenzenesulfonate to 70 parts of deionized water and stirring), and then mechanically stirred and dispersed at a stirring speed of 800 rpm for 3.75 hours to obtain a dispersion.

[0098] Test example

[0099] (1) Distribution test of multi-walled carbon nanotubes on carbon fiber surface

[0100] Test method: The carbon fibers prepared in Examples 1-2 and Comparative Examples 1 and 3 were used as samples, and then a scanning electron microscope was used to observe the distribution of multi-walled carbon nanotubes on the carbon fiber surface of each sample.

[0101] See Figures 2 to 5 It can be seen that Examples 1 and 2 are prepared according to the preparation process provided in the examples of the present application, and the multi-walled carbon nanotubes on the surface of the carbon fiber are relatively dispersed and distributed more evenly; while Comparative Examples 1 and Comparative Example 3 are not prepared according to the preparation process provided in the examples of the present application, and the multi-walled carbon nanotubes on the surface of the carbon fiber are distributed more concentratedly and severely agglomerated.

[0102] (2) Interface bonding strength test of carbon fiber resin composite materials

[0103] Test method: The carbon fibers prepared in Examples 1 to 2 and Comparative Examples 1 to 3 were used as samples, and then each sample was mixed with epoxy resin (E-31) in a mass ratio of 3:2. The carbon fiber resin composite materials were prepared by compression molding technology (temperature control was: heat preservation at 85°C for 2h, heat preservation at 130°C for 2h, and heat preservation at 180°C for 2h). The interlaminar shear strength between the carbon fiber and the resin matrix in each composite material was tested, and the results were statistically reported in Table 1.

[0104] Table 1

[0105] sample Interlaminar shear strength (MPa) Example 1 80 Example 2 79 Comparative Example 1 73 Comparative Example 2 69 Comparative Example 3 72

[0106] Referring to Table 1, it can be seen from the test results of Examples 1 to 2 and Comparative Examples 1 to 3 that the carbon fibers are prepared according to the preparation process provided in the examples of the present application, and the corresponding carbon fibers are compounded with resin materials to form carbon fiber resin composite materials. The carbon fibers and resins in the composite materials have relatively excellent interface bonding strength. Figures 2 to 5 The distribution results of medium-walled carbon nanotubes on the carbon fiber surface are consistent.

[0107] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

Claims

1. A method for preparing a carbon fiber sizing agent containing multi-walled carbon nanotubes, characterized in that: The following steps are involved: The multi-walled carbon nanotubes are placed in an inert atmosphere for heat treatment, wherein the heat treatment temperature is 2000-3000° C. and the treatment time is 1-6 hours; The heat-treated multi-walled carbon nanotubes, sizing agent resin matrix and surfactant solution are mixed, wherein the mixing step is carried out in sequence under ultrasonic and mechanical stirring conditions to obtain a carbon fiber sizing agent containing multi-walled carbon nanotubes.

2. The preparation method according to claim 1, characterized in that The temperature of the heat treatment is 2550-3000°C; the heat treatment step is carried out in a graphite furnace, the real-time temperature of the graphite furnace is T, and during the heating process, when T≤1500°C, the heating rate is C1, when 1500°C<T≤2500°C, the heating rate is C2, and when 2500°C<T≤3000°C, the heating rate is C3, wherein C1>C2>C3.

3. The preparation method according to claim 2, characterized in that Among C1, C2 and C3, the difference in heating rate between any two adjacent ones is 5-6°C / min; Optionally, C1 is 15-18°C / min.

4. The preparation method according to any one of claims 1 to 3, characterized in that The step of mixing the heat-treated multi-walled carbon nanotubes, the sizing agent resin matrix and the surfactant solution comprises: First, the heat-treated multi-walled carbon nanotubes and the surfactant solution are mixed for the first time, wherein the first mixing step is sequentially performed under ultrasonic and mechanical stirring conditions to obtain a dispersion; Then, the dispersion and the sizing agent resin matrix are mixed for the second time.

5. The preparation method according to claim 4, characterized in that In the first mixing step, the ultrasonic power is 200-600W, and the ultrasonic treatment time is 30-60 minutes.

6. The preparation method according to claim 4, characterized in that In the first mixing step, the rotation speed of the mechanical stirring is 500 to 1500 rpm, and the treatment time of the mechanical stirring is 2 to 4 hours.

7. The preparation method according to any one of claims 1 to 3, characterized in that In the step of mixing the heat-treated multi-walled carbon nanotubes, the sizing agent resin matrix and the surfactant solution: Calculated by weight, the added amount of the multi-walled carbon nanotubes is 0.1 to 5 parts, the added amount of the sizing agent resin matrix is 10 to 40 parts, and the added amount of the surfactant solution is 50.5 to 100 parts.

8. The preparation method according to claim 7, characterized in that The surfactant solution comprises: 0.5 to 10 parts of a surfactant and 50 to 90 parts of a solvent.

9. The preparation method according to claim 8, characterized in that Meet at least one of the following conditions A to C: The sizing agent resin matrix A is selected from at least one of epoxy resin and polyurethane; B. The surfactant is selected from at least one of sodium dodecylbenzenesulfonate and Tween-80: C. The solvent is selected from at least one of deionized water and ethanol.

10. A carbon fiber, characterized in that: The invention comprises a carbon fiber matrix and a modified coating located on the surface of the carbon fiber matrix, wherein the modified coating is formed by coating with the carbon fiber sizing agent according to any one of claims 1 to 9 and then curing the coating.

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