A carbon fiber, a composite material, and a method for surface treatment of carbon fiber

Abstract

This application relates to a carbon fiber, a composite material and a carbon fiber surface treatment method, belonging to the technical field of carbon fibers. A carbon fiber surface treatment method includes: sequentially subjecting the carbon fiber to an anodic oxidation treatment and a cleaning and drying treatment to obtain carbon fiber I; wherein, the current density of the anodic oxidation treatment is 3-5 mA / cm 2 ; immersing the carbon fiber I in an aqueous dopamine solution for reaction, and the dopamine undergoes a self-polymerization reaction during this process to coat the surface of the carbon fiber I, thereby obtaining the surface-treated carbon fiber; wherein, the mass fraction of the aqueous dopamine solution is 15-30%. Through this preparation method, after the dopamine undergoes a self-polymerization reaction on the fiber surface, rich active groups can be provided. In subsequent processes, the wetting effect of the resin on the fiber is significantly improved, thereby significantly enhancing the bonding ability between the fiber and the resin. The carbon fiber obtained by this method has a good bonding ability with the resin and a good tensile strength of the multifilament.

Description

Technical Field

[0001] This application relates to the technical field of carbon fiber, and particularly to a carbon fiber, a composite material, and a method for surface treatment of carbon fiber. Background Art

[0002] Carbon fiber is mainly composed of carbon elements and has characteristics such as high temperature resistance, anti-friction, heat conduction, and corrosion resistance. Its shape is fibrous, soft, and can be processed into various fabrics. Due to the preferential orientation of its graphite microcrystal structure along the fiber axis, it has high strength and modulus along the fiber axis direction. Carbon fiber has a small density, so its specific strength and specific modulus are high. The main use of carbon fiber is as a reinforcing material to be compounded with resins, metals, ceramics, carbon, etc. to manufacture advanced composite materials. Therefore, the bonding ability between carbon fiber and the matrix material is particularly important. Good interfacial action can give full play to the ability of carbon fiber. The carbon content of carbon fiber itself is high, generally ≥90%, and for high-modulus carbon fiber, further high-temperature graphitization can increase the carbon content to more than 99%. The higher the carbon content, the lower the surface activity of the fiber. Therefore, it is necessary to introduce active groups on the fiber surface through surface treatment.

[0003] The current mainstream solution in the market is the electrochemical anodic oxidation method, that is, letting the fiber pass through an electrolytic cell with electricity to etch the fiber surface. This method has obvious effects on ordinary carbon fiber, but high-modulus carbon fiber itself has a high carbon content. Electrochemical treatment requires a large amount of electricity to etch the surface. On the one hand, the large amount of electricity consumes a large amount of energy, and on the other hand, it causes certain damage to the fiber surface, thus sacrificing part of the fiber axial properties.

[0004] Chinese Patent Application No. 202110906559.0 discloses a method for surface treatment of pitch-based graphite carbon fiber. The pitch-based graphite carbon fiber is first infiltrated in a polydopamine solution and then subjected to anodic oxidation treatment to finally obtain a surface-treated carbon fiber product. In this method, the polydopamine solution is directly coated on the surface of the fiber, but the polydopamine in the solution is not easy to be directly coated on the fiber surface, but needs to be coated during the self-polymerization process of dopamine; moreover, after the polydopamine is coated and then subjected to electrochemical anodic oxidation treatment, the polydopamine coating layer will be damaged.

[0005] Chinese Patent Application No. 201910784000.8 discloses a processing technology of modified carbon fiber. After the carbon fiber is produced and subjected to electrochemical anodic surface treatment, the obtained fiber is put into a dopamine solution and stirred for 16 - 24 hours, and then washed and dried to obtain a modified carbon fiber product. Generally, the production line speed of carbon fiber exceeds 400 m / h. This method takes too long in the dopamine polymerization coating section and cannot be used for continuous production. Summary of the Invention

[0006] To solve the technical problems in the prior art that the bonding ability between carbon fiber and resin is poor and the strength is damaged easily after being etched by high current, one of the purposes of the embodiments of the present application is to provide a method for treating the surface of carbon fiber.

[0007] Another purpose of the embodiments of the present application is to provide a carbon fiber prepared by the above method for treating the surface of carbon fiber.

[0008] Still another purpose of the embodiments of the present application is to provide a composite material prepared by using the above carbon fiber.

[0009] To achieve the above first purpose, the technical solution adopted in the present application is as follows:

[0010] A method for treating the surface of carbon fiber includes the following steps: subjecting carbon fiber to anodic oxidation treatment and then cleaning and drying treatment in sequence to obtain carbon fiber I. Among them, the current density of the anodic oxidation treatment is 3 - 5 mA / cm 2 . Immerse carbon fiber I in an aqueous dopamine solution for reaction. During this process, dopamine undergoes self-polymerization reaction to coat on the surface of carbon fiber I, thus obtaining the surface-treated carbon fiber. The mass fraction of the aqueous dopamine solution is 15 - 30%.

[0011] Through the above preparation method, after dopamine undergoes self-polymerization reaction on the fiber surface, abundant active groups can be provided. In subsequent processes, the wetting effect of resin on the fiber is significantly improved, thereby significantly enhancing the bonding ability between the fiber and the resin; and it has the advantages of simple overall process, easy operation, energy conservation and emission reduction, etc. Among them, by first performing anodic oxidation treatment and then coating with polydopamine, not only can the polydopamine generated after the self-polymerization reaction of dopamine coat well on the fiber surface, but also the polydopamine coating layer will not be damaged; during the anodic oxidation treatment, the current density of the anodic oxidation treatment is 3 - 5 mA / cm 2 (The currently commonly used current density is all above 6 mA / cm 2 ), so this preparation method can avoid the current high-current treatment process while taking into account the fiber strength to prevent fiber damage. In addition, by controlling the mass fraction of the aqueous dopamine solution to be 15 - 30%, the dissolution efficiency of dopamine in water and the subsequent self-polymerization reaction efficiency on the fiber surface are increased, so that the generated polydopamine can coat on the fiber surface in a shorter time, improving the production efficiency and realizing continuous production.

[0012] In some embodiments of the present application, an alkaline electrolyte is used to perform anodic oxidation treatment on the carbon fiber.

[0013] In some embodiments of the present application, the alkaline electrolyte is selected from an aqueous sodium hydroxide solution or an aqueous ammonium bicarbonate solution.

[0014] In some embodiments of the present application, the electrolyte is an aqueous solution of sodium hydroxide. Sodium hydroxide is a strong electrolyte, which is cheap and easily available. Its aqueous solution has good conductivity and can effectively conduct electric current. This is very important for ion transport and reaction rate in the electrochemical process. Moreover, the aqueous solution of sodium hydroxide is alkaline and has a high pH value. This can provide an appropriate alkaline environment, which is beneficial to the anodizing treatment in the present application. Compared with the aqueous solution of ammonium bicarbonate, the aqueous solution of sodium hydroxide has a smaller odor and is more fully ionized.

[0015] In some embodiments of the present application, the concentration of the aqueous solution of sodium hydroxide is 1-3%. When the concentration of the aqueous solution of sodium hydroxide is 1-3%, the total ion content in the electrolyte is relatively high, the conductivity of the electrolyte is good, so that the degree of electrochemical oxidation is relatively high; and the corrosion of the solution within this range is small.

[0016] In some embodiments of the present application, the time of the anodizing treatment is 30-50 s. Within this range, the anodizing treatment is more sufficient, the surface activity of the fiber is high, and the binding effect between the subsequent polydopamine and the fiber can be improved; in addition, this time range is a suitable range and will not cause excessive etching on the fiber surface.

[0017] In some embodiments of the present application, the conditions of the self-polymerization reaction include: the pH is 8-9; the reaction temperature is 50-60 °C; the reaction time is 3-5 min. Within the above pH, temperature and time ranges, the coating effect of polydopamine is better.

[0018] In some embodiments of the present application, Tris buffer solution or PBS buffer solution is used to adjust the pH value of the reaction solution.

[0019] To achieve the second above-mentioned purpose, the technical solution adopted in the present application is as follows:

[0020] A carbon fiber is prepared by surface treatment using the above method. The carbon fiber has a good binding ability with the resin and a good tensile strength of the multifilament.

[0021] To achieve the third above-mentioned purpose, the technical solution adopted in the present application is as follows:

[0022] A composite material contains the above carbon fiber. Detailed implementation manners

[0023] To make the purpose, technical solution and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Those not specified in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. Those reagents or instruments not specified in the manufacturer are all conventional products that can be obtained through commercial purchase.

[0024] A method for surface treatment of carbon fiber, comprising the following steps:

[0025] (1) Anodize and then clean and dry the carbon fiber successively to obtain Carbon Fiber Ⅰ; wherein, the current density of the anodizing treatment is 3 - 5 mA / cm 2 .

[0026] During the surface treatment of carbon fiber, anodizing is a commonly used method to increase the oxygen content on the carbon fiber surface and form an oxide layer. This can improve the surface properties of carbon fiber and enhance its adhesion performance with other materials. However, an oxide layer will be formed on the carbon fiber surface after anodizing, and this oxide layer may remain some unreacted oxidants, metal ions or other impurities. These residues may have a negative impact on subsequent surface treatment steps, such as reducing the adhesion of the polydopamine coating layer or causing surface contamination. Therefore, the cleaning and drying treatment is to remove the residues and impurities generated during the anodizing process to ensure the cleanliness and purity of the carbon fiber surface. Cleaning can be carried out by using an appropriate solvent or cleaning agent, and drying is to completely remove the solvent or moisture on the surface to make the carbon fiber surface dry for the next polydopamine coating treatment.

[0027] In some embodiments, the carbon fiber is anodized using an alkaline electrolyte solution.

[0028] When anodizing the carbon fiber, the main purpose of using an alkaline electrolyte solution is to achieve a uniform oxidation reaction and promote the formation of the oxide layer. For example: 1) Uniform oxidation reaction: The alkaline electrolyte solution can provide appropriate conductivity and ion transport ability, enabling the electrolyte to be evenly distributed over the entire carbon fiber surface. This helps to ensure that the oxidation reaction proceeds uniformly over the entire surface area, avoiding local oxidation or incomplete oxidation. 2) Promote the formation of the oxide layer: Hydroxide ions (OH-) in the alkaline electrolyte solution participate in the oxidation reaction during anodizing to form the oxide layer. The OH- ions in the alkaline environment can provide the oxygen source required for the oxidation reaction, promote the formation of the oxide layer, and increase the thickness and stability of the oxide layer. 3) Adjust the reaction rate: The ion concentration and pH value in the alkaline electrolyte solution can adjust the rate of the oxidation reaction. By controlling the composition and conditions of the electrolyte solution, the desired oxidation rate and the thickness of the oxide layer can be achieved. This allows the properties and thickness of the oxide layer to be adjusted as needed. In summary, using an alkaline electrolyte solution to anodize the carbon fiber helps to achieve a uniform oxidation reaction, promote the formation of the oxide layer, and adjust the reaction rate, thereby obtaining ideal oxide layer performance and surface characteristics.

[0029] In some embodiments, the electrolyte solution is selected from an aqueous sodium hydroxide solution or an aqueous ammonium bicarbonate solution.

[0030] In some embodiments, the electrolyte is an aqueous sodium hydroxide solution. Compared with an aqueous ammonium bicarbonate solution, the aqueous sodium hydroxide solution has a smaller odor and more complete ionization.

[0031] Sodium hydroxide is a strong electrolyte, inexpensive and readily available. Its aqueous solution has good electrical conductivity and can effectively conduct current. This is very important for ion transport and reaction rate in electrochemical processes. Moreover, the aqueous sodium hydroxide solution is alkaline and has a relatively high pH value. This can provide an appropriate alkaline environment, which is beneficial to the progress of some electrochemical reactions, especially electrode reactions under alkaline conditions.

[0032] In some embodiments, the concentration of the aqueous sodium hydroxide solution is 1-3%. When the concentration of the aqueous sodium hydroxide solution is 1-3%, the total ion content in the electrolyte is relatively high, the conductivity of the electrolyte is good, so that the degree of electrochemical oxidation is relatively high; and the corrosion of the solution within this range is relatively small.

[0033] In some embodiments, the temperature of the electrolyte is 25-30 °C. Too high or too low temperature of the electrolyte will affect the ionization effect of ions in the electrolyte. The ionization effect of ions in the electrolyte is better within the range of 25-30 °C.

[0034] In some embodiments, the time for anodic oxidation treatment is 30-50 s. Within this range, the anodic oxidation treatment is more complete, the surface activity of the fiber is high, which can improve the bonding effect between the subsequent polydopamine and the fiber; in addition, this time range is a suitable range and will not cause excessive etching on the fiber surface.

[0035] In this application, the cleaning and drying treatment includes: cleaning with flowing deionized water for 40-60 s, drying at 120-135 °C, and the drying time is 40-60 s; specifically, the cleaning time, drying temperature and drying time can be selected according to actual situations, and this application does not make any limitations.

[0036] In this application, by controlling the cleaning time to be 40-60 s, the drying temperature to be 120-135 °C, and the drying time to be 40-60 s, without affecting the thermal stability of the carbon fiber, the surface smoothness and roughness of the carbon fiber can be improved, providing better surface conditions for the uniform coating of polydopamine. In addition, under these treatment conditions, the hydrophilicity of the carbon fiber surface can also be increased, improving the adhesion and consistency of the polydopamine coating.

[0037] (2) Immerse the carbon fiber Ⅰ in an aqueous dopamine solution for reaction, and dopamine undergoes a self-polymerization reaction during this process to coat the surface of the carbon fiber Ⅰ, thus obtaining the surface-treated carbon fiber; wherein, the mass fraction of the aqueous dopamine solution is 15-30%.

[0038] In some embodiments, the reaction conditions include: pH is 8 - 9; the reaction temperature is 50 - 60 °C; the reaction time is 3 - 5 min. If the pH value exceeds the range of 8 - 9, the polymerization rate of dopamine will decrease, and even the reaction will not occur. Within the above temperature and time ranges, the coating effect of polydopamine is better. If the reaction time is too short, less polydopamine is coated on the fiber surface, affecting the subsequent bonding between the fiber and the resin; if the time is too long, the thickness of the polydopamine layer on the fiber surface is relatively large, which will also affect the bonding between the fiber and the resin, thus reducing the interlaminar shear strength.

[0039] In some embodiments, Tris buffer solution or PBS buffer solution is used to adjust the pH value of the reaction solution.

[0040] Through the above preparation method, after the self - polymerization reaction of dopamine on the fiber surface, rich active groups can be provided. In the subsequent process, the infiltration effect of the resin on the fiber is significantly improved, thereby significantly enhancing the bonding ability between the fiber and the resin; and it has the advantages of simple overall process, easy operation, energy conservation and emission reduction. Among them, anodic oxidation treatment is carried out first and then polydopamine coating. In this way, not only can the polydopamine generated after the self - polymerization reaction of dopamine be well coated on the fiber surface, but also the polydopamine coating layer will not be damaged; during the anodic oxidation treatment process, the current density of the anodic oxidation treatment is 3 - 5 mA / cm 2 (The currently commonly used current density is all above 6 mA / cm 2 ), so this preparation method can avoid the current large - current treatment process while taking into account the fiber strength to prevent fiber damage. In addition, by controlling the mass fraction of the dopamine aqueous solution to be 15 - 30%, the dissolution efficiency of dopamine in water and the subsequent self - polymerization reaction efficiency on the fiber surface are increased, so that the generated polydopamine can be coated on the fiber surface in a relatively short time, improving the production efficiency.

[0041] A carbon fiber is prepared by surface treatment using the above method. The bonding ability between this carbon fiber and the resin is good, and the tensile strength of the multifilament is good.

[0042] A composite material contains the above - mentioned carbon fiber. The epoxy - based carbon fiber reinforced prepreg can be prepared by the hot - melting method using the above - mentioned carbon fiber, and then the required composite specimen can be made according to the corresponding national standard.

[0043] The features and properties of this application will be further described in detail below in conjunction with the examples.

[0044] Example 1

[0045] This example provides a carbon fiber, and the preparation method is as follows:

[0046] (1) Prepare a dopamine aqueous solution with a mass fraction of 30%;

[0047] (2) Electrochemically anodize the graphitized fiber in a 3% aqueous sodium hydroxide solution at 25 °C for 30 s, applying a current density of 3 mA / cm 2 , wash with flowing deionized water for 50 s and then dry at 125 °C for 50 s;

[0048] (3) Add the same mass of tris(hydroxymethyl)aminomethane (Tris buffer) as dopamine to the dopamine aqueous solution in step (1), then add deionized water to adjust the pH value of the mixed solution to 8.5, with the temperature of the mixed solution being 50 °C. Immerse the fiber dried in step (2) in the above-mentioned mixed solution for surface coating for 3 min, then wash with flowing deionized water for 50 s and dry at 125 °C for 50 s to obtain the carbon fiber with surface polydopamine coating treatment.

[0049] Example 2

[0050] This example provides a carbon fiber, and the preparation method is as follows:

[0051] (1) Prepare a 15% aqueous dopamine solution;

[0052] (2) Electrochemically anodize the graphitized fiber in a 3% aqueous sodium hydroxide solution at 30 °C for 40 s, applying a current density of 3 mA / cm 2 , wash with flowing deionized water for 50 s and then dry at 125 °C for 50 s;

[0053] (3) Add the same mass of tris(hydroxymethyl)aminomethane (Tris buffer) as dopamine to the dopamine aqueous solution in step (1), then add deionized water to adjust the pH value of the mixed solution to 8.5, with the temperature of the mixed solution being 50 °C. Immerse the fiber dried in step (2) in the above-mentioned mixed solution for surface coating for 5 min, then wash with flowing deionized water for 50 s and dry at 125 °C for 50 s to obtain the carbon fiber with surface polydopamine coating treatment.

[0054] Example 3

[0055] This example provides a carbon fiber, and the preparation method is as follows:

[0056] (1) Prepare a 25% aqueous dopamine solution;

[0057] (2) Electrochemically anodize the graphitized fiber in a 1% aqueous sodium hydroxide solution at 30 °C for 50 s, applying a current density of 3 mA / cm 2, after washing with flowing deionized water for 50 s, it is dried at 125 °C for 50 s;

[0058] (3) Add the same mass of tris (Tris buffer) as dopamine to the dopamine aqueous solution in step (1), then add deionized water to adjust the pH value of the mixture to 8.5, and the temperature of the mixed solution is 50 °C. Immerse the fiber dried in step (2) in the above-mentioned mixed solution for surface coating, the treatment time is 5 min, and after treatment, it is washed with flowing deionized water for 50 s and dried at 125 °C for 50 s, then the carbon fiber with surface polydopamine coating treatment is obtained.

[0059] Example 4

[0060] This example provides a kind of carbon fiber, and the preparation method is as follows:

[0061] (1) Prepare a dopamine aqueous solution with a mass fraction of 20%;

[0062] (2) Electrochemically anodize the graphitized fiber with 3% sodium hydroxide aqueous solution at 25 °C for 40 s, and apply a current density of 3 mA / cm 2 , after washing with flowing deionized water for 50 s, it is dried at 125 °C for 50 s;

[0063] (3) Add the same mass of tris (Tris buffer) as dopamine to the dopamine aqueous solution in step (1), then add deionized water to adjust the pH value of the mixture to 8.5, and the temperature of the mixed solution is 50 °C. Immerse the fiber dried in step (2) in the above-mentioned mixed solution for surface coating, the treatment time is 3 min, and after treatment, it is washed with flowing deionized water for 50 s and dried at 125 °C for 50 s, then the carbon fiber with surface polydopamine coating treatment is obtained.

[0064] Example 5

[0065] This example is basically the same as Example 4, the difference is that: the mass fraction of the dopamine aqueous solution is 10%.

[0066] Example 6

[0067] This example is basically the same as Example 4, the difference is that: the mass fraction of the dopamine aqueous solution is 40%.

[0068] Example 7

[0069] This example is basically the same as Example 4, the difference is that: the concentration of the sodium hydroxide aqueous solution is 0.5%.

[0070] Example 8

[0071] This example is basically the same as Example 4, except that the concentration of the sodium hydroxide aqueous solution is 5%.

[0072] Example 9

[0073] This example is basically the same as Example 4, except that in step (3): the dried fibers in step (2) are immersed in the aforementioned mixed solution for surface coating, and the treatment time is 1 min.

[0074] Example 10

[0075] This example is basically the same as Example 4, except that in step (3): the dried fibers in step (2) are immersed in the aforementioned mixed solution for surface coating, and the treatment time is 5 min.

[0076] Example 11

[0077] This example is basically the same as Example 4, except that in step (3): the dried fibers in step (2) are immersed in the aforementioned mixed solution for surface coating, and the treatment time is 8 min.

[0078] Example 12

[0079] This example provides a carbon fiber, and the preparation method is as follows:

[0080] (1) Prepare an aqueous dopamine solution with a mass fraction of 20%;

[0081] (2) Electrochemically anodize the graphitized fibers in a 2% sodium hydroxide aqueous solution at 25°C for 40 s, apply a current density of 6 mA / cm 2 , wash with flowing deionized water for 50 s and then dry at 125°C, and the drying time is 50 s;

[0082] (3) Add the same mass of tris(hydroxymethyl)aminomethane (Tris buffer) as dopamine to the dopamine aqueous solution in step (1), then add deionized water to adjust the pH value of the mixed solution to 8.5, and the temperature of the mixed solution is 50°C. Immerse the dried fibers in step (2) in the aforementioned mixed solution for surface coating, and the treatment time is 5 min. After treatment, wash with flowing deionized water for 50 s and dry at 125°C, and the drying time is 50 s, thus obtaining carbon fibers with surface polydopamine coating treatment.

[0083] Example 13

[0084] This example is basically the same as Example 12, except that in step (2), the applied current density is 1 mA / cm 2 .

[0085] Example 14

[0086] This example is basically the same as Example 12, with the difference that: in step (2), the applied current density is 3 mA / cm 2 .

[0087] Example 15

[0088] This example is basically the same as Example 4, with the difference that: in step (2), the anodization time is 20 s.

[0089] Example 16

[0090] This example is basically the same as Example 4, with the difference that: in step (2), the anodization time is 70 s.

[0091] Comparative Example 1

[0092] This comparative example is basically the same as Example 2, with the difference that: no further dopamine coating treatment is performed, that is, steps (1) and (3) are absent.

[0093] Comparative Example 2

[0094] This comparative example is basically the same as Example 2, with the difference that: the order of steps (2) and (3) is exchanged, that is, polydopamine coating is performed first and then anodization treatment.

[0095] This comparative example provides a carbon fiber, and the preparation method is as follows:

[0096] (1) Prepare an aqueous dopamine solution with a mass fraction of 15%;

[0097] (2) Add the same mass of tris(hydroxymethyl)aminomethane (Tris buffer) as dopamine to the dopamine aqueous solution in step (1), then add deionized water to adjust the pH value of the mixed solution to 8.5, the temperature of the mixed solution is 50 °C, immerse the fiber in the above-mentioned mixed solution for surface coating, the treatment time is 5 min, after treatment, wash with flowing deionized water for 50 s, and dry at 125 °C, the drying time is 50 s, thus obtaining a carbon fiber with surface polydopamine coating treatment.

[0098] (3) Electrochemically anodize the carbon fiber with surface dopamine coating treatment in step (2) in a 3% sodium hydroxide aqueous solution at 30 °C for 40 s, apply a current density of 3 mA / cm 2 , wash with flowing deionized water for 50 s and then dry at 125 °C, the drying time is 50 s; thus obtaining the surface-treated carbon fiber.

[0099] Test Example

[0100] The surface treated carbon fibers obtained in Examples 1-16, Comparative Example 1 and Comparative Example 2 were tested for layer shear strength according to GB / T 1458-2008, and for multifilament tensile strength according to GB / T 3362-2017. The test results are shown in Table 1.

[0101] Table 1

[0102]

[0103]

[0104] By comparing the data of Examples 4-6, it can be seen that when the mass fraction of the dopamine aqueous solution is less than 15%, the bonding ability between the fiber and the resin decreases, and the layer shear is only 51 MPa; when the mass fraction of the dopamine aqueous solution is greater than 30%, the layer shear is improved, but significantly lower than Example 4.

[0105] By comparing the data of Example 4, Example 7 and Example 8, it can be seen that when the concentration of the sodium hydroxide aqueous solution (electrolyte) is less than 1%, the anodizing treatment effect is not obvious, and the layer shear strength is only 55 MPa; when the concentration of the sodium hydroxide aqueous solution (electrolyte) is greater than 3%, the layer shear strength is high, but the tensile strength of the multifilament is slightly reduced from about 4900 MPa to 4735 MPa, and there is a certain hidden risk in the operation of high-concentration sodium hydroxide solution.

[0106] By comparing the data of Example 4 and Examples 9-11, it can be seen that when the coating treatment time is less than 3 minutes, the coating effect of polydopamine on the fiber surface is poor, and although the layer shear strength is improved compared with that of Comparative Example 1, the improvement is small; when the coating treatment time is greater than 5 minutes, the layer shear strength is reduced compared with that of Example 10, indicating that the longer the treatment time is, the better.

[0107] Comparing the data of Examples 12-14, it can be seen that when the current density is less than 3 mA / cm 2 , the layer shear strength is 58MPa. It can be seen that the etching degree of the fiber surface is limited by the small current density. Although the layer shear strength is improved, the degree is limited. When the current density is greater than 5mA / cm 2 The layer shear strength was significantly improved to 79MPa, and the high current density caused certain damage to the fiber surface, resulting in the tensile strength of the multifilament decreasing to 4459MPa.

[0108] By comparing the data of Example 4, Example 15 and Example 16, it can be seen that when the anodizing treatment time is less than 40s, the degree of anodization on the fiber surface is low, resulting in an increase in the layer shear strength of only 52MPa; when the anodizing treatment time is greater than 50s, the fiber surface is etched too much by the current, which has a certain impact on the tensile strength of the multifilament, and the strength drops to 4671MPa.

[0109] In Comparative Example 1, dopamine coating was not carried out, and its shear strength was only 45 MPa, far lower than 73 MPa in Example 2, indicating that the binding ability between the fiber surface provided in Comparative Example 1 and the resin was poor; compared with Comparative Example 1, the fibers in Example 2 were coated with dopamine, and its binding ability with the resin was significantly enhanced. In Comparative Example 2, dopamine coating was carried out first, and then anodic oxidation treatment was carried out. The current caused certain damage to the polydopamine coating layer, and the shear strength of the prepared fiber (59 MPa) was much lower than that of Example 2 (shear strength 73 MPa); the above test data show that the layer shear is improved to a certain extent but the improvement degree is limited by carrying out electrochemical anodic oxidation treatment after dopamine coating first.

[0110] The embodiments described above are some, but not all, of the embodiments of the present application. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application claimed, but merely represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the scope of protection of the present application.

Claims

1. A method for surface treatment of carbon fiber, characterized in that, It includes the following steps: S1. Anodize the carbon fiber, and the current density of the anodizing treatment is 3-5 mA / cm 2 ; S2. Clean and dry the carbon fiber processed in step S1 to obtain carbon fiber I; S3. Immerse the carbon fiber I in an aqueous dopamine solution to cause the dopamine to undergo self-polymerization reaction and coat on the surface of the carbon fiber I, thus obtaining the surface-treated carbon fiber; wherein, the mass fraction of the aqueous dopamine solution is 15-30%; the time of the self-polymerization reaction is 3-5 min; The anodic oxidation treatment of the carbon fiber is carried out using an alkaline electrolyte, the alkaline electrolyte is selected from an aqueous sodium hydroxide solution, and the concentration of the aqueous sodium hydroxide solution is 1-3%; the time of the anodic oxidation treatment is 30-50 s.

2. The method according to claim 1, wherein The conditions of the self-polymerization reaction include: pH is 8-9; the reaction temperature is 50-60 °C.

3. The method according to claim 2, characterized in that, Use Tris buffer or PBS buffer to adjust the pH value of the reaction solution.

4. A carbon fiber, characterized in that, It is prepared by carrying out surface treatment by the method according to any one of claims 1-3.

5. A composite material, characterized in that, It contains the carbon fiber according to claim 4.

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