Anodic oxidation surface treatment process of carbon fiber and surface modified carbon fiber

Abstract

The embodiment of the invention provides an anodic oxidation surface treatment process for carbon fibers and surface modified carbon fibers, and belongs to the technical field of carbon fiber manufacturing. The anodic oxidation surface treatment process for the carbon fibers comprises the following steps: sequentially carrying out first-stage anodic oxidation treatment, first-stage water washing treatment, second-stage anodic oxidation treatment and second-stage water washing treatment on the carbon fibers; wherein the electrolyte in the first-stage anodic oxidation treatment is alkaline electrolyte, and the electrolyte in the second-stage anodic oxidation treatment is acidic electrolyte, or the electrolyte in the first-stage anodic oxidation treatment is acidic electrolyte, and the electrolyte in the second-stage anodic oxidation treatment is alkaline electrolyte; the interface bonding strength between the modified carbon fiber prepared by the anodic oxidation surface treatment process and a resin matrix is relatively excellent.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of carbon fiber manufacturing, in particular to an anodic oxidation surface treatment process of carbon fiber and surface modified carbon fiber. BACKGROUND

[0002] Carbon fiber is mainly composed of graphite microcrystals, and its surface has low chemical activity and poor wettability, which leads to weak physical / chemical bonding between the carbon fiber and the resin matrix material. When the carbon fiber resin composite material is subjected to external force, poor interfacial bonding can easily lead to problems such as delamination and crack propagation of the composite material, thereby greatly reducing the overall performance (such as interlaminar shear strength, impact resistance, etc.) of the composite material.

[0003] Currently, in order to improve the interfacial bonding strength between carbon fiber and resin matrix material, various surface modification methods are usually used, including but not limited to anodic oxidation treatment, liquid oxidation treatment, chemical grafting and plasma treatment, etc. Among them, anodic oxidation treatment is one of the mainstream methods for industrialization at present due to its strong controllability, high efficiency and suitability for continuous production. However, the modification effect of the current anodic oxidation surface treatment process is not good, which leads to low interfacial bonding strength between the modified carbon fiber and the resin matrix material. SUMMARY

[0004] The purpose of the present application is to provide an anodic oxidation surface treatment process of carbon fiber and surface modified carbon fiber, which has excellent interfacial bonding strength between the modified carbon fiber and the resin matrix.

[0005] The embodiments of the present application are implemented as follows: In a first aspect, the embodiments of the present application provide an anodic oxidation surface treatment process of carbon fiber, comprising the following steps: The carbon fiber is sequentially subjected to first-stage anodic oxidation treatment, first-stage water washing treatment, second-stage anodic oxidation treatment and second-stage water washing treatment; wherein the electrolyte in the first-stage anodic oxidation treatment is an alkaline electrolyte, and the electrolyte in the second-stage anodic oxidation treatment is an acidic electrolyte, or the electrolyte in the first-stage anodic oxidation treatment is an acidic electrolyte, and the electrolyte in the second-stage anodic oxidation treatment is an alkaline electrolyte.

[0006] In the above technical solution, when the alkaline electrolyte and the acidic electrolyte are alternately used for multi-stage anodic oxidation treatment of the carbon fiber, the carbon fiber is subjected to water washing treatment after each stage of anodic oxidation treatment, which helps to reduce the residual amount of the electrolyte in the corresponding treatment stage on the surface of the carbon fiber, and can make the surface modified carbon fiber prepared by using the multi-stage anodic oxidation surface treatment process have excellent interfacial bonding strength with the resin matrix.

[0007] In some optional embodiments, the electrolyte in the first-stage anodization treatment is an alkaline electrolyte, and the electrolyte in the second-stage anodization treatment is an acid electrolyte.

[0008] In the technical solution, the strong alkali containing metal ions is used as the electrolyte in the first-stage anodization treatment, and the acid electrolyte is used as the electrolyte in the first-stage anodization treatment. After each anodization treatment stage, water washing treatment is provided. The above arrangement can make the metal ions be washed more times by water, thereby effectively reducing the residual amount of metal ions on the surface of the carbon fiber, so that the carbon fiber resin composite prepared subsequently has the advantages of being not easy to bubble, strong toughness, and not easy to break, etc. in the application process. In addition, compared with using the acid electrolyte as the electrolyte in the first-stage anodization treatment and using the strong alkali containing metal ions as the electrolyte in the second-stage anodization treatment (the alkaline electrolyte is easy to cause the active groups already loaded on the surface of the carbon fiber to fall off synchronously in the process of etching the surface of the carbon fiber), the amount of active groups (such as carboxyl groups) loaded on the surface of the carbon fiber can be more, thereby making the corresponding modified carbon fiber and the resin matrix have more excellent interfacial bonding strength.

[0009] In some optional embodiments, the alkaline electrolyte is at least one selected from sodium hydroxide, potassium hydroxide, barium hydroxide, and calcium hydroxide.

[0010] In the technical solution, the carbon fiber is subjected to anodization treatment by using the above-mentioned alkaline electrolyte, which can effectively increase the surface roughness of the carbon fiber and load an appropriate amount of hydroxyl groups on the surface of the carbon fiber, thereby helping to improve the interfacial bonding strength between the modified carbon fiber and the resin matrix.

[0011] In some optional embodiments, in the step of the first-stage anodization treatment, at least one of the following conditions is met: A. The mass fraction of the alkaline electrolyte in the electrolyte is 0.5-2%.

[0012] B. The treatment electric quantity is 60-100 C / g.

[0013] C. The treatment time is 5-30 s.

[0014] In the technical solution, in the step of the first-stage anodization treatment, the mass fraction of the alkaline electrolyte, the treatment electric quantity, and the treatment time are respectively limited in the above-mentioned appropriate ranges, which can make the carbon fiber maintain excellent strength and toughness while achieving good modification effect.

[0015] In some optional embodiments, the acidic electrolyte is selected from at least one of sulfuric acid, nitric acid, oxalic acid, carbonic acid and citric acid.

[0016] In the technical solution described above, the acidic electrolyte can be used in a variety of types, and a large number of implementation schemes can be provided, thereby facilitating the popularization and application of the technical solution provided by the embodiments of the present application.

[0017] In some optional embodiments, in the step of the second-stage anodic oxidation treatment, at least one of the following conditions is met: D The mass fraction of the acidic electrolyte in the electrolyte is 2-4%.

[0018] E The processing electric quantity is 20-40 C / g.

[0019] F The processing time is 5-30 s.

[0020] In the technical solution described above, in the step of the second-stage anodic oxidation treatment, the mass fraction of the acidic electrolyte, the processing electric quantity and the processing time are respectively limited in the above-mentioned appropriate ranges, so that a better modification effect can be achieved while the carbon fiber itself maintains excellent strength and toughness.

[0021] In some optional embodiments, after the step of the second-stage water washing treatment is completed, third-stage anodic oxidation treatment and third-stage water washing treatment are sequentially performed, wherein the electrolyte in the third-stage anodic oxidation treatment is an ammonium salt.

[0022] In the technical solution described above, after the step of the second-stage water washing treatment is completed, third-stage anodic oxidation treatment and third-stage water washing treatment are sequentially performed, wherein the third-stage anodic oxidation treatment using an ammonium salt can increase the amino active group on the surface of the carbon fiber, thereby further improving the interfacial bonding strength between the modified carbon fiber and the resin matrix, and the third-stage water washing treatment can effectively remove the residual electrolyte on the surface of the carbon fiber.

[0023] In some optional embodiments, the ammonium salt is selected from at least one of ammonium bicarbonate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

[0024] In the technical solution described above, the ammonium salt can be used in a variety of types, and a large number of implementation schemes can be provided, thereby facilitating the popularization and application of the technical solution provided by the embodiments of the present application.

[0025] In some optional embodiments, the duration of the third-stage water washing treatment is not less than that of the first-stage water washing treatment, and the duration of the third-stage water washing treatment is not less than that of the second-stage water washing treatment.

[0026] In the technical solution, the third water washing treatment has a longer time than the first water washing treatment and the second water washing treatment, and can effectively reduce the electrolyte residue on the surface of the carbon fiber after the multi-stage anodic oxidation surface treatment process.

[0027] In some optional embodiments, the water washing time in the first water washing treatment or / and the second water washing treatment is 5-10 s.

[0028] In the technical solution, the water washing time in the first water washing treatment or / and the second water washing treatment is limited in the range, which can effectively remove the alkaline electrolyte and the acidic electrolyte on the surface of the carbon fiber.

[0029] In some optional embodiments, the water washing time in the third water washing treatment is 10-30 s.

[0030] In the technical solution, the water washing time in the third water washing treatment is limited in the range, which can more effectively reduce the electrolyte residue on the surface of the carbon fiber after the multi-stage anodic oxidation surface treatment process.

[0031] In some optional embodiments, the mass fraction of the ammonium salt in the electrolyte in the third anodic oxidation treatment is 0.5-2%, or / and the treatment electric quantity is 20-40 C / g.

[0032] In the technical solution, the concentration of the ammonium salt in the third anodic oxidation treatment and the treatment electric quantity are limited in the suitable ranges, which can load a suitable number of amino active groups on the surface of the carbon fiber.

[0033] In a second aspect, the embodiments of the present application provide a surface modified carbon fiber prepared by the surface treatment process provided in the first aspect.

[0034] In the technical solution, the surface modified carbon fiber is prepared by the surface treatment process provided in the first aspect, so as to have a suitable surface roughness and load a suitable number of active groups, and thus has an excellent interfacial bonding strength with the resin matrix. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. It should be understood that the following drawings only show some embodiments of the present application, and thus should not be considered as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0036] Figure 1A process flow chart of a carbon fiber anodic oxidation surface treatment process provided in the embodiments of the present application is shown in the following figure. Figure 2 A series of cross-sectional views of carbon fiber resin composite materials provided in the present application are shown in the following figures. DETAILED DESCRIPTION

[0037] In order to make the purpose, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below. Unless otherwise specified in the embodiments, the conditions are conventional or recommended by the manufacturer. Unless otherwise specified, the reagents or instruments used are conventional products that can be purchased on the market.

[0038] It should be noted that in the present application, "and / or", such as "feature 1 and / or feature 2", means "feature 1" alone, "feature 2" alone, or "feature 1" plus "feature 2".

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

[0040] In the prior art, during the modification treatment of carbon fibers by anodic oxidation treatment, it is found that the modification effect is poor (i.e., the interfacial bonding strength between the modified carbon fibers and the resin matrix is still low) when a single electrolyte is used for single-stage anodic oxidation treatment. Based on this, it is proposed to use alkaline electrolyte and acidic electrolyte alternately for multi-stage anodic oxidation treatment of carbon fibers, and then uniformly wash with water to complete the entire anodic oxidation surface treatment. The reason why the technicians perform uniform water washing treatment at the end is that the technicians believe that even if there is electrolyte residue on the surface of the carbon fibers during the anodic oxidation process of the carbon fibers using alkaline electrolyte and acidic electrolyte alternately, since the alkaline electrolyte and the acidic electrolyte will neutralize each other, it will not adversely affect the modification effect of the carbon fibers.

[0041] However, in fact, it is not like this. The inventors found that when the multi-stage anodic oxidation treatment of carbon fibers is performed by alternately using alkaline electrolyte and acidic electrolyte, and then uniformly washing with water, the interfacial bonding strength between the modified carbon fibers and the resin matrix is still poor. The inventors studied the reasons for this problem and provided a solution as follows: In a first aspect, the embodiments of the present application provide a carbon fiber anodic oxidation surface treatment process, comprising the following steps: The carbon fiber is sequentially subjected to a first-stage anodic oxidation treatment, a first-stage water washing treatment, a second-stage anodic oxidation treatment and a second-stage water washing treatment; wherein the electrolyte in the first-stage anodic oxidation treatment is an alkaline electrolyte, and the electrolyte in the second-stage anodic oxidation treatment is an acidic electrolyte, or the electrolyte in the first-stage anodic oxidation treatment is an acidic electrolyte, and the electrolyte in the second-stage anodic oxidation treatment is an alkaline electrolyte.

[0042] It should be noted that the meaning of the above "or" is: when the alkaline electrolyte and the acidic electrolyte are alternately used for multi-stage anodic oxidation treatment of the carbon fiber, the alkaline electrolyte can be used first and then the acidic electrolyte, or the acidic electrolyte can be used first and then the alkaline electrolyte, and the specific adjustment can be made according to the actual needs.

[0043] In this application, when the alkaline electrolyte and the acidic electrolyte are alternately used for multi-stage anodic oxidation treatment of the carbon fiber, the carbon fiber is subjected to water washing treatment after each stage of anodic oxidation treatment, which helps to reduce the residual amount of the electrolyte in the corresponding treatment stage on the surface of the carbon fiber, and can make the surface modified carbon fiber prepared by using the multi-stage anodic oxidation surface treatment process have a relatively excellent interfacial bonding strength with the resin matrix.

[0044] It should be noted that the type of carbon fiber is not limited, and can be adjusted as needed, and polyacrylonitrile-based carbon fiber is used as an example in the embodiments of the application.

[0045] The inventors have also found that: after the multi-stage anodic oxidation treatment of the carbon fiber using the alkaline electrolyte and the acidic electrolyte alternately, and then unified water washing, the modified carbon fiber prepared in this way has the problems of poor interfacial bonding strength with the resin matrix, and the composite material formed by the modified carbon fiber and the resin matrix is prone to bubbling and cracking during use.

[0046] Based on this, the inventors have found that in the existing multi-stage anodic oxidation process, in order to better increase the roughness of the surface of the carbon fiber to improve the interfacial bonding strength between the carbon fiber and the resin matrix, various strong alkalis containing metal ions are usually used. The metal ions are easily combined with the surface of the carbon fiber through ionic bonds, intermolecular forces and other forces, and are easily left on the surface of the carbon fiber, which further leads to the problems of bubbling and cracking of the composite material formed by the modified carbon fiber and the resin matrix during application. Therefore, in order to solve the problems of bubbling and cracking of the composite material formed by the modified carbon fiber and the resin matrix during application, the inventors further propose the following improvement scheme: As an example, the electrolyte in the first-stage anodization treatment is an alkaline electrolyte containing metal ions, and the electrolyte in the second-stage anodization treatment is an acid electrolyte.

[0047] In this embodiment, the strong alkali containing metal ions is used as the electrolyte in the first-stage anodization treatment, and the acid electrolyte is used as the electrolyte in the second-stage anodization treatment. Since water washing treatment is provided after each stage of anodization treatment, the metal ions can be washed more times, thereby effectively reducing the residual amount of metal ions on the surface of the carbon fiber, so that the carbon fiber resin composite prepared subsequently has the advantages of being less prone to bubbling, strong toughness, and less prone to breaking, etc. during application. In addition, compared with using the acid electrolyte as the electrolyte in the first-stage anodization treatment and the strong alkali containing metal ions as the electrolyte in the second-stage anodization treatment (the alkaline electrolyte is prone to causing the active groups already loaded on the surface of the carbon fiber to fall off simultaneously during etching of the surface of the carbon fiber), the amount of active groups (such as carboxyl groups) loaded on the surface of the carbon fiber can be greater, thereby enabling the corresponding modified carbon fiber to have a more excellent interfacial bonding strength with the resin matrix.

[0048] In order to better understand the principle of the entire process of first using an alkaline electrolyte for modification and then using an acid electrolyte for modification, the functions of each modification treatment are described as follows: the use of the alkaline electrolyte for anodization treatment of the carbon fiber mainly functions to etch the surface of the carbon fiber, increase the surface roughness, and load a portion of hydroxyl groups on the surface of the carbon fiber; the use of the acid electrolyte for anodization treatment of the carbon fiber mainly functions to load active groups (such as carboxyl groups) on the surface of the carbon fiber, so that the surface of the finally modified carbon fiber has a suitable roughness and loads a greater amount of active groups, thereby enabling the modified carbon fiber to have a more excellent interfacial bonding strength after being combined with the resin matrix.

[0049] It should be noted that the type of the alkaline electrolyte containing metal ions is not limited and can be selected according to conventional methods in the art.

[0050] As an example, the alkaline electrolyte is selected from at least one of sodium hydroxide, potassium hydroxide, barium hydroxide, and calcium hydroxide.

[0051] In this embodiment, the use of the alkaline electrolyte of the above type for anodization treatment of the carbon fiber can effectively increase the surface roughness of the carbon fiber and load an appropriate amount of hydroxyl groups on the surface of the carbon fiber, thereby helping to improve the interfacial bonding strength between the modified carbon fiber and the resin matrix.

[0052] As an example, in the step of the first-stage anodization treatment, at least one of the following conditions is satisfied: A The mass fraction of the alkaline electrolyte in the electrolyte is 0.5-2%, such as but not limited to any one of the point values of 0.5%, 1%, 1.5%, and 2% or a range value between any two of them.

[0053] B The treatment electric quantity is 60-100 C / g, such as but not limited to any one of the point values of 60 C / g, 70 C / g, 80 C / g, 90 C / g, and 100 C / g or a range value between any two of them.

[0054] C The treatment time is 5-30 s, such as but not limited to any one of the point values of 5 s, 10 s, 15 s, 20 s, 25 s, and 30 s or a range value between any two of them.

[0055] In this embodiment, in the step of the first-stage anodization treatment, the mass fraction of the alkaline electrolyte, the treatment electric quantity, and the treatment time are respectively limited in the above-mentioned suitable ranges, which can achieve a better modification effect while making the carbon fiber itself maintain excellent strength and toughness.

[0056] It should be noted that the type of the acidic electrolyte is not limited and can be set according to the conventional selection in the art.

[0057] As an example, the acidic electrolyte is selected from at least one of sulfuric acid, nitric acid, oxalic acid, carbonic acid, and citric acid.

[0058] In this embodiment, the acidic electrolyte can be used in a variety of types, which can provide more implementable schemes, thereby facilitating the popularization and application of the technical solutions provided by the embodiments of the present application.

[0059] As an example, in the step of the second-stage anodization treatment, at least one of the following conditions is satisfied: D The mass fraction of the acidic electrolyte in the electrolyte is 2-4%, such as but not limited to any one of the point values of 2%, 2.5%, 3%, 3.5%, and 4% or a range value between any two of them.

[0060] E The treatment electric quantity is 20-40 C / g, such as but not limited to any one of the point values of 20 C / g, 25 C / g, 30 C / g, 35 C / g, and 40 C / g or a range value between any two of them.

[0061] F The processing time is 5-30 s, for example but not limited to any one of the point values of 5 s, 10 s, 15 s, 20 s, 25 s and 30 s or a range value between any two of them.

[0062] In this embodiment, in the step of the second-stage anodic oxidation treatment, the mass fraction of the acidic electrolyte, the processing electric quantity and the processing time are respectively limited in the above-mentioned suitable ranges, so that the carbon fiber can maintain excellent strength and toughness while a better modification effect is achieved.

[0063] As an example, after the step of the second-stage water washing treatment is completed, the method further comprises sequentially performing a third-stage anodic oxidation treatment and a third-stage water washing treatment, wherein the electrolyte in the third-stage anodic oxidation treatment is an ammonium salt.

[0064] In this embodiment, after the step of the second-stage water washing treatment is completed, the method further comprises sequentially performing a third-stage anodic oxidation treatment and a third-stage water washing treatment, wherein the third-stage anodic oxidation treatment using an ammonium salt can increase the amino active group on the surface of the carbon fiber, so as to further improve the interfacial bonding strength between the modified carbon fiber and the resin matrix, and the third-stage water washing treatment can effectively remove the residual electrolyte on the surface of the carbon fiber.

[0065] It should be noted that the type of ammonium salt is not limited and can be set according to conventional selection in the art.

[0066] As an example, the ammonium salt is selected from at least one of ammonium bicarbonate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

[0067] In this embodiment, the ammonium salt can be used in a variety of types, which can provide more implementable schemes, so as to facilitate the popularization and application of the technical solutions provided by the embodiments of the present application.

[0068] As an example, the duration of the third-stage water washing treatment is not less than that of the first-stage water washing treatment, and the duration of the third-stage water washing treatment is not less than that of the second-stage water washing treatment.

[0069] In this embodiment, the duration of the third-stage water washing treatment is longer than that of the first-stage water washing treatment alone and that of the second-stage water washing treatment alone, so that after the multi-stage anodic oxidation surface treatment process is completed, the residual amount of electrolyte on the surface of the carbon fiber can be effectively reduced.

[0070] As an example, in the step of the first-stage water washing treatment or / and the second-stage water washing treatment, the water washing time is 5-10 s, for example but not limited to any one of the point values of 5 s, 6 s, 7 s, 8 s, 9 s and 10 s or a range value between any two of them.

[0071] In the embodiment, the water washing time in the first water washing process or / and the second water washing process is limited in the above range, which can effectively remove the alkaline electrolyte and the acidic electrolyte on the surface of the carbon fiber.

[0072] As an example, the water washing time in the third water washing process is 10-30 s, for example but not limited to any one of 10 s, 15 s, 20 s, 25 s and 30 s or a range value between any two of them.

[0073] In the embodiment, the water washing time in the third water washing process is limited in the above range, which can more effectively reduce the residual amount of the electrolyte on the surface of the carbon fiber after the multi-stage anodic oxidation surface treatment process.

[0074] As an example, the mass fraction of the ammonium salt in the electrolyte in the third anodic oxidation process is 0.5-2%, for example but not limited to any one of 0.5%, 1%, 1.5% and 2% or a range value between any two of them; or / and, the processing electric quantity is 20-40 C / g, for example but not limited to any one of 20 C / g, 25 C / g, 30 C / g, 35 C / g and 40 C / g or a range value between any two of them.

[0075] In the embodiment, the concentration of the ammonium salt and the processing electric quantity in the third anodic oxidation process are respectively limited in the above suitable ranges, which can load a more suitable amino active group on the surface of the carbon fiber.

[0076] It should be noted that when there is no third anodic oxidation process and no third water washing, the second water washing is the last water washing, and the time of the second water washing can be appropriately increased to ensure the water washing effect.

[0077] It should be noted that the processes or steps not specially mentioned or limited in the anodic oxidation surface treatment process can be selected according to the conventional selection in the art.

[0078] As an example, after the step of the third water washing process is completed, the carbon fiber is further subjected to a sizing, drying and winding process.

[0079] It should be noted that the subsequent sizing, drying and winding processes are all known technologies in the art, and therefore will not be introduced in the embodiment.

[0080] In order to better understand the anodic oxidation surface treatment process, the process flow chart is used for auxiliary explanation, and the specific process can be referred to in Figure 1 .

[0081] In a second aspect, the embodiments of the present application provide a surface modified carbon fiber prepared by the surface treatment process provided in the first aspect.

[0082] In the present application, the surface modified carbon fiber is prepared by the surface treatment process provided in the first aspect, so that it has a relatively appropriate surface roughness and is loaded with a relatively appropriate number of active groups, thereby making it have a relatively excellent interfacial bonding strength with the resin matrix.

[0083] The features and performances of the present application are further described in detail below in combination with embodiments.

[0084] Embodiment 1 The embodiments of the present application provide an anodic oxidation surface treatment process for carbon fiber, which comprises the following steps: S1. The polyacrylonitrile-based carbon fiber is subjected to first-stage anodic oxidation treatment by a first-stage electrolytic tank, wherein the electrolyte is 1% potassium hydroxide by mass fraction, the treatment electric quantity is 80 C / g, and the treatment time is 20 s.

[0085] S2. The above polyacrylonitrile-based carbon fiber is subjected to first-stage water washing treatment by a first-stage water washing tank, wherein the water washing time is 8 s.

[0086] S3. The above polyacrylonitrile-based carbon fiber is subjected to second-stage anodic oxidation treatment by a second-stage electrolytic tank, wherein the electrolyte is 2% sulfuric acid by mass fraction, the treatment electric quantity is 30 C / g, and the treatment time is 20 s.

[0087] S4. The above polyacrylonitrile-based carbon fiber is subjected to second-stage water washing treatment by a second-stage water washing tank, wherein the water washing time is 8 s.

[0088] S5. The above polyacrylonitrile-based carbon fiber is subjected to third-stage anodic oxidation treatment by a third-stage electrolytic tank, wherein the electrolyte is 1% ammonium bicarbonate by mass fraction, the treatment electric quantity is 30 C / g, and the treatment time is 20 s.

[0089] S6. The above polyacrylonitrile-based carbon fiber is subjected to third-stage water washing treatment by a third-stage water washing tank, wherein the water washing time is 20 s.

[0090] S7. The above polyacrylonitrile-based carbon fiber is subjected to sizing, drying and winding into a shaft in sequence to obtain a surface modified carbon fiber.

[0091] Embodiment 2 The embodiments of the present application provide an anodic oxidation surface treatment process for carbon fiber, which is only different from that of Embodiment 1 in that: S1 The polyacrylonitrile-based carbon fiber is subjected to first-stage anodic oxidation treatment by a first-stage electrolytic tank, wherein the electrolyte is 2% sulfuric acid by mass fraction, the treatment electric quantity is 30 C / g, and the treatment time is 20 s.

[0092] S2 The polyacrylonitrile-based carbon fiber is subjected to first-stage water washing treatment by a first-stage water washing tank, wherein the water washing time is 8 s.

[0093] S3 The polyacrylonitrile-based carbon fiber is subjected to second-stage anodic oxidation treatment by a second-stage electrolytic tank, wherein the electrolyte is 1% potassium hydroxide by mass fraction, the treatment electric quantity is 80 C / g, and the treatment time is 20 s.

[0094] Comparative Example 1 The comparative example of the present application provides an anodic oxidation surface treatment process for carbon fiber, comprising the following steps: S1 The polyacrylonitrile-based carbon fiber is subjected to first-stage anodic oxidation treatment by a first-stage electrolytic tank, wherein the electrolyte is 1% potassium hydroxide by mass fraction, the treatment electric quantity is 80 C / g, and the treatment time is 20 s.

[0095] S2 The polyacrylonitrile-based carbon fiber is subjected to second-stage anodic oxidation treatment by a second-stage electrolytic tank, wherein the electrolyte is 2% sulfuric acid by mass fraction, the treatment electric quantity is 30 C / g, and the treatment time is 20 s.

[0096] S3 The polyacrylonitrile-based carbon fiber is subjected to third-stage anodic oxidation treatment by a third-stage electrolytic tank, wherein the electrolyte is 1% ammonium bicarbonate by mass fraction, the treatment electric quantity is 30 C / g, and the treatment time is 20 s.

[0097] S4 The polyacrylonitrile-based carbon fiber is subjected to water washing treatment by a water washing tank, wherein the water washing time is 36 s.

[0098] S5 The polyacrylonitrile-based carbon fiber is subjected to sizing, drying, and winding into a shaft in sequence to obtain a surface-modified carbon fiber.

[0099] Comparative Example 2 The comparative example of the present application provides an anodic oxidation surface treatment process for carbon fiber, comprising the following steps: S1 The polyacrylonitrile-based carbon fiber is subjected to first-stage anodic oxidation treatment by a first-stage electrolytic tank, wherein the electrolyte is 1% potassium hydroxide by mass fraction, the treatment electric quantity is 80 C / g, and the treatment time is 20 s.

[0100] S2 The polyacrylonitrile-based carbon fiber is subjected to second-stage anodic oxidation treatment by a second-stage electrolytic tank, wherein the electrolyte is 2% sulfuric acid by mass fraction, the treatment electric quantity is 30 C / g, and the treatment time is 20 s.

[0101] S3 The polyacrylonitrile-based carbon fiber is subjected to first-stage water washing treatment through a first-stage water washing tank, wherein the water washing time is 8 s.

[0102] S4 The polyacrylonitrile-based carbon fiber is subjected to third-stage anodic oxidation treatment through a third-stage electrolytic tank, wherein the electrolyte is 1% by mass of ammonium bicarbonate, the treatment electric quantity is 30 C / g, and the treatment time is 20 s.

[0103] S5 The polyacrylonitrile-based carbon fiber is subjected to third-stage water washing treatment through a third-stage water washing tank, wherein the water washing time is 28 s.

[0104] S6 The polyacrylonitrile-based carbon fiber is subjected to sizing, drying, and winding into a shaft in sequence to obtain a surface-modified carbon fiber.

[0105] Comparative Example 3 The comparative example of the present application provides an anodic oxidation surface treatment process for carbon fiber, comprising the following steps: S1 The polyacrylonitrile-based carbon fiber is subjected to first-stage anodic oxidation treatment through a first-stage electrolytic tank, wherein the electrolyte is 1% by mass of potassium hydroxide, the treatment electric quantity is 80 C / g, and the treatment time is 20 s.

[0106] S2 The polyacrylonitrile-based carbon fiber is subjected to first-stage water washing treatment through a first-stage water washing tank, wherein the water washing time is 8 s.

[0107] S3 The polyacrylonitrile-based carbon fiber is subjected to second-stage anodic oxidation treatment through a second-stage electrolytic tank, wherein the electrolyte is 2% by mass of sulfuric acid, the treatment electric quantity is 30 C / g, and the treatment time is 20 s.

[0108] S4 The polyacrylonitrile-based carbon fiber is subjected to third-stage anodic oxidation treatment through a third-stage electrolytic tank, wherein the electrolyte is 1% by mass of ammonium bicarbonate, the treatment electric quantity is 30 C / g, and the treatment time is 20 s.

[0109] S5 The polyacrylonitrile-based carbon fiber is subjected to third-stage water washing treatment through a third-stage water washing tank, wherein the water washing time is 28 s.

[0110] S6 The polyacrylonitrile-based carbon fiber is subjected to sizing, drying, and winding into a shaft in sequence to obtain a surface-modified carbon fiber.

[0111] Comparative Example 4 The comparative example of the present application provides an anodic oxidation surface treatment process for carbon fiber, which is different from Comparative Example 1 only in that S4 the polyacrylonitrile-based carbon fiber is subjected to water washing treatment through a water washing tank, wherein the water washing time is 50 s.

[0112] In order to better understand the process differences between various embodiments and comparative examples, the relevant process parameters are summarized and described herein in combination with the table, which can be specifically referred to Table 1.

[0113] Table 1

[0114] It should be noted that “—” in Table 1 indicates that the water washing treatment of the corresponding stage is not performed.

[0115] Test Example (1) Residual amount of metal ions (K) on the surface of carbon fibers Test method: The modified carbon fibers prepared in Examples 1-2 and Comparative Examples 1-4 were used as samples, respectively, and then the content of K ions in each sample was tested by ICP method, and the test results were statistically listed in Table 2.

[0116] Among them, the steps of ICP test are as follows: according to the standard GB / T 30902-2014, first cut 8±0.08g carbon fiber, soak in 50mL concentrated nitric acid for 0.5h, then transfer to microwave digestion instrument for digestion, digestion time 1h, after complete digestion, take out the solution, test after constant volume.

[0117] Table 2

[0118] Referring to Table 2, it can be known from the test results of Examples 1 and Comparative Examples 1-3 that after the surface treatment of carbon fibers with alkaline electrolyte, immediately performing water washing treatment, and after the end of the entire anodic oxidation surface treatment process, the residual amount of metal ions on the surface of carbon fibers can be effectively reduced.

[0119] It can be known from the test results of Examples 1 and 2 that, compared with first performing acid treatment and then performing alkali treatment, first performing alkali treatment and then performing acid treatment can effectively reduce the residual amount of metal ions on the surface of carbon fibers after the end of the entire anodic oxidation surface treatment process.

[0120] It can be known from the test results of Examples 1, Comparative Example 1 and Comparative Example 4 that, compared with performing long-time water washing treatment after the end of the entire anodic oxidation surface treatment process, performing short-time water washing treatment after each stage of anodic oxidation can more effectively reduce the residual amount of metal ions on the surface of carbon fibers.

[0121] (2) Interface bonding strength test of carbon fibers and resin matrix Test method: the modified carbon fibers prepared by example 1~2 and comparative example 1~4 were taken as samples respectively, then each sample was prepared into a composite material with an epoxy resin matrix and the interfacial bonding strength of each composite material was tested, finally the test results were counted in table 3.

[0122] The test standard of the interfacial bonding strength is GB / T 1450.1-2005.

[0123] Table 3

[0124] Referring to table 3, it can be known from the test results of example 1~2 and comparative example 1~3 that water washing treatment after each anodic oxidation treatment can effectively improve the interfacial bonding strength between the modified carbon fiber and the resin matrix.

[0125] It can be known from the test results of example 1 and example 2 that, compared with acid treatment first and then alkali treatment, the former corresponding modified carbon fiber and resin matrix have more excellent interfacial bonding strength.

[0126] It can be known from the test results of comparative example 1 and comparative example 4 that only water washing treatment after the end of the anodic oxidation treatment process, even if the water washing time is increased, it is difficult to further improve the interfacial bonding strength between the modified carbon fiber and the resin matrix.

[0127] (3) cross-sectional view of carbon fiber resin composite material Test method: the modified carbon fibers prepared by example 1~2 and comparative example 1 were taken as samples respectively, then each sample was prepared into a composite material with an epoxy resin matrix and the cross-sectional view of each composite material was tested.

[0128] It can be known from Figure 2 that, compared with acid treatment first and then alkali treatment, the former corresponding modified carbon fiber and resin matrix are combined more closely, the composite material fracture surface is flat and the cracks around the carbon fiber are less, which indicates that the interfacial bonding strength between the former corresponding modified carbon fiber and resin matrix is higher and the metal ion residue is less; in addition, in comparative example 1, only water washing treatment after the end of the anodic oxidation treatment process, the cracks between the modified carbon fiber and the resin matrix are the most, and the carbon fiber pull-out phenomenon (black holes appear in comparative example 1) appears, which indicates that the interfacial bonding strength between the modified carbon fiber and the resin matrix corresponding to comparative example 1 is the lowest and the metal ion residue is the most.

[0129] The embodiments described above are only part of the embodiments of the present application, rather than all the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor are within the scope of protection of the present application.

Claims

1. A process for the anodization surface treatment of carbon fibers, characterized in that, The method comprises the following steps: The carbon fiber is sequentially subjected to a first-stage anodic oxidation treatment, a first-stage water washing treatment, a second-stage anodic oxidation treatment and a second-stage water washing treatment. The electrolyte in the first-stage anodic oxidation treatment is an alkaline electrolyte, and the electrolyte in the second-stage anodic oxidation treatment is an acidic electrolyte, or the electrolyte in the first-stage anodic oxidation treatment is an acidic electrolyte, and the electrolyte in the second-stage anodic oxidation treatment is an alkaline electrolyte.

2. The surface treatment process according to claim 1, characterized in that, The electrolyte in the first-stage anodic oxidation treatment is an alkaline electrolyte, and the electrolyte in the second-stage anodic oxidation treatment is an acidic electrolyte.

3. The surface treatment process of claim 2, wherein, The alkaline electrolyte is at least one of sodium hydroxide, potassium hydroxide, barium hydroxide and calcium hydroxide.

4. The surface treatment process of claim 2, wherein, In the first-stage anodic oxidation treatment, at least one of the following conditions is met: A. The mass fraction of the alkaline electrolyte in the electrolyte is 0.5-2%; B. The processing electric quantity is 60-100 C / g; C. The processing time is 5-30 s.

5. The surface treatment process of claim 2, wherein, The acidic electrolyte is at least one of sulfuric acid, nitric acid, oxalic acid, carbonic acid and citric acid.

6. The surface treatment process of claim 5, wherein, In the second-stage anodic oxidation treatment, at least one of the following conditions is met: D. The mass fraction of the acidic electrolyte in the electrolyte is 2-4%; E. The processing electric quantity is 20-40 C / g; F. The processing time is 5-30 s.

7. The surface treatment process according to any one of claims 1 to 6, characterized in that, After the second-stage water washing treatment, a third-stage anodic oxidation treatment and a third-stage water washing treatment are sequentially performed, wherein the electrolyte in the third-stage anodic oxidation treatment is an ammonium salt. Optionally, the ammonium salt is at least one of ammonium bicarbonate, ammonium dihydrogen phosphate and diammonium hydrogen phosphate.

8. The surface treatment process according to claim 7, characterized in that The duration of the third-stage water washing treatment is not less than that of the first-stage water washing treatment, and the duration of the third-stage water washing treatment is not less than that of the second-stage water washing treatment. Optionally, in the first-stage water washing treatment or / and the second-stage water washing treatment, the water washing time is 5-10 s. Optionally, in the third-stage water washing treatment, the water washing time is 10-30 s.

9. The surface treatment process of claim 7, wherein, In the third-stage anodic oxidation treatment, the mass fraction of the ammonium salt in the electrolyte is 0.5-2%, or / and the processing electric quantity is 20-40 C / g.

10. A surface-modified carbon fiber, characterized by, The surface treatment process is prepared by using any one of claims 1-9.

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