Method and equipment for improving interface performance of high-modulus carbon fiber, surface modified carbon fiber and composite material

Abstract

The invention relates to a method and equipment for improving the interface performance of high-modulus carbon fibers, surface modified carbon fibers and a composite material, and belongs to the technical field of carbon fiber production. The method comprises the following steps: carrying out first-stage anodic oxidation treatment on high-modulus carbon fibers by adopting a strong alkaline electrolyte, wherein the elastic modulus of the high-modulus carbon fibers is 350-400Gpa; carrying out second-stage anodic oxidation treatment on the carbon fibers subjected to the first-stage anodic oxidation treatment by adopting a weakly acidic electrolyte; wherein the electric quantity applied by the first-stage anodic oxidation treatment is greater than the electric quantity applied by the second-stage anodic oxidation treatment. Aiming at the high-modulus carbon fiber, the method adopts two-step anodic oxidation treatment, and the strength of the high-modulus carbon fiber can be kept to a certain extent while the interface performance of the high-modulus carbon fiber is improved by controlling the sequence of specific electrolyte and the applied electric quantity.

Description

Technical Field

[0001] The present application relates to the technical field of carbon fiber production, and in particular to a method and equipment for improving the interface performance of high modulus carbon fiber, surface modified carbon fiber and composite material. Background Art

[0002] During the production process of polyacrylonitrile-based carbon fiber, as the carbonization temperature continues to increase, the oxygen element in the fiber is gradually removed, and the final carbon content exceeds 90%, resulting in a decrease in the surface active functional groups of the carbon fiber, showing an inert characteristic, which is not conducive to the interface bonding between the fiber and the composite material. The highest carbonization temperature of high modulus carbon fiber products is above 2000°C, and the number of surface active functional groups is further reduced, increasing the difficulty of bonding with the tree branch interface. The interlaminar shear strength of the composite material is low, which will cause the overall performance of the composite material to be reduced.

[0003] The conventional method to improve the interfacial properties of carbon fiber is usually to use an anodic oxidation method to perform one or more electrochemical surface treatments on the carbon fiber to introduce oxygen-containing active groups on the carbon fiber surface and improve the interlaminar shear strength of the composite material. When this surface treatment method is applied to high modulus carbon fiber, the total amount of surface treatment electricity is usually further increased, but the increase in surface treatment electricity will increase the degree of carbon fiber surface etching, resulting in a decrease in carbon fiber strength. Therefore, there is an urgent need to develop a method that can both improve the interfacial properties of high modulus carbon fiber and maintain the strength of the carbon fiber. Summary of the invention

[0004] To solve the above problems, the purpose of the embodiments of the present application includes providing a method and equipment for improving the interface performance of high modulus carbon fiber, surface modified carbon fiber and composite material, which can improve the interface performance of high modulus carbon fiber while maintaining the strength of high modulus carbon fiber to a certain extent.

[0005] In a first aspect, the present application provides a method for improving the interface performance of high modulus carbon fiber, comprising the following steps:

[0006] The high modulus carbon fiber is subjected to a first-stage anodizing treatment using a strong alkaline electrolyte; wherein the elastic modulus of the high modulus carbon fiber is 350 to 400 GPa;

[0007] A weakly acidic electrolyte is used to perform a second-stage anodizing treatment on the carbon fiber after the first-stage anodizing treatment;

[0008] The amount of electricity applied in the first stage anodizing treatment is greater than the amount of electricity applied in the second stage anodizing treatment.

[0009] In the above technical solution, a two-step anodizing treatment is used for high modulus carbon fiber, wherein the first-stage anodizing treatment uses a strong alkaline electrolyte and a relatively large surface treatment power to physically etch the surface of the high modulus carbon fiber to increase the surface roughness. Then, the second-stage anodizing treatment uses a weak acid electrolyte and a relatively low surface treatment power to increase the active chemical groups on the fiber surface, thereby significantly improving the interface performance of the high modulus carbon fiber without increasing the total power of the two-stage treatment, while maintaining the strength of the high modulus carbon fiber to a certain extent.

[0010] In some embodiments of the present application, the pH value of the strong alkaline electrolyte is 11-13, and the pH value of the weak acidic electrolyte is 4-6.

[0011] In some embodiments of the present application, the electrolyte in the strong alkaline electrolyte includes at least one of sodium hydroxide, potassium hydroxide or calcium hydroxide, and the electrolyte in the weak acid electrolyte includes at least one of diammonium phosphate or carbonic acid.

[0012] In some embodiments of the present application, the amount of electricity applied in the first-stage anodizing treatment is 40-60 c / g, and the amount of electricity applied in the second-stage anodizing treatment is 20-30 c / g. The time of the first-stage anodizing treatment is 10-20 s, and the treatment temperature is 20-50°C; the time of the second-stage anodizing treatment is 10-20 s, and the treatment temperature is 20-50°C.

[0013] In some embodiments of the present application, after the second-stage anodizing treatment, the method further includes: performing multi-stage water washing, sizing, drying and winding on the carbon fiber obtained after the second-stage anodizing treatment.

[0014] In some embodiments of the present application, the method for preparing high modulus carbon fiber includes:

[0015] The polyacrylonitrile fiber is subjected to a pre-oxidation treatment to obtain a pre-oxidized fiber;

[0016] The preoxidized fiber is sequentially subjected to low-temperature carbonization, high-temperature carbonization and graphitization treatment to obtain high modulus carbon fiber;

[0017] Among them, the temperature of the pre-oxidation treatment is 220°C to 260°C, the temperature of the low-temperature carbonization treatment is 400°C to 900°C, the temperature of the high-temperature carbonization treatment is 1000°C to 1500°C, and the temperature of the graphitization treatment is 1800°C to 2400°C.

[0018] In a second aspect, an embodiment of the present application provides a device used in the above-mentioned method for improving the interfacial properties of high modulus carbon fiber, comprising: a first electrolytic cell and a second electrolytic cell, wherein the first electrolytic cell contains a strong alkaline electrolyte for performing a first-stage anodizing treatment on the high modulus fiber. The second electrolytic cell contains a weak acid electrolyte for performing a second-stage anodizing treatment on the carbon fiber treated by the first electrode cell. The amount of electricity applied in the first-stage anodizing treatment is greater than the amount of electricity applied in the second-stage anodizing treatment.

[0019] In some embodiments of the present application, the above-mentioned equipment also includes: a first water washing tank, a second water washing tank, a third water washing tank and a fourth water washing tank, and the first water washing tank, the second water washing tank, the third water washing tank and the fourth water washing tank are connected in sequence and their heights increase step by step.

[0020] By setting up four washing tanks with gradually increasing heights, the electrolyte soaked in the high modulus fiber can be fully cleaned to prevent the electrolyte from remaining on the fiber surface.

[0021] In a third aspect, the present application provides a surface-modified carbon fiber. The surface-treated carbon fiber is prepared using the above method or device.

[0022] In a fourth aspect, an embodiment of the present application provides a composite material, comprising the above-mentioned surface modified carbon fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the drawings required for use in the embodiments will be briefly introduced below. 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 related drawings can be obtained based on these drawings without paying creative work.

[0024] Figure 1 A process flow chart of a method for improving the interface performance of high modulus carbon fibers provided in an embodiment of the present application.

[0025] Figure 2 A schematic diagram of the structure of a device for improving the interface performance of high modulus carbon fibers provided in an embodiment of the present application.

[0026] Figure markings: 100-anodic oxidation device; 11-first electrolytic cell; 110-first cathode plate; 112-first anode roller; 114-first guide roller; 116-second anode roller; 12-second electrode trough; 120-second cathode plate; 122-third anode roller; 124-third guide roller; 126-fourth anode roller; 200-water washing device; 21-first water washing trough; 211-first guide groove roller; 213-second guide groove roller; 22-second water washing trough; 221-third guide groove roller; 223-fourth guide groove roller; 23-third water washing trough; 231-fifth guide groove roller; 233-sixth guide groove roller; 24-fourth water washing trough; 241-seventh guide groove roller; 243-eighth guide groove roller; 245-ninth guide groove roller; A-wire running direction; C-high modulus carbon fiber. DETAILED DESCRIPTION

[0027] Figure 1 This is a process flow chart of a method for improving the interface performance of high modulus carbon fiber provided in an embodiment of the present application. Figure 1 The method for improving the interface performance of high modulus carbon fiber provided in the embodiment of the present application comprises the following steps:

[0028] S110, first-stage anodizing treatment of high modulus carbon fibers using a strong alkaline electrolyte;

[0029] The pH value of the strong alkaline electrolyte is 11-13, and the electrolyte can be at least one of sodium hydroxide, potassium hydroxide or calcium hydroxide.

[0030] The amount of electricity applied in the first-stage anodizing treatment is 40-60 c / g, the treatment time is 10-20 s, and the treatment temperature can be 20-50° C.

[0031] High modulus carbon fiber refers to carbon fiber with an elastic modulus of 350 to 400 GPa. In the embodiment of the present application, the preparation method of the high modulus carbon fiber may include the following steps:

[0032] The polyacrylonitrile fiber is subjected to a pre-oxidation treatment to obtain a pre-oxidized fiber;

[0033] High modulus carbon fibers can be obtained by subjecting the preoxidized fibers to low-temperature carbonization, high-temperature carbonization and graphitization treatments in sequence.

[0034] Optionally, the density of the polyacrylonitrile fiber is 1.18 g / cm 3 , the single fiber diameter is 8.6μm.

[0035] The temperature of the pre-oxidation treatment can be 220℃~260℃. Preferably, the starting temperature of the pre-oxidation reaction is 230℃ and the ending temperature is 255℃; the running speed of the polyacrylonitrile fiber tow is 520m / h, and the pre-oxidation residence time is 60min. In the pre-oxidation reaction, the tension applied to the tow is 18N, and the density of the obtained pre-oxidized fiber is 1.385g / cm 3 .

[0036] The low-temperature carbonization temperature range may be 400° C. to 900° C. Preferably, the pre-oxidized fiber is sequentially passed through low-temperature carbonization temperature zones of 380° C., 430° C., 460° C., 500° C., 560° C., 650° C., 750° C., and 850° C., the residence time of the fiber is 115 s, and the tension applied to the fiber is 8N.

[0037] The high temperature carbonization temperature range may be 1000° C. to 1500° C. Preferably, the low carbon fiber is sequentially passed through high temperature carbonization temperature zones of 1000° C., 1080° C., 1160° C., 1240° C., 1320° C., and 1400° C., the fiber residence time is 110 s, and the tension applied to the fiber is 50N.

[0038] The graphitization temperature range may be 1800° C. to 2400° C. Preferably, the high carbon fiber is sequentially passed through high temperature graphitization temperature zones of 1800° C., 1900° C., 2050° C., 2150° C., and 2300° C., the residence time of the fiber is 90 seconds, and the tension applied to the fiber is 55N.

[0039] S120, performing a second-stage anodizing treatment on the carbon fiber after the first-stage anodizing treatment using a weakly acidic electrolyte, wherein the amount of electricity applied in the first-stage anodizing treatment is greater than the amount of electricity applied in the second-stage anodizing treatment.

[0040] The pH value of the weak acid electrolyte may be 4-6, and the electrolyte in the weak acid electrolyte includes diammonium dihydrogen phosphate or carbonic acid.

[0041] The amount of electricity applied in the second-stage anodizing treatment is 20 to 30 c / g, the treatment time is 10 to 20 s, and the treatment temperature can be 20 to 50°C.

[0042] Since high modulus carbon fiber has few active groups on its surface, it is inert. Alkaline electrolyte can etch the surface of carbon fiber and increase the surface roughness, while acidic electrolyte mainly adds active groups on the fiber surface. If alkaline electrolyte is used in both steps of anodizing, the active oxygen-containing groups on the surface of high modulus carbon fiber cannot be effectively increased. If a weak alkaline electrolyte is used in the first stage of anodizing, it cannot effectively etch the inert fiber surface, which will further reduce the treatment effect of the acidic electrolyte in the second stage of anodizing. In addition, although strong acid electrolyte can also etch the surface of carbon fiber, for high modulus carbon fiber, a larger surface treatment power is usually required. A higher temperature will be generated during the electrochemical process with a larger power, making the strong acid electrolyte volatile, dangerous, and difficult to operate when the surface treatment power is large. Therefore, it is generally not considered for use in practical applications.

[0043] The embodiment of the present application adopts a two-step anodizing treatment, sets the electrolyte in the first-stage electrolytic cell to be strongly alkaline, and the electrolyte in the second electrolytic cell to be weakly acidic, and controls the amount of electricity applied by the first-stage anodizing treatment to be greater than the amount of electricity applied by the second-stage anodizing treatment. First, the surface of the high modulus carbon fiber is physically etched by a large amount of strong alkaline oxidation to increase the surface roughness, and then a low amount of weak acid oxidation is used to increase the active chemical groups on the surface of the carbon fiber, which can effectively improve the interface performance of the high modulus carbon fiber. At the same time, since the total amount of electricity in the two-step anodizing treatment is not increased, the strength of the carbon fiber is less affected, and the strength can be maintained without a significant decrease while improving the interface performance.

[0044] In an embodiment of the present application, the method further comprises: performing multi-stage water washing on the carbon fiber obtained after the second-stage anodizing treatment. Optionally, the water washing method may include: performing a four-stage water washing treatment on the carbon fiber obtained after the second-stage anodizing treatment. During the four-stage water washing treatment, the heights of the four water washing tanks are gradually increased.

[0045] By adopting multi-stage water washing, the residual electrolyte in the washing tank is reduced step by step, and finally the electrolyte infiltrated in the fiber is fully cleaned to prevent the electrolyte residue from affecting the performance of the carbon fiber composite.

[0046] It can be understood that after washing, the process further includes: sizing, drying and winding the surface-modified carbon fiber.

[0047] Figure 2 This is a schematic diagram of the structure of the device for improving the interface performance of high modulus carbon fiber provided in the embodiment of the present application. Figure 2The embodiment of the present application also provides a device for improving the interfacial properties of high modulus carbon fiber, including an anodizing device 100 and a water washing device 200 connected to the anodizing device 100, the anodizing device 100 includes a first electrolytic cell 11 and a second electrolytic cell 12, wherein the first electrolytic cell 11 contains a strong alkaline electrolyte, and the second electrolytic cell 12 contains a weak acidic electrolyte.

[0048] When the device is used to treat high modulus carbon fiber, the first electrolytic cell 11 is used to perform a first-stage anodizing treatment on it, and then the second electrolytic cell 12 is used to perform a second-stage anodizing treatment on it, and the amount of electricity applied by the first electrolytic cell 11 is controlled to be greater than the amount of electricity applied by the second electrolytic cell 12, and then after treatment by the water washing device 200, surface modified carbon fiber is obtained.

[0049] The first electrolytic cell 11 is provided with a first cathode plate 110 at the bottom, and along the wire running direction A, the first electrolytic cell 11 is provided with a first anode roller 112, two first guide rollers 114 and a second anode roller 116 in sequence, and the two first guide rollers 114 are immersed in a strong alkaline electrolyte. The second electrolytic cell 12 is provided with a second cathode plate 120 at the bottom, and along the wire running direction A, the second electrolytic cell 12 is provided with a third anode roller 122, two third guide rollers 124 and a fourth anode roller 126 in sequence, and the two third guide rollers 124 are immersed in a weakly acidic electrolyte. The first electrolytic cell 11 and the second electrolytic cell 12 are connected via the second anode roller 116 and the third anode roller 122.

[0050] The washing device 200 includes a first washing tank 21, a second washing tank 22, a third washing tank 23 and a fourth washing tank 24 which are connected in sequence, and the surface-treated high modulus carbon fiber C is pulled out by the fourth washing tank 24. Along the wire feeding direction A, the first washing tank 21 is provided with a first guide groove roller 211 and two second guide groove rollers 213 in sequence, the second washing tank 22 is provided with a third guide groove roller 221 and two fourth guide groove rollers 223 in sequence, the third washing tank 23 is provided with a fifth guide groove roller 231 and two sixth guide groove rollers 233 in sequence, and the fourth washing tank 24 is provided with a seventh guide groove roller 241, two eighth guide groove rollers 243 and a ninth guide groove roller 245 in sequence.

[0051] It can be understood that the two second guide groove rollers 213, the two fourth guide groove rollers 223, the two sixth guide groove rollers 233 and the two eighth guide groove rollers 243 are all immersed in the washing liquid, wherein the washing liquid can be desalted water, and the washing temperature is 20-70°C.

[0052] Preferably, the heights of the first water washing tank 21, the second water washing tank 22, the third water washing tank 23 and the fourth water washing tank 24 are gradually increased, that is, the heights of the first guide groove roller 211, the third guide groove roller 221, the fifth guide groove roller 231 and the seventh guide groove roller 241 are gradually increased. The heights of the seventh guide groove roller 241 and the ninth guide groove roller 245 are approximately equal, and the high modulus carbon fiber C is pulled out by the ninth guide groove roller 245.

[0053] The surface modified carbon fiber prepared by the method and the equipment has a tensile strength greater than 6400 MPa, a tensile modulus greater than 380 GPa, and a surface carboxyl content greater than 6%.

[0054] The carbon fiber is mixed with a matrix resin to prepare a composite material, and the interlaminar shear strength of the composite material is greater than 90 MPa and can reach up to 105 MPa. The matrix resin can be an epoxy resin.

[0055] In order to make the purpose, technical scheme and advantages of the embodiments of the present application clearer, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to the conventional conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0056] Example 1

[0057] This embodiment provides a surface-modified carbon fiber, and the preparation method thereof comprises the following steps:

[0058] (1) Density is 1.18 g / cm 3 , polyacrylonitrile fiber with a single fiber diameter of 8.6 μm was pre-oxidized to obtain pre-oxidized fiber. The starting temperature of the pre-oxidation reaction was 230°C, the ending temperature was 255°C, the running speed of the polyacrylonitrile fiber tow was 520 m / h, and the pre-oxidation residence time was 60 min. During the pre-oxidation reaction, the tension applied to the tow was 18 N, and the density of the obtained pre-oxidized fiber was 1.385 g / cm 3 .

[0059] (2) nitrogen is introduced into the low temperature furnace, and the oxygen content of the nitrogen in the low temperature furnace is less than 2 ppm. The pre-oxidized fiber in step (1) is sequentially passed through low temperature carbonization temperature zones of 380°C, 430°C, 460°C, 500°C, 560°C, 650°C, 750°C, and 850°C for low temperature carbonization treatment, the residence time of the fiber is 115 seconds, and the tension applied to the fiber is 8N.

[0060] Nitrogen is introduced into the high temperature furnace, and the oxygen content in the nitrogen in the high temperature furnace is less than 1ppm. The low carbon fiber obtained by low temperature carbonization treatment is sequentially passed through high temperature carbonization temperature zones of 1000℃, 1080℃, 1160℃, 1240℃, 1320℃, and 1400℃ for high temperature carbonization treatment, the residence time of the fiber is 110s, and the tension applied to the fiber is 50N.

[0061] Nitrogen is introduced into the graphite furnace, and the oxygen content in the nitrogen in the graphite furnace is less than 1ppm. The high-carbon fiber obtained by high-temperature carbonization treatment is sequentially graphitized in high-temperature graphitization temperature zones of 1800℃, 1900℃, 2050℃, 2150℃, and 2300℃. The residence time of the fiber is 90s, and the tension applied to the fiber is 55N, so as to obtain high modulus carbon fiber.

[0062] (3) The high modulus fiber after the graphite furnace is subjected to electrochemical surface treatment. The high modulus fiber is pulled by a guide roller and passed through a first electrolytic tank for a first-stage anodizing treatment, and then passed through a second electrolytic tank for a second-stage anodizing treatment. The first electrolytic tank contains a sodium hydroxide electrolyte with a pH of 12, and the electrochemical treatment amount applied in the first-stage anodizing treatment is 50c / g; the second electrolytic tank contains a diammonium phosphate electrolyte with a pH of 5, and the electrochemical treatment amount applied in the second-stage anodizing treatment is 25c / g.

[0063] (4) The high modulus fiber after the electrochemical surface treatment is pulled into a water washing device for four-stage water washing, and then sizing, drying and winding to obtain surface modified carbon fiber.

[0064] Example 2

[0065] This comparative example provides a surface-modified carbon fiber, and its preparation method is substantially the same as the preparation method in Example 1, except that:

[0066] The amount of electrochemical treatment applied in the first anodizing treatment is 60 c / g, and the amount of electrochemical treatment applied in the second anodizing treatment is 30 c / g.

[0067] Comparative Example 1

[0068] This comparative example provides a surface-modified carbon fiber, and its preparation method is substantially the same as the preparation method in Example 1, except that:

[0069] In step (3), the amount of electrochemical treatment power applied in the first stage anodizing treatment is 25 / g, and the amount of electrochemical treatment power applied in the second stage anodizing treatment is 25c / g.

[0070] Comparative Example 2

[0071] This comparative example provides a surface-modified carbon fiber, and its preparation method is substantially the same as the preparation method in Example 1, except that:

[0072] In step (3), the electrochemical treatment amount of electricity applied in the first stage anodizing treatment is 100 c / g, and the electrochemical treatment amount of electricity applied in the second stage anodizing treatment is 100 c / g.

[0073] Comparative Example 3

[0074] This comparative example provides a surface-modified carbon fiber, and its preparation method is substantially the same as the preparation method in Example 1, except that:

[0075] The electrolyte used in the second stage anodizing treatment in step (3) is a strong alkaline sodium hydroxide electrolyte with a pH of 12.

[0076] Comparative Example 4

[0077] This comparative example provides a surface-modified carbon fiber, and its preparation method is substantially the same as the preparation method in Example 1, except that:

[0078] In step (3), the electrolyte used in the first stage anodizing treatment is a strong alkaline sodium hydroxide electrolyte with a pH of 12, and the applied electrochemical treatment power is 100 c / g; the electrolyte used in the second stage anodizing treatment is a strong alkaline sodium hydroxide electrolyte with a pH of 12, and the applied electrochemical treatment power is 100 c / g.

[0079] Comparative Example 5

[0080] This comparative example provides a surface-modified carbon fiber, and its preparation method is substantially the same as the preparation method in Example 1, except that:

[0081] The electrolyte used in the first stage anodizing treatment in step (3) is a weak acid ammonium dihydrogen phosphate electrolyte with a pH of 5; the electrolyte used in the second stage anodizing treatment is a strong base sodium hydroxide electrolyte with a pH of 12.

[0082] Comparative Example 6

[0083] This comparative example provides a surface-modified carbon fiber, and its preparation method is substantially the same as the preparation method in Example 1, except that:

[0084] The electrolyte used in the first stage anodizing treatment in step (3) is a weak acid ammonium dihydrogen phosphate electrolyte with a pH of 5.

[0085] Comparative Example 7

[0086] This comparative example provides a surface-modified carbon fiber, and its preparation method is substantially the same as the preparation method in Example 1, except that:

[0087] The electrolyte used in the first stage anodizing treatment in step (3) is a weak acid ammonium dihydrogen phosphate electrolyte with a pH of 5. The electrochemical treatment power applied in the first and second stage anodizing treatments is 100 c / g.

[0088] Comparative Example 8

[0089] This comparative example provides a surface-modified carbon fiber, and its preparation method is substantially the same as the preparation method in Example 1, except that:

[0090] The carbon fibers are not surface treated, ie step (3) is not included.

[0091] Test example

[0092] The surface modified carbon fibers provided in the examples and comparative examples are made into carbon fiber composite materials, and the composite materials are sequentially subjected to interlaminar shear strength tests, and the interlaminar shear strength tests are tested according to the ASTM D2344 standard. The preparation method of the carbon fiber composite material is as follows: (1) The carbon fiber test yarn is wound on a wooden board wrapped with release paper for a fixed number of turns; (2) It is mixed with AG80 resin and curing agent in a certain proportion, evenly applied to the winding yarn in the previous step, soaked, and kneaded; (3) It is placed in a mold and pressed into a fixed cross-section (constant width and thickness), heated, cooled, and made into an interlaminar shear spline (unidirectional board).

[0093] At the same time, the tensile strength, tensile modulus, and surface carboxyl content of the carbon fibers provided in the embodiments and comparative examples were tested. The tensile strength test was conducted in accordance with the GB / T3362 test standard, the tensile modulus test was conducted in accordance with the GB / T3362 test standard, and the carboxyl content of the carbon fiber surface was detected using X-ray photoelectron spectroscopy (XPS).

[0094] The above test results are shown in Table 1.

[0095] Table 1 Preparation conditions and interface properties of samples in Examples and Comparative Examples

[0096]

[0097]

[0098] As can be seen from Table 1, in Examples 1-2, by controlling the first-stage anodizing treatment to be a strong base with a large amount of electricity, and the second-stage anodizing treatment to be a weak acid with a small amount of electricity, the carbon fiber surface can have abundant oxygen-containing active groups and a high layer shear strength, that is, while improving the interface properties of the high modulus carbon fiber, the strength of the high modulus carbon fiber is maintained to a certain extent. In Example 1, compared with the carbon fiber without surface modification treatment in Comparative Example 8, the layer shear strength of the carbon fiber is increased by about 50%, and the tensile strength is only reduced by about 1%.

[0099] Comparative Examples 1-2 are primary sodium hydroxide electrolyte, secondary ammonium dihydrogen phosphate electrolyte, and surface treatment conditions of excessively high and low charges. Since the high modulus carbon fiber has few active groups on the interface and is inert, the fiber surface cannot be etched due to too low a charge, and the active groups are difficult to adsorb. Although there is no obvious damage to the strength performance of the fiber body, the carboxyl content and layer shear performance are both low, and excessive performance is prone to excessive etching of the fiber surface. Under weak acid electrolyte conditions and excessively high charges, the carboxyl content is obviously increased, but the layer shear performance is affected by both physical riveting and chemical bonds. Therefore, the layer shear performance is not improved even when the fiber is damaged due to the high carboxyl content.

[0100] Comparative Examples 3-4 are both levels of sodium hydroxide strong base electrolyte conditions. The fiber mechanical properties and layer shear properties are compared under different charge conditions. The strong base electrolyte tends to affect the fiber interface more with physical etching during surface treatment, and the content of the generated carboxyl chemical bonds is relatively low compared with the weak acid electrolyte. At the same time, the strong base electrolyte causes greater damage to the fiber than the weak acid electrolyte under the same charge condition. Therefore, under the charge condition of 100+100c / g, not only the tensile strength of the high modulus fiber is only 4576MPa, the layer shear performance is only 79MPa, and the comprehensive performance is significantly reduced.

[0101] Comparative Examples 5-7 use weak acid electrolytes as the first-stage surface treatment electrolytes. The results show that high-charge weak acid electrolytes and low-charge strong base electrolytes have no significant effect on the tensile strength of the fiber body, indicating that the surface treatment has a poor effect on improving the inert surface of high modulus fibers. At the same time, the layer shear performance is only 80-90MPa, which is significantly lower than that under the condition of NaOH+NH4H2PO4. At the same time, under the surface treatment method of first weak acid and then strong base electrolyte conditions, the carboxyl content on the fiber surface is significantly lower, which is speculated to be caused by the etching of the fiber surface area to which the active groups are attached by the secondary strong base electrolyte during the surface treatment etching process. Therefore, it is necessary to place the strong base physical etching electrolyte at the front end of the surface treatment.

[0102] The comparison results show that the first-stage electrochemical treatment uses a strong base NaOH electrolyte configuration, and the second-stage electrochemical treatment uses a weak acid NH4H2PO4 electrolyte configuration. This surface treatment method ensures the strength of the carbon fiber itself under the condition of a large first-stage charge and a small second-stage charge, relative to a total charge of 50+25c / g, and effectively improves the interface performance of the finished high modulus carbon fiber product, ultimately achieving an improvement in the high modulus carbon fiber interface.

[0103] 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 the 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 work are within the scope of protection of the present application.

Claims

1. A method for improving the interface performance of high modulus carbon fiber, characterized in that: The steps include: The high modulus carbon fiber is subjected to a first-stage anodizing treatment using a strong alkaline electrolyte; wherein the elastic modulus of the high modulus carbon fiber is 350 to 400 GPa; Performing a second-stage anodizing treatment on the carbon fiber after the first-stage anodizing treatment using a weakly acidic electrolyte; The amount of electricity applied in the first-stage anodizing treatment is greater than the amount of electricity applied in the second-stage anodizing treatment.

2. The method according to claim 1, characterized in that: The pH value of the strong alkaline electrolyte is 11-13, and the pH value of the weak acid electrolyte is 4-6.

3. The method according to any one of claims 1 to 2, characterized in that: The electrolyte in the strong alkaline electrolyte includes at least one of sodium hydroxide, potassium hydroxide or calcium hydroxide, and the electrolyte in the weak acid electrolyte includes at least one of ammonium dihydrogen phosphate or carbonic acid.

4. The method according to claim 1, characterized in that The amount of electricity applied in the first-stage anodizing treatment is 40 to 60 c / g, and the amount of electricity applied in the second-stage anodizing treatment is 20 to 30 c / g; And / or, the first-stage anodizing treatment lasts for 10 to 20 seconds, and the treatment temperature is 20 to 50°C; the second-stage anodizing treatment lasts for 10 to 20 seconds, and the treatment temperature is 20 to 50°C.

5. The method according to claim 1, characterized in that After the second-stage anodizing treatment, the method further includes: performing multi-stage water washing, sizing, drying and winding on the carbon fiber obtained after the second-stage anodizing treatment.

6. The method according to claim 1, characterized in that The preparation method of the high modulus carbon fiber comprises: The polyacrylonitrile fiber is subjected to a pre-oxidation treatment to obtain a pre-oxidized fiber; The preoxidized fiber is subjected to low-temperature carbonization, high-temperature carbonization and graphitization treatment in sequence to obtain the high modulus carbon fiber; Wherein, the temperature of the pre-oxidation treatment is 220°C to 260°C, the temperature of the low-temperature carbonization treatment is 400°C to 900°C, the temperature of the high-temperature carbonization treatment is 1000°C to 1500°C, and the temperature of the graphitization treatment is 1800°C to 2400°C.

7. An apparatus for use in the method according to any one of claims 1 to 6, characterized in that: include: a first electrolytic cell, wherein a strong alkaline electrolyte is contained in the first electrolytic cell, and the first electrolytic cell is used for performing a first-stage anodizing treatment on the high modulus fiber; a second electrolytic cell, wherein a weakly acidic electrolyte is contained in the second electrolytic cell, and the second electrolytic cell is used to perform a second-stage anodizing treatment on the carbon fibers treated by the first electrolytic cell; The amount of electricity applied in the first-stage anodizing treatment is greater than the amount of electricity applied in the second-stage anodizing treatment.

8. The device according to claim 7, characterized in that Also includes: A first water washing tank, a second water washing tank, a third water washing tank and a fourth water washing tank, wherein the first water washing tank, the second water washing tank, the third water washing tank and the fourth water washing tank are connected in sequence and their heights are gradually increased.

9. A surface-modified carbon fiber, characterized in that: The method is prepared by the method described in any one of claims 1 to 6 or the equipment described in any one of claims 7 to 8.

10. A composite material, characterized in that: The method is prepared by using the surface modified carbon fiber as described in claim 9.

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