Carbon fibers, and preparation method therefor and use thereof

Abstract

Disclosed are carbon fibers, and a preparation method therefor and the use thereof. The preparation method for the carbon fibers comprises: using a polyacrylonitrile precursor as a raw material to prepare graphitized fibers; and sequentially subjecting the graphitized fibers to an electrochemical oxidation surface treatment and sizing same to obtain carbon fibers., wherein the electrochemical oxidation surface treatment comprises: sequentially subjecting the graphitized fibers to a primary surface treatment and a secondary surface treatment, with the primary surface treatment being performed by using an alkaline electrolyte having hydroxide, and the secondary surface treatment being performed by using a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate.

Description

Carbon fiber, its preparation methods and applications

[0001] This disclosure is based on and claims priority to Chinese Patent Application No. 202411539674.9, filed on October 31, 2024, entitled "Carbon Fiber and its Preparation Method and Application", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to, but is not limited to, a carbon fiber, its preparation method, and its application. Background Technology

[0003] Polyacrylonitrile-based high-modulus carbon fiber is widely used in aerospace, defense, and high-end sports equipment due to its high strength, high modulus, corrosion resistance, and low coefficient of thermal expansion. However, after high-temperature graphitization, this carbon fiber exhibits chemical inertness and low adsorption on its surface, making it difficult for the resin matrix to adhere effectively, thus affecting the performance of the composite material. Summary of the Invention

[0004] The following is an overview of the subject matter described in detail in this disclosure. This overview is not intended to limit the scope of the claims.

[0005] One of the purposes of this disclosure is to provide a method for preparing carbon fiber.

[0006] The second objective of this disclosure is to provide a carbon fiber prepared by the aforementioned carbon fiber preparation method.

[0007] A third objective of this disclosure is to provide an application of the carbon fiber described herein in the preparation of composite materials.

[0008] In order to achieve the above-mentioned objectives of this disclosure, the following technical solution is adopted:

[0009] In a first aspect, this disclosure provides a method for preparing carbon fiber, the method comprising:

[0010] Graphitized fibers were prepared using polyacrylonitrile precursor fibers as raw materials.

[0011] The graphitized fibers were subjected to electrochemical oxidation surface treatment and sizing in sequence to obtain carbon fibers;

[0012] The electrochemical oxidation surface treatment includes performing a primary surface treatment and a secondary surface treatment on the graphitized fiber in sequence. The primary surface treatment uses an alkaline electrolyte containing hydroxide ions, and the secondary surface treatment uses a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate.

[0013] The alkaline electrolyte containing hydroxide ions includes at least one of sodium hydroxide and potassium hydroxide.

[0014] In some exemplary embodiments, the electrochemical oxidation surface treatment includes anodizing surface treatment;

[0015] In some exemplary embodiments, the charge of the primary surface treatment is 200C / g to 400C / g, and the charge of the secondary surface treatment is 200C / g to 400C / g;

[0016] In some exemplary embodiments, the mass ratio of the ammonium acetate to the ammonium dihydrogen phosphate is 1:1;

[0017] In some exemplary embodiments, the time for the primary surface treatment is 10s to 30s, and the time for the secondary surface treatment is 10s to 30s;

[0018] In some exemplary embodiments, a graphite roller is provided at the outlet of the electrolyte tank for the secondary surface treatment, and the graphite roller is used to transport graphitized fibers to the washing tank.

[0019] In some exemplary embodiments, the tilt angle between the graphitized fiber and the graphite roller is 30° to 50°, and the fiber bundle tension of the graphitized fiber is 50N to 80N.

[0020] In some exemplary embodiments, the preparation process of the graphitized fiber includes: pre-oxidizing, primary carbonizing, secondary carbonizing and graphitizing the polyacrylonitrile precursor fiber in sequence;

[0021] The pre-oxidation, primary carbonization, secondary carbonization, and graphitization all employ a gradient heating method.

[0022] In some exemplary embodiments, the pre-oxidation temperature is 200°C to 300°C, and the time is 1 hour to 2 hours;

[0023] In some exemplary embodiments, the pre-oxidation is provided with 3 to 4 temperature zones, and the temperature difference between the temperature zones is 5°C to 15°C;

[0024] In some exemplary embodiments, the temperature of the primary carbonization is 400°C to 800°C, and the time is 3 min to 5 min;

[0025] In some exemplary embodiments, the device for primary carbonization is provided with 6 to 8 temperature zones, with a temperature difference between the zones ranging from 40°C to 80°C;

[0026] In some exemplary embodiments, the secondary carbonization temperature is 1000°C to 1600°C, and the time is 2 min to 6 min;

[0027] In some exemplary embodiments, the secondary carbonization device is provided with 5 to 6 temperature zones, with a temperature difference between the temperature zones ranging from 50°C to 150°C;

[0028] In some exemplary embodiments, the graphitization temperature is 2000°C to 2600°C, and the time is 2 min to 6 min;

[0029] In some exemplary embodiments, the graphitized device is provided with four to five temperature zones, with a temperature difference between the zones ranging from 100°C to 200°C.

[0030] In some exemplary embodiments, prior to the sizing, the carbon fiber preparation method further includes washing the graphitized fibers after electrochemical oxidation surface treatment with water.

[0031] The washing time is 100s to 150s;

[0032] In some exemplary embodiments, the water washing adopts a multi-stage water washing method;

[0033] In some exemplary embodiments, a water washing tank is used for washing, and the water washing tank is provided with 4 to 6 sections;

[0034] In some exemplary embodiments, the interior of the washing tank is provided with a plurality of baffles, which are used to separate each section of the washing process.

[0035] In some exemplary embodiments, the height of the plurality of baffles increases along the running direction of the graphitized fibers after electrochemical oxidation surface treatment in the washing tank;

[0036] In some exemplary embodiments, the water flow direction in the washing tank is opposite to the running direction of the graphitized fibers after electrochemical oxidation surface treatment;

[0037] In some exemplary embodiments, a spray pipe is provided above the washing tank, and the pipe has a plurality of openings.

[0038] In some exemplary embodiments, the water-washed graphitized fibers are first dried before the sizing process.

[0039] The temperature of the first drying step is 130°C to 150°C.

[0040] In some exemplary embodiments, the sizing agent used for sizing is an epoxy sizing agent.

[0041] In some exemplary embodiments, the sized fibers are subjected to a second drying process;

[0042] In some exemplary embodiments, the temperature of the second drying is 150°C to 250°C.

[0043] Secondly, this disclosure provides a carbon fiber prepared by the carbon fiber preparation method described above.

[0044] Thirdly, this disclosure provides an application of carbon fiber in the preparation of composite materials.

[0045] Fourthly, this disclosure provides an application of the carbon fiber described above in the preparation of composite materials, wherein the composite material is prepared by the following steps:

[0046] The composite material is obtained by combining carbon fiber and resin matrix.

[0047] The carbon fiber preparation method disclosed herein employs a two-stage surface treatment. The first-stage surface treatment uses an alkaline electrolyte containing hydroxide ions, while the second-stage surface treatment uses a composite electrolyte of ammonium dihydrogen phosphate and ammonium acetate. The alkaline electrolyte containing hydroxide ions oxidizes and etches the surface of the graphitized fibers, refining the surface grains and increasing the specific area. The surface roughness of the graphitized fibers increases after surface treatment. During subsequent composite material preparation, the resin matrix can fully encapsulate and impregnate the carbon fibers, forming a physical interlocking texture. This interlocking texture, after the resin matrix cures, allows for further processing. It can act as an anchoring agent, which is beneficial to the interfacial bonding of composite materials. Simultaneously, the alkaline electrolyte containing hydroxyl groups can effectively remove the weak layers on the surface of graphitized fibers. OH- ions can insert into the edges of the graphite sheets in the graphitized fibers, promoting the peeling of carbon layers in crystalline or amorphous regions. After removing the graphite sheets from the surface of the graphitized fibers, the secondary surface treatment uses a composite electrolyte of ammonium dihydrogen phosphate and ammonium acetate. Ammonium dihydrogen phosphate generates acidic groups after electrolysis, which are located at the edges of the exposed graphite sheets, significantly improving the interfacial properties between the carbon fiber and the resin matrix. Although ammonium dihydrogen phosphate treatment can significantly improve the interlaminar shear strength of carbon fibers, it reduces their tensile properties. Therefore, ammonium acetate electrolyte is used to rapidly oxidize the carbon fiber surface, producing oxidation products. The composite electrolyte of ammonium dihydrogen phosphate and ammonium acetate has a better oxidation effect on carbon fibers, increasing the oxygen-containing and nitrogen-containing functional groups on the carbon fiber surface while maintaining the strength of the carbon fiber itself. Attached Figure Description

[0048] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate embodiments of the present disclosure and, together with the description, serve to explain the principles of these embodiments. In these drawings, similar reference numerals are used to denote similar elements. The drawings described below are some embodiments of the present disclosure, but not all embodiments. Other drawings will be readily available to those skilled in the art based on these drawings without inventive effort.

[0049] Figure 1 is a flowchart illustrating a method for preparing carbon fiber according to an exemplary embodiment. Detailed Implementation

[0050] The technical solutions of the disclosed embodiments will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this disclosure. Based on the embodiments of this disclosure, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this disclosure. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this disclosure can be arbitrarily combined with each other.

[0051] To improve the surface structure of carbon fibers, researchers have explored various surface treatment methods, such as electrochemical oxidation, gas / liquid phase oxidation, sizing, chemical grafting, and plasma treatment. Among these, electrochemical oxidation has become one of the most practical surface treatment technologies due to its mild processing, controllable process, and ability to be performed online.

[0052] Choosing the right electrolyte solution is a crucial factor affecting the treatment effect during electrochemical oxidation. Electrolytes used in the electrochemical oxidation treatment of carbon fiber surfaces can be categorized as acids, alkalis, and salts. Acidic and alkaline electrolytes easily corrode equipment and deteriorate the working environment, while alkali metal salt electrolytes readily remain in the carbon fiber, acting as oxidation catalysts and reducing the carbon fiber's ablation resistance. Furthermore, the factors typically affecting the interfacial bonding between carbon fiber and epoxy resin are the oxidized functional groups and roughness of the carbon fiber surface. However, the original graphite sheets on the carbon fiber surface have weak bonding with the matrix, and directly generating oxygen-containing functional groups (such as hydroxyl and carboxyl groups) on the surface cannot significantly improve interfacial performance.

[0053] The first aspect of this disclosure provides a method for preparing carbon fiber, as shown in Figure 1. The method for preparing carbon fiber includes:

[0054] S110. Graphitized fibers were prepared using polyacrylonitrile precursor fibers as raw materials.

[0055] S120: Graphitized fibers are subjected to electrochemical oxidation surface treatment and sizing in sequence to obtain carbon fibers;

[0056] The electrochemical oxidation surface treatment includes: performing a primary surface treatment and a secondary surface treatment on the graphitized fibers in sequence. The primary surface treatment uses an alkaline electrolyte containing hydroxide ions, and the secondary surface treatment uses a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate.

[0057] In this disclosure, a two-stage surface treatment is employed. The first-stage surface treatment uses an alkaline electrolyte containing hydroxide ions, while the second-stage surface treatment uses a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate. The alkaline electrolyte containing hydroxide ions oxidizes and etches the surface of the graphitized fibers, refining the surface grains and increasing the specific area. The surface roughness of the graphitized fibers increases after the surface treatment. During the subsequent preparation of the composite material, the resin matrix can fully encapsulate and impregnate the carbon fibers, forming a physical interlocking structure. This interlocking structure acts as an anchor after the resin matrix has cured. The electrolyte has a stabilizing effect, which is beneficial to the interfacial bonding of composite materials. Simultaneously, the alkaline electrolyte containing hydroxide ions can effectively remove the weak layers on the surface of graphitized fibers. OH- ions can insert into the edges of the graphite sheets in the graphitized fibers, promoting the peeling of carbon layers in crystalline or amorphous regions. After removing the graphite sheets from the surface of the graphitized fibers, the secondary surface treatment uses a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate. Ammonium dihydrogen phosphate generates acidic groups after electrolysis, which are located at the edges of the exposed graphite sheets, significantly improving the interfacial properties between the carbon fiber and the resin matrix. Although ammonium dihydrogen phosphate treatment can significantly improve the interlaminar shear strength of carbon fibers, it reduces their tensile properties. Therefore, ammonium acetate electrolyte is used to rapidly oxidize the carbon fiber surface, producing oxidation products. The composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate has a better oxidation effect on carbon fibers, increasing the oxygen-containing and nitrogen-containing functional groups on the carbon fiber surface while maintaining the strength of the carbon fiber itself.

[0058] In some exemplary embodiments, the alkaline electrolyte containing hydroxide ions includes at least one of sodium hydroxide and potassium hydroxide;

[0059] Electrochemical oxidation surface treatment includes anodic oxidation surface treatment;

[0060] In some exemplary embodiments, the electrical charge of the primary surface treatment is 200C / g to 400C / g, for example, it can be 200C / g, 250C / g, 300C / g, 350C / g, 400C / g, etc., and the electrical charge of the secondary surface treatment is 200C / g to 400C / g, for example, it can be 200C / g, 250C / g, 300C / g, 350C / g, 400C / g, etc.;

[0061] In some exemplary embodiments, the mass ratio of ammonium acetate to ammonium dihydrogen phosphate is 1:1;

[0062] In some exemplary embodiments, the time for the first-stage surface treatment is 10s to 30s, for example, 10s, 15s, 20s, 25s, 30s, etc.; the time for the second-stage surface treatment is 10s to 30s, for example, 10s, 15s, 20s, 25s, 30s, etc.

[0063] In this disclosure, the degree of oxidation on the carbon fiber surface can be controlled by using specific amounts of electricity and electrolyte time, avoiding excessive oxidation that causes excessive etching of the fiber surface or insufficient oxidation that results in inadequate surface treatment.

[0064] In this disclosure, the electrolyte tank for primary surface treatment and the electrolyte tank for secondary surface treatment are arranged one after the other according to the direction of the filament bundle.

[0065] In some exemplary embodiments, a graphite roller is provided at the outlet of the electrolyte tank for secondary surface treatment. The graphite roller is used to transport graphitized fibers to the washing tank. A waste liquid collection tank with a length of 50 cm is provided below the graphite roller.

[0066] The tilt angle between the graphitized fiber and the graphite roller is 30° to 50°, and can be 40°. This helps the residual electrolyte carried by the fiber to drip into the waste liquid collection tank, which can reduce the amount of water used in the subsequent washing process and improve the washing effect. The fiber bundle tension of the graphitized fiber is 50N.

[0067] In some exemplary embodiments, the polyacrylonitrile precursor fiber is prepared by a dry-jet wet spinning method;

[0068] In some exemplary embodiments, the polyacrylonitrile precursor fiber includes AC65-12K.

[0069] In this disclosure, AC65-12K prepared by dry-jet wet spinning is used as raw material. Its advantage lies in its high fiber performance, which can meet the requirements of the subsequent high-temperature and high-stretch carbonization process.

[0070] In some exemplary embodiments, the preparation process of graphitized fibers includes: pre-oxidizing, carbonizing, carbonizing and graphitizing polyacrylonitrile precursor fibers sequentially.

[0071] Among them, pre-oxidation, primary carbonization, secondary carbonization and graphitization all adopt a gradient heating method;

[0072] In this disclosure, a gradient heating method is used to pre-oxidize, carbonize (i.e., low-temperature carbonization), carbonize (i.e., high-temperature carbonization) and graphitize polyacrylonitrile precursor fibers to obtain graphitized fibers. The advantage of using the gradient heating method is that it can ensure that the carbon fibers are heated uniformly in all parts, avoiding local overheating or undercooling, thereby making the microstructure of the carbon fibers more uniform and reducing the generation of defects.

[0073] In some exemplary embodiments, the pre-oxidation temperature is 200°C to 300°C, for example, 200°C, 250°C, 300°C, etc., and the time is 1 hour to 2 hours, for example, 1 hour, 1.5 hours, 2 hours, etc.

[0074] In some exemplary embodiments, the pre-oxidation is provided with 3 to 4 temperature zones, for example, 3 or 4, etc., and the temperature difference between the temperature zones is 5°C to 15°C, for example, 5°C, 6°C, 7°C, 8°C, 9°C, 10°C, 11°C, 12°C, 13°C, 14°C, 15°C, etc.

[0075] In this disclosure, one temperature zone of the pre-oxidation is an oxidation furnace. In this disclosure, the pre-oxidation can be set up with 3 oxidation furnaces for pre-oxidation. The temperature difference between the 3 oxidation furnaces is 5℃ to 15℃, gradually increasing. The temperature inside each oxidation furnace is constant, and it is necessary to ensure that the furnace temperature of each oxidation furnace is uniform.

[0076] In some exemplary embodiments, the temperature of a single carbonization is 400°C to 800°C, for example, 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, 800°C, etc., and the time is 3 min to 5 min, for example, 3 min, 4 min, 5 min, etc.

[0077] In some exemplary embodiments, the carbonization equipment is provided with 6 to 8 temperature zones, such as 6, 7, 8, etc., and the temperature difference between the temperature zones is 40°C to 80°C, such as 40°C, 60°C, 80°C, etc.

[0078] In this disclosure, the primary carbonization (i.e., low-temperature carbonization) is carried out in a low-temperature carbonization furnace, which has several increasing temperature zones inside.

[0079] In some exemplary embodiments, the temperature of secondary carbonization is 1000°C to 1600°C, for example, 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, etc., and the time is 2 min to 6 min, for example, 2 min, 4 min, 6 min, etc.

[0080] In some exemplary embodiments, the secondary carbonization device is provided with 5 to 6 temperature zones, for example, 5 or 6, and the temperature difference between the temperature zones is 50°C to 150°C, for example, 50°C, 100°C, 150°C, etc.

[0081] In this disclosure, the secondary carbonization (i.e., high-temperature carbonization) is carried out in a high-temperature carbonization furnace, which has several increasing temperature zones inside.

[0082] In some exemplary embodiments, the graphitization temperature is 2000°C to 2600°C, for example, 2000°C, 2100°C, 2200°C, 2300°C, 2400°C, 2500°C, 2600°C, etc., and the time is 2 min to 6 min, for example, 2 min, 4 min, 6 min, etc.

[0083] In some exemplary embodiments, the graphitized device is provided with four to five temperature zones, for example, four or five, with a temperature difference between the zones ranging from 100°C to 200°C. For example, the temperature could be 100°C, 150°C, 200°C, etc.

[0084] In this disclosure, graphitization is performed using a graphitization furnace, which has several progressively increasing temperature zones inside.

[0085] It should be noted that in this disclosure, one oxidation furnace for pre-oxidation is one temperature zone, and the temperature inside each oxidation furnace must be constant; in the low-temperature carbonization, high-temperature carbonization and graphitization steps, a single furnace is used, and several temperature zones with temperature differences are set inside the furnace.

[0086] In some exemplary embodiments, the carbon fiber preparation method further includes washing the graphitized fibers after electrochemical oxidation surface treatment with water before sizing.

[0087] In this disclosure, graphitized fibers are surface-treated using anodizing, impregnated with an electrolyte, and then washed with water. Water washing prevents electrolyte residues from the primary and secondary surface treatments from entering subsequent processes, further improving the interfacial bonding ability of the carbon fibers in the preparation of composite materials.

[0088] In some exemplary embodiments, the washing time is 100s to 150s, for example, it can be 100s, 110s, 120s, 130s, 140s, 150s, etc.

[0089] In some exemplary embodiments, the water washing adopts a multi-stage water washing method;

[0090] In some exemplary embodiments, a water washing tank is used for washing. The water washing tank is provided with 4 to 6 sections, such as 4, 5, or 6 sections. The interior of the water washing tank is provided with several baffles to separate each section of the water washing process, which facilitates better cleaning of surface electrolyte residues. The height of the multiple baffles increases along the running direction of the graphitized fibers after electrochemical oxidation surface treatment in the water washing tank. The height difference between each baffle section is 8 mm to 10 mm. The water flow direction in the water washing tank is opposite to the running direction of the graphitized fibers after electrochemical oxidation surface treatment.

[0091] In some exemplary embodiments, a spray pipe is provided above the washing tank, and the pipe has a plurality of holes; wherein, the diameter of the holes can be 5 mm.

[0092] In some exemplary embodiments, the conduit comprises 304 stainless steel pipes, and the number of conduits is two to four, for example, two, three, four, etc.

[0093] In some exemplary embodiments, the end-wash conductivity of the washing tank is at most 50 μS / cm, and may also be at most 20 μS / cm.

[0094] In some exemplary embodiments, the washed fibers are first dried after washing and before sizing;

[0095] The temperature for the first drying step is between 130°C and 150°C, for example, 130°C, 135°C, 140°C, 145°C, 150°C, etc.

[0096] In some exemplary embodiments, the sizing agent used for sizing is an epoxy sizing agent.

[0097] In some exemplary embodiments, the sized fibers are subjected to a second drying process;

[0098] The temperature for the second drying is between 150°C and 250°C, for example, it can be 150°C, 200°C, 150°C, etc.

[0099] In some exemplary embodiments, the carbon fiber preparation method includes the following steps:

[0100] (1) The dry-jet wet-spun polyacrylonitrile precursor is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0101] (2) The graphitized fiber is subjected to anodizing surface treatment, impregnated with electrolyte, and then washed with water.

[0102] (3) The washed fibers are dried by passing them through a drying roller to remove surface moisture, and then sized and dried to obtain high-strength, high-modulus carbon fibers.

[0103] The second aspect of this disclosure provides a method for preparing carbon fibers.

[0104] In this disclosure, a high-strength, high-modulus carbon fiber with high interfacial properties can be prepared using this carbon fiber preparation method.

[0105] A third aspect of this disclosure provides the application of carbon fiber in the preparation of composite materials, wherein the composite materials are prepared by the following steps:

[0106] A composite material is obtained by combining carbon fiber and a resin matrix.

[0107] In some exemplary embodiments, the resin matrix includes epoxy resin, and high-strength, high-modulus carbon fibers are compounded with epoxy resin to obtain a composite material with significantly improved interfacial properties.

[0108] When preparing composite materials, combining carbon fibers prepared using carbon fiber preparation methods with a resin matrix is ​​beneficial for the interfacial bonding of the composite materials.

[0109] The present disclosure will be further illustrated below by way of examples. Unless otherwise specified, the materials in the examples are prepared according to existing methods or purchased directly from the market.

[0110] Example 1

[0111] This embodiment provides a method for preparing carbon fiber, including the following steps:

[0112] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0113] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is sequentially pre-oxidized in three oxidation furnaces. The temperatures of the three oxidation furnaces are 230℃, 240℃, and 250℃, respectively. The processing time in each oxidation furnace is the same, and the total pre-oxidation time is 1.5h.

[0114] The low-temperature carbonization process includes: the pre-oxidized filament bundles are sequentially passed through 7 temperature zones in a low-temperature carbonization furnace for low-temperature carbonization. The temperatures of the 7 temperature zones are 400℃, 460℃, 520℃, 580℃, 640℃, 700℃, and 760℃, respectively. The processing time for each temperature zone is the same, and the total residence time for low-temperature carbonization is 4 minutes.

[0115] The high-temperature carbonization process includes: the low-temperature carbonized filament bundles are sequentially passed through five temperature zones in a high-temperature carbonization furnace for high-temperature carbonization. The temperatures of the five temperature zones are 1000℃, 1100℃, 1200℃, 1300℃, and 1400℃, respectively. The processing time for each temperature zone is the same, and the total high-temperature carbonization residence time is 4 minutes.

[0116] The graphitization process includes: the carbonized filament bundles are sequentially passed through four temperature zones of a graphitization furnace for graphitization treatment. The temperatures of the four temperature zones are 2000℃, 2150℃, 2300℃, and 2450℃, respectively. The processing time for each temperature zone is the same, and the graphitization time is 4 minutes.

[0117] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0118] The electrolyte for the first-stage surface treatment is sodium hydroxide, with a surface treatment charge of 250 C / g and a treatment time of 20 s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 350 C / g, and a treatment time of 20 s.

[0119] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 40°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0120] The fibers after two-stage electrolysis are washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flows from the rear section to the front section. Four 304 stainless steel pipes are opened above the washing tank for spraying. The stainless steel pipes have several 5 mm diameter holes.

[0121] Step 3: The washed fibers are dried by passing them through a 145℃ drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 200℃ to obtain high-strength, high-modulus carbon fibers with high interface.

[0122] Example 2

[0123] This embodiment provides a method for preparing carbon fiber, which differs from Embodiment 1 in that:

[0124] In step 2, the charge for the secondary surface treatment is 400C / g;

[0125] The remaining steps are the same as in Example 1.

[0126] For example, the carbon fiber preparation method provided in Example 2 includes the following steps:

[0127] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0128] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is sequentially pre-oxidized in three oxidation furnaces. The temperatures of the three oxidation furnaces are 230℃, 240℃, and 250℃, respectively. The processing time in each oxidation furnace is the same, and the total pre-oxidation time is 1.5h.

[0129] The low-temperature carbonization process includes: the pre-oxidized filament bundles are sequentially passed through 7 temperature zones in a low-temperature carbonization furnace for low-temperature carbonization. The temperatures of the 7 temperature zones are 400℃, 460℃, 520℃, 580℃, 640℃, 700℃, and 760℃, respectively. The processing time for each temperature zone is the same, and the total residence time for low-temperature carbonization is 4 minutes.

[0130] The high-temperature carbonization process includes: the low-temperature carbonized filament bundles are sequentially passed through five temperature zones in a high-temperature carbonization furnace for high-temperature carbonization. The temperatures of the five temperature zones are 1000℃, 1100℃, 1200℃, 1300℃, and 1400℃, respectively. The processing time for each temperature zone is the same, and the total high-temperature carbonization residence time is 4 minutes.

[0131] The graphitization process includes: the carbonized filament bundles are sequentially passed through four temperature zones of a graphitization furnace for graphitization treatment. The temperatures of the four temperature zones are 2000℃, 2150℃, 2300℃, and 2450℃, respectively. The processing time for each temperature zone is the same, and the graphitization time is 4 minutes.

[0132] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0133] The electrolyte for the first-stage surface treatment is sodium hydroxide, with a surface treatment charge of 250 C / g and a treatment time of 20 s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 400 C / g, and a treatment time of 20 s.

[0134] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 40°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0135] The fibers after two-stage electrolysis are washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flows from the rear section to the front section. Four 304 stainless steel pipes are opened above the washing tank for spraying. The stainless steel pipes have several 5 mm diameter holes.

[0136] Step 3: The washed fibers are dried by passing them through a 145℃ drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 200℃ to obtain high-strength, high-modulus carbon fibers with high interface.

[0137] Example 3

[0138] This embodiment provides a method for preparing carbon fiber, which differs from Embodiment 1 in that:

[0139] In step 2, the charge for the primary surface treatment is 400C / g;

[0140] The remaining steps are the same as in Example 1.

[0141] For example, the carbon fiber preparation method provided in Example 3 includes the following steps:

[0142] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0143] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is sequentially pre-oxidized in three oxidation furnaces. The temperatures of the three oxidation furnaces are 230℃, 240℃, and 250℃, respectively. The processing time in each oxidation furnace is the same, and the total pre-oxidation time is 1.5h.

[0144] The low-temperature carbonization process includes: the pre-oxidized filament bundles are sequentially passed through 7 temperature zones in a low-temperature carbonization furnace for low-temperature carbonization. The temperatures of the 7 temperature zones are 400℃, 460℃, 520℃, 580℃, 640℃, 700℃, and 760℃, respectively. The processing time for each temperature zone is the same, and the total residence time for low-temperature carbonization is 4 minutes.

[0145] The high-temperature carbonization process includes: the low-temperature carbonized filament bundles are sequentially passed through five temperature zones in a high-temperature carbonization furnace for high-temperature carbonization. The temperatures of the five temperature zones are 1000℃, 1100℃, 1200℃, 1300℃, and 1400℃, respectively. The processing time for each temperature zone is the same, and the total high-temperature carbonization residence time is 4 minutes.

[0146] The graphitization process includes: the carbonized filament bundles are sequentially passed through four temperature zones of a graphitization furnace for graphitization treatment. The temperatures of the four temperature zones are 2000℃, 2150℃, 2300℃, and 2450℃, respectively. The processing time for each temperature zone is the same, and the graphitization time is 4 minutes.

[0147] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0148] The electrolyte for the first-stage surface treatment is sodium hydroxide, with a surface treatment charge of 400 C / g and a treatment time of 20 s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 350 C / g, and a treatment time of 20 s.

[0149] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 40°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0150] The fibers after two-stage electrolysis are washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flows from the rear section to the front section. Four 304 stainless steel pipes are opened above the washing tank for spraying. The stainless steel pipes have several 5 mm diameter holes.

[0151] Step 3: The washed fibers are dried by passing them through a 145℃ drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 200℃ to obtain high-strength, high-modulus carbon fibers with high interface.

[0152] Example 4

[0153] This embodiment provides a method for preparing carbon fiber, which differs from Embodiment 1 in that:

[0154] In step 2, the charge for the secondary surface treatment is 200C / g;

[0155] The remaining steps are the same as in Example 1.

[0156] For example, the carbon fiber preparation method provided in Example 4 includes the following steps:

[0157] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0158] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is sequentially pre-oxidized in three oxidation furnaces. The temperatures of the three oxidation furnaces are 230℃, 240℃, and 250℃, respectively. The processing time in each oxidation furnace is the same, and the total pre-oxidation time is 1.5h.

[0159] The low-temperature carbonization process includes: the pre-oxidized filament bundles are sequentially passed through 7 temperature zones in a low-temperature carbonization furnace for low-temperature carbonization. The temperatures of the 7 temperature zones are 400℃, 460℃, 520℃, 580℃, 640℃, 700℃, and 760℃, respectively. The processing time for each temperature zone is the same, and the total residence time for low-temperature carbonization is 4 minutes.

[0160] The high-temperature carbonization process includes: the low-temperature carbonized filament bundles are sequentially passed through five temperature zones in a high-temperature carbonization furnace for high-temperature carbonization. The temperatures of the five temperature zones are 1000℃, 1100℃, 1200℃, 1300℃, and 1400℃, respectively. The processing time for each temperature zone is the same, and the total high-temperature carbonization residence time is 4 minutes.

[0161] The graphitization process includes: the carbonized filament bundles are sequentially passed through four temperature zones of a graphitization furnace for graphitization treatment. The temperatures of the four temperature zones are 2000℃, 2150℃, 2300℃, and 2450℃, respectively. The processing time for each temperature zone is the same, and the graphitization time is 4 minutes.

[0162] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0163] The electrolyte for the first-stage surface treatment is sodium hydroxide, with a surface treatment charge of 250 C / g and a treatment time of 20 s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 200 C / g, and a treatment time of 20 s.

[0164] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 40°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0165] The fibers after two-stage electrolysis are washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flows from the rear section to the front section. Four 304 stainless steel pipes are opened above the washing tank for spraying. The stainless steel pipes have several 5 mm diameter holes.

[0166] Step 3: The washed fibers are dried by passing them through a 145℃ drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 200℃ to obtain high-strength, high-modulus carbon fibers with high interface.

[0167] Example 5

[0168] This embodiment provides a method for preparing carbon fiber, which differs from Embodiment 1 in that:

[0169] In step 2, the charge for the first-stage surface treatment is 200C / g, and the charge for the second-stage surface treatment is 300C / g;

[0170] The remaining steps are the same as in Example 1.

[0171] For example, the carbon fiber preparation method provided in Example 5 includes the following steps:

[0172] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0173] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is sequentially pre-oxidized in three oxidation furnaces. The temperatures of the three oxidation furnaces are 230℃, 240℃, and 250℃, respectively. The processing time in each oxidation furnace is the same, and the total pre-oxidation time is 1.5h.

[0174] The low-temperature carbonization process includes: the pre-oxidized filament bundles are sequentially passed through 7 temperature zones in a low-temperature carbonization furnace for low-temperature carbonization. The temperatures of the 7 temperature zones are 400℃, 460℃, 520℃, 580℃, 640℃, 700℃, and 760℃, respectively. The processing time for each temperature zone is the same, and the total residence time for low-temperature carbonization is 4 minutes.

[0175] The high-temperature carbonization process includes: the low-temperature carbonized filament bundles are sequentially passed through five temperature zones in a high-temperature carbonization furnace for high-temperature carbonization. The temperatures of the five temperature zones are 1000℃, 1100℃, 1200℃, 1300℃, and 1400℃, respectively. The processing time for each temperature zone is the same, and the total high-temperature carbonization residence time is 4 minutes.

[0176] The graphitization process includes: the carbonized filament bundles are sequentially passed through four temperature zones of a graphitization furnace for graphitization treatment. The temperatures of the four temperature zones are 2000℃, 2150℃, 2300℃, and 2450℃, respectively. The processing time for each temperature zone is the same, and the graphitization time is 4 minutes.

[0177] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0178] The electrolyte for the first-stage surface treatment is sodium hydroxide, with a surface treatment charge of 200C / g and a treatment time of 20s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 300C / g, and a treatment time of 20s.

[0179] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 40°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0180] The fibers after two-stage electrolysis are washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flows from the rear section to the front section. Four 304 stainless steel pipes are opened above the washing tank for spraying. The stainless steel pipes have several 5 mm diameter holes.

[0181] Step 3: The washed fibers are dried by passing them through a 145℃ drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 200℃ to obtain high-strength, high-modulus carbon fibers with high interface.

[0182] Example 6

[0183] This embodiment provides a method for preparing carbon fiber, which differs from Embodiment 2 in that:

[0184] In step 2, the charge for the primary surface treatment is 350 C / g;

[0185] The remaining steps are the same as in Example 2.

[0186] For example, the method for preparing carbon fiber provided in Example 6 includes the following steps:

[0187] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0188] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is sequentially pre-oxidized in three oxidation furnaces. The temperatures of the three oxidation furnaces are 230℃, 240℃, and 250℃, respectively. The processing time in each oxidation furnace is the same, and the total pre-oxidation time is 1.5h.

[0189] The low-temperature carbonization process includes: the pre-oxidized filament bundles are sequentially passed through 7 temperature zones in a low-temperature carbonization furnace for low-temperature carbonization. The temperatures of the 7 temperature zones are 400℃, 460℃, 520℃, 580℃, 640℃, 700℃, and 760℃, respectively. The processing time for each temperature zone is the same, and the total residence time for low-temperature carbonization is 4 minutes.

[0190] The high-temperature carbonization process includes: the low-temperature carbonized filament bundles are sequentially passed through five temperature zones in a high-temperature carbonization furnace for high-temperature carbonization. The temperatures of the five temperature zones are 1000℃, 1100℃, 1200℃, 1300℃, and 1400℃, respectively. The processing time for each temperature zone is the same, and the total high-temperature carbonization residence time is 4 minutes.

[0191] The graphitization process includes: the carbonized filament bundles are sequentially passed through four temperature zones of a graphitization furnace for graphitization treatment. The temperatures of the four temperature zones are 2000℃, 2150℃, 2300℃, and 2450℃, respectively. The processing time for each temperature zone is the same, and the graphitization time is 4 minutes.

[0192] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0193] The electrolyte for the first-stage surface treatment is sodium hydroxide, with a surface treatment charge of 350 C / g and a treatment time of 20 s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 400 C / g, and a treatment time of 20 s.

[0194] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 40°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0195] The fibers after two-stage electrolysis are washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flows from the rear section to the front section. Four 304 stainless steel pipes are opened above the washing tank for spraying. The stainless steel pipes have several 5 mm diameter holes.

[0196] Step 3: The washed fibers are dried by passing them through a 145℃ drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 200℃ to obtain high-strength, high-modulus carbon fibers with high interface.

[0197] Example 7

[0198] This embodiment provides a method for preparing carbon fiber, which differs from Embodiment 1 in that:

[0199] In step 2, two 304 stainless steel spray pipes are opened above the water washing tank;

[0200] The remaining steps are the same as in Example 1.

[0201] For example, the method for preparing carbon fiber provided in Example 7 includes the following steps:

[0202] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0203] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is sequentially pre-oxidized in three oxidation furnaces. The temperatures of the three oxidation furnaces are 230℃, 240℃, and 250℃, respectively. The processing time in each oxidation furnace is the same, and the total pre-oxidation time is 1.5h.

[0204] The low-temperature carbonization process includes: the pre-oxidized filament bundles are sequentially passed through 7 temperature zones in a low-temperature carbonization furnace for low-temperature carbonization. The temperatures of the 7 temperature zones are 400℃, 460℃, 520℃, 580℃, 640℃, 700℃, and 760℃, respectively. The processing time for each temperature zone is the same, and the total residence time for low-temperature carbonization is 4 minutes.

[0205] The high-temperature carbonization process includes: the low-temperature carbonized filament bundles are sequentially passed through five temperature zones in a high-temperature carbonization furnace for high-temperature carbonization. The temperatures of the five temperature zones are 1000℃, 1100℃, 1200℃, 1300℃, and 1400℃, respectively. The processing time for each temperature zone is the same, and the total high-temperature carbonization residence time is 4 minutes.

[0206] The graphitization process includes: the carbonized filament bundles are sequentially passed through four temperature zones of a graphitization furnace for graphitization treatment. The temperatures of the four temperature zones are 2000℃, 2150℃, 2300℃, and 2450℃, respectively. The processing time for each temperature zone is the same, and the graphitization time is 4 minutes.

[0207] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0208] The electrolyte for the first-stage surface treatment is sodium hydroxide, with a surface treatment charge of 250 C / g and a treatment time of 20 s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 350 C / g, and a treatment time of 20 s.

[0209] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 40°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0210] The fibers after two-stage electrolysis are washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flows from the rear section to the front section. Two 304 stainless steel pipes are opened above the washing tank for spraying. The stainless steel pipes have several 5 mm diameter holes.

[0211] Step 3: The washed fibers are dried by passing them through a 145℃ drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 200℃ to obtain high-strength, high-modulus carbon fibers with high interface.

[0212] Example 8

[0213] This embodiment provides a method for preparing carbon fiber, which differs from Embodiment 1 in that:

[0214] In step 2, no 304 stainless steel pipe was used for spraying above the water washing tank.

[0215] For example, the method for preparing carbon fiber provided in Example 8 includes the following steps:

[0216] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0217] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is sequentially pre-oxidized in three oxidation furnaces. The temperatures of the three oxidation furnaces are 230℃, 240℃, and 250℃, respectively. The processing time in each oxidation furnace is the same, and the total pre-oxidation time is 1.5h.

[0218] The low-temperature carbonization process includes: the pre-oxidized filament bundles are sequentially passed through 7 temperature zones in a low-temperature carbonization furnace for low-temperature carbonization. The temperatures of the 7 temperature zones are 400℃, 460℃, 520℃, 580℃, 640℃, 700℃, and 760℃, respectively. The processing time for each temperature zone is the same, and the total residence time for low-temperature carbonization is 4 minutes.

[0219] The high-temperature carbonization process includes: the low-temperature carbonized filament bundles are sequentially passed through five temperature zones in a high-temperature carbonization furnace for high-temperature carbonization. The temperatures of the five temperature zones are 1000℃, 1100℃, 1200℃, 1300℃, and 1400℃, respectively. The processing time for each temperature zone is the same, and the total high-temperature carbonization residence time is 4 minutes.

[0220] The graphitization process includes: the carbonized filament bundles are sequentially passed through four temperature zones of a graphitization furnace for graphitization treatment. The temperatures of the four temperature zones are 2000℃, 2150℃, 2300℃, and 2450℃, respectively. The processing time for each temperature zone is the same, and the graphitization time is 4 minutes.

[0221] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0222] The electrolyte for the first-stage surface treatment is sodium hydroxide, with a surface treatment charge of 250 C / g and a treatment time of 20 s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 350 C / g, and a treatment time of 20 s.

[0223] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 40°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0224] The fiber after two-stage electrolysis is washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flow is from the rear section to the front section.

[0225] Step 3: The washed fibers are dried by passing them through a 145℃ drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 200℃ to obtain high-strength, high-modulus carbon fibers with high interface.

[0226] Example 9

[0227] This embodiment provides a method for preparing carbon fiber, which differs from Embodiment 1 in that:

[0228] In step 2, the electrolyte for the primary surface treatment is KOH;

[0229] The remaining steps are the same as in Example 1.

[0230] For example, the method for preparing carbon fiber provided in Example 9 includes the following steps:

[0231] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0232] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is sequentially pre-oxidized in three oxidation furnaces. The temperatures of the three oxidation furnaces are 230℃, 240℃, and 250℃, respectively. The processing time in each oxidation furnace is the same, and the total pre-oxidation time is 1.5h.

[0233] The low-temperature carbonization process includes: the pre-oxidized filament bundles are sequentially passed through 7 temperature zones in a low-temperature carbonization furnace for low-temperature carbonization. The temperatures of the 7 temperature zones are 400℃, 460℃, 520℃, 580℃, 640℃, 700℃, and 760℃, respectively. The processing time for each temperature zone is the same, and the total residence time for low-temperature carbonization is 4 minutes.

[0234] The high-temperature carbonization process includes: the low-temperature carbonized filament bundles are sequentially passed through five temperature zones in a high-temperature carbonization furnace for high-temperature carbonization. The temperatures of the five temperature zones are 1000℃, 1100℃, 1200℃, 1300℃, and 1400℃, respectively. The processing time for each temperature zone is the same, and the total high-temperature carbonization residence time is 4 minutes.

[0235] The graphitization process includes: the carbonized filament bundles are sequentially passed through four temperature zones of a graphitization furnace for graphitization treatment. The temperatures of the four temperature zones are 2000℃, 2150℃, 2300℃, and 2450℃, respectively. The processing time for each temperature zone is the same, and the graphitization time is 4 minutes.

[0236] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0237] The electrolyte for the first-stage surface treatment is potassium hydroxide, with a surface treatment charge of 250 C / g and a treatment time of 20 s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 350 C / g, and a treatment time of 20 s.

[0238] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 40°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0239] The fibers after two-stage electrolysis are washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flows from the rear section to the front section. Four 304 stainless steel pipes are opened above the washing tank for spraying. The stainless steel pipes have several 5 mm diameter holes.

[0240] Step 3: The washed fibers are dried by passing them through a 145℃ drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 200℃ to obtain high-strength, high-modulus carbon fibers with high interface.

[0241] Example 10

[0242] This embodiment provides a method for preparing carbon fiber, which differs from Embodiment 1 in that:

[0243] In step 1, the pre-oxidation includes: the dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized in four oxidation furnaces at temperatures of 200℃, 215℃, 230℃ and 245℃ respectively. The treatment is the same in each temperature zone, and the total pre-oxidation time is 1 hour.

[0244] The low-temperature carbonization process includes: the pre-oxidized fiber bundle enters the low-temperature carbonization furnace and passes through 6 temperature zones in sequence. The temperatures of the 6 temperature zones are 400℃, 480℃, 560℃, 640℃, 720℃ and 800℃, respectively. The processing time of each temperature zone is the same, and the total residence time of low-temperature carbonization is 3 minutes.

[0245] The high-temperature carbonization process includes: the low-temperature carbonized fiber bundle enters the high-temperature carbonization furnace and passes through 6 temperature zones in sequence. The temperatures of the 6 temperature zones are 1000℃, 1050℃, 1100℃, 1150℃, 1200℃ and 1250℃, respectively. The processing time of each temperature zone is the same, and the total residence time of high-temperature carbonization is 6 minutes.

[0246] The graphitization process includes: the carbonized filament bundles are fed into a graphitization furnace and pass through five temperature zones in sequence. The temperatures of the five temperature zones are 2000℃, 2100℃, 2200℃, 2300℃ and 2400℃, respectively. The processing time for each temperature zone is the same, and the total graphitization time is 6 minutes.

[0247] In step 2, the tilt angle is 30°;

[0248] In step 3, the washed fibers are dried using a 130°C drying roller, and the drying temperature after sizing is 250°C.

[0249] The remaining steps are the same as in Example 1.

[0250] For example, the method for preparing carbon fiber provided in Example 10 includes the following steps:

[0251] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0252] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized in four oxidation furnaces at temperatures of 200℃, 215℃, 230℃ and 245℃ respectively. The treatment is the same in each temperature zone, and the total pre-oxidation time is 1 hour.

[0253] The low-temperature carbonization process includes: the pre-oxidized fiber bundle enters the low-temperature carbonization furnace and passes through 6 temperature zones in sequence. The temperatures of the 6 temperature zones are 400℃, 480℃, 560℃, 640℃, 720℃ and 800℃, respectively. The processing time of each temperature zone is the same, and the total residence time of low-temperature carbonization is 3 minutes.

[0254] The high-temperature carbonization process includes: the low-temperature carbonized fiber bundle enters the high-temperature carbonization furnace and passes through 6 temperature zones in sequence. The temperatures of the 6 temperature zones are 1000℃, 1050℃, 1100℃, 1150℃, 1200℃ and 1250℃, respectively. The processing time of each temperature zone is the same, and the total residence time of high-temperature carbonization is 6 minutes.

[0255] The graphitization process includes: the carbonized filament bundles are fed into a graphitization furnace and pass through five temperature zones in sequence. The temperatures of the five temperature zones are 2000℃, 2100℃, 2200℃, 2300℃, and 2400℃, respectively. The processing time for each temperature zone is the same, and the total graphitization time is 6 minutes.

[0256] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0257] The electrolyte for the first-stage surface treatment is sodium hydroxide, with a surface treatment charge of 250 C / g and a treatment time of 20 s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 350 C / g, and a treatment time of 20 s.

[0258] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 30°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0259] The fibers after two-stage electrolysis are washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flows from the rear section to the front section. Four 304 stainless steel pipes are opened above the washing tank for spraying. The stainless steel pipes have several 5 mm diameter holes.

[0260] Step 3: The washed fibers are dried by passing them through a 130℃ drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 250℃ to obtain high-strength, high-modulus carbon fibers with high interface.

[0261] Example 11

[0262] This embodiment provides a method for preparing carbon fiber, which differs from Embodiment 1 in that:

[0263] In step 1, the pre-oxidation includes: the dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized in four oxidation furnaces in sequence, with temperatures of 285℃, 290℃, 295℃ and 300℃ respectively. The treatment time in each temperature zone is the same, and the total pre-oxidation time is 2 hours.

[0264] The low-temperature carbonization process includes: the pre-oxidized filament bundle enters the low-temperature carbonization furnace and passes through 8 temperature zones in sequence. The temperatures of the 8 temperature zones are 400℃, 440℃, 480℃, 520℃, 560℃, 600℃, 640℃ and 680℃, respectively. The processing time of each temperature zone is the same, and the total residence time of low-temperature carbonization is 5 minutes.

[0265] The high-temperature carbonization process includes: the low-temperature carbonized fiber bundle enters the high-temperature carbonization furnace and passes through 6 temperature zones in sequence. The temperatures of the 6 temperature zones are 1000℃, 1150℃, 1300℃, 1450℃, 1500℃ and 1600℃, respectively. The processing time of each temperature zone is the same, and the total residence time of high-temperature carbonization is 2 minutes.

[0266] The graphitization process includes: the carbonized filament bundles are fed into a graphitization furnace and pass through five temperature zones in sequence. The temperatures of the five temperature zones are 2000℃, 2200℃, 2300℃, 2500℃ and 2600℃, respectively. The processing time for each temperature zone is the same, and the total graphitization time is 2 minutes.

[0267] In step 2, the tilt angle is 50°;

[0268] In step 3, the washed fibers are dried by passing them through a 150°C drying roller. The drying temperature after sizing is 150°C.

[0269] The remaining steps are the same as in Example 1.

[0270] For example, the method for preparing carbon fiber provided in Example 11 includes the following steps:

[0271] Step 1: The dry-jet wet-spun AC65-12K precursor yarn is pre-oxidized, carbonized at low temperature, carbonized at high temperature and graphitized by gradient heating to obtain graphitized fiber.

[0272] The pre-oxidation process includes: the dry-jet wet-spun AC65-12K precursor yarn is sequentially pre-oxidized in four oxidation furnaces at temperatures of 285℃, 290℃, 295℃ and 300℃, with the same treatment time in each temperature zone, and a total pre-oxidation time of 2 hours.

[0273] The low-temperature carbonization process includes: the pre-oxidized filament bundle enters the low-temperature carbonization furnace and passes through 8 temperature zones in sequence. The temperatures of the 8 temperature zones are 400℃, 440℃, 480℃, 520℃, 560℃, 600℃, 640℃ and 680℃, respectively. The processing time of each temperature zone is the same, and the total residence time of low-temperature carbonization is 5 minutes.

[0274] The high-temperature carbonization process includes: the low-temperature carbonized fiber bundle enters the high-temperature carbonization furnace and passes through 6 temperature zones in sequence. The temperatures of the 6 temperature zones are 1000℃, 1150℃, 1300℃, 1450℃, 1500℃ and 1600℃, respectively. The processing time of each temperature zone is the same, and the total residence time of high-temperature carbonization is 2 minutes.

[0275] The graphitization process includes: the carbonized filament bundles are fed into a graphitization furnace and pass through five temperature zones in sequence. The temperatures of the five temperature zones are 2000℃, 2200℃, 2300℃, 2500℃, and 2600℃, respectively. The processing time for each temperature zone is the same, and the total graphitization time is 2 minutes.

[0276] Step 2: The obtained graphitized fibers are subjected to anodizing surface treatment by immersion in the electrolyte in two stages of surface treatment, followed by water washing.

[0277] The electrolyte for the first-stage surface treatment is sodium hydroxide, with a surface treatment charge of 250 C / g and a treatment time of 20 s. The electrolyte for the second-stage surface treatment is a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate, with a mass ratio of ammonium acetate to ammonium dihydrogen phosphate of 1:1, a surface treatment charge of 350 C / g, and a treatment time of 20 s.

[0278] Among them, the electrolyte outlet of the secondary surface treatment passes through a graphite roller, the inclination angle between the fiber and the graphite roller is 50°, there is a 50cm long waste liquid collection tank below the graphite roller, and the fiber tension is 75N.

[0279] The fibers after two-stage electrolysis are washed with water for 125 seconds. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the direction of fiber bundle movement. The height of each baffle differs by 10 mm at each stage. The water flows from the rear section to the front section. Four 304 stainless steel pipes are opened above the washing tank for spraying. The stainless steel pipes have several 5 mm diameter holes.

[0280] Step 3: The washed fibers are dried by passing them through a 150°C drying roller to remove surface moisture. After sizing with an epoxy sizing agent, they are dried at 150°C to obtain high-strength, high-modulus carbon fibers with high interface.

[0281] Examples 12-22

[0282] Examples 12-22 provide the application of carbon fibers prepared by a carbon fiber preparation method in the preparation of composite materials. The carbon fibers prepared in Examples 1-11 are respectively compounded with epoxy resin Huibai WP-S5001 to obtain composite materials with significantly improved interfacial properties as shown in Examples 12-22.

[0283] Comparative Example 1

[0284] This comparative example provides a method for preparing carbon fiber, which differs from Example 1 in that:

[0285] The electrolyte for both primary and secondary surface treatments was sodium hydroxide, with surface treatment charges of 250 C / g and 350 C / g, respectively.

[0286] The remaining steps are the same as in Example 1.

[0287] Comparative Example 2

[0288] This comparative example provides a method for preparing carbon fiber, which differs from Example 1 in that:

[0289] The electrolyte for both primary and secondary surface treatments was sodium hydroxide, and the surface treatment charge was 250 C / g.

[0290] The remaining steps are the same as in Example 1.

[0291] Comparative Example 3

[0292] This comparative example provides a method for preparing carbon fiber, which differs from Example 1 in that:

[0293] In step 2, the electrolyte for the secondary surface treatment is ammonium acetate.

[0294] The remaining steps are the same as in Example 1.

[0295] Comparative Example 4

[0296] This comparative example provides a method for preparing carbon fiber, which differs from Example 1 in that:

[0297] In step 2, the electrolyte for the secondary surface treatment is ammonium dihydrogen phosphate;

[0298] The remaining steps are the same as in Example 1.

[0299] Comparative Examples 5-8

[0300] Comparative Examples 5-8 provide the application of carbon fibers prepared by a carbon fiber preparation method in the preparation of composite materials. The carbon fibers prepared by Comparative Examples 1-4 are respectively compounded with epoxy resin Huibai WP-S5001 to obtain composite materials with significantly improved interfacial properties as shown in Comparative Examples 5-8.

[0301] Test case

[0302] Test samples and test methods:

[0303] The carbon fibers prepared in Examples 1-11 and Comparative Examples 1-4 were used as Sample 1. The tensile strength and tensile modulus of elasticity were tested according to GB / T3362. The O / C and N / C ratios were measured using X-ray photoelectron spectroscopy. The test results are shown in Table 1.

[0304] The composite materials prepared in Examples 12-22 and Comparative Examples 5-8 were used as Sample 2, and interlaminar shear strength tests were conducted according to ASTM D2344. The test results are shown in Table 1.

[0305] Table 1

[0306] As shown in Table 1, when using sodium hydroxide primary charge of 250 C / g and compound secondary charge of 350 C / g in Examples 1 and 12, the tensile strength of the carbon fiber reached 4530 MPa, the modulus reached 488 GPa, the interlaminar shear strength reached 86 MPa, the O / C ratio reached 0.36, and the N / C ratio reached 0.21. Compared with Comparative Examples 1 and 5, which used sodium hydroxide electrolyte in both secondary stages, the fiber strength increased by 14.6%, the interlaminar shear strength increased by 32.3%, the oxygen-containing functional groups increased by 44%, and the nitrogen-containing functional groups increased by 9.5%, achieving a significant improvement in fiber interfacial properties. The data from the examples show that appropriate oxidation can improve the interfacial bonding strength between carbon fiber and epoxy resin, while excessive oxidation will decrease the interfacial bonding strength (i.e., interlaminar shear strength).

[0307] The various embodiments or implementation methods described in this specification are presented in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0308] In the description of this specification, references to the terms "embodiment," "exemplary embodiment," "some implementation," "illustrated implementation," "example," etc., refer to specific features, structures, materials, or characteristics described in connection with an implementation or example that are included in at least one implementation or example of this disclosure.

[0309] In this specification, the illustrative expressions of the terms used do not necessarily refer to the same implementation or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more implementations or examples.

[0310] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this disclosure, and are not intended to limit them. Although this disclosure has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this disclosure. Industrial applicability

[0311] The carbon fiber, its preparation method, and its application disclosed herein utilize a two-stage surface treatment process to remove the weak layer on the fiber surface and then add oxygen-containing and nitrogen-containing functional groups to the fiber surface, thereby improving the interfacial properties of the carbon fiber.

Claims

1. A method for preparing carbon fiber, the method comprising: Graphitized fibers were prepared using polyacrylonitrile precursor fibers as raw materials. The graphitized fibers were subjected to electrochemical oxidation surface treatment and sizing in sequence to obtain carbon fibers; The electrochemical oxidation surface treatment includes performing a primary surface treatment and a secondary surface treatment on the graphitized fiber in sequence. The primary surface treatment uses an alkaline electrolyte containing hydroxide ions, and the secondary surface treatment uses a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate.

2. The carbon fiber preparation method according to claim 1, wherein, The alkaline electrolyte containing hydroxide ions includes at least one of sodium hydroxide and potassium hydroxide; The electrochemical oxidation surface treatment includes anodic oxidation surface treatment; The charge of the primary surface treatment is 200C / g to 400C / g, and the charge of the secondary surface treatment is 200C / g to 400C / g; The mass ratio of ammonium acetate to ammonium dihydrogen phosphate is 1:1; The time for the first-stage surface treatment is 10s to 30s, and the time for the second-stage surface treatment is 10s to 30s; A graphite roller is provided at the outlet of the electrolyte tank for the secondary surface treatment, and the graphite roller is used to transport graphitized fibers to the washing tank. The inclination angle between the graphitized fiber and the graphite roller is 30° to 50°, and the fiber bundle tension of the graphitized fiber is 50N to 80N.

3. The carbon fiber preparation method according to claim 1, wherein, The preparation process of the graphitized fiber includes: pre-oxidizing, carbonizing, carbonizing and graphitizing the polyacrylonitrile precursor fiber in sequence. The pre-oxidation, primary carbonization, secondary carbonization, and graphitization all employ a gradient heating method. The pre-oxidation temperature is 200℃ to 300℃, and the time is 1h to 2h; The pre-oxidation process is configured with 3 to 4 temperature zones, with a temperature difference of 5°C to 15°C between the zones; The temperature for the first carbonization is 400°C to 800°C, and the time is 3 min to 5 min. The equipment for primary carbonization is equipped with 6 to 8 temperature zones, with a temperature difference of 40°C to 80°C between the zones; The secondary carbonization temperature is 1000℃ to 1600℃, and the time is 2 min to 6 min; The secondary carbonization equipment is equipped with 5 to 6 temperature zones, with a temperature difference of 50°C to 150°C between the zones; The graphitization temperature is 2000℃ to 2600℃, and the time is 2 min to 6 min; The graphitization equipment is equipped with 4 to 5 temperature zones, with a temperature difference of 100°C to 200°C between the zones.

4. The carbon fiber preparation method according to claim 1, wherein, Before the sizing process, the carbon fiber preparation method further includes washing the graphitized fibers after electrochemical oxidation surface treatment with water. The washing time is 100s to 150s; The water washing process employs a multi-stage washing method. The washing process is carried out using a water washing tank, which is provided with 4 to 6 sections. The washing tank is equipped with several baffles, which are used to separate each section of the washing process. The height of the multiple baffles increases along the running direction of the graphitized fibers after electrochemical oxidation surface treatment in the washing tank; The water flow direction in the washing tank is opposite to the running direction of the graphitized fibers after electrochemical oxidation surface treatment; A spray pipe is installed above the washing tank, and the pipe has several openings.

5. The carbon fiber preparation method according to claim 4, wherein, Before the sizing process, the washed graphitized fibers are dried for the first time. The temperature of the first drying step is 130°C to 150°C.

6. The carbon fiber preparation method according to claim 1, wherein, The sizing agent used for sizing is an epoxy sizing agent.

7. The carbon fiber preparation method according to claim 1, wherein, The sized fibers undergo a second drying process. The temperature of the second drying process is between 150°C and 250°C.

8. Carbon fiber prepared by the carbon fiber preparation method according to any one of claims 1-7.

9. The use of carbon fiber as described in claim 8 in the preparation of composite materials.

10. The application of carbon fiber according to claim 9 in the preparation of composite materials, wherein, The composite material is prepared using the following steps: The composite material is obtained by combining carbon fiber and resin matrix.

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