Carbon fiber and its preparation method and application

Abstract

The present invention provides a carbon fiber, a preparation method thereof and an application thereof, relating to the technical field of carbon fiber surface modification. The present invention provides a carbon fiber preparation method, which comprises the following steps: using a polyacrylonitrile precursor as a raw material to prepare a graphitized fiber, and then successively performing electrochemical oxidation surface treatment and sizing on the graphitized fiber to obtain a carbon fiber; wherein, the electrochemical oxidation surface treatment includes: successively performing a primary surface treatment and a secondary surface treatment on the graphitized fiber, the primary surface treatment uses an alkaline electrolyte with hydroxide radicals, and the secondary surface treatment uses a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate. The present invention adopts two-stage surface treatment to remove the weak layer on the fiber surface and then increase the oxygen-containing functional groups and nitrogen-containing functional groups on the fiber surface, which can improve the interfacial performance of the carbon fiber.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fiber surface modification, and particularly to a carbon fiber, a preparation method thereof and an application thereof. Background Art

[0002] Polyacrylonitrile-based high-modulus carbon fibers are widely used in the fields of aerospace, national defense and high-end sports equipment due to their high strength, high modulus, corrosion resistance and low coefficient of thermal expansion. However, after such carbon fibers are treated by high-temperature graphitization, their surfaces exhibit chemical inertness and low adsorption, resulting in difficult effective adhesion of the resin matrix, and thus affecting the performance of the composite material. To improve the surface structure of carbon fibers, researchers have explored various surface treatment methods, such as electrochemical oxidation, gas / liquid phase oxidation, sizing method, chemical grafting and plasma treatment, etc. Among them, electrochemical oxidation has become one of the most practical surface treatment technologies because of its mild treatment, controllable process and the realization of online treatment.

[0003] Selecting a suitable electrolyte solution during electrochemical oxidation treatment is an important factor affecting the treatment effect. The electrolytes used for electrochemical oxidation treatment of carbon fiber surfaces can be divided into acids, alkalis and salts. Acid-base electrolytes are likely to corrode equipment and deteriorate the working environment, and the salt electrolytes of alkali metals are extremely likely to remain in the carbon fiber and become oxidation catalysts, reducing the ablation resistance of the carbon fiber. And generally, the factors affecting the interfacial bonding between carbon fiber and epoxy resin are the oxidation functional groups and roughness on 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 groups, carboxyl groups) on the surface cannot significantly improve the interfacial performance.

[0004] In view of this, the present invention is particularly proposed. Summary of the Invention

[0005] One of the purposes of the present invention is to provide a preparation method of carbon fiber to solve at least one of the technical problems existing in the prior art. The carbon fiber preparation method adopts two-stage surface treatment to remove the weak layer on the fiber surface, and then increase the oxygen-containing functional groups and nitrogen-containing functional groups on the fiber surface, which can improve the interfacial performance of the carbon fiber.

[0006] Another purpose of the present invention is to provide a carbon fiber prepared by the above-mentioned carbon fiber preparation method.

[0007] Another purpose of the present invention is to provide an application of the above-mentioned carbon fiber in the preparation of composite materials. When preparing composite materials, the carbon fiber prepared by the above-mentioned carbon fiber preparation method is compounded with the resin matrix, which is beneficial to the interfacial bonding of the composite material.

[0008] In order to achieve the above purposes of the present invention, the following technical solutions are specifically adopted:

[0009] In a first aspect, the present invention provides a method for preparing carbon fibers, and the method for preparing carbon fibers includes the following steps:

[0010] Using polyacrylonitrile precursor as raw material, graphitized fibers are prepared, and then the graphitized fibers are sequentially subjected to electrochemical oxidation surface treatment and sizing to obtain carbon fibers;

[0011] Among them, the electrochemical oxidation surface treatment includes: sequentially performing primary surface treatment and secondary surface treatment on the graphitized fibers. The primary surface treatment uses an alkaline electrolyte with hydroxide ions, and the secondary surface treatment uses a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate.

[0012] Further, the alkaline electrolyte with hydroxide ions includes at least one of sodium hydroxide and potassium hydroxide;

[0013] Preferably, the electrochemical oxidation surface treatment includes anodic oxidation surface treatment;

[0014] Preferably, the charge of the primary surface treatment is 200 - 400 C / g, and the charge of the secondary surface treatment is 200 - 400 C / g;

[0015] Preferably, the mass ratio of ammonium acetate to ammonium dihydrogen phosphate is 1:1;

[0016] Preferably, the time of the primary surface treatment is 10 s to 30 s, and the time of the secondary surface treatment is 10 s to 30 s;

[0017] Preferably, a graphite roller is provided at the outlet of the electrolyte tank for the secondary surface treatment, and the graphite roller is used to convey the graphitized fibers to the water washing tank;

[0018] Preferably, the inclination angle between the graphitized fibers and the graphite roller is 30° to 50°, and the tow tension of the graphitized fibers is 50 N to 80 N.

[0019] Further, the preparation process of the graphitized fibers includes: sequentially performing pre-oxidation, primary carbonization, secondary carbonization and graphitization on the polyacrylonitrile precursor;

[0020] Preferably, the pre-oxidation, the primary carbonization, the secondary carbonization and the graphitization all adopt a gradient heating method;

[0021] Preferably, the temperature of the pre-oxidation is 200 - 300 °C, and the time is 1 h to 2 h;

[0022] Preferably, the pre-oxidation is provided with 3 - 4 temperature zones, and the temperature difference between the temperature zones is 5 - 15 °C;

[0023] Preferably, the temperature of the first carbonization is 400 - 800 °C, and the time is 3 min to 5 min;

[0024] Preferably, the equipment for the first carbonization is provided with 6 - 8 temperature zones, and the temperature difference between the temperature zones is 40 °C to 80 °C;

[0025] Preferably, the temperature of the second carbonization is 1000 - 1600 °C, and the time is 2 min to 6 min;

[0026] Preferably, the equipment for the second carbonization is provided with 5 - 6 temperature zones, and the temperature difference between the temperature zones is 50 °C to 150 °C;

[0027] Preferably, the temperature of the graphitization is 2000 - 2600 °C, and the time is 2 min to 6 min;

[0028] Preferably, the equipment for the graphitization is provided with 4 - 5 temperature zones, and the temperature difference between the temperature zones is 100 °C to 200 °C.

[0029] Further, before the sizing, it also includes washing the graphitized fibers after the electrochemical oxidation surface treatment;

[0030] Preferably, the time for the washing is 100 - 150 s;

[0031] Preferably, the washing adopts a multi - stage washing method;

[0032] Preferably, a washing tank is used for washing, and the washing tank is provided with 4 - 6 sections;

[0033] Preferably, a number of baffles are arranged inside the washing tank, and the baffles are used to separate each section of the washing;

[0034] Preferably, the heights of the multiple baffles increase along the running direction of the graphitized fibers after the electrochemical oxidation surface treatment in the washing tank;

[0035] Preferably, the water flow direction in the washing tank is opposite to the running direction of the graphitized fibers after the electrochemical oxidation surface treatment;

[0036] Preferably, a pipeline for spraying is arranged above the washing tank, and a number of pores are opened on the pipeline.

[0037] Further, before the sizing, the washed graphitized fibers are subjected to the first drying;

[0038] Preferably, the temperature of the first drying is 130 - 150 °C.

[0039] Further, the sizing agent used for the sizing is an epoxy - type sizing agent.

[0040] Further, the fiber after sizing is subjected to a second drying;

[0041] Preferably, the temperature of the second drying is 150°C to 250°C.

[0042] In a second aspect, the present invention provides a carbon fiber obtained by the carbon fiber preparation method described above.

[0043] In a third aspect, the present invention provides an application of a carbon fiber in the preparation of a composite material.

[0044] In a fourth aspect, the present invention provides an application of the carbon fiber in the preparation of a composite material, and the composite material is prepared by the following steps:

[0045] The carbon fiber and the resin matrix are compounded to obtain the composite material.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] The carbon fiber preparation method provided by the present invention adopts two-stage surface treatment. The first-stage surface treatment uses an alkaline electrolyte with hydroxide ions, and the second-stage surface treatment uses a composite electrolyte of ammonium dihydrogen phosphate and ammonium acetate. The alkaline electrolyte with hydroxide ions oxidizes and etches the surface of the graphitized fiber, the surface crystal grains are refined, the specific surface area increases, and the roughness of the surface of the graphitized fiber after surface treatment increases. When preparing the composite material subsequently, the resin matrix can fully wrap and infiltrate the carbon fiber, forming a physical concave-convex interlocking. This concave-convex interlocking can play an anchoring role after the resin matrix is cured, which is beneficial to the interfacial bonding of the composite material; at the same time, the alkaline electrolyte with hydroxide ions can also effectively remove the weak layer on the surface of the graphitized fiber, and OH - ions can be inserted into the edge of the graphite sheet layer of the graphitized fiber, promoting the exfoliation of the carbon layer in the crystalline region or the amorphous region; after removing the graphite sheet layer on the surface of the graphitized fiber, the second-stage surface treatment uses a composite electrolyte of ammonium dihydrogen phosphate and ammonium acetate. Ammonium dihydrogen phosphate generates acidic groups after electrolysis, and the acidic groups are located at the edge of the exposed graphite sheet layer, which can significantly improve the interfacial performance between the carbon fiber and the resin matrix. Although the treatment with ammonium dihydrogen phosphate can greatly improve the interlaminar shear strength of the carbon fiber, it will reduce its tensile performance. Therefore, the surface of the carbon fiber is quickly oxidized by the ammonium acetate electrolyte to generate oxidation products. The composite electrolyte of ammonium dihydrogen phosphate and ammonium acetate has a better oxidation effect on the carbon fiber, can increase the oxygen-containing functional groups and nitrogen-containing functional groups on the surface of the carbon fiber, and at the same time maintain the strength of the carbon fiber body. Specific Embodiments

[0048] Unless otherwise defined herein, scientific and technical terms used in connection with the present invention shall have the meanings commonly understood by one of ordinary skill in the art. The meanings and scopes of the terms shall be clear. However, in any case of potential ambiguity, the definitions provided herein shall prevail over any dictionary or extrinsic definition. In this application, unless otherwise specified, the use of "or" means "and / or". In addition, the use of the term "comprising" and other forms is non-limiting.

[0049] The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0050] In a first aspect of the present invention, a method for preparing carbon fiber is provided. The method for preparing carbon fiber includes the following steps:

[0051] Using polyacrylonitrile precursor as raw material, graphitized fiber is prepared, and then the graphitized fiber is subjected to electrochemical oxidation surface treatment and sizing in sequence to obtain carbon fiber;

[0052] Wherein, the electrochemical oxidation surface treatment includes: sequentially performing primary surface treatment and secondary surface treatment on the graphitized fiber. The primary surface treatment uses an alkaline electrolyte with hydroxide, and the secondary surface treatment uses a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate.

[0053] In the present invention, two-stage surface treatment is adopted. The primary surface treatment uses an alkaline electrolyte with hydroxide, and the secondary surface treatment uses a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate. The alkaline electrolyte with hydroxide oxidizes and etches the surface of the graphitized fiber, refines the surface grains, increases the specific surface area, and increases the roughness of the surface of the graphitized fiber after surface treatment. When preparing the composite material subsequently, the resin matrix can fully wrap and infiltrate the carbon fiber to form a physical concave-convex interlocking. This concave-convex interlocking can play an anchoring role after the resin matrix is cured, which is beneficial to the interfacial bonding of the composite material; at the same time, the alkaline electrolyte with hydroxide can also effectively remove the weak layer on the surface of the graphitized fiber, OH -Ions can be inserted into the edges of the graphite sheets of graphitized fibers, causing the carbon layers to exfoliate in the crystalline or amorphous regions; after removing the graphite sheets on the surface of the graphitized fibers, the secondary surface treatment uses a composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate. Ammonium dihydrogen phosphate electrolyzes to generate acidic groups, which are located at the edges of the exposed graphite sheets and can significantly improve the interfacial properties between the carbon fibers and the resin matrix. Although the treatment with ammonium dihydrogen phosphate can greatly improve the interlaminar shear strength of the carbon fibers, it will reduce their tensile properties. Therefore, an ammonium acetate electrolyte is used to rapidly oxidize the surface of the carbon fibers to produce oxidation products. The composite electrolyte of ammonium acetate and ammonium dihydrogen phosphate has a better oxidation effect on the carbon fibers, can increase the oxygen-containing functional groups and nitrogen-containing functional groups on the surface of the carbon fibers, and at the same time maintain the strength of the carbon fiber body.

[0054] In some preferred embodiments, the basic electrolyte having hydroxide ions includes at least one of sodium hydroxide and potassium hydroxide;

[0055] The electrochemical oxidation surface treatment includes anodic oxidation surface treatment;

[0056] Preferably, the electric quantity of the primary surface treatment is 200 - 400 C / g, for example, it can be 200 C / g, 250 C / g, 300 C / g, 350 C / g, 400 C / g, etc., and the electric quantity of the secondary surface treatment is 200 - 400 C / g, for example, it can be 200 C / g, 250 C / g, 300 C / g, 350 C / g, 400 C / g, etc.;

[0057] Preferably, the mass ratio of the ammonium acetate to the ammonium dihydrogen phosphate is 1:1;

[0058] Preferably, the time of the primary surface treatment is 10 s - 30 s, for example, it can be 10 s, 15 s, 20 s, 25 s, 30 s, etc.; the time of the secondary surface treatment is 10 s - 30 s, for example, it can be 10 s, 15 s, 20 s, 25 s, 30 s, etc.;

[0059] In the present invention, specific electric quantity, electrolyte time can be used to control the oxidation degree of the carbon fiber surface, avoiding over-oxidation causing excessive etching on the fiber surface or insufficient oxidation resulting in insufficient surface treatment effect.

[0060] In the present invention, the electrolyte tank for the primary surface treatment and the electrolyte tank for the secondary surface treatment are arranged one after the other in the wire running direction of the tow.

[0061] Preferably, a graphite roller is arranged at the outlet of the electrolyte tank for the secondary surface treatment. The graphite roller is used to convey the graphitized fibers to the water washing tank, and a waste liquid collection tank with a length of 50 cm is arranged below the graphite roller;

[0062] The inclination angle between the graphitized fiber and the graphite roller is 30° to 50°, preferably 40°, which helps the electrolyte residue carried by the fiber to drip into the waste liquid collection tank, reducing the water consumption for subsequent water washing and improving the water washing effect. The tow tension of the graphitized fiber is 50 N.

[0063] In some preferred embodiments, the polyacrylonitrile precursor is prepared by a dry-jet wet-spinning method;

[0064] Preferably, the polyacrylonitrile precursor includes AC65-12K.

[0065] In the present invention, AC65-12K prepared by the dry-jet wet-spinning method is used as the raw material, and its advantage is that the fiber has high performance and can meet the requirements of the subsequent high-temperature and high-draft carbonization process.

[0066] In some preferred embodiments, the preparation process of the graphitized fiber includes: pre-oxidizing, first carbonizing, second carbonizing, and graphitizing the polyacrylonitrile precursor in sequence;

[0067] Preferably, the pre-oxidation, the first carbonization, the second carbonization, and the graphitization all adopt a gradient heating method;

[0068] In the present invention, the polyacrylonitrile precursor is pre-oxidized, first carbonized (i.e., low-temperature carbonization), second carbonized (i.e., high-temperature carbonization), and graphitized by the gradient heating method to obtain graphitized fibers. The advantage of the gradient heating method is that it can ensure that the carbon fiber is uniformly heated in each part, avoiding local overheating or overcooling, so that the microstructure of the carbon fiber is more uniform and the generation of defects is reduced.

[0069] Preferably, the temperature of the pre-oxidation is 200-300 °C, such as 200 °C, 250 °C, 300 °C, etc., and the time is 1 h to 2 h, such as 1 h, 1.5 h, 2 h, etc.;

[0070] Preferably, the pre-oxidation is provided with 3-4 temperature zones, such as 3, 4, etc., and the temperature difference between the temperature zones is 5-15 °C, such as 5 °C, 6 °C, 7 °C, 8 °C, 9 °C, 10 °C, 11 °C, 12 °C, 13 °C, 14 °C, 15 °C, etc.;

[0071] In the present invention, one temperature zone of the pre-oxidation is one oxidation furnace. Preferably, 3 oxidation furnaces for pre-oxidation are provided in the present invention, and the temperature difference between the 3 oxidation furnaces is 5-15 °C, gradually increasing; the temperature inside each oxidation furnace is constant, and the furnace temperature of each oxidation furnace needs to be ensured to be uniform.

[0072] Preferably, the temperature of the primary carbonization is 400 - 800°C, such as 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, such as 3 min, 4 min, 5 min, etc.;

[0073] Preferably, the equipment for the primary carbonization is provided with 6 - 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.;

[0074] In the present invention, the primary carbonization (i.e., low - temperature carbonization) uses a low - temperature carbonization furnace, and several increasing temperature zones are arranged inside the low - temperature carbonization furnace.

[0075] Preferably, the temperature of the secondary carbonization is 1000 - 1600°C, such as 1000°C, 1100°C, 1200°C, 1300°C, 1400°C, 1500°C, 1600°C, etc., and the time is 2 min to 6 min, such as 2 min, 4 min, 6 min, etc.;

[0076] Preferably, the equipment for the secondary carbonization is provided with 5 - 6 temperature zones, such as 5, 6, etc., and the temperature difference between the temperature zones is 50°C to 150°C, such as 50°C, 100°C, 150°C, etc.;

[0077] In the present invention, the secondary carbonization (i.e., high - temperature carbonization) uses a high - temperature carbonization furnace, and several increasing temperature zones are arranged inside the high - temperature carbonization furnace.

[0078] Preferably, the temperature of the graphitization is 2000 - 2600°C, such as 2000°C, 2100°C, 2200°C, 2300°C, 2400°C, 2500°C, 2600°C, etc., and the time is 2 min to 6 min, such as 2 min, 4 min, 6 min, etc.;

[0079] Preferably, the equipment for the graphitization is provided with 4 - 5 temperature zones, such as 4, 5, etc., and the temperature difference between the temperature zones is 100°C to 200°C. For example, it can be 100°C, 150°C, 200°C, etc.

[0080] In the present invention, the graphitization uses a graphitization furnace, and several increasing temperature zones are arranged inside the graphitization furnace.

[0081] It should be noted that in the present invention, one oxidation furnace for the pre - oxidation is one temperature zone, and the temperature inside each oxidation furnace needs to be constant; in the steps of low - temperature carbonization, high - temperature carbonization and graphitization, a single furnace is used, and several temperature zones with temperature differences are arranged inside the furnace.

[0082] In some preferred embodiments, before the sizing, it further includes washing the graphitized fibers after the electrochemical oxidation surface treatment;

[0083] In the present invention, the graphitized fibers are surface-treated by an anodic oxidation surface treatment method, impregnated with an electrolyte solution, and then washed. Washing can avoid the residual electrolyte from the primary and secondary surface treatments from entering the subsequent processes, and can further improve the interfacial bonding ability of the carbon fibers when preparing composite materials.

[0084] Preferably, the washing time is 100 - 150 s, for example, it can be 100 s, 110 s, 120 s, 130 s, 140 s, 150 s, etc.;

[0085] Preferably, the washing adopts a multi-stage washing method;

[0086] Preferably, a washing tank is used for washing. The washing tank is provided with 4 - 6 stages, for example, it can be 4 stages, 5 stages, 6 stages, etc. A number of baffles are arranged inside the washing tank. The baffles are used to separate each stage of washing to facilitate better cleaning of the residual surface electrolyte. Among them, the heights of the multiple baffles increase along the running direction of the graphitized fibers in the washing tank after the electrochemical oxidation surface treatment, and the height difference between each stage of the baffles is 8 mm - 10 mm. The water flow direction in the washing tank is opposite to the running direction of the graphitized fibers after the electrochemical oxidation surface treatment;

[0087] Preferably, a pipeline for spraying is arranged above the washing tank, and the pipeline is provided with a number of pores; among them, the diameter of the pores is preferably 5 mm;

[0088] Preferably, the pipeline includes a 304 stainless steel pipe, and the number of pipelines is 2 - 4, for example, it can be 2, 3, 4, etc.;

[0089] Preferably, the conductivity of the water at the end of the washing tank is at most 50 us / cm, preferably at most 20 us / cm.

[0090] In some preferred embodiments, after the washing and before the sizing, the washed fibers are dried for the first time;

[0091] Preferably, the temperature of the first drying is 130 - 150 °C, for example, it can be 130 °C, 135 °C, 140 °C, 145 °C, 150 °C, etc.

[0092] In some preferred embodiments, the sizing agent used for sizing is an epoxy-based sizing agent.

[0093] In some preferred embodiments, the sized fibers are dried for the second time;

[0094] Preferably, the temperature of the second drying is 150°C to 250°C, and for example, it can be 150°C, 200°C, 250°C, etc.

[0095] Furthermore, the carbon fiber preparation method includes the following steps:

[0096] (1) For the dry-jet wet-spun polyacrylonitrile precursor filaments, pre-oxidation, low-temperature carbonization, high-temperature carbonization, and graphitization are carried out in a gradient temperature increase manner to obtain graphitized fibers;

[0097] (2) The graphitized fibers are subjected to anodic oxidation surface treatment method, impregnated through an electrolyte solution, and then subjected to a water washing treatment;

[0098] (3) The fibers after the water washing treatment are dried through a drying roller to remove the surface moisture, and then sized and dried to obtain high-strength and high-modulus carbon fibers.

[0099] The second aspect of the present invention provides a carbon fiber prepared by the carbon fiber preparation method described above.

[0100] In the present invention, by using this carbon fiber preparation method, a high-strength and high-modulus carbon fiber with high interface performance can be prepared.

[0101] The third aspect of the present invention provides an application of the carbon fiber in the preparation of a composite material, and the composite material is prepared by the following steps:

[0102] The carbon fiber and a resin matrix are compounded to obtain the composite material.

[0103] Preferably, the resin matrix includes an epoxy resin. The high-strength and high-modulus carbon fiber and the epoxy resin are compounded to obtain a composite material with significantly improved interface performance.

[0104] When preparing the composite material, the carbon fiber prepared by the carbon fiber preparation method described above is compounded with the resin matrix, which is beneficial to the interface combination of the composite material.

[0105] The present invention will be further described below through examples. Unless otherwise specified, the materials in the examples are prepared according to the existing methods or directly purchased from the market.

[0106] Example 1

[0107] This example provides a carbon fiber preparation method, including the following steps:

[0108] Step 1: For the dry-jet wet-spun AC65-12K precursor filaments, pre-oxidation, low-temperature carbonization, high-temperature carbonization, and graphitization are carried out in a gradient temperature increase manner to obtain graphitized fibers;

[0109] The pre-oxidation process includes: the dry-jet wet-spinning AC65-12K precursor is sequentially pre-oxidized in three oxidation furnaces, the temperatures of the three oxidation furnaces are 230°C, 240°C, and 250°C, the treatment time of each oxidation furnace is the same, and the total pre-oxidation time is 1.5h;

[0110] Among them, low-temperature carbonization includes: the pre-oxidized tow passes through 7 temperature zones in the low-temperature carbonization furnace in turn for low-temperature carbonization, the temperatures of the 7 temperature zones are 400°C, 460°C, 520°C, 580°C, 640°C, 700°C, and 760°C, the treatment time of each temperature zone is the same, and the total residence time of low-temperature carbonization is 4 minutes;

[0111] The high-temperature carbonization includes: the filament bundle after low-temperature carbonization is sequentially passed through 5 temperature zones in the high-temperature carbonization furnace for high-temperature carbonization, the temperatures of the 5 temperature zones are 1000°C, 1100°C, 1200°C, 1300°C, and 1400°C, the processing time of each temperature zone is the same, and the total residence time of high-temperature carbonization is 4 minutes;

[0112] Among them, graphitization includes: the filament bundle after high-temperature carbonization is sequentially passed through 4 temperature zones of the graphitization furnace for graphitization treatment, the temperatures of the 4 temperature zones are 2000°C, 2150°C, 2300°C, and 2450°C respectively, the treatment time of each temperature zone is the same, and the graphitization time is 4 minutes.

[0113] Step 2: The prepared graphitized fiber is subjected to an anodic oxidation surface treatment method, and is sequentially impregnated with the electrolyte in the two-stage surface treatment, and then washed with water;

[0114] The electrolyte for the primary surface treatment is sodium hydroxide, the surface treatment charge is 250C / g, and the treatment time is 20s; the electrolyte for the primary surface treatment is a composite electrolyte of ammonium acetate and diammonium phosphate, the mass ratio of ammonium acetate to diammonium phosphate is 1:1, the surface treatment charge is 350C / g, and the treatment time is 20s;

[0115] 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 under the graphite roller, and the tow tension is 75N;

[0116] Among them, the fibers after two-stage electrolysis are washed with water for 125s. The washing tank is a multi-stage washing tank with 5 sections. Each section is composed of baffles from low to high along the running direction of the tow. The height of each baffle differs by 10mm step by step, and the water flows from the back section to the front section. Four 304 stainless steel pipes are opened above the washing tank for spraying, and the stainless steel pipes have several pores with a diameter of 5mm.

[0117] Step 3: Dry the fibers after the water washing treatment through a drying roller at 145°C to remove the surface moisture, then perform sizing treatment with an epoxy sizing agent and dry it. The drying temperature is 200°C to obtain high-strength and high-modulus carbon fibers with a high interface.

[0118] Example 2

[0119] This example provides a method for preparing carbon fibers. The difference from Example 1 is:

[0120] In Step 2, the electric quantity of the secondary surface treatment is 400 C / g;

[0121] The remaining steps are the same as those in Example 1.

[0122] Example 3

[0123] This example provides a method for preparing carbon fibers. The difference from Example 1 is:

[0124] In Step 2, the electric quantity of the primary surface treatment is 400 C / g;

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

[0126] Example 4

[0127] This example provides a method for preparing carbon fibers. The difference from Example 1 is:

[0128] In Step 2, the electric quantity of the secondary surface treatment is 200 C / g;

[0129] The remaining steps are the same as those in Example 1.

[0130] Example 5

[0131] This example provides a method for preparing carbon fibers. The difference from Example 1 is:

[0132] In Step 2, the electric quantity of the primary surface treatment is 200 C / g, and the electric quantity of the secondary surface treatment is 300 C / g;

[0133] The remaining steps are the same as those in Example 1.

[0134] Example 6

[0135] This example provides a method for preparing carbon fibers. The difference from Example 2 is:

[0136] In Step 2, the electric quantity of the primary surface treatment is 350 C / g;

[0137] The remaining steps are the same as those in Example 2.

[0138] Example 7

[0139] This embodiment provides a method for preparing carbon fiber. The difference from Embodiment 1 is as follows:

[0140] In step 2, two 304 stainless steel pipe sprays are opened above the water washing tank.

[0141] The remaining steps are the same as those in Embodiment 1.

[0142] Embodiment 8

[0143] This embodiment provides a method for preparing carbon fiber. The difference from Embodiment 1 is as follows:

[0144] In step 2, 304 stainless steel pipe spray is not used above the water washing tank.

[0145] Embodiment 9

[0146] This embodiment provides a method for preparing carbon fiber. The difference from Embodiment 1 is as follows:

[0147] In step 2, the electrolyte for primary surface treatment is KOH.

[0148] The remaining steps are the same as those in Embodiment 1.

[0149] Embodiment 10

[0150] This embodiment provides a method for preparing carbon fiber. The difference from Embodiment 1 is as follows:

[0151] In step 1, the pre-oxidation includes: the dry-jet wet-spun AC65-12K raw silk passes through four oxidation furnaces for pre-oxidation in sequence, and the temperatures are 200°C, 215°C, 230°C, and 245°C respectively. The treatment in each temperature zone is the same, and the total pre-oxidation time is 1 h.

[0152] Among them, the low-temperature carbonization includes: the pre-oxidized tow enters the low-temperature carbonization furnace and passes through six temperature zones in sequence. The temperatures of the six temperature zones are 400°C, 480°C, 560°C, 640°C, 720°C, and 800°C respectively. The treatment time in each temperature zone is the same, and the total residence time of low-temperature carbonization is 3 min.

[0153] Among them, the high-temperature carbonization includes: the tow after low-temperature carbonization enters the high-temperature carbonization furnace and passes through six temperature zones in sequence. The temperatures of the six temperature zones are 1000°C, 1050°C, 1100°C, 1150°C, 1200°C, and 1250°C respectively. The treatment time in each temperature zone is the same, and the total residence time of high-temperature carbonization is 6 min.

[0154] Among them, the graphitization includes: the tow after high-temperature carbonization enters the graphitization furnace and passes through five temperature zones in sequence. The temperatures of the five temperature zones are 2000°C, 2100°C, 2200°C, 2300°C, and 2400°C respectively. The treatment time in each is the same, and the total time of graphitization is 6 min.

[0155] In Step 2, the inclination angle is 30°.

[0156] In Step 3, the fibers after water washing treatment are dried through a drying roller at 130 °C, and the drying temperature after sizing treatment is 250 °C.

[0157] The remaining steps are the same as those in Example 1.

[0158] Example 11

[0159] This example provides a method for preparing carbon fibers. The difference from Example 1 is as follows:

[0160] In Step 1, the pre-oxidation includes: the dry-jet wet-spun AC65-12K raw silk passes through 4 oxidation furnaces in sequence for pre-oxidation, and the temperatures are 285 °C, 290 °C, 295 °C, and 300 °C respectively. The treatment time in each temperature zone is the same, and the total pre-oxidation time is 2 h.

[0161] Among them, the low-temperature carbonization includes: the pre-oxidized tow enters the low-temperature carbonization furnace and passes through 8 temperature zones in sequence. The temperatures of the 8 temperature zones are 400 °C, 440 °C, 480 °C, 520 °C, 560 °C, 600 °C, 640 °C, and 680 °C respectively. The treatment time in each temperature zone is the same, and the total residence time of low-temperature carbonization is 5 min.

[0162] Among them, the high-temperature carbonization includes: the tow after low-temperature carbonization enters the high-temperature carbonization furnace and passes through 6 temperature zones in sequence. The temperatures of the 6 temperature zones are 1000 °C, 1150 °C, 1300 °C, 1450 °C, 1500 °C, and 1600 °C respectively. The treatment time in each temperature zone is the same, and the total residence time of high-temperature carbonization is 2 min.

[0163] Among them, the graphitization includes: the tow after high-temperature carbonization enters the graphitization furnace and passes through 5 temperature zones in sequence. The temperatures of the 5 temperature zones are 2000 °C, 2200 °C, 2300 °C, 2500 °C, and 2600 °C respectively. The treatment time in each temperature zone is the same, and the total time of graphitization is 2 min.

[0164] In Step 2, the inclination angle is 50°.

[0165] In Step 3, the fibers after water washing treatment are dried through a drying roller at 150 °C, and the drying temperature after sizing treatment is 150 °C.

[0166] The remaining steps are the same as those in Example 1.

[0167] Examples 12 - 22

[0168] Example 12-22 provides an application of carbon fiber prepared by a carbon fiber preparation method in the preparation of a composite material. The carbon fibers prepared in Examples 1-11 are respectively compounded with epoxy resin Huibo WP-S5001 to obtain a composite material with significantly improved interfacial properties in Examples 12-22.

[0169] Comparative Example 1

[0170] This comparative example provides a carbon fiber preparation method, which is different from Example 1 in that:

[0171] The electrolytes for the primary and secondary surface treatments are both sodium hydroxide, and the surface treatment electric quantities are 250 C / g and 350 C / g respectively;

[0172] The remaining steps are the same as those in Example 1.

[0173] Comparative Example 2

[0174] This comparative example provides a carbon fiber preparation method, which is different from Example 1 in that:

[0175] The electrolytes for the primary and secondary surface treatments are both sodium hydroxide, and the surface treatment electric quantities are both 250 C / g;

[0176] The remaining steps are the same as those in Example 1.

[0177] Comparative Example 3

[0178] This comparative example provides a carbon fiber preparation method, which is different from Example 1 in that:

[0179] In Step 2, the electrolyte for the secondary surface treatment is ammonium acetate;

[0180] The remaining steps are the same as those in Example 1.

[0181] Comparative Example 4

[0182] This comparative example provides a carbon fiber preparation method, which is different from Example 1 in that:

[0183] In Step 2, the electrolyte for the secondary surface treatment is ammonium dihydrogen phosphate;

[0184] The remaining steps are the same as those in Example 1.

[0185] Comparative Examples 5-8

[0186] Comparative Examples 5-8 provide an application of carbon fiber prepared by a carbon fiber preparation method in the preparation of a composite material. The carbon fibers prepared in Comparative Examples 1-4 are respectively compounded with epoxy resin Huibo WP-S5001 to obtain a composite material with significantly improved interfacial properties in Comparative Examples 5-8.

[0187] Test Example

[0188] Test samples and test methods:

[0189] The carbon fibers prepared in Examples 1-11 and Comparative Examples 1-4 were used as Sample 1 respectively. The tensile strength and tensile elastic modulus were tested according to GB / T3362, and the O / C and N / C were measured using an X-ray photoelectron spectrometer. The test results are shown in Table 2;

[0190] The composite materials prepared in Examples 12-22 and Comparative Examples 5-8 were used as Sample 2 respectively. The interlaminar shear strength was tested according to ASTM D2344. The test results are shown in Table 2.

[0191] Table 1

[0192]

[0193]

[0194] It can be seen from the data in Table 1 that when the primary charge of sodium hydroxide is 250 C / g and the secondary charge of the compound is 350 C / g in Example 1 and Example 12, the tensile strength of the carbon fiber body reaches 4530 MPa, the modulus reaches 488 GPa, the interlaminar shear strength reaches 86 MPa, the O / C reaches 0.36, and the N / C reaches 0.21. Compared with Comparative Example 1 and Comparative Example 5 where sodium hydroxide electrolyte is used in both stages, the fiber strength is increased by 14.6%, the interlaminar shear is increased by 32.3%, the oxygen-containing functional groups are increased by 44%, and the nitrogen-containing functional groups are increased by 9.5%, realizing a significant improvement in the fiber interface performance; it can be seen from the data of the examples that appropriate oxidation can improve the interfacial bonding strength between the carbon fiber and the epoxy resin, while excessive oxidation will instead decrease the interfacial bonding strength (i.e., the interlaminar shear strength).

[0195] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing carbon fiber, characterized in that, The carbon fiber preparation method includes the following steps: Using polyacrylonitrile precursor as raw material, graphitized fiber is prepared, and then the graphitized fiber is successively subjected to electrochemical oxidation surface treatment and sizing to obtain carbon fiber; Among them, the electrochemical oxidation surface treatment includes: successively performing primary surface treatment and secondary surface treatment on the graphitized fiber. The primary surface treatment uses an alkaline electrolyte with hydroxide, 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 with hydroxide includes at least one of sodium hydroxide and potassium hydroxide.

3. The carbon fiber preparation method according to claim 1, characterized in that The electrochemical oxidation surface treatment includes anodic oxidation surface treatment.

4. The carbon fiber preparation method according to claim 1, characterized in that, The electricity quantity of the primary surface treatment is 200 - 400 C / g, and the electricity quantity of the secondary surface treatment is 200 - 400 C / g.

5. The carbon fiber preparation method according to claim 1, characterized in that, The mass ratio of the ammonium acetate to the ammonium dihydrogen phosphate is 1:

1.

6. The carbon fiber preparation method according to claim 1, characterized in that The time of the primary surface treatment is 10s - 30s, and the time of the secondary surface treatment is 10s - 30s.

7. The method for preparing carbon fiber according to claim 1, wherein A graphite roller is arranged at the outlet of the electrolyte tank for the secondary surface treatment, and the graphite roller is used to convey the graphitized fiber to the water washing tank.

8. The carbon fiber preparation method according to claim 7, wherein, The inclination angle between the graphitized fiber and the graphite roller is 30° - 50°, and the tow tension of the graphitized fiber is 50N - 80N.

9. The carbon fiber preparation method according to claim 1, characterized in that, The preparation process of the graphitized fiber includes: successively performing pre-oxidation, primary carbonization, secondary carbonization and graphitization on the polyacrylonitrile precursor.

10. The carbon fiber preparation method according to claim 9, characterized in that, The pre-oxidation, the primary carbonization, the secondary carbonization and the graphitization all adopt a gradient heating method.

11. The carbon fiber preparation method according to claim 9, characterized in that, The temperature of the pre-oxidation is 200 - 300°C, and the time is 1h - 2h.

12. The carbon fiber preparation method according to claim 9, wherein The pre-oxidation is provided with 3 - 4 temperature zones, and the temperature difference between the temperature zones is 5 - 15°C.

13. The carbon fiber preparation method according to claim 9, characterized in that, The temperature of the primary carbonization is 400 - 800°C, and the time is 3min - 5min.

14. The carbon fiber preparation method according to claim 9, characterized in that, The equipment for the primary carbonization is provided with 6 - 8 temperature zones, and the temperature difference between the temperature zones is 40°C - 80°C.

15. The carbon fiber preparation method according to claim 9, characterized in that, The temperature of the secondary carbonization is 1000 - 1600°C, and the time is 2min - 6min.

16. The carbon fiber preparation method according to claim 9, characterized in that, The equipment for the secondary carbonization is provided with 5 - 6 temperature zones, and the temperature difference between the temperature zones is 50°C - 150°C.

17. The carbon fiber preparation method according to claim 9, characterized in that, The temperature of the graphitization is 2000 - 2600°C, and the time is 2min - 6min.

18. The carbon fiber preparation method according to claim 9, characterized in that The equipment for the graphitization is provided with 4 - 5 temperature zones, and the temperature difference between the temperature zones is 100°C - 200°C.

19. The carbon fiber preparation method according to claim 1, characterized in that, Before the sizing, it also includes washing the graphitized fiber after the electrochemical oxidation surface treatment.

20. The carbon fiber preparation method according to claim 19, characterized in that, The time of the washing is 100 - 150s.

21. The carbon fiber preparation method according to claim 19, characterized in that, The washing adopts a multi-stage washing method.

22. The carbon fiber preparation method according to claim 19, characterized in that, A water washing tank is used for washing, and the water washing tank is provided with 4 - 6 sections.

23. The carbon fiber preparation method according to claim 22, characterized in that, A number of baffles are arranged inside the water washing tank, and the baffles are used to separate each section of the washing.

24. The carbon fiber preparation method according to claim 23, wherein The heights of the multiple baffles increase along the running direction of the graphitized fiber after the electrochemical oxidation surface treatment in the water washing tank.

25. The carbon fiber preparation method according to claim 24, wherein The water flow direction in the water washing tank is opposite to the running direction of the graphitized fiber after the electrochemical oxidation surface treatment.

26. The carbon fiber preparation method according to claim 22, characterized in that, A pipeline for spraying is arranged above the water washing tank, and a number of pores are opened on the pipeline.

27. The carbon fiber preparation method according to claim 19, characterized in that, Before the sizing, the graphitized fiber after washing is subjected to the first drying.

28. The carbon fiber preparation method according to claim 27, characterized in that, The temperature of the first drying is 130 - 150 °C.

29. The carbon fiber preparation method according to claim 1, characterized in that, The sizing agent used for sizing is an epoxy sizing agent.

30. The carbon fiber preparation method according to claim 1, characterized in that, The fibers after sizing are subjected to a second drying.

31. The carbon fiber preparation method according to claim 30, characterized in that, The temperature of the second drying is 150 °C to 250 °C.

32. Carbon fibers prepared by the carbon fiber preparation method according to any one of claims 1 - 31.

33. Use of the carbon fibers according to claim 32 in the preparation of composite materials.

34. The application of carbon fiber according to claim 33 in the preparation of a composite material, characterized in that, The composite material is prepared by the following steps: The carbon fibers and the resin matrix are compounded to obtain the composite material.

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