CN116876203A - Carbon fiber, preparation method thereof and composite material - Google Patents

Abstract

The application relates to a carbon fiber, a preparation method thereof and a composite material, and belongs to the technical field of carbon fiber preparation. The preparation method comprises the following steps: placing the carbonized fiber body obtained through the pre-oxidation reaction and the carbonization reaction in a boride solution, and sequentially carrying out soaking and drying treatment to coat the boride on the surface of the carbonized fiber body; then sequentially carrying out graphitization heat treatment and surface treatment on the carbonized fiber body after the drying treatment to obtain carbon fibers; the surface treatment includes: and sequentially carrying out first-stage electrochemical anodic oxidation treatment and second-stage electrochemical anodic oxidation treatment on the carbonized fiber body subjected to graphitization heat treatment, so that the fiber surface is etched and oxygen-containing functional groups are generated. According to the preparation method, the boron catalyst is introduced into the carbonized fiber body, and then graphitization heat treatment and surface treatment are carried out, so that the carbon fiber with higher modulus and interface performance can be obtained at a low graphitization heat treatment temperature, meanwhile, the graphitization heat treatment time is shortened, the equipment loss is reduced, and the production cost is reduced.

Description

Carbon fiber and preparation method thereof, composite material

Technical field

The present application relates to the technical field of carbon fiber preparation, and in particular to a carbon fiber, its preparation method, and composite materials.

Background technique

As a new type of inorganic fiber material, carbon fiber combines the advantages of carbon materials and textile fibers and has broad application prospects. Its importance in cutting-edge technological fields such as aviation, aerospace, missiles and rockets cannot be ignored. At the same time, it has also become an important new material for industrial upgrading in civilian fields such as high-end sporting goods and medical equipment. In recent years, with the continuous advancement of carbon fiber manufacturing technology and process control technology, various carbon fiber products with different properties have been introduced one after another, becoming a high-profile reinforcing material in composite materials.

After graphitized carbon fiber is treated at high temperature, its tensile modulus can usually reach more than 300GPa. The high modulus makes carbon fiber composite materials have excellent rigidity and dimensional stability, and are widely used in fields that have strict requirements on structural deformation, such as aerospace and civil materials. Such as horn antennas in artificial satellites, civilian fishing rods and mobile phone folding screens. Take Japan's Toray as an example. In 2018, it launched M40X carbon fiber with a tensile strength of 5700MPa and a tensile modulus of 377GPa. In 2020, it launched a new high-modulus carbon fiber with a tensile strength of 4800MPa and a tensile modulus of 390GPa. These two products Carbon fiber is mainly developed to replace traditional high-end aerospace and industrial products. The increase in the modulus of carbon fiber is directly related to the graphitization transformation of its internal structure, which requires a high-temperature graphitization process. Under high temperature conditions of 2000-3000°C, non-carbon components in the fiber are gradually removed, causing the internal structure of the fiber to transform, and ultimately the carbon content of the fiber reaches 99-100%, thereby significantly increasing its modulus. Usually, the interlaminar shear strength of commercial carbon fibers needs to reach about 70MPa to meet the application requirements of composite materials. However, after high-temperature graphitization heat treatment, the oxygen-containing functional groups on the surface of the fiber decrease sharply, and the surface inertness increases significantly, resulting in a reduction in the interfacial properties of the fiber. Moreover, although the traditional high-temperature graphitization process can enhance the modulus, excessive temperature may affect the service life of the equipment and is not suitable for continuous production, resulting in increased production costs.

Contents of the invention

In view of the shortcomings of the existing technology, the purpose of the embodiments of the present application includes providing a method for preparing carbon fibers to simultaneously improve the modulus and interface properties of carbon fibers.

In a first aspect, embodiments of the present application provide a method for preparing carbon fibers, which includes the following steps: placing the carbonized fiber body obtained by sequentially undergoing a pre-oxidation reaction and a carbonization reaction in a boride solution, sequentially soaking and drying it, so that the boron The chemical is coated on the surface of the carbonized fiber body; then the dried carbonized fiber body is sequentially subjected to graphitization heat treatment and surface treatment to obtain carbon fiber; the surface treatment includes: subjecting the carbonized fiber body that has undergone graphitization heat treatment to the first level of electrolysis in sequence Chemical anodizing treatment and second-stage electrochemical anodizing treatment etch the fiber surface and generate oxygen-containing functional groups.

This preparation method introduces a boron catalyst into the carbonized fiber body and then performs graphitization heat treatment, which can obtain higher modulus carbon fibers at low graphitization heat treatment temperature, while reducing graphitization heat treatment time, slowing down equipment losses, and reducing production costs. After graphitization heat treatment, the carbonized fiber body also needs to undergo first-level electrochemical anodizing treatment and second-level electrochemical anodizing treatment to etch the fiber surface and increase oxygen-containing functional groups, and introduce active groups on the fiber surface. Increase the interfacial properties of the fiber and improve the chemical bonding ability of the final graphite fiber and the matrix resin. It can also increase the roughness of the fiber surface, improve the mechanical fitting of the fiber and the matrix resin, and ultimately improve the quality of the graphite fiber made from the graphite fiber. Interlaminar shear strength of composite materials. The carbon fiber preparation method provided by this application can also be used in continuous production to save production costs.

In some embodiments of the present application, in the boride solution, the boride includes boric acid and/or boron carbide powder. Selecting boric acid and/or boron carbide powder as the boride can help optimize the interfacial properties, high temperature resistance and chemical properties of the carbon fiber, thereby improving the performance and stability of the final product. Through boride coating, the interfacial properties and oxidation resistance of carbon fiber can be improved. The boride coating helps protect the fiber and increases its service life.

In some embodiments of the present application, the mass concentration of the boride solution is 5-20%. Controlling the mass concentration of the boride solution within the range of 5% to 20% helps to form a uniform coating on the fiber surface, which can achieve better coverage and reduce interface degradation, thereby improving the durability and durability of the carbon fiber. service life.

In some embodiments of the present application, the boride solution includes a boric acid solution with a mass concentration of 8-12%.

In some embodiments of the present application, the boride solution includes a mixed solution of boron carbide powder and boric acid, where the mass ratio of boron carbide powder and boric acid is 1:(1-3). The ratio of boron carbide powder and boric acid in the mixed solution can adjust the properties of the final carbon fiber produced. Boron carbide powder can promote the graphitization transformation inside the fiber during the graphitization process, increase the carbon content of the fiber, and thereby increase the modulus and hardness of the fiber. Boric acid can be used as an oxidant to help introduce oxygen-containing functional groups during the electrochemical anodization treatment and improve the interfacial properties of the fiber. Controlling the mass ratio of boron carbide powder and boric acid within the range of 1:(1-3) can regulate material properties, enhance interface properties, adapt to different needs, and control production costs.

In some embodiments of the present application, the soaking conditions include: the soaking temperature is 20-25°C, and the soaking time is 10-180s. Controlling the soaking temperature in the range of 20-25°C and the soaking time in the range of 10-180 seconds helps achieve stable interfacial coating formation, protect the fiber structure, improve production efficiency, and ensure product consistency and repeatability while reducing security risks.

In some embodiments of the present application, the graphitization heat treatment includes: subjecting the soaked carbonized fiber body to a gradient graphitization heat treatment with a temperature ranging from 1800°C to 2250°C under an inert gas protective atmosphere, and setting the temperature between 1800°C and 2250°C. Multiple heat treatment temperature zones to provide multiple temperature gradients between 1800-2250°C. Graphitization heat treatment can further improve the crystallinity and modulus of carbon fiber. By performing graphitization heat treatment under multiple temperature gradients, the internal structure of the fiber can be made more uniform and the overall performance can be improved.

In some embodiments of the present application, the inert gas includes any one of nitrogen and argon.

In some embodiments of the present application, the number of heat treatment temperature zones is 3-5, and the temperature difference of each heat treatment temperature zone is 30-300°C. The graphitization heat treatment is divided into 3-5 heat treatment temperature zones, and the temperature difference in each temperature zone is 30-300°C, which helps to achieve finer temperature control and a more uniform graphitization process. This optimizes the structural transformation within the fiber, resulting in a more consistent graphitization effect.

In some embodiments of the present application, the graphitization heat treatment time is 20-40 s. Controlling the graphitization heat treatment time within the range of 20-40s can achieve effective graphitization.

In some embodiments of the present application, during the graphitization heat treatment, the tension applied to the carbonized fiber body is 20-80N. By applying moderate tension in the tension range of 20-80N, the graphitization process of the internal structure of the carbonized fiber can be optimized, ultimately resulting in better graphitization and increased carbon content, thereby increasing the modulus and hardness of the fiber.

In some embodiments of the present application, the total amount of electricity applied in the first-stage electrochemical anodizing treatment and the second-stage electrochemical anodizing treatment is 60-150C/g; and/or, the temperature of the electrochemical anodizing treatment The temperature is 20-60°C; and/or the first-stage electrochemical anodizing treatment time is 15-30s; and/or the second-stage electrochemical anodizing treatment time is 15-30s. Controlling the power, temperature and treatment time of the electrochemical anodizing treatment within the above ranges helps to regulate the properties, thickness and uniformity of the oxide layer, thereby achieving the required interface performance and surface characteristics. This helps improve the surface properties, interfacial adhesion, and overall performance of the carbon fiber.

In some embodiments of the present application, the electric quantity applied in the first-stage electrochemical anodizing treatment is 30-80C/g, and the electric quantity applied in the second-stage electrochemical anodizing treatment is 30-80C/g.

In some embodiments of the present application, the electrolyte used in the electrochemical anodization treatment includes an acidic electrolyte and/or an alkaline electrolyte.

In some embodiments of the present application, the electrolyte used in the electrochemical anodization treatment includes one or more of ammonium bicarbonate, sodium hydroxide, sulfuric acid and nitric acid.

In some embodiments of the present application, the mass concentration of the electrolyte used in the electrochemical anodization treatment is 0.5-8%. Controlling the mass concentration of the electrolyte used in electrochemical anodizing treatment within the range of 0.5-8% can obtain a uniform, dense and high-quality oxide layer, while also contributing to process control, energy efficiency and environmental friendliness.

In some embodiments of the present application, the pre-oxidation reaction includes: pre-oxidizing polyacrylonitrile fibers with a density of 1.15-1.25 g/cm ³ and a single filament diameter of 4-8 μm; wherein, the temperature rise of the pre-oxidation reaction starts The starting temperature is 200°C and the ending temperature is 300°C; the residence time of the pre-oxidation reaction is 30-90min, the tension applied to the fiber bundle is 5-25N, and a pre-oxidized fiber body with a density of 1.32-1.39g/ ^cm3 is obtained. .

In some embodiments of the present application, the carbonization reaction includes: sequentially performing a first carbonization treatment and a second carbonization treatment on the pre-oxidized fiber body to obtain a carbonized fiber body; wherein the step of the first carbonization treatment includes performing a temperature range from 400°C to 700°C. °C gradient heating, the first carbonization treatment time is 1-3 minutes, the second carbonization treatment step includes gradient heating from 900°C to 1500°C, the second carbonization treatment time is 1-3 minutes.

In some embodiments of the present application, the preparation method further includes: sequentially washing, sizing, drying and winding the carbon fiber. The main purpose of water washing is to completely remove the electrolyte, products and other impurities remaining on the fiber surface during the electrochemical anodization process. The use of sizing agents can enhance the adhesion between carbon fibers and composite matrix. The sizing agent can form a thin film on the surface of the fiber to increase the bonding strength between the fiber and the matrix, thus improving the performance of the composite material. The purpose of drying is to remove moisture from the fiber.

In some embodiments of the present application, the mass concentration of the sizing agent used in the sizing step is 1.0-2.5%. Controlling the mass concentration of the sizing agent to 1.0-2.5% can evenly coat the fiber surface with the sizing agent, reduce subsequent processing, and reduce fiber damage.

In some embodiments of the present application, drying conditions include: drying temperature is 140-170°C, and drying time is 0.2-2 minutes.

In a second aspect, embodiments of the present application provide a carbon fiber prepared by the above preparation method.

In a third aspect, embodiments of the present application provide a composite material including the above-mentioned carbon fiber.

Detailed ways

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

A carbon fiber, its preparation method, and composite materials according to the embodiments of the present application will be described in detail below.

The embodiment of the present application provides a carbon fiber, and its preparation method includes the following steps:

(1) Preoxidation reaction

Polyacrylonitrile fiber with a density of 1.15-1.25g/cm ³ and a single filament diameter of 4-8 μm is subjected to a pre-oxidation reaction; where the starting temperature of the pre-oxidation reaction is 200°C and the end temperature is 300°C; pre-oxidation The residence time of the reaction is 30-90min, the tension applied to the fiber bundle is 5-25N, and a pre-oxidized fiber body with a density of 1.32-1.39g/ ^cm3 is obtained. Through the pre-oxidation reaction, polyacrylonitrile fibers can be converted into pre-oxidized fibers to increase the graphitization potential of the fibers. Pre-oxidation can partially oxidize the non-carbon components in the fiber to prepare for subsequent graphitization heat treatment.

(2) Carbonization reaction

The pre-oxidized fiber body with a density of 1.32-1.39g/ ^cm3 obtained in step (1) is sequentially subjected to a first carbonization treatment and a second carbonization treatment to obtain a carbonized fiber body; wherein, the step of the first carbonization treatment includes performing Gradient heating from 400°C to 700°C, the time of the first carbonization treatment is 1-3 minutes, the step of the second carbonization treatment includes gradient heating from 900°C to 1500°C, the time of the second carbonization treatment is 1-3 minutes. The first carbonization treatment and the second carbonization treatment help to further increase the carbon content and crystallinity of the fiber. This can significantly increase the strength and modulus of carbon fiber. At the same time, the gradient heating method can effectively reduce processing time and improve production efficiency.

(3)Boride coating

Press the carbonized fiber body obtained in step (2) into the boride solution through a groove wheel at 20-25°C, and soak it so that a layer of boride is evenly attached to each carbon fiber. The soaking time is 10-180s. ; Soak the carbonized fiber body and then dry it at 80-160°C. After drying, the boride is evenly coated on the surface of the carbon fiber;

(4) Graphitization heat treatment

Then, the dried carbonized fiber body is placed in a graphitization furnace, and a gradient graphitization heat treatment is performed from 1800°C to 2250°C in a nitrogen or argon protective atmosphere, with multiple heat treatments set between 1800-2250°C. temperature zone so that there are multiple temperature gradients between 1800-2250℃. In the graphitization heat treatment, the tension applied to the carbonized fiber body is 20-80N, and the graphitization heat treatment time is 20-40s. Among them, the number of heat treatment temperature zones is 3-5, and the temperature difference of each heat treatment temperature zone is 30-300°C.

Although carbon fiber is a brittle material, when heat treated at temperatures above 1800°C, the graphite crystallites will exhibit a certain degree of thermoplasticity. The carbon fiber can be stretched by 5-10%. The stretching will promote the creep of the graphite crystallites during the graphitization process. Change, eliminate the stress between the turbostratic graphite crystallites, cause the crystallites to shift and rearrange, and increase the orientation of the graphite crystallites along the fiber axis. Different graphitization temperatures correspond to different fiber stresses, and fiber stress is closely related to the growth of the graphitized microcrystalline structure. Under the same temperature conditions, the internal stress of the fiber increases linearly with the increase in tensile strength. Studying its stress control is beneficial to carbon fiber. Increased density, strength and modulus. Usually 1700°C is the initial temperature at which graphitization begins. As fiber graphitization proceeds, the condensation denitrification reaction of small aromatic rings is mainly the process before 1700-2200°C. At this stage, the fiber element composition, porosity and density change, 2200 After ℃, the denitrification reaction is basically completed and the carbon content of the fiber is close to 100%. At this time, the main processes inside the fiber are the migration of carbon atoms, the transposition rearrangement and preferred orientation of the carbon network. This stage makes the fiber graphite layer orderly. Stacking is improved and fiber modulus increases. Catalytic graphitization can reduce the activation energy required for layer stacking, reducing the graphitization temperature by 200-500°C. Therefore, the graphitization heat treatment in this application is to perform graphitization heat treatment with 3-5 temperature gradients at a temperature of 1800-2250°C in a nitrogen or argon protective atmosphere. The treatment time is 20-40 s. At the same time, at different graphitization temperatures The tension range applied to the fiber tow under gradient conditions is 20-80N. By dividing the graphitization heat treatment into 3-5 heat treatment temperature zones, with a temperature difference of 30-300°C in each temperature zone, it helps to achieve finer temperature control and a more uniform graphitization process. This optimizes the structural transformation within the fiber, resulting in a more consistent graphitization effect. At the same time, applying moderate tension in the tension range of 20-80N can optimize the graphitization process of the internal structure of the carbonized fiber, ultimately resulting in better graphitization effect and increased carbon content, thereby increasing the modulus and hardness of the fiber.

As an example, the temperature difference of each temperature zone includes but is not limited to 30°C, 50°C, 100°C, 120°C, 150°C, 180°C, 200°C, 210°C, 230°C, 250°C, 270°C, 300°C . In the graphitization heat treatment, the tension applied to the fiber bundles includes but is not limited to 20N, 30N, 40N, 50N, 60N, 70N, and 80N.

The treatment method proposed in this application is to use boride solution to coat carbon fibers and then perform catalytic graphitization. It can obtain higher modulus graphite fibers at low graphitization heat treatment temperature. The time of graphitization heat treatment is generally 40-60s. This book In the application, the graphitization heat treatment time is reduced to 20-40 seconds, which plays a role in saving energy and reducing consumption.

In this application, the boride includes boric acid and/or boron carbide powder, and the mass concentration of the boride solution is 5-20%. For example, the boride solution is a boric acid solution with a mass concentration of 8-12%, or the boride solution is a mixed solution of boron carbide powder and boric acid, where the mass ratio of boron carbide powder and boric acid is 1:(1-3). Both boric acid and boron carbide powders have good interfacial activity and can interact with the carbon fiber surface to form a uniform and tight coating. This can improve the surface properties of the fibers and enhance the bonding between the fibers and the matrix, thereby improving the performance and stability of carbon fiber composites. Moreover, boron carbide powder has good high temperature resistance, can exist stably during high-temperature graphitization heat treatment, and helps to form a stable interface layer at high temperatures. This is very important to improve the graphitization degree and interfacial properties of carbon fiber. Controlling the mass concentration of the boride solution within the range of 5% to 20% helps to form a uniform coating on the fiber surface, which can achieve better coverage and reduce interface degradation, thereby improving the durability and durability of the carbon fiber. service life.

In this application, the soaking temperature of the carbonized fiber body in the boride solution is 20-25°C, and the soaking time is 10-180s. Soaking at a temperature of 20-25°C (room temperature) can effectively control the rate of interface reaction and prevent excessively fast reactions from causing uneven coating or interface degeneration. This helps ensure the stability of the interfacial bond between fiber and coating, improving the material's performance and durability. At the same time, lower temperatures and relatively short soaking times help avoid overexposure of carbon fibers to chemicals, thereby reducing adverse effects on fiber structure and performance. This helps maintain the fiber's strength, modulus and other key properties.

(5)Surface treatment and post-treatment

The carbonized fiber body that has been graphitized and heat-treated is sequentially subjected to the first-stage electrochemical anodizing treatment and the second-stage electrochemical anodizing treatment using the method of pulse electricity, so that the fiber surface is etched and oxygen-containing functional groups are generated; then the fiber surface is The residual electrolyte and impurities are washed away, and the washed fibers are dried using a drying roller at 100-120°C; then a sizing agent with a mass concentration of 1.0-2.5% is used for sizing, and the sizing amount is controlled at 0.6-1.4% ; Dry the sized fiber in a drying oven at 140-170°C for 0.2-2 minutes, and wind and collect to obtain carbon fiber with high modulus and high interface properties. The above post-processing steps are mainly to prepare the carbon fiber for subsequent application in composite materials.

In this application, the electrolyte used in the electrochemical anodization treatment includes acidic electrolyte and/or alkaline electrolyte. The electrolyte includes, but is not limited to, one or more of ammonium bicarbonate, sodium hydroxide, sulfuric acid and nitric acid. Among them, the mass concentration of the electrolyte used in the electrochemical anodizing treatment is 0.5-8%. Controlling the mass concentration of the electrolyte used in electrochemical anodizing treatment within the range of 0.5-8% can obtain a uniform, dense and high-quality oxide layer, while also contributing to process control, energy efficiency and environmental friendliness.

In this application, the total amount of electricity applied in the first-stage electrochemical anodizing treatment and the second-stage electrochemical anodizing treatment is 60-150C/g, and the amount of electricity applied in each stage of electrochemical anodizing treatment is 30-80C/g. The temperature of the electrochemical anodizing treatment is 20-60°C, the time of the first-stage electrochemical anodizing treatment is 15-30s, and the time of the second-stage electrochemical anodizing treatment is 15-30s. Controlling the power of the electrochemical anodizing process can control the thickness and properties of the oxide layer to a certain extent. The increase in electricity will lead to the thickening of the oxide layer, thereby improving surface hardness, wear resistance and corrosion resistance. Controlling the total electric power within the electric power range of 60-150C/g can make the fiber surface have an oxide layer of appropriate thickness, thereby achieving the required performance. The temperature of the electrochemical process can affect the growth rate and structure of the oxide layer, thereby affecting the performance of the oxide layer. Controlling the temperature of the electrochemical anodizing treatment within the range of 20-60°C can achieve the required performance while maintaining a suitable oxide layer structure. At the same time, the electrochemical anodization treatment time will affect the thickness and structure of the oxide layer, as well as the introduction of functional groups. Controlling the electrochemical anodizing treatment time of each stage within the range of 15-30s can make the oxide layer more uniform and produce an oxide layer of appropriate thickness to achieve the required performance.

As an example, the total electricity applied by the first-stage electrochemical anodizing treatment and the second-stage electrochemical anodizing treatment includes but is not limited to 60C/g, 70C/g, 80C/g, 90C/g, 100C/g, 110C/g, 120C/g, 130C/g, 140C/g, 150C/g.

In this application, the sizing agent used is an aqueous epoxy resin emulsion, such as a bisphenol A-type epoxy resin aqueous emulsion, MU-6019C type aqueous epoxy resin emulsion purchased from Shanghai Runcarbon New Material Technology Co., Ltd.

An embodiment of the present application also provides a composite material, which contains the above-mentioned carbon fiber.

The features and performance of the present application will be described in further detail below in conjunction with examples.

Example 1

This embodiment provides a carbon fiber, and its preparation method includes:

(1) The polyacrylonitrile fiber with a density of 1.18g/cm ³ and a single filament diameter of 5 μm is subjected to a pre-oxidation reaction; the starting temperature of the pre-oxidation reaction is 200°C and the end temperature is 300°C; the pre-oxidation reaction The residence time was 80 min, the tension applied to the fiber bundle was 17N, and a ^preoxidized fiber body with a density of 1.35g/cm was obtained.

(2) The pre-oxidized fiber body with a density of 1.35g/ ^cm3 obtained in step (1) is sequentially subjected to a first carbonization treatment and a second carbonization treatment to obtain a carbonized fiber body; wherein the step of the first carbonization treatment includes Gradient heating from 400°C to 700°C, the first carbonization treatment time is 1.5 minutes, the second carbonization treatment step includes gradient heating from 900°C to 1500°C, the second carbonization treatment time is 1.5 minutes.

(3) Press-immerse the carbonized fiber body obtained in step (2) into a boric acid solution with a mass concentration of 8% at 25°C through a groove wheel, soak for 60 s, and dry at 110°C. Gradient graphitization heat treatment was carried out through four temperature zones of 1850°C, 1970°C, 2150°C, and 2230°C. At the same time, a drafting tension of 76N was applied to the fiber bundles, and the graphitization heat treatment time was 35 seconds; followed by two-stage electrochemical anodization. For surface treatment, the first-stage electrochemical anodizing treatment is performed first, and then the second-stage electrochemical anodizing treatment is performed; among them, in the first-stage electrochemical anodizing treatment, the first-stage electrolyte uses a sulfuric acid solution with a mass concentration of 2%. , the processing power is controlled to 70C/g, and the processing time is 20s; in the second-stage electrochemical anodization treatment, the secondary electrolyte uses a sodium hydroxide solution with a mass concentration of 4.5%, the processing power is 70C/g, and the processing time is 20s; the electrolyte treatment temperature is all 60°C; the surface-treated fibers are washed with water and dried in a drying drum at 110°C, and sizing is performed using bisphenol A-type epoxy resin aqueous emulsion with a mass concentration of 1.6% as the sizing agent. The amount is 1.0%. After sizing, it is dried at 140°C for 1 minute, and then wound and collected to obtain high-performance carbon fiber.

Example 2

This embodiment is basically the same as Embodiment 1, except for step (3).

Step (3): Press the carbonized fiber body obtained in step (2) into a boric acid solution with a mass concentration of 12% at 25°C through a sheave, soak for 60 seconds, dry at 120°C, and then carbonize the dried fiber. The fiber body was subjected to gradient graphitization heat treatment through five temperature zones of 1800°C, 1930°C, 2150°C, 2200°C, and 2230°C. At the same time, a drafting tension of 65N was applied to the fiber bundle, and the graphitization heat treatment time was 30 seconds; then two steps were performed. The first-level electrochemical anodizing surface treatment is performed first, and then the second-level electrochemical anodizing treatment is carried out; among them, in the first-level electrochemical anodizing treatment, the mass concentration of the first-level electrolyte is For 4% sodium hydroxide solution, the processing power is controlled to be 60C/g and the processing time is 20s; in the second-stage electrochemical anodization treatment, the secondary electrolyte uses an ammonium bicarbonate solution with a mass concentration of 5%, and the processing power is 60C/g, the treatment time is 20s; the electrolyte treatment temperature is 50℃; the surface-treated fibers are washed and dried in a drying drum at 120℃, and then treated with a bisphenol A-type epoxy resin aqueous emulsion with a mass concentration of 1.9%. Sizing is performed for the sizing agent, and the sizing amount is 1.3%. After sizing, it is dried at 170°C for 0.5 minutes, and then wound and collected to obtain high-performance carbon fiber.

The remaining examples and comparative examples are basically the same as Example 1, except that the reagents and some parameters in step (3) are different. Please see Table 1 for details.

Table 1

Comparative example 1

This comparative example is basically the same as Example 1, except that the surface treatment in step (3) only carries out the first-stage electrochemical anodizing treatment and does not carry out the second-stage electrochemical anodizing treatment.

Comparative example 2

This comparative example is basically the same as Example 1, except that no surface treatment is performed in step (3), only graphitization heat treatment is performed.

Test example

The carbon fibers provided in Examples 1-20 and Comparative Examples were made into carbon fiber composite materials, and the interlaminar shear strength of the composite materials was tested in sequence. Among them, the preparation method of carbon fiber composite materials is as follows: 1. The carbon fiber experimental wire is wound on a wooden board wrapped with release paper for a fixed number of turns; 2. Mix it with AG80 resin and curing agent in a certain proportion, and evenly apply it on the winding wire in the previous step. , soak and knead well; 3. Put it into a mold and press it into a fixed cross-section (constant width and thickness), heat and cool to make an interlayer shear spline (one-way plate).

At the same time, the tensile strength and tensile modulus of the carbon fibers provided in Examples 1-20 and Comparative Examples were tested. Among them, the tensile strength testing is based on GB/T3362, the tensile modulus testing is based on GB/T3362, and the interlaminar shear strength testing is based on GB/T1450.1-2005. The above performance test results are shown in Table 2.

Table 2

sample Tensile modulus (GPa) Tensile strength(MPa) Interlaminar shear strength (MPa) Example 1 437 4635 100 Example 2 446 4410 91 Example 3 423 4572 87 Example 4 434 4617 98 Example 5 402 4710 81 Example 6 439 4681 101 Example 7 432 4593 96 Example 8 430 4553 96 Example 9 409 4601 95 Example 10 301 5200 98 Example 11 420 3971 89 Example 12 296 4206 87 Example 13 323 4504 91 Example 14 411 4673 88 Example 15 396 4595 93 Example 16 435 4589 85 Example 17 437 4635 83 Example 18 437 4635 55 Example 19 437 4635 81 Comparative example 1 437 4655 45 Comparative example 2 437 4655 35

As can be seen from Table 2, by comparing Examples 1 and 9-10, when the starting temperature and maximum temperature of the graphitization heat treatment are too low, the fiber graphitization effect will be poor and the strength modulus will not increase significantly. The reason is In the same graphitization treatment time, too low temperature leads to the removal of non-carbon elements in the fiber and insufficient transformation of the internal structure of the fiber; a small temperature gradient is not conducive to graphitization temperature control and the uniformity of the graphitization effect. By comparing Examples 1 and 11-13, it can be seen that during graphitization heat treatment, when the tension applied to the fiber tow is greater than 80N, the fiber strength is significantly reduced. The reason may be that when the tension is greater, the fiber tow will be damaged. Seriously, more broken wires are produced, thereby reducing the fiber strength; when the tension applied to the fiber bundle is less than 20N, the fiber modulus increases less. The reason may be that when the tension is small, the turbostratic graphite crystallites cannot be fully eliminated. The stress between them is not conducive to the displacement and rearrangement of graphite crystallites, and the axial orientation cannot be improved, resulting in a small increase in fiber modulus. By comparing Examples 1 and 14-16, it can be seen that when the graphitization heat treatment time is in the range of 20-40s, it is more conducive to improving the fiber modulus. Within this time range, the graphitization heat treatment of the fiber is more complete and the fiber crystallinity is improved. And the degree of orientation is greatly improved; furthermore, under the same temperature gradient and drafting tension, the fiber can be effectively graphitized within the above-mentioned heat treatment time. Extending the treatment time will have less effect on further improving the modulus, but will lead to energy Waste and equipment loss. By comparing Examples 1 and 17-19, it can be seen that when the total electricity applied in the first-stage electrochemical anodizing treatment and the first-stage electrochemical anodizing treatment is 60-150C/g, the obtained fiber interlayer shear strength is relatively high. By comparing Example 1 and Comparative Example 1, it can be seen that when only the first-stage electrochemical anodizing treatment is performed and the second-stage electrochemical anodizing treatment is not performed, the shear strength between carbon fiber layers will be lower; the reason is that the shear strength between the carbon fiber layers is low. The fiber surface with fewer oxygen-containing functional groups introduced on the surface and smooth is less etched.

In Comparative Example 2, no surface treatment was performed, and only graphitization heat treatment was performed, which would result in low interlaminar shear strength of the carbon fiber. The reason is that the oxygen-containing functional groups on the fiber surface after graphitization heat treatment are sharply reduced, and the surface energy is reduced, causing the carbon fiber to be separated from the matrix. The interfacial bonding performance of resin is poor. The surface treatment process can introduce oxygen-containing active functional groups on the surface of the graphitized fiber, and etching can occur on the smooth fiber surface to enhance the mechanical fit between the fiber and the matrix resin material.

The above-described embodiments are part of the embodiments of the present application, but not all of the embodiments. The detailed description of the embodiments of the application is not intended to limit the scope of the application as claimed, but rather to represent selected embodiments of the application. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of this application.

Claims (10)

1. A method for preparing carbon fiber, characterized in that it includes the following steps: Place the carbonized fiber body obtained through the pre-oxidation reaction and the carbonization reaction in sequence in a boride solution for soaking and drying, so that the boride is coated on the surface of the carbonized fiber body; Then, the dried carbonized fiber body is sequentially subjected to graphitization heat treatment and surface treatment to obtain the carbon fiber; The surface treatment includes: sequentially performing a first-stage electrochemical anodizing treatment and a second-stage electrochemical anodizing treatment on the carbonized fiber body that has undergone the graphitization heat treatment to etch the fiber surface and generate oxygen-containing functional groups. . 2. The preparation method according to claim 1, wherein in the boride solution, the boride includes boric acid and/or boron carbide powder; Optionally, the mass concentration of the boride solution is 5-20%; Optionally, the boride solution includes a boric acid solution with a mass concentration of 8-12%; Optionally, the boride solution includes a mixed solution of boron carbide powder and boric acid, wherein the mass ratio of the boron carbide powder and boric acid is 1:(1-3). 3. The preparation method according to claim 1, characterized in that the soaking conditions include: soaking temperature is 20-25°C, and soaking time is 10-180s. 4. The preparation method according to any one of claims 1-3, characterized in that the graphitization heat treatment includes: Under an inert gas protective atmosphere, the soaked carbonized fiber body is subjected to gradient graphitization heat treatment at a temperature from 1800°C to 2250°C, and multiple heat treatment temperature zones are set between 1800°C and 2250°C, so that the temperature is 1800-2250°C. There are multiple temperature gradients between 2250°C; Optionally, the inert gas includes any one of nitrogen and argon. 5. The preparation method according to claim 4, characterized in that the number of the heat treatment temperature zones is 3-5, and the temperature difference of each heat treatment temperature zone is 30-300°C; Optionally, the graphitization heat treatment time is 20-40s; Optionally, in the graphitization heat treatment, the tension applied to the carbonized fiber body is 20-80N. 6. The preparation method according to any one of claims 1-3, characterized in that the surface treatment includes: The total electricity applied by the first-stage electrochemical anodizing treatment and the second-stage electrochemical anodizing treatment is 60-150C/g; and/or, the temperature of the electrochemical anodizing treatment is 20-60°C. ; And/or, the time of the first-stage electrochemical anodizing treatment is 15-30s; and/or, the time of the second-stage electrochemical anodizing treatment is 15-30s; Optionally, the electric quantity applied in the first-stage electrochemical anodizing treatment is 30-80C/g, and the electric quantity applied in the second-stage electrochemical anodizing treatment is 30-80C/g; Optionally, the electrolyte used in the electrochemical anodizing treatment includes an acidic electrolyte and/or an alkaline electrolyte; Optionally, the electrolyte used in the electrochemical anodizing treatment includes one or more of ammonium bicarbonate, sodium hydroxide, sulfuric acid and nitric acid; Optionally, the mass concentration of the electrolyte is 0.5-8%. 7. The preparation method according to any one of claims 1-3, characterized in that the pre-oxidation reaction includes: polypropylene with a density of 1.15-1.25g/ ^cm3 and a single filament diameter of 4-8 μm. Nitrile fiber undergoes a pre-oxidation reaction; wherein, the starting temperature of the pre-oxidation reaction is 200°C and the end temperature is 300°C; the residence time of the pre-oxidation reaction is 30-90min, and the tension applied to the fiber tow is 5-25N to obtain a pre-oxidized fiber body with a density of 1.32-1.39g/ ^cm3 ; Optionally, the carbonization reaction includes: sequentially performing a first carbonization treatment and a second carbonization treatment on the pre-oxidized fiber body to obtain the carbonized fiber body; wherein the step of the first carbonization treatment includes performing 400 Gradient heating from ℃ to 700 ℃, the time of the first carbonization treatment is 1-3 minutes, the step of the second carbonization treatment includes gradient heating from 900 ℃ to 1500 ℃, the time of the second carbonization treatment is 1-3min. 8. The preparation method according to any one of claims 1 to 3, further comprising: washing, sizing, drying and winding the carbon fiber in sequence; Optionally, the mass concentration of the sizing agent used in the sizing step is 1.0-2.5%; Optionally, the drying conditions include: drying temperature is 140-170°C, and drying time is 0.2-2 minutes. 9. A carbon fiber produced by the preparation method according to any one of claims 1 to 8. 10. A composite material, characterized by containing the carbon fiber according to claim 9.