Preparation method of carbon fiber and carbon fiber

Abstract

The invention provides a preparation method of a carbon fiber and the carbon fiber. The preparation method of the carbon fiber comprises the following steps: performing polymerization reaction on a first monomer, a second monomer and a third monomer in a preset mass ratio to prepare a polymerization stock solution; carrying out spinning molding on the polymerization stock solution to obtain a polyacrylonitrile-based precursor with a preset densification degree; the preparation method comprises the following steps: carrying out multi-stage pre-oxidation treatment on polyacrylonitrile-based protofilaments to obtain pre-oxidized fibers; and carrying out carbonization treatment on the pre-oxidized fiber to obtain the carbon fiber. According to the preparation method of the carbon fiber, the polymerization stock solution is prepared through the polymerization reaction, the polymerization stock solution is subjected to spinning forming to obtain the polyacrylonitrile-based precursor, and the polyacrylonitrile-based precursor has the preset densification degree, so that the permeability of an oxygen element in the polyacrylonitrile precursor in the subsequent pre-oxidation treatment process is favorably controlled; therefore, the pre-oxidation degree of the pre-oxidized fiber during the pre-oxidation treatment is controlled, and the mechanical property of the prepared carbon fiber is ensured.

Description

Technical Field

[0001] The present disclosure relates to the technical field of carbon fiber, and in particular to a method for preparing carbon fiber and the carbon fiber. Background Art

[0002] Carbon fiber pre-oxidation is a key step in the carbon fiber production process. The purpose of pre-oxidation is to stabilize the carbon fiber structure through chemical modification so that it can withstand the high temperature in the subsequent carbonization process without decomposition and melting. Therefore, the control of pre-oxidation process conditions plays a vital role in the degree of pre-oxidation and the internal structure of carbon fiber. In the large-scale preparation process of carbon fiber, if the degree of pre-oxidation is too low, the pre-oxidation is insufficient, and the stable structure formed is small, and it cannot withstand the subsequent low-temperature and high-temperature carbonization process, affecting the performance of carbon fiber; if the degree of pre-oxidation is too high, the pre-oxidation is excessive, and oxygen escapes in the form of small molecules during the carbonization process, forming defects in the carbon fiber, affecting the performance of the carbon fiber. Therefore, it is crucial to control the degree of pre-oxidation in the preparation process of carbon fiber. Summary of the invention

[0003] In order to solve the problems existing in the related art, the present disclosure provides a method for preparing carbon fiber and carbon fiber.

[0004] According to a first aspect of an embodiment of the present disclosure, a method for preparing carbon fiber is provided, the method comprising:

[0005] The first monomer, the second monomer and the third monomer in a preset mass ratio are polymerized to obtain a polymerization stock solution;

[0006] Spinning the polymer solution into fibers to obtain polyacrylonitrile-based fibers with a preset degree of densification;

[0007] The polyacrylonitrile-based precursor is subjected to multi-stage pre-oxidation treatment to obtain pre-oxidized fibers;

[0008] The pre-oxidized fiber is carbonized to obtain the carbon fiber.

[0009] In some embodiments of the present disclosure, the step of preparing a polymerization stock solution by polymerizing a first monomer, a second monomer, and a third monomer having a preset mass ratio comprises:

[0010] Carrying out polymerization reaction on 97.0% to 99.8% by mass of the first monomer, 0.1% to 1.5% by mass of the second monomer, and 0.1% to 1.5% by mass of the third monomer to obtain the polymerization stock solution;

[0011] Wherein, the first monomer includes acrylonitrile, the second monomer includes itaconic acid, and the third monomer includes ethylene unsaturated esters.

[0012] In some embodiments of the present disclosure, the polyacrylonitrile-based precursor is subjected to a multi-stage pre-oxidation treatment to obtain a pre-oxidized fiber, comprising:

[0013] The polyacrylonitrile-based precursor is heat treated in a mixed atmosphere of oxygen and nitrogen at a temperature of 200-235° C. for 30-50 minutes to complete a first-stage pre-oxidation treatment; wherein the draft ratio is set to 0.9000-0.9500;

[0014] The polyacrylonitrile-based precursor fibers after the first stage pre-oxidation treatment are heat treated in an air atmosphere at a temperature of 260-270° C. to complete the second stage pre-oxidation treatment;

[0015] The polyacrylonitrile-based precursor fibers after the second stage pre-oxidation treatment are subjected to heat treatment in an air atmosphere at a temperature of 270-280° C. to complete the third stage pre-oxidation treatment to obtain the pre-oxidized fibers;

[0016] The total duration of the second-stage pre-oxidation treatment and the third-stage pre-oxidation treatment is 58-98 minutes.

[0017] In some embodiments of the present disclosure, the flame shrinkage rate of the pre-oxidized fiber is 72%-85%.

[0018] In some embodiments of the present disclosure, the bulk density of the pre-oxidized fiber is 1.3510-1.3570 g / cm 3 The ratio of the core diameter of the skin-core structure in the pre-oxidized fiber to the fiber diameter of the pre-oxidized fiber is 9.7%-11.2%.

[0019] In some embodiments of the present disclosure, the duration ratio of the second stage pre-oxidation treatment to the third stage pre-oxidation treatment is 1:1.0-1.5.

[0020] In some embodiments of the present disclosure, in the mixed atmosphere of oxygen and nitrogen, the volume proportion of oxygen is 20%-60%.

[0021] In some embodiments of the present disclosure, the step of spinning the polymer solution to obtain polyacrylonitrile-based precursor fibers with a preset degree of densification includes:

[0022] The polymerized stock solution is spun into shape, and the drying pressure is set to 0.3-1.0 MPa to obtain polyacrylonitrile-based precursor fibers with a preset densification degree of ΔL=40-50.

[0023] In some embodiments of the present disclosure, the step of carbonizing the pre-oxidized fiber to obtain the carbon fiber comprises:

[0024] In an inert atmosphere, the pre-oxidized fiber is subjected to a carbonization treatment at a first preset temperature and a second preset temperature in sequence to obtain the carbon fiber;

[0025] The first preset temperature is 300-800°C, and the second preset temperature is 1200-1600°C.

[0026] According to a second aspect of an embodiment of the present disclosure, a carbon fiber is provided. The carbon fiber is prepared according to the above-mentioned method for preparing the carbon fiber.

[0027] The beneficial effects of the present disclosure include but are not limited to: the method for preparing carbon fiber provided by the present disclosure, preparing a polymerization stock solution through a polymerization reaction, and spinning the polymerization stock solution to obtain a polyacrylonitrile-based precursor, the polyacrylonitrile-based precursor has a preset degree of densification, and is therefore conducive to controlling the permeability of oxygen elements in the polyacrylonitrile precursor during the subsequent pre-oxidation treatment process, thereby controlling the pre-oxidation degree of the pre-oxidized fiber during the pre-oxidation treatment, thereby ensuring the mechanical properties of the prepared carbon fiber, and avoiding the internal defects and reduced mechanical properties of the prepared carbon fiber caused by the loss of control of the pre-oxidation degree in the pre-oxidation treatment stage.

[0028] It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present disclosure. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The accompanying drawings incorporated into the specification and constituting a part of the specification illustrate embodiments of the present disclosure and are used together with the description to explain the principles of the embodiments of the present disclosure. In these drawings, similar reference numerals are used to represent similar elements. The drawings described below are some embodiments of the present disclosure, rather than all embodiments. For those skilled in the art, other drawings can be obtained based on these drawings without paying creative work.

[0030] Figure 1 The present invention is a schematic diagram of a method for preparing carbon fiber according to an exemplary embodiment of the present invention. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solution and advantages of the present disclosure clearer, the technical solution of the present disclosure will be clearly and completely described in combination with the embodiments of the present disclosure. Obviously, the described embodiments are only part of the embodiments of the present disclosure, not all of the embodiments. Based on the embodiments in the present disclosure, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present disclosure. It should be noted that the embodiments in the present disclosure and the features in the embodiments can be arbitrarily combined with each other without conflict.

[0032] Carbon fiber pre-oxidation is a key step in the carbon fiber production process. The purpose of pre-oxidation is to stabilize the carbon fiber structure through chemical modification so that it can withstand the high temperature in the subsequent carbonization process without decomposition and melting. Therefore, the control of pre-oxidation process conditions plays a vital role in the degree of pre-oxidation and the internal structure of carbon fiber. In the large-scale preparation process of carbon fiber, if the pre-oxidation degree is too low or insufficient, the stable structure formed is small and cannot withstand the subsequent low-temperature and high-temperature carbonization process, affecting the performance of carbon fiber; if the pre-oxidation degree is too high or excessive, oxygen escapes in the form of small molecules during the carbonization process, forming defects in the carbon fiber and affecting the performance of the carbon fiber. Therefore, it is crucial to control the degree of pre-oxidation in the preparation process of carbon fiber. Especially in plateau areas, the oxygen content is low, and it is difficult for oxygen to enter the fiber during the pre-oxidation process. The homogeneous pre-oxidation degree is insufficient, resulting in low mechanical properties of carbon fiber.

[0033] In order to solve the above technical problems, the present disclosure provides a method for preparing carbon fiber, wherein a polymerization stock solution is prepared by polymerization reaction, and the polymerization stock solution is spun into polyacrylonitrile-based precursor, wherein the polyacrylonitrile-based precursor has a preset degree of densification, and is therefore beneficial for controlling the permeability of oxygen elements in the polyacrylonitrile precursor during a subsequent pre-oxidation treatment process, thereby controlling the pre-oxidation degree of the pre-oxidized fiber during the pre-oxidation treatment, thereby ensuring the mechanical properties of the prepared carbon fiber, and avoiding the internal defects and reduced mechanical properties of the prepared carbon fiber caused by the loss of control of the pre-oxidation degree during the pre-oxidation treatment stage.

[0034] An exemplary embodiment of the present disclosure provides a method for preparing carbon fiber, such as Figure 1 As shown, the preparation method comprises:

[0035] S100: preparing a polymerization stock solution by polymerizing a first monomer, a second monomer and a third monomer in a preset mass ratio;

[0036] S200: spinning the polymer solution into a fiber to obtain a polyacrylonitrile-based fiber with a preset degree of densification;

[0037] S300: subjecting polyacrylonitrile-based precursor to multi-stage pre-oxidation treatment to obtain pre-oxidized fibers;

[0038] S400: The pre-oxidized fiber is subjected to carbonization treatment to obtain carbon fiber.

[0039] The method for preparing carbon fiber provided in the present embodiment obtains a polymerization stock solution through a polymerization reaction, and spins the polymerization stock solution to obtain a polyacrylonitrile-based precursor. The polyacrylonitrile-based precursor has a preset degree of densification, and is therefore beneficial for controlling the permeability of oxygen in the polyacrylonitrile precursor during the subsequent pre-oxidation treatment process, thereby controlling the pre-oxidation degree of the pre-oxidized fiber during the pre-oxidation treatment, thereby ensuring the mechanical properties of the prepared carbon fiber and avoiding the internal defects and reduced mechanical properties of the prepared carbon fiber caused by the loss of control of the pre-oxidation degree during the pre-oxidation treatment stage.

[0040] For example, if carbon fiber is prepared in a plateau area, the preset densification degree of the polyacrylonitrile-based precursor can be set to a lower densification degree to reserve more oxygen element permeation channels in the polyacrylonitrile-based precursor, so that oxygen can more easily enter the interior of the polyacrylonitrile-based precursor, thereby solving the problem of low oxygen content in plateau areas and difficulty for oxygen to enter the interior of the polyacrylonitrile-based precursor during pre-oxidation treatment.

[0041] In an exemplary embodiment, a first monomer, a second monomer, and a third monomer having a preset mass ratio are subjected to a polymerization reaction to obtain a polymerization stock solution, including: a first monomer having a mass percentage of 97.0%-99.8%, a second monomer having a mass percentage of 0.1%-1.5%, and a third monomer having a mass percentage of 0.1%-1.5% are subjected to a polymerization reaction to obtain a polymerization stock solution. Wherein, the first monomer includes acrylonitrile, the second monomer includes itaconic acid, and the third monomer includes ethylene unsaturated esters. Wherein, the mass percentage of the first monomer in the polymerization reaction may be 97.0%, 98.0%, 99.0%, or 99.8%. The mass percentage of the first monomer may also be any value between the exemplary mass percentages, for example, the mass percentage of the first monomer may also be any value between 97.5%-99.0% or between 97.2%-99.5%. The mass percentage of the second monomer in the polymerization reaction may be 0.1%, 0.5%, 1.2%, or 1.5%. The mass percentage of the second monomer may also be any value between the exemplary mass percentages, for example, the mass percentage of the second monomer may also be any value between 0.3%-1.2% or between 0.2%-1.3%. The mass percentage of the third monomer in the polymerization reaction may be 0.1%, 0.5%, 1.2% or 1.5%. The mass percentage of the third monomer may also be any value between the exemplary mass percentages, for example, the mass percentage of the third monomer may also be any value between 0.3%-1.2% or between 0.2%-1.3%.

[0042] In this embodiment, 97.0%-99.8% of acrylonitrile, 0.1%-1.5% of itaconic acid and 0.1%-1.5% of ethylene unsaturated esters are polymerized to obtain the polymerization stock solution to be used for subsequent spinning. Acrylonitrile is the main monomer for forming the polyacrylonitrile molecular chain and provides the basic skeleton structure. Itaconic acid contains active functional groups such as carboxyl, which can introduce polar groups during the polymerization process, increase the interaction between molecules, improve the solubility and spinnability of polyacrylonitrile polymer, and promote the cyclization reaction in the subsequent pre-oxidation process. The ethylene unsaturated ester can be at least one of methyl acrylate, ethyl methacrylate, methyl methacrylate or vinyl acetate. Because the ethylene unsaturated ester has a larger ester group, the ethylene unsaturated ester is used as the third monomer in the polymerization reaction to make the resin fiber-forming process, which can leave a molecular oxygen permeation channel, promote the double diffusion reaction in the subsequent pre-oxidation treatment, and reduce or eliminate the skin-core structure in the pre-oxidized fiber.

[0043] In an exemplary embodiment, polyacrylonitrile-based precursor is subjected to multi-stage pre-oxidation treatment to obtain pre-oxidized fibers, including:

[0044] The polyacrylonitrile-based precursor is heat-treated for 30-50 minutes at a temperature of 200-235°C in a mixed atmosphere of oxygen and nitrogen to complete the first stage pre-oxidation treatment; wherein the draft ratio is set to 0.9000-0.9500; wherein the temperature of the first stage pre-oxidation treatment can be 200°C, 210°C, 220°C or 235°C. The temperature of the first stage pre-oxidation treatment can also be any value between the exemplary temperatures, for example, the temperature of the first stage pre-oxidation treatment can also be any value between 210-230°C or between 205-225°C. The time of the first stage pre-oxidation treatment can be 30 minutes, 40 minutes, 45 minutes or 50 minutes. The time of the first stage pre-oxidation treatment can also be any value between the exemplary times, for example, the time of the first stage pre-oxidation treatment can also be any value between 30-45 minutes or between 32-48 minutes. The draft ratio of the first stage pre-oxidation treatment can be 0.9000, 0.9200, 0.9300 or 0.9500. The stretch ratio of the first stage pre-oxidation treatment may also be any value between the exemplary stretch ratios. For example, the stretch ratio of the first stage pre-oxidation treatment may also be any value between 0.9200-0.9300 or between 0.9100-0.9400.

[0045] The polyacrylonitrile-based precursor after the first stage pre-oxidation treatment is heat-treated in an air atmosphere at a temperature of 260-270° C. to complete the second stage pre-oxidation treatment; wherein the temperature of the second stage pre-oxidation treatment may be 260° C., 265° C. or 270° C. The temperature of the second stage pre-oxidation treatment may also be any value between the exemplary temperatures, for example, the temperature of the second stage pre-oxidation treatment may also be any value between 261-268° C. or between 265-269° C.

[0046] The polyacrylonitrile-based precursor fibers after the second stage preoxidation treatment are heat treated in an air atmosphere at a temperature of 270-280° C. to complete the third stage preoxidation treatment to obtain preoxidized fibers; wherein the temperature of the third stage preoxidation treatment may be 270° C., 275° C. or 280° C. The temperature of the third stage preoxidation treatment may also be any value between the exemplary temperatures, for example, the temperature of the third stage preoxidation treatment may also be any value between 271-278° C. or between 275-279° C.

[0047] The total duration of the second-stage pre-oxidation treatment and the third-stage pre-oxidation treatment is 58-98 minutes. The total duration of the second-stage pre-oxidation treatment and the third-stage pre-oxidation treatment can be 58 minutes, 65 minutes, 76 minutes or 98 minutes. The total duration of the second-stage pre-oxidation treatment and the third-stage pre-oxidation treatment can also be any value between the exemplary durations, for example, the total duration of the second-stage pre-oxidation treatment and the third-stage pre-oxidation treatment can also be any value between 68-88 minutes or between 60-90 minutes.

[0048] In this embodiment, the pre-oxidation treatment of the polyacrylonitrile-based precursor includes a first-stage pre-oxidation treatment, a second-stage pre-oxidation treatment, and a third-stage pre-oxidation treatment, which are carried out in sequence. The pre-oxidation treatment is divided into multiple stages to enable the polyacrylonitrile-based precursor to gradually undergo cyclization and oxidation reactions to form a stable fiber structure. The first-stage pre-oxidation treatment is carried out in a mixed atmosphere of oxygen and nitrogen, and the volume ratio of oxygen in the mixed atmosphere of oxygen and nitrogen can be controlled to control the oxygen permeability of the first-stage pre-oxidation treatment. And the first-stage pre-oxidation treatment in this embodiment is carried out at a temperature of 200-235°C, that is, at a lower temperature, which can reduce the formation speed of the dense layer of the polyacrylonitrile-based precursor, and combined with a large draft ratio process of 0.9000-0.9500 and a heat treatment time of 30-50 minutes, oxygen can be more easily introduced into the interior of the polyacrylonitrile-based precursor. The subsequent second-stage pre-oxidation treatment and the third-stage pre-oxidation treatment are carried out in sequence at an elevated temperature, which can make the pre-oxidation reaction of the polyacrylonitrile-based precursor more sufficient and uniform.

[0049] In an exemplary embodiment, the duration ratio of the second stage pre-oxidation treatment to the third stage pre-oxidation treatment is 1:1.0-1.5. The duration ratio of the second stage pre-oxidation treatment to the third stage pre-oxidation treatment may be 1:1.0, 1:1.2, 1:1.3 or 1:1.5. The duration ratio of the second stage pre-oxidation treatment to the third stage pre-oxidation treatment may also be any value between the exemplary duration ratios, for example, the duration ratio of the second stage pre-oxidation treatment to the third stage pre-oxidation treatment may also be any value between 1:1.25-1.4 or 1:1.3-1.45.

[0050] In this embodiment, the total duration of the second-stage pre-oxidation treatment and the third-stage pre-oxidation treatment is controlled to be 58-98 minutes, and the duration ratio of the second-stage pre-oxidation treatment at a lower temperature to the third-stage pre-oxidation treatment at a higher temperature is controlled to be 1:1.0-1.5, which can make the pre-oxidation reaction more sufficient and uniform.

[0051] In an exemplary embodiment, in the mixed atmosphere of oxygen and nitrogen, the volume proportion of oxygen is 20%-60%. The volume proportion of oxygen can be 20%, 30%, 40% or 60%. The volume proportion of oxygen can also be any value between the exemplary volume proportions, for example, the volume proportion of oxygen can also be any value between 30%-40% or between 25%-50%.

[0052] In this embodiment, the polyacrylonitrile-based precursor is heat treated in a mixed atmosphere of oxygen and nitrogen at a temperature of 200-235° C. for 30-50 minutes to complete the first stage pre-oxidation treatment. In the mixed atmosphere of oxygen and nitrogen, the volume proportion of oxygen is controlled to 20%-60%, which can provide an appropriate amount of oxygen to enter the interior of the polyacrylonitrile-based precursor to ensure the oxygen permeability of the first stage pre-oxidation treatment.

[0053] In an exemplary embodiment, the flame shrinkage rate of the pre-oxidized fiber is 72%-85%. The flame shrinkage rate of the pre-oxidized fiber may be 72%, 79%, 80% or 85%. The flame shrinkage rate of the pre-oxidized fiber may also be any value between the exemplary flame shrinkage rates, for example, the flame shrinkage rate of the pre-oxidized fiber may also be any value between 75%-80% or between 73%-82%.

[0054] The 200 mm pre-oxidized fiber is heat-treated by a Bunsen burner, and the flame shrinkage of the pre-oxidized fiber can be obtained by measuring the remaining length Wb of the pre-oxidized fiber after the heat treatment and calculating it by the formula (%) = (Wb / 200)*100%. If the flame shrinkage of the pre-oxidized fiber is too large, it indicates that the pre-oxidation is insufficient, and if the flame shrinkage is too small, it indicates that the pre-oxidation is excessive. In this embodiment, the flame shrinkage of the pre-oxidized fiber is controlled within the range of 72%-85%, which can ensure that the pre-oxidized fiber has a suitable degree of pre-oxidation.

[0055] In an exemplary embodiment, the bulk density of the pre-oxidized fiber is 1.3510-1.3570 g / cm 3 The bulk density of the pre-oxidized fiber can be 1.3510 g / cm 3 , 1.3530g / cm 3 , 1.3540g / cm 3 or 1.3570g / cm 3 The bulk density of the pre-oxidized fiber may also be any value between the exemplary bulk densities, for example, the bulk density of the pre-oxidized fiber may also be 1.3520-1.3560 g / cm 3 Between or 1.3515-1.3555g / cm 3 Any value between .

[0056] In an exemplary embodiment, the ratio of the core diameter of the skin-core structure in the pre-oxidized fiber to the fiber diameter of the pre-oxidized fiber is 9.7%-11.2%. The ratio of the core diameter of the skin-core structure in the pre-oxidized fiber to the fiber diameter of the pre-oxidized fiber may be 9.7%, 10.2%, 10.7% or 11.2%. The ratio of the core diameter of the skin-core structure in the pre-oxidized fiber to the fiber diameter of the pre-oxidized fiber may also be any value between the exemplary ratios, for example, the ratio of the core diameter of the skin-core structure in the pre-oxidized fiber to the fiber diameter of the pre-oxidized fiber may also be any value between 9.9%-11.0% or between 10.0%-10.8%.

[0057] The ratio of the core diameter of the skin-core structure in the pre-oxidized fiber to the fiber diameter of the pre-oxidized fiber is calculated by the following formula:

[0058]

[0059] The bulk density of the pre-oxidized fiber and the ratio of the core diameter of the skin-core structure in the pre-oxidized fiber to the fiber diameter of the pre-oxidized fiber will directly affect the tensile strength and tensile modulus of the carbon fiber. In this embodiment, the bulk density of the pre-oxidized fiber is controlled at 1.3510-1.3570 g / cm 3The ratio of the core diameter of the skin-core structure in the pre-oxidized fiber to the fiber diameter of the pre-oxidized fiber is controlled at 9.7%-11.2%, which can ensure the mechanical properties of the prepared carbon fiber, such as tensile strength and tensile modulus.

[0060] In an exemplary embodiment, the polymer solution is spun into shape to obtain a polyacrylonitrile-based precursor with a preset degree of densification, including: spinning the polymer solution into shape, and setting the drying pressure to 0.3-1.0 MPa to obtain a polyacrylonitrile-based precursor with a preset degree of densification of ΔL=40-50. Wherein, the drying pressure can be 0.3MPa, 0.5MPa, 0.7MPa or 1.0MPa. The drying pressure can also be any value between the exemplary drying pressures, for example, the drying pressure can also be any value between 0.4-0.9MPa or between 0.5-0.8MPa. The preset degree of densification ΔL can be 40, 43, 47 or 50. The preset degree of densification ΔL can also be any value between the exemplary preset degrees of densification ΔL, for example, the preset degree of densification ΔL can also be any value between 42-48 or between 43-49.

[0061] During the spinning process, the polymer solution goes through several processes, including spinning, washing, water drawing, oiling, drying and densification (drying), steam drawing and winding. The drying and densification (drying) heat treatment process uses steam as a medium to heat the roller of the precursor. The pressure of the steam medium is the drying pressure. The regulation of the drying pressure is actually the regulation of the steam pressure and the regulation of the surface temperature of the precursor roller (drying temperature). The reasons for drying and densification may be (1) in the hot environment of the temperature field (temperature greater than the boiling point of water), the liquid water containing oil in the precursor pores is evaporated and vaporized, so that vacuum and negative pressure are instantly formed in the precursor pores, causing the pores between the precursors to collapse and merge or disappear; (2) a large amount of water in the precursor pores escapes, causing the volume of the precursor to shrink. Under the action of the shrinkage force, the pores between the precursors are also merged or eliminated, and the precursors are arranged more closely. By adjusting the drying pressure and drying temperature, the degree of densification of polyacrylonitrile-based precursor fibers can be adjusted, thereby adjusting the degree of retention of holes in the polyacrylonitrile-based precursor fiber bundles, thereby adjusting the degree of pre-oxidation in the carbon fiber preparation process.

[0062] The oxygen content is low, and it is difficult for oxygen to enter the polyacrylonitrile-based precursor in the pre-oxidation stage. The presence of holes leaves a certain physical channel for the entry of oxygen in the pre-oxidation stage. If the degree of densification is too high, it is difficult for oxygen to enter the pre-oxidation stage, and if the degree of densification is too low, the pre-oxidation fiber itself has many defects (too many holes, and the pre-oxidation fiber has many defects), which affects the performance of the final product carbon fiber. In this embodiment, in the spinning and forming stage, the drying pressure is set to 0.3-1.0MPa to obtain a polyacrylonitrile-based precursor with a preset densification degree of ΔL=40-50 (iodine adsorption method). Under the condition of the morphology and performance of the pre-oxidation fiber itself, an appropriate physical channel can be left in the polyacrylonitrile-based precursor for the entry of oxygen in the pre-oxidation stage, so as to facilitate the entry of oxygen into the interior of the polyacrylonitrile-based precursor in the pre-oxidation stage.

[0063] In an exemplary embodiment, the pre-oxidized fiber is subjected to carbonization treatment to obtain carbon fiber, including: in an inert atmosphere, the pre-oxidized fiber is subjected to carbonization treatment at a first preset temperature and a second preset temperature in sequence to obtain carbon fiber. The first preset temperature is 300-800°C, and the second preset temperature is 1200-1600°C. Among them, the first preset temperature can be 300°C, 500°C, 600°C or 800°C. The first preset temperature can also be any value between the exemplary first preset temperatures, for example, the first preset temperature can also be any value between 400-700°C or between 350-600°C. The second preset temperature can be 1200°C, 1300°C, 1400°C or 1600°C. The second preset temperature can also be any value between the exemplary second preset temperatures, for example, the second preset temperature can also be any value between 1300-1500°C or between 1250-1550°C.

[0064] In an inert atmosphere, the pre-oxidized fiber is carbonized at two different preset temperatures. The carbonization treatment at the first preset temperature of 300-800°C can further remove non-carbon elements from the pre-oxidized fiber and form a preliminary carbon structure. The second preset temperature of 1200-1600°C is higher, which can further reorganize and crystallize the carbon atoms in the pre-oxidized fiber, improve the graphitization degree of the prepared carbon fiber, and thus significantly improve the strength, modulus and other mechanical properties of the carbon fiber.

[0065] An exemplary embodiment of the present disclosure provides a carbon fiber, which is prepared according to the method for preparing the carbon fiber provided in the embodiment of the present disclosure. During the pre-oxidation treatment stage of the carbon fiber during the preparation process, the pre-oxidation degree is controlled within an appropriate range, thereby ensuring the mechanical properties of the carbon fiber and avoiding the internal defects of the carbon fiber and the reduction of the mechanical properties caused by the loss of control of the pre-oxidation degree during the pre-oxidation treatment stage.

[0066] In order to explain the technical solution of the present disclosure more clearly, the following specific examples of the method for preparing carbon fiber provided by the exemplary embodiment of the present disclosure are given to prepare the carbon fiber provided by the exemplary embodiment of the present disclosure. It should be noted that the following preparation process is carried out in the plateau area.

[0067] The polymerization stock solution is prepared by polymerizing 97.0% to 99.8% of acrylonitrile, 0.1% to 1.5% of itaconic acid and 0.1% to 1.5% of ethylene unsaturated esters in mass percentage.

[0068] The polymerized stock solution is spun into shape, and the drying pressure is reduced and adjusted to 0.3-1.0 MPa to obtain a polypropylene-based precursor with a preset densification degree of ΔL: 40-50 (iodine adsorption method), thereby providing a physical-level channel for oxygen elements to enter the interior of the carbon fiber in the pre-oxidation stage.

[0069] After the polyacrylonitrile-based raw silk is withdrawn through a withdrawing frame, it is heat treated for 30-50 minutes at a temperature of 200-235°C in a mixed atmosphere of oxygen and nitrogen with an oxygen volume ratio of 20%-60% to complete the first stage pre-oxidation treatment; wherein the draft ratio is set to 0.9000-0.9500.

[0070] The polyacrylonitrile-based precursor fibers that have undergone the first stage pre-oxidation treatment are heat treated in an air atmosphere at a temperature of 260-270° C. to complete the second stage pre-oxidation treatment.

[0071] The polyacrylonitrile-based precursor after the second stage preoxidation treatment is heat treated in an air atmosphere at a temperature of 270-280°C to complete the third stage preoxidation treatment to obtain preoxidized fibers. The total duration of the second stage preoxidation treatment and the third stage preoxidation treatment is 58-98 minutes, and the duration ratio of the second stage preoxidation treatment to the third stage preoxidation treatment is 1:1.0-1.5.

[0072] In an inert atmosphere, the pre-oxidized fiber is carbonized at 300-800° C. and 1200-1600° C. in sequence to obtain carbon fiber.

[0073] The following is a table showing a method for preparing carbon fiber provided by an exemplary embodiment of the present disclosure, a process example for preparing carbon fiber provided by an exemplary embodiment of the present disclosure, and a comparison with the process example for preparing carbon fiber in Comparative Example 1, as shown in Table 1.

[0074] Table 1

[0075]

[0076] The flame shrinkage retention rate of the pre-oxidized fiber in the carbon fiber preparation process of Example 1 to Example 11 and Comparative Example 1, the bulk density of the pre-oxidized fiber, the ratio of the core diameter of the skin-core structure in the pre-oxidized fiber to the fiber diameter of the pre-oxidized fiber, and the performance tests of the prepared carbon fiber, including tensile strength and tensile modulus tests, were performed. The test results are shown in Table 2.

[0077] Table 2

[0078]

[0079] By comparing Examples 1 to 11 and Comparative Example 1, it can be seen that the method for preparing carbon fiber provided by the exemplary embodiment of the present disclosure uses and increases the content of the third monomer, reduces the density of the precursor, reduces the temperature of the first-stage pre-oxidation treatment, increases the concentration of oxygen in the first-stage pre-oxidation treatment atmosphere and increases the drawing, which can improve the pre-oxidation degree of the pre-oxidized fiber, and the performance of the prepared carbon fiber is improved.

[0080] The contents described above may be implemented individually or in combination in various ways, and these variations are all within the protection scope of the present disclosure.

[0081] Finally, it should be noted that in this article, the terms "include", "comprises" or any other variations thereof are intended to cover non-exclusive inclusion, so that a process, method, article or apparatus that includes a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or apparatus.

[0082] The above embodiments are only used to illustrate the technical solutions of the present disclosure, rather than to limit them. Although the present disclosure is described in detail with reference to the above embodiments, a person skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present disclosure.

Claims

1. A method for preparing carbon fiber, characterized in that: The preparation method comprises: The first monomer, the second monomer and the third monomer in a preset mass ratio are polymerized to obtain a polymerization stock solution; Spinning the polymer solution into fibers to obtain polyacrylonitrile-based fibers with a preset degree of densification; The polyacrylonitrile-based precursor is subjected to multi-stage pre-oxidation treatment to obtain pre-oxidized fibers; The pre-oxidized fiber is carbonized to obtain the carbon fiber.

2. The method for preparing carbon fiber according to claim 1, characterized in that: The step of preparing a polymerization stock solution by polymerizing the first monomer, the second monomer, and the third monomer in a preset mass ratio comprises: Carrying out polymerization reaction on 97.0% to 99.8% by mass of the first monomer, 0.1% to 1.5% by mass of the second monomer, and 0.1% to 1.5% by mass of the third monomer to obtain the polymerization stock solution; Wherein, the first monomer includes acrylonitrile, the second monomer includes itaconic acid, and the third monomer includes ethylene unsaturated esters.

3. The method for preparing carbon fiber according to claim 1, characterized in that: The polyacrylonitrile-based precursor is subjected to a multi-stage pre-oxidation treatment to obtain pre-oxidized fibers, comprising: The polyacrylonitrile-based precursor is heat treated in a mixed atmosphere of oxygen and nitrogen at a temperature of 200-235° C. for 30-50 minutes to complete a first-stage pre-oxidation treatment; wherein the draft ratio is set to 0.9000-0.9500; The polyacrylonitrile-based precursor fibers after the first stage pre-oxidation treatment are heat treated in an air atmosphere at a temperature of 260-270° C. to complete the second stage pre-oxidation treatment; The polyacrylonitrile-based precursor fibers after the second stage pre-oxidation treatment are subjected to heat treatment in an air atmosphere at a temperature of 270-280° C. to complete the third stage pre-oxidation treatment to obtain the pre-oxidized fibers; The total duration of the second-stage pre-oxidation treatment and the third-stage pre-oxidation treatment is 58-98 minutes.

4. The method for preparing carbon fiber according to claim 1 or 3, characterized in that: The flame shrinkage of the pre-oxidized fiber is 72%-85%.

5. The method for preparing carbon fiber according to claim 1 or 3, characterized in that: The bulk density of the pre-oxidized fiber is 1.3510-1.3570 g / cm 3 The ratio of the core diameter of the skin-core structure in the pre-oxidized fiber to the fiber diameter of the pre-oxidized fiber is 9.7%-11.2%.

6. The method for preparing carbon fiber according to claim 3, characterized in that: The duration ratio of the second stage pre-oxidation treatment to the third stage pre-oxidation treatment is 1:1.0-1.

5.

7. The method for preparing carbon fiber according to claim 3, characterized in that: In the mixed atmosphere of oxygen and nitrogen, the volume proportion of oxygen is 20%-60%.

8. The method for preparing carbon fiber according to claim 1, characterized in that: The step of spinning the polymer solution to obtain polyacrylonitrile-based precursor fibers with a preset degree of densification comprises: The polymerized stock solution is spun into shape, and the drying pressure is set to 0.3-1.0 MPa to obtain polyacrylonitrile-based precursor fibers with a preset densification degree of ΔL=40-50.

9. The method for preparing carbon fiber according to claim 1, characterized in that: The method of subjecting the pre-oxidized fiber to carbonization to obtain the carbon fiber comprises: In an inert atmosphere, the pre-oxidized fiber is subjected to a carbonization treatment at a first preset temperature and a second preset temperature in sequence to obtain the carbon fiber; The first preset temperature is 300-800°C, and the second preset temperature is 1200-1600°C.

10. A carbon fiber, characterized in that: The carbon fiber is prepared according to the method for preparing the carbon fiber according to any one of claims 1-9.

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