PAN-based carbon fiber precursor, preparation method thereof, and PAN-based carbon fiber

Abstract

The application discloses PAN-based carbon fiber precursor and a preparation method thereof and PAN-based carbon fiber, and relates to the technical field of carbon fiber materials.On the basis of acrylonitrile monomers, a comonomer is introduced, and the acrylonitrile monomers and the comonomer synergistically act, which not only improves the storage stability and spinnability of the spinning dope, but also improves the pre-oxidation reaction activity of the precursor, thereby providing a structural basis for obtaining stable carbon fiber modulus in the subsequent process; the drying treatment eliminates the surface defects and internal residual stress of the precursor, and ensures the uniformity of the diameter and the structural compactness of the PAN-based carbon fiber precursor, and the finally obtained PAN-based carbon fiber has excellent and stable mechanical properties.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber materials technology, and more specifically, to PAN-based carbon fiber precursor and its preparation method, and PAN-based carbon fiber. Background Technology

[0002] Polyacrylonitrile (PAN)-based carbon fiber, with its excellent properties such as lightweight, high strength, high modulus, and corrosion resistance, has become a core material in aerospace, defense, and building reinforcement. As composite structural components develop towards larger sizes and lighter weights, the performance requirements for PAN-based carbon fiber are increasing, especially the need to maintain good mechanical properties and processability even with increased diameter. As the precursor to carbon fiber, the quality of the precursor fiber directly affects the performance of the final carbon fiber. High-quality precursor fibers require high purity, high orientation, high density, and uniform diameter distribution; these characteristics are crucial for subsequent pre-oxidation and carbonization processes.

[0003] However, existing precursor fiber preparation technologies face the following technical bottlenecks in achieving the aforementioned performance indicators: First, when the precursor fiber is formed with increased diameter, uneven solidification rate can easily produce a core-sheath structure, reducing the density and orientation of the precursor fiber, and thus affecting the strength of the carbon fiber; Second, unreasonable selection and ratio of comonomers can lead to poor controllability of the precursor fiber pre-oxidation reaction, ultimately affecting the modulus stability of the carbon fiber.

[0004] Therefore, developing a preparation method that balances high purity, high orientation, and uniform precursor fibers is key to achieving industrialization of PAN-based carbon fibers with increased diameter.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a PAN-based carbon fiber precursor and its preparation method, as well as PAN-based carbon fiber, to solve or improve the above-mentioned technical problems.

[0007] This invention is implemented as follows: In a first aspect, the present invention provides a method for preparing PAN-based carbon fiber precursor, comprising the following steps: Acrylonitrile and comonomers are blended in a certain proportion to obtain polyacrylonitrile copolymer; polyacrylonitrile copolymer is blended with solvent to obtain spinning solution; The spinning solution was treated by a dry-wet method to produce nascent fibers through spinning and coagulation. After undergoing multi-stage stretching and washing treatments, the nascent fibers are then oiled and dried to obtain PAN-based carbon fiber precursors. The mass ratio of acrylonitrile to comonomer is (84-99.6):(0.4-16).

[0008] In an optional embodiment, the comonomer comprises a first monomer and a second monomer in a mass ratio of (0.2-8):(0.2-8); The first monomer is a carboxylic acid compound or an amide compound. The carboxylic acid compound includes at least one of acrylic acid, methacrylic acid, itaconic acid, β-itaconic acid ammonium, isobutylacrylic acid, mesoaconic acid, 2-butenoic acid, maleic acid, and methylmaleic acid. The amide compound includes at least one of acrylamide, methacrylamide, acryloyl oxime, diacetone acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid. The second monomer is a sulfonic acid compound, which includes at least one of methyl allyl sulfonic acid, ammonium methyl allyl sulfonate, ammonium styrene sulfonate, and 2-propenesulfonate-2-methylpropane sulfonic acid.

[0009] In an optional embodiment, the preparation of the polyacrylonitrile copolymer further includes an initiator, the amount of which is 0.1%-1.0% of the total mass of acrylonitrile and comonomer; the initiator is an azo initiator, including at least one of azobisisobutyronitrile, azobisisovalerate, and azodiamidine hydrochloride; And / or, the temperature for preparing the polyacrylonitrile copolymer is 50℃-70℃, and the time is 8h-15h.

[0010] In an optional embodiment, the solvent used in preparing the spinning solution is selected from dimethyl sulfoxide or dimethylacetamide; The solid content of the prepared spinning solution is 14wt%-30wt%, and the intrinsic viscosity is 1.8-2.2.

[0011] In an optional embodiment, the dry-wet method uses a spinneret for dry-wet spinning, with a spinning speed of 10m / min-22m / min; And / or, the coagulation bath used for the coagulation treatment is an organic solvent-water mixture with a mass concentration of 20wt%-40wt%, and the coagulation time is 5s-70s; wherein, the organic solvent is selected from dimethyl sulfoxide or dimethylacetamide.

[0012] In an optional embodiment, the total draw ratio of the multi-stage draw treatment is 10.0 times to 25.0 times, which includes 1.2 times to 2.4 times of coagulation bath draw, 1.0 times to 1.5 times of water washing draw, 1.0 times to 2.0 times of gradient heating water draw and 2.5 times to 4.5 times of steam draw. Among them, the temperature of water washing stretching is 10℃-65℃, the temperature of gradient heating water stretching is 50℃-85℃, and the temperature of steam stretching is 120℃-180℃; And / or, the moisture content of the fiber after washing is 15wt%-20wt%.

[0013] In an optional embodiment, the oiling agent used for oiling is a silicone-containing oil, and the oiling rate is 0.3wt%-1.2wt%. And / or, the drying process employs a gradient roller direct contact drying method, with a drying temperature of 75℃-210℃ and a time of 20s-60s; it includes a first drying roller with a temperature of 75℃-85℃ and a time of 5s-12s; a second drying roller with a temperature of 105℃-115℃ and a time of 5s-12s; a third drying roller with a temperature of 135℃-145℃ and a time of 5s-12s; a fourth drying roller with a temperature of 165℃-175℃ and a time of 5s-12s; and a fifth drying roller with a temperature of 190℃-210℃ and a time of 5s-12s.

[0014] Secondly, the present invention provides a PAN-based carbon fiber precursor, which is prepared by any of the preparation methods described in the foregoing embodiments; The monofilament diameter of PAN-based carbon fiber precursor is 8μm-16μm, the orientation degree is ≥90%, and the density is ≥1.18g / cm³. 3 .

[0015] Thirdly, the present invention provides a PAN-based carbon fiber, which is prepared by pre-oxidation treatment, low-temperature carbonization treatment and high-temperature carbonization treatment of the PAN-based carbon fiber precursor as described in the foregoing embodiments. PAN-based carbon fibers have a tensile strength ≥5500MPa, a modulus of 260GPa-280GPa, and a diameter ≥6.5μm.

[0016] In an optional embodiment, the pre-oxidation treatment is carried out at a gradient temperature of 200°C to 280°C for 60 min to 90 min; And / or, low-temperature carbonization treatment is carried out in an inert atmosphere at 350℃-850℃ for 2min-10min; And / or, high-temperature carbonization is performed in an inert atmosphere at 1100℃-1700℃ for 2-10 minutes.

[0017] The present invention has the following beneficial effects: The method for preparing PAN-based carbon fiber precursor provided by this invention introduces a comonomer on the basis of acrylonitrile monomer. The synergistic effect of acrylonitrile monomer and comonomer not only improves the density of the precursor but also enhances the pre-oxidation reactivity of the precursor, providing a structural basis for obtaining stable carbon fiber modulus in the subsequent process. The drying treatment eliminates surface defects and internal residual stress of the precursor, ensuring the uniformity of the diameter and the density of the PAN-based carbon fiber precursor. The final PAN-based carbon fiber has excellent and stable mechanical properties. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0019] In a first aspect, the present invention provides a method for preparing PAN-based carbon fiber precursor, comprising the following steps: Acrylonitrile and comonomers are blended in a certain proportion to obtain polyacrylonitrile copolymer; polyacrylonitrile copolymer is blended with solvent to obtain spinning solution; The spinning solution was treated by a dry-wet method to produce nascent fibers through spinning and coagulation. After undergoing multi-stage stretching and washing treatments, the nascent fibers are then oiled and dried to obtain PAN-based carbon fiber precursors. The mass ratio of acrylonitrile to comonomer is (84-99.6):(0.4-16).

[0020] This invention introduces a comonomer on the basis of acrylonitrile monomer. The synergistic effect of acrylonitrile monomer and comonomer not only improves the storage stability and spinnability of spinning solution, but also improves the pre-oxidation reaction activity of the precursor fiber, providing a structural basis for obtaining stable carbon fiber modulus in the subsequent process.

[0021] For example, the mass ratio of acrylonitrile to comonomer is selected from any one of 90.8:9.2, 91.7:8.3, 99.1:0.9, 84.0:16.0 and 99.6:0.4, or other values ​​in the range of (84-99.6):(0.4-16).

[0022] By mass percentage, acrylonitrile is 84wt%-99.6wt%, and comonomer is 0.4wt%-16wt%.

[0023] In an optional embodiment, the comonomer comprises a first monomer and a second monomer in a mass ratio of (0.2-8):(0.2-8); The first monomer is a carboxylic acid compound or an amide compound. The carboxylic acid compound includes at least one of acrylic acid, methacrylic acid, itaconic acid, β-itaconic acid ammonium, isobutylacrylic acid, mesoaconic acid, 2-butenoic acid, maleic acid, and methylmaleic acid. The amide compound includes at least one of acrylamide, methacrylamide, acryloyl oxime, diacetone acrylamide, and 2-acrylamido-2-methylpropanesulfonic acid. The second monomer is a sulfonic acid compound, which includes at least one of methyl allyl sulfonic acid, ammonium methyl allyl sulfonate, ammonium styrene sulfonate, and 2-propenesulfonate-2-methylpropane sulfonic acid.

[0024] The first monomer is 0.2wt%-8wt% by mass percentage, and the second monomer is 0.2wt%-8wt%.

[0025] In this embodiment of the invention, the synergy between the first monomer and the second monomer can achieve a dual guarantee of process feasibility and the final mechanical properties of the carbon fiber. Specifically: PAN homopolymers have high cyclization temperatures and concentrated exothermic reactions, which can easily cause fiber burnout. Introducing a carboxylic acid or amide compound as the first monomer can provide proton transfer catalysis, initiating intramolecular cyclization. This promotes intramolecular cyclization of –C≡N, lowers the cyclization temperature, and regulates the exothermic behavior. The introduction of the first monomer also enhances the solubility of PAN in solvents, facilitates mass transfer in the coagulation bath, reduces the core-sheath structure of the nascent fiber, and provides a stable structure for carbon atom rearrangement during subsequent carbonization.

[0026] The second monomer has hydrophilic and strongly ionized groups, and is a hydrophilic comonomer that improves density. It can improve the stability of the spinning solution, which is beneficial to the control of the coagulation rate, and further improve the density of the fiber with increased fiber diameter.

[0027] In an optional embodiment, the preparation of the polyacrylonitrile copolymer further includes an initiator, the amount of which is 0.1%-1.0% of the total mass of acrylonitrile and comonomer; the initiator is an azo initiator, including at least one of azobisisobutyronitrile, azobisisovalerate, and azodiamidine hydrochloride; And / or, the temperature for preparing the polyacrylonitrile copolymer is 50℃-70℃, and the time is 8h-15h.

[0028] The initiator decomposes under heating conditions to generate primary free radicals, which initiate free radical chain polymerization of acrylonitrile and comonomers, thereby generating a polyacrylonitrile copolymer with a predetermined molecular weight and distribution. For example, the amount of initiator can be any one of 0.1%, 0.3%, 0.5%, 0.7%, 0.8%, 0.9% and 1.0% of the total mass of acrylonitrile and comonomers, or other values ​​in the range of 0.1% to 1.0%.

[0029] The temperature for preparing the polyacrylonitrile copolymer can be selected from any one of 50℃, 55℃, 60℃, 65℃ and 70℃, or other values ​​within the range of 50℃-70℃; the time can be selected from any one of 8h, 9h, 10h, 11h, 12h, 13h and 15h, or other values ​​within the range of 8h-15h.

[0030] In an optional embodiment, the solvent used in preparing the spinning solution is selected from dimethyl sulfoxide (DMSO) or dimethylacetamide (DMAC). The solid content of the prepared spinning solution is 14wt%-30wt%, and the intrinsic viscosity is 1.8-2.2.

[0031] It should be noted that after the polyacrylonitrile copolymer is blended with the solvent, it undergoes demonolysis, degassing, and filtration to obtain the spinning solution.

[0032] The purpose of monomer removal, defoaming, and filtration is to remove residual monomers, bubbles, and mechanical impurities, preventing yarn breakage, pore blockage, and defects in the raw yarn. Monomer removal primarily removes unpolymerized acrylonitrile and comonomers, preventing monomer decomposition or bubble generation upon subsequent heating, which could affect the stability, odor, and safety of the spinning solution. Specifically, in this embodiment of the invention, the monomer removal method involves vacuum vaporization to remove residual monomers in an environment with a temperature of 60℃-85℃ and a vacuum degree of -0.090MPa to -0.099MPa. In other embodiments of the invention, other reasonable monomer removal methods can be selected according to actual needs.

[0033] Degassing is used to remove dissolved or trapped air microbubbles from the reaction system, preventing bubbles from entering the spinneret orifice and causing defects such as broken filaments, surface streaks, and internal pores in the filament.

[0034] Filtration is used to remove macromolecular gels, undissolved particles, mechanical impurities, or metal shavings generated during polymerization in the reaction system, in order to avoid defects such as spinneret blockage, filament breakage, surface nodes, or blemishes.

[0035] In an optional embodiment, the dry-wet method uses a spinneret for dry-wet spinning, with a spinning speed of 10m / min-22m / min.

[0036] It should be noted that during the dry-wet spinning process, a dual diffusion behavior of solvent and non-solvent exists during the coagulation stage. The dynamic equilibrium of this process directly determines the cross-sectional structure of the precursor fiber. As the fiber diameter increases, the path of dual diffusion lengthens, and the coagulation processes of the fiber surface and core become significantly asynchronous: if the fiber surface is in direct contact with the coagulation bath, the solvent diffuses rapidly outward and the non-solvent penetrates inward, completing coagulation first and forming a dense structure; in the fiber core, because it is far from the coagulation bath interface, the processes of solvent precipitation and non-solvent penetration are both delayed, and coagulation lags behind that of the surface.

[0037] This difference in solidification rate between the inside and outside of the fiber is amplified as the fiber diameter increases, ultimately leading to a significant core-sheath structural inhomogeneity in the precursor fiber cross-section, with a dense sheath and a porous core. This inhomogeneity directly affects the overall structural uniformity of the precursor fiber, easily causing stress concentration and structural defects during subsequent heat treatment, which is detrimental to the preparation of high-performance carbon fibers. Therefore, this invention improves the cross-sectional structural uniformity of large-diameter precursor fibers and weakens the core-sheath effect by optimizing the dry and wet spinning process and controlling the dual diffusion behavior during the solidification stage. Specifically, by adjusting the composition and ratio of comonomers in the polymerization system, the regularity and interaction of PAN molecular chains are optimized, enhancing the densification ability during the precursor fiber solidification process and weakening the core-sheath structural differences.

[0038] If the spinning speed is too high, it will increase the extrusion swell rate, resulting in large fluctuations in the diameter of the nascent fibers and non-circular cross-sections. During coagulation in the coagulation bath, the skin layer is prone to premature closure, leading to internal solvent retention, radial micropores, and uneven fiber structure, which becomes a source of defects during carbonization. If the spinning speed is unstable, the diameter of the nascent fibers will fluctuate greatly and be uneven. The pre-oxidation or carbonization stages will be asynchronous, easily causing local overburning or insufficient residual carbon.

[0039] For example, the filament spinning speed can be selected from any one of 10 m / min, 12 m / min, 15 m / min, 18 m / min, 20 m / min and 22 m / min, or other values ​​in the range of 10 m / min to 22 m / min.

[0040] The spinneret of this invention has a circular spinneret orifice, and a flow guiding structure is provided at the outlet. In other embodiments of this invention, the spinneret orifice can be reasonably selected according to actual needs. For example, the shape of the spinneret orifice can be square.

[0041] And / or, the coagulation bath used for the coagulation treatment is an organic solvent-water mixture with a mass concentration of 20wt%-40wt%, and the coagulation time is 5s-70s; wherein, the organic solvent is selected from dimethyl sulfoxide or dimethylacetamide.

[0042] The organic solvent is the same as the solvent used in the spinning solution, avoiding the introduction of impurities by using a variety of solvents. The use of an organic solvent-water mixture helps to reduce the chemical potential gradient of the solvent in the coagulation bath, slows down the coagulation rate of the nascent fiber surface, and brings the bidirectional diffusion of solvent and non-solvent into equilibrium, thereby obtaining PAN-based carbon fiber precursors with uniform structure and low defects. It also helps to slow down the coagulation rate, making the fiber cross-section more circular and homogeneous, reducing the core-sheath difference, improving the stretchability of the precursor, reducing the volume shrinkage gradient and radial stress, refining the micropore size and making the distribution more uniform. This facilitates the elimination of pores during the drying process, resulting in fewer structural defects and higher strength in the carbonized fiber.

[0043] In an optional embodiment, the total draw ratio of the multi-stage draw treatment is 10.0 to 25.0 times, which includes 1.2 to 2.4 times of coagulation bath draw, 1.0 to 1.5 times of water washing draw, 1.0 to 2.0 times of gradient heating water draw, and 2.5 to 4.5 times of steam draw.

[0044] Total draw ratio = coagulation bath draw ratio × water washing draw ratio × gradient heating water draw ratio × steam draw ratio.

[0045] Multi-stage drawing process facilitates the gradual orientation of PAN molecular chains along the fiber axis and promotes the formation and refinement of microcrystals. Step-by-step heating and stretching avoids fiber breakage caused by single-stage high-ratio stretching, resulting in precursor fibers with uniform diameter, low porosity, and high molecular orientation, providing a sound structural basis for subsequent pre-oxidation and carbonization to prepare high-strength carbon fibers.

[0046] In this process, the coagulation bath stretching applies a light stretching to make the PAN chains slightly oriented along the axis, which helps to prevent the nascent fibers from swelling or shrinking excessively and lays the foundation for subsequent stretching; however, due to the fact that the fibers are still in a rigid state, the ratio should not be too large.

[0047] During the water washing and stretching stage, water molecules act as plasticizers, enhancing the mobility of chain segments. The PAN molecular chains become clearly oriented along the axial direction, and microcrystals begin to form. This facilitates the simultaneous removal of residual solvents, ensuring that subsequent heat treatment and carbonization are free from interference by low-molecular-weight decomposition products.

[0048] Gradient heating water drawing avoids sudden temperature changes that cause strain differences between the surface and the core, achieving more uniform radial orientation, dispersing the total tensile load, and improving diameter uniformity.

[0049] The chain segments have higher degrees of freedom in the steam drawing stage, which can achieve a larger draw ratio without breaking the filament under lower tension; the grain refinement and crystallinity are further improved in this stage, making up for the orientation upper limit that hot water drawing cannot reach; the steam envelopment is good, the circumferential force is symmetrical, the cross section of the filament is more rounded, and the surface tension is uniform.

[0050] Among them, the temperature of water washing stretching is 10℃-65℃, the temperature of gradient heating water stretching is 50℃-85℃, and the temperature of steam stretching is 120℃-180℃; And / or, the moisture content of the fiber after washing is 15wt%-20wt%.

[0051] The washing and drawing process employs an alternating hot and cold temperature method, specifically alternating between high and low temperatures. This alternating temperature stimulation enables the PAN molecular chains to undergo a "relaxation-orientation-re-relaxation-re-orientation" process during drawing. This ensures efficient solvent removal while avoiding the problems of rapid surface densification and uneven solvent residue in the core that can occur with high-temperature drawing on a single production line. This effectively improves the uniformity and overall density of the raw yarn cross-section. For example, the washing and drawing process in this invention involves eight alternating high and low temperatures, such as 35℃, 10℃, 40℃, 10℃, 45℃, 10℃, 50℃, and 10℃. In other embodiments of this invention, the number of washing and drawing temperature cycles and the specific temperatures can be adjusted as needed.

[0052] The temperature of the gradient heating water traction can be adjusted reasonably as needed, such as the temperature of the gradient heating water traction in this invention being 65℃ or 75℃.

[0053] In an optional embodiment, the oiling agent used for oiling is a silicone-containing oil, and the oiling rate is 0.3wt%-1.2wt%. And / or, the drying process employs a gradient roller direct contact drying method, with a drying temperature of 75℃-210℃ and a time of 20s-60s; it includes a first drying roller with a temperature of 75℃-85℃ and a time of 5s-12s; a second drying roller with a temperature of 105℃-115℃ and a time of 5s-12s; a third drying roller with a temperature of 135℃-145℃ and a time of 5s-12s; a fourth drying roller with a temperature of 165℃-175℃ and a time of 5s-12s; and a fifth drying roller with a temperature of 190℃-210℃ and a time of 5s-12s.

[0054] It should be noted that the present invention adopts a direct contact drying method with the rollers to ensure that the moisture on the fiber surface and inside evaporates simultaneously; the gradient rollers are mainly set with the temperature set according to the gradient. The present invention sets five sets of drying rollers. In other embodiments of the present invention, the number of drying sets can be reasonably adjusted according to the needs.

[0055] Further, in this embodiment of the invention, the temperature and corresponding residence time of each group of drying rollers are as follows: First drying roller: 80℃, residence time 5s-12s; Second drying roller: 110℃, residence time 5s-12s; Third drying roller: 140℃, residence time 5s-12s; Fourth drying roller: 170℃, residence time 5s-12s; Fifth drying roller: 200℃, residence time 5s-12s; The total drying temperature range is 80℃-200℃, and the total drying time is 20s-60s. In other embodiments of the invention, the temperature and corresponding residence time of each group of drying rollers can be reasonably adjusted according to actual needs.

[0056] Secondly, the present invention provides a PAN-based carbon fiber precursor, which is prepared by any of the preparation methods described in the foregoing embodiments; The monofilament diameter of PAN-based carbon fiber precursor is 8μm-16μm, the orientation degree is ≥90%, and the density is ≥1.18g / cm³. 3 .

[0057] It should be noted that traditional PAN-based precursor fibers with small diameters are prone to monofilament breakage and increased fuzz during spinning and subsequent processing, resulting in poor batch stability. The monofilament diameter of traditional PAN-based carbon fiber precursor fibers is 6μm-11μm. The PAN-based carbon fiber precursor fibers obtained in this invention have monofilament diameters of 8μm-16μm, representing a significant increase in diameter. This large-diameter precursor fiber significantly improves the cross-sectional uniformity and mechanical property stability of the monofilaments while ensuring spinning operability, and simultaneously reduces losses during production.

[0058] Thirdly, the present invention provides a PAN-based carbon fiber, which is prepared by pre-oxidation treatment, low-temperature carbonization treatment and high-temperature carbonization treatment of the PAN-based carbon fiber precursor as described in the foregoing embodiments. PAN-based carbon fibers have a tensile strength ≥5500MPa, a modulus of 260GPa-280GPa, and a diameter ≥6.5μm.

[0059] The PAN-based carbon fibers with increased diameter provided in this invention significantly improve the uniformity and stability of single filaments, reduce interface defects and stress concentration during the composite material preparation process, effectively improve the overall mechanical properties and structural reliability of the composite material, and are suitable for high load-bearing and lightweight application scenarios.

[0060] In an optional embodiment, the pre-oxidation treatment is carried out at a gradient temperature of 200℃-280℃ for 60min-90min; the pre-oxidation treatment adopts a gradient temperature increase method, which can be reasonably adjusted as needed, such as 200℃, 230℃ and 260℃.

[0061] And / or, low-temperature carbonization treatment is carried out in an inert atmosphere at 350℃-850℃ for 2min-10min; And / or, high-temperature carbonization is performed in an inert atmosphere at 1100℃-1700℃ for 2-10 minutes.

[0062] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0063] Example 1 This embodiment provides a PAN-based carbon fiber precursor, the preparation method of which includes the following steps: (1) Preparation of spinning solution By mass percentage, 90.8 wt% acrylonitrile, 1.2 wt% methacrylic acid (first monomer) and 8.0 wt% methyl allyl sulfonic acid (second monomer) were mixed, and 0.3% of azobisisobutyronitrile initiator by mass of the total monomers was added. The mixture was polymerized at 68°C for 11 h using DMSO as solvent to obtain polyacrylonitrile copolymer. Polyacrylonitrile copolymer was blended with DMSO, and then subjected to demonolysis, defoaming, and filtration to obtain a spinning solution. The spinning solution had a solid content of 20 wt% and an intrinsic viscosity of 1.92.

[0064] (2) Dry and wet spinning forming The spinning solution was treated by a dry-wet method to produce nascent fibers through spinning and coagulation. In the dry-wet method, a spinneret is used for dry-spinning and wet spinning, with a spinning speed of 12 m / min. The selected spinneret has circular spinneret holes and a flow guiding structure at the outlet.

[0065] In the coagulation process, the coagulation bath was a 36wt% DMSO-water mixed solution, and the coagulation time was 60s, resulting in nascent fibers.

[0066] (3) Multi-stage drawing and washing The nascent fibers obtained in step (2) are subjected to multi-stage stretching and washing treatment.

[0067] The total draw ratio of the multi-stage draw treatment is 16.17 times, specifically including: a coagulation bath draw ratio of 1.4 times; a water washing draw ratio of 1.6 times, with temperatures including eight alternating high and low temperatures: 35℃, 10℃, 40℃, 10℃, 45℃, 10℃, 50℃, and 10℃; a water draw ratio of 1.9 times, with gradient heating in the water draw, including temperatures of 65℃ and 75℃; and a steam draw temperature of 130℃, with a draw ratio of 3.8 times.

[0068] The washing process uses deionized water, and the moisture content of the nascent fibers after washing is 18 wt%.

[0069] (4) Oiling and drying treatment The PAN-based carbon fiber precursor was obtained by oiling and drying the fiber after the water washing treatment in step (3).

[0070] The oiling agent used for the oiling treatment is a silicone-containing oil, with an oiling rate of 1.0 wt%.

[0071] The drying process employs a gradient roller direct contact drying method, with temperatures set in gradients. The drying temperature ranges from 80℃ to 200℃, and the time is 50 seconds. The temperatures and corresponding residence times for each set of drying rollers are as follows: First drying roller: 80℃, residence time 10 seconds; Second drying roller: 110℃, residence time 10 seconds; Third drying roller: 140℃, residence time 10 seconds; Fourth drying roller: 170℃, residence time 10 seconds; Fifth drying roller: 200℃, residence time 10 seconds.

[0072] Testing revealed that the PAN-based carbon fiber precursor obtained in this embodiment had a single filament diameter of 12.5 μm, an orientation degree of 92%, and a density of 1.19 g / cm³. 3 The iodine adsorption value was 18.2 mg / g, and ΔL = 4.2.

[0073] The testing methods for each performance aspect are as follows: The test for monofilament diameter is based on GB / T29762; the test for orientation degree is based on GB / T23442; and the test for density is based on B / T30019.

[0074] Iodine adsorption value test method: Dry the sample at 105℃ for 2h and cool it to room temperature. Weigh 0.5g of the sample and place it in an iodine flask. Add 25mL of 0.1mol / L iodine standard solution, seal and shake for 1h. Let it stand for 30min. Take the supernatant and titrate it with 0.05mol / L sodium thiosulfate standard solution. Calculate the iodine adsorption value (mg / g). The lower the value, the higher the fiber density and the lower the porosity.

[0075] The lightness (L) value of the sample before and after iodine adsorption was determined using a colorimeter (CIELab, D65 light source, 10° field of view): the initial lightness of the sample after drying at 105℃ for 2 hours was measured as L0; then, iodine adsorption equilibrium was achieved according to GB / T12496.8 2015, followed by filtration, washing with water, and re-drying at 105℃ for 30 minutes, and the lightness after adsorption was measured as L1. ΔL = L0 was calculated. The smaller the value of L1; ΔL, the fewer the micropores in the fiber and the higher the density. It can be used in conjunction with the iodine adsorption value to characterize the density.

[0076] This embodiment also provides a PAN-based carbon fiber, which is prepared by pre-oxidation treatment, low-temperature carbonization treatment and high-temperature carbonization treatment of the PAN-based carbon fiber precursor obtained in step (4) above. Among them, the gradient temperature of the pre-oxidation treatment is 200℃, 230℃ and 260℃, and the duration of each gradient temperature is 25min; the low-temperature carbonization treatment is carried out at 600℃ for 8min under nitrogen protection; the high-temperature carbonization treatment is carried out at 1600℃ for 8min under nitrogen protection.

[0077] The obtained PAN-based carbon fiber was tested and found to have a single filament diameter of 7.1 μm, a tensile strength of 5800 MPa, and a modulus of 270 GPa. The tensile strength and modulus were tested in accordance with GB / T3362.

[0078] It should be noted that the test methods for the performance of the following embodiments or comparative examples are the same as those in Example 1, and will not be described again thereafter.

[0079] Example 2 This embodiment provides a PAN-based carbon fiber precursor, the preparation method of which includes the following steps: (1) Preparation of spinning solution By mass percentage, 91.7 wt% acrylonitrile, 8.0 wt% methacrylic acid (first monomer) and 0.3 wt% methyl allyl sulfonic acid (second monomer) were mixed, and 0.2% of azobisisobutyronitrile initiator by mass of the total monomers was added. Using DMAC as solvent, the mixture was polymerized at 60°C for 12 h to obtain polyacrylonitrile copolymer. Polyacrylonitrile copolymer was blended with DMAC, and then subjected to demonolysis, defoaming, and filtration to obtain a spinning solution. The spinning solution had a solid content of 18 wt% and an intrinsic viscosity of 1.85.

[0080] (2) Dry and wet spinning forming The spinning solution was treated by a dry-wet method to produce nascent fibers through spinning and coagulation. In the dry-wet method, a spinneret is used for dry-spinning and wet spinning, with a spinning speed of 16 m / min. The selected spinneret has circular spinneret holes and a flow guiding structure at the outlet.

[0081] In the coagulation process, the coagulation bath was a 30wt% DMAC-water mixed solution, and the coagulation time was 40s, resulting in nascent fibers.

[0082] (3) Multi-stage drawing and washing The nascent fibers obtained in step (2) are subjected to multi-stage stretching and washing treatment.

[0083] The total draw ratio of the multi-stage draw treatment is 15.88 times, specifically including: a coagulation bath draw ratio of 1.5 times; a water washing draw ratio of 1.4 times, with temperatures including eight alternating high and low temperatures: 35℃, 10℃, 40℃, 10℃, 45℃, 10℃, 50℃, and 10℃; a water draw ratio of 1.8 times, with gradient temperature increases including 65℃ and 75℃; and a steam draw temperature of 130℃, with a draw ratio of 4.2 times.

[0084] The washing process uses deionized water, and the moisture content of the nascent fibers after washing is 16wt%.

[0085] (4) Oiling and drying treatment The PAN-based carbon fiber precursor was obtained by oiling and drying the fiber after the water washing treatment in step (3).

[0086] The oiling agent used for the oiling treatment is a silicone-containing oil, with an oiling rate of 0.8 wt%.

[0087] The drying process employs a gradient roller direct contact drying method, with temperatures set in gradients. The drying temperature ranges from 80℃ to 200℃, and the time is 50 seconds. The temperatures and corresponding residence times for each set of drying rollers are as follows: First drying roller: 80℃, residence time 10 seconds; Second drying roller: 110℃, residence time 10 seconds; Third drying roller: 140℃, residence time 10 seconds; Fourth drying roller: 170℃, residence time 10 seconds; Fifth drying roller: 200℃, residence time 10 seconds.

[0088] Testing revealed that the PAN-based carbon fiber precursor obtained in this embodiment had a single filament diameter of 12.1 μm, an orientation degree of 90%, and a density of 1.18 g / cm³. 3 The iodine adsorption value was 21.5 mg / g, and ΔL = 4.8.

[0089] This embodiment also provides a PAN-based carbon fiber, which is prepared by pre-oxidation treatment, low-temperature carbonization treatment and high-temperature carbonization treatment of the PAN-based carbon fiber precursor obtained in step (4) above. Among them, the gradient temperature of the pre-oxidation treatment is 200℃, 230℃ and 260℃, and the duration of each gradient temperature is 25min; the low-temperature carbonization treatment is carried out at 600℃ for 8min under nitrogen protection; the high-temperature carbonization treatment is carried out at 1600℃ for 8min under nitrogen protection.

[0090] The obtained PAN-based carbon fiber was tested and found to have a single filament diameter of 6.8 μm, a tensile strength of 5500 MPa, and a modulus of 260 GPa.

[0091] Example 3 This embodiment provides a PAN-based carbon fiber precursor, the preparation method of which includes the following steps: (1) Preparation of spinning solution By mass percentage, 99.1 wt% acrylonitrile, 0.3 wt% methacrylic acid (first monomer) and 0.6 wt% methyl allyl sulfonic acid (second monomer) were mixed, and 0.22% of the total mass of the monomers was added as an azobisisobutyronitrile initiator. The mixture was polymerized at 70°C for 8 hours using DMSO as a solvent to obtain a polyacrylonitrile copolymer. Polyacrylonitrile copolymer was blended with DMSO, and then subjected to demonolysis, defoaming, and filtration to obtain a spinning solution. The spinning solution had a solid content of 22 wt% and an intrinsic viscosity of 2.02.

[0092] (2) Dry and wet spinning forming The spinning solution was treated by a dry-wet method to produce nascent fibers through spinning and coagulation. In the dry-wet method, a spinneret is used for dry-jet wet spinning, with a spinning speed of 14 m / min. The selected spinneret has circular spinneret holes and a flow guiding structure at the outlet.

[0093] In the coagulation process, the coagulation bath was a 33wt% DMAC-water mixed solution, and the coagulation time was 50s, resulting in nascent fibers.

[0094] (3) Multi-stage drawing and washing The nascent fibers obtained in step (2) are subjected to multi-stage stretching and washing treatment.

[0095] The total draw ratio of the multi-stage draw treatment is 24.02 times, specifically including: a coagulation bath draw ratio of 2.0 times; a water washing draw ratio of 1.6 times, with temperatures including eight alternating high and low temperatures: 35℃, 10℃, 40℃, 10℃, 45℃, 10℃, 50℃, and 10℃; a water draw ratio of 1.9 times, with gradient temperature increases including 65℃ and 75℃; and a steam draw temperature of 130℃, with a draw ratio of 3.95 times.

[0096] The washing process uses deionized water, and the moisture content of the nascent fibers after washing is 19 wt%.

[0097] (4) Oiling and drying treatment The PAN-based carbon fiber precursor was obtained by oiling and drying the fiber after the water washing treatment in step (3).

[0098] The oiling agent used for the oiling treatment is a silicone-containing oil, with an oiling rate of 1.2 wt%.

[0099] The drying process employs a gradient roller direct contact drying method, with temperatures set in gradients. The drying temperature ranges from 80℃ to 200℃, and the time is 50 seconds. The temperatures and corresponding residence times for each set of drying rollers are as follows: First drying roller: 80℃, residence time 10 seconds; Second drying roller: 110℃, residence time 10 seconds; Third drying roller: 140℃, residence time 10 seconds; Fourth drying roller: 170℃, residence time 10 seconds; Fifth drying roller: 200℃, residence time 10 seconds.

[0100] Testing revealed that the PAN-based carbon fiber precursor obtained in this embodiment had a single filament diameter of 11.8 μm, an orientation degree of 93%, and a density of 1.20 g / cm³. 3 The iodine adsorption value was 15.7 mg / g, and ΔL = 3.9.

[0101] This embodiment also provides a PAN-based carbon fiber, which is prepared by pre-oxidation treatment, low-temperature carbonization treatment and high-temperature carbonization treatment of the PAN-based carbon fiber precursor obtained in step (4) above. Among them, the gradient temperature of the pre-oxidation treatment is 200℃, 230℃ and 260℃, and the duration of each gradient temperature is 25min; the low-temperature carbonization treatment is carried out at 600℃ for 8min under nitrogen protection; the high-temperature carbonization treatment is carried out at 1600℃ for 8min under nitrogen protection.

[0102] The obtained PAN-based carbon fiber was tested and found to have a single filament diameter of 6.5 μm, a tensile strength of 6100 MPa, and a modulus of 280 GPa.

[0103] Example 4 This embodiment provides a PAN-based carbon fiber precursor, the preparation method of which includes the following steps: (1) Preparation of spinning solution By mass percentage, 84.0 wt% acrylonitrile, 8.0 wt% methacrylic acid (first monomer) and 8.0 wt% methyl allyl sulfonic acid (second monomer) were mixed, and 1.0% of azobisisobutyronitrile initiator by mass of the total monomers was added. Using DMAC as solvent, the mixture was polymerized at 50°C for 15 h to obtain polyacrylonitrile copolymer. Polyacrylonitrile copolymer was blended with DMAC, and then subjected to demonolysis, defoaming, and filtration to obtain a spinning solution. The spinning solution had a solid content of 14 wt% and an intrinsic viscosity of 1.80.

[0104] (2) Dry and wet spinning forming The spinning solution was treated by a dry-wet method to produce nascent fibers through spinning and coagulation. In the dry-wet method, a spinneret is used for dry-spinning and wet spinning, with a spinning speed of 10 m / min. The selected spinneret has circular spinneret holes and a flow guiding structure at the outlet.

[0105] In the coagulation process, the coagulation bath was a 20wt% DMAC-water mixed solution, and the coagulation time was 70s, resulting in nascent fibers.

[0106] (3) Multi-stage drawing and washing The nascent fibers obtained in step (2) are subjected to multi-stage stretching and washing treatment.

[0107] The total draw ratio of the multi-stage draw treatment is 11.55 times, specifically including: a coagulation bath draw ratio of 1.2 times; a water washing draw ratio of 1.0 times, with temperatures including eight alternating high and low temperatures: 35℃, 10℃, 40℃, 10℃, 45℃, 10℃, 50℃, and 10℃; a water draw ratio of 2.5 times, with gradient temperature increases including 65℃ and 75℃; and a steam draw temperature of 130℃, with a draw ratio of 3.85 times.

[0108] The washing process uses deionized water, and the moisture content of the nascent fibers after washing is 15wt%.

[0109] (4) Oiling and drying treatment The PAN-based carbon fiber precursor was obtained by oiling and drying the fiber after the water washing treatment in step (3).

[0110] The oiling agent used for the oiling treatment is a silicone-containing oil, with an oiling rate of 0.3 wt%.

[0111] The drying process employs a gradient roller direct contact drying method, with temperatures set in gradients. The drying temperature ranges from 80℃ to 200℃, and the time is 50 seconds. The temperatures and corresponding residence times for each set of drying rollers are as follows: First drying roller: 80℃, residence time 10 seconds; Second drying roller: 110℃, residence time 10 seconds; Third drying roller: 140℃, residence time 10 seconds; Fourth drying roller: 170℃, residence time 10 seconds; Fifth drying roller: 200℃, residence time 10 seconds.

[0112] Testing revealed that the PAN-based carbon fiber precursor obtained in this embodiment had a single filament diameter of 16.0 μm, an orientation degree of 90%, and a density of 1.18 g / cm³. 3 The iodine adsorption value was 24.8 mg / g, and ΔL = 4.9.

[0113] This embodiment also provides a PAN-based carbon fiber, which is prepared by pre-oxidation treatment, low-temperature carbonization treatment and high-temperature carbonization treatment of the PAN-based carbon fiber precursor obtained in step (4) above. Among them, the gradient temperature of the pre-oxidation treatment is 200℃, 230℃ and 260℃, and the duration of each gradient temperature is 25min; the low-temperature carbonization treatment is carried out at 600℃ for 8min under nitrogen protection; the high-temperature carbonization treatment is carried out at 1600℃ for 8min under nitrogen protection.

[0114] The obtained PAN-based carbon fiber was tested and found to have a single filament diameter of 7.8 μm, a tensile strength of 5526 MPa, and a modulus of 263 GPa.

[0115] Example 5 This embodiment provides a PAN-based carbon fiber precursor, the preparation method of which includes the following steps: (1) Preparation of spinning solution By mass percentage, 99.6 wt% acrylonitrile, 0.2 wt% methacrylic acid (first monomer) and 0.2 wt% methyl allyl sulfonic acid (second monomer) were mixed, and 0.1 wt% of azobisisobutyronitrile initiator was added. The mixture was polymerized at 70°C for 8 hours using DMSO as solvent to obtain polyacrylonitrile copolymer. Polyacrylonitrile copolymer was blended with DMSO, and then subjected to demonolysis, defoaming, and filtration to obtain a spinning solution. The spinning solution had a solid content of 30 wt% and an intrinsic viscosity of 2.20.

[0116] (2) Dry and wet spinning forming The spinning solution was treated by a dry-wet method to produce nascent fibers through spinning and coagulation. In the dry-wet method, a spinneret is used for dry-jet wet spinning, with a spinning speed of 18 m / min. The selected spinneret has circular spinneret holes and a flow guiding structure at the outlet.

[0117] In the coagulation process, the coagulation bath was a 40wt% DMAC-water mixed solution, and the coagulation time was 30s, resulting in nascent fibers.

[0118] (3) Multi-stage drawing and washing The nascent fibers obtained in step (2) are subjected to multi-stage stretching and washing treatment.

[0119] The total draw ratio of the multi-stage draw treatment is 24.60 times, specifically including: a coagulation bath draw ratio of 2 times; a water washing draw ratio of 1.5 times, with temperatures including eight alternating high and low temperatures: 35℃, 10℃, 40℃, 10℃, 45℃, 10℃, 50℃, and 10℃; a water draw ratio of 2.0 times, with gradient temperature increases including 65℃ and 75℃; and a steam draw temperature of 130℃, with a draw ratio of 4.1 times.

[0120] The washing process uses deionized water, and the moisture content of the nascent fibers after washing is 20wt%.

[0121] (4) Oiling and drying treatment The PAN-based carbon fiber precursor was obtained by oiling and drying the fiber after the water washing treatment in step (3).

[0122] The oiling agent used for the oiling treatment is a silicone-containing oil, with an oiling rate of 1.2 wt%.

[0123] The drying process employs a gradient roller direct contact drying method, with temperatures set in gradients. The drying temperature ranges from 80℃ to 200℃, and the time is 50 seconds. The temperatures and corresponding residence times for each set of drying rollers are as follows: First drying roller: 80℃, residence time 10 seconds; Second drying roller: 110℃, residence time 10 seconds; Third drying roller: 140℃, residence time 10 seconds; Fourth drying roller: 170℃, residence time 10 seconds; Fifth drying roller: 200℃, residence time 10 seconds.

[0124] Testing revealed that the PAN-based carbon fiber precursor obtained in this embodiment had a single filament diameter of 8.0 μm, an orientation degree of 94%, and a density of 1.21 g / cm³. 3 The iodine adsorption value was 14.3 mg / g, and ΔL = 3.8.

[0125] This embodiment also provides a PAN-based carbon fiber, which is prepared by pre-oxidation treatment, low-temperature carbonization treatment and high-temperature carbonization treatment of the PAN-based carbon fiber precursor obtained in step (4) above. Among them, the gradient temperature of the pre-oxidation treatment is 200℃, 230℃ and 260℃, and the total time is 75min; the low-temperature carbonization treatment is carried out at 600℃ for 8min under nitrogen protection; and the high-temperature carbonization treatment is carried out at 1600℃ for 8min under nitrogen protection.

[0126] The obtained PAN-based carbon fiber was tested and found to have a single filament diameter of 6.5 μm, a tensile strength of 6200 MPa, and a modulus of 280 GPa.

[0127] Comparative Example 1 This comparative example provides a PAN-based carbon fiber precursor, which is prepared using the same method as in Example 1, except that it includes the following steps: A binary copolymer system was used, consisting of 95 wt% acrylonitrile and 5 wt% methacrylic acid (first monomer), to prepare PAN-based carbon fiber precursor fibers with a diameter of 9.0 μm, an orientation degree of 85%, and a density of 1.18 g / cm³. 3 The iodine adsorption value was 38.6 mg / g, and ΔL = 8.3.

[0128] This comparative example also provides a PAN-based carbon fiber, prepared using the same process as in Example 1. The obtained PAN-based carbon fiber has a single filament diameter of 7.1 μm, a tensile strength of 4800 MPa, and a modulus of 240 GPa. This comparative example does not add methyl allyl sulfonic acid as a second monomer; it only uses a binary copolymerization system to prepare the precursor fiber. The strength and modulus are significantly lower than those of the product in Example 1 of this invention.

[0129] Comparative Example 2 This comparative example provides a PAN-based carbon fiber precursor, which is prepared using the same method as in Example 1, except that it includes the following steps: A binary copolymer system was used, consisting of 95.5 wt% acrylonitrile and 4.5 wt% methyl allyl sulfonic acid (second monomer), to prepare PAN-based carbon fiber precursor fibers with a single filament diameter of 12.3 μm, an orientation degree of 87%, and a density of 1.18 g / cm³. 3 The iodine adsorption value was 32.1 mg / g, and ΔL = 7.5.

[0130] This comparative example also provides a PAN-based carbon fiber, prepared using the same process as in Example 1. The obtained PAN-based carbon fiber has a single filament diameter of 7.0 μm, a tensile strength of 5200 MPa, and a modulus of 253 GPa. This comparative example does not add the first monomer of methacrylate; it only uses a binary copolymer system to prepare the precursor fiber. The strength and modulus are significantly lower than those of the product in Example 1 of this invention.

[0131] Comparative Example 3 This comparative example provides a PAN-based carbon fiber precursor, which is prepared using the same method as in Example 1, except that it includes the following steps: Step (2) uses conventional wet spinning.

[0132] The prepared PAN-based carbon fibers have residual stress, a diameter deviation of ±0.5 μm, an orientation degree of 87%, an iodine adsorption value of 35.7 mg / g, and ΔL=7.9.

[0133] This comparative example also provides a PAN-based carbon fiber, prepared using the same process as in Example 1. The obtained PAN-based carbon fiber has a single filament diameter of 6.7 μm, a tensile strength of 5300 MPa, and a modulus of 255 GPa. Compared to Example 1, this comparative example uses conventional wet spinning instead of dry-wet spinning, resulting in poor filament size uniformity, significant internal stress, a substantial reduction in fiber orientation and density, and more pore defects. Consequently, the mechanical properties of the prepared carbon fiber are significantly inferior to those of Example 1.

[0134] Comparative Example 4 This comparative example provides a PAN-based carbon fiber precursor, which is prepared using the same method as in Example 1, except that it includes the following steps: Step (1) The solid content of the spinning solution is 12wt%, and the intrinsic viscosity is 1.9.

[0135] The prepared PAN-based carbon fibers had uneven diameters, an orientation degree of 88%, and a density of 1.15 g / cm³. 3 The iodine adsorption value was 41.3 mg / g, and ΔL = 8.7.

[0136] This comparative example also provides a PAN-based carbon fiber, prepared using the same process as in Example 1. The obtained PAN-based carbon fiber has a single filament diameter of 6.8 μm, a tensile strength of 5200 MPa, and a modulus of 252 GPa. Compared to Example 1, this comparative example reduces the solid content of the spinning solution and fine-tunes the intrinsic viscosity, resulting in a significant decrease in both the tensile strength and modulus of the carbon fiber, with mechanical properties far inferior to those of Example 1.

[0137] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing PAN-based carbon fiber precursor, characterized in that, Includes the following steps: Acrylonitrile and comonomers are blended in a certain proportion to obtain a polyacrylonitrile copolymer; the polyacrylonitrile copolymer is blended with a solvent to obtain a spinning solution. The spinning solution was subjected to spinning and coagulation treatment using a dry-wet method to obtain nascent fibers. The nascent fibers are subjected to multi-stage stretching and washing treatments, followed by oiling and drying treatments to obtain PAN-based carbon fiber precursors. The mass ratio of acrylonitrile to comonomer is (84-99.6):(0.4-16).

2. The preparation method according to claim 1, characterized in that, The comonomer comprises a first monomer and a second monomer in a mass ratio of (0.2-8):(0.2-8); Wherein, the first monomer is a carboxylic acid compound or an amide compound, wherein the carboxylic acid compound includes at least one of acrylic acid, methacrylic acid, itaconic acid, β-itaconic acid ammonium, isobutylacrylic acid, mesoaconic acid, 2-butenoic acid, maleic acid and methylmaleic acid; and the amide compound includes at least one of acrylamide, methacrylamide, acryloyl oxime, diacetone acrylamide and 2-acrylamido-2-methylpropanesulfonic acid. The second monomer is a sulfonic acid compound, which includes at least one of methyl allyl sulfonic acid, ammonium methyl allyl sulfonate, ammonium styrene sulfonate, and 2-propenesulfonate-2-methylpropane sulfonic acid.

3. The preparation method according to claim 1, characterized in that, The preparation of the polyacrylonitrile copolymer also includes an initiator, wherein the amount of the initiator is 0.1%-1.0% of the total mass of acrylonitrile and comonomer; the initiator is an azo initiator, including at least one of azobisisobutyronitrile, azobisisovalerate, and azodiamidine hydrochloride; And / or, the temperature for preparing the polyacrylonitrile copolymer is 50℃-70℃, and the time is 8h-15h.

4. The preparation method according to claim 1, characterized in that, When preparing the spinning solution, the solvent used is selected from dimethyl sulfoxide or dimethylacetamide; The solid content of the prepared spinning solution is 14wt%-30wt%, and the intrinsic viscosity is 1.8-2.

2.

5. The preparation method according to claim 1, characterized in that, The dry-wet method uses a spinneret for dry-wet spinning, with a spinning speed of 10m / min-22m / min. And / or, the coagulation treatment uses a coagulation bath of 20wt%-40wt% organic solvent-water mixture, and the coagulation time is 5s-70s; wherein the organic solvent is selected from dimethyl sulfoxide or dimethylacetamide.

6. The preparation method according to claim 1, characterized in that, The total draw ratio of the multi-stage draw treatment is 10.0 to 25.0 times, which includes 1.2 to 2.4 times of coagulation bath draw, 1.0 to 1.5 times of water washing draw, 1.0 to 2.0 times of gradient heating water draw, and 2.5 to 4.5 times of steam draw. Among them, the temperature of water washing stretching is 10℃-65℃, the temperature of gradient heating water stretching is 50℃-85℃, and the temperature of steam stretching is 120℃-180℃; And / or, the moisture content of the fibers after the water washing treatment is 15wt%-20wt%.

7. The preparation method according to claim 1, characterized in that, The oiling agent used in the oiling treatment is a silicone-containing oil, with an oiling rate of 0.3wt%-1.2wt%. And / or, the drying process employs a gradient roller direct contact drying method, with a drying temperature of 75℃-210℃ and a time of 20s-60s; it includes a first drying roller with a temperature of 75℃-85℃ and a time of 5s-12s; a second drying roller with a temperature of 105℃-115℃ and a time of 5s-12s; a third drying roller with a temperature of 135℃-145℃ and a time of 5s-12s; a fourth drying roller with a temperature of 165℃-175℃ and a time of 5s-12s; and a fifth drying roller with a temperature of 190℃-210℃ and a time of 5s-12s.

8. A PAN-based carbon fiber precursor, characterized in that, Prepared by the preparation method according to any one of claims 1-7; The monofilament diameter of PAN-based carbon fiber precursor is 8μm-16μm, the orientation degree is ≥90%, and the density is ≥1.18g / cm³. 3 .

9. A PAN-based carbon fiber, characterized in that, The PAN-based carbon fiber precursor described in claim 8 is obtained by pre-oxidation treatment, low-temperature carbonization treatment, and high-temperature carbonization treatment; The PAN-based carbon fiber has a tensile strength ≥5500MPa, a modulus of 260GPa-280GPa, and a diameter ≥6.5μm.

10. The PAN-based carbon fiber according to claim 9, characterized in that, The pre-oxidation treatment is carried out at a gradient temperature of 200℃-280℃ for 60min-90min; And / or, the low-temperature carbonization treatment is carried out in an inert atmosphere at 350℃-850℃ for 2min-10min; And / or, the high-temperature carbonization treatment is carried out in an inert atmosphere at 1100℃-1700℃ for 2min-10min.