Polyacrylonitrile precursor, polyacrylonitrile carbon fiber, and preparation methods therefor

Abstract

The present disclosure relates to the technical field of carbon fiber, and in particular relates to a polyacrylonitrile precursor and a preparation method therefor, and a polyacrylonitrile carbon fiber and a preparation method therefor. The surface of the polyacrylonitrile precursor is provided with longitudinal grooves arranged in parallel along an axial direction of the fiber. The precursor has an average diameter of 10-20 μm, a breaking strength of 7-15 cN / dtex, an initial modulus of 120-200 cN / dtex, an elongation at break of 10-20%, and a degree of orientation of a crystal region of 75-99%. The polyacrylonitrile precursor of the present invention has a large diameter, a high individual filament breaking strength, a high initial modulus, and a high elongation at break.

Description

Polyacrylonitrile precursor fibers and polyacrylonitrile carbon fibers and their preparation methods Technical Field

[0001] This invention relates to the field of carbon fiber technology, specifically to polyacrylonitrile precursor fibers and their preparation methods, as well as polyacrylonitrile (PAN) carbon fibers and their preparation methods. Background Technology

[0002] Carbon fiber possesses excellent properties such as high specific strength and high specific modulus. There is a desire to produce high-performance, high-quality carbon fibers to meet industrial demands. Carbon fiber is generally prepared from carbon fiber precursors. High-quality carbon fiber precursors should have characteristics such as few surface defects, few pores, dense structure, good tensile strength, and high heat resistance. Many types of precursors can be used to prepare carbon fiber, but currently, approximately 90% of carbon fiber is made from PAN precursors. PAN-based carbon fibers have advantages such as high carbon yield, excellent mechanical properties, and mature processing technology, and have become the main carbon fiber product. Using dimethyl sulfoxide as a solvent to prepare polyacrylonitrile-based carbon fiber precursors has advantages such as low toxicity and high solubility of polyacrylonitrile copolymers in solvents, making it an important solvent system for preparing high-strength, high-modulus, and high-toughness polyacrylonitrile carbon fiber precursors.

[0003] The primary condition for producing high-quality polyacrylonitrile (PA) precursor fibers is the preparation of a high-quality PA solution. A high-quality PA solution, besides possessing long-term stable molecular weight characteristics, solid content, viscosity, and copolymer composition, also includes a sufficiently low impurity content. Impurities in PA solutions typically include mechanical impurities introduced from the external environment, non-solvent impurities, and gel particles generated during equipment operation. These impurities negatively impact the PA solution filter and the dopant extrusion process, and in severe cases, can lead to spinneret blockage, causing a series of spinning abnormalities such as fuzzy nascent fibers and fiber breakage, ultimately necessitating a shutdown for cleaning, severely affecting production efficiency and precursor fiber quality.

[0004] Existing technologies suffer from problems such as small diameter of polyacrylonitrile precursor fibers, low single-filament breaking strength, low initial modulus, and low breaking elongation, as well as small diameter, low breaking strength, low initial modulus, and low breaking elongation of the resulting carbon fibers.

[0005] CN114687010A discloses high-strength, high-modulus, and high-elongation carbon fibers and their preparation methods. This application uses wet spinning, where the spinning solution is coagulated, washed, drawn with hot water, oiled, and dried, followed by steam drawing and heat setting to obtain precursor fibers with a boiling water shrinkage rate of 5.0-6.8%, a breaking elongation of 9.5-11.0%, and a tensile strength of 4.7-5.9 cN / dtex. The precursor fibers are then subjected to pre-oxidation, low-temperature carbonization, high-temperature carbonization, and ultra-high-temperature graphitization to prepare carbon fibers with a tensile strength ≥5.00 GPa, a tensile modulus ≥540 GPa, and a breaking elongation ≥0.90%.

[0006] CN111621878A discloses large-diameter, high-strength, intermediate-modulus and high-strength, high-modulus PAN-based carbon fibers with surface groove structures and their preparation methods. Wet spinning with a spinneret with an aperture of 75-120 μm yields 1K PAN precursor fibers with a diameter of 12-16 μm. These precursor fibers undergo pre-oxidation treatment, followed by low-temperature and high-temperature carbonization to obtain large-diameter, high-strength, intermediate-modulus carbon fibers with a groove structure, a diameter of 8.5-10 μm, a strength of 4.90-6.10 GPa, and a modulus of 270-310 GPa. High-temperature graphitization further yields large-diameter, high-strength, high-modulus carbon fibers with a surface groove structure, a diameter of 7-10 μm, a strength of 3.70-5.50 GPa, and a modulus of 370-688 GPa. The crystal orientation degree of the precursor fibers and carbon fibers in this application is relatively low; it is hoped that the crystal orientation degree of the precursor fibers and carbon fibers in this document can be improved.

[0007] CN109082730A discloses large-diameter PAN carbon fibers and their preparation method, which involves preparing large-diameter PAN precursor fibers with a fineness of 252-716 dtex and a diameter of 16-30 μm by controlling the spinning process conditions. CN109252251A discloses large-diameter dry-wet PAN-based carbon fibers and their preparation method. This method uses dry-wet spinning technology, controlling the diameter of the solidified filaments, washed fibers, and dried and densified fibers to obtain large-diameter dry-wet PAN precursor fibers with a fineness of 120-780 dtex and a diameter of 10-30 μm. This application uses a dry-wet spinning process to control the diameter of the precursor fibers, and further pre-oxidizes and carbonizes them to prepare large-diameter dry-wet carbon fibers. The dry-wet carbon fibers of this application lack grooves on their surface, limiting the application scenarios of the carbon fibers.

[0008] CN112831859A discloses a method for preparing polyacrylonitrile fibers. The method involves using a combination of ionic liquid and a high-boiling-point solvent to swell and dissolve polyacrylonitrile, followed by flash spinning to improve fiber defects and produce denser, finer fibers. This application has produced polyacrylonitrile fibers with diameters of 0.5-5 μm, strengths of 1.8-3.7 cN / dtex, and elongation at break of 15-28%. However, the flash spinning technology employed in this application presents multiple challenges for solvent recovery and requires significantly more energy for both spinning and recovery processes.

[0009] The aim is to overcome the problems existing in the prior art and provide polyacrylonitrile precursor fibers with large diameter, high single filament breaking strength, high initial modulus and high breaking elongation, as well as polyacrylonitrile carbon fibers with large diameter, high breaking strength, high initial modulus and high breaking elongation, and to provide methods for their preparation. Summary of the Invention

[0010] Through in-depth research, the inventors have discovered that PAN spinning solution is one of the key components in the preparation of carbon fibers, significantly impacting the final carbon fiber properties. High-quality PAN solution contributes to the production of high-strength and high-modulus carbon fibers.

[0011] Controlling the number and size of gel particles in the PAN spinning solution is crucial for preparing high-performance carbon fibers. Generally, higher concentration solutions tend to form a larger number of gel particles, while lower concentration solutions tend to form fewer gel particles. Therefore, minimizing gel particle formation is generally desirable.

[0012] However, the inventors unexpectedly discovered, after research, that a specific range of gel particles (as defined herein) within a specific size range in the polyacrylonitrile spinning solution have a significant and beneficial effect on the structure and properties of the polyacrylonitrile precursor and the final carbon fiber. In this invention, gel particles refer to polymeric (polyacrylonitrile polymer) particles in the polyacrylonitrile spinning solution. Specifically, gel particles in the solution refer to soft micro-nano-scale polyacrylonitrile polymer particles with a three-dimensional network structure constructed by physical and / or chemical cross-linking. These gel particles can reversibly bind solvent molecules through their network and reach a swelling equilibrium state. The gel particles exhibit properties such as softness, elasticity, and stimuli responsiveness in the dispersion medium (solvent) and exist stably as insoluble discrete individuals (particles) in the spinning solution. The inventors unexpectedly discovered that the above-mentioned type of gel particles can improve the morphology of PAN fibers, manifested as increased fiber surface roughness; can enhance the mechanical properties of the fibers, including increasing the breaking strength, elongation at break, and initial modulus of the precursor and carbon fibers; it is believed that the polymer chains in the gel particles are interwoven to form a network structure, resulting in better breaking strength of the fibers. It is believed that the presence of gel particles during the pre-oxidation and carbonization process of PAN fibers facilitates the stretching of the precursor fibers and improves the structure of the carbon fibers, thereby enhancing their strength and toughness. It is also believed that these types of gel particles can act as reinforcing agents for polyacrylonitrile precursor fibers and carbon fibers, improving their overall performance.

[0013] The purpose of this invention is to overcome the problems of small diameter, low single-filament breaking strength, low initial modulus, and low breaking elongation of polyacrylonitrile precursor fibers and the resulting carbon fibers, which also exhibit small diameter, low breaking strength, low initial modulus, and low breaking elongation in existing technologies. This invention provides polyacrylonitrile precursor fibers and their preparation methods, as well as polyacrylonitrile carbon fibers and their preparation methods. The polyacrylonitrile precursor fibers of this invention have the characteristics of large diameter, high single-filament breaking strength, high initial modulus, and high breaking elongation, and can be further used to prepare polyacrylonitrile carbon fibers with large diameter, high breaking strength, high initial modulus, and high breaking elongation.

[0014] To achieve the above objectives, the first aspect of the present invention provides a polyacrylonitrile precursor fiber, wherein the surface of the polyacrylonitrile precursor fiber has longitudinal grooves arranged parallel to the fiber axis, and the average diameter of the polyacrylonitrile precursor fiber is 10-20 μm, the tensile strength is 7-15 cN / dtex, the initial modulus is 120-200 cN / dtex, the elongation at break is 10-20%, and the degree of crystal orientation is 75-99%.

[0015] A second aspect of this invention provides a method for preparing the polyacrylonitrile precursor fiber described in the first aspect. The method includes: wet spinning a polyacrylonitrile spinning solution; wherein the amount of gel particles with a particle size (diameter) of 0.15-10 μm in the polyacrylonitrile spinning solution is 2*10. 5 -8*10 7 per mL.

[0016] The third aspect of the present invention provides a method for preparing polyacrylonitrile carbon fiber, the method comprising: subjecting the polyacrylonitrile precursor fiber described in the first aspect to pre-oxidation treatment, low-temperature carbonization treatment, and high-temperature carbonization treatment.

[0017] A fourth aspect of this invention provides a polyacrylonitrile carbon fiber with an average diameter of 5-12 μm, a tensile strength of 4.2-6.5 GPa, an initial modulus of 250-350 GPa, and an elongation at break of 0.8-2.5%. Preferably, the polyacrylonitrile carbon fiber is prepared by the method for preparing polyacrylonitrile carbon fiber described in the third aspect. In some embodiments, preferably, the degree of crystal orientation of the polyacrylonitrile carbon fiber is 75-99%, more preferably 85-95%, and even more preferably 88-95%.

[0018] This invention has the following advantages:

[0019] The polyacrylonitrile precursor fiber of the present invention has a large diameter, high single filament breaking strength, high initial modulus and high breaking elongation.

[0020] This invention, by controlling the presence and quantity of specific gel particles in the polyacrylonitrile spinning solution, can obtain precursor fibers with specific morphology and excellent performance. At the same time, the spinning solution with the above characteristics is matched with the spinning process of this invention, which can effectively reduce the pressure of the spinning assembly, improve spinning stability, and help improve the strength and modulus of the fiber, forming carbon fibers with higher crystal orientation and mechanical properties.

[0021] Carbon fibers prepared using the precursor fibers of this invention exhibit good tensile properties and ultimately form a graphite microcrystalline structure that differs from conventional carbon fibers (manifested as a higher degree of crystal orientation in the carbon fibers), thereby improving the overall properties of the carbon fibers, such as strength and toughness.

[0022] The polyacrylonitrile carbon fibers prepared by the method of this invention have large diameter, high tensile strength, high initial modulus, and high elongation at break.

[0023] The polyacrylonitrile carbon fiber epoxy resin composite material prepared from the polyacrylonitrile carbon fiber of the present invention has excellent mechanical properties and compressive-tensile ratio. Detailed Implementation

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] This invention provides a polyacrylonitrile precursor fiber, wherein the surface of the polyacrylonitrile precursor fiber has longitudinal grooves arranged parallel to the fiber axis, and the average diameter of the polyacrylonitrile precursor fiber is 10-20 μm, the tensile strength is 7-15 cN / dtex, the initial modulus is 120-200 cN / dtex, the elongation at break is 10-20%, and the crystal orientation degree is 75-99%.

[0026] The polyacrylonitrile precursor fiber of the present invention has a large diameter, high single-filament breaking strength, high initial modulus, high breaking elongation and high crystal orientation.

[0027] In some embodiments, the average diameter of the polyacrylonitrile precursor fiber can be 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm and 19 μm, or any range of two of the above values, such as 12-18 μm, preferably 13-17 μm, more preferably 14-16 μm.

[0028] In some embodiments, the tensile strength of the polyacrylonitrile precursor fiber can be 7.5 cN / dtex, 8 cN / dtex, 8.5 cN / dtex, 9 cN / dtex, 9.5 cN / dtex, 10 cN / dtex, 10.5 cN / dtex, 11 cN / dtex, 11.5 cN / dtex, 12 cN / dtex, 12.5 cN / dtex, 13 cN / dtex, 13.5 cN / dtex, 14 cN / dtex, 14.5 cN / dtex, and 15 cN / dtex, or any range of two of the above values, such as 7-14 cN / dtex, preferably 8-15 cN / dtex, and more preferably 12-15 cN / dtex.

[0029] In some embodiments, the initial modulus of the polyacrylonitrile precursor fiber can be 130 cN / dtex, 135 cN / dtex, 140 cN / dtex, 145 cN / dtex, 150 cN / dtex, 155 cN / dtex, 160 cN / dtex, 165 cN / dtex, 170 cN / dtex, 175 cN / dtex, 180 cN / dtex, 185 cN / dtex, 190 cN / dtex, 195 cN / dtex, 200 cN / dtex, or any range of two of the above values, such as 130-200 cN / dtex, preferably 145-200 cN / dtex, and more preferably 170-200 cN / dtex.

[0030] In some embodiments, the elongation at break of the polyacrylonitrile precursor fiber can be 11%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, and 19%, or any range of two of the above values, such as 11-19%, preferably 14-20%, and more preferably 15-20%.

[0031] According to some embodiments of the present invention, the number of individual fibers in the polyacrylonitrile precursor fiber can be 1,000-70,000, preferably 3,000-50,000, and more preferably 6,000-24,000. In some embodiments, the number of individual fibers in the polyacrylonitrile precursor fiber can be 2,000, 3,000, 4,000, 5,000, 6,000, 7,000, 8,000, 9,000, 10,000, 12,000, 14,000, 16,000, 18,000, 20,000, 22,000, 24,000, 26,000, or 28,000. 30,000 roots, 32,000 roots, 34,000 roots, 36,000 roots, 38,000 roots, 40,000 roots, 42,000 roots, 44,000 roots, 46,000 roots, 48,000 roots, 50,000 roots, 52,000 roots, 54,000 roots, 56,000 roots, 58,000 roots, 60,000 roots, or any range of two of the above values, such as 5,000-30,000 roots.

[0032] According to some embodiments of the present invention, the oil content of the polyacrylonitrile precursor fiber can be 0.3-1.0%, preferably 0.5-0.9%. In some embodiments, the oil content of the polyacrylonitrile precursor fiber can be 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or any range of two of the above values, for example, 0.4-1.0%.

[0033] According to some embodiments of the present invention, the crystal orientation degree of the polyacrylonitrile precursor fiber can be 75-99%, preferably 80-95%, and more preferably 86-95%. In some embodiments, the crystal orientation degree of the polyacrylonitrile precursor fiber can be 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range of two of the above values, for example, 85-99%.

[0034] According to some embodiments of the present invention, the surface roughness Ra of the polyacrylonitrile precursor fiber is 15-100 nm, preferably 30-70 nm, and more preferably 50-70 nm. In some embodiments, the surface roughness Ra of the polyacrylonitrile precursor fiber is 16 nm, 18 nm, 20 nm, 22 nm, 24 nm, 26 nm, 28 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, 85 nm, 90 nm, 95 nm, or any range of two of the above values, such as 20-75 nm or 20-70 nm.

[0035] According to the present invention, the surface of the polyacrylonitrile precursor fiber has longitudinal grooves arranged parallel to the fiber axis. In the present invention, the longitudinal grooves are formed by wet spinning of the polyacrylonitrile spinning solution to form the polyacrylonitrile precursor fiber; that is, the polyacrylonitrile precursor fiber of the present invention is a polyacrylonitrile precursor fiber prepared by wet spinning. It is known in the art that the surface of polyacrylonitrile precursor fibers prepared by wet spinning and carbon fibers prepared from the polyacrylonitrile precursor fibers have the aforementioned longitudinal grooves arranged parallel to the fiber axis.

[0036] According to some preferred embodiments of the present invention, the surface of the polyacrylonitrile precursor fiber has longitudinal grooves arranged parallel to the fiber axis, and the average diameter of the polyacrylonitrile precursor fiber is 12-18 μm, preferably 14-16 μm; the breaking strength of the polyacrylonitrile precursor fiber is 8-15 cN / dtex, preferably 12-15 cN / dtex; the initial modulus of the polyacrylonitrile precursor fiber is 145-200 cN / dtex, preferably 170-200 cN / dtex; the breaking elongation of the polyacrylonitrile precursor fiber is 14-20%, preferably 15-20%; and the crystal orientation degree of the polyacrylonitrile precursor fiber is 80-95%, preferably 86-95%.

[0037] This invention provides a method for preparing polyacrylonitrile precursor fibers, comprising: wet spinning a polyacrylonitrile spinning solution; wherein the amount of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 2*10. 5 -8*10 7 per mL.

[0038] The preparation of polyacrylonitrile precursor fibers by wet spinning is known in the art. In this invention, wet spinning processes, spinning conditions, and parameters commonly known in the art can be used, as long as the polyacrylonitrile spinning solution of this invention is used as the wet spinning raw material.

[0039] This invention enables the production of precursor fibers with specific morphology and excellent performance by controlling the presence and quantity of specific gel particles in the polyacrylonitrile spinning solution. At the same time, the spinning solution with this characteristic is matched with the spinning process of this invention, which can effectively reduce the pressure of the spinning assembly, improve spinning stability, and help improve the strength and modulus of the fiber, forming carbon fibers with higher crystallinity and mechanical properties.

[0040] According to some embodiments of the present invention, the amount of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is sufficient to achieve the objective of the present invention as long as it is within the aforementioned range. In some embodiments, the amount of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution can be 3*10 5 cells / mL, 4*10 5 cells / mL, 5*10 5 cells / mL, 6*10 5 cells / mL, 7*10 5 cells / mL, 8*10 5 Cells / mL, 9*10 5 cells / mL, 1*10 6 cells / mL, 2*10 6 cells / mL, 3*10 6 cells / mL, 4*10 6 cells / mL, 5*10 6 cells / mL, 6*10 6 cells / mL, 7*10 6 cells / mL, 8*10 6 cells / mL, 9*10 6 cells / mL, 1*10 7 cells / mL, 2*10 7 cells / mL, 3*10 7 cells / mL, 4*10 7 cells / mL, 4.5*10 7 cells / mL, 5*10 7cells / mL, 5.5*10 7 cells / mL, 6*10 7 cells / mL, 6.5*10 7 cells / mL, 7*10 7 cells / mL, 7.5*10 7 cells / mL, 7.6*10 7 cells / mL, 7.7*10 7 cells / mL, 7.8*10 7 cells / mL, 7.9*10 7 cells / mL, 8.0*10 7 cells / mL, or any range of two of the above values, such as 3.0 x 10⁻⁶. 5 -8*10 7 Cells / mL, preferably 5*10 5 -8.0*10 7 Cells / mL, preferably 1*10 6 -8.0*10 7 Cells / mL, more preferably 8*10 6 -8.0*10 7 per mL.

[0041] According to some embodiments of the present invention, in the polyacrylonitrile spinning solution, the number of gel particles with a particle size of 5-10 μm can account for 0.2-2% of the number of gel particles with a particle size of 0.15-10 μm. In some embodiments, the value of the number of gel particles with a particle size of 5-10 μm in the polyacrylonitrile spinning solution as a percentage of the number of gel particles with a particle size of 0.15-10 μm can be 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, and 2.0%, or any range of two of the above values, for example, 0.5-2%, 0.4-1.6%, or 0.8-1.6%, preferably 0.8-1.9%, and more preferably 1.0-1.8%.

[0042] In this invention, the solid content of the polyacrylonitrile spinning solution can be a conventionally chosen value in the art. The following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the solid content of the polyacrylonitrile spinning solution can be 17.0-22.0 wt%, preferably 18.0-22.0 wt%, more preferably 18.0-20.0 wt%. In some embodiments, the solid content of the polyacrylonitrile spinning solution can be 17.0 wt%, 17.5 wt%, 18.0 wt%, 18.5 wt%, 19.0 wt%, 19.5 wt%, 20.0 wt%, 20.5 wt%, 21.0 wt%, 21.5 wt%, 22.0 wt%, or any range of two of the above values, for example, 18.0-21.0 wt%.

[0043] In this invention, as long as the objective of the invention can be achieved, there are no particular requirements for the viscosity of the polyacrylonitrile spinning solution at 60°C. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the viscosity of the polyacrylonitrile spinning solution at 60°C can be 40-200 Pa·s. In some embodiments, the viscosity of the polyacrylonitrile spinning solution at 60°C can be 40 Pa·s, 50 Pa·s, 60 Pa·s, 70 Pa·s, 80 Pa·s, 90 Pa·s, 100 Pa·s, 110 Pa·s, 120 Pa·s, 130 Pa·s, 140 Pa·s, 150 Pa·s, 160 Pa·s, 170 Pa·s, 180 Pa·s, 190 Pa·s, 200 Pa·s, or any range of two of the above values, for example, 100-190 Pa·s.

[0044] In this invention, as long as the objective of the invention can be achieved, there are no special requirements for the residual monomer content of the polyacrylonitrile spinning solution. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the residual monomer content of the polyacrylonitrile spinning solution can be 500-1700 ppm. In some embodiments, the residual monomer content of the polyacrylonitrile spinning solution can be 500 ppm, 550 ppm, 600 ppm, 650 ppm, 700 ppm, 750 ppm, 800 ppm, 850 ppm, 900 ppm, 950 ppm, 1000 ppm, 1050 ppm, 1100 ppm, 1150 ppm, 1200 ppm, 1250 ppm, 1300 ppm, 1400 ppm, 1500 ppm, 1600 ppm, 1700 ppm, or any range of two of the above values, such as 600-1200 ppm or 600-1100 ppm.

[0045] In this invention, as long as the objective of the invention can be achieved, there are no particular requirements for the weight-average molecular weight of the polyacrylonitrile copolymer in the polyacrylonitrile spinning solution. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the weight-average molecular weight of the polyacrylonitrile copolymer in the polyacrylonitrile spinning solution can be 60,000-120,000 g / mol. In some embodiments, the weight-average molecular weight of the polyacrylonitrile copolymer in the polyacrylonitrile spinning solution can be 60,000 g / mol, 65,000 g / mol, 70,000 g / mol, 75,000 g / mol, 80,000 g / mol, 85,000 g / mol, 90,000 g / mol, 95,000 g / mol, 100,000 g / mol, 105,000 g / mol, 110,000 g / mol, 115,000 g / mol, 120,000 g / mol, or any range of two of the above values, for example, 80,000-120,000 g / mol.

[0046] In this invention, as long as the objective of the invention can be achieved, there are no special requirements regarding the content of polyacrylonitrile copolymer with a molecular weight of not less than 600,000 g / mol in the polyacrylonitrile spinning solution. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the content of polyacrylonitrile copolymer with a molecular weight of not less than 600,000 g / mol in the polyacrylonitrile spinning solution is 0.2-2.0 wt%. In some embodiments, the content of polyacrylonitrile copolymer with a molecular weight of not less than 600,000 g / mol in the polyacrylonitrile spinning solution can be 0.2 wt%, 0.25 wt%, 0.3 wt%, 0.35 wt%, 0.4 wt%, 0.45 wt%, 0.5 wt%, 0.55 wt%, 0.6 wt%, 0.65 wt%, 0.7 wt%, 0.75 wt%, 0.8 wt%, 0.85 wt%, 0.9 wt%, 0.95 wt%, 1 wt%, 1.1 wt%, 1.2 wt%, 1.3 wt%, 1.4 wt%, 1.5 wt%, 1.6 wt%, 1.7 wt%, 1.8 wt%, 1.9 wt%, 2 wt%, or any range of two of the above values, for example, 0.3-1.0 wt%, preferably 0.4-1.0 wt%, more preferably 0.45-0.8 wt%.

[0047] In this invention, the polydispersity of the polyacrylonitrile copolymer in the polyacrylonitrile spinning solution is a conventional choice in the art. The following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the polydispersity of the polyacrylonitrile copolymer in the polyacrylonitrile spinning solution is 2-4. In some embodiments, the polydispersity of the polyacrylonitrile copolymer in the polyacrylonitrile spinning solution can be 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, 4, or any range of two of the above values, for example, 2.1-3.9.

[0048] In this invention, the polyacrylonitrile spinning solution comprises a polyacrylonitrile copolymer dissolved in a first solvent. In this invention, the polyacrylonitrile copolymer in the polyacrylonitrile spinning solution is a copolymer of acrylonitrile and a comonomer, and the type of comonomer can be conventionally chosen in the art. The following is an illustrative description and does not limit the scope of the invention. According to some embodiments of the invention, the comonomer is a compound containing an alkenyl group. For example, the comonomer can be one or more of itaconic acid, vinyl groups, acrylates, vinyl esters, acrylamides, sulfonates, and ammonium salts, preferably itaconic acid.

[0049] According to some embodiments of the present invention, the content of acrylonitrile structural units in the polyacrylonitrile copolymer can be 85-99.5 wt%, for example, the content can be 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 98.5 wt%, and 99 wt%, preferably 95-99 wt%. By adopting the aforementioned preferred embodiments, precursor fibers with specific morphologies and excellent properties can be further obtained.

[0050] According to some embodiments of the present invention, the content of the copolymer monomer structural unit in the polyacrylonitrile copolymer can be 15-0.5 wt%, for example, the content can be 14 wt%, 13 wt%, 12 wt%, 11 wt%, 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1.5 wt%, and 1 wt%, preferably 5-1 wt%.

[0051] In this invention, there are no special requirements for the preparation method of the polyacrylonitrile precursor fiber; any conventional method in the art can be used. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the present invention, the preparation method of the polyacrylonitrile precursor fiber includes the following steps: S1, providing the polyacrylonitrile spinning solution; S2, wet spinning the polyacrylonitrile spinning solution, including filtration and metering followed by spinning, coagulation, hot water drawing, washing, oiling, drying and densification, steam drawing, heat setting, and winding.

[0052] According to some preferred embodiments of the present invention, step S1 includes: mixing acrylonitrile, comonomer, initiator, first solvent and gel particle donor to obtain a mixture, and subjecting the mixture to a polymerization reaction under an inert atmosphere. By employing the aforementioned preferred embodiments, precursor fibers with specific morphologies and excellent properties can be further obtained.

[0053] In this invention, polymerization reaction conditions commonly known in the art can be used. Those skilled in the art can suitably select the reaction temperature and time. According to some embodiments of the invention, the reaction conditions may include a reaction temperature of 50-70°C and / or a reaction time of 15-25 hours.

[0054] According to some embodiments of the present invention, the ratio of the total mass of the acrylonitrile and comonomer to the mass of the solvent can be (18-22):(78-82).

[0055] According to some embodiments of the present invention, the initiator may account for 0.1-10 wt% of the total mass of acrylonitrile and comonomer.

[0056] In this invention, the comonomer is not particularly limited; for example, the comonomer can be a compound containing an alkenyl group. In this invention, the comonomer can be one or more of itaconic acid, vinyl groups, acrylates, vinyl esters, acrylamides, sulfonates, and ammonium salts, such as itaconic acid.

[0057] According to some embodiments of the present invention, based on the total mass of acrylonitrile and comonomer, the content of acrylonitrile can be 85-99.5 wt%, for example, the content can be 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 98.5 wt%, and 99 wt%, preferably 95-99 wt%.

[0058] According to some embodiments of the present invention, based on the total mass of acrylonitrile and comonomer, the content of the comonomer can be 15-0.5 wt%, for example, the content can be 14 wt%, 13 wt%, 12 wt%, 11 wt%, 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1.5 wt%, and 1 wt%, preferably 5-1 wt%.

[0059] In this invention, in step S1, a gel particle donor is provided and the gel particle donor is mixed with acrylonitrile, comonomer, initiator and first solvent to obtain the mixture.

[0060] Those skilled in the art will understand that when a polyacrylonitrile spinning dope is obtained by reacting and polymerizing a polymerization solution containing acrylonitrile, optional comonomer, initiator, and solvent under an inert atmosphere, some gel particles are generated in the spinning dope. However, the inventors of this invention have found that the number of these in-situ generated gel particles (i.e., gel particles directly generated during polymerization) is very likely insufficient to meet the requirements of this application. In this invention, the gel particle donor contains a relatively high number of gel particles; when the gel particle donor is added to the mixture, the number of gel particles in the resulting polyacrylonitrile spinning dope can be increased. Furthermore, the inventors of this invention have found that, with the same or similar number of gel particles, the properties of polyacrylonitrile precursor fibers and carbon fibers prepared from spinning dopes containing exogenous gel particles (i.e., gel particles provided by the gel particle donor) are superior to those prepared from spinning dopes containing only in-situ generated gel particles, such as strength, modulus, and elongation.

[0061] In this invention, the gel particle donor is a mixture comprising a polyacrylonitrile polymer (preferably a polyacrylonitrile copolymer) and a second solvent, wherein a portion of the polyacrylonitrile polymer (preferably a polyacrylonitrile copolymer) is present in the form of gel particles (i.e., the gel particle donor comprises gel particles). As those skilled in the art will understand, the gel particles in this invention are polyacrylonitrile polymer gel particles, preferably polyacrylonitrile copolymer gel particles. According to some embodiments of the present invention, the concentration of polyacrylonitrile polymer (preferably polyacrylonitrile copolymer) in the gel particle donor can be 0.2-2.0 wt.%; for example, the concentration of polyacrylonitrile polymer can be 0.2 wt.%, 0.3 wt.%, 0.4 wt.%, 0.5 wt.%, 0.6 wt.%, 0.7 wt.%, 0.8 wt.%, 0.9 wt.%, 1.0 wt.%, 1.1 wt.%, 1.2 wt.%, 1.3 wt.%, 1.4 wt.%, 1.5 wt.%, 1.6 wt.%, 1.7 wt.%, 1.8 wt.%, 1.9 wt.%, 2.0 wt.%, or any range of two of the above values, for example, 0.2-1.9 wt.%.

[0062] In this invention, when the polyacrylonitrile polymer in the gel particle donor is a polyacrylonitrile copolymer, the polyacrylonitrile copolymer is a copolymer of acrylonitrile and a comonomer, and the type of comonomer can be conventionally selected in the art. According to some embodiments of the invention, the comonomer is a compound containing an alkenyl group, for example, the comonomer can be one or more of itaconic acid, vinyl groups, acrylates, vinyl esters, acrylamides, sulfonates, and ammonium salts, preferably itaconic acid. According to some embodiments of the invention, the content of acrylonitrile structural units in the polyacrylonitrile copolymer in the gel particle donor can be 85-99.5 wt%, for example, the content can be 86 wt%, 87 wt%, 88 wt%, 89 wt%, 90 wt%, 91 wt%, 92 wt%, 93 wt%, 94 wt%, 95 wt%, 96 wt%, 97 wt%, 98 wt%, 98.5 wt%, and 99 wt%, preferably 95-99 wt%. According to some embodiments of the present invention, the content of the copolymer monomer structural unit in the polyacrylonitrile copolymer in the gel particle donor can be 15-0.5 wt%, for example, the content can be 14 wt%, 13 wt%, 12 wt%, 11 wt%, 10 wt%, 9 wt%, 8 wt%, 7 wt%, 6 wt%, 5 wt%, 4 wt%, 3 wt%, 2 wt%, 1.5 wt%, and 1 wt%, preferably 5-1 wt%.

[0063] In some embodiments, the structural unit composition of the polyacrylonitrile copolymer in the gel particle donor is the same as or substantially the same as the structural unit composition of the polyacrylonitrile copolymer in the polyacrylonitrile spinning solution in the polyacrylonitrile precursor preparation method of the present invention.

[0064] According to some embodiments of the present invention, the mass ratio of the gel particle donor to the mass of the first solvent used to prepare the S1 mixture can be (0.010-0.2):1 or (0.010-0.125):1; for example, the mass ratio of the gel particle donor to the mass of the first solvent used to prepare the S1 mixture can be 0.010:1, 0.011:1, 0.012:1, 0.013:1, 0.014:1, 0.015:1, 0.016:1, 0.017:1, 0.018:1, etc. 0.019:1, 0.02:1, 0.025:1, 0.03:1, 0.04:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.11:1, 0.12:1, 0.125:1, 0.13:1, 0.14:1, 0.15:1, 0.16:1, 0.17:1, 0.18:1, 0.19:1, 0.2:1, or any range of two of the above values, such as (0.010-0.15):1.

[0065] According to some embodiments of the present invention, in the gel particle donor, the number of gel particles with a particle size of 5-10 μm can account for 0.2-3.0% of the number of gel particles with a particle size of 0.15-10 μm; for example, the number of gel particles with a particle size of 5-10 μm can account for 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7% of the number of gel particles with a particle size of 0.15-10 μm. %, 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, 2.6%, 2.7%, 2.8%, 2.9%, 3.0%, or any range of two of the above values, such as 0.2-2.9%.

[0066] In some embodiments, the gel particle donor comprises a polyacrylonitrile polymer and a second solvent, and the amount of gel particles with a particle size of 0.15-10 μm in the gel particle donor is 1.6*10. 7 -8*10 9 The concentration of polyacrylonitrile polymer in the gel particle donor is 0.2-2.0 wt.%. Preferably, the polyacrylonitrile polymer in the gel particle donor is a polyacrylonitrile copolymer.

[0067] Those skilled in the art can appropriately adjust the content of gel particles in the gel particle donor and / or the amount or dosage of the gel particle donor to obtain the desired gel particle content in the polyacrylonitrile spinning solution. According to some embodiments of the present invention, the content of gel particles with a particle size of 0.15-10 μm in the gel particle donor can be 1.6*102 7 -8*10 9 The content of gel particles with a particle size of 0.15-10 μm in the gel particle donor can be 1.6*10^6 particles / mL. 7 cells / mL, 2*10 7 cells / mL, 3*10 7 cells / mL, 4*10 7 cells / mL, 5*10 7 cells / mL, 6*10 7 cells / mL, 7*10 7 cells / mL, 8*10 7 cells / mL, 9*10 7 cells / mL, 1*10 8 cells / mL, 2*10 8 cells / mL, 3*10 8 cells / mL, 4*10 8 cells / mL, 5*10 8 cells / mL, 6*10 8 cells / mL, 7*10 8 cells / mL, 8*10 8 cells / mL, 9*10 8 cells / mL, 1*10 9 cells / mL, 2*10 9 cells / mL, 3*10 9 cells / mL, 4*10 9 cells / mL, 5*10 9 cells / mL, 6*10 9 cells / mL, 7*10 9 cells / mL, 8*10 9 cells / mL, or any range of two of the above values, such as 2*10. 7 -8*10 9 per mL.

[0068] In this invention, as long as the purpose of this invention can be achieved, there are no special requirements on the type and source of the gel particle donor. The following is an illustrative description, but it does not limit the scope of this invention.

[0069] According to some embodiments of the present invention, the gel particle donor can be a washing solution. In this invention, the washing solution is a cleaning solution obtained after cleaning the inner walls of the polymerization reactor, the demonolysis reactor, the defoaming reactor, the intermediate storage reactor, baffles, stirring blades, heat exchangers (e.g., reboilers and / or circulating heaters), pipes, and interfaces used in the preparation of polyacrylonitrile spinning dope, wherein a second solvent is used for cleaning. The second solvent can be the same as the first solvent used in the polymerization reaction. As those skilled in the art know, deposits may accumulate on the inner walls of the polymerization reactor, the demonolysis reactor, the defoaming reactor, the intermediate storage reactor, baffles, stirring blades, heat exchangers (e.g., reboilers and / or circulating heaters), pipes, and / or interfaces used in the preparation of polyacrylonitrile spinning dope. These deposits can be white, orange, or yellow, transparent or translucent, solid-like substances or solid resins. During the cleaning process, the deposits can be dispersed and dissolved by the second solvent to obtain the gel particle donor. The second solvent can be the same as the solvent used in the polymerization reaction. In some embodiments, the sediment may be sediment after about 20 to about 250 days, for example about 20 to about 200 days, or for example about 30 to about 185 days after the polymerization reaction has been carried out.

[0070] In some preferred embodiments, the washing solution in this application can be a washing solution obtained after cleaning the inner walls of the polymerization reactor, the monomer removal reactor, the degassing reactor, the intermediate storage reactor, baffles, agitator blades, heat exchangers (e.g., reboilers and / or circulating heaters), pipes and / or interfaces, etc., every about 1 to about 6 months, for example every 2 to about 6 months, or every 3 to about 6 months. In some embodiments, the concentration of the original washing solution may be high, for example, greater than 5.0 wt.%, and therefore the original washing solution can be diluted before use. In some embodiments, the washing solution is a diluted washing solution. The second solvent can be used for dilution.

[0071] In this invention, there is no particular limitation on the amount of the initiator, as long as it can initiate the reaction and polymerization. Various amounts of initiators commonly used in the preparation of polyacrylonitrile spinning solutions can be used in this invention. According to some embodiments of the invention, the initiator accounts for 0.1-10 wt% of the total mass of acrylonitrile and comonomer; for example, the initiator can account for 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1 wt%, 2 wt%, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, or any range of two of the above values, such as 0.1-9 wt%, of the total mass of acrylonitrile and comonomer.

[0072] In this invention, the type of the first solvent is not particularly important as long as the objective of the invention can be achieved. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the first solvent is one or more of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, aqueous zinc chloride solution, and aqueous sodium thiosulfate solution, preferably dimethyl sulfoxide.

[0073] In this invention, the type of the second solvent is not particularly important as long as the objective of the invention can be achieved. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the second solvent is one or more of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, aqueous zinc chloride solution, and aqueous sodium thiosulfate solution, preferably dimethyl sulfoxide.

[0074] In this invention, the first solvent and the second solvent may be the same or different. In some embodiments, preferably, the first solvent and the second solvent are the same.

[0075] In this invention, the initiator can be any conventional choice in the art, as long as it achieves the purpose of the invention. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the initiator can be selected from free radical initiators, preferably from peroxide initiators and azo initiators, more preferably from one or more of azobisisobutyronitrile, azobisisovalerate, dimethyl azobisisobutyrate, azobisisoheptanenitrile, and benzoyl peroxide, and is preferably azobisisobutyronitrile.

[0076] In this invention, as long as the spinning solution is obtained, the reaction conditions in S1 can be conventional conditions in the art. The following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the reaction conditions in S1 may include: a reaction temperature of 50-70°C and a reaction time of 15-25 hours. In some embodiments, the reaction time can be adjusted accordingly with changes in the reaction temperature, and these adjustments are known in the art.

[0077] In this invention, the spinning, coagulation, hot water drawing, washing, oiling, drying and densification, steam drawing, heat setting and winding in S2 are steps known in the art for preparing polyacrylonitrile precursor fibers.

[0078] According to some embodiments of the present invention, the filtration conditions in step S2 include: a filtration accuracy of 2-10 μm, preferably 4-8 μm. In the present invention, filtration accuracy refers to the average pore size of the filter screen.

[0079] According to some embodiments of the present invention, the spinning conditions in S2 include: the spinneret orifice diameter is 60-120 μm, preferably 70-110 μm, and more preferably 80-100 μm. By adopting the aforementioned preferred solutions, the pressure of the spinneret assembly can be effectively reduced, and the spinning stability can be improved.

[0080] According to some embodiments of the present invention, the spinning conditions in S2 include: the spinning pressure of the spinneret is 0.4-2.0 MPa, preferably 0.6-1.8 MPa, and more preferably 0.8-1.6 MPa. By adopting the aforementioned preferred solutions, it is possible to obtain precursor fibers with specific morphologies and excellent performance.

[0081] In this invention, as long as the objective of the invention can be achieved, there are no special requirements for the insulation temperature of the filter components, such as the filter and the gooseneck tube. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the insulation temperature of the filter components and the gooseneck tube is 40-80°C.

[0082] According to some embodiments of the present invention, the draw ratio during solidification can be 0.3-1.5, preferably 0.5-1.2.

[0083] In this invention, commonly known solidification temperatures can be used. The advantages of this invention are illustrated by using 60°C as an example of the solidification temperature of the polyacrylonitrile spinning solution.

[0084] In this invention, the coagulation bath used in the coagulation process is a conventional choice in the art. In some embodiments of this invention, the coagulation bath is an aqueous solution of dimethyl sulfoxide. In some preferred embodiments of this invention, the mass concentration of the coagulation bath can be 35-85%, for example, 40-80%. This invention uses a mixed solvent of water and dimethyl sulfoxide (concentration of about 68 wt.%) as an example to illustrate the advantages of this invention.

[0085] In this invention, the temperature range of the coagulation bath is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. In this invention, the temperature of the coagulation bath during coagulation is a conventional choice in the art. In some embodiments, the temperature of the coagulation bath can be 20–70°C, for example, 25–65°C. The advantages of this invention are illustrated using a coagulation bath temperature of 60°C as an example.

[0086] In this invention, the coagulation can utilize one or more coagulation baths. The total draw ratio of the coagulation can be 0.3-1.5, preferably 0.5-1.2. In some embodiments, when using multiple coagulation baths, the concentration of the dimethyl sulfoxide aqueous solution in the coagulation baths can decrease sequentially.

[0087] In this invention, there are no special requirements for the conditions of hot water stretching as long as the purpose of the invention can be achieved. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the conditions for hot water stretching include a temperature of 80-95°C.

[0088] In this invention, there are no special requirements regarding the number of hot water stretching passes, as long as the objective of the invention can be achieved. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the number of hot water stretching passes is 2-4.

[0089] According to some embodiments of the present invention, the conditions for hot water stretching include: a total stretch ratio of 2.5-6.

[0090] In some embodiments of the present invention, the hot water drawing is preferably multi-stage hot water drawing, for example, three-stage hot water drawing. In some embodiments, more preferably, the temperatures of the three hot water drawing stages are 80-95°C. In some embodiments, the draw ratios of the three hot water drawing stages are 1.4 to 1.8, for example, 1.5 to 1.8.

[0091] In this invention, there are no special requirements for the washing conditions as long as the purpose of the invention can be achieved. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the washing conditions include a temperature of 45-80°C.

[0092] In this invention, as long as the objective of the invention can be achieved, there are no special requirements regarding the number of washing stages. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the number of washing stages is 3-8, and the temperature gradient of the washing increases with the increase of the number of washing stages.

[0093] In some embodiments of this invention, the washing is performed using a hot water bath at a temperature of 45-80°C. No stretching is required during the washing process. In some embodiments of this invention, preferably, the washing process involves multiple washes, such as six washes, with the washing temperature increasing sequentially, and the temperature of each wash potentially differing by, for example, approximately 5°C.

[0094] In this invention, there are no special requirements for the oiling conditions as long as the purpose of the invention can be achieved. The following is an illustrative description, but it does not limit the scope of the invention. According to some embodiments of the invention, the oiling conditions include a temperature of 25-40°C.

[0095] In this invention, as long as the objective of the invention can be achieved, there are no special requirements for the concentration of the oil agent during oiling in step S2. The following is an illustrative description, but it does not limit the scope of the invention. According to some preferred embodiments of the invention, the oiling conditions include: an oil agent concentration of 1.0-4.0 wt.%.

[0096] In this invention, excess oil during the oiling process is squeezed out by the extrusion rollers.

[0097] In some embodiments of this invention, the oiling is performed by immersion. In some embodiments of this invention, the oil bath concentration is 1.0-4.0 wt.%, the temperature is 25-40°C, and the residence time is 0.2-1 s.

[0098] In the preparation of raw fibers, applying an oiling agent to the fibers via an oiling step is known in the art. Various oiling agents commonly known in the art can be used in this oiling step; for example, the oiling agents used may include silicone-free oiling agents, low-silicone oiling agents, and silicone-containing oiling agents, etc.

[0099] In this invention, the drying and densification conditions are conventionally chosen in the art, and the following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the drying and densification conditions include a temperature of 90-130°C.

[0100] In some embodiments, the present invention employs a two-stage drying densification process, wherein each stage of drying densification involves 5-9 drying rollers and a drying time of 30-90 seconds. In some embodiments, the temperature of the first stage of drying densification is lower than the temperature of the second stage of drying densification.

[0101] In this invention, the steam drawing pressure is a conventional choice in the art, and the following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the conditions for steam drawing include: a steam pressure of 0.2-0.6 MPa.

[0102] In this invention, the draw ratio of the steam drawing is a conventional choice in the art, and the following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the conditions for steam drawing include a draw ratio of 1.5-5.0.

[0103] In this invention, the heat setting pressure is a conventional choice in the art, and the following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the heat setting conditions include a steam pressure of 0.05-0.15 MPa.

[0104] In this invention, the draw ratio for heat setting is a conventional choice in the art, and the following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the heat setting conditions include a draw ratio of 0.8-1.1.

[0105] This invention provides a method for preparing polyacrylonitrile carbon fiber, the method comprising: subjecting the polyacrylonitrile precursor fiber of this invention to pre-oxidation treatment, low-temperature carbonization treatment, and high-temperature carbonization treatment.

[0106] The preparation of carbon fibers from polyacrylonitrile precursor fibers is known in the art. This invention can utilize processes, steps, and conditions known in the art for preparing carbon fibers from polyacrylonitrile precursor fibers.

[0107] In this invention, carbon fibers can be prepared using pre-oxidation treatment, low-temperature carbonization treatment, and high-temperature carbonization treatment conditions and processes generally known in the art. It is also known in the art to perform post-treatment after high-temperature carbonization to obtain the final carbon fiber bundles. This invention can employ post-treatments generally known in the art. In this invention, the post-treatment may include surface treatment, washing, sizing, drying, and winding.

[0108] Carbon fibers prepared using the precursor fibers of this invention exhibit good tensile properties and ultimately form a graphite microcrystalline structure that differs from conventional carbon fibers, thereby improving the overall properties of carbon fibers, such as strength and toughness.

[0109] According to some embodiments of the present invention, the conditions for the pre-oxidation treatment include a temperature of 190-350°C. In this invention, the pre-oxidation time can be adjusted accordingly with changes in temperature; for example, the pre-oxidation time can be 45-90 minutes.

[0110] In this invention, the total draw ratio of the pre-oxidation treatment is a conventional choice in the art, and the following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the conditions for the pre-oxidation treatment include: the total draw ratio can be 0-20%.

[0111] In some embodiments of the present invention, the pre-oxidation treatment is carried out in an air atmosphere.

[0112] According to some embodiments of the present invention, the conditions for the low-temperature carbonization treatment include: under an inert atmosphere, the low-temperature carbonization temperature can be 350-850°C. In the present invention, the low-temperature carbonization time can be adjusted accordingly with changes in temperature, for example, the time can be 2-4 minutes.

[0113] In this invention, the draw ratio for the low-temperature carbonization treatment is a conventional choice in the art, and the following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the conditions for the low-temperature carbonization treatment include: the draw ratio can be 0-4%.

[0114] According to some embodiments of the present invention, the conditions for the high-temperature carbonization treatment include: under an inert atmosphere, the high-temperature carbonization temperature can be 1300-1400°C. In the present invention, the high-temperature carbonization time can be adjusted accordingly with changes in temperature, for example, the time can be 2-4 minutes.

[0115] In this invention, the draw ratio for the high-temperature carbonization treatment is a conventional choice in the art, and the following is an illustrative description, but does not limit the scope of the invention. According to some embodiments of the invention, the conditions for the high-temperature carbonization treatment include a draw ratio of -4% to -1%.

[0116] In this invention, the inert atmosphere can be achieved, for example, by using one or more of nitrogen, helium, argon and xenon.

[0117] The present invention provides a polyacrylonitrile carbon fiber with an average diameter of 5-12 μm, a tensile strength of 4.2-6.5 GPa, an initial modulus of 250-350 GPa, and a tensile elongation of 0.8-2.5%.

[0118] In some embodiments, preferably, the polyacrylonitrile carbon fiber has a crystal orientation degree of 75-99%, more preferably 85-95%, and even more preferably 88-95%. In some embodiments, the crystal orientation degree of the polyacrylonitrile carbon fiber can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, or any range of two of the above values, for example, 87-93%.

[0119] In some embodiments, the surface roughness Ra of the polyacrylonitrile carbon fiber is 5-80 nm, preferably 20-60 nm, and more preferably 40-60 nm. In some embodiments, the surface roughness Ra of the polyacrylonitrile carbon fiber can be 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm, 50 nm, 55 nm, 60 nm, 65 nm, 70 nm, 75 nm, 80 nm, or any range of two of the above values, for example, 35-60 nm.

[0120] In some embodiments, preferably, the polyacrylonitrile carbon fiber is prepared by the polyacrylonitrile carbon fiber preparation method described above.

[0121] The polyacrylonitrile carbon fibers prepared by the method of this invention have large diameter, high breaking strength, high initial modulus, and high breaking elongation.

[0122] In this invention, the average diameter of the polyacrylonitrile carbon fiber can be 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, 10 μm, 10.5 μm, 11 μm, 11.5 μm, 12 μm, or any range of two of the above values, for example, 7.5-8.5 μm. According to some preferred embodiments of the invention, the average diameter of the polyacrylonitrile carbon fiber is 7-10 μm, preferably 8-9 μm.

[0123] In this invention, the tensile strength of the polyacrylonitrile carbon fiber can be 4.2 GPa, 4.3 GPa, 4.4 GPa, 4.5 GPa, 4.6 GPa, 4.7 GPa, 4.8 GPa, 4.9 GPa, 5.0 GPa, 5.1 GPa, 5.2 GPa, 5.3 GPa, 5.4 GPa, 5.5 GPa, 5.6 GPa, 5.7 GPa, 5.8 GPa, 5.9 GPa, 6.0 GPa, 6.1 GPa, 6.2 GPa, 6.3 GPa, 6.4 GPa, 6.5 GPa, or any range of two of the above values, for example, 5.1-6.2 GPa. According to some preferred embodiments of the invention, the tensile strength of the polyacrylonitrile carbon fiber is 4.7-6.5 GPa, more preferably 5.2-6.2 GPa.

[0124] In this invention, the initial modulus of the polyacrylonitrile carbon fiber can be 250 GPa, 255 GPa, 260 GPa, 265 GPa, 270 GPa, 275 GPa, 280 GPa, 285 GPa, 290 GPa, 295 GPa, 300 GPa, 305 GPa, 310 GPa, 315 GPa, 320 GPa, 325 GPa, 330 GPa, 335 GPa, 340 GPa, 345 GPa, 350 GPa, or any range of two of the above values, for example, 270-350 GPa. According to some preferred embodiments of the invention, the initial modulus of the polyacrylonitrile carbon fiber is 290-350 GPa.

[0125] In this invention, the elongation at break of the polyacrylonitrile carbon fiber can be 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, 2.1%, 2.2%, 2.3%, 2.4%, 2.5%, or any range of two of the above values, for example, 1.1-2.4%. According to some preferred embodiments of the invention, the elongation at break of the polyacrylonitrile carbon fiber is 1.0-2.4%, preferably 1.7-2.3% or 1.75-2.3%.

[0126] In this invention, the polyacrylonitrile carbon fiber can be used to prepare a polyacrylonitrile carbon fiber epoxy resin composite material, the composite material comprising the polyacrylonitrile carbon fiber of this invention and an epoxy resin. As those skilled in the art will understand, the polyacrylonitrile carbon fiber epoxy resin composite material is a carbon fiber reinforced resin matrix composite material.

[0127] In this invention, the polyacrylonitrile carbon fiber epoxy resin composite material can be prepared by the following method:

[0128] (1) Preparation of resin matrix: The epoxy compound and the curing agent are mixed evenly, and then acetone is added and the mixture is continued to be mixed to obtain a mixture;

[0129] (2) Carbon fiber and resin matrix composite: impregnate carbon fiber into the mixture of step (1) to form a carbon fiber composite prepreg; and dry the prepreg to remove excess solvent;

[0130] (3) Curing treatment: Curing the prepreg at an elevated temperature.

[0131] In this invention, degassing can be performed after the curing process. Post-processing can also be performed after the curing process. The post-processing may include machining, or surface grinding and polishing.

[0132] In some embodiments, the epoxy compound may be an epoxy compound commonly used in the art. Preferably, the epoxy compound may be a trifunctional epoxy compound, such as epoxy resin MY750. In some embodiments, the curing agent may be a curing agent commonly used for epoxy resins, such as an amine curing agent, etc. In some embodiments, the curing agent may be diaminodiphenylmethane, such as 4,4'-diaminodiphenylmethane.

[0133] In some embodiments, the epoxy compound and the curing agent can be mixed in proportions commonly known in the art, for example, the mass ratio of epoxy compound to curing agent can be from 10:1 to 1:2, such as 4:1. In some embodiments, the mixing of the epoxy compound and the curing agent can be carried out at elevated temperatures, such as from 30°C to 50°C, such as about 40°C. In some embodiments, the mass ratio of acetone to epoxy compound can be about (20-5):1, for example, about 10:1.

[0134] In this invention, in step (2), when impregnating the carbon fibers into the mixture of step (1), the volume content of the carbon fibers can be reasonably selected. In some embodiments, the volume content of the carbon fibers can be 20%-80%, for example, about 60%. In this invention, the carbon fibers can adopt various known arrangement structures. In some embodiments, in step (2), the carbon fibers are unidirectionally arranged. In this invention, the drying of the pre-impregnated body can be carried out, for example, at 80°C-100°C, for example, about 90°C, to remove excess solvent.

[0135] In this invention, the curing process may be carried out at a temperature, for example, 100°C to 250°C. Those skilled in the art can suitably select the required curing time. In some embodiments, the curing process may be carried out in stages. In some embodiments, the curing process may be carried out in two stages, wherein the first stage is cured at 110°C to 130°C for 4-12 hours, and then cured at 160°C to 240°C for 1-5 hours.

[0136] According to some embodiments of the present invention, the compressive strength of the polyacrylonitrile carbon fiber epoxy resin composite material prepared from the polyacrylonitrile carbon fiber can be 1550-1700 MPa, preferably 1600-1700 MPa, and the tensile strength can be 1700-2400 MPa, preferably 1850-2250 MPa or 1850-2200 MPa. In the present invention, the compressive strength of the polyacrylonitrile carbon fiber epoxy resin composite material prepared from the polyacrylonitrile carbon fiber can be 1550 MPa, 1560 MPa, 1570 MPa, 1580 MPa, 1590 MPa, 1600 MPa, 1610 MPa, 1620 MPa, 1630 MPa, 1640 MPa, 1650 MPa, 1660 MPa, 1670 MPa, 1680 MPa, 1690 MPa, 1700 MPa, or any range of two of the above values, for example, 1610-1690 MPa. In this invention, the tensile strength of the polyacrylonitrile carbon fiber epoxy resin composite material prepared from the polyacrylonitrile carbon fiber can be 1700MPa, 1720MPa, 1740MPa, 1760MPa, 1780MPa, 1800MPa, 1820MPa, 1840MPa, 1860MPa, 1880MPa, 1900MPa, 1920MPa, 1940MPa, 1960MPa, 1980MPa, 2000MPa, 2020MPa, or 2040MPa. Pa, 2060 MPa, 2080 MPa, 2100 MPa, 2120 MPa, 2140 MPa, 2160 MPa, 2180 MPa, 2200 MPa, 2220 MPa, 2240 MPa, 2250 MPa, 2260 MPa, 2280 MPa, 2300 MPa, 2320 MPa, 2340 MPa, 2360 MPa, 2380 MPa, 2400 MPa, or any range of two of the above values, for example, 1850-2250 MPa. According to some embodiments of the present invention, the polyacrylonitrile carbon fiber epoxy resin composite material prepared from the said polyacrylonitrile carbon fiber has a compressive-to-tensile ratio of 0.60-0.95, preferably 0.75-0.95. In the present invention, the compressive-to-tensile ratio of the polyacrylonitrile carbon fiber composite material is the ratio between compressive strength and tensile strength.In this invention, the compressive-to-tensile ratio of the polyacrylonitrile carbon fiber epoxy resin composite material prepared from the polyacrylonitrile carbon fiber can be 0.60, 0.61, 0.62, 0.63, 0.64, 0.65, 0.66, 0.67, 0.68, 0.69, 0.70, 0.71, 0.72, 0.73, 0.74, 0.75, 0.76, 0.77, 0.78, 0.79, 0.80, 0.81, 0.82, 0.83, 0.84, 0.85, or any range of two of the above values, for example, 0.77-0.92.

[0137] The present invention will be described in detail below through embodiments.

[0138] The groove structure on the surface of polyacrylonitrile precursor and carbon fiber was confirmed by observing the carbon fiber surface at 5000-10000x magnification using a scanning electron microscope.

[0139] Viscosity testing of polyacrylonitrile spinning solution: A rotational rheometer (Anton Paar, MCR302) was used at a temperature of 60 ± 0.01℃. A rotor with a diameter of 25 mm and a spacing of 1 mm was selected. During the test, to prevent water absorption and solvent evaporation from affecting the experimental results, a layer of silicone oil was uniformly applied to the free surface of the sample exposed to air. The change in sample viscosity as a function of shear rate was measured at a shear rate of 0.1 s⁻¹. -1 ~10s -1 The shear rate is taken as 8s. -1 The viscosity at that time is used as the viscosity of the polyacrylonitrile spinning solution.

[0140] Gel particle number and size testing: The number of gel particles in the polyacrylonitrile spinning solution was determined using an Accusizer A7000 SIS particle size analyzer. The test environment was 25±1℃ and the humidity was 20-80%. The particle size analyzer was placed in a cleanroom to minimize the influence of environmental dust and impurities on the test results. The Accusizer A7000 SIS uses single-particle optical sensing technology to achieve particle counting analysis. When a single particle passes through a narrow light-sensing area, it blocks part of the incident light, causing a momentary decrease in the intensity of the incident light reaching the detector. The attenuation of the intensity signal is theoretically proportional to the square of the particle's cross-section—that is, the particle diameter. A calibration curve between particle size and intensity signal magnitude was established using standard particles, and the particle size was calculated based on the calibration curve. The detector was LE400-05, with a particle size detection range of 0.15-400μm, a maximum detection concentration of 10,000 particles per milliliter, a sample volume of 5mL, and a flow rate of 30.0mL / min. Before testing, the polyacrylonitrile spinning solution was diluted with a clean solvent, which was then filtered through a 0.45-micron PTFE membrane to ensure that the number of particles per milliliter of the diluted solution was less than 10,000.

[0141] Diameter testing of polyacrylonitrile precursor and carbon fiber: Microscopic method, according to GB / T3364-2008. Specifically, a section of multifilament approximately 200 mm long is randomly cut from the polyacrylonitrile precursor and carbon fiber multifilament samples to be tested; a small fiber bundle of 0.2-0.3 mm in length is cut from the multifilament using a sharp knife; the cut fiber bundle is placed on a microscope slide, and a small drop of xylene-diluted optical adhesive resin is added; the fibers are dispersed with a clean, pointed needle, and then covered with a microscope coverslip. The transmission microscope has a stage mechanism that allows the observation slide to move in two mutually perpendicular directions; the resolution of the transmission microscope should be at least 2 μm, provided that at least 500x magnification is met.

[0142] The breaking strength, initial modulus and elongation at break of carbon fiber precursor were tested in accordance with GB / T14337-2008.

[0143] The breaking strength, initial modulus and breaking elongation of carbon fiber were determined according to GB / T 3362-2005 Test Method for Tensile Properties of Carbon Fiber Multifilament.

[0144] The oil content of polyacrylonitrile precursor fiber was determined by the following method:

[0145] Weigh a certain mass of polyacrylonitrile precursor fiber (<3g), and record the mass as m3. Dry the polyacrylonitrile precursor fiber in a forced-air oven at 80℃ for 2 hours, weigh the fiber again, and record the mass as m4. The moisture content of the polyacrylonitrile precursor fiber is equal to the ratio of (m3-m4) to m3, expressed as a percentage. Perform Soxhlet extraction on the dried polyacrylonitrile precursor fiber using cyclohexane as the solvent, reflux at 110℃ for 3 hours, remove and air-dry for 1 hour, then dry in a forced-air oven at 105℃ for 2 hours. Weigh the dried polyacrylonitrile precursor fiber and record the mass as m5. The oil content of the polyacrylonitrile precursor fiber is equal to the ratio of (m4-m5) to m3, expressed as a percentage.

[0146] The residual monomer content of the polyacrylonitrile spinning solution was determined according to patent CN 106353306B using the following method:

[0147] (1) Weigh 1.5-2.5g of polyacrylonitrile spinning solution onto a 0.0001g analytical balance and place it in a 250mL iodine flask, accurate to 0.0001g, and record it as M.

[0148] (2) Add 25 mL of dimethyl sulfoxide to the iodine flask described in step (1);

[0149] (3) Add a stirring magnet to the iodine flask, put the stopper on, seal the mouth of the iodine flask with water, and stir on an electromagnetic stirrer at 20-30℃ for 8-10 minutes.

[0150] (4) After the polyacrylonitrile spinning solution is completely dissolved, open the stopper and add 50 mL of deionized water along the wall of the iodine flask, and stir well.

[0151] (5) After the solution in the iodine flask has cooled, add 5 drops of mixed indicator to the iodine flask and titrate with sodium hydroxide solution until pale blue.

[0152] (6) Add 25 mL of 0.1 mol / L sodium sulfite solution to the iodine flask and shake well. Then titrate with standard sulfuric acid solution until the solution turns yellow-green. The endpoint is reached when the solution does not fade in 30 seconds. Record the volume V of standard sulfuric acid solution consumed.

[0153] (7) To eliminate interference from the acidity or alkalinity of the reagents themselves, two blank tests were performed: (a) Add 25 mL of dimethyl sulfoxide and 50 mL of deionized water to a 250 mL iodine flask, stir well, add 5 drops of mixed indicator to the iodine flask, then add 25 mL of 0.1 mol / L sodium sulfite solution and shake well. Titrate with standard sulfuric acid solution until a yellow-green color appears. The endpoint is reached when the color does not fade after 30 seconds. Record the volume V of standard sulfuric acid solution consumed. 01(b) Add 25 mL of dimethyl sulfoxide and 50 mL of deionized water to a 250 mL iodine flask, stir well, add 5 drops of mixed indicator to the iodine flask, and titrate with sodium hydroxide solution until a pale blue color appears; the endpoint is reached when the color does not fade after 30 seconds. Record the volume V of sodium hydroxide solution consumed. 02 ;

[0154] (8) According to the formula AN%=[2×(VV) 01 +V 02 The percentage of residual acrylonitrile in the polyacrylonitrile spinning solution is calculated as follows: () / M]×C×0.05306×100%.

[0155] Where: AN% - residual acrylonitrile monomer content in the sample to be tested;

[0156] V - The volume of sulfuric acid standard solution consumed by the sample to be tested, in mL;

[0157] V 01 V 02 - The volumes of standard acid or base consumed in blank tests (a) and (b), respectively, in mL;

[0158] M - Mass of spinning solution, g;

[0159] The concentration of C-standard sulfuric acid solution, in mol / L;

[0160] 0.05306 - The number of grams equivalent to one mole of acrylonitrile, in g / mol.

[0161] The mixed indicator consists of 0.1 g alizarin R and 0.2 g thymolphthalein dissolved in 100 mL of ethanol; the concentration of the sodium hydroxide alkaline solution is 0.03 mol / L; and the concentration of the standard sulfuric acid solution is 0.0994 mol / L.

[0162] The polydispersity of polyacrylonitrile copolymers was determined by the following method:

[0163] (1) Solvent preparation: Weigh 0.04 mol of lithium bromide (LiBr) and add it to 4 L of dimethylformamide (DMF). Disperse it by ultrasonication and set aside for later use.

[0164] (2) Ten narrow-distribution polyacrylonitrile (PAN) standards were selected, dissolved in the prepared solvent, and tested to obtain calibration curves;

[0165] (3) Dissolve the polyacrylonitrile sample to be tested in solvent to a concentration of 2 mg / mL; filter it using a 0.5 μm syringe filter; inject 100 μL of the sample at a test temperature of 60 °C and a solvent flow rate of 0.8 mL / min, analyze it with a differential detector, and calculate the relative molecular weight and distribution (i.e., polydispersity) of the sample using gel permeation chromatography (GPC) software.

[0166] Among them, DMF, chromatographic grade, was from TEDIA, USA; anhydrous lithium bromide, 99% purity, was from Alfa; and GPC, model HLC-8320, was from TOSOH, Japan. The others were commonly used equipment.

[0167] The orientation degree of the polyacrylonitrile precursor fiber crystal region was tested according to GB / T 23442-2009.

[0168] The orientation degree of polyacrylonitrile carbon fiber crystal regions was tested according to "Study on the Microstructural Characteristics of PAN-based Carbon Fibers" (Journal of Beijing University of Chemical Technology, Vol. 35, No. 5, 2008, authors: Zhang Xin, Ma Lei, Li Changqing, Tong Yuanjian, Xu Lianghua).

[0169] The tensile strength of polyacrylonitrile carbon fiber composites was tested according to GB / T 1447-2005. The compressive strength of polyacrylonitrile carbon fiber composites was tested according to GB / T 1448-2005. The compressive-tensile ratio of polyacrylonitrile carbon fiber composites is the ratio between the compressive strength and tensile strength mentioned above.

[0170] The polyacrylonitrile carbon fiber epoxy resin composite material used for testing in GB / T 1447-2005 and GB / T 1448-2005 is a carbon fiber reinforced resin matrix composite material. The specific preparation process is as follows:

[0171] (1) Resin matrix preparation: The epoxy compound (MY750, Shanghai Kaiyin Chemical Co., Ltd.) and the curing agent (diaminodiphenylmethane) were mixed. MDA-100H (Wanhua Chemical Group) was mixed uniformly at 40°C in a mass ratio of 4:1 and allowed to stand for 10 minutes to avoid the formation of bubbles; acetone (the mass ratio of acetone to epoxy compound (MY750) was 10:1) was added and the mixture was continued to be mixed uniformly at 40°C and allowed to stand for 10 minutes to avoid the formation of bubbles, thus obtaining the mixture.

[0172] (2) Carbon fiber and resin matrix composite: Carbon fiber is impregnated into the mixture of step (1) with a carbon fiber volume content of 60% and the carbon fiber is unidirectionally arranged to form a carbon fiber prepreg; then, the prepreg is dried at 90°C to remove excess solvent.

[0173] (3) Curing and molding: Curing the pre-impregnated body at 120℃ for 8 hours, then heating to 200℃ and curing for 3 hours, and finally degassing for 10-20 minutes to eliminate internal air bubbles.

[0174] (4) Post-processing: Machining is performed to cut into standard samples, and surface grinding and polishing are performed to reduce defects.

[0175] Surface roughness Ra of polyacrylonitrile precursor and polyacrylonitrile carbon fibers was tested using a standard MFP-3D-SA atomic force microscope. The precursor or carbon fiber filaments were fixed to a glass slide with double-sided tape. The atomic force microscope was used in tapping mode at a frequency of 1 Hz and a scanning area of ​​2*2 μm. 2 Since the surfaces of the precursor fiber and carbon fiber are arc-shaped, the arithmetic mean roughness Ra calculated directly according to formula (1) will be affected by the curvature. Therefore, NanoScope software is used to perform a two-stage flattening process on the fiber surface, and then the roughness Ra of the precursor fiber and carbon fiber surface is calculated by formula (1).

[0176] Unless otherwise specified, all raw materials are commercially available products.

[0177] Example 1

[0178] (1) Preparation of stock solution:

[0179] 39 kg of distilled acrylonitrile (AN), 1 kg of itaconic acid (IA), 8 kg of washing solution (containing 0.04 kg of polyacrylonitrile copolymer as a gel particle donor), 152 kg of dimethyl sulfoxide (DMSO), and 0.2 kg of azobisisobutyronitrile (AIBN) were added to a reactor. The reaction was carried out under nitrogen protection at a constant temperature of 60°C for 20 hours to obtain a binary acrylonitrile copolymer spinning solution. The spinning solution was then subjected to reduced pressure (absolute pressure: 20 kPa) to remove residual monomers and bubbles, yielding the polyacrylonitrile copolymer spinning dope.

[0180] The polyacrylonitrile spinning solution has a solid content of 18.4 wt%, a viscosity of 120 Pa·s measured at 60°C, a residual monomer content of 1100 ppm, and a weight-average molecular weight M. w It has a concentration of 91,000 g / mol, a polydispersity of 2.9, and a molecular weight of M. w The copolymer content of not less than 600,000 g / mol is 0.4%. The content of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 1.5 × 10⁻⁶. 6 The proportion of gel particles with a particle size of 5-10 μm to the total gel particles is 1.0% per mL.

[0181] The washing solution is obtained by cleaning the spinning solution preparation device after 90 days of polymerization. The polymerization process includes adding 39 kg of distilled acrylonitrile (AN), 1 kg of itaconic acid (IA), 160 kg of dimethyl sulfoxide (DMSO), and 0.2 kg of azobisisobutyronitrile (AIBN) to the reactor and reacting at a constant temperature of 60°C for 20 hours under nitrogen protection. The concentration of polyacrylonitrile copolymer in the gel particle donor is 0.5 wt.%; the content of gel particles with a particle size of 0.15-10 μm in the gel particle donor is 3.6 x 10⁻⁶. 9 The number of gel particles with a diameter of 5-10 μm in the gel particle donor accounted for 1.8% of the number of gel particles with a diameter of 0.15-10 μm.

[0182] (2) Preparation of precursor fibers:

[0183] (a) Spinning: The polyacrylonitrile spinning solution is metered by a metering pump and filtered by a sintered metal filter before being extruded through a spinneret. The filtration accuracy is 6μm, the spinneret orifice diameter is 90μm, and the spinneret pressure is 1.2MPa.

[0184] The insulation temperature of the filter and gooseneck tube is 60℃.

[0185] (b) Coagulation: The spinning solution is extruded through a spinneret and then coagulated in a coagulation bath (a mixed solvent of water and dimethyl sulfoxide, concentration 68 wt.%). The extrusion temperature is 60°C, the coagulation bath temperature is 50°C, and the draw ratio for coagulation is 0.6. Nascent fibers are obtained using a 12K spinneret.

[0186] (c) Stretching: Three hot water stretching processes were performed at temperatures of 86°C, 90°C and 95°C, with stretching ratios of 1.6, 1.65 and 1.7 respectively, for a total stretching ratio of 4.488.

[0187] (d) Washing: The filament bundle is washed 6 times with a stepped heating method. No stretching is performed during the washing process. The washing temperatures are 45℃, 50℃, 55℃, 60℃, 70℃ and 80℃ respectively.

[0188] (e) Oiling: The oil concentration is 2.5%, the temperature is room temperature, and excess oil is squeezed out by the extrusion roller.

[0189] (f) Drying and densification: It is divided into two stages. The first stage of drying and densification is carried out at a temperature of 95°C, with 8 drying rollers and a drying time of 60s. The second stage of drying and densification is carried out at a temperature of 125°C, with 8 drying rollers and a drying time of 60s.

[0190] (g) Steam drawing and heat setting: The steam drawing pressure is 0.35 MPa and the drawing ratio is 2.7. The heat setting pressure is 0.1 MPa and the heat setting ratio is 0.93 to obtain 12K polyacrylonitrile precursor fiber.

[0191] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15μm. The single filament of the precursor fiber has a breaking strength of 8.62cN / dtex, an initial modulus of 163cN / dtex, a breaking elongation of 14.96%, a surface roughness Ra of 42nm, and a crystal orientation degree of 87%.

[0192] (3) Carbon fiber preparation:

[0193] Polyacrylonitrile precursor fibers were pre-oxidized in five air-atmosphere heating furnaces within the range of 195–345℃, at temperatures of 195℃, 225℃, 237℃, 254℃, and 276℃, respectively; the total heating time was 68 min, and the total draw was 10.0%, yielding pre-oxidized fibers. The obtained pre-oxidized fibers were then subjected to low-temperature and high-temperature carbonization treatments in nitrogen atmosphere. The low-temperature carbonization temperature was 350–850℃, the heat treatment time was 3.0 min, and the draw was 2.0%; the high-temperature carbonization temperature was 1300–1400℃, the heat treatment time was 3.0 min, and the draw was -3.0%.

[0194] Mechanical properties of carbon fibers were tested according to GB / T 3362-2005. The average diameter of the polyacrylonitrile-based carbon fiber was 8.5 μm, the breaking strength was 5.1 GPa, the initial modulus was 291 GPa, and the elongation at break was 1.7%. Testing revealed longitudinal grooves parallel to the fiber axis on the surface of the polyacrylonitrile-based carbon fiber, a surface roughness Ra of 33 nm, and a crystalline orientation degree of 90%. The compressive strength of the polyacrylonitrile-carbon fiber composite was 1625 MPa, the tensile strength was 2196 MPa, and the compression-to-tension ratio was 0.74.

[0195] Example 2

[0196] (1) Preparation of stock solution:

[0197] The washing solution consisted of 12 kg (containing 0.06 kg of polyacrylonitrile copolymer) and 148 kg of dimethyl sulfoxide (DMSO). Other steps were the same as in Example 1.

[0198] The washing solution is the same as in Example 1.

[0199] The polyacrylonitrile spinning solution has a solid content of 18.8 wt%, a viscosity of 160 Pa·s measured at 60℃, a residual monomer content of 980 ppm, a weight-average molecular weight (Mw) of 93,000 g / mol, a polydispersity of 3.1, and a polymer content of 0.5% with a molecular weight (Mw) of not less than 600,000 g / mol. The polyacrylonitrile spinning solution contains 3.0 × 10⁻⁶ gel particles with a particle size of 0.15-10 μm. 7 The proportion of gel particles with a particle size of 5-10 μm to the total gel particles is 1.2% per mL.

[0200] (2) Preparation of precursor fibers:

[0201] The spinneret's spinneret pressure is 1.4 MPa. Everything else is the same as in Example 1.

[0202] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 13.15 cN / dtex, an initial modulus of 183 cN / dtex, a breaking elongation of 16.74%, a surface roughness Ra of 56 nm, and a crystal orientation degree of 89%.

[0203] (3) Carbon fiber preparation:

[0204] The carbon fiber preparation method is the same as in Example 1.

[0205] The polyacrylonitrile-based carbon fiber has an average diameter of 8.5 μm, a tensile strength of 5.6 GPa, an initial modulus of 299 GPa, a breaking elongation of 1.9%, a surface roughness Ra of 47 nm, and a crystalline orientation degree of 91%. The polyacrylonitrile carbon fiber composite has a compressive strength of 1658 MPa, a tensile strength of 2126 MPa, and a compression-to-tension ratio of 0.78.

[0206] Example 3

[0207] (1) Preparation of stock solution:

[0208] The washing solution consisted of 14 kg (containing 0.07 kg of polyacrylonitrile copolymer) and 146 kg of dimethyl sulfoxide (DMSO). Other aspects were the same as in Example 1.

[0209] The washing solution is the same as in Example 1.

[0210] The polyacrylonitrile spinning solution has a solid content of 18.9 wt%, a viscosity of 165 Pa·s measured at 60℃, a residual monomer content of 950 ppm, a weight-average molecular weight (Mw) of 94,000 g / mol, a polydispersity of 3.2, and a polymer content of 0.55% with a molecular weight (Mw) of not less than 600,000 g / mol. The polyacrylonitrile spinning solution contains 3.05 × 10⁻⁶ gel particles with a particle size of 0.15-10 μm. 7The proportion of gel particles with a particle size of 5-10 μm per mL is 1.6% of the total gel particles.

[0211] (2) Preparation of precursor fibers:

[0212] The spinneret's spinneret pressure is 1.5 MPa. Everything else is the same as in Example 1.

[0213] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 14.23 cN / dtex, an initial modulus of 194 cN / dtex, a breaking elongation of 18.89%, a surface roughness Ra of 58 nm, and a crystal orientation degree of 91%.

[0214] (3) Carbon fiber preparation:

[0215] The carbon fiber preparation method is the same as in Example 1.

[0216] The polyacrylonitrile-based carbon fiber has an average diameter of 8.5 μm, a tensile strength of 5.9 GPa, an initial modulus of 305 GPa, a breaking elongation of 2.2%, a surface roughness Ra of 49 nm, and a crystalline orientation degree of 93%. The polyacrylonitrile carbon fiber composite has a compressive strength of 1695 MPa, a tensile strength of 1904 MPa, and a compression-to-tension ratio of 0.89.

[0217] Example 4

[0218] (1) Preparation of stock solution:

[0219] The washing solution consisted of 4 kg (containing 0.02 kg of polyacrylonitrile copolymer) and 156 kg of dimethyl sulfoxide (DMSO). Other parameters were the same as in Example 1.

[0220] The washing solution is the same as in Example 1.

[0221] The polyacrylonitrile spinning solution has a solid content of 18.0 wt%, a viscosity of 80 Pa·s measured at 60℃, a residual monomer content of 1200 ppm, a weight-average molecular weight (Mw) of 88,000 g / mol, a polydispersity of 2.6, and contains 0.28% polymers with a molecular weight (Mw) of not less than 600,000 g / mol. The polyacrylonitrile spinning solution contains 3.0 × 10⁻⁶ gel particles with a particle size of 0.15-10 μm. 5 The proportion of gel particles with a particle size of 5-10 μm to the total gel particles is 0.8% per mL.

[0222] (2) Preparation of precursor fibers:

[0223] The spinneret's spinneret pressure is 1.0 MPa. Everything else is the same as in Example 1.

[0224] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 8.63 cN / dtex, an initial modulus of 146 cN / dtex, a breaking elongation of 14.52%, a surface roughness Ra of 41 nm, and a crystal orientation degree of 86%.

[0225] (3) Carbon fiber preparation:

[0226] The carbon fiber preparation method is the same as in Example 1.

[0227] The polyacrylonitrile-based carbon fiber has an average diameter of 8.5 μm, a tensile strength of 4.7 GPa, an initial modulus of 290 GPa, a breaking elongation of 1.7%, a surface roughness Ra of 32 nm, and a crystalline orientation degree of 92%. The polyacrylonitrile carbon fiber composite has a compressive strength of 1675 MPa, a tensile strength of 2204 MPa, and a compression-to-tension ratio of 0.76.

[0228] Example 5

[0229] (1) Preparation of stock solution:

[0230] The washing solution consisted of 2 kg (containing 0.01 kg of polyacrylonitrile copolymer) and 158 kg of dimethyl sulfoxide (DMSO). Other steps were the same as in Example 1.

[0231] The washing solution is the same as in Example 1.

[0232] The polyacrylonitrile spinning solution has a solid content of 17.9 wt%, a viscosity of 78 Pa·s measured at 60℃, a residual monomer content of 1220 ppm, a weight-average molecular weight (Mw) of 87,000 g / mol, a polydispersity of 2.6, and contains 0.27% polymers with a molecular weight (Mw) of not less than 600,000 g / mol. The polyacrylonitrile spinning solution contains 2.95 × 10⁻⁶ gel particles with a particle size of 0.15-10 μm. 5 The proportion of gel particles with a particle size of 5-10 μm per mL is 0.6% of the total gel particles.

[0233] (2) Preparation of precursor fibers:

[0234] The spinneret's spinneret pressure is 0.9 MPa. Everything else is the same as in Example 1.

[0235] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 7.76 cN / dtex, an initial modulus of 137 cN / dtex, a breaking elongation of 13.74%, a surface roughness Ra of 41 nm, and a crystal orientation degree of 85%.

[0236] (3) Carbon fiber preparation:

[0237] The carbon fiber preparation method is the same as in Example 1.

[0238] The polyacrylonitrile-based carbon fiber has an average diameter of 8.5 μm, a tensile strength of 4.6 GPa, an initial modulus of 289 GPa, a breaking elongation of 1.7%, a surface roughness Ra of 32 nm, and a crystalline orientation degree of 91%. The polyacrylonitrile carbon fiber composite has a compressive strength of 1620 MPa, a tensile strength of 2219 MPa, and a compression-to-tension ratio of 0.73.

[0239] Example 6

[0240] The amount of distilled acrylonitrile (AN) used was 39.8 kg and itaconic acid (IA) was 0.2 kg. Other parameters were the same as in Example 1.

[0241] The solid content of the polyacrylonitrile spinning solution was 18.6 wt%, the viscosity of the solution measured at 60℃ was 135 Pa·s, the residual monomer content was 1020 ppm, and the weight-average molecular weight M was... w It has a concentration of 94,000 g / mol, a polydispersity of 2.6, and a molecular weight of M. w The polymer content of not less than 600,000 g / mol is 0.5%. The content of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 1.52 × 10⁻⁶. 6 The proportion of gel particles with a particle size of 5-10 μm to the total gel particles is 1.1% per mL.

[0242] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 7.82 cN / dtex, an initial modulus of 138 cN / dtex, a breaking elongation of 13.84%, a surface roughness Ra of 40 nm, and a crystal orientation degree of 85%.

[0243] The polyacrylonitrile-based carbon fiber has an average diameter of 8.6 μm, a tensile strength of 4.8 GPa, an initial modulus of 290 GPa, a breaking elongation of 2.1%, a surface roughness Ra of 32 nm, and a crystalline orientation degree of 91%. The polyacrylonitrile carbon fiber composite has a compressive strength of 1585 MPa, a tensile strength of 2171 MPa, and a compression-to-tension ratio of 0.73.

[0244] Example 7

[0245] (1) Preparation of stock solution:

[0246] 39 kg of distilled acrylonitrile (AN), 1 kg of itaconic acid (IA), 10 kg of washing solution (containing 0.05 kg of polyacrylonitrile copolymer), 150 kg of dimethyl sulfoxide (DMSO), and 0.2 kg of azobisisobutyronitrile (AIBN) were added to a reactor. The mixture was reacted at a constant temperature of 60°C for 20 hours under nitrogen protection to obtain a binary acrylonitrile copolymer spinning solution. The spinning solution was then subjected to reduced pressure to remove residual monomers and bubbles, yielding the acrylonitrile copolymer spinning dope.

[0247] The washing solution is the same as in Example 1.

[0248] The solid content of the polyacrylonitrile spinning solution was 18.6 wt%, the viscosity of the solution measured at 60℃ was 138 Pa·s, the residual monomer content was 1050 ppm, and the weight-average molecular weight M was... w It has a concentration of 92,000 g / mol, a polydispersity of 3.0, and a molecular weight of M. w The content of particles with a density of not less than 600,000 g / mol is 0.46%. The content of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 5.05 × 10⁻⁶. 6 The proportion of gel particles with a particle size of 5-10 μm per mL is 1.12% of the total gel particles.

[0249] (2) Preparation of precursor fibers:

[0250] (a) Spinning: The polyacrylonitrile spinning solution is metered by a metering pump and filtered by a sintered metal filter before being extruded through a spinneret. The filtration accuracy is 6μm, the spinneret orifice diameter is 90μm, and the spinneret pressure is 1.35MPa.

[0251] The insulation temperature of the filter and gooseneck tube is 60℃.

[0252] (b) Coagulation: The spinning solution is extruded through a spinneret and then coagulated in a coagulation bath (a mixed solvent of water and dimethyl sulfoxide, concentration 68 wt.%). The extrusion temperature is 60°C, the coagulation bath temperature is 50°C, and the draw ratio for coagulation is 0.6. Nascent fibers are obtained using a 12K spinneret.

[0253] (c) Stretching: Three hot water stretching processes were performed at temperatures of 86°C, 90°C and 95°C, with stretching ratios of 1.6, 1.65 and 1.7 respectively, for a total stretching ratio of 4.488.

[0254] (d) Washing: The filament bundle is washed 6 times with a stepped heating method. No stretching is performed during the washing process. The washing temperatures are 45℃, 50℃, 55℃, 60℃, 70℃ and 80℃ respectively.

[0255] (e) Oiling: The oil concentration is 2.5%, the temperature is room temperature, and excess oil is squeezed out by the extrusion roller.

[0256] (f) Drying and densification: It is divided into two stages. The first stage of drying and densification is carried out at a temperature of 95°C, with 8 drying rollers and a drying time of 60s. The second stage of drying and densification is carried out at a temperature of 125°C, with 8 drying rollers and a drying time of 60s.

[0257] (g) Steam drawing and heat setting: The steam drawing pressure is 0.35 MPa and the drawing ratio is 2.7. The heat setting pressure is 0.1 MPa and the heat setting ratio is 0.93 to obtain 12K polyacrylonitrile precursor fiber.

[0258] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 12.15 cN / dtex, an initial modulus of 174 cN / dtex, a breaking elongation of 15.13%, a surface roughness Ra of 52 nm, and a crystal orientation degree of 88%.

[0259] (3) Carbon fiber preparation:

[0260] Polyacrylonitrile precursor fibers were pre-oxidized in five air-atmosphere heating furnaces within the range of 195–345℃, at temperatures of 195℃, 225℃, 237℃, 254℃, and 276℃, respectively; the total heating time was 68 min, and the total draw was 10.0%, yielding pre-oxidized fibers. The obtained pre-oxidized fibers were then subjected to low-temperature and high-temperature carbonization treatments in nitrogen atmosphere. The low-temperature carbonization temperature was 350–850℃, the heat treatment time was 3.0 min, and the draw was 2.0%; the high-temperature carbonization temperature was 1300–1400℃, the heat treatment time was 3.0 min, and the draw was -3.0%.

[0261] Mechanical properties of carbon fibers were tested according to the national standard GB / T 3362-2005. The average diameter of the polyacrylonitrile-based carbon fiber was 8.5 μm, the breaking strength was 5.4 GPa, the initial modulus was 295 GPa, and the elongation at break was 1.85%. Testing revealed longitudinal grooves parallel to the fiber axis on the surface of the polyacrylonitrile-based carbon fiber, a surface roughness Ra of 40 nm, and a crystalline orientation degree of 91%. The compressive strength of the polyacrylonitrile-carbon fiber composite was 1642 MPa, the tensile strength was 2015 MPa, and the compression-to-tension ratio was 0.81.

[0262] Example 8

[0263] (1) Preparation of stock solution:

[0264] 39 kg of distilled acrylonitrile (AN), 1 kg of itaconic acid (IA), 20 kg of washing solution (containing 0.10 kg of polyacrylonitrile copolymer), 140 kg of dimethyl sulfoxide (DMSO), and 0.2 kg of azobisisobutyronitrile (AIBN) were added to a reactor. The reaction was carried out under nitrogen protection at a constant temperature of 60°C for 20 hours to obtain a binary acrylonitrile copolymer spinning solution. The spinning solution was then subjected to reduced pressure to remove residual monomers and bubbles, yielding the acrylonitrile copolymer spinning dope.

[0265] The washing solution is the same as in Example 1.

[0266] The solid content of the polyacrylonitrile spinning solution was 19.2 wt%, the viscosity of the solution measured at 60℃ was 183 Pa·s, the residual monomer content was 990 ppm, and the weight-average molecular weight M was... w It has a concentration of 95,000 g / mol, a polydispersity of 3.3, and a molecular weight of M. w The content of particles with a density of not less than 600,000 g / mol is 0.67%. The content of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 7.8 × 10⁻⁶. 7 The proportion of gel particles with a particle size of 5-10 μm per mL is 1.7% of the total gel particles.

[0267] (2) Preparation of precursor fibers:

[0268] (a) Spinning: The polyacrylonitrile spinning solution is metered by a metering pump and filtered by a sintered metal filter before being extruded through a spinneret. The filtration accuracy is 6μm, the spinneret orifice diameter is 90μm, and the spinneret pressure is 1.8MPa.

[0269] The insulation temperature of the filter and gooseneck tube is 60℃.

[0270] (b) Coagulation: The spinning solution is extruded through a spinneret and then coagulated in a coagulation bath (a mixed solvent of water and dimethyl sulfoxide, concentration 68 wt.%). The extrusion temperature is 60°C, the coagulation bath temperature is 50°C, and the draw ratio for coagulation is 0.6. Nascent fibers are obtained using a 12K spinneret.

[0271] (c) Stretching: Three hot water stretching processes were performed at temperatures of 86°C, 90°C and 95°C, with stretching ratios of 1.6, 1.65 and 1.7 respectively, for a total stretching ratio of 4.488.

[0272] (d) Washing: The filament bundle is washed 6 times with a stepped heating method. No stretching is performed during the washing process. The washing temperatures are 45℃, 50℃, 55℃, 60℃, 70℃ and 80℃ respectively.

[0273] (e) Oiling: The oil concentration is 2.5%, the temperature is room temperature, and excess oil is squeezed out by the extrusion roller.

[0274] (f) Drying and densification: It is divided into two stages. The first stage of drying and densification is carried out at a temperature of 95°C, with 8 drying rollers and a drying time of 60s. The second stage of drying and densification is carried out at a temperature of 125°C, with 8 drying rollers and a drying time of 60s.

[0275] (g) Steam drawing and heat setting: The steam drawing pressure is 0.35 MPa and the drawing ratio is 2.7. The heat setting pressure is 0.1 MPa and the heat setting ratio is 0.93 to obtain 12K polyacrylonitrile precursor fiber.

[0276] The precursor fiber is 12K with an oil content of 0.71% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 14.68 cN / dtex, an initial modulus of 197 cN / dtex, a breaking elongation of 19.13%, a surface roughness Ra of 65 nm, and a crystal orientation degree of 93%.

[0277] (3) Carbon fiber preparation:

[0278] Polyacrylonitrile precursor fibers were pre-oxidized in five air-atmosphere heating furnaces within the range of 195–345℃, at temperatures of 195℃, 225℃, 237℃, 254℃, and 276℃, respectively; the total heating time was 68 min, and the total draw was 10.0%, yielding pre-oxidized fibers. The obtained pre-oxidized fibers were then subjected to low-temperature and high-temperature carbonization treatments in nitrogen atmosphere. The low-temperature carbonization temperature was 350–850℃, the heat treatment time was 3.0 min, and the draw was 2.0%; the high-temperature carbonization temperature was 1300–1400℃, the heat treatment time was 3.0 min, and the draw was -3.0%.

[0279] Mechanical properties of carbon fibers were tested according to the national standard GB / T 3362-2005. The average diameter of the polyacrylonitrile-based carbon fiber was 8.5 μm, the breaking strength was 6.0 GPa, the initial modulus was 335 GPa, and the elongation at break was 2.15%. Testing revealed longitudinal grooves parallel to the fiber axis on the surface of the polyacrylonitrile-based carbon fiber, a surface roughness Ra of 53 nm, and a crystalline orientation degree of 94%. The compressive strength of the polyacrylonitrile-carbon fiber composite was 1698 MPa, the tensile strength was 1895 MPa, and the compression-to-tension ratio was 0.90.

[0280] Example 9

[0281] In this embodiment, the washing solution (as a gel particle donor) used is the washing solution obtained by cleaning the spinning solution preparation device 30 days after the polymerization process. The polymerization process includes adding 39 kg of distilled acrylonitrile (AN), 1 kg of itaconic acid (IA), 160 kg of dimethyl sulfoxide (DMSO), and 0.2 kg of azobisisobutyronitrile (AIBN) into the reactor, and reacting at a constant temperature of 60°C for 20 hours under nitrogen protection.

[0282] The concentration of polyacrylonitrile copolymer in the gel particle donor is 0.4 wt.%; the content of gel particles with a particle size of 0.15-10 μm in the gel particle donor is 2.0 × 10⁻⁶. 7 The number of gel particles with a diameter of 5-10 μm in the gel particle donor accounted for 1.8% of the number of gel particles with a diameter of 0.15-10 μm.

[0283] (1) Preparation of stock solution:

[0284] 39 kg of distilled acrylonitrile (AN), 1 kg of itaconic acid (IA), 10 kg of washing solution (containing 0.04 kg of polyacrylonitrile copolymer), 150 kg of dimethyl sulfoxide (DMSO), and 0.2 kg of azobisisobutyronitrile (AIBN) were added to a reactor. The mixture was reacted at a constant temperature of 60°C for 20 hours under nitrogen protection to obtain a binary acrylonitrile copolymer spinning solution. The spinning solution was then subjected to reduced pressure to remove residual monomers and bubbles, yielding the polyacrylonitrile copolymer spinning dope.

[0285] The polyacrylonitrile spinning solution has a solid content of 18.3 wt%, a viscosity of 119 Pa·s measured at 60℃, a residual monomer content of 1050 ppm, a weight-average molecular weight (Mw) of 90,000 g / mol, a polydispersity of 3.0, and a polymer content of 0.4% with a molecular weight (Mw) of not less than 600,000 g / mol. The polyacrylonitrile spinning solution contains 1.46 × 10⁻⁶ gel particles with a particle size of 0.15-10 μm. 6 The proportion of gel particles with a particle size of 5-10 μm per mL is 0.9% of the total gel particles.

[0286] (2) Preparation of raw fiber: Same as in Example 1.

[0287] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15μm. The single filament of the precursor fiber has a breaking strength of 8.60cN / dtex, an initial modulus of 161cN / dtex, a breaking elongation of 14.90%, a surface roughness Ra of 40nm, and a crystal orientation degree of 86%.

[0288] (3) Carbon fiber preparation: Same as in Example 1.

[0289] Mechanical properties of carbon fibers were tested according to GB / T 3362-2005. The average diameter of the polyacrylonitrile-based carbon fiber was 8.5 μm, the breaking strength was 5.05 GPa, the initial modulus was 290 GPa, and the elongation at break was 1.7%. Testing revealed longitudinal grooves parallel to the fiber axis on the surface of the polyacrylonitrile-based carbon fiber, a surface roughness Ra of 32 nm, and a crystalline orientation degree of 89%. The compressive strength of the polyacrylonitrile-carbon fiber composite was 1624 MPa, the tensile strength was 2195 MPa, and the compression-to-tension ratio was 0.74.

[0290] Example 10

[0291] In this embodiment, the washing solution (as a gel particle donor) used is the washing solution obtained by cleaning the spinning solution preparation device after 150 days of polymerization. The polymerization process includes adding 39 kg of distilled acrylonitrile (AN), 1 kg of itaconic acid (IA), 160 kg of dimethyl sulfoxide (DMSO), and 0.2 kg of azobisisobutyronitrile (AIBN) to the reactor and reacting for 20 hours at a constant temperature of 60°C under nitrogen protection.

[0292] The concentration of polyacrylonitrile copolymer in the gel particle donor is 0.8 wt.%; the content of gel particles with a particle size of 0.15-10 μm in the gel particle donor is 7.5 × 10⁻⁶. 9 The number of gel particles with a diameter of 5-10 μm in the gel particle donor accounted for 1.8% of the number of gel particles with a diameter of 0.15-10 μm.

[0293] (1) Preparation of stock solution:

[0294] 39 kg of distilled acrylonitrile (AN), 1 kg of itaconic acid (IA), 6 kg of washing solution (containing 0.05 kg of polyacrylonitrile copolymer), 154 kg of dimethyl sulfoxide (DMSO), and 0.2 kg of azobisisobutyronitrile (AIBN) were added to a reactor. The mixture was reacted at a constant temperature of 60°C for 20 hours under nitrogen protection to obtain a binary acrylonitrile copolymer spinning solution. The spinning solution was then subjected to reduced pressure to remove residual monomers and bubbles, yielding the polyacrylonitrile copolymer spinning dope.

[0295] The polyacrylonitrile spinning solution has a solid content of 18.5 wt%, a viscosity of 124 Pa·s measured at 60℃, a residual monomer content of 1120 ppm, a weight-average molecular weight (Mw) of 92,000 g / mol, a polydispersity of 2.8, and a polymer content of 0.43% with a molecular weight (Mw) of not less than 600,000 g / mol. The polyacrylonitrile spinning solution contains 1.51 × 10⁻⁶ gel particles with a particle size of 0.15-10 μm. 6The proportion of gel particles with a particle size of 5-10 μm to the total gel particles is 1.1% per mL.

[0296] (2) Preparation of raw fiber: Same as in Example 1.

[0297] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 8.65 cN / dtex, an initial modulus of 164 cN / dtex, a breaking elongation of 14.97%, a surface roughness Ra of 43 nm, and a crystal orientation degree of 87.5%.

[0298] (3) Carbon fiber preparation: Same as in Example 1.

[0299] Mechanical properties of carbon fibers were tested according to GB / T 3362-2005. The average diameter of the polyacrylonitrile-based carbon fiber was 8.5 μm, the breaking strength was 5.17 GPa, the initial modulus was 292 GPa, and the elongation at break was 1.7%. Testing revealed longitudinal grooves parallel to the fiber axis on the surface of the polyacrylonitrile-based carbon fiber. The surface roughness Ra of the carbon fiber was 33.5 nm, and the crystalline orientation was 90.5%. The compressive strength of the polyacrylonitrile-carbon fiber composite was 1627 MPa, the tensile strength was 2199 MPa, and the compression-to-tension ratio was 0.74.

[0300] Comparative Example 1

[0301] (1) Preparation of stock solution:

[0302] Distilled acrylonitrile (AN) 33.15 kg, itaconic acid (IA) 0.85 kg, dimethyl sulfoxide (DMSO) 166 kg, and azobisisobutyronitrile (AIBN) 0.17 kg were added to a reactor and reacted at a constant temperature of 60°C for 20 hours under nitrogen protection to obtain a binary acrylonitrile copolymer spinning solution. The spinning solution was then subjected to reduced pressure to remove residual monomers and bubbles, yielding the acrylonitrile copolymer spinning dope.

[0303] The solid content of the polyacrylonitrile spinning solution was 15.3 wt%, the viscosity of the solution measured at 60℃ was 50 Pa·s, the residual monomer content was 8500 ppm, and the weight-average molecular weight M was... w It has a concentration of 62,000 g / mol, a polydispersity of 2.6, and a molecular weight of M. w The polymer content of not less than 600,000 g / mol is 0.01%. The content of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 1.60 × 10⁻⁶. 3 The proportion of gel particles with a particle size of 5-10 μm to the total gel particles is 0.02% per mL.

[0304] (2) Preparation of precursor fibers:

[0305] The spinneret's spinneret pressure is 0.3 MPa. Everything else is the same as in Example 1.

[0306] The precursor fiber is 12K with an oil content of 0.92% and an average diameter of 9.7 μm. The single filament of the precursor fiber has a breaking strength of 4.13 cN / dtex, an initial modulus of 112 cN / dtex, a breaking elongation of 11.23%, a surface roughness Ra of 13 nm, and a crystal orientation degree of 72%.

[0307] (3) Carbon fiber preparation:

[0308] The carbon fiber preparation method is the same as in Example 1.

[0309] The polyacrylonitrile-based carbon fiber has an average diameter of 4.2 μm, a tensile strength of 3.8 GPa, an initial modulus of 225 GPa, a breaking elongation of 2.1%, a surface roughness Ra of 11 nm, and a crystalline orientation degree of 70%. The polyacrylonitrile carbon fiber composite has a compressive strength of 1520 MPa, a tensile strength of 2621 MPa, and a compression-to-tension ratio of 0.58.

[0310] Comparative Example 2

[0311] (1) Preparation of stock solution:

[0312] The washing solution consisted of 24 kg (containing 0.12 kg of polyacrylonitrile copolymer) and 136 kg of dimethyl sulfoxide (DMSO). Other parameters were the same as in Example 1.

[0313] The composition of the washing solution is the same as in Example 1.

[0314] The solid content of the polyacrylonitrile spinning solution was 18.6 wt%, the viscosity of the solution measured at 60℃ was 170 Pa·s, the residual monomer content was 1010 ppm, and the weight-average molecular weight M was... w It has a concentration of 121,000 g / mol, a polydispersity of 3.5, and a molecular weight of M. w The polymer content of not less than 600,000 g / mol is 1.5%. The content of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 9.6 × 10⁻⁶. 7 The proportion of gel particles with a particle size of 5-10 μm per mL is 2.4% of the total gel particles.

[0315] (2) Preparation of precursor fibers:

[0316] (a) Spinning: The polyacrylonitrile spinning solution is metered by a metering pump and filtered by a sintered metal filter before being extruded through a spinneret. The filtration accuracy is 6μm, the spinneret orifice diameter is 90μm, and the spinneret pressure is 2.5MPa.

[0317] The insulation temperature of the filter and gooseneck tube is 60℃.

[0318] (b) Coagulation and molding: Too many broken nascent fibers are coagulated in the coagulation bath, and the polyacrylonitrile spinning solution cannot be coagulated and molded normally.

[0319] (g) Steam drawing and heat setting: 12K polyacrylonitrile precursor fibers cannot be obtained.

[0320] (3) Carbon fiber preparation: 12K polyacrylonitrile precursor and carbon fiber cannot be obtained.

[0321] Comparative Example 3

[0322] (1) Preparation of stock solution:

[0323] The washing solution contained 0.2 kg (i.e., 0.001 kg of polyacrylonitrile copolymer) and 159.8 kg of dimethyl sulfoxide (DMSO). Other parameters were the same as in Example 1.

[0324] The washing solution is the same as in Example 1.

[0325] The polyacrylonitrile spinning solution has a solid content of 17.2 wt%, a viscosity of 55 Pa·s measured at 60℃, a residual monomer content of 1500 ppm, a weight-average molecular weight (Mw) of 52,000 g / mol, a polydispersity of 2.93, and a polymer content of 0.05% with a molecular weight (Mw) greater than 600,000 g / mol. The content of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 0.4 × 10⁻⁶. 5 The proportion of gel particles with a particle size of 5-10 μm to the total gel particles is 0.05% per mL.

[0326] (2) Preparation of precursor fibers:

[0327] The spinneret's spinneret pressure is 0.33 MPa. Everything else is the same as in Example 1.

[0328] The precursor fiber is 12K with an oil content of 0.95% and an average diameter of 9.6 μm. The single filament of the precursor fiber has a breaking strength of 4.25 cN / dtex, an initial modulus of 113 cN / dtex, a breaking elongation of 12.25%, a surface roughness Ra of 12 nm, and a crystal orientation degree of 72%.

[0329] (3) Carbon fiber preparation:

[0330] The carbon fiber preparation method is the same as in Example 1.

[0331] The polyacrylonitrile-based carbon fiber has an average diameter of 4.1 μm, a tensile strength of 3.9 GPa, an initial modulus of 226 GPa, a breaking elongation of 2.2%, a surface roughness Ra of 4 nm, and a crystalline orientation degree of 70%. The polyacrylonitrile carbon fiber composite has a compressive strength of 1525 MPa, a tensile strength of 2585 MPa, and a compression-to-tension ratio of 0.59.

[0332] Comparative Example 4

[0333] (1) Preparation of stock solution:

[0334] The washing solution consisted of 22 kg (containing 0.11 kg of polyacrylonitrile copolymer) and 138 kg of dimethyl sulfoxide (DMSO). Other procedures were the same as in Example 1.

[0335] The composition of the washing solution is the same as in Example 1.

[0336] The polyacrylonitrile spinning solution has a solid content of 18.5 wt%, a viscosity of 168 Pa·s measured at 60℃, a residual monomer content of 1005 ppm, a weight-average molecular weight (Mw) of 107,000 g / mol, a polydispersity of 3.4, and a polymer content of 1.3% with a molecular weight (Mw) greater than 600,000 g / mol. The polyacrylonitrile spinning solution contains 9.5 × 10⁻⁶ gel particles with a particle size of 0.15–10 μm. 7 The proportion of gel particles with a particle size of 5-10 μm per mL is 2.3% of the total gel particles.

[0337] (2) Preparation of precursor fibers:

[0338] The spinneret's spinneret pressure is 2.4 MPa. Everything else is the same as in Example 1.

[0339] The insulation temperature of the filter and gooseneck tube is 60℃.

[0340] (b) Coagulation and molding: Too many broken nascent fibers are coagulated in the coagulation bath, and the polyacrylonitrile spinning solution cannot be coagulated and molded normally.

[0341] (g) Steam drawing and heat setting: 12K polyacrylonitrile precursor fibers cannot be obtained.

[0342] (3) Carbon fiber preparation: 12K polyacrylonitrile precursor and carbon fiber cannot be obtained.

[0343] Comparative Example 5

[0344] (1) Preparation of stock solution:

[0345] The washing solution contains 0.5 kg (i.e., 0.002 kg of polyacrylonitrile copolymer) and 159.5 kg of dimethyl sulfoxide (DMSO). Other parameters are the same as in Example 1.

[0346] The composition of the washing solution is the same as in Example 1.

[0347] The polyacrylonitrile spinning solution has a solid content of 17.7 wt%, a viscosity of 74 Pa·s measured at 60℃, a residual monomer content of 1250 ppm, a weight-average molecular weight (Mw) of 85,000 g / mol, a polydispersity of 2.45, and contains 0.25% polymers with a molecular weight (Mw) greater than 600,000 g / mol. The content of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 0.6 × 10⁻⁶. 5 The proportion of gel particles with a particle size of 5-10 μm to the total gel particles is 0.1% per mL.

[0348] (2) Preparation of precursor fibers:

[0349] The spinneret's spinneret pressure is 0.8 MPa. Everything else is the same as in Example 1.

[0350] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 5.21 cN / dtex, an initial modulus of 122 cN / dtex, a breaking elongation of 12.84%, a surface roughness Ra of 14 nm, and a crystal orientation degree of 74%.

[0351] (3) Carbon fiber preparation:

[0352] The carbon fiber preparation method is the same as in Example 1.

[0353] The polyacrylonitrile-based carbon fiber has an average diameter of 8.5 μm, a tensile strength of 4.1 GPa, an initial modulus of 288 GPa, a breaking elongation of 1.5%, a surface roughness Ra of 12 nm, and a crystalline orientation degree of 73%. The polyacrylonitrile carbon fiber composite has a compressive strength of 1530 MPa, a tensile strength of 1681 MPa, and a compression-to-tension ratio of 0.91.

[0354] Comparative Example 6

[0355] (1) Preparation of stock solution:

[0356] 39 kg of distilled acrylonitrile (AN), 1 kg of itaconic acid (IA), 152 kg of dimethyl sulfoxide (DMSO), and 0.2 kg of azobisisobutyronitrile (AIBN) were added to a reactor and reacted at a constant temperature of 60°C for 20 hours under nitrogen protection to obtain a binary acrylonitrile copolymer spinning solution. The spinning solution was then subjected to reduced pressure to remove residual monomers and bubbles, yielding the acrylonitrile copolymer spinning dope.

[0357] The polyacrylonitrile spinning solution has a solid content of 18.2 wt%, a viscosity of 118 Pa·s measured at 60℃, a residual monomer content of 1100 ppm, a weight-average molecular weight (Mw) of 90,000 g / mol, a polydispersity of 3.3, and a content of 0.1% of particles with a molecular weight (Mw) of not less than 600,000 g / mol. The content of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 1.7 × 10⁻⁶. 5 The proportion of gel particles with a particle size of 5-10 μm to the total gel particles is 0.3% per mL.

[0358] (2) Preparation of precursor fibers:

[0359] The spinneret's spinneret pressure is 0.7 MPa. Everything else is the same as in Example 1.

[0360] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 5.06 cN / dtex, an initial modulus of 115 cN / dtex, a breaking elongation of 12.15%, a surface roughness Ra of 13 nm, and a crystal orientation degree of 72%.

[0361] (3) Carbon fiber preparation:

[0362] The carbon fiber preparation method is the same as in Example 1.

[0363] The polyacrylonitrile-based carbon fiber has an average diameter of 8.5 μm, a tensile strength of 4.0 GPa, an initial modulus of 263 GPa, a breaking elongation of 1.3%, a surface roughness Ra of 8 nm, and a crystalline orientation degree of 71%. The polyacrylonitrile carbon fiber composite has a compressive strength of 1525 MPa, a tensile strength of 1713 MPa, and a compression-to-tension ratio of 0.89.

[0364] Comparative Example 7

[0365] (1) Preparation of stock solution:

[0366] The washing solution consisted of 1 kg (containing 0.005 kg of polyacrylonitrile copolymer) and 159 kg of dimethyl sulfoxide (DMSO). Other parameters were the same as in Example 1.

[0367] The washing solution is the same as in Example 1.

[0368] The polyacrylonitrile spinning solution has a solid content of 17.8 wt%, a viscosity of 76 Pa·s measured at 60℃, a residual monomer content of 1230 ppm, a weight-average molecular weight (Mw) of 86,000 g / mol, a polydispersity of 2.5, and contains 0.26% polymers with a molecular weight (Mw) of not less than 600,000 g / mol. The polyacrylonitrile spinning solution contains 1.0 × 10⁻⁶ gel particles with a particle size of 0.15-10 μm. 5The proportion of gel particles with a particle size of 5-10 μm to the total gel particles is 0.3% per mL.

[0369] (2) Preparation of precursor fibers:

[0370] The spinneret's spinneret pressure is 0.8 MPa. Everything else is the same as in Example 1.

[0371] The precursor fiber is 12K with an oil content of 0.7% and an average diameter of 15 μm. The single filament of the precursor fiber has a breaking strength of 6.38 cN / dtex, an initial modulus of 125 cN / dtex, a breaking elongation of 13.63%, a surface roughness Ra of 38 nm, and a crystal orientation degree of 84%.

[0372] (3) Carbon fiber preparation:

[0373] The carbon fiber preparation method is the same as in Example 1.

[0374] The polyacrylonitrile-based carbon fiber has an average diameter of 8.5 μm, a tensile strength of 4.5 GPa, an initial modulus of 289 GPa, a breaking elongation of 1.6%, a surface roughness Ra of 31 nm, and a crystalline orientation degree of 89%. The polyacrylonitrile carbon fiber composite has a compressive strength of 1580 MPa, a tensile strength of 2194 MPa, and a compression-to-tension ratio of 0.72.

[0375] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A polyacrylonitrile precursor fiber, characterized in that, The surface of the polyacrylonitrile precursor fiber has longitudinal grooves arranged parallel to the fiber axis, and the average diameter of the polyacrylonitrile precursor fiber is 10-20 μm, the tensile strength is 7-15 cN / dtex, the initial modulus is 120-200 cN / dtex, the elongation at break is 10-20%, and the crystal orientation degree is 75-99%.

2. The polyacrylonitrile precursor fiber according to claim 1, wherein, The polyacrylonitrile precursor fiber has an average diameter of 12-18 μm, preferably 14-16 μm; and / or The tensile strength of the polyacrylonitrile precursor fiber is 8-15 cN / dtex, preferably 12-15 cN / dtex; and / or The initial modulus of the polyacrylonitrile precursor fiber is 145-200 cN / dtex, preferably 170-200 cN / dtex; and / or The breaking elongation of the polyacrylonitrile precursor fiber is 14-20%, preferably 15-20%; and / or The polyacrylonitrile precursor fiber has 1,000-70,000 individual fibers, preferably 3,000-50,000, and more preferably 6,000-24,000; and / or The oil content of the polyacrylonitrile precursor fiber is 0.3-1.0%, preferably 0.5-0.9%; and / or The polyacrylonitrile precursor fiber has a crystal orientation degree of 80-95%, preferably 86-95%; and / or The surface roughness Ra of the polyacrylonitrile precursor fiber is 15-100 nm, preferably 30-70 nm, and more preferably 50-70 nm.

3. The method for preparing polyacrylonitrile precursor fiber according to any one of claims 1-2, characterized in that, The preparation method includes: wet spinning a polyacrylonitrile spinning solution; wherein the amount of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 2*10. 5 -8*10 7 per mL.

4. The preparation method according to claim 3, wherein, The amount of gel particles with a particle size of 0.15-10 μm in the polyacrylonitrile spinning solution is 5*10. 5 -8*10 7 Cells / mL, preferably 1*10 6 -8*10 7 Cells / mL, more preferably 8*10 6 -8*10 7 pcs / mL; and / or In the polyacrylonitrile spinning solution, the number of gel particles with a particle size of 5-10 μm accounts for 0.2-2% of the number of gel particles with a particle size of 0.15-10 μm, preferably 0.5-2%, more preferably 0.8-1.9%, and more preferably 1.0-1.8%.

5. The preparation method according to claim 3 or 4, wherein, The solid content of the polyacrylonitrile spinning solution is 17.0-22.0 wt%, preferably 18.0-22.0 wt%, more preferably 18.0-20.0 wt%; and / or The viscosity of the polyacrylonitrile spinning solution at 60°C is 40-200 Pa·s, preferably 70-200 Pa·s, more preferably 100-200 Pa·s; and / or The residual monomer content of the polyacrylonitrile spinning solution is 500-1700 ppm, preferably 600-1100 ppm.

6. The preparation method according to any one of claims 3-5, wherein, The polyacrylonitrile spinning solution comprises a polyacrylonitrile copolymer of acrylonitrile and a comonomer, wherein the comonomer is a compound containing an alkenyl group; Preferably, the comonomer is one or more selected from itaconic acid, vinyl groups, acrylates, vinyl esters, acrylamides, sulfonates, and ammonium salts, more preferably itaconic acid; and / or Preferably, the acrylonitrile structural unit content in the polyacrylonitrile copolymer is 85-99.5 wt%, more preferably 95-99 wt%; and / or Preferably, the content of copolymer structural units in the polyacrylonitrile copolymer is 15-0.5 wt%, more preferably 5-1 wt%; and / or Preferably, the weight-average molecular weight of the polyacrylonitrile copolymer is 60,000-120,000 g / mol, more preferably 90,000-120,000 g / mol; and / or Preferably, the content of polyacrylonitrile copolymer with a molecular weight of not less than 600,000 g / mol in the polyacrylonitrile spinning solution is 0.2-2.0 wt%, more preferably 0.4-1.0 wt%, and more preferably 0.45-0.8 wt%; and / or Preferably, the polydispersity of the polyacrylonitrile copolymer is 2-4.

7. The preparation method according to any one of claims 3-6, wherein, The preparation method of the polyacrylonitrile precursor fiber includes the following steps: S1. Provide the polyacrylonitrile spinning solution; and S2. The polyacrylonitrile spinning solution is wet-spun, including filtration and metering followed by spinning, coagulation, hot water drawing, washing, oiling, drying and densification, steam drawing, heat setting and winding.

8. The preparation method according to claim 7, wherein, The S1 step includes: mixing acrylonitrile, comonomer, initiator, first solvent and gel particle donor to obtain a mixture, and carrying out a polymerization reaction in the mixture under an inert atmosphere; Preferably, the polymerization reaction conditions include: a reaction temperature of 50-70°C, and / or a reaction time of 15-25 h; and / or Preferably, in the mixture, the ratio of the total mass of acrylonitrile and comonomer to the mass of solvent is (18-22):(78-82); and / or Preferably, the gel particle donor comprises a polyacrylonitrile polymer and a second solvent, and the amount of gel particles with a particle size of 0.15-10 μm in the gel particle donor is 1.6*10. 7 -8*10 9 More preferably, the concentration of polyacrylonitrile polymer in the gel particle donor is 0.2-2.0 wt.%; and / or Preferably, in the gel particle donor, the number of gel particles with a particle size of 5-10 μm accounts for 0.2-3.0% of the number of gel particles with a particle size of 0.15-10 μm; and / or Preferably, the mass ratio of the gel particle donor to the mass of the first solvent used to prepare the S1 mixture is (0.01-0.2):1; and / or Preferably, the initiator accounts for 0.1-10 wt% of the total mass of acrylonitrile and comonomer.

9. The preparation method according to claim 8, wherein, The first solvent is one or more of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, aqueous zinc chloride solution, and aqueous sodium thiosulfate solution, preferably dimethyl sulfoxide; and / or The initiator is selected from free radical initiators, preferably from peroxide initiators and azo initiators, more preferably from one or more of azobisisobutyronitrile, azobisisovalerate, dimethyl azobisisobutyrate, azobisisoheptanenitrile, and benzoyl peroxide, and preferably azobisisobutyronitrile; and / or The second solvent is one or more of dimethyl sulfoxide, dimethylformamide, dimethylacetamide, nitric acid, aqueous solution of zinc chloride, and aqueous solution of sodium hydrosulfite, preferably dimethyl sulfoxide.

10. The preparation method according to claim 7, wherein, In S2, The filtration conditions include: a filtration accuracy of 2-10 μm, preferably 4-8 μm; and / or The conditions for the spinneret include: the spinneret orifice diameter is 60-120μm, preferably 70-110μm, more preferably 80-100μm; and / or the spinneret pressure is 0.4-2.0MPa, preferably 0.6-1.8MPa, more preferably 0.8-1.6MPa.

11. A method for preparing polyacrylonitrile carbon fiber, characterized in that, The preparation method includes: subjecting the polyacrylonitrile precursor fiber according to any one of claims 1-2 to pre-oxidation treatment, low-temperature carbonization treatment, and high-temperature carbonization treatment.

12. The preparation method according to claim 11, wherein, The pre-oxidation treatment conditions include: a temperature of 190-350℃, and / or a pre-oxidation time of 45-90 min, and / or a total draw ratio of 0-20%; and / or The conditions for the low-temperature carbonization treatment include: under an inert atmosphere, a low-temperature carbonization temperature of 350-850℃, and / or a time of 2-4 min, and / or a draw ratio of 0-4%; and / or The conditions for the high-temperature carbonization treatment include: a high-temperature carbonization temperature of 1300-1400℃ under an inert atmosphere, and / or a time of 2-4 min, and / or a draw ratio of -4% to -1%.

13. Polyacrylonitrile carbon fiber, characterized in that, The polyacrylonitrile carbon fiber has an average diameter of 5-12 μm, a tensile strength of 4.2-6.5 GPa, an initial modulus of 250-350 GPa, and a tensile elongation of 0.8-2.5%, and the crystalline orientation degree of the polyacrylonitrile carbon fiber is 75-99%, preferably 85-95%, and more preferably 88-95%.

14. The polyacrylonitrile carbon fiber according to claim 13, wherein, The surface roughness Ra of the polyacrylonitrile carbon fiber is 5-80 nm, preferably 20-60 nm, more preferably 40-60 nm; and / or The polyacrylonitrile carbon fibers have an average diameter of 7-10 μm, preferably 8-9 μm; and / or The tensile strength of the polyacrylonitrile carbon fiber is 4.7-6.5 GPa, preferably 5.2-6.2 GPa; and / or The initial modulus of the polyacrylonitrile carbon fiber is 290-350 GPa; and / or The breaking elongation of the polyacrylonitrile carbon fiber is 1.0-2.4%, preferably 1.75-2.3%.

15. The polyacrylonitrile carbon fiber according to claim 13 or 14, wherein, The polyacrylonitrile carbon fiber is prepared by the preparation method described in claim 11 or 12.

16. The polyacrylonitrile carbon fiber according to any one of claims 13-15, wherein, The carbon fiber reinforced epoxy resin composite material prepared from the polyacrylonitrile carbon fiber has a compressive strength of 1550-1700 MPa, preferably 1600-1700 MPa, and a tensile strength of 1700-2400 MPa, preferably 1850-2250 MPa; and / or The polyacrylonitrile carbon fiber reinforced epoxy resin composite material prepared from the polyacrylonitrile carbon fiber has a compressive-tensile ratio of 0.60-0.95, preferably 0.75-0.

95.

17. A carbon fiber reinforced epoxy resin composite material comprising an epoxy resin and polyacrylonitrile carbon fiber according to any one of claims 13-16.

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