A polyacrylonitrile-based high-performance carbon fiber precursor, its preparation method and application

Abstract

This invention relates to a method for preparing polyacrylonitrile-based high-performance carbon fiber precursor, mainly addressing the problems of high fiber fineness CV value, low strength, and high strength CV value in existing carbon fiber precursors. This invention employs a wet spinning process, using curved rollers in the drying and densification stage. Simultaneously, at 350–450 kPa, the relationship between steam drawing tension and steam drawing ratio satisfies a linear relationship: y = Ax - 50.6 (400 ≤ A ≤ 800, 1 ≤ x ≤ 5). Wherein, y is the steam drawing tension, and x is the steam drawing ratio. The technical solution adopted in this invention effectively solves the problems of high fiber fineness CV value, low strength, and high strength CV value in carbon fiber precursors, and can be used in the industrial production of polyacrylonitrile-based high-performance carbon fiber precursors.

Description

Technical Field

[0001] This invention belongs to the field of carbon fiber technology, specifically relating to a polyacrylonitrile-based high-performance carbon fiber precursor, its preparation method, and its application. Background Technology

[0002] Carbon fiber, primarily composed of carbon, possesses a range of superior properties unmatched by other materials, including lightweight, high strength, high modulus, electrical conductivity, corrosion resistance, fatigue resistance, high temperature resistance, and a low coefficient of thermal expansion. It is widely used in aerospace, wind turbine blades, sports and leisure, pressure vessels, and transportation construction, making it an indispensable strategic material for national economic development. Data shows that commercial aircraft contribute the most to carbon fiber demand in the aerospace sector, and the Chinese carbon fiber market has maintained a continuous growth trend, increasing from US$482 million in 2016 to US$1.213 billion in 2021. With the increasing demand for carbon fiber, production capacity has also expanded. China's carbon fiber production capacity increased from 25,500 tons in 2017 to 39,400 tons in 2021. However, the supply of imported carbon fiber in the domestic market still far exceeds that of domestically produced carbon fiber.

[0003] The production process and fiber structure of polyacrylonitrile-based carbon fiber are easy to control, facilitating large-scale production with low costs and high overall performance, resulting in a market share exceeding 90%. The preparation process of polyacrylonitrile-based carbon fiber is time-consuming and complex, mainly consisting of three stages: polymerization of polyacrylonitrile copolymers, spinning of polyacrylonitrile precursor fibers, and oxidative carbonization treatment of the fibers. These three stages involve dozens of processes, each with multiple controlled parameters; changes in each parameter affect the subsequent fiber structure and properties. Various spinning processes exist for polyacrylonitrile-based carbon fiber precursor fibers, among which wet spinning is the most widely used due to its ease of control, stable process, and consistent precursor fiber quality. Drying and densification, and steam drawing are two crucial steps in wet spinning. During drying and densification, water molecules escape from the pores within the fiber, causing the micropores to fuse and resulting in a denser fibril arrangement. Appropriate drying and densification conditions can effectively improve fiber densification and homogenization. Steam drawing is beneficial for optimizing the optimal stress state of the molecular chains, playing a significant role in reducing the diameter and fineness of the precursor fiber, increasing its orientation, and enhancing its strength. Many studies have reported on these process conditions, such as Chinese patents CN215261005U, CN113388912A, and CN113957552A, and articles such as "The Influence of Drying and Densification Conditions on the Structure and Properties of PAN Fibers" (High-Tech Fibers and Applications, 2021, No. 5) and "The Influence of Steam Drawing on Precursor Preparation and Subsequent Carbon Fiber Production" (High-Tech Fibers and Applications, 2017, Vol. 42, No. 5). These studies all demonstrate that altering the temperature, drawing, and processing time in these two steps significantly impacts fiber properties. However, none of the aforementioned documents address how these two processes interact, the relationship between appropriate tension and draw ratio during steam drawing, or their impact on the quality of carbon fiber precursor and carbon fiber itself. Therefore, this invention is proposed. Summary of the Invention

[0004] The main technical problem addressed by this invention is the high fineness CV value, low strength, and high strength CV value of carbon fiber precursors in existing technologies. This invention effectively solves these problems by employing a method for manufacturing polyacrylonitrile-based carbon fiber precursors.

[0005] One objective of this invention is to provide a method for preparing polyacrylonitrile-based high-performance carbon fiber precursor, employing a wet spinning process, including drying and densification steps and steam drawing. In the steam drawing step, under a steam pressure of 350–450 kPa (preferably 400 kPa), the relationship between the steam drawing tension y and the steam drawing ratio x satisfies a linear relationship: y = Ax - 50.6, where 400 ≤ A ≤ 800, 1 ≤ x ≤ 5; preferably, 400 ≤ A ≤ 650, 1.5 ≤ x ≤ 3.5.

[0006] According to an embodiment of the present invention, a curved roller is used in the drying and densification step. Considering the equipment manufacturing cost, it is preferable to use a curved roller for the first 10% of the total residence time in the drying and densification stage. Specifically, the radius of curvature R of the curved roller is 10 to 15 times the fiber width before entering the drying and densification stage, preferably 12 to 14 times; the surface roughness Ra of the curved roller is ≤1.3 μm, preferably Ra ≤1 μm; the drying and densification temperature is 95 to 130°C, and the total residence time is 60 to 90 s; preferably, the drying and densification temperature is 100 to 120°C, and the total residence time is 70 to 85 s; no stretching is applied during the drying and densification process.

[0007] In the above technical solution, the curved roller is used in the drying and densification step before the steam drawing step. This can play a role in fiber expansion, increase the uniformity of drying and densification temperature, and thus improve the uniformity of the fiber densification process.

[0008] According to an embodiment of the present invention, the preparation method of the polyacrylonitrile-based high-performance carbon fiber precursor includes wet spinning extrusion of a polyacrylonitrile copolymer solution, followed by solidification molding, hot water stretching, water washing, oiling, drying densification, and steam stretching to obtain the polyacrylonitrile-based carbon fiber precursor.

[0009] The polyacrylonitrile is a copolymer of acrylonitrile and itaconic acid. Preferably, the mass percentage of acrylonitrile monomer in the polyacrylonitrile is 97-99.9%. The polymerization method of the polyacrylonitrile polymer can be solution polymerization, suspension polymerization, emulsion polymerization, etc., with solution polymerization being preferred. When using solution polymerization, dimethyl sulfoxide, dimethylformamide, dimethylacetamide, etc. are used as solvents.

[0010] The solvent in the polyacrylonitrile copolymer solution is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide;

[0011] The concentration of the polyacrylonitrile copolymer solution is 18-23%, preferably 19-21%;

[0012] The viscosity of the polyacrylonitrile-based copolymer solution at 60°C is 40–120 Pa·s, preferably 50–100 Pa·s.

[0013] According to embodiments of the present invention, the solidification molding, hot water stretching, water washing, and oiling can employ commonly used operating steps and process conditions in the art. For example, the solidification molding medium is a mixed solvent of water and a polar aprotic solvent, wherein the polar aprotic solvent is preferably at least one selected from dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide; in the mixed solvent, the polar aprotic solvent and water can be mixed in a commonly used ratio range, for example, the volume of the polar aprotic solvent accounts for 20-60% of the total volume of the mixed solvent; the solidification molding temperature is 45-75°C, and the stretching ratio is 1-2.1; the water washing temperature is 65-75°C, and the stretching ratio is 1-1.3; the oiling can be completed at room temperature; the total stretching ratio during the preparation process is 7.0-10.5, preferably 8.0-10.0.

[0014] A second objective of this invention is to provide a polyacrylonitrile-based high-performance carbon fiber precursor, prepared by the above-described method. Preferably, the fineness of the polyacrylonitrile-based carbon fiber precursor is 0.60–1.20 dtex, more preferably 0.65–1.17 dtex.

[0015] The third objective of this invention is to provide a polyacrylonitrile-based carbon fiber, which is prepared from the aforementioned polyacrylonitrile-based high-performance carbon fiber precursor.

[0016] The tension change of fibers during steam drawing reflects the mechanical properties of the fiber's condensed-state structure. This invention controls the steam pressure to be between 350 and 450 kPa, achieving a linear relationship between the steam drawing tension and the steam drawing ratio: y = Ax - 50.6 (400 ≤ A ≤ 800, 1 ≤ x ≤ 5), where y is the steam drawing tension and x is the steam drawing ratio. This significantly reduces the differences in the condensed-state structure of the fibers after steam drawing. Furthermore, the drying and densification process is one of the key processes in the preparation of carbon fiber precursors. As moisture is removed from the fiber microfibrils during this process, the pores gradually collapse and close, resulting in a denser connection between microfibrils and the formation of dense microfibrils. This leads to significant changes in the fiber's condensed-state structure, microstructure, and surface structure. However, the uneven heat transfer between fibers and within and between individual fibers during this process can cause differences in the condensed-state structure between and within fibers, resulting in a higher precursor fineness CV value, as well as lower carbon fiber strength and a higher strength CV value, affecting the precursor quality and the processability and usability of the carbon fiber. This invention further improves the uniformity of densification by using curved rollers for fiber drying and densification.

[0017] Compared with existing technologies, the present invention uses curved rollers for drying and densification, which can expand the fiber width and improve the uniformity of densification. Furthermore, by controlling the linear relationship between steam drawing tension and steam drawing ratio during the steam drawing process, the resulting carbon fibers have higher mechanical strength and lower CV values. This solves the problems of high fineness CV values ​​of carbon fiber precursors, as well as low strength and high strength CV values ​​in carbon fibers. Moreover, the preparation method of the present invention is simple and easy to implement, and can be widely used in industrial production, with broad application prospects. Detailed Implementation

[0018] The present invention will now be described in detail with reference to specific embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the content of the present invention are still within the scope of protection of the present invention.

[0019] The testing instruments and conditions used in this embodiment are as follows:

[0020] This invention relates to the mechanical property testing of polyacrylonitrile fibers: Mechanical property testing of polyacrylonitrile fibers is conducted according to the national standard GB / T-14337-2008. A 40mm long fiber bundle is taken from the fiber, and approximately 500 fibers are extracted and evenly laid on a felt board for testing. A fiber is randomly selected from the test sample using tweezers, and one end of the fiber is clamped with a 0.1cN tension clamp. The fiber is placed in the instrument's clamp, ensuring axial elongation. The monofilament tensile tester test mode, upper and lower clamp spacing (20mm), tensile speed (20mm / min), and sample quantity (50) are set. The monofilament tensile tester and data acquisition equipment are started to begin the tensile test, obtaining the fineness and CV value of the fiber monofilament.

[0021] Carbon fiber mechanical property testing: The mechanical properties of carbon fiber were tested according to the national standard GB-T3362-2017. Carbon fiber multifilaments were impregnated manually. The multifilaments were fixed on a wire hanger and immersed in epoxy resin for 2–4 minutes. After impregnation, excess resin was removed, and the multifilaments were air-dried at room temperature before being placed in an oven for curing, resulting in 10 cured multifilament samples. The testing machine was set to the specified mode, parameters, and loading rate (100 mm / min). The samples were clamped, ensuring the multifilaments were aligned with the loading axes of the upper and lower clamps. An initial load was applied to the samples (5 N for 1K fiber bundles, 15 N for 3K fiber bundles, and so on). The samples were checked and adjusted. The testing machine and data acquisition equipment were started to begin the test and obtain the strength results of the carbon fiber bundles.

[0022] The viscosity of the spinning solution in this invention is measured using the following method: An Anton Paar Rheolab QC rheometer is used. The spinning solution is filled into a measuring cup, taking care to avoid air bubbles, and the filling amount is slightly higher than the graduation mark inside the cup. The measuring cup is then placed in the rheometer and allowed to stand for 5 minutes until the sample is leveled. The measuring cup is then removed, the rotor is pressed into the measuring cup, and the two are reassembled into the rheometer to begin the test.

[0023] The raw materials used in the examples are either directly available for purchase or prepared according to existing methods.

[0024]

Example 1

[0025] Preparation of polyacrylonitrile copolymer spinning solution:

[0026] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor under nitrogen protection and reacted at 66°C for 22 hours. After removing monomers and bubbles, ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer, resulting in a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 82 Pa·s.

[0027] Preparation of carbon fiber precursor:

[0028] After the spinning solution is extruded via wet spinning, it undergoes a coagulation bath with a 50% concentration of dimethyl sulfoxide aqueous solution at 50°C for a 2-fold stretch. This is followed by hot water stretching, washing, and oiling. The washing temperature is 65°C with a stretch ratio of 1.1, the hot water stretching temperature is 85°C with a stretch ratio of 2.5, and oiling is performed at room temperature. During the drying and densification process, the fiber is held for 10% of its residence time (8s, total residence time 80s) using a curved roller (radius of curvature R = 30cm, surface roughness Ra = 1μm, fiber width 2.5cm before drying and densification). The drying and densification temperature is 105°C, and no stretching is applied. During steam stretching, the steam pressure is 400 kPa, the stretch is 1.5 times, and the tension is 774.4 cN, conforming to the formula y = 550x - 50.6. The polyacrylonitrile-based carbon fiber precursor obtained after steam drawing has a fineness of 0.84 dtex and a CV value of 7.38.

[0029] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. Then, it was sized to obtain carbon fiber. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.85 GPa and the CV value was 5.73.

[0030]

Example 2

[0031] Preparation of polyacrylonitrile copolymer spinning solution:

[0032] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor and reacted at 66°C for 22 hours under nitrogen protection. After removing monomers and bubbles, ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer, resulting in a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 82 Pa·s.

[0033] Preparation of carbon fiber precursor:

[0034] After the spinning solution is extruded via wet spinning, it undergoes a coagulation bath with a concentration of 50% in a 50°C dimethyl sulfoxide aqueous solution at a draw ratio of 1.8. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. During the drying and densification process, the fiber is held for 10% of its residence time (8 seconds) before drying and densification using a curved roller (with a radius of curvature R of 30 cm, a surface roughness Ra of 1 μm, and a fiber width of 2.5 cm before drying and densification). The drying and densification temperature is 105°C, and no drawing is applied. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 2.0, and the tension is 1249.4 cN, conforming to the formula y = 650x - 50.6. The polyacrylonitrile-based carbon fiber precursor obtained after steam drawing has a fineness of 0.75 dtex and a CV value of 13.68.

[0035] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. Then, it was sized to obtain carbon fiber. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.9 GPa and the CV value was 8.92.

[0036]

Example 3

[0037] Preparation of polyacrylonitrile copolymer spinning solution:

[0038] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor under nitrogen protection and reacted at 66°C for 22 hours. After monomer and gas removal, ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer, resulting in a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 83 Pa·s.

[0039] Preparation of carbon fiber precursor:

[0040] After the spinning solution is extruded via wet spinning, it undergoes a coagulation bath with a concentration of 50% in a 50°C dimethyl sulfoxide aqueous solution at a draw ratio of 1.4. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. During the drying and densification process, the fiber is held for 10% of its residence time (8 seconds) before drying and densification using a curved roller (with a radius of curvature R of 30 cm, a surface roughness Ra of 1 μm, and a fiber width of 2.5 cm before drying and densification). The drying and densification temperature is 105°C, and no drawing is applied. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 2.5, and the tension is 1499.4 cN, conforming to the formula y = 620x - 50.6. The polyacrylonitrile-based carbon fiber precursor obtained after steam drawing has a fineness of 0.75 dtex and a CV value of 6.45.

[0041] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. After sizing, carbon fiber was obtained. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.83 GPa and the CV value was 9.21.

[0042]

Example 4

[0043] Preparation of polyacrylonitrile copolymer spinning solution:

[0044] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor under nitrogen protection and reacted at 66°C for 22 hours. After removing monomers and bubbles, ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer, resulting in a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 79 Pa·s.

[0045] Preparation of carbon fiber precursor:

[0046] After the spinning solution is extruded via wet spinning, it undergoes a coagulation bath with a concentration of 50% in a 50°C dimethyl sulfoxide aqueous solution at a draw ratio of 1.2. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. During the drying and densification process, the fiber is held for 10% of its residence time (8 seconds) before drying and densification using a curved roller (with a curvature radius R of 30 cm, a surface roughness Ra of 1 μm, and a fiber width of 2.5 cm before drying and densification). The drying and densification temperature is 105°C, and no drawing is applied. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 3.0, and the tension is 1809.4 cN, conforming to the formula y = 620x - 50.6. The polyacrylonitrile-based carbon fiber precursor obtained after steam drawing has a fineness of 0.78 dtex and a CV value of 9.17.

[0047] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. After sizing, carbon fiber was obtained. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.80 GPa and the CV value was 6.76.

[0048]

Example 5

[0049] Preparation of polyacrylonitrile copolymer spinning solution:

[0050] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor and reacted at 66°C for 22 hours under nitrogen protection. After removing monomers and bubbles, and decarboxyl groups (15%) from the copolymer, a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution was prepared. The viscosity of the copolymer solution at 60°C was 83 Pa·s.

[0051] Preparation of carbon fiber precursor:

[0052] After the spinning solution is extruded via wet spinning, it undergoes a coagulation bath with a concentration of 50% in a 50°C dimethyl sulfoxide aqueous solution, resulting in a draw ratio of 1. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. During the drying and densification process, the fiber is held for 10% of its residence time (8 seconds) before drying and densification using a curved roller (with a radius of curvature R of 30 cm, a surface roughness Ra of 1 μm, and a fiber width of 2.5 cm before drying and densification). The drying and densification temperature is 105°C, and no drawing is applied. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 3.5, and the tension is 1689.4 cN, conforming to the formula y = 497.1x - 50.6. The polyacrylonitrile-based carbon fiber precursor obtained after steam stretching has a fineness of 0.78 dtex and a CV value of 5.45.

[0053] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. After sizing, carbon fiber was obtained. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.80 GPa and the CV value was 7.86.

[0054]

Example 6

[0055] Preparation of polyacrylonitrile copolymer spinning solution:

[0056] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with sodium chlorate-sodium bisulfite as the initiator and water as the solvent. The mixture was added to a reactor and reacted at 60°C for 1 hour under nitrogen protection. After washing and drying, a copolymer powder obtained by aqueous precipitation polymerization was obtained. The powder was dissolved in 20% dimethyl sulfoxide, and after adding ammonia to neutralize 15% of the carboxyl groups in the copolymer, monomers and bubbles were removed to prepare a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 73 Pa·s.

[0057] Preparation of carbon fiber precursor:

[0058] After the spinning solution is extruded via wet spinning, it undergoes a coagulation bath with a concentration of 50% in a 50°C dimethyl sulfoxide aqueous solution, resulting in a draw ratio of 1. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. During the drying and densification process, the fiber is held for 10% of its residence time (8 seconds) before drying and densification using a curved roller (with a radius of curvature R of 30 cm, a surface roughness Ra of 1 μm, and a fiber width of 2.5 cm before drying and densification). The drying and densification temperature is 105°C, and no drawing is applied. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 3.5, and the tension is 1874.4 cN, conforming to the formula y = 550x - 50.6. The polyacrylonitrile-based carbon fiber precursor obtained after steam drawing has a fineness of 1.18 dtex and a CV value of 5.45.

[0059] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. After sizing, carbon fiber was obtained. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.82 GPa and the CV value was 6.42.

[0060]

Example 7

[0061] Preparation of polyacrylonitrile copolymer spinning solution:

[0062] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor and reacted at 66°C for 22 hours under nitrogen protection. After removing monomers and bubbles, ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer, resulting in a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 80 Pa.

[0063] Preparation of carbon fiber precursor:

[0064] After the spinning solution is extruded via wet spinning, it undergoes a coagulation bath with a concentration of 50% in a 50°C dimethyl sulfoxide aqueous solution at a draw ratio of 1.4. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. During the drying and densification process, the fiber is held for 20% of its residence time (16 s) before drying and densification using a curved roller (with a radius of curvature R of 30 cm, a surface roughness Ra of 1 μm, and a fiber width of 2.5 cm before drying and densification) at a drying temperature of 105°C without any drawing. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 2.5, and the tension is 1249.4 cN, conforming to the formula y = 520x - 50.6. The polyacrylonitrile-based carbon fiber precursor obtained after steam drawing has a fineness of 0.75 dtex and a CV value of 7.81.

[0065] The carbon fiber precursor prepared in this way was pre-oxidized in sections at 220℃, 240℃, and 280℃, with a total draw ratio of 1.1. Subsequently, it underwent low-temperature carbonization and high-temperature carbonization in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃, respectively, with a total draw ratio of 1.03. After sizing, the carbon fiber was obtained. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.81 GPa, and the CV value was 8.22. The properties of the fiber prepared in this way are comparable to those in Example 3. However, increasing the proportion of the curved roller would increase the equipment manufacturing cost. Therefore, 10% is the optimal proportion.

[0066]

Example 8

[0067] Preparation of polyacrylonitrile copolymer spinning solution:

[0068] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor and reacted at 66°C for 22 hours under nitrogen protection. After removing monomers and bubbles, ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer, resulting in a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 80 Pa.

[0069] Preparation of carbon fiber precursor:

[0070] After the spinning solution is extruded via wet spinning, it undergoes a coagulation bath with a concentration of 50% in a 50°C dimethyl sulfoxide aqueous solution, resulting in a draw ratio of 1.4. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. During the drying and densification process, the fiber is held for 10% of its residence time (8 seconds) before drying and densification using a curved roller (with a radius of curvature R of 35 cm, a surface roughness Ra of 1 μm, and a fiber width of 2.5 cm before drying and densification). The drying temperature is 105°C, and no drawing is applied. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 2.5, and the tension is 1384.4 cN, conforming to the formula y = 574x - 50.6. The polyacrylonitrile-based carbon fiber precursor obtained after steam drawing has a fineness of 0.74 dtex and a CV value of 8.42.

[0071] The carbon fiber precursor prepared in this way was pre-oxidized in sections at 220℃, 240℃, and 280℃, with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃, with a total draw ratio of 1.03. After sizing, the carbon fiber was obtained. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.85 GPa and the CV value was 7.32.

[0072] Comparative Example 1

[0073] Preparation of polyacrylonitrile copolymer spinning solution:

[0074] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor under nitrogen protection and reacted at 66°C for 22 hours. After removing monomers and bubbles, ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer, resulting in a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 82 Pa.

[0075] Preparation of carbon fiber precursor:

[0076] After wet spinning and extrusion, the spinning solution undergoes a coagulation bath with a concentration of 50% dimethyl sulfoxide (DMSO) at 50°C and a draw ratio of 2. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. Subsequently, during the drying and densification process, the drying and densification temperature is 105°C without any drawing. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 1.5, and the tension is 3125.8 cN, conforming to the formula y = 2117.6x - 50.6. The resulting polyacrylonitrile-based carbon fiber precursor after steam drawing has a fineness of 1.26 dtex and a CV value of 37.38.

[0077] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. The resulting carbon fiber was then sized. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.35 GPa and the CV value was 25.73.

[0078] Comparative Example 2

[0079] Preparation of polyacrylonitrile copolymer spinning solution: Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with sodium chlorate-sodium bisulfite as the initiator and water as the solvent, and added to a reactor. Under nitrogen protection, the reaction was carried out at 60°C for 1 hour. After monomer and degassing, copolymer powder obtained by aqueous precipitation polymerization was obtained. The powder was dissolved in 20% dimethyl sulfoxide, and ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer. After monomer and degassing, a polyacrylonitrile copolymer dimethyl sulfoxide solution with a solid content of 20% was prepared. The viscosity of the copolymer solution at 60°C was 73 Pa·s.

[0080] Preparation of carbon fiber precursor:

[0081] After wet spinning and extrusion, the spinning solution undergoes a coagulation bath with a concentration of 50% dimethyl sulfoxide (DMSO) at 50°C and a draw ratio of 2. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. During the drying and densification process, the temperature is 105°C without any drawing. The steam drawing process uses a steam pressure of 400 kPa, a draw ratio of 1.5, and a tension of 2785.8 cN, conforming to the formula y = 1890.9x - 50.6. The resulting polyacrylonitrile-based carbon fiber precursor has a fineness of 1.23 dtex and a CV value of 29.34.

[0082] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. After sizing, carbon fiber was obtained. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.21 GPa and the CV value was 37.85.

[0083] Comparative Example 3

[0084] Preparation of polyacrylonitrile copolymer spinning solution:

[0085] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor and reacted at 66°C for 22 hours under nitrogen protection. After removing monomers and bubbles, ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer, resulting in a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 81 Pa.

[0086] Preparation of carbon fiber precursor:

[0087] After wet spinning and extrusion, the spinning solution undergoes a coagulation bath with a concentration of 50% dimethyl sulfoxide (DMSO) at 50°C and a draw ratio of 2. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. Subsequently, during the drying and densification process, the drying and densification temperature is 105°C without any drawing. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 1.5, and the tension is 417.4 cN, conforming to the formula y = 312x - 50.6. The resulting polyacrylonitrile-based carbon fiber precursor after steam drawing has a fineness of 1.29 dtex and a CV value of 45.24.

[0088] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. The resulting carbon fiber was then sized. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.1 GPa and the CV value was 35.21.

[0089] Comparative Example 4

[0090] Preparation of polyacrylonitrile copolymer spinning solution:

[0091] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor under nitrogen protection and reacted at 66°C for 22 hours. After removing monomers and bubbles, ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer, resulting in a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 82 Pa.

[0092] Preparation of carbon fiber precursor:

[0093] After the spinning solution is extruded via wet spinning, it undergoes a coagulation bath with a concentration of 50% in a 50°C dimethyl sulfoxide aqueous solution, resulting in a draw ratio of 1.4. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. During the drying and densification process, the fiber is held for 10% of its residence time (8 seconds) before drying and densification using a curved roller (with a curvature radius R of 30 cm, a surface roughness Ra of 1 μm, and a fiber width of 2.5 cm before drying and densification). The drying and densification temperature is 105°C, and no drawing is applied. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 2.5, and the tension is 2356.9 cN, conforming to the formula y = 963x - 50.6. The polyacrylonitrile-based carbon fiber precursor obtained after steam drawing has a fineness of 0.81 dtex and a CV value of 47.98.

[0094] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. The resulting carbon fiber was then sized. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.16 GPa and the CV value was 32.56.

[0095] Comparative Example 5

[0096] Preparation of polyacrylonitrile copolymer spinning solution:

[0097] Acrylonitrile and itaconic acid were mixed in a ratio of 98.2:1.8, with azobisisobutyronitrile as the initiator and dimethyl sulfoxide as the solvent. The mixture was added to a reactor under nitrogen protection and reacted at 66°C for 22 hours. After removing monomers and bubbles, ammonia water was added to neutralize 15% of the carboxyl groups in the copolymer, resulting in a 20% solids content polyacrylonitrile copolymer dimethyl sulfoxide solution. The viscosity of the copolymer solution at 60°C was 82 Pa.

[0098] Preparation of carbon fiber precursor:

[0099] After wet spinning and extrusion, the spinning solution undergoes a coagulation bath with a 50% concentration of dimethyl sulfoxide aqueous solution at 50°C and a draw ratio of 1.4. This is followed by hot water drawing, washing, and oiling. The washing temperature is 65°C with a draw ratio of 1.1, the hot water drawing temperature is 85°C with a draw ratio of 2.5, and oiling is performed at room temperature. Subsequently, during the drying and densification process, the temperature is 105°C, no drawing is applied, and curved rollers are not used. During steam drawing, the steam pressure is 400 kPa, the draw ratio is 2.5, and the tension is 1289.4 cN, conforming to the formula y = 536x - 50.6. The resulting polyacrylonitrile-based carbon fiber precursor after steam drawing has a fineness of 0.79 dtex and a CV value of 38.26.

[0100] The carbon fiber precursor obtained above was pre-oxidized in sections at 220℃, 240℃, and 280℃ with a total draw ratio of 1.1. Subsequently, it was carbonized at low temperature and high temperature in sections at 360℃, 560℃, 660℃ and 1200℃, 1300℃, and 1400℃ respectively with a total draw ratio of 1.03. The resulting carbon fiber was then sized. The mechanical properties of the carbon fiber were tested according to the national standard GB-T3362-2005. The tensile strength of the carbon fiber was 5.34 GPa and the CV value was 41.36.

Claims

1. A method for producing a polyacrylonitrile-based carbon fiber precursor by a wet spinning process including a drying densification step and a steam drawing step, wherein, in the steam drawing step, a relationship between a steam drawing tension y and a steam drawing ratio x under a steam pressure of 350 to 450 KPa satisfies a linear relationship: y = Ax - 50.6, wherein A is a constant of 0.1 to 0.

3. 400≤A≤800, 1≤x≤5, y is in cN; the drying and densification step uses a curved roller, the curvature radius R of the curved roller is 10 to 15 times the fiber width before entering the drying and densification, and the surface roughness Ra of the curved roller is ≤1.3μm.

2. The method of claim 1, wherein the method further comprises, In the steam stretching step, 400≤A≤650, 1.5≤x≤3.

5.

3. The preparation method according to claim 1, characterized in that, Curved rollers are used for the first 10% of the total residence time during the drying and densification stage.

4. The preparation method according to claim 3, characterized in that, The radius of curvature R of the curved roller is 12 to 14 times the width of the fiber before drying and densification; and / or, The surface roughness Ra of the curved roller is ≤1μm; and / or, The drying and densification temperature is 95~130℃, and the total residence time is 60~90s.

5. The preparation method according to claim 4, characterized in that, The drying and densification temperature is 100~120℃, and the total residence time is 70~85s.

6. The method of any one of claims 1 to 5, wherein the method further comprises the step of: The preparation method includes wet spinning and extruding a polyacrylonitrile copolymer solution, followed by solidification molding, hot water stretching, water washing, oiling, drying and densification, and steam stretching to obtain the polyacrylonitrile-based carbon fiber precursor.

7. The preparation method according to claim 6, characterized in that, The polyacrylonitrile is a copolymer of acrylonitrile and itaconic acid; and / or, The solvent in the polyacrylonitrile copolymer solution is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide; and / or The concentration of the polyacrylonitrile copolymer solution is 18-23%; and / or, The viscosity of the polyacrylonitrile-based copolymer solution at 60 °C is 40~120 Pa·s.

8. The preparation method according to claim 7, characterized in that, The polyacrylonitrile contains 97-99.9% acrylonitrile monomer by mass; and / or, The concentration of the polyacrylonitrile copolymer solution is 19-21%; and / or, The viscosity of the polyacrylonitrile-based copolymer solution at 60 °C is 50~100 Pa·s.

9. The preparation method according to claim 6, characterized in that, The solidification medium is a mixture of water and a polar aprotic solvent; and / or, The solidification temperature is 45~75℃, and the draw ratio is 1~2.1; and / or, The washing temperature is 65~75℃, and the draw ratio is 1~1.3; and / or, The hot water stretching temperature is 80~95℃, and the stretching ratio is 1.5~3; and / or, The total draw ratio during the preparation process is 7.0~10.

5.

10. The preparation method according to claim 9, characterized in that, The polar aprotic solvent is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, and N,N-dimethylacetamide; and / or, The total draw ratio during the preparation process is 8.0~10.

0.

11. A polyacrylonitrile-based high-performance carbon fiber precursor, prepared by the preparation method according to any one of claims 1 to 10.

12. The carbon fiber precursor according to claim 11, characterized in that, The fineness of the polyacrylonitrile-based high-performance carbon fiber precursor is 0.60~1.20 dtex.

13. The carbon fiber precursor according to claim 12, characterized in that, The fineness of the polyacrylonitrile-based high-performance carbon fiber precursor is 0.65~1.17 dtex.

14. A polyacrylonitrile-based carbon fiber, prepared from the polyacrylonitrile-based high-performance carbon fiber precursor according to any one of claims 11 to 13.