A low-ash high-performance polyacrylonitrile carbon fiber, its precursor and manufacturing method and use

Abstract

This invention relates to a low-ash, high-performance polyacrylonitrile carbon fiber, its precursor fiber, manufacturing method, and applications. It primarily addresses the problem in existing wet spinning techniques where reducing ash content leads to lower mechanical properties in the final carbon fiber. The invention employs a polyacrylonitrile carbon fiber with a grooved surface. The carbon fiber exhibits a Si / C ratio of 1% to 10% at points from the surface protrusions to the grooves, a Si / C ratio of 0.1% to 1% in the region between the surface grooves and the interior (up to 100 nm), and a Si / C ratio not exceeding 0.05% in regions larger than 100 nm. This technical solution effectively solves the problem and can be used in the industrial production of polyacrylonitrile carbon fiber precursor.

Description

Technical Field

[0001] This invention relates to a low-ash, high-performance polyacrylonitrile carbon fiber and a method for manufacturing the same. The invention also relates to a polyacrylonitrile carbon fiber precursor for manufacturing the aforementioned carbon fiber and a method for manufacturing the same. Background Technology

[0002] Carbon fiber is an inorganic polymer fiber material with a carbon content of over 90%. It possesses a stable chemical structure and is characterized by high strength, high modulus, and low mass. Furthermore, it exhibits excellent properties such as high temperature resistance, corrosion resistance, low coefficient of thermal expansion, excellent heat transfer, good chemical stability, and electrical conductivity. It can be used as a reinforcing material for high-performance composite materials and is widely used in aerospace, building reinforcement, sporting goods, automotive structures, wind turbine blades, the photovoltaic industry, and medical devices. However, the continuous development of aerospace and high-end equipment has placed new performance demands on carbon fiber materials. The requirements for carbon fiber are no longer limited to basic indicators such as strength and modulus. Especially in aerospace applications, specific requirements have been placed on the ash content of carbon fiber.

[0003] The performance of carbon fiber is primarily affected by defects. High-quality oiling agents and proper oiling processes are effective means of preventing defects. After PAN precursor fibers are treated with a specialized oiling agent, a protective film with good heat resistance forms on the fiber surface, separating the monofilaments and preventing them from sticking and twisting during pre-oxidation. However, the production process of high-performance carbon fiber precursor fibers currently mainly uses silicone-containing oiling agents. Some silicon-containing components in these agents have poor decomposition properties at high temperatures, leading to incomplete decomposition of silicon during pre-oxidation and carbonization. The resulting silicon carbide and silicon nitride impurities remain inside the carbon fiber, becoming weak points during stretching or bending, thus severely affecting the quality of the carbon fiber. Furthermore, the silicon oxides generated during pre-oxidation and carbonization are the main source of ash in this process, not only contaminating equipment and shortening its production cycle and lifespan, but also reducing start-up time and causing frequent shutdowns for cleaning to ensure smooth operation.

[0004] There are many precursor fibers that can be used to prepare carbon fibers. Currently, over 90% of the carbon fibers on the market are made from PAN fibers. PAN-based carbon fibers have advantages such as high carbon yield, excellent mechanical properties, and mature processing, making them a major product in the carbon fiber industry. Currently, PAN fibers are mainly prepared by wet spinning and dry-jet wet spinning. In dry-jet wet spinning, the solution is extruded from the spinneret, passes through an air section, and then enters a coagulation bath to solidify. This difference leads to significant variations between dry-jet wet spinning and wet spinning in terms of solution system, spinning process, and spinning equipment, resulting in different morphologies and structures of the precursor fibers and carbon fibers. Dry-jet wet-spun carbon fibers have a smooth surface and a denser structure, while wet-spun carbon fibers have a distinct groove structure on their surface. The height difference between the groove protrusions and depressions can reach tens of nanometers. This uneven groove structure can act as a defect, causing carbon fiber breakage. Therefore, the main structural features affecting breakage in wet-spun and dry-jet wet-spun carbon fibers are also different. In the preparation of PAN fibers, compared with dry-jet wet spinning, wet spinning is a more mature process. The spinning process is stable and easy to control, the residual solvent in the fiber is easy to remove, and the carbon fibers obtained are easier to combine with composite materials. It is an important method for preparing high-performance carbon fiber precursors.

[0005] High-quality carbon fiber precursors must possess characteristics such as few surface defects, minimal pore structure, dense structure, good tensile strength, and high heat resistance. To produce high-performance carbon fibers with controllable silicon content and permeability, the precursor fibers must also exhibit low silicon content, low silicon permeability, and good uniformity of the oil film coating on the fiber surface. During carbon fiber precursor production, the coagulation process is a double-diffusion process, resulting in numerous pores in the nascent fibers. During subsequent stretching and washing, some pores gradually decrease in size or even close. Unclosed pores allow silicone-containing oil to seep into them during the oiling process. Later, during drying and densification, the pores close, making it difficult to completely remove the silicone-containing oil, which remains inside the fiber. This leads to higher ash content during carbonization, and the infiltrated silicon is difficult to completely remove, remaining in the carbon fiber and affecting its final performance.

[0006] Therefore, selecting high-quality oiling agents and controlling the oiling process appropriately are crucial steps in preparing low-ash, high-performance polyacrylonitrile carbon fibers and the precursor fibers used in these fibers. Patent CN113597484A discloses a method for inhibiting the penetration of oiling agents into the fiber surface and suppressing surface porosity in carbon fibers, using SIMS (Secondary Ion Mass Spectrometry) to calculate the Si / C ratio at a certain depth from the fiber surface. However, this patent also explicitly states that this invention cannot be used to improve the strength of wet-spun carbon fibers. Furthermore, wet spinning generally employs a multi-stage coagulation process, with coagulation bath concentration, temperature, and impregnation time completely different from dry-jet wet spinning. Therefore, the coagulation conditions and air residence time described in this patent cannot be used to prepare wet-spun carbon fiber precursor fibers, and thus cannot inhibit the penetration of oiling agents into the fiber surface during the wet spinning process, nor can it suppress inter-fiber adhesion and surface porosity in the carbon fiber. Moreover, wet-spun nascent fibers have a looser structure and larger pores compared to dry-jet wet-spun fibers. During the oiling process, the oiling agent can more easily penetrate into the fiber interior. Therefore, new methods are needed to achieve the goal of inhibiting Si penetration and improving carbon fiber performance.

[0007] Patent CN111088559A discloses a method that uses ultra-low silicone oil or no silicone oil for the first oiling step. After the first drying and densification process, the second oiling step uses a common silicone oil-containing oiling method. However, after the drying and densification process, the fiber becomes dense and the surface pores are closed. During the second oiling process, the oil is difficult to adhere to the fiber surface and will fall off during subsequent drying and steam stretching. This damages the integrity of the oil film and has an adverse effect on the fiber during the pre-oxidation and carbonization process, resulting in low strength and modulus of the prepared carbon fiber.

[0008] Patents CN114622417A and CN112424418A disclose a silicone oil agent for carbon fiber, which solves the problem of fuzzing during the spinning process of the precursor fiber and can effectively protect the carbon fiber, but do not mention the problems of carbonization ash and carbon fiber impurities.

[0009] Patents CN112726207A and CN110863270A disclose a silicone-free agent for manufacturing carbon fiber precursor, which has a very low ash content, but its carbon fiber strength modulus is low and it is not suitable for the preparation process of high-performance carbon fibers.

[0010] Patent CN110863270A discloses a method for reducing the ash content of high-strength polyacrylonitrile-based carbon fibers, which involves impregnating the polyacrylonitrile-based carbon fibers with an organic solvent and treating them with hydrofluoric acid. However, this method has an adverse effect on the performance of the carbon fibers.

[0011] Patent CN103290527A discloses a method for reducing the ash content of polyacrylonitrile-based carbon fibers. Based on a quaternary ammoniation-modified copolymer system, a PAN spinning solution with high hydrophilicity is prepared. Then, by focusing on controlling the swelling degree of the precursor fiber before applying the oiling agent, a low-silicone oiling agent is introduced to control the oil content of the fiber bundle. However, the modified copolymer system is not suitable for preparing high-performance carbon fibers.

[0012] Therefore, in the preparation of high-performance carbon fiber wet spinning, in order to reduce the low ash content of carbon fiber, it often leads to a loss of carbon fiber performance.

[0013] In view of this, the present invention is hereby proposed. Summary of the Invention

[0014] Through in-depth research, the inventors discovered that the extensive penetration and distribution of oils in fibers, which are difficult to remove in subsequent processes, is the main reason for the high ash content in the subsequent pre-oxidation and carbonization processes. Furthermore, it leads to a higher impurity content in the final carbon fibers, affecting their performance. On the other hand, if the Si content in the precursor fiber's sheath is too low, problems such as filament bundling, adhesion, and excessive fuzz can easily occur during pre-oxidation, ultimately reducing the carbon fiber's performance. Further research by the inventors revealed that controlling the penetration depth and gradient of silicon in carbon fibers can effectively balance the technical challenges of high performance and low ash content, resulting in high-performance carbon fibers with low ash content. This led to the present invention.

[0015] One of the main technical problems addressed by this invention is the low mechanical properties of the final carbon fiber obtained in the existing wet spinning process due to the effort to reduce the ash content of the carbon fiber. This invention provides a low-ash, high-performance polyacrylonitrile carbon fiber in which silicon has a specific penetration gradient and silicon content on the fiber surface, which can improve the mechanical properties of the carbon fiber while reducing its ash content.

[0016] The second main technical problem solved by this invention is to provide a method for preparing low-ash, high-performance carbon fiber, which corresponds to solving one of the above-mentioned technical problems. This method has the characteristics of low ash content during the carbonization process, requiring only a shutdown every six months to clean the ash in the equipment, low silicon impurity content in the carbon fiber, and good strength, modulus, and elongation of the carbon fiber.

[0017] The third technical problem that this invention mainly solves is to provide an application of low-ash, high-performance carbon fiber, which corresponds to solving one of the above-mentioned technical problems.

[0018] The fourth technical problem that this invention mainly solves is to provide a polyacrylonitrile precursor for preparing low-ash, high-performance carbon fibers as described in the above-mentioned technical problem.

[0019] The fifth technical problem that this invention mainly solves is to provide a method for preparing polyacrylonitrile precursor fibers, which corresponds to the solution of the fourth technical problem mentioned above.

[0020] To solve one of the above-mentioned technical problems, the present invention adopts the following technical solution: a polyacrylonitrile carbon fiber with a groove structure on its surface; wherein, the carbon fiber has a Si / C ratio of 1% to 10% from the surface protrusion to the groove, a Si / C ratio of 0.1% to 1% in the region between the surface groove and the interior 100nm, and a Si / C ratio of no more than 0.05% in the region greater than 100nm.

[0021] In the above technical solution, preferably, the total silicon content in the carbon fiber is 500 to 1500 ppm, and the lowest relative Si content from the protrusion to the groove area on the fiber surface is not less than 10 times the lowest Si content in the area between the surface groove and the interior 100 nm.

[0022] In the above technical solution, preferably, the number of pores in the region from the fiber surface to a depth of 100 nm obtained by gallium focused ion beam cutting and transmission electron microscopy is less than 20, more preferably less than 10; the average length of the pores is 10-50 nm and the average width is 5-25 nm.

[0023] In the above technical solution, preferably, the orientation deviation angle of the pores along the fiber axis obtained by small-angle X-ray diffraction is less than 4°.

[0024] In the above technical solution, preferably, the polyacrylonitrile carbon fiber is obtained from polyacrylonitrile precursor fiber produced by wet spinning.

[0025] To solve the second technical problem mentioned above, the present invention adopts the following technical solution: a method for manufacturing polyacrylonitrile carbon fiber according to any of the technical solutions for solving the first technical problem mentioned above, comprising the step of obtaining the polyacrylonitrile carbon fiber by carbonizing polyacrylonitrile precursor; characterized in that the polyacrylonitrile precursor is obtained by wet spinning, comprising two consecutive oiling processes, without an intermediate drying and densification stage, wherein the first oiling tank contains a silicone-free oil agent with an oil agent concentration of 0.1% to 5.0%; the second oiling tank contains a silicone-containing oil agent with an oil agent concentration of 0.1% to 5.0%, and the residence time of the second oiling is less than that of the first oiling.

[0026] In the above technical solution, preferably, the average particle size of the silicone-free agent and the silicone-containing agent is independently 50nm to 500nm, and the silicone content of the silicone-containing agent used in the second oil bath is 0.1% to 0.9%.

[0027] In the above technical solution, preferably, the pH difference between the silicone-free agent and the silicone-containing agent is not greater than 1; the ionic polarity of the surfactants in the silicone-free agent and the silicone-containing agent cannot be opposite; the silicone-containing agent is preferably a nonionic surfactant agent.

[0028] In the above technical solution, preferably, the swelling degree of the polyacrylonitrile precursor fiber after water washing before oiling is 80-150%.

[0029] In the above technical solution, preferably, the manufacturing method specifically includes the steps of wet solidification of polyacrylonitrile raw solution, solidification stretching, hot water stretching, water washing, oiling, drying and densification, steam stretching, and steam heat setting to obtain the polyacrylonitrile precursor fiber.

[0030] In the above technical solution, preferably, the single filament fineness of the polyacrylonitrile precursor fiber is 0.7 to 1.0 dtex.

[0031] In the above technical solution, preferably, the polyacrylonitrile precursor fiber is obtained by heat stabilization treatment and carbonization.

[0032] In the above technical solution, preferably, the thermal stabilization treatment is carried out in an air atmosphere at a temperature of 190-270°C and the total draw is not higher than 5%; the carbonization step includes low-temperature carbonization treatment in an inert atmosphere at a temperature of 350-700°C with a draw ratio of 0-4% and high-temperature carbonization treatment in an inert atmosphere at a temperature of 1300-1400°C with a draw ratio of -4--2% of the total draw.

[0033] To solve the third technical problem mentioned above, the present invention adopts the following technical solution: the use of polyacrylonitrile carbon fiber obtained by any of the manufacturing methods of polyacrylonitrile carbon fiber described in any of the technical solutions described in the first technical problem or polyacrylonitrile carbon fiber described in the second technical problem.

[0034] To solve the fourth technical problem mentioned above, the present invention adopts the following technical solution: a polyacrylonitrile precursor fiber, characterized in that in a region with a depth of 0 to 2 μm from the fiber surface, the Si / C ratio calculated by TEM-EDS has a point of 1.0% to 20%, and the Si / C ratio at a depth of 2 μm from the fiber surface is not higher than 0.15%.

[0035] In the above technical solution, preferably, the oil content of the precursor fiber is 0.8% to 2.5%, more preferably 0.9% to 2.0%; the silicon content of the precursor fiber is 0.01% to 0.5%; preferably, the single filament fineness of the polyacrylonitrile precursor fiber is 0.7 to 1.0 dtex.

[0036] To solve the fifth technical problem mentioned above, the present invention adopts the following technical solution: a method for preparing polyacrylonitrile precursor fiber according to any of the technical solutions for solving the fourth technical problem mentioned above, using wet spinning, including two consecutive oiling processes, without an intermediate drying and densification stage. The first oiling tank contains a silicone-free oil agent with an oil concentration of 0.1% to 5.0%; the second oiling tank contains a silicone-containing oil agent with an oil concentration of 0.1% to 5.0%, and the residence time of the second oiling is less than that of the first oiling.

[0037] In the above technical solution, preferably, the average particle size of the non-silicone oil agent and the silicone oil agent is independently 50nm to 500nm, and the silicone content of the silicone oil agent used in the second oil bath is 0.1% to 0.9%.

[0038] In the above technical solution, preferably, the pH difference between the silicone-free agent and the silicone-containing agent is not greater than 1; the ionic polarity of the surfactants in the silicone-free agent and the silicone-containing agent cannot be opposite; the silicone-containing agent is preferably a nonionic surfactant agent.

[0039] In the above technical solution, preferably, the swelling degree of the polyacrylonitrile precursor fiber after water washing before oiling is 80-150%.

[0040] In the above technical solution, preferably, the preparation method specifically includes the steps of wet solidification of polyacrylonitrile stock solution, solidification stretching, hot water stretching, water washing, oiling, drying and densification, steam stretching, and steam heat setting to obtain the polyacrylonitrile precursor fiber.

[0041] The polyacrylonitrile precursor fiber in the technical solution described in the fourth solution to the above-mentioned technical problem, or the polyacrylonitrile precursor fiber prepared in the technical solution described in the fourth solution to the above-mentioned technical problem, can both be used to prepare the low-ash high-performance polyacrylonitrile carbon fiber described in the first solution to the above-mentioned technical problem.

[0042] In the above technical solution, there are no other special limitations on the polyacrylonitrile-based precursor fiber. It can be obtained from polyacrylonitrile spinning solution commonly used in the field through a common spinning process. There are also no special limitations on the polyacrylonitrile spinning solution and spinning process. Compared with the existing technology for preparing polyacrylonitrile fibers, both can achieve the goal of improving the mechanical properties of the fiber. For example, but not limited to, the polyacrylonitrile comonomer is a vinyl-containing monomer. The comonomer is preferably one or more of acrylates, vinyl esters, acrylamides, sulfonates, and ammonium salts.

[0043] The inventors have discovered that by controlling the silicon penetration gradient and silicon content on the fiber surface, the mechanical properties of carbon fibers can be improved while reducing their ash content. Specifically, this involves controlling the Si / C ratio from the surface protrusions to the grooves, with a range of 1% to 10%, a range of 0.1% to 1% Si / C ratio in the region from the surface grooves to the interior within 100 nm, and a Si / C ratio no higher than 0.05% in the region greater than 100 nm. This technical solution effectively solves the problems existing in the prior art. Furthermore, the manufacturing method provided by this invention includes two consecutive oiling processes without an intermediate drying and densification stage. The first oiling tank contains a silicone-free oil agent with a concentration of 0.1% to 5.0%, while the second oiling tank contains a silicone-containing oil agent with a concentration of 0.1% to 5.0%. The residence time of the second oiling process is shorter than that of the first oiling process. This technical solution effectively controls the silicon penetration gradient and silicon content on the fiber surface, enabling the preparation of carbon fiber precursors and carbon fibers with low silicon content and a better silicon penetration gradient. Ultimately, it will be possible to produce carbon fibers with very low ash content and excellent properties such as strength and modulus over a long period of time.

[0044] The swelling of washed fibers is calculated by the weight W after removing the fluid adhering to the washed fibers using a centrifuge (15 min, 3000 rpm) and the weight W0 after drying at 105°C for 2 hours using a hot air dryer. Swelling (wt%) = (W - W0) × 100% / W0.

[0045] The silicon content of carbon fibers was determined by placing the sample in a nitrogen-sealed container made of Teflon, heating and acidifying it with aqua regia, and then quantitatively determining the Si content in the sample using ICP (inductively coupled plasma) atomic emission spectrometry.

[0046] The linear density of the fiber is obtained by cutting the fiber bundle 30cm before the last drafting roller after the steam drafting cavity online using a length-fixing device. Then, the fiber and the length-fixing device are placed together in an oven to dry in order to avoid changes in fiber length during the drying process. Finally, the fiber weight (in grams) after drying is divided by the total fiber length (in 10,000 meters). Ten measurements are taken each time, and the average value is taken.

[0047] The mechanical properties of carbon fiber precursor were measured according to GB / T 14337~2008; the mechanical properties of carbon fiber were measured according to GB / T3362~2017; and the particle size of oil emulsion was determined using a laser particle size analyzer (Malvern, UK, Mastersizer2000).

[0048] The number of fiber pores was determined by cutting the fiber into 100 nm thin slices using low-temperature FIB (Gas-Focused Ion Beam) and observing the colorless, transparent, waist-shaped or elongated pores from the fiber surface to a depth of 100 nm using TEM (Transmission Electron Microscopy). The longer axis was the longer side, and the shorter axis was the shorter side. Then, using a TEM-EDS module, ten lines were drawn along the fiber circumference from the center to the outside, and the Si / C atomic content was scanned. The average Si / C atomic ratio was calculated as the Si / C atomic ratio from the surface protrusions to the grooves, and from the surface grooves to different depths inside the fiber.

[0049] The oil content of the raw yarn is determined according to the following method: A certain amount of raw yarn sample is taken and dried at 105℃ for 2 hours. Its mass is recorded as W1. The sample is placed in a Soxhlet extractor, and several or one of cyclohexane, acetone, and ethanol (or a suitable organic solvent such as a gas) are added. The temperature is raised to 50℃, and extraction is carried out for 4 hours. The sample is then removed, dried at 105℃ for 2 hours, and its mass is recorded as W2. The oil content is calculated according to the following formula: Oil content (wt%) = (W1-W2)×100% / W1.

[0050] Carbon fiber porosity or fibril orientation determination: A straight and neatly arranged bundle of carbon fibers was fixed with tape onto a metal frame with dimensions of 3cm × 2cm × 0.2cm and a central aperture size of 3cm × 2cm. The sample was evenly spread to the same width and measured using a small-angle X-ray scattering (SAXS) device at the Shanghai Synchrotron Radiation Facility (SSRF, BL16B). The distance from the sample to the detector was calibrated using a standard sample (1980mm). Incident X-rays at a wavelength of 0.12398nm were used, and SAXS data were collected using a Mar CCD 165 imaging plate. The obtained data were processed using xPolar (Precision Works NY, Inc., USA) software, and the orientation deviation angle (B) of the fibrils and micropores along the fiber axis was determined. φ Calculated according to the Cauchy-Cauchy formula:

[0051]

[0052] In the formula, s (s=2sinθ / λ) is the scattering vector corresponding to the azimuth scan curve, and B obs B is the angular width of the half-width at half-maximum of the azimuth scan curve. φ The slope is the result of linear fitting of the azimuth scan curve using the formula.

[0053] Number of shutdowns during carbon fiber production: During a six-month continuous production period, the number of times the equipment needs to be shut down for cleaning and maintenance due to a decrease in carbon fiber strength or equipment problems is calculated and evaluated according to the following standards: A: less than 2 times, B: 2-4 times, C: more than 5 times.

[0054] The carbon fiber obtained by adopting the technical solution of the present invention has a good silicon penetration gradient and penetration depth, and the ash content during the carbonization process is significantly less. After six months of continuous production, the tensile strength of the prepared carbon fiber can still reach 5.8 GPa, the modulus can reach 379 GPa, and the elongation can reach 1.5%, achieving good technical results.

[0055] The present invention will be further illustrated below through embodiments. Attached Figure Description

[0056] To more clearly illustrate the technical solution of this invention patent, accompanying drawings have been provided.

[0057] Figure 1 This is a schematic diagram of a single fiber cross-section of the carbon fiber of the present invention.

[0058] Figure 1 In the diagram, 1 represents the raised structure on the carbon fiber surface; 2 represents the grooved structure on the carbon fiber surface; X represents the area from the raised part to the groove on the carbon fiber surface; Y represents the area from the groove on the carbon fiber surface to a depth of 100 nm; and Z represents the area inside the carbon fiber with a depth greater than 100 nm. Detailed Implementation

[0059] The raw materials used in the examples and comparative examples are readily available or prepared according to methods disclosed in the prior art.

[0060]

Example 1

[0061] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0062] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1.2%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0063] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0064] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.2%, and a silicon content of 0.15%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 10%, with the highest Si / C ratio of 0.11% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.5 cN / dtex, 125 cN / dtex, and 12.0%, respectively.

[0065] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0066] The total silicon content in the carbon fiber is 800 ppm. From the surface protrusions to the grooves, the Si / C ratio is 5.8% at some points, 0.5% in the region between the surface grooves and the interior (within 100 nm), and 0.04% in the region larger than 100 nm. The carbon fiber surface contains 10 pores with an average length of 20 nm and an average width of 15 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.74 GPa, a modulus of 370 GPa, and an elongation of 1.52%. After seven months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0067]

Example 2

[0068] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0069] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 3.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 3%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0070] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0071] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.2%, and a silicon content of 0.47%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 19%, with the highest Si / C ratio of 0.14% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 8.1 cN / dtex, 137 cN / dtex, and 11.8%, respectively.

[0072] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0073] The total silicon content in the carbon fiber is 1400 ppm. From the surface protrusions to the grooves, the Si / C ratio is 9% at some points; 0.9% in the region between the surface grooves and the interior (within 100 nm); and 0.05% in the region larger than 100 nm. The carbon fiber surface contains 15 pores with an average length of 42 nm and an average width of 22 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.63 GPa, a modulus of 360 GPa, and an elongation of 1.56%. After six months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0074]

Example 3

[0075] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0076] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.1%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 0.8%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0077] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0078] The precursor fiber has a linear density of 0.85 dtex, an oil content of 0.85%, and a silicon content of 0.09%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 6%, with the highest Si / C ratio of 0.07% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.2 cN / dtex, 119 cN / dtex, and 12.5%, respectively.

[0079] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0080] The total silicon content in the carbon fiber is 620 ppm. From the surface protrusions to the grooves, the Si / C ratio is 4.5% at some points, 0.47% in the region between the surface grooves and the interior (within 100 nm), and 0.03% in the region larger than 100 nm. The carbon fiber surface contains 7 pores with an average length of 15 nm and an average width of 10 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.75 GPa, a modulus of 374 GPa, and an elongation of 1.51%. After 8 months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0081]

Example 4

[0082] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0083] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.1%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.01s, and a fiber bundle width of 30mm.

[0084] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0085] The precursor fiber has a linear density of 0.85 dtex, an oil content of 0.9%, and a silicon content of 0.13%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 9%, with the highest Si / C ratio of 0.1% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.6 cN / dtex, 128 cN / dtex, and 11.2%, respectively.

[0086] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0087] The total silicon content in the carbon fiber is 690 ppm. From the surface protrusions to the grooves, the Si / C ratio is 4.8% at some points; 0.54% in the region between the surface grooves and the interior (within 100 nm); and 0.04% in the region larger than 100 nm. The carbon fiber surface contains 8 pores with an average length of 17 nm and an average width of 13 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.75 GPa, a modulus of 375 GPa, and an elongation of 1.55%. After 8 months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0088]

Example 5

[0089] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0090] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 300nm, a residence time of 0.25s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oil agent with a pH of 7.8, an oil agent concentration of 3%, an oil agent particle size of 300nm, an oil agent silicone content of 0.5%, a residence time of 0.13s, and a fiber bundle width of 25mm.

[0091] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0092] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.8%, and a silicon content of 0.39%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 14%, with the highest Si / C ratio of 0.12% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.4 cN / dtex, 126 cN / dtex, and 11.5%, respectively.

[0093] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0094] The total silicon content in the carbon fiber is 1340 ppm. From the surface protrusions to the grooves, the Si / C ratio is 8% at some points; 0.85% in the region between the surface grooves and the interior (within 100 nm); and 0.04% in the region greater than 100 nm. The carbon fiber surface contains 15 pores with an average length of 35 nm and an average width of 20 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.66 GPa, a modulus of 361 GPa, and an elongation of 1.58%. After six months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0095]

Example 6

[0096] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0097] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.08s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 3%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.05s, and a fiber bundle width of 30mm.

[0098] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0099] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1%, and a silicon content of 0.08%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 5%, with the highest Si / C ratio of 0.05% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.8 cN / dtex, 121 cN / dtex, and 11.8%, respectively.

[0100] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0101] The total silicon content in the carbon fiber is 600 ppm. From the surface protrusions to the grooves, the Si / C ratio is 4.5% at some points, 0.45% in the region between the surface grooves and the interior (up to 100 nm), and 0.03% in the region larger than 100 nm. The carbon fiber surface contains 7 pores with an average length of 15 nm and an average width of 10 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.77 GPa, a modulus of 380 GPa, and an elongation of 1.49%. After 8 months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0102]

Example 7

[0103] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0104] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 14mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oil agent with a pH of 7.8, an oil agent concentration of 1.2%, an oil agent particle size of 300nm, an oil agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 13mm.

[0105] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0106] The precursor fiber has a linear density of 0.85 dtex, an oil content of 0.9%, and a silicon content of 0.1%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 6%, with the highest Si / C ratio of 0.06% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.2 cN / dtex, 127 cN / dtex, and 11.8%, respectively.

[0107] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0108] The total silicon content in the carbon fiber is 650 ppm. From the surface protrusions to the grooves, the Si / C ratio is 4.7% at some points, 0.5% in the region between the surface grooves and the interior (up to 100 nm), and 0.03% in the region larger than 100 nm. The carbon fiber surface contains 10 pores with an average length of 23 nm and an average width of 18 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.68 GPa, a modulus of 364 GPa, and an elongation of 1.55%. After six months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0109]

Example 8

[0110] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0111] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 45mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oil agent with a pH of 7.8, an oil agent concentration of 1.2%, an oil agent particle size of 300nm, an oil agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0112] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0113] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.3%, and a silicon content of 0.14%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 9%, with the highest Si / C ratio of 0.1% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.4 cN / dtex, 128 cN / dtex, and 11.7%, respectively.

[0114] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0115] The total silicon content in the carbon fiber is 690 ppm. From the surface protrusions to the grooves, the Si / C ratio is 4.8% at some points; 0.54% in the region between the surface grooves and the interior (within 100 nm); and 0.04% in the region larger than 100 nm. The carbon fiber surface contains 8 pores with an average length of 17 nm and an average width of 13 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.73 GPa, a modulus of 368 GPa, and an elongation of 1.54%. After seven months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0116]

Example 9

[0117] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0118] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 20mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.06s, and a fiber bundle width of 30mm.

[0119] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0120] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.1%, and a silicon content of 0.12%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 8%, with the highest Si / C ratio of 0.08% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.9 cN / dtex, 136 cN / dtex, and 11.3%, respectively.

[0121] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0122] The total silicon content in the carbon fiber is 670 ppm. From the surface protrusions to the grooves, the Si / C ratio is 4.7% at some points; 0.51% in the region between the surface grooves and the interior (within 100 nm); and 0.04% in the region larger than 100 nm. The carbon fiber surface contains 8 pores with an average length of 16 nm and an average width of 12 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.75 GPa, a modulus of 376 GPa, and an elongation of 1.51%. After 8 months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0123]

Example 10

[0124] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0125] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 100nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oil agent with a pH of 7.8, an oil agent concentration of 1.2%, an oil agent particle size of 200nm, an oil agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0126] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0127] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.4%, and a silicon content of 0.14%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 9%, with the highest Si / C ratio of 0.1% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.7 cN / dtex, 130 cN / dtex, and 11.5%, respectively.

[0128] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0129] The total silicon content in the carbon fiber is 700 ppm. From the surface protrusions to the grooves, the Si / C ratio is 5% at some points; 0.55% in the region between the surface grooves and the interior (within 100 nm); and 0.04% in the region greater than 100 nm. The carbon fiber surface contains 8 pores with an average length of 17 nm and an average width of 13 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.75 GPa, a modulus of 374 GPa, and an elongation of 1.51%. After 8 months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0130]

Example 11

[0131] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0132] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oil agent with a pH of 7.8, an oil agent concentration of 1%, an oil agent particle size of 200nm, an oil agent silicone content of 0.5%, a residence time of 0.04s, and a fiber bundle width of 30mm.

[0133] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0134] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.1%, and a silicon content of 0.07%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 5%, with the highest Si / C ratio of 0.06% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.2 cN / dtex, 120 cN / dtex, and 12.3%, respectively.

[0135] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0136] The total silicon content in the carbon fiber is 550 ppm. From the surface protrusions to the grooves, the Si / C ratio is 4.3% at some points, 0.4% in the region between the surface grooves and the interior (within 100 nm), and 0.02% in the region larger than 100 nm. The carbon fiber surface contains 7 pores with an average length of 15 nm and an average width of 9 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.8 GPa, a modulus of 390 GPa, and an elongation of 1.45%. After 8 months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0137]

Example 12

[0138] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0139] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 0.6%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.88%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0140] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0141] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.3%, and a silicon content of 0.34%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 13%, with the highest Si / C ratio of 0.12% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.5 cN / dtex, 126 cN / dtex, and 11.7%, respectively.

[0142] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0143] The total silicon content in the carbon fiber is 1200 ppm. From the surface protrusions to the grooves, the Si / C ratio is 6.7% at some points; 0.7% in the region between the surface grooves and the interior within 100 nm; and 0.04% in the region larger than 100 nm. The carbon fiber surface contains 14 pores with an average length of 30 nm and an average width of 19 nm. Small-angle X-ray diffraction (SAXD) indicates that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.69 GPa, a modulus of 365 GPa, and an elongation of 1.54%. After six months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0144]

Example 13

[0145] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0146] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.13%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0147] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0148] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.1%, and a silicon content of 0.08%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 7%, with the highest Si / C ratio of 0.07% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.7 cN / dtex, 136 cN / dtex, and 11.3%, respectively.

[0149] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0150] The total silicon content in the carbon fiber is 600 ppm. From the surface protrusions to the grooves, the Si / C ratio is 4.5% at some points, 0.45% in the region between the surface grooves and the interior (within 100 nm), and 0.03% in the region larger than 100 nm. The carbon fiber surface contains 7 pores with an average length of 15 nm and an average width of 10 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.76 GPa, a modulus of 379 GPa, and an elongation of 1.5%. After 8 months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0151]

Example 14

[0152] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation and stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 140% after washing.

[0153] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0154] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0155] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.3%, and a silicon content of 0.4%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 16%, with the highest Si / C ratio of 0.14% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.5 cN / dtex, 134 cN / dtex, and 11.7%, respectively.

[0156] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0157] The total silicon content in the carbon fiber is 1350 ppm. From the surface protrusions to the grooves, the Si / C ratio is 8% at some points; 0.85% in the region between the surface grooves and the interior (within 100 nm); and 0.04% in the region greater than 100 nm. The carbon fiber surface contains 15 pores with an average length of 38 nm and an average width of 20 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.66 GPa, a modulus of 362 GPa, and an elongation of 1.55%. After six months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0158]

Example 15

[0159] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 90% after washing.

[0160] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 100nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1%, an oiling agent particle size of 100nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0161] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0162] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.4%, and a silicon content of 0.16%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 12%, with the highest Si / C ratio of 0.12% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 8.4 cN / dtex, 130 cN / dtex, and 12%, respectively.

[0163] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0164] The total silicon content in the carbon fiber is 900 ppm. From the surface protrusions to the grooves, the Si / C ratio is 6% at some points; 0.63% in the region between the surface grooves and the interior (within 100 nm); and 0.04% in the region greater than 100 nm. The carbon fiber surface contains 12 pores with an average length of 26 nm and an average width of 16 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.7 GPa, a modulus of 377 GPa, and an elongation of 1.52%. After seven months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0165]

Example 16

[0166] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0167] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 8, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 9, an oiling agent concentration of 1%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0168] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0169] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.2%, and a silicon content of 0.14%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 9%, with the highest Si / C ratio of 0.11% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.7 cN / dtex, 135 cN / dtex, and 11.5%, respectively.

[0170] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0171] The total silicon content in the carbon fiber is 700 ppm. From the surface protrusions to the grooves, the Si / C ratio is 5% at some points; 0.55% in the region between the surface grooves and the interior (within 100 nm); and 0.04% in the region greater than 100 nm. The carbon fiber surface contains 8 pores with an average length of 17 nm and an average width of 13 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.75 GPa, a modulus of 375 GPa, and an elongation of 1.51%. After 8 months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0172]

Comparative Example 1

[0173] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0174] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone oil agent with a pH of 7.8, an oil agent concentration of 1.2%, an oil agent particle size of 300nm, an oil agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0175] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0176] The linear density of the precursor fiber is 0.85 dtex, the oil content is 3%, and the silicon content is 0.67%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 34%, with the highest Si / C ratio of 0.5% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 8.1 cN / dtex, 131 cN / dtex, and 11.9%, respectively.

[0177] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0178] The total silicon content in the carbon fiber is 3000 ppm. From the surface protrusions to the grooves, the Si / C ratio is 77% at some points, 10% in the region between the surface grooves and the interior (within 100 nm), and 1% in the region larger than 100 nm. The carbon fiber surface contains 40 pores with an average length of 70 nm and an average width of 45 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.23 GPa, a modulus of 355 GPa, and an elongation of 1.46%. After 2.5 months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0179] [Comparative Example 2]

[0180] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0181] After washing, the fibers first pass through the first oiling tank, which contains water with a pH of 7, an oil concentration of 0%, an oil particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone oil agent with a pH of 7.8, an oil agent concentration of 1.2%, an oil agent particle size of 300nm, an oil agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0182] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0183] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.8%, and a silicon content of 0.55%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 24%, with the highest Si / C ratio of 0.19% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.7 cN / dtex, 131 cN / dtex, and 11.5%, respectively.

[0184] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0185] The total silicon content in the carbon fiber is 2600 ppm. From the surface protrusions to the grooves, the Si / C ratio is 72% at some points; 9.8% in the region between the surface grooves and the interior (within 100 nm); and 1% in the region larger than 100 nm. The carbon fiber surface contains 39 pores with an average length of 66 nm and an average width of 45 nm. Small-angle X-ray diffraction (SAXD) indicates that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.35 GPa, a modulus of 357 GPa, and an elongation of 1.48%. After three months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0186] [Comparative Example 3]

[0187] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0188] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 6, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 8, an oiling agent concentration of 1.2%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0189] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0190] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.8%, and a silicon content of 0.54%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 23%, with the highest Si / C ratio of 0.25% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.7 cN / dtex, 128 cN / dtex, and 11.3%, respectively.

[0191] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0192] The total silicon content in the carbon fiber is 2800 ppm. From the surface protrusions to the grooves, the Si / C ratio is 80% at some points, 13% in the region between the surface grooves and the interior (within 100 nm), and 1.5% in the region larger than 100 nm. The carbon fiber surface contains 50 pores with an average length of 77 nm and an average width of 52 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.05 GPa, a modulus of 361 GPa, and an elongation of 1.39%. After three months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0193] [Comparative Example 4]

[0194] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0195] After washing, the fibers first pass through the first oiling tank, which contains anionic silicone-free oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains cationic silicone oil agent with a pH of 7.8, an oil agent concentration of 1.2%, an oil agent particle size of 300nm, an oil agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0196] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0197] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.9%, and a silicon content of 0.58%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 28%, with the highest Si / C ratio of 0.27% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.7 cN / dtex, 129 cN / dtex, and 11.3%, respectively.

[0198] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0199] The total silicon content in the carbon fiber is 2900 ppm. From the surface protrusions to the grooves, the Si / C ratio is 82% at some points; 15% in the region between the surface grooves and the interior (within 100 nm); and 2% in the region larger than 100 nm. The carbon fiber surface contains 56 pores with an average length of 80 nm and an average width of 60 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5 GPa, a modulus of 358 GPa, and an elongation of 1.37%. After three months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0200] [Comparative Example 5]

[0201] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0202] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which also contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.2%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0203] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0204] The linear density of the precursor fiber is 0.85 dtex, the oil content is 2%, and the silicon content is 0%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 0%, with the highest Si / C ratio of 0% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.5 cN / dtex, 128 cN / dtex, and 11.3%, respectively.

[0205] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0206] The total silicon content in the carbon fiber is 0 ppm. From the surface protrusions to the grooves, the Si / C ratio is 0% at points. The Si / C ratio is also 0% in the region between the surface grooves and the interior (within 100 nm), and 0% in regions larger than 100 nm. The carbon fiber surface contains 64 pores with an average length of 89 nm and an average width of 71 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 4.6 GPa, a modulus of 340 GPa, and an elongation of 1.35%. After seven months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0207] [Comparative Example 6]

[0208] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0209] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 2%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0210] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0211] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.6%, and a silicon content of 0.52%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 22%, with the highest Si / C ratio of 0.19% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.7 cN / dtex, 135 cN / dtex, and 11.3%, respectively.

[0212] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0213] The total silicon content in the carbon fiber is 1600 ppm. From the surface protrusions to the grooves, the Si / C ratio is 20% at some points, 4% in the region between the surface grooves and the interior (within 100 nm), and 0.09% in the region larger than 100 nm. The carbon fiber surface contains 36 pores with an average length of 61 nm and an average width of 40 nm. Small-angle X-ray diffraction (SAXD) indicates that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.36 GPa, a modulus of 361 GPa, and an elongation of 1.43%. After four months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0214] [Comparative Example 7]

[0215] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0216] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 3.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 3.8%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0217] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0218] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.7%, and a silicon content of 0.54%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 24%, with the highest Si / C ratio of 0.22% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.7 cN / dtex, 136 cN / dtex, and 11.3%, respectively.

[0219] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0220] The total silicon content in the carbon fiber is 2000 ppm. From the surface protrusions to the grooves, the Si / C ratio is 45% at some points, 8% in the region between the surface grooves and the interior (within 100 nm), and 1% in the region larger than 100 nm. The carbon fiber surface contains 38 pores with an average length of 65 nm and an average width of 44 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.3 GPa, a modulus of 354 GPa, and an elongation of 1.47%. After three months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0221] [Comparative Example 8]

[0222] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0223] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 300nm, a residence time of 0.08s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oil agent with a pH of 7.8, an oil agent concentration of 1.2%, an oil agent particle size of 300nm, an oil agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0224] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0225] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.6%, and a silicon content of 0.52%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 23%, with the highest Si / C ratio of 0.2% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.7 cN / dtex, 132 cN / dtex, and 11.1%, respectively.

[0226] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0227] The total silicon content in the carbon fiber is 1600 ppm. From the surface protrusions to the grooves, the Si / C ratio is 22% at some points; 4% in the region between the surface grooves and the interior (within 100 nm); and 0.08% in the region larger than 100 nm. The carbon fiber surface contains 35 pores with an average length of 60 nm and an average width of 41 nm. Small-angle X-ray diffraction (SAXD) indicates that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.4 GPa, a modulus of 364 GPa, and an elongation of 1.45%. After four months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0228] [Comparative Example 9]

[0229] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0230] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 300nm, a residence time of 0.25s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oil agent with a pH of 7.8, an oil agent concentration of 1.2%, an oil agent particle size of 300nm, an oil agent silicone content of 0.5%, a residence time of 0.3s, and a fiber bundle width of 30mm.

[0231] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0232] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.7%, and a silicon content of 0.55%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 26%, with the highest Si / C ratio of 0.25% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.7 cN / dtex, 132 cN / dtex, and 11.5%, respectively.

[0233] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0234] The total silicon content in the carbon fiber is 2100 ppm. From the surface protrusions to the grooves, the Si / C ratio is 48% at some points; 9% in the region between the surface grooves and the interior within 100 nm; and 1% in the region larger than 100 nm. The carbon fiber surface contains 39 pores with an average length of 66 nm and an average width of 44 nm. Small-angle X-ray diffraction (SAXD) indicates that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.28 GPa, a modulus of 360 GPa, and an elongation of 1.41%. After three months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0235] [Comparative Example 10]

[0236] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0237] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1.2%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.02s, and a fiber bundle width of 30mm.

[0238] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0239] The linear density of the precursor fiber is 0.85 dtex, the oil content is 1%, and the silicon content is 0.07%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 4%, with the highest Si / C ratio of 0.05% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.5 cN / dtex, 130 cN / dtex, and 11.4%, respectively.

[0240] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0241] The total silicon content in the carbon fiber is 900 ppm. From the surface protrusions to the grooves, the Si / C ratio is 0.7% at some points; 0.08% in the region between the surface grooves and the interior (within 100 nm); and 0.02% in the region larger than 100 nm. The carbon fiber surface contains 60 pores with an average length of 87 nm and an average width of 69 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 4.9 GPa, a modulus of 366 GPa, and an elongation of 1.31%. After seven months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0242] [Comparative Example 11]

[0243] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0244] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 800nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oil agent with a pH of 7.8, an oil agent concentration of 1.2%, an oil agent particle size of 300nm, an oil agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0245] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0246] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.6%, and a silicon content of 0.55%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 28%, with the highest Si / C ratio of 0.16% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.5 cN / dtex, 128 cN / dtex, and 11.3%, respectively.

[0247] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0248] The total silicon content in the carbon fiber is 1600 ppm. From the surface protrusions to the grooves, the Si / C ratio is 35% at some points, 3% in the region between the surface grooves and the interior (within 100 nm), and 0.08% in the region larger than 100 nm. The carbon fiber surface contains 35 pores with an average length of 60 nm and an average width of 40 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 4.8 GPa, a modulus of 350 GPa, and an elongation of 1.3%. After four months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0249]

Comparative Example 12

[0250] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0251] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oil agent with a pH of 7.2, an oil agent concentration of 1.5%, an oil agent particle size of 40nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oil agent with a pH of 7.8, an oil agent concentration of 1.2%, an oil agent particle size of 40nm, an oil agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0252] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0253] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.7%, and a silicon content of 0.63%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 34%, with the highest Si / C ratio of 0.28% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.8 cN / dtex, 136 cN / dtex, and 11.3%, respectively.

[0254] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0255] The total silicon content in the carbon fiber is 2000 ppm. From the surface protrusions to the grooves, the Si / C ratio is 50% at some points, 17% in the region between the surface grooves and the interior (within 100 nm), and 1.3% in the region larger than 100 nm. The carbon fiber surface contains 48 pores with an average length of 69 nm and an average width of 50 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.1 GPa, a modulus of 351 GPa, and an elongation of 1.4%. After three months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0256] [Comparative Example 13]

[0257] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0258] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1.2%, an oiling agent particle size of 300nm, an oiling agent silicone content of 1%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0259] The material then undergoes a four-stage drying and densification process at temperatures of 90℃, 100℃, 115℃, and 130℃, followed by steam stretching at a stretch ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0260] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2.7%, and a silicon content of 0.16%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 12%, with the highest Si / C ratio of 0.12% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.6 cN / dtex, 130 cN / dtex, and 11.5%, respectively.

[0261] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0262] The total silicon content in the carbon fiber is 1750 ppm. From the surface protrusions to the grooves, the Si / C ratio is 30% at some points, 2.8% in the region between the surface grooves and the interior (within 100 nm), and 0.07% in the region larger than 100 nm. The carbon fiber surface contains 36 pores with an average length of 64 nm and an average width of 30 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.35 GPa, a modulus of 356 GPa, and an elongation of 1.47%. After three months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0263]

Comparative Example 14

[0264] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0265] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. They then undergo a four-stage drying and densification treatment at temperatures of 90℃, 100℃, 115℃, and 130℃, respectively. Finally, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1.2%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0266] Then, it undergoes four stages of drying and densification treatment at temperatures of 90℃, 100℃, 115℃ and 130℃, followed by steam stretching with a stretching ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0267] The precursor fiber has a linear density of 0.85 dtex, an oil content of 2%, and a silicon content of 0.4%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 24%, with the highest Si / C ratio of 0.05% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.6 cN / dtex, 132 cN / dtex, and 11.5%, respectively.

[0268] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0269] The total silicon content in the carbon fiber is 1300 ppm. From the surface protrusions to the grooves, the Si / C ratio is 8% at some points; 0.8% in the region between the surface grooves and the interior (within 100 nm); and 0.05% in the region larger than 100 nm. The carbon fiber surface contains 43 pores with an average length of 67 nm and an average width of 41 nm. Small-angle X-ray diffraction (SAXD) indicates that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 5.16 GPa, a modulus of 359 GPa, and an elongation of 1.42%. After six months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0270] [Comparative Example 15]

[0271] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 110% after washing.

[0272] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 14mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1.2%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 8mm.

[0273] Then, it undergoes four stages of drying and densification treatment at temperatures of 90℃, 100℃, 115℃ and 130℃, followed by steam stretching with a stretching ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0274] The precursor fiber has a linear density of 0.85 dtex, an oil content of 1.5%, and a silicon content of 0.34%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 19%, with the highest Si / C ratio of 0.04% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.3 cN / dtex, 120 cN / dtex, and 12.5%, respectively.

[0275] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0276] The total silicon content in the carbon fiber is 1000 ppm. From the surface protrusions to the grooves, the Si / C ratio is 5% at some points; 0.6% in the region between the surface grooves and the interior within 100 nm; and 0.04% in the region larger than 100 nm. The carbon fiber surface contains 53 pores with an average length of 81 nm and an average width of 66 nm. Small-angle X-ray diffraction (SAXD) shows that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 4.7 GPa, a modulus of 349 GPa, and an elongation of 1.29%. After five months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0277] [Comparative Example 16]

[0278] 1. Preparation of low-ash, high-performance polyacrylonitrile carbon fiber precursor: A wet spinning method was adopted. The spinning solution was prepared by copolymerizing acrylonitrile and itaconic acid in dimethyl sulfoxide, with an intrinsic viscosity of 3.5 dL / g and a solid content of 18%. The spinning solution was precisely metered by a metering pump, filtered, and then extruded through a spinneret with 6000 holes and a pore size of 60 μm. It then entered the first coagulation bath, which was a dimethyl sulfoxide aqueous solution, for coagulation at 28℃ and a concentration of 5%. The fiber is initially 1.5% thick, then undergoes three stages of coagulation stretching at temperatures of 30℃, 40℃, and 50℃, with stretch ratios of 1.0, 1.1, and 1.2, respectively; followed by four stages of hot water stretching at temperatures of 95℃, 96℃, 97℃, and 99℃, with stretch ratios of 1.35, 1.50, 1.70, and 2.00, respectively; and finally, a six-stage washing process at temperatures of 70℃, 70℃, 80℃, 80℃, 90℃, and 90℃, resulting in a fiber swelling degree of 160% after washing.

[0279] After washing, the fibers first pass through the first oiling tank, which contains a non-ionic silicone-free oiling agent with a pH of 7.2, an oiling agent concentration of 1.5%, an oiling agent particle size of 300nm, a residence time of 0.15s, and a fiber bundle width of 30mm. Then, they pass through the second oiling tank, which contains a non-ionic silicone-containing oiling agent with a pH of 7.8, an oiling agent concentration of 1.2%, an oiling agent particle size of 300nm, an oiling agent silicone content of 0.5%, a residence time of 0.1s, and a fiber bundle width of 30mm.

[0280] Then, it undergoes four stages of drying and densification treatment at temperatures of 90℃, 100℃, 115℃ and 130℃, followed by steam stretching with a stretching ratio of 3.0 times and a steam pressure of 0.35MPa. Finally, it undergoes heat setting and winding to obtain high-performance polyacrylonitrile carbon fiber precursor.

[0281] The precursor fiber has a linear density of 0.85 dtex, an oil content of 3.2%, and a silicon content of 0.7%. In the region from the fiber surface grooves at a depth of 0–2 μm, the Si / C ratio calculated by TEM-EDS shows a point of 43%, with the highest Si / C ratio of 0.62% at a depth of 2 μm from the fiber surface. The tensile strength, modulus, and elongation are 7.2 cN / dtex, 120 cN / dtex, and 12.4%, respectively.

[0282] 2. Preparation of low-ash high-performance carbon fiber: The precursor fiber obtained in step 1 is pre-oxidized at 180-260℃ with a total pre-oxidation draw ratio of 0.95 to obtain pre-oxidized fiber; then, it is carbonized at low temperature of 300-750℃ and high temperature of 800-1500℃ with a draw ratio of 0.96; then, it is graphitized at 2800℃; finally, it undergoes surface treatment, water washing, sizing, drying at 120℃ and winding to obtain high-strength, high-modulus and high-toughness carbon fiber.

[0283] The total silicon content in the carbon fiber is 3100 ppm. From the surface protrusions to the grooves, the Si / C ratio is 71% at some points; 16% in the region between the surface grooves and the interior (within 100 nm); and 3.7% in the region larger than 100 nm. The carbon fiber surface contains 68 pores with an average length of 83 nm and an average width of 75 nm. Small-angle X-ray diffraction (SAXD) indicates that the pore orientation deviation along the fiber axis is 2°. The carbon fiber has a tensile strength of 4.87 GPa, a modulus of 364 GPa, and an elongation of 1.34%. After two months of continuous production, the carbon fiber strength began to decline, necessitating a shutdown to clean the ash from the primary equipment.

[0284] Table 1

[0285]

[0286] Table 2

[0287]

[0288] Table 3

[0289]

[0290] Table 4

[0291]

Claims

1. A polyacrylonitrile carbon fiber, having a grooved structure on its surface; characterized in that... The carbon fiber has a Si / C ratio of 1% to 10% from the surface protrusions to the grooves. The Si / C ratio in the region between the surface grooves and the interior 100nm is 0.1% to 1%, and the Si / C ratio in the region greater than 100nm is no higher than 0.05%.

2. The polyacrylonitrile carbon fiber according to claim 1, characterized in that... The polyacrylonitrile carbon fiber is obtained from polyacrylonitrile precursor fibers produced by wet spinning.

3. The polyacrylonitrile carbon fiber according to claim 1, characterized in that... The total silicon content in the carbon fiber is 500~1500ppm, and the lowest relative Si content from the protrusion to the groove area on the fiber surface is not less than 10 times the lowest Si content in the area between the surface groove and the interior 100nm.

4. The polyacrylonitrile carbon fiber according to claim 1, characterized in that... Observations using gallium focused ion beam cutting and transmission electron microscopy revealed that the number of pores in a single carbon fiber from the fiber surface to a depth of 100 nm was less than 20; the average length of the pores was 10–50 nm, and the average width was 5–25 nm.

5. The polyacrylonitrile carbon fiber according to claim 4, characterized in that... Observations using gallium focused ion beam cutting and transmission electron microscopy revealed that the number of pores in a single carbon fiber was less than 10, extending from the fiber surface to a depth of 100 nm.

6. The polyacrylonitrile carbon fiber according to claim 4 or 5, characterized in that... The orientation deviation angle of the pores along the fiber axis obtained by small-angle X-ray diffraction is less than 4º.

7. A method for manufacturing polyacrylonitrile carbon fiber according to any one of claims 1 to 6, comprising the step of carbonizing polyacrylonitrile precursor fiber to obtain the polyacrylonitrile carbon fiber; characterized in that... The polyacrylonitrile precursor fiber is produced by wet spinning, which includes two consecutive oiling processes without a drying and densification stage in between. The first oiling tank contains no silicone oil and the oil concentration is 0.1% to 5.0%. The second oiling tank contains silicone oil and the oil concentration is 0.1% to 5.0%. The residence time of the second oiling is shorter than that of the first oiling.

8. The method for manufacturing polyacrylonitrile carbon fiber according to claim 7, characterized in that... The average particle size of the silicone-free agent and the silicone-containing agent are each independently 50nm~500nm, and the silicone content of the silicone-containing agent used in the second oil bath is 0.1%~0.9%.

9. The method for manufacturing polyacrylonitrile carbon fiber according to claim 7, characterized in that... The pH difference between the silicone-free agent and the silicone-containing agent shall not be greater than 1; the ionic polarities of the surfactants in the silicone-free agent and the silicone-containing agent shall not be opposite.

10. The method for manufacturing polyacrylonitrile carbon fiber according to claim 9, characterized in that... The silicone-containing oil agent is a nonionic surfactant oil agent.

11. The method for manufacturing polyacrylonitrile carbon fiber according to claim 7, characterized in that... Before oiling, the swelling degree of the polyacrylonitrile precursor fiber after washing with water is 80~150%.

12. The method for manufacturing polyacrylonitrile carbon fiber according to claim 7, characterized in that... The manufacturing method specifically includes the steps of wet solidification of polyacrylonitrile raw solution, solidification stretching, hot water stretching, water washing, oiling, drying and densification, steam stretching, and steam heat setting to obtain the polyacrylonitrile precursor fiber.

13. The method for manufacturing polyacrylonitrile carbon fiber according to claim 7, characterized in that... The single filament fineness of the polyacrylonitrile precursor fiber is 0.7~1.0 dtex.

14. The method for manufacturing polyacrylonitrile carbon fiber according to claim 7, characterized in that... The polyacrylonitrile precursor fiber is subjected to heat stabilization treatment and carbonization to obtain the polyacrylonitrile carbon fiber.

15. The method for manufacturing polyacrylonitrile carbon fiber according to claim 14, characterized in that... The heat stabilization treatment is carried out in an air atmosphere at a temperature of 190~270℃, with a total draw ratio not exceeding 5%; the carbonization step includes low-temperature carbonization treatment in an inert atmosphere at a temperature of 350~700℃ with a draw ratio of 0~4% and high-temperature carbonization treatment in an inert atmosphere at a temperature of 1300~1400℃ with a draw ratio of -4~-2% of the total draw ratio.

16. Use of a polyacrylonitrile carbon fiber according to any one of claims 1 to 6 or a polyacrylonitrile carbon fiber according to any one of claims 7 to 15, obtained by the manufacturing method of the polyacrylonitrile carbon fiber.

17. A polyacrylonitrile precursor fiber, characterized in that... In the region with a depth of 0~2μm from the fiber surface, the Si / C ratio calculated by TEM-EDS ranges from 1.0% to 20%, and the Si / C ratio at a depth of 2μm from the fiber surface is no higher than 0.15%.

18. The polyacrylonitrile carbon fiber precursor according to claim 17, characterized in that... The raw fiber has an oil content of 0.8% to 2.5% and a silicon content of 0.01% to 0.5%.

19. The polyacrylonitrile carbon fiber precursor according to claim 18, characterized in that... The oil content of the raw silk is 0.9% to 2.0%.

20. The polyacrylonitrile carbon fiber precursor according to claim 18, characterized in that... The single filament fineness of the polyacrylonitrile precursor fiber is 0.7~1.0 dtex.

21. A method for preparing polyacrylonitrile precursor fiber according to any one of claims 17-20, comprising wet spinning, including two consecutive oiling processes with no intermediate drying and densification stage, wherein the first oiling tank contains a silicone-free oil agent with an oil concentration of 0.1% to 5.0%; and the second oiling tank contains a silicone-containing oil agent with an oil concentration of 0.1% to 5.0%, wherein the residence time of the second oiling is less than that of the first oiling.

22. The method for preparing polyacrylonitrile precursor fiber according to claim 21, characterized in that... The average particle size of the silicone-free agent and the silicone-containing agent are each independently 50nm~500nm, and the silicone-containing agent used in the second oil bath has a silicone content of 0.1%~0.9%; and / or, The pH difference between the silicone-free agent and the silicone-containing agent is not greater than 1; the ionic polarities of the surfactants in the silicone-free agent and the silicone-containing agent cannot be opposite; and / or, Before oiling, the polyacrylonitrile precursor fibers, after being washed with water, have a swelling degree of 80-150%; and / or, The preparation method specifically includes the steps of wet solidification of polyacrylonitrile stock solution, solidification stretching, hot water stretching, water washing, oiling, drying and densification, steam stretching, and steam heat setting to obtain the polyacrylonitrile precursor fiber.

23. The method for preparing polyacrylonitrile precursor fiber according to claim 22, characterized in that... The silicone-containing oil agent is a nonionic surfactant oil agent.

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