Polyacrylonitrile carbon fiber and preparation method thereof

Abstract

The invention relates to the technical field of carbon fibers, in particular to polyacrylonitrile carbon fibers and a preparation method thereof. The preparation method comprises the following steps: (1) preparing a polyacrylonitrile precursor of which the K number is not greater than 120; (2) sequentially carrying out pre-oxidation and carbonization on the polyacrylonitrile precursor obtained in the step (1); wherein in the pre-oxidation process, the ratio of the width of the polyacrylonitrile precursor to the K number of the precursor is b, and b is 0.1-2.0 mm. By combining the K number of the polyacrylonitrile precursor with the pre-oxidation process parameters, the polyacrylonitrile carbon fiber with small total number of broken ends and broken end aggregates, low diameter CV value, high tensile strength and low tensile strength CV value is prepared.

Description

Technical Field

[0001] This invention relates to the field of carbon fiber technology, specifically to a polyacrylonitrile carbon fiber and its preparation method. Background Technology

[0002] Carbon fiber is an inorganic polymer fiber with a carbon content of over 92%, composed of polymer precursors or allotropic carbon units. It possesses advantages such as high specific strength, high specific modulus, low density, high temperature resistance, ablation resistance, corrosion resistance, high electrical and thermal conductivity, low thermal expansion, self-lubrication, and good biocompatibility. It is processed into composite materials for downstream applications. Carbon fibers are classified into large and small tows, with those of 48K or greater being considered large-tow carbon fibers. Due to their lower production and downstream application costs, large-tow carbon fibers are mainly used in industrial fields such as wind power, pressure vessels, and civil engineering. Especially with the further expansion of wind power generation into the ocean and the increase in blade length, the demand for large-tow carbon fibers is expected to grow at an annual rate exceeding 16% in the coming years.

[0003] The technological paths chosen by Japan and the United States for large-tow and small-tow carbon fiber materials differ somewhat. Japanese companies have a significant advantage in producing small-tow carbon fiber, while American companies focus on developing large-tow fibers. Currently, globally, there are no more than 15 carbon fiber manufacturers capable of large-scale mass production.

[0004] With the increasing application of large-tow carbon fiber, demand exceeds supply, leading global manufacturers are expanding their production capacity. Toray Industries of Japan, through its acquisition of Zoltek, will reach a capacity of 25,000 tons / year by 2021. SGL of Germany, building on its existing 14,000 tons / year capacity, acquired FISIPE Acrylic Fibers of Portugal, ensuring a low-cost supply of large-tow carbon fiber precursor for its European carbon fiber company. Formosa Plastics of Taiwan closed all its acrylic fiber production lines in 2017 to expand its large-tow carbon fiber production. Mitsubishi of Japan, while reducing costs and prices to penetrate the general-purpose large-tow carbon fiber market, is leveraging its precursor fiber advantages to target the high-performance large-tow application market.

[0005] Polyacrylonitrile (PAN)-based carbon fiber is a synthetic inorganic fiber produced from polyacrylonitrile (PAN) fibers through pre-oxidation and carbonization processes. The mainstream practice in China is to prepare PAN fibers using wet spinning. The preparation of PAN precursor fibers typically involves using oil-based solvents such as dimethylacetamide and dimethyl sulfoxide (DMSO), or inorganic solvents such as sodium thiocyanate and zinc chloride, to create the spinning solution. DMSO is widely used due to its relatively low toxicity and relatively simple and mature processing methods. The high-viscosity spinning solution undergoes a multi-stage coagulation and forming process, followed by hot water drawing, washing, oiling and drying densification, steam drawing, and relaxation heat setting to obtain PAN fibers. The preparation process of PAN precursor fibers is one of the key technologies in carbon fiber production. The overall performance of carbon fibers is closely related to the precursor fiber preparation process, especially the control of the precursor fiber process. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of existing polyacrylonitrile carbon fiber, such as a large number of broken ends and broken end assemblies, high diameter CV value, low tensile strength, and high tensile strength CV value. This invention provides a method for preparing polyacrylonitrile carbon fiber, which produces polyacrylonitrile carbon fiber with fewer broken ends and broken end assemblies, lower diameter CV value, higher tensile strength, and lower tensile strength CV value.

[0007] To achieve the above objectives, the first aspect of the present invention provides a method for preparing polyacrylonitrile carbon fiber, the method comprising the following steps: (1) preparing polyacrylonitrile precursor fiber with a K number not greater than 120; (2) subjecting the polyacrylonitrile precursor fiber of step (1) to pre-oxidation and carbonization in sequence; wherein, during the pre-oxidation process, the ratio of the width of the polyacrylonitrile precursor fiber to the K number of the precursor fiber is b, and b is 0.1-2.0 mm.

[0008] The second aspect of the present invention provides a polyacrylonitrile carbon fiber prepared by the preparation method described in the first aspect.

[0009] Through the above technical solution, the present invention has the following advantages:

[0010] This invention combines the K number of polyacrylonitrile precursor fibers with pre-oxidation process parameters to prepare polyacrylonitrile carbon fibers with fewer broken ends and broken end aggregates, lower diameter CV value, higher tensile strength, and lower tensile strength CV value.

[0011] The polyacrylonitrile carbon fiber prepared by the method of the present invention has a diameter CV value of less than 5%, a tensile strength of 3-6 GPa, and a tensile strength CV value of 2-12%. Attached Figure Description

[0012] Figure 1This is a schematic diagram of the solidification device used in a preferred embodiment of the present invention;

[0013] Explanation of reference numerals in the attached figures

[0014] 1 is an annular spinneret; 2 is a coagulation liquid inlet; 3 is a coagulation liquid outlet; 4 is a gooseneck tube; 5 is a pipeline fixing clamp; 6 is the main body of the coagulation bath. Detailed Implementation

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0016] This invention provides a method for preparing polyacrylonitrile carbon fiber, the method comprising the following steps:

[0017] (1) Preparation of polyacrylonitrile precursor fibers with a K number not greater than 120; (2) Pre-oxidation and carbonization of the polyacrylonitrile precursor fibers in step (1) in sequence; wherein, during the pre-oxidation process, the ratio of the width of the polyacrylonitrile precursor fibers to the K number of the precursor fibers is b, and b is 0.1-2.0 mm.

[0018] This invention combines the K number of polyacrylonitrile precursor fibers with pre-oxidation process parameters to prepare polyacrylonitrile carbon fibers with fewer broken ends and broken end aggregates, lower diameter CV value, higher tensile strength, and lower tensile strength CV value.

[0019] In this invention, the width of the polyacrylonitrile precursor fiber is controlled by a yarn spreading device.

[0020] The yarn spreading device consists of n vertically spaced, horizontally arranged, two rows of drive rollers, with adjacent drive rollers forming an equilateral triangle layout. The diameter of each drive roller is R. r The roller spacing is a, the number of rollers is n, and the width of the polyacrylonitrile precursor fiber is mainly determined by R. r It is determined by a and n.

[0021] According to a preferred embodiment of the present invention, the K number of the polyacrylonitrile precursor fiber can achieve the purpose of the present invention as long as it is within the aforementioned range, for example, 1, 6, 12, 18, 24, 28, 32, 36, 40, 50, 60, 70, 80, 90, 100, 110 and 120, preferably 24-120, more preferably 24-96, and even more preferably 24-48.

[0022] According to a preferred embodiment of the present invention, the object of the present invention can be achieved as long as the value of b is within the aforementioned range, for example, 0.2mm, 0.3mm, 0.4mm, 0.8mm, 1mm, 1.2mm, 1.6mm, 1.8mm and 2mm, preferably 0.3-1.8mm, more preferably 0.5-1.2mm.

[0023] According to a preferred embodiment of the present invention, the diameter CV value of the polyacrylonitrile precursor fiber is 1-8%, for example, it can be 1.5%, 2.5%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, and 7.5%, preferably 2-6%, and more preferably 3-5%. By adopting the aforementioned preferred embodiment, it is possible to further reduce the diameter CV value of the carbon fiber, increase its tensile strength, and reduce its tensile strength CV value.

[0024] According to a preferred embodiment of the present invention, the linear density (CV) value of the polyacrylonitrile precursor fiber is 0.05-5%, for example, it can be 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, and 4.5%, preferably 0.1-4%, and more preferably 0.2-2%. By adopting the aforementioned preferred embodiment, it is possible to further reduce the diameter CV value of the carbon fiber, increase its tensile strength, and reduce its tensile strength CV value.

[0025] According to a preferred embodiment of the present invention, the fineness of the polyacrylonitrile precursor fiber is 0.5-2.0 dtex.

[0026] According to a preferred embodiment of the present invention, the single filament breaking strength of the polyacrylonitrile precursor is 5.5-8.0 cN / dtex.

[0027] According to a preferred embodiment of the present invention, the strength CV value of the polyacrylonitrile precursor fiber is 6-13%.

[0028] According to a preferred embodiment of the present invention, the breaking elongation of the polyacrylonitrile precursor is 11-14%.

[0029] According to a preferred embodiment of the present invention, the elongation at break (CV) of the polyacrylonitrile precursor fiber is 8-15%.

[0030] According to a preferred embodiment of the present invention, the initial modulus of the polyacrylonitrile precursor fiber is 100-145 cN / dtex.

[0031] According to a preferred embodiment of the present invention, the initial modulus CV value of the polyacrylonitrile precursor is 6-13%.

[0032] In this invention, polyacrylonitrile precursor fibers possessing the above-mentioned performance characteristics can all be used in this invention.

[0033] According to a preferred embodiment of the present invention, step (1) includes the following steps: (a) preparation of spinning solution; (b) the spinning solution of step (a) is subjected to spinning and coagulation to obtain nascent fibers, wherein the coagulation method includes: the spinning solution obtained by spinning is aggregated in the coagulation liquid to form nascent fibers; wherein the concentration difference between the coagulation liquid in the central region of the nascent fibers and the concentration difference between the coagulation liquid in the edge region of the nascent fibers is 0.2-2 wt.%, the central region of the nascent fibers refers to a cylindrical region with a height ≤ 4 cm formed within (0-0.15)r of the central axis of the nascent fibers; the edge region of the nascent fibers refers to a ring-like region with a height ≤ 4 cm formed within (0.85-1.1)r of the central axis of the nascent fibers; r is the radius of the circular cross section formed radially on the nascent fibers; (c) the nascent fibers obtained in step (b) are subjected to hot water drawing, washing, oiling, drying and densification, saturated steam drawing, steam heat setting and winding in sequence. By adopting the aforementioned preferred scheme, it is possible to further reduce the diameter CV value of carbon fibers, increase their tensile strength, and reduce their tensile strength CV value.

[0034] In this invention, the central axis of the nascent fiber is the axial segment. One of the base surfaces of the quasi-cylindrical and quasi-annular structures coincides with the spinneret. Height refers to the distance between the two base surfaces, i.e., the distance between the surface of the spinneret and the other base surface.

[0035] In this invention, there are no special requirements for the preparation method of the spinning solution in step (a), which can be a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, step (a) includes: mixing a mixture of acrylonitrile, comonomer, initiator and solvent, reacting under an inert atmosphere, and obtaining the spinning solution after demonomerization, defoaming and solid-liquid separation.

[0036] According to a preferred embodiment of the present invention, the mass percentage of acrylonitrile and comonomer is 97-99.9:0.1-3, for example, the mass ratio can be 97.5:2.5, 98:2, 98.5:1.5, 99:1, and 99.5:0.05. By adopting the aforementioned preferred embodiment, it is possible to further reduce the diameter CV value of the carbon fiber, increase its tensile strength, and reduce its tensile strength CV value.

[0037] In this invention, the mass of the initiator is a conventional choice in the art, as illustrated below, but not limited to the scope of the invention. According to a preferred embodiment of the invention, the initiator is 0.1-1 wt.% of the total mass of acrylonitrile and comonomer.

[0038] In this invention, the mass of the solvent is a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mass ratio of the solvent to the total mass of acrylonitrile and comonomer is 72-82:18-28.

[0039] In this invention, the type of comonomer can be a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the comonomer is a compound containing an alkenyl group, preferably itaconic acid.

[0040] In this invention, as long as the purpose of this invention can be achieved, there are no special requirements for the type of solvent. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the solvent is selected from at least one of dimethyl sulfoxide, N,N-dimethylformamide, N,N-dimethylacetyl, sodium thiocyanate aqueous solution, and zinc chloride aqueous solution, preferably dimethyl sulfoxide.

[0041] In this invention, the initiator can be any conventional choice in the art as long as it can achieve the purpose of this invention. The following is an illustrative description, but it does not limit the scope of this invention. This invention uses azobisisobutyronitrile as an example to illustrate the advantages of the technical solution of this invention.

[0042] In this invention, as long as the reaction solution is obtained, the reaction conditions can be conventional methods in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the reaction conditions include: a reaction temperature of 50-70°C, and a reaction time that is adjusted accordingly with changes in the reaction temperature, for example, a reaction time of 15-25 hours.

[0043] According to a preferred embodiment of the present invention, step (b) is performed in a device, the structural schematic diagram of which is shown below. Figure 1 As shown, the device includes: a coagulation bath body, a coagulation liquid outlet and a coagulation liquid inlet communicating with the coagulation bath body, a spinneret disposed within the coagulation bath body, and a spinning solution feeder communicating with the spinneret; the closest distance between the center of the outlet cross-section of the coagulation liquid inlet, or the plane formed by the center of the cross-section, or the line segment formed by the center of the cross-section, and the surface of the spinneret is 1 / 5 to 1 / 2 of the diameter of the spinneret. By adopting the aforementioned preferred embodiment, the diameter CV value of carbon fibers can be further reduced, their tensile strength can be increased, and their tensile strength CV value can be reduced.

[0044] According to a preferred embodiment of the present invention, the spinneret is an annular spinneret with an outer ring region having through holes and an inner ring region without through holes.

[0045] According to a preferred embodiment of the present invention, the outlet of the coagulation liquid inlet is connected to the inlet of the coagulation liquid outlet, and a driving device is provided on the connecting pipeline. By adopting the aforementioned preferred solution, the diameter CV value of carbon fiber can be further reduced, its tensile strength can be increased, and its tensile strength CV value can be reduced.

[0046] According to a preferred embodiment of the present invention, in step (b), the concentration of the coagulation solution in the central region of the nascent fiber is 52-82 wt.%, for example, 53 wt%, 56 wt%, 58 wt%, 62 wt%, 65 wt%, 68 wt%, 70 wt%, 73 wt%, 78 wt%, and 80 wt%, preferably 60-75 wt.%. By adopting the aforementioned preferred embodiment, it is possible to further reduce the diameter CV value of the carbon fiber, increase its tensile strength, and reduce its tensile strength CV value.

[0047] According to a preferred embodiment of the present invention, in step (b), the concentration of the coagulation solution in the edge region of the nascent fiber is 52-80 wt.%, for example, it can be 54 wt%, 55 wt%, 56 wt%, 57 wt%, 58 wt%, 59 wt%, 60 wt%, 63 wt%, 66 wt%, 68 wt%, 70 wt%, 73 wt%, and 78 wt%, preferably 58-74.8 wt.%. By adopting the aforementioned preferred embodiment, it is possible to further reduce the diameter CV value of the carbon fiber, increase its tensile strength, and reduce its tensile strength CV value.

[0048] According to a preferred embodiment of the present invention, in step (b), the spinning solution is filtered before spinning, and the filtration accuracy is 2-5 μm, for example, the filtration accuracy can be 2.5 μm, 3 μm, 4 μm and 4.5 μm. By adopting the aforementioned preferred solution, the diameter CV value of the carbon fiber can be further reduced, its tensile strength can be increased and its tensile strength CV value can be reduced.

[0049] In this invention, as long as the purpose of this invention can be achieved, there are no special requirements for the insulation temperature of the filter components such as the filter and the gooseneck tube. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the insulation temperature of the filter components and the gooseneck tube is 40-80°C.

[0050] According to a preferred embodiment of the present invention, in step (b), the draw ratio during the solidification process is 0.3-1.5%, for example, it can be 0.4%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.2%, 1.3%, and 1.4%, preferably 0.5-1.2%. By adopting the aforementioned preferred embodiment, it is possible to further reduce the diameter CV value of the carbon fiber, increase its tensile strength, and reduce its tensile strength CV value.

[0051] In this invention, the coagulating liquid is a conventional choice in the art. The advantages of this invention are illustrated by taking a mixed solvent of water and dimethyl sulfoxide as an example.

[0052] In this invention, the concentration of dimethyl sulfoxide in the coagulation solution can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the concentration of dimethyl sulfoxide in the coagulation solution is 50-80 wt%.

[0053] In this invention, the temperature range of the coagulation liquid is relatively wide. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the temperature of the coagulation liquid is 45-65°C, preferably 55-65°C.

[0054] In this invention, as long as the purpose of this invention can be achieved, there are no special requirements for the conditions of hot water stretching in step (c). The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the conditions for hot water stretching include: a temperature of 80-95°C.

[0055] In this invention, as long as the purpose of this invention can be achieved, there are no special requirements for the number of hot water stretching passes in step (c). The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the number of hot water stretching passes is 2-4.

[0056] According to a preferred embodiment of the present invention, the conditions for hot water stretching include: a total stretch ratio of 2.5-6.

[0057] In this invention, as long as the purpose of this invention can be achieved, there are no special requirements for the water washing conditions in step (c). The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the water washing conditions include a temperature of 45-80°C.

[0058] In this invention, as long as the purpose of this invention can be achieved, there are no special requirements for the number of water washing stages. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the number of water washing stages is 3-8, and the temperature gradient of the water washing increases with the increase of the number of water washing stages.

[0059] In this invention, as long as the purpose of this invention can be achieved, there are no special requirements for the oiling conditions in step (c). The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the oiling conditions include a temperature of 25-40°C.

[0060] According to a preferred embodiment of the present invention, the oiling conditions include an oil concentration of 1.0-4.0 wt.%.

[0061] In this invention, excess oil during the oiling process is squeezed out by the extrusion rollers.

[0062] In this invention, the drying and densification conditions are conventional choices in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the drying and densification conditions include a temperature of 90-130°C.

[0063] The present invention employs a two-stage drying and densification process, with 5-9 drying rollers in each stage and a drying time of 30-90 seconds.

[0064] In this invention, the steam drawing pressure is a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the steam drawing conditions include a steam pressure of 0.2-0.6 MPa.

[0065] In this invention, the draw ratio of the steam drawing is a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for steam drawing include a draw ratio of 1.5-5.0.

[0066] In this invention, the heat setting pressure is a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the heat setting conditions include a pressure of 0.05-0.15 MPa.

[0067] In this invention, the draw ratio for heat setting is a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the heat setting conditions include a draw ratio of 0.8-1.1.

[0068] According to a preferred embodiment of the present invention, the pre-oxidation conditions include: a temperature of 180-250°C, and a time that is adjusted accordingly with changes in temperature, for example, a time of 40-80 minutes.

[0069] In this invention, the pre-oxidation is set with 2-5 temperature zones, and the temperature of each temperature zone is set to increase along the material flow direction. The residence time of each temperature zone is 10-20 minutes.

[0070] In this invention, as long as the purpose of this invention can be met, the draw ratio of each temperature zone is not required. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, along the material flow direction, the draw ratio of the first temperature zone is 1-3%, and the draw ratio of the remaining temperature zones is -1% to -3%.

[0071] According to a preferred embodiment of the present invention, the temperature difference between adjacent temperature zones is 10-30°C.

[0072] In this invention, the carbonization method can be a conventional means in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, in step (2), the carbonization includes first performing low-temperature carbonization and then performing high-temperature carbonization.

[0073] In this invention, the conditions for low-temperature carbonization are conventional choices in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the conditions for low-temperature carbonization include: a temperature of 350-850°C, preferably 380-750°C, and a time that is adjusted accordingly with the temperature, for example, a time of 1-15 min, preferably 2-10 min.

[0074] In this invention, the conditions for high-temperature carbonization can be conventional choices in the art as long as they can meet the purpose of this invention. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the conditions for high-temperature carbonization include: a temperature of 1000-1500℃, preferably 1050-1450℃, and a time that is adjusted accordingly with the temperature, for example, a time of 1-15 min, preferably 2-10 min.

[0075] According to a preferred embodiment of the present invention, the low-temperature carbonization is provided with 1-3 temperature zones, and the temperature of each temperature zone is set to increase along the material flow direction, and the residence time of each temperature zone is 20-240s.

[0076] In this invention, there are no special requirements for the draw ratio of each temperature zone of the low-temperature carbonization, as long as it can meet the purpose of this invention. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the draw ratio of each temperature zone of the low-temperature carbonization is 2-7%.

[0077] According to a preferred embodiment of the present invention, the temperature difference between adjacent low-temperature carbonization zones is 50-250°C.

[0078] According to a preferred embodiment of the present invention, the high-temperature carbonization is provided with 1-3 temperature zones; preferably, the temperature of each temperature zone is set to increase gradually along the material flow direction, and the residence time of each temperature zone is 20-240s.

[0079] In this invention, the draw ratio of each temperature zone of high-temperature carbonization can be a conventional choice in the art. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the draw ratio of each temperature zone of high-temperature carbonization is -5.0 to -0.5%.

[0080] According to a preferred embodiment of the present invention, the temperature difference between adjacent high-temperature carbonization zones is 50-250°C.

[0081] This invention provides a polyacrylonitrile carbon fiber prepared by the preparation method described above.

[0082] The polyacrylonitrile carbon fibers prepared by the method of the present invention have a diameter CV value of less than 5%, a tensile strength of 3.0-4.5 GPa, and a tensile strength CV value of 2.0-12.0%.

[0083] The present invention will be described in detail below through embodiments. In the following embodiments,

[0084] The quality assessment method for polyacrylonitrile carbon fiber is as follows: While the polyacrylonitrile carbon fiber is propelled at a speed of 1.5 m / min, the total number of single fiber breaks (hereinafter referred to as fluff) and aggregates of single fiber breaks (hereinafter referred to as fluff balls) in the fiber bundle is counted, and evaluated in three grades. The evaluation criteria are as follows:

[0085] A1: ≤3 in 300m carbon fiber;

[0086] A2: 3-12 in 300m carbon fiber;

[0087] A3: 13-50 in 300m carbon fiber.

[0088] The mechanical properties of polyacrylonitrile precursor fibers were tested according to GB / T 14337-2008.

[0089] Test method for the cross-section of polyacrylonitrile carbon fiber: Fix the carbon fiber in a slicer with a thickness between 0.8-1.5 mm. Determine the number of monofilaments to be used for testing the carbon fiber cross-section based on the size of the slicer slot, generally between 22,000-25,000. Secure the carbon fiber (direction perpendicular to the slicer surface) tightly in the slicer slot, ensuring that the carbon fiber cannot be easily pulled out of the slot. Use a single-edged blade to remove the protruding carbon fiber from both sides of the slicer in one go. Place the slicer on the stage of an optical microscope. Focus the optical microscope and select a magnification of 100 or 200 to observe the cross-section of the carbon fiber. Use a Zeiss upright polarizing optical microscope (model: Axio Scope A1 pol) to photograph the cross-sectional morphology of the carbon fiber. The imaging equipment (camera model: AxioCamMR5) and control software (ZEISS Digital Camera and Control Software, AxioVision 4.8) of the optical microscope system are used. Save the photographed images (file type: JPEG image, format: .jpg) for subsequent analysis.

[0090] Analysis, statistics, and processing of cross-sectional morphology of large-tow carbon fibers:

[0091] The saved carbon fiber cross-section photographs were opened using the control software integrated into the optical fiber microscope. The software's automatic statistical analysis module was used to statistically analyze the cross-sectional morphology characteristics (diameter, area) of 22,000-25,000 fibers in the carbon fiber cross-section photographs, obtaining the average diameter and the CV value of the diameter of the 22,000-25,000 fiber cross-sections. The specific steps are as follows:

[0092] A. Set the applicable intensity for the cross-sectional photograph to 65 to remove noise;

[0093] B. Standardize the histogram of the image obtained from A;

[0094] C. For the image obtained from B, set the boundary threshold to 130 and perform binarization.

[0095] The above methods were used to analyze the cross-sectional morphology of the fibers and obtain statistical information on the fiber cross-section, including the average diameter and diameter CV value of 22,000-25,000 large tow polyacrylonitrile carbon fibers.

[0096] The tensile strength and tensile modulus of polyacrylonitrile carbon fiber were tested in accordance with GB / T 3362-2017.

[0097] The viscosity of polyacrylonitrile spinning solution was tested using a rotational rheometer at a temperature of 60 ± 0.01℃. A rotor with a diameter of 25 mm and a spacing of 1 mm was selected. During the test, to prevent water absorption and solvent evaporation from affecting the experimental results, a layer of silicone oil was uniformly applied to the free surface of the sample exposed to air. The viscosity of the sample was measured as a function of shear rate (0.1 s⁻¹). -1 ~10s -1 The shear rate is taken as 8s. -1 The viscosity at that time is used as the viscosity of the polyacrylonitrile spinning solution.

[0098] The test method for the linear density (CV) value of polyacrylonitrile precursor is as follows:

[0099] Unwind the wound polyacrylonitrile precursor fiber by first unwinding 5 meters. Then, using a 1-meter steel ruler with a minimum scale of 0.5mm-1.0mm, cut a 1m ± 1.0mm section of the precursor fiber and weigh it using an electronic balance with an accuracy of 0.1mg. Unwind the fiber again by 2 meters and cut another 1m ± 1.0mm section, weighing it again. Repeat this process to obtain five 1m ± 1.0mm sections of the precursor fiber. Calculate the average value of these five sections, and then calculate the CV value (expressed as a percentage) of the CV value of the wound polyacrylonitrile precursor fiber.

[0100] Unless otherwise specified, all raw materials are commercially available products.

[0101] Example 1

[0102] (1) Preparation of the stock solution: 1358 kg of distilled acrylonitrile (AN), 42 kg of itaconic acid (IA), 7.0 kg of azobisisobutyronitrile (AIBN), and 5600 kg of dimethyl sulfoxide (DMSO) were added to a reactor and reacted at a constant temperature of 59°C for 20 hours under nitrogen protection to obtain a binary acrylonitrile copolymer spinning solution. Then, after removing residual monomers and bubbles from the spinning solution under reduced pressure, it was filtered through a 5 μm filter material to obtain the acrylonitrile copolymer spinning stock solution.

[0103] (2) Spinning: After the raw liquid is filtered and precisely metered by a metering pump, the raw liquid is squeezed out from the gooseneck tube and enters the coagulation bath for coagulation. A 48K specification spinneret is used, and the filtration accuracy is 3.5μm.

[0104] The insulation temperature of the filter and gooseneck tube is 60℃.

[0105] (3) Coagulation and forming: The coagulation liquid temperature is 59℃, the coagulation liquid concentration at the coagulation bath inlet is 66.6%, and the draw ratio is 0.6. The coagulation liquid concentration in the central region of the nascent fiber is 67.8%; the coagulation liquid concentration in the edge region is 66.7%, and the concentration difference between the two is 1.10%. The central region of the coagulated fiber bundle refers to a cylindrical region with a height of 2.5cm formed within 0.15r from the central axis of the coagulated fiber bundle; the edge region of the coagulated fiber bundle refers to a ring-shaped region with a height of 2.5cm formed within 0.85-1.1r from the central axis of the coagulated fiber bundle.

[0106] (4) Drafting and washing: Three hot water drafting processes are performed at temperatures of 86℃, 90℃, and 95℃. The drafting ratio for each process can be the same or different, with the total drafting ratio controlled at 4.2. After hot water drafting, the yarn bundle undergoes six washing processes using a stepped heating method. No drafting is performed during the washing process. The washing temperatures are 45℃, 50℃, 55℃, 60℃, 70℃, and 80℃, respectively.

[0107] (5) Oiling: The oil concentration is 3% and the temperature is 25℃. Excess oil is squeezed by the extrusion roller.

[0108] (6) Drying and densification: It is divided into two stages. The first stage of drying and densification is carried out at a temperature of 90°C, with 7 drying rollers and a drying time of 50s. The second stage of drying and densification is carried out at a temperature of 120°C, with 7 drying rollers and a drying time of 50s.

[0109] (7) Steam stretching and heat setting: The steam stretching pressure is 0.40 MPa and the stretching ratio is 2.6. The heat setting pressure is 0.1 MPa and the heat setting ratio is 0.90 to obtain 48K polyacrylonitrile precursor fiber.

[0110] (8) Pre-oxidation: Pre-oxidation treatment is carried out in an air atmosphere in a four-temperature zone pre-oxidation furnace. The pre-oxidation temperatures in the four zones are 185℃, 205℃, 225℃ and 240℃, respectively, and the draw ratios are 2%, -1.5%, -1.5% and -1.5%, respectively. The residence time in each temperature zone is 15min. The Rr of the yarn spreading device is 15mm, n=17 and a=12cm. The b value of the polyacrylonitrile precursor during the pre-oxidation process is 1.05mm.

[0111] The pre-oxidation process ran stably for 100 hours, during which the pre-oxidation of the filament bundles was good and no filament bundles burned out in the pre-oxidation furnace.

[0112] (9) Carbonization: Under a nitrogen atmosphere, the pre-oxidized fibers were subjected to low-temperature carbonization treatment in three temperature zones using a low-temperature carbonization furnace. The temperatures for each zone were 455℃, 555℃, and 760℃, with a fiber draw ratio of 4.2% and a fiber residence time of 3.5 min. Under a nitrogen atmosphere, the low-carbon fibers were subjected to high-temperature carbonization treatment in three temperature zones using a high-temperature carbonization furnace. The temperatures for each zone were 1110℃, 1255℃, and 1390℃, with a fiber draw ratio of -3.5% and a fiber residence time of 3.8 min.

[0113] The concentration difference of the coagulated liquid between the central and peripheral regions of the coagulated nascent fibers was 1.0 wt.%.

[0114] The diameter CV value of the polyacrylonitrile precursor fiber is 4.0%, the linear density CV value is 2.05%, and the fineness is 1.34 dtex.

[0115] The breaking strength of the monofilament is 6.72 cN / dtex, with a strength CV of 9.6%; the breaking elongation is 12.7%, with an elongation CV of 11.7%; and the initial modulus is 124 cN / dtex, with an initial modulus CV of 9.8%.

[0116] The carbon fiber tow quality assessment result is A1, with a diameter CV value of 3.6%, a tow tensile strength of 4.2 GPa, and a tensile strength CV value of 4.7%.

[0117] Example 2

[0118] A 72K spinneret was used, and the yarn spreading device was modified accordingly to ensure that the b value was 1.05 mm. Everything else was the same as in Example 1.

[0119] The breaking strength of the monofilament is 6.34 cN / dtex, with a strength CV value of 10.2%; the breaking elongation is 12.7%, with an elongation CV value of 11.9%; and the initial modulus is 124 cN / dtex, with an initial modulus CV value of 10.1%.

[0120] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 3.0%, a tow tensile strength of 4.1 GPa, and a tensile strength CV value of 4.5%.

[0121] Example 3

[0122] A 96K spinneret was used, and the yarn spreading device was modified accordingly to ensure that the b-value was 1.05 mm. Everything else was the same as in Example 1.

[0123] The breaking strength of the monofilament is 6.03 cN / dtex, with a strength CV of 11.2%; the breaking elongation is 12.5%, with an elongation CV of 12.1%; and the initial modulus is 123 cN / dtex, with an initial modulus CV of 10.4%.

[0124] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 3.5%, a tow tensile strength of 4.0 GPa, and a tensile strength CV value of 5.0%.

[0125] Example 4

[0126] A 24K spinneret was used, and the yarn spreading device was modified accordingly to ensure that the b value was 1.05 mm. Everything else was the same as in Example 1.

[0127] The breaking strength of the monofilament is 6.91 cN / dtex, with a strength CV of 8.5%; the breaking elongation is 12.6%, with an elongation CV of 11.5%; and the initial modulus is 125 cN / dtex, with an initial modulus CV of 9.6%.

[0128] The carbon fiber tow quality assessment result is A1, with a diameter CV value of 1.4%, a tow tensile strength of 4.4 GPa, and a tensile strength CV value of 3.8%.

[0129] Example 5

[0130] (8) Pre-oxidation device: The yarn spreading device has Rr = 12mm, n = 9 and a = 10cm. During the pre-oxidation process, the b value of the polyacrylonitrile precursor is 0.3mm. Other parameters are the same as in Example 1.

[0131] The breaking strength of the monofilament is 6.22 cN / dtex, with a strength CV value of 10.1%; the breaking elongation is 12.8%, with an elongation CV value of 11.8%; and the initial modulus is 124 cN / dtex, with an initial modulus CV value of 10.2%.

[0132] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 3.0%, a tow tensile strength of 4.0 GPa, and a tensile strength CV value of 4.5%.

[0133] Example 6

[0134] (8) Pre-oxidation device: The yarn spreading device has Rr = 20 mm, n = 21 and a = 15 cm. During the pre-oxidation process, the b value of the polyacrylonitrile precursor is 1.8 mm. Other parameters are the same as in Example 1.

[0135] The breaking strength of the monofilament is 6.32 cN / dtex, with a strength CV value of 10.0%; the breaking elongation is 12.7%, with an elongation CV value of 11.6%; and the initial modulus is 123 cN / dtex, with an initial modulus CV value of 10.1%.

[0136] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 3.0%, a tow tensile strength of 3.9 GPa, and a tensile strength CV value of 4.4%.

[0137] Example 7

[0138] (8) Pre-oxidation device: The yarn spreading device has Rr = 5mm, n = 3 and a = 6cm. During the pre-oxidation process, the b value of the polyacrylonitrile precursor is 0.1mm. Other parameters are the same as in Example 1.

[0139] The breaking strength of the monofilament is 6.35 cN / dtex, with a strength CV value of 10.3%; the breaking elongation is 12.9%, with an elongation CV value of 12.0%; and the initial modulus is 125 cN / dtex, with an initial modulus CV value of 10.3%.

[0140] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 3.0%, a tow tensile strength of 4.1 GPa, and a tensile strength CV value of 4.6%.

[0141] Example 8

[0142] (3) Coagulation and molding: The temperature of the coagulation liquid is 64℃, so that the concentration of the coagulation liquid in the central region of the nascent fiber is 66.9% and the concentration of the coagulation liquid in the edge region is 66.7%, with a concentration difference of 0.20%.

[0143] Everything else is the same as in Example 1.

[0144] The breaking strength of the monofilament is 6.56 cN / dtex, with a strength CV of 8.8%; the breaking elongation is 12.6%, with an elongation CV of 10.9%; and the initial modulus is 124 cN / dtex, with an initial modulus CV of 8.9%.

[0145] The carbon fiber tow quality assessment result is A1, with a diameter CV value of 0.5%, a tow tensile strength of 4.2 GPa, and a tensile strength CV value of 3.9%.

[0146] Example 9

[0147] (3) Coagulation and molding: The temperature of the coagulation liquid is 52℃, so that the concentration of the coagulation liquid in the central region of the nascent fiber is 68.7% and the concentration of the coagulation liquid in the edge region is 66.7%, with a concentration difference of 2.0%.

[0148] Everything else is the same as in Example 1.

[0149] The breaking strength of the monofilament is 5.95 cN / dtex, with a strength CV value of 11.5%; the breaking elongation is 12.2%, with an elongation CV value of 12.4%; and the initial modulus is 121 cN / dtex, with an initial modulus CV value of 10.7%.

[0150] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 3.5%, a tow tensile strength of 3.5 GPa, and a tensile strength CV value of 5.1%.

[0151] Example 10

[0152] (3) Coagulation and molding: The temperature of the coagulation liquid is 47℃, so that the concentration of the coagulation liquid in the central region of the nascent fiber is 69.0% and the concentration of the coagulation liquid in the edge region is 66.7%, with a concentration difference of 2.3%.

[0153] Everything else is the same as in Example 1.

[0154] The breaking strength of the monofilament is 5.91 cN / dtex, with a strength CV value of 11.9%; the breaking elongation is 12.1%, with an elongation CV value of 12.8%; and the initial modulus is 120 cN / dtex, with an initial modulus CV value of 11.2%.

[0155] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 3.7%, a tow tensile strength of 3.4 GPa, and a tensile strength CV value of 5.3%.

[0156] Example 11

[0157] The concentration of the coagulation solution at the coagulation bath inlet was 52.9%, and the draw ratio was 0.6. The concentration of the coagulation solution in the central region of the nascent fiber was 54.1%, while the concentration in the peripheral region was 53.0%, with a concentration difference of 1.10%.

[0158] Everything else is the same as in Example 1.

[0159] The breaking strength of the monofilament is 6.84 cN / dtex, with a strength CV of 8.4%; the breaking elongation is 12.6%, with an elongation CV of 11.3%; and the initial modulus is 123 cN / dtex, with an initial modulus CV of 8.9%.

[0160] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 2.0%, a tow tensile strength of 4.5 GPa, and a tensile strength CV value of 3.7%.

[0161] Example 12

[0162] The concentration of the coagulation solution at the coagulation bath inlet was 79.8%, and the draw ratio was 0.6. The concentration of the coagulation solution in the central region of the nascent fiber was 81.1%, while the concentration in the peripheral region was 80.0%, with a concentration difference of 1.10%.

[0163] Everything else is the same as in Example 1.

[0164] The breaking strength of the monofilament is 6.85 cN / dtex, with a strength CV of 8.75%; the breaking elongation is 12.5%, with an elongation CV of 11.8%; and the initial modulus is 124 cN / dtex, with an initial modulus CV of 9.9%.

[0165] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 1.7%, a tow tensile strength of 4.6 GPa, and a tensile strength CV value of 3.9%.

[0166] Example 13

[0167] The concentration of the coagulation solution at the coagulation bath inlet was 51.8%, and the draw ratio was 0.6. The concentration of the coagulation solution in the central region of the nascent fiber was 53.1%, while the concentration in the peripheral region was 52.0%, with a concentration difference of 1.10%.

[0168] Everything else is the same as in Example 1.

[0169] The breaking strength of the monofilament is 6.83 cN / dtex, with a strength CV of 8.4%; the breaking elongation is 12.7%, with an elongation CV of 10.6%; and the initial modulus is 122 cN / dtex, with an initial modulus CV of 8.4%.

[0170] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 2.2%, a tow tensile strength of 4.5 GPa, and a tensile strength CV value of 3.7%.

[0171] Example 14

[0172] The solidification and molding process involved a draw ratio of 0.5, and the fineness of the polyacrylonitrile precursor fiber was 1.61 dtex. Other parameters were the same as in Example 1.

[0173] The breaking strength of the monofilament is 6.52 cN / dtex, with a strength CV value of 10.4%; the breaking elongation is 12.1%, with an elongation CV value of 12.1%; and the initial modulus is 118 cN / dtex, with an initial modulus CV value of 10.4%.

[0174] The carbon fiber tow quality assessment result is A1, with a diameter CV value of 1.8%, a tow tensile strength of 4.2 GPa, and a tensile strength CV value of 4.6%.

[0175] Example 15

[0176] The solidification and molding process involved a draw ratio of 1.2, and the fineness of the polyacrylonitrile precursor fiber was 0.66 dtex. Other parameters were the same as in Example 1.

[0177] The breaking strength of the monofilament is 7.68 cN / dtex, with a strength CV of 7.1%; the breaking elongation is 11.2%, with an elongation CV of 9.2%; and the initial modulus is 138 cN / dtex, with an initial modulus CV of 8.0%.

[0178] The carbon fiber tow quality assessment result is A1, with a diameter CV value of 2.3%, a tow tensile strength of 5.7 GPa, and a tensile strength CV value of 3.2%.

[0179] Example 16

[0180] The solidification and molding process involved a draw ratio of 0.4, and the fineness of the polyacrylonitrile precursor fiber was 1.98 dtex. Other parameters were the same as in Example 1.

[0181] The breaking strength of the monofilament is 6.08 cN / dtex, with a strength CV value of 12.3%; the breaking elongation is 12.8%, with an elongation CV value of 13.6%; and the initial modulus is 106 cN / dtex, with an initial modulus CV value of 11.7%.

[0182] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 1.5%, a tow tensile strength of 3.9 GPa, and a tensile strength CV value of 5.5%.

[0183] Example 17

[0184] Solidification and shaping: The central region of the solidified filament bundle refers to a cylindrical region with a height of 1 cm formed within 0.15r of the central axis of the solidified filament bundle; the edge region of the solidified filament bundle refers to a ring-like region with a height of 1 cm formed within 0.85-1.1r of the central axis of the solidified filament bundle. Other aspects are the same as in Example 1.

[0185] The breaking strength of the monofilament is 6.87 cN / dtex, with a strength CV of 8.6%; the breaking elongation is 12.4%, with an elongation CV of 11.8%; and the initial modulus is 122 cN / dtex, with an initial modulus CV of 9.8%.

[0186] The carbon fiber tow quality assessment result is A1, with a diameter CV value of 1.5%, a tow tensile strength of 4.4 GPa, and a tensile strength CV value of 3.8%.

[0187] Example 18

[0188] Solidification and shaping: The central region of the solidified filament bundle refers to a cylindrical region with a height of 4 cm formed within 0.15r of the central axis of the solidified filament bundle; the edge region of the solidified filament bundle refers to a ring-like region with a height of 4 cm formed within 0.85-1.1r of the central axis of the solidified filament bundle. Other aspects are the same as in Example 1.

[0189] The breaking strength of the monofilament is 6.75 cN / dtex, with a strength CV of 9.7%; the breaking elongation is 12.8%, with an elongation CV of 11.4%; and the initial modulus is 123 cN / dtex, with an initial modulus CV of 9.4%.

[0190] The carbon fiber tow quality assessment result is A1, with a diameter CV value of 2.5%, a tow tensile strength of 4.3 GPa, and a tensile strength CV value of 4.3%.

[0191] Example 19

[0192] Solidification and shaping: The central region of the solidified filament bundle refers to a cylindrical region with a height of 4 cm formed within 0.15r of the central axis of the solidified filament bundle; the edge region of the solidified filament bundle refers to a ring-like region with a height of 5 cm formed within 0.85-1.1r of the central axis of the solidified filament bundle. Other aspects are the same as in Example 1.

[0193] The breaking strength of the monofilament is 6.77 cN / dtex, with a strength CV of 9.8%; the breaking elongation is 12.8%, with an elongation CV of 11.4%; and the initial modulus is 122 cN / dtex, with an initial modulus CV of 9.5%.

[0194] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 2.5%, a tow tensile strength of 4.1 GPa, and a tensile strength CV value of 4.4%.

[0195] Example 20

[0196] Spinning: After the raw liquid is filtered and precisely metered by a metering pump, it is extruded from the gooseneck tube and enters the coagulation bath for coagulation. The filtration accuracy is 2.0μm.

[0197] Everything else is the same as in Example 1.

[0198] The breaking strength of the monofilament is 6.89 cN / dtex, with a strength CV of 8.7%; the breaking elongation is 12.4%, with an elongation CV of 11.7%; and the initial modulus is 123 cN / dtex, with an initial modulus CV of 9.8%.

[0199] The carbon fiber tow quality assessment result is A1, with a diameter CV value of 1.6%, a tow tensile strength of 4.4 GPa, and a tensile strength CV value of 3.9%.

[0200] Example 21

[0201] Spinning: After the raw liquid is filtered and precisely metered by a metering pump, it is extruded from the gooseneck tube and enters the coagulation bath for coagulation. The filtration accuracy is 5.0μm.

[0202] Everything else is the same as in Example 1.

[0203] The breaking strength of the monofilament is 6.87 cN / dtex, with a strength CV of 6.7%; the breaking elongation is 12.9%, with an elongation CV of 8.7%; and the initial modulus is 122 cN / dtex, with an initial modulus CV of 7.7%.

[0204] The carbon fiber tow quality assessment result is A1, with a diameter CV value of 2.1%, a tow tensile strength of 4.4 GPa, and a tensile strength CV value of 3.0%.

[0205] Example 22

[0206] Spinning: After the raw liquid is filtered and precisely metered by a metering pump, it is extruded from the gooseneck tube and enters the coagulation bath for coagulation. The filtration accuracy is 6.0μm.

[0207] Everything else is the same as in Example 1.

[0208] The breaking strength of the monofilament is 6.32 cN / dtex, with a strength CV value of 10.6%; the breaking elongation is 12.5%, with an elongation CV value of 12.3%; and the initial modulus is 122 cN / dtex, with an initial modulus CV value of 10.5%.

[0209] The carbon fiber tow quality assessment result is A2, with a diameter CV value of 3.1%, a tow tensile strength of 4.1 GPa, and a tensile strength CV value of 4.7%.

[0210] Comparative Example 1

[0211] A 160K spinneret was used, and the yarn spreading device was modified accordingly to ensure that the b value was 1.05 mm. Everything else was the same as in Example 1.

[0212] The breaking strength of the monofilament is 5.2 cN / dtex, with a strength CV of 16.9%; the breaking elongation is 10.6%, with an elongation CV of 17.5%; and the initial modulus is 96 cN / dtex, with an initial modulus CV of 15.2%.

[0213] The carbon fiber tow quality assessment result is A3, with a diameter CV value of 8.6%, a tow tensile strength of 2.9 GPa, and a tensile strength CV value of 7.9%.

[0214] Comparative Example 2

[0215] (8) Pre-oxidation device: The yarn spreading device has Rr = 30mm, n = 27 and a = 20cm. During the pre-oxidation process, the b value of the polyacrylonitrile precursor is 2.5mm. Other parameters are the same as in Example 1.

[0216] The breaking strength of the monofilament is 5.4 cN / dtex, with a strength CV of 16.1%; the breaking elongation is 10.8%, with an elongation CV of 16.8%; and the initial modulus is 98 cN / dtex, with an initial modulus CV of 14.5%.

[0217] The carbon fiber tow quality assessment result is A3, with a diameter CV value of 7.9%, a tow tensile strength of 3.2 GPa, and a tensile strength CV value of 7.2%.

[0218] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing polyacrylonitrile carbon fiber, characterized in that, The preparation method includes the following steps: (1) preparation of polyacrylonitrile precursor fibers with a K number not greater than 120; (2) pre-oxidation and carbonization of the polyacrylonitrile precursor fibers in step (1) in sequence; wherein, during the pre-oxidation process, the ratio of the width of the polyacrylonitrile precursor fibers to the K number of the polyacrylonitrile precursor fibers is b, and b is 0.1-2 mm.

2. The preparation method according to claim 1, wherein, The K number of the polyacrylonitrile precursor fiber is 24-120, preferably 24-96, and more preferably 24-48; and / or The value of b is 0.3-1.8 mm, preferably 0.5-1.2 mm.

3. The preparation method according to claim 1 or 2, wherein, The diameter CV value of the polyacrylonitrile precursor fiber is 1-8%, preferably 2-6%, more preferably 3-5%; and / or The linear density (CV) of the polyacrylonitrile precursor fiber is 0.05-5%, preferably 0.1-4%, more preferably 0.2-2%; and / or The polyacrylonitrile precursor fiber has a fineness of 0.5-2.0 dtex; and / or The single filament breaking strength of the polyacrylonitrile precursor is 5.5-8.0 cN / dtex; and / or The strength CV value of the polyacrylonitrile precursor fiber is 6-13%; and / or The breaking elongation of the polyacrylonitrile precursor fiber is 11-14%; and / or The breaking elongation (CV) of the polyacrylonitrile precursor fiber is 8-15%; and / or The initial modulus of the polyacrylonitrile precursor fiber is 100-145 cN / dtex; and / or The initial modulus CV value of the polyacrylonitrile precursor fiber is 6-13%.

4. The preparation method according to any one of claims 1-3, wherein, Step (1) includes the following steps: (a) Preparation of spinning solution; (b) The spinning solution from step (a) is spun and solidified to obtain nascent fibers. The solidification method includes: the spinning solution obtained by spinning is aggregated in the solidification liquid to form nascent fibers; wherein the difference between the solidification liquid concentration in the central region of the nascent fibers and the solidification liquid concentration in the edge region of the nascent fibers is 0.2-2 wt.%, the central region of the nascent fibers refers to a cylindrical region with a height ≤ 4 cm formed within (0-0.15)r of the central axis of the nascent fibers; the edge region of the nascent fibers refers to a ring-like region with a height ≤ 4 cm formed within (0.85-1.1)r of the central axis of the nascent fibers; r is the radius of the circular cross-section formed radially by the nascent fibers; (c) The nascent fibers obtained in step (b) are sequentially subjected to hot water drawing, washing, oiling, drying and densification, saturated steam drawing, steam heat setting and winding.

5. The preparation method according to claim 4, wherein, Step (a) includes: mixing a mixture of acrylonitrile, comonomer, initiator, and solvent; reacting under an inert atmosphere; and obtaining a spinning solution after degassing and solid-liquid separation of the reaction solution; preferably, The mass percentage of acrylonitrile and comonomer is 97-99.9:0.1-3; and / or The initiator is 0.1-1 wt.% of the total mass of acrylonitrile and comonomer; and / or The mass ratio of the solvent to the total mass of acrylonitrile and comonomer is 72-82:18-28; and / or The comonomer is an alkenyl compound, preferably itaconic acid; and / or The reaction conditions include a temperature of 50-70°C and / or a time of 15-25 hours.

6. The preparation method according to claim 4 or 5, wherein, Step (b) is performed in an apparatus comprising: a coagulation bath body, a coagulation liquid outlet and a coagulation liquid inlet connected to the coagulation bath body, a spinneret disposed within the coagulation bath body, and a spinning solution feeder connected to the spinneret; the closest distance between the center of the outlet cross-section of the coagulation liquid inlet, or the plane formed by the center of the cross-section, or the line segment formed by the center of the cross-section, and the surface of the spinneret is 1 / 5 to 1 / 2 of the diameter of the spinneret. Preferably, The spinneret is an annular spinneret with an outer ring region having through holes and an inner ring region without through holes; and / or The outlet of the coagulation liquid inlet is connected to the inlet of the coagulation liquid outlet, and a driving device is provided on the connecting pipeline.

7. The preparation method according to any one of claims 4-6, wherein, In step (b), The concentration of the coagulation solution in the central region of the nascent fiber is 52-82 wt.%, preferably 60-75 wt.%; and / or The concentration of the coagulation solution in the edge region of the nascent fibers is 52-80 wt.%, preferably 58-74.8 wt.%; and / or The spinning solution is filtered before spinning, with a filtration accuracy of 2-5 μm; and / or The draw ratio during the solidification and molding process is 0.3-1.5%, preferably 0.5-1.2%.

8. The preparation method according to any one of claims 1-7, wherein, In step (2), the carbonization includes first performing low-temperature carbonization and then high-temperature carbonization. Preferably, The conditions for the low-temperature carbonization include: a temperature of 350-850℃, preferably 380-750℃; and / or a time of 1-15 min, preferably 2-10 min; and / or The conditions for high-temperature carbonization include: a temperature of 1000-1500℃, preferably 1050-1450℃; and / or a time of 1-15 min, preferably 2-10 min.

9. The preparation method according to claim 8, wherein, The low-temperature carbonization process is configured with 1-3 temperature zones; preferably, the temperature of each zone increases progressively along the material flow direction, and / or the residence time in each zone is 20-240 s, and / or the draw ratio of each zone is 2-7%; more preferably, the temperature difference between adjacent zones is 50-250°C; and / or The high-temperature carbonization process is configured with 1-3 temperature zones; preferably, the temperature of each temperature zone increases progressively along the material flow direction, and / or the residence time of each temperature zone is 20-240s, and / or the draw ratio of each temperature zone is -5.0 to -0.5%; more preferably, the temperature difference between adjacent temperature zones is 50-250℃.

10. Polyacrylonitrile carbon fiber prepared by the preparation method according to any one of claims 1-9.

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