A polyacrylonitrile-based carbon fiber precursor, a preparation method and application thereof

Abstract

The application relates to the technical field of carbon fibers, and discloses a polyacrylonitrile-based carbon fiber precursor, a preparation method and application thereof.The method comprises the following steps: (1) spinning and coagulating a spinning dope, and then performing heat drawing to obtain heat-drawn fibers; (2) performing post-treatment on the heat-drawn fibers to obtain a polyacrylonitrile-based carbon fiber precursor; wherein the variation coefficient of the swelling degree of the heat-drawn fibers is less than or equal to 5%. The method can be used for preparing carbon fiber precursors with small differences in single-fiber properties and few broken filaments by controlling the variation coefficient of the swelling degree of the heat-drawn fibers.

Description

Technical Field

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

[0002] Carbon fiber is a fibrous material primarily composed of carbon. Compared to other materials, besides possessing inherent properties such as low density, high temperature resistance, friction resistance, electrical conductivity, thermal conductivity, and corrosion resistance, carbon fiber exhibits a structural characteristic of randomly layered graphite microcrystals with preferred orientation along the fiber axis, resulting in very high strength and modulus along the fiber axis. Composite materials made with carbon fiber as their skeleton structure still boast the highest specific strength and specific modulus among existing engineering materials. Furthermore, its relatively flexible nature allows for the fabrication of various composite structural components using carbon fiber winding and weaving processes, enabling applications in high-end manufacturing fields such as aerospace, hydrogen storage cylinders, and wind turbine blades.

[0003] Since carbon fiber composites are formed by impregnating bundled carbon fibers with resin, the inherent characteristics of the fiber bundle are a crucial factor affecting the composite's performance. Theoretically, the fibers in a fiber bundle should possess relatively uniform properties. However, in reality, because each filament in an industrially produced bundle is in the same position, differences in mass and heat transfer conditions between filaments are inevitable during the forming process. Even from a physical morphology perspective, the thickness of individual filaments can vary by 1-5%, and this difference clearly has a significant impact on the performance of the final composite material. It is generally accepted that defects in the precursor fiber are inherited by the carbon fiber itself, and various defects in the carbon fiber bundle are inherited by the composite material. Therefore, preventing these differences from the outset is extremely important.

[0004] Patent applications CN201710777381.8, CN201780041618.4, CN201880057751.3, CN202122194771.7, and CN202110590805.6 have studied and reported on the uniformity issues in the dopant preparation, coagulation, steam drawing, sizing, and composite material forming steps during fiber forming, and provided optimization solutions. It can be observed that, regardless of the stage, large variability and poor uniformity in monofilaments caused by any factor mean a loss of tensile strength in the final product. Therefore, the various properties of monofilaments within a high-strength fiber bundle must be uniform. It is clear that the consistency of monofilaments not only refers to physical morphology, but high-quality raw fibers also require good consistency in secondary structures such as crystallization, pores, and core-sheath structure. This consistency requires that the monofilaments undergo the same processes during production; that is, the central control indicators for the monofilaments cannot deviate significantly. This includes the uniformity control of processes such as polymerization, steam drawing, sizing, and composite forming, as mentioned in the literature. However, research on the uniformity of fiber control parameters during the hot water drawing process in fiber production is still lacking. Summary of the Invention

[0005] The purpose of this invention is to overcome the problems of large differences in the properties of single fiber filaments and excessive fuzz in the existing wet spinning process, and to provide a polyacrylonitrile-based carbon fiber precursor, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides a method for preparing polyacrylonitrile-based carbon fiber precursor, the method comprising the following steps:

[0007] (1) Spinning solution is spun and solidified, and then hot-drawn to obtain hot-drawn fibers;

[0008] (2) The hot-drawn fibers are post-treated to obtain polyacrylonitrile-based carbon fiber precursors;

[0009] The coefficient of variation of the swelling degree of the thermally drawn fiber is ≤5%.

[0010] Preferably, the swelling degree of the thermally drawn fiber is 80-120%.

[0011] Preferably, the single filament fineness of the thermally drawn fiber is 1-4 Dtex.

[0012] Preferably, the orifice density of the spinneret used during spinning is 80-200 orifices / cm², and more preferably 120-160 orifices / cm².

[0013] Preferably, the spinneret used during spinning is a circular spinneret.

[0014] Preferably, the width of the nascent fibers obtained by coagulation is controlled to be 0.8-1.1 cm / k.

[0015] Preferably, the number of stages of thermal stretching is 3-5.

[0016] Preferably, the method further includes a bundling process before each stage of hot drawing, and the width of the filament after each bundling satisfies the following relationship: 0.8A / Dr≥B≥1.1A / Dr; where B is the width of the filament after this bundling, A is the width of the filament after the previous bundling, and Dr is the drawing ratio of this stage of hot drawing.

[0017] Preferably, the bunching is performed at a distance of 5-10 cm from the inlet of the hot water stretching tank.

[0018] Preferably, the temperature of the thermal stretching is 80-98℃, and the temperature of each stretching stage is not lower than the temperature of the previous stretching stage.

[0019] Preferably, the total thermal stretching ratio is 2-6 times.

[0020] Preferably, the post-processing includes: water washing, oiling, drying and densification, steam stretching and heat setting.

[0021] A second aspect of the present invention provides polyacrylonitrile-based carbon fiber precursors prepared by the method described above.

[0022] A third aspect of the present invention provides the application of the polyacrylonitrile-based carbon fiber precursor described above in the preparation of carbon fibers.

[0023] A fourth aspect of the present invention provides a method for preparing carbon fiber, the method comprising the following steps:

[0024] The polyacrylonitrile-based carbon fiber precursor described above is subjected to pre-oxidation, low-temperature carbonization, and high-temperature carbonization.

[0025] Preferably, the pre-oxidation temperature is 200-260℃;

[0026] Preferably, the temperature for low-temperature carbonization is 400-750°C;

[0027] Preferably, the high-temperature carbonization temperature is 1150-1450℃.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. This invention provides a method for preparing polyacrylonitrile carbon fiber precursor. By controlling the coefficient of variation of the swelling of the thermally drawn fiber, carbon fiber precursor with small differences in monofilament properties and few fuzz can be obtained.

[0030] 2. In the method described in this invention, by optimizing the orifice density of the spinneret, controlling the width of the nascent fiber filaments, and controlling the degree of shrinkage during the thermal stretching process, the uniformity of mass transfer, heat transfer, and deformation during fiber forming is improved, the differences between the single filament structures during the carbon fiber precursor forming process are reduced, and the quality of the obtained carbon fiber precursor is further improved. Detailed Implementation

[0031] The following provides a detailed description of specific embodiments of the present invention. It should be understood that the specific embodiments described herein are for illustrative and explanatory purposes only and are not intended to limit the scope of the invention.

[0032] 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.

[0033] During their research, the inventors of this invention discovered that swelling is a crucial controllable indicator in the preparation of polyacrylonitrile carbon fiber precursor, and currently, swelling is typically monitored only at an average value. In practical research, the inventors found a strong correlation between the coefficient of variation of swelling in the obtained hot-drawn fibers and the final carbon fiber properties. Controlling the coefficient of variation of swelling can improve the uniformity of the fiber filaments, reducing the adverse effects caused by differences between filaments, thereby facilitating the acquisition of higher-quality carbon fibers. Based on this, this invention was completed.

[0034] This invention provides a method for preparing polyacrylonitrile-based carbon fiber precursor, which employs a wet spinning process and includes the following steps:

[0035] (1) Spinning solution is spun and solidified, and then hot-drawn to obtain hot-drawn fibers;

[0036] (2) The hot-drawn fibers are post-treated to obtain polyacrylonitrile-based carbon fiber precursors;

[0037] The coefficient of variation of the swelling degree of the thermally drawn fiber is ≤5%.

[0038] In a preferred embodiment, the spinning solution contains a polyacrylonitrile copolymer and a solvent.

[0039] In a preferred embodiment, the intrinsic viscosity of the polyacrylonitrile copolymer is 1.5-2.8 dL / g.

[0040] In a preferred embodiment, the concentration of the polyacrylonitrile copolymer in the spinning solution is 19-21% by weight.

[0041] More preferably, the polyacrylonitrile copolymer is obtained by copolymerizing acrylonitrile and a second monomer. The second monomer is selected from monomers containing vinyl groups.

[0042] More preferably, the second monomer is selected from itaconic acid or polymethyl methacrylate.

[0043] In a specific embodiment, when the second monomer is selected from an acidic monomer such as itaconic acid, the method further includes a step of treating the spinning solution with ammonia gas before spinning. Ammonia gas can neutralize the carboxyl groups in itaconic acid.

[0044] In a preferred embodiment, the acrylonitrile structural unit content in the polyacrylonitrile copolymer is ≥95% by weight, and the content of the second monomer structural unit is ≥0.6% by weight. More preferably, the acrylonitrile structural unit content in the polyacrylonitrile copolymer is 95-99.4% by weight, and the content of the second monomer structural unit is 0.6-5% by weight.

[0045] In a preferred embodiment, the solvent may be dimethyl sulfoxide (DMSO).

[0046] In a preferred embodiment, a circular spinneret is used during the spinning process.

[0047] In wet spinning, if the spinneret orifice density is too high, it will lead to greater differences in mass transfer during the forming process. This results in a higher solvent concentration inside the spinneret, causing the newly formed fibers to have higher swelling. Conversely, a low spinneret orifice density will cause uneven spinneret pressure during large-diameter spinning, leading to greater fiber fineness variation. Therefore, to further improve the uniformity of hot-drawn fiber monofilaments and reduce the coefficient of variation in monofilament swelling, the orifice density of the spinneret needs to be reasonably controlled. In a preferred embodiment, the orifice density of the spinneret used during spinning is 80-200 orifices / cm², preferably 120-160 orifices / cm².

[0048] More preferably, the spinneret has 1000-12000 holes and a hole diameter of 0.04-0.08 mm.

[0049] In a preferred embodiment, the coagulation bath used during coagulation is an aqueous solution of dimethyl sulfoxide. More preferably, the concentration of dimethyl sulfoxide in the coagulation bath is 45-82% by weight; specifically, it can be 45% by weight, 50% by weight, 55% by weight, 60% by weight, 65% by weight, 70% by weight, 75% by weight, 80% by weight, or 82% by weight.

[0050] In a preferred embodiment, the temperature of the coagulation bath is 25-35°C; specifically, it can be 25°C, 26°C, 27°C, 28°C, 29°C, 30°C, 32°C, 34°C, or 35°C.

[0051] In the method described in this invention, if the fiber width is excessively narrowed upon exiting the coagulation bath, the outer fibers cannot immediately complete bundling and thus adhere to the roller surface under surface tension, leading to fiber breakage. Therefore, to further improve the uniformity of the hot-drawn fiber monofilaments and reduce the coefficient of variation in monofilament swelling, the width of the nascent fiber obtained after coagulation can be reasonably controlled. Preferably, the width of the nascent fiber obtained after coagulation (i.e., the width of the filament at the coagulation exit) is 0.8-1.1 cm / k.

[0052] In a preferred embodiment, the thermal stretching is performed in 3-5 stages.

[0053] In this invention, as the fibers continuously thin during the hot drawing process, the fiber width needs to be continuously narrowed. Insufficient narrowing can easily lead to filament splitting and fuzzing, while excessive narrowing can cause uneven stretching due to increased thickness. Therefore, to further improve the uniformity of hot-drawn fiber monofilaments and reduce structural differences during fiber forming, the narrowing degree during the hot drawing process can be reasonably controlled. In a preferred embodiment, the method further includes a bundling process before each stage of hot drawing; and the fiber width after each bundling satisfies the following relationship: 0.8A / Dr≥B≥1.1A / Dr; where B is the fiber width after this bundling, in cm / k, A is the fiber width after the previous bundling, in cm / k, and Dr is the drawing multiple of this stage of hot drawing; wherein, when performing the first bundling, the fiber width after the previous bundling refers to the fiber width at the solidification exit.

[0054] In one specific implementation, when the number of thermal stretching stages is 3, the specific process of step (1) includes: spinning and solidifying the spinning solution, then performing the first bundling and stage 1 thermal stretching, then performing the second bundling and stage 2 thermal stretching, and then performing the third bundling and stage 3 thermal stretching to obtain thermally stretched fibers; and the width of the fiber after each bundling satisfies the following relationship: 0.8A / Dr≥B≥1.1A / Dr, and the width of the fiber after each bundling satisfies the following relationship: 0.8A / Dr≥B≥1.1A / Dr; where B is the width of the fiber after this bundling, in cm / k, A is the width of the fiber after the previous bundling, in cm / k, and Dr is the stretching multiple of this stage of thermal stretching. For example, when the fiber width at the solidification exit (i.e., the fiber width of the nascent fiber obtained after solidification) is 0.9 cm / k, and the draw ratio of the first-stage hot drawing is 1.3, the fiber width range after the first bundling is:

[0055] In this invention, the fiber width refers to the characteristic of fiber bundle thickness. During the spinning process, fibers are always produced in bundles. The fiber bundle is usually in a flat state during the process. Although the fiber width is a width data, it needs to be considered comprehensively when comparing the transverse dimensions due to the use of different spinneret specifications. Therefore, the fiber width characteristic described in this invention adopts the width-to-number ratio (cm / k) to reflect the stacking state of the fiber bundle during the process.

[0056] In a preferred embodiment, the bundling is performed at a distance of 5-10 cm from the inlet of the hot water stretching tank.

[0057] In a preferred embodiment, the thermal stretching is performed in a hot water stretching tank.

[0058] In a preferred embodiment, the temperature of the thermal stretching is 80-98°C, and the temperature of each stretching stage is not lower than the temperature of the previous stretching stage.

[0059] In a preferred embodiment, the total thermal stretching ratio is 2-6 times.

[0060] In this invention, the coefficient of variation of the swelling degree of the hot-drawn fiber represents the difference in swelling degree between individual fiber filaments. During their research, the inventors discovered that if the difference in swelling degree between individual fiber filaments is large, even if this difference eventually disappears after drying, the structural characteristics of the original filament causing the swelling degree difference will not disappear. Differences in crystallization, pores, and core-sheath structure in the original filament structure are inherited, and these structural differences will be further amplified during subsequent oxidation and carbonization. This leads to a large dispersion coefficient in the performance of individual fibers, resulting in a decrease in carbon fiber quality. Furthermore, the large difference in swelling degree causes an increase in fuzz, further deteriorating fiber quality. Therefore, the method described in this invention improves carbon fiber quality and reduces fuzz production by rationally controlling the coefficient of variation of the swelling degree of the hot-drawn fiber.

[0061] In a preferred embodiment, the coefficient of variation of fiber swelling can be detected using the following method:

[0062] (1) Place the sample to be tested in an ultrafiltration centrifuge tube and centrifuge at 5000g for 6 minutes. Manually separate the fibers and randomly select 10 groups of fiber samples, with 10 monofilaments in each group.

[0063] (2) Test the swelling of each group of fibers separately. The swelling test process is as follows: weigh the sample to be tested and record it as W3, then dry the fiber and weigh it and record it as W4. Swelling = 100*(W3-W4) / W4;

[0064] (3) Calculate the standard deviation SD and average value MN of the swelling of 10 groups of fiber samples, and then calculate the coefficient of variation Cv using the following formula: Cv=(SD / MN)×100%.

[0065] In this invention, in the above-mentioned method for testing the coefficient of variation of swelling of fibers, each sample consists of 10 monofilaments. This not only accurately and intuitively reflects the test results of swelling differences, but also reduces the inconvenience caused by the weighing process due to the light weight of a single filament.

[0066] In a preferred embodiment, the swelling degree of the thermally drawn fiber is 80-120%, more preferably 90-110%; specifically, it can be 80%, 85%, 90%, 95%, 100%, 105%, 110%, 115%, or 120%.

[0067] In a preferred embodiment, the coefficient of variation of the swelling of the thermally drawn fiber is ≤4%.

[0068] In a preferred embodiment, the single filament fineness of the thermally drawn fiber is 1-4 Dtex.

[0069] In a preferred embodiment, the post-processing includes: washing, oiling, drying and densification, steam stretching and heat setting.

[0070] In specific implementations, the conditions for water washing, oiling, drying and densification, steam stretching and heat setting are not subject to special requirements and can be conventional conditions in the field.

[0071] In one specific embodiment, the oiling agent used is amino silicone oil.

[0072] In one specific embodiment, the drying and densification temperature is 110-150°C; specifically, it can be 110°C, 120°C, 130°C, 140°C, or 150°C.

[0073] In one specific embodiment, the steam stretching pressure is 200-350 kPa, and the stretching ratio is 2.

[0074] In one specific embodiment, the pressure during heat setting is 80-180 kPa.

[0075] In this invention, pressure refers to absolute pressure.

[0076] In the method described in this invention, by reasonably controlling the plate density of the spinneret and the width of the nascent fiber obtained by solidification, and by reasonably controlling the shrinkage degree of the thermal stretching process, thermally stretched fibers with good structural consistency are obtained; after further processing, polyacrylonitrile and carbon fiber precursors are obtained.

[0077] A second aspect of the present invention provides polyacrylonitrile-based carbon fiber precursors prepared by the method described above.

[0078] A third aspect of the present invention provides the application of the polyacrylonitrile-based carbon fiber precursor described above in the preparation of carbon fibers.

[0079] A fourth aspect of the present invention provides a method for preparing carbon fiber, the method comprising the following steps:

[0080] The polyacrylonitrile-based carbon fiber precursor described above is subjected to pre-oxidation, low-temperature carbonization, and high-temperature carbonization.

[0081] Preferably, the pre-oxidation temperature is 200-260°C.

[0082] Preferably, the temperature for low-temperature carbonization is 400-750°C.

[0083] Preferably, the high-temperature carbonization temperature is 1150-1450℃.

[0084] The present invention will be described in detail below through embodiments, but the scope of protection of the present invention is not limited thereto.

[0085] The characterization and testing methods used in the following examples and comparative examples are as follows:

[0086] 1. Test method for swelling of thermally drawn fibers: Take 5g of the sample to be tested, place it in an ultrafiltration centrifuge tube and centrifuge it for 6 minutes under a centrifugal force of 5000g. Take it out and weigh it as W1. Then dry the fiber and weigh it as W2.

[0087] Swelling degree = 100*(W1-W2) / W2

[0088] 2. Test method for the coefficient of variation of swelling of hot-drawn fibers:

[0089] (1) Place the sample to be tested in an ultrafiltration centrifuge tube and centrifuge at 5000g for 6 minutes. Manually separate the fibers and randomly select 10 groups of fiber samples, with 10 monofilaments in each group.

[0090] (2) Test the swelling of each group of fibers separately. The swelling test process is as follows: weigh the sample to be tested and record it as W3, then dry the fiber and weigh it and record it as W4. Swelling = 100*(W3-W4) / W4;

[0091] (3) Calculate the standard deviation (SD) and mean (MN) of the swelling of the 10 fiber samples, and then calculate the coefficient of variation (Cv) according to the following formula:

[0092] Cv = (SD / MN) × 100%.

[0093] 3. The method for testing the tensile strength of carbon fiber shall be the same as that described in GB / T 3362-2005.

[0094] Example 1

[0095] (1) The spinning solution is a 20% by weight dimethyl sulfoxide solution of polyacrylonitrile copolymer. The intrinsic viscosity of the polyacrylonitrile copolymer is 1.88 dL / g. The polyacrylonitrile copolymer contains 98.5% by weight acrylonitrile structural units and 1.5% by weight itaconic acid structural units. NH3 is introduced to neutralize the carboxyl groups before spinning. The spinning solution is passed through a circular spinneret (6k holes, 0.060mm hole diameter, and 150 holes / cm²). 2 The yarn is extruded into a coagulation bath (60% by weight dimethyl sulfoxide aqueous solution, temperature 35℃), and the yarn width at the coagulation exit is controlled to be 1 cm / k. Then, a first bundling and first-stage hot drawing are performed, resulting in a yarn width of 0.77 cm / k after the first bundling. The first-stage hot drawing temperature is 90℃ and the draw ratio is 1.3. A second bundling and second-stage hot drawing are then performed, resulting in a yarn width of 0.59 cm / k after the second bundling. The second-stage hot drawing temperature is 92℃ and the draw ratio is 1.3. Finally, a third bundling and third-stage hot drawing are performed. After three rounds of bundling, the filament width is 0.46 cm / k. The temperature for the third stage of hot drawing is 94℃, and the draw ratio is 1.3. Then, a fourth round of bundling and a fourth stage of hot drawing are performed. After the fourth round of bundling, the filament width is 0.35 cm / k. The temperature for the fourth stage of hot drawing is 95℃, and the draw ratio is 1.3. Bundling is performed 10 cm away from the inlet of the hot water drawing tank. After four stages of hot drawing, the total width is 2.1 cm, the swelling degree of the hot-drawn fiber is 95%, the coefficient of variation of the swelling degree of the hot-drawn fiber is 3.1%, and the single filament fineness is 1.6 Dtex.

[0096] (2) After washing the hot-stretched fiber with water, the fiber is coated with amino silicone oil and dried and densified at 140°C. Then it is steam-stretched twice at 350KPa and heat-set at 150KPa to obtain polyacrylonitrile carbon fiber precursor.

[0097] Pre-oxidizing the above-mentioned polyacrylonitrile carbon fiber precursor at 200-240℃, carbonizing at a low temperature of 700℃, and carbonizing at a high temperature of 1350℃ can yield carbon fiber products with no fuzz, a tensile strength of 5.61GPa, and a Young's modulus of 315KPa.

[0098] Example 2

[0099] (1) The spinning solution is a 20% by weight dimethyl sulfoxide solution of polyacrylonitrile copolymer. The intrinsic viscosity of the polyacrylonitrile copolymer is 1.88 dL / g. The polyacrylonitrile copolymer contains 98.5% by weight acrylonitrile structural units and 1.5% by weight itaconic acid structural units. NH3 is introduced to neutralize the carboxyl groups before spinning. The spinning solution is passed through a circular spinneret (6k holes, 0.060mm hole diameter, and 140 holes / cm²). 2 The yarn is extruded into a coagulation bath (60% by weight dimethyl sulfoxide aqueous solution, temperature 35℃), and the yarn width at the coagulation exit is controlled to be 1 cm / k. Then, a first bundling and first-stage hot drawing are performed. After the first bundling, the yarn width is 0.77 cm / k, the first-stage hot drawing temperature is 90℃, and the draw ratio is 1.3. Then, a second bundling and second-stage hot drawing are performed. After the second bundling, the yarn width is 0.57 cm / k, the second-stage hot drawing temperature is 92℃, and the draw ratio is 1.35. Then, a third bundling and... The fiber width after the third stage of hot drawing is 0.41 cm / k, the temperature of the third stage of hot drawing is 94℃, and the draw ratio is 1.4 times. Then, the fiber width after the fourth stage of hot drawing and the fourth stage of hot drawing are carried out. The fiber width after the fourth stage of hot drawing is 0.29 cm / k and the draw ratio is 1.4 times. The bundling is carried out at a distance of 10 cm from the entrance of the hot water drawing tank. After four stages of drawing, the total width is 1.74 cm, the swelling degree of the hot drawn fiber is 90%, the coefficient of variation of the swelling degree of the hot drawn fiber is 2.8%, and the single filament fineness is 1.5 Dtex.

[0100] (2) After washing the hot-stretched fiber with water, the fiber is coated with amino silicone oil and dried and densified at 140°C. Then it is steam-stretched twice at 350KPa and heat-set at 150KPa to obtain polyacrylonitrile carbon fiber precursor.

[0101] Pre-oxidizing the above-mentioned polyacrylonitrile carbon fiber precursor at 200-240℃, carbonizing at a low temperature of 700℃, and carbonizing at a high temperature of 1200-1300℃ can yield carbon fiber products with no fuzz, a tensile strength of 5.75GPa, and a Young's modulus of 307KPa.

[0102] Example 3

[0103] (1) The spinning solution is a 20% by weight dimethyl sulfoxide solution of polyacrylonitrile copolymer. The intrinsic viscosity of the polyacrylonitrile copolymer is 1.88 dL / g. The polyacrylonitrile copolymer contains 98.5% by weight acrylonitrile structural units and 1.5% by weight itaconic acid structural units. NH3 is introduced to neutralize the carboxyl groups before spinning. The spinning solution is passed through a circular spinneret (6k holes, 0.060mm hole diameter, and 140 holes / cm²). 2The yarn is extruded into a coagulation bath (60% by weight dimethyl sulfoxide aqueous solution, temperature 35℃), with the yarn width at the coagulation exit controlled at 0.8 cm / k. Then, a first bundling and first-stage hot drawing are performed, resulting in a yarn width of 0.59 cm / k after the first bundling. The first-stage hot drawing temperature is 90℃ and the draw ratio is 1.35. A second bundling and second-stage hot drawing are then performed, resulting in a yarn width of 0.44 cm / k after the second bundling. The second-stage hot drawing temperature is 92℃ and the draw ratio is 1.35. Finally, a third bundling and third-stage hot drawing are performed. After the third bundling, the filament width is 0.31 cm / k, the temperature of the third-stage hot drawing is 94℃, and the draw ratio is 1.4 times. Then, the fourth bundling and the fourth-stage hot drawing are carried out. After the fourth bundling, the filament width is 0.22 cm / k, the temperature of the fourth-stage hot drawing is 95℃, and the draw ratio is 1.45 times. The bundling is carried out 10 cm away from the inlet of the hot water drawing tank. After four stages of hot drawing, the total width is 1.30 cm, the swelling degree of the hot-drawn fiber is 80%, the coefficient of variation of the swelling degree of the hot-drawn fiber is 2.6%, and the single filament fineness is 1.4 Dtex.

[0104] (2) After the hot-stretched fiber is washed with water, the fiber is coated with amino silicone oil and dried and densified at 140°C. Then it is stretched twice at 350KPa and heat-set at 150KPa to obtain polyacrylonitrile carbon fiber precursor.

[0105] Pre-oxidizing the above-mentioned polyacrylonitrile carbon fiber precursor at 200-240℃, carbonizing at a low temperature of 700℃, and carbonizing at a high temperature of 1200-1300℃ can yield carbon fiber products with no fuzz, a tensile strength of 5.83GPa, and a Young's modulus of 309KPa.

[0106] Example 4

[0107] (1) The spinning solution is a 20% by weight dimethyl sulfoxide solution of polyacrylonitrile copolymer. The intrinsic viscosity of the polyacrylonitrile copolymer is 1.88 dL / g. The polyacrylonitrile copolymer contains 98.5% by weight acrylonitrile structural units and 1.5% by weight itaconic acid structural units. NH3 is introduced to neutralize the carboxyl groups before spinning. The spinning solution is passed through a circular spinneret (6k holes, 0.060mm hole diameter, and 60 holes / cm²). 2The filaments are extruded into a coagulation bath (60% by weight dimethyl sulfoxide aqueous solution, temperature 35℃), with the filament width at the coagulation exit controlled at 1 cm / k. Then, a first bundling and first-stage hot drawing are performed, resulting in a filament width of 0.38 cm / k after the first bundling. The first-stage hot drawing temperature is 90℃, and the draw ratio is 1.1. A second bundling and second-stage hot drawing are then performed, resulting in a filament width of 0.28 cm / k after the second bundling. The second-stage hot drawing temperature is 92℃, and the draw ratio is 1.1. Finally, a third bundling and third-stage hot drawing are performed. After the first bundling, the filament width is 0.20 cm / k, the temperature of the third-stage hot drawing is 94℃, and the draw ratio is 1.1. Then, the fourth bundling and fourth-stage hot drawing are performed. After the fourth bundling, the filament width is 0.15 cm / k, the temperature of the fourth-stage hot drawing is 95℃, and the draw ratio is 1.2. Bundling is performed 10 cm away from the inlet of the hot water drawing tank. After four stages of drawing, the total width is 3.76 cm, the swelling of the hot-drawn fiber is 140%, the coefficient of variation of the swelling of the hot-drawn fiber is 3.8%, and the single filament fineness is 4.8 Dtex.

[0108] (2) After the hot-stretched fiber is washed with water, the fiber is coated with amino silicone oil and dried and densified at 140°C. Then it is stretched twice at 350KPa and heat-set at 150KPa to obtain polyacrylonitrile carbon fiber precursor.

[0109] The above-mentioned polyacrylonitrile carbon fiber precursor is pre-oxidized at 200-240℃, carbonized at a low temperature of 700℃, and carbonized at a high temperature of 1200-1300℃. The resulting carbon fiber product has fewer fuzzy fibers, a tensile strength of 5.31GPa, and a Young's modulus of 294GPa.

[0110] Comparative Example 1

[0111] (1) The spinning solution is a 20% by weight dimethyl sulfoxide solution of polyacrylonitrile copolymer. The intrinsic viscosity of the polyacrylonitrile copolymer is 1.88 dL / g. The polyacrylonitrile copolymer contains 98.5% by weight acrylonitrile structural units and 1.5% by weight itaconic acid structural units. NH3 is introduced to neutralize the carboxyl groups before spinning. The spinning solution is passed through a circular spinneret (6k holes, 0.060mm hole diameter, and 240 holes / cm²). 2The yarn is extruded into a coagulation bath (60% by weight dimethyl sulfoxide aqueous solution, temperature 35℃), and the yarn width at the coagulation exit is controlled to be 1 cm / k. Then, a first bundling and first-stage hot drawing are performed, resulting in a yarn width of 0.77 cm / k after the first bundling. The first-stage hot drawing temperature is 90℃ and the draw ratio is 1.3. A second bundling and second-stage hot drawing are then performed, resulting in a yarn width of 0.59 cm / k after the second bundling. The second-stage hot drawing temperature is 92℃ and the draw ratio is 1.3. A third bundling and third-stage hot drawing are then performed, resulting in a yarn width of 0.46 cm / k after the third bundling. The third-stage hot drawing temperature is 94℃ and the draw ratio is 1.3. Finally, a fourth... The process involves four stages of hot drawing and bundling. After the fourth stage of bundling, the filament width is 0.35 cm / k. The temperature for the fourth stage of hot drawing is 95℃, and the draw ratio is 1.3. Bundling is performed 10 cm from the inlet of the hot water drawing tank. The filament width after each stage of bundling satisfies the following relationship: 0.8A / Dr ≥ B ≥ 1.1A / Dr. Wherein, B is the filament width after this stage of bundling (in cm / k), A is the filament width after the previous stage of bundling (in cm / k), and Dr is the draw ratio for this stage of hot drawing. After four stages of hot drawing, the total width is 2.1 cm, the bulkiness of the fiber after hot drawing is 95%, the coefficient of variation of bulkiness of the hot-drawn fiber is 8.5%, and the single filament fineness is 1.5 Dtex.

[0112] (2) After the hot-stretched fiber is washed with water, the fiber is coated with amino silicone oil and dried and densified at 140°C. Then it is stretched twice at 350KPa and heat-set at 150KPa to obtain polyacrylonitrile carbon fiber precursor.

[0113] Pre-oxidizing the above-mentioned polyacrylonitrile carbon fiber precursor at 200-240℃, carbonizing at a low temperature of 700℃, and carbonizing at a high temperature of 1200-1300℃ can yield carbon fiber products with fewer fuzz, a tensile strength of 5.25GPa, and a Young's modulus of 311KPa.

[0114] Comparative Example 2

[0115] (1) The spinning solution is a 20% by weight dimethyl sulfoxide solution of polyacrylonitrile copolymer. The intrinsic viscosity of the polyacrylonitrile copolymer is 1.88 dL / g. The polyacrylonitrile copolymer contains 98.5% by weight acrylonitrile structural units and 1.5% by weight itaconic acid structural units. NH3 is introduced to neutralize the carboxyl groups before spinning. The spinning solution is passed through a circular spinneret (6k holes, 0.060mm hole diameter, and 140 holes / cm²). 2The yarn is extruded into a coagulation bath (60% by weight dimethyl sulfoxide aqueous solution, temperature 35℃), and the yarn width at the coagulation exit is controlled to be 0.5 cm / k. Then, a first bundling and first-stage hot drawing are performed, resulting in a yarn width of 0.38 cm / k after the first bundling. The first-stage hot drawing temperature is 90℃ and the draw ratio is 1.3. A second bundling and second-stage hot drawing are then performed, resulting in a yarn width of 0.28 cm / k after the second bundling. The second-stage hot drawing temperature is 92℃ and the draw ratio is 1.35. Finally, a third bundling and third-stage hot drawing are performed... After three rounds of bundling, the filament width is 0.20 cm / k. The temperature for the third stage of hot drawing is 94℃, and the draw ratio is 1.4. Then, a fourth round of bundling and a fourth stage of hot drawing are performed. After the fourth round of bundling, the filament width is 0.15 cm / k. The temperature for the fourth stage of hot drawing is 95℃, and the draw ratio is 1.4. Bundling is performed 10 cm away from the inlet of the hot water drawing tank. After four stages of drawing, the total width is 0.87 cm. The swelling degree of the fiber after hot drawing is 90%, the coefficient of variation of the swelling degree of the fiber after hot drawing is 10.5%, and the single filament fineness is 1.5 Dtex.

[0116] (2) After the hot-stretched fiber is washed with water, the fiber is coated with amino silicone oil and dried and densified at 140°C. Then it is stretched twice at 350KPa and heat-set at 150KPa to obtain polyacrylonitrile carbon fiber precursor.

[0117] Pre-oxidizing the above-mentioned polyacrylonitrile carbon fiber precursor at 200-240℃, carbonizing at a low temperature of 700℃, and carbonizing at a high temperature of 1200-1300℃ can yield carbon fiber products with fewer fuzz, a tensile strength of 5.25GPa, and a Young's modulus of 311KPa.

[0118] Comparative Example 3

[0119] (1) The spinning solution is a 20% by weight dimethyl sulfoxide solution of polyacrylonitrile copolymer. The intrinsic viscosity of the polyacrylonitrile copolymer is 1.88 dL / g. The polyacrylonitrile copolymer contains 98.5% by weight acrylonitrile structural units and 1.5% by weight itaconic acid structural units. NH3 is introduced to neutralize the carboxyl groups before spinning. The spinning solution is passed through a circular spinneret (6k holes, 0.060mm hole diameter, and 60 holes / cm²). 2The yarn is extruded into a coagulation bath (60% by weight dimethyl sulfoxide aqueous solution, temperature 35℃), with the yarn width at the coagulation exit controlled at 1 cm / k. Then, a first bundling and first-stage hot drawing are performed, resulting in a yarn width of 0.38 cm / k after the first bundling. The first-stage hot drawing temperature is 90℃, and the draw ratio is 1.3. A second bundling and second-stage hot drawing are then performed, resulting in a yarn width of 0.28 cm / k after the second bundling. The second-stage hot drawing temperature is 92℃, and the draw ratio is 1.3. Finally, a third bundling and third-stage hot drawing are performed. After the third bundling, the filament width is 0.20 cm / k, the temperature of the third-stage hot drawing is 94℃, and the draw ratio is 1.3. Then, the fourth bundling and fourth-stage hot drawing are performed. After the fourth bundling, the filament width is 0.15 cm / k, the temperature of the fourth-stage hot drawing is 95℃, and the draw ratio is 1.3. The bundling is performed 10 cm away from the inlet of the hot water drawing tank. After four stages of drawing, the total width is 0.87 cm, the swelling degree of the hot-drawn fiber is 90%, the coefficient of variation of the swelling degree of the hot-drawn fiber is 9.4%, and the single filament fineness is 1.5 Dtex.

[0120] (2) After the hot-stretched fiber is washed with water, the fiber is coated with amino silicone oil and dried and densified at 140°C. Then it is stretched twice at 350KPa and heat-set at 150KPa to obtain polyacrylonitrile carbon fiber precursor.

[0121] The above-mentioned polyacrylonitrile carbon fiber precursor is pre-oxidized at 200-240℃, carbonized at a low temperature of 700℃, and carbonized at a high temperature of 1200-1300℃. The resulting carbon fiber product has more carbon fiber fuzz, a tensile strength of 4.99GPa, and a Young's modulus of 311KPa.

[0122] Comparative Example 4

[0123] (1) The spinning solution is a 20% by weight dimethyl sulfoxide solution of polyacrylonitrile copolymer. The intrinsic viscosity of the polyacrylonitrile copolymer is 1.88 dL / g. The polyacrylonitrile copolymer contains 98.5% by weight acrylonitrile structural units and 1.5% by weight itaconic acid structural units. NH3 is introduced to neutralize the carboxyl groups before spinning. The spinning solution is passed through a circular spinneret (6k holes, 0.060mm hole diameter, and 60 holes / cm²). 2The yarn is extruded into a coagulation bath (60% by weight dimethyl sulfoxide aqueous solution, temperature 35℃), and the yarn width at the coagulation exit is controlled to be 1 cm / k. Then, a first bundling and first-stage hot drawing are performed, resulting in a yarn width of 0.77 cm / k after the first bundling. The temperature for the first-stage hot drawing is 90℃, and the draw ratio is 1.3. A second bundling and second-stage hot drawing are then performed, resulting in a yarn width of 0.77 cm / k after the second bundling. The temperature for the second-stage hot drawing is 92℃, and the draw ratio is 1.3. Finally, a third bundling and third-stage hot drawing are performed. After the first bundling, the filament width is 0.77 cm / k, the temperature of the third-stage hot drawing is 94℃, and the draw ratio is 1.3. Then, a fourth bundling and a fourth-stage hot drawing are performed. After the fourth bundling, the filament width is 0.77 cm / k, the temperature of the fourth-stage hot drawing is 95℃, and the draw ratio is 1.3. Bundling is performed 10 cm away from the inlet of the hot water drawing tank. After four stages of drawing, the total width is 4.62 cm, the swelling degree of the hot-drawn fiber is 90%, the coefficient of variation of the swelling degree of the hot-drawn fiber is 5.21%, and the single filament fineness is 1.5 Dtex.

[0124] (2) After the hot-stretched fiber is washed with water, the fiber is coated with amino silicone oil and dried and densified at 140°C. Then it is stretched twice at 350KPa and heat-set at 150KPa to obtain polyacrylonitrile carbon fiber precursor.

[0125] The above-mentioned polyacrylonitrile carbon fiber precursor is pre-oxidized at 200-240℃, carbonized at a low temperature of 700℃, and carbonized at a high temperature of 1200-1300℃. The resulting carbon fiber product has more carbon fiber fuzz, a tensile strength of 5.21GPa, and a Young's modulus of 315KPa.

[0126] Test Example 1

[0127] The fuzziness, tensile strength, and Young's modulus of the carbon fibers prepared in the examples and comparative examples are shown in Table 1.

[0128] Table 1

[0129] serial number Wool condition Tensile strength (GPa) Young's modulus (kPa) Example 1 none 5.61 315 Example 2 none 5.75 307 Example 3 none 5.83 309 Example 4 few 5.31 294 Comparative Example 1 few 5.25 311 Comparative Example 2 few 5.11 305 Comparative Example 3 many 4.99 311 Comparative Example 4 many 5.21 315

[0130] As shown in Table 1, the method described in this invention can produce high-quality carbon fiber precursors without fuzz or broken fibers, which can be used to prepare high-performance carbon fibers.

[0131] 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 producing a polyacrylonitrile-based carbon fiber precursor, characterized by, The method comprises the following steps: (1) spinning dope is jetted and coagulated, and then hot drawn to obtain hot drawn fiber; (2) the hot drawn fiber is post-treated to obtain polyacrylonitrile-based carbon fiber precursor; The coefficient of variation of the swelling degree of the hot drawn fiber is less than or equal to 5%. The hole density of the jet plate used in jetting is 80-200 holes per square centimeter. The width of the fiber web of the as-spun fiber obtained by controlling coagulation is 0.8-1.1 cm / k. The number of the hot drawing is 3-5, and the bundling is performed before each hot drawing, and the width of the fiber web after each bundling satisfies the following relationship: 0.8A / Dr≥B≥1.1A / Dr; wherein B is the width of the fiber web after the current bundling, A is the width of the fiber web after the previous bundling, and Dr is the draw ratio of the current hot drawing.

2. The method of claim 1, wherein, The swelling degree of the hot drawn fiber is 80-120%.

3. The method according to claim 1 or 2, characterized in that, The fineness of the monofilament of the hot drawn fiber is 1-4 Dtex.

4. The method of claim 1, wherein, The hole density of the jet plate used in jetting is 120-160 holes per square centimeter.

5. The method of claim 4, wherein, The jet plate used in jetting is a circular jet plate.

6. The method of claim 1, wherein, The width of the fiber web of the as-spun fiber obtained by controlling coagulation is 0.8-1.1 cm / k.

7. The method of claim 1, wherein, The bundling is performed at a distance of 5-10 cm from the inlet of the hot water drawing tank.

8. The method according to claim 1 or 7, characterized in that, The temperature of the hot drawing is 80-98℃, and the temperature of each drawing is not lower than the temperature of the previous drawing.

9. The method according to claim 1 or 7, characterized in that, The total draw ratio of the hot drawing is 2-6.

10. The method of claim 1, wherein, The process of the post-treatment comprises: water washing, oiling, drying densification, steam drawing, and heat setting.

11. The polyacrylonitrile-based carbon fiber precursor prepared by the method of any one of claims 1-10.

12. The use of the polyacrylonitrile-based carbon fiber precursor of claim 11 in the preparation of carbon fiber.

13. A method of producing carbon fibers, characterized by, The method comprises the following steps: The polyacrylonitrile-based carbon fiber precursor of claim 11 is pre-oxidized, low-temperature carbonized, and high-temperature carbonized.

14. The method of claim 13, wherein, The temperature of the pre-oxidation is 200-260℃.

15. The method of claim 13, wherein, The temperature of the low-temperature carbonization is 400-750℃.

16. The method of claim 13, wherein, The temperature of the high-temperature carbonization is 1150-1450℃.