Carbon fiber with micro-groove structure and preparation method thereof

Abstract

The invention discloses a carbon fiber with a micro-groove structure and a preparation method of the carbon fiber. The method comprises the following steps: carrying out dry-wet spinning, solidification drafting, primary drafting, washing, oiling, drying densification, secondary drafting and heat setting on a polyacrylonitrile fiber spinning solution to obtain a polyacrylonitrile precursor; the polyacrylonitrile precursor is subjected to pre-oxidation and carbonization treatment to obtain the carbon fiber, the weight-average molecular weight of a polymer in a polyacrylonitrile fiber spinning solution is 22 thousand to 300 thousand, the molecular weight distribution of the polymer in the spinning solution is 1.5 to 2.5, the trickle linear speed of a spinneret plate for dry-wet spinning is 10 m / min to 16 m / min, and the height of an air layer is 2 mm to 5 mm. By adopting the method, the carbon fiber with the micro-groove structure on the surface can be prepared, and the possibility is provided for realizing both the tensile property and the interface property of the high-performance carbon fiber.

Description

Technical Field

[0001] This invention belongs to the field of fibers, specifically relating to a method for preparing carbon fibers with microgroove structures. Background Technology

[0002] Polyacrylonitrile (PAN)-based carbon fiber is the most widely used and consumed of the three major carbon fiber varieties: PAN-based, viscose-based, and pitch-based. PAN-based carbon fiber is divided into high-strength, high-modulus, and ultra-high-strength high-modulus types. The high-strength type can be further divided into two main categories: dry-wet process and wet process. Carbon fibers prepared by the wet process have a regular groove structure on the surface, while carbon fibers prepared by the dry-wet process have a smooth surface.

[0003] PAN-based carbon fibers exhibit outstanding tensile properties. From the perspective of carbon fiber tensile properties, the surface groove structure, being an open defect, is one of the key factors affecting the high performance of carbon fibers. Carbon fibers prepared using a dry-wet process with a smooth surface can achieve ultra-high strength. Currently, all reported ultra-high strength carbon fibers, both domestically and internationally, are prepared using a dry-wet process, including the T1100 and T1200 grades represented by Toray Industries, Japan. Furthermore, the fine-stream solidification characteristics of the spinnerets in both dry-wet and wet processes result in a more homogeneous radial structure and better axial orientation in the fibers produced by the dry-wet process, which is more conducive to the preparation of high-performance carbon fibers.

[0004] High-performance carbon fibers are typically used in composite materials, and the interfacial bonding ability between carbon fibers and the resin matrix is ​​one of the important factors affecting the performance of composite materials. The surface groove structure of carbon fibers has a strong physical interlocking effect with the resin matrix, which can effectively improve the interfacial bonding ability between the two. On the other hand, a smooth carbon fiber surface has almost no physical interlocking effect, which is not conducive to the realization of the mechanical properties of carbon fibers in composite materials.

[0005] To keep pace with the trend of high-performance carbon fiber, while ensuring its tensile properties, its interfacial properties are also a crucial factor that cannot be ignored. Therefore, developing a carbon fiber that combines the surface processing characteristics of both wet and dry-wet processes is a powerful method to achieve a balance between tensile and interfacial properties. Summary of the Invention

[0006] This invention provides a carbon fiber with a microgroove structure and a method for preparing the same. This method can prepare carbon fibers with a surface microgroove structure, which makes it possible to achieve both tensile and interfacial properties of high-performance carbon fibers.

[0007] In one aspect of the present invention, a method for preparing carbon fibers having a microgroove structure is provided, comprising: Polyacrylonitrile fiber spinning solution is processed by dry and wet spinning, coagulation and stretching, primary stretching, water washing, oiling, drying and densification, secondary stretching and heat setting to obtain polyacrylonitrile precursor fiber. The polyacrylonitrile precursor fiber is pre-oxidized and carbonized to obtain carbon fiber. The polyacrylonitrile fiber spinning solution has a weight-average molecular weight of 220,000-300,000, a molecular weight distribution of 1.5-2.5, a spinneret flow velocity of 10 m / min-16 m / min, and an air layer height of 2 mm-5 mm.

[0008] In some embodiments of the present invention, the preparation method of the polyacrylonitrile fiber spinning solution includes: adding acrylonitrile, itaconic acid, a first initiator, and dimethyl sulfoxide into a polymerization reactor and mixing them for polymerization; when the viscosity of the polymerization system reaches 300 poise-550 poise, adding a second initiator into the polymerization system and continuing the reaction to obtain the polyacrylonitrile fiber spinning solution.

[0009] In some embodiments of the present invention, the molar ratio of acrylonitrile to itaconic acid is (93-99.5):(0.5-7).

[0010] In some embodiments of the present invention, the total amount of the first initiator and the second initiator is 0.1%-1% of the total molar amount of acrylonitrile and itaconic acid.

[0011] In some embodiments of the present invention, the molar ratio of the first initiator to the second initiator is (2-3):(2-3).

[0012] In some embodiments of the present invention, the second initiator is added by continuous dripping, and the dripping is completed within 30 min to 60 min.

[0013] In some embodiments of the present invention, the first initiator and the second initiator each independently comprise azobisisobutyronitrile and / or azobisisoheptanenitrile.

[0014] In some embodiments of the present invention, the viscosity of the polyacrylonitrile fiber spinning solution at 45°C is 700 poise to 1200 poise.

[0015] In some embodiments of the present invention, the solidification stretching includes a first solidification stretching or a second solidification stretching. The first solidification stretching sequentially includes primary solidification, secondary solidification, and tertiary solidification. The primary solidification uses a first solidification bath at a temperature of 20-30°C. The first solidification bath is a mixture of dimethyl sulfoxide and water at a volume ratio of 1:(0.2-0.6). The stretching ratio of the primary solidification is 1.5-4.0 times, and the first solidification time is 0.5 seconds. -2 minutes; the second coagulation bath temperature for the secondary coagulation is 20-50℃, the second coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(0.5-1.5), and the coagulation time for the secondary coagulation is 0.5-2 minutes; the third coagulation bath temperature for the tertiary coagulation is 20-50℃, the third coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(4-7), and the coagulation time for the tertiary coagulation is 0.5-2 minutes. The coagulation bath temperature for the second coagulation stretching is 3-15℃, the coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(3-19), the coagulation stretching ratio is 1.5-4.0 times, and the coagulation time is 0.5-2 minutes.

[0016] In some embodiments of the present invention, the stretching medium for the first-stage stretching is water vapor at 100-110°C, and the stretching ratio is 4-10 times.

[0017] In some embodiments of the present invention, the drying and densification temperature is 110-150°C.

[0018] In some embodiments of the present invention, the stretching medium for the secondary stretching is water vapor at 120-150°C, and the stretching ratio is 2-5 times.

[0019] In some embodiments of the present invention, the heat setting temperature is 110-180°C.

[0020] In some embodiments of the present invention, the pre-oxidation adopts 4-6 temperature zones with gradient heating, the initial temperature of the pre-oxidation treatment is 180-220℃, the final temperature is 250-300℃, and the total pre-oxidation time is 40-100min.

[0021] In some embodiments of the present invention, the draw ratio of the pre-oxidation process is 30-80% of the breaking stress of the pre-oxidized fiber obtained by the pre-oxidation.

[0022] In some embodiments of the present invention, the carbonization treatment includes low-temperature carbonization and high-temperature carbonization. The low-temperature carbonization uses high-purity nitrogen as a protective gas, at a temperature of 300-800°C, for a time of 1.5-6 minutes. The draw ratio of the low-temperature carbonization process is 20-70% of the breaking stress of the fiber obtained by the low-temperature carbonization. The high-temperature carbonization uses high-purity nitrogen as a protective gas, at a temperature of 1200-1800°C, for a time of 1-4 minutes.

[0023] In some embodiments of the present invention, the Ra of the carbon fiber surface is 5nm-25nm.

[0024] In a second aspect of the invention, the invention provides a carbon fiber obtained by means of the method described in the first aspect of the invention.

[0025] This invention utilizes a polyacrylonitrile fiber spinning solution with a polymer weight-average molecular weight of 220,000-300,000 and a polymer molecular weight distribution of 1.5-2.5. The solution is then subjected to dry-wet spinning, with the spinneret's streamline velocity controlled at 10-16 m / min and the air layer height at 2-5 mm. After pre-oxidation and carbonization, carbon fibers with a surface microgroove structure can be prepared, providing a possibility for achieving a balance between the tensile and interfacial properties of high-performance carbon fibers. Attached Figure Description

[0026] Figure 1 Here is a SEM image of the carbon fiber obtained in Example 8; Figure 2 This is a SEM image of the carbon fiber obtained in Comparative Example 6. Detailed Implementation

[0027] The present invention will be further described in detail below with reference to the embodiments. The following embodiments are merely descriptive and not limiting, and should not be used to limit the scope of protection of the present invention.

[0028] The "range" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is understood that ranges of 60-110 and 80-120 are also expected. Furthermore, if minimum range values ​​1 and 2 are listed, and if maximum range values ​​3, 4, and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers, and ranges defined in this way can include endpoints a and b. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0029] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0030] In one aspect of the present invention, a method for preparing carbon fibers with microgroove structures is provided, the method comprising: S100: Polyacrylonitrile fiber precursor is obtained by wet and dry spinning, coagulation and drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting of polyacrylonitrile fiber spinning solution. In this step, the weight-average molecular weight of the polymer in the polyacrylonitrile fiber spinning solution is 220,000-300,000, the molecular weight distribution of the polymer in the spinning solution is 1.5-2.5, the spinneret flow velocity in the dry-wet spinning process is 10 m / min-16 m / min, and the air layer height is 2 mm-5 mm. This invention utilizes a high molecular weight and narrow molecular weight distribution polyacrylonitrile fiber spinning solution, where the macromolecular chains in the spinning solution form numerous physical entanglement points (preparing for a high extrusion swell ratio in the subsequent process). Combined with the high spinneret speed (i.e., high spinneret shear rate, resulting in a high extrusion swell ratio) and relatively short air layer height in the dry-wet spinning process (where extrusion swell does not have time to fully retract), the fine stream of spinning solution enters the coagulation bath. Upon entering the coagulation bath, a normal contraction force occurs. The imbalance between the residual swell effect and the normal contraction force forms a microgroove structure on the fiber surface, providing a possibility for achieving a balance between the tensile and interfacial properties of high-performance carbon fibers.

[0031] In some embodiments of the present invention, the preparation method of the polyacrylonitrile fiber spinning solution includes: using acrylonitrile and itaconic acid as comonomers, azobisisobutyronitrile and / or azobisisoheptanenitrile as the first initiator, and dimethyl sulfoxide as the solvent, adding acrylonitrile, itaconic acid, and dimethyl sulfoxide into a polymerization reactor, stirring evenly, raising the temperature inside the polymerization reactor to 50-65°C, adding the first initiator, and allowing the system inside the polymerization reactor to undergo a free radical polymerization reaction under the action of the first initiator (azobisisobutyronitrile and / or azobisisoheptanenitrile, preferably azobisisobutyronitrile), and testing the viscosity of the polymerization system in the polymerization reactor in real time. When the viscosity of the polymerization system reaches 300-550 poise, adding the second initiator (azobisisobutyronitrile and / or azobisisoheptanenitrile, preferably azobisisoheptanenitrile) to the polymerization system, and continuing the reaction for 6-9 hours after the addition is complete, then terminating the reaction to obtain the polyacrylonitrile fiber spinning solution.

[0032] Furthermore, in the above-mentioned preparation of spinning solution, acrylonitrile and itaconic acid are added in a molar ratio of (93-99.5):(0.5-7); the amount of dimethyl sulfoxide and comonomer added is 19%-23% of the total mass of acrylonitrile and itaconic acid, and the total amount of the first initiator and the second initiator is 0.1-1% of the total molar mass of acrylonitrile and itaconic acid.

[0033] Furthermore, in the above-mentioned preparation of spinning solution, the molar ratio of the first initiator to the second initiator is (2-3):(2-3); and the second initiator is added continuously, and is added at a uniform rate within 30-60 minutes. After the addition is completed, the reaction continues for 6-9 hours, and then the reaction is terminated.

[0034] In some embodiments of the present invention, the above method further includes: treating the polyacrylonitrile fiber spinning solution for desizing and deinitiator removal in the following manner: raising the temperature of the polymerization reactor to 70-75°C, evacuating the vacuum, and after 5-8 hours, lowering the temperature of the polymerization reactor to 65-72°C, continuing to evacuate the vacuum for 4-10 hours, and performing desizing and deinitiator removal treatment.

[0035] The final spinning solution has a solid content of 19%-23%, a weight-average molecular weight of polymer in the solution of 220,000-300,000, a molecular weight distribution of 1.5-2.5, and a viscosity (45℃) of 700 poise-1200 poise.

[0036] In some embodiments of the present invention, the coagulation and drawing process in the preparation of polyacrylonitrile precursor fibers includes a first coagulation and drawing or a second coagulation and drawing. The first coagulation and drawing sequentially includes primary coagulation, secondary coagulation, and tertiary coagulation. The primary coagulation uses a first coagulation bath at a temperature of 20-30°C, and the first coagulation bath is a mixture of dimethyl sulfoxide and water at a volume ratio of 1:(0.2-0.6). The drawing ratio of the primary coagulation is 1.5-4.0 times. The second coagulation time is 0.5-2 minutes; the second coagulation bath temperature for the second stage of coagulation is 20-50℃, and the second coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(0.5-1.5). The coagulation time for the second stage of coagulation is 0.5-2 minutes; the third coagulation bath temperature for the third stage of coagulation is 20-50℃, and the third coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(4-7). The coagulation time for the third stage of coagulation is 0.5-2 minutes. The coagulation bath temperature for the second stage of coagulation and stretching is 3-15℃, and the coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(3-19). The coagulation stretching ratio is 1.5-4.0 times, and the coagulation time is 0.5-2 minutes.

[0037] The entry of the spinning solution into the coagulation bath is a crucial step in controlling the cross-sectional morphology of the fiber. Both the second coagulation drawing (using low temperature and low concentration, with a coagulation bath temperature of 3-15℃ and a volume ratio of dimethyl sulfoxide to water of 1:(3-19)) and the first coagulation drawing (using high temperature and high concentration for the first stage of coagulation, i.e., a first stage coagulation bath temperature of 20-30℃ and a volume ratio of dimethyl sulfoxide to water of 1:(0.2-0.6)) can achieve high roundness of the nascent fiber cross-section. Furthermore, under the first coagulation drawing condition, using gradient coagulation technology helps to slow down the coagulation rate of the fiber sheath, resulting in better radial structural homogeneity of the precursor fiber.

[0038] In some embodiments of the present invention, the stretching medium for the first-stage stretching in the above-mentioned preparation of polyacrylonitrile precursor fibers is water vapor at 100-110°C, and the stretching ratio is 4-10 times; the washing process adopts a multi-stage gradient heating washing process, with the water flow opposite to the fiber direction to facilitate thorough washing, the washing temperature is 50-90°C, the washing time is about 4-10 minutes, and the washing stretching ratio is 97%-101%; the oiling agent in the oiling tank includes an amino-modified silicone oil emulsion with a solid content of 1.5%-2.5%; the drying and densification temperature is 110-150°C; the stretching medium for the second-stage stretching is water vapor at 120-150°C, and the stretching ratio is 2-5 times; the heat setting temperature is 110-180°C, and a stretching ratio of 96%-102% is applied simultaneously.

[0039] In this invention, the method for testing the weight-average molecular weight and molecular weight distribution of the polymer in the spinning solution includes: using a gel permeation chromatography (GPC) instrument manufactured by Waters Corporation, using dimethylformamide as a solvent, and adding an appropriate amount of lithium chloride when preparing the polymer solution.

[0040] In this invention, the method for testing the solid content of spinning solution includes: taking a certain mass of spinning solution, denoted as M, precipitating the polymer in it, drying it, and recording the polymer mass as m when the mass is stable. The ratio of the mass of the dried polymer m to the mass of the spinning solution M is the solid content of the spinning solution.

[0041] In this invention, unless otherwise specified, the viscosity of the polymerization system is the viscosity at 45°C. The testing method includes: using a rotational viscometer to test, adding the spinning solution into the test chamber, circulating water at 45°C through the chamber jacket, starting the test after 30 minutes of water circulation, recording the test data when it is stable, and taking the average value of 3 tests.

[0042] S200: Carbon fiber is obtained by pre-oxidizing and carbonizing the polyacrylonitrile precursor fiber. In some embodiments of the present invention, the pre-oxidation employs 4-6 temperature gradient zones, with an initial pre-oxidation temperature of 180-220°C and a final temperature of 250-300°C. The total pre-oxidation time is 40-100 minutes. The draw ratio of the pre-oxidation process is 30%-80%, preferably 40%-60%, of the breaking stress of the pre-oxidized fiber obtained after pre-oxidation, resulting in a bulk density of 1.32-1.47 g / cm³. 3 Pre-oxidized fibers. The pre-oxidation process, when stretched, promotes the alignment of the generated ring structures towards a preferred orientation, and moderate stretching yields even better results.

[0043] In some embodiments of the present invention, the carbonization treatment includes low-temperature carbonization and high-temperature carbonization. The low-temperature carbonization uses high-purity nitrogen as a protective gas, with an oxygen content of less than 5 ppm, at a temperature of 300-800°C for 1.5-6 minutes. The draw ratio of the low-temperature carbonization process is 20%-70% of the fracture stress of the fiber obtained by the low-temperature carbonization, preferably 40%-50%. Moderate draw is beneficial to the orientation and arrangement of carbon structures in the fiber, thereby improving performance. The high-temperature carbonization uses high-purity nitrogen as a protective gas, with an oxygen content of less than 3 ppm, at a temperature of 1200-1800°C for 1-4 minutes to obtain carbon fibers with a microgroove structure on the surface. The Ra obtained by AFM testing is 5 nm-25 nm.

[0044] The method for testing the Ra surface roughness of carbon fibers using atomic force microscopy (AFM) includes: characterizing the micro-area roughness and surface morphology of the carbon fibers. Before testing, the carbon fiber samples were ultrasonically cleaned for 3 minutes each with acetone, ethanol, and deionized water, and then dried. During sample preparation, double-sided tape was adhered to both sides of a glass slide, and the carbon fiber filaments were vertically taut and adhered to the tape. The sample was then fixed on the sample stage. During testing, the frequency was set to 1 Hz, the tapping mode was used, and the scanning area was 2 μm × μm. Each sample was tested three times, and the average value was taken.

[0045] The method for preparing carbon fibers with microgroove structures according to the present invention has at least one of the following effects: (1) From the perspective of polymerization control: This invention achieves synergistic regulation of the polymer and its molecular weight and molecular weight distribution in the spinning solution by continuously adding initiators in the middle and late stages of polymerization. On the one hand, it allows the PAN molecular chains to grow to the required molecular weight, which is beneficial to the high performance of the fibers. On the other hand, by continuously adding initiators in the middle and late stages, it is beneficial to ensure that the initiators diffuse evenly in the relatively viscous system (avoiding local large-scale initiation). The added initiators can initiate unreacted monomers in the system and can also act as scavengers for long-chain macromolecular free radicals to terminate the reaction, thereby avoiding or alleviating the problems of excessively large molecular weight and excessively wide molecular weight distribution caused by the sharp increase in viscosity of the polymerization system due to gelation effect and bimolecular termination of macromolecular chains. If the initiator is added in a viscosity of less than 300 poise, the molecular weight of the PAN generated in the system is low, and there are a large number of unreacted monomers. The added initiator initiates the monomers, causing the monomers to no longer participate in the addition reaction of the original PAN polymer free radicals, ultimately resulting in a low molecular weight of PAN in the system, which affects the performance of PAN fibers and carbon fibers. If an initiator is added when the viscosity of the system is higher than 550 poise, the polymerization system will be too viscous, and the added initiator will have difficulty colliding with the monomer. The free radicals of the long PAN molecular chain may collide with the initiator and terminate the reaction, or there may be negative effects such as double-click termination of the free radicals of the large PAN molecular chain, resulting in automatic acceleration. In this case, the added initiator will not play a role in controlling the polymerization process.

[0046] (2) From the perspective of carbon fiber tensile properties: This invention retains the process line of dry-jet wet spinning, so that when the fine stream of spinning solution solidifies and generates nascent fibers, it avoids the problem of poor radial structure homogeneity of nascent fibers caused by the high extrusion swell ratio of 3-5 times in wet spinning, which is beneficial to the preparation of high-performance carbon fibers.

[0047] (3) From the perspective of the interfacial properties between carbon fiber and resin matrix: Carbon fibers prepared by wet spinning typically have a regular groove structure on their surface, and their Ra obtained by AFM testing is between 30-50 nm, depending on the process adjustment during preparation. The Ra of the carbon fiber prepared by this invention is between 5-25 nm in AFM testing. In contrast, the Ra of the carbon fiber prepared by conventional dry and wet spinning processes is between 1-3 nm in AFM testing. From the perspective of the physical interlocking of the carbon fiber interface, the interfacial properties of the carbon fiber prepared by this invention are superior to those of carbon fibers prepared by dry and wet spinning processes. After the same anodizing treatment and using the same resin matrix, the interlaminar shear strength of the carbon fiber prepared by this invention is 15%-25% higher than that of carbon fibers prepared by traditional dry and wet spinning processes.

[0048] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and should not be construed as limiting the present invention in any way.

[0049] Example 1 (1) Preparation of spinning solution Acrylonitrile and itaconic acid were blended at a molar ratio of 97:3 and added to a polymerization reactor. Then, dimethyl sulfoxide solvent with a total mass ratio of acrylonitrile to itaconic acid of 3.65:1 was added. When the temperature of the polymerization reactor rose to 62°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.25% of the total molar percentage of acrylonitrile and itaconic acid, was added. When the viscosity of the polymer solution in the reactor (45°C) rose to 350 poise, the initiator (azobisisobutyronitrile) was added dropwise continuously, with the addition completed within 30 minutes. After the reaction continued for 4 hours, the reaction was quickly stopped. Then, the temperature of the polymerization reactor was raised to 74°C and a vacuum was drawn. After 6 hours, the temperature of the polymerization reactor was lowered to 70°C and a vacuum was drawn for another 6 hours to remove monomers and initiators, thus obtaining polyacrylonitrile fiber spinning solution. The solid content of the spinning solution was 20.5%, the weight average molecular weight of the polymer in the solution was 240,000, the molecular weight distribution was 2.3, and the viscosity was 870 poise (tested at 45°C).

[0050] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of the spinning solution: A spinneret with an orifice diameter of 0.150 mm is used, employing a dry-wet spinning process. The linear velocity of the fiber leaving the spinneret is 12 m / min. After passing through a 4 mm high air environment, it enters the first coagulation bath at a temperature of 25°C. The volume ratio of dimethyl sulfoxide to water in the first coagulation bath is 1:0.33, the coagulation time is 1 minute, and the coagulation draw is 3 times. After exiting the first coagulation bath, the coagulated filament enters the second coagulation bath at a temperature of 25°C. The volume ratio of dimethyl sulfoxide to water in the second coagulation bath is 1:1.2, and the coagulation time is 1.5 minutes. After exiting the second coagulation bath, the coagulated filament enters the third coagulation bath at a temperature of 25°C. The volume ratio of dimethyl sulfoxide to water in the third coagulation bath is 1:5.7, and the coagulation time is 1.5 minutes.

[0051] Polyacrylonitrile precursor fibers were obtained by sequentially performing primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting. The solidified fibers exiting the third coagulation bath underwent primary drawing in 100℃ steam with a draw ratio of 4.8. The drawn fibers were then passed through six progressively heated washing baths at temperatures of 50℃ / 60℃ / 70℃ / 75℃ / 80℃ / 85℃, with a washing draw ratio of 98.5%. After conventional washing to remove residual solvent, a solid content of [missing information] was used for [missing information]. A 2% amino-modified silicone oil emulsion was used as an oiling agent for oiling. The filaments were dried and densified by three hot rollers with gradient heating at temperatures of 105℃, 110℃, and 115℃, with a draw ratio of 98%. The dried and densified filaments were then subjected to secondary drawing in superheated steam at 140℃ with a draw ratio of 2.5. The filaments after secondary drawing were heat-set at 150℃ and then wound into a cylinder using a winding machine to obtain polyacrylonitrile carbon fiber precursor.

[0052] (3) Preparation of carbon fibers by pre-oxidation and carbonization Pre-oxidation: The precursor fiber was pre-oxidized and stabilized in air under a gradient heating method in six temperature zones. The pre-oxidation temperatures were 210℃, 225℃, 235℃, 245℃, 255℃, 265℃, and 270℃, with residence times of 6 min, 12 min, 12 min, 12 min, and 6 min, respectively. During pre-oxidation, the fiber draw ratio was controlled at 50% of the corresponding pre-oxidation fiber breaking stress, depending on the degree of pre-oxidation. The total pre-oxidation time was 60 minutes, resulting in a bulk density of 1.37 g / cm³. 3 Pre-oxidized fibers.

[0053] Carbonization: The obtained pre-oxidized fibers are fed into a low-temperature carbonization furnace for low-temperature carbonization treatment. High-purity nitrogen is used as the protective gas, with an oxygen content of 1 ppm. The low-temperature carbonization temperature is 580℃. According to the fiber diameter requirements, the fiber draw ratio during the low-temperature carbonization stage is 40% of the fracture stress of the resulting low-temperature carbonized fiber. The low-temperature carbonization time is 3 minutes. After the fibers exit the low-temperature carbonization furnace, they are fed into a high-temperature carbonization furnace for high-temperature carbonization treatment. High-purity nitrogen is used as the protective gas, with an oxygen content of 1 ppm. The high-temperature carbonization temperature is 1350℃. The high-temperature carbonization time is 3 minutes to obtain polyacrylonitrile carbon fiber.

[0054] Example 2 (1) Preparation of spinning solution Acrylonitrile and itaconic acid were blended at a molar ratio of 97:3 and added to a polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 4:1 to the total mass of acrylonitrile and itaconic acid was added. When the temperature of the polymerization reactor rose to 62°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.15% of the total molar percentage of acrylonitrile and itaconic acid, was added. When the viscosity of the polymer solution in the reactor (45°C) rose to 430 poise, the initiator (azobisisobutyronitrile) was added dropwise continuously, controlling the addition to be completed within 50 minutes. After continuing the reaction for 4 hours, the reaction was quickly stopped. The polymerization reactor temperature was then raised to 74°C and evacuated. After 6 hours, the polymerization reactor temperature was lowered to 70°C and evacuated for another 6 hours. The monomer and initiator were removed to obtain polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 19.3%, a weight-average molecular weight of 263,000, a molecular weight distribution of 1.6, and a viscosity of 930 poise (tested at 45°C).

[0055] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: Using a spinneret with an aperture of 0.150 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 15 m / min. After passing through a 3 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 1.

[0056] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0057] Example 3 (1) Preparation of spinning solution: Same as in Example 2.

[0058] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: Using a spinneret with an aperture of 0.150 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 10 m / min. After passing through a 3 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 1.

[0059] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0060] Example 4 (1) Preparation of spinning solution Acrylonitrile and itaconic acid were blended at a molar ratio of 97:3 and added to a polymerization reactor. Then, dimethyl sulfoxide solvent with a total mass ratio of acrylonitrile to itaconic acid of 3.65:1 was added. When the temperature of the polymerization reactor rose to 62°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.25% of the total molar percentage of acrylonitrile and itaconic acid, was added. When the viscosity of the polymer solution in the reactor (45°C) rose to 510 poise, the initiator (azobisisobutyronitrile) was added dropwise continuously, with the addition controlled to be completed within 45 minutes. After the reaction continued for 4 hours, the reaction was quickly stopped. Then, the temperature of the polymerization reactor was raised to 74°C and a vacuum was drawn. After 6 hours, the temperature of the polymerization reactor was lowered to 70°C and a vacuum was drawn for another 6 hours to remove monomers and initiators, thus obtaining polyacrylonitrile fiber spinning solution. The solid content of the spinning solution was 20.3%, the weight average molecular weight of the polymer in the solution was 230,000, the molecular weight distribution was 2.2, and the viscosity was 760 poise (tested at 45°C).

[0061] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of the spinning solution: A spinneret with an orifice diameter of 0.100 mm is used, employing a dry-wet spinning process. The linear velocity of the fiber leaving the spinneret is 14 m / min. After passing through a 5 mm high air environment, it enters the first coagulation bath at a temperature of 25°C. The volume ratio of dimethyl sulfoxide to water in the first coagulation bath is 1:0.33, the coagulation time is 1 minute, and the coagulation draw is 3 times. After exiting the first coagulation bath, the coagulated filament enters the second coagulation bath at a temperature of 25°C. The volume ratio of dimethyl sulfoxide to water in the second coagulation bath is 1:1.2, and the coagulation time is 1.5 minutes. After exiting the second coagulation bath, the coagulated filament enters the third coagulation bath at a temperature of 25°C. The volume ratio of dimethyl sulfoxide to water in the third coagulation bath is 1:5.7, and the coagulation time is 1.5 minutes.

[0062] Polyacrylonitrile precursor fibers were obtained by sequentially performing primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting. The solidified fibers exiting the third coagulation bath underwent primary drawing in 100°C steam with a draw ratio of 5. The drawn fibers were then passed through six progressively heated washing tanks at temperatures of 50°C, 60°C, 70°C, 75°C, 80°C, and 85°C, with a washing draw ratio of 98.5%. After conventional washing to remove residual solvent, the fibers were further processed using a solids content of 2... A % amino-modified silicone oil emulsion was used as an oiling agent for oiling. The filaments were dried and densified by three hot rollers with gradient heating at temperatures of 105℃, 110℃, and 115℃, respectively, with a draw ratio of 98%. The dried and densified filaments were then subjected to secondary drawing in superheated steam at 140℃ with a draw ratio of 2.4. The filaments after secondary drawing were heat-set at 150℃ and then wound into a cylinder using a winding machine to obtain polyacrylonitrile carbon fiber precursor.

[0063] (3) Preparation of carbon fibers by pre-oxidation and carbonization Pre-oxidation: The precursor fiber was pre-oxidized and stabilized in air under a gradient heating method in four temperature zones. The pre-oxidation temperatures were 210℃, 220℃, 230℃, 235℃, 240℃, 245℃, and 250℃, with residence times of 6 min, 12 min, 12 min, 12 min, and 6 min, respectively. During pre-oxidation, the fiber draw ratio was controlled at 50% of the corresponding pre-oxidation fiber breaking stress, depending on the degree of pre-oxidation. The total pre-oxidation time was 60 minutes, resulting in a bulk density of 1.365 g / cm³. 3 Pre-oxidized fibers.

[0064] Carbonization: The obtained pre-oxidized fibers are fed into a low-temperature carbonization furnace for low-temperature carbonization treatment. High-purity nitrogen is used as the protective gas, with an oxygen content of 1 ppm. The low-temperature carbonization temperature is 600℃. According to the fiber diameter requirements, the fiber stretch ratio during the low-temperature carbonization stage is 50% of the fracture stress of the resulting low-temperature carbonized fiber. The low-temperature carbonization time is 3 minutes. After the fibers exit the low-temperature carbonization furnace, they are fed into a high-temperature carbonization furnace for high-temperature carbonization treatment. High-purity nitrogen is used as the protective gas, with an oxygen content of 1 ppm. The high-temperature carbonization temperature is 1500℃. The high-temperature carbonization time is 3 minutes to obtain polyacrylonitrile carbon fiber.

[0065] Example 5 (1) Preparation of spinning solution Acrylonitrile and itaconic acid were blended at a molar ratio of 98:2 and added to a polymerization reactor. Then, dimethyl sulfoxide solvent with a total mass ratio of acrylonitrile to itaconic acid of 3.44:1 was added. When the temperature of the polymerization reactor rose to 62°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.3% of the total molar percentage of acrylonitrile and itaconic acid, was added. When the viscosity of the polymer solution in the reactor (45°C) rose to 470 poise, 0.30% of the total molar percentage of acrylonitrile and itaconic acid initiator (azobisisobutyronitrile) was added dropwise continuously, with the addition controlled to be completed within 50 minutes. After continuing the reaction for 4 hours, the reaction was quickly stopped. Then, the temperature of the polymerization reactor was raised to 74°C and a vacuum was drawn. After 6 hours, the temperature of the polymerization reactor was lowered to 70°C and a vacuum was drawn for another 6 hours to remove monomers and initiators, thus obtaining polyacrylonitrile fiber spinning solution. The solid content of the spinning solution was 21.7%, the weight average molecular weight of the polymer in the solution was 245,000, the molecular weight distribution was 1.77, and the viscosity was 880 poise (tested at 45°C).

[0066] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: Using a spinneret with an aperture of 0.100 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 12.5 m / min. After passing through a 3 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 4.

[0067] (3) Preparation of carbon fiber by pre-oxidation and carbonization: same as in Example 4.

[0068] Example 6 (1) Preparation of spinning solution Acrylonitrile and itaconic acid were blended at a molar ratio of 99.5:0.5 and added to a polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.88:1 to the total mass of acrylonitrile and itaconic acid was added. When the temperature of the polymerization reactor rose to 62°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.35% of the total molar percentage of acrylonitrile and itaconic acid, was added. When the viscosity of the polymer solution in the reactor (45°C) rose to 550 poise, the initiator (azobisisobutyronitrile) was added dropwise continuously, controlling the addition to be completed within 60 minutes. After continuing the reaction for 4 hours, the reaction was quickly stopped. Then, the temperature of the polymerization reactor was raised to 74°C and a vacuum was drawn. After 6 hours, the temperature of the polymerization reactor was lowered to 70°C and a vacuum was drawn for another 6 hours to remove monomers and initiators, thus obtaining polyacrylonitrile fiber spinning solution. The solid content of the spinning solution was 19.7%, the weight average molecular weight of the polymer in the solution was 220,000, the molecular weight distribution was 1.8, and the viscosity was 890 poise (tested at 45°C).

[0069] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding of spinning solution: Using a spinneret with an aperture of 0.100 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 10.5 m / min. After passing through a 4 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 4.

[0070] (3) Preparation of carbon fiber by pre-oxidation and carbonization: same as in Example 4.

[0071] Example 7 (1) Preparation of spinning solution Same as Example 2; (2) Spinning of dry-jet wet-spun raw yarn Solidification and molding of spinning solution: The dry and wet spinning process was adopted, and the spinneret specifications, the linear velocity of the fiber leaving the spinneret orifice, and the air layer height were the same as in Example 2. The solidification and stretching stage has a solidification bath temperature of 5℃, a volume ratio of dimethyl sulfoxide to water of 1:9, a solidification time of 2 minutes, and a solidification stretching ratio of 3 times.

[0072] Polyacrylonitrile precursor fibers were obtained after primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting. The process conditions for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting were the same as in Example 1.

[0073] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0074] Example 8 (1) Preparation of spinning solution Same as Example 5; (2) Spinning of dry-jet wet-spun raw yarn Solidification and molding of spinning solution: The dry and wet spinning process was adopted, and the spinneret specifications, the linear velocity of the fiber leaving the spinneret orifice, and the air layer height were the same as in Example 5. The solidification and stretching stage has a solidification bath temperature of 5℃, a volume ratio of dimethyl sulfoxide to water of 1:9, a solidification time of 2 minutes, and a solidification stretching ratio of 3 times.

[0075] Polyacrylonitrile precursor fibers were obtained after primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting. The process conditions for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting were the same as in Example 4.

[0076] (3) Preparation of carbon fibers by pre-oxidation and carbonization: Same as in Example 4, the SEM image of the obtained carbon fibers is shown below. Figure 1 As shown, by Figure 1 It can be seen that microgroove structures are formed on the surface of carbon fibers.

[0077] Comparative Example 1 (1) Preparation of spinning solution Acrylonitrile and itaconic acid were blended at a molar ratio of 97:3 and added to a polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to the total acrylonitrile and itaconic acid was added. When the temperature of the polymerization reactor reached 62°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.5% of the total molar percentage of acrylonitrile and itaconic acid, was added. After reacting for 9 hours, the reaction was quickly stopped. The temperature of the polymerization reactor was then raised to 74°C and evacuated. After 6 hours, the temperature was lowered to 70°C, and evacuation was continued for another 6 hours to remove monomers and initiator, yielding a polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 19.6%, a weight-average molecular weight of 200,000, a molecular weight distribution of 3.7, and a viscosity of 650 poise (tested at 45°C).

[0078] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: A spinneret with an aperture of 0.150 mm was used, and a dry-wet spinning process was adopted. The linear velocity of the fiber leaving the spinneret was 10 m / min. After passing through a 5 mm high air environment, the fiber entered the coagulation bath and underwent coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting were the same as in Example 1.

[0079] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0080] Comparative Example 2 (1) Preparation of spinning solution: same as Comparative Example 1.

[0081] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: Using a spinneret with an aperture of 0.100 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 10 m / min. After passing through a 5 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 4.

[0082] (3) Preparation of carbon fiber by pre-oxidation and carbonization: same as in Example 4.

[0083] Comparative Example 3 (1) Preparation of spinning solution: Same as in Example 1; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: Using a spinneret with an aperture of 0.150 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 9 m / min. After passing through a 5 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, water washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, water washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 1.

[0084] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0085] Comparative Example 4 (1) Preparation of spinning solution: Same as in Example 1; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: Using a spinneret with an aperture of 0.150 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 17 m / min. After passing through a 5 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 1.

[0086] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0087] Comparative Example 5 (1) Preparation of spinning solution: Same as in Example 1; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of the spinning solution: A spinneret with an orifice diameter of 0.150 mm was used, employing a dry-wet spinning process. The linear velocity of the fiber leaving the spinneret orifice was 12 m / min. After passing through a 1 mm high air environment, the fiber entered the coagulation bath for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting to obtain polyacrylonitrile precursor fibers. The process conditions for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting were the same as in Example 1. Due to the excessively low air layer height, the liquid capillary action caused the coagulation bath to climb backward along the spinning solution stream to the spinneret, eliminating the air layer and switching the spinning process to a wet process. The final precursor fiber produced had a grooved surface structure. Since the first coagulation bath had a draw ratio of 3, the first coagulation in wet spinning is usually a negative draw. Excessive coagulation draw caused "surface cracking," making the regular grooves on the precursor fiber surface discontinuous and irregular.

[0088] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0089] Comparative Example 6 (1) Preparation of spinning solution: Same as in Example 1; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: Using a spinneret with an aperture of 0.150 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 12 m / min. After passing through a 6 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 1.

[0090] (3) Preparation of carbon fibers by pre-oxidation and carbonization: Same as in Example 1, the SEM image of the obtained carbon fibers is shown below. Figure 2 As shown, by Figure 2 It can be seen that the surface of carbon fiber is relatively smooth.

[0091] Comparative Example 7 (1) Preparation of spinning solution: Same as in Example 4; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: Using a spinneret with an aperture of 0.100 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 9 m / min. After passing through a 5 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, water washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, water washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 4.

[0092] (3) Preparation of carbon fiber by pre-oxidation and carbonization: same as in Example 4.

[0093] Comparative Example 8 (1) Preparation of spinning solution: Same as in Example 4; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding of spinning solution: Using a spinneret with an aperture of 0.100 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 17 m / min. After passing through a 5 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, water washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, water washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 4.

[0094] (3) Preparation of carbon fiber by pre-oxidation and carbonization: same as in Example 4.

[0095] Comparative Example 9 (1) Preparation of spinning solution: Same as in Example 4; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: A spinneret with an aperture of 0.100 mm was used, and a dry-wet spinning process was adopted. The linear velocity of the fiber leaving the spinneret was 14 m / min. After passing through a 1 mm high air environment, the fiber entered the coagulation bath and underwent coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions for coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting were the same as in Example 4.

[0096] Due to the excessively low air layer height, the liquid capillary action causes the coagulation bath to climb backwards along the spinning solution to the spinneret, eliminating the air layer and switching the spinning process to wet spinning. The final produced yarn has a grooved surface structure. Furthermore, because the draw ratio of the first coagulation bath is 3 times, the first coagulation in wet spinning is usually a negative draw. Excessive coagulation draw causes "surface cracking," making the regular grooves on the yarn surface discontinuous and irregular.

[0097] (3) Preparation of carbon fiber by pre-oxidation and carbonization: same as in Example 4.

[0098] Comparative Example 10 (1) Preparation of spinning solution: Same as in Example 4; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and forming of spinning solution: Using a spinneret with an aperture of 0.100 mm, a dry-wet spinning process is adopted. The linear velocity of the fiber leaving the spinneret is 14 m / min. After passing through a 6 mm high air environment, it enters the coagulation bath for coagulation drawing, primary drawing, water washing, oiling, drying and densification, secondary drawing and heat setting to obtain polyacrylonitrile precursor fiber. The process conditions of coagulation drawing, primary drawing, water washing, oiling, drying and densification, secondary drawing and heat setting are the same as in Example 4.

[0099] (3) Preparation of carbon fiber by pre-oxidation and carbonization: same as in Example 4.

[0100] The solid content, weight-average molecular weight, molecular weight distribution, and viscosity of the polyacrylonitrile fiber spinning solutions obtained in Examples 1-6 and Comparative Examples 1-10 were tested, and the test results are shown in Table 1.

[0101] Test method for solid content of polyacrylonitrile fiber spinning solution: Take a certain mass of spinning solution and record it as M. Precipitate the polymer in it, dry it, and when the mass is stable, record the polymer mass as m. The ratio of the mass of dried polymer m to the mass of spinning solution M is the solid content of the spinning solution.

[0102] The test methods for the weight-average molecular weight and molecular weight distribution of polymers in polyacrylonitrile fiber spinning solutions include: testing using a gel permeation chromatography (GPC) instrument manufactured by Waters Corporation, using dimethylformamide as a solvent, and adding an appropriate amount of lithium chloride when preparing the polymer solution.

[0103] The viscosity test method for polyacrylonitrile fiber spinning solution is as follows: The spinning solution is added to the test chamber, and circulating water at 45°C is introduced into the chamber jacket. After 30 minutes of water circulation, the test is started. The test data is recorded when the test data is stable. The average value is taken from 3 tests.

[0104] Table 1

[0105] The carbon fibers of Examples 1-8 and Comparative Examples 1-10 were tested according to GB3362 "Test Standard for Carbon Fiber" and GB / T 3364 "Test Method for Diameter and Number of Carbon Fibers". The carbon fibers obtained in Examples 1-8 and Comparative Examples 1-10 were subjected to anodizing surface treatment. Ammonium bicarbonate was used as the electrolyte (concentration of ammonium bicarbonate in the electrolyte was 3 wt%), the electrolyte conductivity was 30 mS / cm, the electrolysis time was 70 s, and the current density was 0.26 mA / cm². 2 Electrochemical treatment was performed. After treatment, the carbon fibers were sized and dried, and samples were prepared and tested using TDE-85 and C05 resin systems according to the JC / T773 interlaminar shear strength test standard. The test results are shown in Table 2.

[0106] Table 2

[0107] Note: For Comparative Examples 5 and 9, interlaminar shear strength tests were not conducted because the mechanical properties of the carbon fiber were too poor.

[0108] As shown in Table 2, the carbon fibers obtained in Examples 1-8 have both excellent tensile and interfacial properties. In contrast, the carbon fibers obtained in Comparative Examples 1-3, 6, 7, and 10 have excellent tensile properties but poor interfacial properties. Furthermore, the carbon fibers obtained in Comparative Examples 4 and 8 have excellent interfacial properties but poor tensile properties, and the carbon fibers obtained in Comparative Examples 5 and 9 also have poor tensile properties. This demonstrates that the method of the present invention can achieve a balance between the tensile and interfacial properties of carbon fibers.

[0109] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for producing a carbon fiber having a microgroove structure, characterized by, The application relates to a preparation method of polyacrylonitrile carbon fiber. The polyacrylonitrile fiber spinning solution is prepared by the following steps: adding acrylonitrile, itaconic acid, a first initiator and dimethyl sulfoxide into a polymerization kettle to carry out polymerization, adding a second initiator into the polymerization system when the viscosity of the polymerization system reaches 300-550 poise, and continuously reacting to obtain the polyacrylonitrile fiber spinning solution. The molar ratio of the acrylonitrile and the itaconic acid is (93-99.5):(0.5-7); and / or The total amount of the first initiator and the second initiator accounts for 0.1-1% of the total molar amount of the acrylonitrile and the itaconic acid; and / or 2. The method of claim 1, wherein, The molar ratio of the first initiator and the second initiator is (2-3):(2-3); and / or The second initiator is continuously added dropwise and is added dropwise within 30-60 minutes; and / or 3. The method of claim 2, wherein, The first initiator and the second initiator independently comprise azobisisobutyronitrile and / or azobisisoheptyl nitrile; and / or The viscosity of the polyacrylonitrile fiber spinning solution is 700-1200 poise at 45 DEG C. The first coagulation drawing comprises primary coagulation, secondary coagulation and tertiary coagulation, The primary coagulation adopts a first coagulation bath with a temperature of 20-30 DEG C, the first coagulation bath is a mixed solution with a volume ratio of dimethyl sulfoxide to water being 1:(0.2-0.6), the drawing multiple of the primary coagulation is 1.5-4.0, and the time of the primary coagulation is 0.5-2 minutes; The secondary coagulation adopts a second coagulation bath with a temperature of 20-50 DEG C, the second coagulation bath is a mixed solution with a volume ratio of dimethyl sulfoxide to water being 1:(0.5-1.5), and the coagulation time of the secondary coagulation is 0.5-2 minutes; The tertiary coagulation adopts a third coagulation bath with a temperature of 20-50 DEG C, the third coagulation bath is a mixed solution with a volume ratio of dimethyl sulfoxide to water being 1:(4-7), and the coagulation time of the tertiary coagulation is 0.5-2 minutes; 4. The method according to any one of claims 1-3, characterized in that, The secondary coagulation adopts a coagulation bath with a temperature of 3-15 DEG C, the coagulation bath is a mixed solution with a volume ratio of dimethyl sulfoxide to water being 1:(3-19), the drawing multiple of the coagulation is 1.5-4.0, and the coagulation time is 0.5-2 minutes. The drawing medium of the primary drawing is water vapor with a temperature of 100-110 DEG C, and the drawing multiple is 4-10; and / or The drying and densification temperature is 110-150 DEG C; and / or ​ ​ ​ 5. The method of claim 1, wherein, ​ ​ The drawing medium of the secondary drawing is water vapor at 120-150 DEG C, and the draw ratio is 2-5; and / or The heat setting temperature is 110-180 DEG C.

6. The method according to claim 1 or 5, characterized in that, The pre-oxidation uses 4-6 temperature zones with gradient temperature rising, the pre-oxidation starting temperature is 180-220 DEG C, the final temperature is 250-300 DEG C, and the total pre-oxidation time is 40-100 min.

7. The method of claim 6, wherein, The draw ratio of the pre-oxidation process is 30-80% of the breaking stress of the pre-oxidized fiber obtained after the pre-oxidation.

8. The method of claim 1, wherein, The carbonization process includes low-temperature carbonization and high-temperature carbonization, The low-temperature carbonization uses high-purity nitrogen as the protective gas, the temperature is 300-800 DEG C, the time is 1.5-6 min, and the draw ratio of the low-temperature carbonization process is 20-70% of the breaking stress of the fiber obtained after the low-temperature carbonization; The high-temperature carbonization uses high-purity nitrogen as the protective gas, the temperature is 1200-1800 DEG C, and the time is 1-4 min.

9. The method of claim 8, wherein, The Ra of the surface of the carbon fiber is 5 nm-25 nm.

10. A carbon fiber, characterized by, The carbon fiber is obtained by the method of any one of claims 1-9.

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