Rough-diameter high-strength intermediate modulus carbon fiber with microgroove structure and preparation method thereof

Abstract

The application discloses a kind of coarse diameter high-strength middle modulus carbon fibers with microgroove structure and preparation method thereof, which comprises the following steps: polyacrylonitrile fiber spinning solution is spun by dry-wet spinning, solidification drafting, first-stage drafting, washing, oiling, drying densification, second-stage drafting and heat setting to obtain polyacrylonitrile precursor filament;The polyacrylonitrile precursor filament is pre-oxidized and carbonized to obtain carbon fiber, wherein the pH of the polyacrylonitrile fiber spinning solution is 3-4.5, the weight average molecular weight of the polymer in the polyacrylonitrile fiber spinning solution is 190,000-260,000, and the molecular weight distribution of the polymer in the spinning solution is 1.5-2.4;The pH of the coagulation bath used in the solidification drafting process is 3-4.5, and the temperature is 3-10℃;The jet stream line speed of the spinning plate of the dry-wet spinning is 10m / min-16m / min, and the air layer height is 2mm-5mm.Using this method, the coarse diameter of high-strength middle modulus carbon fiber and the surface microgroove morphology structure can be realized, so as to obtain carbon fiber with mechanical properties and interface performance.

Description

Technical Field

[0001] This invention belongs to the field of fibers, specifically relating to a method for preparing coarse-diameter, high-strength, intermediate-modulus carbon fibers with microgrooves. 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 fibers can be classified according to their mechanical properties into high-strength, high-modulus, and ultra-high-strength high-modulus types; and according to their spinning process, they can be divided into two main categories: dry-jet wet spinning (dry-wet method) and wet-jet wet spinning (wet method). Due to the influence of the polymer Balas effect, the carbon fibers prepared by the two processes have different surface morphologies. Dry-wet method carbon fibers do not have groove structures on their surface, while wet method carbon fibers have regular groove structures on their surface.

[0003] High-strength intermediate-modulus T800 carbon fiber is the most widely used variety among high-strength series products. However, the monofilament diameter of commercially available high-strength intermediate-modulus carbon fibers is all around 5μm, which is 40% smaller than the 7μm monofilament diameter of high-strength T700 and T300 carbon fibers. The cross-sectional area is also reduced by nearly half. This decrease in carbon fiber production efficiency and composite material preparation efficiency leads to problems such as poor resin wettability, low strength transfer rate of carbon fiber composites, and imbalances in various composite properties. Furthermore, due to the interlocking effect between the carbon fiber surface grooves and the resin matrix, grooved carbon fibers exhibit certain advantages when used as reinforcements for resin matrices. Therefore, the development of high-strength intermediate-modulus carbon fibers with large diameters and grooved structures is a focus of industry attention. Summary of the Invention

[0004] This invention provides a coarse-diameter high-strength intermediate-modulus carbon fiber with a microgroove structure and its preparation method. This method can achieve both the coarsening of the diameter of the high-strength intermediate-modulus carbon fiber and the consideration of the surface microgroove morphology, thereby obtaining carbon fiber with both mechanical and interfacial properties.

[0005] In one aspect of the invention, a method for preparing coarse-diameter, high-strength, intermediate-modulus carbon fibers with a microgroove structure is provided, comprising: Polyacrylonitrile fiber spinning solution is processed by dry and wet spinning, coagulation and stretching, primary stretching, 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 pH of 3-4.5, the polymer weight-average molecular weight in the polyacrylonitrile fiber spinning solution is 190,000-260,000, and the molecular weight distribution of the polymer in the spinning solution is 1.5-2.4. The coagulation bath used in the coagulation and stretching process has a pH of 3-4.5 and a temperature of 3-10℃. The spinneret of the dry-wet spinning process has a flow velocity of 10m / min-16m / min and an air layer height of 2mm-5mm.

[0006] In some embodiments of the present invention, the preparation method of the polyacrylonitrile fiber spinning solution includes: adding acrylonitrile, itaconic acid, acrylic acid, a first initiator, and dimethyl sulfoxide into a polymerization reactor and mixing them for polymerization; when the viscosity of the polymerization system reaches 350 poise-550 poise, adding a second initiator into the polymerization system and continuing the reaction to obtain the polyacrylonitrile fiber spinning solution.

[0007] In some embodiments of the present invention, the molar ratio of acrylonitrile, itaconic acid and acrylic acid is (92-98):(1-7):(0-1).

[0008] In some embodiments of the present invention, the total amount of the first initiator and the second initiator is 0.2%-1.7% of the total molar amount of acrylonitrile, itaconic acid and acrylic acid.

[0009] In some embodiments of the present invention, the molar ratio of the first initiator to the second initiator is (0.1-0.7):(0.1-1).

[0010] In some embodiments of the present invention, the second initiator is added by continuous dripping, and the dripping is completed within 40 min to 60 min.

[0011] In some embodiments of the present invention, the first initiator and the second initiator each independently comprise azobisisobutyronitrile and / or azobisisoheptanenitrile.

[0012] In some embodiments of the present invention, the solid content of the polyacrylonitrile fiber spinning solution is 19-23%.

[0013] In some embodiments of the present invention, the viscosity of the polyacrylonitrile fiber spinning solution at 45°C is 700 poise to 1150 poise.

[0014] In some embodiments of the present invention, the coagulation bath comprises dimethyl sulfoxide and water, wherein the volume ratio of dimethyl sulfoxide to water is 1:(9-39).

[0015] In some embodiments of the present invention, itaconic acid and / or acrylic acid are added to the coagulation bath to adjust its pH.

[0016] In some embodiments of the present invention, the stretching ratio of the solidification stretching is 1.5-4 times, and the solidification time in the solidification bath is 1-6 minutes.

[0017] 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 4-8 times.

[0018] In some embodiments of the present invention, the drying and densification temperature is 110-150°C.

[0019] In some embodiments of the present invention, the stretching medium for the secondary stretching is water vapor at 130-170°C, and the stretching ratio is 2-5 times.

[0020] In some embodiments of the present invention, the heat setting temperature is 110-180°C.

[0021] In some embodiments of the present invention, the pre-oxidation adopts 3-6 temperature zones with gradient heating, the initial temperature of the pre-oxidation treatment is 200-230℃, the final temperature is 250-300℃, and the total pre-oxidation time is 50-100min.

[0022] 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.

[0023] In some embodiments of the present invention, the bulk density of the pre-oxidized fibers obtained by the pre-oxidation process is 1.32-1.40 g / cm³. 3 .

[0024] 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 1200-1650°C, for a time of 1-5 minutes.

[0025] In some embodiments of the present invention, the Ra of the carbon fiber surface is 5nm-25nm.

[0026] In some embodiments of the present invention, the diameter of the carbon fiber is 6.5-7.5 μm.

[0027] 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.

[0028] This invention utilizes a polyacrylonitrile fiber spinning solution with a polymer weight-average molecular weight of 190,000-260,000, a polymer molecular weight distribution of 1.5-2.4, and a pH of 3-4.5. Dry-wet spinning is then performed, with the spinneret flow rate controlled at 10-16 m / min, the air layer height at 2-5 mm, and the coagulation bath pH at 3-4.5 and temperature at 3-10°C during the coagulation and drawing process. Through pre-oxidation and carbonization, a balance can be achieved between increasing the diameter of high-strength, medium-modulus carbon fibers and maintaining a surface microgroove morphology. This results in carbon fibers with both good mechanical properties (tensile strength ≥5800 MPa, tensile modulus 280-320 GPa) and good interfacial properties. Attached Figure Description

[0029] Figure 1 This is a SEM image of the carbon fiber obtained in Example 1. Detailed Implementation

[0030] 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.

[0031] 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.

[0032] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0033] In one aspect of the present invention, a method for preparing coarse-diameter, high-strength, intermediate-modulus carbon fibers with a microgroove structure 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 190,000-260,000, the molecular weight distribution of the polymer in the spinning solution is 1.5-2.4, the pH of the polyacrylonitrile fiber spinning solution is 3-4.5, the pH of the coagulation bath used in the coagulation and drawing process is 3-4.5, the temperature is 3-10℃, the concentration of the coagulation bath is 2.5wt%-10wt%, the spinneret flow rate of the dry-wet spinning process is 10m / min-16m / min, and the air layer height is 2mm-5mm. This invention employs a high molecular weight and narrow molecular weight distribution polyacrylonitrile (PAN) fiber spinning solution, in which the macromolecular chains form numerous physical entanglement points (preparing for a high extrusion swell ratio in subsequent processes). Combined with the pH of the spinning solution, the pH and temperature of the coagulation bath in the wet-dry spinning process, a high spinneret speed (i.e., a high spinneret shear rate, resulting in a high extrusion swell ratio), and a relatively short air layer height (so that the extrusion swell does not have time to fully retract), the spinning solution enters the coagulation bath in fine streams. Upon entering the coagulation bath, a normal contraction force occurs, and the imbalance between the residual swell effect and the normal contraction force forms fibers with a surface microgroove structure. Simultaneously, the balance between the acidic spinning solution and the acidic coagulation bath regulates the balance between the water diffusion rate and the PAN coagulation rate in the coagulation bath, reducing the radial structural differences in the fibers and facilitating the high performance of coarse-diameter fibers.

[0034] In some embodiments of the present invention, the preparation method of the polyacrylonitrile fiber spinning solution includes: using acrylonitrile-itaconic acid and acrylic acid as comonomers, azobisisobutyronitrile and / or azobisisoheptanenitrile as the first initiator, and dimethyl sulfoxide as the solvent; adding acrylonitrile, itaconic acid, acrylic acid, and dimethyl sulfoxide into a polymerization reactor, stirring evenly; raising the temperature inside the polymerization reactor to 60-65°C; adding the first initiator; and using a combination of a double-ribbed and anchor-type stirring paddle at a stirring speed of 100-200 rpm. The system inside the polymerization reactor is stirred with the first initiator (azobisisobutyronitrile and / or azobisisoheptanenitrile). Under the action of [unclear], a free radical polymerization reaction occurs. The viscosity of the polymerization system in the polymerization reactor is measured in real time. When the viscosity of the polymerization system reaches 350-550 poise (45℃), a second initiator (azobisisobutyronitrile and / or azobisisoheptanenitrile) is added to the polymerization system. (The second initiator is added continuously and at a uniform rate within a time range of 40-60 minutes.) At the same time, the stirring speed is adjusted to 15-40 rpm. After the second initiator is added, the reaction continues for 6-9 hours. When the viscosity of the spinning solution reaches 700-1150 poise (at 45℃), the reaction is terminated.

[0035] Furthermore, in the above-mentioned preparation of the spinning solution, the molar ratio of acrylonitrile, itaconic acid, and acrylic acid is (92-98):(1-7):(0-1); the amount of dimethyl sulfoxide and comonomer added is 19%-22% of the total mass of acrylonitrile, itaconic acid, and acrylic acid as dimethyl sulfoxide, and the total amount of the first initiator and the second initiator added accounts for 0.1-0.7% of the total molar mass of acrylonitrile and itaconic acid.

[0036] Furthermore, in the above-mentioned process of preparing the spinning solution, the molar ratio of the first initiator to the second initiator is (0.1-0.7):(0.1-1).

[0037] 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 72-76°C and evacuating it under vacuum for 5-8 hours, then lowering the temperature of the polymerization reactor to 68-72°C and continuing to evacuate it under vacuum for 4-10 hours to perform desizing and deinitiator removal treatment.

[0038] The final spinning solution has a pH value of 3-4.5, a solid content of 19-23%, a polymer weight-average molecular weight of 190,000-260,000, a polymer molecular weight distribution of 1.5-2.4, and a viscosity of 700-1150 poise (45°C).

[0039] In some embodiments of the present invention, the coagulation bath in the above-mentioned preparation process of polyacrylonitrile precursor fibers includes dimethyl sulfoxide and water, wherein the volume ratio of dimethyl sulfoxide to water is 1:(9-39); and itaconic acid and / or acrylic acid are added to the coagulation bath to adjust its pH, the coagulation stretching ratio is 1.5-4 times, and the coagulation time in the coagulation bath is 1-6 minutes. The dimethyl sulfoxide solution polymerization of acrylonitrile typically involves passing ammonia gas or adding ammonia water during the polymerization process to neutralize the carboxyl groups of itaconic acid or acrylic acid. Simultaneously, adding ammonia water to the coagulation bath adjusts the pH to alkaline, which helps to mitigate the excessively rapid coagulation of the nascent fiber sheath due to excessively rapid water diffusion, thus preventing radial structural differences in the fibers. However, on the one hand, ammonia gas is highly irritating and poses an explosion hazard; ammonia water introduces water during the polymerization process, and water, being a coagulant for PAN, easily generates gel in the polymerization system, affecting polymerization and spinning; on the other hand, ammonia water is volatile, making it difficult to control the pH of the coagulation bath when ammonia is added. This study employed a process that did not involve the addition of ammonia during polymerization and coagulation. Itaconic acid is a dicarboxylic acid, and acrylic acid is also acidic. When it is copolymerized with acrylonitrile, the polymerization solution becomes acidic. This eliminates the need for ammonia addition control during polymerization. Furthermore, the addition of acid in the coagulation bath allows the acidic polymer solution to effectively regulate the coagulation and diffusion rates, thereby improving the homogeneity of the radial structure of the nascent fibers.

[0040] Furthermore, this invention controls the pH of the polyacrylonitrile spinning solution between 3 and 4.5, and also controls the pH of the coagulation bath within this range. This effectively regulates the coagulation and diffusion rates, improving the homogeneity of the radial structure of the nascent fibers. If the pH of the coagulation bath is too high, the acidity of the coagulation bath is too low, failing to effectively control the diffusion of water and match the coagulation rate. If the pH of the coagulation bath is too low, the acidity of the coagulation bath is too high. When the concentration of itaconic acid and / or acrylic acid is high, they are prone to association due to hydrogen bonding, leading to an imbalance of the electrolyte in the coagulation bath and affecting stable coagulation.

[0041] Furthermore, coagulation diffusion affects the roundness of the fiber cross-section and the homogeneity of the fiber's radial structure. If the coagulation bath temperature is too high, rapid diffusion during coagulation will result in voids in the fiber cross-section. If the coagulation bath temperature is too low, slow diffusion during coagulation will lead to a denser fiber. This invention uses a low-temperature coagulation bath, which can effectively control the diffusion rate of the coagulant, thus facilitating the preparation of homogeneous and dense precursor fibers.

[0042] 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 4-8 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 130-170°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.

[0043] 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.

[0044] 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.

[0045] 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.

[0046] In this invention, the method can be used to obtain homogeneous and dense polyacrylonitrile precursor fibers with a single filament diameter of 11.5 μm-13 μm.

[0047] 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 3-6 temperature gradient zones, with an initial pre-oxidation temperature of 200-230°C and a final pre-oxidation temperature of 250-300°C. The total pre-oxidation time is 50-100 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 1.32-1.40 g / cm³. 3 Pre-oxidized fibers.

[0048] 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, thus 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 1200-1650°C for 1-5 minutes to obtain carbon fibers with a microgroove structure on the surface, a diameter of 6.5-7.5 μm, and an Ra of 5 nm-25 nm obtained by AFM testing.

[0049] 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.

[0050] The method of the present invention for preparing coarse-diameter high-strength intermediate-modulus carbon fibers with microgroove structures has at least one of the following effects: (1) From the perspective of polymerization control: Unlike the previous polymerization process of ammonia gas or ammonia water, the present invention achieves pH adjustment of the polymerization solution by adding one or two acidic monomers for copolymerization and synergistically controlling the polymerization and degassing temperatures; at the same time, by continuously adding initiators in the middle and late stages of polymerization, high molecular weight narrow distribution polymers are prepared, which is conducive to the high performance of fibers and the occurrence of extrusion swelling effect, while avoiding or mitigating the gelation effect; the danger of ammonia gas control and the risk of gelation caused by adding ammonia water are eliminated.

[0051] (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 conducive to the preparation of high-performance carbon fibers. (3) From the perspective of carbon fiber monofilament diameter: By adjusting the pH value of spinning solution and coagulation bath, and by using a low-temperature coagulation bath, the balance between the coagulant diffusion rate and coagulation rate of coarse-diameter nascent fibers was adjusted, which provides a guarantee for the preparation of coarse-diameter homogeneous and dense precursor fibers. (4) From the perspective of the interfacial properties between carbon fiber and resin matrix: The Ra value of the carbon fiber surface prepared by the present invention is between 5-25 nm in the AFM test. This is superior to the Ra value of the carbon fiber surface prepared by conventional dry and wet processes, which is between 1-3 nm. From the perspective of the physical interlocking of the carbon fiber interface, the interfacial properties of the carbon fiber prepared by the present invention are superior to those of the carbon fiber prepared by the dry and wet process. After the same anodizing treatment and using the same resin matrix, the interlaminar shear strength of the carbon fiber prepared by the present invention is increased by 14%-26% compared with that of the carbon fiber prepared by the traditional dry and wet process.

[0052] In a second aspect, the present invention provides a carbon fiber obtained by the method described in the first aspect of the present invention. It should be noted that the features and advantages described above for the method of preparing carbon fibers also apply to this carbon fiber, and will not be repeated here.

[0053] 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.

[0054] Example 1 (1) Preparation of spinning solution Acrylonitrile, itaconic acid, and acrylic acid were blended in a molar ratio of 97:2.5:0.5 and added to a polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to the total mass of acrylonitrile, itaconic acid, and acrylic acid was added. When the temperature of the polymerization reactor reached 64°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.25% of the total molar percentage of acrylonitrile, itaconic acid, and acrylic acid, was added. The stirring speed was 180 rpm. When the viscosity of the polymer solution in the reactor (45°C) reached 430 poise, the initiator (azobisisobutyronitrile) was added dropwise continuously, accounting for 0.25% of the total molar percentage of acrylonitrile, itaconic acid, and acrylic acid, and the addition was controlled to be completed within 50 minutes. The stirring speed was controlled to be 30 rpm. After the reaction continued for 4 hours, the reaction was quickly stopped. The polymerization reactor temperature was then raised to 75°C and evacuated. After 6 hours, the polymerization reactor temperature was lowered to 72°C and evacuated for another 6 hours to remove monomers and initiators, resulting in a polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 20.8%, a weight-average molecular weight of 223,000, a molecular weight distribution of 2.1, a pH of 3.55, and a viscosity of 850 poise (tested at 45°C).

[0055] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding 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 14 m / min. After passing through a 3 mm high air environment, the fiber entered the coagulation bath. The coagulation bath temperature was 5℃, and the volume ratio of dimethyl sulfoxide to water in the coagulation bath was 1:19. Itaconic acid was used to adjust the pH value of the coagulation bath to 3.60. The coagulation time was 2 minutes, and the coagulation draw was 3 times. 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 coagulation bath underwent primary drawing in 100℃ steam with a draw ratio of 5. The drawn fibers then passed through six progressively heated washing tanks at temperatures of 50℃ / 60℃ / 70℃ / 75℃ / 80℃ / 85℃, with a washing draw ratio of 99.5%. After conventional washing to remove residual solvent, a 2% solids content was used for further processing. Amino-modified silicone oil emulsion was used as an oiling agent for oiling, and the fibers were dried and densified by three hot rollers with gradient heating at temperatures of 105℃, 110℃, and 115℃, with a draw ratio of 98.5%. The dried and densified fibers were then subjected to secondary drawing in superheated steam at 160℃ with a draw ratio of 2.5. The fibers after secondary drawing were then heat-set at 150℃ and wound into a cylinder using a winding machine to obtain polyacrylonitrile carbon fiber precursor.

[0056] (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 three temperature zones: 220℃, 245℃, and 265℃, with residence times of 10 min, 40 min, and 10 min, respectively. During pre-oxidation, the fiber draw ratio was controlled to 50% of the corresponding pre-oxidized fiber breaking stress, based on the degree of pre-oxidation. The total pre-oxidation time was 60 minutes, yielding a bulk density of 1.365 g / cm³. 3 Pre-oxidized fibers.

[0057] Carbonization: The obtained pre-oxidized fibers are fed into a low-temperature carbonization furnace for low-temperature carbonization treatment, using high-purity nitrogen as the protective gas with an oxygen content of 1 ppm. The low-temperature carbonization temperature is 580℃. Based on 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, and the low-temperature carbonization time is 4 minutes. After exiting the low-temperature carbonization furnace, the fibers are fed into a high-temperature carbonization furnace for high-temperature carbonization treatment, using high-purity nitrogen as the protective gas with an oxygen content of 1 ppm. The high-temperature carbonization temperature is 1450℃, and the high-temperature carbonization time is 4 minutes to obtain polyacrylonitrile carbon fibers. 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.

[0058] 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 64°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.20% of the total molar percentage of acrylonitrile and itaconic acid, was added. The stirring speed was 180 rpm. When the viscosity of the polymer solution in the reactor (45°C) rose to 440 poise, 0.15% of the total molar percentage of acrylonitrile and itaconic acid initiator (azobisisobutyronitrile) was added dropwise continuously, with the addition controlled to be completed within 40 minutes. The stirring speed was controlled to be 25 rpm. After the reaction continued 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 to remove monomers and initiators, resulting in a polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 19.5%, a weight-average molecular weight of 250,000, a molecular weight distribution of 2.3, a pH of 3.45, and a viscosity of 1020 poise (tested at 45°C).

[0059] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding 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 15 m / min. After passing through a 4 mm high air environment, the fiber entered the coagulation bath. The coagulation bath temperature was 5℃, and the volume ratio of dimethyl sulfoxide to water in the coagulation bath was 1:19. Itaconic acid was used to adjust the pH value of the coagulation bath to 3.50. The coagulation time was 2 minutes, and the coagulation draw was 3 times. Polyacrylonitrile precursor fibers were obtained by sequentially performing primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting. The process conditions for primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting were the same as in Example 1.

[0060] (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: 225℃, 240℃, 245℃, and 260℃, with residence times of 10 min, 25 min, 25 min, and 10 min, respectively. During pre-oxidation, the fiber draw ratio was controlled to 50% of the corresponding fiber breaking stress, based on the degree of pre-oxidation. The total pre-oxidation time was 70 minutes, yielding a bulk density of 1.375 g / cm³. 3 Pre-oxidized fibers.

[0061] Carbonization: The obtained pre-oxidized fibers are fed into a low-temperature carbonization furnace for low-temperature carbonization and high-temperature carbonization treatment, wherein the low-temperature carbonization and high-temperature carbonization processes are the same as in Example 1.

[0062] Example 3 (1) The preparation of the spinning solution is the same as in Example 2; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding 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 4 mm high air environment, the fiber entered the coagulation bath. Other parameters of coagulation and drawing were the same as in Example 1. Polyacrylonitrile precursor fibers were obtained by sequentially performing primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting. The primary drawing ratio was 5.5, and other process conditions were the same as in Example 1.

[0063] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0064] Example 4 (1) Preparation of spinning solution Acrylonitrile, itaconic acid, and acrylic acid were blended in a molar ratio of 93.5:6:0.5 and added to a polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to the total mass of acrylonitrile, itaconic acid, and acrylic acid was added. When the temperature of the polymerization reactor rose to 64°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.3% of the total molar percentage of acrylonitrile, itaconic acid, and acrylic acid, was added. The stirring speed was 190 rpm. When the viscosity of the polymer solution in the reactor (45°C) rose to 400 poise, 0.2% of the total molar percentage of acrylonitrile, itaconic acid, and acrylic acid initiator (azobisisobutyronitrile) was added dropwise continuously, controlling the addition to be completed within 45 minutes. The stirring speed was controlled at 35 rpm. After the reaction continued for 4 hours, the reaction was quickly stopped. The polymerization reactor temperature was then raised to 75°C and evacuated. After 6 hours, the polymerization reactor temperature was lowered to 70°C and evacuated for another 6 hours to remove monomers and initiators, resulting in a polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 21%, a weight-average molecular weight of 220,000 for the polymer, a molecular weight distribution of 1.9, a pH of 3.0, and a viscosity of 750 poise (tested at 45°C).

[0065] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding 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 12 m / min. After passing through a 5 mm high air environment, the fiber entered the coagulation bath. The coagulation bath temperature was 6℃, and the volume ratio of dimethyl sulfoxide to water in the coagulation bath was 1:24. Itaconic acid was used to adjust the pH value of the coagulation bath to 3.05. The coagulation time was 3 minutes, and the coagulation draw was 3 times. Polyacrylonitrile precursor fibers were obtained sequentially through primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting. The solidified fibers exiting the coagulation bath underwent primary drawing in 100℃ steam with a draw ratio of 5.2. The drawn fibers were then passed through six progressively heated washing tanks at temperatures of 50℃ / 60℃ / 70℃ / 75℃ / 80℃ / 85℃, with a washing draw ratio of 99.5%. After conventional washing to remove residual solvent, the fibers were then subjected to a 2% solids content washing process. Amino-modified silicone oil emulsion was used as an oiling agent for oiling, and the fibers were dried and densified by three hot rollers with gradient heating. The hot roller temperatures were 105℃ / 110℃ / 115℃, and the draw ratio of the hot rollers was 98.5%. The dried and densified fibers were then subjected to secondary drawing in superheated steam at 150℃ with a draw ratio of 2.4. The fibers after secondary drawing were heat-set at 160℃ and then wound into a cylinder by a winding machine to obtain polyacrylonitrile carbon fiber precursor.

[0066] (3) Preparation of carbon fibers by pre-oxidation and carbonization Pre-oxidation: The pre-oxidation process is the same as in Example 3.

[0067] 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 4 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 4 minutes to obtain polyacrylonitrile carbon fiber.

[0068] 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 mass ratio of 3.44:1 to the total mass of acrylonitrile and itaconic acid was added. When the temperature of the polymerization reactor rose to 64°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.3% of the total molar percentage of acrylonitrile, itaconic acid and acrylic acid, was added. The stirring speed was 180 rpm. When the viscosity of the polymer solution in the reactor (45°C) rose to 450 poise, the initiator (azobisisobutyronitrile) was added dropwise continuously, accounting for 0.3% of the total molar percentage of acrylonitrile and itaconic acid, and the addition was controlled to be completed within 50 minutes. The stirring speed was controlled to be 35 rpm. After the reaction continued for 4 hours, the reaction was quickly stopped. The polymerization reactor temperature was then raised to 75°C and evacuated. After 6 hours, the polymerization reactor temperature was lowered to 70°C and evacuated for another 6 hours to remove monomers and initiators, resulting in a polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 21.7%, a weight-average molecular weight of 236,000, a molecular weight distribution of 1.8, a pH of 4.40, and a viscosity of 850 poise (tested at 45°C).

[0069] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding 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 12.5 m / min. After passing through a 3 mm high air environment, the fiber entered the coagulation bath. Itaconic acid was used to adjust the pH value of the coagulation bath to 4.5. Other conditions of the coagulation process were the same as in Example 4. Polyacrylonitrile precursor fibers were obtained by sequentially performing primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting. The processes and conditions for primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting were the same as in Example 4. (3) Preparation of carbon fiber by pre-oxidation and carbonization: The pre-oxidation and carbonization process is the same as in Example 4.

[0070] Example 6 (1) Preparation of spinning solution Acrylonitrile, itaconic acid, and acrylic acid were blended in a molar ratio of 97.5:2.0:0.5 and added to a polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.88:1 to the total mass of acrylonitrile, itaconic acid, and acrylic acid was added. When the temperature of the polymerization reactor reached 64°C, azobisisobutyronitrile (AIBN) initiator, accounting for 0.15% of the total molar percentage of acrylonitrile, itaconic acid, and acrylic acid, was added. The stirring speed was 130 rpm. When the viscosity of the polymer solution in the reactor (45°C) reached 550 poise, azobisisobutyronitrile (AIBN) initiator, accounting for 0.35% of the total molar percentage of acrylonitrile, itaconic acid, and acrylic acid, was added dropwise over 60 minutes. The stirring speed was controlled at 35 rpm. After the reaction continued for 4 hours, the reaction was quickly stopped. The polymerization reactor temperature was then raised to 75°C and evacuated. After 6 hours, the polymerization reactor temperature was lowered to 70°C and evacuated for another 6 hours to remove monomers and initiators, resulting in a polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 19.7%, a weight-average molecular weight of 240,000, a molecular weight distribution of 1.6, a pH of 4.0, and a viscosity of 880 poise (tested at 45°C).

[0071] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding 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 16 m / min. After passing through a 3 mm high air environment, the fiber entered the coagulation bath. The coagulation bath temperature was 6℃, and the volume ratio of dimethyl sulfoxide to water in the coagulation bath was 1:24. Itaconic acid was used to adjust the pH value of the coagulation bath to 4.0. The coagulation time was 3 minutes, and the coagulation draw was 3 times. Polyacrylonitrile precursor fibers were obtained by sequentially performing primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting. The primary drawing ratio was 4.9, and other process conditions were the same as in Example 1.

[0072] (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: 225℃, 230℃, 240℃, 245℃, 250℃, and 260℃, with a residence time of 10 minutes for each zone. The fiber draw ratio during pre-oxidation was controlled to 50% of the corresponding fiber breaking stress, based on the degree of pre-oxidation. The total pre-oxidation time was 70 minutes, resulting in a bulk density of 1.378 g / cm³. 3 Pre-oxidized fibers.

[0073] Carbonization: The carbonization process is the same as in Example 1.

[0074] Comparative Example 1 (1) Preparation of spinning solution Acrylonitrile, itaconic acid, and acrylic acid were blended in a molar ratio of 97:1:2 and added to a polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to the total mass of acrylonitrile, itaconic acid, and acrylic acid was added. Ammonia water (25 wt% ammonia concentration) was added, which accounted for 25% of the total molar number of carboxyl groups of the comonomer. When the temperature of the polymerization reactor was raised to 64°C, azobisisobutyronitrile (AIBN) initiator, which accounted for 0.5% of the total molar percentage of acrylonitrile, itaconic acid, and acrylic acid, was added to start the reaction. The stirring speed was controlled at 130 rpm for the first 4 hours, and at 30 rpm for the next 5 hours. After continuing the reaction for 9 hours, the reaction was stopped. The polymerization reactor temperature was further increased to 74℃, and a vacuum was drawn. After 6 hours, the polymerization reactor temperature was reduced to 70℃, and a vacuum was drawn for another 6 hours to remove monomers and initiators, thus obtaining polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 19.8%, a weight-average molecular weight of 200,000 for the polymer in the solution, a molecular weight distribution of 3.8, a pH of 4.7, and a viscosity of 680 poise (tested at 45℃).

[0075] (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding 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 7 mm high air environment, the fiber entered the coagulation bath. The coagulation bath temperature was 5℃, and the volume ratio of dimethyl sulfoxide to water in the coagulation bath was 1:19. The pH value of the coagulation bath was adjusted to 8.0 with ammonia water. The coagulation time was 2 minutes, and the coagulation draw was 3 times. Polyacrylonitrile precursor fibers were obtained by sequentially performing primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting. The processes and parameters for primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting were the same as in Example 1.

[0076] (3) Preparation of carbon fibers by pre-oxidation and carbonization Pre-oxidation: The pre-oxidation and carbonization processes are the same as in Example 1.

[0077] Comparative Example 2 (1) Preparation of spinning solution: same as Comparative Example 1.

[0078] (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 10 m / min. After passing through a 7 mm high air environment, the fiber entered the coagulation bath for coagulation and drawing. The pH of the coagulation bath was adjusted to 8 with ammonia water. Then, the fiber underwent primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting in sequence to obtain polyacrylonitrile precursor fiber. The process conditions for coagulation and 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 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: 220℃, 235℃, 245℃, and 255℃, with residence times of 10 min, 20 min, 20 min, and 10 min, respectively. During pre-oxidation, the fiber draw ratio was controlled to 50% of the corresponding fiber breaking stress, based on the degree of pre-oxidation. The total pre-oxidation time was 60 minutes, yielding a bulk density of 1.375 g / cm³. 3 Pre-oxidized fibers.

[0080] 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 1450℃. The high-temperature carbonization time is 3 minutes to obtain polyacrylonitrile carbon fiber.

[0081] Comparative Example 3 (1) Preparation of spinning solution: Same as in Example 1; (2) Spinning of dry-jet wet-spun raw yarn The coagulation and molding of the spinning solution is the same as in Example 1, except that itaconic acid is used to adjust the pH of the coagulation bath to 4.7. Then, polyacrylonitrile precursor fibers were obtained by sequentially performing 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.

[0082] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0083] Comparative Example 4 (1) Preparation of spinning solution: Same as in Example 1; (2) Spinning of dry-jet wet-spun raw yarn The coagulation and molding of the spinning solution is the same as in Example 1, except that itaconic acid is used to adjust the pH of the coagulation bath to 2.7. Then, polyacrylonitrile precursor fibers were obtained by sequentially performing 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.

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

[0085] Comparative Example 5 (1) Preparation of spinning solution: Acrylonitrile, itaconic acid and acrylic acid were mixed in a molar ratio of 99:0.5:0.5 and added to the polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to acrylonitrile, itaconic acid and acrylic acid was added. When the temperature of the polymerization reactor rose to 64°C, azobisisobutyronitrile (AIBN) initiator accounting for 0.25% of the total molar percentage of acrylonitrile, itaconic acid and acrylic acid was added. The stirring speed was 180 rpm. When the viscosity of the polymer solution in the reactor (45°C) rose to 430 poise, the initiator (azobisisobutyronitrile) accounting for 0.25% of the total molar percentage of acrylonitrile, itaconic acid and acrylic acid was added dropwise. The addition was controlled to be completed in 50 min. The stirring speed was controlled to be 30 rpm. After the reaction continued for 4 hours, the reaction was quickly stopped. The polymerization reactor temperature was then raised to 72°C and evacuated. After 6 hours, the polymerization reactor temperature was lowered to 70°C and evacuated for another 6 hours to remove monomers and initiators, resulting in a polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 21.1%, a weight-average molecular weight of 240,000, a molecular weight distribution of 1.6, a pH of 4.7, and a viscosity of 950 poise (tested at 45°C). (2) Spinning of dry-jet wet-spun raw yarn The solidification and molding of the spinning solution is the same as in Example 1; Then, polyacrylonitrile precursor fibers were obtained by sequentially performing 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.

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

[0087] Comparative Example 6 (1) Preparation of spinning solution: Acrylonitrile, itaconic acid and acrylic acid were mixed in a molar ratio of 91:8.5:0.5 and added to the polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to acrylonitrile, itaconic acid and acrylic acid was added. When the temperature of the polymerization reactor rose to 64°C, azobisisobutyronitrile (AIBN) initiator accounting for 0.25% of the total molar percentage of acrylonitrile, itaconic acid and acrylic acid was added. The stirring speed was 180 rpm. When the viscosity of the polymer solution in the reactor (45°C) rose to 430 poise, the initiator (azobisisobutyronitrile) accounting for 0.25% of the total molar percentage of acrylonitrile, itaconic acid and acrylic acid was added dropwise. The addition was controlled to be completed in 50 min. The stirring speed was controlled to be 30 rpm. After the reaction continued for 4 hours, the reaction was quickly stopped. The polymerization reactor temperature was then raised to 75°C and evacuated. After 6 hours, the polymerization reactor temperature was lowered to 73°C and evacuated for another 6 hours to remove monomers and initiators, resulting in a polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 20.5%, a weight-average molecular weight of 192,000, a molecular weight distribution of 2.5, a pH of 2.7, and a viscosity of 650 poise (tested at 45°C). (2) Spinning of dry-jet wet-spun raw yarn The solidification and molding of the spinning solution is the same as in Example 1; Then, polyacrylonitrile precursor fibers were obtained by sequentially performing 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.

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

[0089] Comparative Example 7 (1) Preparation of spinning solution: Acrylonitrile, itaconic acid and acrylic acid were mixed in a molar ratio of 97:2.5:0.5 and added to the polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to the total mass of acrylonitrile, itaconic acid and acrylic acid was added. During the feeding process, ammonia water (25wt% ammonia concentration) was added, which accounted for 50% of the total molar number of carboxyl groups of itaconic acid and acrylic acid. When the temperature of the polymerization reactor rose to 64℃, azobisisobutyronitrile (AIBN) initiator, accounting for 0.25% of the total molar percentage of acrylonitrile, itaconic acid and acrylic acid, was added. The stirring speed was 180 rpm. When the viscosity of the polymer solution in the reactor (45℃) rose to 430 poise, the initiator (azobisisobutyronitrile) accounting for 0.25% of the total molar percentage of acrylonitrile, itaconic acid and acrylic acid was added dropwise. The addition was controlled to be completed in 50 min. The stirring speed was controlled to be 30 rpm. After the reaction continued for 4 hours, the reaction was quickly stopped. The polymerization reactor temperature was then raised to 73°C and evacuated. After 6 hours, the polymerization reactor temperature was lowered to 70°C and evacuated for another 6 hours to remove monomers and initiators, resulting in a polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 20.2%, a weight-average molecular weight of 184,000, a molecular weight distribution of 3.2, a pH of 4.7, and a viscosity of 600 poise (tested at 45°C). (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding of spinning solution: It is the same as in Example 1, except that the pH of the coagulation bath is 7. Then, polyacrylonitrile precursor fibers were obtained by sequentially performing 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.

[0090] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0091] Comparative Example 8 (1) Preparation of spinning solution: Acrylonitrile, itaconic acid and acrylic acid are mixed in a molar ratio of 90:9.5:0.5 and added to the polymerization reactor. Then, dimethyl sulfoxide solvent with a mass ratio of 3.65:1 to acrylonitrile, itaconic acid and acrylic acid is added. When the temperature of the polymerization reactor rises to 64°C, azobisisobutyronitrile (AIBN) initiator accounting for 0.25% of the total molar percentage of acrylonitrile, itaconic acid and acrylic acid is added. The stirring speed is 180 rpm. When the viscosity of the polymer solution in the reactor (45°C) rises to 430 poise, the initiator (azobisisobutyronitrile) accounting for 0.25% of the total molar percentage of acrylonitrile, itaconic acid and acrylic acid is added dropwise. The addition is controlled to be completed in 50 min. The stirring speed is controlled to be 30 rpm. After the reaction continues for 4 hours, the reaction is quickly stopped. The polymerization reactor temperature was then raised to 72°C and evacuated. After 6 hours, the polymerization reactor temperature was lowered to 70°C and evacuated for another 6 hours to remove monomers and initiators, resulting in a polyacrylonitrile fiber spinning solution. The resulting spinning solution had a solid content of 19.8%, a weight-average molecular weight of 178,000, a molecular weight distribution of 3.5, a pH of 2.5, and a viscosity of 580 poise (tested at 45°C). (2) Spinning of dry-jet wet-spun raw yarn The coagulation and molding of the spinning solution is the same as in Example 1, except that the pH of the coagulation bath is 2.5. Then, polyacrylonitrile precursor fibers were obtained by sequentially performing 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.

[0092] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0093] Comparative Example 9 (1) Preparation of spinning solution: Same as in Example 1; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding of spinning solution: It is the same as in Example 1, except that the coagulation bath temperature is 0°C; Then, polyacrylonitrile precursor fibers were obtained by sequentially performing 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.

[0094] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0095] Comparative Example 10 (1) Preparation of spinning solution: Same as in Example 1; (2) Spinning of dry-jet wet-spun raw yarn Coagulation and molding of spinning solution: It is the same as in Example 1, except that the coagulation bath temperature is 15°C; Then, polyacrylonitrile precursor fibers were obtained by sequentially performing 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.

[0096] (3) Preparation of carbon fiber by pre-oxidation and carbonization: Same as in Example 1.

[0097] 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.

[0098] 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.

[0099] 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.

[0100] 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.

[0101] Table 1

[0102] The carbon fibers of Examples 1-6 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 1-6 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.

[0103] Table 2

[0104] As shown in Table 2, the carbon fibers in Examples 1-6 simultaneously meet the following requirements: Ra = 5nm-25nm, diameter = 6.5-7.5μm, tensile strength ≥5800MPa, tensile modulus = 280~320Gpa, and bulk density = ≥1.793 g / cm³. 3 The interlaminar shear strength is not less than 117 MPa, which is obviously higher than the carbon fiber performance obtained in Comparative Examples 1-10. This shows that the present invention uses a polyacrylonitrile fiber spinning solution with a polymer weight-average molecular weight of 190,000-260,000, a polymer molecular weight distribution of 1.5-2.4, and a pH of 3-4.5, and then performs dry and wet spinning. The spinneret flow rate of the dry and wet spinning process is controlled to be 10 m / min-16 m / min, the air layer height is 2 mm-5 mm, and the pH of the coagulation bath used in the coagulation and drawing process is 3-4.5, and the temperature is 3-10℃. After pre-oxidation and carbonization, the high-strength intermediate modulus carbon fiber can achieve both large diameter and surface microgroove morphology.

[0105] 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 preparing coarse-diameter, high-strength, intermediate-modulus carbon fibers with microgroove structures, characterized in that, include: Polyacrylonitrile fiber spinning solution is processed by dry and wet spinning, coagulation and stretching, primary stretching, 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 pH of 3-4.5, the polymer weight-average molecular weight in the polyacrylonitrile fiber spinning solution is 190,000-260,000, and the molecular weight distribution of the polymer in the spinning solution is 1.5-2.

4. The coagulation bath used in the coagulation and stretching process has a pH of 3-4.5 and a temperature of 3-10℃. The spinneret of the dry-wet spinning process has a flow velocity of 10m / min-16m / min and an air layer height of 2mm-5mm.

2. The method according to claim 1, characterized in that, The preparation method of the polyacrylonitrile fiber spinning solution includes: Acrylonitrile, itaconic acid, acrylic acid, a first initiator, and dimethyl sulfoxide are added to a polymerization reactor and mixed for polymerization. When the viscosity of the polymerization system reaches 350 poise-550 poise, a second initiator is added to the polymerization system to continue the reaction and obtain the polyacrylonitrile fiber spinning solution.

3. The method according to claim 2, characterized in that, The molar ratio of acrylonitrile, itaconic acid, and acrylic acid is (92-98):(1-7):(0-1); and / or The total amount of the first initiator and the second initiator is 0.2%-1.7% of the total molar amount of acrylonitrile, itaconic acid, and acrylic acid; and / or The molar ratio of the first initiator to the second initiator is (0.1-0.7):(0.1-1); and / or The second initiator is added continuously, completed within 40-60 minutes; and / or The first initiator and the second initiator each independently comprise azobisisobutyronitrile and / or azobisisoheptanenitrile; and / or The solid content of the polyacrylonitrile fiber spinning solution is 19-23%; and / or The viscosity of the polyacrylonitrile fiber spinning solution at 45°C is 700 poise to 1150 poise.

4. The method according to any one of claims 1-3, characterized in that, The coagulation bath comprises dimethyl sulfoxide and water, wherein the volume ratio of dimethyl sulfoxide to water is 1:(9-39); and / or Itaconic acid and / or acrylic acid are added to the coagulation bath to adjust its pH; and / or The stretching ratio of the solidification stretching is 1.5-4 times, and the solidification time in the solidification bath is 1-6 minutes.

5. The method according to claim 1, characterized in that, The drawing medium for the first-stage drawing is water vapor at 100-110℃, and the drawing ratio is 4-8 times; and / or The drying and densification temperature is 110-150℃; and / or The secondary drawing medium is water vapor at 130-170℃, and the draw ratio is 2-5 times; and / or The heat setting temperature is 110-180℃.

6. The method according to claim 1 or 5, characterized in that, The pre-oxidation process employs 3-6 temperature zones with gradient increases. The initial temperature of the pre-oxidation treatment is 200-230℃, the final temperature is 250-300℃, and the total pre-oxidation time is 50-100 min.

7. The method according to claim 6, characterized in that, 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 process; The bulk density of the pre-oxidized fibers obtained through the aforementioned pre-oxidation process is between 1.32 and 1.40 g / cm³. 3 .

8. The method according to claim 1, characterized in that, The carbonization process includes low-temperature carbonization and high-temperature carbonization. The low-temperature carbonization process uses high-purity nitrogen as a protective gas at a temperature of 300-800℃ for 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 process. The high-temperature carbonization process uses high-purity nitrogen as a protective gas, with a temperature of 1200-1650℃ and a time of 1-5 minutes.

9. The method according to claim 8, characterized in that, The Ra of the carbon fiber surface is 5nm-25nm; and / or The carbon fiber has a diameter of 6.5-7.5 μm.

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

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