Carbon fiber having microgroove structure and method for manufacturing the same

Abstract

The application discloses carbon fiber with micro-groove structure and a preparation method thereof. The method comprises the following steps: obtaining polyacrylonitrile original wire by dry-wet spinning, coagulation drafting, primary drafting, water washing, oiling, drying, secondary drafting and heat setting of polyacrylonitrile fiber spinning solution; and obtaining carbon fiber by pre-oxidation and carbonization treatment of the polyacrylonitrile original wire, wherein 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, and the jet line speed of the spinning plate in the dry-wet spinning is 10 m / min-16 m / min, and the air layer height is 2 mm-5 mm. The carbon fiber with micro-groove structure can be prepared by the method, and the method provides the possibility for realizing the tensile property and interface property of high-performance carbon fiber.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of fibers, and particularly relates to a kind of carbon fibers with micro-groove structure and a preparation method thereof. BACKGROUND

[0002] Polyacrylonitrile (PAN) based carbon fiber is the most widely used variety among PAN-based, viscose-based and pitch-based three carbon fiber varieties. PAN-based carbon fibers are divided into high-strength type, high-model type and ultra-high-strength high-model type, wherein the high-strength type can be divided into dry-wet process and wet process. The carbon fiber prepared by wet process has regular groove structure on the surface, and the carbon fiber prepared by dry-wet process has smooth surface.

[0003] PAN-based carbon fiber has outstanding tensile properties. From the perspective of the tensile properties of carbon fiber, the surface groove structure is an opening defect, which is one of the key factors affecting the high performance of carbon fiber. The carbon fiber prepared by dry-wet process can realize the ultra-high strengthening of carbon fiber, and the ultra-high strength carbon fiber reported at home and abroad at present is prepared by dry-wet process, including T1100 grade and T1200 grade represented by Toray carbon fiber. At the same time, the stream solidification characteristics of dry-wet process and wet process spinneret lead to that the radial structure of dry-wet process fiber is more homogeneous, the axial orientation is better, and it is more conducive to the preparation of high-performance carbon fiber.

[0004] High-performance carbon fiber is usually used in the form of composite material, and the interfacial bonding capacity of carbon fiber and resin matrix is one of the important factors affecting the performance of composite material. The surface groove structure of carbon fiber has strong physical engagement with the resin matrix, which can improve the interfacial bonding capacity of the two. The smooth surface of carbon fiber has little physical engagement, which is not conducive to the exertion of the mechanical properties of carbon fiber in the composite material.

[0005] In order to comply with the development trend of high-performance carbon fiber, ensure the tensile properties of carbon fiber, and at the same time, the interfacial performance is also a key point that cannot be ignored. Therefore, developing a kind of carbon fiber with the surface process characteristics of wet process and dry-wet process carbon fiber is a powerful method to solve the balance of tensile properties and interfacial properties. SUMMARY

[0006] The present application provides a kind of carbon fiber with micro-groove structure and a preparation method thereof, and the carbon fiber with micro-groove structure can be prepared by the method, which provides the possibility for realizing the balance of tensile properties and interfacial properties of high-performance carbon fiber.

[0007] In one aspect of the present application, a method for preparing carbon fiber with micro-groove structure is provided, comprising:

[0008] The polyacrylonitrile fiber spinning solution is subjected to dry-wet spinning, coagulation drafting, primary drafting, water washing, oiling, drying densification, secondary drafting and heat setting to obtain a polyacrylonitrile precursor fiber;

[0009] The polyacrylonitrile precursor fiber is subjected to pre-oxidation and carbonization treatment to obtain a carbon fiber,

[0010] 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 stream line speed of the spinning plate in the dry-wet spinning is 10 m / min-16 m / min, and the air layer height is 2 mm-5 mm.

[0011] In some embodiments of the present application, the preparation method of the polyacrylonitrile fiber spinning solution comprises: mixing acrylonitrile, itaconic acid, a first initiator and dimethyl sulfoxide in a polymerization kettle for polymerization; when the viscosity of the polymerization system reaches 300 poise-550 poise, a second initiator is added to the polymerization system, and the reaction is continued to obtain the polyacrylonitrile fiber spinning solution.

[0012] In some embodiments of the present application, the molar ratio of acrylonitrile to itaconic acid is (93-99.5):(0.5-7).

[0013] In some embodiments of the present application, the total amount of the first initiator and the second initiator accounts for 0.1%-1% of the total molar amount of acrylonitrile and itaconic acid.

[0014] In some embodiments of the present application, the molar ratio of the first initiator to the second initiator is (2-3):(2-3).

[0015] In some embodiments of the present application, the second initiator is added continuously by dropwise addition, and the dropwise addition is completed within 30 min-60 min.

[0016] In some embodiments of the present application, the first initiator and the second initiator each independently comprise azobisisobutyronitrile and / or azobisisoheptyl nitrile.

[0017] In some embodiments of the present application, the viscosity of the polyacrylonitrile fiber spinning solution at 45°C is 700 poise-1200 poise.

[0018] In some embodiments of the present application, the coagulation draft includes a first coagulation draft or a second coagulation draft, the first coagulation draft includes a primary coagulation, a secondary coagulation and a tertiary coagulation in sequence, wherein the first coagulation bath temperature for the primary coagulation is 20-30℃, the first coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(0.2-0.6), the draft ratio of the primary coagulation is 1.5-4.0 times, and the time of the first coagulation is 0.5-2 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 of 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 of the tertiary coagulation is 0.5-2 minutes. The coagulation bath temperature for the second coagulation draft is 3-15℃, the coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(3-19), the draft ratio is 1.5-4.0 times, and the coagulation time is 0.5-2 minutes.

[0019] In some embodiments of the present application, the draft medium for the primary draft is water vapor at 100-110℃, and the draft ratio is 4-10 times.

[0020] In some embodiments of the present application, the dry densification temperature is 110-150℃.

[0021] In some embodiments of the present application, the draft medium for the secondary draft is water vapor at 120-150℃, and the draft ratio is 2-5 times.

[0022] In some embodiments of the present application, the heat setting temperature is 110-180℃.

[0023] In some embodiments of the present application, the pre-oxidation uses 4-6 temperature gradient zones, the pre-oxidation treatment starting temperature is 180-220℃, the final temperature is 250-300℃, and the total pre-oxidation time is 40-100 minutes.

[0024] In some embodiments of the present application, the draft ratio of the pre-oxidation process is 30-80% of the breaking stress of the pre-oxidized fiber obtained by the pre-oxidation.

[0025] In some embodiments of the present application, the carbonization process comprises low-temperature carbonization and high-temperature carbonization, the low-temperature carbonization is performed at a temperature of 300-800℃ for 1.5-6 minutes under the protection of high-purity nitrogen, and the drawing 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 is performed at a temperature of 1200-1800℃ for 1-4 minutes under the protection of high-purity nitrogen.

[0026] In some embodiments of the present application, the Ra of the surface of the carbon fiber is 5nm-25nm.

[0027] In the second aspect of the present application, the present application provides a carbon fiber obtained by the method of the first aspect of the present application.

[0028] By using a polyacrylonitrile fiber spinning solution with a weight average molecular weight of 220,000-300,000 and a molecular weight distribution of 1.5-2.5, and then performing dry-wet spinning and controlling the jet stream line speed of the dry-wet spinning to be 10m / min-16m / min and the air layer height to be 2mm-5mm, and then performing pre-oxidation and carbonization, a carbon fiber with a surface micro-groove structure can be prepared, which makes it possible to achieve a balance between the tensile properties and the interfacial properties of high-performance carbon fibers. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 SEM image of the carbon fiber obtained in Example 8;

[0030] Figure 2 SEM image of the carbon fiber obtained in Comparative Example 6. DETAILED DESCRIPTION

[0031] The present application will be further described in detail below by combining with the examples, the following examples are only descriptive and not limiting, and the protection scope of the present application cannot be limited by the examples.

[0032] "RANGES" disclosed herein are defined, for each specific range of numerals, by a lower and an upper endpoint. The endpoints of the ranges are inclusive and are to be construed as being combined with every interval formed by every lower endpoint with every upper endpoint to form a new range within the area defined by the original endpoints. For example, if a range is recited as 60-120 and 80-110, it is understood that the ranges of 60-110 and 80-120 are also contemplated. In addition, if a minimum range value of 1 and 2 is recited, and if a maximum range value of 3, 4 and 5 is recited, then the following ranges are all contemplated: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In this application, unless otherwise stated, a range of "a-b" is a shorthand manner of disclosing each and every numeral value and range encompassed within the range of a to b, where a and b are both real numbers and the range is inclusive of the endpoints. For example, the numerical range of "0-5" recited herein is to be understood as including every real number in the range of "0-5" that has been recited herein, "0-5" is merely a shorthand manner of disclosing each and every numerical value in the range. In addition, when a parameter is stated to be an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0033] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0034] In one aspect of the present application, a method for preparing carbon fibers with microgroove structure is provided, which comprises:

[0035] S100: obtaining polyacrylonitrile precursor fibers by dry-wet spinning, coagulation drafting, primary drafting, water washing, oiling, drying densification, secondary drafting and heat setting of a polyacrylonitrile fiber spinning solution

[0036] In the step, the weight average molecular weight of the polyacrylonitrile fiber spinning dope is 220,000-300,000, the molecular weight distribution of the polymer in the spinning dope is 1.5-2.5, and the stream line speed of the dry-jet wet spinning spinneret is 10 m / min-16 m / min, and the air layer height is 2 mm-5 mm. By using the polyacrylonitrile fiber spinning dope with high molecular weight and narrow molecular weight distribution, in which the macromolecular chains in the spinning dope form more physical entanglement points (to prepare for high extrusion swell ratio), and by combining the high spinneret speed (i.e. high spinneret shear rate, to obtain high extrusion swell ratio) and the relatively short air layer height (the extrusion swell does not have enough time to fully retract) in the dry-jet wet spinning process, the spinning solution stream enters the coagulation bath, and the normal shrinkage force occurs when the spinning solution stream just enters the coagulation bath, and the imbalance between the residual swell effect and the normal shrinkage force forms the fiber with the surface micro-groove structure, which makes it possible to achieve the balance between the tensile properties and the interfacial properties of the high-performance carbon fiber.

[0037] In some embodiments of the present application, the preparation method of the polyacrylonitrile fiber spinning dope comprises: taking acrylonitrile and itaconic acid as the comonomers, taking azobisdimethylvaleronitrile and / or azobisdimethylhexanonitrile as the first initiator, taking dimethyl sulfoxide as the solvent, adding acrylonitrile, itaconic acid and dimethyl sulfoxide into a polymerization kettle, stirring uniformly, increasing the temperature in the polymerization kettle to 50-65℃, adding the first initiator, and allowing the system in the polymerization kettle to undergo free radical polymerization under the action of the first initiator (azobisdimethylvaleronitrile and / or azobisdimethylhexanonitrile, preferably azobisdimethylvaleronitrile), and testing the viscosity of the polymerization system in the polymerization kettle in real time; when the viscosity of the polymerization system reaches 300 poise-550 poise, adding the second initiator (azobisdimethylvaleronitrile and / or azobisdimethylhexanonitrile, preferably azobisdimethylhexanonitrile) into the polymerization system, and continuing to react for 6-9 hours after the addition is completed, and then stopping the reaction to obtain the polyacrylonitrile fiber spinning dope.

[0038] Further, in the above preparation process of the spinning dope, the molar ratio of acrylonitrile to itaconic acid is (93-99.5):(0.5-7); the addition amount of dimethyl sulfoxide and the comonomers is 19%-23% of the total mass of acrylonitrile and itaconic acid; and the total addition amount of the first initiator and the second initiator accounts for 0.1-1% of the total molar amount of acrylonitrile and itaconic acid.

[0039] Further, in the above preparation process of the spinning dope, the molar ratio of the first initiator to the second initiator is (2-3):(2-3); and the second initiator is added continuously at a uniform speed and is added completely within 30 min-60 min, and the reaction is continued for 6-9 hours after the addition is completed, and then the reaction is stopped.

[0040] In some embodiments of the present application, the method further comprises: performing the single-elimination and initiator-removing treatment on the polyacrylonitrile fiber spinning dope in the following manner: increasing the temperature of the polymerization kettle to 70-75℃, vacuumizing, and then after 5-8h, decreasing the temperature of the polymerization kettle to 65-72℃, continuing vacuumizing for 4-10h, and performing the single-elimination and initiator-removing treatment.

[0041] Finally, a spinning dope with a solid content of 19%-23%, a weight average molecular weight of the polymer in the dope of 220-300 thousand, a molecular weight distribution of 1.5-2.5, and a viscosity (45℃) of 700-1200 poise is obtained.

[0042] In some embodiments of the present application, the coagulation drawing in the process of preparing the polyacrylonitrile precursor fiber comprises a first coagulation drawing or a second coagulation drawing, the first coagulation drawing comprises a first-stage coagulation, a second-stage coagulation and a third-stage coagulation in sequence, wherein the first-stage coagulation adopts a first coagulation bath with a temperature of 20-30℃, the first coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(0.2-0.6), the first-stage coagulation has a drawing ratio of 1.5-4.0, and the first-stage coagulation has a time of 0.5-2 minutes; the second-stage coagulation adopts a second coagulation bath with a temperature of 20-50℃, the second coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(0.5-1.5), the second-stage coagulation has a coagulation time of 0.5-2 minutes; the third-stage coagulation adopts a third coagulation bath with a temperature of 20-50℃, the third coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(4-7), and the third-stage coagulation has a coagulation time of 0.5-2 minutes. The second coagulation drawing adopts a coagulation bath with a temperature of 3-15℃, the coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(3-19), the coagulation drawing has a drawing ratio of 1.5-4.0, and the coagulation has a time of 0.5-2 minutes.

[0043] The entry of the spinning dope into the coagulation bath is a key link for controlling the cross-sectional morphology of the fiber. Both the second coagulation drawing (adopting low temperature and low concentration, the coagulation bath temperature is 3-15℃, and the coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(3-19)) and the first coagulation drawing (the first-stage coagulation adopts high temperature and high concentration, the first-stage coagulation bath temperature is 20-30℃, and the first-stage coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(0.2-0.6)) can achieve the effect of high roundness of the cross section of the nascent fiber. Meanwhile, in the case of the first coagulation drawing, the use of gradient coagulation technology is beneficial to delaying the coagulation rate of the fiber skin, and the radial structure homogeneity of the precursor fiber is more optimal.

[0044] In some embodiments of the present application, the drawing medium for the first drawing in the above process for preparing polyacrylonitrile filaments is water vapor at 100-110 DEG C, the draw ratio is 4-10 times; the water washing process adopts a multi-stage gradient temperature raising water washing process, the water flow is opposite to the fiber direction, which facilitates thorough washing, the water washing temperature is 50-90 DEG C, the washing time is about 4-10 min, and the water washing draw ratio is 97%-101%; the oil agent in the oil agent tank comprises an amino modified silicone oil emulsion with a solid content of 1.5%-2.5%; the drying densification temperature is 110-150 DEG C; the drawing medium for the second drawing is water vapor at 120-150 DEG C, and the draw ratio is 2-5 times; and the heat setting temperature is 110-180 DEG C, while a draw ratio of 96%-102% is applied.

[0045] In the present application, the test method for the weight average molecular weight and the molecular weight distribution of the polymer in the spinning dope comprises: using a gel permeation chromatograph GPC produced by Waters Company to perform the test, using dimethylformamide as a solvent, and adding an appropriate amount of lithium chloride when preparing the polymer solution.

[0046] In the present application, the test method for the solid content of the spinning dope comprises: taking a certain mass of spinning dope, denoted as M, precipitating the polymer therein, drying, and recording the mass of the polymer when the mass is stable, denoted as m, the ratio of the mass m of the dried polymer to the mass M of the spinning dope is the solid content of the spinning dope.

[0047] In the present application, unless otherwise specified, the viscosity of the polymerization system is the viscosity at 45 DEG C, and the test method comprises: using a rotary viscometer to perform the test, adding the spinning dope into a test cavity, circulating water at 45 DEG C into the cavity jacket, starting the test after 30 min of water circulation, recording when the test data are stable, and taking the average of three tests.

[0048] S200: carbonizing the polyacrylonitrile filaments to obtain carbon fibers

[0049] In some embodiments of the present application, the pre-oxidation adopts 4-6 gradient temperature raising temperature zones, the pre-oxidation starting temperature is 180-220 DEG C, the final temperature is 250-300 DEG C, the total pre-oxidation time is 40-100 min, and the draw ratio in the pre-oxidation process is 30%-80% of the breaking stress of the pre-oxidized fiber obtained after the pre-oxidation, preferably 40%-60%, so that the pre-oxidized fiber with a bulk density of 1.32-1.47 g / cm 3 The drawing in the pre-oxidation process is beneficial to the arrangement of the reaction generated ring structure to the preferred orientation direction, and the moderate drawing is more optimal.

[0050] In some embodiments of the present application, the carbonization treatment comprises low-temperature carbonization and high-temperature carbonization, the low-temperature carbonization uses high-purity nitrogen as a protective gas, the oxygen content in the nitrogen is less than 5 ppm, the temperature is 300-800℃, the time is 1.5-6 minutes, the draft ratio of the low-temperature carbonization process is 20%-70% of the breaking stress of the fiber obtained by the low-temperature carbonization, preferably 40%-50%, and moderate draft is conducive to the orientation and arrangement of the carbon structure in the fiber and improves the performance; the high-temperature carbonization uses high-purity nitrogen as a protective gas, the oxygen content in the nitrogen is less than 3 ppm, the temperature is 1200-1800℃, and after 1-4 minutes, carbon fibers with a micro-groove structure on the surface can be obtained, and the Ra obtained by AFM test is 5 nm-25 nm.

[0051] The method for testing the Ra of the carbon fiber surface by AFM comprises: using an atomic force microscope (AFM) to characterize the micro-area roughness and surface morphology of the carbon fiber. Before testing, the carbon fiber sample is cleaned with acetone, ethanol and deionized water in sequence by ultrasonic oscillation for 3 minutes, and then dried. When preparing the sample, double-sided adhesive tape is pasted on both sides of the glass slide, the carbon fiber monofilament is tightly pasted on the double-sided adhesive tape, the sample is fixed on the sample table, the frequency is set to 1 Hz during testing, the tapping mode is used, and the scanning area is 2 μm×μm. Each sample is tested 3 times, and the average value is taken.

[0052] The method for preparing the carbon fiber with a micro-groove structure according to the present application has at least one of the following effects:

[0053] (1) From the perspective of polymerization control: the present application realizes the synergistic control of polymer and polymer 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, PAN molecular chain is lengthened to the required molecular weight, which is beneficial to the high performance of the fiber; on the other hand, by continuously adding initiators in the middle and late stages, the initiators can diffuse uniformly in the relatively sticky system (avoiding local massive initiation), the added initiators can initiate the monomers that have not reacted in the system, and also can act as a trapping agent for long-chain macromolecular radicals, realizing termination reaction, thereby avoiding or alleviating the problems of excessive molecular weight and excessively wide molecular weight distribution caused by the rapid rise of polymer system viscosity due to gelation effect and macromolecular chain double radical termination. If the initiator is added when the viscosity is lower than 300 poise, the PAN molecular weight generated in the system is relatively low, and there are a large number of unreacted monomers, the added initiator initiates the monomers, and the monomers no longer participate in the addition reaction of the original PAN polymer radical, finally resulting in low PAN molecular weight in the system, affecting the performance of PAN fiber and carbon fiber. If the initiator is added when the viscosity is higher than 550 poise, the polymer system is too sticky, and the added initiator is difficult to collide with the monomers, the PAN long-chain macromolecular radical may collide with the initiator to terminate the reaction, or there may be negative effects such as automatic acceleration caused by PAN macromolecular chain radical double-click termination, and the added initiator cannot control the polymerization process.

[0054] (2) From the perspective of carbon fiber tensile performance: the present application retains the main line of dry-jet wet spinning process, so that the spinning solution stream avoids the problem of poor radial structure uniformity of the primary fiber caused by the high extrusion swell ratio of 3-5 times in wet spinning, which is beneficial to the preparation of high-performance carbon fiber.

[0055] (3) From the perspective of carbon fiber and resin matrix interface performance: the surface of the carbon fiber prepared by the conventional wet spinning process has a regular groove structure, and the Ra obtained by AFM test is between 30-50 nm according to the process adjustment in the preparation process. The Ra of the carbon fiber prepared by the present application is between 5-25 nm. The surface of the carbon fiber prepared by the conventional dry-wet process has an AFM test Ra of 1-3 nm. From the perspective of carbon fiber interface physical engagement, the interface performance of the carbon fiber prepared by the present application is better than that of the carbon fiber prepared by the dry-wet process. After the same anodic oxidation treatment and using the same resin matrix, the interlaminar shear strength of the carbon fiber prepared by the present application is increased by 15%-25% compared with that of the carbon fiber prepared by the conventional dry-wet process.

[0056] The present application will be described below with reference to specific examples, it should be noted that these examples are merely descriptive, and should not limit the present application in any way.

[0057] Example 1

[0058] (1) Preparation of the spinning dope

[0059] The acrylonitrile and itaconic acid were blended in a molar ratio of 97:3 and put into a polymerization kettle, then dimethyl sulfoxide solvent was added in a mass ratio of 3.65:1 to the total mass of acrylonitrile and itaconic acid. When the temperature of the polymerization kettle was raised to 62°C, 0.25% of the total moles of acrylonitrile and itaconic acid was added as initiator (azobisisobutyronitrile, AIBN). When the viscosity of the polymer solution in the kettle (45°C) was raised to 350 poise, 0.25% of the total moles of acrylonitrile and itaconic acid was added as initiator (azobisisobutyronitrile, AIBN) in a continuous dropwise manner, and the addition was completed in 30 min. After 4 hours of continuous reaction, the reaction was stopped quickly. Then the temperature of the polymerization kettle was raised to 74°C, and vacuum was applied. After 6 hours, the temperature of the polymerization kettle was reduced to 70°C, and vacuum was continued for 6 hours to remove the single and initiator. The polyacrylonitrile fiber spinning dope was obtained, and the solid content of the obtained spinning dope was 20.5%, the weight average molecular weight of the polymer in the dope was 240,000, the molecular weight distribution was 2.3, and the viscosity was 870 poise (tested at 45°C).

[0060] (2) Spinning of dry-jet wet-spun filaments

[0061] Solidification of the spinning solution: a spinneret with a pore size of 0.150 mm was used, and a dry-jet wet spinning process was adopted. The linear speed of the fiber leaving the spinneret was 12 m / min. After passing through a section of air environment with a height of 4 mm, the fiber entered the first coagulation bath. The temperature of the first coagulation bath was 25°C, the volume ratio of dimethyl sulfoxide to water in the first coagulation bath was 1:0.33, the coagulation time was 1 minute, and the coagulation draft was 3 times. After the coagulation yarn left the first coagulation bath, it entered the second coagulation bath. The temperature of the second coagulation bath was 25°C, the volume ratio of dimethyl sulfoxide to water in the second coagulation bath was 1:1.2, and the coagulation time was 1.5 minutes. After the coagulation yarn left the second coagulation bath, it entered the third coagulation bath. The temperature of the third coagulation bath was 25°C, the volume ratio of dimethyl sulfoxide to water in the third coagulation bath was 1:5.7, and the coagulation time was 1.5 minutes.

[0062] The polyacrylonitrile precursor fiber is obtained after sequentially performing primary drawing, water washing, oiling, drying and densification, secondary drawing and heat setting: the fiber strand coming out of the third coagulation bath is drawn in 100℃ water vapor at a draw ratio of 4.8 times; the drawn fiber strand is passed through six water washing tanks with gradient temperature, the water washing tank temperatures are 50℃ / 60℃ / 70℃ / 75℃ / 80℃ / 85℃ respectively, the water washing draw ratio is 98.5%, after removing residual solvent by conventional water washing, the fiber is oiled by using amino-modified silicone oil emulsion with solid content of 2% as oil agent, and is dried and densified by three hot rollers with gradient temperature, the hot roller temperatures are 105℃ / 110℃ / 115℃ respectively, the draw ratio of the hot roller is 98%; the dried and densified fiber strand is drawn in 140℃ superheated water vapor at a draw ratio of 2.5 times; the twice-drawn fiber strand is heat set at 150℃, and is wound into a bobbin by a yarn collector after heat setting, thereby obtaining the polyacrylonitrile carbon fiber precursor.

[0063] (3) Preparation of carbon fiber by pre-oxidation and carbonization

[0064] Pre-oxidation: the precursor fiber is pre-oxidized and stabilized by using gradient temperature method in air atmosphere in six temperature zones, the pre-oxidation temperatures are 210℃, 225℃, 235℃, 245℃, 255℃, 265℃ and 270℃ respectively, the residence times are 6min, 12min, 12min, 12min, 12min and 6min respectively, the draw ratio of the fiber during pre-oxidation is controlled at 50% of the breaking stress of the corresponding pre-oxidized fiber, the total pre-oxidation time is 60 minutes, and the pre-oxidized fiber with a bulk density of 1.37g / cm 3 is obtained.

[0065] Carbonization: the obtained pre-oxidized fiber is put into a low-temperature carbonization furnace for low-temperature carbonization treatment, high-purity nitrogen is used as protective gas, the oxygen content in the nitrogen is 1PPm, the low-temperature carbonization temperature is 580℃, according to the requirement of fiber diameter, the draw ratio of the fiber during low-temperature carbonization is 40% of the breaking stress of the obtained low-temperature carbonized fiber, the low-temperature carbonization time is 3 minutes; the fiber coming out of the low-temperature carbonization furnace is put into a high-temperature carbonization furnace for high-temperature carbonization treatment, high-purity nitrogen is used as protective gas, the oxygen content in the nitrogen is 1PPm, the high-temperature carbonization temperature is 1350℃, the high-temperature carbonization time is 3 minutes, thereby obtaining the polyacrylonitrile carbon fiber.

[0066] Example 2

[0067] (1) Preparation of spinning solution

[0068] The acrylonitrile and itaconic acid are blended in a molar ratio of 97:3 and fed into a polymerization kettle, and dimethyl sulfoxide solvent is added in a mass ratio of 4:1 to the total mass of the acrylonitrile and itaconic acid. When the temperature of the polymerization kettle is raised to 62°C, 0.15% of the total molar percentage of acrylonitrile and itaconic acid is added as an initiator (azobisisobutyronitrile, AIBN). When the viscosity (45°C) of the polymer solution in the kettle is raised to 430 poise, 0.15% of the total molar percentage of acrylonitrile and itaconic acid is added as an initiator (azobisisobutyronitrile, AIBN) in a continuous dropwise manner, and the addition is completed in 50 min. After the reaction is continued for 4 hours, the reaction is stopped quickly. Then the temperature of the polymerization kettle is raised to 74°C, and vacuum is applied. After 6 hours, the temperature of the polymerization kettle is reduced to 70°C, and vacuum is continued to be applied for 6 hours, to remove the single and initiator. A polyacrylonitrile fiber spinning dope is obtained, and the obtained spinning dope has a solid content of 19.3%, a weight average molecular weight of the polymer in the dope of 263,000, a molecular weight distribution of 1.6, and a viscosity of 930 poise (tested at 45°C).

[0069] (2) Spinning of dry-jet wet-spun filaments

[0070] Coagulation and formation of the spinning solution: a spinneret with a pore size of 0.150 mm is used, and a dry-jet wet spinning process is adopted. The linear speed of the fiber leaving the spinneret is 15 m / min. After passing through a 3 mm high air environment, the fiber enters a coagulation bath for coagulation drafting, primary drafting, washing, oiling, drying densification, secondary drafting, and heat setting to obtain polyacrylonitrile filaments. The process conditions of the coagulation drafting, primary drafting, washing, oiling, drying densification, secondary drafting, and heat setting are the same as in Example 1.

[0071] (3) Pre-oxidation and carbonization to prepare carbon fibers: the same as in Example 1.

[0072] Example 3

[0073] (1) Preparation of the spinning dope: the same as in Example 2.

[0074] (2) Spinning of dry-jet wet-spun filaments

[0075] Coagulation and formation of the spinning solution: a spinneret with a pore size of 0.150 mm is used, and a dry-jet wet spinning process is adopted. The linear speed of the fiber leaving the spinneret is 10 m / min. After passing through a 3 mm high air environment, the fiber enters a coagulation bath for coagulation drafting, primary drafting, washing, oiling, drying densification, secondary drafting, and heat setting to obtain polyacrylonitrile filaments. The process conditions of the coagulation drafting, primary drafting, washing, oiling, drying densification, secondary drafting, and heat setting are the same as in Example 1.

[0076] (3) Pre-oxidation and carbonization to prepare carbon fibers: the same as in Example 1.

[0077] Example 4

[0078] (1) Preparation of the spinning dope

[0079] The acrylonitrile and itaconic acid were blended in a molar ratio of 97:3 and put into a polymerization kettle, then dimethyl sulfoxide solvent was added in a mass ratio of 3.65:1 to the total mass of acrylonitrile and itaconic acid. When the temperature of the polymerization kettle was raised to 62°C, 0.25% of the total moles of acrylonitrile and itaconic acid was added as initiator (azobisisobutyronitrile, AIBN). When the viscosity of the polymer solution in the kettle (45°C) was raised to 510 poise, 0.25% of the total moles of acrylonitrile and itaconic acid was added as initiator (azobisisobutyronitrile, AIBN) in a continuous dropwise manner, and the addition was completed in 45 min. The reaction was continued for 4 hours, and then the reaction was stopped quickly. Then the temperature of the polymerization kettle was raised to 74°C, and vacuum was applied. After 6 hours, the temperature of the polymerization kettle was reduced to 70°C, and vacuum was continued for 6 hours to remove the single and initiator. The polyacrylonitrile fiber spinning dope was obtained, and the solid content of the obtained spinning dope was 20.3%, the weight average molecular weight of the polymer in the dope was 230,000, the molecular weight distribution was 2.2, and the viscosity was 760 poise (tested at 45°C).

[0080] (2) Spinning of dry-jet wet-spun filaments

[0081] Solidification of the spinning solution: a spinneret with a pore size of 0.100 mm was used, and a dry-jet wet spinning process was adopted. The linear speed of the fiber leaving the spinneret was 14 m / min. After passing through a section of air environment with a height of 5 mm, the fiber entered the first coagulation bath. The temperature of the first coagulation bath was 25°C, the volume ratio of dimethyl sulfoxide to water in the first coagulation bath was 1:0.33, the coagulation time was 1 minute, and the coagulation draft was 3 times. After the coagulation yarn left the first coagulation bath, it entered the second coagulation bath. The temperature of the second coagulation bath was 25°C, the volume ratio of dimethyl sulfoxide to water in the second coagulation bath was 1:1.2, and the coagulation time was 1.5 minutes. After the coagulation yarn left the second coagulation bath, it entered the third coagulation bath. The temperature of the third coagulation bath was 25°C, the volume ratio of dimethyl sulfoxide to water in the third coagulation bath was 1:5.7, and the coagulation time was 1.5 minutes.

[0082] The polyacrylonitrile precursor fiber is obtained after sequentially performing primary drawing, water washing, oiling, drying and densification, secondary drawing and heat setting: the fiber strand coming out of the third coagulation bath is drawn in 100℃ water vapor, and the drawing ratio is 5 times; the drawn fiber strand passes through 6 water washing tanks with gradient temperature, and the water washing tank temperatures are 50℃ / 60℃ / 70℃ / 75℃ / 80℃ / 85℃ respectively, the water washing drawing ratio is 98.5%, after removing the residual solvent by conventional water washing, the fiber is oiled by using the amino-modified silicone oil emulsion with solid content of 2% as the oil agent, and is dried and densified by three heat rollers with gradient temperature, and the heat roller temperatures are 105℃ / 110℃ / 115℃ respectively, and the heat roller drawing ratio is 98%; the dried and densified fiber strand is drawn in 140℃ superheated water vapor for the second time, and the drawing ratio is 2.4 times; the fiber strand after the second drawing is heat set at 150℃, and is wound into a bobbin by a yarn collector after heat setting, thereby obtaining the polyacrylonitrile carbon fiber precursor.

[0083] (3) Preparation of carbon fiber by pre-oxidation and carbonization

[0084] Pre-oxidation: the precursor fiber is pre-oxidized and stabilized by using the gradient temperature method in an air atmosphere in 4 temperature zones, and the pre-oxidation temperatures are 210℃, 220℃, 230℃, 235℃, 240℃, 245℃ and 250℃ respectively, and the residence times are 6min, 12min, 12min, 12min, 12min and 6min respectively, and the fiber drawing ratio during pre-oxidation is controlled at 50% of the breaking stress of the corresponding pre-oxidized fiber, and the total pre-oxidation time is 60 minutes, thereby obtaining the pre-oxidized fiber with a bulk density of 1.365g / cm 3 .

[0085] Carbonization: the obtained pre-oxidized fiber is put into a low-temperature carbonization furnace for low-temperature carbonization treatment, high-purity nitrogen is used as the protective gas, the oxygen content in the nitrogen is 1PPm, the low-temperature carbonization temperature is 600℃, according to the requirement of the fiber diameter, the fiber drawing ratio during the low-temperature carbonization stage is 50% of the breaking stress of the obtained low-temperature carbonized fiber, and the low-temperature carbonization time is 3 minutes; after the fiber comes out of the low-temperature carbonization furnace, it is put into a high-temperature carbonization furnace for high-temperature carbonization treatment, high-purity nitrogen is used as the protective gas, the oxygen content in the nitrogen is 1PPm, the high-temperature carbonization temperature is 1500℃, and the high-temperature carbonization time is 3 minutes, thereby obtaining the polyacrylonitrile carbon fiber.

[0086] Example 5

[0087] (1) Preparation of spinning solution

[0088] The acrylonitrile and itaconic acid are blended in a molar ratio of 98:2 and fed into a polymerization kettle, and dimethyl sulfoxide solvent is added in a mass ratio of 3.44:1 to the total mass of acrylonitrile and itaconic acid. When the temperature of the polymerization kettle is raised to 62°C, 0.3% of the total molar percentage of acrylonitrile and itaconic acid is added as initiator azobisisobutyronitrile (AIBN). When the viscosity (45°C) of the polymer solution in the kettle is raised to 470 poise, 0.30% of the total molar percentage of acrylonitrile and itaconic acid is added as initiator (azobisisoheptyl nitrile) in a continuous dropwise manner, and the addition is completed in 50 min. After 4 hours of continuous reaction, the reaction is stopped quickly. Then the temperature of the polymerization kettle is raised to 74°C, vacuum is applied, and after 6 hours the temperature of the polymerization kettle is lowered to 70°C, and vacuum is continued for 6 hours for single-elimination and initiator-elimination treatment, to obtain a polyacrylonitrile fiber spinning dope. The obtained spinning dope has a solid content of 21.7%, a weight average molecular weight of the polymer in the dope of 245,000, a molecular weight distribution of 1.77, and a viscosity of 880 poise (tested at 45°C).

[0089] (2) Spinning of dry-jet wet-spun filaments

[0090] Coagulation and formation of the spinning dope: a spinneret with a pore size of 0.100 mm is used, and a dry-jet wet spinning process is adopted, with a linear speed of the fiber leaving the spinneret of 12.5 m / min. After passing through a section of air environment of 3 mm in height, the fiber enters a coagulation bath for coagulation drafting, primary drafting, washing, oiling, drying densification, secondary drafting, and heat setting to obtain polyacrylonitrile filaments. The process conditions of coagulation drafting, primary drafting, washing, oiling, drying densification, secondary drafting, and heat setting are the same as in Example 4.

[0091] (3) Preparation of carbon fibers by pre-oxidation and carbonization: the same as in Example 4.

[0092] Example 6

[0093] (1) Preparation of the spinning dope

[0094] The acrylonitrile and itaconic acid are blended in a molar ratio of 99.5:0.5 and fed into a polymerization kettle, and dimethyl sulfoxide solvent is added in a mass ratio of 3.88:1 to the total mass of acrylonitrile and itaconic acid. When the temperature of the polymerization kettle is raised to 62°C, 0.35% of the total molar percentage of acrylonitrile and itaconic acid is added as initiator azobisisobutyronitrile (AIBN). When the viscosity (45°C) of the polymer solution in the kettle is raised to 550 poise, 0.35% of the total molar percentage of acrylonitrile and itaconic acid is added as initiator (azobisisobutyronitrile) in a continuous dropwise manner, and the addition is completed in 60 min. After 4 hours of continuous reaction, the reaction is stopped quickly. Then the temperature of the polymerization kettle is raised to 74°C, vacuum is applied, and after 6 hours the temperature of the polymerization kettle is reduced to 70°C, and vacuum is continued for 6 hours for single-elimination and initiator-elimination treatment, to obtain a polyacrylonitrile fiber spinning dope. The obtained spinning dope has a solid content of 19.7%, a weight average molecular weight of the polymer in the dope of 220,000, a molecular weight distribution of 1.8, and a viscosity of 890 poise (tested at 45°C).

[0095] (2) Spinning of dry-jet wet-spun filaments

[0096] Coagulation and formation of the spinning solution: a spinneret with a pore size of 0.100 mm is used, and a dry-jet wet spinning process is adopted, the linear speed of the fiber leaving the spinneret is 10.5 m / min, and after passing through an air layer with a height of 4 mm, the fiber enters a coagulation bath for coagulation drafting, primary drafting, washing, oiling, drying densification, secondary drafting, and heat setting to obtain polyacrylonitrile filaments, wherein the process conditions of coagulation drafting, primary drafting, washing, oiling, drying densification, secondary drafting, and heat setting are the same as in Example 4.

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

[0098] Example 7

[0099] (1) Preparation of the spinning dope

[0100] The same as in Example 2;

[0101] (2) Spinning of dry-jet wet-spun filaments

[0102] Coagulation and formation of the spinning solution: a dry-jet wet spinning process is adopted, the spinneret specification, the linear speed of the fiber leaving the spinneret, and the air layer height are the same as in Example 2;

[0103] The coagulation bath temperature is 5°C, the volume ratio of dimethyl sulfoxide to water in the coagulation bath is 1:9, the coagulation time is 2 minutes, and the coagulation drafting ratio is 3 times.

[0104] Primary drafting, washing, oiling, drying densification, secondary drafting, and heat setting are performed to obtain polyacrylonitrile filaments, wherein the process conditions of coagulation drafting, primary drafting, washing, oiling, drying densification, secondary drafting, and heat setting are the same as in Example 1.

[0105] (3) Pre-oxidation and carbonization to prepare carbon fiber: same as Example 1.

[0106] Example 8

[0107] (1) Preparation of spinning dope

[0108] Same as Example 5;

[0109] (2) Spinning of dry-jet wet-spun filaments

[0110] Solidification of the spinning dope: the dry-jet wet spinning process was used, the spinneret specification, the linear speed of the fiber leaving the spinneret hole, and the air layer height were the same as in Example 5.

[0111] The coagulation bath temperature in the coagulation drawing stage was 5°C, the volume ratio of dimethyl sulfoxide to water in the coagulation bath was 1:9, the coagulation time was 2 minutes, and the coagulation drawing multiple was 3.

[0112] After primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting, polyacrylonitrile filaments were obtained, wherein the coagulation drawing, primary drawing, washing, oiling, drying and densification, secondary drawing, and heat setting process conditions were the same as in Example 4.

[0113] (3) Pre-oxidation and carbonization to prepare carbon fiber: same as Example 4, the SEM image of the carbon fiber obtained is shown in Figure 1 , and it can be seen that a micro-groove structure is formed on the surface of the carbon fiber. Figure 1

[0114] Comparative Example 1

[0115] (1) Preparation of spinning dope

[0116] Acrylonitrile and itaconic acid were blended in a molar ratio of 97:3 and fed into a polymerization kettle, and dimethyl sulfoxide solvent was added in a mass ratio of 3.65:1 to the total mass of acrylonitrile and itaconic acid. When the temperature of the polymerization kettle increased to 62°C, 0.5% of the total molar percentage of acrylonitrile and itaconic acid was added as initiator azobisisobutyronitrile (AIBN), and the reaction was stopped after 9 hours. Then the temperature of the polymerization kettle was increased to 74°C, vacuum was applied, and after 6 hours the temperature of the polymerization kettle was reduced to 70°C, and vacuum was continued for 6 hours for single removal and initiator removal treatment. A polyacrylonitrile fiber spinning dope was obtained, the solid content of the obtained spinning dope was 19.6%, the weight average molecular weight of the polymer in the dope was 200,000, the molecular weight distribution was 3.7, and the viscosity was 650 poise (tested at 45°C).

[0117] (2) Spinning of dry-jet wet-spun filaments

[0118] ​Coagulation and formation of the spinning solution: using a spinneret with a pore diameter of 0.150 mm, a dry-jet wet spinning process was adopted, the linear speed 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 for coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting to obtain the polyacrylonitrile precursor fiber, wherein the process conditions of coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting were the same as in Example 1.

[0119] (3) Pre-oxidation and carbonization to prepare carbon fiber: the same as in Example 1.

[0120] Comparative Example 2

[0121] (1) Preparation of the spinning solution: the same as in Comparative Example 1.

[0122] (2) Spinning of the dry-jet wet-spun precursor fiber

[0123] Coagulation and formation of the spinning solution: using a spinneret with a pore diameter of 0.100 mm, a dry-jet wet spinning process was adopted, the linear speed 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 for coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting to obtain the polyacrylonitrile precursor fiber, wherein the process conditions of coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting were the same as in Example 4.

[0124] (3) Pre-oxidation and carbonization to prepare carbon fiber: the same as in Example 4.

[0125] Comparative Example 3

[0126] (1) Preparation of the spinning solution: the same as in Example 1;

[0127] (2) Spinning of the dry-jet wet-spun precursor fiber

[0128] Coagulation and formation of the spinning solution: using a spinneret with a pore diameter of 0.150 mm, a dry-jet wet spinning process was adopted, the linear speed of the fiber leaving the spinneret was 9 m / min, after passing through a 5 mm high air environment, the fiber entered the coagulation bath for coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting to obtain the polyacrylonitrile precursor fiber, wherein the process conditions of coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting were the same as in Example 1.

[0129] (3) Pre-oxidation and carbonization to prepare carbon fiber: the same as in Example 1.

[0130] Comparative Example 4

[0131] (1) Preparation of the spinning solution: the same as in Example 1;

[0132] (2) Spinning of dry-jet wet-spun filaments

[0133] Solidification and formation of the spinning dope: using a spinneret with a pore diameter of 0.150 mm, a dry-jet wet spinning process was used, the linear speed of the fiber leaving the spinneret was 17 m / min, after passing through a 5 mm high air layer, the fiber entered the coagulation bath for coagulation draft, primary draft, water washing, oiling, drying densification, secondary draft and heat setting to obtain polyacrylonitrile filaments, wherein the process conditions of coagulation draft, primary draft, water washing, oiling, drying densification, secondary draft and heat setting were the same as in Example 1.

[0134] (3) Pre-oxidation and carbonization to prepare carbon fibers: the same as in Example 1.

[0135] Comparative Example 5

[0136] (1) Preparation of the spinning dope: the same as in Example 1;

[0137] (2) Spinning of dry-jet wet-spun filaments

[0138] Solidification and formation of the spinning dope: using a spinneret with a pore diameter of 0.150 mm, a dry-jet wet spinning process was used, the linear speed of the fiber leaving the spinneret was 17 m / min, after passing through a 5 mm high air layer, the fiber entered the coagulation bath for coagulation draft, primary draft, water washing, oiling, drying densification, secondary draft and heat setting to obtain polyacrylonitrile filaments, wherein the process conditions of coagulation draft, primary draft, water washing, oiling, drying densification, secondary draft and heat setting were the same as in Example 1.

[0139] (3) Pre-oxidation and carbonization to prepare carbon fibers: the same as in Example 1.

[0140] Comparative Example 6

[0141] (1) Preparation of the spinning dope: the same as in Example 1;

[0142] (2) Spinning of dry-jet wet-spun filaments

[0143] Coagulation and formation of the spinning solution: using a spinneret with a pore diameter of 0.150 mm, a dry-jet wet spinning process was adopted, the linear speed of the fiber leaving the spinneret was 12 m / min, after passing through a 6 mm high air environment, the fiber entered the coagulation bath for coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting to obtain the polyacrylonitrile precursor fiber, wherein the process conditions of coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting were the same as in Example 1.

[0144] (3) Preparation of carbon fiber by pre-oxidation and carbonization: the same as in Example 1, the SEM image of the obtained carbon fiber is shown in Figure 2 , and it can be seen from Figure 2 that the surface of the carbon fiber is relatively smooth.

[0145] Comparative Example 7

[0146] (1) Preparation of the spinning solution: the same as in Example 4;

[0147] (2) Spinning of the dry-jet wet-spun precursor fiber

[0148] Coagulation and formation of the spinning solution: using a spinneret with a pore diameter of 0.100 mm, a dry-jet wet spinning process was adopted, the linear speed of the fiber leaving the spinneret was 9 m / min, after passing through a 5 mm high air environment, the fiber entered the coagulation bath for coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting to obtain the polyacrylonitrile precursor fiber, wherein the process conditions of coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting were the same as in Example 4.

[0149] (3) Preparation of carbon fiber by pre-oxidation and carbonization: the same as in Example 4.

[0150] Comparative Example 8

[0151] (1) Preparation of the spinning solution: the same as in Example 4;

[0152] (2) Spinning of the dry-jet wet-spun precursor fiber

[0153] Coagulation and formation of the spinning solution: using a spinneret with a pore diameter of 0.100 mm, a dry-jet wet spinning process was adopted, the linear speed of the fiber leaving the spinneret was 17 m / min, after passing through a 5 mm high air environment, the fiber entered the coagulation bath for coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting to obtain the polyacrylonitrile precursor fiber, wherein the process conditions of coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting were the same as in Example 4.

[0154] (3) Preparation of carbon fiber by pre-oxidation and carbonization: the same as in Example 4.

[0155] Comparative Example 9

[0156] (1) Preparation of the spinning dope: same as Example 4;

[0157] (2) Spinning of the dry-jet wet-spun filaments

[0158] Solidification and formation of the spinning dope: using a spinneret with a pore size of 0.100 mm, a dry-jet wet spinning process was adopted, the linear velocity of the fiber leaving the spinneret was 14 m / min, after passing through a 6 mm high air layer, the filaments entered the coagulation bath for coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting to obtain the polyacrylonitrile filaments, wherein the process conditions of the coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting were the same as in Example 4.

[0159] Due to the too low height of the air layer, the liquid capillary effect caused the coagulation bath to climb against the spinneret along the spinning dope stream, the air layer disappeared, and the spinning process was converted to wet spinning. The finally prepared filaments were filaments with groove structures on the surface, and due to the draft ratio of the first coagulation bath being 3 times, the first coagulation of the wet spinning was usually negative draft, and the too high coagulation draft caused the regular grooves on the surface of the "surface broken" filaments to become discontinuous and irregular.

[0160] (3) Preparation of carbon fibers by pre-oxidation and carbonization: same as Example 4.

[0161] Comparative Example 10

[0162] (1) Preparation of the spinning dope: same as Example 4;

[0163] (2) Spinning of the dry-jet wet-spun filaments

[0164] Solidification and formation of the spinning dope: using a spinneret with a pore size of 0.100 mm, a dry-jet wet spinning process was adopted, the linear velocity of the fiber leaving the spinneret was 14 m / min, after passing through a 6 mm high air layer, the filaments entered the coagulation bath for coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting to obtain the polyacrylonitrile filaments, wherein the process conditions of the coagulation draft, primary draft, washing, oiling, drying densification, secondary draft and heat setting were the same as in Example 4.

[0165] (3) Preparation of carbon fibers by pre-oxidation and carbonization: same as Example 4.

[0166] The solid content of the polyacrylonitrile fiber spinning dope, the weight average molecular weight of the polymer, the molecular weight distribution of the polymer and the viscosity of the polyacrylonitrile fiber spinning dope obtained in Examples 1-6 and Comparative Examples 1-10 were tested, and the test results are shown in Table 1.

[0167] The solid content of the polyacrylonitrile fiber spinning solution is tested by the following method: a certain amount of the spinning solution is taken, denoted as M, and the polymer is precipitated and dried, and the mass of the dried polymer is recorded as m. 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.

[0168] The weight average molecular weight and the molecular weight distribution of the polymer in the polyacrylonitrile fiber spinning solution are tested by the following method: a gel permeation chromatograph produced by Waters is used, dimethylformamide is used as the solvent, and an appropriate amount of lithium chloride is added when the polymer solution is prepared.

[0169] The viscosity of the polyacrylonitrile fiber spinning solution is tested by the following method: a rotary viscometer is used, the spinning solution is added to the test cavity, the cavity jacket is connected to circulating water at 45°C, and the water is turned on for 30 minutes before the test is started. The test data is recorded when it is stable, and the average value of three tests is taken.

[0170] Table 1

[0171]

[0172] The carbon fibers obtained in Examples 1-8 and Comparative Examples 1-10 are subjected to performance tests according to GB3362 “Carbon Fiber Test Standard” and GB / T 3364 “Carbon Fiber Diameter and Number Test Method”. The carbon fibers obtained in Examples 1-8 and Comparative Examples 1-10 are subjected to anodic oxidation surface treatment, and are subjected to electrochemical treatment using ammonium bicarbonate as an electrolyte (the concentration of ammonium bicarbonate in the electrolyte is 3 wt%), the electrolyte conductivity is 30 mS / cm, the electrolysis time is 70 s, and the current density is 0.26 mA / cm 2 After the treatment, the carbon fibers are dried after sizing, and are subjected to sample preparation and testing according to JC / T773 interlaminar shear strength test standard using TDE-85 and C05 resin system. The test results are shown in Table 2.

[0173] Table 2

[0174]

[0175] Note: Comparative Example 5 and Comparative Example 9 are not subjected to interlaminar shear strength tests because the mechanical properties of the carbon fibers are too poor.

[0176] As can be seen from the data in Table 2, the carbon fibers obtained in Examples 1-8 have excellent tensile properties and interfacial properties, while the carbon fibers obtained in Comparative Examples 1-3 and 6, 7, and 10 have excellent tensile properties but poor interfacial properties. 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 have poor tensile properties, which shows that the method of the present application can take into account both the tensile properties and the interfacial properties of the carbon fibers.

[0177] The above merely preferred embodiments of the present application and it should be noted that, for the ordinary skilled in the art, several improvements and refinements can be made without departing from the technical principles of the present application, and these improvements and refinements should also be considered within the scope of protection of the present application.

Claims

1. A method for preparing 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 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.

2. The method according to claim 1, characterized in that, The preparation method of the polyacrylonitrile fiber spinning solution includes: Acrylonitrile, itaconic 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 300 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 to itaconic acid is (93-99.5):(0.5-7); and / or The total amount of the first initiator and the second initiator added accounts for 0.1%-1% of the total molar amount of acrylonitrile and itaconic acid; and / or The molar ratio of the first initiator to the second initiator is (2-3):(2-3); and / or The second initiator is added continuously, completed within 30-60 minutes; and / or The first initiator and the second initiator each independently comprise azobisisobutyronitrile and / or azobisisoheptanenitrile; and / or The viscosity of the polyacrylonitrile fiber spinning solution at 45°C is 700 poise to 1200 poise.

4. The method according to any one of claims 1-3, characterized in that, The solidification stretching includes a first solidification stretching or a second solidification stretching. The first solidification stretching includes, in sequence, primary solidification, secondary solidification, and tertiary solidification. The temperature of the first coagulation bath used in the first coagulation is 20-30℃, the first coagulation bath is a mixture of dimethyl sulfoxide and water with a volume ratio of 1:(0.2-0.6), the draw ratio of the first coagulation is 1.5-4.0 times, and the first coagulation time is 0.5-2 minutes. The secondary coagulation process uses a second coagulation bath at a temperature of 20-50°C, which is a mixture of dimethyl sulfoxide and water in a volume ratio of 1:(0.5-1.5). The coagulation time for the secondary coagulation process is 0.5-2 minutes. The temperature of the third coagulation bath used in the three-stage 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 of the three-stage 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 in 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.

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 4-10 times; and / or The drying and densification temperature is 110-150℃; and / or The secondary drawing medium is water vapor at 120-150℃, 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 4-6 temperature zones with gradient increases. The initial temperature of the pre-oxidation treatment is 180-220℃, the final temperature is 250-300℃, and the total pre-oxidation time is 40-100 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.

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 1200-1800℃ and a time of 1-4 minutes.

9. The method according to claim 8, characterized in that, The Ra of the carbon fiber surface is 5nm-25nm.

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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