High-strength high-modulus carbon fiber and method for producing the same

Abstract

The application discloses high-strength and high-modulus carbon fibers and a preparation method thereof. The carbon fibers have a tensile strength of 7000-7700 MPa and a tensile modulus of 350-390 GPa.

Description

Technical Field

[0001] This invention belongs to the field of fiber material preparation, and relates to a high-strength, high-modulus carbon fiber and its preparation method. Background Technology

[0002] Polyacrylonitrile-based carbon fiber has excellent properties that can meet the requirements of lightweight, high strength, high stiffness, dimensional stability and functional / structural integration of aerospace equipment structures. It is a core material for primary and secondary structures at all levels of aircraft and satellites, and is also a key focus of future aerospace material development.

[0003] Currently, polyacrylonitrile-based carbon fiber has undergone two generations of development, supporting the development of the first and second generations of advanced composite materials. The first generation of carbon fiber is represented by high-strength standard models such as T300, T700, AS4, and AS7, with a strength of approximately 3530-4900 MPa, a modulus of approximately 230-248 GPa, and an interlaminar shear strength ≥100 MPa. The second generation of carbon fiber is represented by high-strength medium-modulus models such as T800, IM7, and IM8, with a strength of approximately 5500-6100 MPa, a modulus of approximately 276-305 GPa, and an interlaminar shear strength ≥100 MPa. Compared with the first generation, the second generation of products has an average increase of more than 20% in tensile strength and tensile modulus, while maintaining comparable interlaminar shear strength. This has resulted in a 10-15% weight reduction in composite materials and a significant improvement in equipment performance. In recent years, with the continuous progress of carbon fiber preparation technology in my country, breakthroughs have been made in the engineering preparation technology of the first and second generation carbon fibers, supporting the emergency needs of my country's high-end equipment. However, with the need for equipment upgrading and replacement, there is an urgent need for the third generation of high-strength and high-modulus carbon fibers. Currently, the tensile strength of high-strength carbon fiber has reached 7000 MPa, and the tensile modulus of high-modulus carbon fiber has reached 640 GPa. However, the traditional method of increasing the carbonization (graphitization) temperature for high-modulus carbon fiber often results in a decrease in tensile strength while increasing the tensile modulus. At the same time, high temperature increases the degree of graphitization, which reduces the interlaminar shear strength and limits its application. For example, M40J grade carbon fiber has a modulus of 377 GPa, a tensile strength of 4410 MPa, and an interlaminar shear strength of 80 GPa, while M55 grade carbon fiber has a modulus of 540 GPa, a tensile strength of 4020 MPa, and an interlaminar shear strength of 65 GPa. Therefore, there are still technical problems that need to be solved in the third generation of carbon fiber, which has a tensile strength and tensile modulus that are more than 20% higher than that of the second-generation T800 grade carbon fiber and an interlaminar shear strength that is comparable to that of T800 grade carbon fiber (≥100 MPa). Summary of the Invention

[0004] The purpose of this invention is to overcome the shortcomings of the prior art and provide a high-strength, high-modulus carbon fiber and its preparation method. Using this method, carbon fibers with a tensile strength of 7000-7700 MPa and a tensile modulus of 350-390 GPa can be prepared.

[0005] In one aspect, the present invention provides a high-strength, high-modulus carbon fiber, wherein the tensile strength is 7000-7700 MPa and the tensile modulus is 350-390 GPa.

[0006] Furthermore, the interlaminar shear strength of the carbon fiber is ≥100MPa.

[0007] In another aspect of the present invention, a method for preparing carbon fiber is proposed, comprising: (1) mixing acrylonitrile, itaconic acid, azobisisobutyronitrile and dimethyl sulfoxide for polymerization, and after polymerization, obtaining acrylonitrile copolymer spinning solution by amination, demonolysis, degassing and filtration; (2) subjecting the acrylonitrile copolymer spinning solution to spinning, primary coagulation, secondary coagulation, tertiary coagulation, atmospheric pressure steam drawing, washing, oiling, drying and densification, high pressure saturated steam drawing and heat setting to obtain polyacrylonitrile precursor fiber, wherein the precursor fiber has a single filament fineness of 0.5-0.8 dtex and a crystal orientation degree of 91-94%; (3) subjecting the polyacrylonitrile precursor fiber to pre-oxidation and carbonization to obtain carbon fiber, wherein the oxygen content of the fiber after pre-oxidation is 6wt%-8wt%.

[0008] Further, in step (1), the molar ratio of acrylonitrile to itaconic acid is 100:(0.5-0.8), the polymerization reaction temperature is controlled at 60-70℃, the reaction time is 12-30 hours, the rotational viscosity of the acrylonitrile copolymer spinning solution at 45℃ is 60-80 Pa·s, and the intrinsic viscosity is 1.65-1.95 dL / g.

[0009] Further, in step (2), the spinning process employs a dry-jet wet-spinning method. The coagulation process includes primary coagulation, secondary coagulation, and tertiary coagulation. The primary coagulation bath temperature is 0-40°C, and the primary coagulation bath is a dimethyl sulfoxide aqueous solution, wherein the dimethyl sulfoxide volume content in the dimethyl sulfoxide aqueous solution is 65-75%, and the primary coagulation draw ratio is 2.5-4.0. The secondary coagulation bath temperature is 50-70°C. A dimethyl sulfoxide (DMSO) aqueous solution is used, wherein the DMSO volume content in the aqueous solution is 30-45%, and the secondary solidification draw ratio is 1.2-2.0. The tertiary solidification process uses a DMSO aqueous solution at a temperature of 55-75°C, wherein the tertiary solidification bath uses a DMSO aqueous solution, wherein the DMSO volume content in the aqueous solution is 10-20%, and the tertiary solidification draw ratio is 1.2-2.0. After tertiary solidification, the fiber crystal region orientation degree is 55-65%.

[0010] Furthermore, in step (2), the atmospheric pressure steam drawing is carried out in steam at 95-100℃ with a drawing ratio of 3.5-6; the fiber crystal region orientation degree is controlled to be 75-85%.

[0011] Furthermore, in step (2), the high-pressure saturated steam stretching pressure is 0.4-0.8 MPa, the stretching ratio is 2.5-6, and the fiber crystal region orientation degree is controlled to be 91-95%.

[0012] Furthermore, the heat setting temperature is 180-210℃, the time is 1-5s, and the draw ratio is 1.0-1.1.

[0013] Further, in step (3), the pre-oxidation includes 3-6 progressively increasing temperature zones, with the initial temperature zone at 210-230℃ and the final temperature zone at 230-260℃, for a duration of 30-90 minutes.

[0014] Further, in step (3), the carbonization includes primary carbonization, secondary carbonization, tertiary carbonization, and quaternary carbonization, wherein: the primary carbonization is carried out in a high-purity nitrogen atmosphere, with an initial temperature of 300-400℃, a final temperature of 450-500℃, a time of 2-4 minutes, and a draw ratio of 75-90% of the limiting draw ratio of the primary carbonization process; the secondary carbonization is carried out in a high-purity nitrogen atmosphere, with a secondary carbonization temperature of 600-800℃. The first stage of carbonization is carried out at 00℃ for 3-6 minutes, with a draw ratio of the ultimate draw ratio. The second stage of carbonization is carried out in a high-purity nitrogen atmosphere, with an initial temperature of 900-1000℃ and a final temperature of 1100-1200℃ for 3-6 minutes, with a draw ratio of the ultimate draw ratio. The third stage of carbonization is carried out in a high-purity nitrogen atmosphere, with an initial temperature of 1400-1700℃ and a final temperature of 3-6 minutes, with a draw ratio of the ultimate draw ratio.

[0015] Compared with the prior art, the present invention has the following advantages:

[0016] The method of this invention improves the fineness and orientation of the precursor fiber by progressively controlling the conditions of the spinning coagulation, atmospheric pressure steam drawing, and high pressure saturated steam drawing processes, thereby promoting carbon fiber orientation enhancement. This allows for the production of highly oriented, high-modulus carbon fibers at relatively low carbonization temperatures. Controlling the oxygen content of the pre-oxidized fiber ensures sufficient thermal stability and maintains its shape retention during carbonization. Simultaneously, it prevents excessive carbon fixation due to excessive oxygen, reducing the proportion of amorphous carbon after carbonization and promoting an increase in the graphite carbon proportion, which is beneficial for improving tensile strength and tensile modulus. The chemical structure of pre-oxidized fibers varies at different temperatures during the carbonization process, resulting in different stress limits and different drawability. They can be mainly divided into (1) the cracking stage of linear molecular chain segments and few-ring pre-oxidized ladder structure, (2) the stage of multi-element ladder structure condensation to form crystal nuclei, (3) the stage of rapid removal of nitrogen and oxygen elements, and (4) the stage of rapid growth of graphite microcrystals. In the four key chemical reaction stages of carbonization, the actual draw ratio is limited by the limit draw ratio of each stage. Under the premise of ensuring that the fiber does not fray or break, the growth and orientation of graphite microcrystals are promoted to the maximum extent, thereby improving the tensile modulus of the fiber. At the same time, the matching of multi-level gradient carbonization temperature, time, and draw can achieve fine crystallization of graphite microcrystals, thereby improving the modulus while ensuring the high tensile strength and interlayer shear strength of the fiber. The final product will be carbon fiber with a tensile strength of 7000-7700MPa, a tensile modulus of 350-390GPa, and an interlaminar shear strength of ≥100MPa. Compared with the current second-generation T800 grade carbon fiber, the tensile strength and tensile modulus will be increased by more than 20% simultaneously, and the interlaminar shear strength will be comparable. It is expected to reduce the weight of my country's high-end equipment by 10-15% and further improve the performance of my country's high-end equipment. Detailed Implementation

[0017] 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.

[0018] In one aspect, the present invention provides a high-strength, high-modulus carbon fiber, wherein the carbon fiber has a tensile strength of 7000-7700 MPa and a tensile modulus of 350-390 GPa.

[0019] Furthermore, the interlaminar shear strength of the carbon fiber is ≥100MPa.

[0020] In another aspect, the present invention provides a method for preparing high-strength, high-modulus carbon fibers. According to an embodiment of the present invention, the method includes:

[0021] S1: Acrylonitrile, itaconic acid, azobisisobutyronitrile, and dimethyl sulfoxide are mixed and polymerized. After polymerization, the mixture undergoes amination, demonolysis, degassing, and filtration.

[0022] In this step, acrylonitrile is used as the first monomer, itaconic acid as the second monomer, dimethyl sulfoxide (DMSO) as the solvent, and azobisisobutyronitrile (AIO) as the initiator for polymerization. The molar ratio of acrylonitrile to itaconic acid is 100:(0.5-0.8), the polymerization temperature is 60-70℃, and the reaction time is 12-30 hours. After polymerization, ammonia gas is introduced. Ammonia gas can amidate the itaconic acid to control the hydrophilicity of the acrylonitrile copolymer. Then, under stirring, unreacted monomers in the polymer spinning solution are removed at 60-70℃ and a vacuum degree greater than 0.095 MPa. After 7-9 hours, stirring is stopped, and degassing is performed under a vacuum condition of 55-65℃. The resulting spinning solution has a rotational viscosity of 60-80 Pa·s at 45℃ and an intrinsic viscosity of 1.65-1.95 dL / g.

[0023] The inventors discovered that controlling the intrinsic viscosity of the spinning solution is beneficial for achieving high density and high orientation of the precursor fiber; simultaneously, controlling the rotational viscosity of the spinning solution enables continuous and stable spinning of low-density precursor fibers. Then, dry-jet wet spinning of the spinning solution yields precursor fibers with smooth surfaces and fewer defects. Furthermore, dry-jet wet spinning facilitates high draw ratios, improves orientation, and thus promotes carbon fiber orientation enhancement. Consequently, high-oriented, high-modulus carbon fibers can be obtained at lower carbonization temperatures.

[0024] S2: The spinning solution undergoes spinning, primary coagulation, secondary coagulation, tertiary coagulation, atmospheric pressure steam drawing, washing, oiling, drying and densification, high-pressure saturated steam drawing, and heat setting.

[0025] According to an embodiment of the present invention, the spinneret coagulation adopts a dry-spinning wet-spinning method, which facilitates high draw ratio and improves the orientation of the precursor yarn. After being metered and extruded from the spinneret, the spinning solution forms a fine stream, passes through an air layer, and enters the primary coagulation bath. The air layer height is 3-9 mm. The coagulation process includes primary coagulation, secondary coagulation, and tertiary coagulation. The temperature of the primary coagulation bath in the primary process is 0-40°C, and the primary coagulation bath uses a dimethyl sulfoxide aqueous solution with a dimethyl sulfoxide volume content of 65-75%. The primary coagulation draw ratio is 2.5-4.0. After exiting the primary coagulation bath, the coagulated yarn enters the secondary coagulation bath at a temperature of 5°C. The secondary coagulation bath is set at 0-70℃, using a dimethyl sulfoxide (DMSO) aqueous solution with a DMSO volume content of 30-45% and a secondary coagulation draw ratio of 1.2-2.0. After exiting the secondary coagulation bath, the coagulated filaments enter the tertiary coagulation bath at 55-75℃, using a DMSO aqueous solution with a DMSO volume content of 10-20% and a tertiary coagulation draw ratio of 1.2-2.0. After tertiary coagulation, the fiber crystal orientation is 55-65%.

[0026] The inventors discovered that after three-stage solidification, the fiber crystal region orientation degree is 55-65%, which can provide an orientation basis for subsequent atmospheric pressure steam drawing, thereby improving the overall orientation of the original fiber, while avoiding obvious fuzzing and fiber breakage.

[0027] According to an embodiment of the present invention, the atmospheric pressure steam drawing is carried out in steam at 95-100℃ with a drawing ratio of 3.5-6; the fiber crystal region orientation degree is controlled to be 75-85%. The inventors have found that by controlling the fiber orientation degree to be 75-85% in this process, an orientation basis can be provided for subsequent high-pressure saturated steam drawing, thereby achieving an overall improvement in the orientation of the precursor fiber, while avoiding significant fuzzing and fiber breakage.

[0028] According to an embodiment of the present invention, the high-pressure saturated steam drawing pressure is 0.4-0.8 MPa, the draw ratio is 2.5-6, and the fiber orientation degree is controlled at 91-95%. The inventors have discovered that high-pressure saturated steam facilitates the penetration of water molecules into the fiber interior, resulting in sufficient fiber plasticization, effectively improving drawability and increasing fiber orientation. By controlling the fiber orientation degree to 91-95% during this process, high modulus of carbon fibers can be achieved at a lower carbonization temperature, while simultaneously improving interlaminar shear strength.

[0029] According to an embodiment of the present invention, the heat setting temperature is 180-210°C, the time is 1-5 seconds, and the draw ratio is 1.0-1.1. Thus, by performing heat setting at high temperature for a short time, the highly oriented structure after being drawn under high pressure with saturated water vapor is solidified to a certain extent, preventing deorientation.

[0030] It should be noted that the other conditions in the spinning process are standard conditions in this field and will not be described in detail here.

[0031] S3: Pre-oxidation and carbonization of polyacrylonitrile precursor fibers

[0032] In this step, the polyacrylonitrile precursor obtained above is subjected to pre-oxidation and carbonization treatments in sequence to obtain carbon fibers.

[0033] According to an embodiment of the present invention, the pre-oxidation includes 3-6 progressively increasing temperature zones, with an initial temperature zone of 210-230°C and a final temperature zone of 230-260°C, for a duration of 30-90 minutes. The oxygen content of the resulting pre-oxidized fiber is controlled to be 6wt%-8wt%. The inventors have found that controlling the oxygen content of the pre-oxidized fiber within the above range ensures sufficient thermal stability and maintains the fiber's shape retention during carbonization. Simultaneously, it prevents excessive carbon fixation, reduces the proportion of amorphous carbon after carbonization, promotes an increase in the graphite carbon ratio, and is beneficial for improving tensile strength and tensile modulus.

[0034] According to embodiments of the present invention, the carbonization described above includes primary carbonization, secondary carbonization, tertiary carbonization, and quaternary carbonization.

[0035] The primary carbonization is carried out in a high-purity nitrogen atmosphere. The initial temperature of primary carbonization is 300-400℃, the final temperature is 450-500℃, and the time is 2-4 minutes. The draw ratio is 75-90% of the limit draw ratio of the primary carbonization process. It should be noted that the "limit draw ratio" here refers to the highest draw ratio that does not cause fiber breakage during the primary carbonization process. The inventors have discovered that this stage is the cleavage stage of linear molecular chain segments and 1-3 ring few-ring pre-oxidized ladder structures. If the draw is too small, the orientation of the multi-ring ladder structure is small; if the draw is too large, molecular slippage occurs between the ladder structures, reducing the intermolecular forces. The draw range of this invention ensures that excessive slippage does not occur between the multi-ring ladder macromolecules, improves the orientation and regularity of the multi-ring ladder structure, and is beneficial to the improvement of carbon fiber strength and modulus.

[0036] The secondary carbonization is carried out in a high-purity nitrogen atmosphere at a temperature of 600-800℃ for 3-6 minutes, with a draw ratio of the limiting draw ratio. It should be noted that the "limiting draw ratio" here refers to the highest draw ratio during the secondary carbonization process without fiber breakage. The inventors discovered that this stage is where the multi-element trapezoidal structure condenses to form crystal nuclei. If the temperature is too low, the reaction rate is too slow, which is not conducive to crystal nuclei formation; if the temperature is too high, the crystal growth rate is too fast, easily forming a small number of large crystals. The carbonization temperature and time set in this invention can ensure the formation of a large number of small crystal nuclei, which is beneficial for achieving high crystallinity and fine crystallization of carbon fibers, thereby effectively improving tensile strength and tensile modulus. Using the limiting draw ratio in this stage is beneficial for improving crystal nuclei orientation, thereby improving the microcrystalline orientation of the final carbon fiber and increasing the tensile modulus of the carbon fiber.

[0037] The three-stage carbonization is carried out in a high-purity nitrogen atmosphere. The initial temperature is 900-1000 degrees Celsius, the final temperature is 1100-1200 degrees Celsius, and the time is 3-6 minutes. The draw ratio is the ultimate draw ratio. It should be noted that the "ultimate draw ratio" here refers to the highest draw ratio during the three-stage carbonization process without fiber breakage. The inventors discovered that this stage is a rapid removal stage of nitrogen and oxygen elements, mainly consisting of small molecule gases such as carbon monoxide, carbon dioxide, and nitrogen. If the temperature is too low, the reaction rate is too slow; if the temperature is too high, the small molecule removal rate is too fast, causing increased internal pressure and making it easy to leave large molecular-level pores and increase defects. The temperature and time set in this invention balance the relationship between the small molecule removal rate and graphitization transformation while ensuring the reaction rate. This can reduce molecular-level pores, and at the same time, the ultimate draw ratio is used to maximize the closure of micropores and the improvement of microcrystal orientation, thereby improving strength and modulus.

[0038] The fourth-stage carbonization is carried out in a high-purity nitrogen atmosphere at a temperature of 1400-1600℃ for 3-6 minutes, with a draw ratio of the ultimate draw ratio. It should be noted that the "ultimate draw ratio" here refers to the highest draw ratio during the fourth-stage carbonization process without fiber breakage. The inventors discovered that this stage is the rapid growth stage of graphite crystallites. If the temperature is too low, the degree of graphitization is low, resulting in low modulus; if the temperature is too high, the degree of graphitization is too high, resulting in low surface polarity and low interlaminar shear strength. This stage is the final formation stage of graphite crystallites. Using the ultimate draw ratio can directly improve the orientation of carbon fiber crystallites and effectively increase the modulus.

[0039] Specifically, the chemical structure, stress tolerance limit, and drawability of pre-oxidized fibers differ at different temperatures during the carbonization process. By limiting the actual draw ratio through the limiting draw ratio at each key chemical reaction stage of carbonization, the growth and orientation of graphite crystallites can be effectively promoted. Simultaneously, the matching of the aforementioned multi-stage carbonization temperature, time, and draw ratio can achieve graphite crystal refinement, improving the modulus while ensuring high tensile strength and interlaminar shear strength of the fibers. Therefore, this method can be used to prepare carbon fibers with tensile strength of 7000-7700 MPa, tensile modulus of 350-390 GPa, and interlaminar shear strength ≥100 MPa.

[0040] 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.

[0041] Example 1

[0042] (1) Acrylonitrile is the first monomer, itaconic acid is the second monomer, azobisisobutyronitrile is the initiator, and dimethyl sulfoxide is the solvent for polymerization. The molar ratio of acrylonitrile to itaconic acid is 100:0.5, the polymerization temperature is 65℃, and the reaction time is 24 hours. After polymerization, ammonia is introduced. Ammonia can amidate itaconic acid to control the hydrophilicity of the acrylonitrile copolymer. Then, under stirring, unreacted monomers in the polymer spinning solution are removed at 65℃ and under a vacuum degree greater than 0.095MPa. After 8 hours, stirring is stopped, and degassing is performed under a vacuum at 60℃. After filtration, the spinning solution is obtained. The spinning solution has a rotational viscosity of 71Pa.s and an intrinsic viscosity of 1.78dL / g at 45℃.

[0043] (2) The spinning solution is ejected through a spinneret with an aperture of 115 μm, passes through a 6 mm air layer, and enters the primary coagulation bath at a temperature of 3°C. The primary coagulation bath uses a dimethyl sulfoxide (DMSO) aqueous solution with a volume concentration of 73% and a draw ratio of 2.8. After exiting the primary coagulation bath, the fiber bundle enters the secondary coagulation bath at a temperature of 55°C. The secondary coagulation bath also uses a DMSO aqueous solution with a volume concentration of 40% and a draw ratio of 1.3. After exiting the secondary coagulation bath, the fiber bundle enters the tertiary coagulation bath at a temperature of 60°C. The tertiary coagulation bath also uses a DMSO aqueous solution with a volume concentration of 20%. The three-stage coagulation process involves a draw ratio of 1.3, resulting in a fiber crystal orientation degree of 61%. After exiting the three-stage coagulation bath, the fiber bundle undergoes sequential atmospheric pressure steam drawing, washing, oiling, and drying densification. The atmospheric pressure steam drawing ratio is 4.1 at 100℃, resulting in a fiber crystal orientation degree of 78%. Silicone oil is used as the oiling agent, and the drying densification temperature is 140℃. The dried and densified fiber bundle then undergoes high-pressure steam drawing and heat setting. The high-pressure saturated steam pressure is 0.59 MPa, with a draw ratio of 2.9. After high-pressure steam drawing, the fiber crystal orientation degree is 93%. The heat setting temperature is 200℃, and the heat setting time is 3 seconds. After heat setting, the fiber bundle is wound to obtain the precursor fiber with a fineness of 0.78 dtex.

[0044] (3) The raw fiber was pre-oxidized in air at four temperature ranges: 202℃, 219℃, 231℃, and 249℃, for a total processing time of 70 minutes. The draw ratios for the four pre-oxidation stages were set to 1.04, 1.021, 1.015, and 1.015, respectively, and the oxygen content of the pre-oxidized fiber was 7.1%. The pre-oxidized fiber under nitrogen atmosphere under two temperature ranges: 350℃ and 480℃, for a total processing time of 2 minutes. The limit draw ratio for the first-stage carbonization process was 1.24, and the draw ratio for the first-stage carbonization process was set to 1.12. Then, under nitrogen atmosphere under two temperature ranges: 600℃ and 800℃, for a total processing time of 3 minutes. The limit draw ratio for the second-stage carbonization process was 0.988, and the draw ratio for the second-stage carbonization process was set to 0.988. Finally, under nitrogen atmosphere under two temperature ranges: 350℃ and 480℃, for a total processing time of 3 minutes. Three-stage carbonization was performed at two temperature ranges of 1000℃ and 1150℃ under a nitrogen atmosphere, with a total processing time of 3 minutes. The limiting draw ratio of the three-stage carbonization process was 1.006, and the draw ratio of the three-stage carbonization process was set to 1.006. Finally, four-stage carbonization was performed at two temperature ranges of 1400℃ and 1600℃ under a nitrogen atmosphere, with a total processing time of 3 minutes. The limiting draw ratio of the four-stage carbonization process was 1.005, and the draw ratio of the four-stage carbonization process was set to 1.005. Carbon fibers were thus obtained. The tensile strength and tensile modulus of the prepared carbon fibers were tested according to GB3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilament" and the interlaminar shear strength was tested according to JC / T 773-2010 "Determination of Interlaminar Shear Strength of Fiber Reinforced Plastics by Short Beam Method". The results were: tensile strength 7338 MPa, tensile modulus 367 GPa, and interlaminar shear strength 111 MPa.

[0045] Example 2

[0046] (1) Acrylonitrile is the first monomer, itaconic acid is the second monomer, azobisisobutyronitrile is the initiator, and dimethyl sulfoxide is the solvent for polymerization. The molar ratio of acrylonitrile to itaconic acid is 100:0.8, the polymerization temperature is 65℃, and the reaction time is 24 hours. After polymerization, ammonia is introduced. Ammonia can amidate itaconic acid to control the hydrophilicity of the acrylonitrile copolymer. Then, under stirring, unreacted monomers in the polymer spinning solution are removed at 65℃ and under a vacuum degree greater than 0.095MPa. After 8 hours, stirring is stopped, and degassing is performed under a vacuum at 60℃. After filtration, the spinning solution is obtained. The spinning solution has a rotational viscosity of 63Pa.s and an intrinsic viscosity of 1.72dL / g at 45℃.

[0047] (2) The spinning solution is ejected through a spinneret with an aperture of 115 μm, passes through a 6 mm air layer, and enters the primary coagulation bath at a temperature of 25°C. The primary coagulation bath uses a dimethyl sulfoxide (DMSO) aqueous solution with a DMSO volume concentration of 73% and a primary coagulation draw ratio of 3.3. After exiting the primary coagulation bath, the fiber bundle enters the secondary coagulation bath at a temperature of 55°C. The secondary coagulation bath also uses a DMSO aqueous solution with a DMSO volume concentration of 40% and a secondary coagulation draw ratio of 1.35. After exiting the secondary coagulation bath, the fiber bundle enters the tertiary coagulation bath at a temperature of 60°C. The tertiary coagulation bath also uses a DMSO aqueous solution with a DMSO volume concentration of 20%. The fiber bundle was subjected to three-stage coagulation with a draw ratio of 1.4. After three-stage coagulation, the fiber crystal orientation was 65%. After exiting the three-stage coagulation bath, the fiber bundle underwent atmospheric pressure steam drawing, washing, oiling, and drying densification in sequence. The atmospheric pressure steam drawing ratio was 4.3, and the temperature was 98℃. After atmospheric pressure steam drawing, the fiber crystal orientation was 82%. The oiling agent was silicone oil, and the drying densification temperature was 140℃. The dried and densified fiber bundle underwent high-pressure steam drawing and heat setting. The high-pressure saturated steam pressure was 0.55MPa, and the draw ratio was 3.3. After high-pressure steam drawing, the fiber crystal orientation was 94%. The heat setting temperature was 210℃, and the heat setting time was 2s. After heat setting, the fiber bundle was wound to obtain the precursor fiber with a fineness of 0.68 dtex.

[0048] (3) The raw fiber was pre-oxidized in air at four temperature ranges: 200℃, 215℃, 230℃, and 240℃, for a total processing time of 80 minutes. The draw ratios for the four pre-oxidation stages were set to 1.06%, 1.025, 1.016, and 1.014, respectively, and the oxygen content of the pre-oxidized fiber was 6.3%. The pre-oxidized fiber underwent primary carbonization at two temperature ranges: 350℃ and 480℃, for a total processing time of 2 minutes. The limit draw ratio for the primary carbonization process was 1.30, and the draw ratio for the primary carbonization process was set to 1.15. Then, under nitrogen atmosphere, secondary carbonization was performed at two temperature ranges: 600℃ and 750℃, for a total processing time of 4 minutes. The limit draw ratio for the secondary carbonization process was 0.987, and the draw ratio for the secondary carbonization process was set to 0.987. Finally, under nitrogen atmosphere... Three-stage carbonization was performed at two temperature ranges of 900℃ and 1200℃ for a total processing time of 3.5 minutes. The limiting draw ratio of the three-stage carbonization process was 1.007, and the draw ratio of the three-stage carbonization process was set to 1.007. Finally, four-stage carbonization was performed at two temperature ranges of 1400℃ and 1500℃ under a nitrogen atmosphere for a total processing time of 4 minutes. The limiting draw ratio of the four-stage carbonization process was 1.002, and the draw ratio of the four-stage carbonization process was set to 1.002. Third-generation carbon fibers were thus obtained. The tensile strength and tensile modulus of the prepared carbon fibers were tested according to GB3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilament" and the interlaminar shear strength was tested according to JC / T 773-2010 "Determination of Interlaminar Shear Strength of Fiber Reinforced Plastics by Short Beam Method". The results were: tensile strength 7637 MPa, tensile modulus 355 GPa, and interlaminar shear strength 119 MPa.

[0049] Example 3

[0050] (1) Acrylonitrile is the first monomer, itaconic acid is the second monomer, azobisisobutyronitrile is the initiator, and dimethyl sulfoxide is the solvent for polymerization. The molar ratio of acrylonitrile to itaconic acid is 100:0.5, the polymerization temperature is 65℃, and the reaction time is 24 hours. After polymerization, ammonia is introduced. Ammonia can amidate itaconic acid to control the hydrophilicity of the acrylonitrile copolymer. Then, under stirring, unreacted monomers in the polymer spinning solution are removed at 65℃ and under a vacuum degree greater than 0.095MPa. After 8 hours, stirring is stopped, and degassing is performed under a vacuum at 60℃. After filtration, the spinning solution is obtained. The spinning solution has a rotational viscosity of 71Pa.s and an intrinsic viscosity of 1.78dL / g at 45℃.

[0051] (2) The spinning solution is ejected through a spinneret with an aperture of 115 μm, passes through a 6 mm air layer, and enters the primary coagulation bath at a temperature of 38°C. The primary coagulation bath uses a dimethyl sulfoxide (DMSO) aqueous solution with a volume concentration of 73% DMSO and a primary coagulation draw ratio of 2.6. After exiting the primary coagulation bath, the fiber bundle enters the secondary coagulation bath at a temperature of 60°C. The secondary coagulation bath also uses a DMSO aqueous solution with a volume concentration of 44% DMSO and a secondary coagulation draw ratio of 1.25. After exiting the secondary coagulation bath, the fiber bundle enters the tertiary coagulation bath at a temperature of 60°C. The tertiary coagulation bath also uses a DMSO aqueous solution with a volume concentration of 23% DMSO. The fiber bundle was subjected to three-stage coagulation with a draw ratio of 1.2. After three-stage coagulation, the fiber crystal orientation was 57%. After exiting the three-stage coagulation bath, the fiber bundle underwent atmospheric pressure steam drawing, washing, oiling, and drying densification in sequence. The atmospheric pressure steam drawing ratio was 3.8, and the temperature was 96℃. After atmospheric pressure steam drawing, the fiber crystal orientation was 78%. The oiling agent was silicone oil, and the drying densification temperature was 140℃. The dried and densified fiber bundle underwent high-pressure steam drawing and heat setting. The high-pressure saturated steam pressure was 0.55MPa, and the draw ratio was 2.5. After high-pressure steam drawing, the fiber crystal orientation was 91%. The heat setting temperature was 200℃, and the heat setting time was 3s. After heat setting, the fiber bundle was wound to obtain the precursor fiber with a fineness of 0.78 dtex.

[0052] (3) The raw fiber was pre-oxidized in air at four temperature ranges: 210℃, 225℃, 230℃, and 252℃, for a total processing time of 60 minutes. The draw ratios for the four pre-oxidation stages were set to 1.06, 1.026, 1.017, and 1.015, respectively, and the oxygen content of the pre-oxidized fiber was 7.8%. The pre-oxidized fiber under nitrogen atmosphere was subjected to primary carbonization at two temperature ranges: 350℃ and 500℃, for a total processing time of 2 minutes. The limit draw ratio for the primary carbonization process was 1.21, and the draw ratio for the primary carbonization process was set to 1.12. Then, under nitrogen atmosphere, secondary carbonization was performed at two temperature ranges: 600℃ and 750℃, for a total processing time of 4 minutes. The limit draw ratio for the secondary carbonization process was 0.99, and the draw ratio for the secondary carbonization process was set to 0.99. Finally, under nitrogen atmosphere, 1 Three-stage carbonization was performed at two temperature ranges of 000℃ and 1200℃ for a total processing time of 4 minutes. The limiting draw ratio of the three-stage carbonization process was 0.998, and the draw ratio of the three-stage carbonization process was set to 0.998. Finally, four-stage carbonization was performed at two temperature ranges of 1400℃ and 1680℃ under a nitrogen atmosphere for a total processing time of 3.5 minutes. The limiting draw ratio of the four-stage carbonization process was 0.998, and the draw ratio of the four-stage carbonization process was set to 0.998, thus obtaining third-generation carbon fibers. The tensile strength and tensile modulus of the prepared carbon fibers were tested according to GB3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilament", and the interlaminar shear strength of the prepared carbon fibers was tested according to JC / T 773-2010 "Determination of Interlaminar Shear Strength of Fiber Reinforced Plastics by Short Beam Method". The results were: tensile strength 7067 MPa, tensile modulus 387 GPa, and interlaminar shear strength 102 MPa.

[0053] Comparative Example 1

[0054] (1) Acrylonitrile is the first monomer, itaconic acid is the second monomer, azobisisobutyronitrile is the initiator, and dimethyl sulfoxide is the solvent for polymerization. The molar ratio of acrylonitrile to itaconic acid is 100:1.5, the polymerization temperature is 65℃, and the reaction time is 24 hours. After polymerization, ammonia is introduced. Ammonia can amidate the itaconic acid to control the hydrophilicity of the acrylonitrile copolymer. Then, under stirring, unreacted monomers in the polymer spinning solution are removed at 65℃ and under a vacuum degree greater than 0.095MPa. After 8 hours, stirring is stopped, and degassing is performed under a vacuum at 60℃. After filtration, the spinning solution is obtained. The spinning solution has a rotational viscosity of 90 Pa·s at 45℃ and an intrinsic viscosity of 2.08 dL / g.

[0055] (2) The spinning solution is extruded through a spinneret with an aperture of 115 μm, passes through a 6 mm air layer, and enters the primary coagulation bath to obtain nascent fibers. The primary coagulation bath temperature is 3℃, and the primary coagulation bath uses a dimethyl sulfoxide aqueous solution with a volume concentration of 73% and a primary coagulation draw ratio of 2.1. The fibers then enter the secondary coagulation bath at a temperature of 60℃, using a dimethyl sulfoxide aqueous solution with a volume concentration of 44% and a secondary coagulation draw ratio of 1.05. After exiting the secondary coagulation bath, the fibers enter the tertiary coagulation bath at a temperature of 60℃, using a dimethyl sulfoxide aqueous solution with a volume concentration of 44% and a secondary coagulation draw ratio of 1.05. The fiber tow has a fineness of 23%, a three-stage coagulation draw ratio of 1.1, and a fiber crystal orientation degree of 45% after three-stage coagulation. After exiting the three-stage coagulation bath, the fiber tow undergoes atmospheric pressure steam drawing, washing, oiling, and drying densification in sequence. The atmospheric pressure steam drawing ratio is 3.0, and the temperature is 100℃. After atmospheric pressure steam drawing, the fiber crystal orientation degree is 65%. The oiling agent is silicone oil, and the drying densification temperature is 140℃. The dried and densified fiber tow undergoes high-pressure steam drawing and heat setting. The high-pressure saturated steam pressure is 0.55MPa, and the draw ratio is 2.2. After high-pressure steam drawing, the fiber crystal orientation degree is 82%, and the heat setting temperature is 170℃. After heat setting, the fiber is wound to obtain the precursor fiber with a fineness of 0.84 dtex.

[0056] (3) The raw yarn was pre-oxidized in air at four temperature ranges of 210℃, 225℃, 230℃ and 268℃ for a total treatment time of 60 minutes. The draw ratios of the four pre-oxidation stages were set to 1.01, 1.016, 1.01 and 1.01 respectively, and the oxygen content of the pre-oxidized fiber was 8.9%. The carbonization process employs a three-stage carbonization method. First, the pre-oxidized fiber undergoes primary carbonization at three temperature ranges (350℃, 500℃, and 750℃) under a nitrogen atmosphere for a total processing time of 4 minutes. The limiting draw ratio for the primary carbonization process is 1.26, and the set draw ratio for the primary carbonization process is 0.93. Second, secondary carbonization is performed at two temperature ranges (900℃ and 1200℃) under a nitrogen atmosphere for a total processing time of 4 minutes. The limiting draw ratio for the secondary carbonization process is 0.995, and the set draw ratio for the secondary carbonization process is 0.99. Finally, tertiary carbonization is performed at two temperature ranges (1400℃ and 1900℃) under a nitrogen atmosphere for a total processing time of 3 minutes. The limiting draw ratio for the tertiary carbonization process is 0.99, and the set draw ratio for the tertiary carbonization process is 0.963, thus producing carbon fibers. The tensile strength and tensile modulus of the prepared carbon fiber were tested according to GB3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilament" and the interlaminar shear strength of the prepared carbon fiber was tested according to JC / T 773-2010 "Determination of Interlaminar Shear Strength of Fiber Reinforced Plastics by Short Beam Method". The results were: tensile strength 6567 MPa, tensile modulus 377 GPa, and interlaminar shear strength 81 MPa.

[0057] Comparative Example 2

[0058] (1) Acrylonitrile is the first monomer, itaconic acid is the second monomer, azobisisobutyronitrile is the initiator, and dimethyl sulfoxide is the solvent for polymerization. The molar ratio of acrylonitrile to itaconic acid is 100:0.5, the polymerization temperature is 65℃, and the reaction time is 24 hours. After polymerization, ammonia is introduced. Ammonia can amidate the itaconic acid to control the hydrophilicity of the acrylonitrile copolymer. Then, under stirring, unreacted monomers in the polymer spinning solution are removed at 65℃ and under a vacuum degree greater than 0.095MPa. After 8 hours, stirring is stopped, and degassing is performed under a vacuum at 60℃. After filtration, the spinning solution is obtained. The spinning solution has a rotational viscosity of 71Pa.s and an intrinsic viscosity of 178dL / g at 45℃.

[0059] (2) The spinning solution is extruded through a spinneret with an aperture of 115 μm, passes through a 6 mm air layer, and enters the primary coagulation bath to obtain nascent fibers. The temperature of the primary coagulation bath is 25℃, and the primary coagulation bath uses a dimethyl sulfoxide aqueous solution with a volume concentration of 73% and a primary coagulation draw ratio of 2.1. The fibers then enter the secondary coagulation bath at a temperature of 60℃, using a dimethyl sulfoxide aqueous solution with a volume concentration of 44% and a secondary coagulation draw ratio of 1.0. After exiting the secondary coagulation bath, the fibers enter the tertiary coagulation bath at a temperature of 60℃, using a dimethyl sulfoxide aqueous solution with a volume concentration of 44% and a secondary coagulation draw ratio of 1.0. The fiber orientation degree is 43% after three-stage coagulation with a three-stage coagulation stretching ratio of 1.0. After three-stage coagulation, the fiber tow undergoes atmospheric pressure steam stretching, washing, oiling, and drying densification in sequence. The atmospheric pressure steam stretching ratio is 3.2 at 100℃. After atmospheric pressure steam stretching, the fiber orientation degree is 70%. The oiling agent is silicone oil, and the drying densification temperature is 140℃. The dried and densified fiber tow undergoes high-pressure steam stretching and heat setting. The high-pressure saturated steam pressure is 0.55MPa, the stretching ratio is 2.0, and after high-pressure steam stretching, the fiber orientation degree is 87%. The heat setting temperature is 160℃. After heat setting, the fiber is wound to obtain the precursor fiber with a fineness of 0.81 dtex.

[0060] (3) The precursor fiber was pre-oxidized in air at four temperature ranges: 210℃, 225℃, 225℃, and 225℃, for a total processing time of 100 minutes. The elongation of the four pre-oxidized fibers was set to 1.02, 1.01, 1.01, and 1.01, respectively, and the oxygen content of the pre-oxidized fiber was 4.5%. Carbonization was carried out in two stages. The pre-oxidized fiber was carbonized in nitrogen atmosphere at three temperature ranges: 350℃, 500℃, and 700℃, for a total processing time of 4 minutes. The limit draw ratio of the first carbonization process was 1.32, and the draw ratio of the first carbonization process was set to 0.98. Then, the second carbonization was carried out in nitrogen atmosphere at three temperature ranges: 1300℃, 1600℃, and 1850℃, for a total processing time of 4 minutes. The limit draw ratio of the second carbonization process was 0.995, and the draw ratio of the second carbonization process was set to 0.96, thus obtaining carbon fiber. The tensile strength and tensile modulus of the prepared carbon fiber were tested according to GB3362-2017 "Test Method for Tensile Properties of Carbon Fiber Multifilament" and the interlaminar shear strength of the prepared carbon fiber was tested according to JC / T 773-2010 "Determination of Interlaminar Shear Strength of Fiber Reinforced Plastics by Short Beam Method". The results were: tensile strength 6267 MPa, tensile modulus 364 GPa, and interlaminar shear strength 85 MPa.

[0061] 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 high-strength, high-modulus carbon fibers, characterized in that, include: (1) Acrylonitrile, itaconic acid, azobisisobutyronitrile and dimethyl sulfoxide are mixed and polymerized. After polymerization, ammoniaation, demonolysis, degassing and filtration are performed to obtain acrylonitrile copolymer spinning solution. (2) The acrylonitrile copolymer spinning solution is subjected to spinning, primary coagulation, secondary coagulation, tertiary coagulation, atmospheric pressure steam drawing, washing, oiling, drying and densification, high pressure saturated steam drawing and heat setting to obtain polyacrylonitrile precursor fiber. The precursor fiber has a single filament fineness of 0.5-0.8 dtex and a crystal orientation degree of 91-94%. (3) The polyacrylonitrile precursor fiber is pre-oxidized and carbonized to obtain carbon fiber, wherein the oxygen content of the pre-oxidized fiber is 6wt%-8wt%. In step (1), the molar ratio of acrylonitrile to itaconic acid is 100:(0.5-0.8), the polymerization reaction temperature is controlled at 60-70℃, the reaction time is 12-30 hours, and the rotational viscosity of the acrylonitrile copolymer spinning solution at 45℃ is 60-80 Pa·s, and the intrinsic viscosity is 1.65-1.95 dL / g. In step (2), after three-stage solidification, the fiber crystal region orientation degree is 55-65%. The atmospheric pressure steam drawing is carried out in steam at 95-100℃ with a drawing ratio of 3.5-6, controlling the fiber crystal region orientation degree to be 75-85%. The high-pressure saturated steam drawing pressure is 0.4-0.8MPa with a drawing ratio of 2.5-6, controlling the fiber crystal region orientation degree to be 91-95%. The heat setting temperature is 180-210℃ for 1-5s with a drawing ratio of 1.0-1.

1. In step (3), the pre-oxidation includes 3-6 progressively increasing temperature zones, with the initial temperature zone at 210-230℃ and the final temperature zone at 230-260℃, for a duration of 30-90 minutes. The carbonization includes primary carbonization, secondary carbonization, tertiary carbonization, and quaternary carbonization, wherein: The primary carbonization is carried out in a high-purity nitrogen atmosphere. The initial temperature of primary carbonization is 300-400℃, the final temperature is 450-500℃, the time is 2-4 minutes, and the draw ratio is 75%-90% of the limit draw ratio of the primary carbonization process. The secondary carbonization is carried out in a high-purity nitrogen atmosphere at a temperature of 600-800℃ for 3-6 minutes, with the draw ratio being the ultimate draw ratio. The three-stage carbonization is carried out in a high-purity nitrogen atmosphere. The initial temperature of the three-stage carbonization is 900-1000℃, the final temperature is 1100-1200℃, the time is 3-6 minutes, and the draw ratio is the ultimate draw ratio. The fourth-stage carbonization is carried out in a high-purity nitrogen atmosphere at a temperature of 1400-1700℃ for 3-6 minutes, with a draw ratio of the ultimate draw ratio.

2. The method according to claim 1, characterized in that, In step (2), the spinning is carried out by dry-jet wet spinning. The coagulation process includes primary coagulation, secondary coagulation and tertiary coagulation. The temperature of the primary coagulation bath in the primary coagulation process is 0-40℃. The primary coagulation bath is a dimethyl sulfoxide aqueous solution. The volume content of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 65-75%. The primary coagulation draw ratio is 2.5-4.

0. The secondary coagulation process involves a secondary coagulation bath temperature of 50-70℃, a dimethyl sulfoxide aqueous solution in which the dimethyl sulfoxide volume content is 30-45%, and a secondary coagulation draw ratio of 1.2-2.

0. The temperature of the tertiary solidification bath in the tertiary solidification process is 55-75℃. The tertiary solidification bath uses a dimethyl sulfoxide aqueous solution, wherein the volume content of dimethyl sulfoxide in the dimethyl sulfoxide aqueous solution is 10-20%. The tertiary solidification draw ratio is 1.2-2.

0. The orientation degree of the fiber crystal region after tertiary solidification is 55-65%.

3. A high-strength, high-modulus carbon fiber, characterized in that, The carbon fiber prepared by the method according to claim 1 or 2 has a tensile strength of 7000-7700 MPa, a tensile modulus of 350-390 GPa, and an interlaminar shear strength ≥100 MPa.