High-strength medium-modulus carbon fiber and preparation method thereof

Abstract

The invention relates to a high-strength medium-modulus carbon fiber and a preparation method thereof, belongs to the technical field of carbon fibers, and solves the problem of insufficient carbon fiber strength caused by high residual monomer content, low precursor compactness, poor orientation and insufficient strength in a spinning solution in the prior art. The invention provides a preparation method of a high-strength medium-modulus carbon fiber. A carbon fiber product is obtained through polymerization, monomer removal, ammonification, coagulating bath, water washing, hot water drafting and post-treatment. The weight-average molecular weight of the spinning solution / acrylonitrile-based polymer solution prepared by the preparation method is 20-25 thousand, the polydispersity index (PDI) is 2.0-3.0, and the residual monomer content in the polymer solution is less than or equal to 350ppm; the orientation degree of the precursor is greater than or equal to 93.0%, and the strength of the precursor is greater than or equal to 7.5 cN / dtex; the elasticity modulus of the carbon fiber is 320-340 GPa, the drafting strength is larger than 6100 MPa, the residual amount of dimethyl sulfoxide is smaller than or equal to 320 ppm, and no obvious defect exists when the carbon fiber is observed through a 2000-multiplying-power electrical microscope.

Description

Technical Field

[0001] The present invention relates to the technical field of carbon fiber materials, and particularly relates to a high-strength medium-modulus carbon fiber and a preparation method thereof. Background Art

[0002] Polyacrylonitrile (PAN) carbon fiber is an inorganic material with a carbon content of more than 90%. PAN-based carbon fiber has become the mainstream of carbon fiber production due to its better finished product quality, mechanical properties, and simpler process. A large part of the comprehensive performance of PAN-based carbon fiber depends on the quality of the spinning solution and the densification degree of the precursor fiber.

[0003] Regarding the spinning solution, the preparation of polyacrylonitrile spinning solution with high molecular weight and narrow molecular weight distribution has always been the research focus, which can make the fiber mechanical properties better, reduce the filament breakage phenomenon in continuous production, and improve the production qualification rate.

[0004] To prepare high molecular weight PAN, scholars at home and abroad have developed a series of polymerization methods. According to whether the PAN polymer is soluble in the solvent, the polymerization methods are divided into two categories: homogeneous polymerization (homogeneous solution polymerization) and heterogeneous polymerization (aqueous precipitation polymerization, mixed solvent precipitation polymerization, aqueous suspension polymerization, etc.). At present, these heterogeneous polymerization methods are difficult to be applied in the process because their process flow is complex and there are problems that additives such as emulsifiers, dispersants, organometallic reagents, and ionic liquids are difficult to remove, which have an adverse impact on the quality of carbon fiber.

[0005] At present, the molecular weight of PAN prepared by the homogeneous solution polymerization method mainly used in industry is generally low. Some researchers have tried to improve the molecular weight of PAN obtained by homogeneous solution polymerization by processes such as increasing the monomer concentration, reducing the initiator concentration, and reducing the reaction temperature. However, these methods have the following problems: too high monomer concentration will lead to high system viscosity and serious gelation phenomenon, which is not conducive to subsequent spinning; too low initiator concentration will lead to too slow reaction rate, which is not conducive to industrial production; reducing the temperature will also reduce the reaction rate, and different initiators have different optimal decomposition temperatures, so the reaction temperature should not be too low. Therefore, the polyacrylonitrile spinning solution produced industrially still has problems such as difficult to increase the molecular weight, wide molecular weight distribution, unstable viscosity and molecular weight of different batches, which ultimately affect the mechanical properties of carbon fiber.

[0006] Regarding the properties of the precursor fiber (densification), the precursor fiber is formed by the polymerization reaction of acrylonitrile monomers to form a spinning solution. The spinning solution becomes a single filament stream through a spinneret, and the single filament stream is prepared into the precursor fiber under the action of coagulation double diffusion and the synergistic action of hot water drawing after washing.

[0007] Due to the high sensitivity of spinning solutions with different compositions to coagulation bath and drawing process parameters (temperature, medium, draw ratio, etc.), defects such as poor orientation consistency of the precursor filaments, many pore-type defects, and insufficient densification are likely to occur during the preparation process, thereby affecting the densification degree and strength of the carbon fibers prepared subsequently. Summary of the Invention

[0008] In view of the above analysis, embodiments of the present invention aim to provide a high-strength and medium-modulus carbon fiber and a preparation method thereof to solve at least one of the following technical problems: solving the problems in the prior art that it is difficult to increase the molecular weight of PAN-based spinning solutions, the molecular weight distribution is relatively wide, the viscosity and molecular weight of different batches are unstable; and the defects such as poor orientation consistency of the precursor filaments, many pore-type defects, and insufficient densification, thereby improving the densification degree and strength of the carbon fibers.

[0009] The present invention provides a preparation method of a high-strength and medium-modulus carbon fiber, which specifically includes the following steps:

[0010] S1: Add a material containing acrylonitrile, comonomer and solvent to a polymerization device and regulate the target molecular weight of the acrylonitrile-based polymerization solution;

[0011] S2: Perform a degassing treatment on the acrylonitrile-based polymerization solution that meets the target molecular weight;

[0012] S3: Perform an ammoniation treatment on the degassed acrylonitrile-based polymerization solution to obtain a spinning solution;

[0013] S4: After the spinning solution is extruded through a spinneret, it enters a coagulating liquid for a coagulation bath and is drawn to obtain primary fibers;

[0014] S5: Wash the primary fibers with a multi-stage water washing process with gradually increasing temperature;

[0015] S6: Adopt a multi-stage drawing process to perform hot drawing on the washed fibers, and obtain densified precursor filaments after cooling and treatment;

[0016] S7: Make the densified precursor filaments into high-strength and medium-modulus carbon fibers.

[0017] Specifically, in step S1, according to the viscosity change of the material, determine the timing of adding the remaining initiator and the timing of terminating the reaction after polymerization starts, and regulate the target molecular weight of the acrylonitrile-based polymerization solution by controlling the material temperature and the proportion of the remaining initiator in the total initiator amount.

[0018] Specifically, when the viscosity of the material reaches the first viscosity threshold, add the remaining initiator, and when the viscosity of the material reaches the second viscosity threshold, terminate the reaction; the first viscosity threshold is 200P - 400P; and / or, the second viscosity threshold is 600P - 1000P; the proportion of the remaining initiator in the total initiator amount is 20 - 40%.

[0019] Specifically, the monomer removal treatment in step S2 is as follows:

[0020] The polymerization solution undergoes gas-liquid exchange with the counter-current solvent vapor through multiple perforated partitions. At each perforated partition, the polymerization solution is divided into two parts: one part of the polymerization solution spreads on the perforated partition to form a thin liquid layer and flows downward through the holes on the perforated partition, and the other part of the polymerization solution flows downward from the suspended end on the side of the perforated partition.

[0021] Specifically, the inlet liquid flow rate Q1 of the acrylonitrile-based polymerization solution entering the monomer removal device and the inlet gas flow rate Q2 of the solvent vapor entering the monomer removal device in step S2 satisfy:

[0022] Q2 ≥ k × Q1 × m × α × 1000

[0023] wherein, the unit of Q1 is m 3 / h, the unit of Q2 is L / h, m is the mass percentage of the residual monomer in the carbon fiber polymerization solution; α is the flow coefficient of the solvent vapor, and the value range of α is 1.0 - 1.2; k is the proportionality coefficient, and the value range of k is 1.5 - 1.9.

[0024] Specifically, in the ammoniation treatment in step S3, according to the flow rate Q3 of the polymerization solution and in combination with the following relational expression: M = Q3 × n, the mass M of ammonia gas required to be introduced per 1 kg of the polymerization solution is determined; wherein, the unit of M is mg, the unit of Q3 is m 3 / h, and the value range of n is 1.25 - 3.0.

[0025] Specifically, in the coagulation bath process in step S4, the coagulated filaments are drawn, and the draw ratio is 1.01 - 1.20 times.

[0026] Specifically, in step S5, a flower roll type water washing is adopted, and draw distribution is carried out during the water washing process. When the water washing temperature ≤ 45°C, a draw of 1.01 - 1.03 times is applied; when the water washing temperature > 45°C, a draw of 1.02 - 1.05 times is applied; wherein, the temperature and draw ratio of the next stage of water washing are not less than those of the previous stage of water washing.

[0027] Specifically, in step S6, the hot water temperature ≥ 70°C, and the total hot water draw ratio is 2 - 4 times; the hot water draw is divided into 2 - 6 stages, and the temperature and draw ratio of each stage of hot water gradually increase.

[0028] Specifically, the treatment process of densifying the raw filaments in step S6 includes: oiling, drying, and steam drawing.

[0029] Specifically, the densified raw filaments are made into carbon fibers through processes such as constant tension wire drawing, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and wire winding.

[0030] The present invention also provides a high-strength medium-modulus carbon fiber, which is prepared by the above preparation method;

[0031] The carbon fiber has an elastic modulus of 320 - 340 GPa, a drawing strength > 6100 MPa, a residual dimethyl sulfoxide content ≤ 320 ppm, and no obvious defects observed under an electron microscope at a magnification of 2000.

[0032] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0033] (1) The acrylonitrile-based polymerization solution / spinning solution prepared by the present invention has a high molecular weight and a low molecular weight distribution width. The weight-average molecular weight is 200,000 - 250,000, and the polydispersity index PDI is 2.0 - 3.0; the residual monomer content of the spinning solution ≤ 350 ppm, and the ammoniation uniformity is good, laying a good foundation for improving the performance of subsequent carbon fibers. By adding initiators in batches during the polymerization reaction, determining the appropriate timing for adding the remaining initiators after the polymerization starts according to the change in the viscosity of the material, and through the coordinated control of the material temperature and the proportion of the remaining initiator in the total initiator, the molecular weight of the polymer can be effectively regulated to reach the target level. Compared with traditional indicators such as temperature and reaction time, the change in the viscosity of the material can more accurately reflect the progress of the reaction; while traditional indicators such as conversion rate, although can be used as one of the evaluation indicators of the reaction degree, the determination of the conversion rate is too cumbersome and time-consuming. Obtaining each conversion rate requires sampling the material in the reaction process and drying it for several hours to obtain a solid, and then calculating the conversion rate, which is difficult to apply to industrial production. Compared with traditional indicators such as conversion rate, the viscosity indicator of the present invention has stronger operability. In actual application, it can conveniently grasp the best timing for adding the initiator, thereby significantly improving the stability of the viscosity and molecular weight of different batches of polymerization solutions, and thus laying a solid foundation for the preparation of subsequent high-performance carbon fibers. In some preferred embodiments, based on the above advantages of determining the timing of adding batch initiators according to the viscosity change, the present invention can effectively reduce the number of molecular chain end groups in the polymerization reaction, increase the molecular chain length, reduce the number of small molecules, and obtain a polymerization stock solution with a high molecular weight and a reduced molecular weight distribution width by controlling the viscosity threshold for adding the remaining initiator, the termination viscosity threshold, the polymerization temperature, the temperature rise to the target temperature, the proportion of the remaining initiator in the total initiator, etc.

[0034] (2) In some preferred embodiments, during the degassing process, by optimizing the flow path of the polymerization solution, it is possible to ensure that the polymerization solution spreads out to form a large-area thin liquid layer, having sufficient contact area and sufficient contact time with the solvent vapor, thereby obtaining a good degassing effect. Moreover, the present invention can also avoid problems such as skinning, coking, or gel formation in the polymerization solution that are prone to occur in traditional degassing processes when processing high molecular weight and high viscosity polymerization solutions with greater degassing difficulty. Through further optimization of the flow path of the polymerization solution, the upper-layer polymerization solution flows onto the lower-layer partition plate and then continues to spread and flow, enabling the polymerization solution to have more opportunities for gas-liquid exchange with the solvent vapor and improving the degassing effect. After degassing treatment using the preferred preparation method provided in the embodiments of the present invention, the residual monomer content in the polymerization solution < 100 ppm, preferably, the residual monomer content < 50 ppm, more preferably, the residual monomer content < 30 ppm.

[0035] (3) In some preferred embodiments, during the ammoniation process, the appropriate range of ammonia gas introduction amount is set according to the flow rate of the polymerization solution and in combination with the quantitative relationship, thereby precisely controlling the ammonia gas introduction amount, ensuring the ammoniation effect, improving the ammoniation uniformity, enhancing the hydrophilicity of polyacrylonitrile, stabilizing the ammoniation degree, extending the service life of the spinning solution, and further improving the properties of carbon fibers.

[0036] (4) The densified precursor filaments prepared by the present invention have a high degree of orientation consistency, the precursor filament orientation degree ≥ 91.5%, and the precursor filament strength > 6.5 cN / dtex; the residual dimethyl sulfoxide in the precursor filaments is significantly reduced, and the dimethyl sulfoxide residue in the precursor filaments < 1000 ppm, thereby significantly reducing the pore-type defects in the precursor filaments, improving the densification degree and strength of the precursor filaments; and further improving the comprehensive properties of the subsequently prepared carbon fibers.

[0037] Since the precursor filaments are composed of multiple single filaments, each single filament has a certain diameter, and the solidification and diffusion of the single filaments ejected from the spinneret holes proceed gradually from the outer surface towards the core of the single filaments. During the double-diffusion solidification process, the skin of the single filaments solidifies first and gradually densifies, hindering the double diffusion of the core of the single filaments. Therefore, the dimethyl sulfoxide in the core cannot be released, forming defects. The present invention first realizes solidification fineness by adjusting parameters such as the concentration of the coagulation solution, the coagulation temperature, and the draw ratio. The fibers become thinner in the coagulation bath, which is more conducive to the precipitation of dimethyl sulfoxide in the core of the single filaments, and the densification of the as-spun fibers after solidification is better (that is, the content of dimethyl sulfoxide in the as-spun fibers is reduced).

[0038] (5) More preferably, when using an annular spinneret plate, by controlling the concentration and flow rate of the inner-ring liquid, it is possible to make the contact between the spinning solution and the coagulation liquid (strictly speaking, the inner-ring liquid is also part of the coagulation liquid) more sufficient, the solidification process more uniform, and it is beneficial to improve the orientation and uniformity of the as-spun fibers.

[0039] (6) Further, in the present invention, the number of washing stages in the water washing stage is significantly increased, particularly preferably 16-stage water washing. During the water washing process, the temperature is gradually increased, and the draw ratio is strictly controlled (slightly increased according to the temperature change). In this process, the purpose of washing out the coagulant dimethyl sulfoxide and further improving the fiber densification is achieved simultaneously, and the residual amount of dimethyl sulfoxide in the raw silk is <1000 ppm. Too few washing stages or too low temperature will result in too high sulfoxide content in the fiber bundle. With too few washing stages, the washing time is insufficient, and the sulfoxide residue will be high. With too low water washing temperature, the plasticity of the fiber is poor, which becomes a defect during drawing and affects the densification. Too many washing stages will cause waste of resources and a long process; the water washing temperature should not be too high either. On the one hand, high temperature will cause the residual dimethyl sulfoxide to diffuse rapidly. Although the residual coagulant is removed, it will cause hole-type defects inside or on the surface of the raw silk. On the other hand, when the water washing temperature > 90 °C, the crystallinity in the raw silk will decrease, resulting in changes in the internal structure, and then the strength of the raw silk will decrease. In addition, it will also cause waste of energy.

[0040] (7) Further, the present invention strictly controls the temperature of hot water drawing and divides it into multiple stages / sub-sections, and different draw ratios are set for each stage to achieve the gradual optimization of the internal structure of the raw silk. If the number of stages is too small and the draw ratio for each stage is too large, it will cause wire breakage and form defects. The temperature of each stage increases step by step, and the draw ratio increases with the increase of temperature. The draw ratio also gradually increases. As the temperature increases step by step, the plasticity of the fiber becomes better, the draw ratio gradually increases, the fiber becomes finer and finer, and the densification becomes better.

[0041] Particularly preferably, the hot water drawing is 4 stages; among them, the temperature of the first stage is 70 - 80 °C, and the draw ratio is 1.1 - 1.2 times; the temperature of the second stage is 75 - 85 °C, and the draw is 1.2 - 1.3 times; the temperature of the third stage is 80 - 90 °C, and the draw is 1.3 - 1.4 times; the temperature of the fourth stage is 85 - 95 °C, and the draw is 1.4 - 1.5 times. The preferred scheme has a gentle temperature gradient and a gentle draw ratio, which causes little damage to the fiber drawing and has a higher densification of the fiber.

[0042] Through the linkage of the above steps (corresponding to S4, S5, S6), aiming at the characteristics of the acrylonitrile-based polymer spinning solution and the coagulating solution (dimethyl sulfoxide), the technical objectives and parameter designs of each process section are closely related and work synergistically, and finally the densification control of the raw silk is achieved (low residue, reduced hole-type defects, high orientation consistency), thereby improving the performance of the raw silk and downstream carbon fiber products.

[0043] The finally obtained carbon fiber product has high appearance consistency, high product stability, no structural defects, an elastic modulus of 320 - 340 GPa, a draw strength > 6100 MPa, and a residual amount of dimethyl sulfoxide ≤ 320 ppm.

[0044] (8) The preparation method provided by the present invention has high comprehensive performance of the process products, thereby improving the performance and product stability of the final product carbon fiber.

[0045] (9) The equipment involved in the preparation method provided by the present invention is easy to obtain, the process conditions are mild, the energy consumption is small, and it is suitable for large-scale production and wide promotion.

[0046] In the present invention, the above technical solutions can also be combined with each other to achieve more preferred combination schemes. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can be made obvious from the description, or understood by implementing the present invention. The objectives and other advantages of the present invention can be realized and obtained through the content specifically pointed out in the description and the drawings. Description of the Drawings

[0047] The drawings are only for the purpose of showing specific embodiments and are not considered as limiting the present invention. Throughout the drawings, the same reference signs denote the same components.

[0048] Figure 1 It is a flow chart of a preparation method for high-strength medium-modulus carbon fiber;

[0049] Figure 2 It is a schematic structural diagram of a degassing device provided by an embodiment of the present invention;

[0050] Figure 3 It is a schematic structural diagram of an ammoniation device provided by an embodiment of the present invention;

[0051] Figure 4 It is a schematic structural diagram of a polymerization device provided by an embodiment of the present invention;

[0052] Figure 5 It is a physical photo of a carbon fiber product.

[0053] Reference Signs:

[0054] 100 - degassing device; A - tank body; B - solvent vaporizer; C - real-time viscosity monitoring device; 11 - perforated partition; 12 - polymer solution inlet; 13 - distribution tray; 14 - solvent inlet; 15 - coil; 15a - coil inlet; 15b - coil outlet; 16 - solvent vapor; 17 - vacuum extraction port; 18 - polymer solution outlet; 200 - ammoniation device; 21 - inclined paddle stirrer; 21a - stirring paddle; 21b - rotating shaft; 22 - ammonia gas inlet; 23 - polymer solution inlet; 24 - polymer solution outlet; 25 - first motor; 300 - polymerization device; 31 - stirring device; 32 - inert gas inlet; 33 - inert gas outlet; 34 - second motor; 35 - on-line pressure-viscosity converter; 36 - constant-speed gear pump; 37 - circulating water inlet; 38 - circulating water outlet. Detailed Embodiments

[0055] The preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. The accompanying drawings form a part of this application and are used together with the embodiments of the present invention to explain the principles of the present invention, rather than to limit the scope of the present invention.

[0056] The present invention provides a method for preparing high-strength medium-modulus carbon fiber, which specifically includes the following steps:

[0057] S1: Add the material containing acrylonitrile, comonomer and solvent into the polymerization device and adjust the target molecular weight of the acrylonitrile-based polymerization solution;

[0058] S2: Perform monomer removal treatment on the acrylonitrile-based polymerization solution that meets the target molecular weight;

[0059] S3: Perform ammoniation treatment on the acrylonitrile-based polymerization solution after monomer removal treatment to obtain a spinning solution;

[0060] S4: After the spinning solution is extruded through a spinneret, enter the coagulating bath in the coagulating liquid and perform stretching to obtain nascent fibers;

[0061] S5: Wash the nascent fibers with a multi-stage water washing process with gradually increasing temperature;

[0062] S6: Adopt a multi-stage stretching process to perform hot stretching on the fibers after water washing, and obtain densified raw filaments after cooling and treatment;

[0063] S7: Make the densified raw filaments into high-strength medium-modulus carbon fiber.

[0064] Specifically, in step S1, according to the viscosity change of the material, determine the timing of adding the remaining initiator after polymerization starts and the timing of terminating the reaction, and control by the material temperature and the proportion of the remaining initiator in the total initiator to adjust the target molecular weight of the acrylonitrile-based polymerization solution;

[0065] Among them, determining the timing of adding the remaining initiator after polymerization starts and the timing of terminating the reaction includes:

[0066] Raise the temperature to the polymerization temperature and add part of the initiator;

[0067] Monitor the material viscosity in real time:

[0068] When the material viscosity reaches the first viscosity threshold, add the remaining initiator. When the material viscosity reaches the second viscosity threshold, terminate the reaction to obtain an acrylonitrile-based polymerization solution with the target molecular weight; the first viscosity threshold < the second viscosity threshold.

[0069] Specifically, the first viscosity threshold is 200P - 400P; and / or, the second viscosity threshold is 600P - 1000P;

[0070] The polymerization temperature is 50 - 60°C. When the viscosity of the material reaches the first viscosity threshold, the temperature of the material is raised to the target temperature of 60 - 70°C;

[0071] The proportion of the remaining initiator in the total initiator is 20 - 40%.

[0072] Through the control of the above-mentioned appropriate viscosity threshold, material temperature (polymerization temperature and the target temperature to which it is raised when the threshold is reached), and the proportion of the remaining initiator in the total initiator, it is beneficial to obtain a polyacrylonitrile-based polymerization solution with high molecular weight and narrow distribution while increasing the polymerization reaction rate.

[0073] Exemplarily, the polymerization temperature is 52°C, 54°C, 56°C, 58°C. Preferably, the polymerization temperature is 55 - 60°C.

[0074] Exemplarily, the target temperature is 62°C, 64°C, 67°C, 69°C. Preferably, the target temperature is 66 - 68°C.

[0075] Exemplarily, the first viscosity threshold is 250P, 280P, 330P, 350P, 380P. More preferably, the first viscosity threshold is 300P - 400P.

[0076] Exemplarily, the second viscosity threshold is 650P, 700P, 750P, 800P, 850P, 900P, 950P. Preferably, the second viscosity threshold is 750P - 950P.

[0077] Exemplarily, the proportion of the remaining initiator in the total initiator is 23%, 25%, 27%, 30%, 33%, 35%, 37%. Preferably, the proportion of the remaining initiator in the total initiator is 30 - 40%. It should be noted that by finely controlling the viscosity threshold, material temperature (polymerization temperature and the target temperature to which it is raised when the viscosity threshold is reached), and the proportion of the remaining initiator in the total initiator, while obtaining a polymerization solution with high molecular weight and narrow distribution, the micro-regulation of the molecular weight of the polymerization solution can be achieved.

[0078] In some embodiments, the polymerization temperature is 50 - 52°C, the first viscosity threshold is 200P - 250P. When the viscosity of the material reaches the first viscosity threshold, the target temperature to which it is raised is 68 - 70°C, the proportion of the remaining initiator in the total initiator is 35 - 40%; the second viscosity threshold is 620 - 650P; the molecular weight (MW) of the obtained polyacrylonitrile-based polymerization solution is 200,000 - 220,000, and the polydispersity index (PDI) is 2.5 - 3.0.

[0079] In some embodiments, the polymerization temperature is 54 - 56 °C, the first viscosity threshold is 250P - 300P. When the viscosity of the material reaches the first viscosity threshold, the target temperature to which it is heated is 64 - 66 °C. The proportion of the remaining initiator in the total initiator is 35 - 40%; the second viscosity threshold is 700 - 750P; the molecular weight (MW) of the obtained acrylonitrile-based polymerization solution is 210,000 - 230,000, and the polydispersity index (PDI) is 2.2 - 2.7.

[0080] In some embodiments, the polymerization temperature is 58 - 60 °C, the first viscosity threshold is 250P - 300P. When the viscosity of the material reaches the first viscosity threshold, the target temperature to which it is heated is 60 - 62 °C. The proportion of the remaining initiator in the total initiator is 35 - 40%; the second viscosity threshold is 700 - 750P; the molecular weight (MW) of the obtained acrylonitrile-based polymerization solution is 220,000 - 240,000, and the polydispersity index (PDI) is 2.2 - 2.7.

[0081] In some embodiments, the polymerization temperature is 54 - 56 °C, the first viscosity threshold is 300P - 350P. When the viscosity of the material reaches the first viscosity threshold, the target temperature to which it is heated is 64 - 66 °C. The proportion of the remaining initiator in the total initiator is 30 - 35%; the second viscosity threshold is 800 - 850P; the molecular weight (MW) of the obtained acrylonitrile-based polymerization solution is 230,000 - 250,000, and the polydispersity index (PDI) is 2.0 - 2.5.

[0082] In some embodiments, the polymerization temperature is 54 - 56 °C, the first viscosity threshold is 350P - 400P. When the viscosity of the material reaches the first viscosity threshold, the target temperature to which it is heated is 64 - 66 °C. The proportion of the remaining initiator in the total initiator is 30 - 35%; the second viscosity threshold is 900 - 950P; the molecular weight (MW) of the obtained acrylonitrile-based polymerization solution is 230,000 - 250,000, and the polydispersity index (PDI) is 2.0 - 2.5.

[0083] In some embodiments, the step of real-time monitoring the viscosity of the material includes: setting up a material reflux pipeline, real-time monitoring the pressure of the material at a fixed position in the reflux pipeline, and obtaining the real-time monitored viscosity of the material according to the real-time viscosity value converted from the pressure value.

[0084] Specifically, the material is led out from the polymerization device, and the material flows through the reflux pipeline at a constant temperature and a constant flow rate, and finally converges back to the polymerization device; by real-time monitoring the pressure of the material at a fixed position in the reflux pipeline, and combining with the pressure-viscosity relationship formula, the pressure value is converted into a real-time viscosity value.

[0085] Furthermore, the method for determining the pressure-viscosity relationship includes: by setting multiple data acquisition times, at each data acquisition time, recording the pressure value at a fixed position of the reflux pipeline and the viscosity value obtained by the experimental method, performing mathematical fitting on the pressure value and the viscosity value, and establishing a pressure-viscosity relationship.

[0086] Specifically, the steps for obtaining the viscosity value by the experimental method include: sampling from the polymerization device and measuring the viscosity of the sample using a viscosity measuring instrument. Preferably, the sampling position is adjacent to the position where the material is led out of the polymerization device. Exemplarily, the viscosity measuring instrument includes a falling ball viscometer and a rotational viscometer.

[0087] To ensure the reliability and consistency of the pressure measurement results, the step of making the material flow through the reflux pipeline at a constant temperature and a constant flow rate includes: placing the reflux pipeline in a constant temperature circulating water system and setting a constant speed gear pump on the reflux pipeline. By the constant temperature circulating water system, it is ensured that the temperature of the material remains constant during the flow process, and by controlling the rotation speed of the gear pump, it can be ensured that the material flows through the pipeline at a constant flow rate.

[0088] It can be understood that under the conditions of constant flow rate, constant temperature and a fixed-length pipeline (constant pipeline resistance), by measuring the pressure generated when the polymerization liquid flows through a fixed position of the reflux pipeline and combining with the pressure-viscosity relationship, the viscosity of the material can be obtained. Preferably, the above real-time monitoring of the material viscosity is applicable to materials with a viscosity of 0 - 1000P.

[0089] Preferably, the length of the reflux pipeline is 0.5 - 1.5 meters, and the pipe diameter is 5 - 20 mm. Exemplarily, the length of the reflux pipeline is 1.0 meter, and the pipe diameter is 10 mm.

[0090] In some embodiments, for the acrylonitrile-based polymerization liquid obtained by polymerizing acrylonitrile and comonomers, the pressure-viscosity relationship is:

[0091] y = -0.045x 2 +13.78x - 106.8

[0092] Wherein, y is the viscosity measured by the falling ball method, with the unit of P; x is the pressure, with the unit of Kpa.

[0093] Exemplarily, the viscosity y is the viscosity measured by the falling ball method at 40 - 50 °C. For example, within the ±Δ time range near each data acquisition time t, preferably Δ ≤ 10 min, the pressure values at a fixed position of the reflux pipeline are recorded N times, and samples are taken from the polymerization device N times at the same time points as the recorded pressure values. N temperature points are selected within 40 - 50 °C for viscosity measurement. Through data fitting software (such as EXCEL, Matlab or Python), the viscosity y and the pressure x are fitted, and the fitting criterion is: the coefficient of determination R2 ≥95%, preferably R 2 ≥98%, to obtain a pressure-viscosity relationship, and the model types of the pressure-viscosity relationship include at least one of exponential, linear, logarithmic, polynomial (second order and above), and power. For example, N is 3, and the test conditions are 40°C, 45°C, and 50°C respectively. For example, Δ = 8 min, 5 min, 2 min, 1 min.

[0094] Preferably, the constant temperature is 40-50°C; and / or, the constant flow rate is 1-2 L / h.

[0095] Preferably, the position where the material is led out from the polymerization device is set 10-20 cm below the lower end of the stirring device in the polymerization device, and this position belongs to the position with the best fluidity of the polymerization liquid, which is convenient for timely and accurately monitoring the real-time viscosity of the polymerization liquid in the polymerization kettle.

[0096] In one embodiment, the step of monitoring the pressure of the material at a fixed position in the reflux pipeline in real time and converting the pressure value into a real-time viscosity value in combination with the pressure-viscosity relationship includes: setting an on-line pressure-viscosity converter at the fixed position of the reflux pipeline, and the on-line pressure-viscosity converter includes a pressure detector and a processor;

[0097] The pressure detector is used to collect the pressure signal of the polymerization liquid in the reflux pipeline in real time and transmit the pressure signal to the processor through a line; the processor converts the pressure signal into a viscosity value according to the preset pressure-viscosity relationship and transmits the viscosity value to a display set outside the polymerization device through a line for real-time display.

[0098] Specifically, the ratio of the material and the total amount of the initiator, by weight, acrylonitrile is 20-24 parts, the comonomer is 1-2 parts, the solvent is 73.65-78.85 parts, and the total amount of the initiator is 0.15-0.35 parts. Preferably, the total amount of the initiator is 0.2-0.3 parts.

[0099] Optionally, the comonomer is one or a combination of itaconic acid, acrylic acid, methyl acrylate, methyl methacrylate, ethyl methacrylate, isobutyl acrylic acid, β-butyl itaconate, acrylamide, acrylamide oxime, hydroxyethyl acrylonitrile, α-chloropropionitrile, or diacetone acrylamide. Exemplarily, the comonomer is itaconic acid.

[0100] Optionally, the initiator is at least one of azobisisobutyronitrile, azobisisoheptonitrile, and dimethyl azobisisobutyrate. Exemplarily, the initiator is azobisisobutyronitrile (AIBN).

[0101] Optionally, the solvent is at least one of dimethyl sulfoxide, sodium thiocyanate, and N,N-dimethylformamide. Exemplarily, the solvent is dimethyl sulfoxide.

[0102] In some embodiments, the material further includes a molecular weight regulator; exemplarily, the molecular weight regulator is isopropanol; taking acrylonitrile and comonomers as copolymerization components, the addition amount of the molecular weight regulator is 0.002-0.005% of the total mass of the copolymerization components.

[0103] Specifically, after adding the material to the polymerization device, before starting the polymerization, the material is stirred by a stirring device to make it uniformly mixed. The stirring device is located in the middle of the inner liquid in the polymerization kettle and stirs in the same direction.

[0104] Preferably, the stirring device includes a ribbon agitator and a scraping wall agitator.

[0105] Preferably, before starting the polymerization, the rotation speed of the stirring is 20-80 rpm, and the stirring time is 30-60 min. Exemplarily, the rotation speed of the stirring is 30 rpm, 40 rpm, 50 rpm, 60 rpm, 70 rpm. The stirring time is 35 min, 40 min, 45 min, 50 min, 55 min.

[0106] (a) For the ribbon agitator, it satisfies: S1=(50-70%)S2, S1 = Π×(1 / 2D1) 2 , D1 is the outer diameter of the ribbon, and S2 is the inner cross-sectional area of the polymerization kettle. Exemplarily, S1 / S2 = 55%, 60%, 65%.

[0107] (b) For the scraping wall agitator, it satisfies: L≤10 mm, where L represents the gap between the scraping wall component (such as a scraper or a knife) of the scraping wall agitator and the inner wall of the polymerization kettle. As the polymerization reaction proceeds, the viscosity of the inner liquid in the polymerization kettle continuously increases and becomes a highly viscous liquid. Using a scraping wall agitator and controlling L can effectively prevent the highly viscous liquid from adhering to the inner wall of the polymerization kettle to form wall-hanging rubber blocks.

[0108] During the stirring process, the proportion of the liquid level height h of the inner liquid in the polymerization kettle to the total height H of the polymerization kettle is 10%-90%. Exemplarily, h / H = 20%, 30%, 40%, 50%, 60%, 70%, 80%. Preferably, h / H = 80-90%.

[0109] By selecting the above preferred stirring device and stirring parameters, etc., it can ensure energy-efficiently that the material is uniformly mixed before starting the polymerization.

[0110] Preferably, by weight, acrylonitrile is 22 - 24 parts, the comonomer is 1 - 2 parts, the solvent is 73.7 - 76.8 parts, the stirring speed is 40 - 60 rpm, and the stirring time is 30 - 45 min.

[0111] Preferably, by weight, acrylonitrile is 20 - 22 parts, the comonomer is 1 - 2 parts, the solvent is 74.7 - 77.8 parts, the stirring speed is 50 - 70 rpm, and the stirring time is 45 - 55 min.

[0112] Exemplarily, the uniformity of the material mixture is judged by the uniform temperature of the internal liquid in the polymerization kettle. Specifically, during the stirring process, when the temperature difference of the internal liquid in the polymerization kettle ≤ 1°C, this is used as the basis for judging the mixing uniformity.

[0113] Specifically, the polymerization reaction is carried out under the protection of an inert gas. The flow rate of the inert gas is 50 - 100 L / h; the pressure of the inert gas ≤ 0.1 Mpa. Oxygen in the air has an inhibitory effect on polymerization, and the inert gas can isolate oxygen. Using an inert gas with a suitable flow rate and pressure helps the polymerization reaction.

[0114] Preferably, the inert gas enters the polymerization kettle from one side of the top of the polymerization kettle and flows out of the polymerization kettle from the other side of the top of the polymerization kettle, so that the original air in the polymerization kettle can be better replaced. The inert gas is selected from at least one of nitrogen, argon or helium.

[0115] Exemplarily, the flow rate of the inert gas is 60 L / h, 70 L / h, 75 L / h, 85 L / h.

[0116] Exemplarily, the pressure of the inert gas is 0.07 Mpa, 0.05 Mpa, 0.04 Mpa, 0.02 Mpa, 0.01 Mpa.

[0117] Preferably, the flow rate of the inert gas is 80 - 90 L / h; the pressure of the inert gas is 0.06 - 0.08 Mpa. By precisely controlling the flow rate and pressure of the inert gas, it is beneficial to polymerize to obtain a polymer solution with high molecular weight and narrow distribution.

[0118] Preferably, the initiator is pre - dissolved in the solvent and then added to the polymerization device in batches, which helps to ensure that the initiator reaches a uniform distribution more quickly in the whole reaction system, improves the uniformity of the polymerization reaction rate at different positions in the polymerization device, and is beneficial to obtaining a polymer solution with high molecular weight and narrow distribution. Preferably, for the case where the initiator is 0.15 - 0.35 parts, the solvent used to dissolve the initiator is 5 - 10 parts.

[0119] Specifically, after the polymerization is started, the materials in the polymerization kettle are continuously stirred at a stirring speed of 30 - 80 rpm. Exemplarily, after the polymerization is started, the stirring speed is 35 rpm, 40 rpm, 45 rpm, 50 rpm, 55 rpm, 60 rpm, 65 rpm, 70 rpm, 75 rpm.

[0120] Preferably, after the polymerization is started and before the remaining initiator is added, the stirring speed is 30 - 60 rpm, more preferably 40 - 60 rpm. After the remaining initiator is added, the stirring speed is 50 - 80 rpm, more preferably 50 - 70 rpm.

[0121] Preferably, the de - monomerization treatment in step S2 is as follows:

[0122] The polymerization liquid undergoes gas - liquid exchange with the solvent vapor flowing counter - currently through a multi - layer perforated baffle. At each layer of the perforated baffle, the polymerization liquid is divided into two parts: one part of the polymerization liquid spreads out on the perforated baffle to form a thin liquid layer and flows downward through the holes on the perforated baffle, and the other part of the polymerization liquid flows downward from the suspended end on the side of the perforated baffle.

[0123] By adopting this optimized de - monomerization method, the de - monomerization effect and efficiency can be significantly improved, effectively avoiding the internal scaling or coking of the de - monomerization device and reducing the formation of gels in the polymerization liquid during the de - monomerization process. After the polymerization liquid is introduced into the de - monomerization device, it is evenly distributed on the first - layer perforated baffle through a porous distributor to form a uniform thin liquid layer; the polymerization liquid mainly flows through the holes on the baffle to the next - layer baffle and continues to spread out on the lower - layer baffle to form a thin liquid layer, thereby ensuring that the thin liquid layer of the polymerization liquid on each baffle can undergo efficient gas - liquid exchange with the solvent vapor. At the same time, the excess high - viscosity material can smoothly flow to the next - layer baffle through the channel between the suspended end of the baffle and the inner wall of the tank; this flow path not only ensures the de - monomerization effect but also effectively avoids the scaling and coking on the inner wall of the device, reduces the formation of gels in the polymerization liquid, and guarantees the efficient progress of production. Compared with traditional de - monomerization methods such as falling - film towers and high - gravity rotating beds, the de - monomerization treatment of the present invention significantly reduces the stringent requirements for process parameters and equipment processing precision. Especially when treating acrylonitrile - based polymerization liquids with higher viscosities and higher molecular weights, the present invention shows better adaptability and stability, effectively avoiding the common coking and scaling problems in traditional methods, and significantly reducing the formation of gels in the polymerization liquid during de - monomerization.

[0124] Further preferably, a part of the polymerization liquid flows downward to the next layer of perforated baffle or the polymerization liquid collection area through the holes on the perforated baffle, and the positions of the holes where the polymerization liquid flows out of the adjacent layers of perforated baffles are different. The other part of the polymerization liquid flows from the suspended end on the side of the perforated baffle to the next layer of perforated baffle or the polymerization liquid collection area. In the degassing treatment, by optimizing the flow path of the polymerization liquid as described above, the contact time between the polymerization liquid and the solvent vapor is prolonged, ensuring that unreacted monomers (such as acrylonitrile) are more fully removed, meeting the degassing requirements of the high-viscosity polymerization liquid.

[0125] In some embodiments, in the degassing treatment, the polymerization liquid enters the degassing device from the top or upper part of the degassing device. After passing through the porous distribution, it is distributed onto the first layer of perforated baffle, enabling the polymerization liquid to be more evenly distributed on the first layer of perforated baffle, improving the degassing effect and efficiency.

[0126] It can be understood that the process of the degassing treatment includes: the polymerization liquid enters the degassing device and flows through multiple layers of perforated baffles from top to bottom, forming a continuous liquid film flow; meanwhile, the solvent vapor enters the degassing device and passes through multiple layers of perforated baffles from bottom to top, coming into full contact with the flowing-down polymerization liquid for gas-liquid exchange. The solvent vapor carries the residual volatile monomers in the polymerization liquid and is discharged from the degassing device; the polymerization liquid after the degassing treatment is discharged from the degassing device, completing the degassing process.

[0127] Exemplarily, the degassing treatment is carried out under negative pressure. The vacuum degree of the negative pressure is 100 - 5000 Pa. Exemplarily, the vacuum degrees are 200 Pa, 500 Pa, 800 Pa, 1000 Pa, 2000 Pa, 3000 Pa, 4000 Pa. Preferably, the vacuum degree is 500 - 2000 Pa.

[0128] Preferably, in the degassing treatment, the inlet temperature of the polymerization liquid is 50 - 70 °C, preferably 65 - 70 °C. Exemplarily, the inlet temperatures of the polymerization liquid are 54 °C, 58 °C, 62 °C, 66 °C.

[0129] Preferably, in the degassing treatment, the inlet flow rate of the polymerization liquid is 3 - 5 m 3 / h, preferably 3 - 4 m 3 / h. In the degassing treatment, the temperature of the degassing system is controlled at 50 - 70 °C. More preferably, the temperature of the degassing system gradually increases from top to bottom. Exemplarily, the inlet flow rates of the polymerization liquid are 3.3 m 3 / h, 3.6 m 3 / h, 3.9 m 3 / h, 4.2 m 3 / h, 4.5 m 3 / h, 4.8 m 3 / h.

[0130] Preferably, in the said monomer removal treatment, the inlet temperature of the solvent vapor is 80 - 100 °C; more preferably 90 - 100 °C. Exemplarily, the inlet temperature of the solvent vapor is 84 °C, 88 °C, 92 °C, 96 °C.

[0131] Preferably, in the said monomer removal treatment, the inlet pressure of the solvent vapor is 0.01 - 0.5 Mpa; more preferably 0.2 - 0.3 Mpa. Exemplarily, the inlet pressure of the solvent vapor is 0.05 Mpa, 0.1 Mpa, 0.15 Mpa, 0.25 Mpa, 0.35 Mpa, 0.40 Mpa, 0.45 Mpa.

[0132] In some embodiments, in the monomer removal treatment, the inlet viscosity of the carbon fiber polymerization liquid is 600 - 1000 P, and the weight - average molecular weight is 200,000 - 250,000.

[0133] The inventors found that in the said monomer removal treatment, when the inlet flow rate of the polymerization liquid and the inlet flow rate of the solvent vapor satisfy a specific relationship, a better monomer removal effect can be obtained.

[0134] Specifically, in step S2, the inlet flow rate Q1 of the acrylonitrile - based polymerization liquid entering the monomer removal device and the inlet flow rate Q2 of the solvent vapor entering the monomer removal device satisfy:

[0135] Q2 ≥ k × Q1 × m × α × 1000

[0136] wherein, the unit of Q1 is m 3 / h, the unit of Q2 is L / h, m is the mass percentage of the residual monomer in the carbon fiber polymerization liquid; α is the flow coefficient of the solvent vapor, and the value range of α is 1.0 - 1.2; k is the proportionality coefficient, and the value range of k is 1.5 - 1.9.

[0137] Exemplarily, k = 1.60, 1.65, 1.70, 1.72, 1.74, 1.75, 1.80, 1.85. For example, k = 1.737.

[0138] Preferably, Q1 is 3 - 5 m 3 / h.

[0139] When 3.0 m 3 / h ≤ Q1 < 3.7 m 3 / h, preferably, the value of k is 1.8 - 1.9.

[0140] When 3.7 m 3 / h ≤ Q1 < 4.4 m 3 / h, preferably, the value of k is 1.7 - 1.8.

[0141] When 4.4 m 3 / h ≤ Q1 ≤ 5.0 m3 / h. Preferably, k ranges from 1.6 to 1.7.

[0142] In one embodiment, Q1 = 3m 3 / h, m = 10%, α = 1.0, k = 1.9. When Q2 ≥ 570 L / h, after testing, the residual acrylonitrile (AN) in the polymerized liquid after degassing is less than 100 ppm.

[0143] In one embodiment, Q1 = 4m 3 / h, m = 10%, α = 1.1, k = 1.73. When Q2 ≥ 760 L / h, after testing, the residual acrylonitrile (AN) in the polymerized liquid after degassing is less than 100 ppm.

[0144] In one embodiment, Q1 = 5m 3 / h, m = 9%, α = 1.2, k = 1.60. When Q2 ≥ 860 L / h, after testing, the residual acrylonitrile (AN) in the polymerized liquid after degassing is less than 100 ppm.

[0145] The above embodiments fully verify the reliability of the relationship Q2 ≥ k × Q1 × m × α × 1000.

[0146] In the above embodiments, by precisely controlling the process parameters of degassing, such as the inlet flow rate of the polymerized liquid, the inlet flow rate of the solvent vapor, the inlet temperature of the polymerized liquid, the inlet temperature / pressure of the solvent vapor, etc., it is beneficial to improve the degassing efficiency and effect, avoid skinning or coking of the degassing equipment, and significantly reduce the formation of gels in the polymerized liquid. In some embodiments, the degassing effect is remarkable, the residual monomer content after degassing is less than 100 ppm, and the degassing process is efficient and continuous. The polymerized liquid can continuously enter and flow out of the degassing device according to the working conditions. In addition, the phenomenon of skinning or coking of the equipment is significantly reduced. Through the viewing window on the degassing device, there is no obvious discoloration on the inner wall of the device. In the traditional degassing device, due to uneven heat absorption during the flow of the polymerized liquid, local gels are generated, and even coking occurs on the inner wall of the device, resulting in the filter replacement cycle for removing gels from the polymerized liquid after degassing being only 1 - 2 months, or even shorter. However, with the degassing treatment of the present invention, the formation of gels in the polymerized liquid is significantly reduced, so that the filter replacement cycle is extended to more than 3 months, improving the equipment operation efficiency and service life. The above replacement cycle is based on the condition that the pressure increase reaches half of the filter pressure resistance rating for filter replacement.

[0147] Exemplarily, in the degassing treatment, the solvent vapor is at least one of dimethyl sulfoxide, sodium thiocyanate, and N, N - dimethylformamide. The selected solvent vapor is the same as the solvent in the polymerized liquid.

[0148] In the ammoniation treatment, in the storage tank of the ammoniation device, the polymerization solution remains flowing and the temperature is controlled at 60-65 °C, which is the optimal temperature range for the ammoniation of the acrylonitrile-based polymerization solution. Specifically, the polymerization solution flows into the storage tank of the ammoniation device from the upper part and flows out from the lower part of the storage tank.

[0149] Specifically, in the ammoniation treatment described in step S3, according to the flow rate Q3 of the polymerization solution and combined with the following relational formula: M = Q3 × n, the mass M of ammonia gas required to be introduced per 1 kg of the polymerization solution is determined; where, the unit of M is mg, and the unit of Q3 is m 3 / h, and the value range of n is 1.25-3.0.

[0150] Exemplarily, n = 1.5, 1.8, 2.1, 2.4, 2.7.

[0151] Preferably, the value range of Q3 is 3-5 m 3 / h.

[0152] When 3.0 m 3 / h ≤ Q3 < 3.5 m 3 / h, preferably, the value range of n is 2.0-2.7.

[0153] When 3.5 m 3 / h ≤ Q3 < 4.3 m 3 / h, preferably, the value range of n is 1.25-1.75.

[0154] When 4.3 m 3 / h ≤ Q3 ≤ 5.0 m 3 / h, preferably, the value range of n is 1.6-2.0.

[0155] In an embodiment, Q3 = 3 m 3 / h, then when M satisfies 6-8 mg, after testing, the pH of the ammoniated spinning solution is 8-10, and the ammoniation effect is good.

[0156] In an embodiment, Q3 = 4 m 3 / h, then when M satisfies 5-7 mg, after testing, the pH of the ammoniated spinning solution is 8-10, and the ammoniation effect is good.

[0157] In an embodiment, Q3 = 5 m 3 / h, then when M satisfies 8-10 mg, after testing, the pH of the ammoniated spinning solution is 8-10, and the ammoniation effect is good.

[0158] Preferably, the ammonia gas introduction time is controlled within 5-8 hours.

[0159] In the ammoniation treatment, based on the material ratio provided by the present invention, the ammonia gas introduction amount is precisely controlled according to the flow rate Q3 of the polymerization solution and in combination with the following relational expression: M = Q3 × n, which can not only ensure good ammoniation effect, but also save ammonia gas and ammoniation treatment time.

[0160] Preferably, in the ammoniation treatment, a diagonal blade stirrer is used to stir the polymerization solution. The diagonal blade stirrer includes a plurality of diagonal stirring blades. The inclination angle of the diagonal stirring blades is 40 - 50°, and the diagonal stirring blades are rectangular blades with a length of L and satisfying πL 2 = (50 - 70%)S4, where S4 is the cross-sectional area of the storage tank in the ammoniation device. During the ammoniation treatment, the stirring speed is controlled at 30 - 50 r / min. Exemplarily, during ammoniation, the stirring speed is controlled at 35 r / min, 40 r / min, 45 r / min.

[0161] By using a diagonal blade stirrer to lift the polymerization solution upward, strong axial flow can be generated, causing the polymerization solution to form an up-and-down circulating flow during stirring. This flow pattern helps ammonia gas to be better dispersed in the polymerization solution, improving the mass transfer efficiency and ammoniation effect. By precisely controlling the structural parameters of the diagonal blade stirrer, the up-and-down circulating flow can be better promoted, further improving the mass transfer efficiency and ammoniation effect.

[0162] Preferably, the ammoniation treatment is carried out under a slightly positive pressure, so that ammonia gas can diffuse more effectively and come into full contact with the polymerization solution, while ensuring the safety of the system. Specifically, during the ammoniation process, a pressure slightly higher than the external atmospheric pressure, i.e., a slightly positive pressure, is applied to the inside of the storage tank. The slightly positive pressure is 0 - 2000 Pa, that is, the pressure inside the storage tank is 0 - 2000 Pa higher than the external atmospheric pressure. More preferably, the slightly positive pressure is 100 - 1000 Pa. Exemplarily, the slightly positive pressure is 50 Pa, 200 Pa, 500 Pa, 800 Pa, 1300 Pa, 1500 Pa, 1800 Pa.

[0163] Using the ammoniation treatment provided in the above embodiments of the present invention can ensure that the pH of the obtained carbon fiber spinning solution is 8 - 10, further the pH is 8.4 - 9.8, and preferably the pH is 8.9 - 9.5.

[0164] Furthermore, the molecular weight M of the acrylonitrile-based polymerization solution prepared from S1 - S3 W is 200,000 - 250,000, the polydispersity index PDI is 2.0 - 3.0, the falling ball method viscosity at 40 - 50 °C is 600 - 1000 P, the solid content in the polymerization solution is 19.0 - 21.0%, the polymerization conversion rate ≥ 90%, and the residual monomer content of the polymerized acrylonitrile-based polymerization solution is ≤ 10%. After the monomer removal treatment, the residual monomer content of the acrylonitrile-based polymerization solution is ≤ 350 ppm. After the ammoniation treatment, the pH of the obtained carbon fiber spinning solution is 8 - 10.

[0165] In some embodiments, the molecular weight M of the polymerized acrylonitrile-based polymerization solution W is 210,000 - 250,000, the polydispersity index PDI is 2.1 - 2.6, the falling ball viscosity at 40 - 50 °C is 620 - 910 P, the solid content in the polymerization solution is 19.2 - 20.6%, the polymerization conversion rate is 92 - 95%, the residual monomer content of the polymerized acrylonitrile-based polymerization solution is ≤ 3%, further, the residual monomer content of the polymerized acrylonitrile-based polymerization solution is ≤ 2%, further, the residual monomer content of the polymerized acrylonitrile-based polymerization solution is ≤ 1%. After the monomer removal treatment, the residual monomer content of the acrylonitrile-based polymerization solution is < 100 ppm, more preferably, the residual monomer content after monomer removal is less than 50 ppm, further, the residual monomer content after monomer removal is less than 30 ppm. After the ammoniation treatment, the pH of the obtained carbon fiber spinning solution is 8.4 - 9.8, preferably the pH is 8.9 - 9.5.

[0166] The present invention also provides a production device for a carbon fiber spinning solution, and the production device is used for the production and preparation of the carbon fiber spinning solution (corresponding to steps S1 - S3).

[0167] Specifically, the production device includes a monomer removal device, an ammoniation device, and a polymerization device.

[0168] (1) Monomer removal device:

[0169] The monomer removal device 100 includes a tank A and a multi-layer perforated partition 11 arranged in the tank. The multi-layer perforated partition is arranged in layers from top to bottom along the axial direction of the tank, and each layer of perforated partition is perpendicular to the axial direction of the tank. Each layer of perforated partition includes a fixed end on one side and a suspended end on the other side. The fixed end is conformally fixed to the inner wall of the tank, and the suspended end on the other side extends freely. The suspended end of the upper layer of perforated partition is located on one side of the axial direction of the tank, and the suspended end of the lower layer of perforated partition adjacent to the upper layer of perforated partition is located on the other side of the axial direction of the tank. The suspended ends of the multi-layer perforated partition form an alternating staggered layout in space.

[0170] Compared with the prior art, the present invention sets a multi-layer perforated partition in the monomer removal device. The polymerization solution forms a thin liquid layer on each layer of the partition, and the suspended ends of adjacent partitions are staggered, ensuring the smooth flow of the polymerization solution. This structural design optimizes the flow path of the polymerization solution in the tank. On the one hand, the specific surface area of the material is increased through the thin liquid layer, and on the other hand, the residence time of the liquid in the device is extended, providing more opportunities for the solvent vapor to contact with the residual monomer, thereby significantly improving the monomer removal effect.

[0171] The single-removing device of the present invention designs a channel between the suspended end of each perforated partition plate and the inner wall of the tank body, ensuring that the polymerized liquid can flow smoothly to the next layer after forming a thin liquid layer. This structure not only realizes the uniform distribution and effective guidance of high-molecular-weight and high-viscosity polymerized liquid materials on the partition plate, but also significantly reduces problems such as coking, scaling, or gel formation in the polymerized liquid that are prone to occur in traditional devices when processing such materials. In addition, it effectively avoids blockage inside the single-removing device, improves operation stability, reduces equipment cleaning and maintenance costs, and enhances production efficiency.

[0172] Preferably, the area of each perforated partition plate accounts for 80%-90% of the cross-sectional area of the tank body at that layer position, and the remaining 10-20% serves as a smooth channel for the flow of the polymerized liquid.

[0173] Preferably, the holes of adjacent perforated partition plates are arranged in a staggered layer. The hole positions on each perforated partition plate are offset relative to the hole positions of the directly adjacent perforated partition plate. This setting of staggered hole distribution can further increase the contact area and time between the solvent vapor and the polymerized liquid, thereby improving the gas-liquid exchange efficiency, helping the solvent vapor to more effectively remove the residual monomers in the polymerized liquid. In addition, the staggered holes can optimize the flow path, make the polymerized liquid flow more evenly, reduce the situation of local overheating or overcooling, reduce the risk of coking and scaling, and reduce the formation of gel in the polymerized liquid.

[0174] Preferably, multiple perforated partition plates are distributed parallel and equidistantly from top to bottom along the axial direction of the tank body. By adopting the above-preferred partition plate distribution method, it helps to achieve the uniform flow of the polymerized liquid in the tank body, reduce flow dead zones, reduce the risk of coking and scaling, reduce the formation of gel in the polymerized liquid, and ensure sufficient contact between the solvent vapor and the polymerized liquid, improving the single-removing effect and efficiency.

[0175] Preferably, the distance between the first perforated partition plate and the last perforated partition plate in the tank body accounts for 1 / 2 to 4 / 5 of the total height of the tank body, preferably 60%-70%, such as 2 / 3. This can make more full use of the tank body space, increase the contact time and area between the polymerized liquid and the solvent vapor, improve the single-removing effect and efficiency. By leaving appropriate space above and below, it helps the heat transfer and mass transfer processes to proceed, ensures the uniform distribution of heat and substances throughout the tank body, reduces the dead zone of the polymerized liquid in the tank body, avoids local overheating or overcooling, and is beneficial to reducing the risk of coking and scaling and reducing the formation of gel in the polymerized liquid.

[0176] Furthermore, a polymerized liquid feed port 12 is provided at the top or upper part of the tank body. A perforated distribution plate 13 is provided between the polymerized liquid feed port 12 and the adjacent first perforated partition plate, and the distribution plate 13 is arranged parallel to the first perforated partition plate.

[0177] Preferably, the area ratio of the distribution plate 13 to the first layer of perforated partition plates is 40%-60%, more preferably 45%-55%.

[0178] Preferably, the ratio of the distance between the upper surface of the distribution plate 13 and the lower end of the polymerization liquid feed port 12 to the distance between the lower end of the polymerization liquid feed port 12 and the upper surface of the first layer of perforated partition is 15%-40%; more preferably 20-30%.

[0179] The main function of the distribution plate is to distribute the polymer solution entering from the feed port evenly to the first layer of perforated partitions after being distributed through the porous distribution, so that a uniform thin polymer solution layer is formed on the perforated partitions. By controlling the spatial layout of the distribution plate in the tank body and the area ratio to the adjacent perforated partitions, it is conducive to forming a more uniform thin polymer solution layer, increasing the contact area and time between the polymer solution and the solvent vapor, and improving the removal effect and efficiency.

[0180] By precisely controlling the shape and structural parameters of the perforated partition and the spatial layout in the tank, it is beneficial to improve the monomer removal effect, avoid local overheating or overcooling, further reduce the risk of coking and crusting, and reduce the formation of gel in the polymer solution. The monomer removal device provided by the present invention is used to remove monomers from the polymer solution, which can ensure that the content of residual monomers in the polymer solution after the monomer removal is reduced to less than 100ppm.

[0181] Specifically, the perforated partition has at least one of the following characteristics:

[0182] (a) the number of layers of the perforated partition is 4-8;

[0183] (b) The hole size on each layer of perforated partition is 0.5-2 mm, and the hole spacing is 10-40 mm; illustratively, the hole size is 1 mm, 1.5 mm; the hole spacing is 20 mm, 30 mm.

[0184] (c) The arrangement of the multiple holes on each layer of the perforated partition is preferably a circular array; further, the multiple holes cover the entire perforated partition.

[0185] (d) The spacing between two adjacent layers of perforated partitions is 300-800 mm; preferably 400-600 mm, for example 500 mm;

[0186] (e) The thickness of each layer of perforated partition is 6-12 mm;

[0187] (f) The holes of adjacent perforated partitions are arranged in staggered layers, and the offset distance between the centers of the corresponding holes in adjacent layers is 10-30 mm; preferably, they are arranged in an alternating staggered manner: the odd-numbered layers and the even-numbered layers are kept consistent, but the odd-numbered layers are staggered a certain distance from the even-numbered layers.

[0188] (g) To enable the polymerization solution to spread better into a thin film on the perforated partition plate to improve the monomer removal effect, preferably, the material of the perforated partition plate is selected from 316L stainless steel, 1Cr18NiMo3 stainless steel, and AL-1100 aluminum alloy. The above materials are all existing commercially available alloy grades.

[0189] Furthermore, a solvent vapor inlet is provided at the lower part of the tank body. The monomer removal device further includes a solvent vaporizer B. The upper part of the solvent vaporizer B is connected to the solvent vapor inlet through a pipeline. A solvent inlet 14 is provided at the bottom of the solvent vaporizer B. A coil 15 is provided inside the solvent vaporizer B. One end of the coil 15 is connected to a coil inlet 15a provided at the upper part of the solvent vaporizer B, and the other end of the coil 15 is connected to a coil outlet 15b provided at the lower part of the solvent vaporizer B.

[0190] It can be understood that during operation, the solvent enters the solvent vaporizer B from the solvent inlet 14, water vapor enters the coil from the coil inlet 15a, flows along the coil, and finally flows out from the coil outlet 15b. During the process of the water vapor flowing in the coil, heat is transferred to the solvent outside the coil, vaporizing it into solvent vapor 16, and the solvent vapor 16 flows into the tank body A through the solvent vapor inlet.

[0191] Exemplarily, the solvent vapor inlet is provided below the last layer of perforated partition plate and above the liquid level of the monomer-removed polymerization solution and the liquefied solvent mixture collected at the bottom of the tank body A.

[0192] Specifically, a vacuum extraction port 17 is provided at the upper part or the top of the tank body A. The monomer removal device further includes a liquid ring type vacuum jet device, which is connected to the vacuum extraction port 17 through a pipeline, thereby providing a stable negative pressure inside the tank body A of the monomer removal device and discharging the solvent vapor carrying monomers. Specifically, a heating jacket is provided on the outer wall of the tank body A to make the polymerization solution inside the tank body A reach the required monomer removal temperature.

[0193] Specifically, a polymerization solution discharge port 18 is provided at the lower part or the bottom of the tank body A.

[0194] (2) Ammoniation device:

[0195] The ammoniation device 200 includes a storage tank and an inclined paddle stirrer 21 provided inside the storage tank. The inclined paddle stirrer 21 includes a plurality of stirring paddles 21a arranged in layers along the axial direction of the storage tank, and the plurality of stirring paddles are commonly connected to the same rotating shaft 21b. Preferably, the plurality of stirring paddles are equally spaced along the axial direction of the storage tank.

[0196] Each stirring paddle includes a plurality of inclined stirring paddle blades. Preferably, the inclination angle of the inclined stirring paddle blades is 40 - 50°, and the inclined stirring paddle blades are rectangular paddle blades, and its length is L and satisfies πL 2=(50 - 70%)S4, where S4 is the cross-sectional area of the storage tank. Preferably, πL 2 =(50 - 55%)S4.

[0197] Exemplarily, the inclined paddle agitator includes 2, 3 or 4 agitator paddles, and each agitator paddle includes at least two inclined agitator blades. For example, each agitator paddle includes 3 or 4 inclined agitator blades.

[0198] Preferably, the ammonia gas inlet 22 is arranged within the height range of 1 / 5 to 2 / 5 from the bottom of the storage tank, that is, the area between 1 / 5 height and 2 / 5 height upward from the bottom of the storage tank.

[0199] A polymer liquid inlet 23 is arranged at the upper part or top of the storage tank, and a polymer liquid outlet 24 is arranged at the lower part or bottom of the storage tank; the top end of the rotating shaft 21b of the inclined paddle agitator is driven by a first motor 25.

[0200] (3) Polymerization device:

[0201] The polymerization device 300 includes a polymerization kettle and a stirring device 31 arranged inside the polymerization kettle, and the stirring device 31 is selected from a ribbon agitator and a scraping wall agitator.

[0202] For the ribbon agitator, it satisfies: S1=(50 - 70%)S2, S1 = Π×(1 / 2D1) 2 , where D1 is the outer diameter of the ribbon, and S2 is the inner cross-sectional area of the polymerization kettle. Exemplarily, S1 / S2 = 55%, 60%, 65%.

[0203] For the scraping wall agitator, it satisfies: L≤10mm, where L represents the gap between the scraping wall component (such as a scraper or a knife) of the scraping wall agitator and the inner wall of the polymerization kettle.

[0204] One side of the top of the polymerization device 300 is provided with an inert gas inlet 32, and the other side is provided with an inert gas outlet 33. Preferably, both the inert gas inlet 32 and the inert gas outlet 33 are located within the height range of 1 / 10 to 1 / 5 from the top of the polymerization device downward. The stirring device 31 is driven by a second motor 34.

[0205] In some embodiments, the polymerization device further includes a real-time viscosity monitoring device C, which includes a reflux pipeline. Both ends of the reflux pipeline are communicated with the inside of the polymerization kettle, and an on-line pressure-viscosity converter 35 is arranged on the reflux pipeline. The on-line pressure-viscosity converter includes a pressure detector and a processor. The pressure detector is arranged at a fixed position of the reflux pipeline for real-time collecting the pressure signal of the polymer liquid in the pipeline. The pressure detector is connected with the processor through a line, and the processor is used for converting the collected pressure signal into a viscosity value. Figure 4Among them, T represents the temperature monitoring component, and P represents the pressure monitoring component.

[0206] Furthermore, the processor of the real-time viscosity detection device C is connected to a display located outside the polymerization device through a circuit. After converting the collected pressure signal into a viscosity value, the processor transmits the data to the display through the circuit, thereby real-time displaying the viscosity of the polymerization liquid.

[0207] Preferably, a constant-speed gear pump 36 is provided on the reflux pipeline, and a circulating water system is provided outside the reflux pipeline. For example, the circulating water system is a water tank, and the constant-temperature circulating water enters from one side of the water tank and flows out from the other side. Exemplarily, the constant-temperature circulating water enters the water tank from the circulating water inlet 37 at the bottom of the water tank and flows out of the water tank from the circulating water outlet 38 at the top of the water tank. The constant-speed gear pump and the circulating water system can ensure the constant temperature and flow rate of the polymerization liquid in the reflux pipeline.

[0208] In the method for preparing the carbon fiber spinning solution provided by the embodiment of the present invention, preferably, a material containing acrylonitrile, comonomer, and solvent is added to the above-mentioned polymerization device 300. The deodorization treatment is performed using the above-mentioned deodorization device 100. The ammoniation treatment is performed using the above-mentioned ammoniation device 200.

[0209] It can be understood that the acrylonitrile-based polymerization liquid refers to a polymer solution mainly composed of acrylonitrile monomers formed through a polymerization reaction (such as free radical polymerization).

[0210] Exemplarily, a possible design of the deodorization device 100 (hereinafter simply referred to as the A-type deodorization device) is as follows:

[0211] This embodiment provides a deodorization device 100 for carbon fiber polymerization liquid. The deodorization device 100 includes a tank body A and a multi-layer perforated partition 11 arranged horizontally (i.e., perpendicular to the axial direction of the tank body) inside the tank body A. The multi-layer perforated partitions are arranged in parallel and equidistantly in layers from top to bottom along the axial direction of the tank body. Each layer of perforated partition includes a fixed end on one side and a suspended end on the other side. The fixed end is conformally fixed to the inner wall of the tank body, and the other suspended end extends freely. The suspended end of one layer of perforated partition is located on one side of the axial direction of the tank body, and the suspended ends of adjacent layers of perforated partitions are located on the other side of the axial direction of the tank body. The suspended ends of the multi-layer perforated partitions form an alternating staggered layout in space.

[0212] The area of each layer of perforated partition accounts for 75% of the cross-sectional area of the tank body at that layer position, and the remaining 25% serves as a smooth channel for the polymerization liquid to flow; the holes of adjacent layers of perforated partitions are arranged in an alternating staggered layer distribution, and the dislocation distance between the centers of the corresponding holes of adjacent layers is 10 mm; the aperture size of the holes on each layer of perforated partition is 1.0 mm, the hole pitch is 20 mm, and the holes are arranged in a circular array; the thickness of each layer of perforated partition is 6 mm.

[0213] Inside the tank body A, the distance between the first perforated partition plate and the last perforated partition plate accounts for 1 / 2 of the total height of the tank body; a polymerized liquid inlet 12 is provided at the top of the tank body A, and a perforated distribution plate 13 is provided between the polymerized liquid inlet 12 and the adjacent first perforated partition plate, and the distribution plate 13 is arranged parallel to the first perforated partition plate; the area ratio of the distribution plate 13 to the first perforated partition plate is 30%, and the ratio of the distance between the upper surface of the distribution plate 13 and the lower end of the polymerized liquid inlet 12 to the distance between the lower end of the polymerized liquid inlet 12 and the upper surface of the first perforated partition plate is 50%.

[0214] A solvent vapor inlet is provided at the lower part of the tank body A. The de-monomerization device further includes a solvent vaporizer B. The top of the solvent vaporizer B is connected to the solvent vapor inlet through a pipeline. A solvent inlet 14 is provided at the bottom of the solvent vaporizer B. A coil 15 is arranged inside the solvent vaporizer B. One end of the coil 15 is connected to a coil inlet 15a arranged at the upper part of the solvent vaporizer, and the other end of the coil 15 is connected to a coil outlet 15b arranged at the lower part of the solvent vaporizer; a polymerized liquid outlet 18 is provided at the bottom of the tank body A; the solvent is vaporized into solvent vapor 16 through the solvent vaporizer B and enters the storage tank from the solvent vapor inlet; a vacuum pumping port 17 is provided at the upper part of the tank body A; the de-monomerization device further includes a liquid ring type vacuum jet device, which is connected to the vacuum pumping port 17 through a pipeline, so as to provide a stable negative pressure inside the tank body A in the de-monomerization device and discharge the solvent vapor carrying monomers.

[0215] Exemplarily, another possible design of the de-monomerization device 100 is designed as (hereinafter simply referred to as the B-type de-monomerization device):

[0216] The difference between this design and the previous design is that the area of each perforated partition plate accounts for 85% of the cross-sectional area of the tank body at that layer position, and the remaining 15% is used as a smooth channel for the flow of the polymerized liquid; the misalignment distance between the corresponding hole centers of adjacent layers is 20 mm; inside the tank body A, the distance between the first perforated partition plate and the last perforated partition plate accounts for 70% of the total height of the tank body; the area ratio of the distribution plate 13 to the first perforated partition plate is 50%, and the ratio of the distance between the upper surface of the distribution plate 13 and the lower end of the polymerized liquid inlet 12 to the distance between the lower end of the polymerized liquid inlet 12 and the upper surface of the first perforated partition plate is 30%.

[0217] Further, S4 to S6 are particularly applicable to a spinning solution with dimethyl sulfoxide as the solvent.

[0218] Specifically, the specific process of the coagulation bath in step S4 is as follows:

[0219] Using the wet spinning process, the spinning solution is output by a spinning metering pump, flows through a buffer, enters a spinneret and is ejected into a coagulating bath. The coagulating bath is a mixed solution of dimethyl sulfoxide and water, and the mass fraction of dimethyl sulfoxide is 60-80%, preferably 70-78%, and the coagulation temperature is 20-60°C. The spinning solution is a mixed solution of dimethyl sulfoxide and polyacrylonitrile, and the solid content of 19-21% represents the content of polyacrylonitrile, and the content of dimethyl sulfoxide is 79-81%. The coagulation process is a double-diffusion process, from high concentration to low concentration, that is, dimethyl sulfoxide in the spun filament after passing through the spinneret diffuses into the coagulating bath, and water in the coagulating bath diffuses into the spun filament after passing through the spinneret. Therefore, the concentration of dimethyl sulfoxide in the coagulating bath is lower than that of the corresponding component in the spinning solution. The coagulation temperature is generally equivalent to the temperature of the spinning solution, and the temperature of the spinning solution is generally controlled below 60°C. If the temperature is too high, the viscosity of the spinning solution is low, and the fiber properties are reduced. If the temperature is too low, the viscosity of the spinning solution is too high, and it is not easy to form a spun filament from the spinneret holes, and the spinnability is poor. Therefore, the range of the coagulation temperature is 20-60°C;

[0220] During the coagulation bath process, the coagulated filament is drawn, and the draw ratio is 1.01-1.20 times. When forming fibers by coagulation double diffusion, the nascent filament is particularly "delicate" and the intermolecular force is very small, so it is easy to deform and it is not easy to apply a large uniaxial drawing force. Otherwise, the filament will be damaged, resulting in hairiness and broken filaments, causing irregular deformation. The drawing tension is controlled below 200 mg / monofilament, and the monofilament tension corresponding to a draw ratio of 1.20 times is about 200 mg / monofilament.

[0221] Furthermore, the spinneret is an annular spinneret, and liquid is introduced into its inner ring. The flow rate of the liquid in the inner ring is controlled to be 100-1000 L / h. The inner ring liquid is a mixed solution of dimethyl sulfoxide and water, and the mass fraction of dimethyl sulfoxide is 60-80%, preferably 65-75%;

[0222] When using an annular spinneret, by controlling the concentration and flow rate of the inner ring liquid, the contact between the spinning solution and the coagulating bath (strictly speaking, the inner ring liquid is also part of the coagulating bath) can be made more sufficient, and the coagulation process can be more uniform, which is beneficial to improving the orientation and uniformity of the nascent fiber.

[0223] Among them, the mass fraction of dimethyl sulfoxide in the coagulating bath is greater than that in the inner ring liquid, and the temperatures of the coagulating bath and the inner ring liquid are the same. Driven by the pressure of the metering pump, the spinning solution is extruded from the spinneret and forms a filament flow into the coagulating bath. The filament flow is in a columnar state, and the solvent concentration in the filament flow is greater than that of the coagulating bath. Under the action of the concentration difference, the solvent in the filament flow diffuses into the coagulating bath. The solvent concentration in the inner ring of the columnar filament flow is relatively high. To make the concentration of the coagulating liquid in the inner ring (inner ring liquid) the same as that of the coagulating liquid outside the columnar filament flow, the concentration of the coagulating liquid in the inner ring (inner ring liquid) should be lower than that of the coagulating bath.

[0224] Since the raw silk is composed of multiple filaments, each filament has a certain diameter, and the solidification and diffusion of the filaments ejected from the spinneret holes proceed gradually from the outer surface to the core of the filaments. During the double-diffusion solidification process, the surface of the filaments solidifies first and gradually becomes denser, hindering the double diffusion of the core of the filaments. Therefore, the dimethyl sulfoxide in the core cannot be released, forming defects. First, the present invention realizes the fining of solidification by adjusting parameters such as the concentration of the coagulation solution, the coagulation temperature, and the draw ratio. The fibers become thinner in the coagulation bath, which is more conducive to the precipitation of dimethyl sulfoxide in the core of the filaments, and the densification of the as-spun fibers after solidification is better (that is, the content of dimethyl sulfoxide in the as-spun fibers is reduced); when the temperature of the coagulation bath increases, the densification of the as-spun fibers first increases and then decreases. When the temperature is relatively low, the double diffusion of solidification is relatively gentle, forming dense as-spun fibers. As the temperature increases, the double diffusion becomes intense, and the dense surface layer hinders the double diffusion from proceeding, so the sulfoxide inside the filaments cannot be released, forming hole defects. When the concentration of the coagulation liquid increases, the concentration difference between the coagulation bath and the main body of the spinning solution decreases, and the double diffusion is slow, making the fiber structure regular and the densification strong. When the concentration of the coagulation liquid decreases, the concentration difference between the two becomes larger, and the double diffusion becomes faster, and the filament will become obviously opaque and white because the solidification is too fast, forming defects of fine holes. The purpose of drawing is to make the fibers finer. The finer fibers are conducive to the complete release of sulfoxide in the core of the filaments, conducive to the progress of double diffusion, and improve densification.

[0225] Specifically, in step S5, a flower roller type water washing is adopted, the water flow direction is countercurrent to the fiber direction, and the water washing temperature is gradually increased, and the water washing temperature range is controlled at 30-80 °C;

[0226] During the water washing process, draw distribution is carried out. When the water washing temperature ≤ 45 °C, a draw of 1.01-1.03 times is applied; when the water washing temperature > 45 °C, a draw of 1.02-1.05 times is applied; wherein, the temperature and draw ratio of the next stage of water washing are not less than those of the previous stage of water washing.

[0227] The present invention significantly increases the number of washing stages in the water washing stage, particularly preferably 16 stages of water washing, and gradually raises the temperature during the water washing process, and strictly controls the draw ratio (slightly increasing according to the temperature change). During this process, the purpose of washing out the coagulant dimethyl sulfoxide and further improving the densification of the fiber is achieved, and the residual amount of dimethyl sulfoxide in the raw silk is <1000 ppm. Too few washing stages or too low a temperature will result in too high a sulfoxide content in the fiber bundle. If the number of washing stages is small, the washing time is insufficient, and the sulfoxide residue will be high. If the water washing temperature is too low, the plasticity of the fiber is poor, which becomes a defect during drawing and affects the densification. Too many washing stages will cause waste of resources and a long process; the temperature during water washing should not be too high either. On the one hand, high temperature will cause the residual dimethyl sulfoxide to diffuse rapidly. Although the residual coagulant is removed, it will cause pore-type defects inside or on the surface of the raw silk. On the other hand, when the water washing temperature > 90 °C, the crystallinity in the raw silk will decrease, resulting in a change in the internal structure, and then the strength of the raw silk will decrease. In addition, it will also cause waste of energy.

[0228] Preferably, in step S5, the total number of water washing stages is 16. The temperature of the first stage is set at 30 - 40 °C, and the temperature of each stage of water washing increases by 2 - 4 °C step by step. The temperature of the 16th stage of water washing is 60 - 70 °C.

[0229] Specifically, in step S6, the temperature of the hot water ≥ 70 °C, and the total draw ratio of the hot water drawing is 2 - 4 times; the hot water drawing is divided into 2 - 6 stages, and the temperature and draw ratio of each stage of hot water gradually increase.

[0230] The present invention strictly controls the temperature of the hot water drawing and divides it into multiple stages / sub-stages, and sets different draw ratios for each stage to achieve the gradual optimization of the internal structure of the raw silk. If the number of stages is too small and the draw distribution of each stage is too large, it will cause broken filaments and form defects. The temperature of each stage increases step by step, and the draw ratio increases with the temperature. As the temperature increases step by step, the plasticity of the fiber becomes better, the draw ratio gradually increases, the fiber becomes finer and finer, and the densification becomes better.

[0231] Preferably, in step S6, the hot water drawing is 4 stages;

[0232] Among them, the temperature of the first stage is 70 - 80 °C, and the draw ratio is 1.1 - 1.2 times; the temperature of the second stage is 75 - 85 °C, and the draw is 1.2 - 1.3 times; the temperature of the third stage is 80 - 90 °C, and the draw is 1.3 - 1.4 times; the temperature of the fourth stage is 85 - 95 °C, and the draw is 1.4 - 1.5 times.

[0233] Specifically, the treatment process of the densified raw silk in step S6 includes: oiling, drying, and steam drawing.

[0234] Specifically, the orientation degree of the densified raw silk ≥ 93.0%, and the strength of the raw silk ≥ 7.5 cN / dtex.

[0235] Specifically, the densified precursor filaments are made into carbon fibers through processes such as wire drawing under constant tension, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and wire winding.

[0236] The present invention also provides a high-strength and medium-modulus carbon fiber, which is prepared by the above preparation method;

[0237] The carbon fiber has an elastic modulus of 320 - 340 GPa, a tensile strength > 6100 MPa, a residual content of dimethyl sulfoxide ≤ 320 ppm, and no obvious defects are observed under an electron microscope at a magnification of 2000 times.

[0238] Spinning solution test group (corresponding to steps S1 - S3)

[0239] Example 1:

[0240] This example provides a preparation method for a binary copolymer polyacrylonitrile-based carbon fiber spinning solution, including the following steps:

[0241] S1: Preparation of materials: By weight, 20 parts of acrylonitrile, 1 part of itaconic acid, 0.2 part of azobisisobutyronitrile (AIBN), and 73.7 parts of dimethyl sulfoxide; 0.2 part of AIBN is pre-dissolved in 8 parts of dimethyl sulfoxide as an initiator for free radical polymerization;

[0242] Acrylonitrile, itaconic acid, and dimethyl sulfoxide are added to the polymerization device, and the materials in the polymerization device are stirred by a scraping wall stirrer, with L = 10 mm, a stirring speed of 20 rpm, and a stirring time of 60 min; the proportion of the liquid level height h of the internal liquid in the polymerization device to the total height H of the polymerization device is 80%;

[0243] When the temperature difference of the materials ≤ 1 °C and the temperature is raised to 54 °C, part of the initiator is added first, and the proportion of part of the initiator in the total amount of the initiator is 60%; the viscosity of the materials is monitored in real time. When the viscosity of the materials reaches the first viscosity threshold of 250 P, the materials are heated to the target temperature of 64 °C, and the remaining 40% of the initiator is added; when the viscosity of the materials reaches the second viscosity threshold of 620 P, the reaction is terminated; the polymerization is carried out under nitrogen protection, with a nitrogen flow rate of 50 L / h and a pressure of 0.1 Mpa. During the polymerization, the stirring speed is 30 rpm; the molecular weight and PDI of the acrylonitrile-based polymerization solution obtained after polymerization are shown in Table 1, and they meet the target molecular weight.

[0244] S2. Perform monomer removal on the acrylonitrile-based polymerization solution that meets the target molecular weight; during the monomer removal process, the polymerization solution enters from the top of the Type A monomer removal device, and through porous distribution, it is evenly distributed on the first perforated partition plate, and successively passes through the second to fifth perforated partition plates arranged in an alternating manner to perform gas-liquid exchange with the solvent vapor flowing countercurrently. At each perforated partition plate, the polymerization solution is divided into two parts: one part of the polymerization solution flows through the holes on the perforated partition plate to the next perforated partition plate or the polymerization solution collection area, and the positions of the holes where the polymerization solution flows out of the adjacent perforated partition plates are different; the other part of the polymerization solution flows from the suspended end on the side of the partition plate to the next perforated partition plate or the polymerization solution collection area. Among them, the monomer removal is carried out at 500 Pa, the inlet temperature of the polymerization solution is 50 °C, the inlet flow rate Q1 of the polymerization solution is 3 m 3 / h; the inlet temperature of the solvent vapor is 80 °C. The inlet flow rate of the solvent vapor is 80 L / h, and the pressure of the solvent vapor is 0.5 Mpa;

[0245] S3: Adopt the ammonia bubbling method to introduce ammonia into the polymerized solution after monomer removal for ammoniation treatment; specifically, adjust the temperature of the polymerized solution placed in the storage tank to 60 °C, and then introduce ammonia from the lower 1 / 5 of the storage tank. During the ammoniation process, the temperature is controlled at 60 °C, the micro positive pressure is 100 pa, and a pitched blade agitator is used for stirring, and the stirring speed is 55 r / min; the pitched blade agitator includes 3 stirring paddles, and each stirring paddle includes 3 rectangular pitched stirring blades with an inclination angle of 35 °, and its length is L and satisfies πL 2 = 70% × S4, where S4 is the cross-sectional area of the storage tank; the flow rate Q3 of the polymerization solution is 3 m 3 / h, and calculate the required amount of ammonia according to 4.0 mg of ammonia introduced per 1 kg of the polymerization solution.

[0246] Example 2:

[0247] The difference between this example and Example 1 is that in step S1, when the material temperature difference ≤ 1 °C and the temperature is raised to 58 °C, part of the initiator is added first, and the proportion of part of the initiator in the total amount of the initiator is 65%; monitor the material viscosity in real time. When the material viscosity reaches the first viscosity threshold of 300 P, raise the material temperature to the target temperature of 62 °C and add the remaining 35% of the initiator; when the material viscosity reaches the second viscosity threshold of 710 P, terminate the reaction; in step S2, the inlet flow rate of the solvent vapor is 100 L / h; in step S3, calculate the required amount of ammonia according to 6 mg of ammonia introduced per 1 kg of the polymerization solution; the remaining steps and parameters are similar to those in Example 1.

[0248] Example 3:

[0249] The differences between this embodiment and Embodiment 1 are as follows: In step S1, when the temperature difference of the material ≤ 1°C and the temperature is raised to 54°C, a part of the initiator is added first, and the proportion of the part of the initiator in the total amount of the initiator is 70%; the viscosity of the material is monitored in real time. When the viscosity of the material reaches the first viscosity threshold of 350 P, the material is heated to the target temperature of 66°C, and the remaining 30% of the initiator is added; when the viscosity of the material reaches the second viscosity threshold of 760 P, the reaction is terminated; in step S2, a Type B degassing device is used for degassing treatment, and the inlet flow rate of the solvent vapor is 100 L / h; in step S3, each stirring paddle includes 3 rectangular inclined stirring paddle blades with an inclination angle of 35°, and its length is L and satisfies πL 2 = 50% × S4, where S4 is the cross-sectional area of the storage tank, and the amount of ammonia required is calculated according to 5 mg of ammonia introduced into every 1 kg of the polymerization solution; the remaining steps and parameters are similar to those in Embodiment 1.

[0250] Embodiment 4:

[0251] The differences between this embodiment and Embodiment 1 are as follows: In step S1, when the temperature difference of the material ≤ 1°C and the temperature is raised to 55°C, a part of the initiator is added first, and the proportion of the part of the initiator in the total amount of the initiator is 68%; the viscosity of the material is monitored in real time. When the viscosity of the material reaches the first viscosity threshold of 320 P, the material is heated to the target temperature of 65°C, and the remaining 32% of the initiator is added; when the viscosity of the material reaches the second viscosity threshold of 840 P, the reaction is terminated; in step S2, a Type B degassing device is used for degassing treatment, and the inlet flow rate of the solvent vapor is 80 L / h; in step S3, each stirring paddle includes 3 rectangular inclined stirring paddle blades with an inclination angle of 45°, and its length is L and satisfies πL 2 = 60% × S4, where S4 is the cross-sectional area of the storage tank, and the amount of ammonia required is calculated according to 5 mg of ammonia introduced into every 1 kg of the polymerization solution; the remaining steps and parameters are similar to those in Embodiment 1.

[0252] Embodiment 5:

[0253] The differences between this embodiment and Embodiment 1 are as follows: In step S1, when the temperature difference of the material ≤ 1°C and the temperature is raised to 56°C, a part of the initiator is added first, and the proportion of the part of the initiator in the total amount of the initiator is 65%; the viscosity of the material is monitored in real time. When the viscosity of the material reaches the first viscosity threshold of 300 P, the material is heated to the target temperature of 64°C, and the remaining 35% of the initiator is added; when the viscosity of the material reaches the second viscosity threshold of 810 P, the reaction is terminated; in step S2, a Type B degassing device is used for degassing treatment, and the inlet flow rate Q1 of the polymerization solution is 4 m 3 / h, and the inlet flow rate of the solvent vapor is 170 L / h; in step S3, the flow rate Q3 of the polymerization solution = 4 m 3 / h, and the amount of ammonia required is calculated according to 6.0 mg of ammonia introduced into every 1 kg of the polymerization solution. The remaining steps and parameters are similar to those in Embodiment 1.

[0254] Example 6:

[0255] The difference between this example and Example 1 is as follows: In step S1, when the temperature difference of the material ≤ 1 °C and the temperature is raised to 54 °C, a part of the initiator is added first, and the proportion of the part of the initiator in the total amount of the initiator is 75%; the viscosity of the material is monitored in real time. When the viscosity of the material reaches the first viscosity threshold of 350 P, the material is heated to the target temperature of 64 °C, and the remaining 25% of the initiator is added; when the viscosity of the material reaches the second viscosity threshold of 910 P, the reaction is terminated; in step S2, a Type B degassing device is used for degassing treatment, the inlet flow rate Q1 of the polymerization liquid is 5 m 3 / h, and the inlet flow rate of the solvent vapor is 250 L / h; in step S3, the flow rate Q3 of the polymerization liquid = 5 m 3 / h, and the amount of ammonia required is calculated according to 12.0 mg of ammonia introduced per 1 kg of the polymerization liquid. The remaining steps and parameters are similar to those in Example 1.

[0256] Example 7:

[0257] The difference between this example and Example 1 is as follows: In step S1, when the temperature difference of the material ≤ 1 °C and the temperature is raised to 57 °C, a part of the initiator is added first, and the proportion of the part of the initiator in the total amount of the initiator is 70%; the viscosity of the material is monitored in real time. When the viscosity of the material reaches the first viscosity threshold of 350 P, the material is heated to the target temperature of 67 °C, and the remaining 30% of the initiator is added; when the viscosity of the material reaches the second viscosity threshold of 620 P, the reaction is terminated; the polymerization is carried out under nitrogen protection, the flow rate of nitrogen is 80 L / h, and the pressure is 0.06 Mpa. During the polymerization, before adding the remaining initiator, the stirring speed is 50 rpm; after adding the remaining initiator, the stirring speed is 60 rpm. In step S2, a Type B degassing device is used for degassing treatment, the inlet temperature of the polymerization liquid is 67 °C, and the inlet flow rate Q1 of the polymerization liquid is 5 m 3 / h; the inlet temperature of the solvent vapor is 95 °C. The inlet flow rate of the solvent vapor is 100 L / h, and the pressure of the solvent vapor is 0.3 Mpa; in step S3, the flow rate Q3 of the polymerization liquid = 5 m 3 / h, and the amount of ammonia required is calculated according to 10.0 mg of ammonia introduced per 1 kg of the polymerization liquid. The remaining steps and parameters are similar to those in Example 1.

[0258] Comparative Example 1:

[0259] The difference between this comparative example and Example 1 is as follows: In step S1, when the temperature difference of the material is ≤ 1 °C and the temperature is raised to 70 °C, a part of the initiator is added, and the proportion of this part of the initiator in the total amount of the initiator is 55%. The viscosity of the material is monitored in real time. When the viscosity of the material reaches the first viscosity threshold of 150 P, the remaining 45% of the initiator is added; when the viscosity of the material reaches the second viscosity threshold of 630 P, the reaction is terminated. The remaining steps and parameters are similar to those in Example 1.

[0260] Comparative Example 2:

[0261] The difference between this comparative example and Example 1 is as follows: In step S1, when the temperature difference of the material is ≤ 1 °C and the temperature is raised to 50 °C, a part of the initiator is added, and the proportion of this part of the initiator in the total amount of the initiator is 85%. The viscosity of the material is monitored in real time. When the viscosity of the material reaches the first viscosity threshold of 450 P, the temperature of the material is raised to the target temperature of 55 °C, and the remaining 15% of the initiator is added; when the viscosity of the material reaches the second viscosity threshold of 630 P, the reaction is terminated. The remaining steps and parameters are similar to those in Example 1.

[0262] Comparative Example 3:

[0263] The difference between this comparative example and Example 1 is as follows: In step S1, when the temperature difference of the material is ≤ 1 °C and the temperature is raised to 65 °C, a part of the initiator is added, and the proportion of this part of the initiator in the total amount of the initiator is 90%. The viscosity of the material is monitored in real time. When the viscosity of the material reaches the first viscosity threshold of 450 P, the remaining 10% of the initiator is added; when the viscosity of the material reaches the second viscosity threshold of 560 P, the reaction is terminated. The remaining steps and parameters are similar to those in Example 1.

[0264] Comparative Example 4:

[0265] The difference between this comparative example and Example 1 is as follows: In step S3, the amount of ammonia required is calculated according to 2.0 mg of ammonia being introduced into every 1 kg of the polymerization solution; the remaining steps and parameters are similar to those in Example 1.

[0266] Comparative Example 5:

[0267] The difference between this comparative example and Example 1 is as follows: In step S3, the amount of ammonia required is calculated according to 14.0 mg of ammonia being introduced into every 1 kg of the polymerization solution; the remaining steps and parameters are similar to those in Example 1.

[0268] Comparative Example 6:

[0269] The difference between this comparative example and Example 1 lies in: In step S2, the difference between the used single-removing device and the Type A single-removing device is that the area of the perforated partition plate along the horizontal direction (hereinafter referred to as the horizontal perforated partition plate) of each layer accounts for 50-79% of the cross-sectional area of the tank body at the position of this layer, and an inclined baffle is provided on each layer of the horizontal perforated partition plate. The included angle between the inclined baffle and the horizontal perforated partition plate is 10°-60°. The holes on the horizontal perforated partition plate are within the vertical projection range of the inclined baffle, and the connection line between the inclined baffle and the horizontal perforated partition plate is parallel to the chord corresponding to the two end points of the arc on the horizontal perforated partition plate; the remaining steps and parameters are similar to those in Example 1.

[0270] Table 1 Test results of examples and comparative examples

[0271]

[0272]

[0273] Test group for precursor yarn and carbon fiber preparation (corresponding to S4 to S7)

[0274] The spinning solutions corresponding to Example 1 and Example 4 in the spinning solution test group were respectively selected for the following experiments, that is, five precursor yarns / carbon fibers were obtained in each group of experiments, totaling ten.

[0275] Precursor yarn / carbon fiber 1

[0276] The spinning solution prepared in Example 1 was used.

[0277] S4: The flow rate of the liquid introduced into the inner ring of the spinneret is 200 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 70%; the concentration of dimethyl sulfoxide in the coagulation liquid is controlled at 75%, and the temperature of the coagulation liquid is controlled at 35°C; the draw ratio in the coagulation liquid is 1.10 times;

[0278] S5: The flower roll type water washing method is adopted for water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45°C, a draw of 1.02 times is applied. When the water washing temperature > 45°C, a draw of 1.04 times is applied;

[0279] The number of water washing stages is 16. The first stage is set at 30 degrees, and each stage of water washing increases by 2 degrees step by step. The 16-stage water washing is 60 degrees;

[0280] S6: Four-stage hot drawing is adopted. The first stage is at 70 degrees with a draw of 1.1 times; the second stage is at 80 degrees with a draw of 1.3 times; the third stage is at 90 degrees with a draw of 1.4 times; the fourth stage is at 95 degrees with a draw of 1.5 times; and then the finished precursor yarn 1 is obtained through oiling, drying, and steam drawing;

[0281] S7: The precursor yarn is made into carbon fiber through processes such as constant tension wire drawing, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and wire winding.

[0282] Precursor yarn / carbon fiber 2

[0283] Use the spinning solution prepared in Example 1.

[0284] S4: The flow rate of the liquid introduced into the inner ring of the spinneret is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulating liquid is controlled at 78%, and the temperature of the coagulating liquid is controlled at 40°C; the draw ratio in the coagulating liquid is 1.10 times.

[0285] S5: The water washing method uses a flower roll type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45°C, a draw ratio of 1.03 times is applied; when the water washing temperature > 45°C, a draw ratio of 1.05 times is applied.

[0286] The number of water washing stages is 16. The first stage is set at 45 degrees, and each stage of water washing increases by 2 degrees step by step. The 16th stage of water washing is 75 degrees.

[0287] S6: The hot drawing is carried out in 4 stages. The first stage is at 75 degrees with a draw ratio of 1.15 times; the second stage is at 85 degrees with a draw ratio of 1.2 times; the third stage is at 90 degrees with a draw ratio of 1.3 times; the fourth stage is at 95 degrees with a draw ratio of 1.4 times; then the finished raw silk 2 is obtained through oiling, drying, and steam drawing.

[0288] S7: The raw silk is made into carbon fiber through processes such as constant tension wire drawing, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and wire winding.

[0289] Raw silk / carbon fiber 3

[0290] Use the spinning solution prepared in Example 1.

[0291] S4: The flow rate of the liquid introduced into the inner ring of the spinneret is 200 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 70%; the concentration of dimethyl sulfoxide in the coagulating liquid is controlled at 75%, and the temperature of the coagulating liquid is controlled at 35°C; the draw ratio in the coagulating liquid is 1.10 times.

[0292] S5: The water washing method uses a flower roll type water washing, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45°C, a draw ratio of 1.02 times is applied; when the water washing temperature > 45°C, a draw ratio of 1.04 times is applied.

[0293] The number of water washing stages is 16. The first stage is set at 35 degrees, and each stage of water washing increases by 2 degrees step by step. The 16th stage of water washing is 75 degrees.

[0294] S6: The hot drawing is carried out in 6 stages. The first stage is at 75 degrees with a draw ratio of 1.1 times; the second stage is at 80 degrees with a draw ratio of 1.15 times, the third stage is at 85 degrees with a draw ratio of 1.15 times, the fourth stage is at 90 degrees with a draw ratio of 1.25 times, the fifth stage is at 95 degrees with a draw ratio of 1.25 times, and the sixth stage is at 98 degrees with a draw ratio of 1.3 times; then the finished raw silk 3 is obtained through oiling, drying, and steam drawing.

[0295] S7: The raw silk is made into carbon fiber through processes such as unwinding with constant tension, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and winding.

[0296] Raw silk / carbon fiber 4 (comparative example)

[0297] The spinning solution prepared in Example 1 is used.

[0298] S4: The flow rate of the liquid introduced into the inner ring of the spinneret is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulation liquid is controlled at 78%, and the temperature of the coagulation liquid is controlled at 40°C; the draw ratio in the coagulation liquid is 1.10 times.

[0299] S5: The water washing method uses a flower roll type water wash, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45°C, a draw ratio of 1.03 times is applied, and when the water washing temperature > 45°C, a draw ratio of 1.05 times is applied.

[0300] The number of water washing stages is 10, each stage of water washing is at 65 degrees, and the draw ratio for each stage of water washing is 1.03 times.

[0301] S6: The hot drawing is carried out in 4 stages. The first stage is at 75 degrees with a draw ratio of 1.15 times; the second stage is at 85 degrees with a draw ratio of 1.4 times; the third stage is at 90 degrees with a draw ratio of 1.3 times; the fourth stage is at 95 degrees with a draw ratio of 1.4 times. Then, the finished raw silk 4 is obtained through oiling, drying, and steam drawing.

[0302] S7: The raw silk is made into carbon fiber through processes such as unwinding with constant tension, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and winding.

[0303] Raw silk / carbon fiber 5 (comparative example)

[0304] The spinning solution prepared in Example 1 is used.

[0305] S4: The flow rate of the liquid introduced into the inner ring of the spinneret is 500 L / h, and the mass fraction of dimethyl sulfoxide in the inner ring liquid is 75%; the concentration of dimethyl sulfoxide in the coagulation liquid is controlled at 78%, and the temperature of the coagulation liquid is controlled at 40°C; the draw ratio in the coagulation liquid is 1.10 times.

[0306] S5: The water washing method uses a flower roll type water wash, and the water flow direction is countercurrent to the fiber direction. When the water washing temperature ≤ 45°C, a draw ratio of 1.03 times is applied, and when the water washing temperature > 45°C, a draw ratio of 1.05 times is applied.

[0307] The number of water washing stages is 10, each stage of water washing is at 65 degrees. The draw ratio for each stage of water washing is 1.03 times.

[0308] S6: The hot drawing is carried out in 4 stages. The first stage is at 75 °C with a draw ratio of 1.4 times; the second stage is at 85 °C with a draw ratio of 1.4 times; the third stage is at 90 °C with a draw ratio of 1.2 times; the fourth stage is at 95 °C with a draw ratio of 1.1 times. Then, through oiling, drying, and steam drawing, the finished raw silk 5 is obtained.

[0309] S7: The raw silk is made into carbon fiber through processes such as constant-tension wire drawing, pre-oxidation, low-temperature carbonization, high-temperature carbonization, electrolysis, sizing, drying, and wire winding.

[0310] For the raw silk / carbon fiber 6 - 10, except for using the spinning solution prepared in Example 4, the other parameters are the same as those of the raw silk / carbon fiber 1 - 5, namely 1-6, 2-7, 3-8, 4-9, 5-10.

[0311] Table 2 Test results of the performance of the raw silk and carbon fiber in the preparation test group of the raw silk and carbon fiber

[0312]

[0313]

[0314] * The evaluation of the hole-type defects is based on the observation results of an electron microscope at a magnification of 2000 times.

[0315] In the raw silk 4 and 9, due to the relatively low water washing temperature and the absence of gradient heating and increasing draw ratio, the residual amount of dimethyl sulfoxide is relatively high, resulting in a small amount of hole defects in the elements, and further leading to a decrease in the strength of the raw silk and carbon fiber.

[0316] In the raw silk 5 and 10, on the one hand, the water washing parameters are poor, and on the other hand, due to the hot water drawing step not being operated according to the gradual increase in temperature and the increase in draw ratio, fuzz is generated after the first two stages of drawing, and there is a phenomenon of roll entanglement. The performance of the raw silk and carbon fiber has all decreased.

[0317] In summary, the raw silk / carbon fiber 1, 2, 3, 6, 7, and 8 all have good comprehensive performance. The degree of orientation of the raw silk provided by the present invention is ≥93.0%, and the strength of the raw silk is ≥7.5 cN / dtex; the elastic modulus of the carbon fiber is 320 - 340 GPa, the draw strength > 6100 MPa, the residual amount of dimethyl sulfoxide ≤ 320 ppm, and there are no obvious defects observed by an electron microscope at a magnification of 2000 times.

[0318] The above is only a preferred specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing high-strength medium-modulus carbon fiber, characterized in that: The specific steps include: S1: adding materials including acrylonitrile, comonomer and solvent into a polymerization device and adjusting the target molecular weight of the acrylonitrile-based polymerization liquid; S2: performing a single removal treatment on the acrylonitrile-based polymer solution meeting the target molecular weight; S3: performing an ammoniation treatment on the acrylonitrile-based polymer solution after the removal of the monomers to obtain a spinning solution; S4: the spinning solution is passed through a spinning spinneret and then enters a coagulation liquid bath for coagulation and drawing to obtain primary fibers; S5: washing the spun fiber with water using a multi-stage water washing process with gradually increasing temperature; S6: using a multi-stage drawing process, the washed fiber is subjected to hot water drawing, and then cooled and treated to obtain a densified raw fiber; S7: The densified raw yarn is made into high-strength medium-modulus carbon fiber.

2. The preparation method according to claim 1, characterized in that: In step S1, the timing of adding the remaining initiator after the polymerization is started and the timing of terminating the reaction are determined according to the viscosity change of the material, and the target molecular weight of the acrylonitrile-based polymerization liquid is regulated by controlling the material temperature and the proportion of the remaining initiator in the total amount of initiators.

3. The preparation method according to claim 2, characterized in that: When the viscosity of the material reaches a first viscosity threshold, the remaining initiator is added, and when the viscosity of the material reaches a second viscosity threshold, the reaction is terminated; the first viscosity threshold is 200P~400P; and / or the second viscosity threshold is 600P~1000P; the remaining initiator accounts for 20% to 40% of the total amount of initiator.

4. The preparation method according to claim 1, characterized in that: The order cancellation process in step S2 is as follows: The polymerization liquid exchanges gas and liquid with the solvent vapor flowing upstream through multiple layers of perforated partitions. At each layer of perforated partitions, the polymerization liquid is divided into two parts: one part of the polymerization liquid is spread on the perforated partitions to form a thin liquid layer and flows downward through the holes on the perforated partitions, and the other part of the polymerization liquid flows downward from the suspended end on the side of the perforated partition.

5. The preparation method according to claim 4, characterized in that: In step S2, the liquid inlet flow rate Q1 of the acrylonitrile-based polymerization liquid entering the single-removal device and the gas inlet flow rate Q2 of the solvent vapor entering the single-removal device satisfy: Q2 ≥ k × Q1 × m × α × 1000 Among them, the unit of Q1 is m 3 / h, the unit of Q2 is L / h, m is the mass percentage of residual monomers in the carbon fiber polymerization liquid; α is the flow coefficient of solvent vapor, and the value range of α is 1.0-1.2; k is the proportional coefficient, and the value range of k is 1.5-1.

9.

6. The preparation method according to claim 1, characterized in that: In the ammoniation treatment in step S3, the mass M of ammonia gas required to be introduced per 1 kg of polymerization liquid is determined according to the flow rate Q3 of the polymerization liquid and the following relationship: M = Q3 × n; wherein the unit of M is mg and the unit of Q3 is m 3 / h, the value range of n is 1.25~3.

0.

7. The preparation method according to claim 1, characterized in that: In step S4, the coagulated filaments are drawn during the coagulation bath process, and the drawing ratio is 1.01 to 1.20 times.

8. The preparation method according to claim 1, characterized in that: In step S5, flower roller type water washing is adopted, and stretching distribution is performed during the water washing process. When the water washing temperature is ≤45°C, 1.01 to 1.03 times of stretching is applied; when the water washing temperature is greater than 45°C, 1.02 to 1.05 times of stretching is applied; wherein, the temperature and stretching multiple of the next water washing section are not less than the temperature and stretching multiple of the previous water washing section.

9. The preparation method according to claim 1, characterized in that: In step S6, the hot water temperature is ≥70°C, and the total hot water drawing ratio is 2 to 4 times; the hot water drawing is divided into 2 to 6 sections, and the hot water temperature and the drawing ratio of each section gradually increase.

10. A high-strength medium modulus carbon fiber, characterized in that: The carbon fiber is prepared by the preparation method according to any one of claims 1 to 9; The elastic modulus of the carbon fiber is 320-340 GPa, the tensile strength is greater than 6100 MPa, the residual content of dimethyl sulfoxide is less than or equal to 320 ppm, and no obvious defects are observed under an electrical microscope at a magnification of 2000.

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