Preparation method of high-modulus polyacrylonitrile-based carbon fiber precursor

Abstract

The invention relates to the technical field of polyacrylonitrile-based carbon fibers, and discloses a preparation method of a high-modulus polyacrylonitrile-based carbon fiber precursor, and the production method comprises the following steps: dynamic mixing, swelling, heating dissolution, vacuum defoaming, secondary filtration, spinning and post-treatment. The preparation method provided by the invention solves the problem that polyacrylonitrile powder is not completely dissolved when the polyacrylonitrile powder is dissolved to prepare the stock solution, the solid content and stability of the spinning stock solution are improved, the spinning stock solution without bubbles and gel is prepared, the quality of the polyacrylonitrile-based carbon fiber precursor is further improved, and industrial production of the high-modulus polyacrylonitrile precursor is realized.

Description

Technical Field

[0001] This invention relates to the field of polyacrylonitrile-based carbon fiber technology, and specifically to a method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor. Background Technology

[0002] High-modulus carbon fibers (such as M40J and M60J) are widely used in aerospace, high-end industry, and defense due to their excellent mechanical properties (high modulus, high strength, and low density) and thermal stability. As the core precursor of carbon fibers, the quality of polyacrylonitrile (PAN) precursor fiber directly determines the final performance of the carbon fiber. Currently, the industrial production of high-modulus carbon fibers mainly relies on the preparation of high-performance PAN precursor fiber, and the quality of PAN precursor fiber is highly dependent on the uniformity, solubility, and degassing effect of the spinning solution.

[0003] Traditional methods for preparing PAN spinning solutions can be divided into a one-step homogeneous solution polymerization method and a two-step heterogeneous polymerization method. Among these, the two-step heterogeneous polymerization method has become the mainstream process due to its advantages such as low cost, high single-reactor capacity, and high process flexibility. However, existing technologies still face the following bottlenecks in the preparation of high-modulus carbon fibers:

[0004] 1) Insufficient dissolution efficiency and uniformity of PAN spinning solution

[0005] In the traditional two-step process, the dissolution of PAN powder requires three stages: swelling, dispersion, and dissolution. Due to the rigid structure and high crystallinity of the PAN molecular chain, its dissolution kinetics are slow. In particular, large particles of powder are difficult to swell sufficiently in conventional solvents (such as DMAC and DMSO), which can easily lead to: 1) Incompletely dissolved PAN particles forming microgels or undissolved substances in the spinning solution, resulting in a high breakage rate and many internal defects in the raw yarn; 2) Slow solvent dissolution rate, which is difficult to meet the requirements for preparing solutions with a solid content >20%; 3) DMSO has a freezing point of 18℃, which can easily cause material agglomeration and blockage of equipment channels in low-temperature environments.

[0006] 2) Degassing process has high energy consumption and poor effect.

[0007] Traditional static degassing takes up to tens of hours and has limited effectiveness on high-solids-content raw materials; vacuum degassing equipment is complex, energy-intensive, and difficult to completely eliminate microbubbles, leading to increased spinning breakage rate.

[0008] 3) Distillation separation of mixed solvents (such as DMAC / DMSO) is difficult and the recovery cost is high.

[0009] The aforementioned incompletely dissolved PAN particles or microgels can cause internal defects in the precursor fiber, forming stress concentration points during carbonization and significantly reducing the modulus and strength of the final carbon fiber. Incomplete degassing leads to increased fiber porosity, further deteriorating the mechanical properties of the carbon fiber.

[0010] Patent CN109825891 discloses a process for stepwise swelling and dissolution of ultra-high molecular weight polyethylene powder using a twin-screw extruder. However, when this technology is directly transferred to the PAN system, there are limitations: the rigid structure and high crystallinity of the PAN molecular chain lead to slow dissolution kinetics and difficult solvent diffusion, which easily forms undissolved particles or microgels.

[0011] Patent CN110699762A proposes to complete the dissolution and degassing of PAN slurry in one step using a twin-screw extruder. However, the following problems exist in practical applications: PAN powder is difficult to fully swell within a short residence time (1-30 minutes), resulting in incomplete dissolution; the solvent system is not optimized and still relies on DMAC or mixed solvents, which cannot solve the problems of microgelation and solvent recovery; the degassing efficiency is insufficient, resulting in a high residual rate of bubbles in the original solution (>5%), which affects the uniformity of the precursor fibers. Summary of the Invention

[0012] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor. This method solves the problem of incomplete dissolution of polyacrylonitrile powder during the preparation of the spinning solution, improves the solid content and stability of the spinning solution, prepares a bubble-free and gel-free spinning solution, further improves the quality of polyacrylonitrile-based carbon fiber precursor, and enables large-scale continuous production, meeting the conditions for industrialization.

[0013] To achieve the above objectives, the technical solution of the present invention is: a method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor, the production method comprising the following steps: dynamic mixing, swelling, heating and dissolving, vacuum degassing, secondary filtration, spinning, and post-treatment;

[0014] The dynamic mixing method involves accurately measuring the mass of polyacrylonitrile powder and solvent. The polyacrylonitrile powder is weighed using a differential pressure electronic scale, and the solvent is measured using a liquid mass flow meter 105. After the solvent is cooled to 10-18℃, the solvent and polyacrylonitrile powder are continuously fed into a single-stage twin-screw mixer for helical mixing to produce a slurry, which is then continuously discharged into a slurry tank 106. The temperature inside the cylinder of the single-stage twin-screw mixer does not exceed 20℃, and the material travels within the cylinder for 5-15 minutes.

[0015] The swelling and heating dissolution method is as follows: the temperature inside the slurry tank 106 is controlled at 10-20℃, and the slurry is stirred at 50-100 rpm to ensure that the solvent and polyacrylonitrile powder are in full contact but do not dissolve. The swelling time of the slurry in the slurry tank 106 is 30-120 min. The stirred and mixed slurry is continuously transported to a high-efficiency tubular heat exchanger. After being heated and dissolved by the high-efficiency tubular heat exchanger, the initial stock solution is obtained and continuously discharged to a multi-stage screw vacuum degassing device.

[0016] The vacuum degassing method involves controlling the vacuum degree and temperature of different cylinders in a multi-stage screw vacuum degassing device to vacuum degas the initial raw liquid and evaporate some of the solvent, thereby stabilizing the solid content of the initial raw liquid and continuously discharging it to the raw liquid buffer tank.

[0017] The secondary filtration method involves passing the raw liquid through a first filter and a second filter in sequence to obtain the secondary filtered raw liquid.

[0018] The raw solution after secondary filtration is spun and post-treated to produce high-modulus polyacrylonitrile-based carbon fiber precursor.

[0019] Further; the solvent is a mixed solution of dimethyl sulfoxide (DMSO) and demineralized water (DW); the amount of demineralized water added is 0.5-5 wt%, and the solid content of the slurry obtained by dynamic mixing is 15-20 wt%.

[0020] Furthermore, the multi-stage screw vacuum degassing device is a vertical or horizontal multi-stage twin-screw extruder. In the multi-stage twin-screw extruder, the vacuum degree of the first stage cylinder is 90-98 kPa and the temperature is 70-85℃, while the vacuum degree of the second and third stages cylinders is 80-90 kPa and the temperature is 60-80℃. By adjusting the temperature and vacuum degree, the solid content of the initial stock solution is controlled to be 17%-23%.

[0021] Furthermore, in the secondary filtration, the first filter is a plate and frame or candle filter 114 with a filtration accuracy of 5-15μm; the second filter is a disc filter 116 with a filtration accuracy of 1-5μm.

[0022] Furthermore, the raw solution after secondary filtration is wet-spun. The raw solution is spun through a spinneret and solidified in a coagulation bath. Then, it is drawn in the coagulation bath to obtain nascent precursor fibers. The nascent precursor fibers undergo post-treatment: water washing and drawing, oiling, drying and densification, steam drawing, and heat setting to obtain high-modulus polyacrylonitrile-based carbon fiber precursor fibers.

[0023] Furthermore, the spinneret assembly is a spinneret with 3k-12k orifices, which is immersed 10-25cm below the surface of the solution in the coagulation bath. The raw solution is spun in the coagulation bath solution and solidified in the coagulation bath to obtain nascent fiber filaments. The coagulation bath is a mixture of dimethyl sulfoxide and demineralized water, with a dimethyl sulfoxide concentration of 40-70wt%, a coagulation bath temperature of 40-70℃, and a fiber tow draw ratio of 0.3-0.8 times in the coagulation bath.

[0024] Furthermore, the water washing and stretching is a multi-stage water washing and stretching process, with a water washing and stretching temperature of 45-100℃ and a total stretching ratio of 2-4 times.

[0025] Furthermore, the oiling process involves applying oil to the raw yarn after washing and stretching. The oil used is an organosilicone oil agent with a concentration of 2-4%, an oiling temperature of 20-35℃, and a target oiling rate of 0.5-1.2%.

[0026] Furthermore, the drying and densification process employs multi-stage hot roller drying at a temperature of 100-180℃. During hot roller drying, the filament tow is drawn up to 1-1.5 times. Before steam drawing, a preheating chamber is set at a temperature not lower than 60℃ to preheat the filament tow. The filament tow is kept at a constant temperature and tension before entering the steam drawing chamber. In a saturated steam environment, the dried filament is steam drawn up to 140-180℃ at a pressure of 0.3-0.6 MPa, with a steam drawing up to 2-5 times.

[0027] The beneficial effects of this invention are:

[0028] 1) The method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor of the present invention involves preparing a spinning solution by dynamically mixing polyacrylonitrile powder and solvent, low-temperature stirring and swelling, heating and dissolving, multi-stage degassing and quality improvement, and two-stage filtration. The spinning solution is then used for wet spinning. The polyacrylonitrile powder can fully swell in the solvent, eliminating the problems of agglomeration and incomplete dissolution of polyacrylonitrile powder in the solvent process, effectively improving the uniformity and stability of the solution, and significantly improving the quality of the obtained polyacrylonitrile-based carbon fiber precursor, thus realizing the industrial production of high-modulus polyacrylonitrile precursor.

[0029] 2) High-modulus carbon fiber precursors are prepared by wet spinning. The diffusion rate is slow. By controlling the coagulation and drawing processes in wet spinning, the diameter, crystallinity and microstructure of the fibers can be effectively controlled, so that the fibers formed have good uniformity and high orientation. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of the preparation of the raw solution in the production of high-modulus polyacrylonitrile-based carbon fiber precursor of the present invention;

[0031] Figure 2 This is a schematic diagram of the spinning preparation process in the production of high-modulus polyacrylonitrile-based carbon fiber precursor of the present invention.

[0032] In the diagram: 101. Powder weighing scale; 102. Single-stage twin-screw mixer; 103. Plate heat exchanger; 104. Automatic control valve; 105. Mass flow meter; 106. Slurry tank; 107. Slurry transfer pump; 108. Tubular heat exchanger; 109. Vacuum pump I; 110. Three-stage screw vacuum degassing device; 111. Vacuum pump II; 112. Raw material buffer tank; 113. Raw material transfer pump; 114. Candle filter. ; 115. Feed metering pump; 116. Disc filter; 201. Spinneret assembly; 202. Coagulation bath; 203. Guide roller; 204. Washing and drawing tank; 205. Washing circulation pump; 206. Washing heater; 207. Oil storage tank; 208. Oil circulation pump; 209. Oil heater; 210. Oiling tank; 211. Front heating roller; 212. Steam drawing box; 213. Rear heating roller; 214. Take-up machine. Detailed Implementation

[0033] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention are now described.

[0034] Example 1:

[0035] like Figure 1-2 As shown, a method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor is as follows:

[0036] (1) Dynamic mixing

[0037] The solvent is metered by mass flow meter 105 and its flow rate is regulated by automatic control valve 104. Then, it is cooled to 12°C by plate heat exchanger 103. At the same time, the polyacrylonitrile powder is metered by powder metering scale 101 and fed into a single-stage twin-screw mixer 102 along with the solvent. The mixture is then rotated and mixed to produce a slurry with a polyacrylonitrile content of 18 wt%. The slurry is then continuously fed into slurry tank 106.

[0038] During the mixing process, the mixing speed is controlled at 600 rpm, and the material runs in the cylinder for 8 minutes. At the same time, during the mixing process, circulating water at a temperature of 7°C is used to cool the cylinder of the single-stage twin-screw mixer 102, and the temperature inside the cylinder is controlled at 12°C.

[0039] The solvent is a mixed solution of dimethyl sulfoxide (DMSO) and deionized water (DW); the amount of deionized water added to the solvent is 2 wt%; the purity of the DMSO used is greater than 99.9 wt%. By adding deionized water, the solidification temperature of the slurry is reduced, and the dissolving power of DMSO is also reduced, thus preventing the premature dissolution of polyacrylonitrile powder and effectively avoiding the "agglomeration phenomenon" and "pole climbing phenomenon" caused by dissolving polyacrylonitrile powder in the prior art.

[0040] (2) Swelling

[0041] The slurry tank 106 receives the slurry obtained by dynamic mixing. The temperature inside the slurry tank 106 is controlled at 12°C. The slurry tank 106 is continuously stirred at a stirring speed of 90 rpm to maintain swelling for 80 minutes. Then, it is transported to the tubular heat exchanger 108 by a transfer pump, heated and dissolved to obtain the initial stock solution, and continuously discharged. The dissolved stock solution is sampled and observed under a microscope. No gel or agglomeration is found, indicating complete dissolution.

[0042] The temperature of the tubular heat exchanger 108 is controlled at 80℃, and the residence time of the material is 2 minutes.

[0043] The discharge rate, discharge volume, and material residence time of the slurry in the slurry tank 106 can be adjusted according to the actual production situation, thereby ensuring the stability of continuous production.

[0044] (3) Vacuum degassing

[0045] The fully dissolved initial stock solution is continuously fed into a three-stage screw vacuum degassing unit 110. The vacuum level of the first stage cylinder of the three-stage screw vacuum degassing unit 110 is controlled at 95 kPa and the temperature at 77°C; the vacuum level of the second and third stages is controlled at 86 kPa and the temperature at 72°C. The residence time of the material in the three-stage screw vacuum degassing unit 110 is 1.8 min. After extrusion mixing and vacuum degassing of the initial stock solution, the resulting stock solution is continuously discharged into the stock solution buffer tank 112. The discharge rate, discharge volume, and material residence time are adjusted according to actual production conditions for subsequent spinning. When the stock solution enters the stock solution buffer tank 112, it flows along the inner wall of the tank to avoid the regeneration of bubbles.

[0046] The raw liquid at the outlet of the three-stage screw vacuum degassing unit 110 has a rotational viscosity of 80,000 cP at 50°C, a polyacrylonitrile content and solid content of 19.5 wt%, and a water content of 1.6 wt%.

[0047] (4) Secondary filtration

[0048] The raw liquid in the raw liquid buffer tank 112 is transported to the candle filter 114 by the raw liquid transfer pump 113, and then to the disc filter 116 by the raw liquid metering pump 115. After two filtrations, it is transported to the spinning device.

[0049] The motor of the raw liquid transfer pump 113 and the motor of the raw liquid metering pump 115 are interlocked to maintain the same material conveying volume between the raw liquid transfer pump 113 and the raw liquid metering pump 115, thus ensuring stable raw liquid delivery.

[0050] Among them, the candle filter 114 has a filtration accuracy of 15μm, and the disc filter 116 has a filtration accuracy of 1μm.

[0051] The two-stage filtration process can further improve the uniformity and stability of the solution, thereby enhancing its spinnability.

[0052] (5) Spinning

[0053] The raw solution discharged from the disc filter 116 enters the coagulation bath 202 of the spinning device for wet spinning. The raw solution is spun in the coagulation bath 202 solution through the spinneret 201. After the filament bundle is solidified and shaped in the coagulation bath 202, it is drawn in the coagulation bath 202 to obtain the nascent raw filament.

[0054] The spinneret 201 is a spinneret with 3k holes, and the spinneret is immersed 10cm below the liquid surface of the solution in the coagulation bath 202.

[0055] The solution in coagulation bath 202 is a mixture of DMSO and DW; the concentration of DMSO in the coagulation solution is 45 wt%, and the temperature of coagulation bath 202 is maintained at 66℃.

[0056] The draw ratio of the filament bundle in coagulation bath 202 is 0.5.

[0057] (6) Post-processing

[0058] After the nascent precursor fibers are washed, stretched, oiled, dried and densified, steam stretched and heat-set, high-modulus polyacrylonitrile-based carbon fiber precursor fibers are obtained.

[0059] ① Water washing and drawing: The water washing and drawing process consists of 9 stages, with 9 water washing and drawing tanks 204 connected in series, numbered P1 to P9. Among them, the water washing and drawing temperature range of P1-P6 is 45-60℃, with the temperature increasing sequentially; the water washing and drawing temperature of P7 is 70℃, the water washing and drawing temperature of P8 is 80℃, and the water washing and drawing temperature of P9 is 90℃.

[0060] As the water washing and stretching temperature increases, the stretching ratio of the P1-P9 water washing and stretching tanks 204 also increases. In this embodiment, the total stretching ratio of the water washing and stretching is 3.5 times.

[0061] In the P1-P7 water washing and stretching grooves 204, three guide rollers 203 are used for stretching; in the P8 and P9 stretching grooves, five guide rollers 203 are used for stretching.

[0062] ② Oiling: The raw yarn after washing and stretching is oiled using oiling tank 210. The oil used is an organosilicone oil agent with a concentration of 3% and an oiling temperature of 30℃. The target oiling rate is 1.2%.

[0063] ③ Drying and densification: Four sets of front heating rollers 211 (a total of 8) with a temperature range of 150-180℃ are used to dry the oiled raw yarn. The yarn draw ratio is 1.5 times, and the temperature of the four sets of front heating rollers 211 increases sequentially.

[0064] ④ Steam drawing: The dried and densified raw yarn is introduced into a steam drawing box 202 with a pressure of 0.4 MPa and steam drawing is carried out in a saturated steam environment with a steam temperature of 160℃ and a drawing ratio of 3.

[0065] ⑤ Finally, after the yarn bundle passes through a set of two rear hot rollers 213 at 100℃ for heat setting, it is wound up.

[0066] The polyacrylonitrile precursor fiber obtained in this embodiment has a single filament fineness of 0.8 dtex and a single filament strength of 9.3 cN / dtex. The precursor fiber obtained above is carbonized to obtain a tensile strength of 5120 MPa and an elastic modulus of 395 GPa. The strength and modulus are higher than the market standard for M40J products.

[0067] Furthermore, this embodiment also provides a high-modulus polyacrylonitrile-based carbon fiber precursor production device that works in conjunction with the production method. Specifically, the inlet of the plate heat exchanger 103 is connected to the solvent feed pipeline, and the outlet of the plate heat exchanger 103 is connected to the solvent inlet of the single-stage twin-screw mixer 102. A mass flow meter 105 and an automatic control valve 104 are sequentially installed on the solvent feed pipeline to cool the solvent to a predetermined temperature. After metering, the solvent is fed into the single-stage twin-screw mixer 102 at a predetermined flow rate.

[0068] The outlet of the powder metering scale 101 is connected to the powder inlet of the single-stage twin-screw mixer 102. After accurately metering the polyacrylonitrile powder, it is fed into the single-stage twin-screw mixer 102.

[0069] A single-stage twin-screw mixer 102 is used to dynamically grind and mix solvent and polyacrylonitrile powder to prepare a slurry. The single-stage twin-screw mixer 102 includes a cylinder, and a stirring screw is installed inside the cylinder. The screw has an L / D ratio of 40.

[0070] The discharge port of the single-stage twin-screw mixer 102 is connected to the inlet of the slurry tank 106, and is used to feed the prepared slurry into the slurry tank 106.

[0071] The slurry tank 106 is equipped with an automatic stirrer to agitate the slurry inside the tank during the swelling process, so as to ensure full swelling.

[0072] The outlet of the slurry tank 106 is connected to the inlet of the tubular heat exchanger 108 via the slurry conveying pump 107. The outlet of the tubular heat exchanger 108 is connected to the inlet of the three-stage screw vacuum degassing device 110. This is used to heat the material in the slurry tank 106 and then feed it to the three-stage screw vacuum degassing device 110 for degassing.

[0073] The three-stage screw vacuum degassing device 110 (screw L / D is 60) is equipped with vacuum pump I 109 and vacuum pump II 111 to maintain the vacuum state of the three-stage screw vacuum degassing device 110.

[0074] The outlet of the three-stage screw vacuum degassing device 110 is connected to the raw liquid buffer tank 112, and is used to feed the prepared raw liquid into the raw liquid buffer tank 112.

[0075] The outlet of the raw liquid buffer tank 112 is connected to the candle filter 114 (primary filter) via the raw liquid transfer pump 113. The outlet of the candle filter 114 is connected to the disc filter 116 (secondary filter) via the raw liquid metering pump 115, which is used to perform secondary filtration of the raw liquid.

[0076] The disc filter 116 is connected to the spinneret 201 of the spinning device and is used to spin the raw liquid that has undergone secondary filtration.

[0077] The spinneret 201 is fixedly immersed in a coagulation bath 202 containing coagulation liquid. A guide roller 203 is provided above the liquid surface of the coagulation bath 202 for shaping and drawing the nascent filaments obtained by spinnereting in the coagulation bath 202.

[0078] Nine washing and drawing tanks 204 (P1-P9) are connected in series after the coagulation bath 202. In the washing and drawing tanks 204 P1-P7, three guide rollers 203 are used to draw the filament bundle; in the drawing tanks P8 and P9, five guide rollers 203 are used to draw the filament bundle. At the same time, each washing and drawing tank 204 is equipped with a washing circulation pump 205 and a washing heater 206 to control the water temperature in each washing and drawing tank 204 to a predetermined value.

[0079] An oiling tank 210 is provided after the P9 water washing and stretching tank 204. The oiling tank 210 is equipped with an oil storage tank 207, an oil circulation pump 208, and an oil heater 209 to control the oil dosage and temperature in the oiling tank 210 to a predetermined value so as to apply oil to the filament bundle after water washing and stretching.

[0080] Four sets of front heating rollers 211 are installed after the oiling tank 210, with two front heating rollers in each set, for drying and densifying the oiled filament bundle.

[0081] A steam drawing box 202 is installed after the hot roller to perform steam drawing on the dried and densified filament bundle.

[0082] Two rear heating rollers 213 are installed after the steam drawing box 202, and a take-up machine 214 is installed after the rear heating rollers 213 for drying and taking up the filament bundle.

[0083] Example 2

[0084] like Figure 1-2 As shown, this embodiment provides a method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor, specifically as follows:

[0085] (1) Dynamic mixing

[0086] After being metered by mass flow meter 105, the solvent flow rate is regulated by automatic control valve 104 and then cooled to 15°C by plate heat exchanger 103. At the same time, polyacrylonitrile powder is metered by powder weighing scale 101 and fed into single-stage twin-screw mixer 102 along with the solvent for rotary mixing to produce a slurry with a polyacrylonitrile content of 16.2 wt%. The slurry is then continuously introduced into slurry tank 106.

[0087] During the mixing process, the mixing speed is controlled at 450 rpm, and the material runs in the cylinder for 10 minutes. At the same time, during the mixing process, circulating water at a temperature of 7°C is used to cool the cylinder of the single-stage twin-screw mixer 102, and the temperature inside the cylinder is controlled at 15°C.

[0088] The solvent is a mixed solution of DMSO and DW; the amount of demineralized water added to the solvent is 3 wt%; the purity of the DMSO used is greater than 99.9 wt%. By adding demineralized water, the solidification temperature of the slurry is reduced, and the solubility of dimethyl sulfoxide (DMSO) is also reduced, thus preventing the premature dissolution of polyacrylonitrile powder and effectively avoiding the "agglomeration phenomenon" and "pole climbing phenomenon" caused by dissolving polyacrylonitrile powder in the prior art.

[0089] (2) Swelling

[0090] The slurry tank 106 receives the slurry obtained by dynamic mixing. The temperature inside the slurry tank 106 is controlled at 15°C. The slurry tank 106 is continuously stirred at a stirring speed of 100 rpm to maintain swelling for 100 minutes. Then, it is transported to the tubular heat exchanger 108 by a transfer pump, heated and dissolved to obtain the initial stock solution, and continuously discharged. The dissolved stock solution is sampled and observed under a microscope. No gel or agglomeration is found, indicating complete dissolution.

[0091] The temperature of the tubular heat exchanger 108 is controlled at 83℃, and the residence time of the material is 2.5 min.

[0092] The discharge rate, discharge volume, and material residence time of the slurry in the slurry tank 106 can be adjusted according to the actual production situation, thereby ensuring the stability of continuous production.

[0093] (3) Vacuum degassing

[0094] The fully dissolved initial stock solution is continuously fed into a three-stage screw vacuum degassing unit 110 (screw L / D is 60). The vacuum level of the first stage cylinder of the three-stage screw vacuum degassing unit 110 is controlled at 98 kPa and the temperature at 83°C; the vacuum level of the second and third stages is controlled at 88 kPa and the temperature at 75°C. The residence time of the material in the three-stage screw vacuum degassing unit 110 is 2 minutes. After extrusion mixing and vacuum degassing of the initial stock solution, the resulting stock solution is continuously discharged into the stock solution buffer tank 112. The discharge rate, discharge volume, and material residence time are adjusted according to actual production conditions for subsequent spinning. When the stock solution enters the stock solution buffer tank 112, it flows along the inner wall of the tank to avoid the regeneration of bubbles.

[0095] The raw liquid at the outlet of the three-stage screw vacuum degassing unit 110 has a rotational viscosity of 80,000 cP at 50°C, a polyacrylonitrile content and solid content of 19.5 wt%, and a water content of 1.6 wt%.

[0096] (4) Secondary filtration

[0097] The raw liquid in the raw liquid buffer tank 112 is transported to the candle filter 114 by the raw liquid transfer pump 113, and then to the disc filter 116 by the raw liquid metering pump 115. After two filtrations, it is transported to the spinning device.

[0098] The motor of the raw liquid transfer pump 113 and the motor of the raw liquid metering pump 115 are interlocked to maintain the same material conveying volume between the raw liquid transfer pump 113 and the raw liquid metering pump 115, thus ensuring stable raw liquid delivery.

[0099] Among them, the candle filter 114 has a filtration accuracy of 5μm, and the disc filter 116 has a filtration accuracy of 1μm.

[0100] The secondary filtration step in this embodiment can further improve the uniformity and stability of the raw solution and enhance its spinnability.

[0101] (5) Spinning

[0102] The raw solution discharged from the disc filter 116 enters the coagulation bath 202 of the spinning device for wet spinning. The raw solution is spun in the coagulation bath 202 solution through the spinneret 201. After the filament bundle is solidified and shaped in the coagulation bath 202, it is drawn in the coagulation bath 202 to obtain the nascent raw filament.

[0103] The spinneret 201 is a spinneret with 3k holes, and the spinneret is immersed 8cm below the liquid surface of the solution in the coagulation bath 202.

[0104] The solution in coagulation bath 202 is a mixture of DMSO and DW; the concentration of DMSO in the coagulation solution is 55 wt%, and the temperature of coagulation bath 202 is maintained at 50℃.

[0105] The draw ratio of the filament bundle in coagulation bath 202 is 0.7.

[0106] (6) Post-processing

[0107] After the nascent precursor fibers are washed, stretched, oiled, dried and densified, steam stretched and heat-set, high-modulus polyacrylonitrile-based carbon fiber precursor fibers are obtained.

[0108] ① Water washing: The water washing and stretching is a 9-stage water washing and stretching process, with 9 water washing and stretching tanks 204 connected in series, P1-P9. Among them, the water washing and stretching temperature range of P1-P6 is 50-85℃, the water washing and stretching temperature of P7-P8 is 85-90℃, and the water washing and stretching temperature of P9 is 100℃.

[0109] As the water washing and stretching temperature increases, the stretching ratio of the P1-P9 water washing and stretching tanks 204 also increases. In this embodiment, the total stretching ratio of the water washing and stretching is 2.2 times.

[0110] In the P1-P7 water washing and stretching grooves 204, three guide rollers 203 are used for stretching; in the P8 and P9 stretching grooves, five guide rollers 203 are used for stretching.

[0111] ② Oiling: The raw yarn after washing and stretching is oiled using oiling tank 210; the oil used is an organosilicone oil agent, the oil concentration is 3%, the oiling temperature is 30℃, and the target oiling rate is 1.2%.

[0112] ③ Drying and densification: Four sets of front heating rollers 211 (a total of 8) at a temperature of 220℃ are used to dry the oiled raw yarn, and the yarn draw ratio is 1.5 times.

[0113] ④ Steam drawing: The dried and densified raw yarn is introduced into a steam drawing box 202 with a pressure of 0.5 MPa and steam drawing is carried out in a saturated steam environment with a steam temperature of 160℃ and a drawing ratio of 3.

[0114] ⑤ Finally, after the yarn bundle passes through a set of two rear hot rollers 213 at 100℃ for heat setting, it is wound up.

[0115] The polyacrylonitrile precursor fiber obtained in this embodiment has a single filament fineness of 0.91 dtex and a single filament strength of 8.6 cN / dtex. The precursor fiber obtained above is carbonized to obtain a tensile strength of 4388 MPa and an elastic modulus of 446 GPa. The strength and modulus are higher than the market standard M46J product.

[0116] Unless otherwise stated, all percentages used in this invention are mass percentages.

[0117] Finally, it should be noted that the above descriptions are merely preferred embodiments of the present invention and are not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor, characterized in that, The production method includes the following steps: dynamic mixing, swelling, heating and dissolving, vacuum degassing, secondary filtration, spinning, and post-treatment; The dynamic mixing method is as follows: after the solvent is cooled to 10-18℃, the solvent and polyacrylonitrile powder are continuously fed into a single-stage twin-screw mixer for spiral rotation mixing to produce slurry, which is then continuously discharged into the slurry tank 106. The swelling and heating dissolution method is as follows: the temperature inside the slurry tank 106 is controlled at 10-20℃, the slurry is stirred to ensure that the solvent and polyacrylonitrile powder are in full contact but do not dissolve, the stirred and mixed slurry is continuously transported to the high-efficiency tubular heat exchanger, and after being heated and dissolved by the high-efficiency tubular heat exchanger, the initial stock solution is obtained and continuously discharged to the multi-stage screw vacuum degassing device. The vacuum degassing method involves controlling the vacuum degree and temperature of different cylinders in a multi-stage screw vacuum degassing device to vacuum degas the initial raw liquid and evaporate some of the solvent, thereby stabilizing the solid content of the initial raw liquid and continuously discharging it to the raw liquid buffer tank. The secondary filtration method involves passing the raw liquid through a first filter and a second filter in sequence to obtain the secondary filtered raw liquid. The raw solution after secondary filtration is spun and post-treated to produce high-modulus polyacrylonitrile-based carbon fiber precursor.

2. The method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor according to claim 1, characterized in that: The solvent is a mixed solution of dimethyl sulfoxide and demineralized water; the amount of demineralized water added is 0.5-5 wt%, the solid content of the slurry obtained by dynamic mixing is 15-20 wt%, and the swelling time of the slurry in the slurry tank 106 is 30-120 min.

3. The method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor according to claim 1, characterized in that: The multi-stage screw vacuum degassing device is a multi-stage twin-screw extruder. In the multi-stage twin-screw extruder, the vacuum degree of the first stage cylinder is 90-98 kPa and the temperature is 70-85℃, while the vacuum degree of the second and third stages cylinders is 80-90 kPa and the temperature is 60-80℃.

4. The method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor according to claim 1, characterized in that: In the secondary filtration, the first filter is a plate and frame or candle filter 114 with a filtration accuracy of 5-15μm; the second filter is a disc filter 116 with a filtration accuracy of 1-5μm.

5. The method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor according to claim 1, characterized in that: The raw solution after secondary filtration is wet-spun. The raw solution is spun through a spinneret and formed in a coagulation bath. It is then drawn in the coagulation bath to obtain nascent precursor fibers. The nascent precursor fibers undergo post-treatment: water washing and drawing, oiling, drying and densification, steam drawing, and heat setting to obtain high-modulus polyacrylonitrile-based carbon fiber precursor fibers.

6. The method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor according to claim 5, characterized in that: The spinneret assembly is a spinneret with 3k-12k orifices. The coagulation bath is a mixture of dimethyl sulfoxide and demineralized water. The concentration of dimethyl sulfoxide is 40-70 wt%. The temperature of the coagulation bath is 40-70℃. The draw ratio of the filament bundle in the coagulation bath is 0.3-0.8 times.

7. The method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor according to claim 5, characterized in that: The water washing and stretching is a multi-stage water washing and stretching process, with a water washing and stretching temperature of 45-100℃ and a total stretching ratio of 2-4 times.

8. The method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor according to claim 5, characterized in that: The oiling process involves applying oil to the raw yarn after washing and stretching. The oil used is an organosilicone oil agent with a concentration of 2-4%, an oiling temperature of 20-35℃, and a target oiling rate of 0.5-1.2%.

9. The method for preparing high-modulus polyacrylonitrile-based carbon fiber precursor according to claim 5, characterized in that: The drying and densification process employs multi-stage hot roller drying at a temperature of 100-180℃. During hot roller drying, the filaments are drawn up to 1-1.5 times. Before steam drawing, a preheating chamber is set at a temperature of no less than 60℃ to preheat the filaments. The filaments are kept at a constant temperature and tension before entering the steam drawing chamber. In a saturated steam environment, the dried filaments are steam drawn up to 2-5 times.

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