A method and apparatus for preparing pbi high performance fiber spinning

Abstract

The application belongs to the technical field of high-performance fiber materials, and particularly discloses a method and device for preparing high-performance PBI fiber spinning. The application adopts a mixed solvent system containing phosphorus imidazole salt ionic liquid / DMAc, reduces the PBI dissolving temperature, and keeps a high characteristic viscosity retention rate; through electrostatic auxiliary wet spinning and gradient temperature coagulation forming processes, combined with modified nanoparticles, PBI fibers with high breaking strength and high limiting oxygen index are prepared; and through a solvent recovery process combining two-stage condensation recovery and vacuum rectification, the solvent recovery rate is high.

Description

Technical Field

[0001] This invention relates to the field of high-performance fiber materials technology, specifically to a method and apparatus for preparing PBI (polybenzimidazole) high-performance fiber spinning. Background Technology

[0002] Polybenzimidazole (PBI) fiber, due to its excellent high-temperature resistance, high moisture absorption, and superior mechanical stability, is considered an ideal material to replace asbestos and traditional flame-retardant fibers, and has broad application prospects in aerospace, fire protection, high-temperature filtration, and high-end industrial protection. Traditional PBI fiber preparation processes typically use DMAc as a solvent, which presents the following technical problems: Firstly, there are environmental and health concerns. DMAc is listed as a substance of very high concern under the EU REACH regulation due to its reproductive toxicity. Traditional processes have low solvent recovery rates (approximately 70-80%), compared to the over 90% recovery rate of this invention. This results in insufficient energy efficiency and environmental friendliness, requires the use of large quantities of organic solvents, leads to high costs for waste treatment, and poses significant environmental risks.

[0003] Secondly, there is the issue of spinning stability. PBI molecular chains are highly rigid and do not fully dissociate in traditional solvents. During spinning, the Taylor cones are unstable, easily leading to beading or breakage. The coefficient of variation of fiber diameter is generally greater than 8%, resulting in poor batch-to-batch consistency.

[0004] Third, the mechanical properties are insufficient. The breaking strength of PBI fibers prepared by traditional processes is only 2.0-2.5 cN / dtex, the modulus is low, there is a lack of nano-reinforcing phase to guide the orderly arrangement of molecular chains, the crystallinity is only 30-40%, and the adhesion to composite materials is poor.

[0005] Fourth, tension control is crude. Traditional winding systems lack real-time tension monitoring, and tension fluctuations cannot be automatically adjusted, resulting in uneven fiber diameter, high filament breakage rate, and poor package quality.

[0006] Fifth, the flame retardant properties need to be improved. Although PBI fiber itself has excellent high-temperature resistance, its limiting oxygen index (LOI) still has room for improvement, which limits its application in high-end flame retardant protection fields.

[0007] Therefore, there is an urgent need to develop a new method for preparing high-performance spinning of PBI fibers. Summary of the Invention

[0008] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method and apparatus for preparing high-performance spinning of PBI fibers. By designing and synthesizing a novel phosphorus-containing imidazole salt ionic liquid, forming a mixed solvent system with DMAc, and combining it with nanocomposite modification and online tension monitoring, a stable spinning process with significantly reduced solvent toxicity, improved fiber mechanical properties, enhanced flame retardant properties, and uniform control of fiber diameter can be achieved.

[0009] To achieve the purpose of this invention, a method for preparing PBI high-performance fibers is provided, comprising the following steps: S1. A mixed solvent is obtained by mixing a phosphorus-containing imidazole salt ionic liquid with DMAc. PBI resin is dissolved in the mixed solvent by gradient heating to obtain a spinning solution. The mass ratio of the phosphorus-containing imidazole salt ionic liquid to DMAc is 3:7 to 7:3. S2. The modified nanoparticles are mixed with the spinning solution, and then subjected to high shear dispersion and vacuum degassing treatment to obtain a nanocomposite spinning solution. S3. The nanocomposite spinning solution is formed by electrostatic assisted wet spinning, solidified through a solidification tunnel, and then solidified through a curing tunnel to obtain nascent fibers; the temperature of the solidification tunnel gradually changes from 60°C to 90°C, and the temperature of the curing tunnel is 120-160°C. S4. The nascent fiber is subjected to stretching, washing, oiling, drying and heat setting to obtain PBI high-performance fiber; Preferably, the process further includes step S5, where the waste gas volatilized from the solidification and curing tunnels is treated by two-stage condensation recovery and vacuum distillation to recover the phosphorus-containing imidazole salt ionic liquid and DMAc solvent for recycling.

[0010] Preferably, the phosphorus-containing imidazole salt ionic liquid is composed of phosphorus-containing imidazole cations and anions, and the structural formula of the cation is [MIM-(CH2)3-P(O)(OR)2]. + MIM is 1-methylimidazolium, and R is a C1-C4 alkyl group; the anion is tetrafluoroborate. or hexafluorophosphate .

[0011] Preferably, R is ethyl.

[0012] Preferably, the mass ratio of the phosphorus-containing imidazole salt ionic liquid to DMAc is 5:5.

[0013] Preferably, the PBI resin is pre-swollen at 70-80°C for 2-3 hours, and then heated to 150-170°C for gradient heating and dissolution, with a PBI solid content of 8-15%.

[0014] Preferably, the modified nanoparticles are one-dimensional nanomaterials, including at least one of modified one-dimensional nano-SiO2, modified one-dimensional nano-Al2O3, modified one-dimensional nano-TiO2, or carbon nanotubes. The modified one-dimensional nano-SiO2 is in the form of nanorods or nanowires with an average aspect ratio of 10:1 to 50:1; the modified one-dimensional nano-Al2O3 is in the form of nanorods or whiskers with an average aspect ratio of 10:1 to 30:1; the modified one-dimensional nano-TiO2 is in the form of nanorods or nanowires with an average aspect ratio of 5:1 to 20:1; the mass fraction is 0.5-3%, and surface modification is performed using an aminosilane coupling agent. One-dimensional nanomaterials have a large aspect ratio, enabling them to form an effective three-dimensional network structure in the PBI matrix, significantly improving the mechanical properties of PBI fibers through stress transfer and load sharing mechanisms; simultaneously, the ordered arrangement of one-dimensional nanomaterials along the fiber axis is beneficial for inducing the ordered arrangement of PBI molecular chains, improving the crystallinity and orientation of the fibers.

[0015] The present invention also provides an apparatus for preparing high-performance spinning of PBI fibers, comprising: The dissolution and dispersion system includes a solvent mixing tank, a gradient temperature dissolution vessel, a high-shear dispersion device, and a vacuum degassing device; The spinning forming system includes a magnetic gear pump, a constant temperature conveying pipeline, a two-stage filtration device, a precision metering pump, a spinneret, a high-voltage electrostatic generator, a solidification forming tunnel, and a curing tunnel. The high-voltage electrostatic generator is electrically connected to the spinneret, and the temperature of the solidification forming tunnel can be gradually changed from 60°C to 90°C. The drawing and setting system includes a drawing roller assembly, a washing bath, an oiling bath, a hot air circulating drying oven, and a heat setting machine; The winding system includes a tension sensor, a signal amplifier, a tension controller, a winding motor, and a winding roller; The solvent recovery system includes a two-stage condensation unit and a vacuum distillation unit.

[0016] Preferably, the effective length of the solidification and forming tunnel is 2-4m, with an exhaust gas outlet at the bottom and a spinneret mounting position at the top.

[0017] Preferably, the effective length of the curing channel is 2-4m, the curing temperature is 120-160℃, and the curing time is 30-60 seconds.

[0018] Preferably, the tension sensor has a range of 0-500cN, an accuracy of ±0.1cN, and a response time of less than 10ms; the tension controller has a built-in PID control algorithm with a control accuracy of ±2%.

[0019] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The phosphorus-containing imidazole salt ionic liquid used in this invention has a low freezing point, low volatility, and good thermal stability. It can form a low eutectic solvent system with DMAc, which significantly reduces the dissolution temperature of PBI, reduces energy consumption, and effectively protects the PBI molecular chain, increasing the retention rate of the intrinsic viscosity of the spinning solution. (2) The present invention adopts electrostatic assisted wet spinning technology, which stabilizes the Taylor cone under the action of high voltage electrostatic field, reduces the phenomenon of fuzz and broken fibers in the spinning process, and improves the continuity and stability of the spinning process; at the same time, it combines gradient heating solidification forming process to promote uniform solidification of fibers and reduce the difference between core and sheath structure; the synergistic effect of the two significantly improves the uniformity and mechanical properties of fibers, increases the breaking strength, and enhances the initial modulus. (3) This invention improves the crystallinity, mechanical properties and flame retardant properties of PBI fiber by adding modified nanoparticles and utilizing the small size effect and surface effect of nanoparticles, resulting in a high limiting oxygen index. (4) The present invention utilizes the synergistic effect of phosphorus-containing imidazole salt ionic liquid and modified nanoparticles to endow PBI fibers with excellent comprehensive properties, and all indicators are significantly better than those of PBI fibers prepared by traditional methods. (5) The present invention adopts a solvent recovery process that combines two-stage condensation recovery and vacuum distillation, which has a high solvent recovery rate. Both phosphorus-containing imidazole salt ionic liquid and DMAc solvent can be recycled, which is energy-saving and environmentally friendly. Attached image description: Figure 1 This is a schematic diagram of the overall structure of the PBI fiber spinning device of the present invention.

[0020] Figure 2 This is a schematic diagram of the spinning and forming system structure of the PBI fiber spinning apparatus of the present invention.

[0021] Figure 3 This is a schematic diagram of the drawing and setting system of the PBI fiber spinning apparatus of the present invention.

[0022] Figure 4 This is a schematic diagram of the winding system structure of the PBI fiber spinning apparatus of the present invention.

[0023] Figure 5 This is a schematic diagram of the solvent recovery system of the PBI fiber spinning apparatus of the present invention. Figure reference numerals: 4-Solvent mixing tank, 5-Gradient heating dissolving vessel, 6-Vacuum degassing device, 7-High shear dispersion equipment, 8-Coupling agent hydrolysis device, 9-Magnetic gear pump, 10-Constant temperature conveying pipeline, 11-Two-stage filtration device, 12-Precision metering pump, 13-Spinneret, 14-High voltage electrostatic generator, 15-Coagulation forming tunnel, 16-Curing tunnel, 17-Traction roller assembly, 17a-Exhaust gas outlet, 18-Water washing bath, 19-Oil bath, 20-Hot air circulating drying oven, 2 1-Heat setting machine, 22-Tension sensor, 23-Signal amplifier, 24-Rewinding motor, 25-Winding roller, 26-Tension controller, 27-First-stage condenser, 28-Reduced pressure distillation unit, 29-Exhaust gas pipeline, 30-PBI resin storage tank, 31-Ionic liquid storage tank, 32-DMAc storage tank, 33-Nano particle storage tank, 34-Oil tank, 35-Deionized water tank, 36-Liquid separator, 101-Thermostatic jacket, 111-Primary filter, 112-Fine filter. Detailed Implementation

[0024] The present invention will now be described in detail with reference to specific embodiments and comparative examples. It should be understood that the following embodiments and comparative examples are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention.

[0025] Example 1: Preparation of phosphorus-containing imidazole salt ionic liquid This embodiment provides a method for preparing a phosphorus-containing imidazole salt ionic liquid, comprising the following steps: (1) Preparation of intermediate: 1-methylimidazole and diethyl 3-chloropropylphosphonate were added to reaction vessel 1 at a molar ratio of 1:1.05 and reacted at 80°C for 12 hours. After cooling to room temperature, ethyl acetate was added to precipitate the mixture. The mixture was filtered, washed three times with ethyl acetate, and dried in a vacuum drying oven 3 at 60°C for 24 hours to obtain the phosphorus-containing imidazole chloride intermediate [1-methyl-3-(γ-phosphonate propyl)imidazole]. + Cl - Temperature controller 2 monitors the temperature inside reactor 1 in real time to ensure that the reaction temperature remains stable within the range of 80±2℃.

[0026] (2) Ion exchange: The phosphorus-containing imidazole chloride intermediate and sodium tetrafluoroborate were added to anhydrous ethanol at a molar ratio of 1:1.1 and reacted at 40°C for 8 hours. The precipitate was removed by filtration, and the ethanol was removed by vacuum distillation of the filtrate. The filtrate was then dried at 60°C for 24 hours in a vacuum drying oven to obtain the target product, the phosphorus-containing imidazole ionic liquid [1-methyl-3-(γ-phosphonate propyl)imidazolium]. + [BF4] - .

[0027] Product characteristics: Decomposition temperature (DSC) greater than 285℃; freezing point (DSC) measured at 18-22℃.

[0028] Example 2: Preparation of modified nanoparticles This embodiment provides a method for preparing modified one-dimensional nanoparticles. One-dimensional nanomaterials include: nanorod-shaped SiO2 (which can be prepared using a sol-gel method combined with a template method or an electrospinning method, or commercially available products such as nanorod-shaped SiO2 particles produced by Cabot Corporation and Degussa Corporation in the United States), nanorod-shaped or whisker-shaped Al2O3 (which can be prepared using a fused whisker method or a chemical vapor deposition method; commercially available products include alumina whiskers produced by Teijin Corporation in Japan), and nanorod-shaped TiO2 (which can be prepared using a hydrothermal method or a sol-gel method; commercially available products include nanorod-shaped TiO2 particles produced by Xuancheng Jingrui New Materials Co., Ltd. in China). The following explanation uses the preparation of modified one-dimensional nano-SiO2 (nanorods) as an example.

[0029] This embodiment provides a method for preparing modified one-dimensional nano-SiO2 (nanorobars), including the following steps: T1. Pretreatment: One-dimensional nano-SiO2 (nanorobars, diameter 10-50nm, length 200-800nm, aspect ratio about 15:1) is placed in a vacuum drying oven and dried at 120℃ for 8 hours to remove adsorbed water and residual organic impurities.

[0030] T2. Coupling Agent Hydrolysis: 3-Aminopropyltriethoxysilane (KH-550) coupling agent was added to anhydrous ethanol at a mass-to-volume ratio of 1:15. Deionized water was added dropwise to adjust the pH to 10-11, with the amount of deionized water being 5% of the coupling agent's mass. The mixture was hydrolyzed in a 40°C water bath with stirring for 1 hour to obtain the coupling agent hydrolysate. The aminosilane coupling agent KH-550 was chosen because the amino groups produced after hydrolysis can form hydrogen bonds and van der Waals forces with the tertiary nitrogen atoms and benzimidazole rings in the PBI molecular chain, improving the compatibility and interfacial bonding between the nanoparticles and the PBI matrix.

[0031] T3. Surface treatment: One-dimensional nano-SiO2 (nanorobars) are added to a high-speed mixer (stirring speed 600 rpm), and coupling agent hydrolysate is added dropwise (dropping rate 8 mL / min). After mixing for 30 minutes, the mixture is placed in an 80℃ oven to dry for 4 hours, ground and sieved to obtain modified one-dimensional nano-SiO2 (nanorobars).

[0032] T4. Dispersion and Degassing: Modified one-dimensional nano-SiO2 (nanorobars) are mixed with PBI spinning solution (mass fraction 1.0%) and dispersed under high shear (shear rate 10000s). -1 Vacuum degassing (pressure 0.08 MPa, time 18 hours), filtration, to obtain nanocomposite spinning solution.

[0033] Example 3 The PBI fiber spinning apparatus provided in this embodiment includes five subsystems: a dissolution and dispersion system, a spinning and forming system, a drawing and setting system, a winding system, and a solvent recovery system. These subsystems are organically connected through pipelines and a control system to form a complete continuous PBI fiber production line. The phosphorus-containing imidazole salt ionic liquid prepared in Example 1 is stored in ionic liquid storage tank 31 and used directly.

[0034] Specifically, such as Figure 1 As shown, the dissolution and dispersion system includes a solvent mixing tank 4, a gradient temperature dissolution vessel 5, a high-shear dispersion device 7, a coupling agent hydrolysis device 8, and a vacuum degassing device 6. The solvent mixing tank 4 contains a phosphorus-containing imidazole salt ionic liquid [1-methyl-3-(γ-phosphonate propyl)imidazolium]. + [BF4] - The solvent mixed with DMAc at a mass ratio of 5:5 is equipped with a stirring device and a heating jacket, and is connected to the ionic liquid storage tank 31 and the DMAc storage tank 32 via pipelines. The gradient temperature dissolution vessel 5 is equipped with a temperature program controller and a condenser, with an effective volume of 50L. The pre-swelling stage temperature is 70-80℃, the dissolution stage temperature is 150-170℃, and the condenser (not shown in the figure) has a condensation temperature of 25℃ for recovering the evaporated solvent. The high-shear dispersion device 7 is a high-speed shear disperser with an effective volume of 2L and a shear rate of 5000-15000s. -1 In this embodiment, 10000s is preferred. -1 The coupling agent hydrolysis device 8 includes a hydrolysis tank (effective volume 5L) and a constant temperature water bath (temperature control accuracy ±1℃). The vacuum degassing device 6 has a vacuum degree controlled at 0.05-0.1MPa (preferably 0.08MPa in this embodiment) and an effective volume of 30L. The inlet of the solvent mixing tank 4 is connected to the ionic liquid storage tank 31 and the DMAc storage tank 32 via pipes; the PBI resin storage tank 30 is connected to the gradient temperature dissolution vessel 5 via a screw feeder; and the nanoparticle storage tank 33 is connected to the high shear dispersion device 7 via a quantitative feeding device. The outlet of solvent mixing tank 4 is connected to gradient temperature dissolving vessel 5, the outlet of gradient temperature dissolving vessel 5 is connected to high shear dispersion equipment 7, the outlet of high shear dispersion equipment 7 is connected to vacuum degassing device 6, and the outlet of coupling agent hydrolysis device 8 is connected to high shear dispersion equipment 7. The specific process is as follows: PBI resin is added to gradient temperature dissolving vessel 5 from storage tank 30, mixed solvent is pumped from solvent mixing tank 4 to gradient temperature dissolving vessel 5 for pre-swelling and gradient temperature dissolution; aminosilane coupling agent hydrolysate is pumped from coupling agent hydrolysis device 8 to high shear dispersion equipment 7, and modified nanoparticles are added to high shear dispersion equipment 7 from storage tank 33 for high shear dispersion; after dispersion, they enter vacuum degassing device 6 for processing and are then transported to spinning forming system.

[0035] Specifically, such as Figure 2 As shown, the spinning system includes a magnetic gear pump 9, a constant-temperature delivery pipeline 10, a two-stage filtration device 11, a precision metering pump 12, a spinneret 13, a high-voltage electrostatic generator 14, a solidification and forming tunnel 15, and a curing tunnel 16. The magnetic gear pump 9 has a flow rate of 0.5-5 mL / min and an accuracy of ±2%. It is connected to the constant-temperature delivery pipeline 10, which is equipped with a constant-temperature jacket 101 to circulate a constant-temperature medium, controlling the temperature at 40-50℃ (preferably 45℃ in this embodiment). The two-stage filtration device 11 includes a pre-filter 111 (200 mesh) and a fine filter 112 (400 mesh). The precision metering pump 12 is a piston pump with a flow rate accuracy within ±1%. The spinneret 13 has 100 holes with a spinneret orifice diameter of 0.10-0.25 mm (preferably 0.18 mm in this embodiment). The high-voltage electrostatic generator 14 operates at a voltage of 50-80kV (preferably 60kV in this embodiment). Its positive electrode is connected to the spinneret 13, creating a high-voltage electrostatic field between the spinneret 13 and the grounded electrode at the bottom of the solidification tunnel 15. The voltage gradient is 0.15-0.25kV / cm, which helps stabilize the spinning process. The temperature of the solidification tunnel 15 gradually changes from 60℃ to 90℃, with an effective length of 2-4m (preferably 3m in this embodiment). An exhaust gas outlet 17a is located at the bottom, and a spinneret mounting position is located at the top. The curing tunnel 16 is 2-4m long (preferably 3m in this embodiment), with a curing temperature of 120-160℃ (140℃ in this embodiment) and a curing time of 30-60 seconds (45 seconds in this embodiment). An exhaust gas outlet 17a is provided. The outlet of the vacuum degassing device 6 is connected to the inlet of the magnetic gear pump 9 via a pipe (not shown in the figure). The magnetic gear pump 9 is connected to a two-stage filtration device 11 via a constant-temperature conveying pipe 10. The two-stage filtration device 11 is connected to a precision metering pump 12, which is connected to a spinneret 13. The spinneret 13 is located at the top of the solidification tunnel 15, and the positive electrode of the high-voltage electrostatic generator 14 is connected to the spinneret 13. The outlet of the solidification tunnel 15 is connected to the curing tunnel 16, and the outlet of the curing tunnel 16 is connected to the stretching and shaping system. The exhaust gas outlets 17a of the solidification tunnel 15 and the curing tunnel 16 are connected to the solvent recovery system via an exhaust gas pipe 29. This device employs electrostatic assisted wet spinning technology. The high-voltage electrostatic field serves two purposes: firstly, it stabilizes the Taylor cone, reducing fuzz and breakage during the spinning process and improving the continuity and stability of the spinning process; secondly, it accelerates the evaporation and diffusion of the solvent during the solidification process, reducing the difference between the core and sheath structure and promoting the uniform solidification of the fiber.

[0036] Specifically, such as Figure 3As shown, the drafting and setting system includes a drafting roller group 17, a water washing bath 18, an oil bath 19, a hot air circulating drying oven 20, and a heat setting machine 21. The drafting roller group 17 includes three or more pairs of drafting rollers, consisting of a servo motor-driven driving roller and a driven roller, with a draft ratio of 3-6 times (4.5 times in this embodiment). The water washing bath 18 has a water temperature of 40-60℃ (50℃ in this embodiment) and is equipped with a deionized water tank 35 for water supply. The oil bath 19 has an oil concentration of 5-10% (8% in this embodiment) and is equipped with an oil tank 34 for liquid supply. The hot air circulating drying oven 20 has a drying temperature of 120-150℃ (130℃ in this embodiment). The heat setting machine 21 has a heat setting temperature of 220-280℃ (260℃ in this embodiment). The outlet of the curing tunnel 16 is connected to the inlet of the stretching roller group 17. The outlet of the stretching roller group 17 is connected in sequence to the water washing bath 18, the oiling bath 19, the hot air circulating drying box 20, and the heat setting machine 21. The outlet of the heat setting machine 21 is connected to the winding system.

[0037] Specifically, such as Figure 4 As shown, the winding system includes a tension sensor 22, a signal amplifier 23, a tension controller 26, a winding motor 24, and a winding roller 25. The tension sensor 22 has a range of 0-500 cN, an accuracy of ±0.1 cN, and a response time of less than 10 ms (preferably less than 8 ms in this embodiment). It is installed on the fiber path to monitor tension in real time. The signal amplifier 23 has an adjustable amplification factor of 1-100 times. The tension controller 26 has a built-in PID control algorithm that automatically adjusts the speed of the winding motor 24 based on the signal from the signal amplifier 23, with a control accuracy of ±2%. The winding motor 24 is a servo motor with a power of 0.5-2 kW and a winding speed of 50-200 m / min (100 m / min in this embodiment). The output of tension sensor 22 is connected to signal amplifier 23, signal amplifier 23 is connected to tension controller 26, tension controller 26 is connected to winding motor 24, and winding motor 24 drives winding roller 25 to rotate. Fiber passes under tension sensor 22. The sensor monitors the tension in real time and transmits the amplified signal to tension controller 26. Tension controller 26 automatically adjusts the speed of winding motor 24 according to the deviation to achieve stable tension control.

[0038] Specifically, such as Figure 5As shown, the solvent recovery system includes a first-stage condenser 27, a liquid separator 36, and a vacuum distillation unit 28. The waste gas volatilized from the solidification and solidification tunnel 15 and the curing tunnel 16 first enters the first-stage condenser 27 through the waste gas pipe 29 for cooling and condensation. The phosphorus-imidazolium salt ionic liquid vapor (freezing point approximately 18-22℃) and DMAc solvent vapor (boiling point 165-166℃) are both condensed into liquid at 5℃. The mixture then enters the liquid separator 36 for separation. The liquid separator 36 is equipped with a level gauge and an automatic drain valve. The phosphorus-imidazolium salt ionic liquid layer passes through an outlet pipe and a reflux pump (as shown in the figure). The DMAc solvent layer (not shown) is transported to the ionic liquid storage tank 31 for recycling. The DMAc solvent layer is transported to the DMAc storage tank 32 for recycling via the outlet pipe and reflux pump (not shown in the figure). The cooled tail gas enters the vacuum distillation unit 28, where distillation is performed under a vacuum of 0.085 MPa at a temperature of 80-100℃ to deeply recover residual DMAc solvent. The distilled DMAc vapor is condensed through the condenser and returned to the DMAc storage tank 32 for recycling via the reflux pipe. The overall solvent recovery rate is over 90%.

[0039] It should be noted that the connecting pipes in the attached diagram are not fully shown, and the PBI fibers are merely schematic and do not represent the actual samples prepared.

[0040] Example 4 This example provides a method for preparing PBI high-performance fibers, using the spinning apparatus of Example 3, and specifically includes the following steps: S1. The phosphorus-containing imidazole salt ionic liquid [1-methyl-3-(γ-phosphonate propyl)imidazolium] in ionic liquid storage tank 31 is placed... + [BF4] - DMAc from storage tank 32 is introduced into solvent mixing tank 4 at a mass ratio of 5:5, and the mixture is stirred until homogeneous to obtain a mixed solvent. PBI resin powder is added from PBI resin storage tank 30 to gradient temperature dissolution vessel 5, and the mixed solvent is pumped from solvent mixing tank 4 to gradient temperature dissolution vessel 5, controlling the solid content to 12%. First, a pre-swelling treatment is performed at 70-80℃ for 2.5 hours to fully swell the PBI molecular chains; then, the temperature is raised to 150-170℃ for gradient temperature dissolution for 2 hours. The synergistic effect of the phosphorus-containing imidazole salt ionic liquid and DMAc promotes the complete dissolution of PBI, achieving a PBI dissolution rate of over 90%, yielding the spinning solution. The evaporated solvent is recovered in real time using a condenser. Compared to the traditional DMAc single solvent system with a dissolution temperature of 200℃, the present invention reduces the dissolution temperature to 150-170℃ by adding phosphorus-containing imidazole salt ionic liquid, which is about 30-50℃ lower. This effectively reduces the risk of thermal degradation of PBI molecular chains, and the intrinsic viscosity retention rate of the spinning solution is greater than 85%.

[0041] S2. Take KH-550 modified one-dimensional nano-SiO2 (nanorobar-shaped, approximately 30 nm in diameter, 400 nm in length, aspect ratio approximately 13:1, mass fraction 1.0%) and add it from nanoparticle storage tank 33 to high-shear dispersion device 7, and mix it with spinning solution. High-shear dispersion device 7 operates at a shear rate of 10000 s⁻¹. -1 Disperse for 20 minutes to ensure uniform dispersion of the one-dimensional nanomaterials. After dispersion, proceed to vacuum degassing device 6 and degas at 0.08 MPa for 18 hours to obtain the nanocomposite spinning solution.

[0042] S3, the nanocomposite spinning solution is transported by a magnetic gear pump 9, then conveyed through a constant-temperature conveying pipeline 10 (45℃) to a two-stage filtration device 11 for filtration (200 mesh initial filtration, 400 mesh fine filtration), and then metered by a precision metering pump 12 before being conveyed to the spinneret 13. The spinneret 13 has 100 holes with a spinneret orifice diameter of 0.18mm. A high-voltage electrostatic generator 14 applies a 60kV high-voltage electrostatic field, forming a high-voltage electrostatic field between the spinneret 13 and the grounded electrode at the bottom of the solidification channel 15, with a voltage gradient of approximately 0.2kV / cm. Under the assistance of the high-voltage electrostatic field, the spinning solution is ejected from the spinneret 13, forming a stable jet and entering the solidification channel 15 for solidification. The fiber is solidified in the solidification tunnel 15 (temperature gradually increasing from 60℃ to 90℃), with the volatile liquid containing phosphorus imidazole salt reaching 70-80%; it is then further cured in the curing tunnel 16 (curing temperature 140℃, curing time 45 seconds). The waste gas volatilized from the solidification tunnel 15 and the curing tunnel 16 is transported to the solvent recovery system through the waste gas pipe 29.

[0043] S4. The cured nascent fiber enters the drawing roller group 17 and is drawn in three stages with a drawing ratio of 4.5 times. Then it is washed in a water washing bath 18 (50℃ deionized water), oiled in an oiling bath 19 (8% oil agent), dried in a hot air circulating drying oven 20 (130℃), and finally heat-set in a heat setting machine 21 (260℃) to obtain high-performance PBI fiber.

[0044] After heat setting, the PBI fibers pass sequentially through tension sensor 22 and winding roller 25. Tension sensor 22 (range 0-500cN, accuracy ±0.1cN, response time less than 8ms) monitors fiber tension in real time. The signal is amplified by signal amplifier 23 and transmitted to tension controller 26. Tension controller 26 uses a built-in PID control algorithm to automatically adjust the speed of winding motor 24, achieving stable tension control within ±2% of the set value. The fibers are automatically wound into a tube on winding roller 25, with a fiber diameter variation coefficient of less than 6%.

[0045] The exhaust gas (temperature 60-160℃) from S5, solidification forming tunnel 15, and solidification tunnel 16 first enters the first-stage condenser 27 (5℃ condensation) through exhaust gas pipe 29. Phosphorus imidazole salt ionic liquid vapor (freezing point approximately 18-22℃) and DMAc solvent vapor (boiling point 165-166℃) are both condensed into liquid at 5℃. The mixture enters the separator 36 for separation; the phosphorus imidazole salt ionic liquid returns to the ionic liquid storage tank 31, and the DMAc solvent returns to the DMAc storage tank 32. The cooled tail gas enters the vacuum distillation unit 28, where distillation is performed under a vacuum of 0.085MPa at a distillation temperature of 80-100℃. After deep recovery of residual DMAc solvent, the gas returns to the DMAc storage tank 32. The overall solvent recovery rate reaches over 90%; among them, the high aspect ratio of the one-dimensional nanomaterials enables them to be arranged in an orderly manner along the fiber axis during the spinning process, forming an interpenetrating network structure with the PBI molecular chains, further improving the mechanical properties and thermal stability of the fiber.

[0046] The performance indicators of the PBI high-performance fiber obtained in this embodiment are detailed in Table 1 below.

[0047] Comparative Example 1 PBI fibers were prepared using traditional DMAc as the single solvent, without the addition of phosphorus-containing imidazole salt ionic liquids and modified nanoparticles, following the traditional wet spinning process.

[0048] S1. PBI Dissolution: PBI resin powder is added to DMAc solvent with a solid content of 12% and dissolved under high temperature and high pressure conditions at 200℃ for 4 hours to obtain spinning solution. Traditional DMAc solvents have a high boiling point (165-166℃) and are prone to thermal degradation during dissolution, with an intrinsic viscosity retention rate of only 65-70%.

[0049] S2. Spinning: The spinning solution is filtered and then transported to the spinneret. Traditional wet spinning is used. The coagulation bath is deionized water and the coagulation bath temperature is 25℃. The coagulation speed is relatively slow. The fiber skin structure is dense while the core structure is loose, resulting in more fiber defects.

[0050] S3. Stretching and setting: The nascent fibers are washed and dried, then stretched and set with a stretch ratio of 3 times and a heat setting temperature of 260℃.

[0051] S4. Solvent Recovery: The coagulation bath contains a large amount of DMAc solvent. It is recovered by vacuum distillation, but the recovery rate is only 70-80%, which consumes a lot of energy.

[0052] Comparative Example 2 This comparative example uses a traditional DMAc solvent system to dissolve PBI resin powder in a single step at 200°C for 4 hours, yielding a spinning solution with a mass fraction of 12%. The PBI molecular chains undergo shearing and dissolution at high temperature, with some chains experiencing thermal degradation; the intrinsic viscosity retention rate is 70%. The spinning solution exhibits poor stability, showing slight stratification after 24 hours.

[0053] Comparative Example 3 In this comparative example, PBI fibers were prepared using a traditional DMAc solvent system. PBI fiber samples were obtained, and their limiting oxygen index (LOI) and heat release performance were tested.

[0054] Comparative Example 4-5 Comparative Example 4 used a phosphorus-containing imidazole salt ionic liquid / DMAc mixed solvent system without adding any nanoparticles to obtain a PBI fiber sample.

[0055] Comparative Example 5 used a phosphorus-containing imidazole salt ionic liquid / DMAc mixed solvent system, adding 1.2% by mass of unmodified spherical nano-SiO2 particles (average particle size 30 nm). The nanocomposite PBI fiber sample was prepared using conventional high-speed stirring dispersion (3000 rpm, 30 minutes). Due to the lack of surface modification with a coupling agent, the interfacial bonding between the spherical nano-SiO2 particles and the PBI matrix was weak; furthermore, the conventional high-speed stirring dispersion process resulted in poor dispersion, with the spherical nanoparticles easily agglomerating in the PBI matrix, forming stress concentration points and exhibiting poor dispersion uniformity. This comparative example, using zero-dimensional spherical nanoparticles and employing an outdated dispersion process, contrasts with the one-dimensional nanorods of the example (modified with a coupling agent and dispersed under high shear) to verify the comprehensive influence of the morphology of one-dimensional nanomaterials and the modification and dispersion process on the reinforcing effect.

[0056] The performance of PBI prepared in Example 4 and Comparative Examples 1-5 was tested, and the performance comparison is summarized in Table 1: Table 1 Performance comparison between the examples and comparative examples

[0057] Note: Intrinsic viscosity retention rate: Based on the intrinsic viscosity of the original PBI resin, the intrinsic viscosity of the spinning solution was measured and the retention rate was calculated. Solvent recovery rate: Combined recovery rate of phosphorus-containing imidazole salt ionic liquid and DMAc solvent. Peak heat release rate and char residue: 100% based on Comparative Example 1 (conventional DMAc solvent system). Example 4 used one-dimensional nano-SiO2 (nanorobars, modified with KH-550 and dispersed under high shear); Comparative Example 5 used zero-dimensional spherical nano-SiO2 (unmodified and dispersed by conventional stirring). "—" indicates that the test was not performed.

[0058] (1) The phosphorus-containing imidazole salt ionic liquid / DMAc mixed solvent system of the present invention, combined with the two-stage dissolution process of pre-swelling-gradient heating, significantly reduced the dissolution temperature of PBI (from 200℃ to 160℃), effectively protected the PBI molecular chain (the intrinsic viscosity retention rate increased from 68-70% to 87%), and improved the stability of the spinning solution from 12-24h to 72h. (2) The phosphonoyl group in the phosphorus-containing imidazole salt ionic liquid of the present invention is introduced into the interior of PBI fiber during the spinning process, and the phosphorus content reaches 1.0%, which significantly improves the flame retardant performance of the fiber, increases the limiting oxygen index from 30% to 34%, reduces the peak heat release rate by 16%, and increases the char rate from 43% to 52%; (3) This invention uses one-dimensional nano-SiO2 (nanoro-rod-shaped, aspect ratio of about 13:1) in combination with a high shear dispersion process to make the one-dimensional nanomaterials uniformly dispersed without agglomeration. The aminosilane coupling agent KH-550 forms hydrogen bonds and van der Waals forces with the tertiary nitrogen atoms and benzimidazole rings of the PBI molecular chain, which significantly improves the compatibility and interfacial bonding force between the one-dimensional nanomaterials and the PBI matrix. The high aspect ratio of the one-dimensional nanomaterials enables them to form an effective three-dimensional network structure in the PBI matrix, which significantly improves the mechanical properties of the fiber through stress transfer and load sharing mechanisms. The breaking strength is increased from 2.7 cN / dtex (zero-dimensional spherical nanoparticles, unmodified, conventional stirring dispersion) in Comparative Example 5 to 3.0 cN / dtex (an increase of 11.1%), and from 2.5 cN / dtex (without nanoparticles) in Comparative Example 4 to 3.0 cN / dtex (an increase of 20%). The initial modulus is increased by 11.5-20.8%, and the crystallinity is increased by 3-5 percentage points. (4) The reinforcing effect of one-dimensional nanomaterials is significantly better than that of zero-dimensional spherical nanoparticles: Comparative Example 5 uses zero-dimensional spherical nano-SiO2 (diameter 30nm, unmodified, conventional stirring dispersion), with a fracture strength of only 2.7cN / dtex, weak interfacial bonding, and nanoparticles easily agglomerate to form stress concentration points; while Example 4 uses one-dimensional nano-SiO2 (nanorobars, diameter about 30nm, length about 400nm, aspect ratio about 13:1, KH-550 modified, high shear dispersion), with a fracture strength of 3.0cN / dtex, an increase of 11.1%. This indicates that: ① The high aspect ratio structure of one-dimensional nanomaterials can better transfer stress in the PBI matrix and form an effective reinforcing network, which is significantly better than the point contact reinforcement effect of zero-dimensional spherical nanoparticles; ② The surface modification of the coupling agent significantly enhances the interfacial bonding between the nanomaterials and the PBI matrix; ③ The high shear dispersion process effectively prevents the agglomeration of one-dimensional nanomaterials and maintains the reinforcing effect; (5) This invention integrates the synergistic effect of phosphorus-containing imidazole salt ionic liquid and one-dimensional nanomaterials, and combines electrostatic assisted wet spinning technology and gradient temperature solidification forming process to achieve the optimization of the comprehensive performance of PBI fiber. All performance indicators are significantly better than those of PBI fiber prepared by traditional methods, and the comprehensive performance reaches the international advanced level.

[0059] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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-performance PBI fiber spinning, characterized in that, Includes the following steps: S1. A mixed solvent is obtained by mixing a phosphorus-containing imidazole salt ionic liquid with DMAc. PBI resin is dissolved in the mixed solvent by gradient heating to obtain a spinning solution. The mass ratio of the phosphorus-containing imidazole salt ionic liquid to DMAc is 3:7 to 7:

3. S2. The modified nanoparticles are mixed with the spinning solution, and then subjected to high shear dispersion and vacuum degassing treatment to obtain a nanocomposite spinning solution. S3. The nanocomposite spinning solution is formed by electrostatic assisted wet spinning, solidified through a solidification tunnel, and then solidified through a curing tunnel to obtain nascent fibers; the temperature of the solidification tunnel gradually changes from 60°C to 90°C, and the temperature of the curing tunnel is 120-160°C. S4. The nascent fibers are subjected to stretching, washing, oiling, drying and heat setting to obtain PBI high-performance spinning.

2. The preparation method according to claim 1, characterized in that, The phosphorus-containing imidazole salt ionic liquid is composed of phosphorus-containing imidazole cations and anions, and the structural formula of the cation is as follows: [MIM-(CH2)3-P(O)(OR)2]+ Wherein, MIM is 1-methylimidazolium, and R is a C1-C4 alkyl group; the anion is tetrafluoroborate. or hexafluorophosphate .

3. The preparation method according to claim 1, characterized in that: The mass ratio of the phosphorus-containing imidazole salt ionic liquid to DMAc is 5:

5.

4. The preparation method according to claim 1, characterized in that: The PBI resin is pre-swollen at 70-80℃ for 2-3 hours, and then heated to 150-170℃ for gradient dissolution. The solid content of the PBI resin is 8-15%.

5. The preparation method according to claim 1, characterized in that: The modified nanoparticles are one-dimensional nanomaterials, including modified one-dimensional nanoparticles. SiO2 Modified one-dimensional nano Al2O3 Modified one-dimensional nano TiO2 Or at least one of modified carbon nanotubes; the modified one-dimensional nanotubes SiO2 The modified one-dimensional nanorods or nanowires are in the form of nanorods or nanowires with an average aspect ratio of 10:1 to 50:

1. Al2O3 The modified one-dimensional nanorods or whiskers have an average aspect ratio of 10:1 to 30:

1. TiO2 They are in the form of nanorods or nanowires, with an average aspect ratio of 5:1 to 20:

1. The mass fraction is 0.5-3%, and the surface is modified using an aminosilane coupling agent.

6. An apparatus for preparing high-performance PBI fiber spinning, characterized in that, include: The dissolution and dispersion system includes a solvent mixing tank, a gradient temperature dissolution vessel, a high-shear dispersion device, and a vacuum degassing device; The spinning forming system includes a magnetic gear pump, a constant temperature conveying pipeline, a two-stage filtration device, a precision metering pump, a spinneret, a high-voltage electrostatic generator, a solidification forming tunnel, and a curing tunnel, wherein the high-voltage electrostatic generator is electrically connected to the spinneret; The drawing and setting system includes a drawing roller assembly, a washing bath, an oiling bath, a hot air circulating drying oven, and a heat setting machine; The winding system includes a tension sensor, a signal amplifier, a tension controller, a winding motor, and a winding roller; The solvent recovery system includes a two-stage condensation unit and a vacuum distillation unit.

7. The spinning apparatus according to claim 6, characterized in that: The effective length of the solidification and forming tunnel is 2-4m, with an exhaust gas outlet at the bottom and a spinneret mounting position at the top.

8. The spinning apparatus according to claim 6, characterized in that: The effective length of the curing tunnel is 2-4m, the curing temperature is 120-160℃, and the curing time is 30-60 seconds.

9. The spinning apparatus according to claim 6, characterized in that: The tension sensor has a range of 0-500cN, an accuracy of ±0.1cN, and a response time of less than 10ms; the tension controller has a built-in PID control algorithm with a control accuracy of ±2%.

10. The spinning apparatus according to claim 6, characterized in that: The high-voltage electrostatic generator forms a high-voltage electrostatic field between the spinneret and the grounding electrode at the bottom of the solidification and forming channel, with a voltage gradient of 0.15-0.25 kV / cm.

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