Para-aramid fibers, para-aramid aerogel fibers, and respective methods of making same

Abstract

The present application belongs to the technical field of fiber preparation, and relates to a kind of p-aramid fiber, p-aramid aerogel fiber and respective preparation methods thereof.The preparation method of p-aramid fiber is to spin p-aramid solution to obtain p-aramid fiber, wherein p-aramid is prepared by the reaction of p-phenylenediamine, 2,3-difluoro-p-phenylenediamine and terephthaloyl chloride.The preparation method of p-aramid aerogel fiber is to first prepare p-aramid fiber dispersion, then perform wet spinning to obtain p-aramid hydrogel fiber, and then dry the p-aramid hydrogel fiber to obtain p-aramid aerogel fiber.The present application simultaneously solves the three major pain points of traditional fiber, i.e., light dyeing, weak strength and poor water resistance, and provides technical support for the multi-scenario application of high-performance fibers.

Description

Technical Field

[0001] This invention belongs to the field of fiber preparation technology, and relates to a para-aramid fiber, a para-aramid aerogel fiber, and their respective preparation methods. Background Technology

[0002] Para-aramid aerogel fiber is a novel high-performance fiber material that combines the superior properties of para-aramid (poly(p-phenylene terephthalamide) fiber, PPTA) with the unique structural advantages of aerogel materials. Para-aramid itself possesses properties such as high strength, high modulus, high temperature resistance, fire resistance, and chemical corrosion resistance, while aerogel is known for its extremely low density, high porosity, and excellent thermal insulation properties. The para-aramid aerogel fiber prepared by combining the two not only retains the mechanical strength and thermal stability of aramid fibers but also endows the material with lightweight and highly efficient thermal insulation properties, making it demonstrate enormous application potential in aerospace, protective equipment, high-end civilian applications, and specialized industrial fields.

[0003] However, with the increasing diversification and stringency of application scenarios, the performance requirements for para-aramid aerogel fibers are becoming more comprehensive and sophisticated. Specifically, in order to meet the needs of different application scenarios for product appearance and function, it is particularly necessary to prepare para-aramid aerogel fibers with excellent dyeing properties, mechanical properties, and superhydrophobicity.

[0004] From the perspective of dyeing performance, para-aramid fibers, due to their unique macromolecular structure and tight molecular chain arrangement, make it difficult for dyes to penetrate and adhere, resulting in low color yield and difficulty in achieving dark dyeing effects. Currently, the range of colored para-aramid fibers on the market is limited, failing to meet diverse color demands, and related research reports are relatively scarce, restricting their application expansion in high-end civilian and specialized industrial fields.

[0005] Para-aramid aerogel fibers also face challenges in terms of waterproof performance. Due to their surface characteristics, the material is easily stained by water and other contaminants, and cleaning is difficult. Simple waterproofing treatments not only fail to completely solve the problem but may also negatively impact key properties such as flame retardancy and protection. Therefore, achieving excellent waterproofing in para-aramid aerogel fibers without affecting other key properties has become a pressing technical challenge. For example, patent application CN116769228A utilizes the continuous changes in the cross-linking structure of aramid fibers, polyurethane molecules, and perfluorooctyltrichlorosilane to obtain a uniquely structured hydrophobic, oleophobic, and stain-resistant aramid nanofiber aerogel through the synergistic effect of these three components. However, this preparation method involves complex chemical reactions of multiple substances, making precise control of the reaction process difficult. Moreover, testing revealed that the hydrophobic properties of the resulting aerogel did not reach an ideal level. In practical applications, facing harsh humid environments or water contact conditions, its waterproofing effect may not meet the requirements, hindering its application in high-end para-aramid aerogel fiber fields.

[0006] In terms of mechanical properties, although para-aramid fibers possess high strength and high modulus, it is crucial to ensure that the microstructure of the fibers is not damaged during processing to maintain their original excellent mechanical properties. Furthermore, while the high porosity of aerogel materials imparts lightweight and thermal insulation properties to the fibers, it may also lead to a slight reduction in their mechanical strength.

[0007] Since the properties of para-aramid aerogel fibers mainly depend on para-aramid fibers, this invention first prepares a new type of para-aramid fiber, and then prepares a new type of para-aramid aerogel fiber with excellent dyeing properties, mechanical properties and superhydrophobicity based on it. Summary of the Invention

[0008] The purpose of this invention is to solve the problems existing in the prior art and to provide para-aramid fibers, para-aramid aerogel fibers and their respective preparation methods.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] A method for preparing para-aramid fibers involves spinning a para-aramid solution to obtain para-aramid fibers. The para-aramid is prepared by reacting p-phenylenediamine (CAS: 106-50-3), 2,3-difluoro-p-phenylenediamine, and terephthaloyl chloride (CAS: 100-20-9). The structural formula of 2,3-difluoro-p-phenylenediamine is as follows:

[0011] .

[0012] This invention improves the dyeing properties, mechanical properties, and superhydrophobicity of para-aramid fibers by introducing 2,3-difluoro-p-phenylenediamine into them, for the following reasons:

[0013] Introducing 2,3-difluoro-p-phenylenediamine into para-aramid will result in the presence of -F in the para-aramid. The introduction of -F will lead to a decrease in the overall crystallinity of the para-aramid fiber and an increase in surface roughness, which will increase the surface free energy. This will improve the binding performance between the surface of the para-aramid fiber and dye molecules, which will facilitate the dye to enter the interior of the para-aramid fiber and increase the dye uptake rate. As a result, the dyeing performance (dyeing depth, color fastness, etc.) of the para-aramid fiber will be significantly improved.

[0014] Introducing 2,3-difluoro-p-phenylenediamine into para-aramid introduces two -F atoms onto one side of the benzene ring of the para-aramid. In two adjacent para-aramid fibers, the two -F atoms on one side of the benzene ring of one para-aramid fiber can effectively form F···H hydrogen bonds with the two -H atoms on one side of the benzene ring of the other para-aramid fiber (e.g., Figure 15 As shown, it can increase the hydrogen bonds between para-aramid fiber macromolecules to a certain extent, improve the van der Waals forces between para-aramid molecules, and increase the molecular rigidity. The rigid main chain plays a role, and the polymer chains are stacked in an orderly and dense manner, thus forming higher mechanical properties.

[0015] The hydrophobic aromatic backbone, the strong hydrophobicity of -F and their directional arrangement work together to construct the rough microstructure of the fiber, reduce the critical surface tension of the fiber, and effectively reduce the surface energy of para-aramid fiber, thus giving para-aramid fiber superhydrophobicity.

[0016] As a preferred technical solution:

[0017] The preparation method of para-aramid fiber described above involves the following steps for preparing 2,3-difluoro-p-phenylenediamine: First, 2,3-difluoroaniline (CAS: 4519-40-8) is reacted with concentrated nitric acid in a concentrated sulfuric acid environment to generate 2,3-difluoro-4-nitroaniline. Then, 2,3-difluoro-4-nitroaniline is reacted with hydrogen under palladium-carbon catalysis to generate 2,3-difluoro-p-phenylenediamine.

[0018] In the above-described method for preparing para-aramid fibers, the molar ratio of p-phenylenediamine, 2,3-difluoro-p-phenylenediamine, and terephthaloyl chloride is 1:1~1.3:3.3~3.9.

[0019] The preparation method of para-aramid fiber as described above involves the following steps: First, under nitrogen or inert gas protection, DMAc and LiCl are added to a reaction vessel and stirred. Then, p-phenylenediamine and 2,3-difluoro-p-phenylenediamine are added. After complete dissolution, the temperature is lowered to -4 to 0°C, and terephthaloyl chloride is added. The reaction system temperature is maintained at 25 to 30°C. After the addition is complete, the reaction continues for 20 to 40 minutes. Finally, LiOH is added for neutralization to obtain the para-aramid solution.

[0020] In the above-described method for preparing para-aramid fibers, the molar ratio of p-phenylenediamine, DMAc (N,N-dimethylacetamide), LiCl, and LiOH is 1:100~2000:4~12:6~24.

[0021] In the above-described method for preparing para-aramid fibers, before spinning, the para-aramid solution is centrifuged to remove salt and then placed into a reaction vessel for degassing.

[0022] The spinning process is a dry-wet spinning method. The overall process flow is: spinning → air bath → coagulation bath → stretching → washing → drying → hot stretching → heat setting → oiling → winding.

[0023] During spinning, the temperature of the para-aramid solution is 20~25℃, the metering pump speed is 4~7 r / min, the spinneret specification is φ0.08mm×100~500 holes, the spinning speed is 7~12m / min, the air bath height is 8~14mm, the coagulation bath is a DMAc aqueous solution (volume concentration of 40~70%), the coagulation bath temperature is 30~35℃, the stretching ratio is 2~8, the water washing temperature is 70~80℃, the hot stretching temperature is 300~320℃, the heat setting temperature is 320~350℃, and the heat setting time is 90~180s.

[0024] The present invention also provides a para-aramid fiber, which is prepared by the method for preparing para-aramid fiber as described in any of the preceding claims;

[0025] The crystallinity of para-aramid fiber is 46%~50%, the crystal axis orientation index is 0.90~0.94, the dyeing rate is 94%~98%, the color fastness to washing is grade 5, the color fastness to rubbing is grade 5, the color fastness to sunlight is grade 4~5, the water contact angle is 102.5°~131.15°, the breaking strength is 30~40cN / dtex, the tensile modulus is 1000~1200cN / dtex, and the elongation at break is 3%~3.5%.

[0026] The present invention also provides a method for preparing para-aramid aerogel fibers, wherein a para-aramid fiber dispersion is first prepared, then wet spinning is performed to obtain para-aramid hydrogel fibers, and then the para-aramid hydrogel fibers are dried to obtain para-aramid aerogel fibers, wherein the para-aramid fibers are the para-aramid fibers described above.

[0027] As a preferred technical solution:

[0028] In the preparation method of para-aramid aerogel fiber as described above, the concentration of the para-aramid fiber dispersion is 0.2~2wt%.

[0029] The preparation method of para-aramid aerogel fiber as described above involves the following steps: using a syringe and a micro-injection pump, the para-aramid fiber dispersion is extruded from the needle into a coagulation bath for solidification, thereby obtaining the para-aramid hydrogel fiber. The coagulation bath is located in a coagulation bath pan. During solidification, a constant-speed turntable rotates the coagulation bath pan at a certain speed to prevent the fine streams of the para-aramid fiber dispersion from stacking and sticking together, thus avoiding loss of fiber morphology. During the solidification process, the color of the fine streams of the para-aramid fiber dispersion in the coagulation bath gradually changes from dark red to light yellow.

[0030] In the preparation method of para-aramid aerogel fiber as described above, the diameter of the needle is 200~1000μm, the coagulation bath is a mixture of DMSO (dimethyl sulfoxide) and proton donor, the volume ratio of DMSO to proton donor is 100~1000:1, and the proton donor is deionized water, ethanol or hydrochloric acid.

[0031] In the preparation method of para-aramid aerogel fiber as described above, the drying is carried out by freeze drying or supercritical drying.

[0032] The present invention also provides a para-aramid aerogel fiber, which is prepared by the method for preparing para-aramid aerogel fiber as described in any of the preceding claims;

[0033] The dyeing rate of para-aramid aerogel fiber is 96%~99%, with a color fastness of grade 5 for washing, grade 5 for rubbing, grade 4~5 for light exposure, a water contact angle of 133.25°~137.75°, and a specific surface area of ​​250~300m². 3 / g, with a breaking strength of 1~5cN / dtex, a tensile modulus of 50~100cN / dtex, and an elongation at break of 20%~30%.

[0034] Beneficial effects:

[0035] This invention achieves a breakthrough of "one agent, multiple effects" by modifying para-aramid with 2,3-difluoro-p-phenylenediamine: the fluorine group not only breaks the dense structure of the fiber to improve the dye adsorption capacity and achieve dark dyeing, but also strengthens the mechanical properties through intermolecular hydrogen bonds. At the same time, its hydrophobic properties and surface microstructure work together to give the fiber superhydrophobicity, thereby solving the three major pain points of traditional fibers: light dyeing, weak strength, and poor water resistance, and providing technical support for the multi-scenario application of high-performance fibers. Attached Figure Description

[0036] Figure 1 The flowchart shows the preparation process of 2,3-difluoro-p-phenylenediamine.

[0037] Figure 2 It is 2,3-difluoro-p-phenylenediamine 1 H NMR spectrum;

[0038] Figure 3 It is 2,3-difluoro-p-phenylenediamine 13 C NMR spectrum;

[0039] Figure 4 This is a water contact angle test diagram of para-aramid fiber in Example 1;

[0040] Figure 5 This is a water contact angle test diagram of para-aramid fiber in Example 2;

[0041] Figure 6 This is a water contact angle test diagram of para-aramid fiber in Example 3;

[0042] Figure 7 This is a water contact angle test diagram of para-aramid fiber in Example 4;

[0043] Figure 8 This is a water contact angle test diagram of para-aramid fiber in Example 5;

[0044] Figure 9 This is a water contact angle test diagram of para-aramid aerogel fiber in Example 1;

[0045] Figure 10 This is a water contact angle test diagram of para-aramid aerogel fiber in Example 2;

[0046] Figure 11 This is a water contact angle test diagram of para-aramid aerogel fiber in Example 3;

[0047] Figure 12 This is a water contact angle test diagram of para-aramid aerogel fiber in Example 4;

[0048] Figure 13 This is a water contact angle test diagram of para-aramid aerogel fiber in Example 5;

[0049] Figure 14 This is a schematic diagram illustrating the reaction of p-phenylenediamine, 2,3-difluoro-p-phenylenediamine, and terephthaloyl chloride to produce para-aramid.

[0050] Figure 15 This is a schematic diagram illustrating the intermolecular hydrogen bonding effect of 2,3-difluoro-p-phenylenediamine on para-aramid fibers. Detailed Implementation

[0051] The present invention will be further described below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0052] The following are the test methods for the relevant performance indicators in each embodiment and comparative example:

[0053] Crystallinity and crystal axis orientation index: The fiber was made into powder (average particle size 40 μm) and X-ray diffraction was performed using an X-ray diffraction spectrometer. The test conditions were: CuKα target (wavelength 0.15406 nm), tube voltage 20~60 kV, tube current 20~60 mA, scanning frequency 12 (°) / min, and scanning angle (2θ) 5°~90°, thus obtaining the wide-angle X-ray diffraction spectrum (WAXD) and two-dimensional wide-angle X-ray diffraction spectrum (2D-WXRD) of ANF; by analyzing... The crystallinity of the fiber is calculated by peak fitting of WAXD spectrum. The crystal orientation index (R) is calculated by crystal axis orientation index analysis method from 2D-WXRD spectrum. Specifically, the sharpest diffraction spot on the 2D-WXRD spectrum is selected, and the X-ray azimuth angle is selected from -90° to 90° along the concentric arc direction for scanning and integration. The distribution curve of diffraction intensity in the azimuth angle is obtained. Then, according to the upper half peak width (H) of the curve, the crystal axis orientation index is obtained by using the calculation formula R=(180°-H) / 180°.

[0054] Dye uptake rate: First, measure 1 mL of the dye solution before dyeing and 5 mL of the dye solution after dyeing; then, transfer the measured dye solution before dyeing and the dye solution after dyeing to 25 mL volumetric flasks respectively under the condition of 20 °C, and dilute to the calibration line; subsequently, shake the solution in the volumetric flask well and let it stand for measurement; finally, use a spectrophotometer to measure the absorbance values of the dye solution before dyeing and the dye solution after dyeing respectively at the maximum absorption wavelength of Disperse Red BFL (CAS: 12223 - 43 - 7), and then calculate the dye uptake rate of the aramid fiber based on the measured absorbance values; the dyeing conditions are: time 1 h, dyeing temperature 170 °C, bath ratio 40:1, dye solution concentration 3%, and the pH value of the dye solution is adjusted to 5.5 with glacial acetic acid; the treatment process is: pre-treatment, wash with water at 90 °C for 10 min, post-treatment, wash with water at 90 °C for 10 min, overflow water wash for 10 min, and dry at 70 °C for 1 h.

[0055] Soaping fastness: Tested according to the standard of GB / T 3921 - 2008.

[0056] Rubbing fastness: Tested according to the standard of GB / T 3920 - 2024.

[0057] Light fastness: Tested according to the standard of GB / T 8427 - 2019.

[0058] Water contact angle: The contact angle is measured by a video contact angle measuring instrument. When testing the static contact angle in the experiment, the volume of water is set to 3 μL for testing; the average value of the left and right water contact angles is taken.

[0059] Tensile strength, tensile modulus, elongation at break: Tested using an electronic universal testing machine according to the standard of GB / T 14344 - 2022; among them, the gauge length is 5OO mm and the tensile rate is 250 mm / min.

[0060] Specific surface area: The specific surface area of the aerogel fiber is analyzed by a Barret-Joyner-Halenda (BJH) nitrogen adsorption-desorption instrument (model ASAP2020, produced by Micromeritics Company, USA). Specifically, using the Brunauer-Emmet-Teller (BET) method, under the condition of a temperature of 77 K, by measuring the amount of nitrogen adsorbed by the fiber when the pressure is within the range of 0.05 < P / P0 < 0.3, the specific surface area of the fiber is calculated.

[0061] In the following examples, the preparation process of 2,3-difluoro-p-phenylenediamine is as Figure 1 shown, and the specific preparation process is as follows:

[0062] (1) Preparation of materials;

[0063] 2,3-difluoroaniline;

[0064] Concentrated nitric acid: water is the solvent, and its mass fraction is 68%.

[0065] Concentrated sulfuric acid: solvent is water, mass fraction is 98.3%;

[0066] hydrogen;

[0067] Palladium on carbon (CAS: 7440-05-3);

[0068] (2) Preparation of 2,3-difluoro-p-phenylenediamine;

[0069] First, 2,3-difluoroaniline is reacted with concentrated nitric acid in a concentrated sulfuric acid environment for 12 hours (reaction temperature 80℃) to produce 2,3-difluoro-4-nitroaniline. Then, 2,3-difluoro-4-nitroaniline is reacted with hydrogen under palladium-carbon catalysis for 18 hours (reaction temperature 40℃) to produce 2,3-difluoro-p-phenylenediamine. 1 H NMR spectrum as follows Figure 2 As shown, 13 C NMR spectrum as follows Figure 3 (As shown), the structural formula of 2,3-difluoro-p-phenylenediamine is as follows:

[0070] ;

[0071] The mass ratio of 2,3-difluoroaniline to concentrated nitric acid is 1:100, the volume ratio of concentrated nitric acid to concentrated sulfuric acid is 1:2, the molar ratio of 2,3-difluoro-4-nitroaniline to hydrogen is 1:4, and the mass ratio of hydrogen to palladium on carbon is 1:0.2.

[0072] Example 1

[0073] A method for preparing para-aramid aerogel fibers, the specific steps of which are as follows:

[0074] (1) Preparation of main materials;

[0075] DMAc;

[0076] LiCl;

[0077] p-Phenylenediamine;

[0078] 2,3-Difluoro-p-phenylenediamine;

[0079] terephthaloyl chloride;

[0080] LiOH;

[0081] Coagulation bath a: DMAc aqueous solution, volume concentration of 40%, temperature of 30℃;

[0082] Molecular sieve: 5A molecular sieve;

[0083] DMSO;

[0084] Deionized water;

[0085] Strong base: NaOH;

[0086] Coagulation bath b: a mixture of DMSO and deionized water, with a volume ratio of DMSO to deionized water of 100:1;

[0087] tert-Butanol aqueous solution: concentration 25 wt%;

[0088] (2) Preparation of para-aramid solution;

[0089] First, under nitrogen or inert gas protection, DMAc and LiCl are added to the reactor and stirred. Then, p-phenylenediamine and 2,3-difluoro-p-phenylenediamine are added. After complete dissolution, the temperature is lowered to -4°C, and terephthaloyl chloride is added. The reaction system temperature is maintained at 25°C, and the reaction continues for 20 minutes after the addition is complete. Finally, LiOH is added for neutralization to obtain a para-aramid solution. The process of p-phenylenediamine, 2,3-difluoro-p-phenylenediamine, and terephthaloyl chloride reacting to produce para-aramid is as follows: Figure 14 As shown; wherein, the molar ratio of p-phenylenediamine, DMAc, LiCl, and LiOH is 1:100:4:6, and the molar ratio of p-phenylenediamine, 2,3-difluoro-p-phenylenediamine, and terephthaloyl chloride is 1:1:3.3;

[0090] (3) Preparation of para-aramid fibers;

[0091] (3.1) After centrifuging to remove salt from the para-aramid solution, it is placed into a reaction vessel for degassing;

[0092] (3.2) The para-aramid solution was spun by wet and dry spinning. The overall process flow was as follows: spinning → air bath → coagulation bath a → stretching → washing → drying → hot stretching → heat setting → oiling → winding to obtain para-aramid fibers. During spinning, the temperature of the para-aramid solution was 20℃, the metering pump speed was 4r / min, the spinneret specification was φ0.08mm×100 holes, the spinning speed was 7m / min, the air bath height was 8mm, the stretching ratio was 2, the washing temperature was 70℃, the hot stretching temperature was 300℃, the heat setting temperature was 320℃, and the heat setting time was 90s.

[0093] The crystallinity of para-aramid fiber is 46%, the crystal axis orientation index is 0.9, the dyeing rate is 94%, the color fastness to washing is grade 5, the color fastness to rubbing is grade 5, the color fastness to sunlight is grade 4, and the water contact angle is 102.5° (test results are as follows). Figure 4 As shown), the tensile strength is 30 cN / dtex, the tensile modulus is 1000 cN / dtex, and the elongation at break is 3%.

[0094] (4) Preparation of para-aramid fiber dispersion;

[0095] (4.1) First, place the molecular sieve in a tube furnace and calcine it at 350℃ for 6 hours. Then, take it out and cool it to room temperature in a desiccator. Then, add an appropriate amount of molecular sieve to DMSO, seal and stir for 48 hours, and filter to obtain anhydrous DMSO. Seal and store for later use. Wash the para-aramid fiber with deionized water and dry it in a vacuum oven at 80℃ for 4 hours to constant weight.

[0096] (4.2) Add 10~30g of para-aramid fiber and an equal mass of strong alkali to a three-necked flask, then add anhydrous DMSO, and stir under nitrogen protection until the system changes from colorless and transparent to dark red (generally takes 6~10 days) to obtain a para-aramid fiber dispersion with a concentration of 0.2wt%.

[0097] (5) Preparation of para-aramid hydrogel fibers by wet spinning;

[0098] The para-aramid fiber dispersion was extruded from a needle with a diameter of 200 μm into coagulation bath b for solidification (coagulation bath b is located in a coagulation bath tray, and the coagulation bath tray is rotated by a constant speed turntable during solidification), thus obtaining para-aramid hydrogel fibers.

[0099] (6) Preparation of para-aramid aerogel fibers;

[0100] Para-aramid hydrogel fibers were placed in a beaker, and deionized water with a mass of 10 times that of the fibers was added for static treatment. The deionized water was replaced every 6 hours (with the same mass each time) for a total of 6 replacements. Then, the deionized water was replaced with an equal volume of tert-butanol aqueous solution every 8 hours for a total of 2 replacements. The para-aramid hydrogel fibers were then frozen at -20°C for 10 hours, and then transferred to a freeze dryer. The dryer was operated at a pressure of 0.4 mbar and a cold trap temperature of -40°C for 48 hours to obtain para-aramid aerogel fibers.

[0101] The final obtained para-aramid aerogel fiber had a dyeing rate of 96%, a color fastness to washing of grade 5, a color fastness to rubbing of grade 5, a color fastness to sunlight of grade 4, and a water contact angle of 133.25° (test results are as follows). Figure 9 As shown), the specific surface area is 250m². 3 / g, with a breaking strength of 1cN / dtex, a tensile modulus of 50cN / dtex, and an elongation at break of 20%.

[0102] Comparative Example 1

[0103] A method for preparing para-aramid aerogel fibers differs from Example 1 only in that 2,3-difluoro-p-phenylenediamine is replaced with an equimolar amount of 2,4-diamino-6-fluoro-1,3,5-triazine.

[0104] The para-aramid fiber obtained in step (3) has a water contact angle of 60°, a breaking strength of 22 cN / dtex, a tensile modulus of 700 cN / dtex, and a breaking elongation of 2.8%.

[0105] The final para-aramid aerogel fibers produced had a water contact angle of 62° and a specific surface area of ​​94.7 m². 3 The tensile strength is 0.8 cN / dtex, the tensile modulus is 44 cN / dtex, and the elongation at break is 17%.

[0106] Compared with Example 1, the mechanical and hydrophobic properties of para-aramid fibers and para-aramid aerogel fibers were significantly reduced. This is because the fluorine atoms in 2,4-diamino-6-fluoro-1,3,5-triazine used in Comparative Example 1 were too few, which did not significantly improve the surface energy, and the hydrogen bonding between molecular chains was greatly weakened, thus failing to achieve the superhydrophobic properties of the fibers and reducing the mechanical properties of the fibers.

[0107] Comparative Example 2

[0108] A method for preparing para-aramid aerogel fibers differs from Example 1 only in that 2,3-difluoro-p-phenylenediamine is replaced with an equimolar amount of 4,5-difluorophenyl-1,2-diamine.

[0109] The para-aramid fiber obtained in step (3) has a crystallinity of 11%, a crystal axis orientation index of 0.4, a breaking strength of 11 cN / dtex, a tensile modulus of 400 cN / dtex, and a breaking elongation of 1.3%.

[0110] The final para-aramid aerogel fiber had a breaking strength of 0.4 cN / dtex, a tensile modulus of 22 cN / dtex, and an elongation at break of 13%.

[0111] Compared with Example 1, the crystallinity, crystal orientation index and mechanical properties of para-aramid fiber and para-aramid aerogel fiber decreased significantly. This is because the 4,5-difluorobenzene-1,2-diamine used in Comparative Example 2 is difficult to polymerize effectively, resulting in poor polymer molecular symmetry and low molecular weight, thereby reducing its crystallinity, crystal orientation index and mechanical properties.

[0112] Comparative Example 3

[0113] A method for preparing para-aramid aerogel fibers differs from Example 1 only in that 2,3-difluoro-p-phenylenediamine is replaced with an equimolar amount of 2,3,5,6-tetrafluoro-p-phenylenediamine;

[0114] The para-aramid fiber obtained in step (3) has a water contact angle of 95.7°, a breaking strength of 28 cN / dtex, a tensile modulus of 887 cN / dtex, and a breaking elongation of 2%.

[0115] The final para-aramid aerogel fiber had a water contact angle of 100.1°, a breaking strength of 0.9 cN / dtex, a tensile modulus of 43 cN / dtex, and an elongation at break of 14%.

[0116] Compared with Example 1, the mechanical properties and hydrophobic properties of para-aramid fibers and para-aramid aerogel fibers in Comparative Example 3 were significantly reduced. This is because the excessive number of 2,3,5,6-tetrafluoro-terephthalic acid fluorine atoms used in Comparative Example 3 resulted in low reactivity, low degree of polymerization of the product, and weakened hydrogen bonding between molecular chains, thereby reducing the mechanical properties of the fibers and affecting their hydrophobic properties.

[0117] Example 2

[0118] A method for preparing para-aramid aerogel fibers, the specific steps of which are as follows:

[0119] (1) Preparation of main materials;

[0120] DMAc;

[0121] LiCl;

[0122] p-Phenylenediamine;

[0123] 2,3-Difluoro-p-phenylenediamine;

[0124] terephthaloyl chloride;

[0125] LiOH;

[0126] Coagulation bath a: DMAc aqueous solution, volume concentration of 48%, temperature of 31℃;

[0127] Molecular sieve: 4A molecular sieve;

[0128] DMSO;

[0129] Deionized water;

[0130] Strong base: KOH;

[0131] Coagulation bath b: a mixture of DMSO and ethanol, with a volume ratio of DMSO to ethanol of 250:1;

[0132] tert-Butanol aqueous solution: concentration 75 wt%;

[0133] (2) Preparation of para-aramid solution;

[0134] First, under nitrogen or inert gas protection, DMAc and LiCl are added to the reactor and stirred. Then, p-phenylenediamine and 2,3-difluoro-p-phenylenediamine are added. After complete dissolution, the mixture is cooled to -3°C, and terephthaloyl chloride is added. The reaction system temperature is maintained at 26°C. After the addition is complete, the reaction continues for 25 minutes. Finally, LiOH is added for neutralization to obtain a para-aramid solution. The molar ratio of p-phenylenediamine, DMAc, LiCl, and LiOH is 1:500:6:10, and the molar ratio of p-phenylenediamine, 2,3-difluoro-p-phenylenediamine, and terephthaloyl chloride is 1:1.1:3.4.

[0135] (3) Preparation of para-aramid fibers;

[0136] (3.1) After centrifuging to remove salt from the para-aramid solution, it is placed into a reaction vessel for degassing;

[0137] (3.2) The para-aramid solution was spun by wet and dry spinning. The overall process flow was as follows: spinning → air bath → coagulation bath a → stretching → washing → drying → hot stretching → heat setting → oiling → winding to obtain para-aramid fibers. During spinning, the temperature of the para-aramid solution was 21℃, the metering pump speed was 4r / min, the spinneret specification was φ0.08mm×200 holes, the spinning speed was 8m / min, the air bath height was 9mm, the stretching ratio was 3, the washing temperature was 72℃, the hot stretching temperature was 305℃, the heat setting temperature was 327℃, and the heat setting time was 110s.

[0138] The crystallinity of para-aramid fiber is 47%, the crystal axis orientation index is 0.91, the dyeing rate is 95%, the color fastness to washing is grade 5, the color fastness to rubbing is grade 5, the color fastness to sunlight is grade 4, and the water contact angle is 118.1° (test results are as follows). Figure 5 As shown), the tensile strength is 32 cN / dtex, the tensile modulus is 1050 cN / dtex, and the elongation at break is 3.1%.

[0139] (4) Preparation of para-aramid fiber dispersion;

[0140] (4.1) First, place the molecular sieve in a tube furnace and calcine it at 360°C for 7 hours. Then, take it out and place it in a desiccator to cool to room temperature. Then, add an appropriate amount of molecular sieve to DMSO, seal and stir for 60 hours, and filter to obtain anhydrous DMSO. Seal and store for later use. Wash the para-aramid fiber with deionized water and dry it in a vacuum oven at 83°C for 4.5 hours to constant weight.

[0141] (4.2) Add 10~30g of para-aramid fiber and an equal mass of strong alkali to a three-necked flask, then add anhydrous DMSO, and stir under nitrogen protection until the system changes from colorless and transparent to dark red (generally takes 6~10 days) to obtain a para-aramid fiber dispersion with a concentration of 0.7wt%.

[0142] (5) Preparation of para-aramid hydrogel fibers by wet spinning;

[0143] The para-aramid fiber dispersion was extruded from a needle with a diameter of 400 μm into coagulation bath b for solidification (coagulation bath b is located in a coagulation bath tray, and the coagulation bath tray is rotated by a constant speed turntable during solidification), thus obtaining para-aramid hydrogel fibers.

[0144] (6) Preparation of para-aramid aerogel fibers;

[0145] Para-aramid hydrogel fibers were placed in a beaker, and deionized water with a mass 10 times that of the fibers was added for static treatment. The deionized water was replaced every 10 hours (with the same mass each time) for a total of 8 replacements. Then, an equal volume of tert-butanol aqueous solution was used to replace the deionized water, and the tert-butanol aqueous solution was replaced every 10 hours for a total of 2 replacements. The para-aramid hydrogel fibers were then frozen at -40°C for 6 hours, and then transferred to a freeze dryer. The dryer was controlled at a pressure of 0.6 mbar and a cold trap temperature of -60°C for 24 hours to obtain para-aramid aerogel fibers.

[0146] The final obtained para-aramid aerogel fiber had a dyeing rate of 97%, a color fastness to washing of grade 5, a color fastness to rubbing of grade 5, a color fastness to sunlight of grade 4, and a water contact angle of 133.95° (test results are as follows). Figure 10 As shown), the specific surface area is 260 m². 3 / g, with a breaking strength of 2cN / dtex, a tensile modulus of 60cN / dtex, and an elongation at break of 22%.

[0147] Example 3

[0148] A method for preparing para-aramid aerogel fibers, the specific steps of which are as follows:

[0149] (1) Preparation of main materials;

[0150] DMAc;

[0151] LiCl;

[0152] p-Phenylenediamine;

[0153] 2,3-Difluoro-p-phenylenediamine;

[0154] terephthaloyl chloride;

[0155] LiOH;

[0156] Coagulation bath a: DMAc aqueous solution, volume concentration of 55%, temperature of 32℃;

[0157] Molecular sieve: 3A molecular sieve;

[0158] DMSO;

[0159] Deionized water;

[0160] Strong base: RbOH;

[0161] Coagulation bath b: a mixture of DMSO and hydrochloric acid, with a volume ratio of DMSO to hydrochloric acid of 500:1;

[0162] Ethanol;

[0163] (2) Preparation of para-aramid solution;

[0164] First, under nitrogen or inert gas protection, DMAc and LiCl are added to the reactor and stirred. Then, p-phenylenediamine and 2,3-difluoro-p-phenylenediamine are added. After complete dissolution, the mixture is cooled to -2°C, and terephthaloyl chloride is added. The reaction system temperature is maintained at 28°C. After the addition is complete, the reaction continues for 30 minutes. Finally, LiOH is added for neutralization to obtain a para-aramid solution. The molar ratio of p-phenylenediamine, DMAc, LiCl, and LiOH is 1:1000:8:15, and the molar ratio of p-phenylenediamine, 2,3-difluoro-p-phenylenediamine, and terephthaloyl chloride is 1:1.2:3.5.

[0165] (3) Preparation of para-aramid fibers;

[0166] (3.1) After centrifuging to remove salt from the para-aramid solution, it is placed into a reaction vessel for degassing;

[0167] (3.2) The para-aramid solution was spun by wet and dry spinning. The overall process flow was as follows: spinning → air bath → coagulation bath a → stretching → washing → drying → hot stretching → heat setting → oiling → winding to obtain para-aramid fibers. During spinning, the temperature of the para-aramid solution was 22℃, the metering pump speed was 5r / min, the spinneret specification was φ0.08mm×300 holes, the spinning speed was 9m / min, the air bath height was 11mm, the stretching ratio was 5, the washing temperature was 75℃, the hot stretching temperature was 310℃, the heat setting temperature was 335℃, and the heat setting time was 130s.

[0168] The para-aramid fiber has a crystallinity of 48%, a crystal axis orientation index of 0.92, a dyeing rate of 96%, a color fastness to washing (grade 5), a color fastness to rubbing (grade 5), a color fastness to sunlight (grade 5), and a water contact angle of 120.1° (test results are as follows). Figure 6 As shown in the figure, the tensile strength is 35 cN / dtex, the tensile modulus is 1100 cN / dtex, and the elongation at break is 3.2%.

[0169] (4) Preparation of para-aramid fiber dispersion;

[0170] (4.1) First, place the molecular sieve in a tube furnace and calcine it at 370℃ for 9 hours. Then, take it out and place it in a desiccator to cool to room temperature. Then, add an appropriate amount of molecular sieve to DMSO, seal and stir for 72 hours, and filter to obtain anhydrous DMSO. Seal and store for later use. Wash the para-aramid fiber with deionized water and dry it in a vacuum oven at 85℃ for 5 hours to constant weight.

[0171] (4.2) Add 10~30g of para-aramid fiber and an equal mass of strong alkali to a three-necked flask, then add anhydrous DMSO, and stir under nitrogen protection until the system changes from colorless and transparent to dark red (generally takes 6~10 days) to obtain a para-aramid fiber dispersion with a concentration of 1.1wt%.

[0172] (5) Preparation of para-aramid hydrogel fibers by wet spinning;

[0173] The para-aramid fiber dispersion was extruded from a needle with a diameter of 600 μm into coagulation bath b for solidification (coagulation bath b is located in a coagulation bath tray, and the coagulation bath tray is rotated by a constant speed turntable during solidification), thus obtaining para-aramid hydrogel fibers.

[0174] (6) Preparation of para-aramid aerogel fibers;

[0175] Para-aramid hydrogel fibers were placed in a beaker, and ethanol with a mass of 10 times that of the para-aramid hydrogel fibers was added and allowed to stand. The ethanol was replaced every 6 hours (with the same mass each time) for a total of 10 times. Then, the ethanol inside the hydrogel fibers was gradually replaced with supercritical CO2 using a supercritical drying device. Subsequently, the system was depressurized and cooled to obtain para-aramid aerogel fibers.

[0176] The final obtained para-aramid aerogel fiber had a dyeing rate of 98%, a color fastness to washing of grade 5, a color fastness to rubbing of grade 5, a color fastness to sunlight of grade 4, and a water contact angle of 133.95° (test results are as follows). Figure 11 As shown), the specific surface area is 275 m². 3 / g, with a breaking strength of 3cN / dtex, a tensile modulus of 75cN / dtex, and an elongation at break of 25%.

[0177] Example 4

[0178] A method for preparing para-aramid aerogel fibers, the specific steps of which are as follows:

[0179] (1) Preparation of main materials;

[0180] DMAc;

[0181] LiCl;

[0182] p-Phenylenediamine;

[0183] 2,3-Difluoro-p-phenylenediamine;

[0184] terephthaloyl chloride;

[0185] LiOH;

[0186] Coagulation bath a: DMAc aqueous solution, volume concentration 63%, temperature 33℃;

[0187] Molecular sieve: 4A molecular sieve;

[0188] DMSO;

[0189] Deionized water;

[0190] Strong base: RbOH;

[0191] Coagulation bath b: a mixture of DMSO and hydrochloric acid, with a volume ratio of DMSO to hydrochloric acid of 750:1;

[0192] Ethanol;

[0193] (2) Preparation of para-aramid solution;

[0194] First, under nitrogen or inert gas protection, DMAc and LiCl are added to the reactor and stirred. Then, p-phenylenediamine and 2,3-difluoro-p-phenylenediamine are added. After complete dissolution, the mixture is cooled to -1°C, and terephthaloyl chloride is added. The reaction system temperature is maintained at 29°C. After the addition is complete, the reaction continues for 35 minutes. Finally, LiOH is added for neutralization to obtain a para-aramid solution. The molar ratio of p-phenylenediamine, DMAc, LiCl, and LiOH is 1:1500:10:20, and the molar ratio of p-phenylenediamine, 2,3-difluoro-p-phenylenediamine, and terephthaloyl chloride is 1:1.3:3.7.

[0195] (3) Preparation of para-aramid fibers;

[0196] (3.1) After centrifuging to remove salt from the para-aramid solution, it is placed into a reaction vessel for degassing;

[0197] (3.2) The para-aramid solution was spun by wet and dry spinning. The overall process flow was as follows: spinning → air bath → coagulation bath a → stretching → washing → drying → hot stretching → heat setting → oiling → winding to obtain para-aramid fibers. During spinning, the temperature of the para-aramid solution was 24℃, the metering pump speed was 6r / min, the spinneret specification was φ0.08mm×400 holes, the spinning speed was 10m / min, the air bath height was 12mm, the stretching ratio was 6, the washing temperature was 77℃, the hot stretching temperature was 315℃, the heat setting temperature was 342℃, and the heat setting time was 150s.

[0198] The crystallinity of para-aramid fiber is 49%, the crystal axis orientation index is 0.93, the dyeing rate is 97%, the color fastness to washing is grade 5, the color fastness to rubbing is grade 5, the color fastness to sunlight is grade 5, and the water contact angle is 123.35° (test results are as follows). Figure 7 As shown), the tensile strength is 37 cN / dtex, the tensile modulus is 1150 cN / dtex, and the elongation at break is 3.4%.

[0199] (4) Preparation of para-aramid fiber dispersion;

[0200] (4.1) First, place the molecular sieve in a tube furnace and calcine it at 380℃ for 11 hours. Then, take it out and cool it to room temperature in a desiccator. Then, add an appropriate amount of molecular sieve to DMSO, seal and stir for 84 hours, and filter to obtain anhydrous DMSO. Seal and store for later use. Wash the para-aramid fiber with deionized water and dry it in a vacuum oven at 87℃ for 5.5 hours until constant weight.

[0201] (4.2) Add 10~30g of para-aramid fiber and an equal mass of strong alkali to a three-necked flask, then add anhydrous DMSO, and stir under nitrogen protection until the system changes from colorless and transparent to dark red (generally takes 6~10 days) to obtain a para-aramid fiber dispersion with a concentration of 1.5wt%.

[0202] (5) Preparation of para-aramid hydrogel fibers by wet spinning;

[0203] The para-aramid fiber dispersion was extruded from a needle with a diameter of 800 μm into coagulation bath b for solidification (coagulation bath b is located in a coagulation bath tray, and the coagulation bath tray is rotated by a constant speed turntable during solidification), thus obtaining para-aramid hydrogel fibers.

[0204] (6) Preparation of para-aramid aerogel fibers;

[0205] Para-aramid hydrogel fibers were placed in a beaker, and ethanol with a mass of 10 times that of the para-aramid hydrogel fibers was added and allowed to stand. The ethanol was replaced every 10 hours (with the same mass each time) for a total of 6 times. Then, the ethanol inside the hydrogel fibers was gradually replaced with supercritical CO2 using a supercritical drying device. Subsequently, the system was depressurized and cooled to obtain para-aramid aerogel fibers.

[0206] The final obtained para-aramid aerogel fiber had a dyeing rate of 99%, a color fastness to washing of grade 5, a color fastness to rubbing of grade 5, a color fastness to sunlight of grade 5, and a water contact angle of 137.35° (test results are as follows). Figure 12 As shown), the specific surface area is 285 m². 3 / g, with a breaking strength of 4cN / dtex, a tensile modulus of 90cN / dtex, and an elongation at break of 28%.

[0207] Example 5

[0208] A method for preparing para-aramid aerogel fibers, the specific steps of which are as follows:

[0209] (1) Preparation of main materials;

[0210] DMAc;

[0211] LiCl;

[0212] p-Phenylenediamine;

[0213] 2,3-Difluoro-p-phenylenediamine;

[0214] terephthaloyl chloride;

[0215] LiOH;

[0216] Coagulation bath a: DMAc aqueous solution, volume concentration of 70%, temperature of 35℃;

[0217] Molecular sieve: 3A molecular sieve;

[0218] DMSO;

[0219] Deionized water;

[0220] Strong base: RbOH;

[0221] Coagulation bath b: a mixture of DMSO and hydrochloric acid, with a volume ratio of DMSO to hydrochloric acid of 1000:1;

[0222] Ethanol;

[0223] (2) Preparation of para-aramid solution;

[0224] First, under nitrogen or inert gas protection, DMAc and LiCl are added to the reactor and stirred. Then, p-phenylenediamine and 2,3-difluoro-p-phenylenediamine are added. After complete dissolution, the temperature is lowered to 0°C, and terephthaloyl chloride is added. The reaction system temperature is maintained at 30°C. After the addition is complete, the reaction continues for 40 minutes. Finally, LiOH is added for neutralization to obtain a para-aramid solution. The molar ratio of p-phenylenediamine, DMAc, LiCl, and LiOH is 1:2000:12:24, and the molar ratio of p-phenylenediamine, 2,3-difluoro-p-phenylenediamine, and terephthaloyl chloride is 1:1.3:3.9.

[0225] (3) Preparation of para-aramid fibers;

[0226] (3.1) After centrifuging to remove salt from the para-aramid solution, it is placed into a reaction vessel for degassing;

[0227] (3.2) The para-aramid solution was spun by wet and dry spinning. The overall process flow was as follows: spinning → air bath → coagulation bath a → stretching → washing → drying → hot stretching → heat setting → oiling → winding to obtain para-aramid fibers. During spinning, the temperature of the para-aramid solution was 25℃, the metering pump speed was 7r / min, the spinneret specification was φ0.08mm×500 holes, the spinning speed was 12m / min, the air bath height was 14mm, the stretching ratio was 8, the washing temperature was 80℃, the hot stretching temperature was 320℃, the heat setting temperature was 350℃, and the heat setting time was 180s.

[0228] The para-aramid fiber has a crystallinity of 50%, a crystal axis orientation index of 0.94, a dyeing rate of 98%, a color fastness to washing (grade 5), a color fastness to rubbing (grade 5), a color fastness to sunlight (grade 5), and a water contact angle of 131.35° (test results are as follows). Figure 8 As shown), the tensile strength is 40 cN / dtex, the tensile modulus is 1200 cN / dtex, and the elongation at break is 3.5%.

[0229] (4) Preparation of para-aramid fiber dispersion;

[0230] (4.1) First, place the molecular sieve in a tube furnace and calcine it at 400℃ for 12 hours. Then, take it out and cool it to room temperature in a desiccator. Then, add an appropriate amount of molecular sieve to DMSO, seal and stir for 96 hours, and filter to obtain anhydrous DMSO. Seal and store for later use. Wash the para-aramid fiber with deionized water and dry it in a vacuum oven at 90℃ for 6 hours to constant weight.

[0231] (4.2) Add 10~30g of para-aramid fiber and an equal mass of strong alkali to a three-necked flask, then add anhydrous DMSO, and stir under nitrogen protection until the system changes from colorless and transparent to dark red (generally takes 6~10 days) to obtain a para-aramid fiber dispersion with a concentration of 2wt%.

[0232] (5) Preparation of para-aramid hydrogel fibers by wet spinning;

[0233] The para-aramid fiber dispersion was extruded from a needle with a diameter of 1000 μm into coagulation bath b for solidification (coagulation bath b is located in a coagulation bath tray, and the coagulation bath tray is rotated by a constant speed turntable during solidification) to obtain para-aramid hydrogel fibers.

[0234] (6) Preparation of para-aramid aerogel fibers;

[0235] Para-aramid hydrogel fibers were placed in a beaker, and ethanol with a mass of 10 times that of the para-aramid hydrogel fibers was added and allowed to stand. The ethanol was replaced every 10 hours (with the same mass each time) for a total of 6 times. Then, the ethanol inside the hydrogel fibers was gradually replaced with supercritical CO2 using a supercritical drying device. Subsequently, the system was depressurized and cooled to obtain para-aramid aerogel fibers.

[0236] The final obtained para-aramid aerogel fiber had a dyeing rate of 99%, a color fastness to washing of grade 5, a color fastness to rubbing of grade 5, a color fastness to sunlight of grade 5, and a water contact angle of 137.75° (test results are as follows). Figure 13 As shown), the specific surface area is 300m². 3 / g, with a breaking strength of 5cN / dtex, a tensile modulus of 100cN / dtex, and an elongation at break of 30%.

Claims

1. A method for producing para-aramid fibers, characterized by, The para-aramid solution is spun to obtain para-aramid fibers, wherein the para-aramid is prepared from p-phenylenediamine, 2,3-difluoro-p-phenylenediamine and terephthaloyl chloride, and the structure of 2,3-difluoro-p-phenylenediamine is as follows: ； The preparation process of 2,3-difluoro-p-phenylenediamine is as follows: 2,3-difluoroaniline is first reacted with concentrated nitric acid in a concentrated sulfuric acid environment to generate 2,3-difluoro-4-nitroaniline, and then 2,3-difluoro-4-nitroaniline is reacted with hydrogen under palladium-carbon catalysis to generate 2,3-difluoro-p-phenylenediamine; The para-aramid fibers have a crystallinity of 46% to 50%, a crystal axis orientation index of 0.90 to 0.94, an upper dyeing rate of 94% to 98%, a soaping color fastness of 5 levels, a rubbing color fastness of 5 levels, a sunlight color fastness of 4 to 5 levels, a water contact angle of 102.5° to 131.15°, a breaking strength of 30 to 40 cN / dtex, a tensile modulus of 1000 to 1200 cN / dtex, and an elongation at break of 3% to 3.5%.

2. The method for preparing para-aramid fiber according to claim 1, characterized in that, The molar ratio of p-phenylenediamine, 2,3-difluoro-p-phenylenediamine and terephthaloyl chloride is 1:1 to 1.3:3.3 to 3.

9.

3. The method of claim 2, wherein the poly (p-phenylene terephthalamide) fibers are prepared by the process of claim 1. The preparation process of the para-aramid solution is as follows: first, under the protection of nitrogen or inert gas, DMAc and LiCl are added to a reaction kettle, stirring is started, then p-phenylenediamine and 2,3-difluoro-p-phenylenediamine are added, the temperature is lowered to -4 to 0℃ after complete dissolution, terephthaloyl chloride is added, the temperature of the reaction system is maintained at 25 to 30℃, after the addition is completed, the reaction is continued for 20 to 40 min, finally, LiOH is added for neutralization to obtain the para-aramid solution.

4. The method of claim 3, wherein the poly (p-phenylene terephthalamide) fibers are prepared by the process of claim 1 or 2. The molar ratio of p-phenylenediamine, DMAc, LiCl and LiOH is 1:100 to 2000:4 to 12:6 to 24.

5. The method for preparing para-aramid fiber according to claim 1, characterized in that, Before spinning, the para-aramid solution is centrifuged to remove salt and then loaded into a reaction tank for defoaming; The spinning is dry-wet spinning, and the overall process flow is: spinning jetting→air bath→coagulation bath→stretching→water washing→drying→heat stretching→heat setting→oiling→winding; During spinning, the temperature of the para-aramid solution is 20 to 25℃, the rotating speed of the metering pump is 4 to 7 r / min, the specification of the spinning plate is φ0.08 mm×100 to 500 holes, the spinning speed is 7 to 12 m / min, the air bath height is 8 to 14 mm, the coagulation bath is DMAc aqueous solution, the temperature of the coagulation bath is 30 to 35℃, the stretching multiple is 2 to 8, the water washing temperature is 70 to 80℃, the heat stretching temperature is 300 to 320℃, the heat setting temperature is 320 to 350℃, and the heat setting time is 90 to 180 s.

6. A para-aramid fiber characterized by, The para-aramid fibers are prepared by the preparation method of any one of claims 1 to 5.

7. A method of making para-aramid aerogel fibers, characterized by, The para-aramid fiber dispersion liquid is first prepared, then wet spinning is performed to obtain para-aramid hydrogel fibers, and then the para-aramid hydrogel fibers are dried to obtain para-aramid aerogel fibers, wherein the para-aramid fibers are the para-aramid fibers of claim 6.

8. The method for preparing para-aramid aerogel fiber according to claim 7, characterized in that, The concentration of the para-aramid fiber dispersion liquid is 0.2 to 2 wt%. The preparation process of the para-aramid hydrogel fiber is that a para-aramid fiber dispersion liquid is extruded from a needle head to a coagulation bath for solidification, and the para-aramid hydrogel fiber is obtained, wherein the coagulation bath is located in a coagulation bath tray, and the coagulation bath tray is rotated by a constant-speed rotating disc during the solidification; The diameter of the needle head is 200-1000 μm, the coagulation bath is a mixed liquid of DMSO and a proton donor, the volume ratio of DMSO to the proton donor is 100-1000:1, and the proton donor is deionized water, ethanol or hydrochloric acid; The drying is performed by a freeze-drying method or a supercritical drying method.

9. A para-aramid aerogel fiber, characterized by, The para-aramid aerogel fiber is prepared by the preparation method of any one of claims 7-8. The dye-uptake rate of the para-aramid aerogel fiber is 96% to 99%, the color fastness to soaping is 5 levels, the color fastness to rubbing is 5 levels, the color fastness to sunlight is 4 to 5 levels, the water contact angle is 133.25° to 137.75°, the specific surface area is 250 to 300 m 3 / g, the breaking strength is 1 to 5 cN / dtex, the tensile modulus is 50 to 100 cN / dtex, and the breaking elongation is 20% to 30%.

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