Intrinsically heterogeneous aramid porous fiber and method of making

Abstract

The present application relates to the technical field of gel fiber, in particular to a kind of inside and outside heterogeneous aramid porous fiber and preparation method. By deprotonation of aramid III fiber, the surface of fiber is negatively charged, and then the assembly kinetics of nanofiber is changed by coagulation bath containing protonic acid, to induce multi-level structure assembly, form "shell layer porous, core layer dense" multi-level pore structure, improve the mechanical strength of aramid aerogel fiber, meet the demand of different application fields on fiber size and strength.

Description

Technical Field

[0001] This invention relates to the field of gel fiber technology, specifically to a porous aramid fiber with internal and external heterogeneous structures and its preparation method. Background Technology

[0002] Porous materials possess characteristics such as high specific surface area, high porosity, and low density, and have broad application prospects in fields such as thermal insulation, energy storage and conversion, photoelectrocatalysis, and water treatment. Traditional porous materials are mainly bulk materials, which have disadvantages such as high brittleness, easy cracking, and difficulty in molding and processing, making it difficult to meet their application requirements in wearable and flexible protective equipment. In contrast, fibrous porous materials have excellent flexibility and weavability, expanding their application in fields such as wearable fabrics.

[0003] Current reported methods for preparing porous fibers include phase separation, template method, cryospinning, and microfluidic spinning. Extruding the spinning solution through a spinneret and then undergoing a sol-gel transition promises for the continuous preparation of porous fibers with uniform structures. Aerogel fibers obtained through wet spinning suffer from low mechanical strength (typically below 10 MPa) due to their low density and weak forces within the fiber's internal cross-linking network. On the other hand, aramid fibers possess excellent mechanical properties, resistance to high and low temperatures, good flame retardancy, and good chemical corrosion resistance. Processing aramid fibers into porous structures is more beneficial for their application in high-temperature thermal insulation protective clothing and other flexible protective equipment. Hierarchical porous structures can ensure both high porosity and improved mechanical properties. However, the assembly of Kevlar aramid nanofiber aerogels is isotropic, resulting in poor mechanical properties and failing to achieve the preparation of anisotropic or hierarchical porous fibers. Existing techniques present difficulties in molding and processing, making it challenging to produce porous aramid fibers with uniform structures. Therefore, developing a method for preparing aerogel fibers with high mechanical strength and a hierarchical pore structure remains a challenge and a key challenge for promoting the widespread application of porous aerogel fibers. Summary of the Invention

[0004] To address the above problems, the present invention provides a porous aramid fiber with internal and external heterogeneous structures and a method for its preparation. By deprotonating aramid III fibers to give the nanofiber surface a negative charge, and then altering the assembly dynamics of the nanofibers through coagulation bath acid protons, a multi-level porous structure with a porous shell and a dense core is formed, which improves the mechanical strength of aramid aerogel fibers and expands their application in textile weaving.

[0005] To achieve the above-mentioned objectives, the present invention provides the following technical solution: On one hand, the present invention provides a method for preparing porous aramid fibers with internal and external heterogeneous structures, comprising the following steps: S1. Aramid III fibers were placed in a potassium hydroxide / dimethyl sulfoxide / water system and stirred to carry out a deprotonation reaction, thereby obtaining an aramid III nanofiber spinning solution. S2. The spinning solution is injected into a coagulation bath containing protic acid, which simultaneously imparts a directional stretching effect to the fiber, causing the fiber to solidify and form, thus obtaining nascent gel fiber. S3. Nascent gel fibers are subjected to solvent replacement-drying treatment to obtain heterogeneous aramid porous fibers.

[0006] In some specific embodiments, aramid III fibers are deprotonated in a potassium hydroxide / dimethyl sulfoxide / water system, breaking the hydrogen bond interactions between aramid fiber molecular chains to obtain aramid nanofibers with negatively charged surfaces. Then, through hydrogen proton induction in a proton donor coagulation bath, the aramid III nanofibers not only adsorb positive charges through physical action, promoting the aggregation of aramid III nanofibers, but also chemically adsorb hydrogen protons, achieving protonation reduction of amide bonds, promoting the assembly of hydrogen bonds between molecular chains, realizing the sol-coagulation hierarchical transformation of aramid nanofibers, and assembling into a hierarchical porous structure of aramid nanofibers with "porous shell and dense core".

[0007] Further, in S1, the length of the aramid III fiber is 1-20 mm; for example, 1-15 mm; or 1-12 mm; or 1-10 mm; or 3-10 mm; or 3-8 mm; or 4-7 mm; such as 5 mm.

[0008] Further, in S1, the aramid concentration in the spinning solution is 0.5-5wt%, for example 0.5-4wt%, or 1-4wt%, or 1.5-3wt%, or 1.5-2.5wt%, such as 2wt%.

[0009] Further, in S1, the mass ratio of potassium hydroxide to aramid III fiber is (1-3):1, for example (1-2.5):1, or (1.5-2.5):1, such as 2:1.

[0010] Furthermore, in S2, the coagulation bath is selected from one or more of deionized water, methanol, ethanol, acetone, and ethylene glycol; In some specific embodiments, the protic acid is selected from inorganic or organic acids; protic acids can not only affect the assembly kinetics of nanofibers, but also significantly improve the sol-gel conversion rate, thereby improving production efficiency and fiber quality. In some preferred embodiments, the protic acid is selected from one or more of sulfuric acid, hydrochloric acid, formic acid, acetic acid, oxalic acid, citric acid, phosphoric acid, and tartaric acid; In some preferred embodiments, the protic acid is selected from one or more of sulfuric acid, hydrochloric acid, acetic acid, and phosphoric acid; In some preferred embodiments, the protonated acid is selected from sulfuric acid. The type of acid proton affects the protonation level and assembly kinetics of nanofibers, and also plays a decisive role in the formation of the three-dimensional structure and shape of nanofibers, thereby affecting their final structural properties and functions.

[0011] Furthermore, in S2, when the spinning solution is injected into the coagulation bath containing protic acid, the injection rate is 0.1-1 mL / min; and / or, when imparting directional stretching to the fiber, the traction speed is 400-600 r / min.

[0012] Further, in S3, the concentration of protic acid in the coagulation bath is 0.1-20 wt%, for example 0.5-15 wt%, or 1-15 wt%, or 2-12 wt%, or 2-10 wt%, or 2-8 wt%, or 2-5 wt%. Further, in S3, the solvent replacement includes immersing the nascent gel fibers in a replacement solvent for replacement; the replacement solvent is one or a combination of two or more of water, ethanol, tert-butanol, n-hexane, cyclohexane, and acetone; and / or The drying process is selected from any one or a combination of two or more of the following: freeze drying, supercritical fluid drying, and atmospheric pressure drying.

[0013] Secondly, the present invention provides an internally and externally heterogeneous aramid porous fiber, which is prepared by the above-mentioned method. The internally and externally heterogeneous aramid porous fiber has a core-shell structure, with the core layer having a nanoporous structure and the shell layer having a microporous structure.

[0014] The micron-sized pores in the outer shell of the heterogeneous aramid porous fiber of this invention can deform and absorb some energy, while the nano-sized pores in the core layer prevent crack propagation and improve the mechanical strength of the aerogel fiber through a more efficient stress transmission path or increased surface area.

[0015] The heterogeneous aramid porous fibers prepared by the above scheme have a multi-level porous structure with "porous shell and dense core", and the pore size, morphology and pore diameter distribution of the fiber core and shell can be controlled.

[0016] The types of raw materials, addition ratios, and process parameters can be adjusted according to actual needs to prepare aerogel fiber materials with nanoscale pores in the core layer and microscale pores in the shell layer, thereby obtaining aerogel fiber materials with different hierarchical pore structures according to actual needs.

[0017] Furthermore, the shell layer has a thickness of 25-90 μm, the core layer has a diameter of 30-250 μm, and the fiber porosity is >80%.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention first deprotonates aramid III fibers, and then induces the assembly of charged nanoparticles through hydrogen protons in a coagulation bath. This can effectively promote the gelation assembly efficiency of aramid nanofibers, change the assembly kinetics of aramid nanofibers, and induce multi-level structure assembly. According to actual needs, the types of raw materials, addition ratios, and process parameters in the preparation process can be adjusted to control the pore size, pore morphology, and pore diameter distribution of the fiber core and shell layers, so as to achieve precise control of fiber diameter and morphology and meet the needs of different application fields for fiber size and morphology. (2) The heterogeneous aramid porous fiber provided by the present invention has a multi-level porous structure of "porous shell and dense core", which improves the tensile strength and elongation at break of aerogel fiber and makes the fiber more durable. Attached Figure Description

[0019] Figure 1 This is a scanning electron microscope image of an internally and externally heterogeneous aramid porous fiber according to an embodiment of the present invention; Figure 2 These are scanning electron microscope images of a pair of aramid aerogel fibers according to the present invention. Figure 3 This is a scanning electron microscope image of a pair of aramid aerogel fibers according to the present invention. Figure 4 These are comparative images of the morphology characterization of the aramid aerogel fibers of the present invention; wherein, 4a is the SEM image of Example 2, 4b is the SEM image of Example 4, 4c is the SEM image of Example 9, and 4d is the SEM image of Example 11. Detailed Implementation

[0020] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be described in detail below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally performed under conventional conditions or as recommended by the manufacturer. Unless otherwise specified, the test materials used in the following embodiments were purchased from conventional biochemical reagent stores. Unless otherwise stated, percentages and parts are by weight. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar with the art. Furthermore, any methods and materials similar to or equivalent to those described herein can be applied to the present invention. The preferred embodiments and materials described herein are for illustrative purposes only.

[0021] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0022] Based on this invention, aramid III nanofibers are selected as raw materials. Taking advantage of their negatively charged surface properties, charged nanoparticles are assembled by hydrogen proton induction in a solidification bath to obtain a multi-level porous structure with a porous shell and a dense core.

[0023] Please see Figure 1 The image shown is a scanning electron microscope image of the heterogeneous aramid porous fiber prepared by the present invention. It can be seen that the heterogeneous aramid porous fiber prepared by the present invention exhibits a multi-level porous structure with a porous shell and a dense core. The core is a nanoporous structure and the shell is a microporous structure. The shell thickness is 25-90 μm and the core diameter is 30-250 μm. Based on this invention, heterogeneous aramid porous fibers are prepared by the following steps: aramid III fibers are placed in a potassium hydroxide / dimethyl sulfoxide / water system and stirred to carry out a deprotonation reaction to obtain aramid III nanofiber spinning solution; the spinning solution is injected into a coagulation bath containing protic acid to promote the heterogeneous assembly and solidification of the fibers, while giving the fibers a directional stretching effect, promoting the fibers to solidify and form, and obtaining nascent gel fibers; the nascent gel fibers are subjected to solvent replacement-drying treatment to obtain heterogeneous aramid porous fibers.

[0024] Based on this invention, the length of the aramid III fiber is 1-20 mm; for example, 1-15 mm; or 1-12 mm; or 1-10 mm; or 3-10 mm; or 3-8 mm; or 4-7 mm; such as 5 mm. Because the aramid III structure contains a third monomer, 2-(4-aminophenyl)-5(6)-aminobenzimidazole, this group unit affects the deprotonation preparation of nanofibers and the acid-controlled kinetic regulation. Therefore, the nanofibers prepared with aramid III have a finer diameter, which can increase the cross-linking points of the three-dimensional network of porous fibers. Simultaneously, this group unit allows the polymer molecules to achieve maximum axial orientation during the spinning and stretching process, thereby significantly improving tensile strength and modulus. Compared to aramid II, meta-aramid has a breaking strength and elastic modulus that are 30% and 20% higher, respectively, improving the overall mechanical properties of the fiber.

[0025] Based on the present invention, the aramid concentration in the spinning solution is 1-5 wt%; in some preferred embodiments, the aramid concentration in the spinning solution is 1-5 wt%, or 1-4 wt%, or 1.5-3 wt%, or 1.5-2.5 wt%.

[0026] In some preferred embodiments, the aramid concentration in the spinning solution is 2 wt%.

[0027] Based on the present invention, the mass ratio of potassium hydroxide to aramid III fiber is (1-3):1; In some preferred embodiments, the mass ratio of potassium hydroxide to aramid III fiber is (1.5-3):1, or (1-2.5):1, or (1.5-2.5):1; In some preferred embodiments, the mass ratio of potassium hydroxide to aramid III fiber is 2:1.

[0028] Based on the present invention, the proton donor coagulation bath is selected from one or more of deionized water, methanol, ethanol, acetone, ethylene glycol, inorganic acid, and organic acid; In some specific embodiments, the protic acid is selected from inorganic or organic acids; protic acid pairs can not only affect the assembly kinetics of nanofibers, but also significantly improve production efficiency and fiber quality; In some preferred embodiments, the protic acid is selected from one or more of sulfuric acid, hydrochloric acid, formic acid, acetic acid, trifluoroacetic acid, oxalic acid, citric acid, phosphoric acid, and tartaric acid; In some preferred embodiments, the protic acid is selected from one or more of sulfuric acid, hydrochloric acid, acetic acid, and phosphoric acid; In some preferred embodiments, the protonated acid is selected from sulfuric acid. The type of acid proton affects the protonation level and assembly kinetics of nanofibers, and also plays a decisive role in the formation of the three-dimensional structure and shape of nanofibers, thereby affecting their final structural properties and functions.

[0029] Based on the present invention, when the spinning solution is injected into the coagulation bath, the injection speed is 0.1-1 mL / min; and / or, when imparting a directional stretching effect to the fiber, the traction speed is 400-600 r / min.

[0030] Based on the present invention, the concentration of protic acid in the coagulation bath is 0.1-20 wt%, for example 0.5-15 wt%, or 1-15 wt%, or 2-12 wt%, or 2-10 wt%, or 2-8 wt%, or 2-5 wt%. Based on this invention, the solvent replacement includes immersing the nascent gel fibers in a replacement solvent for replacement; the replacement solvent is one or a combination of two or more of water, ethanol, tert-butanol, n-hexane, hexafluoroisopropanol, cyclohexane, and acetone; and / or Based on the present invention, the drying process is selected from any one or a combination of two or more of freeze drying, supercritical fluid drying, and atmospheric pressure drying.

[0031] In some preferred embodiments, the drying method is selected from supercritical CO2 drying and freeze drying.

[0032] The technical solution of the present invention will be further described in detail below with reference to several preferred embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. It should be understood that the following embodiments are only used to explain the present invention and are not intended to limit the present invention.

[0033] Example 1 Dissolve 8g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.3mL / min and the negative draw winding rate to 500r / min, and extrude the spinning solution into a coagulation bath containing 1% sulfuric acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature and pressure of 35℃ and 9.5MPa, respectively. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 2

[0034] Dissolve 16g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.1mL / min and the negative draw winding rate to 400r / min, and extrude the spinning solution into a coagulation bath containing 2% sulfuric acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature and pressure of 35℃ and 9.5MPa, respectively. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 3

[0035] Dissolve 8g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.1mL / min and the negative draw winding rate to 400r / min, and extrude the spinning solution into a coagulation bath containing 5% sulfuric acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature and pressure of 35℃ and 9.5MPa, respectively. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 4

[0036] Dissolve 16g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 1.5wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.1mL / min and the negative draw winding rate to 400 r / min, and extrude the spinning solution into a coagulation bath containing 2% hydrochloric acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature and pressure of 35℃ and 9.5MPa, respectively. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 5

[0037] Dissolve 16g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.3mL / min and the negative draw winding rate to 500r / min, and extrude the spinning solution into a coagulation bath containing 5% hydrochloric acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature of 35℃ and a pressure of 9.5MPa. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 6

[0038] Dissolve 16g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.1mL / min and the negative draw winding rate to 300r / min, and extrude the spinning solution into a coagulation bath containing 10% hydrochloric acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature and pressure of 35℃ and 9.5MPa, respectively. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 7

[0039] Dissolve 16g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.2mL / min and the negative draw winding rate to 400r / min, and extrude the spinning solution into a coagulation bath containing 2% phosphoric acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature and pressure of 35℃ and 9.5MPa, respectively. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 8

[0040] Dissolve 16g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning apparatus, set the extrusion speed to 0.3mL / min and the negative draw winding rate to 500r / min, and extrude the spinning solution into a coagulation bath containing 5% phosphoric acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then freeze-dry them. Freeze-dry the gel fibers overnight at -20℃, and then freeze-dry them at -45℃ under vacuum. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 9

[0041] Dissolve 16g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.2mL / min and the negative draw winding rate to 300r / min, and extrude the spinning solution into a coagulation bath containing 10% phosphoric acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature of 35℃ and a pressure of 9.5MPa. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 10

[0042] Dissolve 16g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.3mL / min and the negative draw winding rate to 300r / min, and extrude the spinning solution into a coagulation bath containing 5% acetic acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature of 35℃ and a pressure of 9.5MPa. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 11

[0043] Dissolve 16g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.3mL / min and the negative draw winding rate to 500r / min, and extrude the spinning solution into a coagulation bath containing 10% acetic acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature of 35℃ and a pressure of 9.5MPa. After depressurization and cooling, heterogeneous aramid porous fibers are obtained. Example 12

[0044] Dissolve 16g of potassium hydroxide in water, then add 400ml of DMSO to prepare a potassium hydroxide / dimethyl sulfoxide / water system. Add 8g of aramid III fiber with a length of 3-8mm and stir to carry out a deprotonation reaction, obtaining a spinning solution with an aramid concentration of 2wt%. Transfer the spinning solution to a wet spinning device, set the extrusion speed to 0.3mL / min and the negative draw winding rate to 400r / min, and extrude the spinning solution into a coagulation bath containing 20% ​​acetic acid to obtain nascent gel fibers. Use water as a displacement solvent to immerse the aramid gel fibers in water for solvent displacement, and then use supercritical drying at a supercritical temperature and pressure of 35℃ and 9.5MPa, respectively. After depressurization and cooling, heterogeneous aramid porous fibers are obtained.

[0045] Comparative Example 1 Same as Example 2, except that aramid III is replaced with aramid II.

[0046] Comparative Example 2 Same as Example 2, except that aramid III is replaced with meta-aramid.

[0047] The internal and external heterogeneous aramid porous fibers prepared according to the embodiments and comparative examples of the present invention were observed using an electron microscope. Figure 2-3 The images shown are SEM images of cross-sections of aerogel fibers prepared in Comparative Examples 1 and 2. It can be seen that the pore size, pore morphology and pore diameter distribution of aerogel fibers prepared using aramid II and meta-aramid as raw materials are uniform. In contrast, the aerogel fibers prepared in this invention exhibit a multi-level porous structure with a porous shell and a dense core, which takes into account both the mechanical properties and thermal conductivity of aerogel fibers.

[0048] Figure 4 a-4d are SEM images of cross-sections of aerogel fibers prepared in Examples 2, 4, 9 and 11, respectively. It can be seen that aerogel fibers prepared by coagulation baths containing different protic acids can obtain porous aramid fibers with different multilevel structures.

[0049] Refer to Table 1 for the performance tests of the internal and external heterogeneous aramid porous fibers provided in Examples 1-12 of this invention.

[0050] Table 1

[0051] The table above shows the structural parameters, mechanical properties, and porosity of the heterogeneous aramid porous fibers described in Examples 1-12. Combined with the results of electron microscopy scans of each example, the heterogeneous aramid porous fibers provided by this invention exhibit better mechanical strength and porosity. The nanoporous core layer endows the fiber with high mechanical strength, while the microporous shell layer has the characteristics of large specific surface area and high porosity, while also taking into account the mechanical properties and thermal conductivity of aerogel fibers.

[0052] Finally, it should be noted that the above description is only a preferred embodiment of the present invention. Those skilled in the art, under the guidance of the present invention, can make various similar representations without departing from the spirit and claims of the present invention, and such modifications all fall within the protection scope of the present invention.

Claims

1. A method for preparing porous aramid fibers with internal and external heterogeneous structures, characterized in that, Includes the following steps: S1. Aramid III fibers were placed in a potassium hydroxide / dimethyl sulfoxide / water system and stirred to carry out a deprotonation reaction, thereby obtaining an aramid III nanofiber spinning solution. S2. The spinning solution is injected into a coagulation bath containing 0.5-2% sulfuric acid, which simultaneously imparts a directional stretching effect to the fibers to obtain nascent gel fibers; S3. Using water as a displacement solvent, the aramid gel fiber is immersed in water for solvent displacement, and then dried to obtain a porous aramid fiber with a porous shell and a dense core.

2. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that, In S1, the length of the aramid III fiber is 1-20 mm.

3. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that, In S1, the length of the aramid III fiber is 1-15 mm.

4. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that, In S1, the length of the aramid III fiber is 1-12 mm.

5. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that, In S1, the length of the aramid III fiber is 1-10 mm.

6. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that, In S1, the length of the aramid III fiber is 3-10 mm.

7. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that, In S1, the length of the aramid III fiber is 3-8 mm.

8. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that, In S1, the length of the aramid III fiber is 4-7 mm.

9. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that, In S1, the length of the aramid III fiber is 5 mm.

10. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that... In S1, the aramid concentration in the spinning solution is 1-5 wt%.

11. A method for preparing an internally and externally heterogeneous aramid porous fiber according to any one of claims 1-9, characterized in that... In S1, the aramid concentration in the spinning solution is 1-4 wt%.

12. A method for preparing an internally and externally heterogeneous aramid porous fiber according to any one of claims 1-9, characterized in that... In S1, the aramid concentration in the spinning solution is 1.5-3 wt%.

13. A method for preparing an internally and externally heterogeneous aramid porous fiber according to any one of claims 1-9, characterized in that... In S1, the aramid concentration in the spinning solution is 1.5-2.5 wt%.

14. A method for preparing an internally and externally heterogeneous aramid porous fiber according to any one of claims 1-9, characterized in that... In S1, the aramid concentration in the spinning solution is 2 wt%.

15. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that... In S1, the mass ratio of potassium hydroxide to aramid III fiber is (1-3):

1.

16. A method for preparing an internally and externally heterogeneous aramid porous fiber according to any one of claims 1-10, characterized in that... In S1, the mass ratio of potassium hydroxide to aramid III fiber is (1.5-3):

1.

17. A method for preparing an internally and externally heterogeneous aramid porous fiber according to any one of claims 1-10, characterized in that... In S1, the mass ratio of potassium hydroxide to aramid III fiber is (1-2.5):

1.

18. A method for preparing an internally and externally heterogeneous aramid porous fiber according to any one of claims 1-10, characterized in that... In S1, the mass ratio of potassium hydroxide to aramid III fiber is (1.5-2.5):

1.

19. A method for preparing an internally and externally heterogeneous aramid porous fiber according to any one of claims 1-10, characterized in that... In S1, the mass ratio of potassium hydroxide to aramid III fiber is 2:

1.

20. The method for preparing an internally and externally heterogeneous aramid porous fiber according to claim 1, characterized in that... In S2, when the spinning solution is injected into the proton donor coagulation bath, the injection rate is 0.1-1 mL / min.

21. A method for preparing an internally and externally heterogeneous aramid porous fiber according to any one of claims 1, 2, 10, and 20, characterized in that... In S2, when the fiber is given a directional stretching action, the traction speed is 400-600 r / min.

22. A method for preparing an internally and externally heterogeneous aramid porous fiber according to any one of claims 1, 2, 10, 15, and 20, characterized in that... In S3, the drying process is selected from any one or a combination of two or more of freeze drying, supercritical fluid drying, and atmospheric pressure drying.

23. A porous aramid fiber with heterogeneous internal and external structures, characterized in that, The fiber is prepared by the method described in any one of claims 1-22, characterized in that the inner and outer heterogeneous aramid porous fiber has a core-shell structure, the core layer has a nanoporous structure, and the shell layer has a micron-sized pore and nanopore wall structure.

24. The heterogeneous aramid porous fiber according to claim 23, characterized in that: The shell layer has a thickness of 25-90 μm, the core layer has a diameter of 30-250 μm, and a porosity of >80%.

Images