A hollow aramid aerogel fiber and a method of making

Abstract

The present application relates to the technical field of hollow gel fiber, in particular to a kind of hollow aramid aerogel fiber and preparation method.Combining wet spinning and chemical foaming method, the inner diameter, outer diameter and wall thickness of fiber and the size on the hole of fiber wall are regulated, to form the hollow aramid aerogel fiber with high porosity hollow structure fiber, which has high selectivity and high throughput, and also has flame-retardant heat-insulating, high mechanical strength and other properties, to improve and expand the use performance and application range of existing technology hollow aerogel fiber.

Description

Technical Field

[0001] The present invention relates to the technical field of hollow gel fibers, and in particular to a hollow aramid aerogel fiber and a preparation method thereof. Background Art

[0002] Hollow fiber porous fiber is a kind of nanofiber material with a three-dimensional network structure of tubular cavities in the fiber axis. It has ultra-high porosity, large specific surface area, ultra-low density, excellent mechanical properties and wearability. It has important application value in many fields such as textiles, environment, energy conversion and storage, thermal protection, infrared stealth, and electromagnetic shielding.

[0003] Currently, the main technologies for producing hollow porous fibers are shaped spinneret melt spinning and wet coaxial solution spinning. Both shaped spinnerets and coaxial spinning require complex equipment component designs and are limited by the spinneret / spinning head structure, making it difficult to efficiently produce fibers with complex porous structures. CN202410298279.X discloses a hollow aerogel fiber and a preparation method thereof at room temperature and pressure. The patent provides a preparation method for a hollow aerogel fiber, including preparing a hollow fiber with a porous aerogel structure by synchronous non-solvent phase separation inside and outside the fiber at room temperature and pressure. A coaxial extrusion device is used, a non-solvent core liquid is used for the inner core, and a polymer / solvent solution is used for the outer layer. They are then injected into a coagulation bath at the same time for coagulation and molding, and the hollow aerogel fiber is obtained after drying. However, the material prepared by this method has mostly closed pores, and it can be seen from its coagulation principle and morphology photos that the porosity of the material is relatively low, which is not conducive to the performance of the hollow fiber; Chinese invention patent CN201910933044.2 discloses a graphene aerogel hollow fiber, its preparation method and application, but the graphene aerogel material is usually brittle, and the pore structure, morphology and distribution cannot be controlled, making it difficult to simultaneously solve the problems of high selectivity and high flux, and the scope of application is narrow.

[0004] Therefore, how to prepare hollow aramid aerogel fibers with high porosity and adjustable hollow channels to meet application requirements in adsorption, separation, filtration and thermal management is an urgent problem to be solved. Summary of the Invention

[0005] To solve the above problems, the present invention provides a hollow aramid aerogel fiber and a preparation method. By combining wet spinning and chemical foaming methods, the inner diameter, outer diameter and wall thickness of the fiber and the pore size on the fiber wall are regulated to form a hollow structural fiber with high porosity, thereby improving and expanding the performance and application range of aerogel fibers in the existing technology.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] In one aspect, the present invention provides a method for preparing a hollow aramid aerogel fiber, comprising the following steps:

[0008] S1. The aramid fiber is placed in an alkali solution and stirred to obtain an aramid nanofiber dispersion;

[0009] S2. The aramid nanofiber dispersion is added with a foaming agent to obtain a spinning solution;

[0010] S3. Extruding the spinning solution into a mixed coagulation bath to obtain a hollow aramid wet gel fiber;

[0011] S4. The aramid wet gel fiber is subjected to solvent replacement and dried to obtain a hollow aramid aerogel fiber.

[0012] In some specific embodiments, the aramid fiber can be waste aramid fiber.

[0013] In some specific embodiments, wet spinning is combined with a chemical foaming method, and a chemical foaming agent that reacts quickly to generate carbon dioxide is selected and mixed with an aramid nanofiber dispersion to prepare a spinning solution, which is then extruded into an acidic aqueous solution by wet spinning to generate carbon dioxide gas, squeezing the internal solution to form a hollow structural fiber with high porosity.

[0014] Furthermore, in S1, the length of the aramid 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.

[0015] Furthermore, in S1, the alkali-containing solution is a polar organic solution containing an alkaline substance; and the mass volume ratio of the aramid fiber, the alkaline substance and the polar solvent is (1-10) g: (10-20) g: (300-500) mL.

[0016] Furthermore, in S1, the aramid fiber is selected from one or more of para-aramid fiber, heterocyclic aramid fiber, and meta-aramid fiber; aramid nanofiber is selected as the polymer material, which has excellent high strength and high modulus mechanical properties, excellent thermal stability and flame retardancy, high chemical stability and corrosion resistance, so that the prepared high-porosity porous fiber has flame retardancy, heat insulation, high mechanical strength and other properties;

[0017] Furthermore, the alkaline substance is selected from one or more of potassium hydroxide, sodium hydroxide, sodium ethoxide, potassium ethoxide, potassium tert-butoxide or lithium chloride;

[0018] Furthermore, the polar solvent is selected from one or more of DMSO, DMF, NMP or DMAc.

[0019] Furthermore, in S2, the foaming agent is an alkaline foaming agent;

[0020] In some specific embodiments, the foaming agent is selected from one or more of carbonates and bicarbonates; in a preferred embodiment, the foaming agent is selected from one or more of sodium carbonate, sodium bicarbonate, potassium bicarbonate, and ammonium bicarbonate; in a more preferred embodiment, the foaming agent is sodium carbonate.

[0021] Furthermore, in said S2, the amount of the foaming agent added is 0.25-15 wt% of the total mass;

[0022] In some specific embodiments, the amount of the foaming agent added is 0.5-12 wt% of the total mass;

[0023] In some preferred embodiments, the amount of the foaming agent added is 1-10 wt% of the total mass; in a more preferred embodiment, the amount of the foaming agent added is 1-8 wt% of the total mass.

[0024] Furthermore, in S3, the coagulation bath is selected from any 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 coagulation bath is selected from any one or more of sulfuric acid, hydrochloric acid, acetic acid, and phosphoric acid.

[0025] Furthermore, in S4, the drying method is selected from a combination of supercritical CO2 drying, freeze drying, and vacuum drying;

[0026] In some preferred embodiments, the drying method is selected from supercritical CO2 drying and freeze drying.

[0027] In a second aspect, the present invention provides a hollow aramid aerogel fiber, which is prepared by the above method. The middle part of the hollow aramid aerogel fiber is a hollow structure, and the fiber wall is a nanoporous structure.

[0028] Furthermore, the outer diameter of the fiber is 370 μm-430 μm, the inner diameter is 20 μm-300 μm, and the nanopore diameter is less than 200 nm.

[0029] The hollow aramid aerogel fiber provided by the present invention can be modified by filling with functional materials, heat-treated and hydrophobized according to the environment, and can be used in phase change material adsorption, water-oil separation, filtration, seawater desalination, water treatment, high thermal insulation, energy storage and other fields, greatly expanding and improving the application range and performance of aerogels and hollow fiber membranes.

[0030] Compared with the prior art, the present invention has the following beneficial effects:

[0031] (1) The present invention combines a wet spinning method with a chemical foaming method. By adjusting the raw materials and process parameters, a hollow aramid aerogel fiber with high porosity and adjustable hollow channels can be obtained. It has high selectivity and high flux, as well as flame retardancy, heat insulation, high mechanical strength and other properties.

[0032] (2) The method for preparing hollow aramid aerogel fibers with high porosity provided by the present invention does not require complex synthesis technology, has a simple process, low energy consumption, low production cost, and is suitable for large-scale production and application;

[0033] (3) The hollow aramid aerogel fiber provided by the present invention has a hollow structure in the middle and a nanoporous structure in the fiber wall. The fiber wall has a large specific surface area and high porosity, and the hollow tube diameter can be adjusted as needed, which has extremely strong designability. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is an optical photograph of the hollow aramid aerogel fiber of the present invention;

[0035] Figure 2 is a scanning electron microscope image of a hollow aramid aerogel fiber according to an embodiment of the present invention;

[0036] Figure 3 This is a comparative diagram of the morphology characterization of the hollow aramid aerogel fiber of the present invention. DETAILED DESCRIPTION

[0037] In order to make those skilled in the art better understand the technical scheme of the present invention, the present invention is described in detail below in conjunction with specific embodiments. The experimental methods for which specific conditions are not specified in the following examples are usually based on conventional conditions or the conditions recommended by the manufacturer. The test materials used in the following examples, unless otherwise specified, are purchased from conventional biochemical reagent stores. Unless otherwise specified, percentages and parts are calculated by weight. Unless otherwise defined, all professional and scientific terms used in the text have the same meaning as those familiar to those skilled in the art. In addition, any method and material similar to or equivalent to the described content can be applied to the present invention. The preferred implementation methods and materials described in the text are only for demonstration purposes.

[0038] The endpoints of the ranges and any values ​​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 endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0039] Based on the present invention, the hollow aramid aerogel fiber is made of aramid nanofibers and a chemical foaming agent that generates carbon dioxide faster as raw materials. The wet spinning and chemical foaming methods are combined to dissolve the foaming agent in the spinning solution and extrude it into an acidic aqueous solution through wet spinning to generate carbon dioxide gas to squeeze the internal solution, thereby forming a hollow structural fiber with high porosity.

[0040] See Figure 1 , which is a real photo of the hollow aramid aerogel fiber prepared by the present invention.

[0041] See also Figure 2 , which is a scanning electron microscope image of the hollow aramid aerogel fiber prepared by the present invention, it can be seen that the outer diameter of the hollow aramid aerogel fiber prepared by the present invention is 370μm-430μm, the inner diameter is 20μm-300μm, and the nanopore diameter is less than 200nm.

[0042] According to the present invention, the hollow aramid aerogel fiber is prepared by the following steps: placing the aramid fiber in an alkali-containing solution and stirring it to obtain an aramid nanofiber dispersion; adding a foaming agent to the aramid nanofiber dispersion to obtain a spinning solution; extruding the spinning solution into a mixed coagulation bath, wherein the foaming agent generates carbon dioxide gas in the acidic coagulation solution, squeezing the internal solution to form a hollow structure aramid wet gel fiber with high porosity; and subjecting the aramid wet gel fiber to solvent replacement and drying to obtain the hollow aramid aerogel fiber.

[0043] Based on the present invention, the length of the aramid fiber is 1-20 mm; in some preferred embodiments, the length of the aramid fiber is 1-15 mm; or 1-12 mm; or 1-10 mm; or 3-10 mm; or 3-8 mm; or 4-7 mm; in some more preferred embodiments, the length of the aramid fiber is 5 mm.

[0044] According to the present invention, the alkali-containing solution is a polar solution containing an alkaline substance; the mass volume ratio of the aramid fiber, the alkaline substance and the polar solvent is (1-10) g: (10-20) g: (300-500) mL.

[0045] Based on the present invention, the aramid fiber is selected from one or more of para-aramid fiber, heterocyclic aramid fiber, and meta-aramid fiber; in some preferred embodiments, the aramid fiber is selected from para-aramid fiber or heterocyclic aramid fiber; aramid nanofiber is selected as the polymer material, which has excellent high strength and high modulus mechanical properties, excellent thermal stability and flame retardant properties, high chemical stability and corrosion resistance, so that the prepared high-porosity porous fiber has flame retardant, heat insulation, high mechanical strength and other properties.

[0046] Based on the present application, the basic substance is selected from one or more of potassium hydroxide, sodium hydroxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide or potassium tert-butoxide; in specific experiments, it can be reasonably selected according to the situation, which will not be described one by one here.

[0047] Based on the present application, the polar solvent is selected from one or more of DMSO, DMF, NMP or DMAc, which can be reasonably selected according to the situation in specific experiments, which will not be described one by one here.

[0048] Based on the present application, in S2, the foaming agent is a basic foaming agent.

[0049] Based on the present application, the foaming agent is selected from one or more of carbonate and bicarbonate; in some preferred embodiments, the foaming agent is selected from one or more of sodium carbonate, sodium bicarbonate, potassium bicarbonate and ammonium bicarbonate; in some more preferred embodiments, the foaming agent is sodium carbonate.

[0050] Based on the present application, the addition amount of the foaming agent is 0.25-15wt% of the total mass; in some specific embodiments, the addition amount of the foaming agent is 0.5-12wt% of the total mass; in some preferred embodiments, the addition amount of the foaming agent is 1-10wt% of the total mass; in more preferred embodiments, the addition amount of the foaming agent is 1-8wt% of the total mass.

[0051] Based on the present application, the coagulation bath is selected from any one or two 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 coagulation bath is selected from any one or two or more of sulfuric acid, hydrochloric acid, acetic acid and phosphoric acid.

[0052] Based on the present application, the drying method is selected from a combination of one or more of supercritical CO2 drying, freeze drying or normal pressure drying.

[0053] In some preferred embodiments, the drying method is selected from one or more of supercritical CO2 drying and freeze drying.

[0054] The technical solutions of the present application will be further described in detail below in combination with several preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by a person of ordinary skill in the art without making creative efforts fall within the scope of protection of the present application. It should be understood that the following embodiments are only used to explain the present application, and are not used to limit the present application.

[0055] Embodiment 1

[0056] After KOH was dissolved in water, DMSO was added and ultrasonically dispersed. Then, heterocyclic aramid staple fibers with a length of 4-7 mm were added and stirred evenly. After standing for 24 hours, the mixture was stirred evenly for 24 hours to prepare a dark brown-red aramid nanofiber dispersion (ANF). The ratio of aramid staple fibers: KOH: DMSO was 8 g: 16 g: 400 mL. Sodium carbonate was then added to the ANF and stirred for 2 hours to prepare a spinning solution with a sodium carbonate concentration of 1 wt%. The spinning solution was transferred to a wet spinning device and the extrusion speed was set to 6. The spinning solution was extruded into a coagulation bath containing 10wt% acetic acid at a speed of 500r / min and a negative draft winding rate of 500r / min. The spinning solution underwent an in-situ dynamic sol-gel transition in the coagulation bath, and sodium carbonate reacted with the acid to form a hollow aramid gel fiber. The aramid gel fiber was immersed in an ethanol replacement solvent using water as the replacement solvent for solvent replacement. The fiber was then dried using supercritical CO2 at a supercritical temperature and pressure of 35°C and 9.5MPa, respectively. After reducing the pressure and temperature, the hollow aramid aerogel fiber was obtained. The mechanical properties of the obtained hollow aramid aerogel fiber were tested, and the tensile strength of the hollow aramid aerogel fiber was measured to be 4.6MPa.

[0057] Example 2

[0058] After KOH was dissolved in water, DMSO was added and ultrasonically dispersed. Kevlar aramid staple fibers with a length of 4-7 cm were added and stirred evenly. After standing for 24 hours and mechanically stirred for 3 days, a dark brown-red aramid nanofiber dispersion (ANF) was prepared. The ratio of aramid staple fibers: KOH: DMSO was 16 g: 16 g: 400 mL. Sodium carbonate was then added to the ANF and stirred for 4 hours to prepare a spinning solution with a sodium bicarbonate concentration of 2 wt%. The spinning solution was transferred to a wet spinning device and the extrusion speed control was set. The spinning solution was extruded into a coagulation bath containing 10wt% acetic acid at a speed of 600r / min and a negative draft winding rate of 500r / min. The spinning solution underwent an in-situ dynamic sol-gel transition in the coagulation bath, and sodium bicarbonate reacted with the acid to form a foamed hollow aramid gel fiber. The aramid gel fiber was then immersed in the displacement solvent using water for solvent displacement. The fiber was then dried using supercritical CO2 at a supercritical temperature and pressure of 35°C and 9.5MPa, respectively. The hollow aramid aerogel fiber was obtained after the pressure and temperature were reduced. Mechanical properties of the obtained hollow aramid aerogel fiber were tested, and the tensile strength of the hollow aramid aerogel fiber was measured to be 3.4MPa.

[0059] Example 3

[0060] After KOH was dissolved in water, DMSO was added and ultrasonically dispersed. Kevlar aramid staple fibers with a length of 4-7 mm were added and stirred evenly. After standing for 24 hours, mechanical stirring was performed for 3 days to prepare a clear yellow aramid nanofiber dispersion (ANF), wherein the ratio of aramid staple fibers: KOH: DMSO was 8 g: 16 g: 400 mL. Sodium carbonate was then added to the ANF and stirred for 6 hours to prepare a spinning solution with a sodium carbonate concentration of 4 wt%. The spinning solution was transferred to a wet spinning device and an extruder was set. The spinning solution was extruded into a coagulation bath containing 10wt% acetic acid at a controlled speed of 600r / min and a negative draft winding rate of 500r / min. The spinning solution underwent an in-situ dynamic sol-gel transition in the coagulation bath, yielding a hollow aramid gel fiber. Water was used as the displacement solvent, and the aramid gel fiber was immersed in the displacement solvent for solvent displacement. Subsequently, supercritical drying was performed at a supercritical temperature and pressure of 35°C and 9.5MPa, respectively. After reducing the pressure and temperature, the hollow aramid aerogel fiber was obtained. Performance testing of the resulting hollow aramid aerogel fiber revealed a tensile strength of 3.2MPa, a porosity of 95%, and a specific surface area of ​​208.2035m2 / g.

[0061] Example 4

[0062] KOH was dissolved in water, DMSO was added, and after ultrasonic dispersion, 4-7 mm long meta-aramid staple fibers were added and stirred evenly. After standing for 24 hours, the mixture was mechanically stirred for another 24 hours to produce a clear yellow aramid nanofiber dispersion (ANF). The ratio of aramid staple fibers: KOH: DMSO was 32 g: 16 g: 400 mL. Sodium carbonate was then added to the ANF and stirred for 2 hours to produce a spinning solution with a sodium carbonate concentration of 6 wt%. The spinning solution was transferred to a wet spinning apparatus with an extrusion speed of 600 r / min and a negative draft wind-up rate of 500 r / min. The spinning solution was extruded into a coagulation bath containing 20 wt% acetic acid, where it underwent an in-situ dynamic sol-gel transition to produce hollow aramid gel fibers. A 25 wt% aqueous tert-butyl alcohol solution was used as the displacement solvent, and the aramid gel fibers were immersed in the displacement solvent for solvent exchange. Freeze-drying was used to freeze the hydrogel fibers into a solid state at -20°C. The fibers were then dried in a low-temperature vacuum environment for 24 hours to produce hollow aramid aerogel fibers. Performance testing of the resulting hollow aramid aerogel fibers revealed a tensile strength of 3.2 MPa and a porosity of 96%.

[0063] Example 5

[0064] After KOH was dissolved in water, DMSO was added and ultrasonically dispersed. Kevlar aramid staple fibers with a length of 4-7 mm were added and stirred evenly. Mechanical stirring was performed for 3 days to prepare a dark brown-red aramid nanofiber dispersion (ANF), wherein the ratio of aramid staple fibers: KOH: DMSO was 8 g: 16 g: 400 mL. Sodium carbonate was then added to the ANF and stirred for 6 h to prepare a spinning solution with a sodium carbonate concentration of 8 wt%. The spinning solution was transferred to a wet spinning device and the extrusion speed was set. The spinning solution was extruded into a coagulation bath containing 5wt% hydrochloric acid at a controlled speed of 600r / min and a negative draft winding rate of 500r / min. The spinning solution underwent an in-situ dynamic sol-gel transition in the coagulation bath to produce hollow aramid gel fibers. Water was used as the displacement solvent, and the aramid gel fibers were immersed in the displacement solvent for solvent displacement. Subsequently, supercritical drying was performed at a supercritical temperature and pressure of 35°C and 9.5MPa, respectively. After reducing the pressure and temperature, the hollow aramid aerogel fibers were obtained. Mechanical properties of the obtained hollow aramid aerogel fibers were tested, and the tensile strength of the hollow aramid aerogel fibers was measured to be 2.6MPa.

[0065] Example 6

[0066] Potassium tert-butoxide is added to DMAc, and after ultrasonic dispersion, Kevlar aramid staple fibers with a length of 1-3 mm are added and stirred evenly, and mechanically stirred for 3 days to prepare a dark brown-red aramid nanofiber dispersion (ANF), wherein the ratio of aramid staple fiber: potassium tert-butoxide: DMAc is 5g:12g:300mL; sodium carbonate is then added to the ANF and stirred for 8 hours to prepare a spinning solution with a sodium carbonate concentration of 2wt%; the spinning solution is transferred to a wet spinning device, the extrusion speed is set to 600r / min, the negative draft winding rate is set to 500r / min, and the spinning solution is extruded into a coagulation bath containing 5wt% sulfuric acid. The spinning solution undergoes an in-situ dynamic sol-gel transition in the coagulation bath to obtain a hollow aramid gel fiber; water is used as a replacement solvent, the aramid gel fiber is immersed in the replacement solvent for solvent replacement, and then freeze-drying is used to obtain a hollow aramid aerogel fiber. The obtained hollow aramid aerogel fiber was subjected to a mechanical property test, and the tensile strength of the hollow aramid aerogel fiber was measured to be 4.1 MPa.

[0067] Example 7

[0068] Potassium tert-butoxide is added into DMSO, after ultrasonic dispersion, Kevlar aramid short fibers with a length of 1-3 mm are added and stirred uniformly, and mechanical stirring is carried out for 3 days, to prepare a dark brown red aramid nanofiber dispersion (ANF), wherein the ratio of aramid short fibers: potassium tert-butoxide: DMSO is 10g:20g:500mL; potassium bicarbonate is further added into the ANF, and stirring is carried out for 8h, to prepare a spinning solution with a potassium bicarbonate concentration of 7wt%; the spinning solution is transferred into a wet spinning device, the extrusion speed is controlled to be 600r / min, and the negative drawing take-up speed is 500r / min, the spinning solution is extruded into a coagulation bath containing 10wt% formic acid, in-situ dynamic sol-gel transformation of the spinning solution occurs in the coagulation bath, to obtain hollow aramid gel fibers; water is used as a displacement solvent, the aramid gel fibers are immersed into the displacement solvent for solvent displacement, and then supercritical drying is adopted, the temperature and pressure of the supercritical state are 35℃ and 9.5MPa respectively, and after pressure and temperature reduction, hollow aramid aerogel fibers are obtained. The mechanical property of the obtained hollow aramid aerogel fibers is tested, and the tensile strength of the hollow aramid aerogel fibers is 2.6MPa.

[0069] Comparative Example 1

[0070] The same as Example 2, except that sodium carbonate is replaced by isocyanate.

[0071] Comparative Example 2

[0072] The same as Example 5, except that sodium carbonate is replaced by isocyanate.

[0073] Comparative Example 3

[0074] The same as Example 1, except that no sodium carbonate is added.

[0075] The hollow aramid aerogel fibers prepared in the examples and comparative examples of the application are observed by transmission electron microscopy, and the results are shown in Figure 3 . Figure 3 a-3f are respectively the cross-sectional SEM images of the aerogel fibers prepared in Comparative Example 3 and Examples 1-5, it can be seen that the aerogel fibers prepared from ANF without adding sodium carbonate do not have hollow pipes, and the middle pipes of the aerogel fibers gradually increase with the increase of the concentration of sodium carbonate, it can be seen that the hollow pipe diameter can be controlled as needed, and has strong designability, and the fiber wall is a nanoporous structure.

[0076] Figure 3g-3h are SEM images of the cross-section of the aerogel fibers prepared in Comparative Examples 1-2, respectively. It can be seen that the aerogel fibers prepared in Comparative Examples 1-2 did not form a hollow structure. This may be because the isocyanate reacted in the acidic coagulant solution to generate amine and carbon dioxide, and its reaction kinetics with water were slow, and a large amount of carbon dioxide gas could not be generated quickly. Therefore, it is difficult to be suitable for wet spinning and foaming of aramid nanofibers to prepare hollow fibers.

[0077] The hollow aramid aerogel fiber with a multi-level pore structure provided by the present invention has the characteristics of large specific surface area and high porosity. The fiber inner diameter, outer diameter, wall thickness and pore size distribution can be controlled, thereby regulating the pressure difference, flux and selectivity of the medium passing through the tube wall.

[0078] Hollow aramid aerogel fibers can be modified by filling them with functional materials, heat-treated, and hydrophobized according to the use environment. They can also be used in phase change material adsorption, water-oil separation, filtration, seawater desalination, water treatment, high thermal insulation, energy storage and other fields, greatly expanding and improving the application range and performance of aerogels and hollow fiber membranes.

[0079] In addition, the inventors also conducted experiments with other raw materials and conditions listed in this specification, referring to the methods of Examples 1-7, and also produced hollow aramid aerogel fibers with a multi-level pore structure in which the hollow tube diameter can be adjusted as needed, a large specific surface area, and high porosity.

[0080] Finally, it should be noted that the above description is only a preferred embodiment of the present invention. Under the guidance of the present invention, those skilled in the art can make various similar expressions without violating the purpose and claims of the present invention. Such changes fall within the scope of protection of the present invention.

Claims

1. A method for preparing hollow aramid aerogel fibers, characterized in that: The following steps are involved: S1. The aramid fiber is placed in an alkali solution and stirred to obtain an aramid nanofiber dispersion; S2. A foaming agent is added to the aramid nanofiber dispersion to obtain a spinning solution; S3. The spinning solution is extruded and spun into a mixed coagulation bath to obtain a hollow aramid wet gel fiber; S4. The aramid wet gel fiber was solvent-displaced and dried to obtain a hollow aramid aerogel fiber; The foaming agent is selected from one or more of carbonates and bicarbonates; The amount of the foaming agent added is 1-15% of the mass of the spinning solution; The coagulation bath is selected from any one or more of sulfuric acid, hydrochloric acid, formic acid, acetic acid, oxalic acid, citric acid, phosphoric acid, and tartaric acid.

2. The method for preparing a hollow aramid aerogel fiber according to claim 1, characterized in that: In S1, the length of the aramid fiber is 1-20 mm.

3. The method for preparing a hollow aramid aerogel fiber according to claim 1, characterized in that: In S1, the length of the aramid fiber is 1-15 mm.

4. The method for preparing a hollow aramid aerogel fiber according to claim 1, wherein: In S1, the length of the aramid fiber is 1-12 mm.

5. The method for preparing a hollow aramid aerogel fiber according to claim 1, characterized in that: In S1, the length of the aramid fiber is 1-10 mm.

6. The method for preparing a hollow aramid aerogel fiber according to claim 1, characterized in that: In S1, the length of the aramid fiber is 3-10 mm.

7. The method for preparing hollow aramid aerogel fibers according to claim 1, wherein: In S1, the length of the aramid fiber is 3-8 mm.

8. The method for preparing hollow aramid aerogel fibers according to claim 1, wherein: In S1, the length of the aramid fiber is 4-7 mm.

9. The method for preparing hollow aramid aerogel fibers according to claim 1, wherein: In S1, the length of the aramid fiber is 5 mm.

10. The method for preparing hollow aramid aerogel fibers according to claim 1, characterized in that: In S1, the alkali-containing solution is a polar organic solvent containing an alkaline substance; the mass volume ratio of the aramid fiber, the alkaline substance and the polar organic solvent is (1-10) g: (10-20) g: (300-500) mL.

11. The method for preparing hollow aramid aerogel fibers according to claim 10, characterized in that: In S1, the aramid fiber is selected from one or more of para-aramid fiber, heterocyclic aramid fiber, and meta-aramid fiber; the alkaline substance is selected from one or more of potassium hydroxide, sodium hydroxide, sodium ethoxide, potassium ethoxide, sodium tert-butoxide, or potassium tert-butoxide; and the polar organic solvent is selected from one or more of DMSO, DMF, NMP, or DMAc.

12. The method for preparing hollow aramid aerogel fibers according to claim 1, wherein: In S2, the foaming agent is selected from one or more of sodium carbonate, sodium bicarbonate, potassium bicarbonate, and ammonium bicarbonate.

13. The method for preparing hollow aramid aerogel fibers according to claim 1, characterized in that: In S2, the foaming agent is selected from sodium carbonate.

14. The method for preparing hollow aramid aerogel fibers according to claim 1, characterized in that: In S2, the amount of the foaming agent added is 1-8 wt% of the mass of the spinning solution.

15. The method for preparing hollow aramid aerogel fibers according to any one of claims 1 to 14, characterized in that: In S4, the drying method is selected from one or more combinations of supercritical CO2 drying, freeze drying or atmospheric pressure drying.

16. The method for preparing a hollow aramid aerogel fiber according to any one of claims 1 to 14, characterized in that: In S4, the drying method is selected from supercritical CO2 drying and freeze drying.

17. A hollow aramid aerogel fiber, characterized in that: The hollow aramid aerogel fiber is prepared by the method according to any one of claims 1 to 16, characterized in that the middle part of the hollow aramid aerogel fiber is a hollow structure and the fiber wall is a nanoporous structure.

18. The hollow aramid aerogel fiber according to claim 17, characterized in that: The outer diameter of the fiber is 370 μm-430 μm, the inner diameter is 20 μm-300 μm, and the nanopore diameter is less than 200 nm.

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