Multifunctional aerogel fiber based on waste firefighter uniform fabric and preparation method thereof

Abstract

The invention provides a multifunctional aerogel fiber based on a waste firefighter uniform fabric and a preparation method thereof, and belongs to the technical field of textile material recovery. The method comprises the following steps: separating aramid fiber 1313, aramid fiber 1414 and conductive fiber from the waste firefighter uniform; dissolving step by step, and compounding with sulfonated MXene to prepare a spinning solution; forming a gel fiber precursor through wet spinning, and spirally winding and stranding; performing supercritical carbon dioxide treatment to construct a porous structure; and finally coating a functional skin layer. Spiral winding stranding is adopted to replace traditional parallel stranding, interface micro-fusion is generated in combination with supercritical carbon dioxide, and mechanical interlocking and hydrogen bond strengthening between fibers are synchronously achieved; the continuity of the conductive network is enhanced through sulfonated MXene modification, and the solvent system difference is avoided through beam splitting spinning. The prepared aerogel fiber has the characteristics of high strength, high conductivity and high temperature resistance, and solves the problems of poor interface bonding and single function of various fibers in the waste firefighter uniform.

Description

Technical Field

[0001] The present invention belongs to the technical field of textile materials, and particularly relates to a multifunctional aerogel fiber based on waste fire-fighting suit fabric as raw material and a preparation method thereof. Background Art

[0002] Waste fire-fighting suit fabric is mainly made of high-performance fibers such as aramid 1313 and aramid 1414. Due to their excellent high temperature resistance, flame retardancy, chemical corrosion resistance and mechanical strength, these materials are widely used in fire-fighter protective equipment. However, after long-term use, the performance of the fire-fighting suit will gradually decline, resulting in the inability to continue meeting the safety protection standards. Traditional treatment methods for waste fire-fighting suits, such as landfilling or incineration, not only waste resources but also may cause environmental pollution. Therefore, how to efficiently recycle and endow it with new functions has become one of the current research hotspots.

[0003] Currently, the recycling technologies for waste fire-fighting suit fabric mainly focus on three directions: physical reuse, chemical recycling and functional modification. Physical reuse includes mechanical crushing, fiber regeneration and composite material preparation to maintain some properties of the fabric and apply it to low-demand fields. Chemical recycling involves methods such as solvent dissolution, pyrolysis and catalytic degradation to depolymerize high temperature-resistant fibers such as aramid and PBI into monomers or oligomers for resynthesis of new materials. In addition, functional modification technologies are exploring how to endow the recycled fibers with new fire-proof, heat-resistant or mechanical properties through surface modification or composite processing to expand their application fields.

[0004] Independent research on waste aramid 1313 fibers and waste aramid 1414 fibers is relatively extensive. However, research on the mixed use of these two fibers and the mixing with other fibers is relatively less. Therefore, the recycling method for the mixture of aramid 1313, aramid 1414 and other fibers has good prospects. Summary of the Invention

[0005] The present invention overcomes the deficiencies of the prior art and provides a multifunctional aerogel fiber based on waste fire-fighting suit fabric as raw material and a preparation method thereof.

[0006] To achieve the above object, the technical solution adopted by the present invention is: a preparation method for a multifunctional aerogel fiber based on waste fire-fighting suit fabric as raw material, comprising the following steps: S1. Separate the outer fabric including aramid 1313, aramid 1414 and conductive fiber from the waste fire-fighting suit fabric and conduct pretreatment; S2. Dissolve aramid 1414, aramid 1313 and conductive fiber in the outer fabric in sequence to prepare corresponding fiber solutions respectively; S3. Add sulfonated MXene powder to each fiber solution and disperse it to obtain aramid 1313 spinning solution, aramid 1414 spinning solution and conductive fiber spinning solution; S4. Prepare incompletely cured gel fiber precursors from each spinning solution by wet spinning, and perform spiral winding and doubling to obtain doubled gel fibers; S5. Treat the doubled gel fibers with supercritical carbon dioxide to form porous aerogel fibers; S6. Coat a functionalized cortex on the surface of the aerogel fibers to obtain multifunctional aerogel fibers.

[0007] Further, the pretreatment includes: cutting the waste fire-fighting suit fabric into blocks, separating the outer fabric, removing impurities and opening it into a short fiber mixture; sequentially performing alkaline cleaning, water washing, drying and shearing on the short fiber mixture.

[0008] Further, the cleaning solution for alkaline cleaning contains sodium carbonate, sodium dodecyl sulfate and sodium silicate, the cleaning temperature is 60 - 80 °C, and the cleaning time is 3 - 6 h.

[0009] Further, in step S2, the dissolution of aramid 1414 fibers uses a composite solvent of N,N-dimethylacetamide and lithium chloride, and the dissolution temperature is 80 - 90 °C; the dissolution of aramid 1313 fibers uses a mixed solvent of trifluoroacetic acid and N-methylpyrrolidone, and the dissolution temperature is 25 - 30 °C; the dispersion of conductive fibers uses dimethyl sulfoxide solvent and ultrasonic treatment.

[0010] Further, the preparation of sulfonated MXene in step S3 includes: dispersing MXene in N-methylpyrrolidone, adding a sulfonating agent for reaction, the reaction temperature is 60 - 90 °C, and the reaction time is 2 - 6 h.

[0011] Further, in step S4, the coagulation bath for wet spinning includes a mixed solution of ethanol and water, an aqueous solution containing lithium chloride and acetone, and the coagulation bath temperature is 5 - 25 °C; during the spiral winding and doubling process, the tension of each gel fiber precursor is 10 - 25 cN, the doubling speed is 100 - 200 rpm, and the winding spiral angle is 30 - 45°.

[0012] Further, in step S5, the pressure for supercritical carbon dioxide treatment is 15 - 30 MPa, the temperature is 40 - 60 °C, the pressure relief rate is 0.3 - 0.8 MPa / min, and the pore size of the treated fibers is 50 - 200 nm.

[0013] Further, in step S6, the functionalized cortex includes a composite layer of tin oxide and aramid 1414 solution or a composite layer of zinc oxide and aramid 1313 solution, and the coating is carried out using a coaxial needle.

[0014] Furthermore, the addition amount of tin oxide in the composite layer of tin oxide and aramid 1414 solution is 5-8 wt% of the mass of the aramid 1414 solution; the addition amount of zinc oxide in the composite layer of zinc oxide and aramid 1313 solution is 3-5 wt% of the mass of the aramid 1313 solution; the thickness of the coated cortex is 10-30 μm.

[0015] Another technical solution provided by the present invention: A multifunctional aerogel fiber based on waste fire-fighting suit fabric as raw material is prepared by the above preparation method.

[0016] The present invention solves the defects existing in the background technology and has the following beneficial effects: (1) Through the spiral winding and stranding process, supercritical carbon dioxide treatment and sulfonated MXene modification, the present invention solves the problems of poor interfacial bonding and single function of aramid 1313, aramid 1414 and conductive fibers in waste fire-fighting suit fabric, and realizes the integrated preparation of high-strength, high-conductivity and high-temperature resistant aerogel fibers.

[0017] (2) Through the spiral winding and stranding process, three bundles of fibers form a three-dimensional spiral structure. The spiral angle controls the degree of mechanical interlocking between fibers. Aramid 1414 bears the axial load, aramid 1313 dissipates energy through cross-linking, and conductive fibers are embedded in the spiral gaps to form a conductive network. Combining supercritical carbon dioxide treatment further strengthens the interfacial bonding. Carbon dioxide penetrates to the fiber interface to induce molecular chain plasticization and dynamic hydrogen bond reconstruction. Compared with the traditional parallel stranding process, spiral stranding significantly improves the tensile strength, avoids stress concentration caused by fiber loosening, and at the same time supercritical treatment optimizes the pore structure and reduces the material density. In the prior art, the mechanical properties of parallel stranding are limited due to small interfacial contact area and lack of mechanical interlocking. However, through the synergistic effect of the spiral structure and interfacial micro-melting, the present invention breaks through the incompatibility limit of materials and realizes the dual improvement of mechanical properties and lightweight.

[0018] (3) Sulfonated MXene modification forms a hydrogen bond network through sulfonic acid groups and aramid amide bonds, inhibits MXene agglomeration and enhances dispersibility. MXene is uniformly distributed in the conductive fiber spinning solution to form a continuous conductive path, penetrating the honeycomb pores generated by supercritical treatment. Compared with unmodified MXene or traditional hot pressing process, sulfonated MXene significantly improves the continuity and stability of the conductive network, and at the same time the thermal stability of sulfonic acid groups and aramid at high temperature synergistically inhibits fiber oxidation. In the prior art, the poor dispersibility of MXene leads to the fracture of the conductive network and the prominent problem of single function. However, through the synergism of sulfonation modification and spiral structure, the present invention realizes the synchronous optimization of conductivity, high-temperature stability and interfacial bonding strength.

[0019] (4) The combination of spiral winding and supercritical carbon dioxide treatment strengthens the fiber bonding through mechanical interlocking and interfacial microfusion, solving the problem of poor interfacial bonding; the combination of sulfonated MXene modification and split spinning process breaks through the limitation of single function through the construction of hydrogen bond network and conductive path. The spiral structure provides uniform gaps for the penetration of supercritical carbon dioxide, promoting pore expansion and interfacial hydrogen bond reconstruction, while the uniform distribution of sulfonated MXene in the conductive network further depends on the mechanical stability of spiral winding. The combination of the two forms a dual gain mechanism, realizing the synergistic improvement of tensile strength, conductivity and high-temperature stability, and providing an innovative solution for the high-value recycling of waste fire-fighting suit fabrics. Description of the Drawings

[0020] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments recorded in the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings. Figure 1 It is a flow chart of a multifunctional aerogel fiber based on waste fire-fighting suit fabrics as raw materials. Specific Embodiments

[0021] The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the protection scope of the present invention.

[0022] Many specific details are set forth in the following description in order to provide a thorough understanding of the present invention, but the present invention may be practiced in other ways different from those described herein. Therefore, the protection scope of the present invention is not limited by the specific embodiments disclosed below.

[0023] Unless otherwise specified in the following embodiments, all raw materials are commercially available or prepared by conventional methods in the art. Among them, the commercial sources of some materials are purchased from Sinopharm Reagents, including: XMene (aluminum titanium carbide), 98% 200 mesh (Wokai); N-methylpyrrolidone, AR (Wokai); lithium chloride, AR (Zhejiang); trifluoroacetic acid, AR (Hushi); N-methylpyrrolidone, GCS (Wokai); dimethyl sulfoxide, AR (Wokai); p-toluenesulfonyl chloride (sulfonating agent), 99% (TCI); acetone, AR (Hushi); tin oxide, CP (Hushi); zinc oxide, CP (Hushi). The waste fire-fighting suits are sourced from the local fire department. The outer fabric is composed of a blend of 93% aramid 1313, 5% aramid 1414, and 2% conductive fiber (pre-oxidized fiber), with a heat resistance temperature ≥ 260°C, a short-term tolerance of 400°C, a breaking strength ≥ 850 N, and an oxygen index ≥ 30.

[0024] Exemplary method: As Figure 1 shown, a method for preparing multifunctional aerogel fibers using waste fire-fighting suit fabric as a raw material includes the following steps: S1. Separate the outer fabric including aramid 1313 fibers, aramid 1414 fibers, and conductive fibers from the waste fire-fighting suit fabric and perform pretreatment; S2. Dissolve aramid 1414, aramid 1313, and conductive fibers in the outer fabric in sequence to prepare corresponding fiber solutions; S3. Add sulfonated MXene powder to each fiber solution and disperse it to obtain aramid 1313 spinning solution, aramid 1414 spinning solution, and conductive fiber spinning solution; S4. Prepare incompletely cured gel fiber precursors from each spinning solution by wet spinning and perform spiral winding and stranding to obtain stranded gel fibers; S5. Treat the stranded gel fibers with supercritical carbon dioxide to form porous aerogel fibers; S6. Coat a functionalized cortex on the surface of the aerogel fibers to obtain multifunctional aerogel fibers.

[0025] The exemplary method prepares multifunctional aerogel fibers with integrated tensile strength, energy dissipation, and conductivity by independently splitting and spinning aramid 1313, aramid 1414, and conductive fibers and then spiral winding them to avoid phase separation problems caused by differences in solvent systems; at the same time, by using the plasticizing and foaming effects of supercritical carbon dioxide, it synchronously realizes the strengthening of hydrogen bonds at the fiber interface and the construction of a honeycomb-like porous structure, improves the heat insulation performance while reducing the material density, and enhances the interfacial stability by inducing the combination of sulfonated MXene and fibers.

[0026] Next, each step will be described in detail.

[0027] In step S1, the pretreatment includes: cutting the waste fire-fighting suit fabric into blocks, separating the outer fabric, removing impurities, and opening it into a short fiber mixture; sequentially performing alkaline cleaning, water washing, drying, and shearing on the short fiber mixture.

[0028] Specifically, the waste fire-fighting suit fabric includes an outer layer, a middle layer, and a lining. The outer layer is a raw solution 3A fabric, and the main components are aramid 1313, aramid 1414, and conductive fibers.

[0029] In step S1, use an industrial shearing machine to cut the outer fabric of the waste fire-fighting suit into equal-sized blocks with a side length of 10 to 15 cm, strip the outer layer, middle layer, and lining through a mechanical sorting device, and separate the 3A outer fabric. Among them, use a magnetic separator to adsorb metal impurities such as buttons or zippers, and remove plastic linings and obvious damaged non-fiber impurities. Feed the sorted fabric into a variable-frequency opener, adjust the needle roller speed to 800 to 1200 rpm, and open it into a loose short fiber mixture with a fiber length of 10 to 20 mm.

[0030] Prepare an alkaline cleaning solution, which contains 3-8 wt% sodium carbonate, 1-3 wt% sodium dodecyl sulfate, and add 0.5-1 wt% sodium silicate as a corrosion inhibitor. Sodium carbonate provides an alkaline environment to decompose oil stains, sodium dodecyl sulfate acts as a surfactant to reduce the surface tension of the fiber, and sodium silicate corrosion inhibitor protects the aramid amide bond from strong base hydrolysis.

[0031] Immerse the short fiber mixture in the alkaline cleaning solution, heat it to 60-80 °C, and perform ultrasonic-assisted cleaning at a frequency of 40 kHz and a power of 200 W for 3-6 h, and rinse it with deionized water until the pH is 6.5-7.5; transfer the washed fibers to a vacuum drying oven at 50-70 °C and dry them for 4-6 h, and further shear the dried fibers with a rotary shear machine to short fibers with a length of no more than 5 mm.

[0032] In step S2, the dissolution of aramid 1414 fibers uses a composite solvent of N,N-dimethylacetamide and lithium chloride, and the dissolution temperature is 80-90 °C; the dissolution of aramid 1313 fibers uses a mixed solvent of trifluoroacetic acid and N-methylpyrrolidone, and the dissolution temperature is 25-30 °C; the dispersion of conductive fibers uses dimethyl sulfoxide solvent and ultrasonic treatment.

[0033] The method for dissolving aramid 1414 includes: adding a short fiber mixture into a composite solvent of N,N-dimethylacetamide and lithium chloride at a liquid-solid ratio of 10 mL / g, with the lithium chloride concentration being 4-6 wt%, mechanically stirring at 80-90 °C at 200-300 rpm for 3-5 h. After dissolution, filter with a 200-mesh filter screen. The filtrate is the aramid 1414 solution with a concentration of 12-15 wt%; the filter residue includes undissolved aramid 1313 and conductive fibers, which are rinsed 3 times with ethanol and vacuum dried at 50 °C for 2 h. The preparation method of the composite solvent of N,N-dimethylacetamide and lithium chloride is to add lithium chloride powder into N,N-dimethylacetamide, control the lithium chloride concentration to be 4-6 wt%, and mechanically stir until completely dissolved. Lithium chloride destroys the crystalline hydrogen bond network of aramid 1414 through complexation, and the DMAc solvent provides a polar environment to stabilize the dissolved state, and high temperature accelerates the dissociation of molecular chains.

[0034] The method for dissolving aramid 1313 includes: adding the filter residue generated after dissolving aramid 1414 into a mixed solvent with a volume ratio of trifluoroacetic acid to N-methylpyrrolidone of 1:2 at a liquid-solid ratio of 8 mL / g, pre-cooling to 10-15 °C and then heating to 25-30 °C, and stirring at 150-200 rpm for 2-4 h. After filtration, a filtrate and a filter residue are obtained. Sodium bicarbonate powder is slowly added to the filtrate to neutralize to pH 6-7, and the precipitate is removed by centrifugation to obtain an aramid 1313 solution with a concentration of 10-12 wt%; the filter residue includes undissolved conductive fibers. Trifluoroacetic acid protonates the amide group of meta-aramid, reducing the intermolecular force, and N-methylpyrrolidone is used as a co-solvent to reduce the system viscosity and inhibit side reactions.

[0035] The method for dissolving conductive fibers includes: adding the filter residue generated after dissolving aramid 1313 into dimethyl sulfoxide solvent at a liquid-solid ratio of 5 mL / g, ultrasonic treating at a frequency of 40 kHz and a power of 200 W for 1-2 h, and then centrifuging at 5000 rpm for 10 min to remove undispersed particles to obtain a conductive fiber dispersion with a concentration of 4-6 wt%. The ultrasonic cavitation breaks the agglomeration of conductive fibers, and at the same time limits the treatment time to avoid fiber breakage.

[0036] Lithium chloride destroys the hydrogen bond network of para-aramid through complexation, and N,N-dimethylacetamide provides a polar dissolution environment; trifluoroacetic acid protonates the amide group of meta-aramid, and N-methylpyrrolidone reduces the system viscosity and stabilizes the dissolved state; dimethyl sulfoxide disperses the fibers through polar-π interaction, and ultrasonic cavitation breaks the agglomeration.

[0037] In step S3, the preparation of sulfonated MXene includes: dispersing MXene in N-methylpyrrolidone, adding a sulfonating agent for reaction, with the reaction temperature being 60 - 90°C and the reaction time being 2 - 6 h. Specifically, the MXene powder is dispersed in N-methylpyrrolidone at a concentration of 5 - 10 mg / mL, p-toluenesulfonyl chloride is added, and the molar ratio of MXene to the sulfonating agent is controlled to be 1:1 to 1:3. The mixture is refluxed at 60 - 90°C for 2 - 6 h. After the reaction, it is centrifuged at 8000 rpm for 10 min, washed repeatedly with ethanol until neutral, and vacuum dried at 60°C for 6 - 8 h to obtain sulfonated MXene powder. p-Toluenesulfonyl chloride reacts with the surface hydroxyl groups of MXene at high temperature to graft sulfonic acid groups, enhancing the hydrogen bond binding ability with aramid amide bonds.

[0038] When preparing the aramid 1313 spinning solution, 1 - 3 wt% of sulfonated MXene is added to the aramid 1313 solution, and it is mechanically stirred at 150 - 200 rpm at 25 - 30°C for 1 - 2 h, and then ultrasonically treated at a frequency of 40 kHz and a power of 200 W for 30 min to ensure uniform dispersion of MXene.

[0039] When preparing the aramid 1414 spinning solution, 0.5 - 2 wt% of sulfonated MXene is added to the aramid 1414 solution, and it is stirred at 200 - 300 rpm at 80 - 90°C for 2 - 3 h, and then filtered through a 200-mesh sieve to remove undispersed particles.

[0040] When preparing the conductive fiber spinning solution, 3 - 5 wt% of sulfonated MXene is added to the conductive fiber dispersion, ultrasonically treated at a frequency of 40 kHz and a power of 200 W for 1 h, and then filtered and purified with a 0.45-μm pore size filter membrane.

[0041] Low-temperature stirring of the aramid 1313 solution avoids solvent volatilization, and high-temperature stirring of the aramid 1414 promotes the embedding of MXene into the fiber network, while restricting the temperature below 90°C to avoid decomposition of N,N-dimethylacetamide.

[0042] In step S4, the coagulation bath for wet spinning includes a mixed solution of ethanol and water, an aqueous solution containing lithium chloride, and acetone, and the coagulation bath temperature is 5 - 25°C; during the spiral winding and stranding process, the tension of each gel fiber precursor is 10 - 25 cN, the stranding speed is 100 - 200 rpm, and the winding spiral angle is 30 - 45°. In this step, an incompletely cured gel fiber precursor is formed by wet spinning and is subjected to spiral winding and stranding to obtain a gel fiber, providing a basis for an expandable porous structure for subsequent supercritical carbon dioxide treatment.

[0043] In this step, a multi-component wet spinning device is used to perform wet spinning on aramid 1313 spinning solution, aramid 1414 spinning solution, and conductive fiber spinning solution respectively. A three-channel spinneret is used to extrude the spinning solution into a coagulation bath to prepare aramid 1313 gel fiber precursor, aramid 1414 gel fiber precursor, and conductive fiber gel fiber precursor.

[0044] Among them, the aramid 1313 spinning solution is extruded through a spinneret with a pore diameter of 0.1 - 0.3 mm into a coagulation bath with a volume ratio of ethanol to water of 7 to 3, and the bath temperature is 5 - 10 °C; the aramid 1414 spinning solution is extruded through a spinneret with a pore diameter of 0.2 - 0.4 mm, the coagulation bath is an aqueous solution containing 5 wt% lithium chloride, the temperature is 20 - 25 °C, and the draw ratio is 2.0 - 2.5; the conductive fiber spinning solution is extruded through a spinneret with a pore diameter of 0.05 - 0.15 mm into an acetone coagulation bath, the temperature is 15 - 20 °C, and the draw ratio is 1.5 - 2.0. After staying in the above fibers for 30 - 60 s, they are wound at a draw ratio of 1.5 - 2.5, and the speed is 10 - 20 m / min.

[0045] The above three strands of uncured gel fiber precursors are introduced into a stranding machine through a godet wheel system and stranded and wound spirally to prepare stranded gel fibers. Among them, the tension is controlled: 15 - 20 cN for aramid 1313, 20 - 25 cN for aramid 1414, and 10 - 15 cN for conductive fibers; the stranding machine rotates at a speed of 100 - 200 rpm, the traction speed is 1.0 - 1.5 m / min, forming a winding structure with a spiral angle of 30 - 45°, the volume ratio of the three strands is 1 to 1 to 1, the cross-section is circular with a diameter of 0.5 - 1.0 mm, and the internal is an equally divided fan-shaped area.

[0046] In step S5, the pressure of the supercritical carbon dioxide treatment is 15 - 30 MPa, the temperature is 40 - 60 °C, the pressure relief rate is 0.3 - 0.8 MPa / min, and the pore diameter of the treated fiber is 50 - 200 nm. In this step, through the solvation and foaming effects of supercritical carbon dioxide, the gel fibers are transformed into aerogel fibers with high porosity. Supercritical carbon dioxide penetrates into the fiber interior, and nucleation and foaming are triggered by pressure relief. The plasticization effect reduces the glass transition temperature of aramid and promotes the hydrogen bond combination between sulfonic acid groups and amide bonds.

[0047] In this step, the ply gel fiber is immersed in absolute ethanol for 24 - 48 h, and the solvent is changed every 6 h. Subsequently, it is pre - dried at 50 - 70 °C for 2 - 4 h. The ply gel fiber is wound around a porous scaffold and then placed into a reaction kettle. Liquid carbon dioxide is injected until the pressure reaches 8 - 10 MPa, and the temperature is raised to 40 - 60 °C to make the carbon dioxide enter the supercritical state. Then, the pressure is increased to 15 - 30 MPa and maintained for 1 - 3 h. The pressure is released at a rate of 0.3 - 0.8 MPa / min, and the temperature is simultaneously reduced to 25 - 30 °C to form a honeycomb - like porous structure with pore diameters of 50 - 200 nm. The fiber is placed in a vacuum drying oven at 60 - 80 °C and dried for 4 - 8 h. If the pore distribution is uneven, it can be subjected to a secondary supercritical treatment: pressure 10 - 15 MPa, time 30 - 90 min.

[0048] In step S6, the functionalized cortex includes a composite layer of tin oxide and aramid 1414 solution or a composite layer of zinc oxide and aramid 1313 solution. The coating is carried out using a coaxial needle, and the coagulation bath is a mixed solution of ethanol and water. The addition amount of tin oxide in the composite layer of tin oxide and aramid 1414 solution is 5 - 8 wt% of the mass of the aramid 1414 solution; the addition amount of zinc oxide in the composite layer of zinc oxide and aramid 1313 solution is 3 - 5 wt% of the mass of the aramid 1313 solution; the thickness of the coated cortex is 10 - 30 μm.

[0049] Specifically, the preparation method of the tin oxide / aramid cortex spinning solution includes adding 5 - 8 wt% of tin oxide to the aramid 1414 solution, stirring at 300 rpm for 2 h at 80 °C, and performing ultrasonic dispersion at 40 kHz for 30 min; the preparation method of the zinc oxide / aramid cortex spinning solution includes adding 3 - 5 wt% of zinc oxide to the aramid 1313 solution, stirring at 200 rpm for 1 h at 25 °C, and performing ultrasonic treatment at 40 kHz for 1 h. Tin oxide protects the fiber structure through ultraviolet shielding, and zinc oxide enhances the antibacterial performance through contact sterilization.

[0050] In this step, a coaxial needle with a core layer inner diameter of 1.0 - 1.2 mm and a cortex outer diameter of 1.5 - 2.0 mm is used. The aerogel fiber is used as the core layer, and the functionalized cortex spinning solution is used as the cortex spinning solution. The flow rate of the core layer aerogel fiber is controlled at 0.5 - 1.0 mL / min, and the flow rate of the cortex spinning solution is 1.0 - 1.5 mL / min. The aerogel fiber coated with the functionalized cortex enters a coagulation bath with a volume ratio of ethanol to water of 8 to 2, at a temperature of 10 - 15 °C, a draw ratio of 1.2 - 1.5, and a winding speed of 5 - 8 m / min. Finally, the cortex thickness is 10 - 30 μm.

[0051] Exemplary structure: A multifunctional aerogel fiber based on waste fire - fighting suit fabric as raw material is prepared by the above - mentioned exemplary method.

[0052] Example 1:

[0053] S1: Use an industrial shearing machine to cut the outer fabric of waste fire-fighting suits into equal-sized blocks with a side length of 12 cm. Peel off the outer layer, middle layer, and inner lining through a mechanical sorting device to separate the 3A outer fabric. Use a magnetic separator to adsorb metal impurities including buttons and zippers, and remove plastic linings and obvious damaged non-fibrous impurities. Feed the sorted fabric into a variable-frequency opener, adjust the needle roller speed to 1000 rpm, and open it to a loose short fiber mixture with a fiber length of 15 mm; Prepare an alkaline cleaning solution containing 5 wt% sodium carbonate, 2 wt% sodium dodecyl sulfate, and add 0.8 wt% sodium silicate as a corrosion inhibitor. Immerse the short fiber mixture in the alkaline cleaning solution, heat it to 70 °C, and ultrasonically assist the cleaning at a power of 200 W and a frequency of 40 kHz for 4 h. Rinse it with deionized water until the pH value reaches 7.0, and transfer the washed fibers to a vacuum drying oven at 60 °C for drying for 5 h. Use a rotary shearing machine to further cut the dried fibers into short fibers with a length not exceeding 5 mm.

[0054] S2: Add the short fiber mixture to a composite solvent of N,N-dimethylacetamide and 5 wt% lithium chloride at a liquid-solid ratio of 10 mL / g; mechanically stir it at 250 rpm at 90 °C for 4 h. After dissolution, filter it through a 200-mesh filter screen. The filtrate is an aramid 1414 solution with a concentration of 14 wt%. The filter residue includes undissolved aramid 1313 and conductive fibers, which are rinsed 3 times with ethanol and vacuum dried at 50 °C for 2 h.

[0055] Add the filter residue including undissolved aramid 1313 and conductive fibers to a mixed solvent with a volume ratio of trifluoroacetic acid to N-methylpyrrolidone of 1:2 at a liquid-solid ratio of 8 mL / g; pre-cool it to 12 °C and then heat it to 30 °C, and stir it at 180 rpm for 3 h. After filtration, slowly add sodium bicarbonate powder to the filtrate to neutralize it to a pH value of 6.5, and centrifuge to remove the precipitate to obtain an aramid 1313 solution with a concentration of 11 wt%. The filter residue includes undissolved conductive fibers.

[0056] Add the filter residue including undissolved conductive fibers to dimethyl sulfoxide solvent at a liquid-solid ratio of 5 mL / g; ultrasonically treat it at a power of 200 W and a frequency of 40 kHz for 1.5 h, and then centrifuge it at 5000 rpm for 10 min to remove undispersed particles to obtain a conductive fiber dispersion with a concentration of 5 wt%.

[0057] S3: Disperse MXene powder in N-methylpyrrolidone at a concentration of 8 mg / mL, add p-toluenesulfonyl chloride, control the molar ratio of MXene to the sulfonating agent to be 1:1, and reflux and react at 80 °C for 4 h; after the reaction, centrifuge it at 8000 rpm for 10 min, wash it repeatedly with ethanol until neutral, and vacuum dry it at 60 °C for 8 h to obtain sulfonated MXene powder.

[0058] Prepare the aramid 1313 spinning solution: Add 2 wt% sulfonated MXene to the aramid 1313 solution. Stir mechanically at 180 rpm for 1.5 h at 30 °C, and then sonicate at a power of 200 W and a frequency of 40 kHz for 30 min.

[0059] Prepare the aramid 1414 spinning solution: Add 1 wt% sulfonated MXene to the aramid 1414 solution. Stir at 250 rpm for 3 h at 90 °C, and filter through a 200-mesh sieve to remove undispersed particles.

[0060] Prepare the conductive fiber spinning solution: Add 4 wt% sulfonated MXene to the conductive fiber dispersion. Sonicate at a power of 200 W and a frequency of 40 kHz for 1 h, and then filter and purify with a 0.45-μm pore size filter membrane.

[0061] S4: Use a multi-component wet spinning device to perform wet spinning on the aramid 1313 spinning solution, aramid 1414 spinning solution, and conductive fiber spinning solution respectively. Use a three-channel spinneret. Extrude the aramid 1313 spinning solution through a spinneret with a pore size of 0.2 mm into a coagulation bath with a volume ratio of ethanol to water of 7:3 at a bath temperature of 8 °C. Extrude the aramid 1414 spinning solution through a spinneret with a pore size of 0.3 mm into an aqueous coagulation bath containing 5 wt% lithium chloride at a temperature of 22 °C. Extrude the conductive fiber spinning solution through a spinneret with a pore size of 0.1 mm into an acetone coagulation bath at a temperature of 18 °C. After the above fibers stay for 45 s, wind them up at a draw ratio of 2.0 and a speed of 15 m / min.

[0062] Feed the three strands of uncured gel fiber precursors into a stranding machine through a godet wheel system. Control the tension to be 18 cN for aramid 1313 fiber, 22 cN for aramid 1414 fiber, and 12 cN for conductive fiber. The stranding machine rotates at a speed of 150 rpm, and the drawing speed is 1.2 m / min to form a winding structure with a helix angle of 30°. The three strands have a volume ratio of 1:1:1, a circular cross-section with a diameter of 0.8 mm, and an equally divided fan-shaped area inside.

[0063] S5: Immerse the stranded gel fiber in absolute ethanol for 36 h and change the solvent every 6 h. Then pre-dry at 60 °C for 3 h. Wind the stranded gel fiber around a porous support and place it in a reaction kettle, and inject liquid carbon dioxide until the pressure reaches 9 MPa. Heat up to 50 °C to make the carbon dioxide enter the supercritical state, pressurize to 15 MPa and maintain for 2 h. Release the pressure at a rate of 0.5 MPa per minute and cool down to 25 °C synchronously. Place the fiber in a vacuum drying oven at 60 °C and dry for 6 h.

[0064] S6: Add 6 wt% tin oxide to the aramid 1414 solution, stir at 300 rpm for 2 h at 80 °C, and ultrasonically disperse at 40 kHz for 30 min to obtain a functionalized skin spinning solution. Use a coaxial needle with a core layer inner diameter of 1.0 mm and a skin layer outer diameter of 1.8 mm. Take the aerogel fiber as the core layer and the functionalized skin spinning solution as the skin spinning solution. Control the flow rate of the core layer aerogel fiber at 0.8 m / min and the flow rate of the skin spinning solution at 1.2 m / min. The aerogel fiber coated with the functionalized skin layer enters a coagulation bath with a volume ratio of ethanol to water of 8:2, at a temperature of 12 °C, a draw ratio of 1.3, and a winding speed of 6 m / min. The final skin layer thickness is 20 μm.

[0065] Example 2:

[0066] Different from Example 1, in step S3 of this example, the MXene powder is dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride is added, and the molar ratio of MXene to the sulfonating agent is controlled at 1:2. The reaction is refluxed at 80 °C for 4 h; after the reaction, it is centrifuged at 8000 rpm for 10 min, washed repeatedly with ethanol until neutral, and vacuum dried at 60 °C for 8 h to obtain sulfonated MXene powder.

[0067] In step S4 of this example, the stranding machine rotates at a speed of 150 rpm, the traction speed is 1.2 m / min, and a winding structure with a helix angle of 40° is formed. The volume ratio of the three strands is 1:1:1, the cross-section is circular with a diameter of 0.8 mm, and the internal is an equally divided fan-shaped area.

[0068] Example 3:

[0069] Different from Example 1, in step S3 of this example, the MXene powder is dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride is added, and the molar ratio of MXene to the sulfonating agent is controlled at 1:3. The reaction is refluxed at 80 °C for 4 h; after the reaction, it is centrifuged at 8000 rpm for 10 min, washed repeatedly with ethanol until neutral, and vacuum dried at 60 °C for 8 h to obtain sulfonated MXene powder.

[0070] In step S4 of this example, the stranding machine rotates at a speed of 150 rpm, the traction speed is 1.2 m / min, and a winding structure with a helix angle of 45° is formed. The volume ratio of the three strands is 1:1:1, the cross-section is circular with a diameter of 0.8 mm, and the internal is an equally divided fan-shaped area.

[0071] Example 4:

[0072] Different from Example 1, in step S3 of this example, MXene powder is dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride is added, the molar ratio of MXene to the sulfonating agent is controlled to be 1:2, and the mixture is refluxed at 80 °C for 4 h; after the reaction, it is centrifuged at 8000 rpm for 10 min, washed repeatedly with ethanol until neutral, and dried in vacuum at 60 °C for 8 h to obtain sulfonated MXene powder.

[0073] In step S4 of this example, the stranding machine rotates at a speed of 150 rpm, the traction speed is 1.2 m / min, and a winding structure with a helix angle of 30° is formed. The volume ratio of the three strands is 1:1:1, the cross-section is circular with a diameter of 0.8 mm, and the internal is an equally divided fan-shaped area.

[0074] In step S5 of this example, the stranded gel fiber is wound around a porous scaffold and then loaded into a reaction kettle, and liquid carbon dioxide is injected until the pressure reaches 9 MPa. It is heated to 50 °C to make carbon dioxide enter the supercritical state, pressurized to 25 MPa and maintained for 2 h. The pressure is released at a rate of 0.5 MPa per minute, and the temperature is simultaneously lowered to 25 °C. The fiber is placed in a vacuum drying oven at 60 °C and dried for 6 h.

[0075] Example 5:

[0076] Different from Example 1, in step S3 of this example, MXene powder is dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride is added, the molar ratio of MXene to the sulfonating agent is controlled to be 1:2, and the mixture is refluxed at 80 °C for 4 h; after the reaction, it is centrifuged at 8000 rpm for 10 min, washed repeatedly with ethanol until neutral, and dried in vacuum at 60 °C for 8 h to obtain sulfonated MXene powder.

[0077] In step S4 of this example, the stranding machine rotates at a speed of 150 rpm, the traction speed is 1.2 m / min, and a winding structure with a helix angle of 40° is formed. The volume ratio of the three strands is 1:1:1, the cross-section is circular with a diameter of 0.8 mm, and the internal is an equally divided fan-shaped area.

[0078] In step S5 of this example, the stranded gel fiber is wound around a porous scaffold and then loaded into a reaction kettle, and liquid carbon dioxide is injected until the pressure reaches 9 MPa. It is heated to 50 °C to make carbon dioxide enter the supercritical state, pressurized to 25 MPa and maintained for 2 h. The pressure is released at a rate of 0.5 MPa per minute, and the temperature is simultaneously lowered to 25 °C. The fiber is placed in a vacuum drying oven at 60 °C and dried for 6 h.

[0079] Example 6:

[0080] In step S4 of this embodiment, the stranding machine rotates at a speed of 150 rpm, the traction speed is 1.2 m / min, forming a winding structure with a helix angle of 45°. The volume ratio of the three strands is 1:1:1, the cross-section is circular with a diameter of 0.8 mm, and the internal is an equally divided fan-shaped area.

[0081] In step S5 of this embodiment, the stranded gel fibers are wound around a porous scaffold and then loaded into a reaction kettle, and liquid carbon dioxide is injected until the pressure reaches 9 MPa. The temperature is raised to 50 °C to make the carbon dioxide enter the supercritical state, pressurized to 25 MPa and maintained for 2 h. The pressure is released at a rate of 0.5 MPa per minute, and the temperature is synchronously lowered to 25 °C. The fibers are placed in a vacuum drying oven at 60 °C and dried for 6 h.

[0082] Example 7:

[0083] Different from Example 1, in step S3 of this embodiment, the MXene powder is dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, and p-toluenesulfonyl chloride is added. The molar ratio of MXene to the sulfonating agent is controlled to be 1:3, and the reaction is refluxed at 80 °C for 4 h; after the reaction is completed, it is centrifuged at 8000 rpm for 10 min, washed repeatedly with ethanol until neutral, and vacuum dried at 60 °C for 8 h to obtain sulfonated MXene powder.

[0084] In step S5 of this embodiment, the stranded gel fibers are wound around a porous scaffold and then loaded into a reaction kettle, and liquid carbon dioxide is injected until the pressure reaches 9 MPa. The temperature is raised to 50 °C to make the carbon dioxide enter the supercritical state, pressurized to 30 MPa and maintained for 2 h. The pressure is released at a rate of 0.5 MPa per minute, and the temperature is synchronously lowered to 25 °C. The fibers are placed in a vacuum drying oven at 60 °C and dried for 6 h.

[0085] Example 8:

[0086] In step S4 of this embodiment, the stranding machine rotates at a speed of 150 rpm, the traction speed is 1.2 m / min, forming a winding structure with a helix angle of 40°. The volume ratio of the three strands is 1:1:1, the cross-section is circular with a diameter of 0.8 mm, and the internal is an equally divided fan-shaped area.

[0087] In step S5 of this embodiment, the stranded gel fibers are wound around a porous scaffold and then loaded into a reaction kettle, and liquid carbon dioxide is injected until the pressure reaches 9 MPa. The temperature is raised to 50 °C to make the carbon dioxide enter the supercritical state, pressurized to 30 MPa and maintained for 2 h. The pressure is released at a rate of 0.5 MPa per minute, and the temperature is synchronously lowered to 25 °C. The fibers are placed in a vacuum drying oven at 60 °C and dried for 6 h.

[0088] Example 9:

[0089] Different from Example 1, in step S3 of this example, MXene powder is dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride is added, the molar ratio of MXene to the sulfonating agent is controlled to be 1:2, and the mixture is refluxed at 80 °C for 4 h; after the reaction, it is centrifuged at 8000 rpm for 10 min, washed repeatedly with ethanol until neutral, and dried in vacuum at 60 °C for 8 h to obtain sulfonated MXene powder.

[0090] In step S4 of this example, the stranding machine rotates at a speed of 150 rpm, the traction speed is 1.2 m / min, and a winding structure with a helix angle of 45° is formed. The three strands have a volume ratio of 1:1:1, a circular cross-section with a diameter of 0.8 mm, and an equally divided fan-shaped area inside.

[0091] In step S5 of this example, the stranded gel fiber is wound around a porous scaffold and then loaded into a reaction kettle, and liquid carbon dioxide is injected until the pressure reaches 9 MPa. The temperature is raised to 50 °C to make carbon dioxide enter the supercritical state, pressurized to 30 MPa and maintained for 2 h. The pressure is released at a rate of 0.5 MPa per minute, and the temperature is simultaneously lowered to 25 °C. The fiber is dried in a vacuum drying oven at 60 °C for 6 h.

[0092] Comparative Example 1: Different from Example 1, in step S3 of this comparative example, MXene is not sulfonated and modified, in step S4, parallel-stranded three-bundle fibers are used, and in step S5, supercritical carbon dioxide treatment is not performed, but the fiber is prepared by hot pressing.

[0093] Experimental Example 1: The specific process of the multifunctional aerogel fiber used in this experimental example is as follows.

[0094] (1) The experimental group includes the following steps: S1: Use an industrial shearing machine to cut the outer layer fabric of the waste fire suit into equal-sized blocks with a side length of 12 cm. The outer layer, middle layer, and inner lining are peeled off through a mechanical sorting device to separate the 3A outer layer fabric. A magnetic separator is used to adsorb metal impurities including buttons and zippers, and plastic linings and obvious non-fibrous impurities with damage are removed. The sorted fabric is sent into a variable-frequency opener, and the needle roller speed is adjusted to 1000 rpm to open it into a loose short fiber mixture with a fiber length of 15 mm; Prepare an alkaline cleaning solution containing 5 wt% sodium carbonate, 2 wt% sodium dodecyl sulfate, and add 0.8 wt% sodium silicate as a corrosion inhibitor. Immerse the short fiber mixture in the alkaline cleaning solution, heat it to 70 °C, and ultrasonically assist the cleaning at a power of 40 kHz and 200 W for 4 h. Rinse it with deionized water until the pH value is 7.0, and transfer the washed fiber to a vacuum drying oven at 60 °C to dry for 5 h. Use a rotary shear machine to further cut the dried fiber into short fibers with a length not exceeding 5 mm.

[0095] S2: Add the short fiber mixture into the composite solvent of N,N-dimethylacetamide and 5wt% lithium chloride at a liquid-solid ratio of 10 mL / g; mechanically stir at 250 rpm for 4 h at 90 °C. After dissolution, filter with a 200-mesh sieve. The filtrate is the aramid 1414 solution with a concentration of 14wt%. The filter residue includes undissolved aramid 1313 and conductive fibers, which are rinsed 3 times with ethanol and vacuum dried at 50 °C for 2 h.

[0096] Add the filter residue including undissolved aramid 1313 and conductive fibers into the mixed solvent with a volume ratio of trifluoroacetic acid to N-methylpyrrolidone of 1:2 at a liquid-solid ratio of 8 mL / g; pre-cool to 12 °C and then heat up to 30 °C, stir at 180 rpm for 3 h. After filtration, slowly add sodium bicarbonate powder to the filtrate to neutralize to a pH value of 6.5, and centrifuge to remove the precipitate to obtain an aramid 1313 solution with a concentration of 11wt%. The filter residue includes undissolved conductive fibers.

[0097] Add the filter residue including undissolved conductive fibers into dimethyl sulfoxide solvent at a liquid-solid ratio of 5 mL / g; ultrasonically treat at a power of 200 W and a frequency of 40 kHz for 1.5 h, and then centrifuge at 5000 rpm for 10 min to remove undispersed particles to obtain a conductive fiber dispersion with a concentration of 5wt%.

[0098] S3: Disperse the MXene powder in N-methylpyrrolidone at a concentration of 8 mg / mL. Add p-toluenesulfonyl chloride, and control the molar ratio of MXene to the sulfonating agent to be 1:1 to 1:3. Carry out a reflux reaction at 80 °C for 4 h. After the reaction, centrifuge at 8000 rpm for 10 min, wash repeatedly with ethanol until neutral, and vacuum dry at 60 °C for 8 h to obtain sulfonated MXene powder.

[0099] Prepare the aramid 1313 spinning solution: Add 2wt% sulfonated MXene to the aramid 1313 solution. Mechanically stir at 180 rpm for 1.5 h at 30 °C, and ultrasonically treat at a power of 200 W and a frequency of 40 kHz for 30 min.

[0100] Prepare the aramid 1414 spinning solution: Add 1wt% sulfonated MXene to the aramid 1414 solution. Stir at 250 rpm for 3 h at 90 °C, and filter through a 200-mesh sieve to remove undispersed particles.

[0101] Prepare the conductive fiber spinning solution: Add 4wt% sulfonated MXene to the conductive fiber dispersion. Ultrasonically treat at a power of 200 W and a frequency of 40 kHz for 1 h, and then filter and purify with a 0.45-μm pore size filter membrane.

[0102] S4: Use a multi-component wet spinning device to perform wet spinning on the aramid 1313 spinning solution, aramid 1414 spinning solution, and conductive fiber spinning solution respectively. Use a three-channel spinneret. Extrude the aramid 1313 spinning solution through a spinneret with a pore diameter of 0.2 mm into a coagulation bath with a volume ratio of ethanol to water of 7:3, and the bath temperature is 8°C. Extrude the aramid 1414 spinning solution through a spinneret with a pore diameter of 0.3 mm into an aqueous coagulation bath containing 5 wt% lithium chloride, and the temperature is 22°C. Extrude the conductive fiber spinning solution through a spinneret with a pore diameter of 0.1 mm into an acetone coagulation bath, and the temperature is 18°C. After the above fibers stay for 45 s, wind them up at a draw ratio of 2.0 and a speed of 15 m / min.

[0103] Feed the three strands of uncured gel fiber precursors into the stranding machine through the godet wheel system. Control the tensions to be 18 cN for aramid 1313 fiber, 22 cN for aramid 1414 fiber, and 12 cN for conductive fiber. The stranding machine rotates at a speed of 150 rpm, and the traction speed is 1.2 m / min, forming a winding structure with a helix angle of 30 - 45°. The three strands have a volume ratio of 1:1:1, a circular cross-section with a diameter of 0.8 mm, and an equally divided fan-shaped area inside.

[0104] S5: Immerse the stranded gel fiber in absolute ethanol for 36 h, and change the solvent every 6 h. Then pre-dry it at 60°C for 3 h. Wind the stranded gel fiber around a porous support and place it in a reaction kettle, and inject liquid carbon dioxide until the pressure reaches 9 MPa. Heat up to 50°C to make the carbon dioxide enter the supercritical state, pressurize to 15 - 30 MPa and maintain for 2 h. Release the pressure at a rate of 0.5 MPa per minute, and simultaneously cool down to 25°C. Place the fiber in a vacuum drying oven at 60°C and dry it for 6 h.

[0105] S6: Add 6 wt% tin oxide to the aramid 1414 solution. Stir at 300 rpm for 2 h at 80°C, and disperse it ultrasonically at 40 kHz for 30 min to obtain a functionalized skin layer spinning solution. Use a coaxial needle with an inner diameter of 1.0 mm for the core layer and an outer diameter of 1.8 mm for the skin layer. Use the aerogel fiber as the core layer and the functionalized skin layer spinning solution as the skin layer spinning solution. Control the flow rate of the core layer aerogel fiber to be 0.8 m / min and the flow rate of the skin layer spinning solution to be 1.2 m / min. The aerogel fiber coated with the functionalized skin layer enters a coagulation bath with a volume ratio of ethanol to water of 8:2, the temperature is 12°C, the draw ratio is 1.3, and the winding speed is 6 m / min. The final skin layer thickness is 20 μm.

[0106] (2) Blank control group: Compared with the experimental group, in step S3, MXene is not sulfonated and modified. In step S4, three parallel stranded fibers are used. In step S5, instead of supercritical carbon dioxide treatment, the fiber is prepared by hot pressing.

[0107] The experimental steps involved in this experimental example are as follows: Prepare 10 groups of samples according to the above process, corresponding to Examples 1-9 and Comparative Example 1 respectively; Test the tensile strength of the samples with reference to ASTM D3822, test the conductivity of the samples with reference to GB / T 3048.3, test the pore uniformity of the samples with reference to ISO 15901-1, test the density of the samples with reference to ISO 1183, test the conductivity uniformity of the samples with reference to ASTM D257, and test the glass transition temperature of the samples with reference to ISO 11357-2.

[0108] In this experimental example, the parameter comparison table between the experimental group and the control group is shown in Table 1 below, and the experimental performance test results are shown in Table 2 below.

[0109] Table 1 Parameter comparison table between the experimental group and the control group

[0110] Table 2 Experimental performance test results

[0111] Example 5 exhibits the best comprehensive performance, and its parameter combination is a helix angle of 40°, a supercritical pressure of 25 MPa, and a molar ratio of MXene to sulfonating agent of 1:2. The tensile strength of this group reaches 3.4 GPa, the conductivity is 0.45 S / cm, the pore uniformity is 25 nm, the conductivity uniformity is 98%, and the glass transition temperature is increased by 13.2 °C.

[0112] The 40° helix angle forms a three-dimensional network structure through the helical winding of fibers, enabling aramid 1313, 1414 and conductive fibers to form a gradient stress transfer path during stretching. The high-modulus aramid 1414 fibers serve as the main load-bearing skeleton, and the high-toughness aramid 1313 fibers share local stress concentration through the helical winding angle. The conductive fibers are embedded at the interface of the double aramid to construct a continuous conductive network. The 40° helix angle creates an appropriate surface friction during the winding process of the fibers, which not only ensures the interfacial bonding strength of the ply yarns but also avoids the fracture of the conductive fibers caused by excessive friction. This angle also promotes the penetration path of supercritical carbon dioxide inside the fibers to be in a helical diffusion mode. Combined with a pressure of 25 MPa, the supercritical fluid generates anisotropic expansion inside the fibers, forming a long-range ordered nano-porous structure along the helical direction, and the standard deviation of the pore size is only 25 nm.

[0113] A molar ratio of MXene to sulfonating agent of 1:2 promotes the formation of a moderate amount of sulfonic acid group modification on the surface of MXene. On the one hand, the sulfonic acid groups are adsorbed on the amide groups of the aramid molecular chains through electrostatic interaction, forming an MXene-aramid intermolecular hydrogen bond network and enhancing the interfacial stress transfer efficiency; on the other hand, some of the unreacted MXene layers retain the original conductive channels. This balance enables MXene to act as both a reinforcing phase to improve mechanical properties and a conductive filler to construct a percolation network. During the supercritical treatment stage, a pressure of 25 MPa drives carbon dioxide molecules to insert into the MXene layers. The carbon dioxide-philic property of the sulfonic acid groups reduces the interlayer force, promoting the exfoliation and dispersion of MXene in the fiber matrix, and finally forming a conductive path with MXene nanosheets arranged directionally along the helical pore walls, achieving a conductivity uniformity of 98%.

[0114] In Example 1, a conservative parameter combination of a helix angle of 30°, a supercritical pressure of 15 MPa, and a molar ratio of MXene to sulfonating agent of 1:1 was used, with a tensile strength of only 1.6 GPa, a conductivity of 0.12 S / cm, a pore uniformity of 65 nm, and a conductivity uniformity of 72%.

[0115] A 30° helix angle results in an overly high winding tightness of the fibers. During the ply-twisting process, microcracks are generated in the aramid 1414 fibers due to excessive tension. During the subsequent supercritical treatment, a pressure of 15 MPa is not sufficient to completely open these microcracks, but instead causes carbon dioxide to accumulate at the crack tips, forming a local high-pressure area, and finally generating abnormally shaped pores with discrete sizes inside the fibers. This defective structure causes the stress to deflect during transmission, and the cracks expand along the pore edges, significantly reducing the tensile strength. At the same time, the overly dense helical winding restricts the stretching freedom of the conductive fibers, and the conductive fibers undergo buckling deformation during the shrinkage process in the coagulation bath, destroying the continuity of the conductive path.

[0116] A molar ratio of MXene to sulfonating agent of 1:1 results in insufficient sulfonation degree, and only partially covers the surface of the MXene sheets with sulfonic acid groups. In the aramid solution system, the unmodified MXene regions stack face-to-face due to van der Waals forces, forming micron-sized aggregates. After these aggregates are broken by shear forces during the spinning process, fresh unsulfonated surfaces are exposed, generating interfacial repulsion with the aramid molecular chains, resulting in the formation of nanoscale voids at the MXene-aramid interface. During the supercritical treatment stage, a pressure of 15 MPa causes carbon dioxide to preferentially penetrate into these interfacial defects, triggering a local swelling effect and further expanding the void size, finally deteriorating the pore uniformity to 65 nm. The insufficiently sulfonated MXene shows an island distribution in the construction of the conductive path and can only conduct electrons through the tunneling effect, resulting in a low conductivity.

[0117] It can be seen that there is a dynamic coupling relationship between the helix angle and the supercritical pressure: the moderate pore channels formed by the 40° helix angle enable the fluid shear force generated by the 25 MPa supercritical pressure to directionally peel off the MXene sheets and simultaneously eliminate the internal stress of the fibers; while the pore structure reorganization induced by the supercritical treatment, in turn, optimizes the interfacial bonding state of the helically wound fibers. The synergistic effect between the sulfonation degree of MXene and the spinning tension is reflected in that the moderate sulfonic acid group density generated by the 1:2 molar ratio not only ensures the stable dispersion of MXene in the solution, but also enables it to achieve orientation arrangement through hydrogen bond reconstruction under the action of the ply tension.

[0118] Based on the inspiration of the ideal embodiments of the present invention as described above, through the above description, relevant personnel can completely make various changes and modifications without departing from the technical idea of the present invention. The technical scope of the present invention is not limited to the content in the specification, and the technical scope must be determined according to the scope of the claims.

Claims

1. A preparation method of multifunctional aerogel fibers using waste fire-fighting suit fabric as raw material, characterized in that, It includes the following steps: S1. Separate the outer fabric including aramid 1313 fibers, aramid 1414 fibers and conductive fibers from the waste fire-fighting suit fabric, and conduct pretreatment; S2. Dissolve aramid 1414, aramid 1313 and conductive fibers in the outer fabric in sequence to prepare corresponding fiber solutions respectively; S3. Add sulfonated MXene powder to each fiber solution and disperse it to obtain aramid 1313 spinning solution, aramid 1414 spinning solution and conductive fiber spinning solution; S4. Prepare incompletely cured gel fiber precursors from each spinning solution by wet spinning, and conduct spiral winding and stranding to obtain stranded gel fibers; S5. Treat the stranded gel fibers with supercritical carbon dioxide to form porous aerogel fibers; S6. Coat a functionalized cortex on the surface of the aerogel fibers to obtain multifunctional aerogel fibers.

2. The preparation method according to claim 1, characterized in that, The pretreatment includes: cutting the waste fire-fighting suit fabric into blocks, separating the outer fabric, removing impurities and loosening it into a short fiber mixture; sequentially conducting alkaline cleaning, water washing, drying and shearing treatment on the short fiber mixture.

3. The preparation method according to claim 2, characterized in that, The cleaning solution for the alkaline cleaning contains sodium carbonate, sodium dodecyl sulfate and sodium silicate, the cleaning temperature is 60 - 80 °C, and the cleaning time is 3 - 6 h.

4. The preparation method according to claim 1, wherein, In step S2, the dissolution of aramid 1414 fibers uses a composite solvent of N,N-dimethylacetamide and lithium chloride, and the dissolution temperature is 80 - 90 °C; the dissolution of aramid 1313 fibers uses a mixed solvent of trifluoroacetic acid and N-methylpyrrolidone, and the dissolution temperature is 25 - 30 °C; the dispersion of the conductive fibers uses dimethyl sulfoxide solvent and ultrasonic treatment.

5. The preparation method according to claim 1, characterized in that, The preparation of the sulfonated MXene in step S3 includes: dispersing MXene in N-methylpyrrolidone, adding a sulfonating agent for reaction, the reaction temperature is 60 - 90 °C, and the reaction time is 2 - 6 h.

6. The preparation method according to claim 1, characterized in that, In step S4, the coagulation bath for the wet spinning includes a mixed solution of ethanol and water, an aqueous solution containing lithium chloride and acetone, and the coagulation bath temperature is 5 - 25 °C; during the spiral winding and stranding process, the tension of each gel fiber precursor is 10 - 25 cN, the stranding rotation speed is 100 - 200 rpm, and the winding spiral angle is 30 - 45 °.

7. The preparation method according to claim 1, characterized in that, In step S5, the pressure for the supercritical carbon dioxide treatment is 15 - 30 MPa, the temperature is 40 - 60 °C, the pressure relief rate is 0.3 - 0.8 MPa / min, and the pore diameter of the treated fibers is 50 - 200 nm.

8. The preparation method according to claim 1, characterized in that, In step S6, the functionalized cortex includes a composite layer of tin oxide and aramid 1414 solution or a composite layer of zinc oxide and aramid 1313 solution, and the coating is carried out using a coaxial needle.

9. The preparation method according to claim 8, wherein The addition amount of tin oxide in the composite layer of tin oxide and aramid 1414 solution is 5 - 8 wt% of the mass of the aramid 1414 solution; the addition amount of zinc oxide in the composite layer of zinc oxide and aramid 1313 solution is 3 - 5 wt% of the mass of the aramid 1313 solution; the thickness of the coated cortex is 10 - 30 μm.

10. A multifunctional aerogel fiber based on waste fire-fighting suit fabric as raw material, characterized in that, Prepared by the preparation method described in any one of claims 1 - 9.

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