A multifunctional aerogel fiber based on waste firefighting uniform fabric and its preparation method

Abstract

The present invention provides a multifunctional aerogel fiber based on waste firefighting uniform fabric and a preparation method thereof, belonging to the technical field of textile material recycling. The method comprises separating aramid 1313, aramid 1414 and conductive fiber from waste firefighting uniforms; dissolving them in steps and compounding them with sulfonated MXene to prepare spinning solution; forming a gel fiber precursor by wet spinning and spirally winding and plying; constructing a porous structure by supercritical carbon dioxide treatment; and finally coating with a functionalized cortex. The present invention adopts spiral winding and plying to replace traditional parallel plying, combines supercritical carbon dioxide to produce interface micro-melting, and simultaneously realizes mechanical interlocking and hydrogen bond strengthening between fibers; enhances the continuity of the conductive network by modification with sulfonated MXene, and utilizes beam spinning to circumvent the difference in solvent system. The prepared aerogel fiber has high strength, high conductivity and high temperature resistance, which solves the problems of poor interface bonding and single function of multiple fibers in waste firefighting uniforms.

Description

Technical Field

[0001] The present invention belongs to the technical field of textile materials, and in particular relates to a multifunctional aerogel fiber based on waste firefighting clothing fabric as a raw material and a preparation method thereof. Background Art

[0002] The fabrics used for used firefighting uniforms are primarily made from high-performance fibers such as aramid 1313 and aramid 1414. These materials are widely used in firefighter protective gear due to their excellent heat resistance, flame retardancy, chemical corrosion resistance, and mechanical strength. However, after prolonged use, the performance of firefighting uniforms gradually deteriorates, resulting in them no longer meeting safety protection standards. Traditional methods of disposing of used firefighting uniforms, such as landfill or incineration, not only waste resources but also pose environmental risks. Therefore, finding ways to efficiently recycle and repurpose them has become a hot topic of research.

[0003] Currently, recycling technologies for used firefighting uniform fabrics primarily focus on physical reuse, chemical recycling, and functional modification. Physical reuse involves mechanical crushing, fiber regeneration, and composite material preparation, maintaining some of the fabric's properties for use in less demanding applications. Chemical recycling involves methods such as solvent dissolution, thermal decomposition, and catalytic degradation, breaking down high-temperature-resistant fibers like aramid and PBI into monomers or oligomers for resynthesis into new materials. Furthermore, functional modification technologies are exploring how to impart new fire-resistant, heat-resistant, or mechanical properties to recycled fibers through surface modification or composite processing, thereby expanding their application areas.

[0004] While independent research on waste aramid 1313 and 1414 fibers is extensive, relatively little research has been conducted on their combined use, or on blends of other fibers. Therefore, recycling methods for blends of aramid 1313, aramid 1414, and other fibers hold great promise. Summary of the Invention

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

[0006] To achieve the above-mentioned purpose, the technical solution adopted by the present invention is: a method for preparing multifunctional aerogel fibers based on waste firefighting uniform fabrics as raw materials, comprising the following steps:

[0007] S1. Separate the outer fabric including aramid 1313, aramid 1414 and conductive fiber from the waste firefighting uniform fabric and pre-treat it;

[0008] S2, dissolving the aramid 1414 fiber, aramid 1313 fiber and conductive fiber in the outer fabric in sequence to prepare corresponding fiber solutions;

[0009] 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;

[0010] S4, preparing uncured gel fiber precursors from the spinning solutions by wet spinning, and spirally winding and plying the precursors to obtain ply gel fibers;

[0011] S5, treating the plied gel fibers with supercritical carbon dioxide to form porous aerogel fibers;

[0012] S6. A functionalized cortex is coated on the surface of the porous aerogel fiber to prepare a multifunctional aerogel fiber.

[0013] Furthermore, the pretreatment includes: cutting the waste firefighting clothing fabric into blocks, separating the outer fabric, removing impurities and opening it into a short fiber mixture; and sequentially subjecting the short fiber mixture to alkaline cleaning, water washing, drying and shearing treatment.

[0014] Furthermore, the cleaning solution for alkaline cleaning comprises sodium carbonate, sodium lauryl sulfate and sodium silicate, the cleaning temperature is 60-80° C., and the cleaning time is 3-6 hours.

[0015] Furthermore, in step S2, the aramid 1414 fiber is dissolved using a composite solvent of N,N-dimethylacetamide and lithium chloride at a dissolution temperature of 80-90°C; the aramid 1313 fiber is dissolved using a mixed solvent of trifluoroacetic acid and N-methylpyrrolidone at a dissolution temperature of 25-30°C; and the conductive fiber is dispersed using dimethyl sulfoxide solvent and ultrasonic treatment.

[0016] Furthermore, the preparation of sulfonated MXene in step S3 includes: dispersing MXene in N-methylpyrrolidone, adding a sulfonating agent to react, the reaction temperature is 60-90° C., and the reaction time is 2-6 hours.

[0017] Furthermore, the coagulation bath for wet spinning in step S4 includes a mixture 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 plying process, the tension of each gel fiber precursor is 10-25cN, the plying speed is 100-200rpm, and the winding spiral angle is 30-45°.

[0018] Furthermore, in step S5, the pressure of the supercritical carbon dioxide treatment is 15-30 MPa, the temperature is 40-60° C., the pressure release rate is 0.3-0.8 MPa / min, and the pore size of the treated fiber is 50-200 nm.

[0019] Furthermore, in step S6, the functionalized skin layer 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 performed using a coaxial needle.

[0020] Furthermore, the amount of tin oxide added to the composite layer of tin oxide and aramid 1414 solution is 5-8wt% of the mass of the aramid 1414 solution; the amount of zinc oxide added to the composite layer of zinc oxide and aramid 1313 solution is 3-5wt% of the mass of the aramid 1313 solution; and the thickness of the skin after coating is 10-30μm.

[0021] Another technical solution provided by the present invention is a multifunctional aerogel fiber based on waste firefighting clothing fabric as raw material, which is prepared by the above-mentioned preparation method.

[0022] The present invention solves the defects existing in the background technology and has the following beneficial effects:

[0023] The present invention solves the problems of poor interface bonding and single function between aramid 1313, aramid 1414 and conductive fibers in waste firefighting uniform fabrics through a spiral winding plying process, supercritical carbon dioxide treatment and sulfonated MXene modification, and realizes the integrated preparation of high-strength, high-conductivity and high-temperature resistant aerogel fibers.

[0024] Through the spiral winding and plying process, three bundles of fibers form a three-dimensional spiral structure. The spiral angle regulates the degree of mechanical interlocking between the fibers. Aramid 1414 bears the axial load, aramid 1313 dissipates energy through cross-linking, and the conductive fibers are embedded in the spiral gaps to form a conductive network. Combined with supercritical carbon dioxide treatment, the interface bonding is further strengthened. Carbon dioxide penetrates into the fiber interface to induce molecular chain plasticization and dynamic hydrogen bond reconstruction. Compared with the traditional parallel plying process, spiral plying significantly improves the tensile strength and avoids stress concentration caused by loose fibers. At the same time, supercritical treatment optimizes the pore structure and reduces the material density. In the prior art, the mechanical properties of parallel plying are limited due to the small interface contact area and the lack of mechanical interlocking. The present invention breaks through the material incompatibility limitation through the synergistic effect of the spiral structure and interface micro-melting, achieving a dual improvement in mechanical properties and lightweight.

[0025] Sulfonated MXene modification forms a hydrogen bond network through sulfonic acid groups and aramid amide bonds, inhibiting MXene agglomeration and enhancing dispersibility. MXene is evenly distributed in the conductive fiber spinning solution, forming a continuous conductive path that runs through the honeycomb pores generated by supercritical treatment. Compared with unmodified MXene or traditional hot pressing processes, sulfonated MXene significantly improves the continuity and stability of the conductive network. At the same time, the thermal stability of sulfonic acid groups and aramid at high temperatures synergistically inhibits fiber oxidation. In the prior art, poor MXene dispersibility leads to the breakage of the conductive network and the problem of functional singularity is prominent. The present invention, through the synergy of sulfonation modification and helical structure, achieves the simultaneous optimization of conductivity, high-temperature stability and interface bonding strength.

[0026] The combination of spiral winding and supercritical CO2 treatment addresses poor interfacial bonding through mechanical interlocking and interfacial micro-melting to strengthen the fiber bond. Sulfonated MXene modification, combined with a fractional spinning process, overcomes the limitations of single functionality by constructing a hydrogen-bonding network and conductive pathways. The spiral structure provides uniform clearance for supercritical CO2 penetration, promoting pore expansion and interfacial hydrogen bond reconstruction. The uniform distribution of sulfonated MXene within the conductive network further relies on the mechanical stability of the spiral winding. This combination creates a dual-gain mechanism, achieving synergistic improvements in tensile strength, conductivity, and high-temperature stability, providing an innovative solution for the high-value recycling of waste firefighting uniform fabrics. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments described in the present invention. Those skilled in the art can also derive other drawings based on these drawings without inventive efforts.

[0028] Figure 1 This is a flow chart of multifunctional aerogel fiber based on waste firefighting clothing fabric. DETAILED DESCRIPTION

[0029] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0030] In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention may also be implemented in other ways different from those described herein. Therefore, the scope of protection of the present invention is not limited to the specific embodiments disclosed below.

[0031] Unless otherwise specified in the following examples, all raw materials were commercially available or prepared by conventional methods in the art. Some commercial materials were purchased from Sinopharm Reagents, including: XMene (titanium aluminum carbide), 98% 200 mesh (Wokai); N-methylpyrrolidone, AR (Wokai); lithium chloride, AR (Zhejiang); trifluoroacetic acid, AR (Shanghai trial); N-methylpyrrolidone, GCS (Wokai); dimethyl sulfoxide, AR (Wokai); p-toluenesulfonyl chloride (sulfonating agent), 99% (TCI); acetone, AR (Shanghai trial); tin oxide, CP (Shanghai trial); and zinc oxide, CP (Shanghai trial). Used firefighter uniforms were sourced from local fire departments. The outer fabric is a blend of 93% aramid 1313, 5% aramid 1414, and 2% conductive fiber (pre-oxidized fiber). It has a heat resistance temperature of ≥260°C, a short-term resistance of 400°C, a breaking strength of ≥850N, and an oxygen index of ≥30.

[0032] Exemplary methods:

[0033] like Figure 1 As shown, a method for preparing multifunctional aerogel fibers based on waste firefighting uniform fabrics as raw materials comprises the following steps:

[0034] S1. Separate the outer fabric including aramid 1313 fiber, aramid 1414 fiber and conductive fiber from the waste firefighting uniform fabric and pre-treat it;

[0035] S2, dissolving the aramid 1414 fiber, aramid 1313 fiber and conductive fiber in the outer fabric in sequence to prepare corresponding fiber solutions;

[0036] 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;

[0037] S4, preparing uncured gel fiber precursors from the spinning solutions by wet spinning, and spirally winding and plying the precursors to obtain ply gel fibers;

[0038] S5, treating the plied gel fibers with supercritical carbon dioxide to form porous aerogel fibers;

[0039] S6. A functionalized cortex is coated on the surface of the porous aerogel fiber to prepare a multifunctional aerogel fiber.

[0040] The exemplary method circumvents the phase separation problem caused by differences in solvent systems by spinning aramid 1313, aramid 1414 and conductive fibers independently and then spirally winding them to prepare multifunctional aerogel fibers with integrated tensile strength, energy dissipation and conductivity; at the same time, the plasticization and foaming effects of supercritical carbon dioxide are utilized to simultaneously achieve hydrogen bond strengthening at the fiber interface and construction of a honeycomb porous structure, thereby reducing the material density while improving the thermal insulation performance, and enhancing the interface stability by inducing the combination of sulfonated MXene and fibers.

[0041] Below, each step will be described in detail.

[0042] In step S1, the pretreatment includes: cutting the waste firefighting clothing fabric into blocks, separating the outer fabric, removing impurities and opening it into a short fiber mixture; and sequentially subjecting the short fiber mixture to alkaline cleaning, water washing, drying and shearing treatment.

[0043] Specifically, the fabric of the waste firefighting suits includes an outer layer, a middle layer and an inner lining, wherein the outer layer is the original liquid 3A fabric, the main components of which are aramid 1313, aramid 1414 and conductive fiber.

[0044] In step S1, an industrial shear is used to cut the outer fabric of the used firefighter uniforms into uniform pieces with sides measuring 10 to 15 cm. Mechanical sorting equipment is then used to separate the outer layer, middle layer, and lining, separating the 3A outer fabric. A magnetic separator is used to remove metal impurities such as buttons or zippers, and to remove plastic linings and any visibly damaged non-fibrous impurities. The sorted fabric is then fed into a variable frequency opener, with the needle rollers rotating at a speed of 800 to 1200 rpm, to create a loose, short fiber mixture with a fiber length of 10 to 20 mm.

[0045] Prepare an alkaline cleaning solution containing 3-8wt% sodium carbonate, 1-3wt% sodium lauryl sulfate, and 0.5-1wt% sodium silicate as a corrosion inhibitor. The sodium carbonate provides an alkaline environment to break down oil stains, the sodium lauryl sulfate acts as a surfactant to reduce the fiber's surface tension, and the sodium silicate corrosion inhibitor protects the aramid amide bonds from strong alkaline hydrolysis.

[0046] The short fiber mixture is immersed in an alkaline cleaning solution, heated to 60-80°C, and ultrasonically assisted cleaned for 3-6 hours at a frequency of 40kHz and a power of 200W, and rinsed with deionized water to a pH of 6.5-7.5; the cleaned fibers are transferred to a vacuum drying oven at 50-70°C and dried for 4-6 hours, and the dried fibers are further sheared into short fibers with a length not exceeding 5mm using a rotary shearing machine.

[0047] In step S2, the aramid 1414 fiber is dissolved in a composite solvent of N,N-dimethylacetamide and lithium chloride at a dissolution temperature of 80-90°C; the aramid 1313 fiber is dissolved in a mixed solvent of trifluoroacetic acid and N-methylpyrrolidone at a dissolution temperature of 25-30°C; and the conductive fiber is dispersed in dimethyl sulfoxide solvent and ultrasonically treated.

[0048] The method for dissolving aramid 1414 includes adding a short fiber mixture to a combined solvent of N,N-dimethylacetamide and lithium chloride at a liquid-to-solid ratio of 10 mL / g, with a lithium chloride concentration of 4-6 wt%. The mixture is mechanically stirred at 200-300 rpm for 3-5 hours at 80-90°C. After dissolution, the mixture is filtered through a 200-mesh filter, resulting in an aramid 1414 solution with a concentration of 12-15 wt%. The residue, which contains undissolved aramid 1313 and conductive fibers, is rinsed three times with ethanol and vacuum-dried at 50°C for 2 hours. The combined solvent of N,N-dimethylacetamide and lithium chloride is prepared by adding lithium chloride powder to N,N-dimethylacetamide at a lithium chloride concentration of 4-6 wt%. The mixture is mechanically stirred until completely dissolved. The lithium chloride disrupts the crystalline hydrogen bond network of aramid 1414 through complexation. The DMAc solvent provides a polar environment to stabilize the solution, and the high temperature accelerates molecular chain dissociation.

[0049] The method for dissolving aramid 1313 includes adding the residue produced after dissolving aramid 1414 to a mixed solvent consisting of trifluoroacetic acid and N-methylpyrrolidone in a volume ratio of 1:2 at a liquid-to-solid ratio of 8 mL / g. The mixture is precooled to 10-15°C, then heated to 25-30°C and stirred at 150-200 rpm for 2-4 hours. Filtration yields a filtrate and residue, which is then slowly neutralized to a pH of 6-7 by adding sodium bicarbonate powder. The precipitate is then removed by centrifugation to yield a 10-12 wt% aramid 1313 solution. The residue contains undissolved conductive fibers. Trifluoroacetic acid protonates the amide groups of the meta-aramid, reducing intermolecular forces. N-methylpyrrolidone acts as a cosolvent to reduce the viscosity of the system and inhibit side reactions.

[0050] The method for dissolving the conductive fiber includes adding the filter residue produced after dissolving aramid 1313 to a dimethyl sulfoxide solvent at a liquid-to-solid ratio of 5 mL / g, ultrasonically treating the residue at a frequency of 40 kHz and a power of 200 W for 1-2 hours, and then centrifuging the residue at 5000 rpm for 10 minutes to remove undispersed particles, thereby obtaining a conductive fiber dispersion with a concentration of 4-6 wt%. Ultrasonic cavitation breaks up the conductive fiber agglomerates, while limiting the treatment time to prevent fiber breakage.

[0051] Lithium chloride destroys the hydrogen bond network of para-aramid through complexation, N,N-dimethylacetamide provides a polar dissolution environment; trifluoroacetic acid protonates the amide group of meta-aramid, N-methylpyrrolidone reduces the viscosity of the system and stabilizes the dissolved state; dimethyl sulfoxide disperses the fibers through polar-π interaction, and ultrasonic cavitation breaks up agglomerations.

[0052] In step S3, the preparation of sulfonated MXene includes dispersing MXene in N-methylpyrrolidone, adding a sulfonating agent, and reacting at a temperature of 60-90°C for 2-6 hours. Specifically, 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 sulfonating agent is controlled to be 1:1 to 1:3. The reaction is refluxed at 60-90°C for 2-6 hours. After the reaction is completed, the mixture is centrifuged at 8000 rpm for 10 minutes, repeatedly washed with ethanol until neutral, and vacuum dried at 60°C for 6-8 hours to obtain the sulfonated MXene powder. p-Toluenesulfonyl chloride reacts with the hydroxyl groups on the MXene surface at high temperature, grafting sulfonic acid groups and enhancing the hydrogen bonding ability with the aramid amide bond.

[0053] When preparing the aramid 1313 spinning solution, 1-3 wt% sulfonated MXene was added to the aramid 1313 solution, mechanically stirred at 150-200 rpm at 25-30 ° C for 1-2 hours, and ultrasonically treated at 40 kHz frequency and 200 W power for 30 minutes to ensure uniform dispersion of MXene.

[0054] When preparing the aramid 1414 spinning solution, 0.5-2 wt% sulfonated MXene is added to the aramid 1414 solution, stirred at 200-300 rpm at 80-90 ° C for 2-3 hours, and filtered through a 200 mesh filter to remove undispersed particles.

[0055] When preparing the conductive fiber spinning solution, 3-5wt% sulfonated MXene was added to the conductive fiber dispersion, ultrasonically treated at a frequency of 40kHz and a power of 200W for 1h, and then filtered and purified with a 0.45μm pore size filter membrane.

[0056] The aramid 1313 solution was stirred at low temperature to avoid solvent volatilization, while the aramid 1414 solution was stirred at high temperature to promote the embedding of MXene into the fiber network. At the same time, the temperature was limited to below 90 °C to avoid initiating the decomposition of N,N-dimethylacetamide.

[0057] In step S4, the coagulation bath for wet spinning includes a mixture of ethanol and water, an aqueous solution containing lithium chloride, and acetone, with a temperature of 5-25°C. During the spiral winding and plying process, the tension of each gel fiber precursor is 10-25 cN, the plying speed is 100-200 rpm, and the winding helix angle is 30-45°. This step forms an uncured gel fiber precursor through wet spinning and spirally winds and plies the resulting gel fiber, providing an expandable porous structure for subsequent supercritical carbon dioxide treatment.

[0058] 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, and 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.

[0059] The aramid 1313 spinning solution is extruded through a spinneret with an aperture of 0.1-0.3 mm into a coagulation bath containing an ethanol-to-water ratio of 7:3 by volume at a temperature of 5-10°C. The aramid 1414 spinning solution is extruded through a spinneret with an aperture of 0.2-0.4 mm into a coagulation bath containing a 5 wt% lithium chloride aqueous solution at a temperature of 20-25°C and a draft ratio of 2.0-2.5. The conductive fiber spinning solution is extruded through a spinneret with an aperture of 0.05-0.15 mm into an acetone coagulation bath at a temperature of 15-20°C and a draft ratio of 1.5-2.0. These fibers are then held for 30-60 seconds, then wound up at a draft ratio of 1.5-2.5 at a speed of 10-20 m / min.

[0060] The three strands of uncured gel fiber precursor are introduced into a plying machine via a godet system and spirally twisted to form a twisted gel fiber. The tension is controlled to be 15-20 cN for aramid 1313, 20-25 cN for aramid 1414, and 10-15 cN for the conductive fiber. The plying machine rotates at 100-200 rpm and a pulling speed of 1.0-1.5 m / min, forming a twisted structure with a helix angle of 30-45°. The three strands have a volume ratio of 1:1:1, and the cross-section is circular with a diameter of 0.5-1.0 mm, with an interior of equally divided fan-shaped regions.

[0061] In step S5, the supercritical carbon dioxide treatment is performed at a pressure of 15-30 MPa, a temperature of 40-60°C, and a pressure relief rate of 0.3-0.8 MPa / min. The pore size of the treated fiber is 50-200 nm. This step transforms the gel fiber into a high-porosity aerogel fiber through the solvation and foaming effects of the supercritical carbon dioxide. The supercritical carbon dioxide penetrates the fiber interior, triggering nucleation and foaming through pressure relief. The plasticizing effect lowers the glass transition temperature of the aramid fiber and promotes hydrogen bonding between the sulfonic acid groups and the amide bonds.

[0062] In this step, the stranded gel fiber is immersed in anhydrous ethanol for 24-48 hours, with the solvent replaced every 6 hours, and then pre-dried at 50-70°C for 2-4 hours. The stranded gel fiber is wound on a porous support and placed in a reactor. Liquid carbon dioxide is injected to a pressure of 8-10 MPa, and the temperature is raised to 40-60°C to allow the carbon dioxide to enter a supercritical state. The pressure is then increased to 15-30 MPa and maintained for 1-3 hours. The pressure is released at a rate of 0.3-0.8 MPa / min, and the temperature is simultaneously lowered to 25-30°C to form a honeycomb porous structure with a pore size of 50-200 nm. The fiber is placed in a vacuum drying oven at 60-80°C and dried for 4-8 hours. If the pore distribution is uneven, a secondary supercritical treatment can be performed: pressure 10-15 MPa, time 30-90 minutes.

[0063] In step S6, the functionalized skin layer comprises a composite layer of tin oxide and aramid 1414 solution or a composite layer of zinc oxide and aramid 1313 solution. Coating is performed using a coaxial needle and the coagulation bath is a mixture of ethanol and water. The amount of tin oxide added to the composite layer of tin oxide and aramid 1414 solution is 5-8% by weight of the aramid 1414 solution; the amount of zinc oxide added to the composite layer of zinc oxide and aramid 1313 solution is 3-5% by weight of the aramid 1313 solution. The thickness of the coated skin layer is 10-30 μm.

[0064] Specifically, the preparation method for a tin oxide / aramid cortex spinning solution involves adding 5-8 wt% tin oxide to an aramid 1414 solution, stirring at 300 rpm at 80°C for 2 hours, and ultrasonically dispersing at 40 kHz for 30 minutes. The preparation method for a zinc oxide / aramid cortex spinning solution involves adding 3-5 wt% zinc oxide to an aramid 1313 solution, stirring at 200 rpm at 25°C for 1 hour, and ultrasonically treating at 40 kHz for 1 hour. Tin oxide protects the fiber structure through UV shielding, while zinc oxide enhances antibacterial properties through contact sterilization.

[0065] In this step, a coaxial needle with a core inner diameter of 1.0-1.2 mm and a skin outer diameter of 1.5-2.0 mm was used. The aerogel fiber was used as the core layer, and the functionalized skin spinning solution was used as the skin spinning solution. The core aerogel fiber flow rate was controlled at 0.5-1.0 mL / min, and the skin spinning solution flow rate was controlled at 1.0-1.5 mL / min. The aerogel fiber coated with the functionalized skin layer was placed in a coagulation bath with an ethanol to water volume ratio of 8:2, at a temperature of 10-15°C, a draw ratio of 1.2-1.5, and a winding speed of 5-8 m / min, resulting in a final skin thickness of 10-30 μm.

[0066] Example structure:

[0067] A multifunctional aerogel fiber based on waste firefighting clothing fabric is prepared by the above exemplary method.

[0068] Example 1:

[0069] S1: Use an industrial shear to cut the outer fabric of used firefighter uniforms into uniform pieces with a side length of 12 cm. Mechanical sorting equipment is used to separate the outer layer, middle layer, and lining, separating the 3A outer fabric. A magnetic separator is used to remove metal impurities, including buttons and zippers, and to remove plastic linings and visibly damaged non-fiber impurities. The sorted fabric is fed into a variable frequency opener, with the needle roller speed adjusted to 1000 rpm, to open the fabric to a loose, short fiber mixture with a fiber length of 15 mm.

[0070] Prepare an alkaline cleaning solution containing 5wt% sodium carbonate, 2wt% sodium lauryl sulfate, and 0.8wt% sodium silicate as a corrosion inhibitor. Immerse the short fiber mixture in the alkaline cleaning solution, heat to 70°C, and clean it ultrasonically at 40kHz and 200W for 4 hours. Rinse with deionized water to a pH of 7.0, and transfer the cleaned fibers to a vacuum drying oven at 60°C for 5 hours. Use a rotary shear to shear the dried fibers to a length of no more than 5mm.

[0071] S2: Add the short fiber mixture to a mixed solvent of N,N-dimethylacetamide and 5 wt% lithium chloride at a liquid-to-solid ratio of 10 mL / g. Mechanically stir at 250 rpm and 90°C for 4 hours. After dissolution, filter through a 200-mesh filter to obtain a 14 wt% aramid 1414 solution. The filter residue, containing undissolved aramid 1313 and conductive fibers, is rinsed three times with ethanol and vacuum-dried at 50°C for 2 hours.

[0072] The filter residue, containing undissolved aramid 1313 and conductive fibers, was added to a mixture of trifluoroacetic acid and N-methylpyrrolidone (1:2, volume ratio) at a liquid-to-solid ratio of 8 mL / g. The mixture was precooled to 12°C, then heated to 30°C and stirred at 180 rpm for 3 hours. After filtration, sodium bicarbonate powder was slowly added to the filtrate to neutralize it to a pH of 6.5. The precipitate was removed by centrifugation to obtain an 11 wt% aramid 1313 solution. The filter residue contained undissolved conductive fibers.

[0073] The filter residue including the undissolved conductive fibers was added to dimethyl sulfoxide solvent at a liquid-to-solid ratio of 5 mL / g; ultrasonic treatment was performed at 40 kHz and 200 W power for 1.5 h, followed by centrifugation at 5000 rpm for 10 min to remove undispersed particles, thereby obtaining a conductive fiber dispersion with a concentration of 5 wt%.

[0074] S3: MXene powder was dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride was added, and the molar ratio of MXene to sulfonating agent was controlled to be 1:1. The reaction was refluxed at 80°C for 4 hours. After the reaction, the mixture was centrifuged at 8000 rpm for 10 minutes, repeatedly washed with ethanol until neutral, and vacuum dried at 60°C for 8 hours to obtain sulfonated MXene powder.

[0075] Prepare the aramid 1313 spinning solution: Add 2 wt% sulfonated MXene to the aramid 1313 solution. Mechanically stir at 180 rpm for 1.5 h at 30°C, and then ultrasonicate at 40 kHz and 200 W for 30 min.

[0076] Prepare the aramid 1414 spinning solution: Add 1 wt% sulfonated MXene to the aramid 1414 solution. Stir at 250 rpm and 90°C for 3 h. Filter through a 200-mesh filter to remove undispersed particles.

[0077] To prepare the conductive fiber spinning solution, 4 wt% sulfonated MXene was added to the conductive fiber dispersion. The solution was ultrasonically treated at 40 kHz and 200 W for 1 h, and then filtered through a 0.45 μm pore size filter membrane for purification.

[0078] S4: A multi-component wet spinning apparatus was used to wet-spin aramid 1313, aramid 1414, and conductive fiber spinning solutions, respectively. Using a three-channel spinneret, the aramid 1313 spinning solution was extruded through a 0.2 mm pore size spinneret into a coagulation bath containing a 7:3 volume ratio of ethanol to water at 8°C. The aramid 1414 spinning solution was extruded through a 0.3 mm pore size spinneret into a coagulation bath containing 5 wt% lithium chloride in an aqueous solution at 22°C. The conductive fiber spinning solution was extruded through a 0.1 mm pore size spinneret into an acetone coagulation bath at 18°C. The fibers were held for 45 seconds and then wound up at a draw ratio of 2.0 at a speed of 15 m / min.

[0079] Three strands of uncured gel fiber precursor were introduced into a plying machine via a godet system. The tensions were controlled at 18 cN for the aramid 1313 fiber, 22 cN for the aramid 1414 fiber, and 12 cN for the conductive fiber. The plying machine rotated at 150 rpm and a pull-up speed of 1.2 m / min, forming a twisted structure with a helix angle of 30°. The volume ratio of the three strands was 1:1:1, and the cross-section was a circle with a diameter of 0.8 mm, with an interior divided into equally spaced sectors.

[0080] S5: Immerse the stranded gel fibers in anhydrous ethanol for 36 hours, replacing the solvent every 6 hours. Pre-dry at 60°C for 3 hours. Wind the stranded gel fibers around a porous support and place them in a reactor. Liquid carbon dioxide is injected to a pressure of 9 MPa. The temperature is raised to 50°C to induce a supercritical state of carbon dioxide, which is then pressurized to 15 MPa and maintained for 2 hours. The pressure is released at a rate of 0.5 MPa / min while the temperature is simultaneously lowered to 25°C. The fibers are then dried in a vacuum drying oven at 60°C for 6 hours.

[0081] S6: 6 wt% tin oxide was added to the aramid 1414 solution. The solution was stirred at 300 rpm for 2 h at 80°C and ultrasonically dispersed at 40 kHz for 30 min to obtain a functionalized sheath spinning solution. A coaxial needle with a core inner diameter of 1.0 mm and a sheath outer diameter of 1.8 mm was used. The porous aerogel fiber served as the core, and the functionalized sheath spinning solution was used as the sheath spinning solution. The flow rate of the core aerogel fiber was controlled at 0.8 m / min, and the flow rate of the sheath spinning solution was 1.2 m / min. The porous aerogel fiber coated with the functionalized sheath was placed in a coagulation bath with an ethanol to water volume ratio of 8:2 at 12°C, a draw ratio of 1.3, and a winding speed of 6 m / min. The final sheath thickness was 20 μm.

[0082] Example 2:

[0083] Different from Example 1, in step S3 of this example, the MXene powder was dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride was added, the molar ratio of MXene to the sulfonating agent was controlled to be 1:2, and the reaction was refluxed at 80°C for 4 hours. After the reaction, the mixture was centrifuged at 8000 rpm for 10 minutes, repeatedly washed with ethanol until neutral, and vacuum dried at 60°C for 8 hours to obtain sulfonated MXene powder.

[0084] In step S4 of this embodiment, the stranding machine rotates at 150 rpm and the pulling speed is 1.2 m / min, forming a winding structure with a helical angle of 40°. The volume ratio of the three strands is 1:1:1, and the cross-section is a circle with a diameter of 0.8 mm, with the interior being equally divided into sectors.

[0085] Example 3:

[0086] Different from Example 1, in step S3 of this example, the MXene powder was dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride was added, the molar ratio of MXene to the sulfonating agent was controlled to be 1:3, and the reaction was refluxed at 80°C for 4 hours. After the reaction, the mixture was centrifuged at 8000 rpm for 10 minutes, repeatedly washed with ethanol until neutral, and vacuum dried at 60°C for 8 hours to obtain sulfonated MXene powder.

[0087] In step S4 of this embodiment, the stranding machine rotates at 150 rpm and the pulling speed is 1.2 m / min, forming a winding structure with a helical angle of 45°. The volume ratio of the three strands is 1:1:1, and the cross-section is a circle with a diameter of 0.8 mm, with the interior being equally divided into sectors.

[0088] Example 4:

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

[0090] In step S4 of this embodiment, the stranding machine rotates at 150 rpm and the pulling speed is 1.2 m / min, forming a winding structure with a helical angle of 30°. The volume ratio of the three strands is 1:1:1, and the cross-section is a circle with a diameter of 0.8 mm, with the interior being equally divided into sectors.

[0091] In step S5 of this embodiment, the plied gel fiber was wound around a porous support and placed in a reactor. Liquid carbon dioxide was then injected to a pressure of 9 MPa. The temperature was raised to 50°C to induce supercritical carbon dioxide. The pressure was then increased to 25 MPa and maintained for 2 hours. The pressure was then released at a rate of 0.5 MPa / min while the temperature was simultaneously lowered to 25°C. The fiber was then dried in a vacuum drying oven at 60°C for 6 hours.

[0092] Example 5:

[0093] Different from Example 1, in step S3 of this example, the MXene powder was dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride was added, the molar ratio of MXene to the sulfonating agent was controlled to be 1:2, and the reaction was refluxed at 80°C for 4 hours. After the reaction, the mixture was centrifuged at 8000 rpm for 10 minutes, repeatedly washed with ethanol until neutral, and vacuum dried at 60°C for 8 hours to obtain sulfonated MXene powder.

[0094] In step S4 of this embodiment, the stranding machine rotates at 150 rpm and the pulling speed is 1.2 m / min, forming a winding structure with a helical angle of 40°. The volume ratio of the three strands is 1:1:1, and the cross-section is a circle with a diameter of 0.8 mm, with the interior being equally divided into sectors.

[0095] In step S5 of this embodiment, the plied gel fiber was wound around a porous support and placed in a reactor. Liquid carbon dioxide was then injected to a pressure of 9 MPa. The temperature was raised to 50°C to induce supercritical carbon dioxide. The pressure was then increased to 25 MPa and maintained for 2 hours. The pressure was then released at a rate of 0.5 MPa / min while the temperature was simultaneously lowered to 25°C. The fiber was then dried in a vacuum drying oven at 60°C for 6 hours.

[0096] Example 6:

[0097] In step S4 of this embodiment, the stranding machine rotates at 150 rpm and the pulling speed is 1.2 m / min, forming a winding structure with a helical angle of 45°. The volume ratio of the three strands is 1:1:1, and the cross-section is a circle with a diameter of 0.8 mm, with the interior being equally divided into sectors.

[0098] In step S5 of this embodiment, the plied gel fiber was wound around a porous support and placed in a reactor. Liquid carbon dioxide was then injected to a pressure of 9 MPa. The temperature was raised to 50°C to induce supercritical carbon dioxide. The pressure was then increased to 25 MPa and maintained for 2 hours. The pressure was then released at a rate of 0.5 MPa / min while the temperature was simultaneously lowered to 25°C. The fiber was then dried in a vacuum drying oven at 60°C for 6 hours.

[0099] Example 7:

[0100] Different from Example 1, in step S3 of this example, the MXene powder was dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride was added, the molar ratio of MXene to the sulfonating agent was controlled to be 1:3, and the reaction was refluxed at 80°C for 4 hours. After the reaction, the mixture was centrifuged at 8000 rpm for 10 minutes, repeatedly washed with ethanol until neutral, and vacuum dried at 60°C for 8 hours to obtain sulfonated MXene powder.

[0101] In step S5 of this embodiment, the plied gel fiber was wound around a porous support and placed in a reactor. Liquid carbon dioxide was then injected to a pressure of 9 MPa. The temperature was raised to 50°C to induce supercritical CO2. The pressure was then increased to 30 MPa and maintained for 2 hours. The pressure was then released at a rate of 0.5 MPa / min while the temperature was simultaneously lowered to 25°C. The fiber was then dried in a vacuum drying oven at 60°C for 6 hours.

[0102] Example 8:

[0103] In step S4 of this embodiment, the stranding machine rotates at 150 rpm and the pulling speed is 1.2 m / min, forming a winding structure with a helical angle of 40°. The volume ratio of the three strands is 1:1:1, and the cross-section is a circle with a diameter of 0.8 mm, with the interior being equally divided into sectors.

[0104] In step S5 of this embodiment, the plied gel fiber was wound around a porous support and placed in a reactor. Liquid carbon dioxide was then injected to a pressure of 9 MPa. The temperature was raised to 50°C to induce supercritical CO2. The pressure was then increased to 30 MPa and maintained for 2 hours. The pressure was then released at a rate of 0.5 MPa / min while the temperature was simultaneously lowered to 25°C. The fiber was then dried in a vacuum drying oven at 60°C for 6 hours.

[0105] Example 9:

[0106] Different from Example 1, in step S3 of this example, the MXene powder was dispersed in N-methylpyrrolidone at a concentration of 8 mg / mL, p-toluenesulfonyl chloride was added, the molar ratio of MXene to the sulfonating agent was controlled to be 1:2, and the reaction was refluxed at 80°C for 4 hours. After the reaction, the mixture was centrifuged at 8000 rpm for 10 minutes, repeatedly washed with ethanol until neutral, and vacuum dried at 60°C for 8 hours to obtain sulfonated MXene powder.

[0107] In step S4 of this embodiment, the stranding machine rotates at 150 rpm and the pulling speed is 1.2 m / min, forming a winding structure with a helical angle of 45°. The volume ratio of the three strands is 1:1:1, and the cross-section is a circle with a diameter of 0.8 mm, with the interior being equally divided into sectors.

[0108] In step S5 of this embodiment, the plied gel fiber was wound around a porous support and placed in a reactor. Liquid carbon dioxide was then injected to a pressure of 9 MPa. The temperature was raised to 50°C to induce supercritical CO2. The pressure was then increased to 30 MPa and maintained for 2 hours. The pressure was then released at a rate of 0.5 MPa / min while the temperature was simultaneously lowered to 25°C. The fiber was then dried in a vacuum drying oven at 60°C for 6 hours.

[0109] Comparative Example 1:

[0110] Different from Example 1, in this comparative example, MXene is not subjected to sulfonation modification in step S3, three parallel-twisted fibers are used in step S4, and supercritical carbon dioxide treatment is not performed in step S5. Instead, fibers are prepared by hot pressing.

[0111] Experimental Example 1:

[0112] The specific process of the multifunctional aerogel fiber used in this experimental example is as follows.

[0113] (1) Experimental group, including the following steps:

[0114] S1: Use an industrial shear to cut the outer fabric of used firefighter uniforms into uniform pieces with a side length of 12 cm. Mechanical sorting equipment is used to separate the outer layer, middle layer, and lining, separating the 3A outer fabric. A magnetic separator is used to remove metal impurities, including buttons and zippers, and to remove plastic linings and visibly damaged non-fiber impurities. The sorted fabric is fed into a variable frequency opener, with the needle roller speed adjusted to 1000 rpm, to open the fabric to a loose, short fiber mixture with a fiber length of 15 mm.

[0115] Prepare an alkaline cleaning solution containing 5wt% sodium carbonate, 2wt% sodium lauryl sulfate, and 0.8wt% sodium silicate as a corrosion inhibitor. Immerse the short fiber mixture in the alkaline cleaning solution, heat to 70°C, and clean it ultrasonically at 40kHz and 200W for 4 hours. Rinse with deionized water to a pH of 7.0, and transfer the cleaned fibers to a vacuum drying oven at 60°C for 5 hours. Use a rotary shear to shear the dried fibers to a length of no more than 5mm.

[0116] S2: Add the short fiber mixture to a mixed solvent of N,N-dimethylacetamide and 5 wt% lithium chloride at a liquid-to-solid ratio of 10 mL / g. Mechanically stir at 250 rpm and 90°C for 4 hours. After dissolution, filter through a 200-mesh filter to obtain a 14 wt% aramid 1414 solution. The filter residue, containing undissolved aramid 1313 and conductive fibers, is rinsed three times with ethanol and vacuum-dried at 50°C for 2 hours.

[0117] The filter residue, containing undissolved aramid 1313 and conductive fibers, was added to a mixture of trifluoroacetic acid and N-methylpyrrolidone (1:2, volume ratio) at a liquid-to-solid ratio of 8 mL / g. The mixture was precooled to 12°C, then heated to 30°C and stirred at 180 rpm for 3 hours. After filtration, sodium bicarbonate powder was slowly added to the filtrate to neutralize it to a pH of 6.5. The precipitate was removed by centrifugation to obtain an 11 wt% aramid 1313 solution. The filter residue contained undissolved conductive fibers.

[0118] The filter residue including the undissolved conductive fibers was added to dimethyl sulfoxide solvent at a liquid-to-solid ratio of 5 mL / g; ultrasonic treatment was performed at 40 kHz and 200 W power for 1.5 h, followed by centrifugation at 5000 rpm for 10 min to remove undispersed particles, thereby obtaining a conductive fiber dispersion with a concentration of 5 wt%.

[0119] S3: Disperse MXene powder in N-methylpyrrolidone at a concentration of 8 mg / mL. Add p-toluenesulfonyl chloride, adjusting the molar ratio of MXene to sulfonating agent to between 1:1 and 1:3. Reflux at 80°C for 4 hours. After completion of the reaction, centrifuge at 8000 rpm for 10 minutes, wash repeatedly with ethanol until neutral, and dry under vacuum at 60°C for 8 hours to obtain sulfonated MXene powder.

[0120] Prepare the aramid 1313 spinning solution: Add 2 wt% sulfonated MXene to the aramid 1313 solution. Mechanically stir at 180 rpm for 1.5 h at 30°C, and then ultrasonicate at 40 kHz and 200 W for 30 min.

[0121] Prepare the aramid 1414 spinning solution: Add 1 wt% sulfonated MXene to the aramid 1414 solution. Stir at 250 rpm and 90°C for 3 h. Filter through a 200-mesh filter to remove undispersed particles.

[0122] To prepare the conductive fiber spinning solution, 4 wt% sulfonated MXene was added to the conductive fiber dispersion. The solution was ultrasonically treated at 40 kHz and 200 W for 1 h, and then filtered through a 0.45 μm pore size filter membrane for purification.

[0123] S4: A multi-component wet spinning apparatus was used to wet-spin aramid 1313, aramid 1414, and conductive fiber spinning solutions, respectively. Using a three-channel spinneret, the aramid 1313 spinning solution was extruded through a 0.2 mm pore size spinneret into a coagulation bath containing a 7:3 volume ratio of ethanol to water at 8°C. The aramid 1414 spinning solution was extruded through a 0.3 mm pore size spinneret into a coagulation bath containing 5 wt% lithium chloride in an aqueous solution at 22°C. The conductive fiber spinning solution was extruded through a 0.1 mm pore size spinneret into an acetone coagulation bath at 18°C. The fibers were held for 45 seconds and then wound up at a draw ratio of 2.0 at a speed of 15 m / min.

[0124] Three strands of uncured gel fiber precursor were introduced into a plying machine via a godet system. The tensions were controlled at 18 cN for the aramid 1313 fiber, 22 cN for the aramid 1414 fiber, and 12 cN for the conductive fiber. The plying machine rotated at 150 rpm and a pull-up speed of 1.2 m / min, forming a twisted structure with a helix angle of 30-45°. The volume ratio of the three strands was 1:1:1, and the cross-section was a circle with a diameter of 0.8 mm, with an interior divided into equally spaced sectors.

[0125] S5: Immerse the stranded gel fibers in anhydrous ethanol for 36 hours, replacing the solvent every 6 hours. Pre-dry at 60°C for 3 hours. Wind the stranded gel fibers around a porous support and place them in a reactor. Inject liquid carbon dioxide to a pressure of 9 MPa. Raise the temperature to 50°C to induce supercritical CO2, then pressurize to 15-30 MPa and maintain this pressure for 2 hours. Release the pressure at a rate of 0.5 MPa / min while cooling to 25°C. Dry the fibers in a vacuum drying oven at 60°C for 6 hours.

[0126] 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 cortex spinning solution. A coaxial needle with a core inner diameter of 1.0 mm and a cortex outer diameter of 1.8 mm was used. The porous aerogel fiber was used as the core layer, and the functionalized cortex spinning solution was used as the cortex spinning solution. The flow rate of the core aerogel fiber was controlled at 0.8 m / min, and the flow rate of the cortex spinning solution was controlled at 1.2 m / min. The porous aerogel fiber coated with the functionalized cortex was placed in a coagulation bath with an ethanol to water volume ratio of 8:2, a temperature of 12°C, a draw ratio of 1.3, and a winding speed of 6 m / min. The final cortex thickness was 20 μm.

[0127] (2) Blank control group: Compared with the experimental group, MXene was not sulfonated in step S3, three parallel strands of fibers were used in step S4, and supercritical carbon dioxide treatment was not performed in step S5. Instead, fibers were prepared by hot pressing.

[0128] The experimental steps involved in this experimental example are as follows:

[0129] According to the above process, 10 groups of samples were prepared, corresponding to Examples 1-9 and Comparative Example 1 respectively;

[0130] The tensile strength of the samples was tested with reference to ASTM D3822, the electrical conductivity of the samples was tested with reference to GB / T 3048.3, the porosity uniformity of the samples was tested with reference to ISO 15901-1, the density of the samples was tested with reference to ISO 1183, the electrical conductivity uniformity of the samples was tested with reference to ASTM D257, and the glass transition temperature of the samples was tested with reference to ISO 11357-2.

[0131] In this experimental example, the parameter comparison table of 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.

[0132] Table 1 Parameter comparison table of experimental group and control group

[0133]

[0134] Table 2 Experimental performance test results

[0135]

[0136] Example 5 exhibited the best overall performance, with a helix angle of 40°, a supercritical pressure of 25 MPa, and a MXene to sulfonating agent molar ratio of 1:2. This combination achieved a tensile strength of 3.4 GPa, a conductivity of 0.45 S / cm, a pore uniformity of 25 nm, a conductivity uniformity of 98%, and a 13.2°C increase in glass transition temperature.

[0137] The 40° helix angle creates a three-dimensional network structure through the spiral winding of fibers, allowing aramid 1313, 1414, and the conductive fibers to form a gradient stress transfer path when stretched. The aramid 1414 high modulus fiber serves as the main load-bearing skeleton, while the aramid 1313 high-tenacity fiber shares local stress concentration through the spiral winding angle. The conductive fibers are embedded in the interface of the bi-aramid to build a continuous conductive network. The 40° helix angle creates moderate surface friction in the fiber during the winding process, which not only ensures the interfacial bonding strength of the twisted fibers but also avoids excessive friction that may cause the conductive fibers to break. This angle also promotes a spiral diffusion pattern in the permeation path of supercritical carbon dioxide inside the fiber. Combined with a pressure of 25 MPa, the supercritical fluid expands anisotropically inside the fiber, forming a long-range ordered nanopore structure along the spiral direction, with a pore size standard deviation of only 25 nm.

[0138] A 1:2 molar ratio of MXene to sulfonating agent promotes the formation of moderate sulfonic acid group modification on the MXene surface. The sulfonic acid groups electrostatically adsorb onto the amide groups of the aramid molecular chains, forming a hydrogen bond network between the MXene and aramid molecules and enhancing interfacial stress transfer efficiency. Furthermore, some unreacted MXene interlayers retain their original conductive pathways. This balance allows MXene to function both as a reinforcing phase, enhancing mechanical properties, and as a conductive filler, constructing a percolation network. During the supercritical treatment stage, 25 MPa pressure drives CO2 molecules to intercalate between the MXene layers. The CO2-philic nature of the sulfonic acid groups reduces interlayer forces, promoting the exfoliation and dispersion of the MXene within the fiber matrix. Ultimately, conductive pathways are formed, with MXene nanosheets arranged along the spiral pore walls, achieving 98% conductivity uniformity.

[0139] Example 1 uses a conservative parameter combination of a helix angle of 30°, a supercritical pressure of 15 MPa, and a 1:1 ratio of MXene to sulfonating agent. Its tensile strength is only 1.6 GPa, the conductivity is 0.12 S / cm, the pore uniformity is 65 nm, and the conductivity uniformity is 72%.

[0140] The 30° helix angle results in excessively tight fiber winding, resulting in microcracks in the aramid 1414 fibers due to excessive tension during the plying process. During the subsequent supercritical treatment, the 15MPa pressure is insufficient to fully open these microcracks. Instead, carbon dioxide accumulates at the crack tips, forming localized high-pressure zones, ultimately producing discrete, irregular pores within the fibers. This defective structure deflects stress during transmission, allowing cracks to propagate along the pore edges and significantly reducing tensile strength. Furthermore, the overly dense helical winding inhibits the conductive fibers' freedom of extension, causing them to buckle and deform during contraction in the coagulation bath, disrupting the continuity of the conductive pathway.

[0141] The 1:1 molar ratio of MXene to sulfonating agent results in insufficient sulfonation, with the MXene surface only partially covered with sulfonic acid groups. In the aramid solution system, unmodified MXene regions stack face-to-face due to van der Waals forces, forming micron-sized aggregates. These aggregates are broken up by shear forces during the spinning process, exposing fresh, unsulfonated surfaces that repel the aramid molecular chains, leading to the formation of nanoscale voids at the MXene-aramid interface. During the supercritical treatment stage, the 15 MPa pressure causes carbon dioxide to preferentially penetrate these interfacial defects, triggering a localized swelling effect, further expanding the void size, and ultimately deteriorating the pore uniformity to 65 nm. Insufficiently sulfonated MXene forms isolated islands within the conductive pathway, allowing electrons to be conducted only through tunneling, resulting in low conductivity.

[0142] This demonstrates a dynamic coupling between the helix angle and supercritical pressure: the moderate pore channels formed by the 40° helix angle allow the fluid shear force generated by the 25 MPa supercritical pressure to directionally exfoliate the MXene sheets, while simultaneously eliminating stress within the fiber. The pore structure reorganization induced by supercritical treatment, in turn, optimizes the interfacial bonding state of the helically wound fibers. The synergistic effect of the MXene sulfonation degree and spinning tension is reflected in the moderate sulfonic acid group density generated by the 1:2 molar ratio, which not only ensures the stable dispersion of the MXene in solution but also enables its orientation through hydrogen bonding reconstruction under the action of plying tension.

[0143] The above description is based on the ideal embodiment of the present invention. Based on the above description, relevant personnel can make various changes and modifications without departing from the technical scope of this invention. The technical scope of this invention is not limited to the content of the specification and must be determined according to the scope of the claims.

Claims

1. A method for preparing multifunctional aerogel fibers based on waste firefighting uniform fabrics, characterized in that: The following steps are involved: S1. Separate the outer fabric including aramid 1313 fiber, aramid 1414 fiber and conductive fiber from the waste firefighting uniform fabric and pre-treat it; S2, dissolving the aramid 1414 fiber, aramid 1313 fiber and conductive fiber in the outer layer 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, preparing uncured gel fiber precursors from the spinning solutions by wet spinning, and spirally winding and plying the precursors to obtain ply gel fibers; S5, treating the twisted gel fiber with supercritical carbon dioxide to form a porous aerogel fiber; S6, coating the surface of the porous aerogel fiber with a functionalized cortex to prepare a multifunctional aerogel fiber; The preparation of the sulfonated MXene in step S3 includes: dispersing the MXene in N-methylpyrrolidone, adding a sulfonating agent to react, the reaction temperature is 60-90° C., and the reaction time is 2-6 hours; During the spiral winding and plying process in step S4, the tension of each gel fiber precursor is 10-25 cN, the plying speed is 100-200 rpm, and the winding helical angle is 30-45°; The supercritical carbon dioxide treatment in step S5 is performed at a pressure of 15-30 MPa, a temperature of 40-60° C., a pressure relief rate of 0.3-0.8 MPa / min, and a pore size of the treated fiber of 50-200 nm.

2. The preparation method according to claim 1, characterized in that The pretreatment includes: cutting the waste firefighting clothing fabric into blocks, separating the outer fabric, removing impurities and opening it into a short fiber mixture; and sequentially performing alkaline cleaning, water washing, drying and shearing on the short fiber mixture.

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

4. The preparation method according to claim 1, characterized in that In step S2, the aramid 1414 fiber is dissolved in a composite solvent of N,N-dimethylacetamide and lithium chloride at a dissolution temperature of 80-90°C; the aramid 1313 fiber is dissolved in a mixed solvent of trifluoroacetic acid and N-methylpyrrolidone at a dissolution temperature of 25-30°C; and the conductive fiber is dispersed in dimethyl sulfoxide solvent and ultrasonically treated.

5. The preparation method according to claim 1, characterized in that The coagulation bath for wet spinning in step S4 includes a mixture of ethanol and water, an aqueous solution containing lithium chloride and acetone, and the coagulation bath temperature is 5-25°C.

6. The preparation method according to claim 1, characterized in that The functionalized skin layer in step S6 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 performed using a coaxial needle.

7. The preparation method according to claim 6, characterized in that The amount of tin oxide added to the composite layer of tin oxide and aramid 1414 solution is 5-8wt% of the mass of the aramid 1414 solution; the amount of zinc oxide added to the composite layer of zinc oxide and aramid 1313 solution is 3-5wt% of the mass of the aramid 1313 solution; the thickness of the coated skin layer is 10-30μm.

8. A multifunctional aerogel fiber based on waste firefighting uniform fabric as raw material, characterized in that: Prepared by the preparation method according to any one of claims 1 to 7.

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