Flame-retardant intelligent temperature warning fiber based on waste aramid fiber: preparation method and application

Abstract

This invention discloses a flame-retardant intelligent temperature warning fiber based on waste aramid, its preparation method, and its application. The method involves preparing ANF dispersions of first and second concentrations via proton donor-assisted deprotonation; adding a monolayer MXene DMSO dispersion to the first concentration ANF dispersion to obtain an MXene / ANF spinning solution; using the MXene / ANF spinning solution as the core layer and the second concentration ANF dispersion as the sheath layer, coaxial wet spinning is performed to obtain a core-sheath structured ANF@MXene / ANF coaxial composite fiber. The outer layer of the core-sheath structure in this invention not only improves the overall mechanical properties of the fiber but also provides protection for the core layer and isolates most of the air and moisture to delay the oxidation of the MXene in the core layer, effectively enhancing its application value.

Description

Technical Field

[0001] This invention belongs to the field of thermal protection materials technology, and relates to a flame-retardant intelligent temperature warning fiber based on waste aramid, its preparation method and application. Background Technology

[0002] In modern industry, aerospace, national defense, and daily life, extreme high temperatures and flame threats are ubiquitous, highlighting the increasing importance of thermal protection materials. The rapid development of electronic information, functional materials, and high-performance fiber technologies is driving thermal protective textiles towards intelligentization. New materials, such as graphene oxide (GO), carbon nanotubes (CNTs), and MXene, exhibit unique negative temperature coefficient thermistor properties, meaning their electrical resistance drops sharply at high temperatures. This characteristic enables them to automatically sense temperature changes and provide rapid high-temperature warnings in aerospace, security, and emergency rescue applications, surpassing traditional passive protection.

[0003] In recent years, MXene has stood out due to its dual functional advantages, becoming an ideal choice for developing high-efficiency sensors and flame retardants. It not only possesses passive flame retardancy but also provides active fire warnings. Unlike the one-time limitations of GO and CNT-based sensors, MXene undergoes thermal oxidation at high temperatures to transform into a TiO2 network; as the temperature rises, electrons in this network are excited, enabling cyclical changes in resistance, thus giving it repeatable warning capabilities.

[0004] Currently, methods for preparing MXene-based fibers include coating, wet spinning, electrospinning, double crimping, and 3D printing.

[0005] Coating technology: When preparing functional fibers using coating methods, it is necessary to improve interfacial interactions as much as possible to enhance the loading capacity and adhesion stability of MXene. Furthermore, MXene exhibits poor adhesion to certain materials, such as polyethylene terephthalate (PET) fibers.

[0006] Spinning technology: Because MXene is an inorganic compound with small flake size and weak interlayer forces, it is difficult to assemble MXene dispersions into fibers individually through wet spinning. In addition, the tendency of MXene particles or flakes to agglomerate and recombine can lead to inconsistent fiber diameter and morphology, making it crucial to obtain a more stable and uniform spinning solution.

[0007] Double-curl technology: CNT sheet fabrication is costly and poses biosafety concerns. Its application in wearable electronics will face stringent safety requirements and requires further consideration. Furthermore, the fiber length produced by this method is limited, restricting its application to small devices with high electrochemical performance requirements and hindering large-scale commercial use.

[0008] In summary, the unique interlayer structure of MXene results in weak interlayer interactions, directly affecting the overall mechanical properties of the fiber. Furthermore, MXene sheets exhibit poor environmental resistance, easily oxidizing and failing under high temperatures and fires, severely impacting their performance. Additionally, most thermal protection materials focus on a single function; common flame-retardant materials cannot provide temperature change information, while some temperature monitoring and early warning materials are primarily used for temperature measurement and do not possess flame-retardant properties.

[0009] Therefore, developing a smart fiber material that is both tough and environmentally stable, as well as flame-retardant and fire-predictive, can provide stronger protection for thermal protection fields such as fire fighting, aerospace, emergency rescue, metallurgy, and mining, thereby maximizing the protection of people's lives and property. Summary of the Invention

[0010] To address the problems existing in the prior art, this invention provides a flame-retardant intelligent temperature warning fiber based on waste aramid, its preparation method, and its application. A monolayer Ti3C2T fiber is prepared by a gentle etching method using hydrochloric acid (HCl) and lithium fluoride (LiF). x MXene; MXene was mixed with the organic solution dimethyl sulfoxide (DMSO) to prepare monolayer Ti3C2T. x A stable ANF dispersion was prepared by proton donor-assisted deprotonation of waste aramid 1414 para-fiber PPTA. The MXene DMSO dispersion and the ANF dispersion were then uniformly mixed in a certain proportion to prepare an MXene / ANF spinning solution. Finally, using the intrinsically flame-retardant waste aramid nanofiber ANF dispersion as the skin layer and the semiconductor material MXene / ANF as the core layer, the ANF@MXene / ANF coaxial composite fiber with the skin-core structure was obtained by coaxial wet spinning. This composite fiber has a dual function of outer flame retardant protection and inner temperature warning, thereby solving the technical problems of insufficient mechanical properties, poor environmental stability, and single function of MXene as a thermal protection material in the prior art.

[0011] This invention is achieved through the following technical solution:

[0012] A method for preparing a flame-retardant smart temperature warning fiber based on waste aramid fiber includes the following steps:

[0013] S1: KOH, PPTA, water and DMSO are mixed and stirred to obtain an ANF dispersion of first concentration and an ANF dispersion of second concentration, wherein the first concentration is less than the second concentration;

[0014] S2: Add the monolayer MXene DMSO dispersion to the ANF dispersion of the first concentration to prepare the MXene / ANF spinning solution;

[0015] S3: Using the MXene / ANF spinning solution as the core layer and the ANF dispersion of the second concentration as the sheath layer, coaxial wet spinning is performed to obtain the ANF@MXene / ANF coaxial composite fiber with the core-sheath structure.

[0016] Preferably, the concentration of the first concentration of ANF dispersion is 15 mg / mL.

[0017] Preferably, the concentration of the second concentration of ANF dispersion is 30 mg / mL.

[0018] Preferably, in step S1, when KOH, PPTA, water and DMSO are mixed and stirred to prepare ANF dispersions of the first and second concentrations, the stirring temperature is 60°C, the stirring speed is 1200 rpm, and the stirring time is 7 days.

[0019] Preferably, the solid content of the monolayer MXene DMSO dispersion is 5wt%~30wt%.

[0020] Preferably, the preparation of the monolayer MXene DMSO dispersion is specifically as follows: MXene is added to dimethyl sulfoxide, sonicated in an ice bath for 6 hours under nitrogen protection, and then centrifuged at 3000 rpm for 30 minutes to obtain the monolayer MXene DMSO dispersion.

[0021] Preferably, the MXene is prepared by using Ti3AlC2 MAX phase precursor as raw material and etching with lithium fluoride and hydrochloric acid to obtain the MXene.

[0022] Preferably, in step S3, in the coaxial wet spinning, the inner needle is 16G, the outer needle is 12G, and the spinning speeds of the inner and outer needles are 200μL / min and 350μL / min, respectively.

[0023] A flame-retardant smart temperature warning fiber based on waste aramid fiber is prepared by the above-mentioned method.

[0024] The above-mentioned application of a flame-retardant intelligent temperature warning fiber based on waste aramid in fireproof materials.

[0025] Compared with the prior art, the present invention has the following beneficial technical effects:

[0026] A method for preparing flame-retardant intelligent temperature warning fiber based on waste aramid is disclosed. This method uses high-concentration aramid nanofibers (ANF) as the outer spinning solution for coaxial spinning, leveraging the inherent high strength and high modulus properties of aramid. Both the sheath and core layers are based on ANF, achieving seamless bonding through coaxial spinning, enhancing interfacial adhesion, and avoiding mechanical defects caused by MXene interlayer slippage. Furthermore, the highly dense ANF outer layer isolates oxygen and moisture, significantly delaying the oxidation rate of the core layer MXene under high temperature / flame conditions. Moreover, the ANF sheath forms a char layer during combustion, further blocking heat and oxygen penetration into the core layer. The sheath-core structure of this invention not only significantly improves the overall mechanical properties of the fiber but also provides protection for the fiber core layer and isolates most of the air and moisture to delay the oxidation of the core layer MXene. This effectively solves the technical problems of insufficient mechanical properties, poor environmental stability, and limited functionality of MXene as a thermal protection material in existing technologies.

[0027] Furthermore, the concentration of the first concentration of ANF dispersion is 15 mg / mL, and the concentration of the second concentration of ANF dispersion is 30 mg / mL. This allows the fiber sheath to have good overall mechanical properties without clogging the coaxial needle, while the electrical properties of the core layer are less affected.

[0028] Furthermore, in step S1, when KOH, PPTA, water and DMSO are mixed and stirred to prepare ANF dispersions of the first and second concentrations, the stirring temperature is 60°C, the stirring speed is 1200 rpm, and the stirring time is 7 days, which allows the PPTA fibers to be fully dissolved.

[0029] Furthermore, the solid content of the monolayer MXene DMSO dispersion is 5wt%~30wt%, which allows the electrical properties and carrier concentration of the core fiber to achieve the effect of high-temperature alarm.

[0030] Furthermore, the preparation of the monolayer MXene DMSO dispersion is specifically as follows: using Ti3AlC2 MAX phase precursor as raw material, etching is performed using lithium fluoride and hydrochloric acid to obtain MXene, then adding MXene to DMSO, ultrasonically treating in an ice bath under a nitrogen atmosphere for 6 hours, and then centrifuging at 3000 rpm for 30 minutes to obtain the monolayer MXene DMSO dispersion. This allows the MXene DMSO dispersion to be successfully prepared, and the same solvent can better combine with ANF spinning solution, while its concentration can be obtained by wet spinning.

[0031] Furthermore, in step S3, during the coaxial wet spinning process, the inner needle is 16G and the outer needle is 12G. The spinning speeds of the inner and outer needles are 200μL / min and 350μL / min, respectively, which can make the spinning continuous and the fibers more uniform.

[0032] In this invention, the outer layer of the core-sheath structure not only improves the overall mechanical properties of the fiber, but also provides protection for the core layer and isolates most of the air and moisture to delay the oxidation of the MXene in the core layer, effectively enhancing its application value. At the same time, it also realizes the efficient recycling of waste aramid fibers, which is in line with the current concept of green environmental protection. Attached Figure Description

[0033] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a schematic diagram of the process for preparing flame-retardant intelligent temperature warning fiber in a specific embodiment of the present invention;

[0035] Figure 2 This is an exemplary surface morphology super-depth-of-field image of the flame-retardant intelligent temperature warning fiber prepared by the present invention.

[0036] Figure 3 This is an electron microscope image of an exemplary fiber cross-section of the flame-retardant intelligent temperature warning fiber obtained by the present invention.

[0037] Figure 4 This is a schematic diagram of the process preparation of coaxial wet spinning according to the present invention.

[0038] Figure label:

[0039] 1-Coagulation bath; 2-Roller 1; 3-Deionized water; 4-Roller 2; A-ANF spinning solution; B-MXene / ANF spinning solution; C-ANF@MXene / ANF coaxial composite fiber. Detailed Implementation

[0040] To enable those skilled in the art to understand the features and effects of the present invention, the terms and expressions used in the specification and claims are explained and defined in general below. Unless otherwise specified, all technical and scientific terms used herein have the ordinary meaning understood by those skilled in the art regarding the present invention, and in case of conflict, the definitions in this specification shall prevail.

[0041] The theories or mechanisms described and disclosed herein, whether right or wrong, should not in any way limit the scope of the invention, that is, the contents of the invention can be implemented without being limited by any particular theory or mechanism.

[0042] In this document, all features defined by numerical ranges or percentage ranges, such as numerical values, quantities, contents, and concentrations, are for the sake of brevity and convenience only. Accordingly, descriptions of numerical ranges or percentage ranges should be considered as covering and specifically disclosing all possible sub-ranges and individual numerical values ​​(including integers and fractions) within those ranges.

[0043] In this article, unless otherwise specified, “contains,” “includes,” “containing,” “has,” or similar terms cover the meanings of “composed of” and “mainly composed of,” for example, “A contains a” covers the meanings of “A contains a and others” and “A contains only a.”

[0044] For the sake of brevity, not all possible combinations of the technical features in each implementation scheme or embodiment are described herein. Therefore, as long as there is no contradiction in the combination of these technical features, the technical features in each implementation scheme or embodiment can be combined arbitrarily, and all possible combinations should be considered within the scope of this specification.

[0045] Unless otherwise specified in the following examples, all raw materials were commercially available or prepared using conventional methods in the art. Specifically, titanium aluminum carbide (Ti3AlC2) powder was purchased from Foshan Xinxi Technology Co., Ltd., with a specification of 200 mesh; lithium fluoride (LiF) was purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., with a specification of AR; concentrated hydrochloric acid (HCl) was purchased from Sinopharm Chemical Reagent Co., Ltd., with a purity of 97 wt%; dimethyl sulfoxide (DMSO) and potassium hydroxide (KOH) were both purchased from Chengdu Kelong Chemical Co., Ltd., with a specification of AR; waste aramid 1414 para-fiber (PPTA) was purchased from Hubei Jiateng Textile Co., Ltd.; and ammonium chloride (NH4Cl) was purchased from Sinopharm Chemical Reagent Co., Ltd., with a specification of AR.

[0046] like Figure 1 As shown, this invention provides a method for preparing flame-retardant intelligent temperature warning fiber based on waste aramid, comprising the following steps:

[0047] S1: Monolayer Ti3C2T prepared by mild etching with hydrochloric acid (HCl) and lithium fluoride (LiF). x MXene;

[0048] Specifically, Ti3AlC2 MAX phase precursor is used as raw material, and lithium fluoride (LiF) and hydrochloric acid (HCl) are used to etch the Al layer in the MAX phase to prepare monolayer Ti3AlC2 MXene.

[0049] In one specific embodiment, 2g of the MAX phase precursor Ti3AlC2 was used as the raw material. 2g of LiF was slowly added to 40mL of 9.0M HCl aqueous solution. Monolayer Ti3C2T was prepared by sonication, centrifugation, and freeze-drying. x MXene solid powder.

[0050] MXene is a collective term for graphene-like two-dimensional transition metal carbides and nitrides, due to Ti3C2T x MXene is relatively easy to synthesize, has high stability, and exhibits the best electrical conductivity, thus attracting extensive research. In addition, Ti3C2T... x MXene has semiconductor properties, and its resistance drops sharply at high temperatures. This thermistor material with a negative temperature coefficient can automatically monitor temperature changes and provide rapid early warning of high temperatures and fires. It has wide application value in many fields such as fire protection, aerospace, and emergency rescue.

[0051] S2: Prepare monolayer Ti3C2T by mixing MXene with the organic solution dimethyl sulfoxide (DMSO). x MXeneDMSO dispersion;

[0052] Specifically: Dimethyl sulfoxide (DMSO) solvent was added, nitrogen gas was continuously purged for protection, and the mixture was sonicated in an ice bath for 6 hours, followed by centrifugation at 3000 rpm for 30 minutes to obtain a monolayer of Ti3C2T. x DMSO dispersion of MXene layered nanosheets;

[0053] The prepared monolayer Ti3C2T x The concentration of the MXene DMSO dispersion was 35 mg / mL.

[0054] More specifically, step S2 above is as follows:

[0055] S21, Multilayer Ti3C2T x After grinding MXene powder, pour it into a centrifuge tube, add 30 mL of deionized water, centrifuge at 5000 rpm for 5 min, and pour out the supernatant after centrifugation.

[0056] S22. Add 30 mL of DMSO solvent, shake well, and sonicate for 1 hour. Centrifuge at 3000 rpm for 10 minutes. The upper liquid is then a monolayer of Ti3C2T. x MXene DMSO dispersion solution.

[0057] S23. If the upper liquid is clear, pour out the DMSO, add water again and centrifuge at high speed. After centrifugation, pour out the water and add DMSO. Repeat the above steps.

[0058] S3: A stable ANF dispersion was prepared by proton donor-assisted deprotonation of waste aramid 1414 para-fiber PPTA.

[0059] Specifically, a stable ANF dispersion was prepared using a proton donor-assisted deprotonation method. This involved mixing KOH, PPTA, deionized water, and DMSO together and magnetically stirring at 1200 rpm for one week at 60°C. The ratio of KOH, PPTA, and deionized water was 1:(1~2):1.

[0060] In one specific embodiment, KOH, PPTA, deionized water and 40 mL of DMSO were mixed together and magnetically stirred at 1200 rpm for one week at 60°C to obtain a dark red ANF dispersion.

[0061] The concentration of the above ANF dispersion in the core layer of the coaxial composite fiber is 15 mg / mL, and the concentration in the sheath layer is 30 mg / mL.

[0062] S4: Mix MXene DMSO dispersion and ANF dispersion in a uniform ratio to prepare MXene / ANF spinning solution;

[0063] Specifically: Ti3C2T was added to a 15 mg / mL dark red ANF dispersion. x The MXene DMSO dispersion was magnetically stirred at 600 rpm for 48 h at room temperature to finally prepare the MXene / ANF core spinning solution;

[0064] Among them, Ti3C2T x The solid content of the MXene DMSO dispersion is 5wt%~30wt%, preferably 25wt%.

[0065] In one specific embodiment, 5 wt%, 15 wt%, and 25 wt% Ti3C2 MXene DMSO dispersions were added to a 15 mg / mL ANF dispersion, labeled as M5A, M6A, M7A, and M8A, respectively. 15 A, M 25 A; and the MXene / ANF spinning solution was prepared by magnetic stirring at 600 rpm for 6 hours at room temperature.

[0066] The MXene / ANF spinning solution prepared by mixing Ti3C2 MXene DMSO dispersion with ANF dispersion, and the subsequent wet spinning process, result in fibers with excellent thermal stability, mechanical properties, and fire early warning performance. Figures 2-3 As shown, the coaxial fiber has a uniform surface structure and a diameter of 360μm; the core and sheath are tightly fused without obvious gaps or pores, and the interface bonding performance is good; the cross-section as a whole presents a structure with a dense outer layer and a relatively loose inner layer.

[0067] Compared to traditional heat-protective fiber materials, when this smart fiber is exposed to high temperatures or flames, the polymer ANF in the MXene / ANF temperature-sensing fiber core is burned to form a carbon network, and Ti3C2T x MXene nanosheets, through thermal oxidation, can generate TiO2 in situ as an indirect bandgap semiconductor, thereby stimulating the release of charge carriers and significantly increasing the carrier concentration. During this process, the resistance value drops by several orders of magnitude in a very short time, thus enabling circuit conduction and ultimately triggering the response of the fire alarm system.

[0068] S5: Using intrinsically flame-retardant waste aramid nanofiber ANF dispersion as the outer layer and semiconductor material MXene / ANF as the core layer, the ANF@MXene / ANF coaxial composite fiber with the outer layer and core structure is prepared by coaxial wet spinning. This fiber has the dual function of outer flame-retardant protection and inner temperature warning.

[0069] Specifically, the coaxial wet spinning parameters are as follows: constant draw ratio 1.1, coaxial inner needle 16G (inner diameter ≈ 1.15 mm), outer needle 12G (inner diameter ≈ 2.3 mm), spinning speeds connected to the inner and outer needles are 200 and 350 μL / min, respectively. The coaxial fibers are treated with 5 wt% NH4Cl solution, washed three times in deionized water, collected on the spool, and dried at room temperature.

[0070] In a specific embodiment, step S5 above specifically includes:

[0071] S51. The wet spinning pre-prepared solution obtained in steps S3 and S4 is evenly injected into two syringes and installed in the wet spinning machine. The wet spinning parameters are as follows: the injection speeds of the pumps connected to the inner and outer needles are 200 and 350 μL / min, respectively; the draw ratio R is 1.1; and the coagulation bath for wet spinning is deionized water containing 5 wt% NH4Cl.

[0072] S52. Using an intrinsically flame-retardant 30 mg / m LANF dispersion as the skin layer and a semiconductor material MXene / ANF with a mass ratio of 25 wt% as the core layer, coaxial wet spinning is performed, wherein the coaxial inner needle is 16 G (inner diameter ≈ 1.15 mm) and the outer needle is 12 G (inner diameter ≈ 2.3 mm).

[0073] S53. After spinning, the fiber is placed in a coagulation bath for 30 minutes for displacement. Finally, the fiber is washed three times in deionized water and collected on a spool. It is then dried at room temperature to obtain ANF@MXene / ANF coaxial composite fiber with a core-sheath structure.

[0074] The oxidation of C and Ti in MXene forms a dense char layer at high temperatures, acting as a physical barrier to inhibit heat and oxygen transfer. Simultaneously, MXene and ANF form a cross-linked network, further enhancing the overall thermal stability of the ANF@MXene / ANF coaxial composite fiber. Furthermore, this fiber maintains its original shape during combustion without melting or dripping, and extinguishes rapidly after being removed from the alcohol lamp flame. The fiber also exhibits a limiting oxygen index (LOI) of 43.2%, which is 1.44 times higher than that of aramid fiber (LOI 30%) used in commercial fire-fighting clothing. These results demonstrate that the ANF@MXene / ANF coaxial composite fiber possesses excellent flame-retardant properties and has broad application value in specialized industries such as fire fighting, aerospace, and emergency rescue.

[0075] This invention uses Ti3AlC2 MAX phase precursor as raw material and employs lithium fluoride (LiF) and hydrochloric acid (HCl) to gently etch the Al layer in the MAX phase, thereby preparing a monolayer Ti3C2T x MXene was mixed with the organic solution DMSO to prepare Ti3C2T. x A stable ANF dispersion was prepared by dissolving waste aramid 1414 para-fibers (PPTA) in a DMSO / KOH / H2O system using a proton donor-assisted deprotonation method. The MXene / ANF solution was then uniformly mixed with the DMSO and ANF dispersions in a specific ratio. Using the intrinsically flame-retardant waste aramid nanofiber ANF dispersion as the outer layer and the semiconductor material MXene / ANF as the core layer, a smart fiber material with an outer flame-retardant protective layer and an inner temperature warning system was prepared via coaxial wet spinning. When this coaxial fiber with a core-shell structure is subjected to high temperature or flame attack, the outer layer can achieve self-flame retardancy, controlling the spread of flame while protecting the fiber core layer MXene from rapid thermal oxidation, thus achieving continuous alarm. When the temperature is conducted to the core layer, the ANF in the core layer decomposes and catalyzes the oxidation of MXene. Due to the Ti3C2T...x MXene nanosheets are thermally oxidized to TiO2. TiO2 has semiconductor properties; when the temperature rises, electron transitions occur, leading to an increase in carrier density and the generation of a conductive network, thereby enabling rapid fire alarm (<3s).

[0076] Furthermore, this invention utilizes poly-p-phenylene terephthamide (PPTA), traded as Kevlar, an aramid 1414 fiber with a high strength, high modulus, and a thermal decomposition temperature of 560℃, for dissolution and respinning, fully leveraging the excellent flame-retardant and mechanical properties of aramid 1414 fibers. In addition, 35 mg / mL of 25-30 wt% monolayer Ti3C2T is added to the core spinning solution. x MXene DMSO dispersion exhibits enhanced thermal stability and flame retardancy due to the oxidation of C and Ti in MXene under high temperature or flame attack, forming a denser char layer that acts as a physical barrier to inhibit heat and oxygen transfer and slow flame spread. By combining intrinsically flame-retardant aramid nanofibers (ANF) with the two-dimensional layered nanomaterial MXene, a synergistic flame-retardant effect is achieved. This ANF@MXene / ANF composite fiber maintains a char residue of 64.05% at 800℃, while also exhibiting excellent flame retardancy. It only begins to shrink and deform after 170 seconds of exposure to an alcohol lamp, with a damage length of less than 0.5 cm, no melting or dripping, and self-extinguishing upon removal from the flame. Furthermore, the fiber has a limiting oxygen index (LOI) of 43.2%, which is 1.44 times higher than that of aramid fibers (LOI of 30%), making it suitable for applications in specialized industries such as fire fighting, aerospace, and emergency rescue.

[0077] Furthermore, this invention utilizes an intrinsically flame-retardant waste aramid nanofiber ANF dispersion as the outer layer and the semiconductor material MXene / ANF as the core layer to prepare a core-shell structured ANF@MXene / ANF coaxial composite smart fiber. The outer layer of the core-shell structure enhances the overall mechanical properties of the fiber, controls flame spread to achieve self-flame retardancy, and simultaneously provides protection for the fiber core layer, isolating most air and moisture to delay the oxidation of the MXene in the core layer. The presence of ANF in both the core and shell ensures excellent interfacial bonding, thereby improving the overall mechanical properties of the fiber, enhancing chemical stability, reducing fiber deformation and cracking caused by thermal stress, and improving the fiber's heat resistance and thermal stability. This core-shell structured composite fiber material ensures increased charge density in the core layer MXene under high temperatures or fire conditions, effectively generating a conductive network and providing more sensitive and reliable fire warnings.

[0078] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0079] The following examples use instruments and equipment conventional in the art. Experimental methods in the following examples, unless otherwise specified, are generally performed under conventional conditions or as recommended by the manufacturer. All raw materials used in the following examples are conventional commercially available products with specifications conventional in the art. In this specification and the following examples, unless otherwise specified, "%" refers to weight percentage, "parts" refers to parts by weight, and "ratio" refers to weight proportion.

[0080] Comparative Example 1:

[0081] A method for preparing a flame-retardant smart temperature warning fiber based on waste aramid fiber includes the following steps:

[0082] S1: Using 2g of MAX phase precursor Ti3AlC2 as raw material, 2g of LiF was slowly added to 40mL of 9.0M HCl aqueous solution. Monolayer Ti3C2T was prepared by sonication, centrifugation, and freeze-drying. x MXene solid powder.

[0083] S2: Prepare monolayer Ti3C2T by mixing MXene with the organic solution dimethyl sulfoxide (DMSO). x MXene DMSO dispersion;

[0084] S21, Multilayer Ti3C2T x After grinding MXene powder, pour it into a centrifuge tube, add 30 mL of deionized water, centrifuge at 5000 rpm for 5 min, and pour out the supernatant after centrifugation.

[0085] S22. Add 30 mL of DMSO solvent, shake well, and sonicate for 1 hour. Centrifuge at 3000 rpm for 10 minutes. The upper liquid is then a monolayer of Ti3C2T. x MXene DMSO dispersion solution.

[0086] S23. If the upper liquid is clear, pour out the DMSO, add water again and centrifuge at high speed. After centrifugation, pour out the water and add DMSO. Repeat the above steps.

[0087] S3: Using a proton donor-assisted deprotonation method, KOH, PPTA, deionized water and 40 ml DMSO were mixed together and magnetically stirred at 1200 rpm for one week at 60 °C to prepare a 15 mg / mL ANFs dispersion.

[0088] S4: Mix MXene DMSO dispersion and ANF dispersion in a uniform ratio to prepare MXene / ANF solution;

[0089] S41. Add 25wt% Ti3C2 MXene DMSO dispersion to a 15mg / mL ANF dispersion, labeled M. 25 A;

[0090] S42. Stir magnetically at 600 rpm for 6 hours at room temperature to finally prepare the MXene / ANF spinning solution for the fiber core layer.

[0091] S5: A flame-retardant, temperature-predictive MXene / ANF composite fiber was prepared by wet spinning.

[0092] S51. Inject the wet spinning pre-prepared solution obtained in step S4 into a syringe and install it in the wet spinning machine. The wet spinning parameters are: injection speed 200 μL / min, draw ratio R 1.1, spinning needle specification 16G (inner diameter ≈ 1.15 mm), and the coagulation bath for wet spinning is deionized water containing 5 wt% NH4Cl.

[0093] S52. After spinning, the fiber is placed in a coagulation bath for 30 minutes for displacement. Finally, the fiber is washed three times in deionized water and collected on a spool. It is then dried at room temperature to obtain MXene / ANF composite fiber.

[0094] Comparative Example 2:

[0095] The difference between Comparative Example 1 and Comparative Example 2 is:

[0096] S4: Add 15wt% Ti3C2 MXene DMSO dispersion to a 15mg / mL ANF dispersion, labeled M. 15 A. Then, the solution was magnetically stirred at 600 rpm for 6 hours at room temperature to finally prepare the MXene / ANF spinning solution for the fiber core layer.

[0097] Comparative Example 3:

[0098] The difference between Comparative Example 2 and Comparative Example 1 is as follows:

[0099] S4: Add 5wt% Ti3C2 MXene DMSO dispersion, labeled M5A, to 15mg / mL ANF dispersion, and then magnetically stir at 600rpm for 6h at room temperature to prepare MXene / ANF spinning solution for fiber core layer.

[0100] Table 1 shows the performance test results of the composite fibers prepared by methods 1 to 3.

[0101]

[0102] As shown in Table 1, due to insufficient interlayer forces in MXene nanosheets, increasing its content may lead to internal stress or interface defects, as well as the formation of amorphous regions, reducing the crystallinity of the MXene / ANF composite fiber and thus decreasing its strength. In Comparative Example 1, the MXene / ANF fiber exhibited the highest electrical conductivity. By connecting this fiber, a regulated DC power supply, and an alarm lamp in series, a simple fire alarm device was designed. When an alcohol lamp attacks the fiber, MXene, acting as an indirect bandgap semiconductor, generates TiO2 in situ, resulting in a significant increase in carrier concentration. Simultaneously, the resistance value rapidly decreases within a very short time, thus achieving circuit conduction and triggering the LED light of the fire alarm device within 3 seconds. Furthermore, when the MXene content is 35%, the fiber strength is approximately 11 MPa, making it difficult to spin and store.

[0103] Example 1:

[0104] A method for preparing a flame-retardant smart temperature warning fiber based on waste aramid fiber includes the following steps:

[0105] S1: Using 2g of MAX phase precursor Ti3AlC2 as raw material, 2g of LiF was slowly added to 40mL of 9.0M HCl aqueous solution. Monolayer Ti3C2T was prepared by sonication, centrifugation, and freeze-drying. x MXene solid powder.

[0106] S2: Prepare monolayer Ti3C2T by mixing MXene with the organic solution dimethyl sulfoxide (DMSO). x MXene DMSO dispersion;

[0107] S21, Multilayer Ti3C2T x After grinding MXene powder, pour it into a centrifuge tube, add 30 mL of deionized water, centrifuge at 5000 rpm for 5 min, and pour out the supernatant after centrifugation.

[0108] S22. Add 30 mL of DMSO solvent, shake well, and sonicate for 1 hour. Centrifuge at 3000 rpm for 10 minutes. The upper liquid is then a monolayer of Ti3C2T.x MXene DMSO dispersion solution.

[0109] S23. If the upper liquid is clear, pour out the DMSO, add water again and centrifuge at high speed. After centrifugation, pour out the water and add DMSO. Repeat the above steps.

[0110] S3: Using the proton donor-assisted deprotonation method, KOH, PPTA, deionized water and 40 ml DMSO were mixed together and magnetically stirred at 1200 rpm for one week at 60 °C to prepare two ANFs dispersions with concentrations of 15 mg / mL (core) and 30 mg / mL (skin).

[0111] S4: Mix MXene DMSO dispersion and ANF dispersion in a uniform ratio to prepare MXene / ANF solution;

[0112] S41. Add 25wt% Ti3C2 MXene DMSO dispersion to a 15mg / mL ANF dispersion, labeled M. 25 A;

[0113] S42. Stir magnetically at 600 rpm for 6 hours at room temperature to finally prepare the MXene / ANF spinning solution for the fiber core layer.

[0114] S5: Using an intrinsically flame-retardant ANF dispersion as the outer layer and the semiconductor material MXene / ANF as the core layer, a coaxial wet spinning method was used to prepare an ANF@MXene / ANF coaxial composite fiber with an outer flame-retardant protective layer and an inner temperature warning layer. The surface morphology is shown in the super-depth-of-field image and the fiber cross-section is shown in the figure below. Figures 2-3 As shown, by Figures 2-3 It can be seen that the fiber has a uniform surface structure, with a transparent pale yellow outer layer and a black inner layer, exhibiting longitudinal grooves. This is a typical structural feature of fibers prepared by wet spinning. The preparation process of coaxial wet spinning in this embodiment is as follows: Figure 4 As shown;

[0115] S51. The wet spinning pre-prepared solution obtained in steps S3 and S4 is evenly injected into two syringes and installed in the wet spinning machine. The wet spinning parameters are as follows: the injection speeds of the pumps connected to the inner and outer needles are 200 and 350 μL / min, respectively; the draw ratio R is 1.1; and the coagulation bath for wet spinning is deionized water containing 5 wt% NH4Cl.

[0116] S52. Using 30 mg / m LANF dispersion as the skin layer and MXene / ANF semiconductor material with a mass ratio of 25 wt% as the core layer, coaxial wet spinning is performed, wherein the inner needle is 16 G (inner diameter ≈ 1.15 mm) and the outer needle is 12 G (inner diameter ≈ 2.3 mm).

[0117] S53. After spinning, the fibers are placed in a coagulation bath for 30 minutes for displacement. Finally, the fibers are washed three times in deionized water and collected on a spool, then dried at room temperature to obtain ANF@MXene / ANF coaxial composite fibers with a core-shell structure. The surface morphology of the ANF@MXene / ANF coaxial composite fiber core-shell structure is shown in the super-depth-of-field image. Figure 2 As shown.

[0118] Table 2 shows the performance test results of the composite fibers prepared in Comparative Example 1 and Example 1.

[0119]

[0120] As shown in Table 2, compared with Example 1, Comparative Example 1's ANF@MXene / ANF fiber (the product of Example 1) has a continuous and dense outer layer, and both the fiber sheath and core layer are based on ANF, resulting in strong adhesion and good interfacial properties between the fiber sheath and core, effectively enhancing its mechanical strength. Simultaneously, the ANF concentration in the sheath is higher, exhibiting excellent flame retardant properties. While improving strength, Example 1 also shows a certain degree of improvement in the limiting oxygen index. This is because MXene forms tortuous paths within the polymer ANF matrix, thereby slowing down heat and mass transfer between the underlying matrix and the gas region, inhibiting further combustion of the fiber material, and suppressing the release of smoke and heat. This results in a certain degree of synergistic flame retardant effect between MXene and ANF in the ANF@MXene / ANF coaxial composite fiber.

[0121] Furthermore, as can be seen from Comparative Examples 1-3, the fiber exhibits the best initial conductivity when the core layer MXene concentration is 25 wt%, with a resistance decrease of approximately 88.16% within 3 seconds under an alcohol lamp, demonstrating the fastest response speed. Therefore, Example 1, based on Comparative Example 1, prepared a core-shell structured smart fiber material with flame retardancy and fire early warning capabilities through coaxial wet spinning, providing a more effective and reliable method for applications in fire protection, aerospace, emergency rescue, and safety protection.

[0122] In summary, the core-sheath structure in Example 1 provides effective protection for the internal MXene by concentrating a higher concentration of ANF in the sheath, preventing its oxidation, while also giving the fiber higher overall mechanical strength and flexibility.

[0123] Example 2:

[0124] The difference between this embodiment and Embodiment 1 is that:

[0125] S4: Add 15wt% Ti3C2 MXene DMSO dispersion to a 15mg / mL ANF dispersion, labeled M. 15 A. Then, the solution was magnetically stirred at 600 rpm for 6 hours at room temperature to finally prepare the MXene / ANF spinning solution for the fiber core layer.

[0126] S5: Using intrinsic flame-retardant ANF dispersion as the outer layer and semiconductor material MXene / ANF as the core layer, a coaxial ANF@MXene / ANF coaxial composite fiber with flame-retardant protection on the outer layer and temperature warning on the inner layer was prepared by coaxial wet spinning.

[0127] Example 3:

[0128] The difference between this embodiment and Embodiment 1 is that:

[0129] S4: Add 5wt% Ti3C2 MXene DMSO dispersion, labeled M5A, to 15mg / mL ANF dispersion, and then magnetically stir at 600rpm for 6h at room temperature to prepare MXene / ANF spinning solution for fiber core layer.

[0130] S5: Using intrinsic flame-retardant ANF dispersion as the outer layer and semiconductor material MXene / ANF as the core layer, a coaxial ANF@MXene / ANF coaxial composite fiber with flame-retardant protection on the outer layer and temperature warning on the inner layer was prepared by coaxial wet spinning.

[0131] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing flame-retardant intelligent temperature warning fiber based on waste aramid, characterized in that, Includes the following steps: S1: KOH, waste aramid para-fiber PPTA, water and DMSO are mixed and stirred to prepare an ANF dispersion of first concentration and an ANF dispersion of second concentration, wherein the first concentration is less than the second concentration. S2: Add the monolayer MXene DMSO dispersion to the ANF dispersion of the first concentration to prepare the MXene / ANF spinning solution; S3: Using the MXene / ANF spinning solution as the core layer and the ANF dispersion of the second concentration as the sheath layer, coaxial wet spinning is performed to obtain the flame-retardant intelligent temperature warning fiber based on waste aramid. The concentration of the first concentration of ANF dispersion is 15 mg / mL; The concentration of the second concentration of ANF dispersion is 30 mg / mL; The outer layer is an intrinsically flame-retardant ANF layer that covers the core layer to form a continuous and dense outer layer. This outer layer is used to isolate air and moisture to delay the oxidation of the core layer MXene, so that the resulting fiber forms a coaxial composite structure with flame-retardant protection on the outer layer and temperature warning on the inner layer.

2. The method for preparing a flame-retardant intelligent temperature warning fiber based on waste aramid fiber according to claim 1, characterized in that, In step S1, when KOH, waste aramid para-fiber PPTA, water and DMSO are mixed and stirred to prepare ANF dispersions of first and second concentrations, the stirring temperature is 60℃, the stirring speed is 1200rpm, and the stirring time is 7 days; the mass ratio of KOH, PPTA and water is 1:(1~2):

1.

3. The method for preparing a flame-retardant intelligent temperature warning fiber based on waste aramid fiber according to claim 1, characterized in that, A monolayer MXene DMSO dispersion was added to an ANF dispersion of a first concentration to prepare an MXene / ANF spinning solution, wherein the concentration of MXene in the MXene / ANF spinning solution was 5wt%~30wt%.

4. The method for preparing a flame-retardant intelligent temperature warning fiber based on waste aramid fiber according to claim 1, characterized in that, The preparation of the monolayer MXene DMSO dispersion is as follows: MXene is added to dimethyl sulfoxide, and the mixture is sonicated in an ice bath for 6 hours under nitrogen protection, followed by centrifugation at 3000 rpm for 30 minutes to obtain the monolayer MXene DMSO dispersion.

5. The method for preparing a flame-retardant intelligent temperature warning fiber based on waste aramid fiber according to claim 1, characterized in that, The preparation of MXene is specifically as follows: using Ti3AlC2 MAX phase precursor as raw material, and etching with lithium fluoride and hydrochloric acid to obtain MXene.

6. The method for preparing a flame-retardant intelligent temperature warning fiber based on waste aramid fiber according to claim 1, characterized in that, In step S3, during the coaxial wet spinning process, the inner needle is 16G and the outer needle is 12G, with spinning speeds of 200μL / min and 350μL / min for the inner and outer needles, respectively.

7. A flame-retardant intelligent temperature warning fiber based on waste aramid, characterized in that, It is prepared by the preparation method described in any one of claims 1 to 6.

8. The application of the flame-retardant intelligent temperature warning fiber based on waste aramid as described in claim 7 in fireproof materials.

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