Flame-retardant aramid fiber for fabric and preparation method thereof

Abstract

This application relates to the technical field of aramid fibers, specifically disclosing a flame-retardant aramid fiber for fabrics and its preparation method. The preparation method includes the following steps: S1: Immersing para-aramid chopped fibers in pre-hydrolyzed solution A, heating and reacting, separating the solid and liquid, then immersing in pre-hydrolyzed solution B, heating and reacting, separating the solid and liquid, washing, and drying to obtain pretreated para-aramid chopped fibers; S2: Under an inert atmosphere, dissolving m-phenylenediamine in N,N-dimethylacetamide containing calcium chloride, then adding the pretreated para-aramid chopped fibers, mixing evenly, cooling to -15~-10℃, then adding isophthaloyl chloride, reacting for 50~60 min, neutralizing, degassing to obtain a spinning solution, using a wet spinning process, solidifying in a coagulation bath, washing, and stretching to obtain flame-retardant aramid fibers for fabrics. The flame-retardant aramid fibers for fabrics obtained in this application have good mechanical properties and flame-retardant properties.

Description

Technical Field

[0001] This application relates to the technical field of aramid fibers, and more specifically, to a flame-retardant aramid fiber for fabrics and a method for preparing the same. Background Technology

[0002] Aramid fibers, as high-performance polymer materials, include two main categories: fully aromatic polyamide fibers and heterocyclic aromatic polyamide fibers. Among fully aromatic polyamide fibers, based on the connection position between the amide group and the benzene ring, they can be divided into para-aramid (aramid 1414) and meta-aramid (aramid 1313), with meta-aramid and para-aramid being the mainstream aramid fibers.

[0003] Para-aramid fibers have a regular molecular chain structure, making them prone to high orientation and crystallization, thus exhibiting extremely high strength, modulus, and heat resistance. Meta-aramid fibers have serrated molecular chains and contain a large number of meta structures, giving them excellent thermal stability, inherent flame retardancy, chemical corrosion resistance, and flexibility, but their mechanical strength is much lower than that of para-aramid. To obtain materials with more balanced overall performance, existing technologies mostly employ physical blending or composite methods, such as short fiber blending and lamination. However, these methods cannot solve the fundamental problem of poor interfacial compatibility between the two phases, resulting in low stress transfer efficiency, easy interfacial delamination, and performance degradation, and failing to achieve synergistic gains.

[0004] The patent application with publication number CN118029001A discloses a method for preparing para-aramid nanofiber-reinforced modified meta-aramid fibers, including: (1) mixing para-aramid chopped fibers, potassium hydroxide and dimethyl sulfoxide, stirring at room temperature to obtain a para-aramid nanofiber dispersion; then mixing the aramid nanofiber dispersion, alkali and N,N dimethylacetamide to obtain a mixed alkali solution of aramid nanofibers; (2) preparing a poly(m-phenylene isophthalamide) polymerization solution by low-temperature solution polymerization, adding the mixed alkali solution of aramid nanofibers from step (1), neutralizing and mixing evenly to obtain an aramid nanofiber / poly(m-phenylene isophthalamide) composite spinning solution; (3) performing wet spinning on the aramid nanofiber / poly(m-phenylene isophthalamide) composite spinning solution, solidifying it in a coagulation bath, then performing wet stretching, washing, drying, and dry heat stretching to obtain para-aramid nanofiber-reinforced modified meta-aramid fibers.

[0005] In this technical solution, after the para-aramid chopped fibers are treated with strong alkali, there are insufficient surface active groups, resulting in weak interfacial bonding with poly(m-phenylene isophthalamide) and low stress transfer efficiency. The pH fluctuation during the neutralization stage can easily disrupt the dispersion stability of the para-aramid chopped fibers, causing them to re-aggregate, forming microscopic defects and stress concentration points, which limits the synergistic improvement of strength and elongation at break. Summary of the Invention

[0006] To address the problems of poor interfacial compatibility and inability to achieve synergistic gains in mechanical properties in existing physical blending methods, this application provides a flame-retardant aramid fiber for fabrics and its preparation method.

[0007] In a first aspect, this application provides a method for preparing flame-retardant aramid fibers for fabrics, employing the following technical solution:

[0008] A method for preparing flame-retardant aramid fiber for fabrics includes the following steps:

[0009] S1: Immerse para-aramid short-cut fibers in pre-hydrolyzed solution A, heat to 50~70℃, react for 3~5 hours, separate solid and liquid, immerse in pre-hydrolyzed solution B, heat to 50~70℃, react for 4~6 hours, separate solid and liquid, wash, dry, and obtain pretreated para-aramid short-cut fibers.

[0010] S2: Under an inert atmosphere, m-phenylenediamine is dissolved in N,N-dimethylacetamide containing calcium chloride, and then pretreated para-aramid chopped fibers are added. After mixing evenly, the mixture is cooled to -15~-10℃, and then isophthaloyl chloride is added. The mixture is then reacted for 50~60 minutes, neutralized, and degassed to obtain a spinning solution. A wet spinning process is used, followed by solidification in a coagulation bath, washing, and stretching to obtain flame-retardant aramid fibers for fabrics.

[0011] The pre-hydrolyzed solution A comprises monoaminosilane, ethanol, and water;

[0012] The pre-hydrolyzed solution B comprises diaminosilane, tetra(2-hydroxyethoxy)silane, ethanol, and water.

[0013] This technical solution first utilizes the simple molecular structure of monoaminosilane to effectively anchor it onto the surface of para-aramid fibers, forming a strong covalent bond, constructing an anchoring layer, and introducing initial amino sites. Then, diaminosilane and tetrakis(2-hydroxyethoxy)silane are introduced for synergistic hybridization. Specifically, the diaminosilane further extends through condensation grafting, increasing the amino density and imparting interfacial flexibility, while the tetrakis(2-hydroxyethoxy)silane forms a three-dimensional cross-linked network through polyhydroxyl hydrolysis. Ultimately, a gradient functionalized interfacial layer containing amino and hydroxyl groups is constructed on the fiber surface, significantly improving the compatibility and reactivity of the fiber with the subsequent polymerization system.

[0014] In subsequent in-situ polymerization, the surface functional groups of pretreated para-aramid chopped fibers can form a strong interfacial bond with the generated meta-aramid structure. Through wet spinning, the para-aramid core and the meta-aramid modified layer are synergistically integrated. The resulting fiber retains the high strength characteristics of para-aramid and enhances flame retardancy due to the synergistic effect of the meta-aramid component and the surface cross-linking structure. At the same time, the gradient interfacial layer effectively relieves internal and external stresses, improves the mechanical stability and spinning performance of the fiber, and is suitable for the dual requirements of flame retardancy and mechanical properties in the fabric industry.

[0015] Preferably, the total mass ratio of the m-phenylenediamine and isophthaloyl chloride to the pretreated para-aramid chopped fibers is (60~70):(30~40).

[0016] Preferably, the molar ratio of m-phenylenediamine to isophthaloyl chloride is 1:(1.05~1.1).

[0017] Preferably, the mass fraction of calcium chloride in the N,N-dimethylacetamide is 3% to 5%.

[0018] Preferably, the preparation method of the pre-hydrolyzed solution A includes the following steps:

[0019] Mix monoaminosilane, ethanol and water in a mass ratio of (3~5):(85~90):(10~15) until homogeneous, adjust the pH to 5~5.5, and hydrolyze at 20~30℃ for 50~70 min to obtain pre-hydrolyzed solution A.

[0020] Preferably, the monoaminosilane is a silane coupling agent KH550.

[0021] Preferably, the preparation method of the pre-hydrolyzed solution B includes the following steps:

[0022] Diaminosilane, tetra(2-hydroxyethoxy)silane, ethanol and water are mixed evenly in a mass ratio of 2:(1~3):(85~90):(10~15), the pH is adjusted to 5~5.5, and hydrolyzed at 35~45℃ for 60~80 min to obtain pre-hydrolyzed solution B.

[0023] Preferably, the diaminosilane is a silane coupling agent KH-792.

[0024] Preferably, the prehydrolysate B further includes a phosphorus-containing silane, wherein the mass ratio of the phosphorus-containing silane to the diaminosilane is (0.5~1.0):1.

[0025] Preferably, the phosphorus-containing silane is diethylphosphorylethyltriethoxysilane.

[0026] This technical solution introduces phosphorus-containing silane into the pre-hydrolysis solution B. During the pre-hydrolysis process, its silane groups hydrolyze and condense together with tetra(2-hydroxyethoxy)silane and silane coupling agent KH792 in the system, stably anchoring the flame retardant element in the three-dimensional cross-linked interface layer. This not only reduces the migration and precipitation of flame retardant elements, but also promotes the formation of a dense carbon layer on the fiber surface under high temperature conditions. It exerts a flame retardant effect by isolating oxygen and inhibiting the release of combustible gases, forming a synergistic mechanism with the high temperature resistance of aramid itself and the heat insulation effect of silicon.

[0027] Preferably, in step S1, after washing, the fiber is immersed in an aqueous solution of ammonium phytate with a mass concentration of 10%~15%, heated to 50~70℃, mixed for 90~120 min, separated into solid and liquid, washed, and dried to obtain pretreated para-aramid short fibers.

[0028] This technical solution involves post-treating pretreated fibers with an ammonium phytate aqueous solution. The high-density phosphate ions in the ammonium phytate molecules can be firmly adsorbed onto the positively charged aminated fiber surface through strong electrostatic interactions. This increases the total amount of phosphorus, enhancing the ability to form a dense char layer at high temperatures and further improving the flame retardant properties of the fibers. Furthermore, the strong interaction between ammonium phytate and the interface layer avoids the uneven distribution problem that may exist with a single phosphorus source, reduces the migration and loss of flame retardant elements, and ensures the long-lasting flame retardant effect.

[0029] Preferably, the pre-hydrolyzed solution B further includes bismaleimide, wherein the mass ratio of bismaleimide to diaminosilane is (0.05~0.1):1.

[0030] In this technical solution, bismaleimide is added to the pre-hydrolyzed solution B. The bismaleimide remains stable during the interface modification stage, and during subsequent fiber stretching, its maleimide double bonds undergo a thermal addition reaction with the amino groups at the ends of the interface layer, forming a covalent cross-linked network in the fiber-matrix interface region. This "dynamic thermal cross-linking" mechanism effectively dissipates stress, significantly improving fiber strength and modulus while endowing it with excellent toughness and impact resistance.

[0031] Preferably, in step S2, after stretching, the fiber is immersed in pre-decomposition liquid C, heated to 50~70℃, mixed for 1~2 hours, separated from the solid, and dried to obtain flame-retardant aramid fiber for fabrics; the pre-decomposition liquid C includes 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, tetra(2-hydroxyethoxy)silane, ethanol and water.

[0032] Preferably, the method for preparing the pre-decomposition liquid C includes the following steps:

[0033] Mix 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, tetra(2-hydroxyethoxy)silane, ethanol and water thoroughly, adjust the pH to 5-5.5, heat to 35-45℃, hydrolyze for 60-80 min, cool, and obtain pre-decomposition solution C.

[0034] Preferably, the mass ratio of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, tetra(2-hydroxyethoxy)silane, ethanol and water is (10~15):(5~10):(170~180):(20~30).

[0035] This technical solution involves finishing the fiber-forming process using a pre-decomposition solution C. 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, with its excellent reactivity, bonds with and physically anchors to the fiber surface and shallow layers, particularly the amino and hydroxyl groups remaining after pre-treatment. Tetra(2-hydroxyethoxy)silane hydrolyzes to form a protective siloxane film, which both coats the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide to inhibit its migration and firmly anchors the composite coating to the fiber surface through secondary condensation of silanol groups with fiber surface groups. This composite coating exhibits highly efficient synergistic flame retardancy in the early stages of combustion, while the silicon layer provides a thermal barrier. The synergistic effect of these two components, as a highly efficient supplementary flame retardant method, further enhances the limiting oxygen index (LOI) of the fiber and improves its anti-dripping behavior.

[0036] Secondly, this application provides a flame-retardant aramid fiber for fabrics prepared by the above-mentioned preparation method.

[0037] In this technical solution, the flame-retardant aramid fiber used in the fabric has high-strength para-aramid as the core, and the outer layer is modified by in-situ polymerization to form a meta-aramid modified layer. The core and the modified layer are tightly bonded by a gradient composite interface layer constructed by monoaminosilane, diaminosilane and tetra(2-hydroxyethoxy)silane. This not only retains the high tensile strength and modulus of para-aramid, but also achieves an effective balance between mechanical and flame-retardant properties by taking advantage of the excellent flame retardancy of meta-aramid and the stress buffering effect of the interface layer.

[0038] In summary, this application has the following beneficial effects:

[0039] 1. This application first uses monoaminosilane, then diaminosilane and tetra(2-hydroxyethoxy)silane to process para-aramid fibers stepwise to form a gradient cross-linked multifunctional composite interface layer. This interface layer not only achieves strong compatibility with the subsequent in-situ polymerization system through its rich functional groups, but its unique gradient structure can also effectively alleviate the internal and external stress concentration of the fiber during stress and heat processing, laying a solid interface foundation for the final fiber to achieve synergistic improvement in mechanical strength, modulus and toughness.

[0040] 2. This application preferably uses phosphorus-containing silanes to participate in interface construction during the pre-hydrolysis stage, achieving in-situ immobilization and stable existence of phosphorus elements at the interface. During combustion, it efficiently catalyzes the formation of a dense silicon-carbon protective layer. The subsequent ammonium phytate treatment further introduces phosphorus and nitrogen sources, optimizes the uniformity of phosphorus element distribution, and produces a significant expansion flame-retardant synergistic effect, greatly improving the quality of the char layer. Finally, the 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide introduced in the finishing process plays an efficient free radical capture (quenching) role in the gas phase. These three substances play key roles in the condensed phase and the gas phase, respectively, forming a three-dimensional firewall, which fundamentally improves the limiting oxygen index of the fiber and exhibits excellent anti-dripping performance and long-lasting flame retardancy. Detailed Implementation

[0041] The present application will be further described in detail below with reference to the embodiments.

[0042] Unless otherwise specified, the raw materials used in the embodiments and comparative examples of this application are all commercially available.

[0043] The flame-retardant aramid fibers for fabrics prepared in the following examples are particularly suitable for protective fabrics such as fire suits.

[0044] The length distribution of para-aramid chopped fibers is 1~3mm.

[0045] Example 1

[0046] The method for preparing flame-retardant aramid fibers for fabrics in this embodiment includes the following steps:

[0047] S11: Mix 4g of silane coupling agent KH550, 85g of anhydrous ethanol and 15g of deionized water evenly, adjust the pH to 5 with 8% acetic acid, and hydrolyze in a constant temperature water bath at 25℃ for 60min to obtain pre-hydrolyzed solution A.

[0048] S12: Mix 2g of silane coupling agent KH-792, 2g of tetrakis(2-hydroxyethoxy)silane, 85g of anhydrous ethanol and 15g of deionized water evenly, adjust the pH to 5 with acetic acid with a mass fraction of 8%, and hydrolyze in a constant temperature water bath at 40℃ for 70min to obtain pre-hydrolyzed solution B.

[0049] S13: Add 35g of para-aramid chopped fibers to pre-hydrolyzed solution A, stir and mix at 800rpm for 50min, heat to 60℃, react for 4h, cool to room temperature, filter, add to pre-hydrolyzed solution B, heat to 60℃, react for 5h, cool to room temperature, filter, wash twice with deionized water, wash once with anhydrous ethanol, dry at 80℃ to constant weight to obtain pretreated para-aramid chopped fibers;

[0050] S2: Under a nitrogen atmosphere, 21.9 g of m-phenylenediamine was dissolved in 600 g of N,N-dimethylacetamide containing calcium chloride. Then, 35 g of pretreated para-aramid chopped fibers were slowly added and stirred at 500 rpm for 60 min. The mixture was cooled to -10 °C and maintained at this temperature. Then, 43.1 g of isophthaloyl chloride was slowly added at a rate of 1 g / min, while stirring at 500 rpm during the addition process. After the addition was completed, the mixture was stirred for 55 min. After the reaction was completed, the pH of the system was adjusted to 7 using 10% calcium hydroxide. The mixture was then degassed under a vacuum of -0.08 MPa for 60 min to obtain the spinning solution.

[0051] The wet spinning process involves heating the spinning solution to 30°C and extruding it through a spinneret into a coagulation bath (a 10% N,N-dimethylacetamide aqueous solution heated to 30°C before use) to solidify and form nascent fibers. These fibers are then washed four times with deionized water, stretched 2.5 times in an 80°C hot water bath, dried at 100°C for 2 hours, and subsequently stretched 1.5 times on a hot plate at 320°C to obtain flame-retardant aramid fibers for fabrics.

[0052] The mass fraction of calcium chloride in N,N-dimethylacetamide is 4%.

[0053] Example 2

[0054] The method for preparing flame-retardant aramid fibers for fabrics in this embodiment includes the following steps:

[0055] S11: Mix 3g of silane coupling agent KH550, 90g of anhydrous ethanol and 10g of deionized water evenly, adjust the pH to 5.5 with 8% acetic acid, and hydrolyze in a constant temperature water bath at 20℃ for 50min to obtain pre-hydrolyzed solution A.

[0056] S12: Mix 2g of silane coupling agent KH-792, 1g of tetrakis(2-hydroxyethoxy)silane, 90g of anhydrous ethanol and 10g of deionized water evenly, adjust the pH to 5.5 with 8% acetic acid, and hydrolyze in a constant temperature water bath at 35℃ for 60min to obtain pre-hydrolyzed solution B.

[0057] S13: Add 30g of para-aramid chopped fiber to pre-hydrolyzed solution A, stir and mix at 800rpm for 50min, heat to 50℃, react for 5h, cool to room temperature, filter, add to pre-hydrolyzed solution B, heat to 50℃, react for 6h, cool to room temperature, filter, wash twice with deionized water, wash once with anhydrous ethanol, dry at 80℃ to constant weight to obtain pretreated para-aramid chopped fiber;

[0058] S2: Under a nitrogen atmosphere, 23.3 g of m-phenylenediamine was dissolved in 600 g of N,N-dimethylacetamide containing calcium chloride. Then, 30 g of pretreated para-aramid chopped fibers were slowly added and stirred at 500 rpm for 60 min. The mixture was cooled to -15°C and maintained at this temperature. Then, 46.7 g of isophthaloyl chloride was slowly added at a rate of 1 g / min while stirring at 500 rpm. After the addition was complete, the mixture was reacted for 60 min. After the reaction was completed, the pH of the system was adjusted to 7 using 10% calcium hydroxide. The mixture was then degassed under a vacuum of -0.08 MPa for 60 min to obtain the spinning solution.

[0059] The wet spinning process involves heating the spinning solution to 25°C and extruding it through a spinneret into a coagulation bath (a 10% N,N-dimethylacetamide aqueous solution heated to 25°C before use) to solidify and form nascent fibers. These fibers are then washed four times with deionized water and subjected to a first stretching process in an 80°C hot water bath, stretching 2.5 times. The stretched fibers are then dried at 100°C for 2 hours and subsequently stretched 1.5 times on a hot plate at 320°C to obtain flame-retardant aramid fibers for fabrics.

[0060] The mass fraction of calcium chloride in N,N-dimethylacetamide is 3%.

[0061] Example 3

[0062] The method for preparing flame-retardant aramid fibers for fabrics in this embodiment includes the following steps:

[0063] S11: Mix 5g of silane coupling agent KH550, 85g of anhydrous ethanol and 15g of deionized water evenly, adjust the pH to 5.5 with 8% acetic acid, and hydrolyze in a constant temperature water bath at 30℃ for 70min to obtain pre-hydrolyzed solution A.

[0064] S12: Mix 2g of silane coupling agent KH-792, 3g of tetrakis(2-hydroxyethoxy)silane, 85g of anhydrous ethanol and 15g of deionized water evenly, adjust the pH to 5.5 with 8% acetic acid, and hydrolyze in a constant temperature water bath at 45℃ for 80min to obtain pre-hydrolyzed solution B.

[0065] S13: Add 40g of para-aramid chopped fiber to pre-hydrolyzed solution A, stir and mix at 800rpm for 50min, heat to 50℃, react for 5h, cool to room temperature, filter, add to pre-hydrolyzed solution B, heat to 50℃, react for 6h, cool to room temperature, filter, wash twice with deionized water and once with anhydrous ethanol, dry at 80℃ to constant weight to obtain pretreated para-aramid chopped fiber;

[0066] S2: Under a nitrogen atmosphere, 19.9 g of m-phenylenediamine was dissolved in 600 g of N,N-dimethylacetamide containing calcium chloride. Then, 40 g of pretreated para-aramid chopped fibers were slowly added and stirred at 500 rpm for 60 min. The mixture was cooled to -15°C and maintained at this temperature. Then, 41.2 g of isophthaloyl chloride was slowly added at a rate of 1 g / min while stirring at 500 rpm. After the addition was complete, the mixture was reacted for 50 min. After the reaction was completed, the pH of the system was adjusted to 7 using 10% calcium hydroxide. The mixture was then degassed under a vacuum of -0.08 MPa for 60 min to obtain the spinning solution.

[0067] The wet spinning process involves heating the spinning solution to 25°C and extruding it through a spinneret into a coagulation bath (a 10% N,N-dimethylacetamide aqueous solution heated to 25°C before use) to solidify and form nascent fibers. These fibers are then washed four times with deionized water and subjected to a first stretching process in an 80°C hot water bath, stretching 2.5 times. The stretched fibers are then dried at 100°C for 2 hours and subsequently stretched 1.5 times on a hot plate at 320°C to obtain flame-retardant aramid fibers for fabrics.

[0068] The mass fraction of calcium chloride in N,N-dimethylacetamide is 5%.

[0069] Example 4

[0070] The difference between this embodiment and Embodiment 1 is that:

[0071] S12: Mix 2g of silane coupling agent KH-792, 2g of tetrakis(2-hydroxyethoxy)silane, 1g of diethylphosphorylethyltriethoxysilane, 85g of anhydrous ethanol and 15g of deionized water evenly, adjust the pH to 5 with 8% acetic acid, and hydrolyze in a constant temperature water bath at 40℃ for 70min to obtain pre-hydrolyzed solution B;

[0072] Everything else is the same as in Example 1.

[0073] Example 5

[0074] The difference between this embodiment and embodiment 4 is that:

[0075] S13: Add 35g of para-aramid chopped fibers to pre-hydrolyzed solution A, stir and mix at 800 rpm for 50 min, heat to 60℃, react for 4 h, cool to room temperature, filter, add to pre-hydrolyzed solution B, heat to 60℃, react for 5 h, cool to room temperature, filter, wash twice with deionized water and once with anhydrous ethanol, then slowly add 100g of 10% ammonium phytate aqueous solution, stir and mix at 800 rpm for 30 min, heat to 50℃, stir at 300 rpm for 90 min, filter, wash twice with deionized water and once with anhydrous ethanol, dry at 80℃ to constant weight to obtain pretreated para-aramid chopped fibers;

[0076] The rest is the same as in Example 4.

[0077] Example 6

[0078] The difference between this embodiment and embodiment 5 is as follows:

[0079] S12: Mix 2g of silane coupling agent KH-792, 2g of tetrakis(2-hydroxyethoxy)silane, 1g of diethylphosphorylethyltriethoxysilane, 0.1g of bismaleimide, 85g of anhydrous ethanol and 15g of deionized water evenly, adjust the pH to 5 with 8% acetic acid, and hydrolyze in a constant temperature water bath at 40℃ for 70min to obtain pre-hydrolyzed solution B;

[0080] The rest is the same as in Example 5.

[0081] Example 7

[0082] The difference between this embodiment and embodiment 6 is that:

[0083] S12: Mix 2g of silane coupling agent KH-792, 2g of tetrakis(2-hydroxyethoxy)silane, 2g of diethylphosphorylethyltriethoxysilane, 0.2g of bismaleimide, 85g of anhydrous ethanol and 15g of deionized water evenly, adjust the pH to 5 with 8% acetic acid, and hydrolyze in a constant temperature water bath at 40℃ for 70min to obtain pre-hydrolyzed solution B;

[0084] S13: Add 35g of para-aramid chopped fibers to pre-hydrolyzed solution A, stir and mix at 800 rpm for 50 min, heat to 60℃, react for 4 h, cool to room temperature, filter, add to pre-hydrolyzed solution B, heat to 60℃, react for 5 h, cool to room temperature, filter, wash twice with deionized water and once with anhydrous ethanol, then slowly add 100g of 15% ammonium phytate aqueous solution, stir and mix at 800 rpm for 30 min, heat to 70℃, stir at 300 rpm for 120 min, filter, wash twice with deionized water and once with anhydrous ethanol, dry at 80℃ to constant weight to obtain pretreated para-aramid chopped fibers;

[0085] The rest is the same as in Example 6.

[0086] Example 8

[0087] The difference between this embodiment and Embodiment 1 is that:

[0088] S2: Under a nitrogen atmosphere, 21.9 g of m-phenylenediamine was dissolved in 600 g of N,N-dimethylacetamide containing calcium chloride. Then, 35 g of pretreated para-aramid chopped fibers were slowly added and stirred at 500 rpm for 60 min. The mixture was cooled to -10 °C and maintained at this temperature. Then, 43.1 g of isophthaloyl chloride was slowly added at a rate of 1 g / min, while stirring at 500 rpm during the addition process. After the addition was completed, the mixture was stirred for 55 min. After the reaction was completed, the pH of the system was adjusted to 7 using 10% calcium hydroxide. The mixture was then degassed under a vacuum of -0.08 MPa for 60 min to obtain the spinning solution.

[0089] A wet spinning process was employed, in which the spinning solution was heated to 25°C and extruded through a spinneret into a coagulation bath (a 10% N,N-dimethylacetamide aqueous solution, heated to 25°C before use) to solidify and form nascent fibers. These fibers were then washed four times with deionized water and subjected to a first stretching of 2.5 times in an 80°C hot water bath. The stretched fibers were dried at 100°C for 2 hours, followed by a 1.5-fold stretching on a hot plate at 320°C. The fibers were then slowly added to a pre-decomposition solution C and stirred at 800 rpm for 30 minutes. The temperature was then raised to 50°C and stirred at 300 rpm for 2 hours. After filtration, the fibers were washed twice with deionized water and once with anhydrous ethanol, and then dried at 80°C to constant weight to obtain flame-retardant aramid fibers for fabrics.

[0090] The preparation method of pre-decomposition solution C includes the following steps:

[0091] 10g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 5g of tetra(2-hydroxyethoxy)silane, 180g of ethanol and 20g of deionized water were stirred and mixed evenly. The pH was adjusted to 5.5 with 8% acetic acid. The mixture was hydrolyzed in a constant temperature water bath at 35℃ for 60min. After cooling, the pre-decomposition solution C was obtained.

[0092] Everything else is the same as in Example 1.

[0093] Example 9

[0094] The difference between this embodiment and embodiment 8 is as follows:

[0095] S2: Under a nitrogen atmosphere, 21.9 g of m-phenylenediamine was dissolved in 600 g of N,N-dimethylacetamide containing calcium chloride. Then, 35 g of pretreated para-aramid chopped fibers were slowly added and stirred at 500 rpm for 60 min. The mixture was cooled to -10 °C and maintained at this temperature. Then, 43.1 g of isophthaloyl chloride was slowly added at a rate of 1 g / min, while stirring at 500 rpm during the addition process. After the addition was completed, the mixture was stirred for 55 min. After the reaction was completed, the pH of the system was adjusted to 7 using 10% calcium hydroxide. The mixture was then degassed under a vacuum of -0.08 MPa for 60 min to obtain the spinning solution.

[0096] A wet spinning process was employed, in which the spinning solution was heated to 25°C and extruded through a spinneret into a coagulation bath (a 10% N,N-dimethylacetamide aqueous solution, heated to 25°C before use) to solidify and form nascent fibers. These fibers were then washed four times with deionized water and subjected to a first stretching of 2.5 times in an 80°C hot water bath. The stretched fibers were dried at 100°C for 2 hours, followed by a 1.5-fold stretching on a hot plate at 320°C. The fibers were then slowly added to a pre-decomposition solution C and stirred at 800 rpm for 30 minutes. The temperature was then raised to 70°C and stirred at 300 rpm for 1 hour. After filtration, the fibers were washed twice with deionized water and once with anhydrous ethanol, and dried at 80°C to constant weight to obtain flame-retardant aramid fibers for fabrics.

[0097] The preparation method of pre-decomposition solution C includes the following steps:

[0098] 15g of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide, 10g of tetra(2-hydroxyethoxy)silane, 170g of ethanol and 30g of deionized water were stirred and mixed evenly. The pH was adjusted to 5 with 8% acetic acid. The mixture was hydrolyzed in a constant temperature water bath at 40℃ for 80min. After cooling, the pre-decomposition solution C was obtained.

[0099] The rest is the same as in Example 8.

[0100] Comparative Example 1

[0101] The preparation method of the flame-retardant aramid fiber used in this comparative example includes the following steps:

[0102] S11: Mix 4g of silane coupling agent KH550, 85g of anhydrous ethanol and 15g of deionized water evenly, adjust the pH to 5 with 8% acetic acid, and hydrolyze in a constant temperature water bath at 25℃ for 60min to obtain pre-hydrolyzed solution A.

[0103] S12: Add 35g of para-aramid short-cut fiber to pre-hydrolyzed solution A, stir and mix at 800rpm for 50min, heat to 60℃, react for 4h, cool to room temperature, filter, wash twice with deionized water and once with anhydrous ethanol, dry at 80℃ to constant weight to obtain pretreated para-aramid short-cut fiber.

[0104] S2: Under a nitrogen atmosphere, 21.9 g of m-phenylenediamine was dissolved in 600 g of N,N-dimethylacetamide containing calcium chloride. Then, 35 g of pretreated para-aramid chopped fibers were slowly added and stirred at 500 rpm for 60 min. The mixture was cooled to -10 °C and maintained at this temperature. Then, 43.1 g of isophthaloyl chloride was slowly added at a rate of 1 g / min, while stirring at 500 rpm during the addition process. After the addition was completed, the mixture was stirred for 55 min. After the reaction was completed, the pH of the system was adjusted to 7 using 10% calcium hydroxide. The mixture was then degassed under a vacuum of -0.08 MPa for 60 min to obtain the spinning solution.

[0105] The wet spinning process involves heating the spinning solution to 30°C and extruding it through a spinneret into a coagulation bath (a 10% N,N-dimethylacetamide aqueous solution heated to 30°C before use) to solidify and form nascent fibers. These fibers are then washed four times with deionized water, stretched 2.5 times in an 80°C hot water bath, dried at 100°C for 2 hours, and subsequently stretched 1.5 times on a hot plate at 320°C to obtain flame-retardant aramid fibers for fabrics.

[0106] The mass fraction of calcium chloride in N,N-dimethylacetamide is 4%.

[0107] Comparative Example 2

[0108] The difference between this comparative example and Example 1 is as follows:

[0109] S2: Under a nitrogen atmosphere, 21.9 g of m-phenylenediamine was dissolved in 600 g of N,N-dimethylacetamide containing calcium chloride, cooled to -10°C, and maintained at this temperature. Then, 43.1 g of isophthaloyl chloride was slowly added at a rate of 1 g / min, while stirring at 500 rpm. After the addition was complete, the mixture was stirred for 55 min. After the reaction was completed, the pH of the system was adjusted to 7 using 10% calcium hydroxide. Then, 35 g of pretreated para-aramid chopped fibers was slowly added and stirred at 500 rpm for 60 min. The mixture was then degassed under a vacuum of -0.08 MPa for 60 min to obtain the spinning solution.

[0110] The wet spinning process involves heating the spinning solution to 30°C and extruding it through a spinneret into a coagulation bath (a 10% N,N-dimethylacetamide aqueous solution heated to 30°C before use) to solidify and form nascent fibers. These fibers are then washed four times with deionized water, stretched 2.5 times in an 80°C hot water bath, dried at 100°C for 2 hours, and subsequently stretched 1.5 times on a hot plate at 320°C to obtain flame-retardant aramid fibers for fabrics.

[0111] Everything else is the same as in Example 1.

[0112] Performance testing

[0113] The fabrics prepared in Examples 1-9 and Comparative Examples 1-2 were tested for breaking strength, breaking elongation, limiting oxygen index (LOI), dry heat shrinkage at 320℃, and washability using flame-retardant aramid fibers. The results are shown in Table 1.

[0114] Table 1 Performance testing of flame-retardant aramid fibers for fabrics prepared in Examples 1-9 and Comparative Examples 1-2

[0115]

[0116] The comparison between Examples 1-3 and Comparative Examples 1-2 shows that pre-optimization of the multi-level silane / organosilicon hybrid interface layer of para-aramid chopped fibers not only achieves efficient stress transfer and relaxation through strong interfacial bonding, thereby improving fiber breaking strength and elongation at break and reducing dry heat shrinkage, but more importantly, it provides a guarantee for subsequent successful in-situ polymerization, enabling the flame retardant components to achieve uniform molecular-level distribution within the fiber, thus significantly improving the limiting oxygen index and washability.

[0117] A comparison of Examples 1 and 4-7 shows that, based on the optimized interface, the introduction of phosphorus-containing silanes and / or bismaleimide, along with ammonium phytate pretreatment, into pre-decomposition solution B achieves a synergistic gain in flame retardancy and mechanical properties. The synergistic effect of phosphorus-containing silanes and ammonium phytate significantly improves the limiting oxygen index; the thermal crosslinking of bismaleimide significantly strengthens the fiber bulk and interface, jointly contributing to a further increase in breaking strength and a reduction in dry heat shrinkage. Notably, the multi-point strong anchoring of ammonium phytate and the crosslinking network of bismaleimide jointly ensure the long-lasting stability of the flame-retardant components, exhibiting excellent and stable wash resistance.

[0118] The comparison between Example 1 and Examples 8-9 shows that the finishing process of 9,10-dihydro-9-oxa-10-phosphaphenanthrene-10-oxide and tetra(2-hydroxyethoxy)silane does not destroy the stable internal structure, and the elongation at break and dry heat shrinkage remain basically stable. The interfacial bonding force between the surface coating and the fiber body is weaker than the internal bonding during pretreatment. The coating may generate micro-cracks during stretching, resulting in a slight decrease in breaking strength. The flame-retardant coating attached to the surface is prone to slight peeling during washing, resulting in a significantly lower limiting oxygen index retention rate than in Example 1.

[0119] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A method for preparing flame-retardant aramid fibers for fabrics, characterized in that, Includes the following steps: S1: The para-aramid chopped fibers are immersed in pre-hydrolyzed solution A, heated to 50-70℃, reacted for 3-5 hours, and after solid-liquid separation, immersed in pre-hydrolyzed solution B, heated to 50-70℃, reacted for 4-6 hours, and after solid-liquid separation and washing, immersed in 10%-15% ammonium phytate aqueous solution, heated to 50-70℃, mixed for 90-120 minutes, and after solid-liquid separation, washing, and drying, pretreated para-aramid chopped fibers are obtained. S2: Under an inert atmosphere, m-phenylenediamine is dissolved in N,N-dimethylacetamide containing calcium chloride, and then pretreated para-aramid chopped fibers are added. After mixing evenly, the mixture is cooled to -15~-10℃, and then isophthaloyl chloride is added. The mixture is then reacted for 50~60 minutes, neutralized, and degassed to obtain a spinning solution. A wet spinning process is used, followed by solidification in a coagulation bath, washing, and stretching to obtain flame-retardant aramid fibers for fabrics. The pre-hydrolyzed solution A comprises monoaminosilane, ethanol, and water; The pre-hydrolyzed solution B comprises diaminosilane, tetra(2-hydroxyethoxy)silane, phosphorus-containing silane, bismaleimide, ethanol, and water.

2. The method for preparing flame-retardant aramid fiber for fabrics according to claim 1, characterized in that, The total mass ratio of m-phenylenediamine and isophthaloyl chloride to the pretreated para-aramid chopped fibers is (60~70):(30~40).

3. The method for preparing flame-retardant aramid fiber for fabrics according to claim 2, characterized in that, The molar ratio of m-phenylenediamine to isophthaloyl chloride is 1:(1.05~1.1).

4. The method for preparing flame-retardant aramid fiber for fabrics according to claim 1, characterized in that, The preparation method of the pre-hydrolyzed solution A includes the following steps: Mix monoaminosilane, ethanol and water in a mass ratio of (3~5):(85~90):(10~15) until homogeneous, adjust the pH to 5~5.5, and hydrolyze at 20~30℃ for 50~70 min to obtain pre-hydrolyzed solution A.

5. The method for preparing flame-retardant aramid fiber for fabrics according to claim 1, characterized in that, The preparation method of the pre-hydrolyzed solution B includes the following steps: Diaminosilane, tetra(2-hydroxyethoxy)silane, ethanol and water are mixed evenly in a mass ratio of 2:(1~3):(85~90):(10~15), the pH is adjusted to 5~5.5, and hydrolyzed at 35~45℃ for 60~80 min to obtain pre-hydrolyzed solution B.

6. The method for preparing flame-retardant aramid fiber for fabrics according to claim 1, characterized in that, The mass ratio of the phosphorus-containing silane to the diaminosilane is (0.5~1.0):

1.

7. The method for preparing flame-retardant aramid fiber for fabrics according to claim 6, characterized in that, The phosphorus-containing silane is diethylphosphorylethyltriethoxysilane.

8. The method for preparing flame-retardant aramid fiber for fabrics according to claim 1, characterized in that, The mass ratio of bismaleimide to bisaminosilane is (0.05~0.1):

1.

9. A flame-retardant aramid fiber for fabric prepared by the method described in claims 1 to 8.

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