Antibacterial flame-retardant nylon fiber and preparation method thereof

Abstract

The present application relates to the technical field of nylon fiber, and more particularly to an antibacterial and flame-retardant nylon fiber and a preparation method thereof, comprising the following steps: S1, in-situ polymerization modification of nylon chip with phosphorus-nitrogen functional monomer; S2, in-situ construction of copper ion coordination and antibacterial functional layer; S3, surface grafting and thermal crosslinking of the dense crosslinked flame-retardant antibacterial layer of the skin layer; and S4, thermal relaxation and functional activation. The present application realizes chemical bonding and coupling of the antibacterial function and the flame-retardant function at the molecular level through the composite technology of in-situ polymerization covalent grafting, copper-phosphorus-nitrogen ternary coordination chelation and three-dimensional thermal crosslinking of the surface layer, and discards the traditional modification mode of physical blending and simple superposition. Meanwhile, the copper ion can catalyze the phosphorus-nitrogen system to form carbon at high temperature, so that the residual carbon rate is improved, the positive synergy of antibacterial without weakening flame retardant and flame retardant without inhibiting antibacterial is realized, and the core problem of mutual interference and low effect of the existing antibacterial and flame-retardant nylon fiber is solved.

Description

Technical Field

[0001] This invention relates to the field of nylon fiber technology, and in particular to an antibacterial and flame-retardant nylon fiber and its preparation method. Background Technology

[0002] Nylon, also known as nylon or nylon fiber, is one of the earliest synthetic fibers to be industrialized. It has now become the second largest synthetic fiber for apparel after polyester. As an apparel fabric, nylon fiber has good mechanical properties, is lightweight and soft, and is widely used in underwear, socks and other close-fitting fabrics, as well as functional fabrics such as mountaineering clothing and bag fabrics.

[0003] Existing functional modification technologies for nylon mainly employ blend spinning to modify nylon. Currently, in the process of preparing antibacterial and flame-retardant nylon fibers, the antibacterial agent, flame retardant, and nylon chips are directly blended and spun together. This process suffers from problems such as uneven dispersion of functional components, poor compatibility, easy precipitation, and rapid functional decay. Therefore, it is necessary to design an antibacterial and flame-retardant nylon fiber. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of this invention is to provide an antibacterial and flame-retardant nylon fiber and its preparation method.

[0005] The technical solution adopted in this invention is: a method for preparing antibacterial and flame-retardant nylon fiber, comprising the following steps:

[0006] S1. In-situ polymerization modification of nylon chips with phosphorus-nitrogen functional monomers: Dry nylon chips, phosphorus-containing monomers, and nitrogen-containing monomers are mixed in a mass ratio of 100:5-15:5-15. An ester exchange catalyst is added, and the mixture is reactively melt-blended in a twin-screw extruder at 240℃-270℃ for 3-8 minutes. After amide exchange reaction, phosphorus and nitrogen side groups are covalently grafted onto the nylon molecular chain. After water cooling and pelletizing, modified nylon chips are obtained.

[0007] S2. In-situ construction of copper ion coordination and antibacterial functional layer: The modified nylon chips are immersed in an ethanol aqueous solution of copper salt and imidazole ligand, stirred at 50℃-80℃ for 2-6 hours, washed and dried to obtain copper ion coordination modified nylon chips.

[0008] S3. Surface grafting and thermal crosslinking of dense crosslinked flame retardant and antibacterial skin layer: The copper ion coordination modified nylon chips are mixed with ordinary nylon chips and melt-spun to obtain nascent fibers. The nascent fibers are then impregnated with a finishing solution containing crosslinking agent and catalyst and thermally crosslinked to form a three-dimensional crosslinked network skin layer on the fiber surface.

[0009] S4. Thermal relaxation and functional activation: The cross-linked fibers are heat-treated at 120℃-140℃ under tension-free conditions for 30-60 minutes to complete stress relaxation and functional activation, thereby obtaining antibacterial and flame-retardant nylon fibers.

[0010] As a further description of the above technical solution:

[0011] In step S1, the phosphorus-containing monomer is selected from one or more of dimethyl methylphosphonate, hydroxyethylmethylene diphosphonic acid, and vinylphosphonic acid; the nitrogen-containing monomer is selected from one or more of acrylamide, N-hydroxymethylacrylamide, and dimethylaminoethyl methacrylate.

[0012] As a further description of the above technical solution:

[0013] In step S1, the transesterification catalyst is selected from one of tetrabutyl titanate, isopropyl titanate, dibutyltin oxide, and monobutyltin oxide. The amount of the transesterification catalyst used is 0.3%-1.5% of the total mass of the phosphorus-containing monomer and the nitrogen-containing monomer.

[0014] As a further description of the above technical solution:

[0015] In step S2, the copper salt is selected from copper acetate, copper lactate, and copper gluconate, and the concentration is 0.05-0.5 mol / L; the imidazole ligand is selected from 2-methylimidazolium, benzimidazole, and imidazole-2-carboxaldehyde, and the mass ratio of the imidazole ligand to the copper salt is 1-3:1.

[0016] As a further description of the above technical solution:

[0017] In step S2, the ethanol-water solution is composed of ethanol and water, and the volume ratio of ethanol to water is 1:1.

[0018] As a further description of the above technical solution:

[0019] In step S3, the mass ratio of copper ion coordination modified nylon chips to ordinary nylon chips is 30-70:30-70; the melt spinning temperature is 250℃-290℃, and the draw ratio is 2.5-4.0 times; the crosslinking agent is selected from melamine-formaldehyde prepolymer and hexamethoxymethylmelamine, with a concentration of 1-5wt%; the catalyst is selected from ammonium chloride and ammonium dihydrogen phosphate, with a concentration of 0.1-0.5wt%.

[0020] As a further description of the above technical solution:

[0021] In step S3, the impregnation temperature is 80℃-100℃ and the time is 5-20 minutes; the thermal crosslinking temperature is 130℃-160℃, the tension is 1.0-2.0 cN / dtex, and the time is 2-10 minutes.

[0022] An antibacterial and flame-retardant nylon fiber is prepared according to the above-described method for preparing antibacterial and flame-retardant nylon fiber. From the inside out, it consists of a pure nylon core layer, a phosphorus-nitrogen covalently grafted and copper-coordinated intermediate transition layer, and a three-dimensional cross-linked network skin layer.

[0023] The present invention has the following beneficial effects:

[0024] 1. This invention utilizes in-situ polymerization covalent grafting, copper-phosphorus-nitrogen ternary coordination chelation, and surface three-dimensional thermal cross-linking composite technology to achieve chemical bonding and coupling of antibacterial and flame-retardant functions at the molecular level, abandoning the traditional physical blending and simple superposition modification methods. The copper ions at the antibacterial end are doubly bound by phosphorus-nitrogen coordination anchoring and cross-linking networks, achieving controlled slow release, thus extending the copper ion release half-life and improving the antibacterial effect. At the flame-retardant end, the fiber forms a three-layer synergistic flame-retardant system: an outer dense char layer for barrier, a middle expansion and foaming for flame suppression, and an inner covalent char formation for assistance. Compared to traditional single-component flame retardants, this significantly improves the flame-retardant effect. Simultaneously, copper ions can catalyze the rapid char formation of the phosphorus-nitrogen system at high temperatures, increasing the char residue rate. This achieves a positive synergy where antibacterial properties do not weaken flame retardancy, and flame retardancy does not inhibit antibacterial properties, solving the core problem of mutual interference and low effectiveness of existing antibacterial and flame-retardant nylon fibers.

[0025] 2. The antibacterial and flame-retardant functional components of the present invention are fixed by covalent grafting, coordination chelation, and cross-linked network physical coating to form an inseparable whole with the nylon matrix, fundamentally solving the defects of easy precipitation and easy fall-off in traditional blend spinning and finishing, and greatly improving the durability of fiber function. Detailed Implementation

[0026] The present invention provides a method for preparing antibacterial and flame-retardant nylon fiber, comprising the following steps:

[0027] S1. In-situ polymerization modification of nylon chips using phosphorus-nitrogen functional monomers: Dry nylon chips, phosphorus-containing monomers, and nitrogen-containing monomers are mixed at a mass ratio of 100:5-15:5-15. An ester exchange catalyst is added, and the mixture is reactively melt-blended at 240℃-270℃ for 3-8 minutes in a twin-screw extruder. After amide exchange reaction, phosphorus and nitrogen side groups are covalently grafted onto the nylon molecular chain. After water cooling and pelletizing, modified nylon chips are obtained. The phosphorus-containing monomer is selected from one or more of dimethyl methylphosphonate, hydroxyethylmethylene diphosphonic acid, and vinylphosphonic acid. The nitrogen-containing monomer is selected from one or more of acrylamide, N-hydroxymethylacrylamide, and dimethylaminoethyl methacrylate. The ester exchange catalyst is selected from one of tetrabutyl titanate, isopropyl titanate, dibutyltin oxide, and monobutyltin oxide. The amount of ester exchange catalyst is 0.3%-1.5% of the total mass of the phosphorus-containing monomers and nitrogen-containing monomers.

[0028] S2. In-situ construction of copper ion coordination and antibacterial functional layer: Modified nylon chips were immersed in an ethanol-water solution of copper salt and imidazole ligand, and stirred at 50℃-80℃ for 2-6 hours. After washing and drying, copper ion-coordinated modified nylon chips were obtained. The ethanol-water solution consisted of ethanol and water in a volume ratio of 1:1. The copper salt was selected from copper acetate, copper lactate, and copper gluconate, with a concentration of 0.05-0.5 mol / L. The imidazole ligand was selected from 2-methylimidazolium, benzimidazole, and imidazole-2-carboxaldehyde, with a mass ratio of imidazole ligand to copper salt of 1-3:1.

[0029] S3. Surface grafting and thermal crosslinking of the dense crosslinked flame-retardant and antibacterial layer: Copper ion-modified nylon chips are mixed with ordinary nylon chips, and nascent fibers are obtained by melt spinning. The nascent fibers are then impregnated with a finishing solution containing a crosslinking agent and catalyst, and thermally crosslinked to form a three-dimensional crosslinked network skin on the fiber surface. The mass ratio of copper ion-modified nylon chips to ordinary nylon chips is 30-70:30-70; the melt spinning temperature is 250℃-290℃. The elongation ratio is 2.5-4.0 times; the crosslinking agent is selected from melamine-formaldehyde prepolymer and hexamethoxymethylmelamine, with a concentration of 1-5 wt%; the catalyst is selected from ammonium chloride and ammonium dihydrogen phosphate, with a concentration of 0.1-0.5 wt%; the impregnation treatment temperature is 80℃-100℃, and the time is 5-20 minutes; the thermal crosslinking treatment temperature is 130℃-160℃, the tension is 1.0-2.0 cN / dtex, and the time is 2-10 minutes.

[0030] S4. Thermal relaxation and functional activation: The cross-linked fibers are heat-treated at 120℃-140℃ under tension-free conditions for 30-60 minutes to complete stress relaxation and functional activation, thereby obtaining antibacterial and flame-retardant nylon fibers.

[0031] Mechanism of action:

[0032] Antibacterial mechanism: Copper ions disrupt the integrity of bacterial cell membranes by binding to negatively charged groups, and then enter the cell to bind to proteins and nucleic acids, leading to microbial death. This invention utilizes both coordination anchoring (copper ions coordinating with phosphorus and nitrogen atoms) and cross-linking networks to extend the release half-life of copper ions, achieving long-term sustained-release antibacterial action.

[0033] Flame retardant mechanism: When the fiber is heated and burned, the outer cross-linked network first forms a dense carbon layer to prevent oxygen and heat from being transferred inward; the phosphorus-nitrogen coordination network in the middle layer further expands and foams, releasing non-flammable gases such as NH3, N2, and CO2 to dilute the oxygen, while phosphorus compounds promote char formation; the grafted phosphorus-nitrogen groups in the innermost layer also participate in char formation.

[0034] Copper-phosphorus-nitrogen synergistic flame retardancy enhancement: Copper ions can catalyze the cross-linking of phosphate esters into char at high temperatures, thereby reducing the char formation temperature and improving the density and thermal stability of the char layer.

[0035] Gradient interface and good mechanical properties: The three layers are chemically transitioned through covalent and coordination bonds, avoiding the interface delamination problem of traditional core-sheath structures, resulting in uniform stress distribution and meeting the requirements of textile processing.

[0036] Example 1

[0037] A method for preparing antibacterial and flame-retardant nylon fiber includes the following steps:

[0038] S1. In-situ polymerization modification of nylon chips with phosphorus-nitrogen functional monomers: Nylon chips are dried in a vacuum drying oven at 85℃ for 12 hours until the moisture content is ≤0.05%; Nylon chips: dimethyl methylphosphonate: acrylamide = 100:10:10 by mass ratio are mixed, and tetrabutyl titanate is added (the amount is 1.0% of the total mass of phosphorus and nitrogen monomers); The temperature settings of each zone of the twin-screw extruder are 245℃, 255℃, 260℃, 255℃, and 250℃, and reactive melt blending is performed for 5 minutes. Phosphorus and nitrogen side groups are covalently grafted onto the nylon molecular chain through amide exchange reaction; after water cooling and pelletizing, modified nylon chips are obtained.

[0039] S2. In-situ construction of copper ion coordination and antibacterial functional layer: Modified nylon chips were immersed in an ethanol aqueous solution of 0.2 mol / L copper acetate and 2-methylimidazole (mass ratio 1:2) and stirred at 65℃ and 300 r / min for 4 h. Phosphorus-nitrogen functional groups were coordinated and chelated with copper ions to form a 120 nm copper-phosphorus-nitrogen ternary coordination network layer on the surface. After the reaction, the chips were washed three times each with anhydrous ethanol and deionized water, and then vacuum dried at 80℃ for 6 h to obtain copper ion coordination modified nylon chips.

[0040] S3. Surface grafting and thermal crosslinking of dense crosslinked flame-retardant and antibacterial skin layer: Copper ion coordination modified nylon chips and ordinary nylon chips are mixed (mass ratio of copper ion coordination modified nylon chips to ordinary nylon chips is 50:50), and melt-spun at 270℃ (spinneret orifice diameter 0.25mm, orifice number 48), and nascent fibers are obtained by two-stage drawing with 3.0 times; then the nascent fibers are immersed in a finishing solution containing 3wt% melamine-formaldehyde prepolymer and 0.3wt% ammonium chloride, and impregnated at 90℃ for 10min; subsequently, thermal crosslinking is performed at 145℃ and 1.5cN / dtex tension for 5min to form a three-dimensional crosslinked network skin layer on the fiber surface.

[0041] S4. Thermal relaxation and functional activation: The cross-linked fiber is placed in a tension-free relaxation heat setting machine at 130℃ for 45 minutes to eliminate internal stress, improve the cross-linking network, and activate the antibacterial activity of copper ions to obtain the target antibacterial and flame-retardant nylon fiber.

[0042] Example 2

[0043] A method for preparing antibacterial and flame-retardant nylon fiber includes the following steps:

[0044] S1. In-situ polymerization of phosphorus-nitrogen functional monomers to modify nylon chips: Nylon chips were vacuum dried at 85℃ for 12h; nylon chips: hydroxyethylmethylene diphosphonic acid: N-hydroxymethylacrylamide = 100:8:12 by mass ratio, and dibutyltin oxide (0.8%) was added; the mixture was co-mixed at 265℃ in a twin-screw extruder for 4min, and phosphorus and nitrogen side groups were covalently grafted onto the nylon molecular chain through an amide exchange reaction; after water cooling and pelletizing, modified nylon chips were obtained.

[0045] S2. In-situ construction of copper ion coordination and antibacterial functional layer: Modified slices were immersed in a 0.3 mol / L mixture of copper lactate and benzimidazole (mass ratio 1:3) and reacted at 70℃ for 3 h. A 180 nm coordination network layer was formed on the surface, and copper ion coordination modified nylon slices were obtained.

[0046] S3. Surface grafting and thermal crosslinking of dense crosslinked flame-retardant and antibacterial layer: Copper ion coordination modified nylon chips and ordinary nylon chips are mixed (mass ratio of copper ion coordination modified nylon chips to ordinary nylon chips is 60:40), spun at 280℃ and drawn 3.5 times; immersed in a finishing solution containing 4wt% melamine-formaldehyde prepolymer and 0.4wt% ammonium dihydrogen phosphate, impregnated at 95℃ for 8min, thermally crosslinked at 150℃ for 4min, and then thermally crosslinked at 145℃ and 1.5cN / dtex tension for 5min to form a three-dimensional crosslinked network skin on the fiber surface.

[0047] S4. Thermal relaxation and functional activation: Cross-linked fibers are subjected to tension-free heat treatment at 135℃ for 40 minutes to obtain antibacterial and flame-retardant nylon fibers.

[0048] Example 3

[0049] A method for preparing antibacterial and flame-retardant nylon fiber includes the following steps:

[0050] S1. In-situ polymerization of phosphorus-nitrogen functional monomers to modify nylon chips: Nylon chips were vacuum dried at 85℃ for 12h; Nylon chips: vinylphosphonic acid: dimethylaminoethyl methacrylate = 100:12:8 by mass ratio were mixed, and monobutyltin oxide (1.2%) was added; The mixture was stirred for 6min at 250℃ using a twin-screw extruder, and after water cooling and pelletizing, modified nylon chips were obtained.

[0051] S2. In-situ construction of copper ion coordination and antibacterial functional layer: Modified nylon chips were immersed in a mixture of 0.15 mol / L copper gluconate and imidazole-2-carboxaldehyde (mass ratio 1:1) and reacted at 60℃ for 5 h. An 80 nm coordination network layer was formed on the surface, thus obtaining copper ion coordination modified nylon chips.

[0052] S3. Surface grafting and thermal crosslinking of dense crosslinked flame-retardant and antibacterial layer: Copper ion coordination modified nylon chips and ordinary nylon chips are mixed (mass ratio of copper ion coordination modified nylon chips to ordinary nylon chips is 40:60), spun at 265℃ and drawn 2.8 times; immersed in a finishing solution containing 2wt% hexamethoxymethyl melamine and 0.2wt% ammonium chloride, impregnated at 85℃ for 15min, and then thermally crosslinked at 140℃ and 1.5cN / dtex tension for 5min to form a three-dimensional crosslinked network skin on the fiber surface.

[0053] S4. Thermal relaxation and functional activation: Cross-linked fibers are subjected to tension-free heat treatment at 125℃ for 50 minutes to obtain antibacterial and flame-retardant nylon fibers.

[0054] Comparative Example 1 (Traditional physical blending and spinning, without chemical bonding)

[0055] Nylon chips were directly physically blended with silver ion antibacterial agent and phosphorus-based flame retardant at a mass ratio of 100:2:8, melt-spun at 270℃, and drawn 3.0 times without in-situ polymerization, copper coordination, surface crosslinking and thermal relaxation treatment to obtain comparative fibers.

[0056] Comparative Example 2 (no copper ion coordination, only phosphorus-nitrogen modification)

[0057] Step 2, the copper ion coordination process in Example 1, was omitted. The remaining raw materials, processes, and parameters were completely consistent with those in Example 1, and a comparison fiber without copper coordination was obtained.

[0058] Comparative Example 3 (no surface cross-linking, only copper-phosphorus-nitrogen coordination)

[0059] The surface grafting thermal crosslinking process in step 3 of Example 1 is omitted, while the remaining raw materials, processes, and parameters are completely consistent with those in Example 1, resulting in a control fiber without a crosslinked skin.

[0060] Test method:

[0061] Antibacterial performance test:

[0062] Standard: GB / T20944.3-2008 Evaluation of antimicrobial properties of textiles – Part 3: Vibration method

[0063] Bacterial strains: Staphylococcus aureus (ATCC6538), Escherichia coli (ATCC25922)

[0064] Procedure: Weigh 0.75g of fiber sample, add 70mL of phosphate buffer, and inoculate with 1mL of bacterial suspension (concentration 1×10^5 CFU / mL); shake at 24℃ and 150r / min for 18h; calculate the viable count using the plate count method and calculate the inhibition rate according to the formula.

[0065] Wash resistance and antibacterial properties: Washed 50 times with water according to GB / T12490-2007 (40℃, 0.2% standard detergent, 45min each time), and the antibacterial rate was retested.

[0066] Flame retardant performance test:

[0067] Limiting Oxygen Index (LOI): GB / T5454-1997, sample size 150mm×6.5mm×3mm, tested with an oxygen index meter.

[0068] Vertical combustion: GB / T5455-2014, sample size 300mm×80mm, record self-extinguishing time and melt dripping.

[0069] Carbon residue rate: Thermogravimetric analyzer (TGA), nitrogen atmosphere, temperature rise 10℃ / min to 800℃, carbon residue rate was tested.

[0070] Heat release rate: cone calorimeter, radiant power 35kW / m² 2 The peak heat release rate was tested.

[0071] Mechanical property testing:

[0072] Standard: GB / T14337-2008 "Test Method for Tensile Properties of Synthetic Fiber Filaments"

[0073] Procedure: Clamping distance 200mm, tensile speed 200mm / min, test breaking strength and elongation at break.

[0074] Copper ion release half-life test:

[0075] Methods: The fibers were soaked in deionized water at 37℃, and the soaking solution was taken periodically; the copper ion concentration was tested by ICP-OES, the release curve was plotted, and the copper ion release half-life was calculated.

[0076] Table 1 shows the relevant experimental data.

[0077]

[0078] Experimental Analysis:

[0079] Antibacterial performance analysis: As shown in Table 1, Examples 1-3 all achieved an initial inhibition rate of 99.9% against Staphylococcus aureus and Escherichia coli, reaching the highest level of antibacterial performance for textiles. This is due to the copper-phosphorus-nitrogen ternary coordination network formed on the fiber surface, which can rapidly destroy bacterial cell membranes and kill pathogens by relying on the antibacterial active center of copper ions. Moreover, the coordination network is evenly distributed and has sufficient active sites. Combined with the stable complex formed by imidazole ligands and copper ions, the antibacterial timeliness and effectiveness are maximized. In Comparative Example 1, due to the physical blending of silver ions and phosphorus-based flame retardants without coordination and covalent anchoring, the antibacterial agent was unevenly dispersed, resulting in an initial inhibition rate of only 91.8%-92.3%. Comparative Example 2 omitted the copper ion coordination process and had no antibacterial active center, resulting in an initial inhibition rate of only 92.6%-93.5%. Neither of them reached the high-efficiency antibacterial standard. Although Comparative Example 3 retained the copper coordination structure to achieve an initial inhibition rate of 99.9%, the lack of a surface cross-linking network meant that it could only provide short-term antibacterial protection. After 50 standard water washes, Examples 1-3 still maintained an antibacterial rate of ≥95.1% against the two pathogenic bacteria and a functional retention rate of over 95%. This is because copper ions are firmly anchored to phosphorus-nitrogen functional groups through coordination bonds, combined with the physical barrier effect of the three-dimensional cross-linked network on the surface, and the three-layer gradient chemical bonding structure allows the antibacterial components to be integrated with the fiber matrix, fundamentally preventing water loss and achieving controlled slow release. In contrast, Comparative Example 1, due to physical blending without chemical bonding, experienced a large dissolution of silver ions after water washing, resulting in a sharp drop in the antibacterial rate to 59.4%-61.2%. Comparative Example 2, lacking copper ion antibacterial components, had an antibacterial rate of only 67.2%-68.7% after water washing. Comparative Example 3, lacking cross-linked network protection, experienced rapid release of copper ions, resulting in an antibacterial rate of 71.5%-72.3% after water washing. The antibacterial durability of all three examples was far inferior to that of the Examples. In addition, Examples 1-3 have a highly effective killing effect on both Gram-positive and Gram-negative bacteria, with excellent broad-spectrum antibacterial properties. Moreover, the antibacterial performance does not decrease after being placed in a humid environment at room temperature for 6 months. The long-term stability of the copper-phosphorus-nitrogen coordination structure can fully meet the long-term use requirements of intimate apparel and medical textiles.

[0080] Flame retardant performance analysis, as shown in Table 1, reveals that the limiting oxygen indices (LOIs) of Examples 1-3 are 33.5%, 34.2%, and 32.8%, respectively, all ≥32% and significantly higher than the 22% of ordinary nylon, meeting the standard for flame-retardant materials. This is attributed to the combined effect of the synergistic flame retardant system of the fiber core-transition-skin layers, and the rapid formation of a dense char layer by the phosphorus-nitrogen system catalyzed by copper ions at high temperature, which significantly improves the flame retardant efficiency. Comparative Example 1, due to uneven physical blending and poor compatibility of the flame retardant, has an LIO of only 26.7%, still classifying it as a combustible material. Comparative Example 2, lacking copper ion catalysis, suffers from low char formation efficiency in the phosphorus-nitrogen system, resulting in an LIO of only 28.3%. Comparative Example 3, lacking a surface cross-linking network, cannot form a continuous char layer, resulting in an LIO of only 29.6%. None of these three examples meet the flame-retardant standard. In the vertical combustion test, Examples 1-3 exhibited a self-extinguishing time ≤1.5 seconds and no molten dripping, meeting the GB / T5455-2014 B1 flame retardant standard. The core of this is the rapid formation of a rigid, dense char layer from the surface cross-linked network, locking in the molten components. The intermediate phosphorus-nitrogen coordination layer releases non-combustible gases upon heating, diluting oxygen. Furthermore, the synergistic char formation of copper, phosphorus, and nitrogen results in a high-strength, non-detachable char layer, achieving rapid self-extinguishing. In contrast, Comparative Example 1 showed severe molten dripping and a self-extinguishing time exceeding 10 seconds; Comparative Example 2 exhibited a small amount of molten dripping and a self-extinguishing time of 4.8 seconds; and Comparative Example 3 showed significant molten dripping and a self-extinguishing time of 3.2 seconds, all posing significant safety hazards. At 800℃, Examples 1-3 achieved a char residue rate of 36.9%-41.2%, more than 50% higher than Comparative Example 2, with a peak heat release rate of only 162-201 kW / m³. 2 Compared to Comparative Example 1, the carbonization temperature was reduced by more than 40%. This is the result of copper ion catalysis lowering the carbonization temperature and improving carbon layer performance, combined with the synergistic carbonization of the three layers and the uniform carbonization of covalently grafted phosphorus-nitrogen segments. In contrast, Comparative Example 1 had a residual carbon rate of only 18.2% and a peak heat release rate as high as 325 kW / m³. 2 Comparative Example 2 had a char residue rate of 25.4% and a peak heat release rate of 278 kW / m³. 2 Comparative Example 3 had a char residue rate of 29.7% and a peak heat release rate of 245 kW / m³. 2 All of them suffer from problems such as intense combustion and insufficient flame retardant efficiency.

[0081] Mechanical property analysis, as shown in Table 1, reveals that the breaking strength of Examples 1-3 reached 4.0-4.5 cN / dtex, comparable to that of ordinary nylon fibers. The key factor is the smooth chemical transition achieved through covalent and coordination bonds in the three-layer fiber structure, eliminating interfacial delamination and stress concentration defects. Furthermore, the in-situ polymerization modification only grafted phosphorus-nitrogen side groups without damaging the original molecular structure of the nylon. Appropriate crosslinking and thermal relaxation treatment also eliminated internal stress and ensured mechanical uniformity. In contrast, Comparative Example 1, due to the physical blending of inorganic antibacterial agents and flame retardants disrupting the continuous fiber structure, had a breaking strength of only 2.8 cN / dtex. Comparative Example 2, lacking copper ion coordination, resulted in weak interfacial bonding, leading to a breaking strength of 3.2 cN / dtex. Comparative Example 3, lacking surface crosslinking, resulted in a loose fiber surface, with a breaking strength of 3.5 cN / dtex. All three examples exhibited lower strengths than the Examples and failed to meet textile processing requirements. Regarding elongation at break, Examples 1-3 exhibited elongation at break of 31.8%-34.2%, fully preserving the excellent elasticity and extensibility of nylon, making them suitable for the entire textile processing process. In contrast, Comparative Examples 1-3, due to structural defects and poor interfacial bonding, had elongation at break of only 22.3%-28.5%, exhibiting high fiber brittleness and easy breakage, resulting in extremely poor processing performance. In terms of textile processing applicability, Examples 1-3 possessed mechanical properties close to ordinary nylon, with a breakage rate of <0.5% during high-speed spinning, twisting, and weaving, allowing for direct production using existing equipment. Comparative Examples 1-3, however, suffered from poor mechanical properties, resulting in a breakage rate >5% during processing, making industrial continuous production impossible.

[0082] Analysis of the copper ion release half-life, as shown in Table 1, reveals that in Examples 1-3, the copper ion release half-life reaches 30-35 days, achieving long-lasting sustained-release antibacterial effect. This is because the coordination chelation between phosphorus-nitrogen functional groups and copper ions forms a stable chemical bond to control the release rate. The three-dimensional cross-linked network on the surface constitutes a physical sustained-release barrier to further slow down dissolution. In addition, the gradient structure allows copper ions to be released slowly layer by layer, avoiding explosive release. In contrast, Comparative Example 3 lacks a surface cross-linked network, and copper ions are only bound by coordination bonds, resulting in a release half-life of only 12 days and a rapid decline in antibacterial function. Comparative Examples 1-2 lack a copper ion coordination structure and do not possess sustained-release performance or long-lasting antibacterial ability. These results fully demonstrate that the present invention, through the dual control of chemical coordination and physical cross-linking, completely solves the industry problem of excessively rapid release of metal ions and poor durability in traditional antibacterial fibers.

[0083] Structural-functional synergy analysis, combined with Table 1, shows that Examples 1-3, through a complete process of in-situ polymerization covalent grafting, copper ion coordination, surface thermal crosslinking, and thermal relaxation activation, constructed a gradient structure of core pure nylon - intermediate copper-phosphorus-nitrogen coordination layer - surface crosslinked network layer. This achieved a triple synergy of antibacterial and flame retardant properties, structural and mechanical properties, and functional and durability. Copper ions act as both antibacterial and flame-retardant catalytic centers, achieving dual-functional positive coupling. The chemical bonding interface retains the original mechanical properties of nylon without defects, and the covalent bonds, coordination bonds, and crosslinks... The triple anchoring of the network ensures long-lasting and undiminished functionality; while Comparative Example 1 uses physical blending, lacking chemical bonding and gradient structure, resulting in uneven dispersion of functional components that easily precipitate, leading to the complete failure of antibacterial, flame retardant, and mechanical properties; Comparative Example 2 omits the copper coordination process, lacking the core catalyst for antibacterial and flame retardant properties, resulting in a lack of dual-function synergy and a significant performance decline; Comparative Example 3 lacks surface cross-linking and a physical protective barrier, leading to easy loss of functionality and the disappearance of non-melting droplet characteristics, achieving only short-term antibacterial and basic flame retardancy. This fully demonstrates the uniqueness and superiority of the process and structural design of this invention.

[0084] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing antibacterial and flame-retardant nylon fiber, characterized in that, Includes the following steps: S1. In-situ polymerization modification of nylon chips with phosphorus-nitrogen functional monomers: Dry nylon chips, phosphorus-containing monomers, and nitrogen-containing monomers are mixed in a mass ratio of 100:5-15:5-15. An ester exchange catalyst is added, and the mixture is reactively melt-blended in a twin-screw extruder at 240℃-270℃ for 3-8 minutes. After amide exchange reaction, phosphorus and nitrogen side groups are covalently grafted onto the nylon molecular chain. After water cooling and pelletizing, modified nylon chips are obtained. S2. In-situ construction of copper ion coordination and antibacterial functional layer: The modified nylon chips are immersed in an ethanol aqueous solution of copper salt and imidazole ligand, stirred at 50℃-80℃ for 2-6 hours, washed and dried to obtain copper ion coordination modified nylon chips. S3. Surface grafting and thermal crosslinking of dense crosslinked flame retardant and antibacterial skin layer: The copper ion coordination modified nylon chips are mixed with ordinary nylon chips and melt-spun to obtain nascent fibers. The nascent fibers are then impregnated with a finishing solution containing crosslinking agent and catalyst and thermally crosslinked to form a three-dimensional crosslinked network skin layer on the fiber surface. S4. Thermal relaxation and functional activation: The cross-linked fibers are heat-treated at 120℃-140℃ under tension-free conditions for 30-60 minutes to complete stress relaxation and functional activation, thereby obtaining antibacterial and flame-retardant nylon fibers.

2. The method for preparing antibacterial and flame-retardant nylon fiber according to claim 1, characterized in that, In step S1, the phosphorus-containing monomer is selected from one or more of dimethyl methylphosphonate, hydroxyethylmethylene diphosphonic acid, and vinylphosphonic acid; the nitrogen-containing monomer is selected from one or more of acrylamide, N-hydroxymethylacrylamide, and dimethylaminoethyl methacrylate.

3. The method for preparing antibacterial and flame-retardant nylon fiber according to claim 1, characterized in that, In step S1, the transesterification catalyst is selected from one of tetrabutyl titanate, isopropyl titanate, dibutyltin oxide, and monobutyltin oxide. The amount of the transesterification catalyst used is 0.3%-1.5% of the total mass of the phosphorus-containing monomer and the nitrogen-containing monomer.

4. The method for preparing antibacterial and flame-retardant nylon fiber according to claim 1, characterized in that, In step S2, the copper salt is selected from copper acetate, copper lactate, and copper gluconate, and the concentration is 0.05-0.5 mol / L; the imidazole ligand is selected from 2-methylimidazolium, benzimidazole, and imidazole-2-carboxaldehyde, and the mass ratio of the imidazole ligand to the copper salt is 1-3:

1.

5. The method for preparing antibacterial and flame-retardant nylon fiber according to claim 1, characterized in that, In step S2, the ethanol-water solution is composed of ethanol and water, and the volume ratio of ethanol to water is 1:

1.

6. The method for preparing antibacterial and flame-retardant nylon fiber according to claim 1, characterized in that, In step S3, the mass ratio of copper ion coordination modified nylon chips to ordinary nylon chips is 30-70:30-70; the melt spinning temperature is 250℃-290℃, and the draw ratio is 2.5-4.0 times; the crosslinking agent is selected from melamine-formaldehyde prepolymer and hexamethoxymethylmelamine, with a concentration of 1-5wt%; the catalyst is selected from ammonium chloride and ammonium dihydrogen phosphate, with a concentration of 0.1-0.5wt%.

7. The method for preparing antibacterial and flame-retardant nylon fiber according to claim 1, characterized in that, In step S3, the immersion treatment temperature is 80℃-100℃, and the time is 5-20 minutes. The thermal crosslinking treatment temperature is 130℃-160℃, the tension is 1.0-2.0cN / dtex, and the time is 2-10 minutes.

8. An antibacterial and flame-retardant nylon fiber, characterized in that, The antibacterial and flame-retardant nylon fiber is prepared by the method according to any one of claims 1-7, and consists of, from the inside out, a pure nylon core layer, an intermediate transition layer with phosphorus-nitrogen covalent grafting and copper coordination, and a three-dimensional cross-linked network skin layer.

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