Process for the preparation of heterocyclic polyamide composite fibers

Abstract

The application belongs to the technical field of composite fiber preparation, and particularly relates to a preparation method of a heterocyclic polyamide composite fiber, which comprises the following steps: under the protection of inert gas, heterocyclic diamine monomers and terephthaloyl chloride are mixed in a polar solvent in proportion to prepare a heterocyclic polyamide; then amino-modified cellulose nanomaterials, tannic acid modified metal oxides and Schiff base oligomers are mixed to form a composite dispersion liquid, the heterocyclic polyamide, lithium salt and crosslinking agent are added into the composite dispersion liquid to dissolve and degas to obtain a spinning solution, the spinning solution is extruded to a coagulation bath through wet spinning, and then the heterocyclic polyamide composite fiber is prepared through multi-step washing, drying and heat setting treatment.

Description

Technical Field

[0001] This application belongs to the field of composite fiber preparation technology, and particularly relates to a method for preparing heterocyclic polyamide composite fibers. Background Technology

[0002] Polyamide materials, with their excellent mechanical properties, chemical resistance, and processability, occupy an important position in many fields such as textiles, medicine, and filtration. However, the performance defects of traditional polyamide fibers are gradually making it difficult to meet the stringent requirements of high-end applications. Regarding antibacterial properties, insufficient antibacterial properties in polyamide sutures used in medical environments can easily lead to postoperative infections; textiles in humid environments are prone to bacterial growth, producing odors and even causing skin inflammation due to poor fiber antibacterial properties. In terms of high-temperature stability, in scenarios such as high-temperature resistant filter materials in automotive engine compartments and heat insulation fabrics in industrial kilns, traditional polyamide fibers are prone to thermal oxidative degradation at temperatures above 150°C, leading to a sharp drop in material mechanical properties; and in high-temperature protective fabrics in the aerospace field, their temperature resistance is far from sufficient. Regarding mechanical strength, high-end industrial filter cloths need to withstand the impact of high-pressure fluids, and the tensile strength and fatigue resistance of traditional polyamide fibers are insufficient, easily leading to breakage and filtration failure. To improve the functionality of polyamides, researchers have turned their attention to the introduction of heterocyclic groups. Heterocyclic compounds exert their antibacterial effects through mechanisms such as disrupting bacterial cell membranes and inhibiting enzyme activity. The nitrogen atom in the pyridine group possesses a lone pair of electrons, enabling it to form hydrogen bonds with water molecules, significantly enhancing the material's hydrophilicity and improving the dissolution efficiency of antibacterial components. The conjugated structure of the thiazole group enhances its ability to penetrate bacterial cell membranes, resulting in more prominent antibacterial activity. The rigid cyclic structure of the benzimidazole group increases the rigidity and packing density of the polyamide molecular chain, thereby raising the glass transition temperature and thermal decomposition temperature of the material and enhancing its high-temperature stability. However, the polymerization process of heterocyclic monomers faces numerous challenges. Different heterocyclic diamine monomers exhibit significant differences in reactivity. For example, the amino basicity of 2,5-diaminopyridine is stronger than that of 4-aminobenzimidazole. When reacting with diacyl chlorides, the former is more likely to undergo preferential acylation, leading to inconsistent monomer reaction progress in the polymerization system, resulting in localized overreaction or incomplete reaction. This uneven reaction leads to non-uniform polymer molecular chain structure, affecting not only the uniformity of the material's mechanical properties but also causing disordered distribution of antibacterial groups within the molecular chain, reducing antibacterial efficiency. Meanwhile, the compatibility between heterocyclic monomers and the polyamide backbone differs significantly. Some heterocyclic monomers are prone to microphase separation in the polymerization system, further exacerbating the instability of the polymer structure. Wet spinning, as a key process for preparing high-performance fibers, directly determines fiber quality through the stability of the spinning solution and the controllability of the coagulation process. Furthermore, heterocyclic polyamides have unique solubility properties; the strong polarity and rigid structure of the heterocyclic groups in their molecular chains result in poor solubility in conventional solvents. Precise control of the solvent system is necessary. Improper control of dissolution conditions (temperature, time, lithium salt concentration) can lead to incomplete dissolution or degradation of the heterocyclic polyamide, causing the rheological properties of the spinning solution to deviate from the spinning requirements and affecting the mechanical properties of the formed fiber.

[0003] Therefore, how to achieve the synergistic effect of antibacterial components and reinforcing components in the polyamide matrix, while taking into account both the antibacterial and mechanical properties of the material, has become a key bottleneck in expanding its application range. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this application provides a method for preparing heterocyclic polyamide composite fibers, comprising the following steps: under inert gas protection, a heterocyclic diamine monomer and terephthaloyl chloride are mixed in a specific polar solvent in a certain proportion to obtain a heterocyclic polyamide; then, amino-modified cellulose nanomaterials, tannic acid-modified metal oxides and Schiff base oligomers are mixed to form a composite dispersion; heterocyclic polyamide, lithium salt and crosslinking agent are added to the composite dispersion to dissolve and degas to obtain a spinning solution; the spinning solution is wet-spun and extruded into a coagulation bath; and then subjected to multi-step washing, drying and heat setting treatments to obtain heterocyclic polyamide composite fibers.

[0005] To achieve the above objectives, this application adopts the following technical solution:

[0006] This application provides a method for preparing heterocyclic polyamide composite fibers, comprising the following steps: under inert gas protection, a heterocyclic diamine monomer and a diacyl chloride are polymerized in a polar solvent to obtain a heterocyclic polyamide; amino-modified cellulose nanomaterials, tannic acid-modified metal oxides and Schiff base oligomers are mixed to form a composite dispersion; the heterocyclic polyamide, lithium salt and crosslinking agent are added to the composite dispersion to dissolve and degas to obtain a spinning solution; the spinning solution is extruded into a coagulation bath through a wet spinning machine; and after post-treatment, heterocyclic polyamide composite fibers are obtained.

[0007] Preferably, the heterocyclic diamine monomer includes 2,5-diaminopyridine, 2,4-diaminothiazole and 4-aminobenzimidazole, the diacyl chloride is terephthaloyl chloride, and the molar ratio of 2,5-diaminopyridine, 2,4-diaminothiazole, 4-aminobenzimidazole and terephthaloyl chloride is 5:1:1:6.

[0008] Preferably, the polar solvent is anhydrous N-methylpyrrolidone containing 5% anhydrous lithium chloride, and the polymerization reaction is as follows: first react at 0°C for 1-2 hours, then react at room temperature for 3-4 hours, and finally heat to 70-80°C for 4-6 hours.

[0009] Preferably, the preparation process of the amino-modified cellulose nanomaterial includes: dispersing cellulose nanofibers in deionized water, adding silane coupling agent KH550, reacting at 50-60℃ for 3-4 hours, the mass ratio of cellulose nanofibers to deionized water being 1:100, and the content of silane coupling agent KH550 being 10%-20% of the dry weight of cellulose nanofibers.

[0010] Preferably, the preparation process of the tannic acid modified metal oxide includes: dispersing zinc oxide nanoparticles and tannic acid in deionized water, stirring at 30-40°C for 1-2 hours, wherein the mass ratio of zinc oxide nanoparticles to tannic acid is 5:3.

[0011] Preferably, the Schiff base oligomer is prepared by reacting 2-aminohydroquinone and 2,5-dihydroxyterephthalaldehyde in N,N-dimethylformamide, wherein the molar ratio of 2-aminohydroquinone to 2,5-dihydroxyterephthalaldehyde is 1.2:1.

[0012] Preferably, the preparation process of the composite dispersion includes: adding tannic acid-modified metal oxide and amino-modified cellulose nanomaterials to the Schiff base oligomer, and stirring at 40-50°C for 0.5-1 h, wherein the mass ratio of the Schiff base oligomer, tannic acid-modified metal oxide and amino-modified cellulose nanomaterials is 100:(20-30):(20-25).

[0013] Preferably, the preparation process of the spinning solution includes: adding heterocyclic polyamide powder and lithium chloride particles to a composite dispersion, heating to 60-65°C and stirring for 1-2 hours until dissolved, then adding citric acid powder as a crosslinking agent, and continuing to stir for 1.5-2 hours. The mass of the heterocyclic polyamide powder is 25-30% of the mass of the composite dispersion, the mass of the lithium chloride particles is 7-10% of the mass of the heterocyclic polyamide powder, and the mass of the citric acid powder is 2.5-3% of the mass of the heterocyclic polyamide powder.

[0014] Preferably, the coagulation bath comprises deionized water and anhydrous ethanol, mixed in a volume ratio of 7:3, and contains 0.01-0.05% lithium chloride, with a coagulation bath temperature of 30-40°C.

[0015] Preferably, the post-processing includes: washing the fibers in washing baths set sequentially to 40℃, 60℃, and 80℃ for 5-10 min, 5-10 min, and 10-15 min respectively; drying them in a hot air oven at 80-100℃ for 20-30 min; drying them in a vacuum oven at 120℃ and a vacuum degree of -0.08MPa for 1-2 h until constant weight is achieved; and finally heat-setting them at 180℃ for 20-30 min under nitrogen protection.

[0016] Beneficial technical effects:

[0017] The preparation process of the composite dispersion of this invention includes: adding tannic acid-modified metal oxide and amino-modified cellulose nanomaterials to Schiff base oligomers, and stirring at 40-50°C for 0.5-1 h. When the amino-modified cellulose nanomaterials (NH2-CNF), tannic acid-modified zinc oxide (TA-ZnO), and Schiff base oligomers are mixed, the phenolic hydroxyl groups of the tannic acid-modified zinc oxide form hydrogen bonds with the hydroxyl groups of the amino-modified cellulose nanomaterials, effectively inhibiting nanoparticle aggregation and improving dispersion uniformity. Simultaneously, the polyhydroxy structure of tannins forms coordination bonds with zinc oxide and hydrogen bonds with the amino groups of the amino-modified cellulose nanomaterials, further improving the dispersibility of the composite dispersion. During spinning and fiber formation, the amino groups of the amino-modified cellulose nanomaterials react with the aldehyde groups of the Schiff base oligomers to form stable chemical bonds, significantly enhancing the organic-inorganic interfacial bonding force. The rigidity of the amino-modified cellulose nanomaterials and the filling effect of the tannic acid-modified zinc oxide particles effectively improve the fiber breaking strength. In terms of antibacterial properties, the heterocyclic polyamides in the spinning solution introduce heterocyclic groups, which can disrupt bacterial cell membranes and release Zn from tannic acid-modified zinc oxide. 2+ It inhibits DNA replication and forms an antibacterial synergy through dual targets, significantly improving the antibacterial rate of fibers. Attached Figure Description

[0018] Figure 1 This is an appearance diagram of the heterocyclic polyamide composite fiber prepared according to an embodiment of the present invention.

[0019] Figure 2 This is a schematic diagram of the polymerization reaction of heterocyclic diamine monomers and diacyl chlorides in a polar solvent, according to an embodiment of the present invention.

[0020] Figure 3 This is a schematic diagram of the reaction between 2-aminohydroquinone and 2,5-dihydroxyterephthalaldehyde in Example 2 of the present invention. Detailed Implementation

[0021] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the application will be further described in detail below with reference to embodiments. However, this should not be construed as limiting the scope of this application to the following examples. All other embodiments obtained by those skilled in the art without creative effort without departing from the above-described methodological spirit of this application are within the scope of protection of this application.

[0022] The following describes in detail, with reference to different embodiments, a method for preparing heterocyclic polyamide composite fibers provided in this application.

[0023] Example 1:

[0024] A method for preparing heterocyclic polyamide composite fibers includes the following steps:

[0025] 1. Purge a three-necked flask with nitrogen for 30 min, add anhydrous NMP (containing 5% anhydrous LiCl), cool to 0°C in an ice bath, then add 2,5-diaminopyridine, 2,4-diaminothiazole, and 4-aminobenzimidazole sequentially. Stir under nitrogen protection for 20 min, then slowly add terephthaloyl chloride. React at 0°C for 1.5 h, at room temperature for 3.5 h, and then at 75°C for 5 h. Pour the reaction solution into methanol to precipitate, filter, wash three times with methanol, boil in water (80°C, three times, 2 h each time), and dry under vacuum at 100°C for 20 h to obtain a light yellow heterocyclic polyamide powder. The molar ratio of 2,5-diaminopyridine, 2,4-diaminothiazole, 4-aminobenzimidazole, and terephthaloyl chloride is 5:1:1:6. Figure 2 As shown.

[0026] 2. Cellulose nanofibers (CNF) were dispersed in deionized water and modified with silane coupling agent KH550 (reaction at 60℃ for 4 h), stirred at 55℃ for 3.5 h, centrifuged (8000 rpm, 15 min), washed with deionized water until neutral, and freeze-dried to obtain amino-modified CNF (NH2-CNF). The mass ratio of cellulose nanofibers (CNF) to deionized water was 1:100, and KH550 accounted for 15% (wt / wt) of the dry weight of CNF.

[0027] 3. ZnO nanoparticles were dispersed in deionized water, tannic acid (TA) was added, and the mixture was stirred at 35°C for 1.5 h. After centrifugation (8000 rpm, 15 min), the mixture was washed three times with deionized water and then vacuum dried (60°C, 12 h) to obtain TA-ZnO. The mass ratio of ZnO nanoparticles to tannic acid (TA) was 5:3.

[0028] 4.2-Aminohydroquinone was dissolved in DMF (N,N-dimethylformamide), and 2,5-dihydroxyterephthalaldehyde was added. The mixture was stirred at 45°C under nitrogen protection for 15 min to obtain a Schiff base oligomer. TA-ZnO and NH2-CNF were then added, and stirring continued for 0.5 h to form a composite dispersion. The mass ratio of the Schiff base oligomer, TA-ZnO, and NH2-CNF was 100:25:22; the molar ratio of 2-aminohydroquinone to 2,5-dihydroxyterephthalaldehyde was 1.2:1. Figure 3 As shown.

[0029] 5. Slowly add 27% (by weight) of the synthesized heterocyclic polyamide powder to the composite dispersion, along with 8% (by weight) of LiCl particles containing the heterocyclic polyamide powder. Heat to 60°C and stir for 1.5 hours until the solid is completely dissolved. Add 2.7% (by weight) of citric acid powder containing the heterocyclic polyamide powder and continue stirring for 1.5 hours. Transfer the solution to a vacuum degassing tank, set the vacuum level to -0.09 MPa and the temperature to 55°C, and degas for 25 minutes to obtain the spinning solution.

[0030] 6. Add deionized water and anhydrous ethanol to the constant temperature bath, stir evenly, then add 0.03% LiCl, heat to 35℃, and circulate and stir (speed 400r / min) to completely dissolve the LiCl. Set aside. The volume ratio of deionized water to anhydrous ethanol is 7:3 to obtain a coagulation bath.

[0031] 7. Pour the spinning solution into the spinning machine barrel, maintain the barrel temperature at 68℃, and control the extrusion rate (0.9 mL / min) using a metering pump. Once in the coagulation bath, start the winding system. Sequentially inject deionized water into the washing tanks, setting temperatures to 40℃, 60℃, and 80℃ respectively. Wash the fibers in the first tank for 6 minutes, the second for 8 minutes, and the third for 10 minutes. Introduce the washed fibers into a 90℃ hot air oven and dry for 25 minutes. Transfer them to a 120℃ vacuum oven (vacuum degree -0.08 MPa) and dry for 1.5 hours until constant weight. Place the fibers in a nitrogen-protected heat setter and maintain the temperature at 180℃ for 25 minutes (heating rate 5℃ / min). After naturally cooling to 70℃, remove and wind to obtain heterocyclic polyamide composite fibers, such as... Figure 1 As shown.

[0032] Example 2:

[0033] A method for preparing heterocyclic polyamide composite fibers includes the following steps:

[0034] 1. Purge a three-necked flask with nitrogen for 30 min, add anhydrous NMP (containing 5% anhydrous LiCl), cool to 0°C in an ice bath, then add 2,5-diaminopyridine, 2,4-diaminothiazole, and 4-aminobenzimidazole sequentially. Stir under nitrogen protection for 25 min, then slowly add terephthaloyl chloride. React at 0°C for 1 h, at room temperature for 3 h, then at 70°C for 4 h. Pour the reaction solution into methanol to precipitate, filter, wash three times with methanol, boil in water (80°C, three times, 2 h each time), and dry under vacuum at 100°C for 24 h to obtain a light yellow heterocyclic polyamide powder. The molar ratio of 2,5-diaminopyridine, 2,4-diaminothiazole, 4-aminobenzimidazole, and terephthaloyl chloride is 5:1:1:6. Figure 2 As shown.

[0035] 2. Cellulose nanofibers (CNF) were dispersed in deionized water and modified with silane coupling agent KH550 (reaction at 60℃ for 4 h), stirred at 50℃ for 3 h, centrifuged (8000 rpm, 10 min), washed with deionized water until neutral, and freeze-dried to obtain amino-modified CNF (NH2-CNF). The mass ratio of cellulose nanofibers (CNF) to deionized water was 1:100, and KH550 accounted for 10% (wt / wt) of the dry weight of CNF.

[0036] 3. ZnO nanoparticles were dispersed in deionized water, tannic acid (TA) was added, and the mixture was stirred at 30°C for 1 h. After centrifugation (10,000 rpm, 10 min), the mixture was washed three times with deionized water and then vacuum dried (60°C, 12 h) to obtain TA-ZnO. The mass ratio of ZnO nanoparticles to tannic acid (TA) was 5:3.

[0037] 4.2-Aminohydroquinone was dissolved in DMF (N,N-dimethylformamide), and 2,5-dihydroxyterephthalaldehyde was added. The mixture was stirred for 10 min at 40 °C under nitrogen protection to obtain a Schiff base oligomer. TA-ZnO and NH2-CNF were then added, and stirring continued for 0.5 h to form a composite dispersion. The mass ratio of the Schiff base oligomer, TA-ZnO, and NH2-CNF was 100:20:20; the molar ratio of 2-aminohydroquinone to 2,5-dihydroxyterephthalaldehyde was 1.2:1. Figure 3 As shown.

[0038] 5. Slowly add 25% (by weight) of the synthesized heterocyclic polyamide powder to the composite dispersion, along with 7% (by weight) of LiCl particles containing the heterocyclic polyamide powder. Heat to 60°C and stir for 1 hour until the solid is completely dissolved. Add 2.5% (by weight) of citric acid powder containing the heterocyclic polyamide powder and continue stirring for 1.5 hours. Transfer the solution to a vacuum degassing tank, set the vacuum level to -0.09 MPa and the temperature to 50°C, and degas for 20 minutes to obtain the spinning solution.

[0039] 6. Add deionized water and anhydrous ethanol to the constant temperature bath, stir evenly, then add 0.01% LiCl, heat to 30℃, and circulate and stir (speed 500r / min) to completely dissolve the LiCl. Set aside. The volume ratio of deionized water to anhydrous ethanol is 7:3 to obtain a coagulation bath.

[0040] 7. Pour the spinning solution into the spinning machine barrel, maintain the barrel temperature at 65℃, and control the extrusion rate (0.8 mL / min) using a metering pump. Once in the coagulation bath, start the winding system. Sequentially inject deionized water into the washing tanks, setting temperatures to 40℃, 60℃, and 80℃ respectively. Wash the fibers in the first tank for 5 minutes, the second for 5 minutes, and the third for 10 minutes. Introduce the washed fibers into an 80℃ hot air oven and dry for 20 minutes. Transfer them to a 120℃ vacuum oven (vacuum degree -0.08 MPa) and dry for 1 hour until constant weight. Place the fibers in a nitrogen-protected heat setter and maintain the temperature at 180℃ for 20 minutes (heating rate 5℃ / min). After naturally cooling to 60℃, remove and wind to obtain heterocyclic polyamide composite fibers, such as... Figure 1 As shown.

[0041] Example 3:

[0042] A method for preparing heterocyclic polyamide composite fibers includes the following steps:

[0043] 1. Purge a three-necked flask with nitrogen for 30 min, add anhydrous NMP (containing 5% anhydrous LiCl), cool to 0°C in an ice bath, then add 2,5-diaminopyridine, 2,4-diaminothiazole, and 4-aminobenzimidazole sequentially. Stir under nitrogen protection for 30 min, then slowly add terephthaloyl chloride. React at 0°C for 2 h, at room temperature for 4 h, then at 80°C for 6 h. Pour the reaction solution into methanol to precipitate, filter, wash three times with methanol, boil in water (80°C, three times, 2 h each time), and dry under vacuum at 100°C for 24 h to obtain a light yellow heterocyclic polyamide powder. The molar ratio of 2,5-diaminopyridine, 2,4-diaminothiazole, 4-aminobenzimidazole, and terephthaloyl chloride is 5:1:1:6. Figure 2 As shown.

[0044] 2. Cellulose nanofibers (CNF) were dispersed in deionized water and modified with silane coupling agent KH550 (reaction at 60℃ for 4 h). The mixture was stirred at 60℃ for 4 h, centrifuged (8000 rpm, 15 min), washed with deionized water until neutral, and freeze-dried to obtain amino-modified CNF (NH2-CNF). The mass ratio of cellulose nanofibers (CNF) to deionized water was 1:100, and KH550 accounted for 20% (wt / wt) of the dry weight of CNF.

[0045] 3. ZnO nanoparticles were dispersed in deionized water, tannic acid (TA) was added, and the mixture was stirred at 40°C for 2 hours. After centrifugation (10,000 rpm, 10 min), the mixture was washed three times with deionized water and then vacuum dried (60°C, 12 h) to obtain TA-ZnO. The mass ratio of ZnO nanoparticles to tannic acid (TA) was 5:3.

[0046] 4.2-Aminohydroquinone was dissolved in DMF (N,N-dimethylformamide), and 2,5-dihydroxyterephthalaldehyde was added. The mixture was stirred for 15 min at 50 °C under nitrogen protection to obtain a Schiff base oligomer. TA-ZnO and NH2-CNF were then added, and stirring continued for 1 h to form a composite dispersion. The mass ratio of the Schiff base oligomer, TA-ZnO, and NH2-CNF was 100:30:25; the molar ratio of 2-aminohydroquinone to 2,5-dihydroxyterephthalaldehyde was 1.2:1. Figure 3 As shown.

[0047] 5. Slowly add 30% (by weight) of the synthesized heterocyclic polyamide powder to the composite dispersion, along with 10% (by weight) of LiCl particles containing the heterocyclic polyamide powder. Heat to 65°C and stir for 2 hours until the solid is completely dissolved. Add 3% (by weight) of citric acid powder containing the heterocyclic polyamide powder and continue stirring for 2 hours. Transfer the solution to a vacuum degassing tank, set the vacuum level to -0.09 MPa and the temperature to 60°C, and degas for 30 minutes to obtain the spinning solution.

[0048] 6. Add deionized water and anhydrous ethanol to the constant temperature bath, stir evenly, then add 0.05% LiCl, heat to 40℃, and circulate and stir (speed 500r / min) to completely dissolve the LiCl. Set aside. The volume ratio of deionized water to anhydrous ethanol is 7:3 to obtain a coagulation bath.

[0049] 7. Pour the spinning solution into the spinning machine barrel, maintain the barrel temperature at 70℃, and control the extrusion rate (1.0 mL / min) using a metering pump. Once in the coagulation bath, start the winding system. Sequentially inject deionized water into the washing tanks, setting temperatures to 40℃, 60℃, and 80℃ respectively. Wash the fibers in the first tank for 10 minutes, the second for 10 minutes, and the third for 15 minutes. Introduce the washed fibers into a 100℃ hot air oven and dry for 30 minutes. Transfer them to a 120℃ vacuum oven (vacuum degree -0.08 MPa) and dry for 2 hours until constant weight. Place the fibers in a nitrogen-protected heat setter and heat at 180℃ for 30 minutes (heating rate 5℃ / min). After naturally cooling to 80℃, remove and wind to obtain heterocyclic polyamide composite fibers, such as... Figure 1 As shown.

[0050] Comparative Example 1:

[0051] A method for preparing heterocyclic polyamide composite fibers includes the following steps:

[0052] 1. Purge a three-necked flask with nitrogen for 30 min, add anhydrous NMP (containing 5% anhydrous LiCl), cool to 0°C in an ice bath, add 2,5-diaminopyridine, stir for 20 min under nitrogen protection, slowly add terephthaloyl chloride, react at 0°C for 1 h, react at room temperature for 3 h, and then react at 75°C for 5 h. Pour the reaction solution into methanol to precipitate, filter, wash three times with methanol, boil in water (80°C, three times, 2 h each time), and dry under vacuum at 100°C for 20 h to obtain poly(p-phenylene terephthalamide) powder, with a molar ratio of 2,5-diaminopyridine to terephthaloyl chloride of 1:1.2.

[0053] 2. Cellulose nanofibers (CNF) were directly dispersed in deionized water (mass ratio 1:100), stirred for 3 hours, centrifuged (8000 rpm, 15 min), washed with deionized water until neutral, and freeze-dried.

[0054] 3. Add 20% ZnO and 25% CNF dispersion directly to DMF (N,N-dimethylformamide) and stir for 1 hour to form a composite dispersion. Slowly add 25% (by weight of the composite dispersion) of synthesized poly(p-phenylene terephthalamide) powder, along with 7% (by weight of the polymer) of LiCl particles. Heat to 60°C and stir for 1 hour until the solid is completely dissolved. Add 2.5% (by weight of the polymer) of citric acid powder and continue stirring for 1.5 hours. Transfer the solution to a vacuum degassing tank, set the vacuum to -0.09 MPa and the temperature to 50°C, and degas for 20 minutes to obtain the spinning solution.

[0055] 4. Add deionized water and anhydrous ethanol (volume ratio 7:3) to the constant temperature bath, stir evenly, then add 0.01% LiCl, heat to 35℃, and circulate and stir (speed 400r / min) to completely dissolve the LiCl to obtain a coagulation bath for later use.

[0056] 5. Pour the spinning solution into the spinning machine barrel, maintain the barrel temperature at 70℃, control the extrusion rate (1.0mL / min) through a metering pump, and pour it into the coagulation bath. Turn on the winding system, and sequentially inject deionized water into the washing tanks, setting the temperatures to 40℃, 60℃, and 80℃ respectively. Wash the fibers in the first tank for 10 minutes, the second tank for 10 minutes, and the third tank for 15 minutes. Introduce the washed fibers into a 100℃ hot air oven and dry for 20 minutes. Transfer them to a 120℃ vacuum oven (vacuum degree -0.08MPa) and dry for 1 hour to constant weight. Place the fibers in a nitrogen-protected heat setter and heat them at 180℃ for 20 minutes (heating rate 5℃ / min). After naturally cooling to 60℃, remove the fibers and wind them to obtain heterocyclic polyamide composite fibers.

[0057] Comparative Example 2:

[0058] A method for preparing heterocyclic polyamide composite fibers includes the following steps:

[0059] 1. Purge a three-necked flask with nitrogen for 30 min, add anhydrous NMP (containing 5% anhydrous LiCl), cool to 0°C in an ice bath, add 2,4-diaminothiazole, stir for 30 min under nitrogen protection, slowly add terephthaloyl chloride, react at 0°C for 2 h, react at room temperature for 3 h, and then heat to 80°C for 4 h. Pour the reaction solution into methanol to precipitate, filter, wash three times with methanol, boil in water (80°C, three times, 2 h each time), and dry under vacuum at 100°C for 24 h to obtain a heterocyclic polyamide with a molar ratio of 2,4-diaminothiazole and terephthaloyl chloride of 1:1.2.

[0060] 2. Nano-silica (SiO2) was dispersed in deionized water (mass ratio 1:100), stirred for 3 hours, centrifuged (8000 rpm, 10 min), washed with deionized water until neutral, and freeze-dried. Nano-titanium dioxide (TiO2) was dispersed in deionized water without tannic acid treatment, centrifuged directly (8000 rpm, 10 min), washed three times with deionized water, and vacuum-dried (60℃, 12 h).

[0061] 3. Add 30% TiO2 and 20% SiO2 dispersion to DMF (N,N-dimethylformamide) and stir for 1 hour to form a composite dispersion. Slowly add the above-mentioned heterocyclic polyamide at 25% of the mass of the composite dispersion, and simultaneously add 10% of the polymer mass of LiCl particles. Heat to 65°C and stir for 1 hour until the solid is completely dissolved. Add 3% of the polymer mass of citric acid powder and continue stirring for 2 hours. Transfer the solution to a vacuum degassing tank, set the vacuum degree to -0.09 MPa and the temperature to 60°C, and degas for 30 minutes to obtain the spinning solution.

[0062] 4. Add deionized water and anhydrous ethanol (volume ratio 7:3) to the constant temperature bath, stir evenly, then add 0.01% LiCl, heat to 40℃, and circulate and stir (speed 500r / min) to completely dissolve the LiCl to obtain a coagulation bath for later use.

[0063] 5. Pour the spinning solution into the spinning machine barrel, maintain the barrel temperature at 70℃, control the extrusion rate (0.8mL / min) through a metering pump, and enter the coagulation bath. Turn on the winding system, and sequentially inject deionized water into the washing tanks, setting the temperatures to 40℃, 60℃, and 80℃ respectively. Wash the fibers in the first tank for 10 minutes, the second tank for 10 minutes, and the third tank for 15 minutes. Introduce the washed fibers into an 80℃ hot air oven and dry for 30 minutes. Transfer them to a 120℃ vacuum oven (vacuum degree -0.08MPa) and dry for 2 hours until constant weight. Place the fibers in a nitrogen-protected heat setter and keep them at 180℃ for 30 minutes (heating rate 5℃ / min). After naturally cooling to 60℃, remove the fibers and wind them to obtain heterocyclic polyamide composite fibers.

[0064] Weigh the sample in air using an analytical balance. Immerse the sample completely in the medium and weigh its mass in the medium. Record the density of the medium at the test temperature. Clamp both ends of the fiber in the upper and lower clamps of the testing machine, ensuring the fiber is straight and without tension, avoiding excessive clamping that could break the fiber. Start the testing machine and record the force-displacement curve during the tensile process until the fiber breaks.

[0065] Tensile strength (σ): The ratio of the maximum tensile force at break (F_max) to the fiber cross-sectional area (S), σ = F_max / S (Unit conversion: 1 GPa = 1000 MPa = 1000 N / mm²) 2 ).

[0066] Elastic modulus (E): In the linear elastic phase of the stress-strain curve, the ratio of the stress increment to the strain increment is the slope of the initial straight line segment of the curve.

[0067] Elongation at break (ε): The percentage of the elongation (ΔL) at fiber break to the initial gauge length (L0), ε=(ΔL / L0)×100%.

[0068] Antibacterial rate: Place the fiber sample on a bacterial agar plate, and observe the size of the inhibition zone around the sample after incubation. The larger the diameter of the inhibition zone, the stronger the antibacterial ability.

[0069] Table 1. Performance test results of heterocyclic polyamide composite fibers prepared in the examples and comparative examples.

[0070]

[0071] The glass transition temperature of heterocyclic polyamide composite fibers was determined by differential scanning calorimetry (DSC). The processing temperature (limit value) was determined by thermogravimetric analysis (TGA). The pyrolysis temperature was determined by thermogravimetric analysis, with the temperature at which 5% weight loss (Td5%) was taken as the pyrolysis initiation temperature and the temperature at which 50% weight loss (Td50%) was taken as the main pyrolysis temperature. The auto-ignition temperature was determined by gradually increasing the temperature (5℃ / min) in an inert atmosphere (nitrogen) and observing the auto-ignition phenomenon of the fibers without an external ignition source, recording the temperature at which sustained combustion first occurred. The limiting oxygen index (LOI) was determined by adjusting the volume fraction of oxygen in the oxygen-nitrogen mixture (from low to high), igniting the top of the sample with an igniter at each oxygen concentration, and recording the lowest oxygen concentration at which the sample burned for ≥3 min.

[0072] Table 2. Thermal property test results of heterocyclic polyamide composite fibers prepared in the examples and comparative examples.

[0073]

[0074] As shown in Tables 1 and 2, the test results of density, tensile strength, elastic modulus, elongation at break, antibacterial rate, glass transition temperature, processing temperature (limit value), pyrolysis temperature, auto-ignition temperature, and limiting oxygen index of Examples 1-3 are all superior to those of Comparative Examples 1-2. This is because the polyamides of Examples 1-3 are copolymerized from three heterocyclic diamine monomers (2,5-diaminopyridine, 2,4-diaminothiazole, and 4-aminobenzimidazole) with terephthaloyl chloride, introducing three rigid heterocycles—pyridine ring, thiazole ring, and benzimidazole ring—into the molecular backbone. The conjugated system (π-π stacking) and strong polarity (electronegativity of heteroatoms N and S) of these heterocycles significantly enhance the intermolecular interaction forces (hydrogen bonds and dipole interactions), making the molecular chains more tightly packed and improving rigidity and overall integrity. Comparative Example 1 used only 2,5-diaminopyridine, a single heterocyclic monomer, resulting in a limited variety of heterocycles in the molecular chain and weaker conjugation and intermolecular forces. Comparative Example 2 used only 2,4-diaminothiazole, and its polymer had poor compatibility with SiO2 and TiO2, leading to defects in the molecular chain and a decline in mechanical properties. Examples 1-3 used KH550 to amination CNF, allowing the surface amino groups to form hydrogen bonds with the amide bonds (-CONH-) of the polyamide backbone. The amino groups of the amino-modified cellulose nanomaterial reacted with the aldehyde groups of the Schiff base oligomer to form stable chemical bonds, resulting in a tighter interfacial bond between CNF and the polymer matrix. In contrast, the unmodified CNF in Comparative Example 1 had poor compatibility with polyamide, easily forming interfacial gaps and fracturing under stress. Examples 1-3 describe tannic acid-modified ZnO. The phenolic hydroxyl groups of tannic acid coordinate with the ZnO surface, while the polyhydroxyl groups of tannic acid can form hydrogen bonds with the amino groups of NH2-CNF and the amide bonds of polyamides, resulting in more uniform dispersion of ZnO in the system and preventing agglomeration. In contrast, unmodified ZnO in Comparative Example 1 and untreated TiO2 in Comparative Example 2 both experienced stress concentration due to agglomeration, leading to reduced mechanical properties. Regarding antibacterial properties, the heterocyclic polyamides in the spinning solution introduce heterocyclic groups, which can disrupt bacterial cell membranes. This, combined with the ZnO released from the tannic acid-modified zinc oxide, further enhances the antibacterial properties. 2+Inhibiting DNA replication and forming antibacterial synergy through dual targets significantly improves the antibacterial rate of fibers. The polyamide backbone of Examples 1-3 contains heterocyclic rings such as pyridine rings, thiazole rings, and benzimidazole rings. The conjugated system of these heterocyclic rings significantly improves the high-temperature resistance of the molecular chain. The rigid structure of the heterocyclic rings inhibits the movement of the molecular chain at high temperatures, thus resulting in a higher glass transition temperature. The decomposition of heterocyclic rings requires higher energy, so the pyrolysis temperature is much higher than that of the comparative examples. In contrast, the polymers of Comparative Examples 1 and 2 contain only a single heterocyclic ring, with weak conjugation and poor thermal stability. The limiting oxygen index and auto-ignition temperature of Examples 1-3 are significantly higher because the heterocyclic rings decompose at high temperatures to form a dense char layer, blocking heat transfer and oxygen entry. The N in the heterocyclic rings releases N2 during combustion, diluting the oxygen concentration. The cellulose backbone of NH2-CNF carbonizes at high temperatures and combines with the heterocyclic char layer to form a more stable flame-retardant barrier. The polymer of Comparative Example 1 has a low nitrogen content (single heterocyclic ring), while Comparative Example 2 uses SiO2 / TiO2, thus resulting in a low limiting oxygen index and a low auto-ignition temperature.

[0075] The above results demonstrate and describe the basic principles and main features of this application, as well as its advantages.

[0076] Those skilled in the art should understand that this application is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of this application. Various changes and modifications can be made to this application without departing from the spirit and scope thereof, and all such changes and modifications fall within the scope of this application as claimed. The scope of protection of this application is defined by the equivalents of the appended claims.

Claims

1. A method for preparing heterocyclic polyamide composite fibers, characterized in that, Includes the following steps: Heterocyclic polyamides were prepared by polymerizing heterocyclic diamine monomers and diacyl chlorides in a polar solvent under inert gas protection. Ammonia-modified cellulose nanomaterials, tannic acid-modified metal oxides, and Schiff base oligomers were mixed to form a composite dispersion. Heterocyclic polyamides, lithium salts, and crosslinking agents were added to the composite dispersions to dissolve and degas, thus obtaining a spinning solution. The spinning solution was extruded into a coagulation bath via a wet spinning machine and then post-treated to obtain heterocyclic polyamide composite fibers. The preparation process of the amino-modified cellulose nanomaterial includes: dispersing cellulose nanofibers in deionized water, adding silane coupling agent KH550, and reacting at 50-60℃ for 3-4 hours; The mass ratio of cellulose nanofibers to deionized water is 1:100; the content of the silane coupling agent KH550 is 10%-20% of the dry weight of the cellulose nanofibers. The preparation process of the tannic acid-modified metal oxide includes: dispersing zinc oxide nanoparticles and tannic acid in deionized water, stirring at 30-40℃ for 1-2 hours, wherein the mass ratio of zinc oxide nanoparticles to tannic acid is 5:

3. The Schiff base oligomer is prepared by reacting 2-aminohydroquinone and 2,5-dihydroxyterephthalaldehyde in N,N-dimethylformamide, with a molar ratio of 2-aminohydroquinone to 2,5-dihydroxyterephthalaldehyde of 1.2:

1. The preparation process of the composite dispersion includes: adding tannic acid-modified metal oxide and amino-modified cellulose nanomaterials to Schiff base oligomers, and stirring at 40-50℃ for 0.5-1h. The mass ratio of Schiff base oligomers, tannic acid-modified metal oxides and amino-modified cellulose nanomaterials is 100:(20-30):(20-25).

2. The method for preparing heterocyclic polyamide composite fibers according to claim 1, characterized in that, The heterocyclic diamine monomer includes 2,5-diaminopyridine, 2,4-diaminothiazole and 4-aminobenzimidazole, and the diacyl chloride is terephthaloyl chloride. The molar ratio of 2,5-diaminopyridine, 2,4-diaminothiazole, 4-aminobenzimidazole and terephthaloyl chloride is 5:1:1:

6.

3. The method for preparing heterocyclic polyamide composite fibers according to claim 1, characterized in that, The polar solvent is anhydrous N-methylpyrrolidone containing 5% anhydrous lithium chloride. The polymerization reaction is as follows: first react at 0°C for 1-2 hours, then react at room temperature for 3-4 hours, and finally heat to 70-80°C for 4-6 hours.

4. The method for preparing heterocyclic polyamide composite fibers according to claim 1, characterized in that, The preparation process of the spinning solution includes: adding heterocyclic polyamide powder and lithium chloride particles to a composite dispersion, heating to 60-65℃ and stirring for 1-2 hours until dissolved, then adding citric acid powder as a crosslinking agent and continuing to stir for 1.5-2 hours. The mass of the heterocyclic polyamide powder is 25-30% of the mass of the composite dispersion, the mass of the lithium chloride particles is 7-10% of the mass of the heterocyclic polyamide powder, and the mass of the citric acid powder is 2.5-3% of the mass of the heterocyclic polyamide powder.

5. The method for preparing heterocyclic polyamide composite fibers according to claim 1, characterized in that, The coagulation bath comprises deionized water and anhydrous ethanol, mixed in a volume ratio of 7:3, and contains 0.01-0.05% lithium chloride. The coagulation bath temperature is 30-40℃.

6. The method for preparing heterocyclic polyamide composite fibers according to claim 1, characterized in that, The post-processing includes: washing the fibers in washing baths set to 40℃, 60℃, and 80℃ for 5-10 min, 5-10 min, and 10-15 min respectively; drying them in a hot air oven at 80-100℃ for 20-30 min; drying them in a vacuum oven at 120℃ and a vacuum degree of -0.08MPa for 1-2 h until constant weight; and finally heat-setting them at 180℃ for 20-30 min under nitrogen protection.

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