Bio-based modified aramid fiber and preparation method thereof

Abstract

The invention relates to the technical field of aramid fibers, in particular to a bio-based modified aramid fiber and a preparation method thereof. The method comprises the following steps: sequentially preparing lignin aromatic polyol, carboxyl-terminated polylactic acid, chitosan quaternary ammonium salt and a bio-based modified compound; the bio-based modified compound is introduced in the aromatic polyamide precursor synthesis and wet spinning process, and the bio-based modified aramid fiber is finally obtained through coagulating bath interface enrichment and surface finishing bath dipping treatment. On the basis of keeping the inherent high strength and high modulus characteristics of aramid fiber, the obtained fiber remarkably improves the interface bonding strength, bending fatigue resistance and dynamic strength retention rate, and the method is controllable in process, stable in structure, environmentally friendly and suitable for industrial production. The obtained fiber is suitable for the fields of high-strength insulating materials, structural reinforcements and high-performance composite materials in a long-term fatigue load environment.

Description

Technical Field

[0001] This invention relates to the field of aramid fiber technology, specifically to a bio-based modified aramid fiber and its preparation method. Background Technology

[0002] Aramid fiber is a type of high-performance heat-resistant fiber with aromatic polyamide as its main structure. It has high strength, high modulus, low density and excellent heat resistance, and is widely used in protective fabrics, reinforced composite materials, electrical insulation materials and other fields.

[0003] Traditional aramid materials exhibit significant rigidity due to their highly oriented molecular chains, high crystallinity, and dense intermolecular hydrogen bonds. While this results in excellent strength and modulus, it also leads to inert interfacial reaction, high flexural brittleness, and limited fatigue life. In particular, in composite systems, the interfacial adhesion between aramid and the resin matrix is ​​insufficient, making it prone to peeling or interfacial debonding, which in turn significantly reduces the mechanical properties of the final composite material.

[0004] Currently, the main approaches to improve the interfacial properties of aramid fibers include plasma surface activation, chemical grafting modification, and solvent contact modification. However, these methods generally suffer from complex reaction systems, high risk of fiber damage, and easy aging of the modified layer. They not only easily disrupt the ordered molecular structure of aramid fibers, causing a decrease in strength, but also make it difficult to achieve a balance between flexibility and rigidity control, and cannot guarantee that the modified fiber maintains high modulus while also having good bending durability.

[0005] Bio-based compounds, such as polylactic acid, lignin derivatives, or chitosan, contain hydroxyl, carboxyl, and aromatic rings or polysaccharide skeletons in their molecular structure, which can provide various interfacial interactions such as hydrogen bonds, ionic bonds, and van der Waals forces. In recent years, researchers have been trying to introduce bio-based compounds into fibers to improve their overall performance, but the results have been unsatisfactory, and it is difficult to overcome the traditional technical bottleneck of "strength and toughness contradiction".

[0006] Therefore, how to introduce bio-based materials for modification without damaging the orientation of the aramid main chain, and systematically improve the interfacial adhesion, folding resistance and fatigue resistance of aramid fibers, has become an urgent key issue. Summary of the Invention

[0007] In view of this, the purpose of this invention is to propose a bio-based modified aramid fiber and its preparation method, so as to solve the problem that traditional aramid fibers, under the premise of high strength and high modulus, cannot simultaneously achieve good interfacial adhesion, folding resistance and fatigue resistance.

[0008] To achieve the above objectives, the present invention provides a method for preparing bio-based modified aramid fibers, comprising the following steps: S1 Preparation of lignin aromatic polyols: Basic lignin, polyethylene glycol and ethylene carbonate are reacted with anhydrous sodium carbonate as a catalyst under a nitrogen atmosphere at 110-130℃ for 300-420 min to carry out ring-opening esterification. The resulting product is purified and diluted to obtain a lignin aromatic polyol solution. S2 Preparation of Carboxyl-Terminated Polylactic Acid: L-lactic acid was subjected to a polycondensation reaction under nitrogen atmosphere, at 150-170℃ and -0.09MPa for 200-280 min in the presence of stannous octoate and p-toluenesulfonic acid. After the reaction was carried out, the L-lactic acid was redispersed in N-methyl-2-pyrrolidone. Succinic anhydride and 4-dimethylaminopyridine were added and the mixture was stirred at 75-85℃ for 200-280 min to carry out the end-capping reaction, thereby obtaining a carboxyl-terminated polylactic acid solution. S3 Preparation of chitosan quaternary ammonium salt: Chitosan, glacial acetic acid and deionized water are mixed to form a solution, 2,3-epoxypropyltrimethylammonium chloride is added, and the ring-opening quaternization reaction is carried out under alkaline conditions at 55-65℃ for 300-420 min. After dialysis and freeze drying, chitosan quaternary ammonium salt is obtained. S4 Preparation of Bio-based Modified Complex: Chitosan quaternary ammonium salt was dissolved in deionized water, and the pH was adjusted to 5.0-6.0 to form an aqueous solution of chitosan quaternary ammonium salt; carboxyl-terminated polylactic acid solution and lignin aromatic polyol solution were mixed and emulsified to form an emulsion; then, dicyclohexylcarbodiimide and N-hydroxysuccinimide were pre-dissolved and added to the chitosan quaternary ammonium salt aqueous solution and activated at 25-30°C for 10-20 min, and then the emulsion was added dropwise and reacted at 38-42°C for 400-520 min to carry out the crosslinking reaction. The mixture was then dialyzed and lyophilized to obtain the bio-based modified complex. S5 Preparation of Bio-based Modified Spinning Solution: In the presence of N-methyl-2-pyrrolidone and calcium chloride, m-phenylenediamine and isophthaloyl chloride are added and reacted at room temperature under nitrogen atmosphere for 100-140 min to obtain an aromatic polyamide precursor solution; then the temperature is lowered to 4-6℃, and carboxyl-terminated polylactic acid solution, lignin aromatic polyol solution and dicyclohexylcarbodiimide are added and reacted at 4-6℃ for 100-140 min to carry out crosslinking reaction. After filtration and degassing, the bio-based modified spinning solution is obtained. S6 wet spinning: The bio-based modified spinning solution is wet spun, and after being sprayed out, it is solidified in the first coagulation bath and the second coagulation bath to form a bio-based modified aramid precursor. S7 Preparation of Finished Fibers: Bio-based modified aramid precursor fibers are subjected to wet heat stretching and hot air stretching, followed by impregnation in a surface finishing bath and drying to obtain bio-based modified aramid fibers. Preferably, the ratio of alkaline lignin, polyethylene glycol, ethylene carbonate, and anhydrous sodium carbonate in step S1 is 45-55g:90-110g:65-85g:1.5-2.5g.

[0009] Preferably, the average relative molecular mass of the polyethylene glycol in step S1 is 400.

[0010] Preferably, the solid content of the lignin aromatic polyol solution in step S1 is 28wt%-32wt%.

[0011] Preferably, the ratio of L-lactic acid, stannous octoate, p-toluenesulfonic acid, succinic anhydride and 4-dimethylaminopyridine in step S2 is 90-110g:0.4-0.6g:0.4-0.6g:8-12g:0.4-0.6g.

[0012] Preferably, the ratio of chitosan, glacial acetic acid, deionized water, and 2,3-epoxypropyltrimethylammonium chloride used in step S3 is 18-22g:8-12g:950-1000g:35-45g.

[0013] Preferably, the degree of deacetylation of the chitosan in step S3 is ≥90%, and the relative molecular mass is 2×10⁻⁶. 5 .

[0014] Preferably, the dialysis in step S3 is performed using a dialysis bag with a molecular weight cutoff of 3500 Da.

[0015] Preferably, the ratio of chitosan quaternary ammonium salt, carboxyl-terminated polylactic acid solution, lignin aromatic polyol solution, dicyclohexylcarbodiimide, and N-hydroxysuccinimide in step S4 is 8-12g:35-45g:18-22g:5-7g:2.5-3.5g.

[0016] Preferably, the ratio of N-methyl-2-pyrrolidone, calcium chloride, m-phenylenediamine, isophthaloyl chloride, carboxyl-terminated polylactic acid solution, lignin aromatic polyol solution, and dicyclohexylcarbodiimide in step S5 is 55-65g:4.5-5.5g:4.5-5.5g:9-10g:3.5-4.5g:2.5-3.5g:0.25-0.35g.

[0017] Preferably, the aromatic polyamide precursor solution in step S5 has a solid content of 16wt%-20wt%.

[0018] Preferably, in step S6, the spinneret in the wet spinning assembly has 500 holes with a single hole diameter of 0.07-0.09 mm; and the spinning solution temperature is 18-22℃.

[0019] Preferably, in step S6, the first coagulation bath is composed of deionized water and a bio-based modified composite in a weight percentage of 69.7%-69.9%:0.1%-0.3%, with the balance being N-methyl-2-pyrrolidone.

[0020] Preferably, in step S6, the temperature of the first coagulation bath is controlled at 25°C, the pH is 5.0-6.0, and the residence time is 5-10 seconds.

[0021] Preferably, in step S6, the second coagulation bath is composed of deionized water and N-methyl-2-pyrrolidone in a weight percentage of 94%-96%:4%-6%.

[0022] Preferably, in step S6, the temperature of the second coagulation bath is controlled at 25°C, and the residence time is 30-60 seconds.

[0023] Preferably, the wet heat stretching temperature in step S7 is 75-85℃, and the stretching ratio is 1.8-2.2 times.

[0024] Preferably, the hot air stretching temperature in step S7 is 190-210℃, and the stretching ratio is 1.2-1.4 times.

[0025] Preferably, the surface finishing bath in step S7 is composed of glacial acetic acid and a bio-based modified compound in a weight percentage of 0.03%-0.07%:0.03%-0.07%, with the balance being deionized water.

[0026] Preferably, the immersion time in step S7 is 15-25 seconds.

[0027] Preferably, the drying in step S7 involves holding the product in a hot air drying tunnel at 150-170°C for 50-70 seconds, and finally drying it at 80°C.

[0028] Furthermore, the present invention also provides a bio-based modified aramid fiber.

[0029] The beneficial effects of this invention are: This invention introduces a bio-based modification system into the preparation process of aramid fibers, thereby obtaining bio-based modified aramid fibers with balanced and stable comprehensive properties. First, by introducing carboxyl-terminated polylactic acid and undergoing a controlled condensation reaction with the amino or amide groups at the ends of aramid fibers, a flexible-rigid synergistic molecular bridging structure is constructed in the fiber backbone, which enables the fiber to maintain its original high modulus properties while possessing a certain strain release capability, effectively dispersing stress concentration areas and improving structural toughness. Secondly, the lignin aromatic polyol structure and the benzene ring unit in the aramid molecular chain have good coplanar matching characteristics, which can form π-π stacking and hydrogen bonding complex, improve the internal orientation of the fiber and the interfacial polar affinity, and significantly enhance the adhesive interaction between the fiber and the resin or finishing layer, thereby improving the interfacial bonding strength and fatigue stability. Furthermore, the introduction of chitosan quaternary ammonium salt imparts an electrical regulation function to the fiber surface. Its cationic groups form a reversible ionic-hydrogen bond network during coagulation and surface finishing, providing flexible buffering and self-healing capabilities, enabling the fiber to maintain high mechanical integrity under repeated bending, humid heat and stress cycling conditions. Finally, a dense composite structure is formed by introducing bio-based modified composites, and self-assembly and enrichment occur during the coagulation stage of wet spinning to construct a gradient interface layer. This allows the molecular chains, organic matrix, and outer interface to transition layer by layer, avoiding the initiation of microcracks caused by abrupt changes in interface contrast. After spinning, the surface is treated with a surface finishing bath containing bio-based composites, ultimately forming a continuous and reconfigurable functional coating on the fiber surface, which systematically improves the interfacial bonding force and fatigue resistance. Through the aforementioned synergistic mechanism, this invention significantly improves interfacial adhesion, folding resistance, and fatigue resistance while maintaining the inherent high strength and high modulus of aramid fibers. It solves the long-standing technical contradiction of "high rigidity but brittle interface and short fatigue life" in traditional aramid fibers in composite applications, providing a new technical approach for the development of aramid materials towards longer life and multifunctionality. It has significant engineering application value and industrial promotion potential. Detailed Implementation

[0030] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0031] The sources or properties of the raw materials used in the embodiments and comparative examples of this invention are as follows: Alkaline lignin: Sigma-Aldrich, catalog number 370959; Polyethylene glycol: average relative molecular mass 400; Chitosan powder: degree of deacetylation ≥90%, relative molecular mass 2×10 5 Sodium hydroxide solution: 20 wt%.

[0032] Example 1: A bio-based modified aramid fiber, the specific preparation steps are as follows: (1) Preparation of lignin aromatic polyols: Take 45g of alkaline lignin, 90g of polyethylene glycol and 65g of ethylene carbonate, add 1.5g of anhydrous sodium carbonate, purge with nitrogen to replace air and stir at 110℃ for 300min. After the reaction is complete, cool to 80℃ and stand under -0.08MPa vacuum until no obvious bubbles are precipitated. After the product is cooled to room temperature, dilute with N-methyl-2-pyrrolidone to obtain a lignin aromatic polyol solution with a solid content of 28wt%. (2) Preparation of carboxyl-terminated polylactic acid: Take 90g of L-lactic acid, 0.4g of stannous octoate and 0.4g of p-toluenesulfonic acid, and stir the mixture at 150℃ and -0.09MPa for 200min under a nitrogen atmosphere. After the reaction is complete, cool to 70℃, add N-methyl-2-pyrrolidone as a solvent and stir to dissolve. Then add 8g of succinic anhydride and 0.4g of 4-dimethylaminopyridine, and stir the mixture at 75℃ for 200min. After the product is cooled to room temperature, filter it to obtain a carboxyl-terminated polylactic acid solution. (3) Preparation of chitosan quaternary ammonium salt: 18g of chitosan powder was dispersed in a flask containing 950g of deionized water and 8g of glacial acetic acid. The mixture was stirred at room temperature to form a transparent viscous solution. Then, 35g of 2,3-epoxypropyltrimethylammonium chloride was slowly added dropwise. The pH of the system was adjusted to 7.5-8.5 with sodium hydroxide solution. The mixture was stirred at 55℃ for 300min. After the reaction was completed, the mixture was cooled to room temperature. The resulting product was transferred to a dialysis bag with a molecular weight cutoff of 3500Da and dialyzed for 72h. The bag was replaced every 12h. After the dialysis was completed, the resulting solution was freeze-dried at -50℃ to obtain chitosan quaternary ammonium salt. (4) Preparation of bio-based modified complexes: 8g of chitosan quaternary ammonium salt was added to 350g of deionized water, and the pH was adjusted to 5.0-6.0 with glacial acetic acid to form an aqueous solution of chitosan quaternary ammonium salt. Separately, 35g of carboxyl-terminated polylactic acid solution and 18g of lignin aromatic polyol solution were mixed, and 130g of deionized water was added. The mixture was sheared for 90s in a high-speed shear emulsifier to obtain an emulsion. 5g of dicyclohexylcarbodiimide and 2.5g of N-hydroxysuccinimide were added to 8mL of N-methyl-2-pyrrolidone and stirred until completely dissolved to form a pre-solution. The pre-solution was added dropwise to the chitosan quaternary ammonium salt aqueous solution while stirring, and activated at 25°C for 10min. The emulsion was added dropwise to the system while stirring over 40min, and reacted at 38°C for 400min. After the reaction was completed, the product was dialyzed against deionized water for 48h and then freeze-dried to obtain the bio-based modified complex. (5) Preparation of bio-based modified spinning solution: 55g of N-methyl-2-pyrrolidone and 4.5g of anhydrous calcium chloride were added to a reaction vessel and stirred at room temperature until a transparent solution was formed. Under nitrogen protection, 4.5g of m-phenylenediamine was added and completely dissolved. The temperature was then lowered to 10°C, and 9g of isophthaloyl chloride was added dropwise. After the addition was completed, the reaction was stirred for 100min to obtain an aromatic polyamide precursor solution with a solid content of 16wt%. Subsequently, the temperature inside the vessel was lowered to 4°C, and 3.5g of carboxyl-terminated polylactic acid solution and 2.5g of lignin aromatic polyol solution were added. After stirring evenly, 0.25g of dicyclohexylcarbodiimide was added, and the reaction was carried out at 4°C for 100min. After the reaction was completed, the solution was filtered and degassed under a vacuum of -0.08MPa for 120min to obtain a bio-based modified spinning solution. (6) Wet spinning: The bio-based modified spinning solution was pumped into a wet spinning assembly equipped with a 500-hole spinneret with a single hole diameter of 0.07 mm. The temperature of the spinning solution was controlled at 18°C. After being sprayed out, the solution entered a first coagulation bath composed of deionized water, N-methyl-2-pyrrolidone, and the bio-based modified composite in a weight percentage of 69.7%:30%:0.3%. The temperature of the coagulation bath was controlled at 25°C, the pH was 5.0-6.0, and the residence time was 5 seconds to form a precursor fiber. The precursor fiber was then immediately introduced into a second coagulation bath composed of deionized water and N-methyl-2-pyrrolidone in a weight percentage of 94%:6%. The temperature of the second coagulation bath was controlled at 25°C and the residence time was 30 seconds. After washing, the bio-based modified aramid precursor fiber was obtained. (7) Preparation of finished fiber: Bio-based modified aramid precursor fibers were fed into a 75°C hot water bath via guide rollers for a first wet heat stretching, with the stretching ratio controlled at 1.8 times. After wet heat stretching, the fibers were squeezed out of water by rollers and then subjected to a second stretching in a 190°C hot air stretching zone, with the stretching ratio controlled at 1.2 times, to obtain semi-finished fibers. Subsequently, the fibers were transferred to a surface finishing bath composed of deionized water, glacial acetic acid, and bio-based modified composite in a weight percentage of 99.94%:0.03%:0.03%, with the pH controlled at 4.8-5.2. After immersion for 15 seconds, the fibers were removed from the bath and placed in a 150°C hot air drying tunnel for 50 seconds. Finally, the fibers were dried at 80°C and wound up to obtain bio-based modified aramid fibers.

[0033] Example 2: A bio-based modified aramid fiber, the specific preparation steps are as follows: (1) Preparation of lignin aromatic polyols: Take 50g of alkaline lignin, 100g of polyethylene glycol and 75g of ethylene carbonate, add 2g of anhydrous sodium carbonate, purge the air with nitrogen and stir at 120℃ for 360min. After the reaction is complete, cool to 80℃ and stand under -0.08MPa vacuum until no obvious bubbles are precipitated. After the product is cooled to room temperature, dilute with N-methyl-2-pyrrolidone to obtain a lignin aromatic polyol solution with a solid content of 30wt%. (2) Preparation of carboxyl-terminated polylactic acid: Take 100g L-lactic acid, 0.5g stannous octoate and 0.5g p-toluenesulfonic acid, and stir at 160℃ and -0.09MPa for 240min under a nitrogen atmosphere. After the reaction is completed, cool to 80℃, add N-methyl-2-pyrrolidone as a solvent and stir to dissolve, then add 10g succinic anhydride and 0.5g 4-dimethylaminopyridine, and stir at 80℃ for 240min. After the product is cooled to room temperature, filter to obtain a carboxyl-terminated polylactic acid solution. (3) Preparation of chitosan quaternary ammonium salt: 20g of chitosan powder was dispersed in a flask containing 980g of deionized water and 10g of glacial acetic acid. The mixture was stirred at room temperature to form a transparent viscous solution. Then, 40g of 2,3-epoxypropyltrimethylammonium chloride was slowly added dropwise. The pH of the system was adjusted to 7.5-8.5 with sodium hydroxide solution. The mixture was stirred at 60℃ for 360min. After the reaction was completed, the mixture was cooled to room temperature. The resulting product was transferred to a dialysis bag with a molecular weight cutoff of 3500Da and dialyzed for 72h. The bag was replaced every 12h. After the dialysis was completed, the resulting solution was freeze-dried at -50℃ to obtain chitosan quaternary ammonium salt. (4) Preparation of bio-based modified complexes: 10g of chitosan quaternary ammonium salt was added to 390g of deionized water, and the pH was adjusted to 5.0-6.0 with glacial acetic acid to form an aqueous solution of chitosan quaternary ammonium salt. Separately, 40g of carboxyl-terminated polylactic acid solution and 20g of lignin aromatic polyol solution were mixed, and 150g of deionized water was added. The mixture was sheared for 120s in a high-speed shear emulsifier to obtain an emulsion. 6g of dicyclohexylcarbodiimide and 3g of N-hydroxysuccinimide were added to 10mL of N-methyl-2-pyrrolidone and stirred until completely dissolved to form a pre-solution. The pre-solution was added dropwise to the chitosan quaternary ammonium salt aqueous solution while stirring, and activated at 30°C for 15min. The emulsion was added dropwise to the system while stirring over 50min, and reacted at 40°C for 460min. After the reaction was completed, the product was dialyzed against deionized water for 50h and then freeze-dried to obtain the bio-based modified complex. (5) Preparation of bio-based modified spinning solution: 60g of N-methyl-2-pyrrolidone and 5g of anhydrous calcium chloride were added to a reaction vessel and stirred at room temperature until a transparent solution was formed. 5g of m-phenylenediamine was added under nitrogen protection and completely dissolved. The temperature was then lowered to 10°C, and 9.5g of isophthaloyl chloride was added dropwise. After the addition was complete, the reaction was stirred for 120 min to obtain an aromatic polyamide precursor solution with a solid content of 18wt%. Subsequently, the temperature inside the vessel was lowered to 5°C, and 4g of carboxyl-terminated polylactic acid solution and 3g of lignin aromatic polyol solution were added. After stirring evenly, 0.3g of dicyclohexylcarbodiimide was added, and the reaction was carried out at 5°C for 120 min. After the reaction was completed, the solution was filtered and degassed under a vacuum of -0.08MPa for 120 min to obtain a bio-based modified spinning solution. (6) Wet spinning: The bio-based modified spinning solution was pumped into a wet spinning assembly equipped with a 500-hole spinneret with a single hole diameter of 0.08 mm. The temperature of the spinning solution was controlled at 20°C. After being sprayed out, the solution entered a first coagulation bath composed of deionized water, N-methyl-2-pyrrolidone, and the bio-based modified composite in a weight percentage of 69.8%:30%:0.2%. The temperature of the coagulation bath was controlled at 25°C, the pH was 5.0-6.0, and the residence time was 8 s to form a precursor fiber. The precursor fiber was then immediately introduced into a second coagulation bath composed of deionized water and N-methyl-2-pyrrolidone in a weight percentage of 95%:5%. The temperature of the second coagulation bath was controlled at 25°C and the residence time was 45 s. After washing, the bio-based modified aramid precursor fiber was obtained. (7) Preparation of finished fiber: Bio-based modified aramid precursor fibers were fed into an 80°C hot water bath via guide rollers for a first wet heat stretching, with the stretching ratio controlled at 2 times. After wet heat stretching, the fibers were squeezed out of water by rollers and then subjected to a second stretching in a 200°C hot air stretching zone, with the stretching ratio controlled at 1.3 times, to obtain semi-finished fibers. Subsequently, the fibers were transferred to a surface finishing bath composed of deionized water, glacial acetic acid, and bio-based modified composite in a weight percentage of 99.90%:0.05%:0.05%, with the pH controlled at 4.8-5.2. After immersion for 20 seconds, the fibers were removed from the bath and placed in a 160°C hot air drying tunnel for 60 seconds. Finally, the fibers were dried at 80°C and wound up to obtain bio-based modified aramid fibers.

[0034] Example 3: A bio-based modified aramid fiber, the specific preparation steps are as follows: (1) Preparation of lignin aromatic polyols: Take 55g of alkaline lignin, 110g of polyethylene glycol and 85g of ethylene carbonate, add 2.5g of anhydrous sodium carbonate, purge with nitrogen to replace air and stir at 130℃ for 420min. After the reaction is complete, cool to 80℃ and stand under -0.08MPa vacuum until no obvious bubbles are precipitated. After the product is cooled to room temperature, dilute with N-methyl-2-pyrrolidone to obtain a lignin aromatic polyol solution with a solid content of 32wt%. (2) Preparation of carboxyl-terminated polylactic acid: Take 110g L-lactic acid, 0.6g stannous octoate and 0.6g p-toluenesulfonic acid, and stir at 170℃ and -0.09MPa for 280min under a nitrogen atmosphere. After the reaction is completed, cool to 90℃, add N-methyl-2-pyrrolidone as a solvent and stir to dissolve, then add 12g succinic anhydride and 0.6g 4-dimethylaminopyridine, and stir at 85℃ for 280min. After the product is cooled to room temperature, filter to obtain a carboxyl-terminated polylactic acid solution. (3) Preparation of chitosan quaternary ammonium salt: 22g of chitosan powder was dispersed in a flask containing 1000g of deionized water and 12g of glacial acetic acid. The mixture was stirred at room temperature to form a transparent viscous solution. Then, 45g of 2,3-epoxypropyltrimethylammonium chloride was slowly added dropwise. The pH of the system was adjusted to 7.5-8.5 with sodium hydroxide solution. The mixture was stirred at 65℃ for 420min. After the reaction was completed, the mixture was cooled to room temperature. The resulting product was transferred to a dialysis bag with a molecular weight cutoff of 3500Da and dialyzed for 72h. The bag was replaced every 12h. After the dialysis was completed, the resulting solution was freeze-dried at -50℃ to obtain chitosan quaternary ammonium salt. (4) Preparation of bio-based modified complexes: 12g of chitosan quaternary ammonium salt was added to 420g of deionized water, and the pH was adjusted to 5.0-6.0 with glacial acetic acid to form an aqueous solution of chitosan quaternary ammonium salt. Separately, 45g of carboxyl-terminated polylactic acid solution and 22g of lignin aromatic polyol solution were mixed, and 170g of deionized water was added. The mixture was sheared for 150s in a high-speed shear emulsifier to obtain an emulsion. 7g of dicyclohexylcarbodiimide and 3.5g of N-hydroxysuccinimide were added to 12mL of N-methyl-2-pyrrolidone and stirred until completely dissolved to form a pre-solution. The pre-solution was added dropwise to the chitosan quaternary ammonium salt aqueous solution while stirring, and activated at 30°C for 20min. The emulsion was added dropwise to the system while stirring over 60min, and reacted at 42°C for 520min. After the reaction was completed, the product was dialyzed against deionized water for 60h and then freeze-dried to obtain the bio-based modified complex. (5) Preparation of bio-based modified spinning solution: 65g of N-methyl-2-pyrrolidone and 5.5g of anhydrous calcium chloride were added to a reaction vessel and stirred at room temperature until a transparent solution was formed. 5.5g of m-phenylenediamine was added under nitrogen protection and completely dissolved. The temperature was then lowered to 10°C, and 10g of isophthaloyl chloride was added dropwise. After the addition was complete, the reaction was stirred for 140 min to obtain an aromatic polyamide precursor solution with a solid content of 20wt%. Subsequently, the temperature inside the vessel was lowered to 6°C, and 4.5g of carboxyl-terminated polylactic acid solution and 3.5g of lignin aromatic polyol solution were added. After stirring evenly, 0.35g of dicyclohexylcarbodiimide was added, and the reaction was carried out at 6°C for 140 min. After the reaction was completed, the solution was filtered and degassed under a vacuum of -0.08MPa for 120 min to obtain a bio-based modified spinning solution. (6) Wet spinning: The bio-based modified spinning solution was pumped into a wet spinning assembly equipped with a 500-hole spinneret with a single hole diameter of 0.09 mm. The temperature of the spinning solution was controlled at 22°C. After being sprayed out, the solution entered a first coagulation bath composed of deionized water, N-methyl-2-pyrrolidone, and the bio-based modified composite in a weight percentage of 69.9%:30%:0.1%. The temperature of the coagulation bath was controlled at 25°C, the pH was 5.0-6.0, and the residence time was 10 s to form a precursor fiber. The precursor fiber was then immediately introduced into a second coagulation bath composed of deionized water and N-methyl-2-pyrrolidone in a weight percentage of 96%:4%. The temperature of the second coagulation bath was controlled at 25°C and the residence time was 60 s. After washing, the bio-based modified aramid precursor fiber was obtained. (7) Preparation of finished fiber: Bio-based modified aramid precursor fibers were fed into an 85°C hot water bath via guide rollers for a first wet heat stretching, with the stretching ratio controlled at 2.2 times. After wet heat stretching, the fibers were squeezed out of water by rollers and then subjected to a second stretching in a 210°C hot air stretching zone, with the stretching ratio controlled at 1.4 times, to obtain semi-finished fibers. Subsequently, the fibers were transferred to a surface finishing bath composed of deionized water, glacial acetic acid, and a bio-based modified composite in a weight percentage of 99.86%:0.07%:0.07%, with the pH controlled at 4.8-5.2. After immersion for 25 seconds, the fibers were removed from the bath and placed in a 170°C hot air drying tunnel for 70 seconds. Finally, the fibers were dried at 80°C and wound up to obtain bio-based modified aramid fibers.

[0035] Comparative Example 1: The difference from Example 2 is that carboxyl-terminated polylactic acid solution is not added in step (4), and the other steps are the same as in Example 2.

[0036] Comparative Example 2: The difference from Example 2 is that no lignin aromatic polyol solution is added in step (4), and the rest of the steps are the same as in Example 2.

[0037] Comparative Example 3: The difference from Example 2 is that in step (5), carboxyl-terminated polylactic acid solution, lignin aromatic polyol solution and dicyclohexylcarbodiimide are not added to modify the aromatic polyamide precursor solution. The remaining steps are the same as in Example 2.

[0038] Comparative Example 4: The difference from Example 2 is that the first coagulation bath in step (6) does not contain the bio-based modified compound, and the remaining steps are the same as in Example 2.

[0039] Comparative Example 5: The difference from Example 2 is that the surface finishing bath in step (7) does not contain the bio-based modified compound, and the remaining steps are the same as in Example 2.

[0040] Performance testing Tensile strength and modulus: Tested according to GB / T14344-2008 "Test Method for Tensile Properties of Chemical Fiber Filaments" at a temperature of 20°C and a relative humidity of 65%, using an electronic single fiber tensile tester with a tensile speed of 20 mm / min and a sampling length of 20 mm. 100 filaments were tested in each group. Interfacial bond strength: Using an epoxy resin matrix, a single fiber of the example with a length of 5 mm was embedded in the comparative example. After curing, it was pulled out at a speed of 0.5 mm / min using a high-precision universal testing machine. The maximum pull-out force was recorded and converted into interfacial shear strength. Bending fatigue life: The test was conducted according to FZ / T01143-2018 Test method for low temperature folding resistance of coated fabrics. Single filaments were used for the test, with a flexure angle of 22.5° and a flexure frequency of 100 times / min. The number of cycles until fracture was recorded. 50 single filaments were tested in each sample group. Strength retention rate after dynamic fatigue cycles: Monofilament samples obtained from the examples and comparative examples, with a length controlled at 20 mm, were equilibrated for 24 hours at 20°C and 65% relative humidity. The initial tensile strength was then measured. Subsequently, the monofilaments were installed in a dynamic fatigue loading device and subjected to periodic tension. The load amplitude was 5 N, the frequency was 5 Hz, and the loading mode was a full sine wave tension loading. The number of cycles was 10. 4 After the test, the residual tensile strength is measured again and the tensile strength retention rate is calculated; the test is repeated 100 times in parallel, and the average value is taken. The test results are shown in Table 1.

[0041] Table 1 Performance Test Results

[0042] Data Analysis: As can be seen from the data of Examples 1-3 in Table 1, the bio-based modified aramid fibers prepared by the present invention exhibit excellent overall performance. This indicates that while maintaining the inherent high strength and high modulus characteristics of aramid, these modified fibers have obtained better toughness and fatigue resistance, and have good application potential in high-strength electrical insulation materials, structural reinforcement composites, and high-performance fiber systems under fatigue load environments.

[0043] As can be seen from the data of Example 2 and Comparative Example 1 in Table 1, although the modulus of Comparative Example 1 is slightly higher than that of Example 2, its fatigue life and strength retention are significantly insufficient. It is speculated that this is because the polylactic acid chain segment plays a dual role of stress buffering and energy release in the system of the present invention. It effectively reduces local strain concentration without significantly affecting the overall rigidity. When this flexible chain segment is missing, the fiber is difficult to form a reversible buffer for molecular chain movement under repeated bending and tensile loads, which easily leads to inter-chain slippage and microcracks, resulting in a decrease in fatigue life and dynamic retention rate.

[0044] Based on the data from Example 2 and Comparative Example 2 in Table 1, it can be inferred that lignin aromatic polyols in the system likely provide rigid molecular-level support for the fibers and enhance their interaction with the surrounding matrix or interfacial composite layer. The aromatic ring structure in the lignin molecule has high planar rigidity and polar group density, which can improve the orientation degree and crystal region connectivity of the internal chain segments of the fiber through hydrogen bonding, π-π interactions, etc. At the same time, it forms an advantageous energy transfer channel at the interface, which significantly improves the bonding strength and synergistically enhances the mechanical properties and interfacial adhesion.

[0045] From the data in Table 1 of Example 2 and Comparative Example 3, it can be inferred that, due to the lack of chain-end modification treatment, the aramid molecular chains did not form covalent links with the bio-based structure. This resulted in the lack of effective anchoring points at the ends of the molecular chains after fiber formation, weak interfacial bonding, and interruption of energy conduction paths. Under stress, chain segment slippage and microcracks were difficult to buffer and repair, leading to a decrease in both overall strength and fatigue performance. In contrast, Example 2, through chain-end condensation reaction, introduced an "aromatic-polylactic acid" double-chain structure at the ends of the aramid skeleton, forming a more stable molecular network. This may enhance the interpenetrating connections between chain segments and make the load transfer more uniform.

[0046] As can be seen from the data in Table 1 for Example 2 and Comparative Example 4, the addition of the bio-based modified composite in the first coagulation bath plays a key role in forming a stable and tough interfacial structure. This may be because in the process of Example 2, the chitosan quaternary ammonium salt-polylactic acid-lignin ternary composite may form an intermediate layer with gradually changing polarity on the surface in the early stage of fiber coagulation, making the transition between the inner and outer phase structures smooth, effectively buffering stress differences and inhibiting the initiation of microcracks; in contrast, Comparative Example 4 lacks this process, and the fiber surface is directly subjected to the rapid precipitation between solvent and non-solvent, which easily leads to uneven surface density, severe porosity, and decreased interfacial adhesion and fatigue performance.

[0047] As can be seen from the data in Table 1 for Example 2 and Comparative Example 5, the presence of the bio-based modified composite in the surface finishing bath has a significant impact on the final surface density and fatigue resistance. This may be because the composite in the finishing bath interacts with the polar groups on the aramid surface through the cationic groups of chitosan quaternary ammonium salt, forming a dense and reconfigurable ion-hydrogen bond network. The flexible segments of polylactic acid and the rigid segments of lignin aromatic compounds work synergistically to give the finishing layer both flexibility and wear resistance. During fatigue, this layer can rearrange or self-heal, maintaining interface integrity and thus improving strength retention. In contrast, Comparative Example 5 lacks this surface structure, and the exposed fiber surface is prone to interfacial fatigue spalling under cyclic stress and micro-water environment, with a significant decrease in adhesion.

[0048] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing bio-based modified aramid fiber, characterized in that, Includes the following steps: S1 Preparation of lignin aromatic polyols: Basic lignin, polyethylene glycol and ethylene carbonate are subjected to ring-opening esterification in a nitrogen atmosphere at 110-130℃ under the action of anhydrous sodium carbonate to obtain a lignin aromatic polyol solution. S2 Preparation of carboxyl-terminated polylactic acid: L-lactic acid was subjected to polycondensation reaction in nitrogen atmosphere and 150-170℃ under the action of stannous octoate and p-toluenesulfonic acid, and then redispersed in N-methyl-2-pyrrolidone. Succinic anhydride and 4-dimethylaminopyridine were added and the end-capping reaction was carried out at 75-85℃ to obtain a carboxyl-terminated polylactic acid solution. S3 Preparation of chitosan quaternary ammonium salt: Chitosan, glacial acetic acid and deionized water are mixed to form a solution, 2,3-epoxypropyltrimethylammonium chloride is added, and a ring-opening quaternization reaction is carried out under alkaline conditions at 55-65℃. After dialysis and freeze drying, chitosan quaternary ammonium salt is obtained. S4 Preparation of Bio-based Modified Composite: Chitosan quaternary ammonium salt is dissolved in deionized water to form an aqueous solution of chitosan quaternary ammonium salt; carboxyl-terminated polylactic acid solution and lignin aromatic polyol solution are mixed and emulsified to form an emulsion; then dicyclohexylcarbodiimide and N-hydroxysuccinimide are pre-dissolved and added to the chitosan quaternary ammonium salt aqueous solution for activation at 25-30°C, and then the emulsion is added dropwise for crosslinking reaction at 38-42°C to obtain the bio-based modified composite; S5 Preparation of Bio-based Modified Spinning Solution: In the presence of N-methyl-2-pyrrolidone and calcium chloride, m-phenylenediamine and isophthaloyl chloride were added and reacted at room temperature under a nitrogen atmosphere to obtain an aromatic polyamide precursor solution; the temperature was lowered to 4-6℃, and carboxyl-terminated polylactic acid solution, lignin aromatic polyol solution and dicyclohexylcarbodiimide were added and crosslinked at 4-6℃ to obtain a bio-based modified spinning solution; S6 wet spinning: The bio-based modified spinning solution is wet spun, and after being sprayed out, it is solidified in the first coagulation bath and the second coagulation bath to form a bio-based modified aramid precursor. S7 Preparation of finished fibers: Bio-based modified aramid filaments are subjected to wet heat stretching and hot air stretching, then impregnated in a surface finishing bath and dried to obtain bio-based modified aramid fibers. In step S6, the first coagulation bath is composed of deionized water and a bio-based modified composite in a weight percentage of 69.7%-69.9%:0.1%-0.3%, with the balance being N-methyl-2-pyrrolidone. In step S6, the second coagulation bath is composed of deionized water and N-methyl-2-pyrrolidone in a weight percentage of 94%-96%:4%-6%; The surface finishing bath in step S7 is composed of acetic acid and a bio-based modified compound in a weight percentage of 0.03%-0.07%:0.03%-0.07%, with the balance being deionized water.

2. The preparation method according to claim 1, characterized in that, The ratio of alkaline lignin, polyethylene glycol, ethylene carbonate, and anhydrous sodium carbonate in step S1 is 45-55g:90-110g:65-85g:1.5-2.5g.

3. The preparation method according to claim 1, characterized in that, The solid content of the lignin aromatic polyol solution in step S1 is 28wt%-32wt%.

4. The preparation method according to claim 1, characterized in that, In step S2, the ratio of L-lactic acid, stannous octoate, p-toluenesulfonic acid, succinic anhydride, and 4-dimethylaminopyridine is 90-110g:0.4-0.6g:0.4-0.6g:8-12g:0.4-0.6g.

5. The preparation method according to claim 1, characterized in that, The ratio of chitosan, glacial acetic acid, deionized water, and 2,3-epoxypropyltrimethylammonium chloride used in step S3 is 18-22g:8-12g:950-1000g:35-45g.

6. The preparation method according to claim 1, characterized in that, In step S4, the ratio of chitosan quaternary ammonium salt, carboxyl-terminated polylactic acid solution, lignin aromatic polyol solution, dicyclohexylcarbodiimide, and N-hydroxysuccinimide is 8-12g:35-45g:18-22g:5-7g:2.5-3.5g.

7. The preparation method according to claim 1, characterized in that, In step S5, the ratio of N-methyl-2-pyrrolidone, calcium chloride, m-phenylenediamine, isophthaloyl chloride, carboxyl-terminated polylactic acid solution, lignin aromatic polyol solution, and dicyclohexylcarbodiimide is 55-65g:4.5-5.5g:4.5-5.5g:9-10g:3.5-4.5g:2.5-3.5g:0.25-0.35g.

8. The preparation method according to claim 1, characterized in that, The aromatic polyamide precursor solution in step S5 has a solid content of 16wt%-20wt%.

9. The preparation method according to claim 1, characterized in that, In step S6, the spinneret in the wet spinning assembly has 500 holes with a single hole diameter of 0.07-0.09 mm; the spinning solution temperature is 18-22℃.

10. A bio-based modified aramid fiber, characterized in that, It is prepared according to any one of claims 1-9.

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