A high-elongation ternary aramid fiber, its preparation method and application

Abstract

This invention discloses a high-elongation ternary aramid fiber, its preparation method, and its applications. A specific molar ratio of 3,4'-diaminodiphenyl ether and p-phenylenediamine are dissolved in a composite solvent composed of N-methylpyrrolidone and calcium chloride. A twin-screw continuous polycondensation process with multi-stage temperature control and stepped rotation speed is employed, with terephthaloyl chloride added stepwise to achieve controlled polymerization and form a polymer solution. After neutralization, degassing, and filtration to obtain the spinning solution, the ternary aramid fiber is obtained through dry-jet wet spinning. This invention combines continuous polymerization with solution dry-jet wet spinning. By increasing the solid content of the spinning solution, the fiber not only possesses high strength and high toughness but also increases spinning speed and reduces production costs. The introduction of flexible ether bonds into the ternary copolymer structure disrupts the originally highly regular crystalline structure of para-aramid, making the molecular chains more prone to relative sliding and deformation under stress, thereby increasing the fiber's extensibility.

Description

Technical Field

[0001] This invention relates to a high-elongation ternary aramid fiber, its preparation method, and its application. Specifically, it relates to a high-elongation ternary aramid fiber that can be prepared by high-speed spinning, as well as the preparation method and application of the ternary aramid fiber, belonging to the field of special fiber material preparation technology. Background Technology

[0002] Ternary aramid, or aromatic polyamide, is an aromatic polyamide fiber produced by introducing a third monomer into para-aramid fibers through co-condensation and a special spinning process. Compared to para-aramid, it has higher specific strength, higher specific modulus, higher elongation at break, better dimensional stability, and better high-temperature resistance. Due to the presence of flexible chain segments in its molecular structure, it exhibits less performance degradation under repeated stretching and bending cyclic loads, resulting in a longer service life. Its abrasion resistance and fatigue resistance are significantly superior to para-aramid. It can be used to manufacture high-performance ropes and cables, rubber power transmission belts, high-grade friction sealing materials, aircraft structural components, rocket shells, cut-resistant gloves, bulletproof vests, stab-resistant vests, sailing ropes, fishing lines, etc., and is widely used in marine engineering, mining industry, protection, aerospace, sports and leisure, and other fields.

[0003] Currently, domestic production of heterocyclic aramid fibers employs a low-temperature solution-based batch polymerization process. The polymer solution, after filtration and degassing, is directly used for spinning, but the spinning process utilizes wet spinning. Although some high-end military applications have achieved mass engineering applications of heterocyclic aramid fibers, as reported in Chinese patents CN101787582A and CN101921395A, there remains a significant gap compared to foreign countries in fiber performance and preparation technology. This is mainly reflected in: variations in polymer molecular weight across different batches, affecting fiber quality stability; the high cost of lithium chloride in the wet spinning solvent system, making separation and recovery from wastewater difficult; and the lower spinning speed compared to dry and wet methods, resulting in low production efficiency and excessively high production costs, thus hindering its low-cost, large-scale development.

[0004] In the prior art, Chinese patent CN119162686A reports a liquid crystal spinning method for heterocyclic aramid fibers. This method uses a diamine monomer, a third monomer, and terephthaloyl chloride added in two batches, and polymerizes them in stages at different temperatures in a twin-screw polymerization reactor. The resulting polymer powder is dissolved in concentrated sulfuric acid, filtered, and degassed to obtain a liquid crystal spinning solution, which is then used to prepare hybrid aramid fibers via a dry-jet wet spinning process. The tensile strength of this fiber is 5.6–6.4 GPa, the elongation at break is 3.1–5.2%, and the elastic modulus is 160–200 GPa. Another Chinese patent, CN120099662A, reports a method for preparing high elongation at break modified poly(p-phenylene terephthalamide) fibers. This method first dissolves p-phenylenediamine, a third monomer, and a fourth monomer in a solvent to form a premix, adds a portion of terephthaloyl chloride for prepolymerization to obtain a prepolymer, and then continues polymerization with the remaining terephthaloyl chloride to obtain a modified polymer. Subsequently, a spinning solution was prepared using concentrated sulfuric acid as a solvent, and fibers were produced using a dry-jet wet spinning process. By introducing a small amount of 3,4'-diaminodiphenyl ether and a fourth monomer containing a diaminophenoxy functional group, and by optimizing the process parameters, the elongation at break of the produced fibers can reach more than 3.6%, and the breaking strength is greater than 21.5 cN / dtex.

[0005] In summary, existing technologies, through optimizing polymerization processes and monomer structures, employ dry-jet wet spinning to prepare multi-component aramid fibers, which to some extent improve fiber strength and elongation. However, to achieve a comprehensive improvement in fiber performance and production efficiency, the key is to obtain a polymer solution with uniform structure and stable performance before spinning. A stable solution system not only helps to form a highly oriented fiber structure during dry-wet spinning, thereby significantly improving the fiber's tensile strength and elongation at break, but also effectively increases the spinning rate, overcoming the bottlenecks of low efficiency and high cost in existing wet spinning methods. This provides a feasible path for the large-scale and low-cost manufacturing of existing high-performance aramid fibers. Summary of the Invention

[0006] The purpose of this invention is to provide a high-elongation ternary aramid fiber, its preparation method, and its applications. By combining continuous polymerization with solution dry-jet wet spinning, and increasing the solid content of the spinning solution, the fiber not only possesses high strength and high toughness, but also increases spinning speed and reduces production costs. The introduction of flexible ether bonds into the ternary copolymer structure disrupts the originally highly regular crystalline structure of para-aramid, making the molecular chains more prone to relative sliding and deformation under stress, thereby increasing the fiber's stretchability.

[0007] This invention is achieved through the following technical solution: a method for preparing high-elongation ternary aramid fibers, comprising the following steps: S1. P-phenylenediamine and 3,4'-diaminodiphenyl ether monomers are dissolved in a composite solvent system of N-methylpyrrolidone and calcium chloride, and a mixed solution is formed under nitrogen protection; S2. Control the temperature of the mixed solution at -5 to 5℃, add terephthaloyl chloride, and then mix it with a first-stage twin-screw mixer at a speed of 30 to 60 r / min to form a prepolymer mixture; S3. Control the temperature of the prepolymer mixture at 0-20℃ and perform a second-stage twin-screw mixing at a speed of 50-100r / min to form the prepolymer stock solution; S4. Control the temperature of the prepolymer solution at 20-90℃, add terephthaloyl chloride, and then mix it with a third-stage twin-screw mixer at a speed of 100-500 r / min to form a polymer solution; S5. After neutralizing, degassing and filtering the polymer solution to obtain the spinning solution, the ternary aramid fiber is obtained by dry-spray wet spinning.

[0008] In step S1, the molar ratio of p-phenylenediamine and 3,4'-diaminodiphenyl ether is 70:30 to 15:85.

[0009] In the composite solvent system, the calcium chloride content is 0.5–7 wt%, and the water content is ≤100 ppm.

[0010] In step S2, the amount of terephthaloyl chloride added is 60-95% of its total amount, and in step S4, the amount of terephthaloyl chloride added is 5-40% of its total amount.

[0011] In step S4, the solid content of the polymer solution is 5-15%, and the dynamic viscosity is 6-400,000 centipoise.

[0012] In step S5, the dry-jet wet spinning process includes: extruding the spinning solution from the spinneret, stretching and orienting it through a gas layer before solidification, then entering a coagulation bath to form nascent fibers, followed by washing, drying, stretching, and oiling treatments, and finally winding the fibers to obtain ternary aramid fibers.

[0013] The gas layer includes air, nitrogen, argon, helium, or carbon dioxide.

[0014] The coagulation bath is an aqueous solution of N-methylpyrrolidone, wherein the mass concentration of N-methylpyrrolidone is 10-50%.

[0015] The drying process is carried out at a controlled temperature of 100–350°C and a tension of ≥0.2 cN / dtex.

[0016] During the stretching process, the fiber is heated to 350–500°C, and the tension is ≤1 cN / dtex.

[0017] Another technical solution of the present invention is to provide a high elongation ternary aramid fiber, which is obtained by the above preparation method and its performance indicators meet the following requirements: breaking strength of 25-35 cN / dtex, elastic modulus of 500-800 cN / dtex, and breaking elongation of 3.5-7.0%.

[0018] Furthermore, the present invention also provides an application of high elongation ternary aramid fiber, which is used to prepare load-bearing and reinforcing components in heavy machinery, marine engineering or cable systems.

[0019] Compared with the prior art, the present invention has the following advantages and beneficial effects: (1) The present invention uses a composite solvent system composed of N-methylpyrrolidone and calcium chloride. Compared with the composite solvent system of dimethylacetamide and lithium chloride used in wet spinning, calcium chloride is cheaper than lithium chloride and is easy to recycle and reuse, which effectively reduces the overall solvent cost.

[0020] (2) By optimizing the ratio of aromatic diamines and combining it with a multi-stage screw continuous polycondensation process, this invention can stably prepare ternary copolymer aramid polymer solution. Compared with traditional batch polymerization, the polymer solution obtained by this process can have a solid content of 5-15%, and a narrower molecular weight distribution and better controllability, thus laying a solid foundation for the preparation of high-performance fibers.

[0021] (3) The high solids content spinning solution prepared by the present invention is suitable for solution dry and wet spinning processes, breaking the speed limitation of traditional wet spinning. Its spinning speed is increased from 10-30m / min in the original wet process to 30-100m / min, which greatly improves production efficiency and helps to reduce industrial production costs.

[0022] (4) This invention introduces flexible ether bonds into the ternary aramid structure, which disrupts the original highly regular crystalline structure of para-aramid, making the molecular chains more prone to relative sliding and deformation under stress. This slippage and deformation significantly enhance the fiber's extensibility. The final product has a breaking strength of 25–35 cN / dtex, an elastic modulus of 500–800 cN / dtex, and an elongation at break of 3.5–7.0%, which is an excellent level. Attached Figure Description

[0023] Figure 1 This is an image of the ternary aramid fiber I prepared in Example 1 of the present invention. Detailed Implementation

[0024] The invention's objective, technical solution, and beneficial effects will be further explained in detail below.

[0025] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the claimed invention. Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0026] This invention aims to provide a ternary copolymer aramid fiber with excellent comprehensive performance and its preparation method. The method includes the preparation of a ternary aramid polymerization solution and a dry-jet wet spinning process based on the polymerization solution. In the polymerization stage, 3,4'-diaminodiphenyl ether and p-phenylenediamine in a specific molar ratio are dissolved together in a composite solvent composed of N-methylpyrrolidone and calcium chloride. A twin-screw continuous polycondensation process with multi-stage temperature control and stepped rotation speed is used, and terephthaloyl chloride is added stepwise to achieve controlled polymerization, resulting in a high molecular weight, narrowly distributed ternary copolymer aramid solution with a solid content of 5-15% and a dynamic viscosity of 6-400,000 centipoise. In the spinning stage, the obtained polymerization solution is neutralized, degassed, and filtered, and then spun using a dry-jet wet spinning method. The fiber is formed and oriented by combining gas layer stretching and orientation with an N-methylpyrrolidone aqueous solution coagulation bath. After washing, drying, high-temperature stretching, oiling, and winding, the ternary copolymer aramid fiber with excellent comprehensive performance is finally obtained. This fiber is characterized by high strength, high modulus, and high toughness, with a breaking strength of 25–35 cN / dtex, an elastic modulus of 500–800 cN / dtex, and a breaking elongation of 3.5–7.0%, expanding its application potential in high-end fields such as heavy machinery, marine engineering, and cable systems.

[0027] This invention differs significantly from existing technologies in its process route. Existing technologies typically employ a route where resin is first polymerized, then dissolved in sulfuric acid to form a liquid crystal spinning solution, followed by dry-jet wet spinning. For example, CN120099662A introduces a small amount of a third monomer and 10-20% of a fourth flexible monomer into a traditional para-aramid polymerization system. Although the main structure remains para-aramid, the polymerization and spinning processes are the same. By dissolving resin powder in sulfuric acid to form a liquid crystal spinning solution and then using dry-jet wet spinning, the resulting fiber maintains its original strength while exhibiting improved elongation at break. As another example, CN119162686A introduces a benzo[a]heterocyclic rigid third monomer (benzo[a]oxazole, benzo[a]thiazole, benzimidazole, etc.), polymerizes it into resin powder, dissolves it in sulfuric acid to form a liquid crystal spinning solution, and then uses a dry-jet wet spinning process to obtain heterocyclic aramid with superior mechanical properties.

[0028] This invention abandons the traditional multi-step process of "resin-dissolution-spinning," directly obtaining a polymer solution suitable for dry-jet wet spinning through a controlled polycondensation reaction. This solution has a solid content of 5-15% and a dynamic viscosity of 6-400,000 centipoise, achieving a one-step preparation from polymerization to spinning solution, and further realizing an integrated "solution dry-jet wet spinning" process. This approach overcomes the technical limitations of traditional polymer solutions with low solid content, primarily applicable to wet spinning (spinning speeds typically 10-30 m / min), providing a completely new process solution for the efficient and high-performance preparation of aramid fibers.

[0029] In addition to process innovation, this invention also introduces flexible ether bonds into the terpolymer molecular chain by adjusting the ratio of 3,4'-diaminodiphenyl ether monomers. This moderately disrupts the highly regular crystalline structure of para-aramid, making the molecular chain more prone to relative slippage and deformation under stress. This significantly improves the fiber's elongation at break and toughness while maintaining high strength and modulus. This structural adjustment not only endows the fiber with superior overall mechanical properties but also helps to increase spinning speed, reduce production costs, and further enhance the competitiveness of this technology in high-end industrial applications.

[0030] The following is a detailed summary of the technical solution of this invention: The ternary aramid fiber of the present invention uses an N-methylpyrrolidone / calcium chloride composite solvent system. During the polycondensation process of p-phenylenediamine and terephthaloyl chloride, a third monomer, 3,4'-diaminodiphenyl ether, is introduced. Through a multi-stage screw continuous polycondensation process, a polymer solution with a solid content of 5-15%, a dynamic viscosity of 6-400,000 centipoise, and a narrow molecular weight distribution is obtained. This solution is then used for spinning dope preparation and dry-jet wet spinning to finally obtain ternary aramid fiber with excellent comprehensive performance.

[0031] The molecular structure of ternary aramid fiber is shown in formula (1) below: (1) In equation (1), m and n are positive integers, and n∶m = 70∶30~15∶85.

[0033] In the preparation of the polymer solution, firstly, p-phenylenediamine and 3,4'-diaminodiphenyl ether monomers are weighed according to a certain molar ratio and dissolved in a composite solvent system of N-methylpyrrolidone and calcium chloride. The solution is stirred and dissolved uniformly under nitrogen protection to form a mixed solution. Then, the temperature of the mixed solution is lowered to -5 to 5°C. A certain proportion of terephthaloyl chloride is added to the cooled system, and the mixture is stirred at low speed by a first-stage twin-screw mixer. Polycondensation is carried out at -5 to 5°C to form a prepolymer mixture. Then, a medium-speed polycondensation reaction is carried out by a second-stage twin-screw mixer, with the reaction temperature controlled at 0 to 20°C, to form a prepolymer stock solution. Finally, the remaining proportion of terephthaloyl chloride is added, and the mixture is subjected to high-speed shearing by a third-stage twin-screw mixer, with the temperature controlled at 20 to 90°C, to continuously and stably obtain a homogeneous polymer solution with fluid dynamics.

[0034] In practice, the molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether can be controlled between 70:30 and 15:85, with a preferred range of 55:45 to 15:85. Precisely controlling this molar ratio can effectively increase the polymer molecular weight and solution solids content, which not only helps the polymerization solution adapt to the requirements of dry-jet wet spinning processes but also further enhances the strength and elongation properties of the finished fiber, achieving a comprehensive mechanical performance of high strength and high elongation. Secondly, the total amount of terephthaloyl chloride added is typically 1 to 1.005 times that of p-phenylenediamine, added in two steps: the first stage of twin-screw polycondensation and the third stage of high-speed shearing. The first addition accounts for 60 to 95% of the total amount, and the second addition accounts for 5 to 40% of the total amount.

[0035] This invention employs a composite solvent system composed of N-methylpyrrolidone and calcium chloride, which offers lower cost and superior solubility. Specifically, calcium chloride is dissolved in N-methylpyrrolidone, with the calcium chloride content controlled at 0.5–7 wt%, more preferably 1–5 wt%, and the system's water content not exceeding 100 ppm. This composite solvent system plays a crucial role in increasing polymer molecular weight: as the polymerization reaction proceeds, the polymer molecular weight increases to a certain level, after which its solubility in conventional solvents decreases, easily leading to polymer precipitation and hindering further molecular weight growth. This composite solvent effectively enhances the polymer's solubility in the reaction system, creating a favorable environment for continuous molecular chain growth, thereby achieving higher molecular weights while reducing overall solvent costs.

[0036] In this step, the first-stage twin-screw extruder operates at a low to medium speed: 30–60 r / min; the second-stage twin-screw extruder operates at a medium speed: 50–100 r / min; and the third-stage twin-screw extruder operates at a high speed: 100–500 r / min. For example, three twin-screw reactors can be arranged in series, with the stirring speed controlled sequentially to achieve continuous material feeding: low-temperature, low-speed mixing (for material mixing) is performed in the first-stage twin-screw reactor for 10–30 min; low-temperature, medium-speed polycondensation (pre-polymerization of diamine with added terephthaloyl chloride) is performed in the second-stage twin-screw reactor for 15–30 min; and high-temperature, high-speed shearing (to ensure molecular weight growth) is performed in the third-stage twin-screw reactor for 30–60 min. This multi-stage speed control process, through progressively enhanced mechanical shearing and temperature control, ensures effective mixing and full polymerization of the reactants while achieving precise control of the dynamic viscosity of the polymerization solution, providing a qualified polymer solution for subsequent spinning processes.

[0037] Based on the aforementioned composite solvent system, strictly controlled molar ratios of reaction components, continuous nitrogen protection, and the synergistic effect of a multi-stage twin-screw continuous polycondensation process, this invention successfully achieves precise control over the polymerization process, enabling the stable preparation of ternary aramid polymer solutions with a solid content of 5–15%, a dynamic viscosity of 6–400,000 centipoise, and a narrow molecular weight distribution. This solution exhibits excellent spinning adaptability, providing a crucial material foundation for subsequent dry-jet wet-spinning and the preparation of high-performance fibers.

[0038] In the fiber preparation process, the present invention obtains a spinning solution by neutralizing, degassing and filtering the polymer solution obtained in the above preparation process, and then uses a dry-spray wet spinning method to obtain ternary aramid fibers, with a spinning speed of 30-100 m / min.

[0039] Specifically, neutralization involves adding an alkaline washing substance to the polymer solution to neutralize the byproduct hydrochloric acid. Suitable alkaline substances include, but are not limited to, basic inorganic compounds such as sodium hydroxide, potassium hydroxide, calcium hydroxide, calcium oxide, and ammonium hydroxide, with sodium hydroxide being preferred. Organic bases, such as diethylamine, tributylamine, or other amines, can also be used.

[0040] Degassing involves adding the neutralized and dehydrochlorinated polymer solution to a degassing vessel and degassing it at -0.1 MPa to -0.098 MPa and 20 to 50°C for 0.5 to 1 hour, followed by filtration (using a raw liquid filter with a filtration accuracy of 10 to 30 μm) to remove insoluble impurities.

[0041] Dry-jet wet spinning includes: extruding the spinning solution from the spinneret (0.055-0.075mm), stretching and oriented it through a gas layer before solidification, then entering the coagulation bath to form nascent fibers, followed by washing, drying, stretching, and oiling treatments, and finally winding the fibers to obtain ternary aramid fibers.

[0042] In actual operation, the gas layer refers to a gas that does not react with the spinning solution, such as air, nitrogen, argon, helium, or carbon dioxide, with an air layer or nitrogen layer being preferred. Both the coagulation bath and washing process use an aqueous solution of N-methylpyrrolidone. The mass concentration of N-methylpyrrolidone in the coagulation bath is controlled at 10–50%, preferably 20–40%, while the mass concentration of N-methylpyrrolidone in the washing solution is controlled at 0–10%. Furthermore, for the drying and stretching processes, the parameters are typically controlled as follows: during drying, the temperature is controlled at 100–350°C, and the tension is ≥0.2 cN / dtex; during stretching, the fiber is heated to 350–500°C, and the tension is ≤1 cN / dtex.

[0043] The following examples illustrate specific embodiments of the present invention. However, the scope of protection of the present invention is not limited to these examples. The following examples only provide a partial preparation process and adjustments to specific process parameters for ternary aramid fibers; other process steps can be found in the foregoing detailed summary of the invention's technical solution.

[0044] Example 1: Preparation of ternary aramid fiber I (I) Preparation of polymer solutions (1) Raw materials and proportions The composite solvent system consists of N-methylpyrrolidone (water content ≤100 ppm) and calcium chloride, wherein the calcium chloride content is 2 wt%.

[0045] Monomer ratio: The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 1:1.

[0046] The total amount of terephthaloyl chloride added is usually 1.005 times that of p-phenylenediamine, and it is added in two steps: the first addition is 90% of the total amount added, and the second addition is 10% of the total amount added.

[0047] (2) Polymerization process Two diamine monomers were dissolved in a composite solvent and stirred under nitrogen protection to form a homogeneous mixed solution.

[0048] The mixed solution was cooled to -5°C, and the first addition of terephthaloyl chloride was made, followed by introduction into a three-stage twin-screw continuous polycondensation system. First-stage twin-screw extruder: rotation speed 30 r / min, temperature -5 ℃, residence time 15 min, to achieve low-temperature mixing; Second-stage twin-screw extruder: rotation speed 50 r / min, temperature 0 ℃, residence time 15 min, to complete medium-speed pre-condensation; Third-stage twin-screw extruder: Add the remaining terephthaloyl chloride, rotate at 400 r / min, maintain a temperature of 70 ℃, and hold for 45 min to perform high-speed shearing and final polymerization.

[0049] The final product is a homogeneous polymer solution with a solid content of 10%, a dynamic viscosity of 310,000 centipoise at 25 °C, and a narrow molecular weight distribution.

[0050] (ii) Dry-jet wet spinning (1) Preparation of spinning solution Neutralization: Sodium hydroxide is added to the polymer solution, and the neutralization reaction produces hydrochloric acid as a byproduct.

[0051] Degassing: Degassing was performed at -0.1 MPa and 30 ℃ for 0.5 h.

[0052] Filtration: Insoluble matter is removed by a raw material filter (10 μm precision) to obtain the spinning raw material.

[0053] (2) Spinning conditions Spinneret orifice diameter: 0.065 mm; Gas layer medium: air or nitrogen; Spinning speed: 60 m / min.

[0054] (3) Coagulation and washing Coagulation bath: N-methylpyrrolidone aqueous solution, 30% by mass; Washing solution: N-methylpyrrolidone aqueous solution, mass concentration 5%.

[0055] (4) Post-processing Drying temperature: 120 ℃, tension: 0.2 cN / dtex; High-temperature tensile temperature: 400 ℃, tensile strength: 0.6 cN / dtex; Finally, after oiling and winding, ternary aramid fiber I is obtained (see...). Figure 1 ).

[0056] Example 2: Preparation of ternary aramid fiber II Based on Example 1, this embodiment adjusts the parameters in “(1) Raw materials and proportions”, while the rest of the process flow and parameter conditions are the same as in Example 1, and ternary aramid fiber II is obtained.

[0057] In this embodiment, the composite solvent system consists of N-methylpyrrolidone (water content ≤100 ppm) and calcium chloride, wherein the calcium chloride content is 4 wt%.

[0058] Monomer ratio: The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 2:3.

[0059] The total amount of terephthaloyl chloride added is usually 1.003 times that of p-phenylenediamine, and it is added in two steps: the first addition is 95% of the total amount added, and the second addition is 5% of the total amount added.

[0060] The final product is a homogeneous polymer solution with a solid content of 14%, a dynamic viscosity of 380,000 centipoise, and a narrow molecular weight distribution.

[0061] Example 3: Preparation of ternary aramid fiber III Based on Example 1, this embodiment adjusts the parameters in "(2) Polymerization process", while the rest of the process flow and parameter conditions are the same as in Example 1, and ternary aramid fiber III is obtained.

[0062] In this embodiment, the mixed solution is cooled to -5°C, terephthaloyl chloride is added for the first time, and then it enters a three-stage twin-screw continuous polycondensation system: First-stage twin-screw extruder: rotation speed 50 r / min, temperature -5 ℃, residence time 10 min, to achieve low-temperature mixing and pre-condensation; Second-stage twin-screw extruder: rotation speed 80 r / min, temperature 0 ℃, residence time 15 min, to complete medium-speed pre-condensation; Third-stage twin-screw extruder: Add the remaining terephthaloyl chloride, rotate at 500 r / min, maintain a temperature of 85 ℃, and hold for 30 min to perform high-speed shearing and final polymerization.

[0063] The final product is a homogeneous polymer solution with a solid content of 8%, a dynamic viscosity of 250,000 centipoise at 25 °C, and a narrow molecular weight distribution.

[0064] Example 4: Preparation of ternary aramid fiber IV Based on Example 1, this embodiment adjusts the parameters in "(II) Dry-jet wet spinning" while keeping the rest of the process flow and parameter conditions the same as in Example 1, thus producing ternary aramid fiber IV.

[0065] The dry-jet wet spinning parameters in this embodiment are as follows: (1) Preparation of spinning solution Neutralization: Sodium hydroxide is added to the polymer solution, and the neutralization reaction produces hydrochloric acid as a byproduct.

[0066] Degassing: Degassing was performed at -0.996 MPa and 40 ℃ for 0.6 h.

[0067] Filtration: Insoluble matter is removed by a raw solution filter (precision 30 μm) to obtain the spinning raw solution.

[0068] (2) Spinning conditions Spinneret orifice diameter: 0.075 mm; Gas layer medium: air or nitrogen; Spinning speed: 80 m / min.

[0069] (3) Coagulation and washing Coagulation bath: N-methylpyrrolidone aqueous solution, mass concentration 40%; Washing solution: N-methylpyrrolidone aqueous solution, mass concentration 10%.

[0070] (4) Post-processing Drying temperature: 150 ℃, tension: 0.4 cN / dtex; High-temperature tensile temperature: 500 ℃, tension: 0.8 cN / dtex.

[0071] Comparative Example 1: Preparation of Ternary Aramid Fiber No. 1 Based on Example 1, this comparative example adjusts the parameters in "(1) Raw materials and proportions" while keeping the rest of the process flow and parameter conditions the same as in Example 1, and obtains ternary aramid fiber 1#.

[0072] In this embodiment, the composite solvent system consists of N-methylpyrrolidone (water content ≤100 ppm) and calcium chloride, wherein the calcium chloride content is 8 wt%.

[0073] Monomer ratio: The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 9:1.

[0074] The final polymerized mixture precipitates as a solid powder, the polymerization process terminates, and solution dry-jet wet spinning is no longer possible.

[0075] Comparative Example 2: Preparation of Ternary Aramid Fiber 2# Based on Example 1, this comparative example adjusts the parameters in "(2) polymerization process", while the rest of the process flow and parameter conditions are the same as in Example 1, and ternary aramid fiber 2# is obtained.

[0076] In this embodiment, the mixed solution is cooled to 8 °C, terephthaloyl chloride is added for the first time, and then it enters a three-stage twin-screw continuous polycondensation system: First-stage twin-screw extruder: rotation speed 20 r / min, temperature 8 ℃, residence time 5 min; Second-stage twin-screw extruder: rotation speed 40 r / min, temperature 30 ℃, residence time 12 min; Third-stage twin-screw extruder: Add the remaining terephthaloyl chloride, rotate at 80 r / min, maintain a temperature of 90 ℃, and hold for 20 min.

[0077] Comparative Example 3: Preparation of ternary aramid fiber #3 Based on Example 1, this comparative example adjusts the parameters in "(2) Polymerization process", while the rest of the process flow and parameter conditions are the same as in Example 1, and ternary aramid fiber 3# is obtained.

[0078] In this embodiment, the mixed solution is cooled to -5°C, terephthaloyl chloride is added for the first time, and then it enters a two-stage twin-screw continuous polycondensation system: First-stage twin-screw extruder: rotation speed 30 r / min, temperature 5 ℃, residence time 15 min, to achieve low-temperature mixing and pre-condensation; Second-stage twin-screw extruder: Add the remaining terephthaloyl chloride, rotate at 400 r / min, maintain a temperature of 50 ℃, and hold for 45 min to complete the polymerization.

[0079] The polymer solution and ternary aramid fiber obtained in the above embodiments were compared with those in the comparative examples, including the solid content of the polymer solution (the theoretical solid content was obtained by material balance calculation), dynamic viscosity (tested by rotational rheometer method), fiber breaking strength (see GB / T 14344), elastic modulus (see GB / T 14344), and elongation at break (see GB / T 14344), as detailed in Table 1 below.

[0080] Table 1

[0081] Based on the test data in Table 1 above, the following conclusions can be drawn: (1) The ternary aramid fibers prepared in Examples 1 to 4 of this invention possess excellent comprehensive properties, all meeting the performance index range of 25–35 cN / dtex breaking strength, 500–800 cN / dtex elastic modulus, and 3.5–7.0% elongation at break. This performance advantage stems from the use of 3,4'-diaminodiphenyl ether as the third monomer. The flexible ether bonds in its structure effectively reduce the molecular chain stacking density, improve the polymer's solubility in solvents, and facilitate the acquisition of polymers with higher molecular weights. By controlling the diamine monomer ratio and the content of co-solvents, the polymer can exist in solution form at high solid content for dry-jet wet spinning. Compared with wet spinning, the speed is significantly improved, resulting in high production efficiency and reduced costs.

[0082] (2) The comparison between Example 1 and Comparative Example 1 shows that the ratio of 3,4'-diaminodiphenyl ether monomers and the content of co-solvents in the polymerization reaction system have a significant impact on the polymer molecular structure and macroscopic morphology. When the amount of 3,4'-diaminodiphenyl ether added is low (the molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 9:1), the polymer molecular chain is still mainly composed of the rigid structure of para-aramid, requiring a higher content of co-solvents to maintain system stability. As the molecular weight increases to a certain extent, the system will precipitate in the form of a solid mixture, making solution dry-jet wet spinning impossible. The traditional para-aramid production process must be used, dissolving the resin in concentrated sulfuric acid before spinning. The strength of the resulting fiber is similar to that of para-aramid, but the elongation at break is improved due to the introduction of flexible ether bonds.

[0083] (3) The comparison between Example 1 and Comparative Example 2 shows that although Comparative Example 2 also uses a three-stage screw mixer, its stirring speed, temperature and residence time are all beyond the range controlled by the present invention, resulting in uneven mixing of materials and an increase in side reactions during the reaction process. The high-speed shear bonding time is insufficient, which limits the growth of polymer molecular weight and ultimately causes a decrease in the dynamic viscosity of the polymer liquid and the mechanical properties of the fiber.

[0084] (4) The comparison between Example 1 and Comparative Example 3 shows that Comparative Example 3 used a two-stage screw mixer and adjusted the stirring speed, temperature and residence time within the scope of this invention. Due to insufficient mixing of materials under low temperature conditions, polycondensation reaction occurs, resulting in local imbalance of monomer ratio and generation of more oligomers, which affects the further improvement of polymer molecular weight and leads to lower dynamic viscosity of polymer liquid and lower fiber mechanical properties.

[0085] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Any simple modifications or equivalent changes made to the above embodiments based on the technical essence of the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for preparing high-elongation ternary aramid fiber, characterized in that: Includes the following steps: S1. A mixture of p-phenylenediamine and 3,4'-diaminodiphenyl ether monomers in a molar ratio of 70:30 to 15:85 is dissolved in a composite solvent system of N-methylpyrrolidone and calcium chloride, and a mixed solution is formed under nitrogen protection. In the composite solvent system, the calcium chloride content is 0.5-7 wt%, and the water content is ≤100 ppm; S2. Control the temperature of the mixed solution at -5 to 5℃, add 60 to 95% of the total amount of terephthaloyl chloride, and then carry out the first-stage twin-screw stirring and mixing at a speed of 30 to 60 r / min for 10 to 30 min to form a prepolymer mixture; S3. Control the temperature of the prepolymer mixture at 0-20℃ and perform a second-stage twin-screw stirring at a speed of 50-100r / min for 15-30min to form the prepolymer stock solution; S4. Control the temperature of the prepolymer solution at 20-90℃, add the remaining terephthaloyl chloride, and then mix it with a third-stage twin-screw mixer at a speed of 100-500 r / min for 30-60 min to form a polymer solution. S5. After neutralization, degassing, and filtration of the polymer solution to obtain the spinning solution, dry-jet wet spinning is performed to obtain ternary aramid fibers. The performance characteristics of the ternary aramid fiber meet the following requirements: The tensile strength is 25–35 cN / dtex, the elastic modulus is 500–800 cN / dtex, and the elongation at break is 3.5–7.0%.

2. The preparation method according to claim 1, characterized in that: In step S4, the solid content of the polymer solution is 5-15%, and the dynamic viscosity is 6-400,000 centipoise.

3. The preparation method according to claim 1, characterized in that: In step S5, the dry-jet wet spinning process includes: extruding the spinning solution from the spinneret, stretching and orienting it through a gas layer before solidification, then entering a coagulation bath to form nascent fibers, followed by washing, drying, stretching, and oiling treatments, and finally winding the fibers to obtain ternary aramid fibers.

4. The preparation method according to claim 3, characterized in that: The gas layer includes air, nitrogen, argon, helium, or carbon dioxide.

5. The preparation method according to claim 3, characterized in that: The coagulation bath is an aqueous solution of N-methylpyrrolidone, wherein the mass concentration of N-methylpyrrolidone is 10-50%.

6. The preparation method according to claim 3, characterized in that: The drying process is carried out at a controlled temperature of 100–350°C and a tension of ≥0.2 cN / dtex.

7. The preparation method according to claim 3, characterized in that: During the stretching process, the fiber is heated to 350–500°C, and the tension is ≤1 cN / dtex.

8. A high-elongation ternary aramid fiber, characterized in that: It is obtained by any one of the preparation methods of claims 1 to 7.

9. An application of the high elongation ternary aramid fiber as described in claim 8, characterized in that: The high-elongation ternary aramid fibers are used to prepare load-bearing and reinforcing components for heavy machinery, marine engineering, or cable systems.

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