A method for preparing high-performance aramid fiber by low-temperature drawing

Abstract

The application relates to the technical field of chemical fiber production, and discloses a method for preparing high-performance aramid fiber through low-temperature drafting, which comprises the following steps: adding a temporary toughening agent into an aromatic polyamide solution and stirring to obtain a spinning solution, passing through a spinneret, entering a coagulation bath and a washing bath in sequence after passing through an air layer to obtain a nascent fiber; and then drafting, heat-drawing and heat-setting to obtain aramid fiber. Through the introduction of a specific temporary toughening agent into the aromatic polyamide spinning solution, the good mutual solubility of the temporary toughening agent with a spinning solvent and the plasticizing effect on the fiber are utilized, high-multiple drafting of aramid fiber at low temperature is successfully realized, the bottleneck of traditional process technology is broken, the prepared aramid fiber has excellent comprehensive performance, and the aramid fiber has important industrial application value and market prospect.

Description

Technical Field

[0001] This invention relates to the field of chemical fiber production technology, and more specifically, to a method for preparing high-performance aramid fibers by low-temperature drawing. Background Technology

[0002] Aramid fibers, as a type of high-performance synthetic fiber with a unique rigid molecular chain structure, have become indispensable core materials in high-end fields such as aerospace, defense, special protective equipment, and high-performance composite materials due to their excellent breaking strength, elastic modulus, high-temperature stability, and chemical corrosion resistance. Currently, the mainstream industrial preparation process for aramid fibers is solution spinning, including two core routes: wet spinning and dry-jet wet spinning. The key technical steps are concentrated in spinning solution preparation, coagulation and shaping, drawing and orientation, and heat treatment curing. Among these, the drawing process is the core step in controlling the arrangement of molecular chains within the fiber and improving its orientation and crystallinity, directly determining the final mechanical property boundaries of the fiber.

[0003] In traditional aramid fiber manufacturing processes, the presence of numerous rigid aromatic ring structures in the aromatic polyamide molecular chains results in extremely strong intermolecular hydrogen bonding, leading to very poor plasticity in nascent fibers. This makes it difficult for the molecular chains to undergo effective slippage and orientation reconstruction at normal temperatures. To achieve sufficient draw ratios, existing technologies generally employ high-temperature drawing processes, typically reaching temperatures above 200°C, with some processes even reaching 250-300°C. However, high-temperature drawing processes have several insurmountable technical drawbacks: First, the high-temperature environment accelerates the thermal oxidative degradation of the aramid fiber molecular chains, causing defects on the fiber surface, which not only reduces breaking strength and elastic modulus but also affects the fiber's long-term weather resistance. Second, high-temperature drawing requires sophisticated high-temperature heating and control equipment, resulting in high equipment investment costs and significant energy consumption during operation, significantly increasing production costs. Third, under high-temperature conditions, the seals and heating elements of the spinning equipment are prone to wear and tear, increasing maintenance frequency and costs. Furthermore, high temperatures demand extremely high precision in process operation, easily leading to problems such as uneven fiber diameter and orientation fluctuations, which are detrimental to stable industrial-scale production.

[0004] To address the drawbacks of high-temperature drawing, researchers in this field have attempted to improve the plasticity of nascent fibers by optimizing spinning solution formulations and adjusting coagulation bath parameters, but with limited success. Other approaches have tried introducing conventional plasticizers to reduce intermolecular forces, but these plasticizers have poor compatibility with aromatic polyamides, making it difficult to achieve uniform molecular-level dispersion. Furthermore, most have high boiling points and cannot be completely removed during subsequent heat treatment, leaving residues that severely impact the fiber's high-temperature resistance and mechanical stability. Therefore, developing a technology for preparing aramid fibers that achieves high-ratio drawing at low temperatures without residue risk is crucial for overcoming traditional process bottlenecks and promoting quality improvement and cost reduction in the aramid fiber industry. This invention presents an innovative solution to this technical challenge. Summary of the Invention

[0005] In view of this, the present invention proposes a method for preparing high-performance aramid fibers by low-temperature drawing, which aims to solve the problems of poor plasticity of nascent fibers, high energy consumption due to high-temperature drawing, complex process, easy thermal degradation of fibers and unstable product performance in the traditional preparation of aramid fibers.

[0006] This invention proposes a method for preparing high-performance aramid fibers by low-temperature drawing, comprising the following steps: Step 1): An aromatic polyamide solution is prepared by polycondensation reaction of aromatic amide and aromatic acyl chloride; Step 2): Add a temporary toughening agent to the aromatic polyamide solution and stir to obtain the spinning solution; Step 3): The spinning solution is passed through a spinneret, then through an air layer, and then sequentially into a coagulation bath and a water washing bath to obtain nascent fibers; Step 4): The nascent fibers are successively subjected to a drawing process, a hot drawing process, and a heat setting process to obtain aramid fibers; The aromatic amide is m-phenylenediamine or a mixture of aromatic diamines; The aromatic diamine mixture consists of at least one of m-phenylenediamine and other aromatic diamines; The other aromatic diamines include: p-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-di(trifluoromethyl)diaminobiphenyl, 2-(4-aminophenyl)-5-aminobenzimidazole or 2-(4-aminophenyl)-6-aminobenzoxazole; The aromatic acyl chloride is a mixture of isophthaloyl chloride, isophthaloyl chloride and terephthaloyl chloride; The temporary toughening agent is at least one of methyl isopropyl ketone, methyl isobutyl ketone, isopropylidene acetone, diisopropyl ketone, cyclohexanone, dichlorobenzene, 1,2,4-trichlorobenzene, and benzophenone, and the amount of the temporary toughening agent added is 1 to 20 wt% of the aromatic polyamide.

[0007] Preferably, in the aromatic diamine mixture, the molar proportion of m-phenylenediamine is not less than 60%.

[0008] Preferably, in the mixture of isophthaloyl chloride and terephthaloyl chloride, the molar proportion of isophthaloyl chloride is not less than 60%.

[0009] Preferably, the polycondensation reaction temperature in step 1) is -10~25℃, and the reaction time is 6~12 hours; calcium hydroxide, an acid-binding agent, also needs to be added during the reaction, and the amount added is 1.2~2.5 times that of the acyl chloride functional group.

[0010] Preferably, the solvent in step 1) includes at least one of N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), 1-methyl-2-pyrrolidone (NMP), and dimethyl sulfoxide (DMSO).

[0011] Preferably, the aromatic polyamide solution further includes a co-solvent, which is calcium chloride or lithium chloride, and the amount added is 1 wt% to 5 wt% of the aromatic polyamide, and the solid content of the solution is 15 to 30 wt%.

[0012] Preferably, the spinneret has an aperture of 10~50μm and an aspect ratio of 2~4:1.

[0013] Preferably, the height of the air layer is 0.5~10cm.

[0014] Preferably, the coagulation bath is a blend of spinning solution solvent and water, wherein the water volume ratio is 65%~90%, the coagulation bath temperature is controlled at 25~60℃, and the fiber passing time is 5~30s.

[0015] Preferably, the water bath temperature is 40~80℃, and the fiber bath time is 20~60s.

[0016] Preferably, the stretching process involves a stretching temperature of 50-100℃, a stretching ratio of 2-6 times, and a stretching speed of 3-10 m / min.

[0017] Preferably, the stretching temperature of the hot stretching process is 150~300℃, and the stretching ratio is 1.01~2 times.

[0018] Preferably, the heat setting temperature is 350~400℃.

[0019] Another object of the present invention is to provide a method for preparing high-performance aramid fibers by low-temperature stretching.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention introduces a specific temporary toughening agent into the aromatic polyamide spinning solution, leveraging its good miscibility with the spinning solvent and its precise plasticizing effect on the fiber. This successfully achieves a high draw ratio of 2-6 times at low temperatures of 50-100℃ for aramid fibers, overcoming the technical bottleneck of traditional processes requiring high-temperature drawing. By rationally limiting the raw material ratio, the amount of temporary toughening agent added, the spinning conditions, and the drawing / heat treatment parameters, the uniform orientation and high crystallinity of the molecular chains within the fiber are ensured. Example data shows that the aramid fibers prepared by this invention have a crystallinity ≥65%, an orientation degree ≥90%, a breaking strength ≥4.1 cN / dtex, and an elastic modulus ≥7.5 cN / dtex, exhibiting excellent overall performance. Simultaneously, the process has low energy consumption, a simplified procedure, no residue risk, and good compatibility with existing equipment, demonstrating significant industrial application value and market potential. Attached Figure Description

[0021] Various other advantages and benefits will become apparent to those skilled in the art upon reading the following detailed description of preferred embodiments. The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings: Figure 1 This is a tensile curve of the aramid fiber prepared in Example 2; Figure 2 This is a tensile curve of the aramid fiber prepared in Example 4; Figure 3 This is a photograph of the aramid fiber prepared in Example 6. Detailed Implementation

[0022] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0023] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0024] 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. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0025] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0026] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0027] This invention proposes a method for preparing high-performance aramid fibers by low-temperature drawing, comprising the following steps: Step 1): An aromatic polyamide solution is prepared by polycondensation reaction of aromatic amide and aromatic acyl chloride; Step 2): Add a temporary toughening agent to the aromatic polyamide solution and stir to obtain the spinning solution; Step 3): The spinning solution is passed through a spinneret, then through an air layer, and then sequentially into a coagulation bath and a water washing bath to obtain nascent fibers; Step 4): The nascent fibers are successively subjected to a drawing process, a hot drawing process, and a heat setting process to obtain aramid fibers; The aromatic amide is m-phenylenediamine or a mixture of aromatic diamines; The aromatic diamine mixture consists of at least one of m-phenylenediamine and other aromatic diamines; The other aromatic diamines include: p-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-di(trifluoromethyl)diaminobiphenyl, 2-(4-aminophenyl)-5-aminobenzimidazole or 2-(4-aminophenyl)-6-aminobenzoxazole; The aromatic acyl chloride is a mixture of isophthaloyl chloride, isophthaloyl chloride and terephthaloyl chloride; The temporary toughening agent is at least one of methyl isopropyl ketone, methyl isobutyl ketone, isopropylidene acetone, diisopropyl ketone, cyclohexanone, dichlorobenzene, 1,2,4-trichlorobenzene, and benzophenone, and the amount of the temporary toughening agent added is 1 to 20 wt% of the aromatic polyamide.

[0028] In this invention, the structural formula of m-phenylenediamine is: The structural formula of the p-phenylenediamine is: The structural formula of the 2,2'-dimethyl-4,4'-diaminobiphenyl is as follows: The structural formula of 2,2'-bis(trifluoromethyl)diaminobiphenyl is: The structural formula of the 2-(4-aminophenyl)-5-aminobenzimidazole is as follows: The structural formula of the 2-(4-aminophenyl)-6-aminobenzoxazole is as follows: .

[0029] In this invention, the coagulation bath achieves phase separation and solidification of the spinning solution through the dual diffusion of solvent and water, forming nascent fibers with a preliminary structure; the core function of the water washing bath is to remove residual spinning solvent inside the fiber, avoiding the hindrance of molecular chain orientation by solvent residue during subsequent drawing; nascent fiber drawing is a key step in improving the degree of molecular chain orientation, guiding the molecular chains to align along the fiber axis through external force; hot drawing further optimizes the molecular chain orientation structure at a moderately high temperature, eliminating internal stress generated during the drawing process; heat setting simultaneously achieves complete removal of temporary toughening agent and perfection of fiber crystal structure, ultimately obtaining high-performance aramid fibers.

[0030] In this invention, the temporary toughening agent and the spinning solvent form a molecularly uniform dispersion system, which plays a highly efficient plasticizing role inside the nascent fiber. By weakening the hydrogen bonding and van der Waals forces between aromatic polyamide molecular chains, it significantly improves the plasticity and molecular chain slippage ability of the fiber, making high stretching at low temperatures a reality. During the subsequent high-temperature heat treatment, the temporary toughening agent can be completely removed by volatilization or thermal decomposition, and will not remain in the final fiber, thus avoiding negative impacts on fiber performance.

[0031] In this invention, the specific types of temporary toughening agents are also specified because: these compounds have excellent miscibility with spinning solvents, can achieve uniform molecular-level dispersion in spinning solutions, and avoid uneven local plasticization; they have strong plasticizing targeting, can precisely weaken the hydrogen bonding between aromatic polyamide molecular chains, significantly improve fiber plasticity, and do not damage the rigid structure of the molecular chains themselves; their boiling points or thermal decomposition temperatures are lower than the heat setting temperatures, and they can be completely volatilized or decomposed and removed during the heat setting process without any residue.

[0032] In this invention, the amount of temporary toughening agent added is also limited. If the amount added is too low: the plasticizing effect is insufficient, it cannot effectively improve the plasticity of the nascent fiber, the molecular chain slippage is difficult at low temperature, it is difficult to achieve a high stretching ratio of more than 2 times, and the improvement of fiber orientation is limited; if the amount added is too high: some toughening agent is difficult to completely disperse in the spinning solution, resulting in a decrease in the uniformity of the spinning solution, and toughening agent aggregation areas are easily formed inside the fiber after forming; and during the subsequent heat setting process, a large amount of toughening agent will rapidly volatilize and form pores inside the fiber, reducing the fiber density and mechanical properties.

[0033] In this invention, the molar percentage of m-phenylenediamine in the aromatic diamine mixture is preferably not less than 60%, and more preferably not less than 80%.

[0034] In this invention, the reason for limiting the proportion of m-phenylenediamine is that its molecular structure is symmetrical and moderately rigid. After reacting with acyl chloride, the polyamide molecular chains formed have good regularity, which is conducive to the directional arrangement of molecular chains during the stretching process, thereby improving the crystallinity and orientation of the fiber. Other diamines can be introduced as comonomers in appropriate amounts to fine-tune the flexibility of the molecular chains, but if the proportion is too high, it will destroy the regularity of the molecular chains, resulting in a decrease in crystallinity and damage to mechanical properties.

[0035] In this invention, the molar percentage of isophthaloyl chloride in the mixture of isophthaloyl chloride and terephthaloyl chloride is preferably not less than 60%, more preferably not less than 80%.

[0036] The reason for limiting the proportion of isophthaloyl chloride in this invention is that isophthaloyl chloride and m-phenylenediamine have excellent structural matching and moderate reactivity, which can ensure that the polycondensation reaction proceeds fully and forms a high molecular weight aromatic polyamide.

[0037] In this invention, the polycondensation reaction temperature in step 1) is preferably -10~25℃, more preferably -5~20℃; the reaction time is preferably 6~12 hours, more preferably 8~10 hours; calcium hydroxide, an acid-binding agent, is also added during the reaction, and the amount added is preferably 1.2~2.5 times that of the acyl chloride functional group, more preferably 1.5~2.0 times.

[0038] In this invention, the aromatic polyamide solution also includes a co-solvent, which is preferably calcium chloride or lithium chloride, and the amount added is preferably 1 wt% to 5 wt% of the aromatic polyamide, more preferably 2 wt% to 4 wt%.

[0039] In this invention, the solvent of the aromatic polyamide solution is preferably at least one of N,N-dimethylacetamide, N,N-dimethylformamide, 1-methyl-2-pyrrolidone, and dimethyl sulfoxide; the solid content of the solution is preferably 15-30 wt%, more preferably 20-25 wt%. If the solid content is too low, the viscosity of the spinning solution is insufficient, resulting in a loose fiber structure and high internal porosity during forming in the coagulation bath. This makes the fiber prone to breakage due to stress concentration during the drawing process, and the final fiber's crystallinity and mechanical properties will be significantly lower. If the solid content is too high, the viscosity of the spinning solution increases sharply, the fluidity deteriorates, and it becomes difficult to achieve uniform spinning through the small orifices of the spinneret. This easily leads to defects such as uneven fiber diameter, surface streaks, or burrs. At the same time, bubbles are easily generated inside the spinning solution, further deteriorating the fiber forming quality.

[0040] In this invention, the orifice diameter of the spinneret is preferably 10~50μm, more preferably 20~40μm; if the orifice diameter is too small, the spinneret resistance is high, the spinneret is prone to blockage, and the formed fiber is too fine, resulting in insufficient tensile strength during the drawing process and a significant increase in the breakage rate; if the orifice diameter is too large, the fiber diameter is too coarse, and the molecular chain orientation is difficult to be uniform during the subsequent drawing process, resulting in large differences in the properties of the inner and outer layers of the fiber and fluctuations in the overall mechanical properties. In this invention, the aspect ratio of the spinneret is preferably 2 to 4:1, more preferably 3:1. If the aspect ratio is too small, the shearing effect of the spinning solution in the spinneret orifice is insufficient, the molecular chain arrangement is disordered, and the initial structural stability of the formed fiber is poor; if the aspect ratio is too large, the spinning speed is significantly reduced, the production efficiency decreases, and the fiber surface is prone to stripe-like defects due to excessive shear stress.

[0041] In this invention, the height of the air layer is preferably 0.5~10cm, more preferably 2~8cm. The air layer is the transition zone from the spinneret to the coagulation bath of the spinning solution, and its height directly affects the fiber forming quality: if the height is too low, the solvent will not evaporate sufficiently, the phase separation rate in the coagulation bath will be too fast, the fiber surface will solidify rapidly, and the internal solvent will be difficult to diffuse, resulting in stress concentration inside the fiber; if the height is too high, the spinneret will be easily disturbed by the ambient airflow, resulting in bending and swaying, leading to uneven fiber diameter, and even filament bundling.

[0042] In this invention, the coagulation bath is preferably a blend of spinning solution solvent and water, wherein the water volume ratio is preferably 65%~90%, more preferably 70%~80%; the coagulation bath temperature is preferably 25~60℃, more preferably 30~50℃; and the fiber passing time is preferably 5~30s, more preferably 10~20s. The coagulation bath is a blend of spinning solution solvent and water, wherein the water ratio directly determines the coagulation rate: if the water ratio is too low, the coagulation rate is too slow, the spinning solution streams swell excessively in the coagulation bath, resulting in a loose fiber structure with high porosity; if the water ratio is too high, the coagulation rate is too fast, a dense hard shell quickly forms on the fiber surface, the internal solvent cannot diffuse and drain out in time, leading to cracks and pores inside the fiber, making it prone to breakage during subsequent drawing.

[0043] In this invention, the water washing temperature is preferably 40~80℃, more preferably 50~70℃; the fiber washing time is preferably 20~60s, more preferably 30~50s. The function of the water washing is to remove residual spinning solvent and some unbonded toughening agent from inside the fiber. If the temperature is too low: the solubility of solvent and toughening agent in water is low, resulting in incomplete cleaning. Residual substances will hinder the orientation of molecular chains during subsequent drawing, affecting mechanical properties and high-temperature resistance. If the temperature is too high: the fiber is prone to excessive swelling in high-temperature water, destroying the initially formed molecular chain network structure, leading to a significant increase in fiber breakage rate during drawing.

[0044] In this invention, the stretching temperature of the stretching process is preferably 50~100℃, more preferably 60~80℃; the stretching ratio is preferably 2~6 times, more preferably 3~5 times; and the stretching speed is preferably 3~10m / min, more preferably 4~8m / min.

[0045] In this invention, nascent fiber stretching is a crucial step in improving molecular chain orientation. Its parameter settings directly determine the stretching effect and fiber performance stability: If the temperature is too low, the plasticizing effect of the temporary toughening agent is not fully utilized, resulting in poor fiber plasticity, high molecular chain slip resistance, and difficulty in achieving high-ratio stretching. Forced stretching leads to a high fiber breakage rate. Conversely, excessively high temperatures not only increase energy consumption but may also cause some temporary toughening agents to volatilize prematurely, losing their plasticizing effect. Simultaneously, slight oxidation easily occurs on the fiber surface, affecting appearance and weather resistance. If the stretching ratio is too low, the improvement in molecular chain orientation is limited, and the fiber's breaking strength and elastic modulus cannot reach high-performance standards. If the ratio is too high, the internal stress of the fiber exceeds the molecular chain's tolerance limit, easily leading to molecular chain breakage, resulting in decreased fiber breaking strength and abnormally low elongation at break. If the stretching speed is too fast, the fiber is under stress for a short time, resulting in uneven stress transmission, easily causing defects such as uneven fiber thickness and surface burrs, and even stretching breakage. If the speed is too slow, production efficiency is low, and the fiber is prone to creep during stretching, leading to poor orientation stability and large batch-to-batch performance fluctuations.

[0046] In this invention, the stretching temperature of the hot stretching process is preferably 150~300℃, more preferably 180~260℃; the stretching ratio is preferably 1.01~2 times, more preferably 1.2~1.5 times.

[0047] In this invention, thermal stretching is a crucial step in further optimizing molecular chain orientation based on initial stretching. It must be performed at a temperature that maintains a certain level of molecular chain mobility, primarily to allow the plasticizer to volatilize while preserving the fiber's internal density (high temperature increases molecular chain movement). If the temperature is too low, the molecular chain mobility is insufficient, making further orientation reconstruction difficult and resulting in poor stretching optimization. If the temperature is too high, the fiber molecular chains are prone to thermal degradation, leading to a significant decrease in breaking strength and elastic modulus. If the stretching ratio is too low, the orientation optimization effect is weak and cannot compensate for the deficiencies of initial stretching; if the stretching ratio is too high, stress concentration occurs within the fiber, making it prone to breakage or structural defects.

[0048] In this invention, the heat setting temperature is preferably 350~400℃, more preferably 360~380℃.

[0049] In this invention, heat setting serves two important functions: to completely volatilize or decompose the temporary toughening agent; and to promote the orderly arrangement of molecular chains, improve fiber crystallinity, and further optimize and eliminate internal stress. If the temperature is too low, the temporary toughening agent will not be completely removed, and the residual substances will reduce the fiber's high-temperature resistance and mechanical stability, and the crystallinity will be insufficient. If the temperature is too high, the aramid fiber molecular chains will undergo thermal oxidative degradation, resulting in a significant decrease in fiber strength and modulus, as well as abnormal elongation at break.

[0050] Another object of the present invention is to provide a method for preparing high-performance aramid fibers by low-temperature stretching.

[0051] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0052] Example 1 1) Preparation of aromatic polyamide: m-phenylenediamine and isophthaloyl chloride were subjected to a polycondensation reaction in DMAc (calcium hydroxide was used as the acid binder, and the amount added was 1.2 times that of the acyl chloride functional group; lithium chloride was used as the co-solvent, and the amount added was 3wt%). An aromatic polyamide solution with a solid content of 20wt% was prepared by reacting at -5℃ for 10h. 2) Preparation of spinning solution: Add isopropylidene acetone (temporary toughening agent, 8wt%) to the above solution and stir for 2 hours until uniformly dispersed; 3) Spinning and forming: The spinneret has an aperture of 25μm, an aspect ratio of 3:1, an air layer height of 4cm, and a coagulation bath of DMAc and water (75% by volume of water). The temperature of the coagulation bath is 25℃, and the fiber passes through for 30s. The water washing bath temperature is 55℃, and the fiber passes through for 30s to obtain nascent fibers. 4) Stretching and heat treatment: The nascent fiber is stretched at 65℃, with a stretching ratio of 3.5 times and a stretching speed of 5.5m / min; the hot stretching temperature is 200℃, with a stretching ratio of 1.3 times; the heat setting temperature is 365℃, and after holding at the temperature for 30s, it is wound to obtain aramid fiber.

[0053] Example 2 1) Preparation of aromatic polyamide: m-phenylenediamine and p-phenylenediamine (molar ratio 7:3) were mixed and polycondensed with isophthaloyl chloride and terephthaloyl chloride (molar ratio 8:2) in DMAc (the acid binder was calcium hydroxide, and the amount added was 1.5 times that of the acyl chloride functional groups; the cosolvent was calcium chloride, and the amount added was 2wt%). An aromatic polyamide solution with a solid content of 15wt% was prepared under the condition of reaction at 0℃ for 9h. 2) Preparation of spinning solution: Add methyl isobutyl ketone (temporary toughening agent, 1 wt%) to the above solution and stir for 2 hours until uniformly dispersed; 3) Spinning and forming: The spinneret has an aperture of 10μm, an aspect ratio of 2:1, an air layer height of 0.5cm, and the coagulation bath is a blend of DMAc and water (water volume ratio of 65%). The temperature of the coagulation bath is 35℃, and the fiber passage time is 25s. The water washing bath temperature is 40℃, and the fiber passage time is 60s to obtain nascent fibers. 4) Stretching and heat treatment: The nascent fiber is stretched at 50℃, with a stretching ratio of 2 and a stretching speed of 3m / min; the hot stretching temperature is 150℃ and the stretching ratio is 1.01; the heat setting temperature is 350℃, and after holding at the temperature for 30s, it is wound to obtain aramid fiber.

[0054] Figure 1 The figure shows the tensile curve of the aramid fiber prepared in Example 2. As can be seen from the figure, the curve first rises linearly, then grows steadily, and finally breaks after reaching the peak.

[0055] Example 3 1) Preparation of aromatic polyamide: m-phenylenediamine and 4,4'-diaminodiphenyl ether (molar ratio 6:4) were mixed and polycondensed with isophthaloyl chloride and terephthaloyl chloride (molar ratio 9:1) in NMP (the acid binder was calcium hydroxide, and the amount added was 1.8 times that of the acyl chloride functional groups; the cosolvent was lithium chloride, and the amount added was 4wt%). An aromatic polyamide solution with a solid content of 22.5wt% was prepared under the condition of reaction at 10℃ for 8h. 2) Preparation of spinning solution: Add cyclohexanone (temporary toughening agent, 10.5 wt%) to the above solution and stir for 2 hours until uniformly dispersed; 3) Spinning and forming: The spinneret has an aperture of 30μm, an aspect ratio of 3:1, an air layer height of 5cm, and the coagulation bath is a mixture of NMP and water (water volume percentage 77.5%). The temperature of the coagulation bath is 45℃, and the fiber passage time is 18s. The water washing bath temperature is 60℃, and the fiber passage time is 40s, to obtain nascent fibers. 4) Stretching and heat treatment: The nascent fiber is stretched at 75℃, with a stretching ratio of 4 times and a stretching speed of 6.5m / min; the hot stretching temperature is 225℃, with a stretching ratio of 1.5 times; the heat setting temperature is 375℃, and after holding at the temperature for 30s, it is wound to obtain aramid fiber.

[0056] Example 4 1) Preparation of aromatic polyamide: m-phenylenediamine and p-phenylenediamine (molar ratio 9:1) were mixed and polycondensed with isophthaloyl chloride and terephthaloyl chloride (molar ratio 6:4) in DMF (calcium hydroxide was used as the acid binder, and the amount added was 2.0 times that of the acyl chloride functional groups; lithium chloride was used as the cosolvent, and the amount added was 5 wt%). An aromatic polyamide solution with a solid content of 30 wt% was prepared under the condition of reaction at -10℃ for 12 h. 2) Preparation of spinning solution: Add dichlorobenzene (temporary toughening agent, 20wt%) to the above solution and stir for 2 hours until uniformly dispersed; 3) Spinning and forming: The spinneret has an aperture of 50μm, an aspect ratio of 4:1, an air layer height of 10cm, and the coagulation bath is a blend of DMF and water (water volume ratio of 90%). The temperature of the coagulation bath is 55℃, and the fiber passage time is 15s. The water washing bath temperature is 80℃, and the fiber passage time is 20s to obtain nascent fibers. 4) Stretching and heat treatment: The nascent fiber is stretched at 100℃, with a stretching ratio of 6 times and a stretching speed of 10m / min; the hot stretching temperature is 300℃, with a stretching ratio of 2 times; the heat setting temperature is 400℃, and after holding at the temperature for 30s, it is wound to obtain aramid fiber.

[0057] Figure 2 The image shows the tensile curve of the aramid fiber prepared in Example 4, and... Figure 1 compared to, Figure 2 The initial slope of the curve is steeper (higher elastic modulus), the steady growth phase is longer, and the peak value at break is higher. Due to the optimization of process parameters such as solid content and draw ratio, the fiber mechanical properties are superior to those of Example 2.

[0058] Example 5 1) Preparation of aromatic polyamide: m-phenylenediamine and 4,4'-diaminodiphenyl ether (molar ratio 8:2) were mixed and polycondensed with isophthaloyl chloride and terephthaloyl chloride (molar ratio 7:3) in DMSO (the acid binder was calcium hydroxide, and the amount added was 1.6 times that of the acyl chloride functional groups; the cosolvent was lithium chloride, and the amount added was 3wt%). An aromatic polyamide solution with a solid content of 18wt% was prepared under the condition of reaction at 15℃ for 7h. 2) Preparation of spinning solution: Add benzophenone (temporary toughening agent, 5wt%) to the above solution and stir for 2 hours until uniformly dispersed; 3) Spinning and forming: The spinneret has an aperture of 20μm, an aspect ratio of 2.5:1, an air layer height of 3cm, and the coagulation bath is a blend of DMSO and water (70% by volume). The coagulation bath temperature is 40℃, and the fiber passage time is 20s. The water washing bath temperature is 50℃, and the fiber passage time is 30s, to obtain nascent fibers. 4) Stretching and heat treatment: The nascent fiber is stretched at 60℃, with a stretching ratio of 3 times and a stretching speed of 5m / min; the hot stretching temperature is 180℃, with a stretching ratio of 1.2 times; the heat setting temperature is 360℃, and after holding at the temperature for 30s, it is wound to obtain aramid fiber.

[0059] Example 6 1) Preparation of aromatic polyamide: m-phenylenediamine and p-phenylenediamine (molar ratio 7.5:2.5) were mixed and polycondensed with isophthaloyl chloride and terephthaloyl chloride (molar ratio 8.5:1.5) in DMAc (the acid binder was calcium hydroxide, and the amount added was 2.3 times that of the acyl chloride functional groups; the cosolvent was calcium chloride, and the amount added was 2wt%). An aromatic polyamide solution with a solid content of 25wt% was prepared under the condition of reaction at 25℃ for 6h. 2) Preparation of spinning solution: Add methyl isopropyl ketone (temporary toughening agent, 15wt%) to the above solution and stir for 2 hours until uniformly dispersed; 3) Spinning and forming: The spinneret has an aperture of 40μm, an aspect ratio of 3.5:1, an air layer height of 8cm, and the coagulation bath is a blend of DMAc and water (water volume percentage of 85%). The temperature of the coagulation bath is 60℃, and the fiber passage time is 5s. The water washing bath temperature is 70℃, and the fiber passage time is 25s to obtain nascent fibers. 4) Stretching and heat treatment: The nascent fiber is stretched at 90℃, with a stretching ratio of 5 times and a stretching speed of 8m / min; the hot stretching temperature is 280℃, with a stretching ratio of 1.8 times; the heat setting temperature is 390℃, and after holding at the temperature for 30s, it is wound to obtain aramid fiber.

[0060] Figure 3 This is a photograph of the aramid fiber prepared in Example 6.

[0061] Comparative Example 1 Based on Example 3, without the addition of cyclohexanone (temporary toughening agent), all other process parameters are completely consistent with Example 3. The nascent fibers prepared in this way achieve a maximum draw ratio of 1.2 times during the drawing process; further increasing the draw ratio results in filament breakage and fuzzing.

[0062] Comparative Example 2 The stretching step is omitted, and hot stretching and heat setting are performed directly. The remaining process parameters are completely consistent with those in Example 3. Due to the high temperature release of plasticizer, obvious bubbles and fiber breakage occur in the fibers.

[0063] Comparative Example 3 The hot stretching and heat setting steps are omitted, and the remaining process parameters are completely consistent with those in Example 3.

[0064] Performance test results: The performance test results for the embodiments and comparative examples are shown in Table 1 below.

[0065] Table 1. Performance Test Table for Examples and Comparative Examples

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A method for preparing high-performance aramid fibers by low-temperature drawing, characterized in that, Includes the following steps: Step 1): Aromatic amide and aromatic acyl chloride are subjected to a polycondensation reaction in a solvent to obtain an aromatic polyamide solution; Step 2): Add a temporary toughening agent to the aromatic polyamide solution and stir to obtain the spinning solution; Step 3): The spinning solution is passed through a spinneret, then through an air layer, and then sequentially into a coagulation bath and a water washing bath to obtain nascent fibers; Step 4): The nascent fibers are sequentially processed through a drawing process, a hot drawing process, and a heat setting process to obtain aramid fibers; The aromatic amide is m-phenylenediamine or a mixture of aromatic diamines; The aromatic diamine mixture consists of at least one of m-phenylenediamine and other aromatic diamines; The other aromatic diamines include: p-phenylenediamine, 2,2'-dimethyl-4,4'-diaminobiphenyl, 2,2'-di(trifluoromethyl)diaminobiphenyl, 2-(4-aminophenyl)-5-aminobenzimidazole or 2-(4-aminophenyl)-6-aminobenzoxazole; The aromatic acyl chloride is a mixture of isophthaloyl chloride, isophthaloyl chloride and terephthaloyl chloride; The temporary toughening agent is at least one of methyl isopropyl ketone, methyl isobutyl ketone, isopropylidene acetone, diisopropyl ketone, cyclohexanone, dichlorobenzene, 1,2,4-trichlorobenzene, and benzophenone, and the amount of the temporary toughening agent added is 1 to 20 wt% of the aromatic polyamide.

2. The method for preparing high-performance aramid fibers by low-temperature drawing according to claim 1, characterized in that, In the aromatic diamine mixture, the molar percentage of m-phenylenediamine is not less than 60%; In the mixture of isophthaloyl chloride and terephthaloyl chloride, the molar percentage of isophthaloyl chloride is not less than 60%.

3. The method for preparing high-performance aramid fibers by low-temperature drawing according to claim 1 or 2, characterized in that, In step 1), the molar ratio of aromatic amide to aromatic acyl chloride is 1:(1~1.05). The polycondensation reaction temperature is -10~25℃, and the reaction time is 6~12 hours. During the reaction, calcium hydroxide, an acid-binding agent, also needs to be added, and the amount added is 1.2~2.5 times that of the acyl chloride functional group.

4. The method for preparing high-performance aramid fibers by low-temperature drawing according to claim 3, characterized in that, The solvent mentioned in step 1) includes at least one of N,N-dimethylacetamide, N,N-dimethylformamide, 1-methyl-2-pyrrolidone, and dimethyl sulfoxide; The aromatic polyamide solution also includes a co-solvent, which is calcium chloride or lithium chloride, and the amount added is 1 wt% to 5 wt% of the aromatic polyamide, and the solid content of the solution is 15 to 30 wt%.

5. The method for preparing high-performance aramid fibers by low-temperature drawing according to claim 1, 2, or 4, characterized in that, The spinneret has an aperture of 10~50μm and an aspect ratio of 2~4:

1.

6. The method for preparing high-performance aramid fibers by low-temperature drawing according to claim 5, characterized in that, The height of the air layer is 0.5~10cm.

7. The method for preparing high-performance aramid fibers by low-temperature drawing according to claim 1, 2, 4 or 6, characterized in that, The coagulation bath is a mixture of spinning solution solvent and water, wherein the water volume ratio is 65%~90%, the coagulation bath temperature is controlled at 25~60℃, and the fiber passes through for 5~30s. The water bath temperature is 40~80℃, and the fiber passing time is 20~60s.

8. The method for preparing high-performance aramid fibers by low-temperature drawing according to claim 7, characterized in that, The drawing process involves a drawing temperature of 50-100℃, a drawing ratio of 2-6 times, and a drawing speed of 3-10 m / min.

9. The method for preparing high-performance aramid fibers by low-temperature drawing according to claim 1, 2, 4, 6 or 8, characterized in that, The hot drawing process has a drawing temperature of 150~300℃ and a drawing ratio of 1.01~2 times. The heat setting temperature is 350~400℃.

10. High-performance aramid fibers prepared by any one of the low-temperature drawing methods described in claims 1 to 9.

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