Preparation method of special-shaped section aramid fiber

Abstract

The present application relates to a kind of preparation methods of special-shaped section aramid fiber, belong to high-performance chemical fiber technical field.The preparation method is: S1, aramid polymerization stock solution is added with polyvinyl alcohol polymer, and homogeneous mixture is obtained to spinning solution;The mass concentration of polyvinyl alcohol polymer in the spinning solution is 20-30%.S2, spinning solution is sprayed out through spinneret, and successively carried out coagulation bath forming, multi-stage drawing bath drafting, finally through washing, drying, crystallization and shaping to obtain special-shaped section aramid fiber.In the preparation method of special-shaped section aramid fiber of the present application, high mass concentration polyvinyl alcohol is added in meta polymer stock solution, which reduces the coagulation strength and delays the coagulation rate in coagulation bath and drawing bath stage, and the method of using low coagulation bath temperature and combining two-stage stretching and washing process to prepare cashew-shaped section aramid fiber, the strength and elongation of fiber are relatively high, and it has wide application prospect in papermaking field.

Description

Technical Field

[0001] This invention relates to a method for preparing aramid fibers with irregular cross-sections, belonging to the field of high-performance chemical fiber technology. Background Technology

[0002] Meta-aramid fibers (such as Nomex) are widely used in protection, insulation, and filtration due to their excellent heat resistance, flame retardancy, and electrical insulation properties. However, traditional meta-aramid fibers are mostly circular in cross-section, with smooth surfaces and limited interfacial bonding strength with the resin matrix, restricting their application in composite materials. Furthermore, the relatively small specific surface area of ​​circular cross-section fibers leaves room for improvement in fabric coverage, gloss, and capillary effect. The circular cross-section of traditional aramid fibers also limits the cohesion of fiber assemblies and the interfacial properties of composite materials. Irregularly shaped fibers (such as flat, cashew-shaped, and hollow fibers) can significantly increase the specific surface area, improve fiber wettability, adsorption, and bonding strength with the resin matrix, thereby enhancing the overall performance of composite materials.

[0003] Currently, while there are reports on irregularly shaped cross-section fibers, they mostly focus on general-purpose fibers such as polyester and nylon. For rigid-chain polymers like meta-aramid, due to their solution properties, high freezing point, and the difficulty of molecular chain migration during solidification, it is extremely difficult to prepare fibers with regular structures and high irregularity using conventional spinning techniques. Especially for asymmetric cross-sections like cashew nuts, precise control of the double diffusion kinetics during solidification is required, making the technology even more challenging.

[0004] Patent application CN110863257A discloses a method for preparing irregularly shaped fibers. While the high temperature accelerates the coagulation process, it can also lead to excessively rapid coagulation, resulting in significant differences between the fiber's outer and core structures, causing defects. The contours of the irregular cross-section are difficult to maintain perfectly during rapid coagulation, easily deforming and tending towards roundness. Increased internal pores and decreased density negatively impact mechanical properties.

[0005] Therefore, it is of great significance to develop a method for preparing aramid fibers that can precisely control the solidification process, perfectly maintain the shape of irregular cross sections, obtain excellent mechanical properties, and consume less energy. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a method for preparing aramid fibers with irregular cross-sections. Polyvinyl alcohol polymer is added to the raw solution, and a low-temperature coagulation bath is used in conjunction with polyvinyl alcohol to slow down the phase separation rate. Combined with a unique two-stage stretching and washing process, aramid fibers with irregular cross-sections that maintain good cross-sectional shape, have a dense structure, and excellent mechanical properties are prepared.

[0007] The technical solution of this invention to solve the above-mentioned technical problems is as follows: a method for preparing aramid fibers with irregular cross-sections, wherein the preparation method is as follows:

[0008] S1. Add polyvinyl alcohol polymer to aramid polymerization solution and mix evenly to obtain spinning solution;

[0009] S2. The spinning solution is sprayed out through the spinneret and successively undergoes coagulation bath molding, multi-stage stretching bath stretching, and finally water washing, drying, and crystallization to obtain aramid fibers with irregular cross-sections.

[0010] Furthermore, in step S1, the solid content of the aramid polymerization solution is 18-25%, the pH value is 7-8, and [η] = 1.8-2.6.

[0011] Furthermore, the mass concentration of the polyvinyl alcohol polymer in the spinning solution is 20-30%.

[0012] Furthermore, the preparation method of the aramid polymerization solution is as follows:

[0013] Under inert gas protection, diamine is dissolved in dimethylacetamide solvent, cooled to -10~0℃, acyl chloride is added, and low-temperature polycondensation reaction is carried out at 0-20℃. After the reaction is completed, ammonia is added to neutralize, and the reaction temperature is controlled to be at most 5-10℃. The by-product ammonium chloride is removed by circulating filtration to obtain aramid polymerization stock solution.

[0014] Furthermore, the diamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, and diaminodiphenyl ether;

[0015] The acyl chloride is selected from at least one of isophthaloyl chloride and terephthaloyl chloride.

[0016] Furthermore, the weight-average molecular weight of the polyvinyl alcohol polymer is 146,000-186,000.

[0017] Furthermore, the coagulation bath is a 5%-30% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 0-15℃.

[0018] Furthermore, during the solidification bath molding process, the draw ratio is 0.8-1.2.

[0019] Furthermore, the stretching process employs a two-stage stretching bath, and a water washing operation is performed after each stage of stretching.

[0020] The first-stage stretching bath is a 20%-40% dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 15-25℃.

[0021] The second-stage stretching bath is a dimethylacetamide aqueous solution with a mass concentration of 40%~60%, and the temperature of the second-stage stretching bath is 25~35℃.

[0022] Furthermore, the stretching process employs a two-stage stretching bath: the stretching ratio in the first stage stretching bath is 1-2; and the stretching ratio in the second stage stretching bath is 2-3.

[0023] The beneficial effects of this invention are:

[0024] In the preparation method of the irregular cross-section aramid fiber of the present invention, high-quality polyvinyl alcohol is added to the meta-polymer solution to reduce the coagulation strength and slow down the coagulation rate in the coagulation bath and stretching bath stages. Furthermore, the method of preparing cashew-shaped cross-section aramid fiber by using a low coagulation bath temperature and combining it with a two-stage stretching and washing process results in fibers with relatively high strength and elongation, and has broad application prospects in the papermaking field.

[0025] The aramid fibers with irregular cross-sections prepared by the method described in this invention exhibit excellent shape retention. In this preparation method, a low-temperature coagulation bath is used, significantly reducing the dual diffusion rate between the solvent (diformamide) and the non-solvent (water), making the coagulation process smooth and controllable. This allows the spinning solution streams more time to maintain their irregular contours before solidification, effectively avoiding cross-sectional deformation and rounding tendencies caused by excessively rapid coagulation, thus obtaining irregular cross-section fibers with clear contours and extremely high shape retention. The addition of polyvinyl alcohol is equivalent to increasing the concentration of the "solvent" in the coagulation bath, thereby reducing the chemical potential gradient between the coagulation bath and the spinning solution. This makes the dual diffusion process gentle and slow; the slow coagulation process is conducive to forming a more uniform and dense core-sheath structure, reducing internal pores and defects, and laying the foundation for obtaining high mechanical properties. The process combines two-stage stretching and washing. The first stage involves moderate stretching and preliminary washing at a lower temperature to avoid the expansion of defects caused by sudden high temperature and high stretching. The second stage involves high stretching and deep washing at a higher temperature. The high temperature and hot water help diffuse the residual solvent inside the fiber, while the high stretching makes the molecular chains highly oriented and squeezes out water and micropores, further densifying the fiber structure. Attached Figure Description

[0026] Figure 1 This is a magnified image under a microscope of the irregularly shaped aramid fiber obtained in Example 1. Detailed Implementation

[0027] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0028] Unless otherwise defined, 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. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0029] A method for preparing aramid fibers with irregular cross-sections, wherein the preparation method comprises:

[0030] S1. Add polyvinyl alcohol polymer to aramid polymerization solution, mix evenly to obtain spinning solution, and store at room temperature for later use.

[0031] S2. After vacuum degassing, the spinning solution is pumped to the spinneret by a metering pump. The spinneret is shaped in a coagulation bath and stretched in a multi-stage stretching bath. Finally, it is washed, dried, and crystallized to obtain aramid fibers with irregular cross-sections.

[0032] Specifically, in step S1, the solid content of the aramid polymerization solution is 18-25%, the pH value is 7-8, and [η] = 1.8-2.6.

[0033] Specifically, the mass concentration of the polyvinyl alcohol polymer in the spinning solution is 20-30%.

[0034] Specifically, the preparation method of the aramid polymerization solution is as follows:

[0035] Under inert gas protection, diamine is dissolved in dimethylacetamide solvent, cooled to -10~0℃, acyl chloride is added, and low-temperature polycondensation reaction is carried out at 0-20℃. After the reaction is completed, ammonia is added to neutralize, and the reaction temperature is controlled to be at most 5-10℃. The by-product ammonium chloride is removed by circulating filtration to obtain aramid polymerization stock solution.

[0036] Specifically, the diamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, and diaminodiphenyl ether;

[0037] The acyl chloride is selected from at least one of isophthaloyl chloride and terephthaloyl chloride. The molar ratio of the diamine to the acyl chloride is 1:(0.95-1.05).

[0038] In this embodiment of the invention, when preparing the aramid polymerization solution, the diamine used is m-phenylenediamine, and the acyl chloride used is isophthaloyl chloride, with a molar ratio of 1:1 between the diamine and the acyl chloride.

[0039] Specifically, the weight-average molecular weight of the polyvinyl alcohol polymer is 146,000-186,000.

[0040] More specifically, the polyvinyl alcohol polymer used in the embodiments of the present invention is Aladdin's P434368 model.

[0041] Specifically, the coagulation bath is a 5%-30% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 0-15℃.

[0042] Specifically, during the coagulation bath molding process, the draw ratio is 0.8-1.2.

[0043] Specifically, the stretching process uses a two-stage stretch bath, and a water washing operation is performed after each stage of stretching.

[0044] The first-stage stretching bath is a 20%-40% dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 15-25℃.

[0045] The second-stage stretching bath is a dimethylacetamide aqueous solution with a mass concentration of 40%~60%, and the temperature of the second-stage stretching bath is 25~35℃.

[0046] Specifically, the stretching process employs a two-stage stretching bath: the stretching ratio in the first stage stretching bath is 1-2; and the stretching ratio in the second stage stretching bath is 2-3.

[0047] More specifically, the spinnerets used in the embodiments of the present invention all have conventional circular spinneret holes. However, by reasonably controlling the process, it is possible to obtain aramid fibers with irregular cross-sections using conventional spinnerets.

[0048] Example 1

[0049] A method for preparing aramid fibers with irregular cross-sections, wherein the preparation method comprises:

[0050] S1. Add polyvinyl alcohol polymer to aramid polymerization solution, mix evenly to obtain spinning solution, and store at a constant temperature of 25℃.

[0051] The aramid polymerization solution has a solid content of 19%, a pH of 7.0, and [η] = 1.9. The polyvinyl alcohol polymer in the spinning solution has a mass concentration of 30%.

[0052] S2. The spinning solution is stably delivered to the spinneret using a precision metering pump. It then undergoes coagulation and multi-stage stretching in a coagulation bath, a first-stage stretching bath, and a second-stage stretching bath (each stage of stretching is followed by a water washing process). Finally, after washing, drying, and crystallization, shaped cross-section aramid fibers are obtained (a magnified image of the shaped cross-section aramid fibers under a microscope is shown in the image). Figure 1 (As shown).

[0053] The coagulation bath is a 5% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 5°C. During the coagulation bath molding process, the draw ratio is 1.0.

[0054] The first-stage stretching bath is a 20% (w / w) dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 15℃; the stretching ratio in the first-stage stretching bath is 2.0.

[0055] The second-stage stretching bath is a 40% dimethylacetamide aqueous solution, the temperature of the second-stage stretching bath is 25℃, and the stretching ratio in the second-stage stretching bath is 2.5.

[0056] Example 2

[0057] A method for preparing aramid fibers with irregular cross-sections, wherein the preparation method comprises:

[0058] S1. Add polyvinyl alcohol polymer to aramid polymerization solution, mix evenly to obtain spinning solution, and store at a constant temperature of 25℃.

[0059] The aramid polymerization solution has a solid content of 20%, a pH of 7.2, and [η] = 2.3. The polyvinyl alcohol polymer in the spinning solution has a mass concentration of 20%.

[0060] S2. The spinning solution is stably delivered to the spinneret by a precision metering pump. It is then passed through a coagulation bath, a first-stage stretching bath, and a second-stage stretching bath for coagulation and multi-stage stretching (after stretching in each stage, a water washing operation is performed). Finally, after washing, drying, and crystallization, aramid fibers with irregular cross-sections are obtained.

[0061] The coagulation bath is an 8% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 3°C. During the coagulation bath molding process, the draw ratio is 1.0.

[0062] The first-stage stretching bath is a 25% (w / w) dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 12℃; the stretching ratio in the first-stage stretching bath is 1.2.

[0063] The second-stage stretching bath is a 45% dimethylacetamide aqueous solution, the temperature of the second-stage stretching bath is 25℃, and the stretching ratio in the second-stage stretching bath is 2.8.

[0064] Example 3

[0065] A method for preparing aramid fibers with irregular cross-sections, wherein the preparation method comprises:

[0066] S1. Add polyvinyl alcohol polymer to aramid polymerization solution, mix evenly to obtain spinning solution, and store at a constant temperature of 25℃.

[0067] The aramid polymerization solution has a solid content of 21%, a pH of 7.5, and [η] = 2.5. The polyvinyl alcohol polymer in the spinning solution has a mass concentration of 25%.

[0068] S2. The spinning solution is stably delivered to the spinneret by a precision metering pump. It is then passed through a coagulation bath, a first-stage stretching bath, and a second-stage stretching bath for coagulation and multi-stage stretching (after stretching in each stage, a water washing operation is performed). Finally, after washing, drying, and crystallization, aramid fibers with irregular cross-sections are obtained.

[0069] The coagulation bath is a 10% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 12°C. During the coagulation bath molding process, the draw ratio is 1.0.

[0070] The first-stage stretching bath is a 28% dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 10℃; the stretching ratio in the first-stage stretching bath is 1.5.

[0071] The second-stage stretching bath is a 48% dimethylacetamide aqueous solution, the temperature of the second-stage stretching bath is 28℃, and the stretching ratio in the second-stage stretching bath is 3.0.

[0072] Example 4

[0073] A method for preparing aramid fibers with irregular cross-sections, wherein the preparation method comprises:

[0074] S1. Add polyvinyl alcohol polymer to aramid polymerization solution, mix evenly to obtain spinning solution, and store at a constant temperature of 25℃.

[0075] The aramid polymerization solution has a solid content of 18%, a pH of 7.0, and [η] = 1.8. The polyvinyl alcohol polymer in the spinning solution has a mass concentration of 27%.

[0076] S2. The spinning solution is stably delivered to the spinneret by a precision metering pump. It is then passed through a coagulation bath, a first-stage stretching bath, and a second-stage stretching bath for coagulation and multi-stage stretching (after stretching in each stage, a water washing operation is performed). Finally, after washing, drying, and crystallization, aramid fibers with irregular cross-sections are obtained.

[0077] The coagulation bath is a 30% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 15°C. During the coagulation bath molding process, the draw ratio is 1.0.

[0078] The first-stage stretching bath is a 40% dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 25℃; the stretching ratio in the first-stage stretching bath is 1.0.

[0079] The second-stage stretching bath is a 60% dimethylacetamide aqueous solution, the temperature of the second-stage stretching bath is 35℃, and the stretching ratio in the second-stage stretching bath is 2.0.

[0080] Example 5

[0081] A method for preparing aramid fibers with irregular cross-sections, wherein the preparation method comprises:

[0082] S1. Add polyvinyl alcohol polymer to aramid polymerization solution, mix evenly to obtain spinning solution, and store at a constant temperature of 25℃.

[0083] The aramid polymerization solution has a solid content of 25%, a pH of 8.0, and [η] = 2.6. The polyvinyl alcohol polymer in the spinning solution has a mass concentration of 24%.

[0084] S2. The spinning solution is stably delivered to the spinneret by a precision metering pump. It is then passed through a coagulation bath, a first-stage stretching bath, and a second-stage stretching bath for coagulation and multi-stage stretching (after stretching in each stage, a water washing operation is performed). Finally, after washing, drying, and crystallization, aramid fibers with irregular cross-sections are obtained.

[0085] The coagulation bath is an 8% (w / w) dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 0°C. During the coagulation bath molding process, the draw ratio is 1.0.

[0086] The first-stage stretching bath is a 20% dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 15℃; the stretching ratio in the first-stage stretching bath is 1.2.

[0087] The second-stage stretching bath is a 40% dimethylacetamide aqueous solution, the temperature of the second-stage stretching bath is 25℃, and the stretching ratio in the second-stage stretching bath is 3.0.

[0088] Comparative Example 1

[0089] Aramid fibers were prepared using the same method as in Example 1, except that polyvinyl alcohol was not added in Comparative Example 1.

[0090] S1. Use aramid polymerization solution as spinning solution and store at a constant temperature of 25℃.

[0091] The aramid polymerization solution has a solid content of 19%, a pH value of 7.0, and [η] = 1.9.

[0092] S2. The spinning solution is stably delivered to the spinneret using a precision metering pump. It then undergoes coagulation and multi-stage stretching in a coagulation bath, a first-stage stretching bath, and a second-stage stretching bath (each stage of stretching is followed by a water washing process). Finally, after washing, drying, and crystallization, shaped cross-section aramid fibers are obtained (a magnified image of the shaped cross-section aramid fibers under a microscope is shown in the image). Figure 1 (As shown).

[0093] The coagulation bath is a 5% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 5°C. During the coagulation bath molding process, the draw ratio is 1.0.

[0094] The first-stage stretching bath is a 20% (w / w) dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 15℃; the stretching ratio in the first-stage stretching bath is 2.0.

[0095] The second-stage stretching bath is a 40% dimethylacetamide aqueous solution, the temperature of the second-stage stretching bath is 25℃, and the stretching ratio in the second-stage stretching bath is 2.5.

[0096] The aramid fiber obtained in Comparative Example 1 has a circular cross-section.

[0097] Comparative Example 2

[0098] Aramid fibers were prepared using the same method as in Example 1, except that polyvinyl alcohol was not added in Comparative Example 1, and the stretch bath draw ratio was increased.

[0099] S1. Use aramid polymerization solution as spinning solution and store at a constant temperature of 25℃.

[0100] The aramid polymerization solution has a solid content of 19%, a pH value of 7.0, and [η] = 1.9.

[0101] S2. The spinning solution is stably delivered to the spinneret by a precision metering pump. The solution is then passed through a coagulation bath, a first-stage stretching bath, and a second-stage stretching bath for coagulation and multi-stage stretching (after stretching in each stage, the solution is washed with water). Finally, the solution is washed, dried, and crystallized to obtain aramid fiber.

[0102] The coagulation bath is a 5% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 5°C. During the coagulation bath molding process, the draw ratio is 1.0.

[0103] The first-stage stretching bath is a 20% dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 15℃; the stretching ratio in the first-stage stretching bath is 3.0.

[0104] The second-stage stretching bath is a 40% dimethylacetamide aqueous solution, the temperature of the second-stage stretching bath is 25℃, and the stretching ratio in the second-stage stretching bath is 4.0.

[0105] The fibers obtained in this comparative example showed obvious breakage due to excessive stretching.

[0106] Comparative Example 3

[0107] Aramid fibers were prepared using the same method as in Example 3, except that excess polyvinyl alcohol was added in Comparative Example 3.

[0108] S1. Use aramid polymerization solution as spinning solution and store at a constant temperature of 25℃.

[0109] The aramid polymerization solution has a solid content of 21%, a pH of 7.5, and [η] = 2.5. The polyvinyl alcohol polymer in the spinning solution has a mass concentration of 50%.

[0110] S2. The spinning solution is stably delivered to the spinneret by a precision metering pump. The solution is then passed through a coagulation bath, a first-stage stretching bath, and a second-stage stretching bath for coagulation and multi-stage stretching (after stretching in each stage, the solution is washed with water). Finally, the solution is washed, dried, and crystallized to obtain aramid fiber.

[0111] The coagulation bath is a 10% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 12°C. During the coagulation bath molding process, the draw ratio is 1.0.

[0112] The first-stage stretching bath is a 28% dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 10℃; the stretching ratio in the first-stage stretching bath is 1.5.

[0113] The second-stage stretching bath is a 48% dimethylacetamide aqueous solution, the temperature of the second-stage stretching bath is 28℃, and the stretching ratio in the second-stage stretching bath is 3.0.

[0114] The aramid fiber obtained in Comparative Example 3 has a cashew-shaped cross-section.

[0115] Comparative Example 4

[0116] Aramid fibers were prepared using the same method as in Example 1, except that the stretching bath in Comparative Example 4 was only set to a single stage. The specific preparation process is as follows:

[0117] S1. Add polyvinyl alcohol polymer to aramid polymerization solution, mix evenly to obtain spinning solution, and store at a constant temperature of 25℃.

[0118] The aramid polymerization solution has a solid content of 19%, a pH of 7.0, and [η] = 1.9. The polyvinyl alcohol polymer in the spinning solution has a mass concentration of 30%.

[0119] S2. The spinning solution is stably delivered to the spinneret by a precision metering pump. It is then coagulated and stretched in a coagulation bath and a stretching bath. Finally, it is washed, dried, and crystallized to obtain aramid fibers with irregular cross sections.

[0120] The coagulation bath is a 5% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 5°C. During the coagulation bath molding process, the draw ratio is 1.0.

[0121] The stretching bath was a 40% dimethylacetamide aqueous solution, the temperature of the stretching bath was 25℃, and the stretching ratio in the stretching bath was 2.5.

[0122] The aramid fiber obtained in Comparative Example 4 has a circular cross-section.

[0123] Comparative Example 5

[0124] Aramid fibers were prepared using the same method as in Example 1, except that the concentration of the coagulation bath was increased in Comparative Example 5.

[0125] S1. Add polyvinyl alcohol polymer to aramid polymerization solution, mix evenly to obtain spinning solution, and store at a constant temperature of 25℃.

[0126] The aramid polymerization solution has a solid content of 19%, a pH of 7.0, and [η] = 1.9. The polyvinyl alcohol polymer in the spinning solution has a mass concentration of 30%.

[0127] S2. The spinning solution is stably delivered to the spinneret by a precision metering pump. The solution is then passed through a coagulation bath, a first-stage stretching bath, and a second-stage stretching bath for coagulation and multi-stage stretching (after stretching in each stage, the solution is washed with water). Finally, the solution is washed, dried, and crystallized to obtain aramid fiber.

[0128] The coagulation bath is a 60% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 5°C. During the coagulation bath molding process, the draw ratio is 1.0.

[0129] The first-stage stretching bath is a 20% dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 15℃; the stretching ratio in the first-stage stretching bath is 2.

[0130] The second-stage stretching bath is a 40% dimethylacetamide aqueous solution, the temperature of the second-stage stretching bath is 25℃, and the stretching ratio in the second-stage stretching bath is 2.5.

[0131] The aramid fiber obtained in Comparative Example 5 has a circular cross-section.

[0132] The aramid fibers obtained in the above examples and comparative examples were subjected to performance tests, and the test methods involved were GB / T 14337-2022.

[0133] Table 1 Fiber performance test results

[0134]

[0135] The results in Table 1 clearly show that the technical solutions described in this invention (Examples 1-5) have achieved significant progress in fiber cross-sectional shape, mechanical properties, and process stability compared with the comparative examples that deviate from the process parameters of this invention.

[0136] Examples 1-5 successfully controlled the solvent-to-non-solvent exchange rate by adjusting the concentration and viscosity of the aramid polymer solution, as well as the composition and temperature of the coagulation bath, resulting in stable and regular irregular cross-sections of the fibers during coagulation. Furthermore, the irregularly shaped aramid fibers obtained in Examples 1-5 exhibited excellent tensile strength. This was achieved through an optimized multi-stage stretching process, which, under suitable bath concentration and temperature, enabled the full orientation and crystallization of the macromolecular chains.

[0137] A comparison of the experimental results of Comparative Example 1 and Example 1 shows that, since no polyvinyl alcohol polymer was added to the polymer stock solution in Comparative Example 1, the molecular chains of the nascent fibers were disordered and the strength was very low after they came out of the coagulation bath. As a result, the strength of the fibers was significantly lower than that of the embodiment of the present invention. Moreover, the absence of polyvinyl alcohol caused the coagulation process to be too fast, and a dense skin layer was quickly formed on the surface, which limited the development of the cross-sectional shape. In the end, only a conventional circular cross-section could be obtained.

[0138] Although Comparative Example 2 used a higher stretching ratio, structural defects were generated during the solidification stage. These defects were amplified during the subsequent high-stretching process, resulting in limited strength improvement and increased wire breakage rate.

[0139] A comparison of the experimental results of Comparative Example 3 and Example 3 shows that excessive polyvinyl alcohol does not have a significant impact on the cross-section of the fiber, but the fiber performance indicators are greatly reduced.

[0140] A comparison of the experimental results of Comparative Example 4 and Example 1 shows that having one less stretch bath will result in the inability to obtain aramid fibers with irregular cross-sections, and the fiber strength index will decrease significantly.

[0141] A comparison of the experimental results of Comparative Example 5 and Example 1 shows that if the concentration of the coagulation bath is increased, it is impossible to obtain aramid fibers with irregular cross sections, but the impact on the fiber properties is not too significant.

[0142] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0143] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention patent should be determined by the appended claims.

Claims

1. A method for preparing aramid fibers with irregular cross-sections, characterized in that, The preparation method is as follows: S1. Polyvinyl alcohol polymer is added to the aramid polymerization solution and mixed evenly to obtain a spinning solution; the mass concentration of the polyvinyl alcohol polymer in the spinning solution is 20-30%. S2. The spinning solution is sprayed out through the spinneret and successively undergoes coagulation bath molding, multi-stage stretching bath stretching, and finally water washing, drying, and crystallization to obtain aramid fiber with irregular cross section. The coagulation bath is a 5%-30% dimethylacetamide aqueous solution, and the temperature of the coagulation bath is 0-15℃. The stretching process employs a two-stage stretch bath, and a water washing operation is performed after each stage of stretching. The first-stage stretching bath is a 20%-40% dimethylacetamide aqueous solution, and the temperature of the first-stage stretching bath is 15-25℃. The second-stage stretching bath is a dimethylacetamide aqueous solution with a mass concentration of 40%~60%, and the temperature of the second-stage stretching bath is 25~35℃.

2. The method for preparing aramid fiber with irregular cross-section according to claim 1, characterized in that, In step S1, the solid content of the aramid polymerization solution is 18-25%, the pH value is 7-8, and [η] = 1.8-2.

6.

3. The method for preparing aramid fiber with irregular cross-section according to claim 1, characterized in that, The preparation method of the aramid polymerization solution is as follows: Under inert gas protection, diamine is dissolved in dimethylacetamide solvent, cooled to -10~0℃, acyl chloride is added, and low-temperature polycondensation reaction is carried out at 0-20℃. After the reaction is completed, ammonia is added to neutralize, and the reaction temperature is controlled to be at most 5-10℃. The by-product ammonium chloride is removed by circulating filtration to obtain aramid polymerization stock solution.

4. The method for preparing aramid fiber with irregular cross-section according to claim 3, characterized in that, The diamine is selected from at least one of m-phenylenediamine, p-phenylenediamine, and diaminodiphenyl ether; The acyl chloride is selected from at least one of isophthaloyl chloride and terephthaloyl chloride.

5. The method for preparing aramid fiber with irregular cross-section according to claim 1, characterized in that, The weight-average molecular weight of the polyvinyl alcohol polymer is 146,000-186,000.

6. The method for preparing aramid fiber with irregular cross-section according to claim 1, characterized in that, During the solidification bath molding process, the draw ratio is 0.8-1.

2.

7. The method for preparing aramid fiber with irregular cross-section according to claim 1, characterized in that, The stretching process employs a two-stage stretch bath: the stretching ratio in the first stage stretch bath is 1-2; the stretching ratio in the second stage stretch bath is 2-3.

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