Preparation method of high-strength para-aramid fiber

Abstract

The invention belongs to the technical field of aramid fibers, and particularly relates to a preparation method of high-strength para-aramid fibers, which comprises the following steps: in an inert gas environment, mixing para-aramid powder and concentrated sulfuric acid, stirring, and filtering to obtain a spinning solution; preparing nascent fibers from the spinning solution through a dry-jet wet spinning process; the nascent fiber is subjected to quenching treatment on a cooling roller after being dried and subjected to heat setting; and oiling and rolling the quenched nascent fiber to obtain the high-strength para-aramid fiber. According to the preparation method, synergistic modification is carried out on nascent fibers through heat setting and quenching treatment, so that the fibers are subjected to grain refinement, the grain size is reduced, the crystallinity of the fibers is improved, the microstructure of the fibers is optimized, and the structural defects in the fiber crystallization process are reduced; the strength and the mechanical uniformity are obviously improved.

Description

Technical Field

[0001] This invention relates to the field of aramid fiber technology, and specifically to a method for preparing high-strength para-aramid fibers. Background Technology

[0002] Aramid fiber, especially para-aramid (PPTA), is a high-performance synthetic fiber with excellent properties such as high strength, high modulus, high temperature resistance, and chemical corrosion resistance. Due to its unique molecular structure and superior mechanical properties, aramid fiber is widely used in aerospace, military protection, automotive industry, and sporting goods. For example, aramid fiber plays an irreplaceable role in products such as bulletproof vests, bulletproof helmets, tire cords, and high-strength ropes.

[0003] However, in the existing common spinning process of para-aramid, aramid fibers are prone to forming large grains and many structural defects during conventional heat treatment, such as uneven internal structure and low crystallinity, which prevents the fiber from achieving optimal mechanical properties, and its mechanical properties need to be further improved.

[0004] Patent CN 114351276 A discloses a high-strength para-aramid fiber and its preparation method. The high-strength para-aramid multifilament fiber is prepared by one-step polymerization + sizing treatment + heat setting. The process is stable, low-cost and suitable for industrialization. However, the tensile strength is only 24cN / dtex, the strength improvement is limited, and it is highly dependent on the heat setting process.

[0005] Patent CN 112281223 A discloses a high-strength and high-toughness para-aramid fiber and its manufacturing method. By controlling the temperature of the spinning solution, the temperature of the coagulation bath, and the low-tension treatment, the high-strength and high-toughness para-aramid fiber is prepared. The fiber has a high elongation at break (≥4.0%), which keeps the fiber with high toughness and stable performance. However, the tensile strength is only 23cN / dtex, and the strength improvement is limited. Summary of the Invention

[0006] The purpose of this invention is to provide a method for preparing high-strength para-aramid fibers. By heat setting and quenching treatment, the nascent fibers are synergistically modified, inducing grain refinement during recrystallization, reducing grain size, increasing fiber crystallinity, improving fiber grain uniformity, optimizing fiber microstructure, and reducing structural defects during fiber crystallization. While maintaining the toughness of para-aramid fiber products, its strength and mechanical uniformity are significantly improved, thereby improving the product performance of the fibers.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: A method for preparing high-strength para-aramid fiber includes the following steps: (1) Under an inert gas environment, para-aramid powder is mixed and stirred with concentrated sulfuric acid, and impurities are filtered out to obtain spinning solution; (2) The spinning solution is processed into nascent fibers by dry-jet wet spinning process; (3) After the nascent fibers are dried and heat-set, they are quenched on a cooling roller; (4) The quenched nascent fibers are oiled and wound up to obtain high-strength para-aramid fibers.

[0008] Preferably, in step (1), the intrinsic viscosity of the para-aramid powder is 7.5~8.5 dL / g; the stirring temperature is 80~100℃; and the mass concentration of para-aramid in the spinning solution is 16~24 wt%.

[0009] Preferably, in step (2), the dry-jet wet spinning process includes the following steps: the spinning solution is squeezed by a metering pump and the filament bundle is sprayed out from the small hole of the spinneret. The filament bundle is frozen and solidified after passing through an air layer and a coagulation bath. Then, it is washed with water, alkali washed, and washed with water again to obtain nascent fibers.

[0010] More preferably, the spinneret orifice diameter is 0.1 mm, the air layer is 2-7 mm, the coagulation bath temperature is 0-10°C, and the sulfuric acid concentration in the coagulation bath is 4-10%.

[0011] Preferably, in step (3), the drying temperature is 130~170℃, the fiber tension is controlled at 1~2cN / dtex during the drying process, the drying time is 4~8 seconds, and the moisture content of the filament bundle is controlled at 10~15%; the heat setting temperature is 200-300℃, the heat setting time is 0.5~2 seconds, and the fiber tension is controlled at 2~4cN / dtex during the heat setting process.

[0012] Preferably, in step (3), the quenching temperature is -10℃ to 5℃, the quenching time is 0.5 to 2 seconds, and the fiber tension is controlled at 2 to 4 cN / dtex during the quenching process.

[0013] Preferably, the high-strength para-aramid fiber filament has a grain size of 6~14nm, a tensile strength of 26.5~28.5cN / dtex, an elongation at break of 3.5~4.2%, and a CV value of less than 4%.

[0014] Compared with the prior art, the present invention has the following beneficial effects: In existing traditional para-aramid spinning processes, the single high-temperature heat setting post-treatment step leads to the formation of large grains and numerous structural defects in the aramid fibers, such as uneven internal structure and low crystallinity, resulting in suboptimal mechanical properties. Compared to existing technologies, this invention introduces quenching treatment into the heat treatment process of para-aramid spinning. Through heat setting and quenching, the nascent fibers are synergistically modified. Rapid cooling after high-temperature setting induces grain refinement during recrystallization, reducing grain size, increasing fiber crystallinity, improving grain uniformity, optimizing the fiber's microstructure, and reducing structural defects during crystallization. While maintaining the toughness of the para-aramid fiber product, its strength and mechanical uniformity are significantly improved, thereby enhancing the fiber's overall performance.

[0015] In the fiber industry, fiber strength and fiber toughness are core attributes of high-performance fibers. The toughness of aramid fibers is determined by both strength and elongation at break. In traditional aramid fiber manufacturing processes, to improve product toughness, it is necessary to control fiber crystallinity to retain more amorphous regions and increase grain size to improve product elongation at break. However, low fiber crystallinity and excessively large grain size can lead to a decrease in product strength. Therefore, it is difficult to achieve both high strength and high toughness in fiber products prepared by traditional processes. This invention improves fiber crystallinity and reduces internal structural defects through the synergistic effect of heat setting and quenching treatment, reducing crystal size, increasing grain boundary density, and forming fine and dense grains. High-density grain boundaries can hinder dislocation (molecular chain slip) and crack propagation and provide more sliptable interfaces, thereby enhancing fiber strength while ensuring fiber elongation at break. This significantly improves the strength of para-aramid fiber products while maintaining their toughness.

[0016] Quenching treatment, through precise control of the microstructure of aramid fibers, utilizes rapid cooling to induce fiber recrystallization, achieving grain refinement and uniform distribution, and effectively reducing crystal structure defects. This high degree of microstructural uniformity directly translates into stable macroscopic mechanical properties, significantly reducing the performance dispersion between monofilaments and between different segments of monofilaments. This greatly improves the mechanical uniformity and quality reliability within and between fiber batches, becoming a key process for reducing its mechanical property CV value (coefficient of variation).

[0017] Grain size and the ratio of amorphous regions are core microscopic factors controlling fiber strength and toughness. Smaller grain size increases grain boundary density, hindering molecular chain slippage and crack propagation, thus increasing fiber strength; grain size and strength are positively correlated. However, grain size and toughness exhibit an inverted U-shaped relationship. Controlling grain size within a certain range allows for grain boundary slippage and uniform fibrillation, achieving efficient energy absorption and improving fiber toughness. However, excessively small grain size leads to overloading of internal grain boundaries, resulting in brittle fracture and decreased fiber toughness. During cryogenic quenching, controlling the quenching temperature is a key parameter for controlling grain size. The quenching temperature should ideally be controlled between -10℃ and 5℃. Excessively high temperatures result in incomplete grain refinement, leading to substandard strength and toughness; excessively low temperatures damage the internal structure, causing fiber embrittlement. A suitable quenching temperature is crucial for significantly improving the strength of para-aramid fibers while maintaining their toughness.

[0018] The aramid filament fibers obtained by this invention have a grain size of 6~12nm; a tensile strength of 26.5~28.5cN / dtex, which is 10~20% higher than the standard for high-strength superior products; a breaking elongation of 3.5~4.2%, which meets the national standard; and a CV (coefficient of variation) value of less than 4%, indicating a significant improvement in the overall performance of the fiber. Attached Figure Description

[0019] Figure 1 The images show the XRD patterns of the conventional para-aramid fiber sample from Comparative Example 1, the high-strength para-aramid sample from Example 1, and the Taparan® 629 (1000D) para-aramid sample from Taihe New Materials. Detailed Implementation

[0020] The technical features of the present invention are described below with reference to specific experimental schemes and accompanying drawings, but the present invention is not limited thereto. Unless otherwise specified, the experimental methods described in the following embodiments are conventional methods; the reagents, equipment, and instruments used are commercially available unless otherwise specified. Product performance tests on the products obtained in the examples and comparative examples were conducted according to the national standard GB / T42823-2023 Para-aramid filament.

[0021] Test method for fiber mechanical properties: A certain amount of para-aramid fiber filament is taken, the linear density of the fiber is tested, and twisting is performed according to the linear density and international standards. The twisted aramid filament is fixed on the tensile testing fixture of a tensile testing machine, and its mechanical properties are measured 5 times. The average value is taken, and the CV value is calculated. Tensile testing machine model: YG(B)026HC-250; Twisting machine model: YG155A yarn twist meter. Example 1

[0022] The present invention discloses a method for preparing high-strength para-aramid fibers, comprising the following steps: (1) Under nitrogen sealing at a temperature of 85℃, para-aramid powder with an intrinsic viscosity of 8.0 dL / g was mixed and stirred with sulfuric acid with a concentration of 100.2%, and impurities were filtered out to obtain a spinning solution with a para-aramid concentration of 20 wt%. (2) The spinning solution is squeezed by a metering pump and the filament bundle is ejected from the spinneret with an aperture of 0.08 mm. The filament bundle passes through a 4 mm air layer and is stretched at a draw ratio of 3. It is then frozen in a coagulation bath at 5 °C. The sulfuric acid concentration in the coagulation bath is 8%. The filament bundle is then washed with water, alkali washed with 3% sodium bicarbonate solution, and washed with water again to obtain nascent fibers. (3) Dry the nascent fiber at 150°C for 5 seconds. During the drying process, the fiber tension is controlled within the range of 1~2 cN / dtex and the fiber moisture content is controlled within the range of 10~15%. Then heat-set the fiber on a high-temperature heating roller at 260°C for 1 second. During the heat-setting process, the fiber tension is controlled within the range of 2~4 cN / dtex and the moisture content is controlled within the range of 5~8%. Then quench the heat-set fiber on a cooling roller at -5°C for 1 second. During the quenching process, the fiber tension is controlled within the range of 2~4 cN / dtex. (4) The quenched fiber is oiled and wound up to obtain high-strength para-aramid fiber.

[0023] The performance test results of high-strength para-aramid fiber products show that the fiber grain size is 10nm; the tensile strength of the fiber is 28.5cN / dtex, which is 20% higher than the standard for high-strength superior grade products; the breaking elongation of the fiber is 3.8%, and the CV value is 2.5%. The comprehensive mechanical properties exceed the national standard for high-strength superior grade products. Example 2

[0024] (1) Under nitrogen sealing at a temperature of 85℃, para-aramid powder with an intrinsic viscosity of 8.0 dL / g was mixed and stirred with sulfuric acid with a concentration of 100.2%, and impurities were filtered out to obtain a spinning solution with a para-aramid concentration of 20 wt%. (2) The spinning solution is squeezed out from the spinneret with an aperture of 0.08 mm by a metering pump. The filament bundle passes through a 4 mm air layer and is quickly stretched at a draw ratio of 3. It is then frozen in a coagulation bath at 5 °C. The sulfuric acid concentration in the coagulation bath is 8%. The filament bundle is then washed with water, alkali washed with 3% sodium bicarbonate solution, and washed with water again to obtain nascent fibers. (3) Dry the nascent fiber at 150°C for 5 seconds. During the drying process, the fiber tension is controlled within the range of 1~2 cN / dtex and the fiber moisture content is controlled within the range of 10~15%. Then heat-set the fiber on a high-temperature heating roller at 260°C for 1 second. During the heat-setting process, the fiber tension is controlled within the range of 2~4 cN / dtex and the moisture content is controlled within the range of 5~8%. Then quench the heat-set fiber on a cooling roller at 0°C for 1 second. During the quenching process, the fiber tension is controlled within the range of 2~4 cN / dtex. (4) The quenched fiber is oiled and wound up to obtain high-strength para-aramid fiber.

[0025] The performance test results of high-strength para-aramid fiber products show that the fiber grain size is 12nm; the tensile strength of the fiber is 27.8cN / dtex, which is 18% higher than the standard for high-strength superior grade products; the breaking elongation of the fiber is 4.0%, and the CV value is 2.8%. The comprehensive mechanical properties exceed the national standard for high-strength superior grade products. Example 3

[0026] (1) Under nitrogen sealing at a temperature of 85℃, para-aramid powder with an intrinsic viscosity of 8.0 dL / g was mixed and stirred with sulfuric acid with a concentration of 100.2%, and impurities were filtered out to obtain a spinning solution with a para-aramid concentration of 20 wt%. (2) The spinning solution is squeezed out from the spinneret with an aperture of 0.08 mm by a metering pump. The filament bundle passes through a 4 mm air layer and is quickly stretched at a draw ratio of 3. It is then frozen in a coagulation bath at 5 °C. The sulfuric acid concentration in the coagulation bath is 8%. The filament bundle is then washed with water, alkali washed with 3% sodium bicarbonate solution, and washed with water again to obtain nascent fibers. (3) Dry the nascent fiber at 150°C for 5 seconds. During the drying process, the fiber tension is controlled within the range of 1~2 cN / dtex and the fiber moisture content is controlled within the range of 10~15%. Then heat-set the fiber on a high-temperature heating roller at 260°C for 1 second. During the heat-setting process, the fiber tension is controlled within the range of 2~4 cN / dtex and the winding speed is 300 m / min. The moisture content is controlled within the range of 5~8%. Then quench the heat-set fiber on a cooling roller at 5°C for 1 second. During the quenching process, the fiber tension is controlled within the range of 2~4 cN / dtex and the winding speed is 300 m / min. (4) The quenched fiber is oiled and wound up to obtain high-strength para-aramid fiber.

[0027] The performance test results of high-strength para-aramid fiber products show that the fiber grain size is 14nm; the tensile strength of the fiber is 26.2cN / dtex, which is 11.5% higher than the standard for high-strength superior grade products; the breaking elongation of the fiber is 4.2%, and the CV value is 3.2%. The comprehensive mechanical properties exceed the national standard for high-strength superior grade products. Example 4

[0028] (1) Under nitrogen sealing at a temperature of 85℃, para-aramid powder with an intrinsic viscosity of 8.0 dL / g was mixed and stirred with sulfuric acid with a concentration of 100.2%, and impurities were filtered out to obtain a spinning solution with a para-aramid concentration of 20 wt%. (2) The spinning solution is squeezed out from the spinneret with an aperture of 0.08 mm by a metering pump. The filament bundle passes through a 4 mm air layer and is quickly stretched at a draw ratio of 3. It is then frozen in a coagulation bath at 5 °C. The sulfuric acid concentration in the coagulation bath is 8%. The filament bundle is then washed with water, alkali washed with 3% sodium bicarbonate solution, and washed with water again to obtain nascent fibers. (3) Dry the nascent fiber at 150°C for 5 seconds. During the drying process, the fiber tension is controlled within the range of 1~2 cN / dtex and the fiber moisture content is controlled within the range of 10~15%. Then heat-set the fiber on a high-temperature heating roller at 260°C for 1 second. During the heat-setting process, the fiber tension is controlled within the range of 2~4 cN / dtex and the moisture content is controlled within the range of 5-8%. Then quench the heat-set fiber on a cooling roller at -10°C for 1 second. During the quenching process, the fiber tension is controlled within the range of 2~4 cN / dtex. (4) The quenched fiber is oiled and wound up to obtain high-strength para-aramid fiber.

[0029] The performance test results of high-strength para-aramid fiber products show that the fiber grain size is 6nm; the tensile strength of the fiber is 26.5cN / dtex, which is 13% higher than the standard for high-strength superior grade products; the breaking elongation of the fiber is 3.2%, and the CV value is 3.6%. The comprehensive mechanical properties exceed the national standard for high-strength superior grade products. Example 5

[0030] (1) Under nitrogen sealing at a temperature of 85℃, para-aramid powder with an intrinsic viscosity of 8.0 dL / g was mixed and stirred with sulfuric acid with a concentration of 100.2%, and impurities were filtered out to obtain a spinning solution with a para-aramid concentration of 20 wt%. (2) The spinning solution is squeezed out from the spinneret with an aperture of 0.08 mm by a metering pump. The filament bundle passes through a 4 mm air layer and is quickly stretched at a draw ratio of 3. It is then frozen in a coagulation bath at 5 °C with a sulfuric acid concentration of 8%. The filament bundle is then washed with water, alkali washed with 3% sodium bicarbonate solution, and washed with water again to obtain nascent fibers. (3) Dry the nascent fiber at 150°C for 5 seconds, during which the fiber tension is controlled within the range of 1~2 cN / dtex and the fiber moisture content is controlled within the range of 10~15%; then heat set on a high-temperature heating roller at 300°C for 1 second, during which the fiber tension is controlled within the range of 2~4 cN / dtex and the moisture content is controlled within the range of 5~8%; then quench the heat-set fiber on a cooling roller at -5°C for 1 second, during which the fiber tension is controlled within the range of 2~4 cN / dtex. (4) The quenched fiber is oiled and wound up to obtain high-strength para-aramid fiber.

[0031] The performance test results of high-strength para-aramid fiber products show that the fiber grain size is 12nm; the tensile strength of the fiber is 26.8cN / dtex, which is 14% higher than the standard for high-strength superior grade products; the breaking elongation of the fiber is 4.0%, and the CV value is 3.2%. The comprehensive mechanical properties exceed the national standard for high-strength superior grade products. Example 6

[0032] (1) Under nitrogen sealing at a temperature of 85℃, para-aramid powder with an intrinsic viscosity of 8.0 dL / g was mixed and stirred with sulfuric acid with a concentration of 100.2%, and impurities were filtered out to obtain a spinning solution with a para-aramid concentration of 20 wt%. (2) The spinning solution is squeezed out from the spinneret with an aperture of 0.08 mm by a metering pump. The filament bundle passes through a 4 mm air layer and is quickly stretched at a draw ratio of 3. It is then frozen in a coagulation bath at 5 °C. The sulfuric acid concentration in the coagulation bath is 8%. The filament bundle is then washed with water, alkali washed with 3% sodium bicarbonate solution, and washed with water again to obtain nascent fibers. (3) Dry the nascent fiber at 150°C for 5 seconds. During the drying process, the fiber tension is controlled within the range of 1~2 cN / dtex and the fiber moisture content is controlled within the range of 10~15%. Then heat-set the fiber on a high-temperature heating roller at 220°C for 1 second. During the heat-setting process, the fiber tension is controlled within the range of 2~4 cN / dtex and the moisture content is controlled within the range of 5~8%. Then quench the heat-set fiber on a cooling roller at -5°C for 1 second. During the quenching process, the fiber tension is controlled within the range of 2~4 cN / dtex. (4) The quenched fiber is oiled and wound up to obtain high-strength para-aramid fiber.

[0033] The performance test results of high-strength para-aramid fiber products show that the fiber grain size is 8nm; the tensile strength of the fiber is 27.2cN / dtex, which is 16% higher than the standard for high-strength superior grade products; the breaking elongation of the fiber is 3.6%, the CV value is 3%, and the comprehensive mechanical properties exceed the national standard for high-strength superior grade products. Comparative Example 1

[0034] (1) Under nitrogen sealing at a temperature of 85℃, para-aramid powder with an intrinsic viscosity of 8.0 dL / g was mixed and stirred with sulfuric acid with a concentration of 100.2%, and impurities were filtered out to obtain a spinning solution with a para-aramid concentration of 20 wt%. (2) The spinning solution is squeezed out from the spinneret with an aperture of 0.08 mm by a metering pump. The filament bundle passes through a 4 mm air layer and is quickly stretched at a draw ratio of 3. It is then frozen in a coagulation bath at 5 °C. The sulfuric acid concentration in the coagulation bath is 8%. The filament bundle is then washed with water, alkali washed with 3% sodium bicarbonate solution, and washed with water again to obtain nascent fibers. (3) Dry the nascent fiber at 150°C for 5 seconds. During the drying process, the fiber tension is controlled within the range of 1~2 cN / dtex and the fiber moisture content is controlled within the range of 10~15%. Then heat-set the fiber on a high-temperature heating roller at 260°C for 1 second. During the heat-setting process, the fiber tension is controlled within the range of 2~4 cN / dtex and the moisture content is controlled within the range of 5~8%. Then heat-set the fiber at room temperature at 25°C for 3 seconds for natural cooling. During the cooling process, the fiber tension is controlled within the range of 1~2 cN / dtex. (4) The quenched fiber is oiled and wound up to obtain conventional para-aramid fiber.

[0035] The performance test results of para-aramid fiber products show that the fiber grain size is 18nm; the tensile strength of the fiber is 18.6cN / dtex; the elongation at break of the fiber is 3.7%; the CV value is 5%; the overall mechanical properties can only reach the level of qualified conventional fibers, and the mechanical stability is not high. Comparative Example 2

[0036] (1) Under nitrogen sealing at a temperature of 85℃, para-aramid powder with an intrinsic viscosity of 8.0 dL / g was mixed and stirred with sulfuric acid with a concentration of 100.2%, and impurities were filtered out to obtain a spinning solution with a para-aramid concentration of 20 wt%. (2) The spinning solution is squeezed out from the spinneret with an aperture of 0.08 mm by a metering pump. The filament bundle passes through a 4 mm air layer and is quickly stretched at a draw ratio of 3. It is then frozen in a coagulation bath at 5 °C. The sulfuric acid concentration in the coagulation bath is 8%. The filament bundle is then washed with water, alkali washed with 3% sodium bicarbonate solution, and washed with water again to obtain nascent fibers. (3) Dry the nascent fiber at 150°C for 5 seconds. During the drying process, the fiber tension is controlled within the range of 1~2 cN / dtex and the fiber moisture content is controlled within the range of 10~15%. Then heat-set the fiber on a high-temperature heating roller at 260°C for 1 second. During the heat-setting process, the fiber tension is controlled within the range of 2~4 cN / dtex and the moisture content is controlled within the range of 5-8%. Then quench the heat-set fiber on a cooling roller at 10°C for 1 second. During the quenching process, the fiber tension is controlled within the range of 2~4 cN / dtex. (4) The quenched fiber is oiled and wound up to obtain high-strength para-aramid fiber.

[0037] The performance test results of para-aramid fiber products show that the fiber grain size is 15nm; the tensile strength of the fiber is 22cN / dtex; the elongation at break of the fiber is 3.8%; the CV value is 6%; the comprehensive mechanical properties can only reach the level of qualified high-strength fiber products; and the mechanical stability is not high. The insufficient quenching temperature results in incomplete grain refinement and low crystallinity, which affects the final performance of the fiber. Comparative Example 3

[0038] (1) Under nitrogen sealing at a temperature of 85℃, para-aramid powder with an intrinsic viscosity of 8.0 dL / g was mixed and stirred with sulfuric acid with a concentration of 100.2%, and impurities were filtered out to obtain a spinning solution with a para-aramid concentration of 20 wt%. (2) The spinning solution is squeezed out from the spinneret with an aperture of 0.08 mm by a metering pump. The filament bundle passes through a 4 mm air layer and is quickly stretched at a draw ratio of 3. It is then frozen in a coagulation bath at 5 °C. The sulfuric acid concentration in the coagulation bath is 8%. The filament bundle is then washed with water, alkali washed with 3% sodium bicarbonate solution, and washed with water again to obtain nascent fibers. (3) Dry the nascent fiber at 150°C for 5 seconds. During the drying process, the fiber tension is controlled within the range of 1~2 cN / dtex and the fiber moisture content is controlled within the range of 10~15%. Then heat-set the fiber on a high-temperature heating roller at 260°C for 1 second. During the heat-setting process, the fiber tension is controlled within the range of 2~4 cN / dtex and the moisture content is controlled within the range of 5-8%. Then quench the heat-set fiber on a cooling roller at -20°C for 1 second. During the quenching process, the fiber tension is controlled within the range of 2~4 cN / dtex. (4) The quenched fiber is oiled and wound up to obtain high-strength para-aramid fiber.

[0039] The performance test results of para-aramid fiber products show that the fiber grain size is 4nm; the tensile strength of the fiber is 23cN / dtex, the elongation at break of the fiber is 2.8%, the CV value is 8%, and the overall mechanical properties can only reach the level of qualified high-strength fibers. The toughness is low and the mechanical stability is poor. The excessively low quenching temperature makes the grains too fine, which leads to damage to the internal structure and severe fiber embrittlement.

[0040]

[0041] As can be seen from the data in the table above, the para-aramid fiber products prepared in the embodiments of the present invention have a better crystal structure, significantly smaller grain size, and significantly reduced fiber structural defects compared with para-aramid fibers produced by traditional processes. The grain size of the aramid filament fiber is 6~14nm; the tensile strength is 26.5~28.5cN / dtex, which is 10~20% higher than the standard for high-strength superior products; the breaking elongation of the fiber is 3.5~4.2%, which meets the national standard for high-strength superior products; the CV value is less than 4%, the mechanical properties of the fiber are significantly improved, and it has better mechanical uniformity, resulting in a significant improvement in the overall performance of the fiber.

[0042] Appendix Figure 1 Compared to traditional production processes and the benchmark product for isoaramid fibers in the existing domestic market (Taparan® 629 from Taihe New Materials), this product is superior. ， The peak intensity of the sample after low-temperature quenching in Example 1 was significantly improved, indicating that quenching treatment helps to improve the crystallinity of the fiber.

[0043] This invention optimizes the heat treatment process of aramid fibers by introducing a quenching process and through the synergistic effect of high-temperature annealing and low-temperature quenching. This induces grain refinement during the recrystallization process, reduces grain size, and further improves fiber crystallinity. This effectively improves the crystal structure of para-aramid fibers, reduces internal structural defects, and significantly improves the strength, toughness, and mechanical uniformity of the fibers, thereby enhancing product performance. This process has the advantages of simple operation and suitability for large-scale industrial production, and has broad application prospects.

[0044] The above examples are merely preferred results of this invention and are not intended to limit the invention. Any technical solutions obtained by equivalent substitutions or modifications based on the principles of this invention are within the protection scope of this invention.

Claims

1. A method for preparing high-strength p-aramid fiber, characterized by, The method comprises the following steps: (1) mixing and stirring para-aramid powder with concentrated sulfuric acid under inert gas environment, filtering out impurities to obtain a spinning dope; (2) preparing a nascent fiber through dry-jet wet spinning process of the spinning dope; (3) drying and heat setting the nascent fiber, and then quenching the nascent fiber on a cooling roller; (4) oiling and winding the nascent fiber after quenching to obtain high-strength para-aramid fiber.

2. The method for preparing high-strength para-aramid fiber according to claim 1, characterized in that, In the step (1), the para-aramid powder has a specific viscosity of 7.5-8.5 dL / g; the stirring temperature is 80-100℃; and the mass concentration of the para-aramid in the spinning dope is 16-24 wt%.

3. The method for preparing high-strength para-aramid fiber according to claim 1, characterized in that, In the step (2), the dry-jet wet spinning process comprises the following steps: extruding the spinning dope through a metering pump, spraying the fiber bundle from the spinneret orifice, freezing and solidifying the fiber bundle into a shape after passing through an air layer and a coagulation bath, and then washing with water, washing with alkali, and washing with water again to obtain a nascent fiber.

4. The method for preparing high-strength para-aramid fiber according to claim 3, characterized in that, The spinneret orifice has a diameter of 0.1 mm, the air layer has a thickness of 2-7 mm, the coagulation bath has a temperature of 0-10℃, and the sulfuric acid in the coagulation bath has a concentration of 4-10%.

5. The method for preparing high-strength para-aramid fiber according to claim 1, characterized in that, In the step (3), the drying temperature is 130-170℃, the fiber tension is controlled at 1-2 cN / dtex during the drying process, the drying time is 4-8 seconds, and the moisture content of the fiber bundle is controlled at 10-15%; the heat setting temperature is 200-300℃, the heat setting time is 0.5-2 seconds, and the fiber tension is controlled at 2-4 cN / dtex during the heat setting process.

6. The method for preparing high-strength para-aramid fiber according to claim 1, characterized in that, In the step (3), the quenching temperature is -10℃-5℃, the quenching time is 0.5-2 seconds, and the fiber tension is controlled at 2-4 cN / dtex during the quenching process.

7. The method for preparing high-strength para-aramid fiber according to claim 1, characterized in that, The high-strength para-aramid fiber has a fiber grain size of 6-14 nm, a tensile strength of 26.5-28.5 cN / dtex, an elongation at break of 3.5-4.2%, and a CV value of less than 4%.

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