A method of dry spinning high performance aramid

Abstract

The application relates to a method for dry spinning high-performance aramid fiber, comprising the following steps: (1) dissolving terephthaloyl chloride and diamine in a mixed solvent under the condition of a protective gas to obtain a reaction system; (2) adding calcium hydroxide or ammonia gas into the reaction system after the reaction system in step (1) is reacted to obtain aramid spinning solution; (3) after the aramid spinning solution in step (2) is defoamed, the aramid spinning solution is metered and delivered to a spinning component and then enters a duct, is extruded and wound to obtain nascent fiber; (4) the nascent fiber in step (3) is washed by multiple ultrasonic waves and is subjected to water bath drawing; and (5) the washed fiber prepared in step (4) is subjected to drying and hot drawing, oiling treatment to obtain high-performance aramid fiber. The aramid fiber prepared in the application has higher molecular chain orientation degree and more compact internal structure, and thus has more excellent mechanical properties, and has wide application prospects in the fields of aerospace, special protection, electrical insulation and the like.

Description

Technical Field

[0001] This invention belongs to the field of high-performance fiber materials technology, and specifically relates to a method for dry spinning high-performance aramid fibers. Background Technology

[0002] Aramid fiber, also known as aromatic polyamide fiber, is one of the four key high-performance fibers that my country is focusing on developing, along with carbon fiber, ultra-high molecular weight polyethylene fiber, and basalt fiber. Based on the position of the amide unit on the benzene ring, aramid fibers can be further divided into meta-aramid and para-aramid. The abundant hydrogen bonds and benzene ring units in the aramid molecular chain endow this material with excellent mechanical properties, outstanding flame retardancy, and resistance to acid and alkali corrosion, leading to its widespread application in aerospace, defense, special protection, and electrical insulation.

[0003] Currently, domestic aramid production mostly employs wet spinning or dry-jet wet spinning. In this process, after the spinning solution enters the coagulation bath, the solvent diffuses into the coagulation bath while the coagulant diffuses into the spinning stream, thus solidifying the filaments. However, to ensure stable fiber formation, wet spinning or dry-jet wet spinning typically involves long residence times in the coagulation bath, resulting in slow spinning rates, low production efficiency, and often requiring negative drafting in the coagulation bath. Furthermore, the coagulant remaining inside the fiber during the dual diffusion process can easily form micropores within the fiber during drying, restricting its mechanical properties. In contrast, dry spinning offers faster rates (≥500 m / min), and only unidirectional solvent diffusion occurs during fiber formation, making it easier to produce dense and uniform fibers. Of particular note is that the polymer solution stream, after being extruded through a spinneret, can withstand more than 20 times the required draft in a high-temperature tunnel and maintains good molecular chain orientation after coagulation, thus producing fibers with superior mechanical properties.

[0004] However, there is currently limited research on dry spinning of aramid fibers in China. The main reason is that, unlike traditional polymer solutions, aramid spinning solutions often generate large amounts of HCl during polymerization. To neutralize this byproduct, alkaline calcium hydroxide or ammonia needs to be added to the system, forming CaCl2 or NH4Cl in the solution. These salts need to be removed during fiber spinning; otherwise, they severely affect the overall performance of the fiber. In dry spinning, the rapid evaporation of the surface solvent in the high-temperature channel causes the spinning stream to solidify quickly, forming a dense skin layer that hinders the evaporation of internal CaCl2 or NH4Cl, making it difficult to remove even after prolonged washing. Therefore, how to quickly and efficiently remove residual salts from nascent aramid fibers is one of the major bottlenecks restricting the dry spinning of aramid. For example, invention patent application CN201010192686.0 discloses a method for preparing aramid III fibers by dry spinning; however, this application does not mention how to effectively remove salts. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a method for dry spinning high-performance aramid fibers. The aramid fibers prepared by this method have higher molecular chain orientation and denser internal structure, and therefore have better mechanical properties, and have broad application prospects in aerospace, special protection, electrical insulation and other fields.

[0006] This invention provides a method for dry spinning high-performance aramid fibers, comprising the following steps:

[0007] (1) Under protective gas conditions, diformyl chloride and diamine are dissolved in a mixed solvent at a molar ratio of 1.05-1:1 to obtain a reaction system with a mass fraction of 22-25%.

[0008] (2) React the reaction system of step (1) at 0-5℃ for 18-24 h, and add calcium hydroxide or ammonia to the reaction system to obtain aramid spinning solution;

[0009] (3) After degassing the aramid spinning solution from step (2), it is metered and conveyed to the spinneret and then enters the duct, where it is extruded and wound to obtain nascent fibers; wherein, by adjusting the duct temperature and residence time, the residual solvent content inside the wound nascent fibers is ensured to be 10-15 wt%;

[0010] (4) The nascent fibers from step (3) are subjected to multi-stage ultrasonic water washing and water bath stretching; the multi-stage ultrasonic water washing and water bath stretching refer to: setting up four ultrasonic water washing stages, each with a length of 1-3m, and a water washing temperature of 50-80℃, wherein DMSO is added to the first stage water washing bath and its concentration is controlled to be 1-5 wt%; the stretching ratios of the four stages water baths are 1.0, 1.2-1.4, 1.2-1.4 and 1.2-1.4 respectively;

[0011] (5) The washed fibers prepared in step (4) are dried, hot-stretched, and oiled to obtain high-performance aramid fibers.

[0012] Preferably, the diformyl chloride in step (1) has one of the following structures:

[0013] .

[0014] Preferably, the diamine in step (1) has one of the following structures:

[0015] .

[0016] Preferably, the mixed solvent in step (1) is N,N-dimethylacetamide DMAc and N-methyl-pyrrolidone NMP or N,N-dimethylacetamide DMAc and N-vinyl-pyrrolidone NVP; wherein the volume fraction of NMP or NVP is 15-30%.

[0017] Preferably, the intrinsic viscosity of the aramid spinning solution in step (2) is 1.0-2.5 dL·g. -1 .

[0018] Preferably, the control of the tunnel temperature and residence time in step (3) refers to the following: the tunnel is heated in three sections from the top, namely 100-120℃, 180-200℃ and 240-280℃; the total residence time of the aramid spinning solution in the tunnel is 3-5s.

[0019] Preferably, the aramid spinning solution extrusion rate in step (3) is 10-20 m / min; the nascent fiber winding speed is 500-600 m / min.

[0020] Preferably, the drying temperature in step (5) is 100-120℃; the hot stretching temperature is 220-300℃; and the hot stretching ratio is 1.5-3.0 times.

[0021] Preferably, the high-performance aramid in step (5) has a tensile strength of 5-10 cN / dtex, a modulus of 100-200 cN / dtex, and an elongation at break of 40%-70%.

[0022] Beneficial effects

[0023] (1) The present invention uses dry spinning to prepare aramid. By controlling the temperature of the tunnel and the residence time, the amount of residual solvent in the nascent fiber can be 10-15 wt%. This residual solvent plays an important role in promoting the removal of salt substances in the fiber through double diffusion with water during the subsequent water washing process.

[0024] (2) The present invention can effectively remove residual salt substances inside the aramid filament by using a multi-stage ultrasonic water washing process. In particular, the addition of trace amounts of DMSO in the first stage water washing bath can effectively destroy the hydrogen bond network of the dense surface of the aramid, thereby facilitating the diffusion of salt substances. In addition, through multi-stage water washing and stretching, the orientation of molecular chains is further optimized, and the mechanical properties of the fiber are improved.

[0025] (3) The present invention uses DMAc / NMP or DMAc / NVP mixed solvent to synthesize aramid. On the one hand, the excellent solvation ability of NMP and NVP is beneficial to the synthesis of high molecular weight aramid. On the other hand, the higher boiling point of NMP and NVP compared to DMAc makes it easier to form solvent residue in the cured fiber during dry forming, which inhibits excessive densification during dry spinning and thus facilitates the rapid diffusion and removal of salt substances in the fiber during the washing process. Attached Figure Description

[0026] Figure 1 Photograph of the aramid fiber prepared in Example 1.

[0027] Figure 2 SEM images of cross-sections of aramid fibers prepared for Example 1 (left) and Comparative Example 1 (right). Detailed Implementation

[0028] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0029] In the examples, diformyl chloride was provided by THICA (Shanghai) Chemical Industry Development Co., Ltd., and diamine was provided by Tianjin Zhongtai Materials Technology Co., Ltd.; commercially available wet-spun meta-aramid was provided by Taihe New Materials Group Co., Ltd.

[0030] Example 1

[0031] Under nitrogen protection, isophthaloyl chloride (IPC) and m-phenylenediamine (m-PDA) were dissolved in a DMAc / NMP mixed solvent (NMP volume fraction 15 vol%) to obtain the reaction system; the molar ratio of IPC / m-PDA was controlled at 1.01:1, and the mass fraction of the reaction system was 22 wt%; after reacting at 0 ℃ for 18 h, ammonia gas was introduced into the reaction system to ensure that all HCl was converted to NH4Cl. The polymer solution was degassed and stored for later use, which is the aramid spinning solution; the above aramid spinning solution was metered and extruded into the duct through a spinneret, and nascent fibers were obtained through extrusion and winding; the temperatures of the three sections of the duct were controlled at 100 ℃, 180 ℃, and 240 ℃, the total residence time of the aramid spinning solution in the duct was 5 s, the extrusion rate was 10 m / min, the winding speed was 500 m / min, and the solvent residue inside the nascent fibers was controlled at 13%. The nascent fibers were ultrasonically washed and stretched in four stages of a water bath. The mass fraction of DMSO in the first stage of the water bath was controlled at 3 wt%, the washing length was 2 m, the washing temperature was 50 ℃, and the stretching ratios of the four stages of the water bath were 1.0, 1.2, 1.2 and 1.2, respectively. Finally, the nascent fibers were thoroughly dried at 120 ℃ and then hot-stretched 1.5 times at 220 ℃ to obtain aramid.

[0032] Example 2

[0033] Under nitrogen protection, IPC and m-PDA were dissolved in a DMAc / NMP mixed solvent (NMP volume fraction 15 vol%) to obtain the reaction system; the molar ratio of IPC / m-PDA was controlled at 1.02:1, and the mass fraction of the reaction system was 25 wt%; after reacting at 0℃ for 18 h, ammonia gas was introduced into the reaction system to ensure that all HCl was converted to NH4Cl. The polymer solution was degassed and stored for later use, which is the aramid spinning solution; the above aramid spinning solution was metered and extruded into the channel through a spinneret, and nascent fibers were obtained through extrusion and winding; the temperatures of the three sections of the channel were controlled at 100 ℃, 180 ℃ and 240 ℃, the total residence time of the aramid spinning solution in the channel was 5 s, the extrusion rate was 10 m / min, the winding speed was 500 m / min, and the solvent residue inside the nascent fibers was controlled at 13%. The nascent fibers were ultrasonically washed and stretched in four stages of a water bath. The mass fraction of DMSO in the first stage of the water bath was controlled at 3 wt%, the washing length was 2 m, the washing temperature was 80 ℃, and the stretching ratios of the four stages of the water bath were 1.0, 1.3, 1.3 and 1.3, respectively. Finally, the nascent fibers were thoroughly dried at 120 ℃ and then hot-stretched 2.0 times at 250 ℃ to obtain aramid.

[0034] Example 3

[0035] Under nitrogen protection, 2,5-furandicarboxylic acid chloride (2,5-FDC) and m-PDA were dissolved in a DMAc / NMP mixed solvent (NMP volume fraction 15 vol%) to obtain the reaction system. The molar ratio of 2,5-FDC / m-PDA was controlled at 1.01:1, and the mass fraction of the reaction system was 22 wt%. After reacting at 0 ℃ for 18 h, ammonia gas was introduced into the reaction system to ensure that all HCl was converted to NH4Cl. The polymer solution was degassed and stored for later use, which is the aramid spinning solution. The above aramid spinning solution was metered and extruded into the duct through a spinneret. After extrusion and winding, nascent fibers were obtained. The temperatures of the three sections of the duct were controlled at 100 ℃, 180 ℃, and 240 ℃, respectively. The total residence time of the aramid spinning solution in the duct was 5 s, the extrusion rate was 10 m / min, the winding speed was 500 m / min, and the solvent residue inside the nascent fibers was controlled at 13%. The nascent fibers were ultrasonically washed and stretched in four stages of a water bath. The mass fraction of DMSO in the first stage of the water bath was controlled at 3 wt%, the washing length was 2 m, the washing temperature was 50 ℃, and the stretching ratios of the four stages of the water bath were 1.0, 1.2, 1.2 and 1.2, respectively. Finally, the nascent fibers were thoroughly dried at 120 ℃ and then hot-stretched 1.5 times at 220 ℃ to obtain aramid.

[0036] Example 4

[0037] Under nitrogen protection, IPC and m-PDA were dissolved in a DMAc / NVP mixed solvent (NVP volume fraction 15 vol%) to obtain the reaction system; the molar ratio of IPC / m-PDA was controlled at 1:1, and the mass fraction of the reaction system was 22 wt%; after reacting at 0 ℃ for 24 h, Ca(OH)2 was added to the reaction system to ensure that all HCl was converted to CaCl2. The polymer solution was degassed and stored for later use, which is the aramid spinning solution; the above aramid spinning solution was metered and extruded into the channel through a spinneret, and nascent fibers were obtained through extrusion and winding; the temperatures of the three sections of the channel were controlled at 120 ℃, 200 ℃ and 280 ℃, the total residence time of the aramid spinning solution in the channel was 5 s, the extrusion rate was 10 m / min, the winding speed was 600 m / min, and the solvent residue inside the nascent fibers was controlled at 15%. The nascent fibers were ultrasonically washed and stretched in four stages of a water bath. The mass fraction of DMSO in the first stage of the water bath was controlled at 3 wt%, the washing length was 2 m, the washing temperature was 80 ℃, and the stretching ratios of the four stages of the water bath were 1.0, 1.4, 1.4 and 1.4, respectively. Finally, the nascent fibers were thoroughly dried at 120 ℃ and then hot-stretched 2.0 times at 250 ℃ to obtain aramid.

[0038] Comparative Example 1

[0039] Under nitrogen protection, IPC and m-PDA were dissolved in DMAc solvent, and the other steps were the same as in Example 1.

[0040] Comparative Example 2

[0041] The temperatures of the three sections of the tunnel were controlled at 100 ℃, 150 ℃ and 180 ℃ respectively, and the other steps were the same as in Example 1.

[0042] Comparative Example 3

[0043] The nascent fibers were washed and stretched in a four-stage non-ultrasonic water bath, with other steps being the same as in Example 1.

[0044] Comparative Example 4

[0045] DMSO is not added to the first water bath, and the other steps are the same as in Example 1.

[0046] Performance comparison of aramid fibers

[0047] sample Tensile strength (cN / dtex) Initial modulus (cN / dtex) Elongation at break (%) Example 1 6.8 125 62 Example 2 8.2 169 55 Example 3 7.2 140 58 Example 4 9.8 193 44 Comparative Example 1 3.1 73 127 Comparative Example 2 2.9 65 136 Comparative Example 3 4.5 99 101 Comparative Example 4 4.2 84 107 Commercially available wet-spun meta-aramid fibers 4.2 72 45

[0048] Examples 1-4 prepared aramid fibers with excellent mechanical properties. Compared with Example 1, Comparative Example 1 did not add NMP components with higher boiling points, resulting in low solvent residue in the nascent filament prepared by dry spinning. This made it difficult to effectively remove internal salt components during the subsequent washing process, leading to poor fiber performance. In Comparative Example 2, when the tunnel temperature was not controlled within the optimal range, the high solvent residue in the nascent filament also damaged the dense internal structure of the dry-spun aramid, ultimately resulting in poor fiber mechanical properties. Comparative Example 3 used non-ultrasonic washing, which was not conducive to salt diffusion and removal, resulting in poor fiber performance. In Comparative Example 4, no trace amount of DMSO was added to the first washing bath. Pure water was insufficient to destroy the dense structure and rich hydrogen bond network on the fiber surface, and it was also not conducive to the diffusion of internal salt components, resulting in poor washing effect and fiber performance lower than that of Example 1. Furthermore, compared with commercially available meta-aramid, the dry-spun meta-aramid prepared in Example 1, with the same chemical structure, exhibited higher mechanical properties.

Claims

1. A method of dry spinning high performance aramid fiber, characterized by, It comprises the following steps: (1) Dissolving diformyl chloride and diamine in a mixed solvent under the condition of protective gas, to obtain a reaction system, the mass fraction of the reaction system is 22-25%; (2) Reacting the reaction system of step (1) at 0-5℃ for 18-24 h, adding calcium hydroxide or ammonia gas to the reaction system to obtain aramid spinning solution; (3) After defoaming treatment, the aramid spinning solution of step (2) is metered to a spinning pack and then enters a duct, and then is extruded and wound to obtain a nascent fiber; wherein, by controlling the duct temperature and residence time, the residual solvent content in the nascent fiber obtained by winding is 10-15 wt%; (4) The nascent fiber of step (3) is washed by multiple ultrasonic waves and is subjected to water bath drawing; the multiple ultrasonic washing and water bath drawing are as follows: four sections of ultrasonic washing are set, each with a length of 1-3 m, and the washing temperature is 50-80℃, wherein DMSO is added in the first washing bath, and the concentration is controlled to be 1-5 wt%; the four sections of water bath drawing are 1.0, 1.2-1.4, 1.2-1.4 and 1.2-1.4, respectively; (5) The washed fiber prepared in step (4) is dried and heat-drawn, and is subjected to oiling treatment to obtain high-performance aramid fiber.

2. The method of claim 1, wherein, The diformyl chloride in step (1) is one of the following structures: 。 3. The method of claim 1, wherein, The diamine in step (1) is one of the following structures: 。 4. The method of claim 1, wherein, The mixed solvent in step (1) is N,N-dimethylacetamide DMAc and N-methyl-pyrrolidone NMP, or N,N-dimethylacetamide DMAc and N-vinyl-pyrrolidone NVP; wherein, the volume fraction of NMP or NVP is 15-30%.

5. The method of claim 1, wherein, The inherent viscosity of the aramid spinning solution in the step (2) is 1.0-2.5 dL·g -1 .

6. The method of claim 1, wherein, The control of duct temperature and residence time in step (3) means that the duct is heated in three sections from top to bottom, which are 100-120℃, 180-200℃ and 240-280℃, respectively; the total residence time of aramid spinning solution in the duct is 3-5 s.

7. The method of claim 1, wherein, The extrusion rate of aramid spinning solution in step (3) is 10-20 m / min; the winding speed of nascent fiber is 500-600 m / min.

8. The method of claim 1, wherein, The drying temperature in step (5) is 100-120℃; the heat-drawing temperature is 220-300℃, and the heat-drawing multiple is 1.5-3.0 times.

9. The method of claim 1, wherein, The tensile strength of high-performance aramid fiber in step (5) is 5-10 cN / dtex, the modulus is 100-200 cN / dtex, and the elongation at break is 40%-70%.

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