Method for spinning high-performance aramid fiber by dry method

Abstract

The invention relates to a method for spinning high-performance aramid fiber by a dry method, which comprises the following steps: (1) under the condition of protective gas, dissolving dicarbonyl chloride and diamine in a mixed solvent to obtain a reaction system; (2) after the reaction of the reaction system in the step (1), adding calcium hydroxide or ammonia gas into the reaction system to obtain an aramid fiber spinning solution; (3) defoaming the aramid fiber spinning solution obtained in the step (2), metering, conveying to a spinning assembly, then entering a channel, and extruding and winding to obtain nascent fibers; (4) carrying out multi-section ultrasonic water washing on the nascent fiber obtained in the step (3), and carrying out water bath drafting; and (5) carrying out drying, hot drafting and oiling treatment on the washed fiber prepared in the step (4) to obtain the high-performance aramid fiber. The aramid fiber prepared by the method has higher molecular chain orientation degree and a more compact internal structure, so that the aramid fiber 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] The present application belongs to the technical field of high-performance fiber materials, and particularly relates to a method for dry spinning high-performance aramid fiber. BACKGROUND

[0002] Aramid fiber, also known as aramid fiber, has the English name Aramid fiber. It is listed together with carbon fiber, ultra-high molecular weight polyethylene fiber and basalt fiber as the four high-performance fibers that China focuses on developing. According to the position of amide units on the benzene ring, aramid fiber can be divided into meta-aramid fiber and para-aramid fiber. Due to the rich hydrogen bonds and benzene ring units in the molecular chain of aramid fiber, this type of material has excellent mechanical properties, outstanding flame retardance, acid and alkali corrosion resistance and other characteristics, and has been widely used in the fields of aerospace, national defense and military industry, special protection, electrical insulation and the like.

[0003] At present, domestic aramid fiber production mostly adopts wet spinning or dry-jet wet spinning, that is, after the spinning solution enters the coagulation bath, the solvent in the spinning solution diffuses to the coagulation bath and the coagulant diffuses to the spinning stream, so that the yarn is solidified. However, in order to ensure the stable formation of the fiber, the wet spinning or dry-jet wet spinning usually stays in the coagulation bath for a long time, the spinning speed is slow, the production efficiency is low, and usually negative draft is needed in the coagulation bath; in addition, the coagulant remaining in the fiber during the double diffusion process is easy to form micropore defects in the fiber during the drying process, which restricts the mechanical properties of the fiber. Relatively speaking, the dry spinning speed is fast (spinning speed ≥ 500 m / min), and only one-way diffusion of the solvent occurs during the fiber forming process, which is more likely to prepare fibers with dense and uniform structure. It is particularly worth noting that the polymer solution stream can withstand more than 20 times of draft after extrusion through the spinneret in the high-temperature duct, and can maintain good molecular chain orientation after coagulation, therefore, the prepared fiber has higher mechanical properties.

[0004] However, there are few dry spinning methods for aramid fibers in China at present. The main reason is that, different from traditional polymer solution, aramid spinning solution polymerization often forms a large amount of HCl. In order to neutralize the by-product, it is necessary to add basic calcium hydroxide or ammonia gas in the system, so as to form CaCl2 or NH4Cl in the solution. Such salt needs to be removed during fiber spinning formation, otherwise it will seriously affect the comprehensive performance of the fiber. In dry spinning, the surface of the spinning stream will quickly solidify to form a dense skin layer due to the rapid volatilization of the surface solvent in the high-temperature duct, thereby hindering the volatilization of the internal CaCl2 or NH4Cl, which is difficult to remove even after a long time of washing. Therefore, how to quickly and efficiently remove the residual salt from the aramid as-spun fiber is one of the important bottlenecks restricting the dry spinning of aramid fibers. For example, the patent application No. CN201010192686.0 discloses a method for preparing aramid III fiber by dry spinning. However, the application document does not mention how to effectively remove the salt. SUMMARY

[0005] The technical problem to be solved by the present application is to provide a method for dry spinning high-performance aramid fiber. The aramid fiber prepared by the method has higher molecular chain orientation degree and more compact internal structure, and thus has more excellent mechanical properties, and has a wide application prospect in the fields of aerospace, special protection, electrical insulation, etc.

[0006] The present application provides a method for dry spinning high-performance aramid fiber, comprising the following steps:

[0007] (1) Dissolving the dichloroform and the diamine in a mixed solvent under the condition of a protective gas, to obtain a reaction system, wherein the mass fraction of the reaction system is 22-25%, and the molar ratio of dichloroform to diamine is 1.05-1:1;

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

[0009] (3) After defoaming treatment of the aramid spinning solution of step (2), metering the aramid spinning solution to a spinning assembly and then into a duct to obtain an as-spun fiber by extrusion and winding. The duct temperature and residence time are controlled to ensure that the residual solvent content in the as-spun fiber obtained by winding is 10-15wt%;

[0010] (4) the nascent fiber prepared in step (3) is subjected to multi-stage ultrasonic washing and water bath drawing; the multi-stage ultrasonic washing and water bath drawing refer to that four stages of ultrasonic washing are set, each stage has a length of 1-3 m, the washing temperature is 50-80℃, and DMSO is added in the first stage of washing bath and the concentration of DMSO is controlled to be 1-5 wt%; the drawing multiples of the four stages of water bath drawing are 1.0, 1.2-1.4, 1.2-1.4 and 1.2-1.4, respectively;

[0011] (5) the washed fiber prepared in step (4) is subjected to drying, heat drawing and oiling to obtain high-performance aramid fiber.

[0012] Preferably, the dicarboxylic acid in step (1) is one of the following structures: .

[0013] Preferably, the diamine in step (1) is one of the following structures: .

[0014] 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%.

[0015] Preferably, the intrinsic viscosity of the aramid spinning solution in step (2) is 1.0-2.5 dL·g -1 .

[0016] Preferably, the regulation of the temperature and residence time of the duct in step (3) refers to that the duct is heated in three stages from top to bottom, and the heating temperatures are 100-120℃, 180-200℃ and 240-280℃, respectively; the total residence time of the aramid spinning solution in the duct is 3-5 s.

[0017] Preferably, the extrusion rate of the aramid spinning solution in step (3) is 10-20 m / min; the winding speed of the nascent fiber is 500-600 m / min.

[0018] Preferably, 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.

[0019] Preferably, the tensile strength of the 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%.

[0020] Beneficial effects

[0021] (1) The present application can make the residual solvent amount in the nascent fiber be 10-15 wt% by adopting dry spinning process and by controlling the temperature of the nozzle and the residence time, and this part of residual solvent plays an important role in promoting the removal of salt substances in the fiber through double diffusion with water in the subsequent washing process.

[0022] (2) The present application can effectively remove the residual salt substances in the nascent aramid fiber by adopting multi-stage ultrasonic washing process, and in particular, the addition of trace amount of DMSO in the first washing bath can effectively destroy the hydrogen bond network of the dense surface layer of aramid, thereby facilitating the diffusion of salt substances; in addition, through multi-stage washing and drawing, the orientation of molecular chains is further optimized, and the mechanical properties of the fiber are improved.

[0023] (3) The present application can synthesize aramid by adopting DMAc / NMP or DMAc / NVP mixed solvent, on the one hand, the excellent solvating ability of NMP and NVP is conducive to the synthesis of high molecular weight aramid, on the other hand, NMP and NVP have higher boiling point than DMAc, which is easy to form solvent residues in the solidified fiber during dry forming, that is, to inhibit the excessive densification during dry spinning forming, thereby facilitating the rapid diffusion and removal of salt substances in the fiber during the washing process. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The photo of aramid prepared for Example 1.

[0025] Figure 2 The cross-sectional SEM photos of aramid prepared for Example 1 (left) and Comparative Example 1 (right). DETAILED DESCRIPTION

[0026] The present application will be further described below in conjunction with specific examples. It should be understood that these examples are only used to illustrate the present application and not used to limit the scope of the present application. In addition, it should be understood that after reading the content taught by the present application, those skilled in the art can make various modifications or changes to the present application, and these equivalent forms also fall within the scope defined by the appended claims of the present application.

[0027] The dicyan chloride in the examples was provided by TCI (Shanghai) Chemical Industry Development Co., Ltd., and the diamine was provided by Tianjin Zhongtai Material Technology Co., Ltd.; the commercially available wet-spun meta-aramid was provided by Taihe New Material Group Co., Ltd.

[0028] Example 1

[0029] IPC and m-PDA were dissolved in DMAc / NMP mixed solvent (NMP volume fraction was 15 vol%) under nitrogen protection to obtain a reaction system; the molar ratio of IPC / m-PDA was controlled to be 1.01:1, and the mass fraction of the reaction system was 22 wt%; after reaction at 0 ℃ for 18 h, ammonia was introduced into the reaction system to ensure that all HCl was converted into NH4Cl, and the polymer solution was stored after degassing, which was aramid spinning solution; the aramid spinning solution was extruded into a duct through a spinneret after metering, and nascent fibers were obtained through extrusion and winding; the temperatures of the three sections of the duct were controlled to be 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, and the winding speed was 500 m / min, and the residual amount of solvent in the nascent fiber was controlled to be 13 wt%; the nascent fiber was ultrasonically washed and drawn in four washing baths, the mass fraction of DMSO in the first washing bath was controlled to be 3 wt%, the washing lengths were all 2 m, the washing temperature was 50 ℃, and the drawing multiples of the four washing sections were 1.0, 1.2, 1.2 and 1.2 respectively; finally, the nascent fiber was fully dried at 120 ℃, and aramid was obtained after hot drawing at 220 ℃ by 1.5 times.

[0030] Example 2

[0031] IPC and m-PDA were dissolved in DMAc / NMP mixed solvent (NMP volume fraction was 15 vol%) under nitrogen protection to obtain a reaction system; the molar ratio of IPC / m-PDA was controlled to be 1.02:1, and the mass fraction of the reaction system was 25 wt%; after reaction at 0 ℃ for 18 h, ammonia was introduced into the reaction system to ensure that all HCl was converted into NH4Cl, and the polymer solution was stored after degassing, which was aramid spinning solution; the aramid spinning solution was extruded into a duct through a spinneret after metering, and nascent fibers were obtained through extrusion and winding; the temperatures of the three sections of the duct were controlled to be 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, and the winding speed was 500 m / min, and the residual amount of solvent in the nascent fiber was controlled to be 13 wt%; the nascent fiber was ultrasonically washed and drawn in four washing baths, the mass fraction of DMSO in the first washing bath was controlled to be 3 wt%, the washing lengths were all 2 m, the washing temperature was 80 ℃, and the drawing multiples of the four washing sections were 1.0, 1.3, 1.3 and 1.3 respectively; finally, the nascent fiber was fully dried at 120 ℃, and aramid was obtained after hot drawing at 250 ℃ by 2.0 times.

[0032] Example 3

[0033] Under nitrogen protection, 2,5-furandicarbonyl chloride (2,5-FDC) and m-PDA were dissolved in a DMAc / NMP mixed solvent (NMP volume fraction was 15 vol%) to obtain a reaction system. The molar ratio of 2,5-FDC / m-PDA was controlled to be 1.01:1, and the mass fraction of the reaction system was 22 wt%. After reacting at 0°C for 18 h, ammonia was introduced into the reaction system to ensure that all HCl was converted into NH4Cl. The polymer solution was degassed and stored for later use to obtain the aramid spinning solution. The above aramid spinning solution was metered and extruded from a spinneret into a shaft, and spun fibers were obtained by extrusion and winding. The temperatures of the three sections of the shaft were controlled to be 100°C, 180°C, and 240°C, respectively. The total residence time of the aramid spinning solution in the shaft was 5 s, the extrusion rate was 10 m / min, the winding speed was 500 m / min, and the residual solvent content in the spun fibers was controlled to be 13 wt%; the as-spun fibers were ultrasonically washed and stretched in four-stage washing baths, with the DMSO mass fraction in the first washing bath being controlled at 3 wt%, the washing length being 2 m, the washing temperature being 50 ℃, and the four-stage washing stretching ratios being 1.0, 1.2, 1.2, and 1.2, respectively; finally, the as-spun fibers were fully dried at 120 ℃ and then hot stretched 1.5 times at 220 ℃ to obtain aramid.

[0034] Example 4

[0035] Under nitrogen protection, IPC and m-PDA were dissolved in a DMAc / NVP mixed solvent (NVP volume fraction was 15 vol%) to obtain a reaction system; the molar ratio of IPC / m-PDA was controlled to be 1:1, and the mass fraction of the reaction system was 22 wt%; Ca(OH)2 was added to the reaction system after reacting at 0 ℃ for 24 h to ensure that all HCl was converted into CaCl2. The polymer solution was degassed and stored for later use, which was the aramid spinning solution; the above-mentioned aramid spinning solution was extruded into the shaft through the spinneret after metering, and the spun fiber was obtained by extrusion and winding; the temperatures of the three sections of the shaft were controlled to be 120 ℃, 200 ℃ and 280 ℃ respectively, the total residence time of the aramid spinning solution in the shaft was 5 s, the extrusion rate was 10 m / min, the winding speed was 600 m / min, and the residual solvent content in the spun fiber was controlled to be 15 wt%; the as-spun fibers were ultrasonically washed and drawn in four-stage water washing baths, the DMSO mass fraction in the first-stage water washing bath was controlled to be 3 wt%, the washing length was 2 m, the washing temperature was 80 ℃, and the four-stage water washing drawing ratios were 1.0, 1.4, 1.4 and 1.4, respectively; finally, the as-spun fibers were fully dried at 120 ℃ and then hot-drawn at 250 ℃ for 2.0 times to obtain aramid.

[0036] Comparative Example 1 IPC and m-PDA were dissolved in DMAc solvent under nitrogen protection, and other steps were the same as example 1.

[0037] Comparative example 2 The temperature of the three sections of the duct was controlled at 100 ℃, 150 ℃ and 180 ℃ respectively, and other steps were the same as example 1.

[0038] Comparative example 3 The nascent fiber was washed and drawn in four non-ultrasonic washing baths, and other steps were the same as example 1.

[0039] Comparative example 4 No DMSO was added in the first washing bath, and other steps were the same as example 1.

[0040] Performance comparison of aramid fibers

[0041] 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 Commercial wet-spun para-aramid fiber 4.2 72 45

[0042] Examples 1-4 prepared aramid fibers with excellent mechanical properties. Compared with example 1, in comparative example 1, no NMP component with higher boiling point was added, so the solvent residue in the nascent fiber prepared by dry spinning was low, and it was difficult to effectively remove the salt components in the fiber in the later washing process, and the fiber performance was poor; in comparative example 2, when the duct temperature was not in the best process range, the solvent residue in the nascent fiber was high, which would also destroy the dense internal structure of the dry-spun aramid fiber, and the mechanical properties of the final fiber were poor; in comparative example 3, non-ultrasonic washing was used, which was not conducive to the diffusion and removal of salt, and the fiber performance was poor; in comparative example 4, no trace of DMSO component was added in the first washing bath, and pure water was difficult to destroy the dense structure and rich hydrogen bond network on the surface of the fiber, and also not conducive to the diffusion of internal salt components, the washing effect was poor, resulting in the fiber being lower than example 1. In addition, compared with the commercially available meta-aramid, the dry-spun meta-aramid prepared in example 1 with the same chemical structure has higher mechanical properties.

Claims

1. A method for dry spinning high-performance aramid fiber, characterized in that: The steps include: (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, wherein the mass fraction of the reaction system is 22-25%; (2) reacting the reaction system of step (1) at 0-5°C for 18-24 hours, adding calcium hydroxide or ammonia to the reaction system to obtain an aramid spinning solution; (3) After degassing, the aramid spinning solution of step (2) is metered and transported to the spinneret assembly and then into the tunnel, where it is extruded and wound to obtain spun fibers; wherein, by regulating the tunnel temperature and residence time, the residual solvent content in the wound spun fibers is ensured to be 10-15 wt%; (4) The spun fiber of step (3) is subjected to multi-stage ultrasonic water washing and water bath drawing; the multi-stage ultrasonic water washing and water bath drawing refer to: setting four sections of ultrasonic water washing, each of which has a length of 1-3 m and a water washing temperature of 50-80°C, wherein DMSO is added to the water bath of the first section and its concentration is controlled to be 1-5 wt%; the four water bath drawing multiples 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, heat-stretched, and oiled to obtain high-performance aramid.

2. The method according to claim 1, characterized in that The diformyl chloride in step (1) is one of the following structures: 。 3. The method according to claim 1, characterized in that The diamine in step (1) is one of the following structures: 。 4. The method according to 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 the NMP or NVP is 15-30%.

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

6. The method according to claim 1, characterized in that The control of the tunnel temperature and residence time in step (3) means that the tunnel is heated in three sections from the top, namely 100-120°C, 180-200°C and 240-280°C; the total residence time of the aramid spinning solution in the tunnel is 3-5 s.

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

8. The method according to claim 1, characterized in that The drying temperature in step (5) is 100-120°C; the hot stretching temperature is 220-300°C, and the hot stretching ratio is 1.5-3.0 times.

9. The method according to claim 1, characterized in that 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%.

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