Modified para-aramid stock solution, preparation method and para-aramid fiber thereof

Abstract

The invention relates to the technical field of high-molecular polymerization and molding, in particular to a modified para-aramid stock solution, a preparation method and para-aramid fibers.The preparation method comprises the steps that under the inert gas condition, diamine and a chlorosilane polycondensation agent react in a weakly-alkaline polar aprotic solvent, and a silanization modified diamine solution is obtained; the diamine comprises diaminodiphenyl ether and p-phenylenediamine; adding paraphthaloyl chloride into the silanization modified diamine solution to carry out a copolymerization reaction, and after the reaction is finished, carrying out neutralization treatment to obtain the modified para-aramid stock solution. According to the preparation method of the modified para-aramid stock solution, the modified diamine does not need to be independently purified, the high-viscosity modified para-aramid stock solution can be directly obtained, and the modified para-aramid stock solution is high in polymer specific concentration logarithmic viscosity and high in molecular weight, so that a high-quality and stable-quality para-aramid fiber product is more favorably obtained.

Description

Technical Field

[0001] The present invention relates to a modified para-aramid spinning solution, a preparation method thereof, and para-aramid fibers, belonging to the technical field of polymer polymerization and molding. Background Art

[0002] Para-aramid fibers were successfully developed and first industrialized by DuPont in the 1960s. It is a new type of organic synthetic fiber with excellent properties such as high strength, high modulus, high temperature resistance, acid and alkali resistance, and light weight. It is mainly used in fields such as rubber-reinforced products, bulletproof fabrics, composite structural materials, cable materials, heat insulation and sound insulation, and radiation-proof structural boards. With the continuous increase in the personalized demand for aramid in industries such as electronic communication, national defense and military, lightweight materials, and 5G, the para-aramid industry has developed rapidly, and the market space has great potential.

[0003] The para-aramid molecular chain has a large rigidity, poor impact resistance and fatigue resistance, and is prone to splitting and other phenomena during use, which to a certain extent limits its wide application. The patent with the publication number CN104350190B discloses a polymerization and spinning production method of modified para-aramid, and a high-toughness para-aramid fiber is prepared by a dry-jet wet-spinning process. However, inevitably, p-phenylenediamine is extremely easy to oxidize during the process, resulting in a decrease in the end-group activity, a decline in the quality of the polymerization solution, and the fiber quality. The patent with the publication number CN118047945B discloses a high-viscosity aromatic polyamide copolymer spinning solution, a preparation method thereof, and an application. The preparation method is as follows: under the protection of an inert gas, p-phenylenediamine and triethylamine are dissolved in an organic solvent, and a chlorosilane compound is added dropwise, stirred evenly, and reacted under heating conditions. After the reaction is completed, silanized p-phenylenediamine is obtained through post-treatment; a composite solvent containing a polar amide solvent and a co-solvent is prepared. Under the protection of an inert gas, in the composite solvent, the silanized p-phenylenediamine, diaminodiphenyl ether, and terephthaloyl chloride are subjected to a polymerization reaction. After the reaction is completed, the high-viscosity aromatic polyamide copolymer spinning solution is obtained through neutralization treatment. This patent proposes to modify p-phenylenediamine by silanization, solving the problem that p-phenylenediamine is easy to oxidize during the reaction, thereby preparing a high-viscosity aromatic polyamide copolymer spinning solution. However, in this process, the reaction process time of silanized p-phenylenediamine is relatively long, the operation is complex, and the purification process of silanized p-phenylenediamine is relatively troublesome. The purification and storage environment requirements for silanized p-phenylenediamine are high. Silanized p-phenylenediamine is easily decomposed when encountering water in the air, which easily leads to large differences in the properties of para-aramid fibers spun in different batches, resulting in large differences in products between different batches. Moreover, most of the solvents used in the modification process are carcinogenic substances such as benzene and xylene, which are relatively dangerous and costly in actual production.

[0004] In view of the above problems, a modified para-aramid spinning dope, a preparation method thereof and para-aramid fibers are provided, which are of great significance for solving diamine oxidation, increasing the molecular weight of polymers, improving fiber quality, and reducing environmental pollution. Summary of the Invention

[0005] Aiming at the deficiencies of the existing technology, the present invention provides a modified para-aramid spinning dope, a preparation method thereof and para-aramid fibers. The preparation method of the modified para-aramid spinning dope does not require separate purification of the modified diamine, and a high-viscosity modified para-aramid spinning dope can be directly obtained. The polymer inherent viscosity in the modified para-aramid spinning dope is high, and the molecular weight is high, which is more conducive to obtaining high-quality and stable para-aramid fiber products.

[0006] The technical solution of the present invention to solve the above technical problems is as follows: A preparation method of a modified para-aramid spinning dope, the preparation method is: S1. In-situ silanization modification of diamine: Under the condition of an inert gas, in a weakly basic polar aprotic solvent, diamine reacts with a chlorosilane polycondensation agent to obtain a silanized modified diamine solution; the diamine includes diaminodiphenyl ether and p-phenylenediamine. S2. Copolymerization reaction: Terephthaloyl chloride is added to the silanized modified diamine solution for copolymerization reaction. After the reaction is completed, neutralization treatment is carried out to obtain the modified para-aramid spinning dope.

[0007] Further, in step S1, the diaminodiphenyl ether is at least one of 3,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl ether; The chlorosilane polycondensation agent is at least one of tetrachlorosilane, trimethylchlorosilane, dimethylchlorosilane, and methylchlorosilane.

[0008] Further, the weakly basic polar aprotic solvent is at least one of N-methylpyrrolidone and N,N-dimethylacetamide.

[0009] Further, the molar ratio of the chlorosilane polycondensation agent to the diamine is 1:(16 - 160); The molar ratio of p-phenylenediamine to diaminodiphenyl ether is 1:(0.8 - 1.2).

[0010] The molar ratio of terephthaloyl chloride to diamine is 1:(0.98 - 1.02).

[0011] Further, the specific operation of step S1 is: Under inert gas conditions, a solubilizing salt, diaminodiphenyl ether, and a chlorosilane polycondensing agent are added to a weakly basic polar aprotic solvent, and the temperature in the reaction system is controlled to be 5°C - 30°C, and the reaction is stirred for 10 - 20 min; then p-phenylenediamine is added to the system and the reaction continues for 20 - 30 min to obtain a silanized modified diamine solution.

[0012] Further, the solubilizing salt is at least one of calcium chloride and lithium chloride, and the dosage of the solubilizing salt is 0.25 - 5% of the mass of the weakly basic polar aprotic solvent.

[0013] Further, the polymerization reaction temperature in step S2 is -5~10°C, and the polymerization reaction time is 3 - 8 h.

[0014] The present invention also discloses a modified para-aramid dope, and the modified para-aramid dope is prepared according to the preparation method described in the present invention; The solid content of the modified para-aramid dope is 4 - 7 wt%, the spinning viscosity of the modified para-aramid dope is 3000 - 7000 Po, and the intrinsic viscosity of the polymer in the modified para-aramid dope is 3.4 - 4.0 dL / g.

[0015] The present invention also discloses a para-aramid fiber, and the para-aramid fiber is prepared by using a dry-jet wet spinning process with the modified para-aramid dope; The modified para-aramid dope is prepared according to the preparation method described in the present invention.

[0016] Further, the strength of the para-aramid fiber is 24 - 30 cN / dtex, the elongation at break is 4.5 - 6.5%, and the modulus is 545 - 750 cN / dtex.

[0017] The beneficial effects of the present invention are: In the preparation method of the modified para-aramid dope of the present invention, in a weakly basic polar aprotic solvent, a diamine reacts with a chlorosilane polycondensing agent to obtain a silanized modified diamine solution. The intermediate silanized modified diamine does not need to be purified, reducing the operation complexity, and avoiding the loss of reaction activity of the silanized modified diamine due to contact with the external environment during the purification process. The silanized modified diamine in the system of the present invention can exist more stably, and the silanized modified diamine has high activity and can react with acyl chloride in situ quickly, reducing the reaction time. The entire preparation process of the modified para-aramid dope has higher controllability and good repeatability, and is suitable for industrial stable production. The modified para-aramid dope can be directly spun to finally obtain para-aramid fibers with more excellent properties. The fibers prepared by dry-jet wet spinning of the modified para-aramid dope can be applied in fields such as rubber reinforcement, automotive hoses, and conveyor belts due to their excellent toughness and wear resistance.

[0018] In the preparation method of the modified para-aramid spinning dope of the present invention, in a weakly basic polar aprotic solvent, in-situ silanization modification of diamine is carried out, and subsequent copolymerization reaction can be directly carried out to prepare a spinning dope; in addition, during the in-situ silanization modification reaction of diamine, a small amount of hydrochloric acid by-product will be generated, and the weakly basic polar aprotic solvent which is the main component in the system can play a role in neutralizing and absorbing the acidic product (hydrochloric acid), thus promoting the forward reaction of the reaction, without the need to additionally add a basic acid-binding agent to the system, and thus without the need for subsequent salt removal operation, simplifying the process operation; in addition, all reaction raw materials and reaction products are dispersed in the weakly basic polar aprotic solvent, so that the acidic product generated by the reaction can be absorbed more quickly, which is more conducive to the reaction conversion, and the silanized modified diamine solution can be obtained quickly without high-temperature heating conditions, reducing energy consumption, shortening the production cycle, and being more conducive to industrial application.

[0019] In addition, in the preparation method of the modified para-aramid spinning dope of the present invention, the same solvent system is used for the in-situ silanization modification of diamine and the copolymerization reaction, so there is no need to purify the silanized modified diamine, which is equivalent to realizing a one-pot method for preparation. While simplifying the operation process, it can avoid the denaturation and inactivation losses of the silanized modified diamine caused by purification and storage. Therefore, only a small amount of chlorosilane polycondensation agent is needed to meet the modification requirements of diamine, and finally a suitable spinning dope can be obtained. Moreover, the small amount of chlorosilane polycondensation agent used can make the reaction in the in-situ silanization modification reaction system of diamine more stable, avoiding the problem of uncontrollable large heat release in the system. Therefore, there is no need to add raw materials by dropping during the reaction process, and the operation is simpler; moreover, each reactant and product can be better dispersed in the solvent system, thereby improving the reaction efficiency and reducing the reaction energy consumption.

[0020] In the preparation method of the present invention, the introduction of diaminodiphenyl ether can greatly improve the flexibility of the polymer molecular chain structure, increase the solubility of the polymer in the system, and the polymerization stock solution can be directly spun. Compared with the traditional preparation process of para-aramid, the use of concentrated sulfuric acid as a spinning solvent is avoided, and the corrosion resistance requirements for equipment can be greatly reduced. In addition, in the conventional method, when unmodified diaminodiphenyl ether, p-phenylenediamine and terephthaloyl chloride are polymerized, p-phenylenediamine has a higher reaction activity and will react with terephthaloyl chloride first, and then diaminodiphenyl ether reacts with terephthaloyl chloride, resulting in a block structure of the final polymer. In the preparation method of the modified para-aramid stock solution of the present invention, during the in-situ silanization modification of diamine, both diaminodiphenyl ether and p-phenylenediamine are subjected to in-situ silanization modification of diamine, so that both diaminodiphenyl ether and p-phenylenediamine contain structures modified by silyl groups, so that both silyl group-modified diaminodiphenyl ether and silyl group-modified p-phenylenediamine have high activity to carry out polymerization reaction with terephthaloyl chloride, so that in the molecular chain structure of the finally prepared polymer, the structures of diaminodiphenyl ether and p-phenylenediamine are more evenly distributed, further improving the performance of para-aramid fiber.

[0021] Furthermore, in the in-situ silanization modification of diamine of the present invention, first let diaminodiphenyl ether react with a chlorosilane condensing agent for a period of time, and then add p-phenylenediamine for silanization modification reaction, which can further balance the reaction activity difference between diaminodiphenyl ether and p-phenylenediamine, so that both diaminodiphenyl ether and p-phenylenediamine contain structures modified by silyl groups, and then a polymer with a more uniform molecular structure arrangement is obtained, and finally para-aramid fibers with relatively high strength performance, elongation performance and modulus performance are obtained. Description of the Drawings

[0022] Figure 1 Infrared spectrum of the polymer dry material prepared in Example 1; Figure 2 Dynamic thermomechanical curve of the para-aramid fiber prepared in Example 1. Detailed Description of the Invention

[0023] The following is a detailed description of the specific embodiments of the present invention. The present invention can be implemented in many other ways different from those described herein. Those skilled in the art can make similar improvements without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed.

[0024] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0025] A method for preparing a modified para-aramid stock solution, the preparation method is as follows: S1. In-situ silanization modification of diamine: Under inert gas conditions, in a weakly basic polar aprotic solvent, diamine reacts with a chlorosilane polycondensing agent to obtain a silanized modified diamine solution; the diamine includes diaminodiphenyl ether and p-phenylenediamine. S2. Copolymerization reaction: Add terephthaloyl chloride to the silanized modified diamine solution for copolymerization reaction. After the reaction is completed, neutralization treatment is carried out to obtain the modified para-aramid spinning solution.

[0026] Specifically, in step S1, the diaminodiphenyl ether is at least one of 3,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl ether. The chlorosilane polycondensing agent is at least one of tetrachlorosilane, trimethylchlorosilane, dimethylchlorosilane, and methylchlorosilane.

[0027] Specifically, the weakly basic polar aprotic solvent is at least one of N-methylpyrrolidone and N,N-dimethylacetamide.

[0028] Taking 3,4'-diaminodiphenyl ether as the diaminodiphenyl ether and trimethylchlorosilane as the chlorosilane polycondensing agent as an example, the reaction principles of steps S1 and S2 are as follows: .

[0029] Specifically, the molar ratio of the chlorosilane polycondensing agent to diamine is 1:(16 - 160); The molar ratio of p-phenylenediamine to diaminodiphenyl ether is 1:(0.8 - 1.2).

[0030] The molar ratio of terephthaloyl chloride to diamine is 1:(0.98 - 1.02).

[0031] Specifically, the specific operation of step S1 is as follows: Under inert gas conditions, add a solubilizing salt, diaminodiphenyl ether, and a chlorosilane polycondensing agent to a weakly basic polar aprotic solvent, control the temperature in the reaction system to be 5°C - 30°C, and stir and react for 10 - 20 min; then add p-phenylenediamine to the system and continue to react for 20 - 30 min to obtain a silanized modified diamine solution.

[0032] Specifically, the solubilizing salt is at least one of calcium chloride and lithium chloride, and the dosage of the solubilizing salt is 0.25% - 5% of the mass of the weakly basic polar aprotic solvent.

[0033] Specifically, the polymerization reaction temperature in step S2 is -5~10°C, and the polymerization reaction time is 3 - 8 h.

[0034] More specifically, after the polymerization reaction is completed, a neutralizing agent is added for neutralization. The neutralizing agent is any one of calcium hydroxide, calcium oxide, and calcium carbonate, and the temperature in the system is controlled not to exceed 90 °C during the neutralization process.

[0035] The present invention also discloses a modified para-aramid spinning solution, which is prepared according to the preparation method described in the present invention; The solid content of the modified para-aramid spinning solution is 4-7 wt%, the spinning viscosity of the modified para-aramid spinning solution is 3000-7000 Po, the intrinsic viscosity of the polymer in the modified para-aramid spinning solution is 3.4-4.0 dL / g, the measurement temperature of the intrinsic viscosity is 30 °C, and the dissolution medium used is concentrated sulfuric acid with a mass concentration of 98%.

[0036] The present invention also discloses a para-aramid fiber, and the para-aramid fiber is prepared by using a dry-jet wet spinning process with the modified para-aramid spinning solution; The modified para-aramid spinning solution is prepared according to the preparation method described in the present invention.

[0037] Preferably, the strength of the para-aramid fiber is 24-30 cN / dtex, the elongation at break is 4.5-6.5%, and the modulus is 545-750 cN / dtex.

[0038] More specifically, the dry-jet wet spinning process method used in the embodiments of the present invention is as follows: The modified para-aramid spinning solution enters a coagulation bath through a spinneret plate with 200 holes, a pore diameter of 0.2 mm, and a length-diameter ratio of 3 to form a nascent fiber. The coagulation bath is an aqueous NMP solution with a mass concentration of 30%, and the temperature of the coagulation bath is 10 °C; the height of the air bath is adjusted to 10 mm. The nascent fiber is then stretched in a stretching bath, the stretching ratio is 1.5, the stretching bath is an aqueous NMP solution with a mass concentration of 10%, and the temperature of the stretching bath is 10 °C. Then, after passing through a series of water washing and drying devices, it is thermally stretched 9 times at 500 °C in a nitrogen atmosphere, and then heat-set on a hot roller at 400 °C. After oiling, it is wound up to obtain the modified para-aramid fiber, and the winding speed is 100 m / min.

[0039] Example 1 S1. In-situ silanization modification of diamine: Under the protection of an inert gas and mechanical stirring conditions, 3,4'-diaminodiphenyl ether, calcium chloride, and silicon tetrachloride are added to N-methylpyrrolidone, the temperature in the system is controlled at 25 °C, and the stirring reaction is carried out for 15 min; then p-phenylenediamine is added to the system, and the stirring reaction is continued for 25 min. The solution in the system is in a clear state, and a silanized modified diamine solution is obtained; Among them, the molar ratio of silicon tetrachloride to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:32; The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 1:1; The addition amount of calcium chloride is 0.75% of the mass of the N-methylpyrrolidone.

[0040] S2. Copolymerization reaction: Cool the silanized modified diamine solution to -5°C, and then add terephthaloyl chloride in three portions for copolymerization reaction. The molar ratio of terephthaloyl chloride to diamine is 1:1; mechanically stir at 100 r / min for 5 h; finally, slowly raise the temperature to 90°C and add calcium hydroxide to neutralize to pH 7 to obtain the modified para-aramid spinning dope; the solid content of the modified para-aramid spinning dope is 6.4%, the spinning viscosity is 5000 Po, the intrinsic viscosity of the polymer measured after washing and drying with water is 4.0 dL / g, and the infrared spectrum of the polymer is as Figure 1 shown.

[0041] S3. Spinning: The modified para-aramid spinning dope enters the coagulation bath through a spinneret plate with 200 holes, a pore diameter of 0.2 mm, and a length-diameter ratio of 3 to form a nascent fiber. The coagulation bath is an aqueous solution of NMP with a mass concentration of 30%, and the temperature of the coagulation bath is 10°C; the height of the air bath is adjusted to 10 mm. The nascent fiber is then stretched in a stretching bath, and the stretching ratio is 1.5. The stretching bath is an aqueous solution of NMP with a mass concentration of 10%, and the temperature of the stretching bath is 10°C. Then it passes through a series of water washing and drying devices, is thermally stretched 9 times at 500°C in a nitrogen atmosphere, and then undergoes heat setting treatment on a hot roller at 400°C. After oiling, it is wound up to obtain the modified para-aramid fiber, and the winding speed is 100 m / min. The dynamic thermomechanical curve of the para-aramid fiber is as Figure 2 shown.

[0042] Example 2 S1. In-situ silanization modification of diamine: Under the protection of inert gas and mechanical stirring, add 3,4'-diaminodiphenyl ether, calcium chloride, and trimethylchlorosilane to N-methylpyrrolidone, control the temperature in the system to 30°C, and stir and react for 10 min; then add p-phenylenediamine to the system and continue to stir and react for 30 min. The solution in the system is in a clear state to obtain the silanized modified diamine solution; Among them, the molar ratio of trimethylchlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:32; The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 1:1; The addition amount of calcium chloride is 0.25% of the mass of the N-methylpyrrolidone.

[0043] S2. Copolymerization reaction: Cool the silanized modified diamine solution to -5°C, then add terephthaloyl chloride in three portions for copolymerization reaction. The molar ratio of terephthaloyl chloride to diamine is 1:1. Stir mechanically at 100 r / min for 5 h. Finally, slowly raise the temperature to 90°C and add calcium hydroxide to neutralize to pH 7 to obtain the modified para-aramid spinning dope. The solid content of the modified para-aramid spinning dope is 6.4%, the spinning viscosity is 3000 Po, and the intrinsic viscosity of the polymer measured after washing and drying is 3.4 dL / g.

[0044] S3. Spinning: The modified para-aramid spinning dope enters the coagulation bath through a spinneret with 200 holes, a pore diameter of 0.2 mm, and a length-to-diameter ratio of 3 to form a nascent fiber. The coagulation bath is an aqueous NMP solution with a mass concentration of 30%, and the temperature of the coagulation bath is 10°C. The height of the air bath is adjusted to 10 mm. The nascent fiber is then stretched in a stretching bath with a stretching ratio of 1.5. The stretching bath is an aqueous NMP solution with a mass concentration of 10%, and the temperature of the stretching bath is 10°C. After that, it passes through a series of water washing and drying devices, is thermally stretched 9 times at 500°C under a nitrogen atmosphere, and then undergoes heat setting treatment on a hot roller at 400°C. After oiling, it is wound up to obtain the modified para-aramid fiber, and the winding speed is 100 m / min.

[0045] Example 3 S1. In-situ silanization modification of diamine: Under the protection of inert gas and mechanical stirring, add 3,4'-diaminodiphenyl ether, lithium chloride, and dimethylchlorosilane to N,N-dimethylacetamide, control the temperature in the system to 5°C, and stir and react for 20 min. Then add p-phenylenediamine to the system and continue to stir and react for 30 min. The solution in the system is in a clear state to obtain the silanized modified diamine solution. Among them, the molar ratio of dimethylchlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:16. The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 1:0.8. The addition amount of lithium chloride is 5% of the mass of the N,N-dimethylacetamide.

[0046] S2. Copolymerization reaction: Cool the silanized modified diamine solution to 0°C, then add terephthaloyl chloride in three portions for copolymerization reaction. The molar ratio of terephthaloyl chloride to diamine is 1:1.02. Stir mechanically at 100 r / min for 8 h. Finally, slowly raise the temperature to 80°C and add calcium carbonate to neutralize to pH 7 to obtain the modified para-aramid spinning dope. The solid content of the modified para-aramid spinning dope is 5.5%, the spinning viscosity is 4200 Po, and the intrinsic viscosity of the polymer measured after washing and drying is 3.6 dL / g.

[0047] S3. Spinning: The modified para-aramid dope enters a coagulation bath through a spinneret plate with 200 holes, a pore diameter of 0.2 mm, and a length-to-diameter ratio of 3 to form a nascent fiber. The coagulation bath is an aqueous NMP solution with a mass concentration of 30%, and the temperature of the coagulation bath is 10°C. The height of the air bath is adjusted to 10 mm. The nascent fiber is then stretched in a stretching bath, with a stretching ratio of 1.5. The stretching bath is an aqueous NMP solution with a mass concentration of 10%, and the temperature of the stretching bath is 10°C. Subsequently, it passes through a series of water washing and drying devices, is thermally stretched 9 times at 500°C in a nitrogen atmosphere, and then undergoes heat setting treatment on a hot roller at 400°C. After oiling, it is wound up to obtain modified para-aramid fiber, and the winding speed is 100 m / min.

[0048] Example 4 S1. In-situ silanization modification of diamine: Under the protection of an inert gas and mechanical stirring, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, calcium chloride, and methylchlorosilane are added to N,N-dimethylacetamide, and the temperature in the system is controlled at 15°C, and the reaction is stirred for 10 min. Then, p-phenylenediamine is added to the system, and the reaction is continued to stir for 20 min. The solution in the system is in a clear state, and a silanized modified diamine solution is obtained. Among them, the molar ratio of methylchlorosilane to diamine (3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, and p-phenylenediamine) is 1:160. The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl ether is 1:0.9:0.1. The addition amount of lithium chloride is 2% of the mass of the N,N-dimethylacetamide.

[0049] S2. Copolymerization reaction: The silanized modified diamine solution is cooled to 10°C, and then p-phthaloyl chloride is added in three portions for copolymerization reaction. The molar ratio of p-phthaloyl chloride to diamine is 1:0.98. Mechanical stirring is carried out at 100 r / min for 3 h. Finally, the temperature is slowly raised to 90°C and sodium hydroxide is added to neutralize to pH 7 to obtain a modified para-aramid dope. The solid content of the modified para-aramid dope is 4.0%, the spinning viscosity is 3100 Po, and the intrinsic viscosity of the polymer measured after water washing and drying is 3.4 dL / g.

[0050] S3. Spinning: The modified para-aramid dope enters the coagulation bath through a spinneret plate with 200 holes, a pore diameter of 0.2 mm, and a length-diameter ratio of 3 to form a nascent fiber. The coagulation bath is an aqueous NMP solution with a mass concentration of 30%, and the temperature of the coagulation bath is 10°C; the height of the air bath is adjusted to 10 mm. The nascent fiber is then stretched in a stretching bath, with a stretching ratio of 1.5. The stretching bath is an aqueous NMP solution with a mass concentration of 10%, and the temperature of the stretching bath is 10°C. After that, it passes through a series of water washing and drying devices, and is hot-stretched 9 times at 500°C in a nitrogen atmosphere. Subsequently, it is heat-set on a hot roller at 400°C. After oiling, it is wound up to obtain modified para-aramid fibers, and the winding speed is 100 m / min.

[0051] Example 5 S1. In-situ silanization modification of diamine: Under the protection of inert gas and mechanical stirring, 3,4'-diaminodiphenyl ether, p-phenylenediamine, calcium chloride, and tetrachlorosilane are added to N-methylpyrrolidone. The temperature in the system is controlled at 25°C, and the reaction is stirred for 40 min. The solution in the system is in a clear state, and a silanized modified diamine solution is obtained; Among them, the molar ratio of tetrachlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:32; The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 1:1; The addition amount of calcium chloride is 0.75% of the mass of the N-methylpyrrolidone.

[0052] S2. Copolymerization reaction: The temperature of the silanized modified diamine solution is lowered to -5°C, and then terephthaloyl chloride is added in three portions for copolymerization reaction. The molar ratio of terephthaloyl chloride to diamine is 1:1; mechanical stirring is carried out at 100 r / min, and the reaction is carried out for 5 h; finally, it is slowly heated to 90°C and calcium hydroxide is added to neutralize to pH 7 to obtain a modified para-aramid dope; the solid content of the modified para-aramid dope is 7.6%, the spinning viscosity is 4970 Po, and the intrinsic viscosity of the polymer measured after water washing and drying is 3.5 dL / g.

[0053] S3. Spinning: The modified para-aramid spinning dope enters a coagulation bath through a spinneret plate with 200 holes, a pore diameter of 0.2 mm, and a length-to-diameter ratio of 3 to form nascent filaments. The coagulation bath is an aqueous NMP solution with a mass concentration of 30%, and the temperature of the coagulation bath is 10°C; the height of the air bath is adjusted to 10 mm. The nascent filaments are then stretched in a stretching bath with a stretching ratio of 1.5. The stretching bath is an aqueous NMP solution with a mass concentration of 10%, and the temperature of the stretching bath is 10°C. After passing through a series of water washing and drying devices, it is hot stretched 9 times at 500°C in a nitrogen atmosphere, and then heat-set on a hot roller at 400°C. After oiling, it is wound up to obtain modified para-aramid fibers, and the winding speed is 100 m / min.

[0054] Comparative Example 1 Para-aramid fibers were prepared by the same method as in Example 1, except that: the amount of tetrachlorosilane was increased. In this Comparative Example 1, the molar ratio of tetrachlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) was 1:13, and other conditions were the same as in Example 1.

[0055] The modified para-aramid spinning dope (spinning solution) obtained by the preparation method of this Comparative Example 1 had a dynamic viscosity of 9000 Po, and the intrinsic viscosity of the polymer measured after washing and drying with water was 4.2 dL / g.

[0056] Due to the high viscosity of the spinning solution, dry-jet wet spinning could not be carried out.

[0057] Comparative Example 2 Para-aramid fibers were prepared by the same method as in Example 1, except that: the amount of tetrachlorosilane was decreased. In this Comparative Example 2, the molar ratio of tetrachlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) was 1:212, and other conditions were the same as in Example 1.

[0058] Comparative Example 3 Para-aramid fibers were prepared by the same method as in Example 1, except that: no tetrachlorosilane was added in this Comparative Example 3.

[0059] During the spinning process, the hot stretching was 5-fold stretching. It was found in the experiment that: when the hot stretching exceeded 5 times, serious wire breakage occurred.

[0060] Comparative Example 4 Para-aramid fibers were prepared by the same method as in Example 1, except that: in this Comparative Example 4, on the condition that the total molar amount of diamine was the same as that in Example 1, the usage ratio of 3,4'-diaminodiphenyl ether was decreased. In this Comparative Example 4, the molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether was 4:1.

[0061] It was found in the experiment that the solubility of the polymer in the system was poor, and dry-jet wet spinning could not be directly carried out. The intrinsic viscosity of the polymer measured after washing and drying with water was 1.5 dL / g.

[0062] Comparative Example 5 Para-aramid fibers were prepared by the same method as in Example 1, except that: in this Comparative Example 5, when the total molar amount of diamine was the same as that in Example 1, the dosage ratio of 3,4'-diaminodiphenyl ether was increased, and the molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether in this Comparative Example 4 was 0.25:1.

[0063] During the spinning process, the hot drawing was 9 times drawing. Although the elongation rate was high, the fiber strength was low and could not meet the application requirements.

[0064] Comparative Example 6 Para-aramid fibers were prepared by the same method as in Example 1, except that: in this Comparative Example 6, the dosage ratio of the solubilizing salt in Step S1 was increased, and the addition amount of calcium chloride was 8% of the mass of N-methylpyrrolidone.

[0065] During the spinning process, the hot drawing was 4 times drawing. It was found in the experiment that when the hot drawing exceeded 4 times, the problem of serious wire breakage occurred.

[0066] Comparative Example 7 Para-aramid fibers were prepared by the same method as in Example 1, except that: in Step S1 of this Comparative Example 7, no solubilizing salt was added.

[0067] It was found in the experiment that the obtained modified para-aramid stock solution was turbid light yellow, the solubility of the polymer in the system was poor, dry-jet wet spinning could not be carried out, and the intrinsic viscosity of the polymer measured after washing and drying was 1.2 dL / g.

[0068] Comparative Example 8 Para-aramid fibers were prepared by the same method as in Example 1, except that: in Step S1 of this Comparative Example 8, toluene was used as the solvent, and a purification operation was added after the end of Step S1. The specific operation process is as follows: S1. In-situ silanization modification of diamine: Under the protection of inert gas and mechanical stirring conditions, 3,4'-diaminodiphenyl ether, tetrachlorosilane, and triethylamine were added to toluene, the temperature in the system was controlled at 25°C, and the stirring reaction was carried out for 15 min; then p-phenylenediamine was added to the system, and the stirring reaction was continued for 25 min to obtain a silanized modified diamine solution; Then, under the protection of inert gas, the solid in the silanized modified diamine solution was filtered off, then the solvent was removed by atmospheric distillation, and then vacuum distillation was carried out at 170°C to obtain silanized modified diamine.

[0069] Among them, the molar ratio of tetrachlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) was 1:32; The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 1:1; The molar ratio of diamine to triethylamine is 1:3.

[0070] S2. Copolymerization reaction: Dissolve the silanized modified diamine and calcium chloride in N-methylpyrrolidone, cool down to -5°C, and then add terephthaloyl chloride in three portions for copolymerization reaction. The molar ratio of terephthaloyl chloride to diamine is 1:1; the addition amount of calcium chloride is 0.75% of the mass of N-methylpyrrolidone. Stir mechanically at 100 r / min for 5 h; finally, slowly heat up to 90°C and add calcium hydroxide to neutralize to pH 7 to obtain the modified para-aramid spinning dope. The solid content of the modified para-aramid spinning dope is 6.4%, the spinning viscosity is 1700 Po, and the intrinsic viscosity of the polymer measured after washing and drying is 2.7 dL / g.

[0071] S3. Spinning: Same as Example 1, but during the spinning process, the hot drawing is 6-fold drawing. It is found in the experiment that when the hot drawing exceeds 6-fold, serious wire breakage problems occur.

[0072] Example 9 Prepare para-aramid fibers by the same method as in Example 1, except that in step S1 of this Comparative Example 8, 3,4'-diaminodiphenyl ether is not silane-modified. The specific preparation process is as follows: S1. In-situ silanization modification of diamine: Under the protection of inert gas and mechanical stirring, add p-phenylenediamine, calcium chloride, and silicon tetrachloride to N-methylpyrrolidone, control the temperature in the system to 25°C, and stir and react for 25 min; the solution in the system is in a clear state to obtain a silanized modified diamine solution; The addition amount of calcium chloride is 0.75% of the mass of N-methylpyrrolidone.

[0073] S2. Copolymerization reaction: Cool the silanized modified diamine solution to -5°C, then add 3,4'-diaminodiphenyl ether, and then add terephthaloyl chloride in three portions for copolymerization reaction. The molar ratio of terephthaloyl chloride to diamine is 1:1; the molar ratio of silicon tetrachloride to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:32; the molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 1:1. Stir mechanically at 100 r / min for 5 h; finally, slowly heat up to 90°C and add calcium hydroxide to neutralize to pH 7 to obtain the modified para-aramid spinning dope; the solid content of the modified para-aramid spinning dope is 7.6%, the spinning viscosity is 3400 Po, and the intrinsic viscosity of the polymer measured after washing and drying is 3.2 dL / g.

[0074] S3. Spinning: Same as Example 1.

[0075] The poly(p-phenylene terephthalamide) dope, polymer, and poly(p-phenylene terephthalamide) fibers prepared in the above examples and comparative examples were subjected to performance tests. The specific test results are shown in Table 1 below. The test methods involved are as follows: The detection method for the intrinsic viscosity (IV) is as follows: After washing and drying the poly(p-phenylene terephthalamide) dope, a polymer sulfuric acid solution with a concentration of 0.5 g / dL (mass fraction 98%) is prepared. The efflux times of the solvent and the solution are measured at 30 °C using an Ubbelohde viscometer with a capillary inner diameter of 1.07 mm, and then calculated according to the intrinsic viscosity calculation formula.

[0076] The performance test of poly(p-phenylene terephthalamide) fibers refers to GB / T 14344-2022.

[0077] Table 1 Performance test results

[0078] It can be seen from the above experimental results that the poly(p-phenylene terephthalamide) fibers prepared in Examples 1-5 using the preparation method described in the present invention have better strength, modulus, and elongation properties. Moreover, the preparation process is simple, without excessive intermediate purification operations, does not require high-temperature heating, and has low energy consumption. In addition, it can also be seen from the comparison of the results of Example 1 and Example 5 that when the diamine is in-situ silanized and modified, 3,4'-diaminodiphenyl ether and p-phenylenediamine are separately added at different time periods, which is more conducive to obtaining high-performance poly(p-phenylene terephthalamide) fibers. Because allowing 3,4'-diaminodiphenyl ether and the chlorosilane condensing agent to react for a period of time first, and then adding p-phenylenediamine for silanization modification reaction can further balance the reaction activity differences between 3,4'-diaminodiphenyl ether and p-phenylenediamine, so that both 3,4'-diaminodiphenyl ether and p-phenylenediamine contain structures modified by silyl groups, and then a polymer with a more uniform molecular structure arrangement is obtained, and finally poly(p-phenylene terephthalamide) fibers with relatively high strength, elongation, and modulus properties are obtained.

[0079] Figure 1 , 2 are the infrared spectrum and dynamic thermomechanical curve of the poly(p-phenylene terephthalamide) fibers prepared in Example 1 respectively. From Figure 1 it can be seen that: 1644 cm -1 , 1541 cm -1 are amide bond absorption peaks, 1515 cm -1 is the benzene ring vibration peak, 1100 cm -1 is the ether bond absorption peak, proving that the polymer molecular chain contains a 3,4'-diaminodiphenyl ether flexible chain segment.

[0080] From Figure 2It can be seen that the glass transition temperature of the modified para-aramid fiber is between 270°C and 330°C. Compared with the 340°C of the PPTA fiber, the molecular chain is more flexible, and the prepared fiber has stronger toughness.

[0081] From the comparison of the results of Comparative Example 1 and Example 1, it can be seen that if the dosage of the chlorosilane polycondensing agent is increased, the viscosity of the modified para-aramid spinning solution will be too high, and the dry-jet wet spinning operation cannot be carried out, and thus para-aramid fibers cannot be obtained.

[0082] From the comparison of the results of Comparative Example 2 and Example 1, it can be seen that if the dosage of the chlorosilane polycondensing agent is reduced, the performance of the para-aramid fiber will decrease significantly. Therefore, using the dosage of the chlorosilane polycondensing agent defined in the present invention is more conducive to obtaining para-aramid fibers with excellent performance.

[0083] From the comparison of the results of Comparative Example 3 and Example 1, it can be seen that if the chlorosilane polycondensing agent is not added, it is very difficult to perform high-magnification hot stretching during the spinning process because the unmodified diamine is easily oxidized, its activity decreases, the prepared polymer has a low IV value and a low molecular weight, and high-magnification stretching cannot be carried out. Therefore, if the chlorosilane polycondensing agent is not added, the strength, modulus and elongation performance of the para-aramid fiber will all decrease significantly.

[0084] From the comparison of the results of Comparative Example 4 and Example 1, it can be seen that if the dosage ratio of 3,4'-diaminodiphenyl ether is reduced, the solubility of the polymer in the weakly alkaline polar aprotic solvent is poor, and the spinning solution cannot be directly subjected to dry-jet wet spinning.

[0085] From the comparison of the results of Comparative Example 5 and Example 1, it can be seen that if the dosage ratio of 3,4'-diaminodiphenyl ether is increased, the polymer has a low IV value, and it is very difficult to perform high-magnification hot stretching during the spinning process, ultimately resulting in a significant decrease in the strength and modulus performance of the para-aramid fiber. This is because 3,4'-diaminodiphenyl ether is a flexible chain segment and p-phenylenediamine is a rigid chain segment. When the proportion of the flexible chain segment increases, the strength and modulus of the fiber will be greatly reduced.

[0086] From the comparison of the results of Comparative Example 6 and Example 1, it can be seen that if the dosage of the solubilizing salt is increased, high-magnification hot stretching cannot be achieved during the spinning process, and the strength, modulus and elongation performance of the para-aramid fiber decrease significantly. This is because when the content of the solubilizing salt is too high, Ca 2+ complexes with the amino group, reducing the amino group activity, resulting in a decrease in the polymer molecular weight and inability to perform high-fold drawing, thus significantly reducing the fiber performance.

[0087] From the comparison of the results of Comparative Example 7 and Example 1, it can be seen that if the solubilizing salt is not added, the modified para-aramid spinning solution is turbid light yellow, the polymer has poor solubility in the system, and dry-jet wet spinning cannot be carried out.

[0088] It can be seen from the comparison of the results of Comparative Example 8 and Example 1 that: if toluene solvent is used in Step S1, during the in-situ silanization modification process of diamine, it is necessary to add the acid-binding agent triethylamine, and the purification process of the silanized modified diamine needs to be increased. The properties of the resulting para-aramid fibers all decrease significantly. This is because: firstly, in the toluene system, under the same reaction principle, reaction temperature and reaction time conditions, the reaction modification effect of silanization is not as sufficient as that in a weakly basic polar aprotic solvent; secondly, during the purification process of the silanized modified diamine, the silanized modified diamine is very prone to instability problems because the Si-N bond is extremely susceptible to trace moisture in the environment, which affects the activity of the diamine during the copolymerization reaction process, resulting in poor polymer performance and a decrease in the properties of the para-aramid fibers.

[0089] It can be seen from the comparison of the results of Comparative Example 9 and Example 1 that: if the silane modification of diaminodiphenyl ether is not carried out, the strength, modulus and elongation properties of the para-aramid fibers will all decrease significantly. Because if the silane modification of diaminodiphenyl ether is not carried out, when the diamine copolymerizes with terephthaloyl chloride, the silane-modified p-phenylenediamine with higher activity will first polymerize with terephthaloyl chloride, and diaminodiphenyl ether will react subsequently, resulting in a block structure for the final polymer. In the preparation method of the modified para-aramid spinning solution of the present invention, during the in-situ silanization modification process of diamine, both diaminodiphenyl ether and p-phenylenediamine are subjected to in-situ silanization modification of diamine, so that both diaminodiphenyl ether and p-phenylenediamine contain structures modified by silyl groups, thereby enabling both the silyl group-modified diaminodiphenyl ether and the silyl group-modified p-phenylenediamine to have high activity to polymerize with terephthaloyl chloride, so that in the molecular chain structure of the finally prepared polymer, the structures of diaminodiphenyl ether and p-phenylenediamine are more evenly distributed, further improving the properties of the para-aramid fibers.

[0090] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of brevity of description, all possible combinations of the various technical features in the above embodiments are not exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, it should be considered as falling within the scope described in this specification.

[0091] For those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. The protection scope of the present invention is subject to the appended claims.

Claims

1. A preparation method of a modified para-aramid spinning solution, characterized in that, The preparation method is as follows: S1. In-situ silanization modification of diamine: Under an inert gas condition, in a weakly basic polar aprotic solvent, diamine reacts with a chlorosilane polycondensing agent to obtain a silanized modified diamine solution; the diamine includes diaminodiphenyl ether and p-phenylenediamine; S2. Copolymerization reaction: Add terephthaloyl chloride to the silanized modified diamine solution for copolymerization reaction. After the reaction ends, perform neutralization treatment to obtain the modified para-aramid spinning dope.

2. The preparation method of a modified para-aramid spinning dope according to claim 1, characterized in that, In step S1, the diaminodiphenyl ether is at least one of 3,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl ether; The chlorosilane polycondensing agent is at least one of tetrachlorosilane, trimethylchlorosilane, dimethylchlorosilane, and methylchlorosilane.

3. The preparation method of a modified para-aramid spinning dope according to claim 1, wherein The weakly basic polar aprotic solvent is at least one of N-methylpyrrolidone and N,N-dimethylacetamide.

4. The preparation method of a modified para-aramid dope according to claim 1, characterized in that, The molar ratio of the chlorosilane polycondensing agent to diamine is 1:(16 - 160); The molar ratio of p-phenylenediamine to diaminodiphenyl ether is 1:(0.8 - 1.2); The molar ratio of terephthaloyl chloride to diamine is 1:(0.98 - 1.02).

5. The preparation method of a modified para-aramid spinning solution according to claim 1, wherein, The specific operation of step S1 is as follows: Under an inert gas condition, add a solubilizing salt, diaminodiphenyl ether, and a chlorosilane polycondensing agent to a weakly basic polar aprotic solvent, control the temperature in the reaction system to be 5°C - 30°C, stir and react for 10 - 20 min; then add p-phenylenediamine to the system and continue to react for 20 - 30 min to obtain a silanized modified diamine solution.

6. The preparation method of a modified para-aramid spinning dope according to claim 5, characterized in that, The solubilizing salt is at least one of calcium chloride and lithium chloride, and the dosage of the solubilizing salt is 0.25 - 5% of the mass of the weakly basic polar aprotic solvent.

7. The preparation method of a modified para-aramid spinning dope according to claim 1, characterized in that, The polymerization reaction temperature in step S2 is -5~10°C, and the polymerization reaction time is 3 - 8 h.

8. A modified para-aramid spinning dope, characterized in that, The modified para-aramid spinning dope is prepared by the preparation method according to any one of claims 1 - 7; The solid content of the modified para-aramid spinning dope is 4wt% - 7wt%, the spinning viscosity of the modified para-aramid spinning dope is 3000 - 7000 Po, and the intrinsic viscosity of the polymer in the modified para-aramid spinning dope is 3.4 - 4.0 dL / g.

9. A para-aramid fiber, characterized in that, Use the dry-jet wet spinning process on the modified para-aramid spinning dope to obtain the para-aramid fiber; The modified para-aramid spinning dope is prepared by the preparation method according to any one of claims 1 - 7.

10. The para-aramid fiber according to claim 9, wherein, The strength of the para-aramid fiber is 24 - 30 cN / dtex, the elongation at break is 4.5 - 6.5%, and the modulus is 545 - 750 cN / dtex.

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