A modified para-aramid stock solution, preparation method and para-aramid fiber thereof

Abstract

The present invention relates to the technical field of polymer polymerization and molding, and specifically to a modified para-aramid stock solution, a preparation method, and para-aramid fiber thereof. The preparation method comprises: reacting a diamine with a chlorosilane condensation agent in a weakly alkaline polar aprotic solvent under inert gas conditions to obtain a silylated modified diamine solution; the diamine comprises diaminodiphenyl ether and para-phenylenediamine; adding terephthaloyl chloride to the silylated modified diamine solution for copolymerization, and after completion of the reaction, neutralizing the solution to obtain the modified para-aramid stock solution. The preparation method of the modified para-aramid stock solution does not require separate purification of the modified diamine, and a high-viscosity modified para-aramid stock solution can be directly obtained. The polymer in the modified para-aramid stock solution has a high inherent viscosity and a high molecular weight, which is more conducive to obtaining a high-quality and stable para-aramid fiber product.

Description

Technical Field

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

[0002] Para-aramid fiber, successfully developed and first industrialized by DuPont in the United States in the 1960s, is a new type of organic synthetic fiber boasting excellent properties such as high strength, high modulus, high-temperature resistance, acid and alkali resistance, and lightweight. It is primarily used in rubber-reinforced products, bulletproof fabrics, composite structural materials, cable materials, thermal and acoustic insulation, and radiation-resistant structural panels. With increasing demand for customized aramid in industries such as electronics and communications, national defense, lightweight materials, and 5G, the para-aramid industry is experiencing rapid growth and possesses enormous market potential.

[0003] Para-aramid has high molecular chain rigidity, poor impact and fatigue resistance, and is prone to splitting during use, which to some extent limits its widespread application. Patent publication number CN104350190B discloses a method for the polymerization and spinning of modified para-aramid, using a dry-jet wet-spinning process to produce high-toughness para-aramid fiber. However, para-phenylenediamine is easily oxidized during the process, resulting in reduced end group activity, lowering the quality of the polymer stock solution and the fiber. Patent publication number CN118047945B discloses a high-viscosity aromatic polyamide copolymer stock solution, a preparation method, and an application thereof. The preparation method comprises: dissolving p-phenylenediamine and triethylamine in an organic solvent under inert gas protection, adding a chlorosilane compound dropwise, stirring evenly, reacting under heating conditions, and obtaining silylated p-phenylenediamine through post-treatment after the reaction; preparing a composite solvent containing a polar amide solvent and a cosolvent, and polymerizing the silylated p-phenylenediamine, diaminodiphenyl ether, and terephthaloyl chloride in the composite solvent under inert gas protection. After the reaction, neutralization is performed to obtain the high-viscosity aromatic polyamide copolymer stock solution. This patent proposes to modify p-phenylenediamine by silanization, which solves the problem of easy oxidation of p-phenylenediamine during the reaction process, thereby preparing a high-viscosity aromatic polyamide copolymer stock solution. However, in this process, the reaction process of silanized p-phenylenediamine is relatively long and the operation is complicated. In addition, the purification process of silanized p-phenylenediamine is relatively troublesome. The purification and storage environment of silanized p-phenylenediamine are demanding. Silanized p-phenylenediamine is easily decomposed when it encounters water in the air, which can easily lead to large differences in the performance of p-aramid fibers spun from different batches, resulting in large differences in products between different batches. In addition, the solvents used in the modification process are mostly carcinogenic substances such as benzene and xylene, which are more dangerous and costly in the actual production process.

[0004] In response to the above problems, a modified para-aramid stock solution, a preparation method and para-aramid fiber are provided, which are of great significance for solving diamine oxidation, increasing polymer molecular weight, improving fiber quality and reducing environmental pollution. Summary of the Invention

[0005] The present invention addresses the deficiencies in the prior art and provides a modified para-aramid stock solution, a preparation method, and para-aramid fibers thereof. The preparation method of the modified para-aramid stock solution does not require the separate purification of modified diamine, and a high-viscosity modified para-aramid stock solution can be directly obtained. The polymer in the modified para-aramid stock solution has a high inherent logarithmic viscosity and a high molecular weight, 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 method for preparing a modified para-aramid stock solution, the preparation method comprising:

[0007] S1, diamine in-situ silanization modification:

[0008] Under inert gas conditions, in a weakly alkaline polar aprotic solvent, a diamine reacts with a chlorosilane polycondensation agent to obtain a silylated modified diamine solution; the diamine includes diaminodiphenyl ether and p-phenylenediamine;

[0009] S2. Copolymerization reaction:

[0010] Terephthaloyl chloride is added to the silylated modified diamine solution to carry out copolymerization reaction. After the reaction is completed, neutralization treatment is performed to obtain the modified para-aramid stock solution.

[0011] Furthermore, in step S1, the diaminodiphenyl ether is at least one of 3,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl ether;

[0012] The chlorosilane polycondensation agent is at least one of tetrachlorosilane, trimethylchlorosilane, dimethylchlorosilane and monomethylchlorosilane.

[0013] Furthermore, the weakly alkaline polar aprotic solvent is at least one of N-methylpyrrolidone and N,N-dimethylacetamide.

[0014] Furthermore, the molar ratio of the chlorosilane polycondensation agent to the diamine is 1:(16-160);

[0015] The molar ratio of p-phenylenediamine to diaminodiphenyl ether is 1:(0.8-1.2).

[0016] The molar ratio of the terephthaloyl chloride to the diamine is 1:(0.98-1.02).

[0017] Furthermore, the specific operations of step S1 are:

[0018] Under inert gas conditions, a solubilizing salt, diaminodiphenyl ether and a chlorosilane polycondensation agent are added to a weakly alkaline polar aprotic solvent, the temperature in the reaction system is controlled at 5°C-30°C, and the reaction is stirred for 10-20 minutes; then p-phenylenediamine is added to the system and the reaction is continued for 20-30 minutes to obtain a silanized modified diamine solution.

[0019] Furthermore, the dissolution-advancing salt is at least one of calcium chloride and lithium chloride, and the amount of the dissolution-advancing salt is 0.25-5% of the mass of the weakly alkaline polar aprotic solvent.

[0020] Furthermore, the polymerization reaction temperature of step S2 is -5~10°C, and the polymerization reaction time is 3-8h.

[0021] The present invention also discloses a modified para-aramid stock solution, which is prepared according to the preparation method of the present invention;

[0022] The solid content of the modified para-aramid stock solution is 4-7wt%, the spinning viscosity of the modified para-aramid stock solution is 3000-7000 Po, and the intrinsic viscosity of the polymer in the modified para-aramid stock solution is 3.4-4.0 dL / g.

[0023] The present invention also discloses a para-aramid fiber, which is prepared by using a modified para-aramid stock solution through a dry-jet wet spinning process;

[0024] The modified para-aramid stock solution is prepared according to the preparation method of the present invention.

[0025] Furthermore, the para-aramid fiber has a strength of 24-30 cN / dtex, an elongation of 4.5-6.5%, and a modulus of 545-750 cN / dtex.

[0026] The beneficial effects of the present invention are:

[0027] The method for preparing the modified para-aramid stock solution of the present invention is as follows: in a weakly alkaline polar aprotic solvent, diamine reacts with a chlorosilane condensation agent to obtain a silylated modified diamine solution; the intermediate silylated modified diamine does not need to be purified, thereby reducing the complexity of the operation and preventing the silylated modified diamine from losing its reactivity due to contact with the external environment during the purification process; the silylated modified diamine in the system of the present invention can exist more stably, and the silylated modified diamine has high activity and can react quickly with acyl chloride in situ, thereby reducing the reaction time. The preparation process of the entire modified para-aramid stock solution is more controllable and has good repeatability, and is suitable for industrial stable production. The modified para-aramid stock solution can be directly spun to ultimately obtain para-aramid fibers with even better performance. The fibers prepared from the modified para-aramid stock solution by dry-jet wet spinning have excellent toughness and wear resistance and can be applied in the fields of rubber reinforcement, automotive hoses, conveyor belts, etc.

[0028] In the method for preparing a modified para-aramid stock solution of the present invention, in-situ silylation modification of diamine is carried out in a weakly alkaline polar aprotic solvent, and a subsequent copolymerization reaction can be directly carried out to prepare a spinning stock solution. In addition, a small amount of hydrochloric acid byproduct is generated during the in-situ silylation modification reaction of diamine. The weakly alkaline polar aprotic solvent, which is the main component of the system, can neutralize and absorb the acidic product (hydrochloric acid), thereby promoting the forward reaction. There is no need to add an additional alkaline acid-binding agent to the system, and thus no subsequent salt removal operation is required, simplifying the process operation. In addition, all reaction raw materials and reaction products are dispersed in the weakly alkaline polar aprotic solvent, so that the acidic product generated by the reaction can be more quickly absorbed, thereby facilitating reaction conversion. The reaction can be quickly completed to obtain a silylated modified diamine solution without high-temperature heating conditions, thereby reducing energy consumption, shortening the production cycle, and being more conducive to industrial application.

[0029] In addition, in the preparation method of the modified para-aramid stock solution of the present invention, the in-situ silylation modification of diamine and the copolymerization reaction use the same solvent system, so there is no need to purify the silylation modified diamine, which is equivalent to realizing a one-pot preparation. While simplifying the operating process, the denaturation and inactivation loss of the silylation modified diamine caused by purification and storage can be avoided. Therefore, only a small amount of chlorosilane polycondensation agent is needed to meet the modification requirements of the diamine, and finally a suitable spinning solution is obtained. Moreover, the small amount of chlorosilane polycondensation agent used can make the reaction in the in-situ silylation modification reaction system of the diamine more stable, avoiding the problem of uncontrollable heat release in the system, so the reaction process does not need to add raw materials by the dropwise addition method, and the operation is simpler; and each reactant and product can be better dispersed in the solvent system, thereby improving the reaction efficiency and reducing the reaction energy consumption.

[0030] The introduction of diaminodiphenyl ether into the preparation method of the present invention significantly improves the flexibility of the polymer molecular chain structure and increases the polymer solubility in the system. The polymer stock solution can be directly spun. Compared with traditional para-aramid preparation processes, it avoids the use of concentrated sulfuric acid as a spinning solvent, significantly reducing the corrosion resistance requirements for equipment. Furthermore, in conventional methods, when unmodified diaminodiphenyl ether, p-phenylenediamine, and terephthaloyl chloride are polymerized, p-phenylenediamine has a higher reactivity and reacts first with terephthaloyl chloride, followed by diaminodiphenyl ether and terephthaloyl chloride, resulting in a block structure in the final polymer. In the preparation method of the modified para-aramid stock solution described in the present invention, during the diamine in-situ silylation modification process, both diaminodiphenyl ether and p-phenylenediamine are subjected to diamine in-situ silylation modification, so that both diaminodiphenyl ether and p-phenylenediamine contain structures modified by silyl groups, thereby making the silyl-modified diaminodiphenyl ether and silyl-modified p-phenylenediamine both highly active in the polymerization reaction with terephthaloyl chloride, so that the diaminodiphenyl ether and p-phenylenediamine structures are more evenly distributed in the molecular chain structure of the finally prepared polymer, further improving the performance of the para-aramid fiber.

[0031] Furthermore, in the in-situ silylation modification process of diamines described in the present invention, diaminodiphenyl ether and a chlorosilane polycondensation agent are first allowed to react for a period of time, and then p-phenylenediamine is added for a silylation modification reaction. This can further balance the difference in the reactivity of diaminodiphenyl ether and p-phenylenediamine, so that both diaminodiphenyl ether and p-phenylenediamine contain structures modified by silane groups, thereby obtaining a polymer with a more uniform molecular structure arrangement, and ultimately obtaining a p-aramid fiber with relatively high strength, elongation and modulus properties. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is the infrared spectrum of the polymer dry material obtained in Example 1;

[0033] Figure 2 This is the dynamic thermomechanical curve of the para-aramid fiber prepared in Example 1. DETAILED DESCRIPTION

[0034] The present invention can be implemented in many other ways than those described herein, and those skilled in the art can make similar improvements without violating the scope of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which the present invention belongs. The terms used are only for describing specific embodiments and are not intended to limit the present invention.

[0036] A method for preparing a modified para-aramid stock solution, the preparation method comprising:

[0037] S1, diamine in-situ silanization modification:

[0038] Under inert gas conditions, in a weakly alkaline polar aprotic solvent, a diamine reacts with a chlorosilane polycondensation agent to obtain a silylated modified diamine solution; the diamine includes diaminodiphenyl ether and p-phenylenediamine;

[0039] S2. Copolymerization reaction:

[0040] Terephthaloyl chloride is added to the silylated modified diamine solution to carry out copolymerization reaction. After the reaction is completed, neutralization treatment is performed to obtain the modified para-aramid stock solution.

[0041] Specifically, in step S1, the diaminodiphenyl ether is at least one of 3,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl ether;

[0042] The chlorosilane polycondensation agent is at least one of tetrachlorosilane, trimethylchlorosilane, dimethylchlorosilane and monomethylchlorosilane.

[0043] Specifically, the weakly basic polar aprotic solvent is at least one of N-methylpyrrolidone and N,N-dimethylacetamide.

[0044] Taking the diaminodiphenyl ether as 3,4'-diaminodiphenyl ether and the chlorosilane polycondensation agent as trimethylchlorosilane as an example, the reaction principles of steps S1 and S2 are as follows:

[0045] .

[0046] Specifically, the molar ratio of the chlorosilane polycondensation agent to the diamine is 1:(16-160);

[0047] The molar ratio of p-phenylenediamine to diaminodiphenyl ether is 1:(0.8-1.2).

[0048] The molar ratio of the terephthaloyl chloride to the diamine is 1:(0.98-1.02).

[0049] Specifically, the specific operations of step S1 are:

[0050] Under inert gas conditions, a solubilizing salt, diaminodiphenyl ether and a chlorosilane polycondensation agent are added to a weakly alkaline polar aprotic solvent, the temperature in the reaction system is controlled at 5°C-30°C, and the reaction is stirred for 10-20 minutes; then p-phenylenediamine is added to the system and the reaction is continued for 20-30 minutes to obtain a silanized modified diamine solution.

[0051] Specifically, the dissolution-advancing salt is at least one of calcium chloride and lithium chloride, and the amount of the dissolution-advancing salt is 0.25-5% of the mass of the weakly alkaline polar aprotic solvent.

[0052] Specifically, the polymerization reaction temperature in step S2 is -5-10°C, and the polymerization reaction time is 3-8 hours.

[0053] 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. During the neutralization process, the temperature in the system is controlled not to exceed 90°C.

[0054] The present invention also discloses a modified para-aramid stock solution, which is prepared according to the preparation method of the present invention;

[0055] The solid content of the modified para-aramid stock solution is 4-7wt%, the spinning viscosity of the modified para-aramid stock solution is 3000-7000 Po, the intrinsic viscosity of the polymer in the modified para-aramid stock solution is 3.4-4.0 dL / g, the measuring temperature of the intrinsic viscosity is 30°C, and the dissolving medium used is concentrated sulfuric acid with a mass concentration of 98%.

[0056] The present invention also discloses a para-aramid fiber, which is prepared by using a modified para-aramid stock solution through a dry-jet wet spinning process;

[0057] The modified para-aramid stock solution is prepared according to the preparation method of the present invention.

[0058] Preferably, the para-aramid fiber has a strength of 24-30 cN / dtex, an elongation of 4.5-6.5%, and a modulus of 545-750 cN / dtex.

[0059] More specifically, the dry-jet wet spinning process used in the embodiment of the present invention is:

[0060] The modified para-aramid stock solution passes through a 200-hole spinneret with a pore size of 0.2 mm and an aspect ratio of 3 and enters a coagulation bath to form spun yarn. The coagulation bath is a 30% NMP aqueous solution at a temperature of 10°C. The air bath is adjusted to a height of 10 mm. The spun yarn is then stretched in a stretching bath with a draw ratio of 1.5. The stretching bath is a 10% NMP aqueous solution at a temperature of 10°C. The yarn then passes through a series of washing and drying devices, heat-stretched 9 times at 500°C in a nitrogen atmosphere, and then heat-set on a 400°C hot roller. After oiling, the fiber is wound up at a speed of 100 m / min to obtain the modified para-aramid fiber.

[0061] Example 1

[0062] S1, diamine in-situ silanization modification:

[0063] Under inert gas protection and mechanical stirring, 3,4'-diaminodiphenyl ether, calcium chloride, and tetrachlorosilane were added to N-methylpyrrolidone, the temperature in the system was controlled at 25°C, and the reaction was stirred for 15 minutes. Then, p-phenylenediamine was added to the system, and the stirring reaction was continued for 25 minutes. The solution in the system was clear, thereby obtaining a silanized modified diamine solution.

[0064] The molar ratio of tetrachlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:32;

[0065] The molar ratio of p-phenylenediamine and 3,4'-diaminodiphenyl ether is 1:1;

[0066] The added amount of calcium chloride is 0.75% of the mass of the N-methylpyrrolidone.

[0067] S2. Copolymerization reaction:

[0068] The silanized modified diamine solution was cooled to -5°C, and then terephthaloyl chloride was added three times for copolymerization reaction, with the molar ratio of terephthaloyl chloride to diamine being 1:1; mechanical stirring was carried out at 100 r / min, and the reaction was carried out for 5 hours; finally, the temperature was slowly raised to 90°C, and calcium hydroxide was added to neutralize the solution to a pH of 7 to obtain a modified para-aramid stock solution; the solid content of the modified para-aramid stock solution was 6.4%, the spinning viscosity was 5000 Po, and the intrinsic viscosity of the polymer after washing and drying was measured to be 4.0 dL / g. The infrared spectrum of the polymer was as follows: Figure 1 shown.

[0069] S3, Spinning:

[0070] The modified para-aramid stock solution passes through a spinneret with 200 holes, a pore size of 0.2 mm, and an aspect ratio of 3 and enters a coagulation bath to form nascent silk, wherein the coagulation bath is an NMP aqueous solution with a mass concentration of 30%, and the coagulation bath temperature is 10°C; the air bath height is adjusted to 10 mm, and the nascent silk is then stretched in a stretching bath with a stretching ratio of 1.5, and the stretching bath is an NMP aqueous solution with a mass concentration of 10%, and the stretching bath temperature is 10°C. After that, it passes through a series of water washing and drying devices, and is heat stretched 9 times at 500°C in a nitrogen atmosphere, and then heat-set on a 400°C hot roller, and is oiled and wound to obtain the modified para-aramid fiber, with a winding speed of 100 m / min. The dynamic thermomechanical curve of the para-aramid fiber is shown in FIG. Figure 2 shown.

[0071] Example 2

[0072] S1, diamine in-situ silanization modification:

[0073] Under inert gas protection and mechanical stirring, 3,4'-diaminodiphenyl ether, calcium chloride, and trimethylsilyl chloride were added to N-methylpyrrolidone, the temperature in the system was controlled at 30°C, and the reaction was stirred for 10 minutes. Then, p-phenylenediamine was added to the system, and the stirring reaction was continued for 30 minutes. The solution in the system was clear, thereby obtaining a silanized modified diamine solution.

[0074] The molar ratio of trimethylchlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:32;

[0075] The molar ratio of p-phenylenediamine and 3,4'-diaminodiphenyl ether is 1:1;

[0076] The added amount of calcium chloride is 0.25% of the mass of the N-methylpyrrolidone.

[0077] S2. Copolymerization reaction:

[0078] The silanized modified diamine solution was cooled to -5°C, and then terephthaloyl chloride was added three times for copolymerization reaction, wherein the molar ratio of terephthaloyl chloride to diamine was 1:1; mechanical stirring was performed at 100 r / min, and the reaction was carried out for 5 hours; finally, the temperature was slowly raised to 90°C, and calcium hydroxide was added to neutralize the solution to a pH of 7 to obtain a modified para-aramid stock solution; the solid content of the modified para-aramid stock solution was 6.4%, the spinning viscosity was 3000 Po, and the intrinsic viscosity of the polymer after washing and drying was measured to be 3.4 dL / g.

[0079] S3, Spinning:

[0080] The modified para-aramid stock solution passes through a 200-hole spinneret with a pore size of 0.2 mm and an aspect ratio of 3 and enters a coagulation bath to form spun yarn. The coagulation bath is a 30% NMP aqueous solution at a temperature of 10°C. The air bath is adjusted to a height of 10 mm. The spun yarn is then stretched in a stretching bath with a draw ratio of 1.5. The stretching bath is a 10% NMP aqueous solution at a temperature of 10°C. The yarn then passes through a series of washing and drying devices, heat-stretched 9 times at 500°C in a nitrogen atmosphere, and then heat-set on a 400°C hot roller. After oiling, the fiber is wound up at a speed of 100 m / min to obtain the modified para-aramid fiber.

[0081] Example 3

[0082] S1, diamine in-situ silanization modification:

[0083] Under inert gas protection and mechanical stirring, 3,4'-diaminodiphenyl ether, lithium chloride, and dimethylchlorosilane were added to N,N-dimethylacetamide, the temperature in the system was controlled at 5°C, and the reaction was stirred for 20 minutes. Then, p-phenylenediamine was added to the system, and the stirring reaction was continued for 30 minutes. The solution in the system was clear, thereby obtaining a silanized modified diamine solution.

[0084] The molar ratio of dimethylchlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:16;

[0085] The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether is 1:0.8;

[0086] The amount of lithium chloride added is 5% of the mass of the N,N-dimethylacetamide.

[0087] S2. Copolymerization reaction:

[0088] The silanized modified diamine solution was cooled to 0°C, and then terephthaloyl chloride was added three times for copolymerization reaction, wherein the molar ratio of terephthaloyl chloride to diamine was 1:1.02; mechanical stirring was performed at 100 r / min, and the reaction was carried out for 8 hours; finally, the temperature was slowly raised to 80°C, and calcium carbonate was added to neutralize the solution to a pH of 7 to obtain a modified para-aramid stock solution; the modified para-aramid stock solution had a solid content of 5.5%, a spinning viscosity of 4200 Po, and an intrinsic viscosity of 3.6 dL / g after washing and drying the polymer.

[0089] S3, Spinning:

[0090] The modified para-aramid stock solution passes through a 200-hole spinneret with a pore size of 0.2 mm and an aspect ratio of 3 and enters a coagulation bath to form spun yarn. The coagulation bath is a 30% NMP aqueous solution at a temperature of 10°C. The air bath is adjusted to a height of 10 mm. The spun yarn is then stretched in a stretching bath with a draw ratio of 1.5. The stretching bath is a 10% NMP aqueous solution at a temperature of 10°C. The yarn then passes through a series of washing and drying devices, heat-stretched 9 times at 500°C in a nitrogen atmosphere, and then heat-set on a 400°C hot roller. After oiling, the fiber is wound up at a speed of 100 m / min to obtain the modified para-aramid fiber.

[0091] Example 4

[0092] S1, diamine in-situ silanization modification:

[0093] Under inert gas protection and mechanical stirring, 3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether, calcium chloride, and monomethylchlorosilane were added to N,N-dimethylacetamide, the temperature in the system was controlled at 15°C, and the reaction was stirred for 10 minutes; then p-phenylenediamine was added to the system, and the stirring reaction was continued for 20 minutes. The solution in the system was clear, thereby obtaining a silanized modified diamine solution;

[0094] The molar ratio of monomethylchlorosilane to diamines (3,4'-diaminodiphenyl ether, 4,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:160;

[0095] The molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether and 4,4'-diaminodiphenyl ether is 1:0.9:0.1;

[0096] The amount of lithium chloride added is 2% of the mass of the N,N-dimethylacetamide.

[0097] S2. Copolymerization reaction:

[0098] The silanized modified diamine solution was cooled to 10°C, and then terephthaloyl chloride was added three times for copolymerization reaction, wherein the molar ratio of terephthaloyl chloride to diamine was 1:0.98; mechanical stirring was performed at 100 r / min, and the reaction was carried out for 3 hours; finally, the temperature was slowly raised to 90°C, and sodium hydroxide was added to neutralize the solution to a pH of 7 to obtain a modified para-aramid stock solution; the solid content of the modified para-aramid stock solution was 4.0%, the spinning viscosity was 3100 Po, and the intrinsic viscosity of the polymer after washing and drying was measured to be 3.4 dL / g.

[0099] S3, Spinning:

[0100] The modified para-aramid stock solution passes through a 200-hole spinneret with a pore size of 0.2 mm and an aspect ratio of 3 and enters a coagulation bath to form spun yarn. The coagulation bath is a 30% NMP aqueous solution at a temperature of 10°C. The air bath is adjusted to a height of 10 mm. The spun yarn is then stretched in a stretching bath with a draw ratio of 1.5. The stretching bath is a 10% NMP aqueous solution at a temperature of 10°C. The yarn then passes through a series of washing and drying devices, heat-stretched 9 times at 500°C in a nitrogen atmosphere, and then heat-set on a 400°C hot roller. After oiling, the fiber is wound up at a speed of 100 m / min to obtain the modified para-aramid fiber.

[0101] Example 5

[0102] S1, diamine in-situ silanization modification:

[0103] Under inert gas protection and mechanical stirring, 3,4'-diaminodiphenyl ether, p-phenylenediamine, calcium chloride, and tetrachlorosilane were added to N-methylpyrrolidone. The temperature in the system was controlled at 25°C and stirred for 40 minutes. The solution in the system was clear, thereby obtaining a silanized modified diamine solution.

[0104] The molar ratio of tetrachlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:32;

[0105] The molar ratio of p-phenylenediamine and 3,4'-diaminodiphenyl ether is 1:1;

[0106] The added amount of calcium chloride is 0.75% of the mass of the N-methylpyrrolidone.

[0107] S2. Copolymerization reaction:

[0108] The silanized modified diamine solution was cooled to -5°C, and then terephthaloyl chloride was added three times for copolymerization reaction, with the molar ratio of terephthaloyl chloride to diamine being 1:1; mechanical stirring was performed at 100 r / min, and the reaction was carried out for 5 hours; finally, the temperature was slowly raised to 90°C, and calcium hydroxide was added to neutralize the solution to a pH of 7 to obtain a modified para-aramid stock solution; the modified para-aramid stock solution had a solid content of 7.6%, a spinning viscosity of 4970 Po, and an intrinsic viscosity of 3.5 dL / g after washing and drying the polymer.

[0109] S3, Spinning:

[0110] The modified para-aramid stock solution passes through a 200-hole spinneret with a pore size of 0.2 mm and an aspect ratio of 3 and enters a coagulation bath to form spun yarn. The coagulation bath is a 30% NMP aqueous solution at a temperature of 10°C. The air bath is adjusted to a height of 10 mm. The spun yarn is then stretched in a stretching bath with a draw ratio of 1.5. The stretching bath is a 10% NMP aqueous solution at a temperature of 10°C. The yarn then passes through a series of washing and drying devices, heat-stretched 9 times at 500°C in a nitrogen atmosphere, and then heat-set on a 400°C hot roller. After oiling, the fiber is wound up at a speed of 100 m / min to obtain the modified para-aramid fiber.

[0111] Comparative Example 1

[0112] The para-aramid fiber was 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.

[0113] The modified para-aramid stock solution (spinning solution) obtained by the preparation method of Comparative Example 1 had a dynamic viscosity of 9000 Po, and the intrinsic viscosity of the polymer after washing and drying was measured to be 4.2 dL / g.

[0114] Due to the high viscosity of the spinning solution, dry-jet wet spinning cannot be performed.

[0115] Comparative Example 2

[0116] Para-aramid fiber was prepared by the same method as in Example 1, except that the amount of tetrachlorosilane was reduced. 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.

[0117] Comparative Example 3

[0118] Para-aramid fibers were prepared using the same method as in Example 1, except that tetrachlorosilane was not added in this comparative example 3.

[0119] During the spinning process, the thermal stretching is 5 times. Experiments have shown that when the thermal stretching exceeds 5 times, serious yarn breakage problems occur.

[0120] Comparative Example 4

[0121] The para-aramid fiber was prepared by the same method as in Example 1, except that: in this comparative example 4, while the total molar number of diamines was the same as in Example 1, the amount of 3,4'-diaminodiphenyl ether was reduced, and the molar ratio of paraphenylenediamine to 3,4'-diaminodiphenyl ether in this comparative example 4 was 4:1.

[0122] The experiment found that the polymer had poor solubility in the system and could not be directly subjected to dry-jet wet spinning. After washing and drying the polymer, the intrinsic viscosity was measured to be 1.5 dL / g.

[0123] Comparative Example 5

[0124] Para-aramid fiber was prepared by the same method as in Example 1, except that in Comparative Example 5, while the total molar number of diamine was the same as in Example 1, the amount of 3,4'-diaminodiphenyl ether was increased, and the molar ratio of para-phenylenediamine to 3,4'-diaminodiphenyl ether in Comparative Example 4 was 0.25:1.

[0125] During the spinning process, the thermal stretching is 9 times. Although the elongation is high, the fiber strength is low and cannot meet the application requirements.

[0126] Comparative Example 6

[0127] The para-aramid fiber was prepared by the same method as in Example 1, except that in this comparative example 6, the amount of the solubilizing salt in step S1 was increased, and the amount of calcium chloride added was 8% of the mass of the N-methylpyrrolidone.

[0128] During the spinning process, the thermal stretching is 4 times. Experiments have shown that when the thermal stretching exceeds 4 times, serious yarn breakage problems occur.

[0129] Comparative Example 7

[0130] The para-aramid fiber was prepared by the same method as in Example 1, except that no solubilizing salt was added in step S1 of this comparative example 7.

[0131] The modified para-aramid stock solution was found to be turbid and light yellow in color. The polymer had poor solubility in the system and could not be subjected to dry-jet wet spinning. After washing and drying, the intrinsic viscosity of the polymer was measured to be 1.2 dL / g.

[0132] Comparative Example 8

[0133] Para-aramid fiber was prepared by the same method as in Example 1, except that toluene was used as a solvent in step S1 of this comparative example 8, and a purification operation was added after step S1. The specific operation process is as follows:

[0134] S1, diamine in-situ silanization modification:

[0135] Under inert gas protection and mechanical stirring, 3,4'-diaminodiphenyl ether, tetrachlorosilane, and triethylamine were added to toluene, the temperature in the system was controlled at 25°C, and the reaction was stirred for 15 minutes; then p-phenylenediamine was added to the system, and the stirring reaction was continued for 25 minutes to obtain a silanized modified diamine solution;

[0136] Then, under inert gas protection, the solid in the silanized modified diamine solution is filtered out, the solvent is removed by atmospheric distillation, and then the silanized modified diamine is obtained by reduced pressure distillation at 170°C.

[0137] The molar ratio of tetrachlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) is 1:32;

[0138] The molar ratio of p-phenylenediamine and 3,4'-diaminodiphenyl ether is 1:1;

[0139] The molar ratio of diamine to triethylamine is 1:3.

[0140] S2. Copolymerization reaction:

[0141] A silanized modified diamine and calcium chloride were dissolved in N-methylpyrrolidone and cooled to -5°C. Terephthaloyl chloride was then added in three separate batches for copolymerization. The molar ratio of terephthaloyl chloride to diamine was 1:1. The amount of calcium chloride added was 0.75% of the mass of the N-methylpyrrolidone. The mixture was mechanically stirred at 100 rpm for 5 hours. Finally, the temperature was slowly raised to 90°C, and calcium hydroxide was added to neutralize the mixture to a pH of 7, yielding a modified para-aramid stock solution. The modified para-aramid stock solution had a solids content of 6.4% and a spinning viscosity of 1700 pJ / s. After washing and drying, the polymer had an intrinsic viscosity of 2.7 dL / g.

[0142] S3, Spinning:

[0143] The same as Example 1, but during the spinning process, the hot stretching is 6 times. It was found in the experiment that when the hot stretching exceeded 6 times, serious problem of broken yarn occurred.

[0144] Example 9

[0145] The para-aramid fiber was prepared by the same method as in Example 1, except that in step S1 of this comparative example 8, 3,4'-diaminodiphenyl ether was not subjected to silane modification. The specific preparation process was as follows:

[0146] S1, diamine in-situ silanization modification:

[0147] Under inert gas protection and mechanical stirring, p-phenylenediamine, calcium chloride, and tetrachlorosilane were added to N-methylpyrrolidone. The temperature in the system was controlled at 25°C and the reaction was stirred for 25 minutes. The solution in the system was clear, and a silanized modified diamine solution was obtained.

[0148] The added amount of calcium chloride is 0.75% of the mass of the N-methylpyrrolidone.

[0149] S2. Copolymerization reaction:

[0150] The silanized modified diamine solution was cooled to -5°C, then 3,4'-diaminodiphenyl ether was added, followed by terephthaloyl chloride, which was then added in three separate steps for copolymerization. The molar ratio of terephthaloyl chloride to diamine was 1:1; the molar ratio of tetrachlorosilane to diamine (3,4'-diaminodiphenyl ether and p-phenylenediamine) was 1:32; and the molar ratio of p-phenylenediamine to 3,4'-diaminodiphenyl ether was 1:1. The reaction was mechanically stirred at 100 rpm for 5 hours. Finally, the temperature was slowly raised to 90°C, and calcium hydroxide was added to neutralize the solution to a pH of 7, yielding a modified para-aramid stock solution. The modified para-aramid stock solution had a solids content of 7.6% and a spinning viscosity of 3400 Po. After washing and drying, the polymer had an intrinsic viscosity of 3.2 dL / g.

[0151] S3, Spinning:

[0152] Same as Example 1.

[0153] The para-aramid stock solutions, polymers and para-aramid 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:

[0154] The intrinsic viscosity (IV) is determined by washing and drying the para-aramid stock solution, preparing a 0.5 g / dL concentrated sulfuric acid solution (98% by mass) of the polymer, and measuring the outflow time of the solvent and solution at 30°C using an Ubbelohde viscometer with a capillary inner diameter of 1.07 mm. The intrinsic viscosity is then calculated using the intrinsic viscosity calculation formula.

[0155] The performance test of para-aramid fiber refers to GB / T 14344-2022.

[0156] Table 1 Performance test results

[0157]

[0158] From the above experimental results, it can be seen that the para-aramid fibers prepared by the preparation method of the present invention in Examples 1-5 have better strength, modulus and elongation properties, and the preparation process is simple to operate, does not require excessive intermediate purification operations, does not require high-temperature heating, and has low energy consumption. In addition, it can be seen from the results of Examples 1 and 5 that when the diamine is in situ silylated, adding 3,4'-diaminodiphenyl ether and p-phenylenediamine separately at different time periods is more conducive to obtaining high-performance para-aramid fibers. This is because first allowing diaminodiphenyl ether and the chlorosilane polycondensation agent to react for a period of time before adding p-phenylenediamine for silylation modification can further balance the difference in reactivity between diaminodiphenyl ether and p-phenylenediamine, thereby making diaminodiphenyl ether and p-phenylenediamine both contain structures modified by silane groups, thereby obtaining a polymer with a more uniform molecular structure arrangement, and ultimately obtaining a para-aramid fiber with relatively high strength, elongation and modulus properties.

[0159] Figure 1 、 2 The infrared spectrum and dynamic thermomechanical curve of the para-aramid fiber prepared in Example 1 are respectively Figure 1 It can be seen that: 1644 cm -1 、1541cm -1 is the amide bond absorption peak, 1515 cm -1 is the benzene ring vibration peak, 1100cm -1 It is the ether bond absorption peak, proving that the polymer molecular chain contains diaminodiphenyl ether flexible chain segments.

[0160] from Figure 2It can be seen that the glass transition temperature of the modified para-aramid fiber is between 270℃-330℃, which is 340℃ compared with PPTA fiber. The molecular chain is more flexible and the prepared fiber has stronger toughness.

[0161] From the comparison of the results of Comparative Example 1 and Example 1, it can be seen that if the amount of the chlorosilane polycondensation agent is increased, the viscosity of the modified para-aramid stock solution will be too high, making it impossible to perform dry-jet wet spinning and thus unable to obtain para-aramid fibers.

[0162] From the comparison of the results of Comparative Example 2 and Example 1, it can be seen that if the amount of the chlorosilane polycondensation agent is reduced, the performance of the para-aramid fiber will be significantly reduced. Therefore, using the amount of the chlorosilane polycondensation agent defined in the present invention is more conducive to obtaining para-aramid fiber with excellent performance.

[0163] From the comparison of the results of Comparative Example 3 and Example 1, it can be seen that if the chlorosilane condensation agent is not added, it is difficult to perform high-ratio thermal stretching during the spinning process, because the unmodified diamine is extremely susceptible to oxidation and its activity decreases, and the prepared polymer has a low IV value and a low molecular weight, and cannot be stretched at a high ratio. Therefore, if the chlorosilane condensation agent is not added, the strength, modulus and elongation properties of the para-aramid fiber will be significantly reduced.

[0164] From the comparison of the results of Comparative Example 4 and Example 1, it can be seen that if the usage 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.

[0165] From the comparison of the results of Comparative Example 5 and Example 1, it can be seen that if the usage ratio of 3,4'-diaminodiphenyl ether is increased, the IV value of the polymer is low, and it is difficult to perform high-ratio hot stretching during the spinning process, which ultimately leads to a significant decrease in the strength and modulus properties of the para-aramid fiber. This is because 3,4'-diaminodiphenyl ether is a flexible segment and para-phenylenediamine is a rigid segment. An increase in the proportion of flexible segments will greatly reduce the strength and modulus of the fiber.

[0166] From the comparison of the results of Comparative Example 6 and Example 1, it can be seen that if the amount of solubilizing salt is increased, high-ratio hot stretching cannot be achieved during the spinning process, and the strength, modulus and elongation properties of the para-aramid fiber are significantly reduced. This is because the solubilizing salt content is too high, Ca 2+ It complexes with amino groups, reduces the activity of amino groups, causes the molecular weight of polymer to decrease, and makes high-drawing impossible, thus significantly reducing the fiber performance.

[0167] From the comparison of the results of Comparative Example 7 and Example 1, it can be seen that if no solubilizing salt is added, the modified para-aramid stock solution is turbid and light yellow, the polymer has poor solubility in the system, and dry-jet wet spinning cannot be performed.

[0168] From the comparison of the results of Comparative Example 8 and Example 1, it can be seen that if toluene solvent is used in step S1, the acid binding agent triethylamine needs to be added during the in-situ silylation modification of the diamine, and the purification process of the silylated modified diamine needs to be increased. The various properties of the ultimately obtained para-aramid fiber are significantly reduced. This is because: first, in the toluene system, under the same reaction principle, reaction temperature and reaction time conditions, the silylation reaction modification effect is not as sufficient as the modification in a weakly alkaline polar aprotic solvent; in addition, during the purification process of the silylated modified diamine, the silylated modified diamine is prone to instability because the Si-N bond is easily affected by trace moisture in the environment, which affects the activity of the diamine during the copolymerization reaction, deteriorates the polymer properties, and also reduces the performance of the para-aramid fiber.

[0169] From the comparison of the results of Comparative Example 9 and Example 1, it can be seen that if the diaminodiphenyl ether is not silane-modified, the strength, modulus and elongation properties of the para-aramid fiber will be significantly reduced. This is because if the diaminodiphenyl ether is not silane-modified, when the diamine and terephthaloyl chloride are copolymerized, the silane-modified p-phenylenediamine is more active and will polymerize with terephthaloyl chloride first, and the diaminodiphenyl ether will react subsequently, so that the final polymer structure is a block structure. In the preparation method of the modified para-aramid stock solution described in the present invention, during the diamine in-situ silylation modification process, both diaminodiphenyl ether and p-phenylenediamine are subjected to diamine in-situ silylation modification, so that both diaminodiphenyl ether and p-phenylenediamine contain structures modified by silyl groups, thereby making the silyl-modified diaminodiphenyl ether and silyl-modified p-phenylenediamine both highly active in the polymerization reaction with terephthaloyl chloride, so that the diaminodiphenyl ether and p-phenylenediamine structures are more evenly distributed in the molecular chain structure of the finally prepared polymer, further improving the performance of the para-aramid fiber.

[0170] The technical features of the above-described embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0171] For those skilled in the art, several variations and improvements may be made without departing from the scope of the present invention, which all fall within the scope of protection of the present invention. The scope of protection of the present invention shall be based on the appended claims.

Claims

1. A method for preparing a modified para-aramid stock solution, characterized in that: The preparation method is: S1, diamine in-situ silanization modification: Under inert gas conditions, in a weakly alkaline polar aprotic solvent, a diamine reacts with a chlorosilane polycondensation agent to obtain a silylated modified diamine solution; the diamine includes diaminodiphenyl ether and p-phenylenediamine; S2. Copolymerization reaction: adding terephthaloyl chloride to the silylated modified diamine solution to carry out copolymerization reaction, and after the reaction is completed, neutralizing the solution to obtain the modified para-aramid stock solution; The specific operations of step S1 are: Under inert gas conditions, a solubilizing salt, diaminodiphenyl ether, and a chlorosilane polycondensation agent are added to a weakly alkaline polar aprotic solvent, the temperature in the reaction system is controlled at 5°C-30°C, and the reaction is stirred for 10-20 minutes; then p-phenylenediamine is added to the system and the reaction is continued for 20-30 minutes to obtain a silanized modified diamine solution; The dissolution-promoting salt is at least one of calcium chloride and lithium chloride, and the amount of the dissolution-promoting salt is 0.25-5% of the mass of the weakly alkaline polar aprotic solvent; The weakly alkaline polar aprotic solvent is at least one of N-methylpyrrolidone and N,N-dimethylacetamide; 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).

2. The method for preparing a modified para-aramid stock solution 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 polycondensation agent is at least one of tetrachlorosilane, trimethylchlorosilane, dimethylchlorosilane and monomethylchlorosilane.

3. The method for preparing a modified para-aramid stock solution according to claim 1, characterized in that: The molar ratio of the terephthaloyl chloride to the diamine is 1:(0.98-1.02).

4. The method for preparing a modified para-aramid stock solution according to claim 1, characterized in that: The polymerization reaction temperature of step S2 is -5~10°C, and the polymerization reaction time is 3-8h.

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

6. A para-aramid fiber, characterized in that: Using a dry-jet wet spinning process to prepare the para-aramid fiber from the modified para-aramid stock solution; The modified para-aramid stock solution is prepared according to the preparation method according to any one of claims 1 to 4.

7. The para-aramid fiber according to claim 6, characterized in that: The para-aramid fiber has a strength of 24-30 cN / dtex, an elongation of 4.5-6.5%, and a modulus of 545-750 cN / dtex.

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