Highly flame-retardant aramid fiber prepared by low-temperature solution polycondensation method and preparation method thereof

Abstract

The present invention provides a method for preparing highly flame-retardant aramid fiber by intermittent polycondensation of low-temperature solution, characterized in that the method comprises the following steps: (1) dissolving calcium chloride; (2) dissolving p-phenylenediamine; (3) reacting terephthaloyl chloride and p-phenylenediamine; (4) reacting isophthaloyl chloride and p-phenylenediamine; (5) after the reaction is completed, separating the generated polymer, washing and drying to obtain modified poly (p-phenylene terephthalamide); (6) preparing modified aramid fiber. The modified aramid fiber prepared by the present invention has a breaking strength of >20.1 cN·dtex. ‑1 , elongation at break ≥ 10%, limiting oxygen index ≥ 32%. The present invention also provides an aramid fiber prepared by the above method.

Description

Technical Field

[0001] The invention relates to the field of aramid synthesis, and in particular to a highly flame-retardant aramid fiber and a preparation method thereof. Background Art

[0002] Aramid (polyphenylene phthalate) is an artificial synthetic fiber with many excellent properties such as high strength, high modulus, high temperature resistance, acid and alkali resistance, light weight, insulation, aging resistance, and long life cycle. Therefore, it is widely used in composite materials, bulletproof products, building materials, special protective clothing, electronic equipment and other fields.

[0003] Among them, aramid 1313 (poly(m-phenylene isophthalamide)) and aramid 1414 (poly(p-phenylene terephthalamide)) are the two most important aramids. Due to their excellent performance, they have been used more and more widely in recent years, and their synthesis and modification research have received more and more attention. The main methods for synthesizing aramid include interfacial polycondensation, direct polycondensation, gas phase polymerization, ester exchange, and low-temperature solution polycondensation, and the low-temperature solution polycondensation is the most effective and applicable synthesis method.

[0004] CN104530422A discloses a method for preparing polyaromatic amide, wherein m-phenylenediamine, terephthaloyl chloride and isophthaloyl chloride are subjected to solution polymerization in a polar solvent inert to aprotons, wherein the amount of the polar solvent inert to aprotons is 10 to 12 times the mass of m-phenylenediamine; the molar ratio of isophthaloyl chloride to terephthaloyl chloride is 70 to 50:30 to 50, the reaction temperature of the solution polymerization reaction is 0 to 10°C, and after reacting for 5 to 8 hours, a combined antioxidant is added to the reaction solution, and after the reaction solution is stirred evenly, it is added to the stirred water to precipitate a copolymer, and the copolymer is filtered, washed with water, and dried to obtain a polyaromatic amide copolymer, and the specific viscosity of the copolymer is 0.8 to 1.6. The performance of the product obtained by this method is not significantly improved, the reaction time is long, and water is used in the precipitation process, which will cause the product precipitation process to be too fast, the uniformity is poor, and the solvent recovery is difficult. Summary of the invention

[0005] In view of the shortcomings of the prior art, the present invention provides a highly flame-retardant aramid fiber (aramid 1414) with strong practicality, simple operation and excellent performance and a preparation method thereof.

[0006] To achieve the above objectives, the present invention is implemented through the following technical solutions:

[0007] A method for preparing highly flame-retardant aramid fiber, which is prepared by a low-temperature solution intermittent polycondensation method, and the preparation method comprises the following steps:

[0008] (1) Add the dehydrated solvent and dried calcium chloride to a reactor with a reflux condenser, then connect the reactor to a vacuum system, maintain the system pressure between -0.02 and -0.005 MPa, stir to dissolve the calcium chloride, add a reflux condenser to reduce solvent loss and reduce costs, and add a reflux condenser to reduce solvent loss;

[0009] (2) adding p-phenylenediamine to the mixed solution obtained in step (1), and cooling the mixture to -5 to 0° C. after the p-phenylenediamine is dissolved;

[0010] (3) adding terephthaloyl chloride to the mixed solution obtained in step (2) in batches, with the feeding time being 0.5 to 1.5 hours. The hydrogen chloride generated during the reaction is separated from the system by vacuum and then absorbed by a water absorption tower to obtain hydrochloric acid as a byproduct. The vacuum system is used to remove hydrogen chloride while reducing bubbles in the liquid, thereby improving product quality.

[0011] (4) adding isophthaloyl chloride and hexamethylenetetramine to the reaction solution obtained in step (3), and simultaneously starting to add tetraethyl urea, and then continuing the reaction for 0.5 to 1.5 hours;

[0012] (5) After the reaction is completed, the generated polymer is separated, washed and dried to obtain modified poly(p-phenylene terephthalamide), and the solvent can be reused after separation by distillation;

[0013] (6) The modified poly(p-phenylene terephthalamide) obtained in step (5) is dissolved in concentrated sulfuric acid to prepare a spinning solution, and the spinning solution is sprayed, coagulated, washed, dried, formed, stretched, washed twice, dried, and high-temperature shaped to obtain modified aramid fiber.

[0014] Furthermore, in step (1), the solvent is a mixed solution of tetramethylurea and tetraethylurea, the volume ratio of tetramethylurea to tetraethylurea is 2-9:1, and the amount of calcium chloride added is 0.3-0.4 times the molar number of p-phenylenediamine. The mixed solvent of the present invention has better solubility for the synthesized modified poly (p-phenylene terephthalamide) and the raw materials, can prevent the polymer from precipitating prematurely during the molecular weight growth process, delay the gelation time, and hinder the reaction; at the same time, a p-phenylenediamine solution with a higher concentration can be prepared, and the collision between molecules during the reaction process is more frequent and the efficiency is higher. When the reaction is close to the end, the condensation reaction is more thorough, the final molecular weight distribution is narrower, the obtained product has a higher viscosity, and the performance is better.

[0015] Furthermore, the molar ratio of terephthaloyl chloride in step (3) to p-phenylenediamine in step (2) is (0.96-0.98):1.

[0016] Furthermore, in step (4), the amount of isophthaloyl chloride added is 0.05 to 0.06 times the molar number of p-phenylenediamine, the amount of tetraethyl urea added is 0.2 to 0.3 times the volume of the solvent in step (1), and the amount of urotropine added is 0.05 to 0.1 times the mass of calcium chloride. Finally, the sum of the molar numbers of isophthaloyl chloride and terephthaloyl chloride is more than 1 times that of p-phenylenediamine. Since the two benzene rings in poly (p-phenylene terephthalamide) are rigid groups, the rigidity of the molecular chain is very strong and the molecular chain is very regular, and the symmetry is excellent, so poly (p-phenylene terephthalamide) is insoluble in general organic solvents, which places high demands on the industrial fiber-forming process and increases the production cost very much. In the final stage of the polymerization reaction, a certain amount of urotropine is added. Due to the symmetry of urotropine, urotropine can be well dissolved in the reaction solution and play a catalytic role. At the same time, the reaction rate at the end of the reaction is accelerated, the reaction at the end of the reaction is promoted to be complete, and the viscosity of the solution is reduced. Isophthaloyl chloride is added for condensation reaction, which destroys the symmetry of the final product to a certain extent, resulting in weakened symmetry, weakened rigidity, improved toughness, and enhanced elongation at break, while other properties are not affected. The tetraethyl urea added in step (4) can reduce the solubility of the product in the solvent, promote the uniform precipitation rate of the product, improve the uniformity, and reduce the viscosity of the solution. The prepared product has better performance and improved flame retardant properties.

[0017] Furthermore, the modified aramid fiber prepared in step (6) has a breaking strength of >20.1 cN·dtex -1 , elongation at break ≥ 10%, limiting oxygen index ≥ 32%.

[0018] The solubility of the modified poly(p-phenylene terephthalamide) obtained in the final step (5) in sulfuric acid can be increased by more than 9%, and the dissolution time can be shortened by more than 25%, thereby reducing the use of concentrated sulfuric acid and the discharge of three wastes.

[0019] At the same time, the present invention also provides an aramid fiber prepared by any of the above methods, the aramid fiber has excellent performance, improved limiting oxygen index, and good performance indicators such as breaking strength, breaking elongation, and regain.

[0020] The protective clothing fabric prepared by adopting the aramid fiber prepared by the present invention has excellent performance and excellent flame retardancy. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0022] Example 1

[0023] A method for preparing highly flame-retardant aramid fiber by low-temperature solution intermittent polycondensation method, characterized in that it comprises the following steps:

[0024] (1) Add 4.5 L of dehydrated tetramethylurea, 0.5 L of tetraethylurea, and 11.7 g of dry calcium chloride to a 10 L reactor equipped with a reflux condenser. Then, connect the reactor to a vacuum system, maintain the system pressure between -0.02 and -0.01 MPa, and stir to dissolve the calcium chloride.

[0025] (2) adding 37.85 g (0.35 mol) of p-phenylenediamine to the mixed solution obtained in step (1), and cooling the mixture to -5 to 0° C. after the p-phenylenediamine is dissolved;

[0026] (3) 68.21 g (0.336 mol) of terephthaloyl chloride was added to the mixed solution obtained in step (2) in batches, and the addition time was 0.5 h. The hydrogen chloride generated during the reaction was separated from the system by vacuum and then absorbed in a water absorption tower to obtain hydrochloric acid as a byproduct;

[0027] (4) Add 3.55 g (0.0175 mol) of isophthaloyl chloride, 0.6 g of urotropine, and 1 L of tetraethyl urea to the reaction solution obtained in step (3), and then continue the reaction for 0.5 h;

[0028] (5) After the reaction is completed, the generated polymer is separated, washed and dried to obtain modified poly(p-phenylene terephthalamide). The solvent can be reused after separation by distillation. The remaining solid after evaporation is mainly hexamethylenetetramine hydrochloride and calcium chloride. After enrichment, the hexamethylenetetramine can be reused after alkali washing, extraction and evaporation.

[0029] (6) The modified poly(p-phenylene terephthalamide) obtained in step (5) is dissolved in concentrated sulfuric acid for 19.5 minutes to prepare a spinning solution with a solid content of 25.3%. The spinning solution is sprayed, coagulated, washed, dried, formed, stretched, washed twice, dried, and high-temperature shaped to obtain modified aramid fiber. The solubility of the modified poly(p-phenylene terephthalamide) in sulfuric acid can be increased by 15%, and the dissolution time can be reduced by 35%.

[0030] The modified aramid fiber obtained in step (6) is used as a raw material to make special protective clothing fabrics, and performance tests are carried out. The afterflaming time in both the warp and weft directions is 0 s, the smoldering time in both the warp and weft directions is 0 s, and the damage length in both the warp and weft directions is less than 32 cm.

[0031] Example 2

[0032] A method for preparing highly flame-retardant aramid fiber by low-temperature solution intermittent polycondensation method, characterized in that it comprises the following steps:

[0033] (1) Add 3.75 L of dehydrated tetramethyl urea, 1.25 L of tetraethyl urea, and 14.8 g of dry calcium chloride to a 10 L reactor equipped with a reflux condenser. Then, connect the reactor to a vacuum system, maintain the system pressure between -0.01 and -0.005 MPa, and stir to dissolve the calcium chloride.

[0034] (2) adding 37.85 g (0.35 mol) of p-phenylenediamine to the mixed solution obtained in step (1), and cooling the mixture to -5 to 0° C. after the p-phenylenediamine is dissolved;

[0035] (3) 69.63 g (0.343 mol) of terephthaloyl chloride was added to the mixed solution obtained in step (2) in batches over a period of 1.5 h. The hydrogen chloride produced during the reaction was separated from the system by vacuum and then absorbed in a water absorption tower to obtain hydrochloric acid as a byproduct;

[0036] (4) Add 4.26 g (0.021 mol) of isophthaloyl chloride, 1.48 g of urotropine, and 1.5 L of tetraethyl urea to the reaction solution obtained in step (3), and then continue the reaction for 1.5 h;

[0037] (5) After the reaction is completed, the generated polymer is separated, washed and dried to obtain modified poly(p-phenylene terephthalamide), and the solvent can be reused after separation by distillation;

[0038] (6) The modified poly(p-phenylene terephthalamide) obtained in step (5) is dissolved in concentrated sulfuric acid for 21 minutes to prepare a spinning solution with a solid content of 24.6%. The spinning solution is sprayed, coagulated, washed, dried, formed, stretched, washed twice, dried, and high-temperature shaped to obtain modified aramid fiber. The solubility of the modified poly(p-phenylene terephthalamide) in sulfuric acid can be increased by 12% and the dissolution time can be reduced by 30%.

[0039] The modified aramid fiber obtained in step (6) is used as a raw material to make special protective clothing fabrics, and performance tests are carried out. The afterflaming time in both the warp and weft directions is 0 s, the smoldering time in both the warp and weft directions is 0 s, and the damage length in both the warp and weft directions is less than 35 cm.

[0040] Example 3

[0041] A method for preparing highly flame-retardant aramid fiber by low-temperature solution intermittent polycondensation method, characterized in that it comprises the following steps:

[0042] (1) Add 3.75 L of dehydrated tetramethyl urea, 1.25 L of tetraethyl urea, and 14.8 g of dry calcium chloride to a 10 L reactor equipped with a reflux condenser, then connect the reactor to a vacuum system, maintain the system pressure between -0.01 and -0.005 MPa, and stir to dissolve the calcium chloride;

[0043] (2) adding 37.85 g (0.35 mol) of p-phenylenediamine to the mixed solution obtained in step (1), and cooling the mixture to -5 to 0° C. after the p-phenylenediamine is dissolved;

[0044] (3) 69.63 g (0.343 mol) of terephthaloyl chloride was added to the mixed solution obtained in step (2) in batches over a period of 1.5 h. The hydrogen chloride produced during the reaction was separated from the system by vacuum and then absorbed in a water absorption tower to obtain hydrochloric acid as a byproduct;

[0045] (4) Add 4.26 g (0.021 mol) of isophthaloyl chloride, 1.3 g of urotropine, and 1.25 L of tetraethyl urea to the reaction solution obtained in step (3), and then continue the reaction for 1.5 h;

[0046] (5) After the reaction is completed, the generated polymer is separated, washed and dried to obtain modified poly(p-phenylene terephthalamide), and the solvent can be reused after separation by distillation;

[0047] (6) The modified poly(p-phenylene terephthalamide) obtained in step (5) is dissolved in concentrated sulfuric acid for a dissolution time of 22.2 minutes to prepare a spinning solution with a solid content of 24.2%. The spinning solution is spun, coagulated, washed, dried, formed, stretched, washed twice, dried, and high-temperature shaped to obtain modified aramid fiber. The solubility of the modified poly(p-phenylene terephthalamide) in sulfuric acid can be increased by 10% and the dissolution time can be reduced by 26%.

[0048] The modified aramid fiber obtained in step (6) is used as a raw material to make special protective clothing fabrics, and performance tests are carried out. The afterflaming time in both the warp and weft directions is 0 s, the smoldering time in both the warp and weft directions is 0 s, and the damage length in both the warp and weft directions is less than 37 cm.

[0049] Comparative Example 1

[0050] Only the modified poly(p-phenylene terephthalamide) in step (6) of Example 1 was replaced by commercially available poly(p-phenylene terephthalamide), and the rest was the same as Example 1. The final dissolution time was 30 min, the spinning solution concentration was 22%, and the aramid fiber was used as a raw material to make a special protective clothing fabric. The performance test showed that the afterflaming time in both the warp and weft directions was 0 s, the smoldering time in both the warp and weft directions was greater than 8 s, and the damaged length in both the warp and weft directions was greater than 60 cm.

[0051] Comparative Example 2

[0052] Only the solvent in step (1) of Example 1 was replaced by N,N-dimethylacetamide. The other steps were the same as Example 1. The properties of the obtained product are shown in Table 1.

[0053] Comparative Example 3

[0054] Only in step (4) of Example 1, urotropine was not added. The other steps were the same as in Example 1. The reaction time in step (4) needed to be increased to more than 3 hours to complete the reaction. The properties of the obtained product are shown in Table 1.

[0055] The performance comparison of the aramid fibers prepared in the examples of the present invention and the comparative examples is shown in Table 1:

[0056] Table 1 Comparison of the properties of aramid fibers prepared in the embodiments of the present invention and the comparative examples

[0057]

[0058]

[0059] It can be seen from the data of Comparative Example 1 in the above table that the breaking strength of the modified aramid fiber prepared by the present invention is equivalent to that of the commercially available one, but the breaking elongation is significantly improved, the limiting oxygen index is significantly improved, the flame retardancy is good, and the special protective clothing fabric further prepared has better performance; it can be seen from the data of Comparative Example 2 that due to the better symmetry of the solvent of the present invention, the raw materials and the prepared products have better solubility, high reaction activity, and the prepared product performance is more excellent; it can be seen from the data of Comparative Example 3 that the addition of hexamine reduces the reaction time, and the final product performance is better.

Claims

1. A method for preparing highly flame-retardant aramid fiber, characterized in that: The preparation is carried out by a low-temperature solution intermittent polycondensation method, and the preparation method comprises the following steps: (1) Add dehydrated solvent and dry calcium chloride into the reactor, then connect the reactor to the vacuum system, maintain the system pressure between -0.02 and -0.005 MPa, and stir to dissolve the calcium chloride; (2) adding p-phenylenediamine to the mixed solution obtained in step (1), and cooling the mixture to -5 to 0°C after the p-phenylenediamine is dissolved; (3) adding terephthaloyl chloride to the mixed solution obtained in step (2) in batches, with the addition time being 0.5 to 1.5 hours. The hydrogen chloride generated during the reaction is separated from the system by vacuum and then absorbed in a water absorption tower to obtain hydrochloric acid as a byproduct; (4) adding isophthaloyl chloride and urotropine to the reaction solution obtained in step (3), and simultaneously starting to add tetraethyl urea, and then continuing the reaction for 0.5 to 1.5 hours; (5) After the reaction is completed, the generated polymer is separated, washed and dried to obtain modified poly(p-phenylene terephthalamide); (6) dissolving the modified poly(p-phenylene terephthalamide) obtained in step (5) in concentrated sulfuric acid to prepare a spinning solution, spinning, coagulating, washing, drying, shaping, stretching, washing twice, drying, and high-temperature shaping to obtain modified aramid fiber; In the step (1), the solvent is a mixed solution of tetramethylurea and tetraethylurea, the volume ratio of tetramethylurea to tetraethylurea is 2-9:1, and the amount of calcium chloride added is 0.3-0.4 times the molar number of p-phenylenediamine.

2. The method for preparing highly flame-retardant aramid fiber according to claim 1, characterized in that: The molar ratio of terephthaloyl chloride in step (3) to p-phenylenediamine in step (2) is (0.96-0.98):

1.

3. The method for preparing highly flame-retardant aramid fiber according to claim 1, characterized in that: In step (4), the amount of phthaloyl chloride added is 0.05 to 0.06 times the molar number of p-phenylenediamine, the amount of tetraethyl urea added is 0.2 to 0.3 times the volume of the solvent in step (1), and the amount of hexamethylenetetramine added is 0.05 to 0.1 times the mass of calcium chloride.

4. The method for preparing highly flame-retardant aramid fiber according to claim 1, characterized in that: The solvent after separating the polymer in step (5) can be reused after distillation separation.

5. Aramid fiber prepared by the method according to any one of claims 1 to 4.

6. The aramid fiber according to claim 5, characterized in that The aramid fiber breaking strength is greater than 20.1 cN•dtex -1 , elongation at break ≥10%, limiting oxygen index ≥32%.

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