An oxidation-resistant meta-aramid fiber and its preparation method

Abstract

The present invention discloses an oxidation-resistant meta-aramid fiber and a preparation method thereof, comprising the following steps: Step 1, reacting carboxylated carbon nanotubes with modified copolyamide, then adding modified meta-aramid powder, and drying to obtain composite reinforced nano-powder; Step 2, mixing the composite reinforced nano-powder, poly(m-phenylene isophthalamide), hydrogen chloride and N,N-dimethylacetamide to prepare a composite meta-aramid spinning solution, and obtaining the oxidation-resistant meta-aramid fiber by a wet spinning process; by doping the composite reinforced nano-powder in the meta-aramid fiber, the performance of the oxidation-resistant meta-aramid fiber is enhanced by the composite reinforced nano-powder modified by carbon nanotubes, the oxidation-resistant ability of the oxidation-resistant meta-aramid fiber is improved by using the antioxidant property of the carbon nanotubes, and at the same time the physical properties of the carbon nanotubes themselves also improve the mechanical strength of the oxidation-resistant meta-aramid fiber, and the obtained oxidation-resistant meta-aramid fiber has good heat-oxygen aging performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of meta-aramid, and specifically relates to an oxidation-resistant meta-aramid fiber and a preparation method thereof. Background Art

[0002] Meta-aramid has good thermal stability and chemical stability, with high breaking strength and toughness, and excellent mechanical properties. It is often used in the military field and the national economy in the form of structural composites and has become an irreplaceable key material. However, the π-π bond between benzene rings in meta-aramid fiber is easily oxidized to cause yellowing, which affects the quality of meta-aramid fiber.

[0003] Patent CN113789583A discloses an anti-yellowing meta-aramid precipitated fiber and its preparation method and application. By gradually adding isophthaloyl chloride and a modifier containing tetramethylpiperidineamine to a solution of m-phenylenediamine, and then adding an anti-yellowing agent and performing precipitation molding and washing, meta-aramid fiber with excellent anti-yellowing performance and anti-thermal oxidation performance is obtained; however, this scheme introduces metal ions, resulting in a reduction in the performance of downstream products of meta-aramid fiber and limited application scenarios.

[0004] Patent CN117265686A discloses an oxidation-resistant meta-aramid fiber and its preparation method. By polymerizing m-phenylenediamine and isophthaloyl chloride, and dicycloheptane monomers and isophthaloyl chloride separately and then mixing them, and then polymerizing with isophthaloyl chloride and reacting with bis-tert-butylbenzoyl chloride monomers, an oxidation-resistant meta-aramid fiber is obtained through a wet spinning process; it has good antioxidant ability and is suitable for industrial production; however, this scheme improves the antioxidant ability of meta-aramid polymer by changing the polymer structure of meta-aramid, which has an impact on the mechanical strength of meta-aramid fiber. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem of how to improve the antioxidant ability and mechanical strength of meta-aramid fiber, and to provide an oxidation-resistant meta-aramid fiber and a preparation method thereof.

[0006] The purpose of the present invention can be achieved by the following technical solutions:

[0007] A preparation method of an oxidation-resistant meta-aramid fiber, comprising the following steps:

[0008] Step 1: Hydrolytically modify copolyamide and meta-aramid powder with phosphoric acid to obtain modified copolyamide and modified meta-aramid powder.

[0009] Step 2: Mix the carboxylated carbon nanotubes with N,N-dimethylacetamide in a reaction kettle and perform ultrasonic treatment. Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide to the reaction kettle, perform ultrasonic treatment, then add the modified copolyamide, perform ultrasonic treatment and then magnetic stirring, then add the modified meta-aramid powder, perform ultrasonic treatment and then magnetic stirring. After centrifugation at a speed of 10,000 rpm, wash the precipitate with ethanol, and dry to obtain the composite reinforced nano powder.

[0010] Step 3: Mix the composite reinforced nano powder, poly(m-phenylene isophthalamide), hydrogen chloride and N,N-dimethylacetamide to prepare a composite meta-aramid spinning solution, and use the wet spinning process to obtain oxidation-resistant meta-aramid fibers.

[0011] In Step 2, the ultrasonic treatment time is 30 - 40 min, and the magnetic stirring time is 20 - 24 h.

[0012] Furthermore, the dosage ratio of the carboxylated carbon nanotubes, N,N-dimethylacetamide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide, modified copolyamide and modified meta-aramid powder in Step 2 is 5 - 8 g: 100 - 150 mL: 3 - 4 mL: 5 - 7 mL: 3 - 5 g: 3 - 5 g.

[0013] Furthermore, the mixing mass ratio of the composite reinforced nano powder, poly(m-phenylene isophthalamide), hydrogen chloride and N,N-dimethylacetamide in Step 3 is 3 - 4: 15 - 20: 1 - 4: 75 - 85.

[0014] Furthermore, the preparation method of the carboxylated carbon nanotubes is as follows:

[0015] Take carbon nanotubes and mix them with the mixed acid solution in a reaction kettle by ultrasonic treatment for 1 - 2 h, heat them in a water bath to 70 - 80 °C, stir and condense and reflux for 1 - 1.5 h, wash with deionized water after centrifugation, and dry to obtain the carboxylated carbon nanotubes.

[0016] The mixed acid solution is prepared by mixing 98 wt% sulfuric acid and 68 wt% nitric acid according to a molar ratio of 3:1.

[0017] Furthermore, the dosage ratio of the carbon nanotubes and the mixed acid solution is 5 - 10 g: 150 - 170 mL.

[0018] Furthermore, the method for phosphoric acid hydrolysis modification in Step 1 is:

[0019] Mix the meta-aramid powder with phosphoric acid solution at a mass ratio of 30 - 35 times in a reaction kettle, transfer it to a high-speed disperser and mix at a speed of 4500 - 5000 rpm for 5 - 6 min. After filtration, heat the meta-aramid powder in the reaction kettle to 100 - 110 °C and react for 30 - 40 min. Wash the meta-aramid powder with deionized water and dry it to obtain the modified meta-aramid powder.

[0020] Further, the meta-aramid powder is prepared by freezing the meta-aramid short fibers in liquid nitrogen for 5 - 7 min, then grinding them in a planetary ball mill at 500 - 600 rpm for 4 - 5 h, and separating the nano-scale powder with a screening shaker. The phosphoric acid solution is a 50 wt% aqueous phosphoric acid solution.

[0021] Further, the method for phosphoric acid hydrolysis modification of the modified copolyamide is the same as that of the meta-aramid powder.

[0022] Further, the preparation method of the copolyamide is as follows:

[0023] Dissolve p-phenylenediamine, trimellitic acid and p-aminobenzoic acid in a mixed solvent of pyridine and N,N-dimethylacetamide in a reaction kettle. After complete dissolution, add triphenyl phosphite and heat to 100 - 110 °C under nitrogen protection and react for 3 - 5 h. Then slowly pour it into deionized water to obtain a polymer. Wash the polymer with absolute ethanol, reflux it in hot water, and dry it under vacuum at 90 - 100 °C for 10 - 12 h to obtain the copolyamide.

[0024] Further, the dosage ratio of p-phenylenediamine, trimellitic acid, p-aminobenzoic acid, pyridine, N,N-dimethylacetamide, and triphenyl phosphite is 10 - 12 g : 20 - 25 g : 13 - 15 g : 20 - 25 mL : 200 - 250 mL : 90 - 100 g.

[0025] The beneficial effects of the present invention:

[0026] (1) The oxidation-resistant meta-aramid fiber prepared by the present invention is doped with composite reinforcing nano-powder in the meta-aramid fiber, so that the performance of the oxidation-resistant meta-aramid fiber is enhanced by the composite reinforcing nano-powder modified by carbon nanotubes. The antioxidant property of carbon nanotubes is used to improve the oxidation resistance of the oxidation-resistant meta-aramid fiber. At the same time, the physical properties of carbon nanotubes themselves also improve the mechanical strength of the oxidation-resistant meta-aramid fiber, and the obtained oxidation-resistant meta-aramid fiber has good heat and oxygen aging resistance.

[0027] (2) The preparation method of the present invention prepares a copolymerized polyamide that is easily soluble and modifies it with phosphoric acid. The copolymerized polyamide is grafted onto carboxylated carbon nanotubes through an amide dehydration condensation reaction to improve the dispersibility of the carboxylated carbon nanotubes in organic solvents. Then, the remaining carboxyl groups on the copolymerized polyamide are subjected to an amide dehydration condensation reaction with the phosphoric acid-modified meta-aramid powder. The copolymerized polyamide is used to composite the carbon nanotubes and the meta-aramid powder, improving the dispersibility of the carbon nanotubes in the composite meta-aramid spinning solution, thereby enhancing the oxidation resistance and mechanical strength of the meta-aramid fiber by using highly dispersed carbon nanotubes.

[0028] (3) The preparation method of the present invention does not change the principle of the wet spinning of meta-aramid fibers. The method is simple and easy to obtain, without the need to change the equipment and parameters of the wet spinning process. Only by prefabricating the composite reinforcing nano-powder and then mixing the composite reinforcing nano-powder as the raw material of the wet spinning process with the meta-aramid spinning solution for spinning, the oxidation-resistant meta-aramid fiber can be obtained, and it has strong market application ability. Specific Embodiments

[0029] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0030] Example 1: A preparation method of an oxidation-resistant meta-aramid fiber, comprising the following steps:

[0031] Step 1: Dissolve 10 g of p-phenylenediamine, 20 g of trimellitic acid, and 13 g of p-aminobenzoic acid in a mixed solvent of 20 mL of pyridine and 200 mL of N,N-dimethylacetamide in a reaction kettle. After complete dissolution, add 90 g of triphenyl phosphite and heat to 100 °C under nitrogen protection for 3 h. Then slowly pour it into deionized water to obtain a polymer. Wash the polymer with absolute ethanol and reflux it in hot water, and vacuum dry it at 90 °C for 10 h to obtain a copolymerized polyamide.

[0032] Step 2: Mix 8 g of the copolymerized polyamide with 240 g of a 50 wt% phosphoric acid solution in a reaction kettle, transfer it to a high-speed disperser and mix at a speed of 4500 rpm for 5 min. After filtration, heat the copolymerized polyamide in the reaction kettle to 100 °C for 30 min. Wash the copolymerized polyamide with deionized water until the last washing liquid is neutral, and then vacuum dry it at 90 °C for 8 h to obtain a modified copolymerized polyamide.

[0033] Step 3: Mix 8 g of meta-aramid powder with 240 g of 50 wt% phosphoric acid solution in a reaction kettle, transfer it to a high-speed disperser and mix at a speed of 4500 rpm for 5 min. After filtration, heat the meta-aramid powder in the reaction kettle to 100 °C and react for 30 min. Wash the meta-aramid powder with deionized water until the last washing liquid is neutral, and then dry it in vacuo at 90 °C for 8 h to obtain modified meta-aramid powder.

[0034] The meta-aramid powder is obtained by freezing meta-aramid short fibers in liquid nitrogen for 5 min, then grinding them in a planetary ball mill at 500 rpm for 4 h, and separating the nano-scale powder with a screening shaker.

[0035] Step 4: Take 5 g of carbon nanotubes and ultrasonically mix them with 150 mL of mixed acid solution in a reaction kettle for 1 h. The mixed acid solution is prepared by mixing 98 wt% sulfuric acid and 68 wt% nitric acid according to a molar ratio of 3:1. Heat it in a water bath to 70 °C, stir and condense and reflux for 1 h. After centrifugation, wash the precipitate with deionized water until the last washing liquid is neutral, and dry it at 70 °C for 10 h to obtain carboxylated carbon nanotubes.

[0036] Step 5: Ultrasonically mix 5 g of carboxylated carbon nanotubes with 100 mL of N,N-dimethylacetamide in a reaction kettle for 30 min. Add 3 mL of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and 5 mL of N-hydroxysuccinimide to the reaction kettle, ultrasonically treat for 30 min, then add 3 g of modified copolyamide, magnetically stir for 20 h, then add 3 g of modified meta-aramid powder, ultrasonically treat for 30 min and then magnetically stir for 20 h. After centrifugation at a speed of 10000 rpm, wash the precipitate with ethanol and dry it at 50 °C for 1 h to obtain composite reinforced nano powder.

[0037] Step 6: Mix 30 g of composite reinforced nano powder, 150 g of poly(m-phenylene isophthalamide), 10 g of hydrogen chloride and 750 g of N,N-dimethylacetamide to prepare a composite meta-aramid spinning solution, and use a wet spinning process to prepare oxidation-resistant meta-aramid fibers.

[0038] Example 2: A method for preparing oxidation-resistant meta-aramid fibers, comprising the following steps:

[0039] Step 1: Dissolve 11 g of p-phenylenediamine, 22.5 g of trimellitic acid and 14 g of p-aminobenzoic acid in a mixed solvent of 22.5 mL of pyridine and 225 mL of N,N-dimethylacetamide in a reaction kettle. After complete dissolution, add 95 g of triphenyl phosphite, heat to 105 °C under nitrogen protection and react for 4 h, then slowly pour it into deionized water to obtain a polymer. Wash the polymer with absolute ethanol, reflux it in hot water, and dry it in vacuo at 95 °C for 11 h to obtain copolyamide.

[0040] Step 2: Mix 9 g of the copolyamide with 300 g of a 50 wt% phosphoric acid solution in a reaction kettle, transfer it to a high-speed disperser and mix at a speed of 4700 rpm for 5.5 min. After filtration, heat the copolyamide in the reaction kettle to 105 °C and react for 35 min. Wash the copolyamide with deionized water until the last washing liquid is neutral, and then vacuum dry it at 95 °C for 9 h to obtain the modified copolyamide.

[0041] Step 3: Mix 9 g of the meta-aramid powder with 300 g of a 50 wt% phosphoric acid solution in a reaction kettle, transfer it to a high-speed disperser and mix at a speed of 4700 rpm for 5.5 min. After filtration, heat the meta-aramid powder in the reaction kettle to 105 °C and react for 35 min. Wash the meta-aramid powder with deionized water until the last washing liquid is neutral, and then vacuum dry it at 95 °C for 9 h to obtain the modified meta-aramid powder.

[0042] The meta-aramid powder is obtained by subjecting the meta-aramid short-cut fibers to cryogenic treatment in liquid nitrogen for 6 min, then grinding them in a planetary ball mill at 550 rpm for 4.5 h, and separating the nano-scale powder using a screening shaker.

[0043] Step 4: Take 7.5 g of carbon nanotubes and ultrasonically mix them with 160 mL of a mixed acid solution in a reaction kettle for 1.5 h. The mixed acid solution is prepared by mixing 98 wt% sulfuric acid and 68 wt% nitric acid in a molar ratio of 3:1. Heat it in a water bath to 75 °C, stir and condense and reflux for 1.25 h. After centrifugation, wash the precipitate with deionized water until the last washing liquid is neutral, and dry it at 75 °C for 11 h to obtain carboxylated carbon nanotubes.

[0044] Step 5: Ultrasonically mix 6.5 g of the carboxylated carbon nanotubes with 125 mL of N,N-dimethylacetamide in a reaction kettle for 35 min. Add 3.5 mL of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and 6 mL of N-hydroxysuccinimide to the reaction kettle, ultrasonically treat for 35 min, then add 4 g of the modified copolyamide, magnetically stir for 22 h, then add 4 g of the modified meta-aramid powder, ultrasonically treat for 35 min and then magnetically stir for 22 h. After centrifugation at a speed of 10,000 rpm, wash the precipitate with ethanol and dry it at 55 °C for 1.5 h to obtain the composite reinforced nano-powder.

[0045] Step 6: Mix 35 g of the composite reinforced nano-powder, 175 g of poly(m-phenylene isophthalamide), 25 g of hydrogen chloride and 800 g of N,N-dimethylacetamide to prepare a composite meta-aramid spinning solution, and use the wet spinning process to obtain the oxidation-resistant meta-aramid fiber.

[0046] Example 3: A method for preparing an oxidation-resistant meta-aramid fiber, comprising the following steps:

[0047] Step 1: Dissolve 12 g of p-phenylenediamine, 25 g of trimellitic acid, and 15 g of p-aminobenzoic acid in a mixed solvent of 25 mL of pyridine and 250 mL of N,N-dimethylacetamide in a reaction kettle. After complete dissolution, add 100 g of triphenyl phosphite, heat to 110 °C under nitrogen protection, and react for 5 h. Then slowly pour it into deionized water to obtain a polymer. Wash the polymer with absolute ethanol, reflux it in hot water, and dry it in vacuo at 100 °C for 12 h to obtain a copolyamide.

[0048] The copolyamide has good solubility and dispersibility in organic solvents and contains amide groups, which facilitates grafting reactions with other groups and is conducive to the dispersion of substances grafted to the copolyamide in the organic solvent of meta-aramid fibers.

[0049] Step 2: Mix 10 g of the copolyamide with 350 g of 50 wt% phosphoric acid solution in a reaction kettle, transfer it to a high-speed disperser, and mix at a speed of 5000 rpm for 6 min. After filtration, heat the copolyamide in the reaction kettle to 110 °C and react for 40 min. Wash the copolyamide with deionized water until the last washing liquid is neutral, and then dry it in vacuo at 100 °C for 10 h to obtain a modified copolyamide.

[0050] Step 3: Mix 10 g of meta-aramid powder with 350 g of 50 wt% phosphoric acid solution in a reaction kettle, transfer it to a high-speed disperser, and mix at a speed of 5000 rpm for 6 min. After filtration, heat the meta-aramid powder in the reaction kettle to 110 °C and react for 40 min. Wash the meta-aramid powder with deionized water until the last washing liquid is neutral, and then dry it in vacuo at 100 °C for 10 h to obtain a modified meta-aramid powder.

[0051] The meta-aramid powder is obtained by freezing meta-aramid short fibers in liquid nitrogen for 7 min, then grinding them at 600 rpm for 5 h using a planetary ball mill, and separating out nano-scale powder using a screening shaker.

[0052] Utilize the oxidation property of phosphoric acid itself to oxidize and hydrolyze some amide bonds in the surface structures of the copolyamide and the meta-aramid powder to form amino and carboxyl groups, enhancing the reactive grafting ability on the surfaces of the modified copolyamide and the modified meta-aramid powder. The phosphoric acid remaining on the surfaces of the copolyamide and the modified meta-aramid will dehydrate and polymerize into diphosphoric acid at a temperature of 100 - 110 °C. The diphosphoric acid reacts with the amide bonds in the copolyamide structure, improving the surface activity of the modified copolyamide and the modified meta-aramid and enhancing the interfacial bonding performance between the modified copolyamide and carbon nanotubes in subsequent reactions.

[0053] Step 4: Take 10 g of carbon nanotubes and ultrasonically mix them with 170 mL of mixed acid solution in a reaction kettle for 2 h. The mixed acid solution is prepared by mixing 98 wt% sulfuric acid and 68 wt% nitric acid in a molar ratio of 3:1. Heat it in a water bath to 80 °C, stir and condense for reflux for 1.5 h. After centrifugation, wash the precipitate with deionized water until the last washing solution is neutral, and dry it at 80 °C for 12 h to obtain carboxylated carbon nanotubes.

[0054] Step 5: Ultrasonically mix 8 g of carboxylated carbon nanotubes with 150 mL of N,N-dimethylacetamide in a reaction kettle for 40 min. Add 4 mL of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and 7 mL of N-hydroxysuccinimide to the reaction kettle, ultrasonically treat for 40 min, then add 5 g of modified copolyamide, stir magnetically for 24 h, then add 5 g of modified meta-aramid powder, ultrasonically treat for 40 min and then stir magnetically for 24 h. After centrifugation at a speed of 10000 rpm, wash the precipitate with ethanol and dry it at 60 °C for 2 h to obtain composite reinforced nano powder.

[0055] Step 6: Mix 40 g of composite reinforced nano powder, 200 g of poly(m-phenylene isophthalamide), 40 g of hydrogen chloride and 850 g of N,N-dimethylacetamide to prepare a composite meta-aramid spinning solution, and use the wet spinning process to obtain oxidation-resistant meta-aramid fibers.

[0056] After ultrasonically dispersing the carboxylated carbon nanotubes in N,N-dimethylacetamide, under the action of 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide, the carboxyl groups of the carboxylated carbon nanotubes are converted into semi-stable reactive amine esters, and then react with the amino groups on the added modified copolyamide to form stable amide bonds, grafting the modified copolyamide on the surface of the carboxylated carbon nanotubes. Utilize the good solubility of the modified copolyamide in N,N-dimethylacetamide to improve the dispersion of the carboxylated carbon nanotubes in N,N-dimethylacetamide, reduce the agglomeration of the carboxylated carbon nanotubes and reduce the phenomenon of coagulation; then by adding phosphoric acid-modified meta-aramid powder, the carboxyl groups on the surface of the modified meta-aramid powder react with the remaining amino groups on the modified copolyamide to form stable amide bonds, enabling the carbon nanotubes to adhere to the surface of the modified meta-aramid powder under the bonding action of the modified copolyamide and the adhesion ability on the surface of the modified copolyamide. By mixing the modified meta-aramid powder with the meta-aramid spinning solution, since the modified meta-aramid powder does not dissolve in the organic solvent, utilize the dispersion of the modified meta-aramid powder in the organic solvent, with the modified meta-aramid powder as the carrier, to make the modified meta-aramid powder fuse into the meta-aramid fibers, thereby compounding the carbon nanotubes with the meta-aramid fibers, enabling the carbon nanotubes to replace part of the benzene rings to form π-π bonds with the meta-aramid, reducing the easily oxidized bond positions between the benzene rings, and improving the antioxidant property of the meta-aramid fibers.

[0057] Comparative Example 1: The difference from Example 1 is that in Step 5, the modified copolyamide is not added.

[0058] Comparative Example 2: The difference from Example 1 is that in Step 5, the modified meta-aramid powder is not added.

[0059] Comparative Example 3: The difference from Example 1 is that in Step 6, the composite reinforcing nano powder is not added.

[0060] The sources of some reagents in the examples and comparative examples are as follows:

[0061] The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 10 - 15 nm and a length of less than 100 μm, and are commercially available.

[0062] p-Phenylenediamine, trimesic acid, p-aminobenzoic acid, and triphenyl phosphite are purchased from Sinopharm Chemical Reagent Co., Ltd.

[0063] The chopped meta-aramid fibers have a length of 3 - 12 mm and a density of 1.38 g / cm 3 , and are purchased from Zhongfang Special Fiber Co., Ltd.

[0064] N,N-Dimethylacetamide, pyridine, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, and N-hydroxysuccinimide are all purchased from Sigma-Aldrich.

[0065] Perform performance tests on the products obtained in Examples 1 - 3 and Comparative Examples 1 - 3. Cut the meta-aramid fibers of the same size obtained by the conventional wet spinning process in each example and comparative example into fiber bundles with a length of 100 mm, add them to a sealed container containing 40 mL of methanol, ultrasonically treat them at 60 °C for 1 h, filter the solution with a 0.45 μm filter head, and dry to obtain the test samples. Take 1 g of fiber bundles for performance tests respectively. The test method is as follows: Under the conditions of a temperature of 20 °C and a relative humidity of 65%, condition for 16 h, and use an electronic single fiber strength tester to test the breaking strength and breaking elongation of the fibers according to GB / T 14337-2008. The clamping distance is 20 mm, and the stretching speed is 20 mm / min;

[0066] Perform performance tests again after thermo-oxidative aging treatment of the fiber bundles. The method of thermo-oxidative aging treatment is as follows: Wind the fiber bundles and place them in a crucible, place the crucible in a high-temperature oven, the treatment temperature is 300 °C, and the treatment time is 500 h. After the fiber bundles are cooled, take out the fiber bundles to test the breaking strength and breaking elongation, and calculate the breaking strength retention rate and breaking elongation retention rate of the fiber bundles compared with the fiber bundles without thermo-oxidative aging treatment. The results are shown in Table 1:

[0067] Table 1

[0068] Project Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Comparative Example 3 Breaking strength cN / dtex 6.08 6.10 6.11 5.56 5.92 5.54 Elongation at break % 35.5 35.6 35.8 32.1 33.2 32.9 Retention rate of breaking strength % 68.4 68.5 68.8 56.3 63.7 58.6 Retention rate of elongation at break % 56.9 57.2 57.3 41.5 52.6 42.4

[0069] As can be seen from Table 1, the oxidation-resistant meta-aramid fiber prepared by the present invention has significantly improved breaking strength and elongation at break compared with the blank comparative example 3, and has a high retention rate of breaking strength and elongation at break after 500 h of thermal-oxidative aging, indicating that the oxidation-resistant meta-aramid fiber prepared by the present invention has good antioxidant ability; in Comparative Example 1, due to the absence of modified copolyamide, the carboxylated carbon nanotubes have insufficient dispersibility in N,N-dimethylacetamide, poor binding degree with the modified meta-aramid, low dispersion degree in the composite meta-aramid spinning solution, and agglomeration phenomenon, so the obtained oxidation-resistant meta-aramid fiber has poor mechanical properties and low oxidation resistance; in Comparative Example 2, due to the absence of modified meta-aramid powder, the binding strength with the oxidation-resistant meta-aramid fiber spun by wet spinning is low when preparing the composite meta-aramid spinning solution and it is easy to fall off, so the performance is low and the oxidation resistance is insufficient.

[0070] It should be noted that in this article, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device.

[0071] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the present invention, and the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A preparation method of oxidation-resistant meta-aramid fiber, characterized in that, It includes the following steps: Step 1: Respectively subject copolyamide and meta-aramid powder to phosphoric acid hydrolysis modification to obtain modified copolyamide and modified meta-aramid powder; Step 2: Mix carboxylated carbon nanotubes with N,N-dimethylacetamide in a reaction kettle and perform ultrasonic treatment. Add 1-ethyl-(3-dimethylaminopropyl)carbodiimide and N-hydroxysuccinimide to the reaction kettle, perform ultrasonic treatment, then add modified copolyamide, perform ultrasonic treatment and then magnetic stirring. Then add modified meta-aramid powder, perform ultrasonic treatment and then magnetic stirring. After centrifugation at a speed of 10000 rpm, wash the precipitate with ethanol, and dry to obtain composite reinforced nano powder; Step 3: Mix the composite reinforced nano powder, poly(m-phenylene isophthalamide), hydrogen chloride and N,N-dimethylacetamide to prepare a composite meta-aramid spinning solution, and use a wet spinning process to obtain oxidation-resistant meta-aramid fiber; In Step 2, the ultrasonic treatment time is 30-40 min, and the magnetic stirring time is 20-24 h; The preparation method of the copolyamide is as follows: Dissolve p-phenylenediamine, trimellitic acid and p-aminobenzoic acid in a mixed solvent of pyridine and N,N-dimethylacetamide in a reaction kettle. After complete dissolution, add triphenyl phosphite and heat to 100-110 °C under nitrogen protection and react for 3-5 h. Then slowly pour it into deionized water to obtain a polymer. Wash the polymer with absolute ethanol, reflux in hot water, and vacuum dry to obtain copolyamide.

2. The preparation method of an oxidation-resistant meta-aramid fiber according to claim 1, characterized in that, In Step 2, the dosage ratio of the carboxylated carbon nanotubes, N,N-dimethylacetamide, 1-ethyl-(3-dimethylaminopropyl)carbodiimide, N-hydroxysuccinimide, modified copolyamide and modified meta-aramid powder is 5-8 g: 100-150 mL: 3-4 mL: 5-7 mL: 3-5 g: 3-5 g; 3. The preparation method of an oxidation-resistant meta-aramid fiber according to claim 1, characterized in that, In Step 3, the mixing mass ratio of the composite reinforced nano powder, poly(m-phenylene isophthalamide), hydrogen chloride and N,N-dimethylacetamide is 3-4: 15-20: 1-4: 75-85; 4. The preparation method of an oxidation-resistant meta-aramid fiber according to claim 1, characterized in that The preparation method of the carboxylated carbon nanotubes is as follows: Take carbon nanotubes and mix them ultrasonically with a mixed acid solution in a reaction kettle for 1-2 h, heat them in a water bath to 70-80 °C, stir and condense and reflux for 1-1.5 h. After centrifugation, wash them with deionized water and dry to obtain carboxylated carbon nanotubes; The mixed acid solution is prepared by mixing 98 wt% sulfuric acid and 68 wt% nitric acid according to a molar ratio of 3:1; 5. The preparation method of an oxidation-resistant meta-aramid fiber according to claim 4, characterized in that, The dosage ratio of the carbon nanotubes and the mixed acid solution is 5-10 g: 150-170 mL; 6. The preparation method of an oxidation-resistant meta-aramid fiber according to claim 1, characterized in that, The method of phosphoric acid hydrolysis modification in Step 1 is as follows: Mix meta-aramid powder with a phosphoric acid solution 30-35 times its mass in a reaction kettle, transfer it to a high-speed disperser and mix it at a speed of 4500-5000 rpm for 5-6 min. After filtration, heat the meta-aramid powder in the reaction kettle to 100-110 °C and react for 30-40 min. Wash the meta-aramid powder with deionized water and dry to obtain modified meta-aramid powder.

7. The preparation method of an oxidation-resistant meta-aramid fiber according to claim 6, characterized in that, The meta-aramid powder is prepared by freeze-treating meta-aramid short fibers in liquid nitrogen for 5 - 7 min, then grinding them with a planetary ball mill at 500 - 600 rpm for 4 - 5 h, and separating out nano-scale powder with a screening shaker. The phosphoric acid solution is a 50 wt% aqueous phosphoric acid solution.

8. The preparation method of an oxidation-resistant meta-aramid fiber according to claim 1, characterized in that, The dosage ratio of p-phenylenediamine, trimellitic acid, p-aminobenzoic acid, pyridine, N,N-dimethylacetamide, and triphenyl phosphite is 10 - 12 g : 20 - 25 g : 13 - 15 g : 20 - 25 mL : 200 - 250 mL : 90 - 100 g.

9. An oxidation-resistant meta-aramid fiber, characterized in that, Prepared by the preparation method according to any one of claims 1 - 8.