High-strength modified meta-aramid fiber and method for preparing the same

Abstract

The application relates to the technical field of aramid, in particular to a high-strength modified meta-aramid fiber and a preparation method thereof. The application overcomes the problems of poor mechanical properties and poor ultraviolet resistance of meta-aramid fibers. In the application, MPD and DDS are used as diamine solids to react with IPC in a polymerization solvent to generate PMIA; f-BNNS is prepared by surface activation treatment of BNNS; ultraviolet-resistant nano TiO2 is prepared by surface grafting activation treatment of TiO2; PMIA, composite nano suspension and DDSM are mixed in NMP to prepare modified polymer spinning solution after defoaming; and the high-strength modified meta-aramid fiber with good mechanical properties and ultraviolet resistance is obtained after dry spraying-wet spinning, gradient cleaning, three-stage heat stretching, heat setting, heat baking and winding.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of aramid, in particular to a high-strength modified meta-aramid fiber and a preparation method thereof. BACKGROUND

[0002] The meta-aramid has a higher elongation at break due to its flexible molecular chain, and has good ductility and toughness. This characteristic makes the meta-aramid better buffer external force and reduce the phenomenon of broken ends and lint in textile processing, thereby showing higher tensile strength and tensile modulus.

[0003] However, their compressive strength and compressive modulus are much lower than the tensile properties, usually only 10-20% of the tensile strength. In aramid fibers, the highly oriented rigid molecular chains can effectively bear stress under tensile load along the fiber axis, but the molecular chains are mainly connected by hydrogen bonds and van der Waals forces, which are much weaker than the main chain covalent bond. Therefore, under compressive load, the existing meta-aramid fibers are prone to buckling or twisting of the rigid molecular chains, and the microfibril structure also tends to be unstable. The weak lateral interaction cannot effectively prevent this instability, resulting in compression failure of the material at a much lower stress than the tensile limit. At the same time, the chemical structure of aramid, especially the amide bond and benzene ring structure, is sensitive to ultraviolet light energy of a specific wavelength. Ultraviolet irradiation can cause photochemical reaction, resulting in a decrease in the strength of aramid fibers and yellowing, which severely limits the performance durability of aramid fibers.

[0004] Therefore, how to significantly improve the compression resistance and ultraviolet resistance of meta-aramid fibers while maintaining or even improving their excellent tensile properties is one of the technical problems to be solved in the field.

[0005] To this end, a high-strength modified meta-aramid fiber and a preparation method thereof are provided. SUMMARY

[0006] The present application aims to provide a high-strength modified meta-aramid fiber and a preparation method thereof, MPD and DDS as diamine solids react with IPC in a polymerization solvent to generate PMIA; f-BNNS is prepared by surface activation treatment of BNNS; ultraviolet-resistant nano-TiO2 is prepared by surface grafting activation treatment of TiO2; the PMIA, the composite nano-suspension and the DDSM are mixed in NMP, deaerated to prepare a modified polymer spinning solution, and after dry-jet wet spinning, gradient cleaning, three-stage hot stretching, heat setting, heat baking and winding, a high-strength modified meta-aramid fiber is obtained.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0008] The application provides a preparation method of high-strength modified meta-aramid fiber.

[0009] Preferably, the specific preparation method of the poly-m-phenylendiamine isophthaloyl chloride copolymer is as follows: under nitrogen protection, 80-90 parts of N-methyl pyrrolidone (NMP) is mixed with 42 parts of anhydrous lithium chloride at room temperature and a rotating speed of 200-300 rpm to prepare a polymerization solvent; in a low-temperature reactor at 0-5℃, m-phenylenediamine (MPD) and 4,4'-diamino diphenyl sulfone (DDS) are added to the polymerization solvent, and stirred for 1 h to obtain a mixed solution; 20 parts of isophthaloyl chloride (IPC) is dissolved in 40 parts of N-methyl pyrrolidone (NMP) solution to prepare an acid chloride solution; under stirring at a rotating speed of 1500-2000 rpm at 0-10℃, the acid chloride solution is added to the mixed solution at a rate of 0.3-0.5 parts / min, and after the addition is completed, the stirring (polymerization reaction) is continued for 4 h to form a reaction liquid; during the reaction, the molar ratio of the diamine solid (MPD 70%+DDS 30%) to isophthaloyl chloride (IPC) is controlled to be 1.0-1.3:1.0; the diamine solid is 70wt% of m-phenylenediamine (MPD) and 30wt% of 4,4'-diamino diphenyl sulfone (DDS); the reaction liquid is poured into deionized water for precipitation and filtration to obtain a fibrous polymer; the fibrous polymer is washed with ethanol for 3 times, and vacuum dried at 60℃ for 24 h to obtain the poly-m-phenylendiamine isophthaloyl chloride copolymer (PMIA).

[0010] Preferably, the specific preparation method of the functionalized boron nitride nanosheet (f-BNNS) is as follows: 1 part of hexagonal boron nitride powder is added into 5 parts of concentrated sulfuric acid, and ultrasonic stripping is performed under the conditions of ice bath, 200 W, and 40 kHz for 30 min. Then, 0.2 parts of 1.0-1.5 wt% potassium permanganate aqueous solution is added dropwise at a rate of 0.05 parts / min. After the dropwise addition is completed, the reaction is stirred at 30-40°C for 4 h to obtain a hydroxylated boron nitride reaction solution. The hydroxylated boron nitride reaction solution is poured into 20 parts of deionized water, and the precipitate is collected after centrifugation at 8000 rpm for 10-15 min. After freeze-drying, hydroxylated boron nitride powder (BNNS) is obtained. 1 part of the hydroxylated boron nitride powder is dispersed in 8 parts of anhydrous ethanol, and a suspension is formed after ultrasonic treatment (200 W, 30 kHz) for 30 min. After 0.15 parts of silane coupling agent γ-aminopropyl triethoxysilane (KH550) is added to the suspension, 1 part of concentrated ammonia solution (pH = 11) is added dropwise, and the reaction is refluxed at 60°C for 6 h. After the reaction is completed, centrifugation is performed at 10000 rpm for 10 min, and the solid is washed with anhydrous ethanol for 3 times. The washed solid is dispersed in 10 parts of anhydrous ethanol, ultrasonic dispersion (200 W, 40 kHz) is performed for 10 min, and freeze-drying is performed at -50°C for 24 h to obtain the functionalized boron nitride nanosheet (f-BNNS).

[0011] Preferably, the silane coupling agent is any one of γ-aminopropyl triethoxysilane (KH550), 3-glycidyloxypropyl trimethoxysilane (KH560), and 3-aminopropyl trimethoxysilane (APTS).

[0012] Preferably, the specific preparation method of the ultraviolet-resistant nano-TiO2 is as follows: 1 part of 20-50 nm titanium dioxide powder (TiO2) is dispersed in 5 parts of deionized water, and ultrasonic treatment (200 W, 40 kHz) is performed for 30 min. Then, 0.5 parts of 1M concentrated hydrochloric acid is added, and the mixture is stirred at 80°C for 2 h. After centrifugation (8000 rpm, 10 min), the precipitate is washed with deionized water until neutral, and freeze-drying is performed to obtain activated TiO2. 1 part of the activated TiO2 is dispersed in 8 parts of anhydrous ethanol, and ultrasonic dispersion (200 W, 30 kHz) is performed for 30 min. Then, 0.10-0.20 parts of γ-mercaptopropyl trimethoxysilane (KH590) is added dropwise at a rate of 0.05 parts / min, and 0.3-0.5 parts of concentrated hydrochloric acid (37 wt%) is added to adjust the pH of the system to 4.0-5.0. The reaction is refluxed at 60°C for 6 h. After the reaction is completed, centrifugation is performed (10000 rpm, 10 min), and the precipitate is collected. The precipitate is washed with anhydrous ethanol and deionized water alternately for 3 times. The washed solid is dispersed in 5 parts of anhydrous ethanol, ultrasonic treatment (200 W, 30 kHz) is performed for 10 min, and freeze-drying is performed at -50°C for 24 h to obtain the ultraviolet-resistant nano-TiO2.

[0013] Preferably, the specific preparation method of the composite nanosuspension is as follows: 0.3-0.8 parts of functionalized boron nitride nanosheet (f-BNNS), 0.5-1.0 parts of UV-resistant nano-TiO2, and 15-20 parts of N-methyl pyrrolidone (NMP) are stirred at a speed of 800 rpm for 30 min to obtain a preliminary dispersion solution; the preliminary dispersion solution is sheared and dispersed by a high-shear dispersion emulsifier at a speed of 8000-12000 rpm for 1.5-2.0 h at 30°C; and after the dispersion is completed, the composite nanosuspension is obtained by centrifugal separation (5000 rpm, 10 min).

[0014] Preferably, the specific preparation method of the modified polymer spinning solution is as follows: 15 parts of the composite nanosuspension is added to 25-30 parts of poly-m-phenylene isophthalamide copolymer (PMIA) and 100 parts of N-methyl pyrrolidone (NMP) at a rate of 1.0 parts / min under nitrogen protection, followed by the addition of 0.35-0.40 parts of flexible crosslinking comonomer, stirring at a speed of 1200-1500 rpm for 2 h at 55-70°C to obtain a modified copolymer solution; the modified copolymer solution is degassed at 0.08-0.10 MPa and a speed of 200-300 rpm for 10 min to obtain a modified polymer spinning solution with a viscosity of 8000-12000 mPa·s; the flexible crosslinking comonomer is 4,4'-diaminodiphenyl methane (DDSM).

[0015] Preferably, the specific preparation method of the high-strength modified meta-aramid fiber is as follows: the modified polymer spinning solution is pressed into a spinneret (pore size: 100 μm) by a gear pump at a flow rate of 1.0-1.5 parts / min, extruded under an extrusion pressure of 0.2-0.5 MPa, and immediately enters a 40°C constant-temperature air bath, the air bath zone has a length of 10 cm, the stretching air flow speed is 1.0-1.3 m / s, the humidity is maintained at 40-60% RH, and the residence time is 0.5-2.0 s to form a surface gel fiber; the surface gel fiber is immersed in a 12-15 wt% N-methyl pyrrolidone (NMP) aqueous solution coagulation bath, the coagulation bath temperature is 25°C, phase separation occurs through the double diffusion of solvent (NMP)-non-solvent (deionized water), NMP is extracted into water, and the polymer coagulates into a coagulation fiber; the coagulation fiber is washed by three-stage countercurrent water washing tanks, and gradient cleaning is performed using 60-70°C deionized water (first-stage water washing: 60°C deionized water, flow rate 2 L / min, residence time 40 s; second-stage water washing: 70°C deionized water, flow rate 3 L / min, residence time 30 s; third-stage water washing: 70°C deionized water, 40 kHz ultrasonic assistance, flow rate 4 L / min, residence time 20 s), and the residual NMP content of the fiber after washing is ≤30 ppm.

[0016] After washing, the fibers (50 μm in diameter) were subjected to three-stage thermal drawing (first-stage drawing: drawing in a 95℃ hot water bath at a drawing rate of 10 m / min, with a drawing ratio of 2.5; second-stage drawing: drawing by a hot roller (surface lubricated with silicon oil) at 285℃ at a drawing rate of 15 m / min, with a drawing ratio of 2.0; third-stage drawing: drawing by a hot plate (under nitrogen protection) at 300℃ at a drawing rate of 20 m / min, with a drawing ratio of 1.5;), to obtain drawn fibers with a diameter of 15 μm;

[0017] The drawn fibers were subjected to heat setting treatment in a 320℃ tubular furnace (under nitrogen protection) at a draw ratio of 1.05 for 90-120 s, and then were subjected to heat drying at 80℃ for 10 min, and were wound by a winder at a tension of 0.5-1.0 cN / dtex and a linear velocity of 25 m / min, to obtain high-strength modified meta-aramid fibers.

[0018] In another aspect, the present application provides a high-strength modified meta-aramid fiber, which is prepared by the preparation method according to any one of the above.

[0019] Unless otherwise specified, the "parts" mentioned in the present application are "parts by weight".

[0020] Compared with the prior art, the present application has the following beneficial effects:

[0021] 1. By precisely controlling the solvent polarity, monomer composition, reaction temperature, feeding rate, stirring intensity and molar ratio in the polymerization stage, the preparation of a high-molecular-weight, high-regularity copolymer PMIA is realized. The introduction of the composite nano-suspension and 4,4'-diaminodiphenyl methane in the modified polymer spinning solution and the subsequent specific dry-jet wet spinning and three-stage thermal drawing process form multiple synergistic effects, which not only ensure the high axial orientation of the molecular chain, but also significantly improve the compactness and perfection of the crystalline region in the fiber, ultimately endowing the high-strength modified meta-aramid fiber with excellent tensile properties.

[0022] 2. In the preparation of f-BNNS, the active groups in the silane coupling agent react with the hydroxyl groups on the surface of the hydroxylated boron nitride to graft organic functional groups, and the generated f-BNNS enhances the chemical bonding effect with the PMIA matrix, improving the dispersity and compatibility within the modified polymer spinning solution; in the preparation of the ultraviolet-resistant nano-TiO2, the mercapto groups of KH590 are grafted on the surface of TiO2, serving as a free radical trapping agent, and after activation by hydrochloric acid and precise pH control, the modified nano-TiO2 with good ultraviolet resistance is generated; in the preparation of the composite nano-suspension, the f-BNNS and the ultraviolet-resistant nano-TiO2 are high-shear dispersed in NMP in a certain proportion, and the high-strength modified meta-aramid fiber prepared by blending with the PMIA matrix and DDSM, spinning, and subsequent treatment processes still maintains good ultraviolet resistance in a high-energy radiation environment.

[0023] 3. The composite nano-suspension is added into PMIA and NMP at a specific rate, while flexible cross-linking comonomer DDSM is added, and the reaction is carried out under specific temperature control and stirring; the nanoparticles are uniformly dispersed in the PMIA matrix to form a physical reinforcing network; the DDSM forms flexible segments and cross-linking structures between molecular chains; and then defoaming is carried out to prepare a uniform and stable modified polymer spinning solution. The modified polymer spinning solution is subjected to spinning and post-processing processes, which further promotes the high orientation of molecular chains and nanoparticles and the densification of the fiber structure in the modified meta-aramid fiber. The highly ordered and dense structure, as well as the synergistic enhancement of the modified polymer matrix by nanoparticles and DDSM, makes the high-strength modified meta-aramid fiber not prone to mass loss when facing friction; when facing chemical corrosion, it can effectively resist solvent penetration and molecular chain degradation, thereby maintaining high friction resistance and chemical corrosion resistance.

[0024] 4. The synergistic effect between post-processing processes significantly improves the compressive strength and compressive modulus of the high-strength modified meta-aramid fiber. On the one hand, the NMP concentration in the coagulation bath slows down the phase separation process, allowing the polymer chains to arrange regularly and form a uniform and dense initial condensed state structure of the fiber; on the other hand, high-temperature heat setting not only enhances the orientation degree and crystallinity of the macromolecular chains within the fiber, but also creates conditions for cross-linking reactions between the DDSM and PMIA macromolecular segments, thereby strengthening the chemical network cross-linking effect; at the same time, the nanoparticles in the composite nano-suspension have a physical reinforcing effect. In addition, fine adjustment of the spinning stage parameters and appropriate winding tension also play a key role in the formation and maintenance of the structure of the high-strength modified meta-aramid fiber, ultimately significantly improving the ability of the high-strength modified meta-aramid fiber to resist compressive deformation. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 Effect diagram of the ability of the high-strength modified meta-aramid fiber of the present application examples 10-12 and comparative examples 17-20 to resist compressive deformation. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0027] Please refer to Figure 1 The present application provides a high-strength modified meta-aramid fiber and a preparation method thereof, and the technical solutions are as follows:

[0028] The substances involved in the present application are as follows:

[0029] M-phenylenediamine CAS: 108-45-2; 4,4'-diaminodiphenyl sulfone CAS: 80-08-0; isophthaloyl dichloride CAS: 99-63-8; N-methyl pyrrolidone CAS: 872-50-4; potassium permanganate CAS: 7722-64-7; gamma-aminopropyl triethoxysilane CAS: 919-30-2; 3-glycidyloxypropyl trimethoxysilane CAS: 2530-83-8; 3-aminopropyl trimethoxysilane CAS: 13822-56-5; gamma-mercaptopropyl trimethoxysilane CAS: 4420-74-0; hexagonal boron nitride powder (30 nm) purchased from Qingdao Huabang Nanometer Technology Co., Ltd.

[0030] Example 1

[0031] Under the protection of nitrogen, 90 parts of N-methyl pyrrolidone (NMP) was mixed with 42 parts of anhydrous lithium chloride at room temperature and a stirring speed of 200 rpm to prepare a polymerization solvent; 10.58 parts of m-phenylenediamine (MPD) and 4.54 parts of 4,4'-diaminodiphenyl sulfone (DDS) were added to the polymerization solvent in a 0°C low-temperature reactor, and stirred for 1 h to obtain a mixed solution; 20 parts of isophthaloyl dichloride (IPC) was dissolved in 40 parts of N-methyl pyrrolidone (NMP) solution to prepare an acid chloride solution; the acid chloride solution was added to the mixed solution at a rate of 0.5 parts / min under stirring at a speed of 2000 rpm at 5°C, and after the addition was completed, the stirring (polymerization reaction) was continued for 4 h to form a reaction liquid; the molar ratio of the diamine solid (MPD 70% + DDS 30%) to isophthaloyl dichloride (IPC) was controlled to be 1.1:1.0 during the reaction; the diamine solid was 70 wt% of m-phenylenediamine (MPD) and 30 wt% of 4,4'-diaminodiphenyl sulfone (DDS); the reaction liquid was poured into deionized water for precipitation and filtration to obtain a fibrous polymer; the fibrous polymer was washed with ethanol for 3 times and vacuum dried at 60°C for 24 h to obtain a poly-m-phenylenediamine isophthaloyl diamine copolymer (PMIA).

[0032] 1 part of hexagonal boron nitride powder was added to 5 parts of concentrated sulfuric acid, and after ultrasonic exfoliation in an ice bath at 200 W and 40 kHz for 30 min, 0.2 parts of a 1.5 wt% potassium permanganate aqueous solution was added at a rate of 0.05 parts / min, and after the addition was completed, the stirring reaction was continued at 30°C for 4 h to obtain a hydroxylated boron nitride reaction liquid; the hydroxylated boron nitride reaction liquid was poured into 20 parts of deionized water, and after centrifugation at a speed of 8000 rpm for 10 min, the precipitate was collected and freeze-dried to obtain a hydroxylated boron nitride powder;

[0033] Disperse 1 part of hydroxylated boron nitride powder in 8 parts of absolute ethanol, and ultrasonicate for 30 min under the condition of 200 W and 30 kHz to form a suspension; add 0.15 parts of silane coupling agent γ-aminopropyl triethoxysilane (KH550) to the suspension, and then drop 1 part of concentrated ammonia (pH = 11), and reflux at 60°C for 6 h; after the reaction is completed, centrifuge at 10,000 rpm for 10 min and wash with absolute ethanol for 3 times; disperse the washed solid precipitate in 10 parts of absolute ethanol, ultrasonicate for 10 min (200 W, 40 kHz), and freeze-dry (-50°C, 24 h) to obtain functionalized boron nitride nanosheets (f-BNNS).

[0034] Disperse 1 part of 20 nm titanium dioxide powder (TiO2) in 5 parts of deionized water, and ultrasonicate for 30 min (200 W, 40 kHz); add 0.5 parts of 1M concentrated hydrochloric acid, and stir at 80°C for 2 h; after centrifugation (8000 rpm, 10 min), wash with deionized water until neutral, and freeze-dry to obtain activated TiO2; disperse 1 part of the activated TiO2 in 8 parts of absolute ethanol, and ultrasonicate for 30 min (200 W, 30 kHz); drop 0.20 parts of γ-mercaptopropyl trimethoxysilane (KH590) at a rate of 0.05 parts / min, and then add 0.3 parts of concentrated hydrochloric acid to adjust the pH of the system to 5.0, and reflux at 60°C for 6 h; after the reaction is completed, centrifuge (10000 rpm, 10 min) and collect the precipitate, and wash with absolute ethanol and deionized water alternately for 3 times; disperse the washed solid in 5 parts of absolute ethanol, ultrasonicate for 10 min (200 W, 30 kHz), and freeze-dry (-50°C, 24 h) to obtain ultraviolet-resistant nano-TiO2.

[0035] Disperse 0.8 parts of functionalized boron nitride nanosheets (f-BNNS), 0.5 parts of ultraviolet-resistant nano-TiO2, and 20 parts of N-methyl pyrrolidone (NMP) at a rotation speed of 800 rpm for 30 min to obtain a preliminary dispersion solution; use a high-shear dispersion emulsifier to shear disperse the preliminary dispersion solution at a rotation speed of 8000 rpm and a temperature of 20-40°C for 2.0 h; after the dispersion is completed, centrifuge (5000 rpm, 10 min) to obtain a composite nanosuspension.

[0036] Under nitrogen protection, 15 parts of the composite nano-suspension was added into 25 parts of poly-m-phenylene isophthalamide (PMIA) and 100 parts of N-methyl pyrrolidone (NMP) at a rate of 1.0 parts / min, followed by the addition of 0.35 parts of flexible crosslinking comonomer, stirring at 55°C for 2h at a speed of 1500 rpm to obtain a modified copolymer solution; the modified copolymer solution was subjected to defoaming treatment at 0.08 MPa and a speed of 300 rpm for 10 min to obtain a modified polymer spinning solution; the flexible crosslinking comonomer was 4,4'-diaminodiphenyl methane (DDSM).

[0037] The modified polymer spinning solution was pressed into a spinneret (pore diameter: 100 μm) by a gear pump at a flow rate of 1.0 parts / min, extruded under an extrusion pressure of 0.5 MPa and immediately entered a constant-temperature air bath at 40°C, the air bath zone had a length of 10 cm, the stretching air flow rate was 1.3 m / s, the humidity was maintained at 50% RH, and the residence time was 2.0 s to form a surface gel fiber; the surface gel fiber was immersed in a 15 wt% N-methyl pyrrolidone (NMP) aqueous solution coagulation bath at a temperature of 25°C, and phase separation occurred by double diffusion of the solvent (NMP)-non-solvent (deionized water), NMP was extracted into water, and the polymer was coagulated into a coagulation fiber; the coagulation fiber was subjected to three-stage countercurrent water washing tanks, and gradient cleaning was performed using deionized water at 60-70°C (first-stage water washing: deionized water at 60°C, flow rate 2 L / min, residence time 40 s; second-stage water washing: deionized water at 70°C, flow rate 3 L / min, residence time 30 s; third-stage water washing: deionized water at 70°C, 40 kHz ultrasonic assistance, flow rate 4 L / min, residence time 20 s), and the residual NMP content of the fiber after washing was ≤30 ppm;

[0038] The fiber (diameter: 50 μm) after washing was subjected to three-stage heat stretching (first-stage stretching: stretching in a 95°C hot water bath at a stretching rate of 10 m / min, stretching multiple: 2.5 times; second-stage stretching: stretching by a hot roller (surface lubricated with silicone oil) at a stretching rate of 15 m / min, stretching multiple: 2.0 times; third-stage stretching: stretching by a hot plate (under nitrogen protection) at a stretching rate of 20 m / min, stretching multiple: 1.5 times); and a stretched fiber with a diameter of 15 μm was obtained.

[0039] The stretched fiber was subjected to treatment in a 320°C tubular furnace (under nitrogen protection) at a draft ratio of 1.05 for 120 s, and then subjected to heat drying at 80°C for 10 min, and then wound up by a winder at a tension of 0.5 cN / dtex and a linear speed of 25 m / min to obtain a high-strength modified meta-aramid fiber.

[0040] Examples 2-4

[0041] The preparation method and parameters of Example 1 were used as reference, with the specific differences shown in Table 1; NMP in Table 1 is N-methyl pyrrolidone; mixed rotation speed is the rotation speed of the preparation of the polymerization solvent; temperature one is the low-temperature reactor temperature; temperature two and stirring speed are the temperature and stirring speed during the preparation of the reaction solution; drop rate is the drop rate of the acyl chloride solution; diamine solid is 70 wt% m-phenylenediamine (MPD) and 30 wt% 4,4'-diaminodiphenyl sulfone (DDS); and IPC is m-phthaloyl dichloride.

[0042] Comparative Example 1

[0043] The preparation method and parameters of Example 4 were used as reference, except that anhydrous calcium chloride was used instead of anhydrous lithium chloride in the polymerization solvent.

[0044] Comparative Example 2

[0045] The preparation method and parameters of Example 4 were used as reference, except that the diamine solid was 50 wt% m-phenylenediamine (MPD) and 50 wt% 4,4'-diaminodiphenyl sulfone (DDS).

[0046] Comparative Example 3

[0047] The preparation method and parameters of Example 4 were used as reference, except that the molar ratio of the diamine solid (MPD 70% + DDS 30%) to m-phthaloyl dichloride (IPC) was controlled to be 0.8:1.0 during the reaction.

[0048] Comparative Example 4

[0049] The preparation method and parameters of Example 4 were used as reference, except that the acyl chloride solution was added to the mixed solution at a rate of 1.0 parts / min.

[0050] Comparative Example 5

[0051] The preparation method and parameters of Example 4 were used as reference, except that the reaction of the reaction solution in the low-temperature reactor (temperature one) was replaced by reaction at room temperature.

[0052] Comparative Example 6

[0053] The preparation method and parameters of Example 4 were used as reference, except that m-phthaloyl dichloride (IPC) was dissolved in anhydrous ethanol solution to prepare the acyl chloride solution.

[0054] Test Example 1: Mechanical Property Test

[0055] The tensile strength and tensile modulus of the sample were tested by an electronic universal testing machine; according to the ASTM D638 standard, the sample was cut into dumbbell shape (thickness 0.5 mm, gauge length 25 mm), after equilibrating at 25℃, 50% humidity for 24 h, the tensile test was carried out at a rate of 5 mm / min; the specific test results are shown in Table 2.

[0056] Table 1 Parameters of Examples 1-4 and Comparative Examples 1-6

[0057]

[0058]

[0059] Table 2 Mechanical property test of Examples 1-4 and Comparative Examples 1-6

[0060]

[0061] As shown in Table 2, the tensile strength of Examples 1-4 is higher than 7.3 cN / dtex, and the tensile modulus is greater than 445 cN / dtex; this shows that the high-strength modified meta-aramid fiber prepared has good tensile properties. In Comparative Example 1, the anhydrous lithium chloride in the polymerization solvent is replaced by anhydrous calcium chloride; because the coordination ability of calcium chloride is weak, and its solubility in NMP solution is poorer than that of anhydrous lithium chloride, the ionic strength of the polymerization solvent and the mixed solution decreases; the polymer chains precipitate in the reaction solution in advance, forming fibrous polymers with uneven molecular weight distribution. This structural defect reduces the uniformity of the modified polymer spinning solution, and micro-pore defects are easily produced in the dry-jet wet spinning process, ultimately resulting in a decrease in the tensile strength and tensile modulus of the modified meta-aramid fiber produced. In Comparative Example 2, the solid diamine is adjusted to 50wt% MPD and 50wt% DDS, and the proportion of DDS is increased; the introduction of too many rigid sulfonyl groups in the mixed solution hinders the movement of the chain segments, and the polymer chains are loosely packed in the polymerization reaction, resulting in a loose structure of the fibrous polymer produced, which reduces the crystallinity of the modified polymer spinning solution; the stress transfer efficiency is reduced in the subsequent spinning and stretching process, and the tensile strength and tensile modulus of the modified meta-aramid fiber obtained are reduced. In Comparative Example 3, the molar ratio of the solid diamine (MPD 70% + DDS 30%) to IPC is 0.8:1.0, which results in an excess of IPC and a deficiency of solid diamine, causing the polymerization reaction to terminate prematurely, and an oligomer terminated by acyl chloride groups is produced, and the molecular weight of the fibrous polymer obtained is significantly reduced; the low-molecular-weight fibrous polymer cannot form effective physical entanglement points and regular molecular chain structures, and the performance of PMIA is poor, and the strength and modulus of the modified meta-aramid fiber obtained by spinning are also greatly reduced.

[0062] The reaction system in Comparative Example 4 has a too fast dropping speed of the acyl chloride solution, which results in a too high local concentration of the acyl chloride monomer, a violent and uncontrollable heat release of the polymerization reaction, a hydrolysis and crosslinking of most of the acyl chloride, a large amount of gel, an impeded forward reaction, a non-uniform generated fibrous polymer and PMIA, a reduced spinnability of the modified polymer spinning solution, an increased internal defect of the prepared modified meta-aramid fiber, and a reduced tensile strength and modulus of the modified meta-aramid fiber.

[0063] In Examples 1-4, the regularity and crystallinity of the poly-m-phenylene isophthalamide copolymer are ensured by precisely controlling the polar coordination environment of the polymerization system, the monomer ratio and the reaction kinetics. The NMP / lithium chloride polymerization solvent system inhibits hydrogen bonding aggregation by strong polarity, and makes the diamine monomers of MPD (70%) and DDS (30%) uniformly dispersed at a low temperature of 0-5°C to have a high-efficiency interfacial polycondensation reaction with the acyl chloride groups of isophthaloyl chloride (IPC). A suitable dropping speed combined with high-speed stirring can avoid the hydrolysis of acyl chloride caused by a too high local concentration, and promote the directional growth of the molecular chain to form a high-molecular-weight polymer. The precise control of the diamine / acyl chloride molar ratio ensures the balance of the chain end groups, reduces the termination reaction, and improves the polymerization degree. The subsequent spinning stage uses a dry-jet-wet spinning combined with a three-stage heat stretching process to further induce the axial orientation of the molecular chain, and the synergistic effect of the composite nano-suspension and 4,4'-diaminodiphenyl methane enhances the compactness of the internal crystalline region of the fiber. The finally prepared high-strength modified meta-aramid fiber has a strong tensile property.

[0064] Examples 5-8

[0065] The preparation method and parameter conditions of Example 6 were referred to, and the specific differences are shown in Table 3; the stirring temperature and centrifugal time in Table 3 are the stirring temperature and centrifugal time in the process of preparing the hydroxylated boron nitride powder; KH590 is γ-mercaptopropyltrimethoxysilane; f-BNNS in Table 4 is functionalized boron nitride nanosheet; and NMP is N-methyl pyrrolidone.

[0066] Comparative Example 7

[0067] The preparation method and parameter conditions of Example 8 were referred to, except that no silane coupling agent was added when preparing f-BNNS, and the f-BNNS was directly washed with ethanol and then freeze-dried.

[0068] Comparative Example 8

[0069] The preparation method and parameter conditions of Example 8 were referred to, except that γ-mercaptopropyltrimethoxysilane (KH590) was replaced by tetraethyl orthosilicate (TEOS) in the preparation of the ultraviolet-resistant nano-TiO2.

[0070] Comparative Example 9

[0071] The preparation method and parameter conditions of Example 8 were referred to, except that the concentration of the potassium permanganate aqueous solution was increased to 3.0wt% in the preparation of f-BNNS.

[0072] Comparative Example 10

[0073] The preparation method and parameter conditions of Example 8 were referred to, except that the ultraviolet-resistant nano-TiO2 was replaced by ordinary TiO2 powder (30nm).

[0074] Comparative Example 11

[0075] The preparation method and parameter conditions of Example 8 were referred to, except that the washing step was omitted in the preparation of the ultraviolet-resistant nano-TiO2.

[0076] Comparative Example 12

[0077] The preparation method and parameter conditions of Example 8 were referred to, except that 1.5 parts of f-BNNS and 0.2 parts of ultraviolet-resistant nano-TiO2 were added in the preparation of the composite nanosuspension.

[0078] Test Example 2: Ultraviolet Resistance Test

[0079] The tensile strength and elongation at break of the sample before irradiation were tested by using an electronic universal testing machine; after the sample was irradiated in a QUV accelerated aging test machine (ultraviolet irradiance was set to 0.71W / m2 / nm at a wavelength of 340nm, and the cumulative irradiation time was 100h), the tensile strength and elongation at break of the sample after irradiation were measured by using an electronic universal testing machine; the tensile strength retention rate and elongation at break retention rate of the sample were calculated; and the specific test results are shown in Table 4.

[0080] Table 3 Preparation parameters of Examples 4-8 and Comparative Examples 7-12

[0081]

[0082]

[0083] Table 4 Preparation parameters and UV resistance performance test of Examples 4-8, Comparative Examples 7-12

[0084]

[0085] As shown in the data of Table 4, the retention rates of tensile strength and elongation at break of the high-strength modified meta-aramid fibers prepared in Examples 4-8 are all higher than 86.0% and 78.0%, respectively, after the QUV accelerated aging test; this indicates that the UV resistance performance of the meta-aramid fibers is effectively improved by adding the composite nano-suspension to the PMIA matrix in Examples 5-8, and the high-strength modified meta-aramid fibers prepared have good UV resistance performance.

[0086] In Comparative Example 7, no silane coupling agent is added during the preparation of f-BNNS, which results in that the surface of the hydroxylated boron nitride powder is not grafted with amino groups, and the BNNS cannot form a strong interfacial bond with the aramid matrix through the bridging action of the silane coupling agent; the stability of the generated f-BNNS is reduced, which causes the interfacial compatibility of the composite nano-suspension with PMIA to decrease significantly, the f-BNNS is not uniformly dispersed in the PMIA matrix, micro defects are generated during the spinning process, and the UV resistance performance (retention rates of tensile strength and elongation at break) of the finally prepared modified meta-aramid fiber is reduced. In Comparative Example 8, KH590 is replaced by TEOS during the preparation of the UV-resistant nano-TiO2; after the hydrolysis of TEOS, an inorganic silica layer is mainly formed on the surface of TiO2, and this coating does not have the mercapto group (UV-resistant functional group) possessed by KH590; therefore, it cannot effectively capture high-energy free radicals generated by radiation, so as to fail to play a role in protecting the PMIA matrix, which results in that the UV resistance performance of the finally prepared modified meta-aramid fiber is reduced. In Comparative Example 9, the concentration of the potassium permanganate aqueous solution is increased to 3.0 wt% during the preparation of f-BNNS; a high concentration of potassium permanganate will excessively oxidize boron nitride, not only introducing excessive hydroxyl groups, but also damaging the two-dimensional sheet structure of BNNS, causing the size of f-BNNS to decrease and the defects to increase; thus, the mechanical properties of BNNS itself and the reinforcing effect of f-BNNS in the PMIA matrix are weakened, which causes the mechanical properties and UV resistance performance of the modified meta-aramid fiber to be reduced simultaneously.

[0087] Comparative Example 10 replaces the UV-resistant nano-TiO2 with ordinary TiO2 powder; the ordinary TiO2 powder without surface modification treatment lacks thiol and other UV-resistant functional groups, and cannot effectively capture radiation-induced free radicals, and cannot provide radiation protection for the PMIA matrix; on the contrary, it will become a stress concentration point in the aggregation process, thereby reducing the mechanical properties and UV resistance of the modified meta-aramid fiber. Comparative Example 11 omits the washing step in the preparation of UV-resistant nano-TiO2, resulting in the failure to remove impurities such as unreacted KH590, hydrolysis byproducts, and hydrochloric acid used to adjust the pH in the system after the reaction; these substances not only adsorb on the surface of TiO2 to hinder the progress of the reaction, but also seriously affect the UV resistance of the UV-resistant nano-TiO2; in the subsequent polymerization reaction of the UV-resistant nano-TiO2 and the PMIA matrix and the spinning process, it catalyzes the degradation of PMIA, resulting in a simultaneous decrease in the mechanical properties and UV resistance of the modified meta-aramid fiber ultimately prepared. In Comparative Example 12, the amount of f-BNNS is too high in the preparation of the composite nano-suspension, and self-aggregation occurs, resulting in a too high viscosity of the composite nano-suspension, which cannot be uniformly dispersed in the shearing process; and the amount of UV-resistant nano-TiO2 is insufficient, which weakens the UV resistance of the composite nano-suspension; ultimately resulting in a simultaneous decrease in the UV resistance and mechanical properties of the modified meta-aramid fiber prepared by spinning after the polymerization of the composite nano-suspension with PMIA and DDSM.

[0088] Examples 4-8 from the surface chemical design of nanoparticles to the optimization of macroscopic composite process, multi-scale cooperation makes the high-strength modified meta-aramid fiber have excellent UV resistance. In the preparation of f-BNNS, the active groups in the silane coupling agent react with the hydroxyl groups on the surface of hydroxylated boron nitride to graft organic functional groups, and the generated f-BNNS enhances the chemical bonding effect with the PMIA matrix, and improves the dispersity and compatibility within the modified polymer spinning solution; in the preparation of UV-resistant nano-TiO2, the thiol groups of KH590 are grafted on the surface of TiO2 to act as a free radical trapping agent, and after activation by hydrochloric acid and accurate pH control, modified nano-TiO2 with good UV resistance is generated; in the preparation of the composite nano-suspension, f-BNNS and UV-resistant nano-TiO2 are proportionally dispersed in NMP by high shear, and the high-strength modified meta-aramid fiber prepared by blending with the PMIA matrix and DDSM, spinning, and subsequent treatment process still maintains good UV resistance in a high-energy radiation environment.

[0089] Examples 9-10

[0090] The preparation method and parameters of Reference Example 8 are referred to, and the specific differences are shown in Table 5; in Table 5, PMIA is poly-m-phenylene isophthalamide copolymer; DDSM is flexible crosslinking comonomer 4,4'-diaminodiphenyl methane; temperature three and stirring speed are the temperature and stirring speed in the preparation process of the modified copolymer solution.

[0091] Comparative Example 13

[0092] The preparation method and parameters of Example 10 were referred to, except that no composite nano-suspension was added in the preparation of the modified polymer spinning solution.

[0093] Comparative Example 14

[0094] The preparation method and parameters of Example 10 were referred to, except that no 4,4'-diaminodiphenyl methane (DDSM) was added in the preparation of the modified polymer spinning solution.

[0095] Comparative Example 15

[0096] The preparation method and parameters of Example 10 were referred to, except that the composite nano-suspension and flexible crosslinking comonomer were directly added into PMIA and NMP in the preparation of the modified polymer spinning solution.

[0097] Comparative Example 16

[0098] The preparation method and parameters of Example 10 were referred to, except that the modified copolymer solution was not subjected to defoaming treatment in the preparation of the modified polymer spinning solution.

[0099] Stability performance test of Test Example 3

[0100] Friction resistance performance test: using a Martindale abrasion tester, the sample was subjected to 1000 cycles of friction test under a fixed pressure (9 kPa), and the mass after 1000 cycles of abrasion was recorded, and the mass loss rate (%) was calculated;

[0101] Chemical corrosion resistance performance test: using an electronic universal testing machine, the initial tensile strength and elongation at break of the sample were tested; the sample was immersed in 5wt% acetone solvent, and after soaking at 25°C for 72 hours, the tensile strength and elongation at break were measured again; the mechanical property retention rate of the sample was calculated, and the mechanical property retention rate was the retention percentage of the tensile strength and elongation at break; the specific test results are shown in Table 6.

[0102] Table 5 Preparation parameters of Examples 8-10 and Comparative Examples 13-16

[0103]

[0104] Table 6 Stability performance test of Examples 8-10 and Comparative Examples 13-16

[0105]

[0106]

[0107] As shown in the data of Table 6, the mass loss rates of Examples 8-10 are all less than 5.0%, and the mechanical property retention rates are all higher than 83.5%; this shows that the prepared high-strength modified meta-aramid fibers have good friction resistance and chemical corrosion resistance. In Comparative Example 13, no composite nano-suspension is added in the preparation of the modified polymer spinning solution; this results in the lack of nano-scale reinforcing phase in the modified polymer spinning solution, and the flexible crosslinking comonomer DDSM cannot provide sufficient mechanical strength for PMIA, the physical crosslinking and interface reinforcing effect of the modified meta-aramid fiber formed after the spinning, stretching and other post-processing steps are weakened; this makes the surface of the modified meta-aramid fiber easy to peel off and wear during friction, and the mass loss rate increases; at the same time, the modified meta-aramid fiber is more susceptible to chemical corrosion, causing the breakage and swelling of the macromolecular chains, and leading to the decrease of the mechanical property retention rate. In Comparative Example 14, no DDSM is added in the preparation of the modified polymer spinning solution; the crosslinking density between the PMIA molecular chains and the composite nano-suspension is insufficient; the modified polymer spinning solution formed lacks effective crosslinking points and flexible buffers during spinning and stretching, so that the modified meta-aramid fiber is easy to produce cracks and expand under the action of friction, and cannot effectively disperse stress and prevent the deepening of the corrosion medium during chemical corrosion, resulting in the decrease of the wear resistance and corrosion resistance. In Comparative Example 15, the composite nano-suspension and DDSM are directly and completely added to PMIA and NMP in the preparation of the modified polymer spinning solution; this one-time rapid addition method causes the nano-particles to compete with DDSM for adsorption on the PMIA molecular chains, induces the aggregation of the modified polymer spinning solution, and the reaction is uneven; the aggregation of the nano-particles weakens the reinforcing effect of the nano-particles in the PMIA matrix, and the excessive accumulation of DDSM hinders the uniformity of the crosslinking reaction, finally resulting in the uneven viscosity of the spinning solution; the surface gel fiber is not completely phase-separated in the coagulation bath, the internal defects increase, the modified meta-aramid fiber is easy to produce micro-cracks when subjected to friction, the mass loss rate increases, and the mechanical properties decrease after chemical corrosion. In Comparative Example 16, the modified copolymer solution is not subjected to defoaming treatment in the preparation of the modified polymer spinning solution; the bubbles remaining in the generated spinning solution are converted into holes and defects in the fiber during the subsequent spinning and fiber formation processes. These holes and defects not only reduce the effective bearing area of the modified meta-aramid fiber, making it easy to break at the defects when subjected to stress, and increasing the mass loss rate; but also provide a penetration channel for the chemical corrosion medium, accelerating the destruction of the molecular chain structure of the modified meta-aramid fiber, and decreasing the mechanical property retention rate after chemical corrosion.

[0108] Embodiment 8-10 The composite nano-suspension is added into PMIA and NMP at a specific rate, while flexible cross-linking comonomer DDSM is added, and the reaction is carried out under specific temperature control and stirring; the nanoparticles are uniformly dispersed in the PMIA matrix to form a physical reinforcing network; the flexible chain segment and cross-linking structure are formed between the molecular chains of DDSM; and then defoaming is carried out to prepare a uniform and stable modified polymer spinning solution. The modified polymer spinning solution is subjected to spinning and post-treatment processes, which further promotes the high orientation of the molecular chains and nanoparticles and the densification of the fiber structure in the modified meta-aramid fiber. This highly ordered and dense structure, as well as the synergistic enhancement of the modified polymer matrix by nanoparticles and DDSM, makes the high-strength modified meta-aramid fiber not prone to mass loss when subjected to friction; when subjected to chemical corrosion, it can effectively resist solvent penetration and molecular chain degradation, thereby maintaining high friction resistance and chemical corrosion resistance.

[0109] Embodiment 11-12

[0110] Referring to the preparation method and parameter conditions of Embodiment 10, the specific differences are shown in Table 7; in Table 7, the flow rate is the flow rate of the modified polymer spinning solution through the gear pump into the spinneret.

[0111] Comparative Example 17

[0112] Referring to the preparation method and parameter conditions of Embodiment 12, except that the dry-jet wet spinning (air bath + coagulation bath) is replaced by single coagulation bath spinning, i.e., the modified polymer spinning solution is directly extruded and immersed in a 25°C deionized water coagulation bath to coagulate into a coagulated fiber.

[0113] Comparative Example 18

[0114] Referring to the preparation method and parameter conditions of Embodiment 12, except that the gradient cleaning process of the coagulated fiber is omitted.

[0115] Comparative Example 19

[0116] Referring to the preparation method and parameter conditions of Embodiment 12, except that the three-stage heat stretching is replaced by one-step heat stretching (300°C hot plate stretching).

[0117] Comparative Example 20

[0118] Referring to the preparation method and parameter conditions of Embodiment 12, except that the stretched fiber is not subjected to heat setting treatment.

[0119] Test Example 4 Mechanical Property Test

[0120] An electronic universal testing machine is used to measure the compression strength and compression modulus of the sample; the specific test results are shown in Table 8 and Table 9. Figure 1

[0121] Table 7 Preparation Parameters of Embodiments 10-12​

[0122]

[0123] Preparation parameters and mechanical property tests of Examples 10-12 and Comparative Examples 17-20

[0124]

[0125]

[0126] As shown in Table 8 and Figure 1 The data show that the compressive strength of Examples 10-12 is greater than 1.50 cN / dtex, and the compressive modulus is greater than 300 cN / dtex; this shows that Examples 10-12, through the mutual action between processes, make the high-strength modified meta-aramid fibers prepared have high compressive strength and compressive modulus. Comparative Example 17 uses single coagulation bath spinning instead of dry-jet wet spinning, resulting in a lack of pre-gelation of the fiber surface layer in the air bath stage. The dry-jet stage can promote the rapid formation of a dense gel layer on the surface of the fiber by controlling humidity and residence time, and direct immersion in the coagulation bath will destroy the gradient balance of NMP-deionized water double diffusion, making the polymer phase separation rate out of control, forming a non-uniform pore structure. This structural defect will weaken the interfacial bonding strength of the fiber body and the surface layer, making it difficult to achieve the coordinated orientation of molecular chains during the three-stage heat stretching, ultimately leading to a decrease in the compressive strength and compressive modulus of the modified meta-aramid fiber. Comparative Example 18 omits the gradient cleaning process, resulting in excessive residual NMP content; the unremoved NMP acts as a plasticizer and remains in the amorphous region of the fiber, competing with the hydrogen bond network of the PMIA molecular chain for binding sites, reducing intermolecular forces; at the same time, during the three-stage heat stretching process, the micro-bubbles generated by the volatilization of the residual NMP will destroy the continuous phase structure of the fiber, resulting in ineffective transmission of the stretching process to the molecular chain segments, ultimately leading to a decrease in the compressive strength and compressive modulus of the modified meta-aramid fiber.

[0127] Comparative Example 19 changed the three-step hot drawing to one-step hot drawing (only 300°C hot plate drawing). The three-step hot drawing realized the molecular chain segmental orientation and crystallization optimization through step-by-step temperature rising (95°C→285°C→365°C) and step-by-step drawing ratio (2.5→2.0→1.5): the first-stage drawing preliminarily untangled at low temperature, the second-stage drawing promoted chain segment slipping at medium temperature, and the third-stage high-temperature drawing locked the highly oriented structure. While the one-step high-temperature drawing could quickly increase the orientation degree, the molecular chains did not experience step-by-step relaxation and rearrangement, resulting in uneven internal stress distribution, and some chain segments were not fully untangled before being forced to stretch, which caused the modified meta-aramid fiber to easily produce micro-cracks or local amorphous regions, resulting in a significant decrease in the compression modulus of the modified meta-aramid fiber due to structural defects. Comparative Example 20 did not perform the heat setting treatment. Heat setting eliminated the residual stress in the drawing process, promoted the crystallization of the molecular chains, and stabilized the oriented structure. If this step is omitted, the internal stress of the fiber that has not been relaxed will become a crack initiation point when stressed; at the same time, the proportion of amorphous regions is high, and the intermolecular force is weak. In addition, the nitrogen protection in the heat setting stage can prevent high-temperature oxidative degradation, and the absence of it can cause some chain segments to break, resulting in a significant decrease in the compression strength and modulus of the modified meta-aramid fiber due to structural instability and stress concentration.

[0128] Examples 10-12 improved the compression strength and modulus of the high-strength modified meta-aramid fiber through the synergistic effect between processes. On the one hand, the NMP concentration in the coagulation bath slowed down the phase separation process, allowing the polymer chains to arrange regularly, forming a uniform and dense initial condensed state structure of the fiber; on the other hand, the high-temperature heat setting not only enhanced the orientation degree and crystallinity of the macromolecular chains in the fiber, but also created conditions for the crosslinking reaction between the DDSM and PMIA macromolecular segments, thereby strengthening the chemical network crosslinking effect; at the same time, the nanoparticles in the composite nanosuspension played a physical strengthening effect. In addition, the fine adjustment of the spinning stage parameters and the appropriate winding tension also played a key role in the formation and maintenance of the structure of the high-strength modified meta-aramid fiber, which ultimately significantly improved the ability of the high-strength modified meta-aramid fiber to resist compression deformation.

[0129] Although embodiments of the present application have been shown and described, it is to be understood that various modifications, substitutions, replacements and changes can be made to these embodiments without departing from the principles and spirit of the present application, and the scope of the present application is defined by the appended claims and their equivalents.

Claims

1. A method of making a high-strength modified meta-aramid fiber, characterized by: The specific preparation method of the high-strength modified meta-aramid fiber is as follows: mixing poly-m-phenylene isophthalamide copolymer, composite nano suspension and 4,4'-diamino diphenyl methane in N-methyl pyrrolidone, defoaming to prepare modified polymer spinning solution, and obtaining coagulation fiber through dry jet-wet spinning; the coagulation fiber is subjected to post-treatment process to obtain the high-strength modified meta-aramid fiber; wherein, the poly-m-phenylene isophthalamide copolymer is synthesized by reaction of N-methyl pyrrolidone, anhydrous lithium chloride, diamine solid and acyl chloride solution; the composite nano suspension is prepared by functionalized boron nitride nanosheet obtained by modification of hydroxylated boron nitride powder by silane coupling agent and ultraviolet-resistant nano TiO2 obtained by modification of activated TiO2 by γ-mercaptopropyl trimethoxysilane; The hydroxylated boron nitride powder is obtained by adding hexagonal boron nitride powder into concentrated sulfuric acid and ultrasonicating, then dropping 1.0-1.5 wt% potassium permanganate aqueous solution, stirring at 30-40℃, centrifuging for 10-15 min, collecting the precipitate and freeze-drying; The activated TiO2 is obtained by dispersing 20-50 nm titanium dioxide powder in deionized water, ultrasonicating, adding concentrated hydrochloric acid and stirring, centrifuging, washing, and freeze-drying; the activated TiO2 is dispersed in anhydrous ethanol, ultrasonicating, then dropping 0.10-0.20 parts of γ-mercaptopropyl trimethoxysilane, adding 0.3-0.5 parts of concentrated hydrochloric acid to adjust the pH of the system to 4.0-5.0, refluxing, then centrifuging and collecting the precipitate, washing, ultrasonicating and freeze-drying to obtain the ultraviolet-resistant nano TiO2; The composite nano suspension is obtained by stirring 0.3-0.8 parts of the functionalized boron nitride nanosheet, 0.5-1.0 parts of the ultraviolet-resistant nano TiO2 and 15-20 parts of the N-methyl pyrrolidone, shearing and dispersing at 8000-12000 rpm for 1.5-2.0 h, and centrifuging; The specific preparation method of the poly-m-phenylene isophthalamide copolymer is as follows: under nitrogen protection, 80-90 parts of the N-methyl pyrrolidone is mixed with 42 parts of the anhydrous lithium chloride at 200-300 rpm to prepare a polymerization solvent; the diamine solid is added to the polymerization solvent at 0-5℃ to obtain a mixed solution; m-phenylenediamine chloride is dissolved in the N-methyl pyrrolidone to prepare the acyl chloride solution; the acyl chloride solution is added to the mixed solution at a rate of 0.3-0.5 parts / min at 0-10℃ and 1500-2000 rpm to form a reaction liquid; the reaction liquid is poured into deionized water to precipitate and filter to obtain fibrous polymer, which is washed and dried to obtain the poly-m-phenylene isophthalamide copolymer; the molar ratio of the diamine solid to the m-phenylenediamine chloride is 1.0-1.3:1.

0. The specific preparation method of the modified polymer spinning solution is as follows: under nitrogen protection, the composite nanosuspension is added into 25-30 parts of the poly-m-phenylene isophthalamide copolymer and the N-methyl pyrrolidone, then 0.35-0.40 parts of the 4, 4'-diamino diphenyl methane is added, and a modified copolymer solution is obtained by stirring at 55-70℃ and 1200-1500 rpm; the modified copolymer solution is subjected to defoaming treatment at 0.08-0.10 MPa and 200-300 rpm to obtain the modified polymer spinning solution with a viscosity of 8000-12000 mPa·s; The specific preparation method of the high-strength modified meta-aramid fiber is as follows: the modified polymer spinning solution is pressed into a spinneret at a flow rate of 1.0-1.5 parts / min, and then extruded at 0.2-0.5 MPa, immediately enters an air bath, and is stretched by a gas flow at a speed of 1.0-1.3 m / s, under a humidity of 40-60%, and stays for 0.5-2.0 s to form a surface gel fiber; the surface gel fiber is immersed in a coagulation bath of 12-15 wt% N-methyl pyrrolidone aqueous solution, and a coagulation fiber is obtained after phase separation; the coagulation fiber is subjected to gradient cleaning, three-stage heat stretching, heat setting for 90-120 s, and then heat drying, and finally wound at a tension of 0.5-1.0 cN / dtex to obtain the high-strength modified meta-aramid fiber.

2. The method for preparing high-strength modified meta-aramid fiber according to claim 1, characterized in that: The specific preparation method of the functionalized boron nitride nanosheet is as follows: the hydroxylated boron nitride powder is dispersed in anhydrous ethanol to form a suspension by ultrasonic treatment; after adding the silane coupling agent into the suspension and dropwise adding concentrated ammonia water for reflux reaction, centrifugation, washing, and freeze-drying, the functionalized boron nitride nanosheet is obtained.

3. The method for preparing high-strength modified meta-aramid fiber according to claim 2, characterized in that: The silane coupling agent is any one of γ-aminopropyl triethoxysilane, 3-glycidyl ether propyl trimethoxysilane, and 3-aminopropyl trimethoxysilane.

4. A high-strength modified meta-aramid fiber, characterized by: The high-strength modified meta-aramid fiber is prepared by the preparation method of any one of claims 1-3.

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