A modified meta-aramid composite fiber and a method for preparing the same

Abstract

The present application relates to the technical field of meta-aramid fiber materials, in particular to a modified meta-aramid composite fiber and a preparation method thereof.The present application solves the problem that the anti-static performance and insulation performance of the meta-aramid fiber in the prior art cannot be considered simultaneously.The present application modifies meta-phenylenediamine and isophthaloyl chloride by using dodecanediamine and 3,5-diaminobenzoic acid to obtain a modified copolymer;obtains a core layer structure by modifying carbon nanotubes by aniline polymerization and a shell layer structure by modifying polyphenyl ether to prepare a functional core-shell structure;blends the modified copolymer, the functional core-shell structure and other additives to obtain a spinning solution after modifying nanosilica with silane;uses a dry-wet spinning process and performs stretching and heat setting to obtain an aramid composite fiber;modifies the copolymer to improve the mechanical properties and heat resistance of the composite fiber, and cooperates with the electrically-conductive and insulating design of the core-shell structure, so that the composite fiber has anti-static and insulation performance and is suitable for the application of electrical work protective clothing.

Description

Technical Field

[0001] This invention relates to the field of meta-aramid fiber materials technology, specifically to a modified meta-aramid composite fiber and its preparation method. Background Technology

[0002] Meta-aramid fibers possess excellent thermal and chemical stability, high tensile strength and toughness, and superior mechanical properties. They are widely used as structural composite materials in protective clothing, high-temperature filter materials, insulating paper, and honeycomb structural materials, becoming an irreplaceable key material. Protective clothing made from meta-aramid composite fibers is crucial equipment for ensuring worker safety. Due to the inherent good thermal and mechanical properties of meta-aramid, it maintains structural stability in high-temperature environments, providing a certain level of protection for workers. However, with the increasing complexity of electrical work environments, the requirements for the antistatic and insulating properties of protective clothing are becoming increasingly stringent. Existing meta-aramid composite fibers struggle to achieve an ideal balance between these two aspects.

[0003] Traditional meta-aramid fibers have some inherent limitations that restrict their further use in the field of protective clothing. On the one hand, in order to meet the requirements of antistatic properties, conductive components are usually added to the fibers. However, the traditional method of adding conductive components can easily lead to uneven dispersion of conductive particles, forming local conductive areas inside the fibers. This not only affects the insulation performance, but may also cause safety hazards due to charge concentration during use.

[0004] On the other hand, overemphasizing insulation performance often sacrifices antistatic performance. If the proportion of insulating material is increased or highly insulating raw materials are used during fiber preparation, the insulation effect can be improved, but the charge is difficult to conduct and dissipate, leading to static electricity accumulation, which in turn causes equipment failure, or even serious accidents such as fire or explosion.

[0005] In summary, a series of modification treatments have been applied to meta-aramid materials to meet their further application requirements in the field of protective clothing, including improved mechanical properties and heat resistance. However, the problem of not being able to simultaneously achieve both antistatic and insulation properties remains.

[0006] To this end, a modified meta-aramid composite fiber and its preparation method are proposed. Summary of the Invention

[0007] The purpose of this invention is to provide a modified meta-aramid composite fiber and its preparation method. This invention involves modifying m-phenylenediamine and isophthaloyl chloride with dodecanediamine and 3,5-diaminobenzoic acid to obtain a modified copolymer; preparing a functional core-shell structure by polymerizing and modifying carbon nanotubes to obtain a core layer structure and modifying polyphenylene ether to obtain a shell structure; modifying nano-silica with silane, blending it with the modified copolymer, the functional core-shell structure, and other auxiliaries to obtain a spinning solution; and using a dry-wet spinning process followed by stretching and heat setting to obtain the aramid composite fiber. By modifying the copolymer to improve the mechanical and heat resistance properties of the composite fiber, and synergistically combining the conductive-insulating design of the core-shell structure, the composite fiber possesses antistatic and insulating properties, making it suitable for use in electrical work protective clothing.

[0008] To achieve the above objectives, the present invention provides the following technical solution:

[0009] This invention provides a method for preparing modified meta-aramid composite fibers, the preparation of which includes the following steps:

[0010] The modified copolymer was dissolved to obtain a homogeneous solution; modified nano-silica was added to the functional core-shell structure dispersion and ultrasonically dispersed to obtain a pre-dispersion; an auxiliary agent was added to the homogeneous solution and mixed evenly to obtain a mixed solution; the pre-dispersion was added to the mixed solution, stirred and vacuum degassed to obtain a spinning solution; then, the solution was subjected to dry and wet spinning, two-stage stretching, heat setting treatment, and cooling and winding to obtain aramid composite fiber;

[0011] The modified copolymer was prepared by adding isophthaloyl chloride to m-phenylenediamine, dodecanediamine, and 3,5-diaminobenzoic acid.

[0012] Modified nano-silica was obtained by modifying nano-silica with glycidyl etheroxypropyltrimethoxysilane;

[0013] The functional core-shell structure dispersion was obtained by the polymerization reaction of the core layer structure of polyaniline-modified carbon nanotubes and the shell structure of glycidyl etheroxypropyltrimethoxysilane-modified polyphenylene ether.

[0014] Preferably, the preparation of the modified polymer includes the following steps:

[0015] Calcium chloride was slowly added to methylpyrrolidone and stirred to disperse, thus obtaining a mixed solvent. Dodecanediamine and 3,5-diaminobenzoic acid were dissolved in methylpyrrolidone to obtain a pre-reactant. m-Phenylenediamine was dissolved in the mixed solvent and slowly added to the pre-reactant. The temperature was raised to 15-20°C, and isophthaloyl chloride methylpyrrolidone solution was added dropwise. The modification reaction was carried out for 4-6 hours to obtain a reaction system. Methanol was added to the reaction system, and the mixture was centrifuged and washed with deionized water to obtain a precipitate. The precipitate was dried under vacuum to obtain a modified copolymer.

[0016] Preferably, the molar ratio of m-phenylenediamine to isophthaloyl chloride is 1:1; the molar ratio of dodecanediamine to m-phenylenediamine is 0.1-0.15:1; and the molar ratio of 3,5-diaminobenzoic acid to m-phenylenediamine is 0.1-0.2:1.

[0017] Preferably, the preparation of the functional core-shell structure includes the following steps:

[0018] Methylpyrrolidone was added to the shell structure and stirred until homogeneous to obtain a shell solution. The core structure was dissolved in methylpyrrolidone and ultrasonically dispersed to obtain a core dispersion. The core dispersion was added to the shell solution and dispersed by high-speed shearing to obtain a mixed system. The mixed system was transferred to a reactor, azobisisobutyronitrile was added, and the temperature was raised to 80-90℃. The polymerization reaction was carried out for 4-6 hours to obtain a functional core-shell structure dispersion. The mass ratio of the shell structure to the core structure was 2-5:1.

[0019] Preferably, the preparation of the core layer structure includes the following steps:

[0020] Carbon nanotubes with an average particle size of 80-100 nm were placed in a beaker, and a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 was added for acidification. The mixture was then refluxed and stirred. The nanotubes were then washed with deionized water until neutral, centrifuged, and vacuum dried to obtain acidified carbon nanotubes.

[0021] Acidified carbon nanotubes were dispersed in a 95% ethanol solution and ultrasonically dispersed to obtain a suspension. Ammonium persulfate was dissolved in deionized water to obtain an ammonium persulfate solution. Aniline monomer was added to the suspension, and under nitrogen protection, the temperature was controlled at 3-5℃. The ammonium persulfate solution was added dropwise, and the reaction was stirred for 15-18 hours to obtain modified carbon nanotubes. The modified carbon nanotubes were then obtained by separation and centrifugation, washing with alternating ethanol and deionized water, and vacuum drying. The mass ratio of aniline monomer to carbon nanotubes was 0.5-0.8:1, and the molar ratio of ammonium persulfate to aniline monomer was 0.8-1.2:1.

[0022] Preferably, the preparation of the shell structure includes the following steps:

[0023] Polyphenylene ether was dissolved in tetrahydrofuran to obtain a polyphenylene ether solution; glycidyl etheroxypropyltrimethoxysilane was dissolved in 95% ethanol solution, and glacial acetic acid was added to adjust the pH value. The solution was stirred and dissolved to obtain a silane solution; the polyphenylene ether solution was added to the silane solution, and the reaction was carried out under heat and stirred to obtain a reaction system; the reaction system was poured into methanol to precipitate, separated and centrifuged, washed with deionized water, and vacuum dried to obtain a shell structure; the polyphenylene ether type was Noryl SE1.

[0024] Preferably, the preparation of modified nano-silica includes the following steps:

[0025] Nano-sized silica with an average particle size of 50-80 nm was added to a 95% ethanol solution and ultrasonically dispersed. The pH was adjusted by adding glacial acetic acid to obtain a dispersion. Glycidyl etheroxypropyltrimethoxysilane was dissolved in a 95% ethanol solution, and the pH was adjusted by adding glacial acetic acid. The solution was stirred and stirred to obtain a solution. The solution was slowly added to the dispersion and stirred to obtain a modified product. The modified product was centrifuged, washed with ethanol, and vacuum dried to obtain modified nano-silica.

[0026] Preferably, in the preparation of aramid composite fibers, the ultrasonic dispersion power is 300-500W; the ultrasonic dispersion time is 1-2h; the stirring and blending temperature is 60-80℃; the stirring and blending time is 3-5h; the heat setting temperature is 250-300℃; and the heat setting time is 20-40s.

[0027] Preferably, in the dry-wet spinning process, the spinning temperature is controlled at 60-80℃, the spinning speed at 100-200m / min, and the orifice diameter of the spinneret is adjusted to 0.1-0.2mm according to the fiber diameter requirements. The spun spinning solution first enters the dry coagulation zone, where the temperature is controlled at 30-50℃ and the residence time is 1-3s, allowing the spinning solution to initially coagulate and form a shape. Then, a wet coagulation bath is used, which consists of NMP and water in a mass ratio of 1:2, at a temperature of 25-30℃, with a fiber residence time of 5-10min to obtain nascent fibers. The nascent fibers are then subjected to two stages of stretching treatment: the first stage stretching ratio is 2-3 times at a temperature of 60-80℃, and the second stage stretching ratio is 3-4 times at a temperature of 80-100℃ to obtain stretched fibers.

[0028] This invention also provides a modified meta-aramid composite fiber, which is prepared by any of the methods described above; the modified meta-aramid composite fiber is prepared by a spinning solution through dry and wet spinning, two-stage stretching, heat setting treatment and cooling winding; by mass concentration, the spinning solution includes 15-20% modified copolymer, 5-8% functional core-shell structure, 3-5% modified nano silica, 0.8% zinc stearate, 0.5% antioxidant 1010, 0.6% triphenyl phosphate, and the balance being NMP.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] 1. This invention introduces flexible long chains through dodecanediamine, increasing the interchain spacing, reducing intermolecular forces, and improving chain segment flexibility. Simultaneously, 3,5-diaminobenzoic acid introduces rigid benzene rings and amino groups, enhancing hydrogen bonding and rigidity between molecular chains. The synergistic effect of these two substances modifies meta-aramid fibers, thereby improving the overall mechanical properties of the fiber. Simultaneously, it synergistically modifies nano-silica, uniformly dispersing it in the fiber matrix to form a good interfacial bond with the polymer matrix, dispersing stress and achieving a strengthening and toughening effect. The core-shell structure enhances the fiber's electrical conductivity, thermal conductivity, and mechanical properties, while the shell structure improves compatibility and dispersibility with the matrix. The pre-dispersion process further improves compatibility with the polymer matrix and increases interfacial bonding. The synergistic use of the core-shell structure further enhances the overall mechanical properties of the fiber. The introduction of a two-stage stretching process further eliminates interfiber stress, maintaining a balance between breaking strength and elongation at break, thus improving the mechanical properties of the composite fiber.

[0031] 2. This invention utilizes the synergistic effect of 3,5-diaminobenzoic acid and dodecanediamine to ensure the fiber's flexibility while maintaining sufficient rigidity and stability between molecular chains. This makes the fiber less prone to deformation and structural damage at high temperatures, thus improving its heat resistance. Furthermore, the introduction of modified nano-silica acts as a reinforcement and thermal stabilizer in the fiber, dispersing heat, inhibiting the thermal motion of molecular chains, and synergistically enhancing heat resistance with other components. The synergistic effect of the shell and core layers forms a stable and efficient heat conduction and reinforcement system, effectively resisting thermal damage at high temperatures and improving heat resistance. Finally, the pre-dispersion liquid mixing process ensures uniform dispersion of all components, promoting interfacial bonding and interaction, improving the synergistic dispersion and interaction mechanisms between components, further enhancing the fiber's heat resistance while maintaining good mechanical properties.

[0032] 3. This invention uses modified carbon nanotubes as the core layer, which has good conductivity and can provide a pathway for charge conduction. The shell structure maintains the insulation performance of the fiber to a certain extent, preventing leakage and maintaining the insulation performance of the fiber surface. The core layer structure has conductivity and a stable supporting role, but its dispersion in the matrix is ​​poor. The shell structure helps to disperse and avoid agglomeration, while improving the insulation effect. The core and shell structures work together to ensure the balance of dispersion and performance. By controlling the mass ratio of the core layer to the shell layer, chemical improvement and physical dispersion processes are introduced to further improve the uniform dispersion and interaction of components in the matrix, thereby improving and balancing the antistatic and insulation properties and expanding the application range of the composite fiber. Attached Figure Description

[0033] Figure 1 The graph shows the change in the breaking strength retention rate of the composite fibers obtained in Examples 7-9, Comparative Examples 1, 4, 8, and 11 of this invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Please see Figure 1 This invention provides a modified meta-aramid composite fiber and its preparation method, the technical solution of which is as follows:

[0036] Example 1

[0037] Calcium chloride was slowly added to methylpyrrolidone solvent and dispersed by stirring at 40°C to obtain a mixed solvent with a mass concentration of 8%. Dodecanediamine and 3,5-diaminobenzoic acid were dissolved in methylpyrrolidone to obtain a pre-reactant. Under nitrogen protection, m-phenylenediamine was dissolved in the mixed solvent, and the pre-reactant was slowly added and stirred until dissolved. The temperature was raised to 20°C, and a methylpyrrolidone solution of isophthaloyl chloride was slowly added dropwise. The modification reaction was carried out at 500 rpm for 5 h to obtain a reaction system. Methanol was added to the reaction system, and the mixture was stirred at 400 rpm for 2 h. The mixture was then separated by centrifugation and washed three times with deionized water to obtain a precipitate. The precipitate was placed in a vacuum drying oven and dried under vacuum at 60°C for 5 h to obtain a modified copolymer. The molar ratio of m-phenylenediamine to isophthaloyl chloride was 1:1; the molar ratio of dodecanediamine to m-phenylenediamine was 0.15:1; and the molar ratio of 3,5-diaminobenzoic acid to m-phenylenediamine was 0.2:1.

[0038] Carbon nanotubes were placed in a beaker and acidified by adding a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1. The mixture was then refluxed and stirred at 60°C for 2 hours. After washing repeatedly with deionized water until neutral, the mixture was centrifuged and vacuum dried in a vacuum drying oven at 50°C for 10 hours to obtain acidified carbon nanotubes.

[0039] Acidified carbon nanotubes were dispersed in a 95% ethanol solution and ultrasonically dispersed at 300W for 60 min to obtain a uniform suspension. Ammonium persulfate was dissolved in deionized water to prepare a 0.1 mol / L ammonium persulfate solution. Aniline monomer was added to the suspension, with a mass ratio of aniline monomer to carbon nanotubes of 0.6:1. Under nitrogen protection and with the temperature controlled at 5℃, the ammonium persulfate solution was slowly added dropwise over 30 min. After the addition was complete, the mixture was kept at this temperature and stirred for 16 h to obtain modified carbon nanotubes. The modified carbon nanotubes were obtained by separation and centrifugation, followed by washing with alternating ethanol and deionized water three times, and vacuum drying at 60℃ for 15 h. The molar ratio of ammonium persulfate to aniline was 1.0:1.

[0040] 50 parts of polyphenylene ether were dissolved in tetrahydrofuran to obtain a polyphenylene ether solution; 5 parts of KH560 were dissolved in 95% ethanol solution, and glacial acetic acid was added to adjust the pH to 5. The solution was stirred to obtain a silane solution; the polyphenylene ether solution was heated to 60℃, and the silane solution was slowly added. After the addition was completed, the mixture was kept at the temperature and stirred for 6 hours to obtain a reaction system; the reaction system was poured into methanol to precipitate, separated and centrifuged, washed with deionized water, and dried under vacuum at 50℃ for 8 hours to obtain a shell structure;

[0041] Methylpyrrolidone was added to the shell structure and stirred until homogeneous to obtain a shell solution. The core structure was dissolved in methylpyrrolidone and ultrasonically dispersed to obtain a core dispersion. The core dispersion was added to the shell solution and dispersed under high-speed shear at 2000 rpm for 2 hours to obtain a mixed system. The mixed system was transferred to a reactor, and 0.3% AIBN was added. The temperature was raised to 80°C, and the polymerization reaction was carried out for 5 hours to obtain a functional core-shell structure dispersion, which was then set aside for later use. The mass ratio of the shell structure to the core structure was 3:1.

[0042] 100 parts of nano-silica were added to a 95% ethanol solution and ultrasonically dispersed. The pH was adjusted to 4 with glacial acetic acid to obtain a dispersion. 10 parts of KH5605- were dissolved in a 95% ethanol solution, and the pH was adjusted to 4 with glacial acetic acid. The mixture was stirred to dissolve and obtain a solution. The solution was slowly added to the dispersion, and the temperature was raised to 60℃. The modification reaction was stirred for 4 hours to obtain a modified product. The modified product was centrifuged, washed 5 times with ethanol, and vacuum dried at 80℃ for 10 hours to obtain modified nano-silica.

[0043] The modified copolymer was added to NMP, heated to 90℃ at 200 rpm, and stirred for 4 hours to obtain a homogeneous solution, which was then kept at this temperature for later use. Modified nano-silica was added to the functional core-shell structure dispersion, and ultrasonic dispersion was carried out at 400 W and 30 kHz for 2 hours to obtain a homogeneous pre-dispersion, with intervals paused during the ultrasonic process. Zinc stearate, antioxidant 1010, and triphenyl phosphate were added to the homogeneous solution at 200 rpm, and stirred for 30 minutes to obtain a homogeneous mixture. The pre-dispersion was slowly added to the mixture, heated to 70℃, and stirred for 4 hours, with short-term ultrasonic dispersion during this period, ultrasonication for 5 minutes every 30 minutes of stirring. After stirring was completed, a mixture was obtained. The mixture was placed under vacuum conditions (vacuum degree less than -0.09 MPa) and slowly stirred to degas, obtaining a spinning solution. The modified copolymer has a mass concentration of 18%, the functional core-shell structure has a mass concentration of 6%, the modified nano-silica has a mass concentration of 4%, zinc stearate has a mass concentration of 0.8%, antioxidant 1010 has a mass concentration of 0.5%, triphenyl phosphate has a mass concentration of 0.6%, and the balance is NMP.

[0044] The spinning solution is delivered to the spinneret of the spinning machine through a metering pump, and the nascent fiber is obtained by dry and wet spinning process. The nascent fiber is then subjected to two stages of stretching treatment to obtain stretched fiber. Then, it is subjected to heat setting treatment, under nitrogen protection, with the temperature controlled at 280℃ and held for 30 seconds. The modified meta-aramid composite fiber is obtained by cooling and winding.

[0045] Examples 2-6 follow the same preparation method and parameter conditions as Example 1, with differences shown in Table 1.

[0046] Table 1. Parameter variations in Examples 1-6

[0047]

[0048] Comparative Example 1 is the same as Example 1, except that the copolymer is not modified.

[0049] Comparative Example 2 is the same as Example 1, except that only dodecanediamine was used for modification.

[0050] Comparative Example 3 is the same as Example 1, except that it is modified with only 3,5-diaminobenzoic acid.

[0051] Comparative Example 4 is the same as Example 1, except that no modified nano-silica is added.

[0052] Comparative Example 5 is the same as Example 1, except that the nano-silica is not modified.

[0053] Comparative Example 6 is the same as Example 1, except that it is only stretched at 60°C, and the stretching ratio is 4.

[0054] Comparative Example 7 is the same as Example 1, except that it is only stretched at 100°C, and the stretching ratio is 4.

[0055] Comparative Example 8 is the same as Example 1, except that no functional core-shell structure is added.

[0056] Comparative Example 9 is the same as Example 1, except that no core-shell structure is introduced, and only a core layer structure is used.

[0057] Comparative Example 10 is the same as Example 1, except that no core-shell structure is introduced, and only a shell structure is used.

[0058] Comparative Example 11 is the same as Example 1, except that the spinning solution is obtained by direct blending without the pre-dispersion liquid mixing process.

[0059] Experiment Example 1 Mechanical Property Testing

[0060] The modified meta-aramid composite fibers obtained in Examples 1-6 and Comparative Examples 1-11 were tested for breaking strength and breaking elongation according to GB / T14337-2008. The test results are shown in Table 2.

[0061] Table 2 Test results of Examples 1-6 and Comparative Examples 1-11

[0062] Example Fracture strength / cN / dtex Elongation at break / % Example 1 34.8 22.6 Example 2 34.5 21.8 Example 3 34.2 22.4 Example 4 33.5 21.5 Example 5 34.6 22.5 Example 6 34.5 22.1 Comparative Example 1 18.6 32.5 Comparative Example 2 23.5 26.8 Comparative Example 3 26.4 20.6 Comparative Example 4 22.8 25.2 Comparative Example 5 20.7 18.6 Comparative Example 6 20.2 30.2 Comparative Example 7 20.8 26.5 Comparative Example 8 19.6 25.3 Comparative Example 9 21.6 20.2 Comparative Example 10 22.3 22.6 Comparative Example 11 21.8 15.8

[0063] The results in Table 2 show that, compared to the examples, the comparative examples could not maintain a balance between breaking strength and elongation at break, further affecting the application of the composite fiber in subsequent processes. The results of Comparative Examples 1-3 show that without modification of the copolymer, the mechanical properties of the composite fiber are poor. The unmodified copolymer has high molecular chain regularity, high rigidity, strong intermolecular forces, and lacks flexibility. Under stress, the molecular chains are difficult to slip and orient, and stress concentration easily leads to fiber breakage, reducing breaking strength. Simultaneously, the elongation at break also decreases due to the rigidity of the molecular chains, making stretching difficult. The introduction of flexible long chains with dodecanediamine can increase the inter-chain spacing, reduce intermolecular forces, and improve chain segment flexibility. 3,5-Diaminobenzene... Formic acid enhances the rigidity of molecular chains and intermolecular hydrogen bonding. By controlling the dosage of both, the mechanical properties of composite fibers are synergistically improved. Comparative examples 4-5 show that without modified nano-silica, the fiber has more internal defects, and cracks propagate rapidly under stress, leading to a decrease in breaking strength. Furthermore, without the toughening effect of nano-silica, the fiber's resistance to deformation is weakened, and the elongation at break also decreases. Without nano-silica modification, due to its high surface energy, it is prone to agglomeration, resulting in poor dispersion in the fiber matrix. Agglomerated particles become stress concentration points, reducing the fiber's mechanical properties. Additionally, the weak interfacial bonding between unmodified nano-silica and the polymer matrix prevents effective stress transfer, causing particles to easily detach from the matrix under stress. Debonding further reduces tensile strength and elongation at break. In Comparative Examples 6-7, the lack of multi-stage stretching and the lower stretching temperature limit the mobility of molecular chains, preventing them from aligning as neatly as in two-stage stretching. This results in a loose internal fiber structure, incomplete crystallization, and weak intermolecular forces, leading to low tensile strength. Higher stretching temperatures make it difficult to achieve fine orientation and perfect crystallization of molecular chains, resulting in numerous defects and stress concentration points within the fiber. Furthermore, high-temperature stretching may cause degradation or thermal damage to some molecular chains, further reducing fiber strength. Comparative Examples 8-10 show that without the addition of a functional core-shell structure, the fiber cannot effectively disperse stress and enhance mechanical properties, leading to a decrease in both tensile strength and elongation at break. The fiber's mechanical properties are reduced, while the core-shell structure has a reinforcing effect, and the shell structure can improve its dispersibility in the matrix and its interfacial bonding with the matrix. The use of a single component has poor compatibility with the fiber matrix, uneven dispersion in the spinning solution, and easy agglomeration to form defects. These defects form stress concentration points in subsequent processing, thereby reducing the mechanical properties of the fiber. According to Comparative Example 11, without pre-dispersion treatment, the dispersion uniformity of the functional core-shell structure and modified nano-silica becomes poor, forming agglomerates, which in turn form stress concentration points in the fiber. In addition, when directly blended, the components cannot fully contact and interact with each other, the interfacial bonding force is weak, and the stress cannot be evenly distributed throughout the fiber system, which reduces the fiber's load-bearing capacity and breaking strength.Due to poor interfacial bonding, the components cannot deform synergistically during stretching, leading to localized fiber damage, which limits the fiber's tensile properties and reduces its elongation at break.

[0064] Example 7 is the same as Example 1;

[0065] Examples 8-11 follow the same preparation method and parameter conditions as Example 1, with differences shown in Table 3.

[0066] Table 3 Parameter changes in Examples 7-11

[0067]

[0068] Experiment Example 2: Heat Resistance Test

[0069] The composite fibers obtained in Examples 7-11, Comparative Examples 1-5, and Comparative Examples 8-11 were subjected to thermal aging tests. The composite fibers were wound in a crucible and placed in a high-temperature oven at 300°C for 500 hours. After cooling, the composite fibers were removed and their breaking strength was tested. The rate of retention of breaking strength of the composite fibers compared to those without thermal aging treatment was calculated. The test results are shown in Table 4. Figure 1 The graph shows the changes in fracture strength retention rate for Examples 7-9, Comparative Examples 1, 4, 8, and 11.

[0070] Table 4. Test results of Examples 7-11, Comparative Examples 1-5, and Comparative Examples 8-11

[0071] Example Fracture strength retention rate / % Example 7 92.5 Example 8 91.8 Example 9 91.7 Example 10 92.2 Example 11 92.3 Comparative Example 1 52.4 Comparative Example 2 62.8 Comparative Example 3 68.5 Comparative Example 4 56.8 Comparative Example 5 61.7 Comparative Example 8 46.8 Comparative Example 9 58.2 Comparative Example 10 62.8 Comparative Example 11 58.6

[0072] As shown in Table 4, the comparative examples exhibited a lower breaking strength retention rate and significantly reduced heat resistance compared to the examples. The results of Comparative Examples 1-3 indicate that the modification of the copolymer with dodecanediamine and 3,5-diaminobenzoic acid optimizes the molecular chain structure. The flexible segments of dodecanediamine alleviate stress concentration between molecular chains, while the rigid groups introduced by 3,5-diaminobenzoic acid enhance the inter-chain forces and thermal stability. The unmodified copolymer exhibits high molecular chain regularity and rigidity, making it difficult to disperse heat through minor adjustments during heating, leading to thermal degradation and oxidation, and damaging the internal structure of the fiber. The lack of synergy between 3,5-diaminobenzoic acid and dodecanediamine prevents the maintenance of sufficient rigidity and stability between molecular chains while ensuring flexibility, making the fiber more prone to deformation and structural damage at high temperatures, thus reducing heat resistance. In Comparative Examples 4-5, the modified nano-silica plays a reinforcing and thermal stabilizing role in the fiber, dispersing heat... The addition of functional core-shell structures in Comparative Examples 8-10 results in fibers lacking efficient heat conduction and stable structural support without the addition of functional core-shell structures. Without these structures, the fibers lack a thermally stable reinforcing phase, making the molecular chains more susceptible to disorder and degradation at high temperatures. Furthermore, unmodified nano-silica has high surface energy, making it prone to aggregation and poor dispersibility within the fiber, thus failing to effectively provide reinforcement and thermal stability. These aggregates also form thermal stress concentration points, accelerating structural damage at high temperatures. In Comparative Examples 11, without the addition of functional core-shell structures, the fibers lack efficient heat conduction and stable structural support. The core layer in the functional core-shell structure has high thermal conductivity, rapidly dispersing heat, while the shell layer improves compatibility with the matrix and enhances structural stability, thereby improving the thermal stability of the matrix. Comparative Example 11 shows that direct blending leads to uneven dispersion of components and poor interfacial bonding, resulting in uneven heat transfer at high temperatures. This easily leads to localized overheating and stress concentration, consequently causing poor structural stability, reduced breaking strength retention, and decreased heat resistance at high temperatures.

[0073] Example 12 is the same as Example 1;

[0074] Examples 13-16 follow the preparation method and parameter conditions of Example 1, with differences shown in Table 5.

[0075] Table 5. Parameter changes in Examples 12-16

[0076]

[0077] Comparative Example 8 is the same as Example 1, except that no functional core-shell structure is added.

[0078] Comparative Example 9 is the same as Example 1, except that no core-shell structure is introduced, and only a core layer structure is used.

[0079] Comparative Example 10 is the same as Example 1, except that no core-shell structure is introduced, and only a shell structure is used.

[0080] Comparative Example 11 is the same as Example 1, except that the spinning solution is obtained by direct blending without the pre-dispersion liquid mixing process.

[0081] Comparative Example 12 is the same as Example 1, except that the carbon nanotubes are not modified with aniline.

[0082] Comparative Example 13 is the same as Example 1, except that the polyphenylene ether is not subjected to silane modification treatment.

[0083] Comparative Example 14 is the same as Example 1, except that the mixed system is not subjected to high-speed shear dispersion treatment.

[0084] Comparative Example 15 is the same as Example 1, except that no ultrasonic dispersion process is introduced during the preparation of the spinning solution.

[0085] Comparative Example 16 is the same as Example 1, except that the mass ratio of the shell structure to the core structure is 8:1.

[0086] Comparative Example 17 is the same as Example 1, except that the mass ratio of the shell structure to the core structure is 1:2.

[0087] Experimental Example 3: Antistatic and Insulation Properties

[0088] The composite fibers prepared in Examples 12-16 and Comparative Examples 8-17 were subjected to antistatic insulation performance tests. The dielectric strength of the composite fibers was tested according to GB / T1408.1-2016, and the surface resistivity of the composite fibers was tested according to GB / T 1410-2006. The test results are shown in Table 6.

[0089] Table 6 Test results of Examples 12-16 and Comparative Examples 8-17

[0090]

[0091]

[0092] As shown in Table 6, the comparative examples, compared to the examples, cannot maintain a balance between insulation and antistatic properties, affecting the normal use of the protective clothing when the composite fibers are applied to electrical protective clothing. The results of Comparative Examples 8-10 show that the core layer in the functional core-shell structure is a modified carbon nanotube, which has good conductivity and can provide a pathway for charge conduction. Combined with Comparative Example 12, aniline-modified carbon nanotubes can enhance its conductivity. Without modification, the carbon nanotubes have poor conductivity and low charge conduction efficiency. The absence of carbon nanotubes results in a lack of efficient conductive paths in the fiber, making it difficult for charges to conduct quickly. Rapid dissipation leads to increased surface resistivity and decreased antistatic performance. The introduction of the shell structure maintains the insulation performance of the fiber and prevents leakage. Combined with Comparative Example 13, silane-modified polyphenylene ether improves its compatibility and dispersibility with other components, facilitating charge conduction. Without modification, the shell is not tightly bonded to other components, easily leading to gaps and defects, affecting the formation of the overall conductive network, increasing surface resistivity, impacting antistatic performance, and reducing dielectric strength. Comparative Example 11 shows that pre-dispersed liquid mixing ensures uniform dispersion of each component, avoiding uneven dispersion caused by direct blending, and improving the conductive properties. Uneven component distribution hinders charge conduction, increases surface resistivity, and deteriorates antistatic properties. Simultaneously, localized aggregation of conductive components creates potential conductivity hazards, reduces dielectric strength, and impairs insulation performance. Comparative Example 14 shows that high-speed shear dispersion ensures uniform dispersion of the core-shell structure within the fiber matrix, forming a uniform conductive network. This avoids uneven component dispersion, which leads to discontinuous conductive networks, difficulty in charge conduction, increased surface resistivity, decreased dielectric strength, and reduced antistatic and insulation properties. In Comparative Example 15, the introduction of ultrasonic dispersion further refines the components, promoting uniform dispersion and interaction. While this facilitates the formation of a good conductive network, it also reduces the dispersion of surface components, increases surface resistivity, and causes conductive particles to agglomerate, reducing dielectric strength and affecting insulation performance. In Comparative Examples 16-17, changes in the mass ratio of the core and shell structures disrupted the mechanism by which the core and shell structures synergistically enhance antistatic and insulation performance, affecting the overall performance balance. Polyphenylene ether itself is an insulating material with good dielectric properties and heat resistance. By coating it onto the surface of carbon nanotubes through a core-shell structure, the carbon nanotubes are isolated, and the overall conductivity / insulation performance is regulated. Too many shells encapsulating the core hinder charge conduction and may introduce more insulating impurities. Although the dielectric strength increases, the antistatic performance decreases significantly, disrupting the overall performance balance. Too few shells cannot effectively encapsulate and isolate the core, resulting in reduced dielectric strength, impaired insulation performance, and disruption of the balance.

[0093] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing modified meta-aramid composite fibers, characterized in that: The preparation of the aramid composite fiber includes the following steps: The modified copolymer is dissolved to obtain a homogeneous solution; modified nano-silica is added to the functional core-shell structure dispersion and ultrasonically dispersed to obtain a pre-dispersion; an auxiliary agent is added to the homogeneous solution, and then the pre-dispersion is added, mixed and stirred, and vacuum degassed to obtain a spinning solution; then, the solution is spun by dry and wet spinning, stretched in two stages, heat-set, cooled and wound to obtain the aramid composite fiber. The modified copolymer was prepared by adding isophthaloyl chloride to m-phenylenediamine, dodecanediamine, and 3,5-diaminobenzoic acid. The modified nano-silica was obtained by modifying nano-silica with glycidyl etheroxypropyltrimethoxysilane. The functional core-shell structure dispersion is obtained by the polymerization reaction of the core layer structure of polyaniline-modified carbon nanotubes and the shell structure of glycidyl etheroxypropyltrimethoxysilane-modified polyphenylene ether.

2. The method for preparing modified meta-aramid composite fiber according to claim 1, characterized in that: The preparation of the modified copolymer includes the following steps: Calcium chloride was slowly added to methylpyrrolidone and stirred to disperse, thus obtaining a mixed solvent. Dodecanediamine and 3,5-diaminobenzoic acid were dissolved in methylpyrrolidone to obtain a pre-reactant. The m-phenylenediamine was dissolved in the mixed solvent and slowly added to the pre-reactant. The temperature was raised to 15-20°C, and isophthaloyl chloride methylpyrrolidone solution was added dropwise. The modification reaction was carried out for 4-6 hours to obtain a reaction system. Methanol was added to the reaction system, and the mixture was centrifuged and washed with deionized water to obtain a precipitate. The precipitate was vacuum dried to obtain the modified copolymer.

3. The method for preparing modified meta-aramid composite fiber according to claim 2, characterized in that: The molar ratio of m-phenylenediamine to m-phenylenediamine is 1:1; the molar ratio of dodecanediamine to m-phenylenediamine is 0.1-0.15:1; and the molar ratio of 3,5-diaminobenzoic acid to m-phenylenediamine is 0.1-0.2:

1.

4. The method for preparing modified meta-aramid composite fiber according to claim 1, characterized in that: The preparation of the functional core-shell structured dispersion includes the following steps: Methylpyrrolidone is added to the shell structure and stirred until homogeneous to obtain a shell solution; the core structure is dissolved in the methylpyrrolidone and ultrasonically dispersed to obtain a core dispersion; the core dispersion is added to the shell solution and dispersed by high-speed shearing to obtain a mixed system; the mixed system is transferred to a reactor, azobisisobutyronitrile is added, the temperature is raised to 80-90℃, and the polymerization reaction is carried out for 4-6 hours to obtain the functional core-shell structure dispersion; wherein the mass ratio of the shell structure to the core structure is 2-5:

1.

5. The method for preparing a modified meta-aramid composite fiber according to claim 4, characterized in that: The preparation of the core layer structure includes the following steps: Carbon nanotubes were placed in a beaker and acidified by adding a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:

1. The mixture was then refluxed and stirred. The nanotubes were washed with deionized water until neutral, centrifuged, and vacuum dried to obtain acidified carbon nanotubes. The acidified carbon nanotubes were dispersed in a 95% ethanol solution and ultrasonically dispersed to obtain a suspension. Ammonium persulfate was dissolved in deionized water to obtain an ammonium persulfate solution. Aniline monomer was added to the suspension, and under nitrogen protection, the temperature was controlled at 3-5°C. The ammonium persulfate solution was added dropwise, and the mixture was stirred and reacted for 15-18 hours to obtain modified carbon nanotubes. The modified carbon nanotubes were then obtained by separation and centrifugation, alternating washing with ethanol and deionized water, and vacuum drying. The mass ratio of aniline monomer to carbon nanotubes was 0.5-0.8:1, and the molar ratio of ammonium persulfate to aniline monomer was 0.8-1.2:

1.

6. The method for preparing a modified meta-aramid composite fiber according to claim 4, characterized in that: The preparation of the shell structure includes the following steps: Polyphenylene ether was dissolved in tetrahydrofuran to obtain a polyphenylene ether solution; glycidyl etheroxypropyltrimethoxysilane was dissolved in 95% ethanol solution, and glacial acetic acid was added to adjust the pH value. The solution was stirred and dissolved to obtain a silane solution; the polyphenylene ether solution was added to the silane solution, and the reaction was carried out under heat and stirred to obtain a reaction system; the reaction system was poured into methanol to precipitate, separated and centrifuged, washed with deionized water, and vacuum dried to obtain the shell structure.

7. The method for preparing modified meta-aramid composite fiber according to claim 1, characterized in that: In the preparation of the aramid composite fiber, the ultrasonic dispersion power is 300-500W; the ultrasonic dispersion time is 1-2h; the blending temperature is 60-80℃; the blending time is 3-5h; the heat setting temperature is 250-300℃; and the heat setting time is 20-40s.

8. A modified meta-aramid composite fiber, characterized in that: The modified meta-aramid composite fiber is prepared by the method described in any one of claims 1-7; the modified meta-aramid composite fiber is prepared by a spinning solution through dry and wet spinning, two-stage stretching, heat setting treatment and cooling winding; by mass concentration, the spinning solution includes 15-20% modified copolymer, 5-8% functional core-shell structure; 3-5% modified nano silica; 0.8% zinc stearate; 0.5% antioxidant 1010; 0.6% triphenyl phosphate, with the balance being NMP.

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