Modified meta-aramid composite fiber and preparation method thereof

Abstract

The invention 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 invention solves the problem that the antistatic property and insulating property of the meso-position aramid fiber cannot be considered at the same time in the prior art. The preparation method comprises the following steps: modifying m-phenylenediamine and isophthaloyl dichloride through dodecane diamine and 3, 5-diaminobenzoic acid to obtain a modified copolymer; preparing a functional core-shell structure from a core-layer structure obtained by polymerizing and modifying the carbon nano tube with aniline and a shell-layer structure obtained by modifying the polyphenyl ether; the preparation method comprises the following steps: modifying nano silicon dioxide silane, blending the modified nano silicon dioxide silane with a modified copolymer, a functional core-shell structure and other auxiliaries to prepare a spinning solution, and carrying out stretching and heat setting by adopting a dry-wet spinning process to prepare aramid composite fibers; the mechanical property and heat resistance of the composite fiber are improved by modifying the copolymer, and the composite fiber has antistatic and insulating properties by cooperating with the conductive-insulating design of the core-shell structure, and is suitable for being applied to electrical operation protective clothing.

Description

Technical Field

[0001] The present invention relates to the technical field of meta-aramid fiber materials, in particular to a modified meta-aramid composite fiber and a preparation method thereof. Background Art

[0002] Meta-aramid has excellent thermal and chemical stability, high breaking strength and toughness, and excellent mechanical properties. It is often used in the form of structural composite materials in protective clothing, high-temperature filter materials, insulating paper, honeycomb structural materials, and other fields, and has become an irreplaceable key material. Among them, protective clothing made of meta-aramid composite fibers has become a key equipment to ensure the safety of workers. Due to the excellent thermal stability and mechanical properties of meta-aramid itself, it can maintain structural stability in high-temperature environments and provide a certain degree of protection for workers. However, with the increasing complexity of electrical working environments, the requirements for the antistatic and insulating properties of protective clothing are becoming increasingly stringent. Existing meta-aramid composite fibers have difficulty achieving 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, conductive components are usually added to the fibers to meet anti-static requirements. However, the traditional method of adding conductive components easily leads to uneven dispersion of conductive particles, forming local conductive areas inside the fibers, which not only affects the insulation performance, but may also cause safety hazards due to charge concentration during use.

[0004] On the other hand, over-emphasizing insulation performance often sacrifices anti-static performance. If the proportion of insulating materials is increased or high-insulation raw materials are used during the fiber preparation process, although the insulation effect can be improved, the charge is difficult to conduct and dissipate, resulting in static electricity accumulation, which in turn causes equipment failure and even serious accidents such as fire or explosion.

[0005] In summary, a series of modification treatments have been performed on meta-aramid materials to meet their further application in the field of protective clothing, including improved mechanical properties and heat resistance. However, there is still the problem that antistatic and insulation properties cannot be taken into account at the same time.

[0006] Therefore, a modified meta-aramid composite fiber and a preparation method thereof are proposed. Summary of the Invention

[0007] The present invention aims to provide a modified meta-aramid composite fiber and a preparation method thereof. The method comprises modifying meta-phenylenediamine and isophthaloyl chloride with dodecanediamine and 3,5-diaminobenzoic acid to obtain a modified copolymer; preparing a functional core-shell structure by polymerizing carbon nanotubes to obtain a core layer structure and modifying a polyphenylene ether to obtain a shell layer structure; modifying nanosilica with silane and blending it with the modified copolymer, the functional core-shell structure, and other additives to prepare a spinning solution; and producing an aramid composite fiber using a dry-wet spinning process, followed by stretching and heat setting. The copolymer modification improves the mechanical properties and heat resistance of the composite fiber, and the conductive-insulating design of the core-shell structure synergizes to impart antistatic and insulating properties to the composite fiber, making it suitable for use in protective clothing for electrical work.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] In one aspect, the present invention provides a method for preparing a modified meta-aramid composite fiber. The preparation of the aramid composite fiber comprises the following steps:

[0010] The modified copolymer is dissolved to obtain a uniform solution; the modified nano-silica is added to the functional core-shell structure dispersion, and ultrasonic dispersion is performed to obtain a pre-dispersion solution; an auxiliary agent is added to the uniform solution, and the mixture is mixed to obtain a mixed solution; the pre-dispersion solution is added to the mixed solution, the mixture is blended and stirred, and vacuum degassed to obtain a spinning solution; and the aramid composite fiber is obtained by dry-wet spinning, two-stage stretching, heat setting treatment, cooling and winding.

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

[0012] The modified nano-silica is obtained by modifying the nano-silica with glycidyloxypropyltrimethoxysilane;

[0013] The functional core-shell structure dispersion is obtained by polymerization reaction of a core structure of polyaniline-modified carbon nanotubes and a shell structure of glycidyloxypropyltrimethoxysilane-modified polyphenylene ether.

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

[0015] Slowly adding calcium chloride into methyl pyrrolidone, stirring and dispersing to obtain a mixed solvent; dissolving dodecanediamine and 3,5-diaminobenzoic acid in methyl pyrrolidone to obtain a pre-reactant; dissolving m-phenylenediamine in the mixed solvent, slowly adding the pre-reactant, heating to 15-20° C., dropwise adding isophthaloyl chloride methyl pyrrolidone solution, and carrying out a modification reaction for 4-6 hours to obtain a reaction system; adding methanol to the reaction system, centrifuging, washing with deionized water to obtain a precipitate; and vacuum drying the precipitate to obtain a modified copolymer.

[0016] Preferably, the molar ratio of m-phenylenediamine to m-phthaloyl 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 comprises the following steps:

[0018] Methyl pyrrolidone is added to the shell structure and stirred evenly to obtain a shell solution; the core structure is dissolved in methyl pyrrolidone and ultrasonically dispersed to obtain a core dispersion; the core dispersion is added to the shell solution and dispersed at high speed shear to obtain a mixed system; the mixed system is transferred to a reactor, azobisisobutyronitrile is added, the temperature is raised to 80-90° C., and a polymerization reaction is carried out for 4-6 hours to obtain a functional core-shell structure dispersion; wherein the mass ratio of the shell structure to the core structure is 2-5:1.

[0019] Preferably, the preparation of the core layer structure comprises 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, and refluxed with stirring; then, the acidified carbon nanotubes were washed with deionized water until neutral, centrifuged, and vacuum dried to obtain the acidified carbon nanotubes;

[0021] Acidified carbon nanotubes are dispersed in a 95% ethanol solution and ultrasonically dispersed to obtain a suspension; ammonium persulfate is dissolved in deionized water to obtain an ammonium persulfate solution; aniline monomer is added to the suspension, and under nitrogen protection, the temperature is controlled at 3-5°C, the ammonium persulfate solution is added dropwise, and the mixture is stirred and reacted for 15-18 hours to obtain modified carbon nanotubes; the core layer structure is then obtained by separation and centrifugation, alternately washing with ethanol and deionized water, and vacuum drying; wherein the mass ratio of aniline monomer to carbon nanotubes is 0.5-0.8:1; and the molar ratio of ammonium persulfate to aniline monomer is 0.8-1.2:1.

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

[0023] Polyphenylene ether is dissolved in tetrahydrofuran to obtain a polyphenylene ether solution; glycidyloxypropyltrimethoxysilane is dissolved in 95% ethanol solution, glacial acetic acid is added to adjust the pH value, and the mixture is stirred and dissolved to obtain a silane solution; the polyphenylene ether solution is added to the silane solution, and the mixture is stirred and reacted to obtain a reaction system; the reaction system is poured into methanol for precipitation, separated by centrifugation, washed with deionized water, and vacuum dried to obtain a shell structure; the polyphenylene ether model is Noryl SE1.

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

[0025] Nano-silica with an average particle size of 50-80 nm is added to a 95% ethanol solution, uniformly dispersed by ultrasonication, and glacial acetic acid is added to adjust the pH to obtain a dispersion; glycidyloxypropyltrimethoxysilane is dissolved in a 95% ethanol solution, glacial acetic acid is added to adjust the pH, and the solution is stirred and dissolved to obtain a solution; the solution is slowly added to the dispersion, and the modification reaction is stirred to obtain a modified product; the modified product is centrifuged, washed with ethanol, and vacuum dried to obtain the modified nano-silica.

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

[0027] Preferably, in the dry-wet spinning process, the spinning temperature is controlled at 60-80°C, the spinning speed is 100-200m / min, and the aperture of the spinneret is adjusted to 0.1-0.2mm according to the fiber diameter requirements; the ejected spinning solution first enters the dry coagulation zone, the temperature is controlled at 30-50°C, and the residence time is 1-3s, so that the spinning solution is initially coagulated and formed; then a wet coagulation bath is performed, the wet coagulation bath consists of NMP and water in a mass ratio of 1:2, the temperature is 25-30°C, and the fiber residence time is 5-10min to obtain the nascent fiber; the nascent fiber is sequentially subjected to two-stage stretching treatment, the first-stage stretching ratio is 2-3 times, the temperature is 60-80°C, and the second-stage stretching ratio is 3-4 times, and the temperature is 80-100°C to obtain the stretched fiber.

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

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] 1. The present invention introduces flexible long chains through dodecanediamine, increases the distance between molecular chains, reduces the intermolecular force, and improves the flexibility of the chain segments. At the same time, 3,5-diaminobenzoic acid can introduce rigid benzene rings and amino groups, enhances the hydrogen bonding and rigidity between molecular chains, and utilizes the synergistic effect of the two to modify the meta-aramid fiber, thereby improving the overall mechanical properties of the fiber; at the same time, the synergistically modified nano-silica is uniformly dispersed in the fiber matrix, forms a good interface bond with the polymer matrix, and disperses the stress to achieve an enhanced toughening effect; the core layer structure in the functional core-shell structure enhances the electrical conductivity, thermal conductivity and mechanical properties of the fiber, and the shell layer structure improves the compatibility and dispersibility with the matrix. The pre-dispersion process is utilized to improve the compatibility with the polymer matrix, increase the interface bonding force, and synergistically utilize the core-shell structure to further improve the overall mechanical properties of the fiber; a two-stage stretching process is introduced to further eliminate the stress between fibers, maintain the balance between breaking strength and breaking elongation, and improve the mechanical properties of the composite fiber.

[0031] 2. The present invention ensures the flexibility of the fiber while maintaining sufficient rigidity and stability between molecular chains through the synergistic effect of 3,5-diaminobenzoic acid and dodecanediamine, so that the fiber is not easily deformed and structurally damaged at high temperatures, and the heat resistance is improved; in addition, modified nano-silica is introduced to play a reinforcing and thermal stabilizing role in the fiber, which can disperse heat, inhibit thermal motion of molecular chains, and synergize with other components to enhance heat resistance; the synergistic effect of the shell layer and the core layer is utilized to form a stable and efficient heat conduction and reinforcement system, so that the fiber effectively resists thermal damage at high temperatures and has improved heat resistance; finally, through the pre-dispersion liquid mixing process, the components are evenly dispersed, the interface bonding and interaction are promoted, the synergistic dispersion and interaction mechanism between the components are improved, and the heat resistance of the fiber is further improved while maintaining good mechanical properties.

[0032] 3. The present invention uses modified carbon nanotubes as the core layer, which has good conductivity and can provide a path for charge conduction; the shell structure maintains the insulation performance of the fiber to a certain extent, prevents leakage, and maintains the insulation performance of the fiber surface; the core structure has conductivity and stable support, but has poor dispersion in the matrix, and the shell structure is used to help disperse it, avoid agglomeration, and improve the insulation effect at the same time; the core-shell structure is used to synergistically ensure dispersion and performance balance, and then by controlling the mass ratio of the core layer to the shell layer, chemical improvements and physical dispersion processes are introduced to further improve the uniform dispersion and interaction of the components in the matrix, so that the antistatic and insulation properties are improved and balanced, and the application range of the composite fiber is increased. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a graph showing the change in the breaking strength retention rate of the composite fibers obtained in Examples 7-9, Comparative Example 1, Comparative Example 4, Comparative Example 8, and Comparative Example 11 of the present invention. DETAILED DESCRIPTION

[0034] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0035] See also Figure 1 The present invention provides a modified meta-aramid composite fiber and a preparation method thereof, and the technical solution is as follows:

[0036] Example 1

[0037] Calcium chloride was slowly added to a methyl pyrrolidone solvent and stirred at 40°C to obtain a mixed solvent with a mass concentration of 8%. Dodecanediamine and 3,5-diaminobenzoic acid were dissolved in methyl pyrrolidone to obtain a pre-reactant. Under nitrogen protection, m-phenylenediamine was dissolved in the mixed solvent, the pre-reactant was slowly added, and the mixture was stirred to dissolve. The mixture was heated to 20°C, and a solution of isophthaloyl chloride in methyl pyrrolidone was slowly added dropwise. The reaction was carried out at 500 rpm for 5 hours to obtain a modified copolymer. Methanol was added to the reaction system and stirred at 400 rpm for 2 hours. The mixture was then centrifuged and washed three times with deionized water to obtain a precipitate. The precipitate was placed in a vacuum drying oven and dried in vacuo at 60°C for 5 hours 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] The carbon nanotubes 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, and refluxed at 60°C for 2 hours; then, the mixture was repeatedly washed with deionized water until neutral, and then centrifuged and dried in a vacuum drying oven at 50°C for 10 hours to obtain the acidified carbon nanotubes;

[0039] The acidified carbon nanotubes were dispersed in a 95% ethanol solution and ultrasonically dispersed at 300W for 60 minutes to obtain a 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, wherein the mass ratio of aniline monomer to carbon nanotubes was 0.6:1. Under nitrogen protection, the temperature was controlled at 5°C, and the ammonium persulfate solution was slowly added dropwise for 30 minutes. After the addition was completed, the mixture was stirred and reacted for 16 hours to obtain modified carbon nanotubes. The core layer structure was obtained by separation and centrifugation, alternating washing with ethanol and deionized water for 3 times, and vacuum drying at 60°C for 15 hours. 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, glacial acetic acid was added to adjust the pH to 5, and the solution was stirred to obtain a silane solution; the polyphenylene ether solution was heated to 60°C, the silane solution was slowly added dropwise, and the mixture was stirred and reacted for 6 hours to obtain a reaction system; the reaction system was poured into methanol for precipitation, separated and centrifuged, washed with deionized water, and dried in vacuo at 50°C for 8 hours to obtain a shell structure;

[0041] Methyl pyrrolidone was added to the shell structure and stirred to obtain a shell solution; the core structure was dissolved in methyl pyrrolidone and ultrasonically dispersed to obtain a core dispersion; the core dispersion was added to the shell solution and dispersed under a high-speed shear device at a speed of 2000 rpm for 2 hours to obtain a mixed system; the mixed system was transferred to a reactor, 0.3% by mass of 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 set aside; wherein 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, uniformly dispersed by ultrasonication, and glacial acetic acid was added to adjust the pH value to 4 to obtain a dispersion; 10 parts of KH5605 were dissolved in a 95% ethanol solution, glacial acetic acid was added to adjust the pH value to 4, and the solution was stirred to dissolve; the solution was slowly added to the dispersion, the temperature was raised to 60° C., and the modification reaction was stirred for 4 hours to obtain a modified product; the modified product was centrifuged, washed with ethanol 5 times, and vacuum dried at 80° C. for 10 hours to obtain modified nano-silica;

[0043] The modified copolymer was added to NMP, heated to 90°C at 200rpm, stirred and dissolved for 4h to obtain a uniform solution, and kept warm for later use; modified nano-silica was added to the functional core-shell structure dispersion, and the ultrasonic dispersion power was maintained at 400W and the frequency was 30kHz. The ultrasonic dispersion was carried out for 2h to obtain a uniform pre-dispersion liquid, and intervals were kept during the ultrasonic process; zinc stearate, antioxidant 1010, and triphenyl phosphate were added to the uniform solution at 200rpm, stirred for 30min, and mixed to obtain a mixed solution; the pre-dispersion liquid was slowly added to the mixed solution, heated to 70°C, and blended and stirred for 4h. During this period, short-time ultrasonic dispersion was adopted, and ultrasonication was carried out for 5min every 30 minutes of stirring. After stirring, a mixed solution was obtained; the mixed solution was placed under vacuum conditions with a vacuum degree of less than -0.09MPa, and slowly stirred and degassed to obtain a spinning solution. The mass concentration of the modified copolymer is 18%, the mass concentration of the functional core-shell structure is 6%, the mass concentration of the modified nano-silica is 4%, the mass concentration of zinc stearate is 0.8%, the mass concentration of antioxidant 1010 is 0.5%, the mass concentration of triphenyl phosphate is 0.6%, and the balance is NMP.

[0044] The spinning solution is transported to the spinneret of the spinning machine through a metering pump, and the dry-wet spinning process is used to form fibers to obtain spun fibers; the spun fibers are sequentially subjected to two-stage stretching treatments to obtain stretched fibers; and then heat-setting treatment is performed under nitrogen protection at a controlled temperature of 280°C for 30 seconds, and the modified meta-aramid composite fibers are obtained by cooling and winding.

[0045] Examples 2-6 refer to the preparation methods and parameter conditions of Example 1, with the differences shown in Table 1.

[0046] Table 1 Parameter changes of Examples 1-6

[0047]

[0048] Comparative Example 1 refers to Example 1, except that the copolymer is not subjected to modification treatment.

[0049] Comparative Example 2 refers to Example 1, except that only dodecanediamine was used for modification.

[0050] Comparative Example 3 refers to Example 1, except that only 3,5-diaminobenzoic acid is used for modification treatment.

[0051] Comparative Example 4 refers to Example 1, except that modified nano-silica is not added.

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

[0053] Comparative Example 6 refers to Example 1, except that it is only stretched at 60°C with a stretching ratio of 4.

[0054] Comparative Example 7 refers to Example 1, except that it is only stretched at 100°C with a stretching ratio of 4.

[0055] Comparative Example 8 refers to Example 1, except that the functional core-shell structure is not added.

[0056] Comparative Example 9 refers to Example 1, except that the core-shell structure is not introduced and only the core-layer structure is used.

[0057] Comparative Example 10 refers to Example 1, except that the core-shell structure is not introduced and only the shell structure is used.

[0058] Comparative Example 11 refers to Example 1, except that the spinning solution is directly blended without going through the pre-dispersion liquid mixing process.

[0059] Experimental Example 1 Mechanical Properties Test

[0060] The modified meta-aramid composite fibers prepared 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 Breaking 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] From the results in Table 2, it can be seen that the comparative example cannot maintain a balance between the breaking strength and the breaking elongation compared with the embodiment, which further affects the further application of the composite fiber in the subsequent process; from the results of comparative examples 1-3, it can be seen that without modifying the copolymer, the mechanical properties of the composite fiber are poor, the unmodified copolymer molecular chain has high regularity, high rigidity, strong intermolecular force, and lacks flexible adjustment; when subjected to force, it is difficult for the molecular chain to slip and orient relative to each other, and stress concentration can easily lead to fiber breakage, thereby reducing the breaking strength. At the same time, the breaking elongation also becomes smaller due to the difficulty of stretching the rigid molecular chain; the introduction of flexible long chains by dodecanediamine can increase the molecular chain spacing, reduce the intermolecular force, and improve the segment flexibility; 3,5-diaminobenzene Formic acid enhances the rigidity of the molecular chain and the effect of intermolecular hydrogen bonds. By controlling the amount of the two, the mechanical properties of the composite fiber are synergistically improved. The results of comparative examples 4-5 show that when modified nano-silica is not added, the internal defects of the fiber increase, and the cracks tend to expand rapidly when subjected to stress, resulting in a decrease in breaking strength. In addition, without the toughening effect of nano-silica, the fiber's ability to resist deformation is weakened, and the elongation at break is also reduced. Without the modification of nano-silica, due to its high surface energy, it is easy to agglomerate, and its dispersion in the fiber matrix is poor. The agglomerated particles will become stress concentration points, reducing the mechanical properties of the fiber. In addition, the unmodified nano-silica has a weak interface with the polymer matrix and cannot effectively transfer stress. When subjected to stress, the particles and the matrix are easily Debonding leads to further reduction of breaking strength and elongation at break; in comparative examples 6-7, multi-stage stretching treatment is not used, and the lower stretching temperature makes the molecular chain activity limited, and it is not possible to fully arrange the molecular chains as regular as two-stage stretching. The internal structure of the fiber is loose, the crystallization is imperfect, and the force between the molecular chains is weak, resulting in low breaking strength; higher stretching temperature makes it difficult to achieve fine orientation and perfect crystallization of the molecular chains, and there are more defects and stress concentration points inside the fiber. In addition, high-temperature stretching may cause degradation or thermal damage of some molecular chains, further reducing the strength of the fiber; the results of comparative examples 8-10 show that without adding a functional core-shell structure, the fiber cannot effectively disperse stress and enhance mechanical properties, and the breaking strength and elongation at break will be reduced. Reduced, while the core layer structure has a reinforcing effect, the shell structure can improve its dispersibility in the matrix and the interface bonding with the matrix, the use of a single component has poor compatibility with the fiber matrix, uneven dispersion in the spinning solution, easy to agglomerate to form defects, forming stress concentration points in the subsequent processing process, thereby reducing the mechanical properties of the fiber, combined with Comparative Example 11, without pre-dispersion treatment, resulting in poor dispersion uniformity of the functional core-shell structure and modified nano-silica, forming agglomerates, and then forming stress concentration points in the fiber; in addition, when directly blended, the components cannot fully contact and interact with each other, the interface bonding force is weak, and the stress cannot be evenly distributed in the entire fiber system, which reduces the bearing capacity of the fiber and reduces the breaking strength;Due to poor interfacial bonding, the components cannot deform synergistically during the stretching process, and the fiber is prone to local damage, which limits the tensile properties of the fiber and reduces the elongation at break.

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

[0065] Examples 8-11 refer to the preparation methods and parameter conditions of Example 1, with the differences shown in Table 3.

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

[0067]

[0068] Experimental Example 2 Heat Resistance Test

[0069] The composite fibers prepared in Examples 7-11, Comparative Examples 1-5, and Comparative Examples 8-11 were subjected to a heat aging test. The composite fibers were wound in a crucible and placed in a high-temperature oven at a treatment temperature of 300°C for 500 hours. After cooling, the composite fibers were taken out and the breaking strength was tested. The breaking strength retention rate of the composite fibers compared to the untreated fibers was calculated. The test results are shown in Table 4. Figure 1 This is a graph showing the change in breaking strength retention rate of Examples 7-9, Comparative Example 1, Comparative Example 4, Comparative Example 8, and Comparative Example 11.

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

[0071] Example Breaking 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] It can be seen from the results in Table 4 that the comparative example shows a lower breaking strength retention rate than the embodiment, and the heat resistance is significantly reduced; the results of comparative examples 1-3 show that the modification of the copolymer by dodecanediamine and 3,5-diaminobenzoic acid can optimize the molecular chain structure, the flexible chain segment of dodecanediamine can relieve stress concentration between molecular chains, and the rigid groups introduced by 3,5-diaminobenzoic acid enhance the interaction force between molecular chains and thermal stability. The molecular chain of the unmodified copolymer has high regularity and high rigidity. When heated, it is difficult for the molecular chain to disperse heat through slight adjustments, and it is easy to thermally degrade and thermally oxidize, destroying the internal structure of the fiber; lacking the synergy of 3,5-diaminobenzoic acid and dodecanediamine, it is impossible to maintain sufficient rigidity and stability between molecular chains while ensuring flexibility, making the fiber more prone to deformation and structural damage at high temperatures, and the heat resistance is reduced; in comparative examples 4-5, the modified nano-silica plays a reinforcing and thermal stabilizing role in the fiber, which can disperse heat The amount of modified nanosilica is high, and the thermal motion of the molecular chain is inhibited. When it is not added, the fiber lacks a thermally stable reinforcing phase, and the molecular chain is more easily disordered and degraded due to thermal action at high temperature. In addition, the surface energy of unmodified nanosilica is high, it is easy to agglomerate, and its dispersion in the fiber is poor, and it cannot effectively play the role of reinforcement and thermal stability. The agglomerates will also form thermal stress concentration points, which accelerate the structural damage of the fiber at high temperature. In comparative examples 8-10, no functional core-shell structure is added, and the fiber lacks efficient heat conduction and stable structural support. The core layer in the functional core-shell structure has high thermal conductivity and can quickly disperse heat. The shell layer improves the compatibility with the matrix and enhances the structural stability, thereby improving the thermal stability of the matrix. The results of comparative example 11 show that direct blending leads to uneven dispersion of the components, poor interface bonding, uneven heat transfer at high temperature, and easy local overheating and stress concentration, which in turn makes the structural stability of the fiber worse at high temperature, the breaking strength retention rate is reduced, and the heat resistance is reduced.

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

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

[0075] Table 5 Parameter changes of Examples 12-16

[0076]

[0077] Comparative Example 8 refers to Example 1, except that the functional core-shell structure is not added.

[0078] Comparative Example 9 refers to Example 1, except that the core-shell structure is not introduced and only the core-layer structure is used.

[0079] Comparative Example 10 refers to Example 1, except that the core-shell structure is not introduced and only the shell structure is used.

[0080] Comparative Example 11 refers to Example 1, except that the spinning solution is directly blended without going through the pre-dispersion liquid mixing process.

[0081] Comparative Example 12 refers to Example 1, except that the carbon nanotubes are not subjected to aniline modification treatment.

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

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

[0084] Comparative Example 15 refers to Example 1, except that the ultrasonic dispersion process is not introduced during the preparation of the spinning solution.

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

[0086] Comparative Example 17 refers to 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 Performance

[0088] The antistatic insulation performance of the composite fibers prepared in Examples 12-16 and Comparative Examples 8-17 was tested. The dielectric strength of the composite fibers was tested according to GB / T 1408.1-2016; 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] From the results in Table 6, it can be seen that the comparative example cannot maintain the balance of insulation performance and antistatic performance compared with the embodiment, which affects the normal use of the protective clothing when the composite fiber is used in the process of electric power protective clothing; the results of comparative examples 8-10 show that the core layer in the functional core-shell structure is modified carbon nanotubes, which has good conductivity and can provide a path for charge conduction. Combined with comparative example 12, aniline-modified carbon nanotubes can enhance their conductivity. Without modification, the carbon nanotubes have poor conductivity and low charge conduction efficiency. The lack of carbon nanotubes leads to the lack of efficient conductive paths in the fibers, making it difficult for charges to be quickly transferred. The shell structure is introduced to maintain the insulation performance of the fiber and prevent leakage. In combination with Comparative Example 13, silane-modified polyphenylene ether can improve its compatibility and dispersibility with other components, which is beneficial to charge conduction. Without modification, the shell layer is not tightly combined with other components, and gaps and defects are prone to occur, which affects the formation of the overall conductive network, increases the surface resistivity, affects the antistatic performance, and reduces the dielectric strength. The results of Comparative Example 11 show that the pre-dispersion liquid mixing can make the components evenly dispersed, avoid the uneven dispersion caused by direct blending, and the conductive component The distribution of the components is uneven, the charge conduction is blocked, the surface resistivity increases, the antistatic performance deteriorates, and the conductive components are locally aggregated, forming a conductive hidden danger, reducing the dielectric strength, and destroying the insulation performance; the results of Comparative Example 14 show that the high-speed shear dispersion makes the core-shell structure evenly dispersed in the fiber matrix, forming a uniform conductive network, avoiding uneven dispersion of the components, resulting in discontinuous conductive network, difficult charge conduction, increased surface resistivity, reduced dielectric strength, and decreased antistatic ability and insulation performance; In Comparative Example 15, the introduction of ultrasonic dispersion can further refine the components, promote uniform dispersion and interaction , which is conducive to the formation of a good conductive network, the surface component dispersion effect is reduced, the surface resistivity is increased, and insufficient dispersion will cause the conductive particles to agglomerate, reduce the dielectric strength, and affect the insulation performance; in Comparative Examples 16-17, by changing the mass ratio of the core layer structure and the shell layer structure, the imbalance of the core-shell mass ratio destroys the mechanism of the core-shell structure to synergistically improve the antistatic and insulation performance, affecting the balance of performance; polyphenylene ether itself is an insulating material with good dielectric properties and heat resistance. It is coated on the surface of carbon nanotubes through the core-shell structure to isolate the carbon nanotubes and regulate the overall conductive / insulating performance. Too many shell layers wrap the core layer, hindering charge conduction, and may introduce more insulating impurities. Although the dielectric strength has increased, the antistatic performance has dropped significantly, and the overall performance balance has been destroyed; too few shell layers cannot effectively wrap and isolate the core layer, the dielectric strength is reduced, the insulation performance is damaged, and the balance is destroyed.

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

Claims

1. A method for preparing a modified meta-aramid composite fiber, characterized in that: The preparation of the aramid composite fiber comprises the following steps: The modified copolymer is dissolved to obtain a uniform solution; the modified nano-silica is added to the functional core-shell structure dispersion, and ultrasonic dispersion is performed to obtain a pre-dispersion solution; an auxiliary agent is added to the uniform solution, and then the pre-dispersion solution is added, mixed and stirred, and vacuum degassed to obtain a spinning solution; and the aramid composite fiber is obtained by dry-wet spinning, two-stage stretching, heat setting treatment, cooling and winding. The modified copolymer is prepared by adding isophthaloyl chloride to m-phenylenediamine, dodecanediamine and 3,5-diaminobenzoic acid; The modified nano-silica is obtained by modifying nano-silica with glycidyloxypropyltrimethoxysilane; The functional core-shell structure dispersion is obtained by polymerization of a core structure of polyaniline-modified carbon nanotubes and a shell structure of glycidyloxypropyltrimethoxysilane-modified polyphenylene ether.

2. The method for preparing a modified meta-aramid composite fiber according to claim 1, wherein: The preparation of the modified polymer comprises the following steps: Slowly adding calcium chloride to methyl pyrrolidone, stirring and dispersing to obtain a mixed solvent; dissolving the dodecanediamine and the 3,5-diaminobenzoic acid in the methyl pyrrolidone to obtain a pre-reactant; dissolving the m-phenylenediamine in the mixed solvent, slowly adding the pre-reactant, heating to 15-20° C., dropwise adding a solution of isophthaloyl chloride in methyl pyrrolidone, and carrying out a modification reaction for 4-6 hours to obtain a reaction system; adding methanol to the reaction system, centrifuging, and washing with deionized water to obtain a precipitate; and vacuum drying the precipitate to obtain the modified copolymer.

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

1.

4. The method for preparing a modified meta-aramid composite fiber according to claim 1, wherein: The preparation of the functional core-shell structure comprises the following steps: Methyl pyrrolidone is added to the shell structure and stirred evenly to obtain a shell solution; the core layer structure is dissolved in the methyl pyrrolidone and ultrasonically dispersed to obtain a core layer dispersion; the core layer dispersion is added to the shell solution and high-speed shear dispersion is performed to obtain a mixed system; the mixed system is transferred to a reactor, azobisisobutyronitrile is added, the temperature is raised to 80-90° C., and a polymerization reaction is performed for 4-6 hours to obtain the functional core-shell structure dispersion; wherein the mass ratio of the shell structure to the core layer 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 comprises the following steps: The carbon nanotubes 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, and refluxed with stirring; then, the carbon nanotubes were washed with deionized water until neutral, centrifuged, and vacuum dried to obtain the acidified carbon nanotubes; The acidified carbon nanotubes are dispersed in a 95% ethanol solution and subjected to ultrasonic dispersion to obtain a suspension; ammonium persulfate is dissolved in deionized water to obtain an ammonium persulfate solution; aniline monomer is added to the suspension, and under nitrogen protection, the temperature is controlled at 3-5°C, the ammonium persulfate solution is added dropwise, and the mixture is stirred for reaction for 15-18 hours to obtain modified carbon nanotubes; the core layer structure is then obtained by separation and centrifugation, alternately washing with ethanol and deionized water, and vacuum drying; wherein the mass ratio of the aniline monomer to the carbon nanotubes is 0.5-0.8:1; and the molar ratio of the ammonium persulfate to the aniline monomer is 0.8-1.2:

1.

6. The method for preparing a modified meta-aramid composite fiber according to claim 4, wherein: The preparation of the shell structure comprises the following steps: The polyphenylene ether is dissolved in tetrahydrofuran to obtain a polyphenylene ether solution; glycidyloxypropyltrimethoxysilane is dissolved in a 95% ethanol solution, glacial acetic acid is added to adjust the pH value, and the solution is stirred to obtain a silane solution; the polyphenylene ether solution is added to the silane solution, and the mixture is stirred to react at a temperature of 100°C to obtain a reaction system; the reaction system is poured into methanol for precipitation, separated by centrifugation, washed with deionized water, and vacuum dried to obtain the shell structure.

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

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

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