Method for modifying high-elongation heterocyclic aramid fibers

Abstract

This invention discloses a method for modifying high-elongation heterocyclic aramid fibers, belonging to the field of high-performance organic fiber surface treatment technology. The method includes: preparing a polymerization solution, preparing a polymerization spinning solution, filtering and degassing, metering extrusion, coagulation molding, stretching, and washing; then sequentially performing oiling treatment, roller drying, and hot stretching; followed by impregnation with a surface treatment agent composed of glycerol triglycidyl ether and sorbitol polyglycidyl ether; and finally, continuous drying in a non-contact hot drying tunnel followed by winding to obtain high-elongation modified heterocyclic aramid fibers. The oiling agent used in the oiling treatment includes fatty alcohol polyoxyethylene ether phosphate. This invention significantly improves the interfacial adhesion between the fiber and rubber or epoxy resin while maintaining the original strength and elongation of the fiber, improves the dispersion and smoothness of the fiber bundle, reduces static electricity generation, and does not increase production costs or reduce production efficiency.

Description

Technical Field

[0001] This invention relates to the field of high-performance organic fiber surface treatment technology, specifically to a method for modifying high-elongation heterocyclic aramid fibers. Background Technology

[0002] High-elongation heterocyclic aramid fibers refer to a type of para-aramid fiber containing aromatic heterocycles and ether structures in the main chain. By introducing 4,4′-diaminodiphenyl ether or 3,4′-diaminodiphenyl ether structural units into the typical aromatic heterocycle structure, the proportion of rigid molecular chain structure is reduced while preparing a high molecular weight polymerization spinning solution. The product is then produced by wet spinning process, with a strength ≥3.5GPa and an elongation at break of over 6%.

[0003] Heterocyclic aramid fibers possess excellent properties such as lightweight, high strength and modulus, high heat resistance, and solvent resistance, exhibiting superior mechanical properties compared to typical aramid II fibers. However, the following technical challenges exist in the manufacturing process of heterocyclic aramid fibers: The inertness of the fiber surface leads to poor interfacial adhesion. Heterocyclic aramids tend to form a skin structure during the wet spinning process, with extremely high axial orientation and crystallinity, resulting in a dense, smooth, and chemically inert fiber surface structure. This leads to poor adhesion when bonded to matrices such as rubber or epoxy resin. Existing surface modification techniques, such as plasma treatment, radiation treatment, acid and alkali etching, direct fluorination, and covalent grafting, can improve interfacial adhesion to some extent, but they suffer from drawbacks such as long processing times, complex processes, the need for organic solvents, and damage to the mechanical properties of the fiber itself.

[0004] The problem of fiber bundle cohesion affects subsequent processing. During the heat treatment stretching and orientation process of high elongation heterocyclic aramid fibers, due to the large stretching ratio of the fiber bundle, the individual filaments of the bundle are prone to cohesion due to electrostatic and hydrogen bonding. This makes the fiber bundle hard, tightly cohesive, and not loose. In the later impregnation process, problems such as insufficient and uneven impregnation occur, which seriously affects the composite effect of fiber and matrix resin.

[0005] While existing surface coating technologies (such as silane coupling agent treatment) can improve the interfacial bonding between fibers and the matrix, the adhesion between the coating and the fiber relies on physical adsorption, and is prone to peeling due to friction and aging during long-term use, resulting in insufficient stability. Although technologies such as direct fluorination can improve interfacial shear strength, some amide bonds will inevitably be broken during the treatment process, affecting the mechanical properties of the fiber itself.

[0006] Since downstream applications are mainly tire cords, tensile cores for industrial synchronous belts, and automotive belt skeleton materials that are composited with rubber or epoxy, improving the bonding performance of high-elongation heterocyclic aramid fibers with rubber and epoxy resin, while solving the problem of fiber bundle cohesion to ensure uniform dispersion of monofilaments, are currently critical manufacturing process issues that urgently need to be addressed. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of existing high-elongation heterocyclic aramid fibers, such as poor interfacial adhesion and difficulty in dispersion of fiber bundles, and to provide a modification method for high-elongation heterocyclic aramid fibers that simultaneously improves fiber bundle dispersion and interfacial adhesion without increasing production costs or reducing production efficiency.

[0008] The objective of this invention is achieved through the following technical solution: On one hand, the present invention provides a method for modifying high-elongation heterocyclic aramid fibers, comprising the sequential steps of preparing a polymerization solution, preparing a polymerization spinning solution, filtering and degassing, metering extrusion, coagulation molding, stretching, and washing. The method is characterized in that the washed fibers are oiled, dried by roller drying, and then hot-stretched. The hot-stretched fibers undergo surface treatment, are continuously dried in a non-contact hot drying tunnel, and finally wound to obtain high-elongation modified heterocyclic aramid fibers. The oiling process involves impregnating the washed fibers with a fatty alcohol polyoxyethylene ether phosphate solution. The surface treatment involves impregnating the heat-stretched fibers with a mixture of glycerol triglycidyl ether and sorbitol polyglycidyl ether. Furthermore, in the oiling process, the immersion time is at least 2 seconds, and the fatty alcohol polyoxyethylene ether phosphate solution is a solution diluted with deionized water to a concentration of 2‰-5%. Furthermore, the drying temperature of the roller dryer is 90-150℃, the drying time is at least 60 seconds, and the moisture content of the fiber after drying is no more than 7%. Furthermore, the hot stretching treatment is carried out in a nitrogen atmosphere, the stretching temperature is 400-500℃, the stretching ratio is 80%, and the hot stretching time is at least 15 seconds. Furthermore, in the mixture, the mass ratio of glycerol triglycidyl ether to sorbitol polyglycidyl ether is 2.5-3.5:1.5-0.5, and the mixture is diluted with deionized water to a mass percentage concentration of 40%. Furthermore, in the surface treatment, the impregnated fibers are flattened by a polytetrafluoroethylene pressure roller; Furthermore, the non-contact hot drying tunnel continuous drying is a two-stage hot air drying, wherein the first stage drying temperature is 90-120℃ and the drying time is 20-25 seconds; The second stage of drying is at a temperature of 120-150℃ and a drying time of 25-30 seconds. After continuous drying in the non-contact hot drying tunnel, the fiber moisture content is less than or equal to 1%.

[0009] On the other hand, the present invention provides a high elongation modified heterocyclic aramid fiber.

[0010] Furthermore, the high-elongation modified heterocyclic aramid fiber has improved tow dispersion and interfacial adhesion properties.

[0011] This invention uses fatty alcohol polyoxyethylene ether phosphate (MOA9P) for oiling treatment, which can significantly reduce the surface resistance of fibers and rapidly dissipate static electricity. At the same time, its long-chain alkyl groups form a lubricating layer on the fiber surface, reducing the coefficient of friction between fibers and promoting the transformation of the fiber bundle from a cohesive state to a loosely dispersed state. The amphiphilic structure of MOA9P is beneficial for transforming the hydrophobic fiber surface into a wettable polar surface, which is conducive to the uniform spreading and penetration of subsequent surface treatment agents.

[0012] Based on this, a surface treatment agent composed of glycerol triglycidyl ether (GTE) and sorbitol polyglycidyl ether (SGE) was used for modification. GTE has a small molecular weight and good permeability, which can penetrate deep into the fiber surface and shallow layer; SGE molecules contain multiple glycidyl ether groups, which is beneficial for forming multi-point bonds with rubber or epoxy resin matrix.

[0013] In this application, the MOA9P oiling treatment and the GTE / SGE surface treatment work together to achieve the technical effect of improving interfacial adhesion performance while maintaining the fiber's bulk strength and elongation.

[0014] The beneficial effects of this invention are: 1. This invention uses a self-circulating oiling method to apply a specially formulated oil (MOA-9P), which significantly reduces the fiber bundle agglomeration rate, improves fiber bundle dispersion, and makes the fiber texture soft, which is beneficial for the full wetting of monofilaments during subsequent impregnation. A uniform and extremely thin oil film is formed on the surface of the monofilaments, which does not block the fiber surface structure and is beneficial for the adhesion of fibers to epoxy ethers, resins, etc. during subsequent impregnation. No glue forms on the surface of the dryer rollers, which does not affect the continuous production of fibers.

[0015] 2. This invention utilizes a non-contact continuous drying tunnel surface treatment method, combined with a special surface treatment agent, to significantly improve the properties of the finished fiber in terms of rubber peel strength, H-pull-out force, and interlayer shear force.

[0016] 3. This invention does not increase manufacturing costs or reduce production efficiency. It only optimizes part of the spinning process, which can simultaneously improve the dispersion and interfacial adhesion properties of high-elongation heterocyclic aramid fiber bundles. This has important value and significance for the development of high-elongation heterocyclic aramid fibers. Attached Figure Description

[0017] Figure 1This invention describes the modification process route for high-elongation heterocyclic aramid fibers. Detailed Implementation

[0018] The technical solutions in some embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments provided in this application, all other embodiments obtained by those skilled in the art are within the scope of protection of this application.

[0019] Example 1 A surface treatment method for high elongation heterocyclic aramid fibers includes the following steps: S1. Add 555 L of DMAC (dimethylacetamide) solvent with a moisture content of 135 ppm to a 1000 L polymerization reactor.

[0020] S2. Then, add 21.5 kg of anhydrous lithium chloride, which has been calcined at 400°C for 1 hour in advance, to the polymerization reactor containing solvent. This means that the content of anhydrous lithium chloride in the solvent system is about 3.7%.

[0021] S3. After stirring and dissolving in the polymerization reactor for 1 hour, the moisture content was measured to be 223 ppm.

[0022] S4. Based on the requirement that the total solid content of the four reactants in the polymer material is 6%, p-phenylenediamine (PPDA), 2-(4-aminophenyl)-5-aminobenzimidazole (APBIA), and 4,4'-diaminodiphenyl ether (4,4-ODA) are added to the polymerization reactor in a molar ratio of 1:1:1. The mass of the materials added is calculated based on the molecular weight of the materials.

[0023] S5. Start the polymerization reactor and stir to dissolve the material for 1 hour, maintaining the reactor temperature at 25°C. Use chilled brine through the reactor jacket to cool the material inside the reactor down to 0°C.

[0024] S6. Based on the requirement that the total solid content of the four reactants in the polymer material is 6%, calculate the total mass of terephthaloyl chloride added to the material by means of the molecular weight of the material, and add 98.5% of the theoretical total mass of terephthaloyl chloride (TPC) into the polymerization reactor for prepolymerization reaction.

[0025] S7. After stirring the reaction, based on the change in dynamic viscosity of the polymer reactants, the remaining portion of the theoretical total mass of terephthaloyl chloride (TPC) is added to the polymerization reactor in multiple batches for telomerization reaction.

[0026] S8. Sampling and testing: The dynamic viscosity of the polymerization spinning solution is 55,000 centipoise, indicating the reaction is complete.

[0027] S9. The obtained polymer spinning solution is extruded through a twin-screw extruder into a plate and frame filter for filtration and degassing, and then transferred to the spinning section storage tank. The plate and frame filter has a filtration accuracy of 1000 mesh.

[0028] S10. The polymer spinning solution is injected into an 800-hole spinneret with a hole diameter of 0.08mm through a micro metering pump. The spinneret is subjected to initial coagulation and forming in a coagulation bath according to the 1500D linear density specification, while being stretched. The stretching ratio is 80%, and the coagulation solution is an aqueous solution with a 55% DMAC content.

[0029] S11, the nascent fibers are washed in a washing machine using deionized water with a conductivity controlled below 20μS. They are then dried once more using drying rollers at a surface temperature of 110℃.

[0030] S12. Feed the nascent fibers into the guide roller of the oiling machine. The oiling machine uses a self-circulating oil replenishment system. The fibers are immersed and oiled in the oil tank of the oiling machine. The oiling agent is a mixture of MOA9P and deionized water with a concentration of 5‰.

[0031] S13. After oiling, the nascent fibers are continuously drawn into the heat treatment drying tunnel. The nascent fibers are thermally stretched by controlling the stretch ratio before and after the heat treatment drying tunnel. The length of the heat treatment drying tunnel is 11 meters, the internal temperature of the drying tunnel is 450℃, nitrogen atmosphere protection is provided, the fiber running speed is 40 meters / minute, and the stretch ratio is 80%.

[0032] S14. The heat-treated and stretched fibers are then drawn into a surface treatment machine. The surface treatment machine uses a self-circulating oiling system. After the fibers are impregnated with the surface treatment agent, they are smoothed by PTFE rollers. The surface treatment uses a mixture of glycerol triglycidyl ether (GTE) and sorbitol polyglycidyl ether (SGE) at a mass ratio of 2.5:1.5, diluted with 60°C deionized water to a concentration of 40%.

[0033] S15. After surface treatment, the fibers continuously enter the drying tunnel for non-contact drying. The drying tunnel consists of two independent sections. The first section has a drying temperature of 90-120℃ and a drying time of 20-25 seconds; the second section has a drying temperature of 120-150℃ and a drying time of 25-30 seconds. After the fibers undergo low-temperature drying to remove moisture in the first section, they are continuously fed into a winding machine for winding and testing after high-temperature cyclization and reinforcement in the second section. The testing items include filament agglomeration rate, rubber peel strength, H-pull force, and interlayer shear force of the fabric.

[0034] Example 2 The difference between Example 2 and Example 1 is as follows: In S1, the added DMAC solvent has a moisture content of 155 ppm; In S3, the moisture content after stirring and dissolving in the polymerization reactor was 285 ppm. In S10, the traction stretching ratio during initial solidification is 100%. In S14, the surface treatment uses a mixture of GTE and SGE in a 3:1 mass ratio.

[0035] The remaining steps and parameters are the same as in Example 1.

[0036] Example 3 The difference between Example 3 and Example 1 is as follows: In S1, the moisture content of the added DMAC solvent is 199 ppm; In S3, the moisture content after stirring and dissolving in the polymerization reactor was 279 ppm. In S14, the surface treatment uses a mixture of GTE and SGE in a mass ratio of 3.5:0.5.

[0037] The remaining steps and parameters are the same as in Example 1.

[0038] Comparative Example 1 The difference between Comparative Example 1 and Example 1 is that: in step S1, the moisture content of the added DMAC solvent was 189 ppm; in S3, the moisture content after stirring and dissolving in the polymerization reactor was 233 ppm; and there was no oiling or surface treatment. All other steps and parameters were the same as in Example 1.

[0039] Comparative Example 2 The difference between Comparative Example 2 and Example 3 is that in S3, the moisture content after stirring and dissolving in the polymerization reactor was 256 ppm; no surface treatment was performed. All other steps and parameters were the same as in Example 3.

[0040] Comparative Example 3 The difference between Comparative Example 3 and Example 3 is as follows: In S3, the moisture content after stirring and dissolving in the polymerization reactor was 256 ppm; in S14, the surface treatment was performed by diluting GTE with 60°C deionized water to a concentration of 40%. The remaining steps and parameters were the same as in Example 3.

[0041] Comparative Example 4 The difference between Comparative Example 4 and Example 3 is as follows: In S3, the moisture content after stirring and dissolving in the polymerization reactor was 256 ppm; in S14, the surface treatment involved mixing GTE and propylene glycol diglycidyl ether (PGDGE) at a mass ratio of 3.5:0.5, and diluting with deionized water at 60°C to a concentration of 40%. The remaining steps and parameters were the same as in Example 3.

[0042] Comparative Example 5 The difference between Comparative Example 5 and Example 3 is as follows: In S3, the moisture content after stirring and dissolving in the polymerization reactor was 256 ppm; in S12, the nascent fibers were fed into the guide roller of the oiling machine, which used a self-circulating oil replenishment system. The fibers were immersed and oiled in the oil tank of the oiling machine, and the oiling agent was prepared by mixing MOA-3P with deionized water at a concentration of 5‰. The remaining steps and parameters were the same as in Example 3.

[0043] Comparative Example 6 The difference between Comparative Example 6 and Example 3 is as follows: In S3, the moisture content after stirring and dissolving in the polymerization reactor was 256 ppm; in S14, the nascent fibers were fed into the guide roller of the oiling machine, which used a self-circulating oil replenishment system. The fibers were immersed and oiled in the oil tank of the oiling machine, and the oiling agent was prepared by mixing isotridecyl alcohol polyoxyethylene ether phosphate with 60°C deionized water at a concentration of 5‰. The remaining steps and parameters were the same as in Example 3.

[0044] Comparative Example 7 The difference between Comparative Example 7 and Example 3 is as follows: In step S1, the moisture content of the added DMAC solvent is 169 ppm; in S3, the moisture content after stirring and dissolving in the polymerization reactor is 228 ppm; in S14, the surface treatment is performed by diluting SGE with isopropanol to a concentration of 40%. The remaining steps and parameters are the same as in Example 3.

[0045] Comparative Example 8 The difference between Comparative Example 8 and Example 3 is as follows: In step S1, the moisture content of the added DMAC solvent is 177 ppm; in S3, the moisture content after stirring and dissolving in the polymerization reactor is 268 ppm; in S15, the surface-treated fibers are dried using a contact-type continuous drying roller at a drying temperature of 140°C for ≥2 minutes. All other steps and parameters are the same as in Example 3.

[0046] The data for each embodiment and comparative example are shown in Table 1.

[0047] Table 1 Example 1 25.51 6.8% 55230 0.5 4.3 223 33 Example 2 25.29 6.6% 67410 0.4 4.6 218 31 Example 3 25.26 6.8% 77260 0.4 4.4 219 31 Comparative Example 1 25.31 6.6% 74180 30.5 3.3 90 22 Comparative Example 2 25.24 6.9% 77320 0.4 3.8 105 25 Comparative Example 3 25.24 6.9% 77320 0.4 3.9 132 25 Comparative Example 4 25.24 6.9% 77320 0.4 3.7 128 24 Comparative Example 5 22.45 6.2% 77320 25.0 3.9 145 25 Comparative Example 6 23.15 6.3% 77320 0.5 3.8 135 26 Comparative Example 7 25.35 6.9% 69340 0.4 3.8 139 26 Comparative Example 8 25.16 6.8% 65895 0.4 3.5 125 24 As can be seen from the above data, through Comparative Examples 1 and 2, it can be seen that when high elongation heterocyclic aramid fibers are not treated with oiling agent such as fatty alcohol polyoxyethylene ether phosphate (MOA9P) in an impregnation tank, the fiber bundle agglomeration rate is significantly improved, and the fiber bundles exhibit a cohesive and non-loose state. Even after surface treatment, the performance of various aspects will significantly decrease when compounded with rubber.

[0048] Comparative Examples 3 and 4 show that after the fibers are oiled with fatty alcohol polyoxyethylene ether phosphate (MOA-9P) oil, when mixed with single-component GTE or PGDGE, the composite performance with rubber is improved to a certain extent. However, the peel strength and interlaminar shear force are still significantly different from those of the present invention. The main principle is that GTE has strong penetration ability and can reduce the surface tension of high-elongation heterocyclic aramid fibers, but its anchoring performance is weak. When used alone or mixed with other low-functionality active epoxy monomers, the fiber surface structure is simple, and the anchoring and cross-linking effects are insufficient.

[0049] As can be seen from Comparative Example 5, when the fiber is oiled with fatty alcohol polyoxyethylene ether phosphate (MOA-3P) oiling agent, the fiber bundle agglomeration rate is significantly improved, the fiber bundle is in a cohesive and non-loose state, a large amount of glue appears on the surface of the drying roller, and the mechanical properties of the fiber are significantly reduced due to its adhesion and pulling with the roller surface during the drying process.

[0050] As can be seen from Comparative Example 6, when the fiber is oiled with isotridecyl alcohol polyoxyethylene ether phosphate oil, the fiber bundle agglomeration rate decreases and no glue appears on the surface of the drying roller. However, the mechanical properties of the fiber decrease, and the composite properties with rubber, peel strength, and interlaminar shear force are still significantly different from those of the present invention. The main reason is that the oil film formed by isotridecyl alcohol polyoxyethylene ether phosphate on the surface of high-elongation heterocyclic aramid fiber is uneven and not dense. Under the special process of high-ratio stretching during heat treatment of high-elongation heterocyclic aramid, the fiber bundle slips, resulting in uneven stretching, which affects the mechanical properties. In addition, the high temperature of heat treatment of high-elongation heterocyclic aramid also causes partial precipitation of isotridecyl alcohol polyoxyethylene ether phosphate, affecting the subsequent composite performance.

[0051] As can be seen from Comparative Example 7, the surface treatment only uses SGE as a single component treatment agent. Due to its high concentration, it is difficult to dissolve in deionized water, so isopropanol is required for dilution. However, the subsequent composite performance is also significantly different from that of the present invention. The main reason is that the SGE film is too thick and has high molecular inertness, which causes the fiber surface to be completely sealed, and the fiber cannot form a cross-linked structure with rubber and other composite materials.

[0052] As can be seen from Comparative Example 8, the composite performance of the surface-treated fibers was not significantly improved by unsegmented contact drying. The main reason is that the moisture could not evaporate slowly in the one-stage high-temperature drying and contact extrusion. It rapidly vaporized at high temperature, carrying GTE which was quickly heated and floated to the surface, making it difficult to combine with the fiber surface. The SGE after high-temperature curing formed cavities or uneven oil films, thus affecting the subsequent composite performance.

[0053] This invention uses MOA-9P to oil the fibers, resulting in a dispersed and loose fiber structure without affecting their mechanical properties. The fibers are then dried and pre-cyclized using a continuous, segmented hot-drying tunnel with a mixture of GTE and SGE oils. This effectively removes moisture while GTE's strong penetrability allows it to penetrate the fiber surface and form chemical bonds, and SGE's high functionality enables it to form a high-density cross-linked network on the fiber surface. The synergistic effect of these two components creates a multi-dimensional network structure on the fiber surface, significantly improving anchoring and cross-linking properties, and substantially enhancing the interfacial adhesion between the fiber and rubber or epoxy resin.

[0054] The above description is merely a preferred embodiment of the present invention. It should be understood that the present invention is not limited to the forms disclosed herein and should not be construed as excluding other embodiments. It can be used in various other combinations, modifications, and environments, and can be altered within the scope of the concept described herein through the above teachings or related technologies or knowledge. Modifications and variations made by those skilled in the art that do not depart from the spirit and scope of the present invention should be within the protection scope of the appended claims.

Claims

1. A method for modifying high-elongation heterocyclic aramid fibers, comprising the sequential steps of preparing a polymerization solution, preparing a polymerization spinning solution, filtering and degassing, metering extrusion, coagulation molding, drawing, and washing, characterized in that, The washed fibers are oiled and dried by roller drying. The dried fibers are then hot-stretched, surface-treated, and continuously dried in a non-contact hot drying tunnel before being wound up to obtain high-elongation modified heterocyclic aramid fibers. The oiling process involves impregnating the washed fibers with a fatty alcohol polyoxyethylene ether phosphate solution. The surface treatment involves impregnating the heat-stretched fibers with a mixture of glycerol triglycidyl ether and sorbitol polyglycidyl ether.

2. The modification method according to claim 1, characterized in that, In the oiling process, the immersion time is at least 2 seconds, and the fatty alcohol polyoxyethylene ether phosphate solution is a solution diluted with deionized water to a concentration of 2‰-5%.

3. The modification method according to claim 1, characterized in that, The drying temperature of the roller dryer is 90-150℃, the drying time is at least 60 seconds, and the moisture content of the fiber after drying is no more than 7%.

4. The modification method according to claim 1, characterized in that, The hot stretching treatment is carried out in a nitrogen atmosphere, with a stretching temperature of 400-500℃, a stretching ratio of 80%, and a hot stretching time of at least 15 seconds.

5. The modification method according to claim 1, characterized in that, In the mixture, the mass ratio of glycerol triglycidyl ether to sorbitol polyglycidyl ether is 2.5-3.5:1.5-0.5, and the mixture is diluted with deionized water to a mass percentage concentration of 40%.

6. The modification method according to claim 1, characterized in that, In the surface treatment, the impregnated fibers are flattened by a polytetrafluoroethylene pressure roller.

7. The modification method according to claim 1, characterized in that, The non-contact hot drying tunnel is a two-stage hot air drying process, in which the first stage drying temperature is 90-120℃ and the drying time is 20-25 seconds. The second stage of drying is at a temperature of 120-150℃ and a drying time of 25-30 seconds. After continuous drying in the non-contact hot drying tunnel, the fiber moisture content is less than or equal to 1%.

8. A high-elongation modified heterocyclic aramid fiber obtained by the modification method according to any one of claims 1-7.

9. The high-elongation modified heterocyclic aramid fiber according to claim 8, characterized in that, The high-elongation modified heterocyclic aramid fibers have improved tow dispersion and interfacial adhesion properties.

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