Preparation process of PTFE (Polytetrafluoroethylene) fiber for enhanced dust removal filter bag

Abstract

The invention relates to the technical field of PTFE fiber preparation, in particular to a preparation process of PTFE fibers for an enhanced dust removal filter bag. The invention aims to solve the problem that the mechanical property and the dust removal property of the existing PTFE fiber are difficult to consider at the same time. The preparation method comprises the following steps: pre-mixing and extruding polytetrafluoroethylene, polyphenyl ether, fluororubber and perfluoropolyether to prepare modified polytetrafluoroethylene; modifying nano titanium dioxide and carbon nanotubes respectively, and blending the modified nano titanium dioxide and carbon nanotubes with PFA to obtain a nano filler; carrying out modification treatment on the chopped carbon fibers to obtain a modified micron material; through a skin-core composite spinning production line, a core layer containing PFA, a modified micron material and a nano filler and a shell layer containing modified polytetrafluoroethylene and an auxiliary agent are subjected to melt extrusion, spinning is performed through a composite spinneret plate, and then multi-stage hot stretching, multi-section sintering and heat setting treatment are performed to obtain PTFE fibers; the PTFE fiber prepared by the process has excellent mechanical properties and dust removal performance, and can meet the application requirements in the fields of dust removal filter bags and the like.

Description

Technical Field

[0001] The invention relates to the technical field of PTFE fiber preparation, in particular to a process for preparing PTFE fibers for enhanced dust removal filter bags. Background Art

[0002] Due to its excellent chemical stability, high and low temperature resistance, low friction coefficient, and hydrophobicity, polytetrafluoroethylene (PTFE) fiber has broad application prospects in industrial filtration, specialty textiles, medical treatment, and other fields. It plays a particularly important role in the manufacture of dust filter bags for high-temperature and corrosive environments. However, traditional PTFE fibers often face a prominent problem in practical applications: it is often difficult to balance their excellent mechanical properties, including strength and wear resistance, with efficient dust removal performance. Because PTFE's macromolecular chains are flexible and easily oriented and crystallized, excessive crystallinity or excessive molecular chain orientation can improve fiber strength, but it may lead to a dense fiber structure and reduced porosity, thereby affecting its air permeability and fine particle capture efficiency when used as a filter material. Conversely, the porous structure constructed to improve dust removal performance often sacrifices the mechanical strength of the fiber, making the filter bag easily damaged during use and shortening its lifespan.

[0003] To improve the overall performance of PTFE fibers, researchers have attempted various modification methods, including blending, filler reinforcement, surface treatment, and spinning process optimization. For example, by introducing nanofillers and changing stretching process parameters, researchers aim to create a specific microstructure within the PTFE fiber, thereby achieving a balance between mechanical strength and filtration performance. However, due to their poor compatibility with the PTFE matrix, these introduced fillers tend to aggregate, forming stress concentration points, reducing material uniformity, and thus affecting the overall performance of the fiber, limiting its further application.

[0004] In summary, the modification methods of polytetrafluoroethylene fibers in the existing technology often focus on improving a single performance and ignore the coordinated optimization of multiple performances. When applied to dust removal filter bags, it is still difficult to balance mechanical properties and dust removal performance, resulting in insufficient comprehensive performance in actual applications and reduced service life.

[0005] Therefore, a preparation process of PTFE fiber for enhanced dust filter bags was proposed. Summary of the Invention

[0006] The present invention aims to provide a process for preparing PTFE fibers for enhanced dust filter bags. The process involves premixing polytetrafluoroethylene with polyphenylene ether, fluororubber, and perfluoropolyether, followed by twin-screw extrusion to produce modified polytetrafluoroethylene. Nano-titanium dioxide and carbon nanotubes are then modified and blended with PFA to produce nanofillers. Chopped carbon fibers are then modified to produce modified micron materials. A core layer containing PFA, modified micron materials, and nanofillers is melt-extruded with a shell layer containing modified polytetrafluoroethylene and additives through a sheath-core composite spinning line. The fibers are then spun through a composite spinneret and subjected to multi-stage heat stretching, multi-stage sintering, and heat-setting to produce PTFE fibers. The PTFE fibers produced by this process exhibit excellent mechanical and dust removal properties, meeting application requirements in fields such as dust filter bags.

[0007] To achieve the above object, the present invention provides the following technical solutions:

[0008] The present invention provides a process for preparing PTFE fibers for enhanced dust removal filter bags, the preparation process comprising the following steps:

[0009] The core layer material is obtained by melt-extruding a perfluoroalkoxy resin, a modified micron material, a nanofiller and a compatibilizer; the shell layer material is obtained by melt-extruding the modified polytetrafluoroethylene and an additive; the shell layer material and the core layer material are passed through a composite spinneret, and the spinning material is obtained by cooling the spinning material;

[0010] The spinning material is subjected to multi-stage heat stretching, multi-stage sintering and heat setting treatment to obtain PTFE fiber;

[0011] Among them, the modified micron material is prepared by a silane coupling agent-modified short-cut carbon fiber;

[0012] Modified polytetrafluoroethylene is obtained by melt blending polytetrafluoroethylene and a modifier;

[0013] The nanofiller is obtained by melt-blending modified carbon nanotubes, modified nano titanium dioxide, perfluoroalkoxy resin and a compatibilizer;

[0014] The modified carbon nanotubes are obtained by treating the carbon nanotubes with a silane coupling agent.

[0015] The modified nano titanium dioxide is obtained by modifying the nano titanium dioxide with a silane coupling agent.

[0016] Preferably, the compatibilizer is maleic anhydride grafted ethylene-tetrafluoroethylene copolymer; the first silane coupling agent is (3,3,3-trifluoropropyl)trimethoxysilane; the second silane coupling agent is methacryloxypropyltrimethoxysilane; the auxiliary agents include sodium bicarbonate, citric acid, magnesium oxide and zinc oxide; the modifiers include polyphenylene ether particles, fluororubber FKM and perfluoropolyether.

[0017] Preferably, the preparation of the spinning material includes the following process:

[0018] By weight, 100 parts of perfluoroalkoxy resin, 20-30 parts of modified micron material, 10-15 parts of nano filler, and 5-8 parts of maleic anhydride grafted ethylene-tetrafluoroethylene copolymer are melt-extruded through a core layer extruder to obtain a core layer material;

[0019] By weight, 100 parts of modified polytetrafluoroethylene, 3-5 parts of sodium bicarbonate, 2-4 parts of citric acid, 2-3 parts of magnesium oxide, and 3-5 parts of zinc oxide are melt-extruded through a shell extruder to obtain a shell material;

[0020] By volume, the shell layer material and the core layer material are passed through a composite spinneret, spun, and air-cooled to obtain a spinning material; wherein the volume ratio of the shell layer material to the core layer material is 5-7:3-5.

[0021] Preferably, the core layer melt extrusion parameters are: feed zone 280-300°C, compression zone 310-330°C, metering zone 320-340°C, die head temperature 310-330°C, and core layer pressure 8-12MPa; core layer melt extrusion parameters are: feed zone 300-330°C, compression zone 320-350°C, metering zone 340-360°C, die head temperature 330-360°C, and pressure 10-15MPa.

[0022] Preferably, the core layer extruder and the shell layer extruder are both single-screw extruders with a screw diameter of 30-65 mm and an aspect ratio of 28:1-32:1; the core layer screw compression ratio is 2.5-3.5:1; the shell layer screw compression ratio is 1.5-2.5:1; the shell layer extruder uses a PTFE-specific screw design; it is air-cooled with an air temperature of 20-25°C; the air flow rate is 0.8-1.5 m / s; and the cooling zone length is 0.5-2 m.

[0023] Preferably, the composite spinneret is a skin-core structure, the spinning speed is 150-250 m / min, the number of spinnerets is 24-72 holes, the core layer spinneret outlet diameter is 0.3-0.5 mm; the shell layer spinneret outlet width is 0.15-0.3 mm; the spinneret capillary length to diameter ratio is 3:1-5:1.

[0024] Preferably, the multi-stage hot stretching includes the following processes:

[0025] The spinning material is first pre-stretched at a stretching temperature of 120-180°C and a stretching ratio of 1.2-2.0 times; then stretched at a medium temperature of 220-260°C and a stretching ratio of 2-4 times; and finally stretched at a high temperature of 300-330°C and a stretching ratio of 1.5-3 times.

[0026] Preferably, the multi-stage sintering process includes: a nitrogen flow rate of 5 L / min, heating to 200-250°C at a heating rate of 5-10°C / min in the first stage, and keeping warm for 30-60 minutes; heating to 300-330°C at a heating rate of 3-5°C / min in the second stage, and keeping warm for 30-45 minutes; heating to 360-380°C at a heating rate of 3-5°C / min in the third stage, and keeping warm for 10-15 minutes.

[0027] Preferably, the preparation of the modified micron material includes the following process:

[0028] (3,3,3-trifluoropropyl)trimethoxysilane is added to a 95% ethanol aqueous solution, stirred evenly, acetic acid is added to adjust the pH value to 4, and the temperature is raised to 50°C and stirred for 1 hour to obtain a silane solution; short-cut carbon nanofibers are added to the silane solution, and stirred to react under ultrasonic assistance; then separated and centrifuged, washed alternately with ethanol and deionized water for 5 times, and vacuum dried at 100°C for 3 hours to obtain a modified micron material; wherein (3,3,3-trifluoropropyl)trimethoxysilane accounts for 0.8-1.5% of the total mass of the short-cut carbon fibers.

[0029] Preferably, the chopped fibers have an average diameter of 100-200 nm and a length of 50-80 μm; the particle size of nano-titanium dioxide is 20-50 nm; and the carbon nanotubes are multi-walled carbon nanotubes with an outer diameter of 10-30 nm and a length of 10-20 μm.

[0030] Preferably, the preparation of the nanofiller includes the following process:

[0031] The invention discloses a method for preparing multi-walled carbon nanotubes by adding multi-walled carbon nanotubes to a mixed solvent of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, performing oxidation treatment at 60°C, separating and centrifuging, washing with deionized water five times until neutral, and vacuum drying to obtain acidified carbon nanotubes; adding a silane solution to the acidified carbon nanotubes, stirring and reacting under ultrasonic assistance; separating and centrifuging again, washing with ethanol and deionized water alternately five times, and vacuum drying to obtain modified carbon nanotubes; and adding 5-8 parts of the modified carbon nanotubes, 10-20 parts of modified nano-titanium dioxide, 5-8 parts of maleic anhydride grafted ethylene-tetrafluoroethylene copolymer, 70-80 parts of perfluoroalkoxy resin, and 0.5 part of PVP to a twin-screw extruder for melt blending at a melt extrusion temperature of 280-320°C to obtain a nanofiller.

[0032] Preferably, the preparation of modified nano-titanium dioxide includes the following process:

[0033] 5 parts by mass of methacryloyloxypropyltrimethoxysilane were added to a 95% aqueous ethanol solution, acetic acid was added to adjust the pH value to acidic, and the mixture was stirred at 30°C for 20 minutes to obtain a modified solution; 100 parts of nano-titanium dioxide were added to 200 ml of anhydrous ethanol, ultrasonically dispersed for 30 minutes, and then the modified solution was added. The mixture was heated to 70°C for reaction, centrifuged, washed alternately with deionized water and ethanol three times, and vacuum dried to obtain modified nano-titanium dioxide.

[0034] Preferably, the preparation of modified polytetrafluoroethylene includes the following process:

[0035] 100 parts by mass of dry polytetrafluoroethylene powder, 20-25 parts of polyphenylene ether particles, 5-10 parts of fluororubber (FKM), and 5-8 parts of perfluoropolyether are added to a high-speed mixer, and pre-mixed three times at room temperature in the high-speed mixer for 20 minutes each time with a mixing interval of 5 minutes each time to uniformly disperse the mixture; the mixture is melt-blended and granulated through a co-rotating twin-screw extruder to obtain an extrudate; the extrudate is cooled in a cooling water tank, pelletized, and vacuum-dried at 100° C. for 10 hours to obtain modified polytetrafluoroethylene;

[0036] Preferably, in the melt extrusion process, the temperature of the feed zone is controlled at 200-250° C., the temperature of the compression melting zone is controlled at 280-320° C., the temperature of the homogenization zone is controlled at 320-340° C., and the temperature of the die head is controlled at 330-340° C.; the screw speed is maintained at 150-200 rpm, high shear melt blending is performed for 20 minutes, and the extrudate is quickly passed through the high temperature zone to reduce thermal degradation to obtain the extrudate;

[0037] Preferably, the melt index (MFI@380°C, 21.6kg) of the modified polytetrafluoroethylene is 3-8g / 10min.

[0038] Compared with the prior art, the present invention has the following beneficial effects:

[0039] 1. The present invention improves the melt processability of PTFE by modifying it, laying the foundation for uniform compounding with fillers and melt spinning; the skin-core structure is synergistically used to optimize the material selection and ratio of the skin layer and the core layer, achieving a good match between strength and toughness. Among them, carbon fiber has high strength and high modulus, and carbon nanotubes also have excellent mechanical properties. Their good dispersion and interface bonding in the PFA matrix can effectively bear the load; finally, through multi-stage stretching and hot stretching, multi-stage sintering treatment and heat setting treatment, the compatibility of the polytetrafluoroethylene matrix and the core layer reinforcement material is improved through the synergistic effect between multiple components and processes, giving the fiber structure stability and higher mechanical properties.

[0040] 2. The present invention fills the fiber micropores with carbon nanotubes to form a nano-scale filtration barrier; nano-titanium dioxide adsorbs particles and refines the pore size, synergistically realizing the dual mechanism of "nano-screening + adsorption interception"; in addition, sodium bicarbonate and citric acid are introduced to generate carbon dioxide through reaction to form uniform micropores (pore size 0.2-0.5μm) in the shell layer, forming a gradient structure of "outer layer fine pore interception + inner layer coarse pore support" with the micron-scale carbon fiber skeleton of the core layer to avoid a decrease in filtration efficiency, and finally through multi-stage stretching to orient the axial pores of the fiber to improve the filtration efficiency; multi-stage sintering treatment promotes PTFE crystallization to form a rigid pore structure to ensure the stability of the pore structure, and the synergistic effect of the three is used to further improve the air permeability and filtration efficiency of the fiber.

[0041] 3. The present invention modifies polytetrafluoroethylene through polyphenylene ether, utilizes interface modification to improve the rigidity and creep resistance of PTFE, reduces adhesive wear, and simultaneously introduces perfluoropolyether and fluororubber FKM to form a dynamic lubricating film, thereby reducing the friction coefficient. In addition, the elastic buffering effect provided by fluororubber improves the toughness and fatigue resistance of the material, which is beneficial to the improvement of wear resistance. A core layer is formed by combining nanofillers and micron-sized reinforcing fibers to construct a "rigid-flexible interlocking" skeleton. Carbon fibers bear the main load, and carbon nanotubes fill microgaps and enhance the electrical and thermal conductivity of the interface, thereby suppressing the influence of local overheating of friction on the fibers. At the same time, the "micro-bearing effect" of nano-titanium dioxide reduces contact stress, and rigid particles fill the PTFE micropores, thereby reducing the friction contact area, suppressing crack propagation, and increasing the surface hardness. The shell layer of the modified polytetrafluoroethylene synergistically resists surface wear, forming a gradient wear-resistant layer, thereby further improving the friction resistance of the fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1 This is a flow chart of the preparation process of polytetrafluoroethylene fiber according to Example 1 of the present invention. DETAILED DESCRIPTION

[0043] 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.

[0044] The polytetrafluoroethylene powder of the present invention is selected from suspended PTFE powder and has an average particle size of 80-150 μm; the intrinsic viscosity of the polyphenylene ether particles is in the range of 0.4-0.6 dL / g (25° C., chloroform); the average molecular weight of the perfluoropolyether is 5000-8000 g / mol; the maleic anhydride grafting rate of the maleic anhydride-grafted ethylene-tetrafluoroethylene copolymer is 0.5-2.5wt%, and the melt index (MFI@297° C., 5kg) of the ethylene-tetrafluoroethylene copolymer is 10-30 g / 10min; the PFA resin is a perfluoroalkoxy resin and has a melt index (MFI@372° C., 5kg) of 5-15 g / 10min; and the KH570 is methacryloxypropyltrimethoxysilane.

[0045] See also Figure 1 , Figure 1 This is a flow chart of the preparation process of polytetrafluoroethylene fiber according to Example 1 of the present invention. The present invention provides a process for preparing PTFE fiber for enhanced dust filter bags, and the technical solution is as follows:

[0046] Example 1

[0047] 100 parts by mass of dry polytetrafluoroethylene powder, 20 parts by mass of polyphenylene ether particles, 5 parts by mass of fluororubber FKM and 5 parts by mass of perfluoropolyether were added to a high-speed mixer, and pre-mixed in the high-speed mixer three times at room temperature for 20 minutes each time, with a mixing interval of 5 minutes between each time to ensure that the components were fully and evenly dispersed to obtain a mixture; the mixture was melt-blended and granulated through a co-rotating twin-screw extruder to obtain an extrudate; the extrudate was cooled in a cooling water tank, pelletized, and vacuum-dried at 100°C for 10 hours to obtain modified polytetrafluoroethylene.

[0048] (3,3,3-trifluoropropyl)trimethoxysilane is added to a 95% ethanol aqueous solution, stirred evenly, acetic acid is added to adjust the pH value to 4-5, and the temperature is raised to 50°C and stirred for 1 hour to obtain a silane solution; short-cut carbon nanofibers are slowly added to the silane solution, and under ultrasonic assistance, stirred at 50-70°C for 3-5 hours; then separated and centrifuged, washed alternately with ethanol and deionized water 5 times, and vacuum dried at 100°C for 3 hours to obtain a modified micron material; (3,3,3-trifluoropropyl)trimethoxysilane accounts for 1.2% of the total mass of the short-cut carbon fibers.

[0049] 5 parts by mass of KH570 were added to 10 ml of a 95% aqueous ethanol solution, acetic acid was added to adjust the pH to acidic, and the mixture was stirred at 30°C for 20 minutes to obtain a modified solution. 100 parts of nano-titanium dioxide with a particle size of 20-50 nm were added to 200 ml of anhydrous ethanol, ultrasonically dispersed for 30 minutes, and the modified solution was slowly added. The mixture was heated to 70°C and reacted for 3 hours. The mixture was centrifuged and washed alternately with deionized water and ethanol three times, and vacuum dried at 100°C for 8 hours to obtain the modified nano-titanium dioxide.

[0050] The multi-walled carbon nanotubes were added to a mixed solvent of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, oxidized at 60-70°C for 1-2h, separated and centrifuged, washed with deionized water 5 times until neutral, and vacuum dried at 80°C for 5h to obtain acidified carbon nanotubes; silane solution was slowly added to the acidified carbon nanotubes, and stirred at 50-70°C for 3-5h under ultrasonic assistance; wherein the mass ratio of multi-walled carbon nanotubes to (3,3,3-trifluoropropyl)trimethoxysilane was 50:1; further separated and centrifuged, washed alternately with ethanol and deionized water 5 times, and vacuum dried at 100°C for 3h to obtain modified carbon nanotubes; 6 parts of modified carbon nanotubes, 15 parts of modified nano-titanium dioxide, 8 parts of maleic anhydride grafted ethylene-tetrafluoroethylene copolymer, 80 parts of PFA and 0.5 parts of PVP as dispersants were added to a twin-screw extruder for melt blending and extrusion to obtain nanofillers;

[0051] The invention relates to a method for preparing a sheath-core composite spinning production line and two single-screw extruders for spinning. 100 parts of PFA, 25 parts of modified micron material, 15 parts of nanofiller, and 6 parts of maleic anhydride grafted ethylene-tetrafluoroethylene copolymer are passed through the core layer extruder to melt extrude the core layer material as a core layer. 100 parts of modified polytetrafluoroethylene, 4 parts of sodium bicarbonate, 3 parts of citric acid, 2 parts of magnesium oxide, and 4 parts of zinc oxide are passed through the shell layer extruder to melt extrude the shell layer material as a shell layer. The shell layer material and the core layer material are passed through a composite spinneret, the volume ratio of the shell layer to the core layer is maintained at 6:4, the spinning speed is 200 m / min, and the spinning material is cooled in air to obtain a spinning material.

[0052] The spinning material is subjected to multi-stage hot stretching, first pre-stretching, the stretching temperature is 160°C, and the stretching ratio is 1.5 times; then medium-temperature stretching, the stretching temperature is 240°C, and the stretching ratio is 3 times; finally high-temperature stretching, the stretching temperature is 320°C, and the stretching ratio is 2.5 times to obtain a stretched fiber; the stretched fiber is subjected to multi-stage sintering treatment, the nitrogen flow rate is 5L / min, the first stage is heated to 240°C at a heating rate of 8°C / min, and kept warm for 60 minutes; the second stage is heated to 320°C at a heating rate of 5°C / min, and kept warm for 30 minutes; the third stage is heated to 380°C at a heating rate of 3°C / min, kept warm for 10 minutes, and cooled to 30°C at 8°C / min to obtain a sintered fiber; the sintered fiber is heat-set at a heat-setting temperature of 280°C and the control time is 3 minutes to obtain PTFE fiber.

[0053] Examples 2-5 refer to the preparation methods and parameter conditions of Example 1, with the differences shown in Table 1.

[0054] Table 1 Parameter changes of Examples 1-5

[0055]

[0056] Comparative Example 1 refers to Example 1, except that polyphenylene ether particles are not used to modify the polytetrafluoroethylene powder.

[0057] Comparative Example 2 refers to Example 1, except that perfluoropolyether and fluororubber FKM are not used, and polyphenylene ether and polytetrafluoroethylene are melt-extruded.

[0058] Comparative Example 3 refers to Example 1, except that multiple room temperature premixing is not used.

[0059] Comparative Example 4 refers to Example 1, except that no modified chopped carbon fiber is added.

[0060] Comparative Example 5 refers to Example 1, except that no modified carbon nanotubes are added.

[0061] Comparative Example 6 refers to Example 1, except that modified nano-titanium dioxide is not introduced.

[0062] Comparative Example 7 refers to Example 1, except that no core layer material is used and the fiber is obtained only by modifying polytetrafluoroethylene.

[0063] Comparative Example 8 refers to Example 1, except that no skin-core structure is used, and the product is obtained directly through melt blending and spinning.

[0064] Comparative Example 9 refers to Example 1, except that it does not undergo multi-stage heat stretching, but only high-temperature stretching, and the stretching ratio is 7 times.

[0065] Comparative Example 10 refers to Example 1, except that it does not undergo multi-stage heat stretching, but only low-temperature stretching, and the stretching ratio is 7 times.

[0066] Comparative Example 11 refers to Example 1, except that no heat setting treatment is performed.

[0067] Comparative Example 12 refers to Example 1, except that it does not undergo multi-stage sintering treatment.

[0068] Experimental Example 1 Fracture Performance Test

[0069] The PTFE fibers prepared in Examples 1-5 and Comparative Examples 1-12 were tested for breaking strength and breaking elongation according to the GB T3916-2013 test standard. The test results are shown in Table 2.

[0070] Table 2 Test results of Examples 1-5 and Comparative Examples 1-12

[0071] Example Breaking strength / MPa Elongation at break / % Example 1 42 86.2 Example 2 40 85.8 Example 3 41 86.2 Example 4 40 86.4 Example 5 42 85.6 Comparative Example 1 26 58.6 Comparative Example 2 32 48.2 Comparative Example 3 36 65.2 Comparative Example 4 25 56.7 Comparative Example 5 36 60.2 Comparative Example 6 32 60.8 Comparative Example 7 24 55.6 Comparative Example 8 30 66.7 Comparative Example 9 22 42.5 Comparative Example 10 25 50.4 Comparative Example 11 33 85.2 Comparative Example 12 28 60.2

[0072] The results in Table 2 show that in the comparative examples, the changes in the components and process conditions have a significant adverse effect on the mechanical properties of the fibers. In comparative examples 1-3, no polyphenylene ether particles, perfluoropolyether, and fluororubber-modified polytetrafluoroethylene are added, and the mechanical properties are significantly reduced compared to the examples. The rigid molecular chains of polyphenylene ether can be embedded between polytetrafluoroethylene molecules, thereby enhancing the interfacial bonding force through physical entanglement and promoting filler dispersion by reducing the melt viscosity. Without the modification treatment, the PTFE matrix has poor fluidity, and the filler is easily agglomerated during the subsequent melt extrusion process, forming stress concentration points, and significantly reducing the fiber strength. The elastic segments of FKM can absorb tensile energy, and perfluoropolyether reduces the stress concentration points through lubrication. Processing heat damage, without adding, the modified system shows rigid brittle fracture characteristics, and the strength is significantly reduced; in addition, perfluoropolyether, as a fluorine-based lubricant, can reduce the friction heat between polytetrafluoroethylene and the equipment. After its absence, thermal degradation in the high-temperature zone is aggravated, resulting in the breakage of the main chain, the decrease in molecular weight and the deterioration of mechanical properties; due to the compatibility gap between the two, multiple pre-mixing is to ensure the uniform distribution of polyphenylene ether particles and polytetrafluoroethylene, while reducing the extruder load, avoiding local overheating, damaging the polytetrafluoroethylene matrix, and thus improving the compatibility between the two, improving the melt index of the matrix, and facilitating the subsequent processing process; the results of comparative examples 4-7 show that without introducing the skin-core structure or without utilizing the synergistic reinforcement effect of the filler components, the fiber The mechanical properties of the fiber are significantly reduced; short-cut carbon fiber, as a micron-sized reinforcement, bears most of the tensile load. Without it, the nanofiller cannot form an effective skeleton support due to size limitations, and the load is almost entirely borne by the matrix, resulting in poor mechanical properties; after acidification and silane modification, the surface carboxyl groups of carbon nanotubes form hydrogen bonds with the matrix, and the high aspect ratio can bridge adjacent carbon fibers to form a "micron-nano load transfer network", in which short-cut carbon fiber acts as a skeleton to bear the main tensile load, and carbon nanotubes bridge adjacent carbon fibers through high aspect ratio to form a stress transfer chain. At the same time, nanoscale pores absorb submicron particles, achieving a dual improvement in mechanical reinforcement and filtration accuracy, improving interfacial stress transfer efficiency, and avoiding the generation of microcracks. Raw; modified nano titanium dioxide as a heterogeneous nucleating agent can refine the crystallization of polytetrafluoroethylene, improve the crystallinity and molecular chain orientation. If it is not added, the coarse grains formed are easy to slip, which can easily cause crack propagation during stretching and reduce the overall mechanical properties. Since a single shell structure cannot disperse concentrated loads, the introduced skin-core structure uses the core layer to bear the main stress and the shell layer to buffer the surface stress. The introduction of high-temperature resistant polymers and a high proportion of fillers in the core layer improves the overall compatibility and mechanical strength of the fiber. Combined with Comparative Example 8, the core layer in the skin-core structure can be enriched with more than 70% of reinforcing fillers. When directly blended, the fillers are evenly dispersed but the concentration is reduced, the effective load-bearing filler per unit cross-sectional area is reduced, and the mechanical strength is reduced.In addition, when directly blended, the melt compatibility of PTFE and PFA in spinning is poor. The skin-core structure avoids direct mixing of the two through layered melting, thereby improving the overall mechanical properties. From the results of 9-10, it can be seen that high temperature is close to the melting point of polytetrafluoroethylene, which leads to rapid orientation of the molecular chain. However, excessively high temperature aggravates the breakage of the molecular chain, forming an "orientation-breakage" competition, and ultimately a large number of microcracks are generated inside the fiber, which greatly reduces the strength. At low temperatures, the molecular chain orientation is insufficient, the residual stress is not eliminated, the fiber is easy to break, and the tensile properties deteriorate. Pre-stretching is a preparation for subsequent high-magnification stretching. Medium-temperature stretching is the main orientation stage, and high-temperature stretching is helpful. Further improving the crystal form and eliminating some defects synergistically improve the mechanical properties of the fiber. In Comparative Example 12, without multi-stage sintering, the pore structure is unstable, the inorganic filler in the shell is not fully bonded, the wear resistance is poor, and the fiber is easily brittle. High-temperature sintering fully fuses the PTFE particles, eliminates interfaces, forms a continuous network structure, and simultaneously eliminates internal stress accumulated during the stretching process, giving the fiber structure stability and higher mechanical properties. In Comparative Example 11, without heat setting treatment, the molecular chains relax, residual stress remains, the fiber dimensional stability is poor, the elongation fluctuates greatly, and it is easy to deform after long-term use, further affecting the overall performance of the fiber.

[0073] Example 6 is the same as Example 1;

[0074] Examples 7-9 refer to the preparation methods and parameter conditions of Example 1, with the differences shown in Table 3.

[0075] Table 3 Parameter changes of Examples 6-9

[0076]

[0077] Comparative Example 12 refers to Example 1, except that it does not undergo multi-stage sintering treatment.

[0078] Comparative Example 13 refers to Example 1, except that the temperature is raised to 360° C. at a heating rate of 10° C. / min and sintered for 15 minutes.

[0079] Comparative Example 14 refers to Example 1, except that the temperature is raised to 200° C. at a heating rate of 3° C. / min and sintered for 60 min.

[0080] Comparative Example 15 refers to Example 1, except that no sodium bicarbonate is added.

[0081] Comparative Example 16 refers to Example 1, except that citric acid is not added.

[0082] Comparative Example 17 refers to Example 1, except that sodium bicarbonate and citric acid are not added.

[0083] Comparative Example 18 refers to Example 1, except that sodium bicarbonate and citric acid are added during the core layer extrusion process.

[0084] Experimental Example 2: Air permeability and dust removal performance

[0085] The polytetrafluoroethylene fibers prepared in Examples 6-9, Comparative Examples 5-8, and Comparative Examples 12-18 were filtered through an airflow containing particles of 0.1-0.5 μm at a filtration rate of 2.5 cm / s. The particle concentrations before and after the airflow passed through the samples were measured using a particle counter, and the filtration efficiency was calculated using a formula. Under a pressure differential of 100 Pa, the air flow rate per unit area of the fiber sample per unit time was measured to represent the air permeability. The test results are shown in Table 4.

[0086] Table 4 Test results of Examples 6-9, Comparative Examples 5-8, and Comparative Examples 12-18

[0087]

[0088]

[0089] From the results in Table 4, it can be seen that the adjustment of components and processes in the comparative examples has a significant impact on the air permeability and filtration performance of the fiber. From the results of comparative examples 5-6, it can be seen that the high specific surface area and nanoscale pores of the modified carbon nanotubes are the key to capturing 0.1-0.5μm particles. After the loss, the number of micropores in the fiber decreases and the proportion of macropores increases, resulting in an increase in the particle penetration rate, but a decrease in the filtration accuracy; nano-titanium dioxide refines the pore size by filling the pores. After the loss, the average pore size of the fiber increases, and it is unable to effectively intercept submicron particles. The increase in pore size reduces the air permeability resistance and increases the air permeability, but the filtration efficiency decreases with the increase in pore size; from the results of comparative examples 7-8, it can be seen that the core layer contains modified carbon fibers and nanofillers, which provide mechanical support and skeleton pores. Gap, when no core layer is added, pure modified PTFE fiber is easy to break during stretching, pore collapse, filtration efficiency decreases due to the reduction of effective pores, and the collapsed pores hinder airflow, and air permeability decreases; the introduction of the skin-core structure realizes functional zoning through the shell porous layer and the core support layer, and direct melt blending and spinning leads to random distribution of pores, uneven pore size of the filter layer, and particles easily penetrate from the macropores, and air permeability also decreases due to uneven pore distribution; the results of comparative examples 12-14 show that during the multi-stage sintering process, citric acid begins to dehydrate and partially decompose at low temperature, and the generated gas helps to form the initial microporous structure. In addition, the slower heating and sufficient holding time help the gas to slowly escape, forming a more uniform pore process. Under medium temperature conditions, the modified PTFE matrix begins to soften and has a certain fluidity, which helps the PTFE particles to initially bond and fuse around the formed pores, thereby stabilizing the pore structure and preventing serious collapse during subsequent high-temperature sintering; under the action of high temperature, the PTFE particles fully melt and diffuse and connect with each other to form a strong porous network skeleton, maximizing the retention of porosity and pore size uniformity; the rapid heating process causes local overheating, excessive melting of PTFE, and the formation of a large pore structure with a wide pore size distribution and poor connectivity, which reduces the filtration accuracy; when the heating rate is too slow and the temperature is low, it is lower than the PTFE crystallization temperature, the fiber is not fully crystallized, and is in an amorphous state, the pores collapse and there is no fixed pore structure, and the filtration efficiency and air permeability decreased significantly; the results of comparative examples 15-18 show that sodium bicarbonate reacts with citric acid to generate carbon dioxide, which is the core of the shell foaming to form a porous structure. Without the addition process, the shell does not foam at all and has a solid structure. It relies only on the micropores of the core layer for filtration, but the core layer accounts for a low proportion and has irregular pores, and the filtration efficiency is greatly reduced; when there is no sodium bicarbonate, the shell cannot produce gas by citric acid alone, resulting in a dense shell, hindering the passage of airflow, and reducing the air permeability and filtration efficiency; when there is no citric acid, the gas production is insufficient, the porosity of the shell is too low, and the filtration and air permeability performance are reduced; sodium bicarbonate and citric acid produce gas in the core layer, resulting in a loose core layer structure, but the shell is still a solid structure, and the filtration still depends on the shell structure, and the filtration efficiency and overall air permeability remain low.

[0090] Example 10 is the same as Example 1;

[0091] Examples 11-14 refer to the preparation method and parameter conditions of Example 1, with the differences shown in Table 5.

[0092] Example 10-14 parameter changes

[0093]

[0094] Comparative Example 19 refers to Example 1, except that magnesium oxide is not added.

[0095] Comparative Example 20 refers to Example 1, except that zinc oxide is not added.

[0096] Comparative Example 21 refers to Example 1, except that the nanofiller is not first obtained by melt extrusion, but the modified micron material, modified carbon nanotubes and modified nano titanium dioxide are directly melt-extruded with the PFA matrix to obtain the shell material.

[0097] Experimental Example 3 Wear resistance test

[0098] The PTFE fibers prepared in Examples 10-14, Comparative Examples 1-5, and Comparative Examples 19-21 were tested according to the GB / T21196.1-2007 test method. The wear resistance of the fibers was reflected by the number of wear times, mass loss, and appearance change under a load of 12 kPa. The test results are shown in Table 6.

[0099] Table 6 Test results of Examples 10-14, Comparative Examples 1-5, and Comparative Examples 19-21

[0100]

[0101]

[0102] The results in Table 6 show that, from the results of Comparative Examples 1-3, the wear resistance of the fiber material obtained by modifying polytetrafluoroethylene is significantly reduced compared with that in the embodiment. Polyphenylene ether, as a rigid dispersed phase, enhances the interfacial bonding force and can form an island structure when blended with polytetrafluoroethylene. In addition, the heat resistance of polyphenylene ether inhibits the high-temperature softening of polytetrafluoroethylene. After its absence, the strength of the polytetrafluoroethylene matrix decreases, and plastic deformation easily occurs during friction. Frictional heat aggravates material wear. Perfluoropolyether is a low molecular weight lubricant, and fluororubber provides elastic damping. The absence of both causes the shell polytetrafluoroethylene to change from "self-lubricating wear" to "adhesive wear", and the friction performance decreases. Multiple premixing ensures that the modifier is evenly dispersed in the matrix to avoid agglomeration of components caused by insufficient mixing. , the uneven structure leads to local stress concentration and increased wear rate; in comparative examples 4-7, the wear resistance of the fiber is significantly reduced by changing the core layer components, the short-cut carbon fiber is modified by silane and combined with the PTFE interface to form a rigid skeleton that bears the friction stress. After the loss, the fiber matrix is prone to interlayer slippage, and the wear mechanism changes from "fatigue wear" to "adhesive wear". In addition, the conductivity of carbon fiber can transfer friction static electricity and reduce electrostatic adsorption wear; carbon nanotubes fill the gaps between PTFE molecular chains in nanometer size to form a "molecular reinforcement network", which improves the surface hardness. At the same time, the high aspect ratio hinders the slippage of molecular chains and improves the wear resistance; modified nano-titanium dioxide forms hydrogen bonds with PTFE to enhance the interfacial bonding force and at the same time acts as "Solid lubricant" reduces the friction factor, and its inherent photocatalytic activity can decompose the oxides produced by friction, further reducing the wear rate; the results of comparative examples 19-20 show that magnesium oxide, as an alkaline filler, can neutralize the acidic degradation products produced during the friction process and inhibit corrosion wear. Without it, the acidic environment accelerates the breakage of the PTFE molecular chain and the wear rate increases. In addition, the high melting point of magnesium oxide improves the heat resistance of the material, avoids the local softening phenomenon caused by frictional heating, and improves the wear resistance; zinc oxide has pressure-sensitive conductivity, and synergistically acts with carbon nanotubes and carbon fibers to evenly distribute friction static electricity and reduce material damage caused by discharge. After it is missing, static electricity adsorbs wear debris to form an abrasive layer, which aggravates the fiber volume wear. In addition, the micro-rigid particles of zinc oxide ( The particle size of 1-2 μm is selected to polish the friction interface and reduce the roughness, and the surface becomes rougher after the particle is lost. In Comparative Example 21, micron particles and nanoparticles are directly blended, which easily leads to filler agglomeration and greatly reduces the compatibility with the PFA matrix. In addition, the formation of agglomerates acts as hard points to plow the grinding surface, further reducing the wear resistance. In the process of pre-preparing nanofillers, high shear force is used to achieve nano-scale dispersion of modified carbon nanotubes and modified nano-titanium dioxide in PFA, and then micron-sized carbon fibers are introduced. Nanofillers are used to improve the bonding between the micron fibers and the PTFE matrix interface. At the same time, micron fibers are used to bear the main load to achieve multi-scale synergistic enhancement, avoid local stress concentration caused by uneven dispersion, and thus improve the wear resistance of the fiber.

[0103] 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 process for preparing PTFE fibers for enhanced dust filter bags, characterized by: The preparation comprises the following processes: The core layer material is obtained by melt-extruding the perfluoroalkoxy resin, the modified micron material, the nanofiller and the compatibilizer; The modified polytetrafluoroethylene and the auxiliary agent are melt-extruded to obtain a shell material; the shell material and the core material are passed through a composite spinneret, and the spinning and cooling are performed to obtain a spinning material; The spinning material is subjected to heat stretching, sintering and heat setting treatment to obtain the PTFE fiber; Wherein, the modified micron material is prepared from a silane coupling agent-modified short-cut carbon fiber; The modified polytetrafluoroethylene is obtained by melt blending polytetrafluoroethylene and a modifier; The nanofiller is obtained by melt blending modified carbon nanotubes, modified nano titanium dioxide, the perfluoroalkoxy resin and the compatibilizer; The modified carbon nanotubes are obtained from the silane coupling agent-modified carbon nanotubes; The modified nano titanium dioxide is obtained by modifying the nano titanium dioxide with a silane coupling agent.

2. The process for preparing PTFE fiber for enhanced dust filter bags according to claim 1, characterized in that: The compatibilizer is maleic anhydride grafted ethylene-tetrafluoroethylene copolymer; the first silane coupling agent is (3,3,3-trifluoropropyl)trimethoxysilane; the second silane coupling agent is methacryloxypropyltrimethoxysilane; the auxiliary agents include sodium bicarbonate, citric acid, magnesium oxide and zinc oxide; the modifier includes polyphenylene ether particles, fluororubber FKM and perfluoropolyether.

3. The process for preparing PTFE fiber for enhanced dust filter bags according to claim 1, characterized in that: The preparation of the spinning material includes the following processes: The perfluoroalkoxy resin, 20-30 parts of the modified micron material, 10-15 parts of the nanofiller, and 5-8 parts of maleic anhydride grafted ethylene-tetrafluoroethylene copolymer are melt-extruded through a core layer extruder to obtain the core layer material. The modified polytetrafluoroethylene, 3-5 parts of sodium bicarbonate, 2-4 parts of citric acid, 2-3 parts of magnesium oxide, and 3-5 parts of zinc oxide are passed through a shell extruder as a shell layer, and melt-extruded to obtain the shell layer material; By volume, the shell layer material and the core layer material are passed through a composite spinneret, spun, and air-cooled to obtain the spinning material; wherein the volume ratio of the shell layer material to the core layer material is 5-7:3-5.

4. The process for preparing PTFE fiber for enhanced dust filter bags according to claim 1, characterized in that: The hot stretching process includes the following steps: The spinning material is pre-stretched through a multi-stage hot stretching process, with a stretching temperature of 120-180°C and a stretching ratio of 1.2-2.0 times; then pre-stretched through a medium-temperature stretching process, with a stretching temperature of 220-260°C and a stretching ratio of 2-4 times; and finally pre-stretched through a high-temperature stretching process, with a stretching temperature of 300-330°C and a stretching ratio of 1.5-3 times.

5. The process for preparing PTFE fiber for enhanced dust filter bags according to claim 3, characterized in that: The preparation of the modified micron material includes the following processes: (3,3,3-trifluoropropyl)trimethoxysilane is added to an ethanol aqueous solution, stirred evenly, acetic acid is added to adjust the pH value, and the temperature is increased with stirring to obtain a silane solution; short-cut carbon nanofibers are added to the silane solution, and stirred to react under the assistance of ultrasound; then separated and centrifuged, washed alternately with ethanol and deionized water, and vacuum dried to obtain the modified micron material; wherein the (3,3,3-trifluoropropyl)trimethoxysilane accounts for 0.8-1.5% of the total mass of the short-cut carbon fibers.

6. The process for preparing PTFE fiber for enhanced dust filter bags according to claim 5, characterized in that: The silane solution for preparing the nanofiller comprises the following process: The method comprises the following steps: adding multi-walled carbon nanotubes to a mixed solvent of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, performing oxidation treatment, separating and centrifuging, washing with deionized water until neutral, and vacuum drying to obtain acidified carbon nanotubes; adding the silane solution to the acidified carbon nanotubes, stirring and reacting under ultrasound assistance; separating and centrifuging again, washing with ethanol and deionized water alternately, and vacuum drying to obtain modified carbon nanotubes; and adding 5-8 parts of the modified carbon nanotubes, 10-20 parts of modified nano-titanium dioxide, 5-8 parts of maleic anhydride grafted ethylene-tetrafluoroethylene copolymer, 70-80 parts of perfluoroalkoxy resin, and PVP to a twin-screw extruder for melt blending and extrusion to obtain the nanofiller.

7. The process for preparing PTFE fiber for enhanced dust filter bags according to claim 6, characterized in that: The preparation of the modified nano titanium dioxide includes the following processes: Methacryloxypropyltrimethoxysilane was added to an ethanol aqueous solution in parts by mass, acetic acid was added to adjust the pH value to acidic, and the mixture was stirred to obtain a modified solution; The nano-titanium dioxide is added to anhydrous ethanol, ultrasonically dispersed, the modified solution is added, the temperature is increased for reaction, the process is centrifuged, the process is alternately washed with deionized water and ethanol, and vacuum dried to obtain the modified nano-titanium dioxide.

8. The process for preparing PTFE fiber for enhanced dust filter bags according to claim 1, characterized in that: The preparation of the modified polytetrafluoroethylene includes the following processes: The method comprises the following steps: adding dried polytetrafluoroethylene powder, 20-25 parts of polyphenylene ether particles, 5-10 parts of fluororubber FKM, and 5-8 parts of perfluoropolyether to a high-speed mixer, pre-mixing at room temperature in the high-speed mixer, and uniformly dispersing the mixture; passing the mixture through a co-rotating twin-screw extruder for melt blending and granulation to obtain an extrudate; cooling the extrudate through a cooling water tank, pelletizing, and vacuum drying to obtain the modified polytetrafluoroethylene.

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