Preparation process of enhanced PTFE fiber for dust removal filter bag

Abstract

The present application relates to the technical field of PTFE fiber preparation, in particular to a preparation process of PTFE fiber for reinforced dust removal filter bag. The present application aims to solve the problem that the mechanical properties and dust removal performance of the existing PTFE fiber are difficult to be considered simultaneously. The present application prepares modified polytetrafluoroethylene by pre-mixing extrusion of polytetrafluoroethylene, polyphenyl ether, fluoro rubber and perfluoropolyether; then, nano titanium dioxide and carbon nanotube are respectively modified and treated, and then blended with PFA to prepare nano filler; the chopped carbon fiber is modified and treated to obtain modified micron material; through the core-sheath composite spinning line, the core layer containing PFA, modified micron material and nano filler is melt-extruded with the shell layer of modified polytetrafluoroethylene and auxiliary agent, and then spun through the composite spinneret, and then subjected to multi-stage hot stretching, multi-section sintering and heat setting to obtain PTFE fiber; the PTFE fiber prepared by the process has excellent mechanical properties and dust removal performance, and can meet the application requirements in the field of dust removal filter bag and the like.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of PTFE fiber preparation, in particular to a preparation process of PTFE fiber for reinforced dust removal filter bag. BACKGROUND

[0002] Polytetrafluoroethylene (PTFE) fiber has a wide application prospect in the fields of industrial filtration, special textiles, medical treatment, etc. due to its excellent chemical stability, high and low temperature resistance, low friction coefficient and hydrophobicity, especially in the manufacture of dust removal filter bags in high temperature and corrosive environment. However, the traditional PTFE fiber often faces a prominent problem in practical application: its excellent mechanical properties, including strength and wear resistance, and high dust removal performance are often difficult to balance. Since the macromolecular chain of PTFE is flexible and easy to orient and crystallize, high crystallinity or excessive orientation of molecular chain can improve the strength of the fiber, but may also lead to dense fiber structure and reduced porosity, thereby affecting the air permeability and fine particle capture efficiency of the fiber as a filter material. On the contrary, the porous structure constructed to improve the dust removal performance often sacrifices the mechanical strength of the fiber, making the filter bag prone to breakage and shortening its service life during use.

[0003] At present, in order to improve the comprehensive performance of PTFE fiber, researchers have tried various modification methods, including blending modification, filling enhancement, surface treatment and optimization of spinning process, etc. For example, by introducing nano fillers, changing the stretching process parameters, etc., a specific microstructure is formed inside the PTFE fiber, so as to balance the mechanical strength and filtration performance to a certain extent. However, the introduced fillers are prone to agglomeration due to poor compatibility with the polytetrafluoroethylene matrix, 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 fiber in the prior art often focus on the improvement of a single performance, ignoring the synergistic optimization of multiple performances. When applied to dust removal filter bags, the mechanical properties and dust removal performance are difficult to balance, resulting in insufficient comprehensive performance in actual application and reducing the service life.

[0005] Therefore, a preparation process of PTFE fiber for reinforced dust removal filter bag is proposed. SUMMARY

[0006] The application aims to provide a preparation process of PTFE fiber for enhanced dust removal filter bag.

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

[0008] The application provides a preparation process of PTFE fiber for enhanced dust removal filter bag, which comprises the following processes:

[0009] The core layer material is obtained by melt extrusion of perfluoroalkoxy resin, modified micron material, nano filler and compatibilizer; the shell layer material is obtained by melt extrusion of modified polytetrafluoroethylene and additives; and the shell layer material and the core layer material are extruded through a composite spinneret to obtain a spinning material.

[0010] The PTFE fiber is obtained by multi-stage hot stretching, multi-section sintering and heat setting of the spinning material.

[0011] The modified micron material is prepared from silane coupling agent 1 and short carbon fibers.

[0012] The modified polytetrafluoroethylene is obtained by melt blending of polytetrafluoroethylene and modifiers.

[0013] The nano filler is obtained by melt blending of modified carbon nanotubes, modified nano titanium dioxide, perfluoroalkoxy resin and compatibilizer.

[0014] The modified carbon nanotubes are obtained from silane coupling agent 1 and carbon nanotubes.

[0015] The modified nano titanium dioxide is obtained from silane coupling agent 2 and nano titanium dioxide.

[0016] Preferably, the compatibilizer is maleic anhydride grafted ethylene-tetrafluoroethylene copolymer; the silane coupling agent 1 is (3,3,3-trifluoropropyl)trimethoxysilane; the silane coupling agent 2 is methacryloyloxypropyltrimethoxysilane; the additives include sodium bicarbonate, citric acid, magnesium oxide and zinc oxide; and the modifiers include polyphenylene ether particles, fluororubber FKM and perfluoropolyether.

[0017] Preferably, the preparation of the spinning material comprises the following processes:

[0018] The perfluoroalkoxy resin 100 parts, modified micron material 20-30 parts, nano filler 10-15 parts, maleic anhydride grafted ethylene-tetrafluoroethylene copolymer 5-8 parts as the core layer are melt extruded by the core layer extruder to obtain the core layer material;

[0019] The modified polytetrafluoroethylene 100 parts, sodium bicarbonate 3-5 parts, citric acid 2-4 parts, magnesium oxide 2-3 parts, and zinc oxide 3-5 parts as the shell layer are melt extruded by the shell layer extruder to obtain the shell layer material.

[0020] The shell layer material and the core layer material are processed by a composite spinneret, and air cooling is performed to obtain a spun material; 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: feeding zone 280-300℃, compression zone 310-330℃, metering zone 320-340℃, die temperature 310-330℃, and the core layer pressure is 8-12MPa; the core layer melt extrusion parameters are: feeding zone 300-330℃, compression zone 320-350℃, metering zone 340-360℃, die temperature 330-360℃, and the pressure is 10-15MPa.

[0022] Preferably, the core layer extruder and the shell layer extruder are both single-screw extruders, the screw diameter is 30-65mm, and the length-diameter ratio is 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 is designed with a PTFE special screw; air cooling is performed at an air temperature of 20-25℃ and an air flow rate of 0.8-1.5m / s; the cooling zone length is 0.5-2m.

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

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

[0025] The spun material is first pre-stretched at a stretching temperature of 120-180℃ and a stretching multiple of 1.2-2.0 times; then it is stretched at a medium temperature of 220-260℃ and a stretching multiple of 2-4 times; finally, it is stretched at a high temperature of 300-330℃ and a stretching multiple of 1.5-3 times.

[0026] Preferably, the multi-stage sintering process comprises: nitrogen flow of 5 L / min, the first stage is heated to 200-250℃ at a heating rate of 5-10℃ / min, and the temperature is kept for 30-60 min; the second stage is heated to 300-330℃ at a heating rate of 3-5℃ / min, and the temperature is kept for 30-45 min; the third stage is heated to 360-380℃ at a heating rate of 3-5℃ / min, and the temperature is kept for 10-15 min.

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

[0028] (3,3,3-trifluoropropyl)trimethoxysilane is added into 95% aqueous ethanol solution, stirred uniformly, acetic acid is added to adjust the pH value to 4, and the temperature is raised to 50℃ for stirring for 1h to obtain a silane solution; the short-cut carbon nanofiber is added into the silane solution, and the stirring reaction is assisted by ultrasonic; then, the separation and centrifugation are carried out, the ethanol and deionized water are alternately washed for 5 times, and the vacuum drying is carried out at 100℃ for 3h 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 fiber.

[0029] Preferably, the short-cut fiber has an average diameter of 100-200nm and a length of 50-80μm; the particle size of the nanometer titanium dioxide is 20-50nm; and the carbon nanotube is selected from a multi-walled carbon nanotube, wherein the outer diameter is 10-30nm and the length is 10-20μm.

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

[0031] The multi-walled carbon nanotube is added into a mixed solvent of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, and the oxidation treatment is carried out at 60℃, and the separation and centrifugation are carried out, and the deionized water is washed for 5 times until neutral, and the vacuum drying is carried out to obtain the acidified carbon nanotube; the silane solution is added into the acidified carbon nanotube, and the stirring reaction is assisted by ultrasonic; then, the separation and centrifugation are carried out, the ethanol and deionized water are alternately washed for 5 times, and the vacuum drying is carried out to obtain the modified carbon nanotube; the modified carbon nanotube 5-8 parts, the modified nanometer titanium dioxide 10-20 parts, the maleic anhydride grafted ethylene-tetrafluoroethylene copolymer 5-8 parts, the perfluoroalkoxy resin 70-80 parts and the PVP 0.5 part are added into a twin-screw extruder for melt blending, and the melt extrusion temperature is 280-320℃ to obtain the nanofiller.

[0032] Preferably, the preparation of the modified nanometer titanium dioxide comprises the following process:

[0033] In 95% ethanol solution, 5 parts of methacryloxypropyl trimethoxysilane is added, acetic acid is added to adjust the pH value to be acidic, and stirring treatment is carried out at 30 DEG C for 20 min to obtain a modified solution; 100 parts of nano-titanium dioxide is added into 200 ml of anhydrous ethanol, ultrasonic dispersion is carried out for 30 min, the modified solution is added, the temperature is raised to 70 DEG C for reaction, centrifugal separation is carried out, and deionized water and ethanol are alternately washed for 3 times to obtain modified nano-titanium dioxide.

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

[0035] In a high-speed mixer, 100 parts of dry polytetrafluoroethylene powder, 20-25 parts of polyphenyl ether particles, 5-10 parts of fluororubber FKM and 5-8 parts of perfluoropolyether are added, pre-mixed for 3 times at room temperature in the high-speed mixer, each time for 20 min, and each mixing interval is 5 min, and uniform dispersion is obtained to obtain a mixture; the mixture is subjected to melt blending and granulation through a co-rotating twin-screw extruder to obtain an extruded material; the extruded material is cooled through a cooling water tank, granulated, and vacuum dried at 100 DEG C for 10 h to obtain the modified polytetrafluoroethylene.

[0036] Preferably, in the melt extrusion process, the temperature of the feeding area is controlled to be 200-250 DEG C, the temperature of the compression melting area is controlled to be 280-320 DEG C, the temperature of the homogenization area is controlled to be 320-340 DEG C, and the temperature of the die head is controlled to be 330-340 DEG C; the screw rotation speed is maintained to be 150-200 rpm, high-shear melt blending is carried out for 20 min, and the extruded material is quickly passed through a high-temperature area to reduce thermal degradation.

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

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

[0039] 1、The present application improves the melt processability of PTFE through modification, lays a foundation for uniform compounding with fillers and melt spinning, and optimizes the material selection and proportion of the skin layer and the core layer through the use of the skin-core structure to realize good matching of strength and toughness, wherein the carbon fiber has high strength and high modulus, and the carbon nanotube also has excellent mechanical properties, and good dispersion and interface combination of them in the PFA matrix can effectively bear the load; finally, through multi-stage hot drawing and heat drawing, multi-stage sintering treatment and heat setting treatment, the compatibility of the polytetrafluoroethylene matrix and the core layer reinforcing material is improved through the synergistic effect of multiple components and processes, and the fiber structure stability and higher mechanical properties are given.

[0040] 2, The application forms a nanometer level filtering barrier by filling the fiber micropore with carbon nanotubes; the nanometer titanium dioxide adsorbs microparticles and refines the pore size, and cooperatively realizes the dual mechanism of "nanometer sieving + adsorption interception"; in addition, sodium bicarbonate and citric acid are introduced, and carbon dioxide is generated by reaction to form uniform micropores (pore size 0.2-0.5 μm) in the shell layer, and a gradient structure of "outer fine pore interception + inner coarse pore support" is formed with the micrometer level carbon fiber skeleton in the core layer, so as to avoid the decline of the filtering efficiency, and finally the fiber axial porosity is directionally arranged through multi-stage stretching to improve the filtering efficiency; the multi-stage sintering treatment promotes the crystallization of PTFE to form a rigid pore structure, ensures the stability of the pore structure, and further improves the air permeability and filtering efficiency of the fiber by the synergistic effect of the three.

[0041] 3, The application improves the rigidity and creep resistance of PTFE by modifying polytetrafluoroethylene with polyphenyl ether, improves the rigidity and creep resistance of PTFE by interface modification, reduces adhesive wear, and at the same time introduces perfluoropolyether and fluororubber FKM to form a dynamic lubricating film to reduce the friction coefficient; the core layer formed by the combination of nanofiller and micron level reinforcing fiber constructs a "rigid and flexible interlocking" skeleton, the carbon fiber bears the main load, the carbon nanotube fills the micro gap and enhances the interface conductivity and thermal conductivity, and at the same time the "micro bearing effect" of the nanometer titanium dioxide reduces the contact stress, the rigid particles fill the PTFE micropore, reduce the friction contact area, inhibit the crack propagation and improve the surface hardness, and the modified shell layer of PTFE cooperatively resists surface wear to form a gradient wear-resistant layer, further improving the friction resistance of the fiber. BRIEF DESCRIPTION OF DRAWINGS

[0042] Figure 1 The preparation process flow chart of the polytetrafluoroethylene fiber of the embodiment 1 of the application. DETAILED DESCRIPTION

[0043] The technical solutions in the embodiments of the application will be described clearly and completely below with reference to the drawings in the embodiments of the application. Obviously, the described embodiments are only part of the embodiments of the application, rather than all the embodiments of the application. Based on the embodiments in the application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the application.

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

[0045] Referring to Figure 1 , Figure 1 It is a preparation process flow chart of the polytetrafluoroethylene fiber of the embodiment 1 of the present application. The present application provides a preparation process of the PTFE fiber for the reinforced dust removal filter bag, and the technical scheme is as follows:

[0046] Embodiment 1

[0047] In mass parts, 100 parts of dry polytetrafluoroethylene powder, 20 parts of polyphenyl ether particles, 5 parts of fluororubber FKM and 5 parts of perfluoropolyether are added into a high-speed mixer, and pre-mixed for 3 times at room temperature, each time for 20 min, and each mixing interval is 5 min, so as to ensure that each component is fully and uniformly dispersed to obtain a mixture; the mixture is subjected to melt blending and granulation through a co-rotating twin-screw extruder to obtain an extruded material; the extruded material is cooled through a cooling water tank, granulated, and vacuum dried at 100 DEG C for 10 h to obtain modified polytetrafluoroethylene.

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

[0049] In mass parts, 5 parts of KH570 are added into 10 ml of 95% ethanol aqueous solution, acetic acid is added to adjust the pH value to be acidic, and stirred at 30 DEG C for 20 min to obtain a modified solution; 100 parts of nano-titanium dioxide with a particle size of 20-50 nm are added into 200 ml of anhydrous ethanol, ultrasonically dispersed for 30 min, slowly added into the modified solution, heated to 70 DEG C, reacted for 3 h, separated by centrifugation, washed with deionized water and ethanol alternately for 3 times, and vacuum dried at 100 DEG C for 8 h to obtain modified nano-titanium dioxide.

[0050] The multi-walled carbon nanotubes are added into a mixed solvent of concentrated sulfuric acid and concentrated nitric acid with a volume ratio of 3:1, and oxidized at 60-70℃ for 1-2h, separated by centrifugation, washed with deionized water for 5 times until neutral, and vacuum dried at 80℃ for 5h to obtain acidified carbon nanotubes; the acidified carbon nanotubes are slowly added into a silane solution, and reacted at 50-70℃ for 3-5h under ultrasonic assistance; the mass ratio of the multi-walled carbon nanotubes to (3,3,3-trifluoropropyl) trimethoxysilane is 50:1; then the mixture is separated by centrifugation, washed with ethanol and deionized water alternately for 5 times, and vacuum dried at 100℃ for 3h to obtain modified carbon nanotubes; the modified carbon nanotubes 6 parts, modified nano-titanium dioxide 15 parts, maleic anhydride grafted ethylene-tetrafluoroethylene copolymer 8 parts, PFA 80 parts, and 0.5 part of PVP as a dispersant are added into a twin-screw extruder for melt blending, and extruded to obtain a nanofiller;

[0051] The PFA 100 parts, modified micron material 25 parts, and nanofiller 15 parts are melt-extruded by a core-shell composite spinning line through two single-screw extruders to obtain a core layer material; the modified polytetrafluoroethylene 100 parts, sodium bicarbonate 4 parts, citric acid 3 parts, magnesium oxide 2 parts, and zinc oxide 4 parts are melt-extruded by a shell layer extruder to obtain a shell layer material; the shell layer material and the core layer material are passed through a composite spinneret to maintain a volume ratio of the shell layer to the core layer of 6:4, and the spinning speed is 200 m / min to cool in air to obtain a spun material;

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

[0053] Example 2-5 refers to the preparation method and parameter conditions of Example 1, and the differences are 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 fluoroelastomer FKM are not used, and polyphenylene ether is melt-extruded with polytetrafluoroethylene.

[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 modified short carbon fibers are not added.

[0060] Comparative Example 5 refers to Example 1, except that modified carbon nanotubes are not added.

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

[0062] Comparative Example 7 refers to Example 1, except that core-shell material is not used, and the fiber is obtained only by modified polytetrafluoroethylene.

[0063] Comparative Example 8 refers to Example 1, except that core-sheath structure is not used, and is obtained directly by melt blending and spinning treatment.

[0064] Comparative Example 9 refers to Example 1, except that multiple-stage hot stretching is not used, and only high-temperature stretching is used, with a stretching ratio of 7 times.

[0065] Comparative Example 10 refers to Example 1, except that multiple-stage hot stretching is not used, and only low-temperature stretching is used, with a stretching ratio of 7 times.

[0066] Comparative Example 11 refers to Example 1, except that heat setting treatment is not performed.

[0067] Comparative Example 12 refers to Example 1, except that multiple-stage sintering treatment is not used.

[0068] Experimental Example 1: Breaking property test

[0069] The PTFE fibers prepared in Examples 1-5 and Comparative Examples 1-12 were tested for breaking strength and elongation at break according to the test standard GB T3916-2013, and 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 Breaking elongation / % 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] From the results of Table 2, in the comparative examples, the mechanical properties of the fibers are obviously adversely affected by the changes in the components and process conditions. In Comparative Examples 1-3, no polyphenyl ether particles, perfluoropolyether, and fluororubber modified polytetrafluoroethylene are added, and the mechanical properties are obviously reduced compared to the examples. The rigid molecular chain of the polyphenyl ether can be embedded between the polytetrafluoroethylene molecules, enhancing the interfacial bonding force through physical entanglement, and promoting the dispersion of the filler by reducing the melt viscosity. Without modification, the PTFE matrix has poor flowability, and the filler is prone to agglomeration during the later melt extrusion process, forming stress concentration points, which significantly reduces the fiber strength. The elastic segment of FKM can absorb tensile energy, and the perfluoropolyether reduces processing heat damage through lubrication. Without the latter, the modified system exhibits brittle fracture characteristics, and the strength is significantly reduced. In addition, as a fluorine-based lubricant, perfluoropolyether can reduce the frictional heat between polytetrafluoroethylene and the equipment. The absence of it intensifies thermal degradation in the high-temperature zone, leading to main chain rupture and a decrease in molecular weight, resulting in poor mechanical properties. Due to the poor compatibility of the two, multiple pre-mixing is necessary to ensure uniform distribution of polyphenyl ether particles and polytetrafluoroethylene, while reducing the load on the extruder and avoiding local overheating, which damages the polytetrafluoroethylene matrix, thereby improving the compatibility of the two and the melt index of the matrix, which is beneficial to the subsequent processing process. As shown in Comparative Examples 4-7, without introducing a skin-core structure or utilizing the synergistic reinforcement of the filler components, the mechanical properties of the fibers are significantly reduced. As a micron-level reinforcing agent, chopped carbon fibers bear 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, forming a "micron-nanometer load transfer network." The chopped carbon fibers act as the skeleton to bear the main tensile load, and the carbon nanotubes bridge adjacent carbon fibers through their high aspect ratio, forming a stress transfer chain. Meanwhile, the nanoscale pores adsorb submicron particles, achieving dual improvement in mechanical reinforcement and filtration precision, improving the efficiency of interfacial stress transfer and avoiding the generation of microcracks. Modified nanometer titanium dioxide acts as a heterogeneous nucleating agent, which can refine the polytetrafluoroethylene crystals, increase the crystallinity and molecular chain orientation, and form coarse grains that are prone to slip and crack propagation during stretching, reducing the overall mechanical properties. Due to the inability of a single shell structure to disperse concentrated loads, the introduction of a skin-core structure allows the core layer to bear the main stress and the shell layer to buffer the surface stress. By introducing a high proportion of fillers and a high-temperature resistant polymer in the core layer, the overall compatibility and mechanical strength of the fiber are improved. In combination with Comparative Example 8, the core layer in the skin-core structure can enrich more than 70% of the reinforcing fillers. When directly blended, the fillers are uniformly dispersed but the concentration is reduced, the effective load-bearing fillers in the unit cross-sectional area are reduced, and the mechanical strength is decreased.In addition, when directly blended, the PTFE and PFA in the spinning have poor melt compatibility, the skin-core structure avoids direct mixing of the two by delamination melting, and improves the overall mechanical properties. As can be seen from the results of 9-10, high temperature close to the melting point of polytetrafluoroethylene causes rapid orientation of molecular chains, however, too high temperature causes the molecular chain to break, forming an "orientation-breakage" competition, and finally a large number of microcracks are generated inside the fiber, and the strength is greatly reduced; at low temperature, the molecular chain is not fully oriented, and the residual stress is not eliminated, and the fiber is prone to breakage, and the tensile properties are poor; pre-stretching prepares for subsequent high-stretching, medium-temperature stretching is the main orientation stage, and high-temperature stretching helps to further improve the crystal form and eliminate part of the defects, and the mechanical properties of the fiber are improved under the synergistic effect; in Comparative Example 12, without multi-stage sintering, the pore structure is unstable, the inorganic filler in the shell layer is not fully combined, the wear resistance is poor, and the fiber is prone to brittle fracture; high-temperature sintering makes the PTFE particles fully fuse, eliminates the interface, forms a continuous network structure, and eliminates the internal stress accumulated during stretching, and gives the fiber structural stability and higher mechanical properties; in Comparative Example 11, without heat setting treatment, the molecular chain relaxes, the residual stress remains, the fiber size stability is poor, the elongation fluctuates greatly, and the fiber is prone to deformation during long-term use, which further affects the overall performance of the fiber.

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

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

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

[0076]

[0077] Comparative Example 12 refers to Example 1, and the difference is that it does not pass through multi-stage sintering treatment.

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

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

[0080] Comparative Example 15 refers to Example 1, and the difference is that it does not add sodium bicarbonate.

[0081] Comparative Example 16 refers to Example 1, and the difference is that it does not add citric acid.

[0082] Comparative Example 17 refers to Example 1, and the difference is that it does not add sodium bicarbonate and citric acid.

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

[0084] 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 subjected to a filtration test at a filtration speed of 2.5 cm / s, and the air flow containing 0.1-0.5 μm particles was passed through the fiber samples. The particle concentration before and after the air flow passed through the samples was measured by means of a particle counter, and the filtration efficiency was calculated by a formula. The air flow per unit area of the fiber sample per unit time was measured at a pressure difference of 100 Pa, and the air permeability was determined. 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 of Table 4, it can be seen that in the comparative examples, the adjustment of components and process has a significant influence on the air 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 0.1-0.5 pm particles. After the absence of the modified carbon nanotubes, the number of micropores in the fiber decreases, the proportion of macropores increases, resulting in the increase of particle penetration rate, and the decrease of filtration precision. The nanometer titanium dioxide refines the pore size by filling the pores. After the absence of the nanometer titanium dioxide, the average pore size of the fiber increases, and the sub-micron particles cannot be effectively intercepted. The increase of pore size reduces the air permeation resistance and increases the air permeability, but the filtration efficiency decreases with the increase of pore size. From the results of Comparative Examples 7-8, it can be seen that the modified carbon fibers and nanometer fillers in the core layer provide mechanical support and skeleton pores. Without the core layer, the pure modified PTFE fiber is prone to breakage during stretching, the pores collapse, and the filtration efficiency decreases due to the decrease of effective pores. In addition, the collapsed pores hinder the airflow, and the air permeability decreases. The introduction of the skin-core structure realizes the functional partitioning through the porous shell layer and the support layer of the core layer. Direct melt blending spinning leads to random distribution of pores, uneven pore size of the filtration layer, and easy penetration of particles from the large pores. The air permeability also decreases due to the uneven distribution of pores. From the results of Comparative Examples 12-14, it can be seen that during the multi-stage sintering process, citric acid starts to dehydrate and partially decompose at low temperature, and the generated gas helps to form the initial microporous structure. In addition, the slow heating and sufficient holding time help the gas to slowly escape, and the process is uniform. At medium temperature, the modified PTFE matrix starts to soften and has a certain fluidity, which helps the PTFE particles to preliminarily bond and fuse around the already formed pores, thereby stabilizing the pore structure and preventing serious collapse during subsequent high-temperature sintering. Under high temperature, the PTFE particles are fully melted and diffused to form a solid porous network skeleton, which maximizes the porosity and uniformity of the pore size. The rapid heating process leads to local overheating, excessive melting of PTFE, and the formation of a large-pore structure with wide pore size distribution and poor connectivity, resulting in a decrease in filtration precision. When the heating rate is too slow and the temperature is too low, the fiber is amorphous and not fully crystallized below the crystallization temperature of PTFE, the pores collapse, and there is no fixed pore structure, resulting in a significant decrease in filtration efficiency and air permeability. From the results of Comparative Examples 15-18, it can be seen that the reaction of sodium bicarbonate and citric acid to generate carbon dioxide is the core of the foaming of the shell layer to form a porous structure. Without sodium bicarbonate, the shell layer does not foam at all, and the shell layer is a solid structure, relying only on the micropores of the core layer for filtration, but the core layer has a low proportion and irregular pores, resulting in a significant decrease in filtration efficiency. Without sodium bicarbonate, the shell layer cannot generate gas relying only on citric acid, resulting in a dense shell layer that hinders the airflow, and a decrease in air permeability and filtration efficiency. Without citric acid, the gas production is insufficient, the porosity of the shell layer is too low, and the filtration and air permeability performance decrease. The generation of gas in the core layer by sodium bicarbonate and citric acid leads to a loose structure of the core layer, but the shell layer 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 were prepared according to the method and parameters of Example 1 with the differences shown in Table 5.

[0092] Parameter changes of Examples 10-14

[0093]

[0094] Comparative Example 19 was prepared according to Example 1 with the difference that magnesium oxide was not added.

[0095] Comparative Example 20 was prepared according to Example 1 with the difference that zinc oxide was not added.

[0096] Comparative Example 21 was prepared according to Example 1 with the difference that the nanofiller was not obtained by melt extrusion first, but the modified micron material, modified carbon nanotube and modified nanometer titanium dioxide were directly melt extruded with PFA matrix to obtain the shell material.

[0097] Abrasion resistance test of Example 3

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

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

[0100]

[0101]

[0102] From the results of Table 6, it can be seen that the results of Comparative Examples 1-3 show that the wear resistance of the fiber material is significantly reduced by modifying polytetrafluoroethylene. Polystyrene as a rigid dispersed phase enhances the interfacial bonding force and forms an island structure with polytetrafluoroethylene. In addition, the heat resistance of polystyrene inhibits the softening of polytetrafluoroethylene at high temperatures, and the strength of the polytetrafluoroethylene matrix decreases, making it prone to plastic deformation during friction, which exacerbates material wear. Perfluoropolyether is a low molecular weight lubricant, and fluororubber provides elastic damping. The absence of both causes the shell layer of polytetrafluoroethylene to change from "self-lubricating wear" to "adhesive wear", resulting in a decrease in friction performance. Multiple pre-mixing ensures uniform dispersion of the modifier in the matrix, avoiding agglomeration of components due to insufficient mixing, and non-uniform structure leading 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. Short carbon fibers are modified with silane to form a rigid skeleton that bears the frictional stress. The absence of the fiber matrix makes it prone to interlayer slip, and the wear mechanism changes from "fatigue wear" to "adhesive wear". In addition, the electrical conductivity of carbon fibers can transfer frictional static electricity, reducing electrostatic adsorption wear. Carbon nanotubes fill the intermolecular chain gaps of PTFE with nanoscale dimensions, forming a "molecular-level reinforcing network" to improve surface hardness. The high aspect ratio hinders molecular chain slipping, improving wear resistance. Modified nano-titanium dioxide forms hydrogen bonds with PTFE, enhancing interfacial bonding. As a "solid lubricant", it reduces the friction coefficient. Its inherent photocatalytic activity can decompose the oxides generated during friction, further reducing the wear rate. As an alkaline filler, magnesium oxide can neutralize acidic degradation products generated during friction, inhibiting corrosion wear. Without it, the acidic environment accelerates the breakdown of PTFE molecular chains, increasing the wear rate. In addition, the high melting point of magnesium oxide improves the material's heat resistance, preventing local softening caused by friction heating and improving wear resistance. Zinc oxide has pressure-sensitive conductivity and works synergistically with carbon nanotubes and carbon fibers to evenly distribute frictional static electricity, reducing material damage caused by electrical discharge. Without it, electrostatic adsorption of wear debris forms a grinding layer, exacerbating the volume wear of the fiber. In addition, the micro-rigid particles of zinc oxide (with a particle size of 1-2 μm) can polish the friction interface, reducing roughness. Without it, the surface is rougher. In Comparative Example 21, directly blending micron particles and nanoparticles can easily lead to filler agglomeration, greatly reducing the compatibility of the PFA matrix. In addition, the formation of agglomerates acts as hard points to plow against the grinding surface, further reducing wear resistance. During the preparation of the nano-filler, high shear forces are used to achieve nanoscale dispersion of modified carbon nanotubes and modified nano-titanium dioxide in PFA. Then, micron-sized carbon fibers are introduced to improve the interfacial bonding between the micron fibers and the PTFE matrix using the nano-filler. At the same time, micron fibers bear the main load, achieving multi-scale synergistic reinforcement, avoiding local stress concentration caused by uneven dispersion, and further improving the wear resistance of the fiber.

[0103] While embodiments of the application have been shown and described, it is to be understood that the embodiments described are merely exemplary of the principles and application of the present application. Numerous modifications and adaptions can be effected without departing from the spirit and scope of the present application, which is not limited to the exact construction and arrangement described. It is intended, therefore, to cover all modifications and adaptions that fall within the scope of the claims and their equivalents.

Claims

1. A process for the production of PTFE fibers for enhanced dust filtration bags, characterized by: The preparation comprises the following processes: The perfluoroalkoxy resin, modified micron material, nanofiller and compatibilizer are melt-extruded to obtain a core layer material; The modified polytetrafluoroethylene and the auxiliary agent are melt-extruded to obtain a shell layer material; the shell layer material and the core layer material are passed through a composite spinneret, spun and cooled to obtain a spun material; The auxiliary agent comprises sodium bicarbonate, citric acid, magnesium oxide and zinc oxide; The spun material is subjected to multi-stage heat stretching, multi-stage sintering treatment and heat setting treatment to obtain the PTFE fiber; The multi-stage heat stretching comprises: first, pre-stretching the spun material, the stretching temperature being 120-180℃ and the stretching multiple being 1.2-2.0 times; then, middle-temperature stretching, the stretching temperature being 220-260℃ and the stretching multiple being 2-4 times; finally, high-temperature stretching, the stretching temperature being 300-330℃ and the stretching multiple being 1.5-3 times; The multi-stage sintering treatment process comprises: nitrogen flow being 5L / min, the first stage being heated to 200-250℃ at a heating rate of 5-10℃ / min and being kept for 30-60min; the second stage being heated to 300-330℃ at a heating rate of 3-5℃ / min and being kept for 30-45min; the third stage being heated to 360-380℃ at a heating rate of 3-5℃ / min and being kept for 10-15min; The modified micron material is prepared from the silane coupling agent one and modified short carbon fibers; The modified polytetrafluoroethylene is obtained by melt blending polytetrafluoroethylene and a modifier; The modifier comprises polyphenyl ether particles, fluororubber FKM and perfluoropolyether; The nanofiller is obtained by melt blending modified carbon nanotubes, modified nanometer titanium dioxide, the perfluoroalkoxy resin, the compatibilizer and PVP; The modified carbon nanotubes are obtained from the silane coupling agent one and modified carbon nanotubes; The modified nanometer titanium dioxide is obtained from the silane coupling agent two and modified nanometer titanium dioxide; The dry polytetrafluoroethylene powder, the polyphenyl ether particles, the fluororubber FKM and the perfluoropolyether are added into a high-speed mixer in mass fractions of 20-25 parts, 5-10 parts and 5-8 parts respectively, pre-mixed at room temperature in the high-speed mixer and uniformly dispersed to obtain a mixture; the mixture is subjected to melt blending and granulation by a co-rotating twin-screw extruder to obtain an extruded material; the extruded material is cooled by a cooling water tank, granulated and vacuum dried to obtain the modified polytetrafluoroethylene.

2. A process for the preparation of PTFE fibers for enhanced dust filtration bags as claimed in claim 1, wherein: The compatibilizer is maleic anhydride grafted ethylene-tetrafluoroethylene copolymer; the silane coupling agent one is (3,3,3-trifluoropropyl)trimethoxysilane; and the silane coupling agent two is methacryloyloxypropyltrimethoxysilane.

3. The process for the preparation of PTFE fibers for enhanced dust filtration bags as claimed in claim 1, wherein the process is characterized by: The preparation of the spun material comprises the following processes: The perfluoroalkoxy resin, the modified micron material, the nanofiller and the maleic anhydride grafted ethylene-tetrafluoroethylene copolymer are melt-extruded by a core layer extruder to obtain the core layer material; The modified polytetrafluoroethylene, sodium bicarbonate 3-5 parts, citric acid 2-4 parts, magnesium oxide 2-3 parts, zinc oxide 3-5 parts are taken as the shell layer and melt-extruded through a shell extruder to obtain the shell layer material; The shell layer material and the core layer material are taken through a composite spinneret, subjected to spinning treatment, and air-cooled to obtain the spun material; wherein the volume ratio of the shell layer material to the core layer material is 5-7:3-5.

4. The process for the preparation of PTFE fibers for enhanced dust filtration bags as claimed in claim 1, wherein: The preparation of the modified micro material comprises the following processes: (3,3,3-trifluoropropyl) trimethoxysilane is added into an ethanol aqueous solution, stirred uniformly, acetic acid is added to adjust the pH value, and the mixture is stirred at an elevated temperature to obtain a silane solution; short-cut carbon nanofibers are added into the silane solution, and the mixture is stirred under ultrasonic assistance; then the mixture is separated and centrifuged, washed with ethanol and deionized water alternately, and vacuum-dried to obtain the modified micro material; wherein the (3,3,3-trifluoropropyl) trimethoxysilane accounts for 0.8-1.5% of the total mass of the short-cut carbon fibers.

5. The process for the preparation of PTFE fibers for enhanced dust filtration bags as claimed in claim 1, wherein: The preparation of the silane solution for preparing nanofillers comprises the following processes: In terms of mass parts, multi-walled carbon nanotubes are added into a mixed solvent of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1, subjected to oxidation treatment, separated and centrifuged, washed with deionized water until neutral, and vacuum-dried to obtain acidified carbon nanotubes; the silane solution is added into the acidified carbon nanotubes, and the mixture is stirred under ultrasonic assistance; then the mixture is separated and centrifuged, washed with ethanol and deionized water alternately, and vacuum-dried to obtain modified carbon nanotubes; the modified carbon nanotubes 5-8 parts, modified nanometer titanium dioxide 10-20 parts, maleic anhydride grafted ethylene-tetrafluoroethylene copolymer 5-8 parts, perfluoroalkoxy resin 70-80 parts, and the PVP are added into a twin-screw extruder for melt blending and extrusion to obtain the nanofillers.

6. The process for the preparation of PTFE fibers for enhanced dust filtration bags as claimed in claim 1, wherein: The preparation of the modified nanometer titanium dioxide comprises the following processes: In terms of mass parts, methacryloxypropyl trimethoxysilane is added into an ethanol aqueous solution, acetic acid is added to adjust the pH value to be acidic, and the mixture is stirred to obtain a modified solution; Nanometer titanium dioxide is added into anhydrous ethanol, ultrasonically dispersed, the modified solution is added, the mixture is reacted at an elevated temperature, centrifuged, washed with deionized water and ethanol alternately, and vacuum-dried to obtain the modified nanometer titanium dioxide.

Images