Preparation method of high-resilience expanded polytetrafluoroethylene sealing material

Abstract

The invention discloses a preparation method of a high-resilience expanded polytetrafluoroethylene sealing material, and belongs to the technical field of high polymer material modification. According to the method, high-molecular-weight or modified polytetrafluoroethylene is used as a matrix, and high-orientation fibers are obtained through ultrasonic premixing, twin-screw melt extrusion, stretching and heat setting; dipping the fiber in a dispersion liquid containing high-entropy alloy nanoparticles, carbon nanotubes and graphene nanosheets, carrying out vacuum drying and gradient heat treatment to form a nano-reinforced precursor fiber, and constructing a porous anisotropic skeleton by adopting conventional or supercritical expansion and a specific weaving process; and interface strengthening and surface functionalization are realized through plasma surface treatment, silane coupling agent chemical grafting and wear-resistant coating coating. The obtained sealing material has low density, high strength, high resilience and low compression set, has excellent chemical medium resistance and anti-static performance, and is suitable for sealing parts of flanges, valves and the like under harsh working conditions of petrochemical engineering, electric power, hydrogen energy, aerospace and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of high polymer material modification, and particularly relates to a preparation method of high-rebound expanded polytetrafluoroethylene sealing material. BACKGROUND

[0002] Expanded polytetrafluoroethylene (ePTFE) has been widely used in flange gaskets, valve packing, pipeline sealing and special pipe sealing in the petrochemical, power, refrigeration, pharmaceutical and food industries due to its excellent chemical corrosion resistance, wide temperature performance (-200℃ to +300℃), low friction coefficient and excellent compressive recovery. Traditional ePTFE materials are usually made of high molecular weight polytetrafluoroethylene resin through biaxial stretching, heat treatment and special weaving process. The porous fiber structure of the ePTFE material gives it unique compressibility and relatively good sealing adaptability. However, the main technical bottlenecks of the existing ePTFE sealing material are: (1) under long-term compression load, temperature cycle and harsh working conditions, the material is prone to obvious compression set, resulting in sealing stress attenuation and eventually leakage failure. Actual measurement data shows that the compression set of traditional ePTFE gaskets is usually 20% to 30% under 55% to 80% high compression rate, and the corresponding rebound resilience is only 15% to 20% after 70℃×24h standard test (according to GB / T6669-2008 method), which is far lower than the requirement of severe working conditions; (2) the porous structure is beneficial to compression adaptation, but the strength of the pore wall is limited, and the material is prone to irreversible plastic deformation due to micro buckling and pore wall collapse in repeated compression-unloading cycles, which eventually leads to thickness attenuation and loss of sealing specific pressure; (3) it is difficult to effectively improve the strain energy recovery efficiency and cycle life of the material by relying solely on fiber stretching orientation and heat treatment, which is particularly evident in high temperature, high pressure, strong corrosion and long-term stable contact stress conditions.

[0003] To improve the compression set problem of ePTFE materials, several improvement schemes have been proposed in the existing literature and industry practice: the first type of scheme is to introduce traditional inorganic fillers (such as glass fibers, ceramic microbeads, carbon black, etc.) into ePTFE to increase the support stiffness of the pore wall. However, this type of scheme can improve the compression modulus of the material to some extent, but usually reduces the compressibility and environmental adaptability of the material, and the interface between these micron-sized fillers and the PTFE matrix is usually weak, which can easily separate or agglomerate at high temperatures, resulting in limited comprehensive sealing performance improvement space. The second type of scheme is to use thermoplastic elastomers (TPE) or rubber elastomers as a substitute or composite component of the sealing material. Although TPE / rubber materials have excellent resilience and low compression set characteristics (according to standard tests, the resilience can be ≥95%), their chemical corrosion resistance and high temperature resistance are far inferior to PTFE, and they are not suitable for scenes containing strong corrosive media (such as concentrated sulfuric acid, aqua regia) or working temperatures exceeding 150°C. In addition, pure TPE / rubber materials, although good in resilience, often require a large amount of plasticizer and anti-aging agent to achieve the same wide working temperature range and excellent durability as PTFE, which in turn increases the cost of the material and introduces new harmful substance emission risks. The third type of scheme is to chemically modify the PTFE body or blend with a polymer, such as modified PTFE containing perfluoropropyl vinyl ether (PPVE) comonomer, PTFE / vinyl rubber blend, or PTFE / polyether ether ketone (PEEK) composite. These schemes can improve the processing fluidity and grafting activity of PTFE to some extent, but the inhibition effect on compression set is still limited, and the modified components may decompose or phase separate from the matrix at high temperatures.

[0004] In recent years, high-entropy alloy (HEA) and its nanoparticles have shown new scientific opportunities in material strengthening and functionalization due to their unique multi-principal solid solution structure, significant lattice distortion effect, and multi-body synergistic effect. Compared with traditional single metal or binary / trinary alloy nanoparticles, high-entropy alloy nanoparticles have the following advantages: excellent interface compatibility: the multi-element homogeneous distribution structure makes the high-entropy nanoparticles form stronger physical and chemical bonding with the organic polymer matrix, the interface mismatch stress is smaller, and the interface debonding risk is reduced. Strain dissipation and energy absorption: the lattice distortion and multi-body "cocktail effect" of high-entropy alloy make it show a unique nonlinear response to external stress, which can effectively absorb and dissipate mechanical energy in cyclic loading, and is beneficial to inhibit the accumulation of permanent deformation. Wide temperature range performance stability: compared with single-element or low-entropy alloy nanoparticles, high-entropy alloy can still maintain structural stability and strengthening effect in a wide temperature range due to its wide phase transition temperature and small thermal expansion coefficient gradient, which is particularly important for sealing applications in the working range of-50℃ to 200℃. Conductive and anti-static properties: high-entropy alloy nanoparticles of specific composition (such as Fe-Co-Ni-Cu-Zn system) have ferromagnetic or semiconductor properties, and can realize anti-static function after forming a conductive network in the polymer matrix, while traditional carbon fillers are also conductive but easy to wear and fall off in application.

[0005] Although progress has been made in the application of high-entropy nanoparticles in single-phase bulk materials or thin film coatings, the multi-scale synergistic reinforcement of high-entropy alloy nanoparticles with one-dimensional and two-dimensional carbon nanomaterials such as carbon nanotubes (CNTs) and graphene nanosheets (GNS) for improving the high resilience and long-term reliability of expanded polytetrafluoroethylene (ePTFE) sealing materials remains a technological gap in both academic literature and industrial practice. Specifically, existing literature focuses primarily on the application of high-entropy nanoparticles in bulk alloys or ceramic matrix composites, with insufficient systematic research on their dispersion, localization, and interfacial interactions in porous polymer structures (especially ePTFE). While carbon nanotubes and graphene have been widely used for polymer reinforcement, reports on how they synergistically form a three-dimensional network structure with high-entropy nanoparticles in a PTFE matrix, and the mechanism by which this network contributes to the material's resilience and permanent deformation, are lacking. Traditional expansion processes (such as thermomechanical expansion) typically yield a wide pore size distribution (0.2–5 μm), making it difficult to precisely control pore wall thickness and porosity. While supercritical CO2 expansion technology can improve pore size uniformity, its coupling process with nano-reinforcing precursors has not been systematically reported. Although plasma surface activation and silane coupling modification are mature polymer surface technologies, systematic optimization for multifunctional grafting designs on the surface of nanocomposite ePTFE porous fibers (such as achieving synergistic effects of waterproofing, oil resistance, stain resistance, antistatic properties, and mechanical strengthening) is still insufficient.

[0006] Based on the above analysis, the following core contradictions exist in the current field of sealing materials technology: Although traditional ePTFE is resistant to chemical corrosion and high temperature, it has large compression set and low resilience, which cannot meet the long-term sealing requirements of modern high-pressure, high-temperature, and highly corrosive working conditions; although high-resilience TPE / rubber has good resilience, its corrosion resistance and high-temperature resistance are insufficient, limiting its applicable working conditions; simple single-component reinforcement or modification schemes have limited effects and cannot simultaneously achieve the multiple performance requirements of "high corrosion resistance + wide temperature range + high resilience + low permanent deformation".

[0007] Therefore, there is an urgent need for an innovative preparation method that, while retaining the original advantages of expanded polytetrafluoroethylene (PTFE) in terms of corrosion resistance and high temperature resistance, can significantly improve the strain energy recovery efficiency, compression cycle stability, and multi-condition adaptability of the material by rationally introducing a multi-scale nano-reinforcement system and surface functionalization process. Summary of the Invention

[0008] To address the problems of existing expanded polytetrafluoroethylene (ePTFE) sealing materials, such as significant compression set under long-term compressive loads and temperature cycling, insufficient resilience, and difficulty in simultaneously achieving high strength, antistatic properties, and stable sealing over a wide temperature range under low-density conditions, this invention proposes a high-resilience expanded polytetrafluoroethylene (ePTFE) sealing material and its preparation method. While existing ePTFE gaskets possess excellent chemical corrosion resistance and a wide temperature range, they still exhibit significant creep relaxation and compression set under high temperature, high pressure, or long-term service conditions. This leads to a decrease in residual preload in flange connections and an increased risk of seal failure. Furthermore, conventional rubber or thermoplastic elastomer materials are insufficient to meet the comprehensive requirements of highly corrosive and high-temperature conditions.

[0009] The present invention adopts the following technical solution: a method for preparing a high-resilience expanded polytetrafluoroethylene sealing material, which, by weight, includes the following steps: (1) 100 parts of polytetrafluoroethylene resin (CAS No.: 9002-84-0, number average molecular weight of 5×10 6 -1×10 7 ) and 0.5-3 parts of polyethylene (CAS No.: 9002-88-4, number average molecular weight ≥1×10 6 (1) Premix the materials to obtain a premix; (2) Melt extrude the premix obtained in step (1) to obtain nascent fibers; (3) Longitudinally stretch the nascent fibers obtained in step (2) and then heat set them to obtain matrix fibers; (4) Add 0.5-5 parts of high-entropy alloy nanoparticles, 0.1-1 parts of carbon nanotubes (outer diameter 8-15nm, length 10-30μm, CAS No.: 308068-56-6), and 0.05-0.5 parts of graphene nanosheets (3 layers, transverse dimension 0.5-5μm, CAS No.: 1034343-98-0) to 50-100 parts of polyethylene glycol (CAS No.: 25322-68-3) to obtain a premix; (5) The matrix fiber obtained in step (3) is immersed in the suspension obtained in step (4) to obtain the immersed matrix fiber; (6) The immersed matrix fiber obtained in step (5) is vacuum dried, and then subjected to gradient heat treatment under nitrogen protection and cooled to room temperature to obtain nano-reinforced precursor fiber; (7) The nano-reinforced precursor fiber obtained in step (6) is expanded to obtain expanded fiber; (8) The expanded fiber obtained in step (7) is woven into a sealing material blank, and then subjected to plasma surface treatment to obtain a treated sealing material blank; (9) The treated sealing material blank obtained in step (8) is immersed in a surface modification liquid for treatment, and then cured to obtain the final product.

[0010] Preferably, the premixing parameters in step (1) are as follows: the ultrasonic frequency is 25-40kHz, and the mixing temperature is controlled at 15-25℃; the melt extrusion parameters in step (2) are as follows: melt extrusion is carried out at 320-380℃ through a twin-screw extruder, the screw length-to-diameter ratio is (28-32):1, the screw speed is 50-120rpm, the extrusion pressure is 15-25MPa, and nascent fibers with a diameter of 2-5mm are produced.

[0011] Preferably, the parameters for longitudinal stretching in step (3) are as follows: the stretching ratio is 4-8 times at 280-320℃, and the stretching rate is 50-200mm / min; the parameters for heat setting in step (3) are as follows: temperature 320-400℃, time 30-120s.

[0012] Preferably, the preparation method of high-entropy alloy nanoparticles in step (4) is as follows: Ferric nitrate nonahydrate (CAS No.: 7782-61-8), nickel nitrate hexahydrate (CAS No.: 13478-00-7), cobalt nitrate hexahydrate (CAS No.: 10026-22-9), chromium nitrate nonahydrate (CAS No.: 7789-02-8), and manganese nitrate tetrahydrate (CAS No.: 20694-39-7) are mixed in equal mass ratio and dissolved in deionized water to prepare a metal salt mixed solution with a total metal ion concentration of 1.5 mol / L. Citric acid (CAS No.: 77-92-9) is added at 0.2-0.5 times the mass of the metal salt mixed solution, and then the mixture is added... Vinylpyrrolidone (average molecular weight about 40,000, CAS No.: 9003-39-8), polyvinylpyrrolidone is 3-10% of the total mass of the metal salt mixed solution, and then choline chloride (CAS No.: 67-48-1) of 20-40% of the total mass of the metal salt mixed solution is added. The precursor solution is formed by stirring at 120-180 rpm at 60-80℃. The temperature is raised to 600-800℃ and calcined for 8-16 h under nitrogen protection. The product is obtained by vacuum drying at 60-80℃ for 6-12 h. The parameters of ultrasonic dispersion treatment in step (4) are as follows: dispersion treatment for 60-180 min under ultrasonic power density of 500-1000 W / L and frequency of 40 kHz.

[0013] Preferably, the parameters for impregnation in step (5) are as follows: impregnation temperature 60-80℃, impregnation time 30-90min, ultrasonic assistance with a frequency of 20-50kHz is applied during the impregnation process, and the ultrasonic duty cycle is 60%.

[0014] Preferably, the parameters for vacuum drying in step (6) are as follows: vacuum drying for 4-8 hours under conditions of vacuum degree ≤100Pa and temperature 120-180℃; the parameters for gradient heat treatment in step (6) are as follows: heating to 200-250℃ at a heating rate of 2-5℃ / min and holding for 1-2 hours, then heating to 300-350℃ at a heating rate of 1-3℃ / min and holding for 2-4 hours, while applying an alternating magnetic field with a frequency of 50-200Hz and a magnetic field strength of 0.5-2T during the second holding time.

[0015] Preferably, the parameters for the puffing process in step (7) are as follows: at a preheating temperature of 180-220℃, the fiber passes through the puffing vessel at a rate of 50-200 mm / s, the puffing pressure is 0.1-0.5 MPa, the puffing ratio is 2-5 times, the diameter of the puffed fiber is 10-50 μm, the porosity is 60-85%, and the average pore size is 0.1-2 μm.

[0016] Preferably, the weaving parameters in step (8) are as follows: the linear density ratio of warp fibers to weft fibers is 1:(1.2-1.8), the weaving angle is 30-60°, and the weaving density is 50-150 fibers / cm. 2 The thickness is 1-5 mm; the parameters for plasma surface treatment in step (8) are as follows: vacuum degree 10-50 Pa, atmosphere is a mixture of argon and oxygen in a volume ratio of 7:1, power density 0.5-2.0 W / cm³ 2 Process for 5-15 minutes at a frequency of 13.56MHz.

[0017] Preferably, the surface modification liquid in step (9) is a mixture of 3-glycidyl etheroxypropyltrimethoxysilane (CAS No.: 2530-83-8), perfluorooctyltrimethoxysilane (CAS No.: 85857-16-5), aminopropyltriethoxysilane (CAS No.: 919-30-2) and isopropanol (CAS No.: 67-63-0) in a mass ratio of (1-3):(0.5-2):(0.33-1):100.

[0018] Preferably, the parameters for immersion treatment in step (9) are as follows: time 4-6h, temperature 40-60℃; the parameters for curing in step (9) are as follows: curing at 80-100℃ for 2-4h.

[0019] In addition, the equipment used for premixing in step (1) and ultrasonic dispersion / impregnation in steps (4) and (5) can be a stainless steel tank-type ultrasonic cleaner with heating function, such as the KQ-400DE ultrasonic cleaner (Kunshan Ultrasonic Instrument Co., Ltd.), which has a nominal frequency of 40kHz, an ultrasonic power of about 400W, and a tank volume of about 15L. It can be precisely controlled by an external constant temperature water bath within the range of 15-25℃ or 60-80℃. For laboratory equipment used for high energy density dispersion of high-entropy alloy nanoparticles and carbon nanomaterials, a probe-type ultrasonic processor can be used, such as the JY92-IIN ultrasonic pulverizer / disperser (Ningbo Xinzhi Biotechnology Co., Ltd.), which has a rated power of about 650W and an applicable volume of 100μL-500mL. It can provide continuous or pulsed ultrasonic modes around 40kHz, making it easy to obtain an equivalent power density of 500-1000W / L. In step (2), the twin-screw extruder used for melt extrusion is a co-rotating parallel twin-screw structure. The barrel is divided into 5-7 independent temperature control zones, with the temperature of each zone increasing sequentially from the feed end to the discharge end. Typical settings are 320 / 340 / 350 / 360 / 370-380℃. The length of the screw shear section accounts for 40%-60% of the total length, which is beneficial for achieving uniform plasticization and degassing of PTFE / PE melt under a pressure of 15-25MPa. In actual industrial scale-up, a twin-screw extrusion production line suitable for FEP / PTFE processing can be used, such as a twin-screw extruder for FEP / PTFE profiles (brand name such as "nanhaiya", produced in Zhejiang). Its screw diameter is about 60mm, the screw length-to-diameter ratio is about 30-33:1, the maximum screw speed can reach 600rpm, and it is equipped with a barrel electric heating and air cooling system, which can meet the requirements of continuous and stable extrusion of nascent fibers under the conditions of 320-380℃ and 50-120rpm in this invention. In step (3), longitudinal stretching can be performed using an online hot stretching device. After the fiber is preheated in hot air or an infrared heating zone at 280-320℃ for 30-90s, it is stretched through a multi-roller stretching system at a stretching ratio of 4-8 times and a stretching rate of 50-200mm / min. After stretching, it is immediately placed in a heat setting channel at 320-400℃ and held for 30-120s. It is then rapidly cooled by forced air cooling or oil cooling to stabilize the axial orientation structure of the fiber. In step (6), vacuum drying can be performed using a benchtop vacuum drying oven, such as the DZF-6050 vacuum drying oven (Shanghai Yiheng Scientific Instruments Co., Ltd.). Its temperature control range is usually room temperature +10℃ to 200-250℃, with a temperature fluctuation of about ±1℃. When equipped with a 2XZ-4 rotary vane vacuum pump, the ultimate vacuum degree can reach about ≤133Pa, which matches the drying conditions of ≤100Pa, 120-180℃, and 4-8h required by this invention.Gradient heat treatment can be performed in a tube furnace or box furnace equipped with programmed temperature control and an external alternating magnetic field module. 99.999% high-purity nitrogen gas is introduced into the furnace cavity at a flow rate of 50-200 mL / min. The temperature is increased to 200-250℃ at a rate of 2-5℃ / min and held for 1-2 hours. Then, the temperature is increased to 300-350℃ at a rate of 1-3℃ / min and held for 2-4 hours. The alternating magnetic field can be generated by an external electromagnet or solenoid coil with a magnetic field strength of 0.5-2T and a frequency of 50-200Hz. It is applied synchronously with the second stage of holding time to promote the directional distribution of nanoparticles near the fiber pore walls and the rearrangement of the interface structure. The expansion vessel in step (7) is a continuous or semi-continuous expansion device with a preheating section and a pressure holding section. It can be filled with CO2 or inert gas with a purity of 99.5% or higher. The preheating temperature is 180-220℃, the residence time in the expansion section is 0.5-5s, and the outlet is equipped with a throttling or limiting orifice to stabilize the expansion pressure at 0.1-0.5MPa. If necessary, an online laser diameter gauge can be used to monitor the fiber diameter to ensure that the fiber diameter after expansion is stable within the range of 10-50μm, porosity of 60-85%, and average pore size of 0.1-2μm. In step (8), the plasma surface treatment can be carried out using radio frequency plasma cleaning / treatment equipment with a working frequency of 13.56MHz, a vacuum chamber ultimate vacuum of 1-2Pa, and a process vacuum degree controlled at 10-50Pa. It supports the introduction of two or more mixed gases, such as argon and oxygen. The actual device can be the NE-PE13F type vacuum plasma surface treatment instrument (Shenzhen Nann Technology Co., Ltd.). This type of equipment is a small vacuum radio frequency plasma system, which is suitable for surface activation and cleaning of polymer fiber fabrics in scientific research institutions and enterprise R&D. It can be used at the 7:1 argon / oxygen volume ratio and 0.5-2.0W / cm set in this invention. 2 Stable operation under power density and 5-15 min processing conditions. The weaving process can be carried out using a multi-shuttle circular knitting machine or a flat loom, controlling the warp and weft tension at 0.05-0.2 cN / dtex to avoid secondary compaction of the high-porosity expanded fibers during the weaving process; the formed sealing material blank can be pre-dried with hot air at 80-120℃ for 10-30 min before plasma treatment to remove residual moisture and low molecular weight substances on the surface.

[0020] This invention introduces a multi-scale nano-reinforcement system composed of high-entropy alloy nanoparticles, carbon nanotubes, and graphene nanosheets, and coordinates it with a porous framework of highly oriented expanded polytetrafluoroethylene fibers. This creates a continuous and stable three-dimensional support and conductive network within the material, significantly suppressing pore wall buckling and microscopic plastic collapse, and improving strain energy storage and release efficiency. Consequently, it maintains low compressive settling and high resilience even under high compression ratios and multiple cyclic loading. Test results in Examples 1-8 show that the material of this invention exhibits low compressive settling and high resilience even at densities of 0.32-0.78 g / cm³. 3Within a given range, the material exhibits a tensile strength of ≥25 MPa and an elongation at break of ≥300%, with a compression set of only 2.9-4.2% and a springback rate as high as 95.2-97.8%, significantly superior to the 10.5-13.2% compression set and 81.2-84.5% springback rate of the comparative samples. This demonstrates the effectiveness of the multi-scale nano-reinforcement and fiber-oriented structural design. This invention achieves directional and uniform distribution of high-entropy alloy nanoparticles and carbon nanofillers within the fibers and near the pore walls by superimposing an alternating magnetic field during vacuum drying and gradient heat treatment. This avoids agglomeration and the formation of fragile phase boundary regions, further improving the structural stability and fatigue life of the material during cyclic compression. Test results show that within a wide temperature range of -50℃ to 200℃, the sealing performance of the material remains stable, and the compression-rebound behavior does not show significant attenuation, which is beneficial for maintaining the specific pressure and sealing reliability of flanges, valves, and other sealing components under long-term service conditions. This invention controls pore size distribution (0.1-2 μm), porosity (60-85%), warp and weft density, and weaving angle through the coupling of supercritical or conventional CO2 expansion with a specific weaving process. This results in a porous anisotropic skeleton that maintains sufficient compressive deformation space while possessing high structural strength and stress transfer efficiency, achieving a balance between low density and high mechanical properties. Compared to unexpanded or expanded samples with parameters deviating from the range, the density of the product from this invention is significantly reduced while tensile strength and resilience are significantly improved, indicating that the selected expansion and weaving window effectively optimizes the synergy between the macro- and micro-structures. This invention enhances the interfacial bonding between the nanofiller and the PTFE matrix through plasma surface activation and chemical grafting with multi-component silane coupling agents, followed by a wear-resistant coating and surface modification design with fluorinated segments. Simultaneously, it constructs a multifunctional interfacial layer on the fiber and pore wall surfaces, providing waterproof, oil-proof, stain-proof, and antistatic functions. The surface resistivity of the resulting material is controlled at 10⁻⁶. 6 -10 9 Within the Ω / sq range, it meets both anti-static safety requirements and avoids the defects of traditional high-conductivity filler systems, such as easy wear and shedding, and media contamination. It is suitable for sealing scenarios containing flammable, explosive, or electrostatically sensitive fluid media. Research on high-entropy alloys and their nanostructures in lightweight porous structures to enhance energy absorption and recovery capabilities also provides theoretical support and experimental evidence for achieving high resilience and low damage in this invention. In summary, while maintaining the chemical resistance, high temperature resistance, and low friction properties of expanded polytetrafluoroethylene (ePTFE), this invention achieves a comprehensive performance combination of "low density + high strength + high resilience + low compression set + anti-static" through synergistic design including multi-scale nano-reinforcement, gradient thermo-magnetic field treatment, controllable expansion weaving, and multifunctional surface modification. This overcomes the technical bottlenecks of traditional ePTFE sealing materials, such as large compression set, low resilience, and single function, and can provide a more long-term stable and reliable sealing solution in harsh working conditions such as petrochemical, power, hydrogen energy, and aerospace. Attached Figure Description

[0021] Figure 1 This is the energy spectrum distribution of different main metal elements in the high-entropy alloy nanoparticles prepared in Example 1.

[0022] Figure 2 This is the infrared spectrum of the high-entropy alloy nanoparticles prepared in Example 1.

[0023] Figure 3 This is the infrared spectrum of the final product prepared in Example 1.

[0024] Figure 4 This is a scanning electron microscope image of the final product prepared in Example 1. Detailed Implementation

[0025] The present invention will now be described in detail through specific embodiments. However, these illustrative embodiments are for purposes and uses only to illustrate the invention and do not constitute any limitation on the actual scope of protection of the invention, nor are they intended to restrict the scope of protection of the invention to these embodiments. For parameter ranges not mentioned, intermediate values ​​are selected. Also, for mass ratios not explicitly stated or mentioned, the mass ratio after addition generally refers to the mass ratio. Furthermore, in the present invention, the unit of mass is grams (g).

[0026] Example 1

[0027] Preparation of high-resilience expanded polytetrafluoroethylene sealing material: (1) First, take polytetrafluoroethylene resin (CAS No.: 9002-84-0, number average molecular weight is 7.5×10 6 100g of polyethylene (CAS No.: 9002-88-4, number average molecular weight is 2×10) 61.75g ​​was premixed, the ultrasonic frequency was 32.5kHz, the mixing temperature was controlled at 20℃, and a premix was obtained; (2) the obtained premix was melt-extruded, and melt-extruded at 350℃ through a twin-screw extruder, the screw length-to-diameter ratio was 30:1, the screw speed was 85rpm, the extrusion pressure was 20MPa, and a nascent fiber with a diameter of 3.5mm was made; (3) the obtained nascent fiber was longitudinally stretched, the stretching ratio was 6 times at 280-320℃, and the stretching rate was 125mm / min; then heat setting treatment was performed at 360℃ for 75s to obtain the matrix fiber; (4) the preparation method of high entropy alloy nanoparticles is as follows: take iron nitrate nonahydrate (CAS No.: 7782-61-8), nickel nitrate hexahydrate (CAS No.: 13478-00-7), cobalt nitrate hexahydrate (CAS No.: 10026-22-9), chromium nitrate nonahydrate (CA 20g each of S No.: 7789-02-8 and manganese nitrate tetrahydrate (CAS No.: 20694-39-7) were mixed in equal mass ratio and dissolved in deionized water to prepare 500g of a mixed metal salt solution with a total metal ion concentration of 1.5mol / L. Then, 175g of citric acid (CAS No.: 77-92-9), which was 0.35 times the mass of the mixed metal salt solution, was added. After mixing, polyvinylpyrrolidone (average molecular weight approximately 40,000) was added. The metal salt mixture solution (CAS No.: 9003-39-8) was 6.5% (32.5g) of total mass, followed by choline chloride (CAS No.: 67-48-1) (150g) at 30% of total mass. The mixture was stirred at 150 rpm at 70°C to form a precursor solution. Under nitrogen protection, the solution was heated to 700°C and calcined for 12 hours. The product was then vacuum dried at 70°C for 9 hours to obtain high-entropy alloy nanoparticles. The transmission electron microscopy (TEM) image is shown below. Figure 1 As shown, and its infrared spectrum is as follows. Figure 2As shown; 2.75g of high-entropy alloy nanoparticles, 0.55g of carbon nanotubes (outer diameter 8-15nm, length 10-30μm, CAS No.: 308068-56-6) and 0.275g of graphene nanosheets (3 layers, transverse dimension 0.5-5μm, CAS No.: 1034343-98-0) were added to 75g of polyethylene glycol (CAS No.: 25322-68-3) and ultrasonically dispersed for 120min under ultrasonic power density of 750W / L and frequency of 40kHz to form a suspension; (5) the obtained matrix fiber was immersed in the obtained suspension at an immersion temperature of 70℃ and an immersion time of 60min. During the immersion process, ultrasonic assistance at a frequency of 35kHz was applied and the ultrasonic duty cycle was 60% to obtain the immersed matrix fiber; (6) the obtained immersed matrix fiber was vacuum dried under vacuum conditions of ≤100Pa and 150℃. Dry for 6 hours; then perform gradient heat treatment under nitrogen protection, raise the temperature to 225℃ at a rate of 3.5℃ / min and hold for 1.5 hours, then raise the temperature to 325℃ at a rate of 2℃ / min and hold for 3 hours. At the same time, apply an alternating magnetic field with a frequency of 125Hz and a magnetic field strength of 1.25T during the second holding time, and cool to room temperature to obtain nano-reinforced precursor fibers; (7) The obtained nano-reinforced precursor fibers are expanded. At a preheating temperature of 200℃, they are passed through an expansion tank at a rate of 125mm / s. The expansion pressure is 0.3MPa, the expansion ratio is 3.5 times, the diameter of the expanded fiber is 30μm, the porosity is 72.5%, and the average pore size is 1.05μm to obtain expanded fibers; (8) The obtained expanded fibers are woven into a sealing material blank. The linear density ratio of the warp fibers to the weft fibers is 1:1.5, the weaving angle is 45°, and the weaving density is 100 fibers / cm. 2 The thickness is 3 mm; then plasma surface treatment is performed under a vacuum of 30 Pa, an atmosphere of argon and oxygen in a volume ratio of 7:1, and a power density of 1.25 W / cm³. 2 The sealed material blank was treated at a frequency of 13.56MHz for 10 minutes to obtain the treated sealed material blank; (9) The surface modification liquid was a mixture of 3-glycidyl etheroxypropyltrimethoxysilane (CAS No.: 2530-83-8), perfluorooctyltrimethoxysilane (CAS No.: 85857-16-5), aminopropyltriethoxysilane (CAS No.: 919-30-2) and isopropanol (CAS No.: 67-63-0) in a mass ratio of 2:1.25:0.665:100; the obtained sealed material blank was immersed in the surface modification liquid for 5 hours at a temperature of 50℃; then cured at 90℃ for 3 hours to obtain the final product, the infrared spectrum and scanning electron microscope image of which are shown in the figure. Figure 3 and Figure 4 As shown.

[0028] The resulting high-resilience expanded polytetrafluoroethylene sealing material has the following physical parameters: density 0.55 g / cm³. 3 Tensile strength 32.5 MPa, elongation at break 350%, compression set 3.5% (70℃×24h), resilience 96.5%, thermal decomposition temperature 470℃, surface resistivity 5×10⁻⁶ 7 Ω / sq, with stable sealing performance within a temperature range of -50℃ to 200℃.

[0029] The specific parameters for Examples 2-8 and Comparative Examples 1-8 are listed in the following tables. The tables are designed according to the progress of the steps, and each table reflects different parameter values ​​for the examples / comparative examples, covering all endpoint values ​​and intermediate values ​​(the remaining unlisted parameters are the same as in Example 1).

[0030] Table 1: Parameters of step (1)

[0031]

[0032] Table 2: Parameters of step (2)

[0033]

[0034] Table 3: Parameters of step (3)

[0035]

[0036] Table 4: Parameters of step (4) (Preparation of high-entropy alloy nanoparticles)

[0037]

[0038] Table 5: Parameters of step (4) (II) (Continued in the preparation of high-entropy alloy nanoparticles)

[0039]

[0040] Table 6: Parameters (III) of Step (4) (Suspension Components)

[0041]

[0042] Table 7: Parameters of step (5)

[0043]

[0044] Table 8: Parameters (I) of Step (6)

[0045]

[0046] Table 9: Parameters (II) of Step (6)

[0047]

[0048] Table 10: Parameters of step (7)

[0049]

[0050] Table 11: Parameters (I) of Step (8)

[0051]

[0052] Table 12: Parameters (II) of Step (8)

[0053]

[0054] Table 13: Parameters (I) of Step (9) (Mass ratio of surface modification liquid)

[0055]

[0056] Table 14: Parameters (II) of Step (9)

[0057]

[0058] To verify the performance of the high-resilience expanded polytetrafluoroethylene sealing material described in this invention, multi-dimensional tests were conducted on the products prepared in Examples 1-8 and Comparative Examples 1-8. The tests included density, tensile strength, elongation at break, compression set, resilience, thermal decomposition temperature, and surface resistivity. All test data were based on actual material properties (e.g., density 0.3-0.8 g / cm³). 3 Excellent (compression set ≤5% is considered excellent). Test methods are as follows: Density test: measured using an electronic densitometer (model: MH-300A) according to GB / T1033.1-2008 standard. Tensile strength and elongation at break test: tested using a universal testing machine (model: Instron 5567) according to GB / T 1040.3-2006 standard, with a tensile speed of 50 mm / min. Compression set test: tested at 70℃ for 24 hours according to GB / T 6669-2008 standard. Resilience test: tested using a rebound hammer according to GB / T 1681-2009 standard. Thermal decomposition temperature test: using a thermogravimetric analyzer (model: TGA Q500), with a heating rate of 10℃ / min, under a nitrogen atmosphere. Surface resistivity test: Measured using a surface resistivity meter (model: ZC-90) in accordance with GB / T 31838.3.1-2019 standard.

[0059] Table 15: Performance Test Results (Part 1)

[0060]

[0061] Table 16: Performance Test Results (Part Two)

[0062]

[0063] The test results show that the performance of the products in the examples is superior to that in the comparative examples, with densities ranging from 0.32 to 0.78 g / cm³. 3 The compression set is 2.9-4.2%, and the resilience is 95.2-97.8%, exhibiting excellent performance. The comparative sample, due to missing or incorrect measurements, shows a significant decrease in performance (e.g., density 0.82-1.20 g / cm³). 3 The compression set is 10.5-13.2%, and the springback is 81.2-84.5%. This demonstrates the superiority of the preparation method of the present invention.

[0064] The above description, in conjunction with specific embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, several simple deductions or substitutions can be made without departing from the concept of the present invention, and all such deductions or substitutions should be considered to fall within the scope of protection defined by the claims submitted herein.

Claims

1. A process for the production of a high-resilience expanded polytetrafluoroethylene sealing material, characterized by: The method comprises the following steps: (1) mixing 100 parts of polytetrafluoroethylene resin with 0.5-3 parts of polyethylene to obtain a premix; (2) melt-extruding the premix obtained in step (1) to obtain nascent fibers; (3) longitudinally stretching the nascent fibers obtained in step (2) and then performing heat setting treatment to obtain matrix fibers; (4) adding 0.5-5 parts of high-entropy alloy nanoparticles, 0.1-1 parts of carbon nanotubes and 0.05-0.5 parts of graphene nanosheets into 50-100 parts of polyethylene glycol, and performing ultrasonic dispersion treatment to form a suspension; (5) immersing the matrix fibers obtained in step (3) in the suspension obtained in step (4) to obtain immersed matrix fibers; (6) vacuum drying the immersed matrix fibers obtained in step (5), and then performing gradient heat treatment under nitrogen protection, and cooling to room temperature to obtain a nano-enhanced precursor fiber; (7) performing puffing treatment on the nano-enhanced precursor fiber obtained in step (6) to obtain puffed fibers; (8) weaving the puffed fibers obtained in step (7) into a sealing material blank, and then performing plasma surface treatment to obtain a treated sealing material blank; and (9) immersing the treated sealing material blank obtained in step (8) in a surface modification liquid for treatment, and then solidifying to obtain a final product.

2. The method for preparing the high-resilience expanded polytetrafluoroethylene sealing material according to claim 1, characterized in that: In step (1), the parameters for the premixing are as follows: the ultrasonic frequency is 25-40 kHz, and the mixing temperature is controlled at 15-25 ℃; in step (2), the parameters for the melt-extruding are as follows: melt-extruding through a double-screw extruder at 320-380 ℃, the screw length-diameter ratio is (28-32):1, the screw rotation speed is 50-120 rpm, the extrusion pressure is 15-25 MPa, and nascent fibers with a diameter of 2-5 mm are prepared.

3. The method for preparing the high-resilience expanded polytetrafluoroethylene sealing material according to claim 1, characterized in that: In step (3), the parameters for the longitudinal stretching are as follows: the stretching ratio is 4-8 times at 280-320 ℃, and the stretching rate is 50-200 mm / min; and the parameters for the heat setting treatment in step (3) are as follows: the temperature is 320-400 ℃, and the time is 30-120 s.

4. The method for preparing the high-resilience expanded polytetrafluoroethylene sealing material according to claim 1, characterized in that: In step (4), the high-entropy alloy nanoparticles are prepared by the following method: mixing iron nitrate nonahydrate, nickel nitrate hexahydrate, cobalt nitrate hexahydrate, chromium nitrate nonahydrate and manganese nitrate tetrahydrate in an equal mass ratio, dissolving them in deionized water to prepare a mixed metal salt solution with a total metal ion concentration of 1.5 mol / L, adding 0.2-0.5 times the mass of the mixed metal salt solution of citric acid, mixing, then adding polyvinylpyrrolidone which accounts for 3-10% of the total mass of the mixed metal salt solution, and then adding 20-40% of the total mass of the mixed metal salt solution of choline chloride, stirring at a rotation speed of 120-180 rpm at 60-80 ℃ to form a precursor solution, heating to 600-800 ℃ under nitrogen protection and calcining for 8-16 h, and vacuum drying the product at 60-80 ℃ for 6-12 h to obtain the high-entropy alloy nanoparticles; and the parameters for the ultrasonic dispersion treatment in step (4) are as follows: ultrasonic power density 500-1000 W / L, frequency 40 kHz, and dispersion treatment time 60-180 min.

5. The method for preparing the high-resilience expanded polytetrafluoroethylene sealing material according to claim 1, characterized in that: The parameters of the impregnation in step (5) are as follows: impregnation temperature 60-80℃, impregnation time 30-90min, and ultrasonic assistance with a frequency of 20-50kHz is applied during the impregnation process, and the duty cycle of the ultrasonic is 60%.

6. The method for preparing the high-resilience expanded polytetrafluoroethylene sealing material according to claim 1, characterized in that: The parameters of the vacuum drying in step (6) are as follows: vacuum degree ≤100Pa, temperature 120-180℃, and vacuum drying is performed for 4-8h; the parameters of the gradient heat treatment in step (6) are as follows: the temperature is raised to 200-250℃ at a rate of 2-5℃ / min, and the first holding time is 1-2h, then the temperature is raised to 300-350℃ at a rate of 1-3℃ / min, and the second holding time is 2-4h, and an alternating magnetic field with a frequency of 50-200Hz and a magnetic field strength of 0.5-2T is applied during the second holding time.

7. The method for preparing the high-resilience expanded polytetrafluoroethylene sealing material according to claim 1, characterized in that: The parameters of the puffing treatment in step (7) are as follows: the preheating temperature is 180-220℃, the speed through the puffing kettle is 50-200mm / s, the puffing pressure is 0.1-0.5MPa, the puffing ratio is 2-5, the fiber diameter after puffing is 10-50μm, the porosity is 60-85%, and the average pore size is 0.1-2μm.

8. The method for preparing the high-resilience expanded polytetrafluoroethylene sealing material according to claim 1, characterized in that: The parameters of weaving in step (8) are as follows: the linear density ratio of warp fibers to weft fibers is 1: (1.2-1.8), the weaving angle is 30-60°, and the weaving density is 50-150 roots / cm 2 ; the thickness is 1-5 mm; the parameters of plasma surface treatment in step (8) are as follows: the vacuum degree is 10-50 Pa, the mixed gas of argon and oxygen with a volume ratio of 7:1 is used as the atmosphere, the power density is 0.5-2.0 W / cm 2 , the frequency is 13.56 MHz, and the treatment time is 5-15 min.

9. The method for preparing the high-resilience expanded polytetrafluoroethylene sealing material according to claim 1, characterized in that: The surface modification liquid in step (9) is a mixed liquid of 3-glycidyloxypropyltrimethoxysilane, perfluorooctyltrimethoxysilane, aminopropyltriethoxysilane, and isopropyl alcohol with a mass ratio of (1-3):(0.5-2):(0.33-1):

100.

10. The method for preparing the high-resilience expanded polytetrafluoroethylene sealing material according to claim 1, characterized in that: The parameters of the immersion treatment in step (9) are as follows: time 4-6h, temperature 40-60℃; the parameters of the solidification in step (9) are as follows: solidification at 80-100℃ for 2-4h.

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