Expanded polytetrafluoroethylene composite film and its preparation method

Abstract

This invention relates to the field of polytetrafluoroethylene (ePTFE) membrane technology. Addressing the problem that existing expanded PTFE films cannot meet the high-performance standards of superhydrophobicity and superoleophobicity, this invention specifically discloses an expanded PTFE composite membrane and its preparation method. The expanded PTFE composite membrane includes an ePTFE base membrane and an fPTFE / SiO2 particle composite layer disposed on the surface of the ePTFE base membrane. The fPTFE / SiO2 particle composite layer includes a PTFE composite and SiO2 particles. The PTFE composite comprises polyethylene oxide and PTFE in a dry weight ratio of 1:10-30, and the SiO2 particles have a particle size of 100-1000 nm. By coating the ePTFE base membrane with PTFE and SiO2 particles to construct the fPTFE / SiO2 particle composite layer, and then modifying the membrane surface with silica-fluorination, the distribution of SiO2 particles can be specifically controlled to impart superhydrophobic and superoleophobic properties to the expanded PTFE composite membrane, with both water and oil contact angles >150°.

Description

Technical Field

[0001] This invention relates to the field of polytetrafluoroethylene (PTFE) membrane technology, and more specifically, to an expanded polytetrafluoroethylene (ePTFE) composite membrane and its preparation method. Background Technology

[0002] Expanded PTFE (ePTFE) is made from polytetrafluoroethylene resin through special processing methods such as stretching. It possesses a network structure formed by interconnected microfibers, which create numerous micropores, giving it excellent elasticity and flexibility. In addition to the excellent physicochemical properties inherent in PTFE, ePTFE's porous structure also provides excellent waterproof and breathable properties, making it widely used in hygiene control, energy conservation, and environmental protection. Due to its unique physicochemical structure, ePTFE films exhibit excellent water resistance and strong oleophilicity, and are widely used in chemical production as polymer membrane materials for oil-water phase separation. However, it is prone to wetting when in contact with oils, organic solvents, or surfactants. Furthermore, the introduction of other functional components into the ePTFE membrane often affects the pore formation and the uniformity of the microporous structure.

[0003] To address the problems faced by expanded polytetrafluoroethylene (ePTFE) films in practical applications, existing technologies have proposed improving the hydrophobic and oleophobic properties of ePTFE films through surface modification and other treatments.

[0004] For example, patent CN104691069A provides a protective clothing polytetrafluoroethylene composite film, including a polytetrafluoroethylene film layer and a PU coating. The PU coating includes a bottom layer and a top layer, which are respectively coated on the top and bottom surfaces of the polytetrafluoroethylene film layer. The polytetrafluoroethylene film layer is made of the following raw materials in parts by weight: 85-95 parts polytetrafluoroethylene resin, 5-8 parts silicone powder, 2-4 parts polyetheretherketone, and 3.5-6.5 parts lubricant. The PU coating is made of the following raw materials in parts by weight: 100 parts PU resin, 10-15 parts polyethylene wax, 5-10 parts nano titanium dioxide, and 10-18 parts N,N-dimethylformamide. For example, patent CN113527760A provides a method for manufacturing an expanded polytetrafluoroethylene (ePTFE)-silica aerogel composite thermal insulation film material. The method includes: mixing a silicon source and solvent at room temperature; slowly adding a catalyst and continuing stirring to obtain an aerogel precursor (sol); mixing the aerogel precursor (sol), solvent, and surfactant; stirring in an ice bath to obtain a coating liquid; ultrasonically treating the ePTFE film, followed by drying; and then treating it using a plasma gas treatment method to obtain an ePTFE film; uniformly coating the treated ePTFE film with the coating liquid to obtain an ePTFE film coated with the aerogel precursor (sol); and drying to obtain the expanded polytetrafluoroethylene (ePTFE)-silica aerogel composite thermal insulation film material.

[0005] However, according to the standards in this field, such as "Physical Chemistry" and GB / T 30693-2014 "Determination of the Contact Angle between Plastic Films and Water", the hydrophobic and oleophobic ePTFE film mentioned above, although its hydrophobic and oleophobic properties have been significantly improved through modification treatment, still cannot meet the high performance standard and application requirements of superhydrophobic and superoleophobic properties with a water-oil contact angle of ≥150°, which limits the application of expanded polytetrafluoroethylene film in more fields and scenarios. Summary of the Invention

[0006] The purpose of this invention is to solve the problem that existing expanded polytetrafluoroethylene films cannot meet the high-performance standards of superhydrophobic and superoleophobic.

[0007] This invention is achieved through the following technical solution:

[0008] This invention provides an expanded polytetrafluoroethylene (ePTFE) composite membrane, comprising an ePTFE base membrane and an fPTFE / SiO2 particle composite layer disposed on the surface of the ePTFE base membrane; the fPTFE / SiO2 particle composite layer comprises a polytetrafluoroethylene composite and SiO2 particles, the polytetrafluoroethylene composite comprising polyethylene oxide and polytetrafluoroethylene in a dry weight ratio of 1:10-30, and the SiO2 particles having a particle size of 100-1000 nm.

[0009] Preferably, the thickness of the expanded polytetrafluoroethylene composite film is 10-100 μm.

[0010] Preferably, the expanded polytetrafluoroethylene composite membrane has a water contact angle >150° and an oil contact angle >150°.

[0011] This invention provides a method for preparing the above-mentioned expanded polytetrafluoroethylene composite film, comprising the following steps:

[0012] S1 Prepare polytetrafluoroethylene composite mixture and SiO2 particle suspension respectively. Take ePTFE base film and use a dual syringe to coat the surface of ePTFE base film with polytetrafluoroethylene composite mixture and SiO2 particles through surface modification treatment. Dry to obtain the initial ePTFE composite film.

[0013] S2 The pre-prepared ePTFE composite membrane is placed at 300-400℃ and sintered for 5-15 minutes, followed by surface fluorination treatment to obtain the expanded polytetrafluoroethylene composite membrane.

[0014] Preferably, in step S1, the surface modification treatment is performed by synchronous or asynchronous electrospinning.

[0015] Furthermore, if synchronous electrospinning is used, the two syringes start spinning simultaneously. After the syringe for polytetrafluoroethylene spinning solution stops spinning for 0-2 hours, the syringe for SiO2 particle spinning solution stops spinning.

[0016] Furthermore, if asynchronous electrospinning is used, the syringe for polytetrafluoroethylene spinning solution starts spinning first, and after spinning for 0.5-2 hours, the syringe for SiO2 particle spinning solution starts spinning again. After the syringe for polytetrafluoroethylene spinning solution stops spinning for 0-2 hours, the syringe for SiO2 particle spinning solution stops spinning again.

[0017] Preferably, in step S2, the surface fluorination treatment includes the following steps:

[0018] The sintered membrane material is placed in a fluorination modification solution and impregnated for 5-8 hours. After the reaction is completed, it is taken out and placed in an oven to dry at 50-80℃ for 1.5-3 hours to obtain the expanded polytetrafluoroethylene composite membrane.

[0019] Preferably, the fluorinated modification solution comprises silica, ammonia, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and a solvent.

[0020] The technical solution of the present invention has the following beneficial effects:

[0021] The expanded polytetrafluoroethylene composite membrane of the present invention directly constructs an fPTFE / SiO2 particle composite layer on an ePTFE base membrane using a dual-injector electrospinning technique, followed by silica-fluorination modification of the membrane surface, achieving the following beneficial effects:

[0022] During the spinning process of the dual syringe, polytetrafluoroethylene (PTFE) spinning fibers and SiO2 particles intertwine to construct a lotus leaf-like uneven structure on the surface of the ePTFE membrane. When water droplets fall on the membrane surface, the tiny protrusions and the air in the gaps lift the droplets, preventing the composite membrane from being wetted. Furthermore, the fluorination modification of the SiO2 particles enables the membrane surface to obtain extremely low surface energy.

[0023] During the preparation process, the spinning sequence and duration of each needle can be controlled by using a dual-injector spinning method, achieving a gradient distribution of SiO2 particles in the fPTFE layer. In the initial stage, the syringe spraying the polytetrafluoroethylene spinning solution begins spinning, which increases the interfacial strength between the fPTFE layer and the ePTFE base film, reducing particle clogging of micropores. In the later stage of spinning, the syringe spraying the SiO2 particle spinning solution ends last, increasing the distribution density of SiO2 particles on the fPTFE layer surface, thereby improving the droplet contact angle. By controlling the specific spinning process, the composite membrane can be endowed with superhydrophobic and superoleophobic properties, i.e., a water contact angle greater than 150° and an oil contact angle greater than 150°. The operation is simple and easy to scale up for continuous production. Furthermore, since the gradient distribution of SiO2 does not significantly clog micropores, and the membrane permeability can be controlled by adjusting the pore structure of ePTFE and fPTFE, the composite membrane exhibits excellent overall performance. Attached Figure Description

[0024] Figure 1 This is a scanning electron microscope image of the expanded polytetrafluoroethylene composite film of the present invention, magnified 6000 times.

[0025] Figure 2 This is a scanning electron microscope image of the expanded polytetrafluoroethylene composite film of the present invention, magnified 24,000 times.

[0026] Figure 3 This is a diagram showing the water contact angle of the expanded polytetrafluoroethylene composite membrane in this invention.

[0027] Figure 4 This is a diagram showing the oil contact angle of the expanded polytetrafluoroethylene composite film in this invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, they are performed according to conventional conditions or conditions recommended by the manufacturer; where the manufacturers of the instruments, equipment, reagents, or raw materials used are not specified, they are all conventional products that can be purchased commercially.

[0029] This invention provides an expanded polytetrafluoroethylene composite film, the preparation method of which includes the following steps:

[0030] (1) Prepare polytetrafluoroethylene spinning solution and SiO2 particle spinning solution respectively:

[0031] Take polyethylene oxide (PEO), polytetrafluoroethylene (PTFE) emulsion with a solid content of 50-75%, and deionized water respectively, and control the dry weight ratio of polyethylene oxide to PTFE to be 1:10-30. Stir for 6-12 hours and mix until there are no solid particles in the system. If the viscosity is high and a large number of bubbles appear, put it in a vacuum mixer to eliminate the bubbles and obtain the PTFE spinning solution.

[0032] Take silica with a particle size of 100-1000nm, disperse it in deionized water, and prepare a silica spinning solution with a mass concentration of 5-20%.

[0033] (2) Pretreatment of ePTFE base film:

[0034] Take a uniaxially or biaxially stretched ePTFE base film and rinse it with distilled water 3-4 times to remove impurities from the surface of the ePTFE base film. After rinsing, place the ePTFE base film in an oven at 80-100℃ for 2-5 hours to dry it and remove moisture.

[0035] (3) Electrospinning of the ePTFE base film surface:

[0036] Using a dual-injector system, polytetrafluoroethylene (PTFE) spinning solution and SiO2 particle spinning solution are electrospun onto the surface of the pretreated ePTFE base film to form an fPTFE layer and a SiO2 layer. The thickness of the fPTFE layer and the distribution of SiO2 particles in the fPTFE layer are controlled by adjusting parameters such as the spinning time of each injector. After spinning, the film is placed in an oven and dried at 40-60℃ for 6-12 hours to remove moisture, thus obtaining the initial ePTFE composite film.

[0037] The specific processing conditions for electrospinning are as follows: the electrospinning voltage is 10-30kV; the receiving voltage is 1-3kV, the receiving speed is 80-140r / min, and the receiving distance is 10-40cm; the injection speed of electrospinning is 0.1-0.2mm / min, the translation speed is 400-500mm / min, and the moving distance is 200mm; the spinning time for each syringe is 4-6h.

[0038] Regarding the use of dual syringes for spinning, the specific order of processing the two syringes during spinning can be carried out in the following ways:

[0039] One method is to use synchronous spinning: two syringes start spinning simultaneously. After the syringe for polytetrafluoroethylene spinning solution stops spinning for 0-2 hours, the syringe for SiO2 particle spinning solution stops spinning. Those skilled in the art can select to set the injection speed of the two syringes to the same or different values ​​according to further specific needs.

[0040] Secondly, asynchronous spinning is adopted: the syringe of polytetrafluoroethylene spinning solution starts spinning first, and after spinning for 0.5-2 hours, the syringe of SiO2 particle spinning solution starts spinning again; similarly, after the syringe of polytetrafluoroethylene spinning solution stops spinning for 0-2 hours, the syringe of SiO2 particle spinning solution stops spinning again. Those skilled in the art can select to set the injection speed of the two syringes to the same or different values ​​according to further specific needs.

[0041] (4) Sintering and modification treatment of the initial ePTFE composite membrane:

[0042] The pre-prepared ePTFE composite membrane obtained by electrospinning is placed in a muffle furnace, fixed on all sides, and sintered at 300-400℃ for 5-15 minutes to remove polyethylene oxide. The sintered membrane has high mechanical strength, peel strength, high porosity, and high hydrostatic pressure resistance.

[0043] The sintered membrane material is then placed in a fluorinated modification solution and impregnated for 5-8 hours. After the reaction is complete, it is removed and placed in an oven to dry at 50-80℃ for 1.5-3 hours to obtain expanded polytetrafluoroethylene composite membrane.

[0044] The fluorination modification solution includes solvents such as silica, ammonia, 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTES), and ethanol, which are mixed by stirring.

[0045] The expanded polytetrafluoroethylene composite membrane proposed in this invention is prepared by the above method. Its membrane thickness can be adjusted by material selection, spinning amount, etc., and the thickness is 10-100μm. It has been measured that the water contact angle of the expanded polytetrafluoroethylene composite membrane is greater than 150°, the water roll-off angle is less than 10°, the oil contact angle is greater than 150°, the oil roll-off angle is less than 10°, the peel strength is 2-4N / mm, and the hydrostatic pressure resistance is 110-120MPa.

[0046] Example 1

[0047] Step 1: Take the biaxially stretched ePTFE base film, rinse it 3 times with distilled water, and then place it in an 80℃ oven to dry for 4 hours to obtain a clean ePTFE base film for later use.

[0048] Step 2: Mix PEO and PTFE emulsion with a solid content of 60% at a dry weight ratio of 1:22 and stir for 8 hours to obtain a homogeneous polytetrafluoroethylene spinning solution for later use. Disperse particles with a diameter of approximately 500 nm in deionized water to prepare a silica spinning solution with a silica mass concentration of 10 wt% for later use. Disperse silica in ethanol, then add ammonia and 1H,1H,2H,2H-perfluorodecyltriethoxysilane sequentially, and stir until homogeneous to obtain a fluorinated modified solution.

[0049] Step 3: Inject the PTFE spinning solution into a 5mL syringe, using a 16G stainless steel needle; separately inject the silica dispersion into another 5mL syringe, using a 21G stainless steel needle. Using a dual-syringe electrospinning device, employ synchronous spinning to spin the PTFE spinning solution and SiO2 particle spinning solution onto the cleaned ePTFE substrate surface, i.e., both spinning solutions begin spinning simultaneously. The spinning time for the PTFE spinning solution is 4 hours, and the spinning time for the SiO2 particle spinning solution is 6 hours. The electrospinning settings are as follows: electrospinning voltage 15kV, receiving voltage 2kV, receiving speed 140r / min, receiving distance 15cm, electrospinning injection speed 0.12mm / min, translation speed 400mm / min, and moving distance 200mm.

[0050] Step 4: Fix the spun composite film onto an iron plate, place it in a muffle furnace, sinter at 350℃ for 10 min, and then raise the temperature to 380℃ for 5 min; after taking it out, place the sintered composite film in a fluorination modification solution and react for 6 h, then take it out and dry it in a 60℃ oven for 2 h to obtain an expanded polytetrafluoroethylene composite film with superhydrophobic and superoleophobic properties.

[0051] The thickness of the expanded polytetrafluoroethylene composite film was measured to be 65.4 μm, and as... Figure 1As shown, scanning electron microscopy revealed that the fibers on the membrane surface were interwoven into a network, with the average diameter of a single fiber being approximately 1.1 μm. Performance tests showed that the expanded polytetrafluoroethylene composite membrane had a water contact angle of 156°, a water roll-off angle of 4°, an oil contact angle of 152°, an oil roll-off angle of 5°, a peel strength of 2.56 N / mm, and a hydrostatic pressure resistance of 118 kPa.

[0052] Example 2

[0053] The difference between this embodiment and Embodiment 1 is that: in the electrospinning process, synchronous spinning is used, the spinning time of the polytetrafluoroethylene spinning solution is 4 hours, and the spinning time of the SiO2 particle spinning solution is 5 hours.

[0054] The expanded polytetrafluoroethylene composite film prepared in this embodiment has a thickness of 64.3 μm, a water contact angle of 152°, a water roll-off angle of 4°, an oil contact angle of 150°, an oil roll-off angle of 5°, a peel strength of 2.54 N / mm, and a hydrostatic pressure resistance of 116 kPa.

[0055] Example 3

[0056] The difference between this embodiment and Embodiment 1 is that asynchronous spinning is used in the electrospinning process. The polytetrafluoroethylene spinning solution starts spinning first, and after 2 hours of spinning, the SiO2 particle spinning solution starts spinning. The polytetrafluoroethylene spinning solution stops spinning after 4 hours, and the SiO2 particle spinning solution stops spinning 2 hours after that.

[0057] The expanded polytetrafluoroethylene composite film prepared in this embodiment has a thickness of 73.8 μm, a water contact angle of 153°, a water roll-off angle of 4°, an oil contact angle of 150°, an oil roll-off angle of 6°, a peel strength of 2.70 N / mm, and a hydrostatic pressure resistance of 120 kPa.

[0058] Example 4

[0059] The difference between this embodiment and Embodiment 1 is that the dry weight ratio of PEO and PTFE emulsions in the polytetrafluoroethylene spinning solution is 1:10.

[0060] The expanded polytetrafluoroethylene composite film prepared in this embodiment has a thickness of 63.1 μm, a water contact angle of 152°, a water roll-off angle of 4°, an oil contact angle of 150°, an oil roll-off angle of 6°, a peel strength of 2.54 N / mm, and a hydrostatic pressure resistance of 112 kPa.

[0061] Example 5

[0062] The difference between this embodiment and Embodiment 1 is that the dry weight ratio of PEO and PTFE emulsions in the polytetrafluoroethylene spinning solution is 1:28.

[0063] The expanded polytetrafluoroethylene composite film prepared in this embodiment has a thickness of 67.9 μm, a water contact angle of 153°, a water roll-off angle of 4°, an oil contact angle of 152°, an oil roll-off angle of 5°, a peel strength of 2.51 N / mm, and a hydrostatic pressure resistance of 114 kPa.

[0064] Example 6

[0065] The difference between this embodiment and Embodiment 1 is that the sintering process is carried out at 350°C for 5 minutes.

[0066] The expanded polytetrafluoroethylene composite film prepared in this embodiment has a thickness of 65.7 μm, a water contact angle of 152°, a roll-off angle of 4°, an oil contact angle of 150°, an oil roll-off angle of 6°, a peel strength of 2.59 N / mm, and a hydrostatic pressure resistance of 116 kPa.

[0067] Example 7

[0068] The difference between this embodiment and Embodiment 1 is that the sintering process is carried out at 350°C for 15 minutes.

[0069] The expanded polytetrafluoroethylene composite film prepared in this embodiment has a thickness of 65.0 μm, a water contact angle of 151°, a water roll-off angle of 4°, an oil contact angle of 150°, an oil roll-off angle of 6°, a peel strength of 2.53 N / mm, and a hydrostatic pressure resistance of 112 kPa.

[0070] Example 8

[0071] The difference between this embodiment and Embodiment 1 is that the silica mass concentration in the silica spinning solution is 5 wt%.

[0072] The expanded polytetrafluoroethylene composite film prepared in this embodiment has a thickness of 63.2 μm, a water contact angle of 153°, a water roll-off angle of 4°, an oil contact angle of 150°, an oil roll-off angle of 6°, a peel strength of 2.55 N / mm, and a hydrostatic pressure resistance of 110 kPa.

[0073] Example 9

[0074] The difference between this embodiment and Embodiment 1 is that the silica mass concentration in the silica spinning solution is 20 wt%.

[0075] The expanded polytetrafluoroethylene composite film prepared in this embodiment has a thickness of 68.1 μm, a water contact angle of 154°, a water roll-off angle of 4°, an oil contact angle of 152°, an oil roll-off angle of 5°, a peel strength of 2.58 N / mm, and a hydrostatic pressure resistance of 114 kPa.

[0076] Example 10

[0077] The difference between this embodiment and Embodiment 1 is that the silica particle size in the silica spinning solution is approximately 1000 nm.

[0078] The expanded polytetrafluoroethylene composite film prepared in this embodiment has a thickness of 70.2 μm, a water contact angle of 153°, a water roll-off angle of 4°, an oil contact angle of 151°, an oil roll-off angle of 5°, a peel strength of 2.62 N / mm, and a hydrostatic pressure resistance of 117 kPa.

[0079] Example 11

[0080] The difference between this embodiment and Embodiment 1 is that the silica particle size in the silica spinning solution is approximately 100 nm.

[0081] The expanded polytetrafluoroethylene composite film prepared in this embodiment has a thickness of 64.1 μm, a water contact angle of 151°, a water roll-off angle of 4°, an oil contact angle of 150°, an oil roll-off angle of 6°, a peel strength of 2.56 N / mm, and a hydrostatic pressure resistance of 114 kPa.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that synchronous spinning was used, and the spinning time of both the polytetrafluoroethylene spinning solution and the SiO2 particle spinning solution was 4 hours, that is, the spinning was stopped synchronously.

[0084] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 63.2 μm, the water contact angle was 148°, the water roll-off angle was 5°, the oil contact angle was 145°, the oil roll-off angle was 7°, the peel strength was 2.51 N / mm, and the hydrostatic pressure resistance was 115 kPa.

[0085] Comparative Example 2

[0086] The difference between this comparative example and Example 1 is that a single syringe was used to mix the polytetrafluoroethylene spinning solution and the SiO2 particle spinning solution before spinning, and the silica mass concentration in the SiO2 particle spinning solution was 10wt%, and the spinning time was 4h.

[0087] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 62.5 μm, the water contact angle was 147°, the water roll-off angle was 5°, the oil contact angle was 140°, the oil roll-off angle was 12°, the peel strength was 2.48 N / mm, and the hydrostatic pressure resistance was 111 kPa.

[0088] Comparative Example 3

[0089] The difference between this comparative example and Example 1 is that the spinning time of the polytetrafluoroethylene spinning solution is 10 hours, and the spinning time of the SiO2 particle spinning solution is 11 hours.

[0090] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 104 μm, the water contact angle was 148°, the water roll-off angle was 5°, the oil contact angle was 140°, the oil roll-off angle was 12°, the peel strength was 2.51 N / mm, and the hydrostatic pressure resistance was 120 kPa.

[0091] Comparative Example 4

[0092] The difference between this comparative example and Example 1 is that the spinning time of the polytetrafluoroethylene spinning solution is 1 hour, and the spinning time of the SiO2 particle spinning solution is 2 hours.

[0093] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 23.2 μm, the water contact angle was 132°, the water roll-off angle was 10°, the oil contact angle was 122°, the oil droplet roll-off angle was not possible, the peel strength was 2.43 N / mm, and the hydrostatic pressure resistance was 89 kPa.

[0094] Comparative Example 5

[0095] The difference between this comparative example and Example 1 is that the polytetrafluoroethylene spinning solution was spun first, and the spinning was stopped after 2 hours. Then the SiO2 particle spinning solution was spun again, and the spinning was stopped after 2 hours.

[0096] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 20.2 μm, the water contact angle was 121°, the water roll-off angle was 10°, the oil contact angle was 107°, the oil droplet roll-off angle was not rolling, the peel strength was 2.41 N / mm, and the hydrostatic pressure resistance was 84 kPa.

[0097] Comparative Example 6

[0098] The difference between this comparative example and Example 1 is that asynchronous spinning is used. The polytetrafluoroethylene spinning solution starts spinning first, and after spinning for 2 hours, the SiO2 particle spinning solution starts spinning. The spinning time for both spinning solutions is 10 hours. That is, the polytetrafluoroethylene spinning solution stops spinning for 2 hours first, and then the SiO2 particle spinning solution stops spinning.

[0099] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 100.5 μm, the water contact angle was 148°, the water roll-off angle was 5°, the oil contact angle was 140°, the oil roll-off angle was 12°, the peel strength was 2.41 N / mm, and the hydrostatic pressure resistance was 117 kPa.

[0100] Comparative Example 7

[0101] The difference between this comparative example and Example 1 is that the dry weight ratio of PEO and PTFE emulsions in the polytetrafluoroethylene spinning solution is 1:4.

[0102] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 50.4 μm, the water contact angle was 135°, the water roll-off angle was 8°, the oil contact angle was 122°, the oil droplet roll-off angle was not possible, the peel strength was 2.21 N / mm, and the hydrostatic pressure resistance was 87 kPa.

[0103] Comparative Example 8

[0104] The difference between this comparative example and Example 1 is that the dry weight ratio of PEO and PTFE emulsions in the polytetrafluoroethylene spinning solution is 1:32.

[0105] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 69.6 μm, the water contact angle was 146°, the water roll-off angle was 9°, the oil contact angle was 135°, the oil roll-off angle was 15°, the peel strength was 2.51 N / mm, and the hydrostatic pressure resistance was 113 kPa.

[0106] Comparative Example 9

[0107] The difference between this comparative example and Example 1 is that the sintering process was carried out at 350°C for 3 minutes.

[0108] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 64.9 μm, the water contact angle was 145°, the water roll-off angle was 6°, the oil contact angle was 137°, the oil roll-off angle was 14°, the peel strength was 2.36 N / mm, and the hydrostatic pressure resistance was 103 kPa.

[0109] Comparative Example 10

[0110] The difference between this comparative example and Example 1 is that the sintering process was carried out at 350°C for 20 minutes.

[0111] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 65.1 μm, the water contact angle was 140°, the water roll-off angle was 7°, the oil contact angle was 132°, the oil roll-off angle was 15°, the peel strength was 2.33 N / mm, and the hydrostatic pressure resistance was 105 kPa.

[0112] Comparative Example 11

[0113] The difference between this comparative example and Example 1 is that the silica mass concentration in the silica spinning solution is 0.1 wt%.

[0114] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 52.5 μm, the water contact angle was 127°, the water roll-off angle was 10°, the oil contact angle was 108°, the oil droplet roll-off angle was not rolling, the peel strength was 2.23 N / mm, and the hydrostatic pressure resistance was 99 kPa.

[0115] Comparative Example 12

[0116] The difference between this comparative example and Example 1 is that the silica mass concentration in the silica spinning solution is 30 wt%.

[0117] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 55.8 μm, the water contact angle was 137°, the water roll-off angle was 8°, the oil contact angle was 118°, the oil droplet roll-off angle was not rolling, the peel strength was 2.43 N / mm, and the hydrostatic pressure resistance was 102 kPa.

[0118] Comparative Example 13

[0119] The difference between this comparative example and Example 1 is that the silica particles in the silica spinning solution have a diameter of approximately 10 nm.

[0120] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 60.8 μm, the water contact angle was 148°, the water roll-off angle was 5°, the oil contact angle was 138°, the oil roll-off angle was 14°, the peel strength was 2.47 N / mm, and the hydrostatic pressure resistance was 108 kPa.

[0121] Comparative Example 14

[0122] The difference between this comparative example and Example 1 is that the silica particles in the silica spinning solution have a diameter of approximately 2000 nm.

[0123] The thickness of the expanded polytetrafluoroethylene composite film prepared in this comparative example was measured to be 70.3 μm, the water contact angle was 145°, the water roll-off angle was 6°, the oil contact angle was 140°, the oil roll-off angle was 12°, the peel strength was 2.55 N / mm, and the hydrostatic pressure resistance was 110 kPa.

[0124] Test case (one)

[0126] Samples: Examples 1-2, Comparative Examples 1-4

[0127] The hydrophobic and oleophobic properties of the above samples were measured, and the results are summarized in Table 1 below:

[0128] Table 1 Performance test results of samples with different spinning times

[0129]

[0130] As shown in Table 1, changes in spinning time affect the thickness and macroscopic properties of the superhydrophobic and superoleophobic expanded polytetrafluoroethylene (ePTFE) composite membrane. When the spinning time is controlled within 4-6 hours, the performance of the composite membrane meets the range described in the claims. Furthermore, when using synchronous electrospinning, spinning the silica solution for an additional 1-2 hours allows the silica particles to fully entangle with the ePTFE fibers, resulting in a uniform and dense distribution on the composite membrane surface, thus achieving optimal superhydrophobic and superoleophobic properties. If the spinning time is too long, the thickness of the composite membrane will exceed 100 μm. At this point, excessive silica particle aggregation and uneven distribution prevent the membrane from achieving its optimal hydrophobic and oleophobic properties. Conversely, if the spinning time is too short, the thickness of the composite membrane is around 20 μm. This results in an incomplete and unstable fiber network, making the composite membrane prone to breakage from the ePTFE layer during interfacial peeling, leading to low peel strength and poor hydrostatic pressure resistance. (two)

[0132] Samples: Example 3, Comparative Examples 5-6

[0133] The hydrophobic and oleophobic properties of the above samples were measured, and the results are summarized in Table 2 below:

[0134] Table 2 Performance test results of samples with different spinning methods

[0135]

[0136] As can be seen from Table 2 above, the syringe that sprays PTFE spinning solution first starts spinning in the initial stage, which can improve the interfacial strength between the fPTFE layer and the ePTFE base film and reduce the clogging of micropores by particles. Therefore, the peel strength and hydrostatic pressure resistance are optimal at this time. In the later stage of spinning, the needle that sprays SiO2 particle spinning solution ends last, which can increase the distribution density of SiO2 particles on the surface of the fPTFE layer and improve the contact angle of the droplets. (three)

[0138] Samples: Examples 4-5, Comparative Examples 7-8

[0139] The hydrophobic and oleophobic properties of the above samples were measured, and the results are summarized in Table 3 below:

[0140] Table 3 Performance test results of samples with different spinning methods

[0141]

[0142] As shown in Table 3 above, changes in the emulsion formulation will affect the fiber structure of the composite membrane, which will significantly affect the macroscopic properties of the composite membrane. When the ratio of PEO to PTFE is controlled between 1:10 and 30, the performance of the composite membrane meets the range described in the claims. When the ratio of PEO to PTFE is less than 1:10, the PTFE content is too low, the viscosity of the spinning solution is too high, which will make the spinning process unstable, the fiber structure incomplete, and the fiber diameter difference large. The high viscosity of the spinning solution also makes it difficult for the fPTFE layer fibers to pass through the micropores of the ePTFE membrane and form entanglement with the fibers, resulting in a significant reduction in peel strength. In addition, when the ratio of PEO to PTFE exceeds 1:30, the PEO content is too low and cannot completely encapsulate the PTFE particles, resulting in an incomplete fiber structure, large fiber diameter difference, uneven stress transmission, and poor adhesion between the fiber membrane and the ePTFE layer interface, thus reducing the peel strength of the composite membrane. (Four)

[0144] Samples: Examples 6-7, Comparative Examples 9-10

[0145] The hydrophobic and oleophobic properties of the above samples were measured, and the results are summarized in Table 4 below:

[0146] Table 4 Performance test results of samples with different sintering times

[0147]

[0148] As shown in Table 4 above, changes in sintering time affect the tensile strength, interfacial peel strength, and hydrostatic pressure resistance of the composite membrane. When the sintering time is controlled between 5 and 15 minutes at 350°C, the performance of the composite membrane meets the ranges described in the claims. When the sintering time is less than 5 minutes, the bonding between resin particles and between the ePTFE and fPTFE membranes is insufficient, resulting in low interfacial peel strength of the composite membrane. In addition, insufficient sintering time also leads to instability in the fiber membrane structure, causing the mechanical strength of the composite membrane to be lower than the range described in the claims. When the sintering time exceeds 15 minutes, the excessive heat treatment time will cause partial resin degradation, which also leads to a decrease in the peel strength and hydrostatic pressure resistance of the composite membrane. (five)

[0150] Samples: Examples 8-9, Comparative Examples 11-12

[0151] The hydrophobic and oleophobic properties of the above samples were measured, and the results are summarized in Table 5 below:

[0152] Table 5 Performance test results of samples with different silicon concentrations

[0153]

[0154] As shown in Table 5, the addition of 5-20 wt% SiO2 significantly improved the water contact angle and oil contact angle of the composite membrane. This is because the increased surface roughness and the introduction of SiO2 nanoparticles create a micro-nano-scale rough structure on the fiber surface. The optimal SiO2 concentration is 10%, achieving a maximum water contact angle of 156° and an oil contact angle of 152°, where the balance between roughness and low surface energy is optimal. Excessive SiO2 may lead to particle aggregation, which in turn reduces uniformity. (six)

[0156] Samples: Examples 10-11, Comparative Examples 13-14

[0157] The hydrophobic and oleophobic properties of the above samples were measured, and the results are summarized in Table 6 below:

[0158] Table 6 Performance test results of samples with different silicon particle sizes

[0159]

[0160] As can be seen from Table 6, the particle size of silica also has a certain impact on the hydrophobic and oleophobic properties of the composite membrane. When the particle size is 10 nm, the surface roughness of the membrane is insufficient, which leads to a decrease in both oil and water contact angles. When the particle size is 2000 nm, the particle size of silica is larger than that of a single PTFE fiber, which affects the fiber filamentation and distribution, and similarly, both hydrophobic and oleophobic properties decrease.

[0161] The above experiments show that the present invention directly constructs an fPTFE / SiO2 particle composite layer on an ePTFE base film using a dual-injector electrospinning technique, then modifies the film surface with silica-fluorination, and modifies the specific process in electrospinning. The resulting expanded polytetrafluoroethylene composite film exhibits significant improvements in hydrophobic and oleophobic properties, and both achieve superhydrophobic and superoleophobic performance with water contact angles greater than 150° and oil contact angles greater than 150°.

[0162] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing an expanded polytetrafluoroethylene composite film, characterized in that, Includes the following steps: S1 Prepare polytetrafluoroethylene composite mixture and SiO2 particle suspension respectively. Take ePTFE base film and use a dual syringe to coat the surface of ePTFE base film with polytetrafluoroethylene composite mixture and SiO2 particles through surface modification treatment. Dry to obtain the initial ePTFE composite film. S2 The pre-made ePTFE composite membrane is placed at 300-400℃ and sintered for 5-15 minutes, and then subjected to surface fluorination treatment to obtain the expanded polytetrafluoroethylene composite membrane. In step S1, the surface modification treatment is performed by synchronous or asynchronous electrospinning; If synchronous electrospinning is used, the two syringes start spinning simultaneously. After the syringe for polytetrafluoroethylene spinning solution stops spinning for 0-2 hours, the syringe for SiO2 particle spinning solution stops spinning. If asynchronous electrospinning is used, the syringe for polytetrafluoroethylene spinning solution starts spinning first. After spinning for 0.5-2 hours, the syringe for SiO2 particle spinning solution starts spinning again. After the syringe for polytetrafluoroethylene spinning solution stops spinning for 0-2 hours, the syringe for SiO2 particle spinning solution stops spinning again.

2. The method for preparing the expanded polytetrafluoroethylene composite film according to claim 1, characterized in that, In step S2, the surface fluorination treatment includes the following steps: The sintered membrane material is placed in a fluorination modification solution and impregnated for 5-8 hours. After the reaction is completed, it is taken out and placed in an oven to dry at 50-80℃ for 1.5-3 hours to obtain the expanded polytetrafluoroethylene composite membrane.

3. The method for preparing the expanded polytetrafluoroethylene composite film according to claim 2, characterized in that, The fluorinated modification solution comprises silica, ammonia, 1H,1H,2H,2H-perfluorodecyltriethoxysilane, and a solvent.

4. An expanded polytetrafluoroethylene composite film prepared by the preparation method according to any one of claims 1 to 3, characterized in that, Includes an ePTFE base film and an fPTFE / SiO2 particle composite layer disposed on the surface of the ePTFE base film; The fPTFE / SiO2 particle composite layer includes a polytetrafluoroethylene composite and SiO2 particles. The polytetrafluoroethylene composite includes polyethylene oxide and polytetrafluoroethylene in a dry weight ratio of 1:10-30, and the SiO2 particles have a particle size of 100-1000 nm.

5. The expanded polytetrafluoroethylene composite film according to claim 4, characterized in that, The thickness of the expanded polytetrafluoroethylene composite film is 10-100 μm.

6. The expanded polytetrafluoroethylene composite film according to claim 4, characterized in that, The expanded polytetrafluoroethylene composite membrane has a water contact angle >150° and an oil contact angle >150°.

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