A method for preparing a hydrophobic-modified anti-fouling polytetrafluoroethylene membrane

Abstract

The application discloses a kind of preparation methods of pollution-resistant polytetrafluoroethylene film based on hydrophobic modification, belong to super-hydrophobic material technical field.Aiming at the problems such as insufficient hydrophobicity of existing PTFE film, nanometer particles are easy to aggregate and fall off, the application is first with dimethylsilane cage poly silyl silsesquioxane, fluorinated alkyl acrylate and epoxy group-containing unsaturated compound carry out silicon hydrogen addition reaction, then grafting with polyacrylic polymer to obtain POSS-PAA modified polymer, after emulsification is made into emulsion and is mixed with PTFE and PVA to be spun into emulsion, by electrostatic spinning and under protective atmosphere segmented heat treatment, obtain the polytetrafluoroethylene film.The application realizes the uniform dispersion of nanometer component by fluorine-containing POSS and polyacrylic acid bridge, and constructs micro-nano double-scale rough surface and pore structure, gives the film super-hydrophobicity and anti-pollution performance, while guaranteeing structure stability and high flux, suitable for membrane distillation, gas-liquid contactor, waterproof breathable material and other fields.

Description

Technical Field

[0001] This invention belongs to the field of superhydrophobic materials technology, and particularly relates to a method for preparing an antifouling polytetrafluoroethylene membrane based on hydrophobic modification. Background Technology

[0002] Polytetrafluoroethylene (PTFE) is a fluorinated polymer material with excellent chemical stability, resistance to high and low temperatures, corrosion resistance, and low surface energy. Due to its good hydrophobicity, fouling resistance, and long-term stability, it is widely used in membrane distillation, gas-liquid contactors, oil-water separation, waterproof and breathable materials, air filtration, and battery separators. Especially in membrane distillation, the membrane material not only needs high porosity and excellent mass transfer performance, but also high hydrophobicity and fouling resistance to avoid performance degradation caused by membrane wetting and fouling blockage.

[0003] In recent years, electrospinning technology has attracted widespread attention due to its ability to prepare nanofiber membranes with high porosity, high specific surface area, and low mass transfer resistance. PTFE nanofiber membranes prepared by electrospinning have a large effective mass transfer area and a short diffusion path, which is beneficial for improving flux performance in membrane distillation and gas transport processes. However, although existing PTFE nanofiber membranes have a certain degree of hydrophobicity, their surface water contact angle is usually only about 100-120°, making it difficult to achieve a superhydrophobic state (contact angle greater than 150°). During long-term operation, membrane wetting still easily occurs, leading to decreased separation efficiency and shortened service life.

[0004] To further improve the hydrophobic properties of PTFE membranes, existing technologies typically employ methods such as surface coating with low surface energy materials, introducing fluorinated nanoparticles, or constructing micro / nano rough structures. While constructing surface rough structures with nanoparticles can effectively increase the contact angle of the membrane surface, the nanoparticles often lack stable bonding with the PTFE matrix, making them prone to detachment during long-term operation. This not only leads to a decrease in hydrophobic properties but may also cause membrane structure damage. Furthermore, nanoparticles exhibit poor dispersion in polymer systems, easily agglomerating and locally enriching, thus affecting fiber forming quality and membrane structure uniformity.

[0005] Furthermore, some existing modification methods require secondary surface treatment or subsequent coating after membrane preparation, which is not only complex but also makes it difficult to achieve integrated bonding between the modified components and the PTFE fiber network, resulting in insufficient stability of the modified layer. For long-term operating conditions such as membrane distillation and gas-liquid contactors, how to achieve uniform dispersion and stable fixation of the modified components while maintaining the excellent chemical stability of PTFE, and at the same time construct nanofiber membranes with high porosity, micro-nano dual-scale rough structure, and superhydrophobic surface, remains a pressing technical problem to be solved in this field.

[0006] Therefore, developing a method for preparing polytetrafluoroethylene (PTFE) membranes that can stably introduce hydrophobic nanostructures, improve the hydrophobicity and antifouling properties of the membrane surface, prevent nanoparticle shedding, and simultaneously achieve high porosity and high mass transfer performance is of significant research importance and application value. Summary of the Invention

[0007] In order to overcome the shortcomings of the prior art, this invention proposes a method for preparing an antifouling polytetrafluoroethylene (PTFE) membrane based on hydrophobic modification, addressing the problems of insufficient hydrophobicity, limited antifouling performance, easy agglomeration and detachment of nanoparticles, and poor long-term operational stability of existing PTFE nanofiber membranes.

[0008] To achieve the above objectives, the following technical solution is adopted: This invention provides a method for preparing a hydrophobically modified antifouling polytetrafluoroethylene membrane, comprising the following steps:

[0009] S1. Dimethylsilyl cage polysilsesquioxane, fluoroalkyl acrylate compound and epoxy-containing unsaturated compound are added to a first organic solvent and subjected to hydrosilylation reaction under the action of platinum catalyst to obtain fluoroepoxide polysilsesquioxane.

[0010] S2. The fluorinated epoxidized polysilsesquioxane and the polyacrylic acid polymer are dissolved in a second organic solvent and reacted. After the reaction is completed, the solvent is removed to obtain the POSS-PAA modified polymer.

[0011] S3. Dissolve the POSS-PAA modified polymer in a third organic solvent, add deionized water, emulsifier and dispersant, emulsify by high-speed shearing, and then remove the third organic solvent by rotary evaporation to obtain a POSS modified emulsion.

[0012] S4. Mix polytetrafluoroethylene, polyvinyl alcohol and the POSS modified emulsion, and adjust the solid content to 15~40wt% to obtain a spinning emulsion.

[0013] S5. Electrospinning the spinning emulsion while controlling the ambient humidity at 30-60% to obtain a precursor nanofiber membrane.

[0014] S6. The precursor nanofiber membrane is subjected to the following heat treatments in sequence under a protective atmosphere: pretreatment, pore-forming treatment and sintering treatment, to obtain a hydrophobically modified antifouling polytetrafluoroethylene nanofiber membrane.

[0015] In the above preparation process, the present invention first utilizes a hydrosilylation reaction between fluorinated acrylate and epoxy-containing unsaturated compounds and dimethylsilyl cage-like polysilsesquioxane (POSS), simultaneously introducing fluorinated segments and epoxy active groups onto the POSS surface. The fluorinated segments are used to reduce the surface free energy of the material, while the cage-like structure of POSS provides a nanoscale rough structure. Subsequently, the epoxy groups undergo a ring-opening reaction with the carboxyl groups in the polyacrylic polymer, allowing POSS to be grafted onto the polyacrylic polymer chain, forming a POSS-PAA modified polymer with good dispersibility.

[0016] Since polyacrylic acid segments can form a stable interface with polytetrafluoroethylene emulsion, they can effectively improve the dispersion uniformity of POSS in the polytetrafluoroethylene system and avoid the problems of agglomeration, phase separation and local defects that occur in the traditional direct doping process of nanoparticles.

[0017] During subsequent electrospinning and heat treatment, the polyvinyl alcohol and polyacrylic acid components gradually pyrolyze, while the polytetrafluoroethylene and POSS structures remain stable, thereby forming a large number of uniformly distributed microporous structures and nano-protrusion structures inside and on the fiber surface. The resulting micro / nano dual-scale rough interface can form a stable air layer on the surface, improving the hydrophobic properties of the membrane surface; at the same time, the pore network formed by pyrolysis can reduce mass transfer resistance and improve the permeation performance of the membrane material.

[0018] Furthermore, the POSS nanostructure is not obtained through post-construction surface coating, but rather by constructing a stable composite structure together with the polytetrafluoroethylene network during fiber formation. This avoids the problems of nanoparticle shedding and hydrophobic layer failure, thereby improving the structural stability and service life of the membrane material during long-term operation.

[0019] Further, in step S1, the fluoroalkyl acrylate compound is selected from one or more of perfluorobutyl ethyl acrylate, perfluorohexyl ethyl acrylate, perfluorooctyl ethyl acrylate, and perfluorodecyl ethyl acrylate.

[0020] Further, in step S1, the epoxy-containing unsaturated compound is one or more of glycidyl methacrylate, glycidyl acrylate, and allyl glycidyl ether; the first organic solvent is one or more of toluene, chloroform, or tetrahydrofuran.

[0021] Further, in step S1, the ratio of the total molar number of silane groups to the total molar number of unsaturated double bonds is 1:(0.9~1.2), the molar ratio of fluoroalkyl acrylate to epoxy-containing unsaturated compounds is 3:1~10:1, the amount of platinum catalyst used is 0.01~0.5 mol% of the total molar number of unsaturated double bonds, the reaction temperature is 70~100℃, and the reaction time is 6~18h.

[0022] Further, in step S2, the polyacrylic polymer is selected from one or more of polyacrylic acid, polymethacrylic acid, polyacrylic acid-maleic acid copolymer, and polymethacrylic acid-acrylic acid copolymer; the weight-average molecular weight of the polyacrylic polymer is 10,000 to 500,000.

[0023] Further, in step S2, the molar ratio of epoxy groups to carboxyl groups is 1:(0.5~3), the grafting reaction temperature is 60~120℃, and the reaction time is 2~12h; the POSS structural unit accounts for 5~40wt% of the total mass of the modified polymer in the obtained POSS-PAA modified polymer; the second organic solvent is one or more of N,N-dimethylformamide, dioxane, or toluene.

[0024] Further, in step S3, the third organic solvent is one or more of acetone, tetrahydrofuran, or dichloromethane; the amount of deionized water added is 3 to 15 times the mass of the POSS-PAA modified polymer; the amount of emulsifier added is 0.5 to 8 wt% of the mass of the POSS-PAA modified polymer; the amount of dispersant added is 0.1 to 5 wt% of the mass of the POSS-PAA modified polymer; the high-speed shearing speed is 3000 to 10000 rpm, and the time is 20 to 90 min.

[0025] Further, in step S3, the emulsifier is selected from one or more of Tween 80, Tween 60, polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether, and polyoxyethylene castor oil ether.

[0026] Further, in step S3, the dispersant is selected from one or more of sodium polyacrylate, polyvinylpyrrolidone, sodium carboxymethyl cellulose, and sodium lignosulfonate.

[0027] Further, in step S4, the mass ratio of polytetrafluoroethylene, polyvinyl alcohol, and POSS-PAA modified polymer, based on the mass of solid matter, is (60-90):(5-25):(2-20); the degree of polymerization of the polyvinyl alcohol is 1000-3000, and the degree of alcoholysis is 85-99%.

[0028] Furthermore, step S5 employs an electrospinning process with a spinning voltage of 10~40kV, a receiving distance of 5~30cm, and a liquid supply rate of 0.1~5mL / h.

[0029] Further, in step S6, the protective atmosphere is nitrogen or argon, and the heat treatment includes: heating to 80-150°C at a rate of 1-5°C / min and holding for 0.5-2.5 h; heating to 250-320°C at a rate of 1-5°C / min and holding for 0.5-2 h; heating to 340-390°C at a rate of 2-8°C / min and holding for 0.1-2 h; and then cooling to room temperature at a rate of 1-5°C / min.

[0030] The beneficial effects of this invention are:

[0031] (1) This invention introduces fluorine-containing segments into the POSS structure and uses the POSS nanocage structure to construct a micro-nano dual-scale rough interface, so that the membrane surface has both low surface energy and high surface roughness characteristics, thereby improving the hydrophobic properties and liquid penetration pressure of the polytetrafluoroethylene membrane and effectively suppressing the occurrence of membrane wetting.

[0032] (2) The present invention utilizes polyacrylic acid polymers as interfacial bridging components between POSS and polytetrafluoroethylene, so that POSS can be uniformly dispersed in the polytetrafluoroethylene fiber network, avoiding the agglomeration and local defects caused by direct doping of traditional nanoparticles, while preventing particle shedding, improving the stability of membrane structure and long-term operational reliability.

[0033] (3) During the heat treatment process, polyvinyl alcohol and polyacrylic acid components are pyrolyzed to form a uniform pore structure, while heat-resistant and stable POSS and polytetrafluoroethylene are retained in the membrane skeleton, thereby obtaining a nanofiber structure with high porosity, multi-level channels and low mass transfer resistance. This structure can improve the efficiency of water vapor and gas transport, and improve membrane flux and permeation performance.

[0034] (4) The high porosity superhydrophobic nanofiber network constructed in this invention can effectively reduce the adsorption and deposition of organic pollutants, oil stains and colloidal particles on the membrane surface. At the same time, the presence of an air layer further reduces the probability of contact between pollutants and the membrane surface, thereby giving the membrane excellent antifouling performance and self-cleaning ability, and improving the membrane flux retention rate and service life.

[0035] (5) The present invention can achieve the control of membrane material structure by combining electrospinning and heat treatment, without the need for additional surface coating or complex post-treatment processes, and the preparation process is relatively simple. Attached Figure Description

[0036] Figure 1 The images are scanning electron microscope (SEM) images of the polytetrafluoroethylene films obtained in Example 3 and Comparative Examples 1-3.

[0037] Figure 2The graph shows the test results of water contact angle and water penetration pressure of the polytetrafluoroethylene membranes obtained in Examples 1-3 and Comparative Examples 1-3;

[0038] Figure 3 The stress-strain curves of the polytetrafluoroethylene films obtained in Examples 1-3 and Comparative Examples 1-3 are shown.

[0039] Figure 4 The graph shows the mechanical property test results of the polytetrafluoroethylene films obtained in Examples 1-3 and Comparative Examples 1-3;

[0040] Figure 5 The graph shows the membrane distillation flux test results of the polytetrafluoroethylene membranes obtained in Examples 1-3 and Comparative Examples 1-3 under different NaCl concentration conditions.

[0041] Figure 6 The graph shows the membrane distillation flux change of the polytetrafluoroethylene membranes obtained in Examples 1-3 and Comparative Examples 1-3 under 3.5 wt% NaCl conditions for 72 h of continuous operation.

[0042] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. Detailed Implementation

[0043] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar to those skilled in the art. Furthermore, any methods and materials similar to or equivalent to those described herein may be applied to this invention. The preferred embodiments and materials described herein are for illustrative purposes only and do not limit the scope of this application.

[0045] Unless otherwise specified, the experimental methods used in the following examples are conventional methods, and the experimental materials used in the following examples are commercially available. The platinum-based catalyst used in this application is a Karstedt catalyst.

[0046] Example 1

[0047] A method for preparing a hydrophobically modified antifouling polytetrafluoroethylene membrane includes the following steps:

[0048] S1. Dimethylsilyl cage polysilsesquioxane, fluoroalkyl acrylate compound and epoxy-containing unsaturated compound are added to a first organic solvent and subjected to hydrosilylation reaction under the action of platinum catalyst to obtain fluoroepoxide polysilsesquioxane.

[0049] Wherein, the fluoroalkyl acrylate compound is perfluorobutyl ethyl acrylate; the epoxy-containing unsaturated compound is glycidyl methacrylate; the first organic solvent is toluene; the ratio of the total molar number of silane groups to the total molar number of unsaturated double bonds is 1:0.9, the molar ratio of the fluoroalkyl acrylate to the epoxy-containing unsaturated compound is 3:1, the amount of the platinum-based catalyst is 0.01 mol% of the total molar number of unsaturated double bonds, the reaction temperature is 70℃, and the reaction time is 6 h;

[0050] S2. The fluorinated epoxidized polysilsesquioxane and the polyacrylic acid polymer are dissolved in a second organic solvent and reacted. After the reaction is completed, the solvent is removed to obtain the POSS-PAA modified polymer.

[0051] Wherein, the polyacrylic acid polymer is polyacrylic acid; the weight-average molecular weight of the polyacrylic acid polymer is 10,000; the molar ratio of epoxy groups to carboxyl groups is 1:0.5, the grafting reaction temperature is 60℃, and the reaction time is 2h; the POSS structural unit accounts for 5wt% of the total mass of the modified polymer in the obtained POSS-PAA modified polymer; the second organic solvent is N,N-dimethylformamide;

[0052] S3. Dissolve the POSS-PAA modified polymer in a third organic solvent, add deionized water, emulsifier and dispersant, emulsify by high-speed shearing, and then remove the third organic solvent by rotary evaporation to obtain a POSS modified emulsion.

[0053] The third organic solvent is acetone; the amount of deionized water added is 3 times the mass of the POSS-PAA modified polymer; the amount of emulsifier added is 0.5 wt% of the mass of the POSS-PAA modified polymer; the amount of dispersant added is 0.1 wt% of the mass of the POSS-PAA modified polymer; the high-speed shearing speed is 3000 rpm and the time is 20 min; the emulsifier is selected from Tween 80; the dispersant is sodium polyacrylate.

[0054] S4. Mix polytetrafluoroethylene, polyvinyl alcohol and the POSS modified emulsion, and adjust the solid content to 15 wt% to obtain a spinning emulsion.

[0055] The mass ratio of polytetrafluoroethylene, polyvinyl alcohol, and POSS-PAA modified polymer, based on solid mass, is 60:5:2; the degree of polymerization of the polyvinyl alcohol is 1000, and the degree of alcoholysis is 85%.

[0056] S5. Electrospin the spinning emulsion with a spinning voltage of 10kV, a receiving distance of 5cm, a liquid supply rate of 0.1mL / h, and an ambient humidity of 30% to obtain a precursor nanofiber membrane.

[0057] S6. The precursor nanofiber membrane is subjected to the following heat treatments in a nitrogen protective atmosphere: the temperature is increased to 80°C at a rate of 1°C / min and held for 0.5h; the temperature is increased to 250°C at a rate of 1°C / min and held for 0.5h; the temperature is increased to 340°C at a rate of 2°C / min and held for 0.1h; and then the temperature is decreased to room temperature at a rate of 1°C / min to obtain a hydrophobic modified antifouling polytetrafluoroethylene nanofiber membrane.

[0058] Example 2

[0059] A method for preparing a hydrophobically modified antifouling polytetrafluoroethylene membrane includes the following steps:

[0060] S1. Dimethylsilyl cage polysilsesquioxane, fluoroalkyl acrylate compound and epoxy-containing unsaturated compound are added to a first organic solvent and subjected to hydrosilylation reaction under the action of platinum catalyst to obtain fluoroepoxide polysilsesquioxane.

[0061] Wherein, the fluoroalkyl acrylate compound is perfluorodecyl ethyl acrylate; the epoxy-containing unsaturated compound is allyl glycidyl ether; the first organic solvent is toluene; the ratio of the total molar number of silane groups to the total molar number of unsaturated double bonds is 1:1.2, the molar ratio of the fluoroalkyl acrylate to the epoxy-containing unsaturated compound is 10:1, the amount of the platinum-based catalyst is 0.5 mol% of the total molar number of unsaturated double bonds, the reaction temperature is 100℃, and the reaction time is 18 h;

[0062] S2. The fluorinated epoxidized polysilsesquioxane and the polyacrylic acid polymer are dissolved in a second organic solvent and reacted. After the reaction is completed, the solvent is removed to obtain the POSS-PAA modified polymer.

[0063] Wherein, the polyacrylic acid polymer is a polymethacrylic acid-acrylic acid copolymer; the weight-average molecular weight of the polyacrylic acid polymer is 500,000; the molar ratio of epoxy groups to carboxyl groups is 1:3, the grafting reaction temperature is 120℃, and the reaction time is 12h; the POSS structural unit accounts for 40wt% of the total mass of the modified polymer in the obtained POSS-PAA modified polymer; the second organic solvent is dioxane;

[0064] S3. Dissolve the POSS-PAA modified polymer in a third organic solvent, add deionized water, emulsifier and dispersant, emulsify by high-speed shearing, and then remove the third organic solvent by rotary evaporation to obtain a POSS modified emulsion.

[0065] Wherein, the third organic solvent is tetrahydrofuran; the amount of deionized water added is 15 times the mass of the POSS-PAA modified polymer; the amount of emulsifier added is 8 wt% of the mass of the POSS-PAA modified polymer; the amount of dispersant added is 5 wt% of the mass of the POSS-PAA modified polymer; the high-speed shearing speed is 10000 rpm, and the time is 90 min; the emulsifier is polyoxyethylene castor oil ether; and the dispersant is sodium lignosulfonate.

[0066] S4. Mix polytetrafluoroethylene, polyvinyl alcohol and the POSS modified emulsion, and adjust the solid content to 40 wt% to obtain a spinning emulsion.

[0067] The mass ratio of polytetrafluoroethylene, polyvinyl alcohol, and POSS-PAA modified polymer is 90:25:20 based on the mass of solid matter; the degree of polymerization of polyvinyl alcohol is 3000, and the degree of alcoholysis is 99%.

[0068] S5. Electrospinning the spinning emulsion with a spinning voltage of 40kV, a receiving distance of 30cm, a liquid supply rate of 5mL / h, and an ambient humidity of 60% to obtain a precursor nanofiber membrane.

[0069] S6. The precursor nanofiber membrane is subjected to the following heat treatments in a protective atmosphere of argon: the temperature is increased to 150°C at a rate of 5°C / min and held for 2.5 h; the temperature is increased to 320°C at a rate of 1~5°C / min and held for 2 h; the temperature is increased to 390°C at a rate of 8°C / min and held for 2 h; then the temperature is decreased to room temperature at a rate of 5°C / min to obtain a hydrophobic modified antifouling polytetrafluoroethylene nanofiber membrane.

[0070] Example 3

[0071] A method for preparing a hydrophobically modified antifouling polytetrafluoroethylene membrane includes the following steps:

[0072] S1. Dimethylsilyl cage polysilsesquioxane, fluoroalkyl acrylate compound and epoxy-containing unsaturated compound are added to a first organic solvent and subjected to hydrosilylation reaction under the action of platinum catalyst to obtain fluoroepoxide polysilsesquioxane.

[0073] Wherein, the fluoroalkyl acrylate compound is perfluorohexylethyl acrylate; the epoxy-containing unsaturated compound is glycidyl acrylate; the first organic solvent is toluene; the ratio of the total molar number of silane groups to the total molar number of unsaturated double bonds is 1:1.05, the molar ratio of the fluoroalkyl acrylate to the epoxy-containing unsaturated compound is 6.5:1, the amount of the platinum-based catalyst is 0.25 mol% of the total molar number of unsaturated double bonds, the reaction temperature is 85℃, and the reaction time is 12 h;

[0074] S2. The fluorinated epoxidized polysilsesquioxane and the polyacrylic acid polymer are dissolved in a second organic solvent and reacted. After the reaction is completed, the solvent is removed to obtain the POSS-PAA modified polymer.

[0075] The polyacrylic acid polymer is a polyacrylic acid-maleic acid copolymer; the weight-average molecular weight of the polyacrylic acid polymer is 250,000; the molar ratio of epoxy groups to carboxyl groups is 1:1.75; the grafting reaction temperature is 90℃; and the reaction time is 7h. The POSS structural unit accounts for 22.5 wt% of the total mass of the modified polymer in the obtained POSS-PAA modified polymer; the second organic solvent is toluene.

[0076] S3. Dissolve the POSS-PAA modified polymer in a third organic solvent, add deionized water, emulsifier and dispersant, emulsify by high-speed shearing, and then remove the third organic solvent by rotary evaporation to obtain a POSS modified emulsion.

[0077] The third organic solvent is dichloromethane; the amount of deionized water added is 9 times the mass of the POSS-PAA modified polymer; the amount of emulsifier added is 4.25 wt% of the mass of the POSS-PAA modified polymer; the amount of dispersant added is 2.5 wt% of the mass of the POSS-PAA modified polymer; the high-speed shearing speed is 6500 rpm and the time is 55 min; the emulsifier is Tween 60; and the dispersant is polyvinylpyrrolidone.

[0078] S4. Mix polytetrafluoroethylene, polyvinyl alcohol and the POSS modified emulsion, and adjust the solid content to 28 wt% to obtain a spinning emulsion.

[0079] The mass ratio of polytetrafluoroethylene, polyvinyl alcohol, and POSS-PAA modified polymer is 80:10:10 based on the mass of solid matter; the degree of polymerization of the polyvinyl alcohol is 2000, and the degree of alcoholysis is 92%.

[0080] S5. The spinning emulsion is electrospun at a spinning voltage of 25kV, a receiving distance of 17cm, a liquid supply rate of 2.5mL / h, and an ambient humidity of 45% to obtain a precursor nanofiber membrane.

[0081] S6. The precursor nanofiber membrane is subjected to the following heat treatments in a nitrogen protective atmosphere: the temperature is increased to 120°C at a rate of 3°C / min and held for 1.5h; the temperature is increased to 300°C at a rate of 2°C / min and held for 1.5h; the temperature is increased to 360°C at a rate of 6°C / min and held for 1.5h; then the temperature is decreased to room temperature at a rate of 2°C / min to obtain a hydrophobic modified antifouling polytetrafluoroethylene nanofiber membrane.

[0082] Comparative Example 1

[0083] The difference between this comparative example and Example 1 is that steps S1, S2, and S3 are omitted; only polytetrafluoroethylene and polyvinyl alcohol are used in S4 (without adding POSS-PAA modified polymer), and polytetrafluoroethylene accounts for 95 wt% of the total solid mass, while polyvinyl alcohol accounts for 5 wt%. All other parameters are exactly the same as in Example 1.

[0084] Comparative Example 2

[0085] The difference between this comparative example and Example 1 is that: in S1, octavinyl cage-like polysilsesquioxane (without dimethylsilyl and fluorinated segments) is used, and no hydrosilylation reaction is performed to directly obtain unmodified POSS; in S2, unmodified POSS and polyacrylic acid are only physically mixed (stirred at room temperature); in S3, a POSS / PAA physical blend emulsion is prepared, and all other steps (including the proportions of each component, spinning and heat treatment conditions) are consistent with those in Example 1.

[0086] Comparative Example 3

[0087] The difference between this comparative example and Example 1 is that in S6, the precursor nanofiber membrane is dried at 80°C for 2 hours, and the pore-forming treatment at 250°C (0.5 hours) and sintering treatment at 340°C (0.1 hours) are omitted. All other steps (from S1 to S5) and parameters are exactly the same as in Example 1.

[0088] Results Analysis

[0089] The microstructure of the polytetrafluoroethylene films prepared in Example 3 and Comparative Examples 1-3 was observed using scanning electron microscopy. The scanning electron microscopy images are shown below. Figure 1 As shown. From Figure 1As can be seen, the polytetrafluoroethylene (PTFE) membrane prepared in Example 3 exhibits a uniform and continuous three-dimensional nanofiber network structure with a relatively uniform fiber diameter distribution. The fibers intertwine to form numerous interconnected channels. High-magnification images reveal that the fiber surface is not smooth but rather uniformly distributed with numerous nanoscale protrusions and fine rough structures. The surface of Comparative Example 1 is mainly composed of PTFE fibers. Although it can still form a certain fiber network, the fiber surface is relatively smooth and lacks obvious nanoscale rough structures. Furthermore, because the heat treatment process relies solely on PVA for pore formation, fewer surface microstructures are formed, resulting in a significantly lower overall roughness compared to Example 3. Therefore, its surface can only provide limited air trapping capacity, making it difficult to construct a stable superhydrophobic interface. The SEM image of Comparative Example 2 shows obvious granular agglomeration structures on the fiber surface, with particle enrichment in some areas, and the bonding between the particles and fibers is not tight enough. This indicates that the unmodified POSS has poor dispersibility in the system and is prone to phase separation and agglomeration during spinning and heat treatment. Although the surface roughness was improved, the distribution of the rough structure was uneven, easily leading to local defects, and it lacked the low surface energy effect brought by fluorinated segments. Comparative Example 3, while introducing POSS-PAA modification components, omitted the high-temperature pore-forming and sintering processes. SEM images show that the fiber structure still maintains a relatively complete original spinning morphology, the fiber surface is relatively dense, and no obvious micropores or nano-protrusions are formed; adhesion exists in some areas between fibers. This indicates that pore-forming and sintering treatments play an important role in the removal of sacrificial components such as PVA and PAA, and in the formation of micro / nano structures. Without heat treatment, POSS cannot be fully exposed on the fiber surface, making it impossible to construct a complete micro / nano dual-scale rough interface; therefore, the membrane porosity, mass transfer performance, and hydrophobic properties are significantly limited. A comprehensive comparison of Example 3 with Comparative Examples 1-3 reveals that Example 3 successfully constructed a uniform and stable micro / nano dual-scale rough structure on the PTFE fiber surface through the synergistic effect of POSS surface fluorination modification, PAA interface bridging, and subsequent heat treatment pore-forming. This structure simultaneously features high porosity, continuous mass transfer channels, and low surface energy.

[0090] The static water contact angle of the membrane surface was determined using a contact angle meter. Before testing, the sample membrane was cut into 20 mm × 20 mm pieces and placed at 25℃ and 50% relative humidity for 24 h. A 5 μL droplet of deionized water was slowly added to the membrane surface using a microsyringe. Images were acquired and the contact angle calculated within 5 seconds of the droplet contacting the membrane surface. Five different locations were randomly selected for testing on each sample, and the average value was taken as the final result.

[0091] The liquid penetration pressure was measured using a self-made liquid penetration pressure testing device. The membrane sample was fixed in the test cell, with an effective test area of ​​9.6 cm². 2The test solution was deionized water, and the feed-side pressure was gradually increased using nitrogen pressurization. The pressure started at 0 kPa and increased gradually at a rate of 5 kPa / min. The pressure at which continuous water droplet permeation was first observed on the membrane permeation side was defined as the water penetration pressure. Each sample was tested in triplicate, and the average value was taken as the final result.

[0092] The above water contact angle and water penetration pressure test results are as follows: Figure 2 As shown.

[0093] From the appendix Figure 2 It can be seen that the polytetrafluoroethylene membranes prepared in Examples 1-3 all exhibited significantly higher water contact angles and water penetration pressures than those in Comparative Examples 1-3. Combined with... Figure 1 SEM analysis of the results showed that in Example 3, the POSS modified with fluorinated segments was uniformly dispersed in the PTFE fiber network. During heat treatment, it formed a large number of nanoscale protrusions and a micro / nano dual-scale rough interface. Simultaneously, the fluorinated segments reduced the surface free energy of the membrane, thus forming a stable wetting state. This allowed the membrane surface to trap more air layers, resulting in superhydrophobic properties and higher liquid penetration pressure. In contrast, Comparative Example 1 did not introduce POSS modification, resulting in a smoother fiber surface and a lack of nanoscale rough structures. In Comparative Example 2, the unmodified POSS agglomerated, leading to an uneven distribution of rough structures. Although Comparative Example 3 contained POSS, the lack of pore-forming and sintering processes prevented POSS from being fully exposed on the fiber surface, thus failing to form the micro / nano dual-scale structure seen in Example 3, resulting in a significant decrease in hydrophobic properties. Therefore, the polytetrafluoroethylene membrane prepared by the method of this invention improves the membrane's hydrophobicity and anti-wetting ability.

[0094] Tensile tests were conducted using an electronic universal testing machine. The membrane samples were cut to dimensions of 50 mm in length and 10 mm in width. Before testing, the samples were equilibrated for 24 hours at 25°C and 50% relative humidity. The clamping distance was set to 30 mm, and the tensile rate was set to 10 mm / min. Load and displacement data were recorded in real-time during the test, and stress-strain curves were obtained. At least five parallel samples were tested for each group of samples. The stress-strain curves are shown below. Figure 3 As shown. The stress-strain curve is attached. Figure 3 As shown in the attached figure. The tensile strength elongation at break was calculated. Figure 4 As shown.

[0095] From the appendix Figure 3 and attached Figure 4As can be seen, the stress-strain curves of Examples 1-3 are generally above those of the comparative examples, with Example 3 exhibiting the highest tensile strength and high elongation at break. This indicates that the membrane material prepared by this invention possesses both high strength and good toughness. The reason for this may be that the PAA segments act as an interfacial bridge between POSS and PTFE, allowing POSS to be uniformly embedded within the fiber skeleton, forming a stable stress transfer network; the POSS cage structure itself has a rigid nano-reinforcing effect; and the continuous fiber network and sintering nodes formed after heat treatment further enhance the bonding strength between fibers. In contrast, Comparative Example 2, due to POSS agglomeration, easily forms stress concentration points during stress, resulting in a significant decrease in both strength and elongation; Comparative Example 3 lacks a sintering process, resulting in insufficient fiber cross-linking, thus, although it has a high elongation at break, its tensile strength is significantly lower. The results show that this invention not only improves the hydrophobic properties of the membrane but also maintains or even enhances the mechanical stability of the membrane material, which is beneficial for the structural stability during long-term membrane distillation operation.

[0096] The membrane distillation flux at different salt concentrations was tested using a direct contact membrane distillation apparatus. The effective membrane area was 40 cm², the hot-side feed temperature was 60±1 ℃, the cold-side temperature was 20±1 ℃, and the circulation flow rate was 0.5 L / min. The feed solutions were prepared as follows: pure water, 1 wt% NaCl, 3.5 wt% NaCl, 7 wt% NaCl, and 10 wt% NaCl. Data was recorded after the system had been running stably for 30 minutes. The test results are attached. Figure 5 As shown.

[0097] From the appendix Figure 5 It can be seen that as the NaCl concentration increased from 0 wt% to 10 wt%, the membrane distillation flux of all samples decreased. This is due to the decrease in solution vapor pressure and the enhancement of concentration polarization caused by the increase in salt concentration. However, under all concentration conditions, each Example 3 exhibited a higher membrane distillation flux. Taking 3.5 wt% NaCl as an example, the flux of Example 3 was more than twice that of Comparative Example 1. Combined with SEM results analysis, it can be seen that a high porosity, hierarchical pores, and uniformly connected nanofiber network was formed in Example 3, allowing water vapor to diffuse rapidly through the membrane pores, thus reducing mass transfer resistance. At the same time, the superhydrophobic interface can effectively prevent liquid from entering the pores, ensuring the stable progress of the gas-phase mass transfer process. In contrast, Comparative Example 1 lacked a nano-rough structure, Comparative Example 2 suffered from particle agglomeration and blockage, and Comparative Example 3 lacked sufficient pore formation. Therefore, the pore structure of Comparative Example 1 was not as developed as that of Example 3, resulting in a significant decrease in flux. Therefore, the micro-nano dual-scale pore structure constructed in this invention can improve the mass transfer efficiency in the membrane distillation process.

[0098] Long-term membrane distillation performance was tested according to the above-described membrane distillation flux testing method. The feed solution was 3.5 wt% NaCl solution, and the test was conducted continuously for 72 hours. The remaining test procedures were the same as those described in the previous membrane distillation flux test. Instantaneous membrane distillation flux was recorded every 12 hours. The test results are attached. Figure 6 As shown.

[0099] From the appendix Figure 6 As can be seen, after 72 hours of continuous operation under 3.5 wt% NaCl conditions, the changes in each embodiment were not significant, while Comparative Example 1 showed the most significant decrease, exhibiting obvious instability in the later stages. This difference mainly stems from the differences in membrane surface structure and wetting behavior. The superhydrophobic micro / nano structures on the surface of the embodiments can form a stable air layer on the membrane surface, reducing the contact opportunities between salt crystals, organic pollutants, and colloidal particles and the membrane surface, thereby reducing fouling deposition and pore blockage. Simultaneously, the uniformly dispersed POSS structure forms a stable composite network with the PTFE framework, making it less prone to particle shedding and surface structure damage, thus maintaining a high flux over a long period. In contrast: Comparative Example 1 lacks a superhydrophobic structure and is prone to pore wetting; Comparative Example 2, due to POSS aggregation forming local defects, is prone to local wetting and fouling accumulation; Comparative Example 3, due to its imperfect pore structure, has lower mass transfer efficiency and insufficient antifouling ability. Therefore, during long-term operation, the membrane of this invention exhibits superior antifouling performance, antiwetting performance, and operational stability.

[0100] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

[0101] The present invention and its embodiments have been described above. This description is not restrictive, and the embodiments shown are only one of the embodiments of the present invention. The actual application is not limited to this. In conclusion, if those skilled in the art are inspired by this description and design similar methods and embodiments without departing from the spirit of the present invention, they should all fall within the protection scope of the present invention.

Claims

1. A method for preparing an antifouling polytetrafluoroethylene membrane based on hydrophobic modification, characterized in that: Includes the following steps: S1. Dimethylsilyl cage polysilsesquioxane, fluoroalkyl acrylate compound and epoxy-containing unsaturated compound are added to a first organic solvent and subjected to hydrosilylation reaction under the action of platinum catalyst to obtain fluoroepoxide polysilsesquioxane. S2. The fluorinated epoxidized polysilsesquioxane and the polyacrylic acid polymer are dissolved in a second organic solvent and reacted. After the reaction is completed, the solvent is removed to obtain the POSS-PAA modified polymer. S3. Dissolve the POSS-PAA modified polymer in a third organic solvent, add deionized water, emulsifier and dispersant, emulsify by high-speed shearing, and then remove the third organic solvent by rotary evaporation to obtain a POSS modified emulsion. S4. Mix polytetrafluoroethylene, polyvinyl alcohol and the POSS modified emulsion, and adjust the solid content to 15~40wt% to obtain a spinning emulsion. S5. Electrospinning the spinning emulsion while controlling the ambient humidity at 30-60% to obtain a precursor nanofiber membrane. S6. The precursor nanofiber membrane is subjected to the following heat treatments in sequence under a protective atmosphere: pretreatment, pore-forming treatment and sintering treatment, to obtain a hydrophobically modified antifouling polytetrafluoroethylene nanofiber membrane.

2. The preparation method according to claim 1, characterized in that: In step S1, the fluoroalkyl acrylate compound is selected from one or more of perfluorobutyl ethyl acrylate, perfluorohexyl ethyl acrylate, perfluorooctyl ethyl acrylate, and perfluorodecyl ethyl acrylate.

3. The preparation method according to claim 2, characterized in that: In step S1, the epoxy-containing unsaturated compound is one or more of glycidyl methacrylate, glycidyl acrylate, and allyl glycidyl ether; the first organic solvent is one or more of toluene, chloroform, or tetrahydrofuran.

4. The preparation method according to claim 2, characterized in that: In step S1, the ratio of the total molar number of silane groups to the total molar number of unsaturated double bonds is 1:(0.9~1.2), the molar ratio of fluoroalkyl acrylate to epoxy-containing unsaturated compounds is 3:1~10:1, the amount of platinum catalyst used is 0.01~0.5 mol% of the total molar number of unsaturated double bonds, the reaction temperature is 70~100℃, and the reaction time is 6~18h.

5. The preparation method according to claim 1, characterized in that: In step S2, the polyacrylic polymer is selected from one or more of polyacrylic acid, polymethacrylic acid, polyacrylic acid-maleic acid copolymer, and polymethacrylic acid-acrylic acid copolymer; the weight average molecular weight of the polyacrylic polymer is 10,000 to 500,000.

6. The preparation method according to claim 1, characterized in that: In step S2, the molar ratio of epoxy groups to carboxyl groups is 1:(0.5~3), the grafting reaction temperature is 60~120℃, and the reaction time is 2~12h; the POSS structural unit accounts for 5~40wt% of the total mass of the modified polymer in the obtained POSS-PAA modified polymer; the second organic solvent is one or more of N,N-dimethylformamide, dioxane, or toluene.

7. The preparation method according to claim 1 or 6, characterized in that: In step S3, the third organic solvent is one or more of acetone, tetrahydrofuran, or dichloromethane; the amount of deionized water added is 3 to 15 times the mass of the POSS-PAA modified polymer; the amount of emulsifier added is 0.5 to 8 wt% of the mass of the POSS-PAA modified polymer; the amount of dispersant added is 0.1 to 5 wt% of the mass of the POSS-PAA modified polymer; the high-speed shearing speed is 3000 to 10000 rpm, and the time is 20 to 90 min.

8. The preparation method according to claim 7, characterized in that: In step S3, the emulsifier is selected from one or more of Tween 80, Tween 60, polyoxyethylene octylphenol ether, polyoxyethylene nonylphenol ether, and polyoxyethylene castor oil ether; the dispersant is selected from one or more of sodium polyacrylate, polyvinylpyrrolidone, sodium carboxymethyl cellulose, and sodium lignosulfonate.

9. The preparation method according to claim 1, characterized in that: In step S4, the mass ratio of polytetrafluoroethylene, polyvinyl alcohol, and POSS-PAA modified polymer, based on the mass of solid matter, is (60-90):(5-25):(2-20); the degree of polymerization of polyvinyl alcohol is 1000-3000, and the degree of alcoholysis is 85-99%.

10. The preparation method according to claim 1, characterized in that: Step S5 employs an electrospinning process with a spinning voltage of 10~40kV, a receiving distance of 5~30cm, and a liquid supply rate of 0.1~5mL / h. In step S6, the protective atmosphere is nitrogen or argon, and the heat treatment includes: heating to 80-150°C at a rate of 1-5°C / min and holding at that temperature for 0.5-2.5 hours. Heat to 250-320℃ at a rate of 1-5℃ / min and hold for 0.5-2h; heat to 340-390℃ at a rate of 2-8℃ / min and hold for 0.1-2h; then cool to room temperature at a rate of 1-5℃ / min.

Images