Modified PTFE microporous filter membrane and preparation method thereof

Abstract

The invention relates to the technical field of microfiltration membranes, in particular to a modified PTFE microfiltration membrane and a preparation method thereof. The preparation method of the modified PTFE microporous filter membrane comprises the following steps: firstly, carrying out oxygen plasma treatment on a PTFE membrane, and introducing an oxygen-containing active group on the surface of the PTFE membrane; carrying out covalent grafting by utilizing a silane coupling agent to form a silane layer with amino at the tail end; then, a polyvinyl alcohol hydrogel middle layer is constructed on the surface of the membrane through crosslinking; and finally, loading a polyion compound hydrogel functional layer formed by electrostatically compounding polyanions and a quaternary ammonium salt copolymer and carrying out Fe < 3 + > coordination crosslinking to obtain the modified PTFE microporous filtering membrane. The firm, uniform and functionalized composite hydrophilic coating is constructed on the surface of the PTFE membrane through a multi-stage chemical bonding strategy, so that the obtained membrane has super-hydrophilicity, high water flux, excellent pollution resistance, good salt resistance and long-term use stability, and the application prospect of the PTFE membrane in the hydrophilic filtration fields of water treatment, biological separation and the like is remarkably expanded.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of microporous filter membranes, and particularly relates to a modified PTFE microporous filter membrane and a preparation method thereof. BACKGROUND

[0002] Polytetrafluoroethylene (PTFE) microporous membranes are widely used in water treatment, biological medicine, air filtration and other fields due to their excellent chemical stability, thermal stability and high porosity. However, the PTFE molecular chain is highly symmetrical and has extremely low surface energy (water contact angle > 100°), showing strong hydrophobicity, which makes it difficult to wet in the water phase system and the effective flux is extremely low, which seriously limits its application in liquid phase separation. In order to improve its hydrophilicity, the existing technology often uses methods such as surface coating, plasma treatment, chemical grafting or blending modification.

[0003] However, the traditional modification strategy still faces multiple challenges: (1) Single plasma or silane treatment can introduce hydrophilic groups, but the modified layer is easy to age and fall off, and has poor long-term stability; (2) Direct coating of hydrophilic polymers (such as PVA, PEG) often relies on physical adsorption, and has weak binding force with the PTFE substrate, and is easy to peel off in the water flow shear or cleaning process; (3) If the functional coating (such as anti-pollution, antibacterial layer) is directly constructed on the surface of PTFE, it is difficult to form a uniform and firm interface due to the lack of effective anchoring sites; (4) The multi-layer composite structure often causes pore blockage, flux decline, and even loss of the original high permeability advantage of PTFE membrane due to poor compatibility between layers and insufficient cross-linking.

[0004] Therefore, it is urgent to develop a new modification strategy that can realize efficient functionalization of the PTFE surface and maintain its high flux performance, especially to solve the contradiction between interface bonding strength, coating stability and permeability. SUMMARY

[0005] The purpose of the present application is to provide a modified PTFE microporous filter membrane and a preparation method thereof, which solves the technical problem of realizing efficient functionalization of the PTFE surface and maintaining its high flux performance in the prior art.

[0006] In order to achieve the above purpose, the technical scheme adopted by the present application is as follows: The present application provides a preparation method of a modified PTFE microporous filter membrane, comprising the following steps: Step (1) wash the PTFE microporous membrane with anhydrous ethanol and deionized water for 3-5 times, then dry at 35-45℃, and then coat a layer of hydrophilic polymer on the surface of the PTFE microporous membrane at a power density of 0.51 W / cm 2The surface-activated PTFE microporous membrane is obtained by radio frequency oxygen plasma treatment for 25-35 min; In the above process, the plasma treatment enriches the hydrophilic oxygen-containing groups, providing reaction sites for subsequent silane grafting.

[0007] Step (2) dissolving 3-aminopropyltrimethoxysilane in a volume ratio of 95:5 of ethanol aqueous solution to obtain a silane solution of 1-2 mg / mL; immersing the surface-activated PTFE microporous membrane in the silane solution at a bath ratio of 1:50 g / mL for 4-6 h, rinsing with ethanol after taking out, and then vacuum drying at 35-45 °C for 3-5 h to obtain a silane-modified PTFE membrane; In the above process, in the ethanol aqueous solution, 3-aminopropyltrimethoxysilane is hydrolyzed to form silanol, and the silanol reacts with the oxygen-containing groups generated on the membrane surface by plasma treatment to form a covalently bonded silane layer.

[0008] Step (3) immersing the silane-modified PTFE membrane in PVA solution after being fully wetted with anhydrous ethanol, room temperature soaking for 2-4 h, then transferring to the crosslinking solution at a bath ratio of 1:40 g / mL, room temperature reaction for 10-14 h, after the reaction is completed, the membrane is immersed and washed with deionized water, and the water is changed every 4-6 hours, a total of 4-6 times, to obtain a PVA hydrogel coated microporous membrane; In the above process, under weak acidic conditions, the dialdehyde group of glutaraldehyde first reacts with the primary amino group at the end of the silane layer to form an imine bond (-N=CH-), achieving covalent bridging of the PTFE substrate and the PVA layer; at the same time, the other aldehyde group of glutaraldehyde reacts with the hydroxyl group on the PVA molecular chain to form an acetal, achieving crosslinking between PVA molecules, thereby constructing a stable three-dimensional hydrogel network on the membrane surface.

[0009] Step (4) immersing the PVA hydrogel coated microporous membrane fully wetted with deionized water in the polyion complex hydrogel dispersion liquid at a bath ratio of 1:30 g / mL, room temperature soaking for 2-4 h, then transferring it to the Fe 3+ crosslinking solution, room temperature reaction for 6-8 h, and fully rinsing with deionized water to obtain a modified PTFE microporous filter membrane.

[0010] In the above process, Fe 3+ forms a coordination bond with the -SO3 - group of poly(2-acrylamide-2-methylpropanesulfonic acid), generating additional physical crosslinking points, enhancing the mechanical strength of the hydrogel; improving the salt resistance of the network, and strengthening the interface bonding between the polyion complex hydrogel layer and the PVA bottom layer.

[0011] Furthermore, the crosslinked aqueous solution is an aqueous solution containing 0.125 g / mL glutaraldehyde and 0.02 g / mL tartaric acid.

[0012] Furthermore, the Fe 3+ The crosslinking solution is an aqueous solution of 1.1-1.3 w / v% Fe(NO3)3·9H2O.

[0013] Furthermore, the method for preparing the PVA solution includes the following steps: PVA was dissolved in a DMSO-water mixture with a volume ratio of 1:3 and stirred vigorously at 90-100℃ for 3-5 hours to obtain a 0.3-0.6 wt% PVA solution.

[0014] Furthermore, the preparation method of the polyionic complex hydrogel dispersion includes the following steps: S1: Dissolve poly(2-acrylamide-2-methylpropanesulfonic acid), a mixture of quaternary ammonium monomers, a photoinitiator, and NaCl in deionized water. Adjust the pH to 6.5-7.0 with NaOH solution. In the resulting solution, the concentration of poly(2-acrylamide-2-methylpropanesulfonic acid) is 1.5 w / v, the total concentration of quaternary ammonium monomers is 0.7 w / v, and the concentration of NaCl is 2.9 w / v. After stirring at 60-70℃ for 20-30 min, cool to room temperature and irradiate under 365nm ultraviolet light for 11-13 h to form a hydrogel.

[0015] S2: Cut the hydrogel into small pieces and soak them in deionized water for 2 days, changing the water 3 times a day for purification. After taking them out, add 4 mol / L NaCl solution at a ratio of 1:20 g / mL of wet weight of purified hydrogel to solution volume. Swell at 65-75℃ for 3 hours, then stir vigorously at 85-95℃ for 2.5-4.5 hours. Then further dilute with 4 mol / L NaCl solution and sonicate for 40-60 minutes to obtain a 0.6 w / v% polyionomer hydrogel dispersion.

[0016] Furthermore, the quaternary ammonium salt monomer mixture is obtained by mixing allyltrimethylammonium chloride and [2-(methacryloyloxy)ethyl]trimethylammonium chloride at a mass ratio of 1:9.

[0017] Furthermore, the photoinitiator is Irgacure 2959, accounting for 0.5% of the total mass of the quaternary ammonium salt monomer mixture.

[0018] In the above process, under UV irradiation, allyltrimethylammonium chloride copolymerizes with [2-(methacryloyloxy)ethyl]trimethylammonium chloride to form a cationic network, while simultaneously forming a polyionic complex hydrogel with poly(2-acrylamide-2-methylpropanesulfonic acid) chains through electrostatic interactions. 3+Further with -SO3 - Coordination strengthens the network layer and may lead to physical entanglement or secondary interactions with the underlying layer through interfacial penetration, enhancing network stability and forming a physically cross-linked polyionic complex hydrogel. To obtain a uniform and stable hydrogel dispersion, the blocky gel is chopped, depolymerized under high ionic strength, and then ultrasonically dispersed.

[0019] Furthermore, the preparation method of the poly(2-acrylamide-2-methylpropanesulfonic acid) includes the following steps: Prepare a 20.7 w / v% aqueous solution of 2-acrylamide-2-methylpropanesulfonic acid, add 0.5% by mass of the photoinitiator Irgacure 2959, deoxygenate by purging with nitrogen, and irradiate under 365 nm ultraviolet light for 2-4 h. The product is precipitated with ethanol, filtered, washed three times with ethanol, and vacuum dried at 45-55 °C to constant weight to obtain poly(2-acrylamide-2-methylpropanesulfonic acid).

[0020] The modified PTFE microporous filter membrane was prepared using the method for preparing the conductive polymer material.

[0021] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are: 1. The modified PTFE microporous filter membrane prepared by this invention exhibits high hydrophilicity and long-lasting stability. This invention utilizes oxygen plasma treatment to efficiently introduce oxygen-containing active groups onto the surface of inert PTFE, providing reliable reaction sites for subsequent chemical grafting. 3-Aminopropyltrimethoxysilane is used as the key bridging molecule; the silanol generated from its hydrolysis covalently binds to the active sites on the PTFE surface, forming a robust silane layer that prevents coating detachment. The primary amino groups at the ends of the silane layer covalently bridge with the upper PVA hydrogel network via a Schiff base reaction with glutaraldehyde, constructing an integrated and stable structure. This results in a low coating detachment rate under long-term hydraulic scouring, achieving durable hydrophilic functionality.

[0022] 2. The modified PTFE microporous filter membrane prepared by this invention exhibits high flux and antifouling performance. By optimizing the PVA concentration and crosslinking degree, a continuous, uniform, and extremely thin hydrophilic network is formed on the PTFE surface. This provides initial hydrophilicity and, more importantly, acts as an anti-clogging layer, effectively preventing the outer polyelectrolyte complex from penetrating and clogging the microporous structure of PTFE, thus maintaining high-purity water flux while achieving superhydrophilicity. Glutaraldehyde, as a bifunctional crosslinking agent, forms imine bonds with the -NH2 of the silane layer for interlayer linkage and forms acetal bonds with the -OH of PVA (intralayer crosslinking), constructing a stable three-dimensional hydrogel network with high mechanical strength and controllable swelling, laying the foundation for the functional top layer. Top-layer functionalization is achieved by constructing a polyionic complex hydrogel with physical-chemical dual crosslinking: firstly, anionic poly(2-acrylamide-2-methylpropanesulfonic acid) and a cationic quaternary ammonium salt copolymer network generated by in-situ photopolymerization form a stable polyionic complex through electrostatic interaction; subsequently, Fe... 3+ With the -SO3 on the poly(2-acrylamido-2-methylpropanesulfonic acid) chain - Strong coordination crosslinking of the functional groups further strengthens the network and endows it with excellent salt resistance. The strong hydrophilic hydration layer and steric hindrance effectively resist the adsorption of organic pollutants such as proteins.

[0023] 3. This invention provides high reactivity and charge density through allyltrimethylammonium chloride, and chain flexibility and film uniformity through [2-(methacryloyloxy)ethyl]trimethylammonium chloride. The complementary structures effectively balance functional density and permeability, avoiding the brittleness, swelling or flux decay problems that are prone to occur in traditional single quaternary ammonium salt modification.

[0024] 4. The modified PTFE microporous filter membrane prepared by this invention exhibits excellent stability in salt ion environments; the Fe introduced in this invention... 3+ Coordination crosslinking is a non-electrostatic, robust physical crosslinking method that remains stable even under high ionic strength, effectively maintaining the structure of the hydrogel network. This solves the industry problem of the drastic performance degradation of traditional hydrophilic modified membranes in salt-containing systems. This invention, through a gradient design involving plasma activation, silane bridging, and hydrogel composites, successfully constructs a composite functional layer on the surface of a PTFE microporous membrane that possesses strong interfacial bonding, superhydrophilicity, high permeability, long-lasting antifouling properties, and excellent salt resistance. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a line graph showing the water contact angle of the modified PTFE microporous filter membrane of the present invention; Figure 2 This is a bar chart showing the pure water flux of the modified PTFE microporous filter membrane of the present invention; Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Example 1

[0028] This embodiment discloses a method for preparing a PVA solution, including the following steps: PVA was dissolved in a DMSO-water mixture with a volume ratio of 1:3 and stirred vigorously at 90-100℃ for 3-5 hours to obtain a 0.45wt% PVA solution. Example 2

[0029] This embodiment discloses a method for preparing poly(2-acrylamide-2-methylpropanesulfonic acid), including the following steps: Prepare a 20.7 w / v% aqueous solution of 2-acrylamide-2-methylpropanesulfonic acid, add 0.5% by mass of the photoinitiator Irgacure 2959, deoxygenate by purging with nitrogen, and irradiate under 365 nm ultraviolet light for 2-4 h. The product is precipitated with ethanol, filtered, washed three times with ethanol, and vacuum dried at 45-55 °C to constant weight to obtain poly(2-acrylamide-2-methylpropanesulfonic acid). Example 3

[0030] This embodiment discloses a method for preparing a polyionic composite hydrogel dispersion, including the following steps: S1: The poly(2-acrylamide-2-methylpropanesulfonic acid), quaternary ammonium salt monomer mixture, photoinitiator, and NaCl prepared in Example 2 were dissolved in deionized water, and the pH was adjusted to 6.5-7.0 with NaOH solution. In the resulting solution, the concentration of poly(2-acrylamide-2-methylpropanesulfonic acid) was 1.5 w / v, the total concentration of quaternary ammonium salt monomer was 0.7 w / v, and the concentration of NaCl was 2.9 w / v. After stirring at 60-70℃ for 20-30 min, the solution was cooled to room temperature and irradiated under 365nm ultraviolet light for 11-13 h to form a hydrogel.

[0031] The quaternary ammonium salt monomer mixture was obtained by mixing allyltrimethylammonium chloride and [2-(methacryloyloxy)ethyl]trimethylammonium chloride at a mass ratio of 1:9.

[0032] The photoinitiator was Irgacure 2959, accounting for 0.5% of the total mass of the quaternary ammonium salt monomer mixture.

[0033] S2: Cut the hydrogel into small pieces and soak them in deionized water for 2 days (changing the water 3 times a day) for purification. After taking them out, add 4 mol / L NaCl solution at a ratio of 1:20 g / mL of wet weight of purified hydrogel to solution volume. Swell at 65-75℃ for 3 hours, then stir vigorously at 85-95℃ for 2.5-4.5 hours. Then further dilute with 4 mol / L NaCl solution and sonicate for 40-60 minutes to obtain a 0.6 w / v% polyionomer hydrogel dispersion.

[0034] The ammonium salt monomer mixture is allyltrimethylammonium chloride and [2-(methacryloyloxy)ethyl]trimethylammonium chloride in a mass ratio of 1:9. Example 4

[0035] This embodiment discloses a method for preparing a modified PTFE microporous filter membrane, including the following steps: Step (1) Take a PTFE microporous membrane with a pore size of 0.22 μm and a thickness of 120 μm, cut it into 5 cm × 5 cm sheets, wash it four times each with anhydrous ethanol and deionized water, and vacuum dry it at 40 °C for 2 h; then place it in an RF plasma treatment machine in an oxygen atmosphere with a power density of 0.51 W / cm². 2 After 30 minutes of treatment, a surface-activated PTFE microporous membrane was obtained. Step (2) At room temperature, 3-aminopropyltrimethoxysilane was dissolved in a 95:5 volume ratio of ethanol to water to prepare a 1.5 mg / mL silane solution; the surface-activated PTFE microporous membrane was immersed in the solution at a bath ratio of 1 g: 50 mL and reacted in the dark for 5 h; after removal, it was rinsed 3 times with anhydrous ethanol and dried under vacuum at 40 °C for 4 h to obtain a silane-modified PTFE membrane.

[0036] Step (3) After fully wetting the silane-modified PTFE membrane with anhydrous ethanol, immerse it in the 0.45wt% PVA solution prepared in Example 1 at a bath ratio of 1g:40mL and soak it at room temperature for 3h; after taking it out, transfer it to the crosslinking aqueous solution at the same bath ratio and react at room temperature for 12h; after the reaction is completed, place the membrane in deionized water and change the water every 5h for a total of 5 times to obtain a PVA hydrogel-coated microporous membrane; The cross-linked aqueous solution contains 0.125 g / mL glutaraldehyde and 0.02 g / mL tartaric acid.

[0037] Step (4) After fully wetting the PVA hydrogel-coated microporous membrane with deionized water, immerse it in the 0.6 w / v% polyionotropic complex hydrogel dispersion prepared in Example 3 at a bath ratio of 1 g: 30 mL and soak it at room temperature for 3 h; then transfer it to a 1.21 w / v% Fe(NO3)3·9H2O aqueous solution and crosslink it at room temperature for 7 h; after taking it out, rinse it with deionized water until it is colorless and transparent to obtain the modified PTFE microporous filter membrane. Example 5

[0038] This embodiment is basically the same as embodiment 4, except that: In step (3), the concentration of the PVA solution is 0.3 wt%; In step (4), the polyionic composite dispersion was soaked for 2 hours, and Fe 3+ The cross-linking time was 6 hours, and all other conditions remained unchanged. Example 6

[0039] This embodiment is basically the same as embodiment 4, except that: In step (2), the concentration of the silane solution is 2 mg / mL, and the grafting time is 6 h; The cross-linking reaction time in step (3) is 14 hours; Fe in step (4) 3+ The crosslinking solution concentration was 1.3 w / v, and all other conditions remained unchanged. Example 7

[0040] This embodiment is basically the same as embodiment 4, except that: The PVA solution was prepared with pure water at a concentration of 0.45 wt% and stirred at 95°C for 5 hours; the NaCl concentration in the polyionic composite dispersion was 2.9 w / v%, and the rest was the same as in Example 4.

[0041] Comparative Example 1 This comparative example omits step (1) plasma treatment, and the remaining steps are the same as in Example 4; that is, the original PTFE membrane is directly grafted with silane; subsequent steps (3)-(4) remain unchanged.

[0042] Comparative Example 2 This comparative example omits step (4) of the polyionopolymer layer and Fe. 3+ Crosslinking, the remaining steps are the same as in Example 4; That is, after obtaining the PVA hydrogel coating film in step (3), it is directly rinsed and dried, without further polyelectrolyte composite and Fe... 3+ Crosslinking.

[0043] Comparative Example 3 In this comparative example, glutaraldehyde in step (3) is replaced with an equal mass of deionized water (i.e., no crosslinking agent), and the rest is the same as in Example 4; that is, PVA is only physically adsorbed on the silane layer, without covalent bridging and the formation of a three-dimensional network.

[0044] Comparative Example 4 This comparative example omits the entire step (3) of constructing the PVA hydrogel coating; the remaining steps are the same as in Example 4. That is, after obtaining the silane-modified PTFE membrane in step (2), it is directly wetted with deionized water; The modified membrane was immersed in a 0.6 w / v% polyionic composite hydrogel dispersion at a bath ratio of 1 g: 30 mL and soaked at room temperature for 3 h; then transferred to a 1.21 w / v% Fe(NO3)3·9H2O solution for crosslinking for 7 h, rinsed and dried to obtain the modified membrane.

[0045] Test methods and test results: The static sessile drop method was used, and the contact angle was measured using a contact angle meter. Using a dead-end filtration device, the test pressure is 1.0 bar (nitrogen pressurization), and the test temperature is 25±1℃. First, the membrane is pre-pressurized at 1.0 bar for 30 minutes to compact it. The permeate is collected for 30 minutes, weighed, and converted into flux to test the pure water flux. Anti-protein contamination performance: Flux recovery test after bovine serum albumin (BSA) contamination; Contamination solution: 1.0 g / L bovine serum albumin (BSA, dissolved in 10 mM PBS buffer, pH 7.4). Salt tolerance test: Salt solution: 3.5wt% NaCl aqueous solution; Test conditions: 1.0 bar, 25℃, dead-end mode.

[0046] Coating stability (coating peeling rate) test: The constant-weight membrane was immersed in 100 mL of deionized water and shaken in a shaker (100 rpm) for 24 h; the membrane was then removed and vacuum dried at 40 °C to constant weight, obtaining the dry weight. Simultaneously, the immersion solution was filtered through a 0.22 μm filter membrane, and the filtrate was collected. The total organic carbon (TOC) content in the filtrate was determined using a total organic carbon (TOC) analyzer and converted into the mass of peeled polymer. Finally, the coating peeling rate was calculated. The test results are shown in Table 1: Table 1

[0047] Based on the performance data comparison of Examples 4-7 and Comparative Examples 1-4 in Table 1, the modified PTFE microporous filter membrane prepared by the present invention has excellent comprehensive performance, specifically manifested as high flux, superhydrophilicity, strong antifouling, high salt resistance and excellent coating stability.

[0048] A comparison of Comparative Example 1 and Examples 4-7 shows that the surface of the untreated PTFE membrane is extremely hydrophobic, making it impossible to effectively graft silane and subsequent coatings. Its pure water flux is extremely low, its antifouling and salt resistance are almost completely lost, and the coating peeling rate is high. This demonstrates that oxygen plasma treatment is a necessary prerequisite for constructing robust, high-performance composite coatings. It lays the foundation for all subsequent chemical bonding steps by introducing active sites onto the inert PTFE surface.

[0049] A comparison of Comparative Example 2 and Example 4 shows that the membrane lacking the top polyionic composite hydrogel layer, while exhibiting acceptable hydrophilicity and high flux, suffers from significantly reduced antifouling and salt resistance. This indicates that the membrane, composed of poly(2-acrylamide-2-methylpropanesulfonic acid), quaternary ammonium salt copolymer network, and Fe... 3+ The top layer, composed of coordination crosslinks, is the core structure that endows the membrane with long-term antifouling and salt resistance. The PVA bottom layer mainly provides hydrophilicity and bridging, while the top layer is responsible for achieving specific separation and stabilization functions.

[0050] The comparison between Comparative Example 3 and Example 4 shows that without the use of glutaraldehyde crosslinking agent, PVA is only physically adsorbed onto the silane layer and cannot form a stable three-dimensional network. This results in poor coating adhesion and a significant reduction in its anti-fouling and salt resistance properties.

[0051] The comparison between Comparative Example 4 and Example 4 shows that without the PVA hydrogel interlayer, directly loading the polyionic composite onto silanized PTFE resulted in a comprehensive degradation of membrane performance and severe coating peeling. This reveals the dual crucial role of the PVA layer as a flexible buffer layer and a homogenization platform: it covalently bridges the hydrophobic PTFE substrate with the hydrophilic functional top layer, greatly enhancing interlayer adhesion; and its uniform solution characteristics prevent the outer particle dispersion from directly clogging the PTFE membrane pores, thus ensuring high throughput while achieving functionalization.

[0052] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

[0053] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to specific implementations. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for preparing a modified PTFE microporous filter membrane, characterized in that, Includes the following steps: Step (1) The PTFE microporous membrane is cleaned, dried, and then subjected to plasma treatment to obtain a surface-activated PTFE microporous membrane; Step (2) At room temperature, 3-aminopropyltrimethoxysilane is dissolved in an aqueous ethanol solution to obtain a silane solution of 1-2 mg / mL; the surface-activated PTFE microporous membrane is immersed in the silane solution, taken out and rinsed with ethanol, and then vacuum dried to obtain a silane-modified PTFE membrane. Step (3) After the silane-modified PTFE membrane is fully wetted with anhydrous ethanol, it is immersed in PVA solution at room temperature, then taken out and transferred to crosslinking aqueous solution for reaction at room temperature. After the reaction is completed, the membrane is rinsed with deionized water to obtain PVA hydrogel-coated microporous membrane. Step (4) The PVA hydrogel-coated microporous membrane, fully wetted with deionized water, is immersed in the polyionomer hydrogel dispersion at a bath ratio of 1:30 g / mL and soaked at room temperature. Then, it is transferred to Fe... 3+ After reacting at room temperature in a crosslinking solution, the membrane is rinsed to obtain a modified PTFE microporous filter membrane.

2. The method for preparing the modified PTFE microporous filter membrane according to claim 1, characterized in that, In step (1), the cleaning method is as follows: wash with anhydrous ethanol and deionized water 3-5 times in sequence; the drying temperature is 35-45℃; the plasma treatment method is as follows: at a power density of 0.51W / cm². 2 Radiofrequency oxygen plasma treatment was performed for 25-35 minutes.

3. The method for preparing the modified PTFE microporous filter membrane according to claim 1, characterized in that, In step (2), the volume ratio of ethanol to water in the ethanol-water solution is 95:5; the immersion conditions are: immersion bath ratio of 1:50 g / mL and immersion time of 4-6 h; the vacuum drying method is: vacuum drying at 35-45℃ for 3-5 h.

4. The method for preparing the modified PTFE microporous filter membrane according to claim 1, characterized in that, In step (3), the immersion conditions are as follows: the immersion bath ratio is 1:40 g / mL, the immersion time is 2-4 h, the room temperature reaction time is 10-14 h, the soaking and rinsing method is: the membrane is soaked and rinsed with deionized water, and the water is changed every 4-6 hours, for a total of 4-6 times; the crosslinking aqueous solution is an aqueous solution containing 0.125 g / mL glutaraldehyde and 0.02 g / mL tartaric acid.

5. The method for preparing the modified PTFE microporous filter membrane according to claim 1, characterized in that, In step (4), the immersion bath ratio is 1:30 g / mL; the immersion time at room temperature is 2-4 hours; Fe 3+ The crosslinking solution is an aqueous solution of 1.1-1.3 w / v% Fe(NO3)3·9H2O; the reaction time is 6-8 h at room temperature; rinsing method: rinse thoroughly with deionized water.

6. The method for preparing the modified PTFE microporous filter membrane according to claim 1, characterized in that, In step (3), the method for preparing the PVA solution includes the following steps: PVA was dissolved in a DMSO-water mixture with a volume ratio of 1:3 and stirred vigorously at 90-100℃ for 3-5 hours to obtain a 0.3-0.6 wt% PVA solution.

7. The method for preparing the modified PTFE microporous filter membrane according to claim 1, characterized in that, In step (4), the preparation method of the polyionic complex hydrogel dispersion includes the following steps: S1: Dissolve poly(2-acrylamide-2-methylpropanesulfonic acid), a mixture of quaternary ammonium salt monomers, a photoinitiator, and NaCl in deionized water, adjust the pH to 6.5-7.0 with NaOH solution to obtain a mixed solution, stir and cool to room temperature, and irradiate with ultraviolet light to form a hydrogel; S2: Cut the hydrogel into small pieces, soak them in deionized water for purification, remove them and add NaCl solution to swell them, then stir vigorously, then further dilute with NaCl solution and sonicate to obtain a 0.6 w / v% polyionic complex hydrogel dispersion.

8. The method for preparing the modified PTFE microporous filter membrane according to claim 7, characterized in that, In step S1, the quaternary ammonium salt monomer mixture is allyltrimethylammonium chloride and [2-(methacryloyloxy)ethyl]trimethylammonium chloride in a mass ratio of 1:9; the photoinitiator is Irgacure. 2959, accounting for 0.5% of the total mass of the quaternary ammonium salt monomer mixture; in the mixed solution, the concentration of poly(2-acrylamide-2-methylpropanesulfonic acid) is 1.5 w / v, the total concentration of quaternary ammonium salt monomer is 0.7 w / v, and the concentration of NaCl is 2.9 w / v; stirring conditions: stirring temperature is 60-70℃, stirring time is 20-30 min; ultraviolet irradiation method: irradiation under 365nm ultraviolet light for 11-13 h; in step S2, the soaking method in deionized water is: soaking for 2 days, changing the water 3 times a day; the NaCl solution concentration is 4 mol / L; the amount of NaCl solution added is based on the ratio of the wet weight of the purified hydrogel to the volume of the solution of 1:20 g / mL; swelling method: swelling at 65-75℃ for 3 h; vigorous stirring method: vigorous stirring at 85-95℃ for 2.5-4.5 h; ultrasonic treatment time is 40-60 min.

9. The method for preparing the modified PTFE microporous filter membrane according to claim 7, characterized in that, The preparation method of the poly(2-acrylamide-2-methylpropanesulfonic acid) includes the following steps: Prepare a 20.7 w / v% aqueous solution of 2-acrylamide-2-methylpropanesulfonic acid, add 0.5% by mass of the photoinitiator Irgacure 2959, deoxygenate by purging with nitrogen, and irradiate under 365 nm ultraviolet light for 2-4 h. The product is precipitated with ethanol, filtered, washed three times with ethanol, and vacuum dried at 45-55 °C to constant weight to obtain poly(2-acrylamide-2-methylpropanesulfonic acid).

10. A modified PTFE microporous filter membrane prepared by the method according to any one of claims 1-9.

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