Dual hydrogel surface modified polytetrafluoroethylene (PTFE) hydrophilic anti-fouling hollow fiber membrane with zwitter-ion brush and preparation method of hydrophilic anti-fouling hollow fiber membrane

Abstract

The invention provides a double hydrogel surface modified PTFE hydrophilic anti-fouling hollow fiber membrane with a zwitter-ion brush and a preparation method of the hydrophilic anti-fouling hollow fiber membrane. The hydrophilic and anti-fouling properties of the PTFE hollow fiber membrane can be remarkably improved. The preparation method comprises the following steps: step 1, putting pretreated PTFE membrane filaments into a PVA (Polyvinyl Alcohol) solution for dipping; step 2, dipping in a glutaraldehyde / citric acid solution; step 3, balancing in water; step 4, dipping in a PIC hydrogel solution; step 5, dipping in the iron ion-containing solution again; and step 6, balancing in water. According to the modification method disclosed by the invention, the water flux of the PTFE hollow fiber membrane can be remarkably improved, and the modified dual-hydrophilic polymer has high stain resistance.

Description

Technical Field

[0001] The invention relates to the technical field of PTFE hollow fiber membrane modification, and in particular to a double hydrogel surface-modified polytetrafluoroethylene (PTFE) hydrophilic antifouling hollow fiber membrane with a zwitterionic brush and a preparation method thereof. Background Art

[0002] Membrane separation technology is increasingly widely used in separation and purification processes due to its advantages of high separation efficiency, low energy consumption, good economic and environmental benefits, low investment cost, and continuous use. In recent years, perfluoropolymers represented by polytetrafluoroethylene (PTFE) have attracted the attention of many researchers with their unique comprehensive properties. In particular, due to the large electronegativity and low polarizability of fluorine atoms, it has a small van der Waals radius and a strong CF bond, which makes PTFE have ultra-high toughness, chemical inertness and hydrophobicity. These excellent properties make PTFE very suitable for various harsh application scenarios. However, the practical application of PTFE membranes is limited by two major problems: wettability and fouling resistance. The strong hydrophobicity of the membrane will cause pollution problems in water treatment, and pollution will reduce the separation efficiency and the performance of the membrane, thereby increasing the operating cost and even causing failures. Therefore, the development of a hollow fiber membrane with both high hydrophilicity and high fouling resistance has broad application prospects.

[0003] The hydrophilic modification methods of PTFE hollow fiber membranes reported so far mainly include chemical modification, plasma treatment, high-energy radiation grafting, atomic layer deposition (ALD), surface coating, etc. Zhou et al. [Zhou Qingying, Liu Sihua, She Jingguo, et al. In-situ aeration-assisted polydopamine / polyethyleneimine copolymerization and deposition for rapid and uniform membrane modification [J]. Journal of Membrane Science, 2022, 657, 120662] designed a new in-situ aeration-assisted polydopamine / polyethyleneimine copolymerization deposition method. Aeration provides a good hydrophilic modification environment for hollow fiber membranes, and the performance of polydopamine / polyethyleneimine coatings can be simply controlled by adjusting polymerization and deposition parameters. The fiber membrane modified by this method has good hydrophilicity, but the cost of the modified raw materials is high, and the stability of polydopamine is poor. It is easy to oxidize and denature during surface treatment, which reduces the acid and alkali resistance of the fiber membrane. Wang Qingyu et al. [Wang Qingyu, Xu Mei, Zeng Fanfu, Xu Baiyu, Qian Cheng. A PTFE membrane for highly polluted wastewater treatment and preparation method [P]. CN114471169A, 2022-05-13.] A polymer containing carboxyl or hydroxyl groups is used to modify the surface of the hollow fiber membrane, and the filter membrane filaments are formed into an external pressure membrane assembly and then a hydrophilic polymer modified solution is passed through the pressurized circulation, and the external pressure membrane assembly and the mixed solution are activated together to prepare a hydrophilic polymer membrane material. This method is simple to operate, but the water flux of the modified fiber membrane is low, and the single hydrophilic modification has poor stain resistance. Therefore, the hydrophilic modified PTFE hollow fiber membrane reported so far is difficult to achieve high water flux and good stain resistance in practical applications. Summary of the invention

[0004] One of the purposes of the present invention is to provide a method for preparing a hydrophilic antifouling hollow fiber membrane of polytetrafluoroethylene (PTFE) modified by double hydrogel surface with zwitterionic brushes. The obtained fiber membrane has excellent antifouling effect compared with a single-layer modified fiber membrane.

[0005] The preparation method comprises the following steps:

[0006] Step 1: After the PTFE hollow fiber membrane substrate is treated with plasma, it is impregnated with a silane solution and dried at room temperature;

[0007] Step 2: Immersing the fiber membrane obtained in step 1 in a PVA solution, wherein the mass fraction of PVA in the PVA solution is 0.2-0.6 wt %;

[0008] Step 3: The fiber membrane obtained in step 2 is taken out and immersed in a mixed solution of glutaraldehyde (GA) and citric acid (CA), wherein the mass concentration of glutaraldehyde in the mixed solution of glutaraldehyde and citric acid is 0.12-0.13 g / ml, and the mass concentration of citric acid is 0.019-0.021 g / ml;

[0009] Step 4: The fiber membrane obtained in step 3 is taken out and balanced in water to obtain a PTFE hollow fiber membrane S-PTFE after the glutaraldehyde cross-linked PVA polymer monolayer is hydrophilically modified;

[0010] Step 5: The S-PTFE obtained in step 4 is taken out and immersed in a polyampholyte hydrogel solution with a mass fraction of 0.003-0.01 wt%, preferably 0.006 wt%;

[0011] Step 6: The fiber membrane obtained in step 5 is taken out and immersed in an iron ion solution having an iron ion concentration of 0.05 to 0.2 mol / L, more preferably 0.1 mol / L;

[0012] Step 7: The fiber membrane obtained in step 6 is taken out and balanced in water to obtain the PTFE hollow fiber membrane D-PTFE after the iron ion cross-linked PVA / PIC polymer double hydrophilic modification.

[0013] As a preferred embodiment, the outer diameter of the PTFE hollow fiber membrane substrate is 2.2 to 2.3 mm, the wall thickness is 0.4 to 0.5 mm, and the average pore size is 0.27 to 0.32 μm.

[0014] As a preferred embodiment, the plasma pretreatment process in step 1 is to place the PTFE hollow fiber membrane in a commercial plasma surface treatment machine for atmospheric pressure plasma treatment for 30 to 40 minutes. After the plasma treatment, the chemical bonds on the surface of the PTFE membrane are activated, and combined with free radicals, a large number of hydrophilic groups hydroxyl groups are introduced into the surface.

[0015] Optionally, in order to obtain a fiber membrane with a cleaner and drier surface, before placing the PTFE hollow fiber membrane in a commercial plasma surface treatment machine for treatment, the following processes may be optionally included: a. washing the PTFE hollow fiber membrane in anhydrous ethanol and then drying it; b. placing the PTFE hollow fiber membrane in an ultraviolet ozone cleaning machine for cleaning.

[0016] As a preferred embodiment, the silane solution in step 1 is a mixed solution of water, ethanol and AEAPTS (N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane); wherein the mass fraction of AEAPTS in the mixed solution is 0.1 to 0.15 wt %; and the volume ratio of ethanol to water is 4:1.

[0017] As a preferred embodiment, the immersion time of the silane treatment is 4 to 5 hours.

[0018] AEAPTS silane is hydrolyzed to generate silanol -Si-OH, which can dehydrate and condense with the hydroxyl groups on the surface of PTFE to form -Si-O- covalent bonds, so that AEAPTS silane is firmly anchored on the surface of PTFE to obtain a PTFE hollow fiber membrane treated with silane.

[0019] As a preferred implementation, before immersing in the PVA solution in step 2, the PTFE hollow fiber membrane treated with silane is firstly soaked in anhydrous ethanol.

[0020] Optionally, the anhydrous ethanol infiltration process is to infiltrate the PTFE hollow fiber membrane treated with silane and dried in anhydrous ethanol for 4 to 5 hours at room temperature. The dry PTFE fiber membrane has low surface tension and strong hydrophobic effect. Infiltrating the fiber membrane with anhydrous ethanol can give the fiber membrane stronger wettability. When impregnating the PVA hydrophilic polymer solution, the hydrophilic polymer can better wet the membrane pores, giving the PTFE hollow fiber membrane a better hydrophilic modification effect.

[0021] As a preferred implementation manner, the mass fraction of PVA in the PVA solution in step 2 is 0.2-0.6wt%.

[0022] As a preferred embodiment, the solvent in the PVA solution in step 2 is a mixed solvent of dimethyl sulfoxide and water in a volume ratio of 3:1.

[0023] As a preferred embodiment, the preparation method of the PVA solution is: dissolving PVA in a mixed solvent of dimethyl sulfoxide and water, stirring at 90 to 95° C. for 2 to 4 hours to obtain the PVA solution.

[0024] As a preferred embodiment, in step 1, the temperature for immersing the PVA solution is room temperature, and the immersion time is 2 to 4 hours.

[0025] The PVA molecular chain modified layer with a higher content has a strong chemical cross-linking effect and is relatively strong and tough. It can maintain large deformation without causing polymer damage, and the large amount of hydroxyl groups in PVA can significantly improve the hydrophilicity. Therefore, the design of the PVA modified layer is typically helpful for the strong surface adhesion between the hydrophilic polymer and the substrate and the high resistance to environmental corrosion damage.

[0026] As a preferred embodiment, in step 3, the immersion temperature of the GA / CA solution is room temperature, and the immersion time is 8 to 13 hours.

[0027] When the fiber membrane immersed in the PVA solution is taken out and immersed in the GA / CA solution, the carbonyl group C=O on one end of GA will react with the amino group -NH2 on the AEAPTS silane to form an imine bond by Schiff base reaction, and at the same time, the carbonyl group C=O on the other end will react with the hydroxyl group on the PVA to form an acetalization reaction, so that the PVA is connected to the AEAPTS silane through GA. In addition, the carbonyl group C=O on the glutaraldehyde GA is a strong polar group. Since the C atom has a strong positive charge, it is easy to react with a nucleophilic reagent. PVA contains a large number of hydrophilic groups, and the O atom on the hydroxyl group has a lone pair of electrons and has a strong nucleophilicity. Under acidic conditions, GA reacts with the membrane surface and the hydroxyl group in PVA to form cross-linking, so that the PVA hydrogel layer is further firmly anchored on the surface of the PTFE membrane, and a PVA single-layer modified PTFE hollow fiber membrane S-PTFE with super hydrophilic properties is obtained.

[0028] As a preferred implementation, in step 4, the water balance time is 20 to 25 hours, and the water is changed every 5 hours.

[0029] As a preferred embodiment, the undried fiber membrane is directly impregnated with the polyampholyte hydrogel solution in step 5. The undried fiber membrane has the best wetting effect, retains the water channel to the greatest extent, and can fully contact the PVA modified layer with the PIC hydrogel when impregnated with the PIC hydrogel solution.

[0030] As a preferred embodiment, the polyampholyte hydrogel solution in step 5 contains PNaSS (poly sodium p-styrene sulfonate), PMPTC (poly N,N,N-trimethyl-3-(2-methylallylamino)-1-propylammonium chloride) and NaCl.

[0031] As a preferred embodiment, the total monomer concentration of the PNaSS and PMPTC is 1.5-1.6 mol / L, and the molar ratio of NaSS (sodium p-styrene sulfonate) and MPTC (N,N,N-trimethyl-3-(2-methylallylamino)-1-propylammonium chloride) units is 1:0.85-0.95.

[0032] As a preferred embodiment, the method for preparing the polyampholyte hydrogel solution comprises the following steps:

[0033] Step a, adding PNaSS, MPTC, initiator, and sodium chloride NaCl into deionized water, stirring and dissolving to obtain a uniform solution;

[0034] Step b, placing the mixed solution obtained in step a in a mold to initiate polymerization of MPTC to obtain an initial hydrogel of an amphoteric electrolyte composite polymer PIC;

[0035] Step c, balancing the PIC initial hydrogel obtained in step b in deionized water to obtain a PIC hydrogel;

[0036] Step d, placing the PIC hydrogel obtained in step c in a 3.5-4.5 mol / L NaCl solution to fully dissolve it, thereby obtaining a PIC hydrogel solution.

[0037] As a preferred embodiment, the concentration of NaCl in the uniform solution obtained in step a above is 0.3-0.5 mol / L.

[0038] As a preferred embodiment, the concentration of the initiator in the uniform solution obtained in the above step a is 0.001-0.002 mol / L.

[0039] As a preferred embodiment, the initiator used in the above step a is KA (α-ketoglutaric acid); and the polymerization initiation method in step b is ultraviolet light initiation.

[0040] The initiator initiated the polymerization of MPTC to produce PMPTC. Due to the presence of NaCl, the two polyelectrolytes could not form coordination, and the initial hydrogel of PIC was mainly formed by entanglement of polymer chains. The isoelectric point ratio of NaSS and MPTC units was 1:0.9. Near this ratio, the coordination effect of the synthesized initial hydrogel after water equilibrium was the best, and the comprehensive mechanical properties of the hydrogel were the best.

[0041] As a preferred embodiment, the conditions for preparing a uniform solution in step a are stirring and dissolving, the stirring temperature is 60 to 70° C., and the stirring time is 25 to 35 minutes.

[0042] As a preferred embodiment, the balancing method in step b is to balance the obtained PIC initial hydrogel in water for 2 to 3 days, and change the water every 12 hours.

[0043] As a preferred embodiment, the PIC hydrogel in step c is shredded before being placed in the NaCl solution to accelerate dissolution.

[0044] As a preferred embodiment, the dissolution conditions in the above step d are 80-90° C., and the solution is stirred and dissolved for 2-3 hours.

[0045] In order to obtain an ion brush layer with both lubricity and strength, S-PTFE was modified with a polyampholyte hydrogel solution. It is difficult for polymers to form a highly entangled structure by blending in a solution. The PNaSS polymer and MPTC monomer are mixed and polymerized to obtain a PIC initial hydrogel with a certain strength. After equilibration in water, it has more entangled structures, so an initial hydrogel with good mechanical properties can be obtained. When it is dissolved in a high-concentration sodium chloride solution, the electrostatic interaction and low entanglement are mainly destroyed, and a more complex entangled structure is retained, so that the PIC hydrogel solution can enter the PVA modified layer by immersion while retaining a certain strength. After entering the PVA modified layer, the hydrophilic groups in the PIC hydrogel can combine with the hydroxyl groups on the PVA modified layer to produce hydrogen bonds, so that the PIC hydrogel is anchored on the PVA modified layer. In this process, the system is in a high concentration of NaCl, which shields the electrostatic interaction. The formation of the PIC hydrogel modified layer still mainly relies on hydrogen bonds. However, as the immersion time increases, the hydrogen bond anchoring positions that the PVA layer can provide decrease, and the modified layer formed by a small amount of PIC hydrogel in the outermost layer is relatively loose, forming the original structure of the ion brush.

[0046] As a preferred embodiment, the iron ion solution in step 6 is ferric nitrate nonahydrate solution.

[0047] Iron ions can form ionic coordination with the negatively charged sulfonate groups on PNaSS in the PIC hydrogel, causing ionic crosslinking of PNaSS in the PIC, which is further fixed on the membrane surface. Since the PIC layer formed in step 5 is not uniform, but has a structure similar to a gradient density, that is, the density close to the PVA layer is higher and the density far from the PVA layer is lower, the crosslinking density formed by iron ions here is also different. PMPTC cannot compete with iron ions in a high concentration of iron ion solution, so it is mainly fixed on the membrane surface by hydrogen bonds and polymer chain entanglement.

[0048] As a preferred embodiment, in step 7, the water balance time is 24 to 30 hours, and the water is changed every 6 hours. During the water balance process, excess and partially weakly coordinated iron ions are removed, strongly coordinated iron ions are retained, and the vacant sulfonate radicals are further coordinated with some of the weakly coordinated iron ions that have not been removed to produce strong ion coordination, and the positively charged groups in PMPTC replace some of the weakly coordinated iron ions and produce ion coordination with the partially vacant sulfonate radicals, and the two act synergistically to further strengthen the PIC modified layer. In the outermost layer of the membrane, the PIC hydrogel layer is relatively sparse, and is still relatively loose after ionic crosslinking. Some polymer segments are anchored in the outermost layer through ionic coordination, hydrogen bonding, chain entanglement, etc., and the unanchored segments form zwitterionic brushes.

[0049] The second object of the present invention is to provide a double hydrogel surface-modified polytetrafluoroethylene (PTFE) hydrophilic antifouling hollow fiber membrane with zwitterionic brushes, which is obtained by the above-mentioned preparation method.

[0050] The present invention further assembles a PIC ion brush layer on the surface of the PVA modified layer, and the PIC hydrogel first generates hydrogen bonds with the PVA modified layer through hydrophilic groups, and then the PIC hydrogel layer is cross-linked by iron ions, and the PIC hydrogel layer is strengthened while being connected to the PVA hydrogel layer, thereby obtaining a PTFE hollow fiber membrane D-PTFE with a zwitterionic brush having super hydrophilicity. When D-PTFE is in a water environment, the PVA / PIC dual hydrophilic polymer can rapidly swell in water and retain a large amount of water, so that the hydrophilicity of the fiber membrane is greatly improved, and its water flux is significantly increased, and the outermost PIC hydrogel layer will gradually disperse to form a zwitterionic brush, giving D-PTFE stronger antifouling performance. The synergistic effects of hydrogen bonds, GA chemical crosslinking, iron ion coordination crosslinking, imine bonds, etc. in the fiber membrane cause a strong interfacial interaction to be generated between the modified hydrogel layer and the PTFE interface, giving D-PTFE stronger chemical stability.

[0051] The invention provides a method for preparing a double hydrogel surface-modified PTFE hydrophilic anti-fouling hollow fiber membrane with zwitterionic brushes. The process is simple and the operation is convenient. The prepared fiber membrane D-PTFE has both high water flux and anti-fouling performance. A large number of hydrophilic groups contained in the PVA / PIC double hydrogel enable the modified layer to retain a large amount of water after swelling after absorbing water, thereby giving the modified fiber membrane a high water flux. The synergistic effects of imine bonds, hydrogen bonds, GA chemical crosslinking, iron ion coordination crosslinking and the like on the modified layer of the fiber membrane enable strong interfacial interactions between the modified hydrogel layers and between the modified hydrogel layer and the PTFE interface, thereby giving the D-PTFE stronger chemical stability. At the same time, the outermost PIC hydrogel layer will further swell and disperse in an aqueous environment to form a zwitterionic brush, and synergistically act with the hydration layer formed by the hydrophilic layer to further improve the anti-fouling performance of the fiber membrane. This will become a common method for preparing hydrophilic and anti-fouling PTFE hollow fiber membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 The following is a schematic diagram of the experimental process and corresponding principles of this application; wherein:

[0053] (a) is a schematic diagram of the preparation process of the dual polymer hydrophilic modified PTFE hollow fiber membrane of the present application embodiment;

[0054] (b) is a schematic diagram of the synthesis reaction mechanism of S-PTFE in the embodiment of the present application;

[0055] (c) is a schematic diagram of the reaction mechanism for preparing D-PTFE from S-PTFE in an embodiment of the present application. DETAILED DESCRIPTION

[0056] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0057] In the following embodiments:

[0058] The PTFE hollow fiber membrane used for hydrophilic modification was purchased from Hairui Membrane Technology Co., Ltd., with an outer diameter of 2.2-2.3 mm, a wall thickness of 0.4-0.5 mm, and an average pore size of 0.27-0.32 μm.

[0059] The plasma pretreatment process is to wash the dried PTFE hollow fiber membrane in anhydrous ethanol and then dry it, then put it into an ultraviolet ozone cleaning machine for cleaning for 15 to 20 minutes, and then put it into a plasma surface treatment machine for normal pressure plasma treatment for 30 to 40 minutes to obtain a plasma pretreated PTFE hollow fiber membrane.

[0060] The silane treatment process is to immerse the plasma pretreated PTFE hollow fiber membrane in a silane solution at room temperature and then dry it at room temperature. The silane solution is a mixed solution of AEAPTS, ethanol and water, wherein the mass fraction of AEAPTS in the mixed solution is 0.1wt%, and the volume ratio of ethanol to water is 4:1.

[0061] The preparation process of PIC hydrogel solution is to add PNaSS, MPTC, initiator and NaCl into deionized water, stir and dissolve the uniform solution, place it in a mold, initiate MPTC polymerization, obtain PIC initial hydrogel, place it in deionized water for equilibrium, obtain PIC hydrogel, and then place the obtained PIC hydrogel in NaCl solution to fully dissolve it to obtain PIC hydrogel solution. The total monomer concentration of PNaSS and MPTC is 1.5 mol / L, the molar ratio of NaSS and MPTC units is 1:0.9, the concentration of NaCl is 0.5 mol / L, the concentration of initiator is 0.0015 mol / L, the initiator is KA, the initiation method is ultraviolet light initiation, the NaCl concentration used to dissolve PIC hydrogel is 4 mol / L, and the dissolution condition is 90℃.

[0062] The experimental process and corresponding principles are as follows Figure 1 shown.

[0063] Example 1

[0064] Step 1: The PTFE hollow fiber membrane treated with silane and dried was fully moistened with anhydrous ethanol and then immersed in a 0.6 wt% PVA solution at room temperature for 3 hours;

[0065] Step 2: The fiber membrane obtained in step 1 is taken out and immersed in a GA / CA cross-linking solution (wherein the mass concentration of GA is 0.13 g / ml and the mass concentration of CA is 0.021 g / ml) at room temperature for 12 hours;

[0066] Step 3: The fiber membrane obtained in step 2 is taken out and placed in deionized water for 24 hours to obtain a PTFE hollow fiber membrane S-PTFE after the GA cross-linked PVA polymer single layer hydrophilic modification;

[0067] Step 4: The S-PTFE hollow fiber membrane obtained in step 3 is taken out and immersed in a PIC hydrogel solution with a mass fraction of 0.006wt% at room temperature for 3 hours;

[0068] Step 5: The fiber membrane obtained in step 4 is taken out and immersed in an aqueous solution with an iron ion concentration of 0.1 mol / L at room temperature for 12 hours;

[0069] Step 6: The fiber membrane obtained in step 5 is taken out and placed in deionized water for 24 hours. After swelling equilibrium, it is dried to obtain the PTFE hollow fiber membrane D-PTFE after the iron ion cross-linked PVA / PIC polymer double hydrophilic modification.

[0070] Example 2

[0071] Step 1: The PTFE hollow fiber membrane treated with silane and dried was fully moistened with anhydrous ethanol and then immersed in a 0.4 wt% PVA solution at room temperature for 3 hours;

[0072] Step 2: The fiber membrane obtained in step 1 is taken out and immersed in a GA / CA cross-linking solution (wherein the mass concentration of GA is 0.125 g / ml and the mass concentration of CA is 0.02 g / ml) at room temperature for 12 hours;

[0073] Step 3: The fiber membrane obtained in step 2 is taken out and placed in deionized water for 24 hours to obtain a PTFE hollow fiber membrane S-PTFE after the GA cross-linked PVA polymer monolayer is hydrophilically modified;

[0074] Step 4: The S-PTFE hollow fiber membrane obtained in step 3 is taken out and immersed in a PIC hydrogel solution with a mass fraction of 0.006 wt % at room temperature for 3 hours;

[0075] Step 5: The fiber membrane obtained in step 4 is taken out and immersed in a cross-linking solution with an iron ion concentration of 0.1 mol / L at room temperature for 12 hours;

[0076] Step 6: The fiber membrane obtained in step 5 is taken out and placed in deionized water for 24 hours. After swelling equilibrium, it is dried to obtain the PTFE hollow fiber membrane D-PTFE after the iron ion cross-linked PVA / PIC polymer double hydrophilic modification.

[0077] Example 3

[0078] Step 1: The PTFE hollow fiber membrane treated with silane and dried was fully moistened with anhydrous ethanol and then immersed in a 0.2 wt% PVA solution at room temperature for 3 hours;

[0079] Step 2: The fiber membrane obtained in step 1 is taken out and immersed in a GA / CA cross-linking solution (wherein the mass concentration of GA is 0.12 g / ml and the mass concentration of CA is 0.019 g / ml) at room temperature for 12 hours;

[0080] Step 3: The fiber membrane obtained in step 2 is taken out and placed in deionized water for 24 hours to obtain a PTFE hollow fiber membrane S-PTFE after the GA cross-linked PVA polymer monolayer is hydrophilically modified;

[0081] Step 4: The S-PTFE hollow fiber membrane obtained in step 3 is taken out and immersed in a PIC hydrogel solution with a mass fraction of 0.006 wt % at room temperature for 3 hours;

[0082] Step 5: The fiber membrane obtained in step 4 is taken out and immersed in a cross-linking solution with an iron ion concentration of 0.1 mol / L at room temperature for 12 hours;

[0083] Step 6: The fiber membrane obtained in step 5 is taken out and placed in deionized water for 24 hours. After swelling equilibrium, it is dried to obtain the PTFE hollow fiber membrane D-PTFE after the iron ion cross-linked PVA / PIC polymer double hydrophilic modification.

[0084] Example 4

[0085] Step 1: The PTFE hollow fiber membrane treated with silane and dried was fully moistened with anhydrous ethanol and then immersed in a 0.6 wt% PVA solution at room temperature for 3 hours;

[0086] Step 2: The fiber membrane obtained in step 1 is taken out and immersed in a GA / CA cross-linking solution (wherein the mass concentration of GA is 0.13 g / ml and the mass concentration of CA is 0.021 g / ml) at room temperature for 12 hours;

[0087] Step 3: The fiber membrane obtained in step 2 is taken out and placed in deionized water for 24 hours to obtain a PTFE hollow fiber membrane S-PTFE after the GA cross-linked PVA polymer monolayer is hydrophilically modified;

[0088] Step 4: The S-PTFE hollow fiber membrane obtained in step 3 is taken out and immersed in a PIC hydrogel solution with a mass fraction of 0.01wt% at room temperature for 3 hours;

[0089] Step 5: The fiber membrane obtained in step 4 is taken out and immersed in a cross-linking solution with an iron ion concentration of 0.2 mol / L at room temperature for 12 hours;

[0090] Step 6: The fiber membrane obtained in step 5 is taken out and placed in deionized water for 24 hours. After swelling equilibrium, it is dried to obtain the PTFE hollow fiber membrane D-PTFE after the iron ion cross-linked PVA / PIC polymer double hydrophilic modification.

[0091] Example 5

[0092] Step 1: The PTFE hollow fiber membrane treated with silane and dried was fully moistened with anhydrous ethanol and then immersed in a 0.6 wt% PVA solution at room temperature for 3 hours;

[0093] Step 2: The fiber membrane obtained in step 1 is taken out and immersed in a GA / CA cross-linking solution (wherein the mass concentration of GA is 0.13 g / ml and the mass concentration of CA is 0.021 g / ml) at room temperature for 12 hours;

[0094] Step 3: The fiber membrane obtained in step 2 is taken out and placed in deionized water for 24 hours to obtain a PTFE hollow fiber membrane S-PTFE after the GA cross-linked PVA polymer monolayer is hydrophilically modified;

[0095] Step 4: The S-PTFE hollow fiber membrane obtained in step 3 is taken out and immersed in a PIC hydrogel solution with a mass fraction of 0.003 wt% at room temperature for 3 hours;

[0096] Step 5: The fiber membrane obtained in step 4 is taken out and immersed in a cross-linking solution with an iron ion concentration of 0.05 mol / L at room temperature for 12 hours;

[0097] Step 6: The fiber membrane obtained in step 5 is taken out and placed in deionized water for 24 hours. After swelling equilibrium, it is dried to obtain the PTFE hollow fiber membrane D-PTFE after the iron ion cross-linked PVA / PIC polymer double hydrophilic modification.

[0098] Comparative Example 1

[0099] Step 1: The PTFE hollow fiber membrane treated with silane and dried was fully moistened with anhydrous ethanol and then immersed in a 0.6 wt% PVA solution at room temperature for 3 hours;

[0100] Step 2: The fiber membrane obtained in step 1 is taken out and immersed in a GA / CA cross-linking solution (wherein the mass concentration of GA is 0.13 g / ml and the mass concentration of CA is 0.021 g / ml) at room temperature for 12 hours;

[0101] Step 3: The fiber membrane obtained in step 2 is taken out and placed in deionized water for 24 hours to obtain a PTFE hollow fiber membrane S-PTFE after the GA cross-linked PVA polymer single layer hydrophilic modification.

[0102] Comparative Example 2

[0103] Step 1: The PTFE hollow fiber membrane treated with silane and dried was fully moistened with anhydrous ethanol and then immersed in a 0.6 wt% PVA solution at room temperature for 3 hours;

[0104] Step 2: The fiber membrane obtained in step 1 is taken out and immersed in a GA / CA cross-linking solution (wherein the mass concentration of GA is 0.13 g / ml and the mass concentration of CA is 0.021 g / ml) at room temperature for 12 hours;

[0105] Step 3: The fiber membrane obtained in step 2 is taken out and placed in deionized water for 24 hours to obtain a PTFE hollow fiber membrane S-PTFE after the GA cross-linked PVA polymer monolayer is hydrophilically modified;

[0106] Step 4: The S-PTFE hollow fiber membrane obtained in step 3 is taken out and immersed in a PIC hydrogel solution with a mass fraction of 0.006 wt % at room temperature for 3 hours;

[0107] Step 5: The fiber membrane obtained in step 4 is taken out and placed in deionized water for 24 hours. After swelling equilibrium, it is dried to obtain a PTFE hollow fiber membrane PTFE / PVA / PIC after metal ion-free cross-linked PVA / PIC polymer dual hydrophilic modification.

[0108] Comparative Example 3

[0109] Step 1: The PTFE hollow fiber membrane treated with silane and dried was fully moistened with anhydrous ethanol and then immersed in a PIC solution with a mass fraction of 0.4 wt% at room temperature for 3 hours;

[0110] Step 2: The fiber membrane obtained in step 1 is taken out and immersed in a cross-linking solution with an iron ion concentration of 0.1 mol / L at room temperature for 12 hours;

[0111] Step 3: The fiber membrane obtained in step 2 is taken out and placed in deionized water for 24 hours to obtain a PTFE hollow fiber membrane PTFE / PIC after the iron ion cross-linked PIC polymer single layer is hydrophilically modified.

[0112] Pollution resistance test:

[0113] Step 1: Cut the hydrophilically modified and dried PTFE hollow fiber membrane into samples with a length of 11 cm and test the outer diameter D of the fiber membrane.

[0114] Step 2: Seal one end of the sample obtained in step 1 and fix the other end on a homemade water flux tester, so that the effective length in the middle is 10 cm, and ensure good air tightness between the sample and the tester.

[0115] Step 3: Immerse the sample fixed in step 2 completely in a water tank filled with deionized water and test it at 25°C. Adjust the test pressure of the water flux tester to stabilize at 0.06MPa. Start timing after the solution is stably drawn out through the fiber membrane. Pre-press for 30 minutes and then adjust the flux to 600L·m -2 ·h -1 , record the initial pressure after the flux stabilizes, and record the solution volume V every 2 minutes w1 , test for 10 minutes.

[0116] Step 4: Replace the deionized water in the water tank in step 3 with 0.5 g / L bovine serum albumin solution, keep the pressure unchanged, and test at 25°C. Start timing after the solution is stably drawn out through the fiber membrane, and record the solution volume V every 2 minutes. p , test for 30 minutes.

[0117] Step 5: Remove the fiber membrane after the test in step 4, backwash it with deionized water for 5 minutes, then replace the bovine serum albumin solution in the water tank in step 4 with deionized water, keep the pressure unchanged, and test it at 25°C. Start timing after the solution is stably drawn out through the fiber membrane, and record the solution volume V every 2 minutes. w2 , test for 10 minutes.

[0118] Step 6: Calculate the water flux J of the fiber membrane by the ratio of the volume of deionized water extracted to the product of the test time and the test membrane area. The calculation formula is as follows:

[0119]

[0120] Where J is the flux of a single fiber membrane during the test, in units of L·m -2 ·h -1 The results obtained from the data of steps 3, 4, and 5 are the initial flux of deionized water J w1 , bovine serum albumin solution flux J p , deionized water recovery flux J w2 ; V is the volume of the solution extracted, in L, and the results obtained from the data in steps 3, 4, and 5 are the initial volume of deionized water V w1 , volume of bovine serum albumin solution V p , deionized water recovery volume V w2 ; △T is the test time, in h; S is the membrane area, in m 2 ; D is the outer diameter of the fiber membrane, in m.

[0121] Step 7: Use the J calculated in step 6 w1 With J w2 The flux recovery rate FRR of the membrane before and after the bovine serum albumin solution test was calculated by the ratio of the following formula:

[0122]

[0123] Use the J calculated in step 6 w2 and J p The difference between w1 The reversible fouling ratio R of the membrane before and after the test in bovine serum albumin solution was calculated by the ratio of r , the calculation formula is as follows:

[0124]

[0125] Use the J calculated in step 6 w1 and J w2 The difference between w1 The irreversible fouling ratio R of the membrane before and after the test in bovine serum albumin solution was calculated by the ratio of ir , the calculation formula is as follows:

[0126]

[0127] The water flux and antifouling performance of the hydrophilic modified PTFE hollow fiber membranes obtained in the above examples and comparative examples are shown in Table 1 below:

[0128] Table 1: Water flux and antifouling performance of hydrophilic modified PTFE hollow fiber membrane

[0129]

[0130] Examples 1 to 3 are iron ion cross-linked PVA / PIC polymer dual hydrophilic modified PTFE hollow fiber membrane D-PTFE prepared by changing the mass fraction of PVA when the iron ion concentration is 0.1 mol / L and the mass fraction of PIC hydrogel is 0.006wt%. Examples 4 to 5 are iron ion cross-linked PVA / PIC polymer dual hydrophilic modified PTFE hollow fiber membrane D-PTFE prepared by changing the mass fraction of PIC hydrogel when the mass fraction of PVA is 0.6wt%. Comparative Example 1 is a PTFE hollow fiber membrane S-PTFE after hydrophilic modification of a single layer of PVA polymer prepared using only PVA with a mass fraction of 0.6wt%. Comparative Example 2 is a PTFE hollow fiber membrane PTFE / PVA / PIC after metal ion cross-linked PVA / PIC dual hydrophilic modified prepared by using a metal ion-free cross-linking solution with a mass fraction of PVA of 0.6wt% and a mass fraction of PIC of 0.006wt%. Comparative Example 3 is a PTFE hollow fiber membrane PTFE / PIC obtained by hydrophilically modifying a PIC single hydrogel by crosslinking with iron ions while using only PIC with a mass fraction of 0.4 wt%.

[0131] According to the data in Table 1:

[0132] It can be seen from Examples 1 to 5 and Comparative Example 1 that the bovine serum albumin solution flux of D-PTFE (151.13 to 213.81 L·m -2 ·h -1 ), recovery water flux (405.54~477.40L·m -2 ·h -1 ), flux recovery rate (68.28% to 81.03%), reversible scaling ratio (38.59% to 49.09%), and irreversible scaling ratio (18.89% to 31.72%) were significantly better than the bovine serum protein solution flux (146.71 L·m -2 ·h -1 ), recovery water flux (308.09L·m -2 ·h -1), flux recovery rate (51.29%), reversible scaling ratio (26.91%), and irreversible scaling ratio (48.71%). This is because the PIC hydrogel layer forms polyampholyte ion brushes on the surface of the PTFE membrane, which can block pollutants and reduce the pollution of the membrane itself. When the PVA mass fraction is 0.2wt% to 0.6wt%, the membrane pores can be modified more comprehensively, the hydrophilicity of the fiber membrane can be greatly improved, and the cross-linking of GA enhances the strength of the PVA modified layer, so that the membrane can retain a larger pore size after swelling with water, so that the S-PTFE fiber membrane has a higher initial water flux; at the same time, when the PIC mass fraction is 0.003wt% to 0.01wt%, a thin and loose PIC hydrogel layer can be constructed on the PVA hydrogel layer through hydrogen bond anchoring. The outermost PIC hydrogel will disperse after swelling with water to form a polyampholyte ion brush. When pressurized, the ion brush keeps swinging, so that the fiber membrane can resist the contamination of bovine serum albumin and reduce the degree of contamination of the fiber membrane during the bovine serum albumin solution testing process.

[0133] It can be seen from Examples 1 to 5 and Comparative Example 2 that the bovine serum albumin solution flux of D-PTFE (151.13 to 213.81 L·m -2 ·h -1 ), recovery water flux (405.54~477.40L·m -2 ·h -1 ), flux recovery rate (68.28% ~ 81.03%), reversible scaling ratio (38.59% ~ 49.09%), and irreversible scaling ratio (18.89% ~ 31.72%) are significantly better than those of the bovine serum protein solution flux (83.86 L·m -2 ·h -1 ), recovery water flux (168.61L·m -2 ·h -1), flux recovery rate (29.51%), reversible scaling ratio (14.86%), and irreversible scaling ratio (70.49%). This is because the iron ions produce ionic crosslinking in the PIC hydrogel layer, which strengthens the PIC hydrogel layer and enables the hydrogel layer to maintain a larger pore size after absorbing water and swelling. Iron ions can produce coordinated ion crosslinking of PNaSS in PIC hydrogel, thereby making the loose PIC hydrogel layer dense and further strengthening the hydrogel layer, so that the D-PTFE modified by the double hydrogel can still maintain a relatively large pore size after absorbing water and swelling, so that the D-PTFE has a higher initial water flux; at the same time, due to the different coordination degrees produced by iron ions, the crosslinking effects produced are also different. The outermost hydrogel layer of the modified layer is the sparsest, and the crosslinking effect produced is relatively weak. The polymer chains are not completely fixed and will disperse after swelling in water to form a relatively stable polyampholyte ion brush. If the PIC hydrogel layer is not crosslinked by iron ions and is only fixed by weak hydrogen bonds, the polyampholyte ion brush structure on the surface of the modified layer will be destroyed during the flux test, which will significantly reduce the anti-fouling ability of the fiber membrane.

[0134] From Examples 1 to 5 and Comparative Example 3, it can be seen that the bovine serum albumin solution flux (181.14 L·m -2 ·h -1 ), recovery water flux (401.12L·m -2 ·h -1 ), flux recovery rate (68.79%), reversible scaling ratio (37.71%), irreversible scaling ratio (32.21%) and D-PTFE bovine serum albumin solution flux (151.13~213.81L·m -2 ·h -1 ), recovery water flux (405.54~477.40L·m -2 ·h -1), flux recovery rate (68.28%~81.03%), reversible scaling ratio (38.59%~49.09%), and irreversible scaling ratio (18.89%~31.72%) are similar, but the initial pressure required for PTFE / PIC (0.055MPa) is much higher than the initial pressure of D-PTFE (0.02~0.025MPa). This is because when the PIC content is high, a thick and continuous PIC hydrogel layer will be formed on the surface of the substrate to improve the hydrophilicity of the fiber membrane. After the iron ion cross-linking, the body strength of the PIC hydrogel modified layer is greatly increased, making it stably fixed on the membrane surface, which also causes it to deform as a whole after drying. The PTFE hollow fiber membrane substrate also has good body strength, but its deformation before and after drying is smaller. The different deformation degrees of the PIC hydrogel layer and the PTFE substrate cause the interface connection between the two to be partially separated. Therefore, the membrane pores of the dried fiber membrane cannot be completely wetted, and a greater pressure is required to allow water to pass through the membrane pores. After the PTFE fiber membrane is first modified by the first layer of PVA, its hydrophilicity is greatly improved. When the PIC mass fraction is 0.003wt%~0.01wt%, a thin and loose PIC hydrogel layer can be constructed on the PVA hydrogel layer through hydrogen bond anchoring, which can be firmly anchored on the membrane surface after iron ion cross-linking. The outermost PIC hydrogel will disperse after absorbing water and swelling to form a polyampholyte ion brush, which makes the fiber membrane have both ultra-high hydrophilicity and polyampholyte ion brush structure, and can be more easily re-wetted after drying.

[0135] The above embodiments are merely examples of the technical solutions of the present invention. The modification method of the double hydrogel surface-modified PTFE hydrophilic antifouling hollow fiber membrane with zwitterionic brushes involved in the present invention is not limited to the contents described in the above embodiments, but is subject to the scope defined in the claims. Any modification, supplement or equivalent replacement made by a technician in the field of the present invention based on the embodiment is within the scope of protection required by the claims of the present invention.

Claims

1. A method for preparing a double hydrogel surface-modified polytetrafluoroethylene (PTFE) hydrophilic antifouling hollow fiber membrane with a zwitterionic brush, characterized in that: The steps include: Step 1: After the PTFE hollow fiber membrane substrate is treated with plasma, it is immersed in a silane solution and dried at room temperature; Step 2: Immersing the fiber membrane obtained in step 1 in a PVA solution, wherein the mass fraction of PVA in the PVA solution is 0.2-0.6 wt %; Step 3: The fiber membrane obtained in step 2 is taken out and immersed in a mixed solution of glutaraldehyde and citric acid, wherein the mass concentration of glutaraldehyde in the mixed solution of glutaraldehyde and citric acid is 0.12-0.13 g / ml, and the mass concentration of citric acid is 0.019-0.021 g / ml; Step 4: The fiber membrane obtained in step 3 is taken out and balanced in water to obtain a PTFE hollow fiber membrane S-PTFE after the glutaraldehyde cross-linked PVA polymer monolayer is hydrophilically modified; Step 5: The S-PTFE obtained in step 4 is taken out and immersed in a polyampholyte hydrogel solution with a mass fraction of 0.003 to 0.01 wt%; Step 6: The fiber membrane obtained in step 5 is taken out and immersed in an iron ion solution having an iron ion concentration of 0.05 to 0.2 mol / L; Step 7: The fiber membrane obtained in step 6 is taken out and balanced in water to obtain the PTFE hollow fiber membrane D-PTFE after the iron ion cross-linked PVA / PIC polymer double hydrophilic modification.

2. The preparation method according to claim 1, characterized in that: The silane solution in step 1 is a mixed solution of water, ethanol and N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane AEAPTS; wherein the mass fraction of AEAPTS in the mixed solution is 0.1 to 0.15 wt%.

3. The preparation method according to claim 1, characterized in that: Step 2: Before impregnating with the PVA solution, the PTFE hollow fiber membrane treated with silane is first impregnated with anhydrous ethanol.

4. The preparation method according to claim 1, characterized in that: The solvent of the PVA solution in step 2 is a mixed solvent of dimethyl sulfoxide and water.

5. The preparation method according to claim 1, characterized in that: The polyampholyte hydrogel solution in step 5 contains PNaSS, PMPTC and NaCl.

6. The preparation method according to claim 5, characterized in that: The total monomer concentration of the PNaSS and PMPTC is 1.5-1.6 mol / L, and the molar ratio of the NaSS and MPTC units is 1:0.85-0.

95.

7. The preparation method according to claim 5, characterized in that: The preparation method of the polyampholyte hydrogel solution comprises the following steps: Step a, adding PNaSS, MPTC, initiator, and sodium chloride NaCl into deionized water, stirring and dissolving to obtain a uniform solution; Step b, placing the mixed solution obtained in step a in a mold to initiate polymerization of MPTC to obtain an initial hydrogel of an amphoteric electrolyte composite polymer PIC; Step c, balancing the PIC initial hydrogel obtained in step b in water to obtain a PIC hydrogel; Step d, placing the PIC hydrogel obtained in step c in a 3.5-4.5 mol / L NaCl solution to fully dissolve it, thereby obtaining a PIC hydrogel solution.

8. The preparation method according to claim 7, characterized in that: The concentration of NaCl in the uniform solution obtained in step a is 0.3-0.5 mol / L; the concentration of the initiator in the uniform solution obtained in step a is 0.001-0.002 mol / L.

9. The preparation method according to claim 7, characterized in that: The dissolving condition of step d is 80-90°C.

10. A double hydrogel surface-modified polytetrafluoroethylene (PTFE) hydrophilic antifouling hollow fiber membrane with zwitterionic brushes, characterized in that: The preparation method according to any one of claims 1 to 9 is used to obtain the

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