A zwitterionic-brush dual-hydrogel surface-modified polytetrafluoroethylene (ptfe) hydrophilic antifouling hollow fiber membrane and a preparation method thereof

Abstract

The application provides a zwitterionic brush double hydrogel surface modified polytetrafluoroethylene (PTFE) hydrophilic antifouling hollow fiber membrane and a preparation method thereof, which can significantly improve the hydrophilicity and antifouling performance of the PTFE hollow fiber membrane. The preparation method comprises the following steps: step 1, putting pretreated PTFE membrane filaments into a PVA solution for immersion; step 2, immersing a glutaraldehyde / citric acid solution; step 3, balancing in water; step 4, immersing a PIC hydrogel solution; step 5, immersing an iron ion-containing solution again; and step 6, balancing in water. The modification method can significantly improve the water flux of the PTFE hollow fiber membrane, and the modified double hydrophilic polymer has high antifouling performance.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of modification of PTFE hollow fiber membranes, in particular to a zwitterionic brush modified PTFE hollow fiber membrane with dual hydrogel surface and a preparation method thereof. BACKGROUND

[0002] Membrane separation technology is widely used in separation and purification processes due to its high separation efficiency, low energy consumption, economic and environmental benefits, low investment cost, and continuous use. In recent years, polytetrafluoroethylene (PTFE) has attracted the attention of many researchers due to its unique comprehensive performance. In particular, due to the large electronegativity and low polarizability of fluorine atoms, it has a small van der Waals radius and a strong C-F bond, making PTFE have super 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 can cause pollution problems in water treatment, which can reduce the separation efficiency and the performance of the membrane, thereby increasing the operating cost and even causing failure. Therefore, developing a hollow fiber membrane with high hydrophilicity and high fouling resistance has broad application prospects.

[0003] The main methods for hydrophilic modification of PTFE hollow fiber membranes reported so far include chemical modification, plasma treatment, high-energy radiation grafting, atomic layer deposition (ALD), and surface coating. 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 novel in-situ aeration-assisted polydopamine / polyethyleneimine copolymerization and deposition method. The aeration provided a good hydrophilic modification environment for the hollow fiber membrane, and the performance of the polydopamine / polyethyleneimine coating could be simply controlled by adjusting the polymerization and deposition parameters. The modified fiber membrane has good hydrophilicity, but the cost of the raw materials for modification is high, and the stability of polydopamine is poor, which can be easily oxidized and denatured during surface treatment, reducing the acid and alkali resistance of the fiber membrane. Wang Qingyu et al. [Wang Qingyu, Xu Mei, Zeng Fufu, Xu Baiyu, Qian Chong. A PTFE membrane for high-pollution wastewater treatment and a preparation method [P]. CN114471169A, 2022-05-13.] used a polymer containing carboxyl or hydroxyl groups to modify the surface of the hollow fiber membrane. The filter membrane was formed into an outer pressure membrane assembly, and the modified solution was circulated under pressure. The outer pressure membrane assembly and the mixed solution were 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 pollution resistance. Therefore, the hydrophilic modified PTFE hollow fiber membranes reported so far are difficult to achieve high water flux and good pollution resistance in practical applications. SUMMARY

[0004] One of the purposes of the present application is to provide a preparation method of a zwitterionic brush double hydrogel surface modified polytetrafluoroethylene (PTFE) hydrophilic and anti-fouling hollow fiber membrane. The obtained fiber membrane has excellent anti-fouling effect compared with 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 by plasma, it is immersed in a silane solution and dried at room temperature;

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

[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 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 equilibrated in water to obtain a PVA polymer monolayer hydrophilic modified PTFE hollow fiber membrane S-PTFE crosslinked by glutaraldehyde;

[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%, and further preferably 0.006 wt%;

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

[0012] Step 7: The fiber membrane obtained in step 6 is taken out and equilibrated in water to obtain a PTFE hollow fiber membrane D-PTFE double hydrophilic modified by PVA / PIC polymer crosslinked by iron ions.

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

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

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

[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 0.1-0.15 wt%; and the volume ratio of ethanol to water is 4:1.

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

[0018] The AEAPTS silane hydrolyzes to form silicon hydroxyl-Si-OH, which can dehydrate and condense with the hydroxyl on the PTFE surface to form a-Si-O- covalent bond, so that the AEAPTS silane is firmly anchored on the PTFE surface, and a silane-treated PTFE hollow fiber membrane is obtained.

[0019] As a preferred embodiment, before step 2, the silane-treated PTFE hollow fiber membrane is first infiltrated with anhydrous ethanol.

[0020] Optionally, the anhydrous ethanol infiltration process is to immerse the silane-treated and dried PTFE hollow fiber membrane in anhydrous ethanol at room temperature for 4-5 hours. The surface tension of the dried PTFE fiber membrane is low, and the hydrophobic effect is strong. By infiltrating the fiber membrane with anhydrous ethanol, the fiber membrane can be given stronger wettability, and when the PVA hydrophilic polymer solution is infiltrated, the hydrophilic polymer can better wet the membrane pores, giving the PTFE hollow fiber membrane better hydrophilic modification effect.

[0021] As a preferred embodiment, 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 to dissolve PVA in a mixed solvent of dimethyl sulfoxide and water, and stir at 90-95℃ for 2-4 hours to obtain the PVA solution.

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

[0025] The PVA molecular chain modification layer with high content has strong chemical crosslinking effect, is relatively strong and tough, can maintain large deformation without damage to the polymer, and a large number of hydroxyl groups in PVA can significantly improve the hydrophilicity, so the design of PVA modification layer can typically help the strong surface adhesion between the hydrophilic polymer and the substrate and the high environmental corrosion resistance.

[0026] As a preferred embodiment, in step 3, the temperature for infiltrating the GA / CA solution is room temperature, and the infiltration time is 8-13 hours.

[0027] When the fiber membrane immersed in the PVA solution is taken out and continuously immersed in the GA / CA solution, the carbonyl group C=O at one end of GA will react with the amino group -NH2 on the AEAPTS silane to form a Schiff base imine bond, and at the same time, the carbonyl group C=O at the other end will react with the hydroxyl group on the PVA to form an acetal, so that the PVA is connected to the AEAPTS silane through the GA. In addition, the carbonyl group C=O on the glutaraldehyde GA is a strong polar group. Since the C atom has strong positive charge, it is easy to react with nucleophiles. The PVA contains a large number of hydrophilic groups, i.e. hydroxyl groups, and the O atom on the hydroxyl group has a lone pair of electrons, which has strong nucleophilicity. Under acidic conditions, the GA reacts with the hydroxyl groups on the membrane surface and in the PVA to form an acetal, which further stabilizes the PVA hydrogel layer and anchors it on the surface of the PTFE membrane, thereby obtaining a PVA single-layer modified PTFE hollow fiber membrane S-PTFE with superhydrophilic properties.

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

[0029] As a preferred embodiment, step 5 directly uses the fiber membrane without drying to immerse in the polyamphoteric electrolyte hydrogel solution. The fiber membrane without drying has the best wetting effect, and the water channels are maximally retained, so that the PVA modified layer can fully contact the PIC hydrogel when the PIC hydrogel solution is immersed.

[0030] As a preferred embodiment, the polyamphoteric electrolyte hydrogel solution in step 5 contains PNaSS (sodium p-styrenesulfonate), PMPTC (poly N,N,N-trimethyl-3-(2-methylallyl amido)-1-propyl ammonium chloride) and NaCl.

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

[0032] As a preferred embodiment, the preparation method of the polyamphoteric electrolyte hydrogel solution comprises the following steps:

[0033] Step a: PNaSS, MPTC, initiator and sodium chloride NaCl are added to deionized water, and after stirring and dissolving, a uniform solution is obtained;

[0034] Step b: The mixed solution obtained in step a is placed in a mold, and MPTC is polymerized to obtain an amphoteric electrolyte composite polymer PIC initial hydrogel;

[0035] Step c: the PIC initial hydrogel obtained in step b is equilibrated in deionized water to obtain a PIC hydrogel;

[0036] Step d: the PIC hydrogel obtained in step c is placed in a 3.5-4.5 mol / L NaCl solution to fully dissolve the PIC hydrogel to obtain a PIC hydrogel solution.

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

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

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

[0040] The initiator initiates the polymerization of MPTC to produce PMPTC. Due to the presence of NaCl, the two polyelectrolytes cannot form coordination and mainly rely on the entanglement of polymer chains to form the PIC initial hydrogel. The ratio of the isoelectric points of NaSS and MPTC units is 1:0.9. Near this ratio, the coordination effect of the synthesized initial hydrogel bubble after equilibration is best, and the comprehensive mechanical properties of the hydrogel are optimal.

[0041] As a preferred embodiment, the preparation conditions of the uniform solution in step a are stirring and dissolution, the stirring temperature is 60-70°C, and the stirring time is 25-35 minutes.

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

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

[0044] As a preferred embodiment, the dissolution conditions in step d are 80-90°C, and the stirring and dissolution time is 2-3 hours.

[0045] In order to obtain the ion brush layer with both lubricity and strength, the S-PTFE is modified by the polyampholyte hydrogel solution. It is difficult to form high entanglement structure by blending in solution, so the PIC initial hydrogel with certain strength is obtained by mixing PNaSS polymer and MPTC monomer and then polymerizing. After the bubble balance, the PIC initial hydrogel has more entanglement structure, so that the PIC hydrogel solution can be immersed into the PVA modified layer while retaining 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 high concentration of NaCl, which shields the electrostatic interaction, and the formation of the PIC hydrogel modified layer still mainly relies on hydrogen bonds. With the increase of the immersion time, the hydrogen bond anchoring position provided by the PVA layer decreases, and a small amount of PIC hydrogel forms a loose modified layer in the outermost layer to form the original structure of the ion brush.

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

[0047] The iron ion can form ion coordination with the negatively charged sulfonate in the PNaSS of the PIC hydrogel, so that the PNaSS in the PIC is ion crosslinked and further fixed on the membrane surface. Since the PIC layer formed in step 5 is not uniform, but has a structure similar to the gradient density, i.e. the density near the PVA layer is higher, and the density far from the PVA layer is lower, so the crosslinking density formed by the iron ion is also different. And PMPTC cannot compete with iron ion in high concentration of iron ion solution, so at this time it mainly relies on hydrogen bond and polymer chain entanglement to be fixed on the membrane surface.

[0048] As a preferred embodiment, in step 7, the time of the bubble balance is 24-30 hours, and the water is changed every 6 hours. During the bubble balance process, the excess and part of the weakly coordinated iron ions are removed, the strongly coordinated iron ions are retained, and the vacant sulfonate and part of the weakly coordinated iron ions that are not removed further coordinate to produce strong ion coordination. The positively charged groups in PMPTC replace part of the weakly coordinated iron ions and form ion coordination with part of the vacant sulfonate, and the two synergistically further reinforce the PIC modified layer. In the outermost layer of the membrane, the PIC hydrogel layer is relatively sparse, and after ion crosslinking it is still relatively loose, part of the polymer chain segments are anchored in the outermost layer by ion coordination, hydrogen bond, chain entanglement and other effects, and the unanchored chain segments form the zwitterionic brush.

[0049] The second object of the present application is to provide a double hydrogel surface modified polytetrafluoroethylene (PTFE) hydrophilic anti-fouling hollow fiber membrane with zwitterionic brushes.

[0050] The present application further assembles a PIC ion brush layer on the surface of the PVA modified layer, the PIC hydrogel is connected to the PVA modified layer by hydrogen bonds generated by hydrophilic groups, and the PIC hydrogel layer is crosslinked by iron ions, thereby enhancing the connection between the PIC hydrogel layer and the PVA hydrogel layer and toughening the PIC hydrogel layer, and a PTFE hollow fiber membrane D-PTFE with superhydrophilicity and zwitterionic brushes is obtained. When the D-PTFE is in a water environment, the PVA / PIC double hydrophilic polymer can rapidly swell in water while retaining a large amount of water, so that the hydrophilicity of the fiber membrane is greatly improved, and the water flux is significantly increased. The outermost PIC hydrogel layer gradually disperses to form zwitterionic brushes, thereby giving the D-PTFE stronger anti-fouling performance. The synergistic effect of hydrogen bonds, GA chemical crosslinking, iron ion coordination crosslinking, and imine bonds in the fiber membrane enables strong interfacial interaction between the modified hydrogel layer and the PTFE interface, thereby giving the D-PTFE stronger chemical stability.

[0051] The preparation method of the double hydrogel surface modified PTFE hydrophilic anti-fouling hollow fiber membrane with zwitterionic brushes provided by the present application has a simple process and is easy to operate. The prepared fiber membrane D-PTFE has high water flux and anti-fouling performance. The large number of hydrophilic groups in the PVA / PIC double hydrogel enable the modified layer to retain a large amount of water after water absorption and swelling, thereby giving the modified fiber membrane high water flux. The synergistic effect of imine bonds, hydrogen bonds, GA chemical crosslinking, and iron ion coordination crosslinking on the modified layer of the fiber membrane enables strong interfacial interaction between the modified hydrogel layers and between the modified hydrogel layer and the PTFE interface, thereby giving the D-PTFE stronger chemical stability. Meanwhile, the outermost PIC hydrogel layer further swells and disperses in a water environment to form zwitterionic brushes, which synergistically act with the hydration layer formed by the hydrophilic layer, thereby further improving the anti-fouling performance of the fiber membrane. This will become a universal method for preparing hydrophilic anti-fouling PTFE hollow fiber membranes. BRIEF DESCRIPTION OF DRAWINGS

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

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

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

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

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

[0057] In the following examples:

[0058] The hydrophilically modified PTFE hollow fiber membrane used in the examples was purchased from Haire Membrane Technology Co., Ltd. The outer diameter was 2.2-2.3 mm, the wall thickness was 0.4-0.5 mm, and the average pore size was 0.27-0.32 microns.

[0059] The plasma pretreatment process was as follows: the dry PTFE hollow fiber membrane was washed in anhydrous ethanol and then dried, and then placed in an ultraviolet ozone cleaning machine for cleaning for 15-20 minutes, and then placed in a plasma surface treatment machine for atmospheric plasma treatment for 30-40 minutes to obtain a plasma pretreated PTFE hollow fiber membrane.

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

[0061] The PIC hydrogel solution was prepared as follows: PNaSS, MPTC, initiator, and NaCl were added to deionized water, and the obtained uniform solution was placed in a mold to initiate polymerization of MPTC, thereby obtaining a PIC initial hydrogel, which was then placed in deionized water to equilibrate, thereby obtaining a PIC hydrogel, and then the obtained PIC hydrogel was placed in a NaCl solution to fully dissolve, thereby obtaining a PIC hydrogel solution. The total monomer concentration of PNaSS and MPTC was 1.5 mol / L, the molar ratio of NaSS to MPTC units was 1:0.9, the concentration of NaCl was 0.5 mol / L, the concentration of the initiator was 0.0015 mol / L, the initiator was KA, the initiation method was ultraviolet light initiation, the concentration of NaCl used to dissolve the PIC hydrogel was 4 mol / L, and the dissolution condition was 90°C.

[0062] The experimental process and the corresponding principles are shown in Figure 1 .

[0063] Example 1

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

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

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

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

[0068] Step 5: The fiber membrane obtained in step 4 was taken out and then 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 was taken out and then placed in deionized water for 24 hours, and after swelling equilibrium, drying was performed to obtain an iron ion cross-linked PVA / PIC polymer double hydrophilic modified PTFE hollow fiber membrane D-PTFE.

[0070] Example 2

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

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

[0073] Step 3: The fiber membrane obtained in step 2 was taken out and then placed in deionized water for 24 hours to obtain a GA cross-linked PVA polymer single-layer hydrophilic modified PTFE hollow fiber membrane S-PTFE;

[0074] Step 4: The S-PTFE hollow fiber membrane obtained in step 3 was 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 was taken out and then 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 was taken out and then placed in deionized water for 24 hours, and after swelling equilibrium, drying was performed to obtain an iron ion cross-linked PVA / PIC polymer double hydrophilic modified PTFE hollow fiber membrane D-PTFE.

[0077] Example 3

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

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

[0080] Step 3: The fiber membrane obtained in Step 2 was taken out and then immersed in deionized water for 24 hours to obtain a GA crosslinked PVA polymer single-layer hydrophilic modified PTFE hollow fiber membrane S-PTFE;

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

[0082] Step 5: The fiber membrane obtained in Step 4 was taken out and then immersed in a crosslinking solution with a concentration of 0.1mol / L of iron ions at room temperature for 12 hours;

[0083] Step 6: The fiber membrane obtained in Step 5 was taken out and then immersed in deionized water for 24 hours, and after swelling equilibrium, it was dried to obtain a PVA / PIC polymer double hydrophilic modified PTFE hollow fiber membrane D-PTFE.

[0084] Example 4

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

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

[0087] Step 3: The fiber membrane obtained in Step 2 was taken out and then immersed in deionized water for 24 hours to obtain a GA crosslinked PVA polymer single-layer hydrophilic modified PTFE hollow fiber membrane S-PTFE;

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

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

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

[0091] Example 5

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

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

[0094] Step 3: The fiber membrane obtained in step 2 was taken out and placed in deionized water for 24 hours to obtain the PTFE hollow fiber membrane S-PTFE with single-layer hydrophilic modification of GA cross-linked PVA polymer;

[0095] Step 4: The S-PTFE hollow fiber membrane obtained in step 3 was 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 was taken out and immersed in a cross-linking solution with a concentration of 0.05 mol / L of iron ions at room temperature for 12 hours;

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

[0098] Comparative Example 1

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

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

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

[0102] Comparative Example 2

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

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

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

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

[0107] Step 5: The fiber membrane obtained in step 4 was taken out and placed in deionized water for 24 hours, and then dried to obtain the PTFE / PVA / PIC double hydrophilic modified PTFE hollow fiber membrane after swelling equilibrium.

[0108] Comparative Example 3

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

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

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

[0112] Pollution resistance performance test:

[0113] Step 1: The hydrophilic modified and dried PTFE hollow fiber membrane was cut into a sample with a length of 11 centimeters, and the fiber membrane outer diameter D was tested.

[0114] Step 2: One end of the sample obtained in step 1 is sealed and fixed on a self-made water flux tester, so that the effective length in the middle is 10 cm, and the air tightness between the sample and the tester is good.

[0115] Step 3: The sample fixed in step 2 is completely immersed in a water tank containing deionized water, and the test is carried out at 25℃. The test pressure of the water flux tester is adjusted to be stable at 0.06 MPa. After the solution is stably extracted through the fiber membrane, timing starts. After pre-pressing for 30 minutes, the flux is adjusted to 600 L·m -2 ·h -1 . The initial pressure after the flux is stable is recorded, and the solution volume V w1 is recorded every 2 minutes. The test is carried out for 10 minutes.

[0116] Step 4: The deionized water in the water tank in step 3 is replaced with a 0.5 g / L bovine serum albumin solution, and the pressure is kept unchanged. The test is carried out at 25℃. After the solution is stably extracted through the fiber membrane, timing starts. The solution volume V p is recorded every 2 minutes. The test is carried out for 30 minutes.

[0117] Step 5: The fiber membrane after the test in step 4 is taken out and backwashed with deionized water for 5 minutes. The bovine serum albumin solution in the water tank in step 4 is replaced with deionized water, and the pressure is kept unchanged. The test is carried out at 25℃. After the solution is stably extracted through the fiber membrane, timing starts. The solution volume V w2 is recorded every 2 minutes. The test is carried out for 10 minutes.

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

[0119]

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

[0121] Step 7: The ratio of the difference between J w1 and J w2 to J w2 was used to calculate the flux recovery rate (FRR) of the membrane before and after the test in the BSA solution, and the calculation formula was as follows:

[0122]

[0123] Step 6: The ratio of the difference between J w2 and J p to J w1 was used to calculate the reversible fouling ratio (R r ) of the membrane before and after the test in the BSA solution, and the calculation formula was as follows:

[0124]

[0125] Step 6: The ratio of the difference between J w1 and J w2 to J w1 was used to calculate the irreversible fouling ratio (R ir ) of the membrane before and after the test in the BSA solution, and the calculation formula was as follows:

[0126]

[0127] The water flux and anti-fouling performance of the hydrophilic modified PTFE hollow fiber membranes obtained in the above examples and comparative examples were as follows Table 1:

[0128] Table 1: Water flux and anti-fouling performance of hydrophilic modified PTFE hollow fiber membranes

[0129]

[0130] Examples 1-3 are iron ion cross-linked PVA / PIC polymer double hydrophilic modified PTFE hollow fiber membranes D-PTFE prepared by changing the mass fraction of PVA with the iron ion concentration of 0.1 mol / L and the mass fraction of PIC hydrogel of 0.006 wt.%. Examples 4-5 are iron ion cross-linked PVA / PIC polymer double hydrophilic modified PTFE hollow fiber membranes D-PTFE prepared by changing the mass fraction of PIC hydrogel with the mass fraction of PVA of 0.6 wt.%. Comparative Example 1 is a PVA polymer single layer hydrophilic modified PTFE hollow fiber membrane S-PTFE prepared by using PVA with the mass fraction of 0.6 wt.%. Comparative Example 2 is a PTFE / PVA / PIC hydrogel hydrophilic modified PTFE hollow fiber membrane prepared by using a cross-linking solution without metal ions with the mass fraction of PVA of 0.6 wt.% and the mass fraction of PIC of 0.006 wt.%. Comparative Example 3 is a PIC single hydrogel hydrophilic modified PTFE hollow fiber membrane PTFE / PIC prepared by using PIC with the mass fraction of 0.4 wt.% and cross-linking with iron ions.

[0131] According to the data in Table 1:

[0132] It can be seen from Examples 1-5 and Comparative Example 1 that the bovine serum albumin solution flux (151.13-213.81 L·m -2 ·h -1 ), the recovered water flux (405.54-477.40 L·m -2 ·h -1 ), the flux recovery rate (68.28%-81.03%), the reversible fouling ratio (38.59%-49.09%), and the irreversible fouling ratio (18.89%-31.72%) of the D-PTFE are significantly better than the bovine serum albumin solution flux (146.71 L·m -2 ·h -1 ), the recovered water flux (308.09 L·m -2 ·h -1), flux recovery rate (51.29%), reversible fouling ratio (26.91%), irreversible fouling ratio (48.71%). This is because the PIC hydrogel layer forms a polyampholyte ion brush on the surface of the PTFE membrane, which can block pollutants and reduce pollution to the membrane itself. When the PVA mass fraction is 0.2wt%-0.6wt%, the membrane pores can be comprehensively modified, the hydrophilic 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 still retain a large pore size after water absorption and swelling, so that the S-PTFE fiber membrane has a high initial water flux; at the same time, 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 bonding anchoring, and the outermost PIC hydrogel will disperse after water absorption and swelling, forming a polyampholyte ion brush, which constantly swings under pressure, so that the fiber membrane can resist the pollution of bovine serum albumin, and reduce the degree of pollution of the fiber membrane during the bovine serum albumin solution test.

[0133] As can be seen from Examples 1-5 and Comparative Example 2, the bovine serum albumin solution flux of the D-PTFE (151.13-213.81 L·m -2 ·h -1 ), the recovery water flux (405.54-477.40 L·m -2 ·h -1 ), the flux recovery rate (68.28%-81.03%), the reversible fouling ratio (38.59%-49.09%), and the irreversible fouling ratio (18.89%-31.72%) are all significantly better than the bovine serum albumin solution flux (83.86 L·m -2 ·h -1 ), the recovery water flux (168.61 L·m -2 ·h -1), flux recovery rate (29.51%), reversible fouling ratio (14.86%), irreversible fouling ratio (70.49%). This is because the iron ions produce ionic crosslinking in the PIC hydrogel layer, reinforcing the PIC hydrogel layer, so that the hydrogel layer can still maintain a larger pore size after water absorption and swelling. Iron ions can produce coordination ionic crosslinking in PNaSS in the PIC hydrogel, so that the loose PIC hydrogel layer becomes dense, further reinforcing the hydrogel layer, so that the D-PTFE after double hydrogel modification can still maintain a larger pore size after water absorption and swelling, so that the D-PTFE has a higher initial water flux; at the same time, due to the different degrees of coordination produced by iron ions, the crosslinking effect is also different, the outermost hydrogel layer of the modified layer is the sparsest, and the crosslinking effect is relatively weak, and the polymer chain is not completely fixed, and will be dispersed after water absorption and swelling, forming a relatively stable polyelectrolyte ion brush. If the PIC hydrogel layer is not crosslinked by iron ions, but only relies on the weak hydrogen bond effect to fix, the polyelectrolyte ion brush structure on the surface of the modified layer will be damaged during the flux test process, so that the antifouling ability of the fiber membrane is significantly reduced.

[0134] As can be seen from Examples 1-5 and Comparative Example 3, the bovine serum albumin solution flux of the PIC single hydrophilic polymer modified PTFE / PIC (181.14 L·m -2 ·h -1 ) is higher than that of the D-PTFE (151.13-213.81 L·m -2 ·h -1 ), and the bovine serum albumin solution flux recovery rate (68.79%) is higher than that of the D-PTFE (0.00-0.00%). -2 ·h -1 ·h -2 ·h -1), flux recovery (68.28%~81.03%), reversible fouling ratio (38.59%~49.09%), irreversible fouling ratio (18.89%~31.72%) were similar, but the initial pressure required by PTFE / PIC (0.055 MPa) was much higher than that of D-PTFE (0.02~0.025 MPa). 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 iron ion crosslinking, the bulk strength of the PIC hydrogel modified layer increases significantly, which makes it stable and fixed on the membrane surface. This also makes it produce overall deformation after drying. The PTFE hollow fiber membrane substrate also has good bulk strength, but its deformation before and after drying is smaller. The different deformation degrees of PIC hydrogel layer and PTFE substrate lead to the partial separation of the interface connection between the two. Therefore, the membrane pores of the fiber membrane after drying cannot be completely wetted, and a larger pressure is required to make water pass through the membrane pores. The PTFE fiber membrane is first modified by the first heavy PVA, and 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 bonding anchoring. After iron ion crosslinking, it can be firmly anchored on the membrane surface. The outermost PIC hydrogel will disperse after water absorption and swelling, forming a polyzwitterionic ion brush. This makes the fiber membrane have both superhydrophilicity and polyzwitterionic ion brush structure, and it can be more easily repeated wetting after drying.

[0135] The above examples are only illustrative of the technical solutions of the present application. The modification method of the PTFE hydrophilic and antifouling hollow fiber membrane with double hydrogel surface modification with zwitterionic brush involved in the present application is not limited to the content described in the above examples, but is subject to the scope defined in the claims. Any modification or supplement or equivalent replacement made by the skilled person in the art on the basis of the examples is within the scope claimed by the claims of the present application.

Claims

1. A method for preparing a zwitterionic-brush dual hydrogel surface-modified polytetrafluoroethylene (PTFE) hydrophilic antifouling hollow fiber membrane, characterized in that, It comprises the following steps: Step 1: after the PTFE hollow fiber membrane substrate is treated by plasma, it is immersed in a silane solution and dried at room temperature; Step 2: the fiber membrane obtained in step 1 is immersed in a PVA solution, and 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, and the mass concentration of glutaraldehyde in the mixed solution 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 hydrophilic modification of a single layer of a PVA polymer crosslinked by glutaraldehyde; Step 5: the S-PTFE obtained in step 4 is taken out and immersed in a polyamphoteric electrolyte hydrogel solution with a mass fraction of 0.003-0.01 wt%; Step 6: the fiber membrane obtained in step 5 is taken out and immersed in an iron ion-containing solution with an iron ion concentration of 0.05-0.2 mol / L; Step 7: the fiber membrane obtained in step 6 is taken out and balanced in water to obtain a PTFE hollow fiber membrane D-PTFE after double hydrophilic modification of a PVA / PIC polymer crosslinked by iron ions; In step 5, the polyamphoteric electrolyte hydrogel solution contains PNaSS, PMPTC and NaCl, the total monomer concentration of PNaSS and PMPTC is 1.5-1.6 mol / L, and the molar ratio of NaSS and MPTC units is 1:0.85-0.95; the preparation method of the polyamphoteric electrolyte hydrogel solution comprises the following steps: Step a: PNaSS, MPTC, initiator and sodium chloride NaCl are added to deionized water, and after stirring and dissolving, a uniform solution is obtained; Step b: the mixed solution obtained in step a is placed in a mold to initiate polymerization of MPTC to obtain an amphoteric electrolyte composite polymer PIC initial hydrogel; Step c: the PIC initial hydrogel obtained in step b is balanced in water to obtain a PIC hydrogel; Step d: the PIC hydrogel obtained in step c is placed in a 3.5-4.5 mol / L NaCl solution to fully dissolve to obtain a PIC hydrogel solution.

2. The production method according to claim 1, characterized by, 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 0.1-0.15 wt%.

3. The preparation method according to claim 1, characterized in that, Before step 2, the PTFE hollow fiber membrane treated by silane is first immersed in anhydrous ethanol.

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

5. The production method according to claim 1, characterized by, 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.

6. The preparation method according to claim 1, characterized in that, The dissolution condition of step d is 80-90℃.

7. A zwitterionic-brush dual hydrogel surface-modified polytetrafluoroethylene (PTFE) hydrophilic antifouling hollow fiber membrane, characterized in that, The preparation method is obtained by any one of claims 1-6.

Images