A Dual-Network Polymer Hydrophilic Modification Method for a High Water Flux and Corrosion-Resistant PTFE Hollow Fiber Membrane

Abstract

The present invention discloses a hydrophilic modification method for a high water flux and corrosion-resistant polytetrafluoroethylene (PTFE) hollow fiber membrane double-network polymer, including: Step 1, surface silanization treatment of the PTFE hollow fiber membrane; Step 2, impregnation with a hydrophilic polymer polyvinyl alcohol / sodium alginate solution; Step 3, impregnation with an iron ion-containing solution; Step 4, equilibration in water. The modification method of the present invention can significantly improve the water flux of the PTFE hollow fiber membrane. The modified double-network hydrophilic polymer has high mechanical properties and strong interfacial interaction with the PTFE substrate, and the modified fiber membrane has strong corrosion resistance.

Description

Technical Field

[0001] The present invention relates to the field of PTFE hollow fiber membrane modification, and specifically relates to a double-network polymer hydrophilic modification method for a high water flux and corrosion-resistant PTFE hollow fiber membrane. Background Art

[0002] Membrane separation technology is an advanced application of materials science in medium separation technology. Polytetrafluoroethylene (PTFE) hollow fiber microporous membranes have received extensive attention because of their large packing density, long service life, excellent chemical stability, corrosion resistance, and high lubricity and non-stickiness, and can be used for sewage treatment under various harsh conditions. However, since PTFE itself lacks hydrophilic groups and has many hydrophobic units, the water flux is very low during the water filtration process. At the same time, the surface energy of the PTFE hollow fiber membrane is very low, and the surface hydrophobic units are easy to adsorb organic substances such as grease and proteins, and must be restored through chemical cleaning. The commonly used surface hydrophilic chemical modification methods have poor chemical cleaning resistance and corrosion resistance. Therefore, designing a PTFE hollow fiber membrane with high water flux and corrosion resistance has broad application prospects.

[0003] At present, the hydrophilic modification methods of PTFE hollow fiber membranes mainly include wet chemical method, high-energy radiation grafting method, plasma treatment method, surface coating method, etc. Xiong et al. [Xiong S, Jia X, Mi K, et al. Upgrading polytetrafluoroethylene hollow-fiber membranes by CFD-optimized atomic layer deposition[J]. Journal of Membrane Science, 2021, 617, 118610] determined the parameters by hydrodynamic assistance and used the method of atomic layer deposition of uniform ultra-thin alumina coating to functionalize and modify PTFE hollow fiber membranes. The fiber membranes after atomic layer deposition treatment maintained the original pore size, improved the wettability, antifouling property and separation performance of the fiber membranes. However, the water flux of this modification method is not high and the operation is complex. The combination of inorganic atoms and organic membranes is weak and the hydrophilic modification stability is not good, which is not suitable for large-scale production and application. Li Hao et al. [Li Hao, Liu Guochang, Guo Chungang, Chen Jiangrong, Che Zhenning, Lv Jinglie. A hydrophilic PTFE hollow fiber membrane and its preparation method[P]. CN111111470A, 2020-05-08.] designed a modification method in which a polydopamine layer is covered on the surface of the PTFE hollow fiber membrane and then a hydrophilic functional layer is constructed on the surface of the polydopamine layer. The polydopamine layer can cover the inner / outer surface of the fiber membrane. The calcium carbonate-hydrophilic modified PTFE hollow fiber membrane is prepared by sequentially and repeatedly immersing the fiber membrane in calcium chloride solution and sodium carbonate solution. This method is simple to operate and the water flux of the modified fiber membrane is high. However, the cost of the modification raw materials is relatively high, the polydopamine is easily oxidized and denatured and the surface treatment stability is not good, and the acid and alkali resistance of the modified fiber membrane is poor. Therefore, the hydrophilic modified PTFE hollow fiber membranes reported at present are difficult to achieve high water flux and good acid and alkali corrosion resistance in practical applications. Summary of the Invention

[0004] The object of the present invention is to provide a double-network polymer hydrophilic modification method for PTFE hollow fiber membranes with simple process, easy operation, easily available raw materials, low cost and high water flux and corrosion resistance.

[0005] The specific steps of the technical solution are as follows:

[0006] A double-network polymer hydrophilic modification method for PTFE hollow fiber membranes with high water flux and corrosion resistance, comprising the following steps:

[0007] Step 1: The PTFE hollow fiber membrane pretreated by plasma is then treated with silane to obtain S-PTFE;

[0008] Step 2: The S-PTFE fiber membrane obtained in Step 1 is impregnated with a polyvinyl alcohol / sodium alginate oxide (hereinafter referred to as: PVA / OSA) solution;

[0009] Step 3: The fiber membrane obtained in Step 2 is taken out and impregnated with an iron ion solution;

[0010] Step 4: The fiber membrane obtained in Step 3 is equilibrated in water to obtain the PTFE hollow fiber membrane M-PTFE after hydrophilic modification of the iron ion-crosslinked PVA / OSA double network polymer.

[0011] As a preferred embodiment, the outer diameter of the PTFE hollow fiber membrane described in Step 1 is 2.2 to 2.3 mm, the wall thickness is 0.4 to 0.6 mm, and the average pore diameter is 0.35 to 0.45 microns.

[0012] As a preferred embodiment, in Step 1, before the PTFE hollow fiber membrane is treated with silane, it is subjected to plasma pretreatment. After plasma treatment, the chemical bonds on the surface of the PTFE membrane are activated, and a large number of hydrophilic groups, hydroxyl groups, are introduced on the surface by combining with free radicals.

[0013] The plasma pretreatment process 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; alternatively, before placing the PTFE hollow fiber membrane in the commercial plasma surface treatment machine for treatment, the plasma pretreatment process may optionally further include the following processes: a, washing the PTFE hollow fiber membrane in absolute ethanol and then drying; b, cleaning the PTFE hollow fiber membrane in an ultraviolet ozone cleaner. The PTFE hollow fiber membrane can obtain a clean and dry fiber membrane surface after washing and drying with absolute ethanol and ultraviolet / ozone cleaning.

[0014] Furthermore, the above pretreatment process is to place the dry PTFE hollow fiber membrane in absolute ethanol for washing and then drying, then place it in an ultraviolet ozone cleaner for cleaning for 15 to 20 minutes, and after cleaning, place it in a commercial plasma surface treatment machine for atmospheric pressure plasma treatment for 30 to 40 minutes to obtain a plasma-pretreated PTFE hollow fiber membrane.

[0015] As a preferred embodiment, the process of the silane treatment is that the PTFE hollow fiber membrane is impregnated with a silane solution at room temperature and then dried. Optionally, the mass fraction of the silane solution is 0.48 - 0.52 wt%. Optionally, the solvent of the silane solution is an ethanol aqueous solution with a volume ratio of 4:1. Optionally, the silane in step 1 is N-β-(aminoethyl)-γ-aminopropyltrimethoxysilane (AEAPTS). Optionally, the silane solution is a mixed solution of AEAPTS, ethanol and water, wherein the mass fraction of AEAPTS in the mixed solution is 0.48 - 0.52 wt%, and the volume ratio of ethanol to water is 4:1. Optionally, the impregnation time of the silane treatment is 4 - 6 hours; the drying temperature is 50 - 70 °C; the drying time is 4 - 6 hours. When the plasma-pretreated fiber membrane is immersed in the AEAPTS silane solution, AEAPTS silane hydrolyzes to form silanol groups -Si-OH, which undergo dehydration condensation with the hydroxyl groups on the PTFE surface to form -Si-O- covalent bonds. Together with the intermolecular hydrogen bonds, strong interfacial interactions are generated, enabling the AEAPTS silane to firmly adhere to the PTFE surface, resulting in the silane-modified PTFE hollow fiber membrane S-PTFE.

[0016] As a preferred embodiment, in step 2, before impregnating the PVA / OSA solution, the silane-treated PTFE hollow fiber membrane is first fully wetted with absolute ethanol. Optionally, the process of wetting with absolute ethanol is to immerse the silane-treated PTFE hollow fiber membrane in absolute ethanol at room temperature for 4 - 5 hours. The surface tension of the dry S-PTFE fiber membrane is low and the hydrophobic effect is strong. By wetting the fiber membrane with absolute ethanol, stronger wettability can be imparted to the fiber membrane, enabling the hydrophilic polymer to better wet the membrane pores when impregnating the PVA / OSA hydrophilic polymer solution, and endowing the PTFE hollow fiber membrane with a better hydrophilic modification effect.

[0017] As a preferred embodiment, the preparation method of the PVA / OSA solution in step 2 includes the following steps:

[0018] Step a, under light-shielding conditions, sodium alginate (SA) and sodium periodate are dissolved in a mixed solvent of dimethyl sulfoxide and water with a volume ratio of 1:3, and an oxidation reaction is carried out for 5 - 6 hours;

[0019] Step b, ethylene glycol is added to the mixed solution obtained in step a, and stirring is continued for 1 - 2 hours to terminate the oxidation reaction, obtaining an oxidized sodium alginate (OSA) solution;

[0020] Step c, polyvinyl alcohol (PVA) is added to the OSA solution obtained in step b, and stirred until dissolved to obtain the PVA / OSA solution.

[0021] Further, in the reaction system for preparing the PVA / OSA solution described above, the addition amount of PVA accounts for 0.167 - 0.33 wt% of the total amount of the reaction system; the mass fraction ratio of OSA to PVA is 1:(4 - 6), and more preferably 1:5. When the content of iron ions for coordinating and crosslinking the OSA molecular chain network is relatively low, it is relatively hard and brittle, and the intermolecular chain interactions are easily opened under external force, resulting in energy dissipation; when the content of the PVA molecular chain network is relatively high, it has relatively strong chemical crosslinking and is relatively strong and tough, and can maintain large deformations without polymer damage. Therefore, the design of the double-network polymer PVA / OSA brings typical help for the strong surface adhesion between hydrophilic polymers and substrates and high resistance to environmental corrosion damage performance.

[0022] Further, in the reaction system for preparing the PVA / OSA solution described above, the addition amount of SA accounts for 0.033 - 0.067 wt% of the total amount of the reaction system; the addition amount of sodium periodate accounts for 0.036 - 0.072 wt% of the total amount of the reaction system; more preferably, the molar ratio of SA to sodium periodate is 1:1.

[0023] Further, in the reaction system for preparing the PVA / OSA solution described above, the addition amount of ethylene glycol accounts for 0.055 - 0.11 wt% of the total amount of the reaction system.

[0024] As a preferred embodiment, in step 2, the temperature for impregnating the PVA / OSA solution is room temperature, and the impregnation time is 2 - 4 hours.

[0025] As a preferred embodiment, the iron ion-containing solution in step 3 comprises ferric nitrate nonahydrate, glutaraldehyde GA, and citric acid monohydrate CA. Among them, in the iron ion-containing solution, the mass concentration of GA is 0.12 - 0.13 g / ml, the mass concentration of CA is 0.019 - 0.021 g / ml, and the molar concentration of ferric nitrate nonahydrate is 0.08 - 0.12 mol / L. When the fiber membrane impregnated with the PVA / OSA solution is taken out and continued to be impregnated in the iron ion-containing solution, the carbonyl group C=O on glutaraldehyde GA is a strongly polar group. Since the C atom has a strong positive charge, it is easy to react with nucleophiles. And a large number of hydrophilic groups hydroxyl are contained in some unoxidized glycoside chain segments of PVA and OSA. The O atom on the hydroxyl group has a lone pair of electrons and has strong nucleophilicity. Under the catalysis of citric acid monohydrate, the hydroxyl groups on PVA and OSA react with the carbonyl group on GA to form a chemically crosslinked PVA / OSA double-network polymer. Among them, the PVA and OSA molecular chains form a stable double-network interpenetrating structure, and iron ions with high ionization energy form a strong coordination interaction with the carboxylate group -COO - on OSA to form a stable iron ion coordination crosslinked OSA molecular chain network.

[0026] As a preferred embodiment, in step 3, the temperature for immersing the iron ion solution is room temperature, and the immersion time is 10 to 15 hours.

[0027] As a preferred implementation, in step 4, the water balance time is 20 to 24 hours, and the water is changed every 4 hours.

[0028] The present invention also provides a high water flux corrosion-resistant PTFE hollow fiber membrane, which is prepared by the above method.

[0029] The carbonyl group C=O, a strong polar group in OSA, reacts with the primary amine group -NH2 in AEAPTS silane to form a Schiff base reaction, so that the iron ion cross-linked PVA / OSA double network polymer and AEAPTS silane are connected by a -C=N covalent bond, which cooperates with the hydrogen bonds between the interface molecules to give the iron ion cross-linked PVA / OSA double network polymer and S-PTFE strong interfacial bonding properties, thereby obtaining a more stable and firm iron ion cross-linked PVA / OSA double network polymer hydrophilic modified PTFE hollow fiber membrane M-PTFE. When M-PTFE is in a water environment, the PVA / OSA double network hydrophilic polymer can swell rapidly in water and retain a large amount of water, which greatly improves the hydrophilicity of the fiber membrane and gives the fiber membrane a high water flux. At the same time, the design of the iron ion coordinated double network polymer with stronger mechanical properties and the strong interfacial interaction between the double network polymer and PTFE interface give M-PTFE stronger chemical stability and corrosion resistance.

[0030] The invention provides a method for modifying the hydrophilicity of a double-network polymer of a PTFE hollow fiber membrane with high water flux and corrosion resistance. The modification process is simple and easy to control. The modified fiber membrane M-PTFE has both high water flux and corrosion resistance. The hydrophilic groups rich in the PVA / OSA double-network polymer enable the hydrophilic polymer to swell rapidly in water while retaining a large amount of water, thereby giving the modified fiber membrane high water flux. At the same time, through the design of the iron ion coordinated double-network polymer with stronger mechanical properties and the strong interface interaction between the polymer and the PTFE interface, the polymer has a more stable structure and high adhesion performance with the interface, thereby giving the modified fiber membrane stronger corrosion resistance. This will become a common method for preparing a hydrophilic PTFE hollow fiber membrane with high water flux and corrosion resistance.

[0031] Compared with the prior art, the present invention has the following advantages and significant progress:

[0032] 1) The preparation process of the present invention is simple, the production cycle is short, the process conditions are simple, the raw materials are easily available, and the production cost is low.

[0033] 2) The present invention constructs a high-performance and high water flux dual-network polymer hydrophilic modified PTFE hollow fiber membrane with synergistic hydrogen bonds and coordination bonds through the coordination of metal ions and polymers. The highly hydrophilic dual-network polymer endows the fiber membrane with high water flux, and the strong coordination of metal ions and the Schiff base reaction between interfaces endow the dual-network polymer with strong mechanical properties and strong interfacial interaction with the PTFE substrate, having strong corrosion resistance and broad application prospects in the field of hydrophilic modified PTFE hollow fiber membranes for water treatment. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 (a) is a schematic diagram of the preparation process of the dual-network polymer hydrophilic modified PTFE hollow fiber membrane of the present application;

[0035] Figure 1 (b) and (c) are schematic diagrams of the hydrophilic modification principle of the dual-network polymer hydrophilic modified PTFE hollow fiber membrane of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0036] The following specifically describes the embodiments of the present invention in detail with reference to the drawings.

[0037] In the following examples:

[0038] The PTFE hollow fiber membrane used for hydrophilic modification is purchased from Hairui Membrane Technology Co., Ltd., with an outer diameter of 2.2 - 2.3 mm, a wall thickness of 0.4 - 0.6 mm, and an average pore diameter of 0.35 - 0.45 microns.

[0039] The plasma pretreatment process is to wash the dried PTFE hollow fiber membrane in absolute ethanol and then dry it, and then put it into an ultraviolet ozone cleaning machine for cleaning for 15 - 20 minutes. After cleaning, it is put into a plasma surface treatment machine for atmospheric pressure plasma treatment for 30 - 40 minutes to obtain a plasma-pretreated PTFE hollow fiber membrane.

[0040] The AEAPTS silane solution is a mixed solution of AEAPTS, ethanol, and water, where the mass fraction of AEAPTS in the mixed solution is 0.48 - 0.52 wt%, and the volume ratio of ethanol to water is 4:1.

[0041] The preparation method of the PVA / OSA solution is as follows:

[0042] Under light-shielding conditions, SA and sodium periodate are dissolved in a mixed solvent of dimethyl sulfoxide and water with a volume ratio of 1:3 for an oxidation reaction for 5 to 6 hours; ethylene glycol is added to the resulting mixed solution, and stirring is continued for 1 to 2 hours to terminate the oxidation reaction, obtaining an OSA solution; polyvinyl alcohol PVA is added to the obtained OSA solution and stirred to dissolve to obtain the PVA / OSA solution, wherein the molar ratio of SA to sodium periodate is 1:1; PVA is 1750-type PVA with a degree of alcoholysis of 99%; the mass fraction ratio of OSA to PVA is 1:5.

[0043] The experimental process and the corresponding principle are as Figure 1 shown.

[0044] Example 1

[0045] Step 1: The dried PTFE hollow fiber membrane after plasma pretreatment is placed in an AEAPTS silane solution with a mass fraction of 0.5 wt% and impregnated at room temperature for 4 hours, and then dried to obtain a silane-modified PTFE hollow fiber membrane S-PTFE;

[0046] Step 2: The S-PTFE obtained in Step 1 is fully wetted with absolute ethanol and then impregnated in a PVA / OSA hydrophilic polymer solution with a total mass fraction of 0.2 wt% (where the mass fraction of PVA is 0.167 wt% and the mass fraction of OSA is 0.033 wt%) at room temperature for 2 hours;

[0047] Step 3: The fiber membrane obtained in Step 2 is taken out and placed again in a crosslinking solution with an iron ion concentration of 0.1 mol / L (where the mass concentration of GA is 0.125 g / ml and the mass concentration of CA is 0.02 g / ml) and impregnated at room temperature for 12 hours;

[0048] Step 4: The fiber membrane obtained in Step 3 is taken out and placed in deionized water for 24 hours. After swelling equilibrium, it is dried to obtain an iron ion-crosslinked PVA / OSA double-network polymer hydrophilically modified PTFE hollow fiber membrane M-PTFE.

[0049] Example 2

[0050] Step 1: The dried PTFE hollow fiber membrane after plasma pretreatment is placed in an AEAPTS silane solution with a mass fraction of 0.48 wt% and impregnated at room temperature for 4 hours, and then dried to obtain a silane-modified PTFE hollow fiber membrane S-PTFE;

[0051] Step 2: The S-PTFE obtained in Step 1 is fully wetted with absolute ethanol and then impregnated in a PVA / OSA hydrophilic polymer solution with a total mass fraction of 0.3 wt% (where the mass fraction of PVA is 0.25 wt% and the mass fraction of OSA is 0.05 wt%) at room temperature for 3 hours;

[0052] Step 3: Take out the fiber membrane obtained in Step 2, and put it into a crosslinking solution with an iron ion concentration of 0.1 mol / L (where the mass concentration of GA is 0.12 g / ml and the mass concentration of CA is 0.019 g / ml) and immerse it at room temperature for 13 hours;

[0053] Step 4: Take out the fiber membrane obtained in Step 3, and then put it into deionized water for 24 hours. After swelling equilibrium, dry it to obtain the PTFE hollow fiber membrane M-PTFE hydrophilically modified by iron ion crosslinked PVA / OSA double network polymer.

[0054] Example 3

[0055] Step 1: Put the dried PTFE hollow fiber membrane after plasma pretreatment into an AEAPTS silane solution with a mass fraction of 0.52 wt% and immerse it at room temperature for 4 hours, and then dry it to obtain the silane modified PTFE hollow fiber membrane S-PTFE;

[0056] Step 2: Fully immerse the S-PTFE obtained in Step 1 with absolute ethanol and then immerse it in a PVA / OSA hydrophilic polymer solution with a total mass fraction of 0.4 wt% (where the mass fraction of PVA is 0.33 wt% and the mass fraction of OSA is 0.067 wt%) at room temperature for 4 hours;

[0057] Step 3: Take out the fiber membrane obtained in Step 2, and put it into a crosslinking solution with an iron ion concentration of 0.1 mol / L (where the mass concentration of GA is 0.13 g / ml and the mass concentration of CA is 0.021 g / ml) and immerse it at room temperature for 15 hours;

[0058] Step 4: Take out the fiber membrane obtained in Step 3, and then put it into deionized water for 24 hours. After swelling equilibrium, dry it to obtain the PTFE hollow fiber membrane M-PTFE hydrophilically modified by iron ion crosslinked PVA / OSA double network polymer.

[0059] Example 4

[0060] Step 1: Put the dried PTFE hollow fiber membrane after plasma pretreatment into an AEAPTS silane solution with a mass fraction of 0.51 wt% and immerse it at room temperature for 4 hours, and then dry it to obtain the silane modified PTFE hollow fiber membrane S-PTFE;

[0061] Step 2: Fully immerse the S-PTFE obtained in Step 1 with absolute ethanol and then immerse it in a PVA / OSA hydrophilic polymer solution with a total mass fraction of 0.2 wt% (where the mass fraction of PVA is 0.167 wt% and the mass fraction of OSA is 0.033 wt%) at room temperature for 4 hours;

[0062] Step 3: Take out the fiber membrane obtained in Step 2, and put it into a crosslinking solution with an iron ion concentration of 0.08 mol / L (where the mass concentration of GA is 0.125 g / ml and the mass concentration of CA is 0.02 g / ml) and immerse it at room temperature for 15 hours;

[0063] Step 4: Take out the fiber membrane obtained in Step 3, put it into deionized water for 24 hours, and after swelling equilibrium, dry it to obtain the PTFE hollow fiber membrane M-PTFE hydrophilically modified by iron ion cross-linked PVA / OSA double network polymer.

[0064] Example 5

[0065] Step 1: Put the dried PTFE hollow fiber membrane after plasma pretreatment into an AEAPTS silane solution with a mass fraction of 0.49 wt% and immerse it at room temperature for 4 hours, and then dry it to obtain the silane-modified PTFE hollow fiber membrane S-PTFE;

[0066] Step 2: Fully immerse the S-PTFE obtained in Step 1 with absolute ethanol and then immerse it in a PVA / OSA hydrophilic polymer solution with a total mass fraction of 0.2 wt% (where the mass fraction of PVA is 0.167 wt% and the mass fraction of OSA is 0.033 wt%) at room temperature for 4 hours;

[0067] Step 3: Take out the fiber membrane obtained in Step 2, and put it into a crosslinking solution with an iron ion concentration of 0.12 mol / L (where the mass concentration of GA is 0.125 g / ml and the mass concentration of CA is 0.02 g / ml) and immerse it at room temperature for 15 hours;

[0068] Step 4: Take out the fiber membrane obtained in Step 3, put it into deionized water for 24 hours, and after swelling equilibrium, dry it to obtain the PTFE hollow fiber membrane M-PTFE hydrophilically modified by iron ion cross-linked PVA / OSA double network polymer.

[0069] Comparative Example 1

[0070] Step 1: Put the dried PTFE hollow fiber membrane after plasma pretreatment into an AEAPTS silane solution with a mass fraction of 0.5 wt% and immerse it at room temperature for 4 hours, and then dry it to obtain the silane-modified PTFE hollow fiber membrane S-PTFE;

[0071] Step 2: Fully immerse the S-PTFE obtained in Step 1 with absolute ethanol and then immerse it in a PVA hydrophilic polymer solution with a mass fraction of 0.2 wt% at room temperature for 4 hours;

[0072] Step 3: Take out the fiber membrane obtained in Step 2, and put it into a crosslinking solution with an iron ion concentration of 0.10 mol / L (where the mass concentration of GA is 0.125 g / ml and the mass concentration of CA is 0.02 g / ml) and immerse it at room temperature for 15 hours;

[0073] Step 4: Take out the fiber membrane obtained in Step 3, put it into deionized water for 24 hours, dry it after swelling equilibrium to obtain the PTFE hollow fiber membrane PTFE / PVA after hydrophilic modification of the PVA single network polymer.

[0074] Comparative Example 2

[0075] Step 1: Put the dried PTFE hollow fiber membrane after plasma pretreatment into an AEAPTS silane solution with a mass fraction of 0.5 wt%, immerse it at room temperature for 4 hours, and then dry it to obtain the silane-modified PTFE hollow fiber membrane S-PTFE;

[0076] Step 2: Fully immerse the S-PTFE obtained in Step 1 with absolute ethanol and then immerse it in an OSA hydrophilic polymer solution with a mass fraction of 0.2 wt% at room temperature for 4 hours;

[0077] Step 3: Take out the fiber membrane obtained in Step 2, and put it into a crosslinking solution with an iron ion concentration of 0.10 mol / L (where the mass concentration of GA is 0.125 g / ml and the mass concentration of CA is 0.02 g / ml) and immerse it at room temperature for 15 hours;

[0078] Step 4: Take out the fiber membrane obtained in Step 3, put it into deionized water for 24 hours, dry it after swelling equilibrium to obtain the PTFE hollow fiber membrane PTFE / OSA after hydrophilic modification of the OSA single network polymer.

[0079] Comparative Example 3

[0080] Step 1: Put the dried PTFE hollow fiber membrane after plasma pretreatment into an AEAPTS silane solution with a mass fraction of 0.5 wt%, immerse it at room temperature for 4 hours, and then dry it to obtain the silane-modified PTFE hollow fiber membrane S-PTFE;

[0081] Step 2: Fully immerse the S-PTFE obtained in Step 1 with absolute ethanol and then immerse it in a PVA / OSA hydrophilic polymer solution with a total mass fraction of 0.2 wt% (where the mass fraction of PVA is 0.167 wt% and the mass fraction of OSA is 0.033 wt%) at room temperature for 2 hours;

[0082] Step 3: Take out the fiber membrane obtained in Step 2, and put it into a metal-ion-free crosslinking solution (where the mass concentration of GA is 0.125 g / ml and the mass concentration of CA is 0.02 g / ml) and immerse it at room temperature for 12 hours;

[0083] Step 4: Take out the fiber membrane obtained in Step 3, and then put it into deionized water for 24 hours. After swelling equilibrium, dry it to obtain the PTFE hollow fiber membrane modified hydrophilically by metal-ion-free crosslinked PVA / OSA double-network polymer, namely PTFE / PVA / OSA.

[0084] Water flux test:

[0085] Step 1: Cut the dried PTFE hollow fiber membrane modified hydrophilically into specimens with a length of 10 cm, and measure the outer diameter D of the fiber membrane;

[0086] Step 2: Seal one end of the specimen obtained in Step 1, and fix the other end on a self-made water flux tester to ensure good airtightness between the specimen and the tester;

[0087] Step 3: Immerse the specimen fixed in Step 2 completely in a water tank filled with deionized water at 25 °C, adjust the test negative pressure of the water flux tester to be stable at -0.02 MPa. After the deionized water is stably pumped out through the fiber membrane, start timing, and record the volume V of the deionized water pumped out in the first 5 minutes;

[0088] Step 4: Calculate the water flux J of the fiber membrane by the ratio of the volume of the deionized water pumped out to the product of the test time and the test membrane area w , and the calculation formula is as follows:

[0089]

[0090] In the formula, J w is the water flux during the test of a single fiber membrane, with the unit of L·m -2 ·h -1 ; V is the volume of the deionized water pumped out, with the unit of L; ΔT 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.

[0091] Corrosion resistance test:

[0092] Step 1: Test the water flux J of the sample by using the above water flux test method w ;

[0093] Step 2: Immediately immerse the fiber membranes after testing the water flux in Step 1 in sulfuric acid solution with pH = 2 and sodium hydroxide solution with pH = 12 for 5 days respectively;

[0094] Step 3: Take out the fiber membranes after soaking in the acid and alkali solutions in Step 2, dry them, and then test the secondary water flux J of the fiber membranes again under the same conditions w1 ;

[0095] Step 4: The water flux decay rate FDR is used to test the corrosion resistance of the fiber membrane, and the calculation formula is as follows:

[0096]

[0097] Wherein, J w is the initial water flux of a single fiber membrane in the first test, with the unit of L·m -2 ·h -1 ; J w1 is the water flux of the fiber membrane after being soaked in acid / alkali solution for 5 days, dried, and then subjected to a second test, with the unit of L·m -2 ·h -1 .

[0098] The water fluxes and corrosion resistances of the hydrophilic modified PTFE hollow fiber membranes obtained in the above examples and comparative examples are shown in Table 1 below:

[0099] Table 1: Water fluxes and corrosion resistances of hydrophilic modified PTFE hollow fiber membranes Note: In Comparative Example 2, only a small amount of dripping deionized water permeated through the surface of the fiber membrane and adhered to the wall under a negative pressure of -0.02 MPa, and the effective initial water flux of the fiber membrane could not be continuously pumped and tested.

[0100] Examples 1 to 3 are iron ion cross-linked PVA / OSA double-network polymer hydrophilic modified PTFE hollow fiber membranes M-PTFE prepared by changing the total mass fraction of PVA / OSA when the iron ion concentration is 0.1 mol / L. Examples 4 to 5 are iron ion cross-linked PVA / OSA double-network polymer hydrophilic modified PTFE hollow fiber membranes M-PTFE prepared by changing the iron ion concentration when the total mass fraction of PVA / OSA is 0.2 wt%. Comparative Example 1 is a PVA single-network polymer hydrophilic modified PTFE hollow fiber membrane PTFE / PVA with a mass fraction of 0.2 wt% when the iron ion concentration is 0.1 mol / L. Comparative Example 2 is an OSA single-network polymer hydrophilic modified PTFE hollow fiber membrane PTFE / OSA with a mass fraction of 0.2 wt% when the iron ion concentration is 0.1 mol / L. Comparative Example 3 is a metal ion-free cross-linked PVA / OSA double-network polymer hydrophilic modified PTFE hollow fiber membrane PTFE / PVA / OSA prepared by using a metal ion-free cross-linking solution when the total mass fraction of PVA / OSA is 0.2 wt%.

[0101] According to the data in Table 1:

[0102] It can be seen from Examples 1 to 5 and Comparative Example 1 that the initial water fluxes of the samples M-PTFE of the present invention are 1234.08 - 1290.87 L·m-2 ·h -1 ) The acid-resistant water flux decay rate (11.42 - 13.21%) and the strong-alkali-resistant water flux decay rate (5.38 - 7.31%) are both significantly better than the initial water flux (906.36 L·m -2 ·h -1 ) of the acid-resistant water flux decay rate (18.44%) and the strong-alkali-resistant water flux decay rate (23.53%) of the PVA single-network polymer hydrophilic modified PTFE / PVA. This is due to the design of introducing iron ions to crosslink the PVA / OSA double-network polymer. The introduction of the hydrophilic polysaccharide polymer OSA makes the polymer have stronger hydration. At the same time, when the mass fraction ratio of OSA to PVA is 1:5, the relatively low-content iron ion coordination crosslinked OSA molecular chain network is relatively hard and brittle, and it is more likely to open the intermolecular interaction under external force to generate energy dissipation; while the relatively high-content PVA molecular chain network has a relatively strong and tough chemical crosslinking effect, which can maintain large deformation without polymer damage, making the iron ion crosslinked PVA / OSA double-network polymer have stronger mechanical properties and anti-swelling properties than the PVA single-network polymer. After the polymer absorbs water and swells in the membrane pores, it also retains a larger pore size, and the initial water flux of M-PTFE is higher; the Schiff base reaction occurs between the aldehyde group on OSA and the amino group on AEAPTS silane, making the iron ion crosslinked PVA / OSA double-network polymer have a stronger interfacial bonding effect with the PTFE-based membrane. Synergistic with the stronger mechanical properties of the double-network polymer, M-PTFE makes the hydrophilic modified polymer not easily fall off and be damaged when soaked in strong acid / alkali solutions, and has better corrosion resistance. The carboxyl group -COO in OSA - The ionization degree increases with the increase of the pH of the solution, the hydrophilicity of OSA increases, and at the same time the crosslinking degree between iron ions and -COO - increases, the mechanical properties of the PVA / OSA double-network polymer are stronger, and the crosslinked structure is more stable and not easily damaged. Therefore, the strong-alkali corrosion resistance of M-PTFE is better than the strong-acid corrosion resistance.

[0103] It can be seen from Examples 1 - 5 and Comparative Example 2 that only a small amount of deionized water in the form of drops penetrated the surface of the fiber membrane and hung on the wall during the initial water flux test of the OSA single-network polymer hydrophilic modified PTFE / OSA sample, indicating that the membrane pores of the fiber membrane were not blocked. The hydrophilicity of the OSA single-network polymer hydrophilic modified PTFE / OSA sample was insufficient, resulting in the inability to continuously pump water to test the effective initial water flux of the fiber membrane.

[0104] It can be seen from Examples 1 - 5 and Comparative Example 3 that the initial water flux (1234.08 - 1290.87 L·m -2 ·h -1) The acid-resistant water flux decay rate (11.42 - 13.21%) and the strong-base-resistant water flux decay rate (5.38 - 7.31%) are both superior to the initial water flux (1096.59 L·m -2 ·h -1 ) of the crosslinked PTFE / PVA / OSA without metal ions, the acid-resistant water flux decay rate (18.83%), and the strong-base-resistant water flux decay rate (10.24%). This is because M-PTFE crosslinks the carboxylate group -COO in OSA with iron ions - . Compared with the crosslinking of PTFE / PVA / OSA without metal ions, since iron ions are trivalent metal ions, they can crosslink with more carboxylate groups from different molecular chains ((COO)3M). Therefore, the crosslinking effect of trivalent iron ions is superior to that of the double-network polymer without metal ion crosslinking. The double-network polymer of iron ion crosslinked PVA / OSA has stronger mechanical properties and anti-swelling properties. M-PTFE has stronger hydrophilicity, and the crosslinked structure is more stable and not easily damaged in strong acid and strong base solutions. Therefore, M-PTFE also has stronger corrosion resistance.

[0105] The above embodiments are only illustrative examples of the technical solutions of the present invention. The hydrophilic modification method of the high-water-flux and corrosion-resistant PTFE hollow fiber membrane double-network polymer involved in the present invention is not limited only to the content described in the above embodiments, but is subject to the scope defined by the claims. Any modification, supplement, or equivalent substitution made by those skilled in the art to the present invention on the basis of this embodiment is within the scope protected by the claims of the present invention.

Claims

1. A method for hydrophilic modification of a double-network polymer of a high water flux and corrosion-resistant polytetrafluoroethylene (PTFE) hollow fiber membrane, characterized in that It includes the following steps: Step 1: The PTFE hollow fiber membrane pretreated by plasma is further treated with silane to obtain S-PTFE; Step 2: The S-PTFE fiber membrane obtained in Step 1 is impregnated with a polyvinyl alcohol / sodium alginate oxidized solution PVA / OSA; Step 3: The fiber membrane obtained in Step 2 is taken out and impregnated with an iron ion-containing solution, and the iron ion-containing solution contains ferric nitrate nonahydrate, glutaraldehyde GA, and citric acid monohydrate CA; Step 4: The fiber membrane obtained in Step 3 is equilibrated in water to obtain a PTFE hollow fiber membrane M-PTFE modified with hydrophilicity of an iron ion-crosslinked PVA / OSA double-network polymer.

2. The modification method according to claim 1, wherein The plasma pretreatment described 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.

3. The modification method according to claim 1, wherein The silane treatment described in Step 1 is to soak the PTFE hollow fiber membrane pretreated by plasma in a silane solution and then take it out and dry it.

4. The modification method according to claim 1, wherein In Step 2, before impregnating with the PVA / OSA solution, the PTFE hollow fiber membrane treated with silane is first infiltrated with absolute ethanol.

5. The modification method according to claim 1, characterized in that, The preparation method of the PVA / OSA solution described in Step 2 is as follows: Polyvinyl alcohol PVA is added to the sodium alginate oxidized solution OSA, stirred and dissolved to obtain the PVA / OSA solution.

6. The modification method according to claim 5, wherein In the reaction system for preparing the PVA / OSA solution, the mass fraction of PVA is 0.167 to 0.33 wt%.

7. The modification method according to claim 5, characterized in that, In the reaction system for preparing the PVA / OSA solution, the mass fraction ratio of OSA to PVA is 1:(4 to 6).

8. The modification method according to claim 1, wherein The iron ion-containing solution contains: GA with a mass concentration of 0.12 to 0.13 g / ml, CA with a mass concentration of 0.019 to 0.021 g / ml, and ferric nitrate nonahydrate with a molar concentration of 0.08 to 0.12 mol / L.

9. A high water flux and corrosion-resistant PTFE hollow fiber membrane, characterized in that, It is prepared by using the method described in any one of Claims 1 to 8.

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