Hydrophilic polymer chain interpenetrating microgel modified PVDF high water flux anti-fouling filtration membrane and preparation method and application thereof

Abstract

The application discloses a hydrophilic polymer chain interpenetrating microgel modified PVDF high water flux anti-fouling filter membrane and a preparation method and application thereof, and comprises the following steps: uniformly dissolving and mixing poly-2-acrylamide-2-methylpropane sulfonic acid (PAMPS) microgel, acrylamide (AAm) monomer, polyvinylidene fluoride (PVDF), a pore former, a crosslinking agent, an initiator and a solvent to obtain a prepolymer solution; polymerizing and crosslinking the obtained prepolymer solution to obtain a casting solution; and performing film forming treatment on the obtained casting solution after vacuum degassing to obtain the hydrophilic polymer chain interpenetrating microgel modified PVDF high water flux anti-fouling filter membrane. The modification method can significantly improve the wetting performance, water permeability and anti-fouling performance of the PVDF flat membrane, and the construction of the PDN double network hydrophilic polymer chain interpenetrating microgel particle modified PVDF enables the modified flat membrane to withstand long-time cyclic oil-water separation tests and severe chemical environment immersion tests, and the hydrophilic polymer is not easy to fall off, and the modified flat membrane has excellent hydrophilic modification stability.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of PVDF flat membrane modification, in particular to a hydrophilic polymer chain interpenetrating microgel modified PVDF high water flux anti-fouling filtration membrane and its preparation method and application. BACKGROUND

[0002] Separation membrane is one of the important frontiers in the field of membrane science. PVDF (polyvinylidene fluoride) membrane is the main raw material for organic-water filtration system due to its excellent chemical stability and mechanical robustness. Its carbon backbone has stable C-C and C-F bonds, making it suitable for purification in harsh wastewater environments such as high temperature, strong acid / strong base and organic solvents. However, the strong electronegativity and low polarizability of fluorine atoms result in low surface energy and strong hydrophobicity of the membrane. The hydrophobic units easily adsorb organic matter such as oil and protein, causing the blockage of membrane pores, thus leading to rapid flux decline, poor wetting performance and inability to maintain separation efficiency in water treatment process. Therefore, designing a PVDF flat membrane with high water flux and high anti-fouling performance has broad application prospects.

[0003] Currently, the hydrophilic modification methods of PVDF flat membrane mainly include surface modification and bulk modification. Surface modification mainly reduces the deposition of organic matter on the surface by grafting hydrophilic polymers on the surface of PVDF membrane. Jia Guowen et al. [Jia Guowen, Ma Junqing, Miao Lixiao, Zhu Zhen-tao, Liu Lei, Zhao Xin-xin. A surface modified PVDF anti-fouling hydrophilic membrane and its one-step preparation process and application [P]. CN202011164302.4 2020-10-27] by immersing the PVDF base membrane in a mixed solution of graphene oxide and dopamine hydrochloride, the graphene oxide is adhered to the surface of the PVDF membrane through the dopamine layer, the modified PVDF flat membrane has good wetting property and separation performance, but the composite layer on the surface of this modification method has poor stability in variable environment and is easy to age and fall off. The water flux is not high and the anti-fouling ability is weak, which is not suitable for large-scale production and application. For bulk modification, Zhang Xiaowei et al. [Zhang Xiaowei, Zhang Longhui, Ni Xiaolu, Shen Zhilin, Ye Daling. Preparation method of hydrophilic polyvinylidene fluoride microfiltration membrane [P]. CN202210335289.7 2022-08-05] designed a styrene maleic anhydride copolymer and polyethylene glycol to modify PVDF. The modified pore-forming agent improves the hydrophilicity due to the unique amphiphilicity of the styrene maleic anhydride copolymer, thus improving the hydrophilicity of the PVDF membrane. The modified flat membrane has good hydrophilicity, but the water flux of the modified flat membrane is limited, and the discussion on anti-fouling performance only stays on the hydrophilicity and hydrophobicity. Therefore, the current reported surface modification and bulk modification are difficult to simultaneously improve the water flux and anti-fouling performance of PVDF flat membrane in practical application. SUMMARY

[0004] One of the purposes of the present application is to provide a preparation method of a hydrophilic polymer chain interpenetrating microgel modified PVDF high water flux anti-fouling filtration membrane, which has the advantages of simple process, easy operation, easily available raw materials, low cost, high water flux, strong anti-fouling ability, etc.

[0005] The specific steps are as follows:

[0006] A preparation method of a hydrophilic polymer chain interpenetrating microgel modified PVDF high water flux anti-fouling filtration membrane, comprising the following steps:

[0007] Step 1: dissolve and mix PAMPS (poly 2-acrylamido-2-methylpropane sulfonic acid) microgel, AAm (acrylamide) monomer, PVDF, pore-forming agent, crosslinking agent, initiator, and solvent uniformly to obtain a pre-polymer solution;

[0008] Step 2: polymerize and crosslink the pre-polymer solution obtained in step 1 to obtain a hydrophilic polymer chain interpenetrating microgel modified PVDF casting solution;

[0009] Step 3: vacuum degassing the casting solution obtained in step 2, and then performing film forming treatment to obtain a hydrophilic polymer chain interpenetrating microgel modified PVDF high water flux anti-fouling filtration membrane.

[0010] Further, the particle size of the PAMPS microgel in a dry state is not less than 500 mesh.

[0011] Further, the temperature for vacuum degassing is 60-80℃, the negative pressure is -0.08 to -0.1 MPa, and the time for vacuum degassing is 30-90 min.

[0012] Further, the preparation method of the PAMPS microgel is to dissolve and mix AMPS (2-acrylamido-2-methylpropane sulfonic acid) monomer, initiator, crosslinking agent, and solvent to obtain a mixed solution, then initiate polymerization and crosslinking of the monomers in the mixed solution to obtain PAMPS gel containing a highly crosslinked network; the prepared PAMPS gel is dried, ball milled, and then passed through a 500 mesh sieve to obtain PAMPS microgel.

[0013] Further, in the above preparation method of PAMPS microgel, the concentration of AMPS monomer in the mixed solution is 0.9-1.1 mol / L, the concentration of crosslinking agent is 3.8-4.2 mol% of the concentration of AMPS monomer, and the concentration of initiator is 0.05-0.15 mol% of the concentration of AMPS monomer. A high content of crosslinking agent can provide a large number of crosslinking sites, and the presence of crosslinking sites can increase the spacing between the internal networks of the microgel.

[0014] Further, in the preparation method of the PAMPS microgel, the crosslinking agent is MBAA (N, N-dimethyl acrylamide), the initiator is KA (2-ketoglutaric acid), and the solvent is water, and the polymerization and crosslinking are initiated under ultraviolet light.

[0015] The preparation method of the PAMPS gel is, for example, as follows: AMPS monomer, MBAA crosslinking agent and photo-initiator KA are added to 10-15 mL of water under a 65℃ water bath environment, and stirred in the dark for 15-25 min to make them completely dissolved, and then polymerized under ultraviolet light (365 nm 4W cm -1 ) for 8-10 h.

[0016] Further, in the pre-polymerization solution obtained in step 1, the mass fraction of PVDF is 16.5wt%-17.5wt%, and further preferably 16.8wt%-17.2wt%; the mass fraction of PAMPS microgel is 0.025wt%-0.1wt%, and further preferably 0.03wt%-0.06wt%; the mass fraction of AAm monomer is 0.4wt%-1.9wt%, and further preferably 0.5687wt%-1.1374wt%; and the mass fraction of the pore-forming agent is 2wt%-4wt%, and further preferably 2.8wt%-3.2wt%.

[0017] Further, in the pre-polymerization solution obtained in step 1, the amount of the crosslinking agent is 0.01%-0.03% of the molar amount of the AAm monomer; and the amount of the initiator is 0.01%-0.03% of the molar amount of the AAm monomer. A lower content of the crosslinking agent and the initiator helps the second network PAAm (polyacrylamide) to form a network with fewer crosslinking points and longer main chains. The longer molecular chains are more likely to form an interpenetrating network structure with the molecular chains of the PAMPS microgel and PVDF. The PAMPS microgel acts as a “rivet” to rivet the hydrophilic PAAm long chains in the hydrophobic PVDF segments, and then the PAAm and PVDF form an interpenetrating network structure to achieve the purpose of bulk hydrophilic modification.

[0018] Further, the pore-forming agent is PVP (polyvinylpyrrolidone); the crosslinking agent is MBAA; the initiator is selected from KA or APS (ammonium persulfate); and the solvent is DMAc (N, N-dimethylacetamide).

[0019] Further, when the initiator is a thermal initiator such as APS, the polymerization and crosslinking conditions of the pre-polymerization solution in step 2 are as follows: stirring reaction under a 60-90℃ water bath environment, and preferably 80℃, for 6-12 h; when the initiator is a photo-initiator such as KA, the polymerization and crosslinking conditions of the pre-polymerization solution in step 2 are as follows: polymerization under ultraviolet light (for example, 365 nm 4W cm -1 ) for 8-10 h.

[0020] Further, the film forming process comprises the following steps:

[0021] (1) leveling of the casting solution;

[0022] (2) misting pretreatment of the casting solution surface with a poor solvent;

[0023] (3) solidification of the film in a coagulation bath.

[0024] Further, the casting solution is leveled on the glass substrate.

[0025] Further, the leveling method includes, but is not limited to, doctor blade coating, spray coating, spin coating, and flow coating.

[0026] Further, the thickness of the leveled casting solution is 100-300 μm, preferably 200 μm. The thickness of the formed film is generally slightly less than the thickness of the selected doctor blade. Therefore, when the thickness is less than 100 μm, the thickness of the formed film is too small, resulting in poor mechanical properties. When the thickness is greater than 300 μm, the film pores are prone to collapse, and the water flux is low.

[0027] As a preferred embodiment, a doctor blade can be used to uniformly coat the casting solution on the glass substrate to form a film.

[0028] Further, the misting pretreatment is to make the surface of the coating solution stay in a misting poor solvent droplet bath, so that the film surface appears phase separation and produces sponge-like pores.

[0029] Further, the poor solvent is water, and the coagulation bath solution is water. For example, a water mist produced by a humidifier can be used to treat the leveled casting solution surface. The intensity of the water mist is 3 mL·min -1 , and the residence time is 5-10 min.

[0030] Further, step (3) is to immerse the flat film obtained in step (2) in water until the phase separation reaches equilibrium. The water balance time is 20-24 hours, and the water is changed every 4-6 hours.

[0031] The second object of the present application is to provide a hydrophilic polymer chain interpenetrated microgel modified PVDF high water flux anti-fouling filtration membrane, which is prepared by the above method.

[0032] The third object of the present application is to provide the application of the above-mentioned hydrophilic polymer chain interpenetrated microgel modified PVDF high water flux anti-fouling filtration membrane, which can be used in gas filtration, liquid filtration, adsorbent material, anti-adhesion coating, oil transportation, and oil spill interception.

[0033] In traditional P-DN gels, PAAm acts as long chains, linking PAMPS microgels to form an interpenetrating network and sacrificial bonds. In this invention, however, the PAMPS microgels, due to their larger network porosity and particle size (larger than the membrane pores), act as anchors for the hydrophilic PAAm chains within the membrane. The long PAAm chains are entangled with the PVDF chains. During phase separation, as pores form, the hydrophilic PAAm chains migrate towards the pore surface and interface, but the presence of the PAMPS microgel anchors restricts the precipitation of the long PAAm chains. This creates a locally heterogeneous structure. The hydrophilic modified PAAm segments enriched in the pores and on the surface significantly increase the hydrophilicity of the PVDF membrane, resulting in a substantial increase in water flux. Furthermore, the presence of the PAMPS microgels makes PAAm less prone to detachment during cleaning, thus greatly improving the antifouling performance of the PVDF membrane during multiple separation cycles.

[0034] This invention provides a method for modifying PVDF high-flux antifouling filter membranes with hydrophilic polymer chain interpenetrating microgels. The modification process is simple and easy to control. The modified PVDF / PDN flat sheet membrane possesses both high water flux and high antifouling properties. The abundant hydrophilic groups in the PDN dual-network polymer allow the hydrophilic polymer to migrate into the membrane pores and surface during phase separation, endowing the modified flat sheet membrane with high water flux. Simultaneously, the PDN dual network contains a large number of interpenetrating networks and sacrificial bonds, which improve the mechanical strength of the membrane while restricting the release of hydrophilic PAAm chains, thus giving the flat sheet membrane excellent antifouling properties. This will become a common method for preparing hydrophilically modified high-flux antifouling PVDF filter membranes with hydrophilic polymer chain interpenetrating microgels.

[0035] Compared with the prior art, the present invention has the following advantages and significant progress:

[0036] 1) The preparation process of this invention is simple, the production cycle is short, the process conditions are simple, the raw materials are readily available, and the production cost is low.

[0037] 2) This invention constructs a PDN dual network by combining PAMPS microgels and PAAm chains, and forms an interpenetrating structure with PVDF chains. The highly hydrophilic PAAm chains are enriched on the surface of the membrane and in the membrane pores, giving the fiber membrane high water flux. The PAMPS microgels restrict the release of PAAm chains, and the membrane exhibits high antifouling performance during multiple cycle separation processes. It has broad application prospects in the field of hydrophilic modified PVDF flat sheet membranes for water treatment. Attached Figure Description

[0038] Figure 1 This is a schematic diagram illustrating the preparation method and principle of the hydrophilic polymer chain interpenetrating microgel modified PVDF flat sheet membrane of this application, wherein (a) is a schematic diagram of the preparation process; and (b) is a schematic diagram of the hydrophilic modification principle. Detailed Implementation

[0039] The specific embodiments of the present application are described in detail below with reference to the accompanying drawings.

[0040] In the following examples:

[0041] The PVDF powder for hydrophilic modification was purchased from Sanai New Material Technology Co., Ltd., and the brand was FR904.

[0042] The preparation method of the PAMPS gel was as follows: 0.9-1.1 mol / L of AMPS monomer, 3.8-4.2 mol% of the monomer concentration of MBAA crosslinking agent, and 0.05-0.15 mol% of the monomer concentration of the photoinitiator KA were added to 10-15 mL of water under the condition of a 65°C water bath, and stirred in the dark for 15-25 min, so that they were completely dissolved, and then polymerized under ultraviolet light (365 nm 4 W cm-1) for 8-10 h.

[0043] The preparation method of the PDN hydrophilic polymer chain interpenetrating microgel modified PVDF casting solution was as follows: polyvinylpyrrolidone PVP, PAMPS microgel, acrylamide AAm, ammonium sulfate APS, crosslinking agent N,N-methylene bisacrylamide MBAA, and 17 g of PVDF were added to 80 g of DMAc, and stirred at 80°C for 8 h.

[0044] The experimental process and the corresponding principle are shown in Figure 1 .

[0045] Example 1

[0046] Step 1: 1 mol / L of AMPS monomer, 4 mol% of the monomer concentration of the crosslinking agent MBAA, and 0.1 mol% of the monomer concentration of the initiator KA were added to 15 mL of water under the condition of a 65°C water bath, and stirred in the dark for 20 min, so that they were completely dissolved, and then polymerized under ultraviolet light (365 nm 4 W cm -1 ) for 8 h. A high-crosslinking PAMPS gel was obtained. After drying at 90°C, using a ball mill to grind for 3 h, and passing through a 500-mesh sieve, a PAMPS microgel with a particle size of less than 30 μm was obtained.

[0047] Step 2: 0.05 g of the PAMPS microgel obtained in step 1, 0.7582 g of acrylamide AAm, 0.1 mol% of the monomer molar amount of N,N-methylene bisacrylamide MBAA, 0.1 mol% of the monomer molar amount of the thermal initiator APS, 3 g of the pore-forming agent PVP, and 17 g of PVDF were added to 80 g of DMAc solvent, and reacted at 80°C under the condition of a water bath and 300 rpm mechanical stirring for 8 h to obtain a PDN double network hydrophilic polymer chain interpenetrating microgel particle modified PVDF casting solution.

[0048] Step 3: The casting solution obtained in step 2 was cast on a glass plate at a speed of 7-8 cm·s-1 The film is evenly scraped onto a glass plate at a speed of 200 μm (using a scraper for film thickness), allowed to stand in the air for 30 seconds to level, and then subjected to a uniform 2-minute deionized water mist pre-phase separation treatment on the surface of the casting solution (mist output of 3 mL / min). -1 ).

[0049] Step 4: Soak the pretreated flat sheet membrane obtained in Step 3 in deionized water for 24 hours, changing the water every 6 hours to remove residual unreacted small molecules and obtain a PDN dual-network hydrophilic polymer chain interpenetrating microgel particle modified PVDF filter membrane after phase separation.

[0050] Example 2

[0051] Step 1: In a 65℃ water bath, add 1 mol / L AMPS monomer, 4 mol% crosslinking agent MBAA, and 0.1 mol% initiator KA to 15 mL of water. Stir for 20 min in the dark until completely dissolved, then expose to ultraviolet light (365 nm, 4W cm⁻¹). -1 Polymerization was carried out at 90°C for 8 hours to obtain highly cross-linked PAMPS gel. After drying at 90°C, the gel was milled using a ball mill for 3 hours and then passed through a 500-mesh sieve to obtain PAMPS microgels with a particle size of less than 30 μm.

[0052] Step 2: Add 0.048 g of PAMPS microgel obtained in Step 1, 0.9099 g of acrylamide AAM, 0.09 mol% of N,N-methylenebisacrylamide MBAA, 0.09 mol% of thermal initiator APS, 3 g of pore-forming agent PVP, and 17 g of PVDF to 80 g of DMAc solvent. React at 80 °C in a water bath with mechanical stirring at 300 rpm for 8 h to obtain PVDF casting solution modified with PDN dual-network hydrophilic polymer chain interpenetrating microgel particles.

[0053] Step 3: Pour the casting solution obtained in Step 2 into the solution at a flow rate of 7-8 cm. -1 The film is evenly scraped onto a glass plate at a speed of 200 μm (using a scraper for film thickness), allowed to stand in the air for 30 seconds to level, and then subjected to a uniform 2-minute deionized water mist pre-phase separation treatment on the surface of the casting solution (mist output of 3 mL / min). -1 ).

[0054] Step 4: Place the pretreated flat sheet membrane obtained in Step 3 into deionized water for 24 hours, changing the water every 6 hours, to remove residual unreacted small molecules and obtain a PDN dual-network hydrophilic polymer chain interpenetrating microgel particle modified PVDF filter membrane after phase separation.

[0055] Example 3

[0056] Step 1: 1 mol / L AMPS monomer, 4 mol% crosslinking agent MBAA, 0.1 mol% initiator KA were added to 15 mL water under 65°C water bath environment, stirred in the dark for 20 min, and then polymerized under UV light (365 nm 4W cm -1 ) for 8 h after complete dissolution. High crosslinking degree PAMPS gel was obtained. After drying at 90°C and grinding for 3 h using a ball mill, the PAMPS microgel with a particle size of less than 30 μm was obtained by passing through a 500 mesh sieve.

[0057] Step 2: 0.046 g of PAMPS microgel obtained in step 1, 0.8719 g of acrylamide AAm, 0.08 mol% of N,N-methylene bisacrylamide MBAA based on the molar amount of monomer, 0.08 mol% of thermal initiator APS based on the molar amount of monomer, 3 g of pore-forming agent PVP, and 17 g of PVDF were added to 80 g of DMAc solvent. The reaction was carried out at 80°C for 8 h under 300 rpm mechanical stirring to obtain a PDN double network hydrophilic polymer chain interpenetrating microgel particle modified PVDF casting solution.

[0058] Step 3: The casting solution obtained in step 2 was uniformly scraped on a glass plate at a speed of 7-8 cm -1 (s) with a thickness of 200 μm selected for the film scraper), and then placed in air for 30 s to level, and then the surface of the casting solution was uniformly treated with a 2 min deionized water mist pre-phase separation (the mist output was 3 mL min -1 ).

[0059] Step 4: The pre-treated flat membrane obtained in step 3 was placed in deionized water for 24 hours, and the water was changed every 6 hours to remove residual unreacted small molecule substances to obtain a PDN double network hydrophilic polymer chain interpenetrating microgel particle modified PVDF filtration membrane after phase separation.

[0060] Example 4

[0061] Step 1: 1 mol / L AMPS monomer, 4 mol% crosslinking agent MBAA, 0.1 mol% initiator KA were added to 15 mL water under 65°C water bath environment, stirred in the dark for 20 min, and then polymerized under UV light (365 nm 4W cm -1 ) for 8 h after complete dissolution. High crosslinking degree PAMPS gel was obtained. After drying at 90°C and grinding for 3 h using a ball mill, the PAMPS microgel with a particle size of less than 30 μm was obtained by passing through a 500 mesh sieve.

[0062] Step 2: 0.052 g of PAMPS microgel obtained in step 1, acrylamide AAm 0.9857 g, monomer molar amount of 0.11% of N,N-methylene bisacrylamide MBAA, monomer molar amount of 0.11% of thermal initiator APS, 3 g of pore-forming agent PVP, 17 g of PVDF were added to 80 g of DMAc solvent, and the reaction was carried out at 80°C under water bath with 300 rpm mechanical stirring for 8 h to obtain a PDN double network hydrophilic polymer chain interpenetrating microgel particle modified PVDF casting solution.

[0063] Step 3: The casting solution obtained in step 2 was uniformly scraped on a glass plate at a speed of 7-8 cm -1 , with a thickness of 200 μm selected for the film scraper, and was left to level in air for 30 s, and then the surface of the casting solution was uniformly pre-separated by 2 min deionized water mist (the mist output was 3 mL min -1 ).

[0064] Step 4: The pre-treated flat membrane obtained in step 3 was placed in deionized water for 24 hours, and the water was changed every 6 hours to remove residual unreacted small molecule substances to obtain a PDN double network hydrophilic polymer chain interpenetrating microgel particle modified PVDF filtration membrane after phase separation.

[0065] Example 5

[0066] Step 1: 1 mol / L of AMPS monomer, 4 mol% of crosslinking agent MBAA based on the monomer concentration, and 0.1 mol% of initiator KA based on the monomer concentration were added to 15 mL of water under the condition of 65°C water bath, and stirred in the dark for 20 min, and then polymerized under ultraviolet light (365 nm 4 W cm -1 ) for 8 h after complete dissolution. A high crosslinking degree PAMPS gel was obtained. After drying at 90°C and grinding with a ball mill for 3 h, the PAMPS microgel with a particle size of less than 30 μm was obtained after passing through a 500 mesh sieve.

[0067] Step 2: 0.054 g of PAMPS microgel obtained in step 1, acrylamide AAm 1.0236 g, monomer molar amount of 0.12% of N,N-methylene bisacrylamide MBAA, monomer molar amount of 0.12% of thermal initiator APS, 3 g of pore-forming agent PVP, 17 g of PVDF were added to 80 g of DMAc solvent, and the reaction was carried out at 80°C under water bath with 300 rpm mechanical stirring for 8 h to obtain a PDN double network hydrophilic polymer chain interpenetrating microgel particle modified PVDF casting solution.

[0068] Step 3: The casting solution obtained in step 2 was uniformly scraped on a glass plate at a speed of 7-8 cm -1at a speed of 7-8 cm / s, and then left to stand for 30 s in air. The surface of the casting solution was then uniformly pre-phase separated by spraying deionized water for 2 min at a rate of 3 mL / min. -1

[0069] Step 4: The pre-treated flat membrane obtained in step 3 was placed in deionized water for 24 hours, and the water was changed every 6 hours to remove residual unreacted small molecule substances to obtain a phase-separated PDN double network hydrophilic polymer chain interpenetrated microgel particle modified PVDF filtration membrane.

[0070] Comparative Example 1

[0071] Step 1: 1 mol / L AMPS monomer, 4 mol% crosslinking agent MBAA, and 0.1 mol% initiator KA were added to 15 mL of water under the condition of a 65°C water bath, and stirred in the dark for 20 min. After complete dissolution, the solution was subjected to ultraviolet light (365 nm, 4 W cm -1 ) for 8 h. A high crosslinking degree PAMPS gel was obtained. After drying at 90°C, using a ball mill to grind for 3 h, and then passing through a 500 mesh sieve, PAMPS microgels with a particle size of less than 30 μm were obtained.

[0072] Step 2: 0.05 g of PAMPS microgels obtained in step 1, 3 g of a pore-forming agent PVP, and 17 g of PVDF were added to 80 g of DMAc solvent, and the mixture was stirred at 80°C under the condition of a 300 rpm mechanical stirrer for 8 h to obtain a PAPMS strong microgel modified PVDF casting solution.

[0073] Step 3: The casting solution obtained in step 2 was uniformly spread on a glass plate at a speed of 7-8 cm / s (the thickness of the film spreader was selected to be 200 μm), and then left to stand for 30 s in air. The surface of the casting solution was then uniformly pre-phase separated by spraying deionized water for 2 min at a rate of 3 mL / min. -1 -1 .

[0074] Step 4: The pre-treated flat membrane obtained in step 3 was placed in deionized water for 24 hours, and the water was changed every 6 hours to remove residual unreacted small molecule substances to obtain a phase-separated PAPMS microgel modified PVDF filtration membrane.

[0075] Comparative Example 2

[0076] ​​Step 1: 0.7582 g of acrylamide AAm, 0.1 mol% of N,N-methylenebisacrylamide MBAA by monomer molar mass, 0.1 mol% of thermal initiator APS by monomer molar mass, 3 g of pore-forming agent PVP, 17 g of PVDF were added into 80 g of DMAc solvent, and a PAAm hydrophilic modified PVDF casting solution was obtained by mechanical stirring at 80°C for 8 h.

[0077] Step 2: The casting solution obtained in step 1 was uniformly spread on a glass plate at a speed of 7-8 cm / s (the thickness of the film applicator was selected to be 200 μm), and the casting solution was leveled in air for 30 s, and then the surface of the casting solution was uniformly pre-separated by a 2 min deionized water mist (the misting amount was 3 mL / min -1 ). -1

[0078] Step 3: The pre-treated flat membrane obtained in step 2 was placed in deionized water for 24 hours, and the water was changed every 6 hours to remove residual unreacted small molecule substances to obtain a phase-separated PAAm hydrophilic modified PVDF filtration membrane.

[0079] Anti-fouling performance test:

[0080] Step 1: A Tween-80 stabilized oil-in-water emulsion was prepared to simulate real wastewater for evaluating the oil-water separation performance of the membrane: 1 g of mineral oil was added to 1000 mL of deionized water, 0.2 g of Tween-80 was used as an emulsifier, and then a high-speed reflux stirrer was used to stir at 6000 rpm for 4 h to obtain an oil-in-water emulsion.

[0081] Step 2: The membrane was first compacted at 0.1 MPa negative pressure for 30 min at room temperature to achieve a stable water flux, and then the oil-water separation test was started. Each cycle was defined as first testing the deionized water flux for 15 min, and then filtering the oil-in-water emulsion obtained in step 1 for 60 min.

[0082] Step 3: The membrane after separation in step 2 was immersed in a 3‰ sodium hypochlorite (NaCIO) solution and ultrasonically washed for 10 min, and three cycles were continuously tested, and the oil and water fluxes in the three cycles were recorded as J p1 , J p2 , J p3 , J w1 , J w2 , J w3 .

[0083] Step 4: The anti-fouling performance of the filtration membrane was determined by the flux recovery rate FRR and the flux decay rate FDR after the second cycle, and the calculation formula was as follows:

[0084] ​

[0085] In the formula, J w1 This is the stable water flux measured during the first test of the filter membrane, in L·m. -2 ·h -1 ·bar -1 J w2 This is the steady-state water flux of the filter membrane during the second test, measured in L·m. -2 ·h -1 ·bar -1 J p1 The oil-water flux of the filtration membrane during its first test is expressed in L·m. -2 ·h -1 ·bar -1 .

[0086] Water flux test:

[0087] Step 1: The PVDF filter membrane modified by PDN hydrophilic polymer chain interpenetrating microgel was cut into 5cm×5cm samples.

[0088] Step 2: Fix the sample obtained in Step 1 on an area S of 1.32 × 10 -3 m 2 On the water flux tester, ensure good airtightness between the sample and the tester.

[0089] Step 3: Add an appropriate amount of deionized water to the measuring cup above the sample fixed in Step 2, adjust the test negative pressure P of the water flux tester to stabilize at -0.1MPa, start timing after the deionized water is stably extracted through the flat membrane, pre-pressurize for 30 minutes, perform the first oil-water separation cycle, and take the stable water flux of the first water cycle.

[0090] Step 4: Calculate the water flux J of the filtration membrane by the ratio of the volume of deionized water extracted to the product of the test time, the test membrane area, and the test pressure. w The calculation formula is as follows:

[0091]

[0092] In the formula, J w This is the pure water flux during the initial oil-water separation process, measured in L·m⁻¹. -2 ·h -1 ·bar -1 V represents the volume of deionized water extracted, in liters (L); ΔT represents the test time, in hours (h); and S represents the membrane area, in square meters (m²). 2 P represents the applied pressure, measured in bar.

[0093] The water flux and antifouling properties of the hydrophilic modified PVDF filter membranes obtained in the above embodiments and comparative examples are shown in Table 1 below:

[0094] Table 1: Water flux and anti-fouling performance of hydrophilic modified PVDF filtration membrane

[0095]

[0096] Examples 1-5 are PDN hydrophilic macromolecular chain interpenetrating microgel modified PVDF filtration membranes prepared by controlling the total mass of the casting solution base system to be 100 g, changing the content of PAMPS microgel and the content of the second network monomer acrylamide AAm (the proportion of the two components remains the same) under other conditions being the same; Comparative Example 1 is a PAMPS microgel modified PVDF filtration membrane prepared by canceling the addition of the monomer, initiator and crosslinking agent forming the second network on the basis of Example 1; Comparative Example 2 is a PAAm single network modified PVDF filtration membrane prepared by canceling the addition of PAMPS microgel on the basis of Example 1, only allowing PAAm to form a single network.

[0097] According to the data in Table 1:

[0098] From Examples 1-5 and Comparative Example 1, it can be seen that the stable water flux (2024.78-2186.52 L·m -2 ·h -1 ·bar -1 ), the second and third oil-water separation cycle flux recovery rate (81.7-85.5%) and the second oil-water separation cycle flux attenuation rate (79.2-79.9%) of the inventive sample PVDF / PDN-0.05 are significantly better than the stable water flux (1773.24 L·m -2 ·h -1 ·bar -1 ), the second and third oil-water separation cycle flux recovery rate (65.8%) and the second oil-water separation cycle flux attenuation rate (90.0%) of the PAMPS microgel modified PVDF filtration membrane. This is because a small amount of residual hydrophilic pore-forming agent PVP in the original PVDF / PVP membrane is quickly lost during multiple cycles and washing processes. The PAMPS microgel alone has poor compatibility with the PVDF base membrane network due to its strong hydrophilicity, and the PAMPS microgel is prone to agglomeration during phase separation, while in the PVDF / PAMPS-0.05 membrane, only random dispersion and inlay of PAMPS microgel occur, and a continuous and dense hydration layer cannot be formed on the surface of the membrane to resist oil pollution.

[0099] From Examples 1-5 and Comparative Example 2, it can be seen that the stable water flux (2024.78-2186.52 L·m -2 ·h -1 ·bar -1), the flux recovery rate of the second and third oil-water separation cycles (81.7-85.5%), and the flux attenuation rate of the second oil-water separation cycle (79.2-79.9%) were all significantly better than those of the PAAm single-network modified PVDF filtration membrane, the stable water flux (1890.10 L·m -2 ·h -1 ·bar -1 ), the flux recovery rate of the second and third oil-water separation cycles (71.9%), and the flux attenuation rate of the second oil-water separation cycle (84.5%). This is because the PVDF / PAAm-0.05 membrane has a mechanically weak PAAm single-network gel as the modified hydrophilic polymer, which is easily destroyed by flow shear and ultrasonic washing with a strong oxidant during multiple cycles and washing processes, and thus gradually flows away and separates from the membrane surface. The above factors all cause the hydrophilic modification of the membrane to gradually fail, the hydrophobic PVDF membrane matrix to gradually be exposed to the high-concentration oil pollution environment and thus to be contaminated and clogged.

[0100] The above examples are merely illustrative of the technical solutions of the present application. The method for modifying the high-water-flux and high-anti-pollution PVDF filtration membrane by using a hydrophilic polymer chain interpenetrating microgel is not limited to the content described in the above examples, but is subject to the scope defined in the claims. Any modification, supplement, or equivalent replacement made by a person skilled in the art on the basis of the examples is within the scope of the claims of the present application.

Claims

1. A method for preparing a hydrophilic polymer chain interpenetrating microgel modified PVDF high water flux antifouling filtration membrane, characterized in that, Comprising the following steps: Step 1: dissolving and mixing uniformly poly 2-acrylamide-2-methylpropane sulfonic acid PAMPS microgel, acrylamide AAm monomer, polyvinylidene fluoride PVDF, porogen, crosslinking agent, initiator, solvent to obtain a pre-polymer solution; in the obtained pre-polymer solution, the mass fraction of PVDF is 16.8 wt%-17.2 wt%; the mass fraction of PAMPS microgel is 0.03 wt%-0.06 wt%; the mass fraction of AAm monomer is 0.5687 wt%-1.1374 wt%; the porogen is polyvinylpyrrolidone PVP, and the mass fraction is 2.8 wt%-3.2 wt%; the amount of crosslinking agent is 0.01%-0.03% of the molar amount of AAm monomer; the amount of initiator is 0.01%-0.03% of the molar amount of AAm monomer; Step 2: polymerizing and crosslinking the pre-polymer solution obtained in step 1 to obtain a hydrophilic high molecular chain interpenetrating microgel modified PVDF casting solution; Step 3: vacuum degassing the casting solution obtained in step 2 and then performing film forming treatment to obtain a hydrophilic high molecular chain interpenetrating microgel modified PVDF high water flux anti-fouling filtration membrane.

2. The production method according to claim 1, characterized by, In step 1, the particle size of the PAMPS microgel in the dry state is not less than 500 mesh.

3. The production method according to claim 1, characterized by, In step 1, the crosslinking agent is N,N-methylene bisacrylamide MBAA; the initiator is alpha-ketoglutaric acid KA; and the solvent is N,N-dimethylacetamide DMAc.

4. The method of claim 1, wherein, In step 3, the film forming treatment comprises the following steps: (1) leveling the casting solution; (2) atomizing the surface of the casting solution to perform pretreatment on the poor solvent, so that the surface of the coating solution stays in the bath of atomized poor solvent droplets, and sponge-like pores are generated on the surface of the film due to phase separation; (3) solidifying the film in the coagulation bath.

5. The preparation method according to claim 4, characterized in that, The thickness of the casting solution after leveling is 100-300 μm.

6. The preparation method according to claim 4, characterized in that, The poor solvent is water; and the coagulation bath is water.

7. A hydrophilic polymer chain interpenetrated microgel modified PVDF high water flux antifouling filtration membrane, characterized in that, Prepared by the method of any one of claims 1-6.

8. The hydrophilic high molecular chain interpenetrating microgel modified PVDF high water flux anti-fouling filtration membrane of claim 7 is applied in the fields of gas filtration, liquid filtration, adsorbent material, anti-adhesion coating, oil transportation, and oil spill interception.

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