High-performance pvdf ultrafiltration membrane and preparation method thereof

Abstract

This invention relates to the field of polymer materials technology and provides a high-performance PVDF ultrafiltration membrane and its preparation method, comprising the following steps: dissolving PVDF in a solvent, adding ethyl 2-bromoisobutyrate, CuBr / tris-(2-dimethylaminoethyl)amine and N-isopropylacrylamide for reaction; subsequently adding polyethylene glycol methacrylate, heating and reacting, followed by precipitation and drying to obtain a triblock copolymer; mixing the triblock copolymer with PVDF, adding it to a mixed solvent containing ionic liquid, dissolving and degassing to obtain a casting solution; casting the casting solution onto a substrate, coating it using a temperature-controlled doctor blade, then immersing the substrate in a coagulation bath, and after coagulation, washing and drying to obtain the PVDF ultrafiltration membrane. The ultrafiltration membrane has high flux and good retention rate, and also exhibits good temperature-sensitive response performance.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and more specifically, to a high-performance PVDF ultrafiltration membrane and its preparation method. Background Technology

[0002] Membrane technology, with its advantages of high selectivity, simple operation, energy saving, and environmental friendliness, plays a unique role in water treatment, chemical production, pharmaceuticals, medical treatment, and energy development. Polyvinylidene fluoride (PVDF) series resins possess outstanding resistance to weathering, ozone, and ultraviolet radiation, as well as excellent chemical stability. At room temperature, they are not corroded by acids, strong oxidants, or halogens; general organic solvents also have no effect on them. Therefore, they are used to research and prepare PVDF separation membranes for application in water treatment fields such as industrial wastewater treatment, municipal wastewater treatment, greywater reuse, and pure water purification, as well as in waste gas treatment and gas separation.

[0003] However, the symmetrical distribution of fluorine atoms on the molecular chain of pure PVDF membranes results in low surface energy and strong hydrophobicity, making it prone to pollutant adsorption during oily wastewater separation. This leads to decreased membrane flux and shortened lifespan. Furthermore, its pore structure is difficult to precisely control, creating a technical bottleneck where high flux and high rejection rate are difficult to achieve simultaneously. To address these issues, existing technologies often employ copolymer modification to prepare high-performance PVDF ultrafiltration membranes. For example, Chinese patent CN101003004A discloses a method for preparing a high-flux, antifouling PVDF ultrafiltration membrane by grafting PEGMA containing hydrophilic functional groups onto PVDF, thereby improving its hydrophilicity. Under conditions of high organic matter rejection rate, the addition of 10% ethanol or 0.1 mol / L sodium chloride coagulation bath and carboxyl-containing carbon nanotubes can significantly improve membrane flux, restore flux, and enhance antifouling performance. It improves the hydrophilicity of the membrane through copolymer modification, which alleviates the membrane fouling problem to some extent. However, this technical solution still has many drawbacks, such as poor controllability of the copolymer. It adopts a conventional atom transfer radical polymerization (ATRP) system, which leads to the risk of small molecule leaching during long-term use of the membrane. This makes it impossible for the membrane flux and rejection rate to meet the usage requirements, limiting its application in biopharmaceutical, food, and other scenarios with high purity requirements. Summary of the Invention

[0004] Based on the above problems, the purpose of this invention is to provide a high-performance PVDF ultrafiltration membrane and its preparation method, so that the ultrafiltration membrane has high flux, good retention rate, and good temperature-sensitive response performance.

[0005] The embodiments of the present invention are achieved through the following technical solutions: A method for preparing a high-performance PVDF ultrafiltration membrane includes the following steps: (1) Preparation of PVDF-b-PEGMA-b-PNIPAM triblock copolymer: PVDF was dissolved in an organic solvent, and ethyl 2-bromoisobutyrate, CuBr / tris-(2-dimethylaminoethyl)amine, and monomer N-isopropylacrylamide were added. The mixture was reacted under nitrogen protection for a period of time. Then, polyethylene glycol methacrylate was added, and the mixture was heated and reacted for a period of time. After the reaction was completed, the mixture was precipitated and dried under vacuum to obtain PVDF-b-PEGMA-b-PNIPAM triblock copolymer. (2) Preparation of casting solution: The triblock copolymer obtained in step (1) is mixed with PVDF and added to a mixed solvent containing ionic liquid. After dissolution, the resulting solution is degassed for 2-4 hours without mixing to obtain a casting solution. (3) Coupling to form a film: The casting solution obtained in step (2) is cast onto the substrate, coated with a temperature-controlled scraper, and the temperature of the temperature-controlled scraper is controlled to be lower than that of the casting solution. The substrate is then quickly transferred to a sealed chamber and kept under a nitrogen atmosphere. The substrate is then immersed in a coagulation bath. After coagulation, it is washed and dried to obtain the PVDF ultrafiltration membrane.

[0006] The present invention also provides a high-performance PVDF ultrafiltration membrane, which is prepared by the above preparation method.

[0007] The technical solutions of the embodiments of the present invention have at least the following advantages and beneficial effects: 1. The PVDF-b-PEGMA-b-PNIPAM triblock copolymer prepared in this invention provides excellent mechanical strength and chemical stability through PVDF segments, permanent hydrophilicity through PEGMA segments, which can significantly reduce the hydrophobicity of the membrane surface and reduce pollutant adsorption, and thermosensitive response through PNIPAM segments, which lay the foundation for the in-situ self-cleaning function of the membrane. By bringing PNIPAM segments close to the PVDF backbone, thermosensitive transitions can drive synergistic conformational changes in PEGMA segments, resulting in a faster response speed.

[0008] 2. In preparing the casting solution, the present invention utilizes a mixed solvent containing ionic liquid to not only achieve the full dissolution of PVDF and triblock copolymer to form a uniform and stable casting solution, but also promotes the formation of PVDF β crystal form, greatly improving the mechanical strength of the membrane, while improving the hydrophilicity of the membrane, thus providing a basis for the phase separation control of the subsequent film formation process.

[0009] 3. This invention employs a composite film-forming process that couples thermally induced phase separation with non-solvent-induced phase separation and combines it with vapor-induced phase separation. Through multi-stage phase separation control, the membrane structure is precisely controlled, forming a composite membrane structure of "dense temperature-sensitive skin and through-ordered finger pores". This improves the membrane flux and rejection rate, while also endowing the membrane with temperature-sensitive response properties. Attached Figure Description

[0010] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0011] Figure 1 The image is a SEM image obtained by scanning electron microscopy (SEM) at 8000x magnification of the PVDF ultrafiltration membrane of Example 1 of the present invention. Detailed Implementation

[0012] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0013] The following is a detailed description of a high-performance PVDF ultrafiltration membrane and its preparation method provided by an embodiment of the present invention.

[0014] A method for preparing a high-performance PVDF ultrafiltration membrane includes the following steps: (1) Preparation of PVDF-b-PEGMA-b-PNIPAM triblock copolymer: PVDF was dissolved in an organic solvent, and ethyl 2-bromoisobutyrate, CuBr / tris-(2-dimethylaminoethyl)amine, and N-isopropylacrylamide (NIPAM) monomer were added. The mixture was reacted at 40-50°C for 4-6 hours under nitrogen protection. Subsequently, polyethylene glycol methacrylate (PEGMA) was added, and the temperature was raised to 60-70°C to continue the reaction for 8-12 hours. After the reaction was completed, the mixture was precipitated and dried under vacuum to obtain PVDF-b-PEGMA-b-PNIPAM triblock copolymer. The PEGMA segment has a number-average molecular weight of 2000-5000, and the PNIPAM segment has a number-average molecular weight of 3000-8000. The organic solvent is one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), tetrahydrofuran (THF), acetone, acetonitrile, chloroform, dichloromethane, methanol, ethanol, and ethyl acetate. The mass ratio of PVDF, ethyl 2-bromoisobutyrate, CuBr, tris-(2-dimethylaminoethyl)amine, N-isopropylacrylamide, and polyethylene glycol methacrylate is 100:0.5-1.5:0.2-0.8:0.6-1.6:15-25:20-35. This step uses PVDF as the hydrophobic substrate and adds ethyl 2-bromoisobutyrate as the initiator. Under the action of the catalyst CuBr / tris-(2-dimethylaminoethyl)amine, it undergoes a reversible atom transfer radical initiation reaction, introducing active bromine atoms into the PVDF molecular chain ends to form PVDF-Br with bromine-retaining end groups. The active bromine end groups of PVDF-Br initiate the polymerization of NIPAM, grafting PNIPAM segments onto the ends of the PVDF chains. The reaction continues after adding PEGMA, grafting PEGMA segments onto the ends of the PNIPAM segments, ultimately forming "PVDF (hydrophobic framework) - b-PEGMA (permanent hydrophilic segment) - b-PNIPAM (temperature-sensitive responsive chain)". The triblock copolymer of PNIPAM and PEGMA segments brings the PNIPAM segments close to the PVDF backbone, and during thermosensitive transitions, it drives the PEGMA segments to undergo synergistic conformational changes, achieving a faster response speed. The PVDF segments of this invention provide excellent mechanical strength and chemical stability, the PEGMA segments have permanent hydrophilicity, which can significantly reduce the hydrophobicity of the membrane surface and reduce pollutant adsorption, and the PNIPAM segments have thermosensitive response characteristics, laying the foundation for the in-situ self-cleaning function of the membrane. This step ensures good compatibility between the triblock copolymer and PVDF by limiting the molecular weight of the polymer segments and the proportion of each substance, avoiding copolymer agglomeration that leads to membrane pore blockage, while ensuring a balance between the hydrophilicity and mechanical strength of the membrane.

[0015] (2) Preparation of casting solution: The triblock copolymer obtained in step (1) is mixed with PVDF at a mass ratio of 0.15~0.35:1, and added to a mixed solvent containing ionic liquid to prepare a casting solution with a total polymer concentration of 18~22wt%. After stirring and dissolving at 70~80℃ for 6~8h, the resulting solution is degassed for 2~4h without mixing. The mixed solvent is an organic solvent and an imidazole ionic liquid in a volume ratio of 1:0.2~0.5. The organic solvent is one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAC), N,N-dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and tetrahydrofuran (THF), preferably N-methylpyrrolidone. The imidazole ionic liquid is one of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate, preferably 1-ethyl-3-methylimidazolium acetate. In this step, the use of a mixed solvent containing ionic liquids not only achieves the full dissolution of PVDF and triblock copolymer to form a uniform and stable casting solution, but also promotes the formation of PVDF β crystals, greatly improving the mechanical strength of the membrane and improving the hydrophilicity of the membrane, thus providing a basis for the phase separation control of the subsequent film formation process. (3) Coupling to form a film: The casting solution obtained in step (2) is cast onto a substrate (such as a primary surface optical mirror or a stainless steel plate). An 8-inch wide temperature-controlled scraper is used to scrape a liquid film with a thickness of 200-250 μm onto the substrate. The scraper temperature is controlled to be 10-15°C lower than the casting solution temperature to form a temperature gradient between the casting solution and the scraper. This temperature gradient can induce rapid thermal phase separation on the surface of the liquid film, achieving surface pre-phase separation and laying the foundation for the formation of a dense skin layer. Subsequently, the substrate with the liquid film is quickly transferred to a sealed chamber and a nitrogen atmosphere with a relative humidity of 75-85% and a temperature of 50-55°C is introduced and maintained for 60-120 seconds. Phase separation is induced by steam. Water vapor, as a non-solvent, exchanges with the organic solvent on the surface of the liquid film. At the same time, the minimum critical dissolution temperature of the PNIPAM chain segment is utilized to induce phase separation of PNI. The PAM segments contract and aggregate on the surface of the liquid membrane, forming a dense temperature-sensitive skin. This skin can improve the membrane's rejection rate and impart temperature-sensitive response properties. Subsequently, the substrate is immersed in a coagulation bath at 15-20°C for 24 hours. The liquid membrane temperature drops sharply from 50-55°C to 15-20°C. This sudden temperature change further induces thermal phase separation inside the liquid membrane. This, combined with non-solvent-induced phase separation, induces the formation of a through-hole ordered finger-like pore structure, which can improve the membrane flux. The coagulation bath consists of deionized water and the imidazole ionic liquid described in step (2). The concentration of the imidazole ionic liquid is 10-20 wt%. The difference in diffusion rate between the ionic liquid and water, as well as the sudden temperature change, induce the formation of a through-hole ordered finger-like pore structure. After coagulation, the membrane is washed with deionized water and vacuum dried at 25-30°C to obtain the PVDF ultrafiltration membrane.

[0016] This step employs a composite film-forming process that couples thermally induced phase separation with non-solvent-induced phase separation and combines it with vapor-induced phase separation. Through multi-stage phase separation control, the membrane structure is precisely controlled, forming a composite structure of "dense temperature-sensitive skin and through-ordered finger pores".

[0017] The present invention also provides a high-performance PVDF ultrafiltration membrane prepared by the above preparation method.

[0018] Example 1 This embodiment provides a method for preparing a high-performance PVDF ultrafiltration membrane, including the following steps: Step (1): Preparation of PVDF-b-PEGMA-b-PNIPAM triblock copolymer 100g of PVDF powder (Solvate 6010) was dissolved in 1000g of N,N-dimethylacetamide, and 1.0g of ethyl 2-bromoisobutyrate, 0.5g of CuBr, 1.0g of tris-(2-dimethylaminoethyl)amine, and 20g of N-isopropylacrylamide were added. The mixture was reacted at 45℃ for 5h under nitrogen protection. Subsequently, 25g of PEGMA with a molecular weight of 3000 was added, and the temperature was raised to 65℃ for another 10h. The mixture was then precipitated with methanol and dried under vacuum at 40℃ for 24h to obtain a triblock copolymer. GPC tests showed that the number average molecular weight (Mn) was 45000, the polydispersity index (PDI) was 1.25, the number average molecular weight (Mn) of PEGMA segments was 3200, the number average molecular weight (Mn) of PNIPAM segments was 4500, and the hydrophilic segment ratio was 28%.

[0019] Step (2): Preparation of casting solution Take 6g of the above copolymer and mix it with 24g of PVDF. Add it to a mixed solvent of 70g of 1-ethyl-3-methylimidazolium acetate and 100g of N-methylpyrrolidone to prepare a casting solution with a polymer concentration of 20wt%. Then, stir and dissolve the solution at 75°C for 7h. After that, degas the resulting solution for 3h without mixing. Step (3): Film formation The casting solution obtained in step (2) was kept at 60°C for 30 min and cast onto the primary surface optical mirror. At the same time, an 8-inch wide scraper was used and the scraper temperature was set to 48°C to scrape a 230 μm liquid film onto the primary surface optical mirror. The optical mirror with the liquid film was then transferred to a sealed chamber and purged with a nitrogen atmosphere of 80% relative humidity and 50°C for 100 s. The optical mirror was then immersed in a coagulation bath at 18°C ​​(containing 15 wt% 1-ethyl-3-methylimidazolium acetate) and coagulated for 24 h. It was then washed with deionized water and vacuum dried at 28°C for 16 h to obtain the PVDF ultrafiltration membrane.

[0020] Example 2 The difference between this embodiment and Embodiment 1 is that: In step (1), 15g of NIPAM and 20g of PEGMA were used. GPC testing showed: Mn=42000, PDI=1.22, PEGMA segment Mn=2800, and PNIPAM segment Mn=3500. In step (2), 4.5g of copolymer and 25.5g of PVDF are used; In step (3), the scraper temperature is 46℃.

[0021] Example 3 The difference between this embodiment and Embodiment 1 is that: In step (1), the amount of NIPAM used is 25g and the amount of PEGMA used is 35g; according to GPC test: Mn=48000, PDI=1.28; PEGMA segment Mn=3800, PNIPAM segment Mn=5500; In step (2), 8g of copolymer and 22g of PVDF are used; In step (3), the scraper temperature is 50°C.

[0022] Comparative Example 1 This comparative example uses the method of Example 1 in CN109621756A to prepare a PVDF ultrafiltration membrane.

[0023] Comparative Example 2 In step (2), no mixed solvent containing ionic liquid was used; the solvent was pure N-methylpyrrolidone. In step (3), the coagulation bath was pure water.

[0024] Experimental Example 1 - Thermosensitivity Test The PVDF ultrafiltration membranes prepared in each embodiment and comparative example were tested for pure water flux at 25℃, 32℃, and 40℃, respectively. The test method was based on the national standard GB / T 32360-2015 Ultrafiltration Membrane Test Method. The tests were conducted and the results were calculated. The results are shown in Table 1. Table 1 - Pure water flux test results of PVDF ultrafiltration membranes obtained in each embodiment and comparative example

[0025] Meanwhile, the PVDF ultrafiltration membrane of Example 1 was subjected to a cycle stability test. It was cycled 10 times at 25℃, 32℃, and 40℃ to test its flux recovery rate. The test method was based on the national standard GB / T 32360-2015 Ultrafiltration Membrane Test Method. The flux recovery rates were 98.2%, 97.5%, 97.8%, 98.0%, 97.6%, 98.3%, 97.9%, 98.1%, 97.7%, and 98.0%, respectively; the average recovery rate was 97.9%.

[0026] Experiment Example 2 This experiment tested the performance of the PVDF ultrafiltration membranes obtained in each embodiment and comparative example, and the results are shown in Table 2. The BSA rejection rate was tested and calculated according to the national standard GB / T 32360-2015 "Test Methods for Ultrafiltration Membranes". Mechanical strength (tensile strength, elongation at break): According to the national standard GB / T 1040.3-2006 "Determination of Tensile Properties of Plastics Part 3: Test Conditions for Films and Sheets", a universal testing machine was used to test the tensile strength (MPa) and elongation at break (%) at a tensile rate of 5 mm / min. Table 2 - Performance test results of PVDF ultrafiltration membranes obtained in each embodiment and comparative example

[0027] As can be seen from the results in Table 1-2, the PVDF ultrafiltration membrane prepared in the present invention has excellent water flux. Even after 10 temperature difference cycles, it still has a good flux recovery rate, which proves that the PVDF ultrafiltration membrane prepared in Example 1 has good temperature-sensitive response performance and excellent structural reversibility. Furthermore, the PVDF ultrafiltration membrane prepared in the embodiments of the present invention has a significantly better BSA rejection rate and mechanical strength than the comparative examples. This proves that the temperature-sensitive skin formed by the ultrafiltration membrane prepared in the present invention is in a hydrated and open state at the operating temperature, but the pore size distribution is extremely narrow, which can achieve a high rejection effect under high flux. The triblock copolymer formed and the uniform and stable casting solution play a crucial role in improving the mechanical strength.

[0028] Experimental Example 3 The polyethersulfone film prepared in Example 1 was subjected to scanning electron microscopy at 8000x magnification. The results are shown in [Figure 1]. Figure 1 ,Depend on Figure 1As can be seen, the SEM micrographs reveal a unique composite structure of a "dense thermosensitive skin and interconnected, ordered finger-like pores." As shown in the figure, a continuous, uniform, and relatively dense skin layer can be observed. This structure is the result of the combined effect of thermally induced phase separation on the surface layer induced by a temperature gradient created by a temperature-controlled scraper, combined with subsequent vapor-induced phase separation in a nitrogen atmosphere at specific temperature and humidity. During this process, the PNIPAM thermosensitive segments in the triblock copolymer shrink and aggregate on the surface, synergistically forming this dense skin layer. This provides the membrane with excellent selective separation performance (BSA rejection rate up to 96.5%) and thermosensitive response characteristics. Beneath the dense skin layer are numerous large, uniform, and well-connected finger-like pores that grow vertically downwards from the skin layer. The formation of these finger-like pores stems from the synergistic effect of rapid thermally induced phase separation and non-solvent-induced phase separation occurring when the liquid membrane is immersed in a low-temperature coagulation bath. This gradient structure, with a dense upper surface and a continuous, ordered, interconnected finger-like pore layer below, is key to achieving a synergistic improvement in high throughput and high rejection rate. The structure shown in the figure is continuous, uniform and stable, which also confirms the good compatibility between the triblock copolymer and PVDF and the uniformity and stability of the casting solution. This is the structural basis for the membrane to have high mechanical strength (tensile strength 28.3 MPa).

[0029] The above are merely preferred embodiments of the present invention and are not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing high performance PVDF ultrafiltration membrane, characterized in that, Includes the following steps: (1) Preparation of PVDF-b-PEGMA-b-PNIPAM triblock copolymer: PVDF was dissolved in an organic solvent, and ethyl 2-bromoisobutyrate, CuBr / tris-(2-dimethylaminoethyl)amine, and monomer N-isopropylacrylamide were added. The mixture was reacted under nitrogen protection for a period of time. Then, polyethylene glycol methacrylate was added, and the mixture was heated and reacted for a period of time. After the reaction was completed, the mixture was precipitated and dried under vacuum to obtain PVDF-b-PEGMA-b-PNIPAM triblock copolymer. (2) Preparation of casting solution: The triblock copolymer obtained in step (1) is mixed with PVDF and added to a mixed solvent containing ionic liquid. After dissolution, the resulting solution is degassed without mixing to obtain a casting solution. (3) Coupling to form a film: The casting solution obtained in step (2) is cast onto the substrate, coated with a temperature-controlled scraper, and the temperature of the temperature-controlled scraper is controlled to be lower than that of the casting solution. The substrate is then quickly transferred to a sealed chamber and kept under a nitrogen atmosphere. The substrate is then immersed in a coagulation bath. After coagulation, it is washed and dried to obtain the PVDF ultrafiltration membrane.

2. The method of claim 1, wherein the high performance PVDF ultrafiltration membrane is prepared by the steps of: In step (1), the number-average molecular weight of the PEGMA segments is 2000~5000, and the number-average molecular weight of the PNIPAM segments is 3000~8000.

3. The method of claim 1, wherein the high performance PVDF ultrafiltration membrane is prepared by the steps of: In step (1), the organic solvent is one of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, tetrahydrofuran, acetone, acetonitrile, chloroform, dichloromethane, methanol, ethanol, and ethyl acetate.

4. The method of claim 1, wherein the high performance PVDF ultrafiltration membrane is prepared by the steps of: In step (1), the mass ratio of PVDF, ethyl 2-bromoisobutyrate, CuBr, tris-(2-dimethylaminoethyl)amine, N-isopropylacrylamide, and polyethylene glycol methacrylate is 100:0.5~1.5:0.2~0.8:0.6~1.6:15~25:20~35.

5. The method of claim 1, wherein the high performance PVDF ultrafiltration membrane is prepared by the steps of: In step (1), the molar ratio of CuBr to tris-(2-dimethylaminoethyl)amine is 1~2:

1.

6. The method of claim 1, wherein the high performance PVDF ultrafiltration membrane is prepared by the steps of: In step (2), the triblock copolymer and PVDF are mixed at a mass ratio of 0.15 to 0.35:

1.

7. The method for preparing a high-performance PVDF ultrafiltration membrane according to claim 1, characterized in that, In step (2), the mixed solvent is an organic solvent and an imidazole ionic liquid with a volume ratio of 1:0.2~0.

5.

8. The method for preparing a high-performance PVDF ultrafiltration membrane according to claim 1, characterized in that, In step (2), the organic solvent is one of N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran; the imidazole ionic liquid is one of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium chloride, 1-ethyl-3-methylimidazolium bromide, and 1-ethyl-3-methylimidazolium trifluoromethanesulfonate.

9. The method for preparing the high-performance PVDF ultrafiltration membrane according to claim 8, characterized in that, In step (3), the temperature of the temperature control scraper is controlled to be 10-15°C lower than the temperature of the casting solution. The coagulation bath is deionized water and the imidazole ionic liquid mentioned in step (2), and the concentration of the imidazole ionic liquid is 10-20 wt%.

10. A high-performance PVDF ultrafiltration membrane, characterized in that, It is prepared by any one of the preparation methods of claims 1 to 9.

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