An asymmetric polyethersulfone filter membrane, its preparation method and application

Abstract

This invention discloses an asymmetric polyethersulfone filter membrane, its preparation method, and its applications. The invention controls the content of non-solvents in the casting solution to be greater than the content of solvents, and combines vapor-induced phase separation (VIPS), thermally induced phase separation (TIPS), and immersion precipitation-induced phase separation (LIPS) to induce differential phase separation between the upper and lower layers of the coating simultaneously, resulting in an asymmetric polyethersulfone filter membrane with a three-layer structure and an inverted V-shaped cross-section. This asymmetric polyethersulfone filter membrane exhibits high sterilization rate, high filtration flux, and high loading capacity.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, specifically to an asymmetric polyethersulfone filter membrane, its preparation method, and its application. Background Technology

[0002] In numerous industries such as biopharmaceuticals, food and beverage, and ultrapure water preparation for electronics, sterilization filtration is crucial. Common sterilization filtration membrane materials include nylon, polyethersulfone (PES), polyvinylidene fluoride (PVDF), and polytetrafluoroethylene (PTFE). Among them, PES sterilization membranes are widely used in biopharmaceuticals and other fields due to their good chemical stability, low protein adsorption, high filtration flux, and resistance to gamma rays. However, traditional PES sterilization membranes suffer from difficulties in balancing retention precision and flux. Their low structural asymmetry makes it easy for impurities to accumulate on the membrane surface and in the internal pores during filtration, causing rapid fouling. Frequent replacements not only increase operating costs but also affect production continuity. While multilayer composite membranes can effectively improve membrane structural asymmetry and filtration performance, their preparation requires multiple complex processes, the use of various casting solutions, and extremely high equipment precision. Problems such as loose bonding and uneven component miscibility between layers can easily occur, resulting in large fluctuations in membrane performance and low yield rates, making it difficult to consistently meet the demands for high-precision sterilization and high-flux filtration.

[0003] To achieve a PES sterilization membrane with high sterilization rate, high filtration flux, and high load capacity simultaneously, the membrane must possess both suitable and uniform pore size separation and a significant asymmetric structure. Currently, most commercially available PES sterilization membranes, both domestically and internationally, reduce membrane asymmetry to ensure effective sterilization. This results in weak dirt-holding capacity, low filtration flux, rapid flux decay over long-term use, short lifespan, and frequent replacements, increasing operating costs. For example, patent applications CN117563441A, CN117398865A, and CN117358075A disclose an "hourglass-shaped" asymmetric structure for PES sterilization membranes. This structure includes a macroporous pre-filtration layer and a microporous retention layer, with the effective retention layer located in the middle of the cross-section. Its key features are high mechanical strength and high-precision sterilization rate. However, due to the relatively small size of the macroporous pre-filtration layer, its primary dirt-holding area is relatively small, resulting in a low filtration load and short lifespan. Similarly, the Micro series membrane products involved in patent CN101227965A also all have an hourglass-shaped asymmetric structure, which also suffers from the disadvantage of low filtration capacity. Therefore, while ensuring high-precision sterilization of PES filter membranes, improving the asymmetry of the membrane structure is a key factor in simultaneously increasing their filtration flux and capacity. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide an asymmetric polyethersulfone filter membrane, its preparation method and application, which can obtain an asymmetric polyethersulfone filter membrane with high sterilization rate, high filtration flux and loading capacity.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] This invention discloses an asymmetric polyethersulfone filter membrane, which comprises a protective layer, a separation layer and a pre-filter layer from top to bottom, with the average pore size relationship being pre-filter layer > protective layer > separation layer.

[0007] As a preferred technical solution, the protective layer is a porous protective layer with an average pore size of 0.8-1.5 μm; the separation layer is a separation layer composed of continuous dense small pores with an average pore size of 0.20-0.25 μm; the pre-filter layer is a double continuous gradient increasing macroporous layer with an average pore size of 5.7-6.0 μm; and the asymmetry ratio of the pre-filter layer to the separation layer is 24-29.

[0008] As a preferred technical solution, the thickness ratio of the protective layer, the separation layer and the pre-filter layer is 1:3:3-6, the three-layer structure has a continuous transition without obvious interfaces, and the cross-section is inverted V-shaped.

[0009] This invention discloses a method for preparing an asymmetric polyethersulfone filter membrane, comprising the following steps:

[0010] (1) Solution preparation: According to the weight, 10-18 parts of polyethersulfone, 3-8 parts of sulfonated polyethersulfone, 25-40 parts of solvent, 30-40 parts of non-solvent additive and 5-20 parts of pore-forming agent are mixed and dissolved to obtain a homogeneous casting solution; wherein, the content of non-solvent additive is greater than the content of solvent.

[0011] (2) Debubbling and coating: The homogeneous casting solution is coated onto the support;

[0012] (3) Primary film formation process: The coating accompanying the support is subjected to differential synchronous induction between the upper and lower layers; the upper surface of the coating is subjected to double induction using heated steam on the air side, with a steam temperature of 50-90℃ and a steam relative humidity of 50-90%; the lower surface of the coating is subjected to low-temperature induction through the base plate in contact with it, with a base plate temperature of 20-50℃, thus obtaining the primary film.

[0013] (4) Curing: The nascent membrane is immersed in a water coagulation bath along with the support to solidify into a membrane, and then washed and dried to obtain an asymmetric polyethersulfone filter membrane.

[0014] As a preferred technical solution, the solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, 2-pyrrolidone, and dimethyl sulfoxide.

[0015] As a preferred technical solution, the non-solvent additive is one or more of ethylene glycol monomethyl ether, 2-methoxyestradiol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, diethylene glycol monomethyl ether, and small molecule polyethylene glycol.

[0016] As a preferred technical solution, the pore-forming agent is one or more of polyacrylic acid, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, polyethylene glycol, polyvinylpyridine, polyethyleneimine, polyoxazoline, and block polyether.

[0017] As a preferred technical solution, in step (3), the steam temperature is 50-65℃, the steam relative humidity is 60-80%, and the bottom plate temperature is 20-40℃.

[0018] As a preferred technical solution, in step (3), the differential synchronization induction time between the upper and lower layers is 5-60s.

[0019] The present invention also discloses the application of the aforementioned asymmetric polyethersulfone filter membrane in filtration and sterilization.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention controls the content of non-solvents in the casting solution to be greater than the content of solvents, and combines vapor-induced phase separation (VIPS), thermally induced phase separation (TIPS), and immersion precipitation-induced phase separation (LIPS) to induce differential phase separation between the upper and lower layers of the coating simultaneously, resulting in an asymmetric polyethersulfone filter membrane with an inverted V-shaped three-layer structure. This asymmetric polyethersulfone filter membrane has high sterilization rate, high filtration flux, and high loading capacity, with the following specific advantages:

[0022] 1. The film-forming process is easy to control, and the film structure has a stable and uniform transition, which is conducive to large-scale and batch production.

[0023] 2. Highly efficient sterilization: It has a dense and uniform separation layer to ensure the sterility of the product;

[0024] 3. Significant flux advantage: Under the same pressure, the flux is 30%-50% higher than that of traditional PES sterilization membranes, reducing filtration costs and time;

[0025] 4. Long service life: The unique highly asymmetric structure significantly improves the dirt holding capacity, delays clogging, slows down flux decline, and allows the flux to be effectively restored after cleaning, reducing the frequency of membrane replacement. Attached Figure Description

[0026] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the following figures are provided for illustration:

[0027] Figure 1A, B, and C are SEM images of the cross-section, macropore surface on the release membrane side, and micropore surface on the vapor side of the asymmetric polyethersulfone filter membrane prepared in Example 1, respectively.

[0028] Figure 2 This is a cross-sectional SEM image of the asymmetric polyethersulfone filter membrane prepared in Example 2.

[0029] Figure 3 The image shows a cross-sectional SEM image of the asymmetric polyethersulfone filter membrane prepared in Comparative Example 1.

[0030] Figure 4 The image shows a cross-sectional SEM image of the asymmetric polyethersulfone filter membrane prepared in Comparative Example 2.

[0031] Figure 5 This is a cross-sectional SEM image of the asymmetric polyethersulfone filter membrane prepared in Comparative Example 3. Detailed Implementation

[0032] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0033] In this invention, "asymmetry" refers to a membrane or region in which the diameter of the pores varies continuously or discontinuously along the thickness direction of the membrane or region. The control methods for generating asymmetric polyethersulfone filter membranes in this invention include specific solution composition requirements and differential synchronous induction process control between upper and lower layers.

[0034] The solution composition includes 10-18 parts polyethersulfone, 3-8 parts sulfonated polyethersulfone, 25-40 parts solvent, 30-40 parts non-solvent additives, and 5-20 parts pore-forming agent, wherein the content of non-solvent additives is greater than that of solvent. The differential synchronous induction process for the upper and lower layers requires dual induction using heated steam on the air side of the upper coating surface, with a steam temperature of 50-90℃ and a relative humidity of 50-90%; low-temperature induction is performed on the support side of the lower coating surface through a contact plate, with a plate temperature of 20-50℃.

[0035] Based on the specific solution composition requirements and the differentiated synchronous induction process control of the upper and lower layers, the steam in contact with the upper coating is heated. Through the synergistic induction of vapor-induced phase separation (VIPS) and thermally induced phase separation (TIPS), the upper surface of the coating rapidly separates phases and quickly reaches a gel state, simultaneously forming a porous protective layer and a dense separation layer with nascent pore morphology, with the protective layer located above the separation layer. Simultaneously, delayed phase separation occurs on the lower surface of the coating due to cooling, and the phase separation domain gradually expands and grows, forming a nascent pre-filtration layer with macroporous morphology. At this point, the overall nascent membrane morphology exhibits high asymmetry. To effectively preserve this highly asymmetric structure, the entire nascent membrane is rapidly immersed in a non-solvent coagulation bath to solidify into a three-layer asymmetric polyethersulfone filter membrane with an inverted V-shaped cross-section.

[0036] In the asymmetric polyethersulfone filter membrane of the present invention, the upper layer has a porous protective layer and a separation layer composed of continuous dense micropores, and the lower layer has a macroporous pre-filtration layer with a double continuous gradient increase. The average pore size relationship is pre-filtration layer > protective layer > separation layer. The average pore size of the protective layer is 0.8-1.5 μm, the average pore size of the separation layer is 0.20-0.25 μm, and the average pore size of the pre-filtration layer is 5.7-6.0 μm. The asymmetry ratio of the pre-filtration layer to the separation layer is 24-29. The thickness ratio of the three layers from top to bottom is 1:3:3-6. The three layers have a continuous transition without obvious interfaces, and the cross-section is inverted V-shaped.

[0037] The average pore size of the protective layer, separation layer, and pre-filter layer can be characterized by using SEM to scan the membrane cross-section structure in sections, and then measured and calculated using computer software (Nano measure 2.0); the asymmetry ratio is calculated as follows: average pore size of pre-filter layer / average pore size of separation layer.

[0038] This invention unexpectedly discovered that the asymmetric polyethersulfone filter membrane with the above-mentioned membrane structure possesses high sterilization rate, high filtration flux, and high loading capacity. The pre-filtration layer is composed of a continuous, porous, gradient three-dimensional network of pores, effectively trapping large particulate impurities in the filtered liquid and increasing the membrane's dirt-holding capacity. The separation layer is composed of continuous, dense small pores, effectively ensuring bacterial retention. The protective layer primarily protects the separation layer, reducing filtration resistance while simultaneously ensuring the separation layer's retention effect. However, a larger average pore size in the pre-filtration layer is not always better. If the average pore size is too large, resulting in too many pores, the pre-filtration layer becomes too porous. Most of the liquid pressure acts on the pre-filtration layer, and an overly porous pre-filtration layer is prone to compression due to liquid pressure, leading to a decrease in the overall flux and loading capacity of the membrane. Simultaneously, the protective layer should not be too thick, and the pores should not be too dense; otherwise, the effective components in the liquid may ultimately fail to reach the membrane's internal pores. By controlling the thickness of each layer of the asymmetric polyethersulfone filter membrane, this invention can ensure that the asymmetric polyethersulfone filter membrane has excellent retention capacity and can provide good dirt holding effect.

[0039] Example 1

[0040] (1) Mix 35 parts of N-methylpyrrolidone and 38 parts of small molecule polyethylene glycol (relative molecular mass of 400), heat the mixture to 70°C and stir until uniform, then cool to 50°C, add 14 parts of polyethersulfone (BASF E6020P), 3 parts of sulfonated polyethersulfone (sulfonation degree 10%) and 10 parts of block polyether (PE6400, relative molecular mass of 2900 g / mol) and continue stirring to dissolve. After 8 hours, a homogeneous solution is obtained. Vacuum degassing and maintain constant temperature of 30°C to obtain a homogeneous casting solution.

[0041] (2) The casting solution is applied to the release film with a doctor blade at a gap of 300 μm to obtain a solution coating.

[0042] (3) The lower surface of the solution coating is placed on a stainless steel base plate at 25°C to cool along with the release film. At the same time, the upper surface of the coating is subjected to double induction for 30 seconds with hot air at 60°C and 80%RH to obtain the nascent film.

[0043] (4) The nascent membrane was placed in a deionized water coagulation bath at 60°C to solidify into a membrane, and finally washed and dried to obtain an asymmetric polyethersulfone filter membrane.

[0044] The prepared polyethersulfone antibacterial membrane has a thickness of 110-120 μm. Figure 1A, B, and C are SEM images of the cross-section, macroporous surface of the release membrane side, and microporous surface of the asymmetric polyethersulfone filter membrane prepared in Example 1, respectively. The images show that the cross-section of the polyethersulfone sterilization membrane has a significant inverted V-shaped highly asymmetric three-layer structure. The upper layer is a porous protective layer, the lower layer is a dense separation layer, and the lower layer is a pre-filter layer with a double continuous gradient increasing macroporous structure. The thickness ratio from top to bottom is 1:3:6. After measurement and calculation, it was found that the average pore size of the protective layer is 1.5 μm, the average pore size of the separation layer is 0.20 μm, the average pore size of the pre-filter layer is 5.7 μm, and the asymmetry ratio of the pre-filter layer to the separation layer is 28.5.

[0045] Example 2

[0046] (1) Mix 36 parts of N,N-dimethylacetamide and 38 parts of diethylene glycol, heat the mixture to 60°C and stir until homogeneous, then add 11 parts of polyethersulfone (BASF E6020P), 6 parts of sulfonated polyethersulfone (sulfonation degree 5%) and 9 parts of polyethylene glycol (molecular weight 6000 g / mol) and continue stirring to dissolve. After 8 hours, a homogeneous solution is obtained. Vacuum degassing and maintain constant temperature of 40°C to obtain a homogeneous casting solution.

[0047] (2) The casting solution is applied to the release film with a doctor blade at a gap of 400 μm to obtain a solution coating.

[0048] (3) The lower surface of the solution coating is placed on a stainless steel base plate at 40°C to cool along with the release film. At the same time, the upper surface of the coating is subjected to double induction for 10 seconds with hot air at 65°C and 70%RH to obtain the nascent film.

[0049] (4) The nascent membrane was placed in a deionized water coagulation bath at 70°C to solidify into a membrane, and finally washed and dried to obtain an asymmetric polyethersulfone filter membrane.

[0050] The prepared polyethersulfone antibacterial membrane has a thickness of 120-130 μm. Figure 2 The image shows a cross-sectional SEM image of the asymmetric polyethersulfone filter membrane prepared in Example 2. The image reveals a distinct inverted V-shaped, highly asymmetric three-layer structure: an upper porous protective layer, a dense separation layer below, and a pre-filter layer with a double-gradient increasing macroporous structure. The thickness ratio from top to bottom is 1:3:3. Measurements and calculations show that the average pore size of the protective layer is 0.98 μm, the average pore size of the separation layer is 0.25 μm, and the average pore size of the pre-filter layer is 6.0 μm. The asymmetry ratio between the pre-filter layer and the separation layer is 24.

[0051] Example 3

[0052] (1) Mix 25 parts of N-methylpyrrolidone and 32 parts of triethylene glycol, heat the mixture to 60°C and stir until homogeneous, then add 10 parts of polyethersulfone (BASF E6020P), 4 parts of sulfonated polyethersulfone (sulfonation degree 5%) and 9 parts of polyvinyl acetate (molecular weight 6000 g / mol) and continue stirring to dissolve. After 8 hours, a homogeneous solution is obtained. Vacuum degassing is performed and the temperature is maintained at 30°C to obtain a homogeneous casting solution.

[0053] (2) The casting solution is applied to the release film with a doctor blade at a gap of 400 μm to obtain a solution coating.

[0054] (3) The lower surface of the solution coating is placed on a stainless steel base plate at 20°C to cool along with the release film. At the same time, the upper surface of the coating is subjected to double induction for 20 seconds with hot air at 50°C and 60%RH to obtain the nascent film.

[0055] (4) The nascent membrane was placed in a deionized water coagulation bath at 70°C to solidify into a membrane, and finally washed and dried to obtain an asymmetric polyethersulfone filter membrane.

[0056] The prepared polyethersulfone sterilization membrane has a thickness of 110-120 μm. The cross-section of the polyethersulfone sterilization membrane has a significant inverted V-shaped highly asymmetric three-layer structure: an upper porous protective layer, a dense separation layer below, and a pre-filter layer with a double continuous gradient increasing macroporous structure. The thickness ratio from top to bottom is 1:3:4. Measurements and calculations show that the average pore size of the protective layer is 1.0 μm, the average pore size of the separation layer is 0.20 μm, and the average pore size of the pre-filter layer is 5.7 μm. The asymmetry ratio of the pre-filter layer to the separation layer is 28.5.

[0057] Comparative Example 1

[0058] (1) Mix 65 parts of N,N-dimethylacetamide and 6 parts of water, heat the mixture to 70°C and stir until homogeneous, then add 12 parts of polyethersulfone (BASF E6020P), 4 parts of sulfonated polyethersulfone (sulfonation degree 10%) and 13 parts of polyvinylpyrrolidone and continue stirring to dissolve. After 8 hours, a homogeneous solution is obtained. Vacuum degassing is performed and the temperature is maintained at 50°C to obtain a homogeneous casting solution.

[0059] (2) Apply the casting solution onto the release film with a doctor blade at a gap of 350 μm to obtain a solution coating;

[0060] (3) The lower surface of the solution coating is placed on a stainless steel base plate at 20°C to cool along with the release film. At the same time, the upper surface of the coating is subjected to double induction for 20 seconds with hot air at 55°C and 75%RH to obtain the nascent film.

[0061] (4) The nascent membrane was placed in a deionized water coagulation bath at 60°C to solidify into a membrane, and finally washed and dried to obtain an asymmetric polyethersulfone filter membrane.

[0062] The prepared polyethersulfone antibacterial membrane has a thickness of 115-130 μm. Figure 3 The image shows a cross-sectional SEM image of the asymmetric polyethersulfone filter membrane prepared in Comparative Example 1. The polyethersulfone sterilization membrane cross-section shows a significant positive V-shaped highly asymmetric two-layer structure. The upper layer is a macroporous pre-filtration layer with a double continuous gradient decreasing, and the lower layer is a dense separation layer. The thickness ratio from top to bottom is 2:6.

[0063] Comparative Example 2

[0064] (1) Mix 40 parts of N,N-dimethylacetamide and 4 parts of water, heat the mixture to 70°C and stir until homogeneous, then add 10 parts of polyethersulfone (BASF E6020P), 4 parts of sulfonated polyethersulfone (sulfonation degree 10%) and 10 parts of polyvinylpyrrolidone and continue stirring to dissolve. After 8 hours, a homogeneous solution is obtained. Vacuum degassing is performed and the temperature is maintained at 50°C to obtain a homogeneous casting solution.

[0065] (2) Apply the casting solution onto the release film with a doctor blade at a gap of 350 μm to obtain a solution coating;

[0066] (3) The lower surface of the solution coating is placed on a stainless steel base plate at 30°C to cool along with the release film. At the same time, the upper surface of the coating is subjected to double induction for 20 seconds with hot air at 50°C and 60%RH to obtain the nascent film.

[0067] (4) The nascent membrane was placed in a deionized water coagulation bath at 60°C to solidify into a membrane, and finally washed and dried to obtain an asymmetric polyethersulfone filter membrane.

[0068] The prepared polyethersulfone antibacterial membrane has a thickness of 115-120 μm. Figure 4 The image shows a cross-sectional SEM image of the asymmetric polyethersulfone filter membrane prepared in Comparative Example 2. The polyethersulfone sterilization membrane cross-section shows a significant positive V-shaped highly asymmetric two-layer structure. The upper layer is a macroporous pre-filtration layer with a double continuous gradient decreasing, and the lower layer is a dense separation layer. The thickness ratio from top to bottom is 2:8.

[0069] Comparative Example 3

[0070] (1) The composition and stirring and dissolving method of the casting solution are the same as those in Example 3. After stirring and dissolving for 8 hours, a homogeneous solution is obtained. Vacuum degassing and constant temperature of 40°C are maintained to obtain a homogeneous casting solution.

[0071] (2) The casting solution is applied to the release film with a doctor blade at a gap of 400 μm to obtain a solution coating.

[0072] (3) The lower surface of the solution coating is heated on a stainless steel base plate at 50°C along with the release film, while the upper surface of the coating is steam-induced for 10s with steam at 35°C and 70%RH to obtain the nascent film.

[0073] (4) The nascent membrane was placed in a deionized water coagulation bath at 70°C to solidify into a membrane, and finally washed and dried to obtain an asymmetric polyethersulfone filter membrane.

[0074] The prepared polyethersulfone antibacterial membrane has a thickness of 110-120 μm. Figure 5 The image shows a cross-sectional SEM image of the asymmetric polyethersulfone filter membrane prepared in Comparative Example 3. The cross-section of the polyethersulfone sterilization membrane has an asymmetric three-layer structure: the upper layer is a porous protective layer, the lower layer is a dense separation layer, and the lower layer is a macroporous pre-filtration layer with a double continuous gradient. The thickness ratio from top to bottom is 3:2:4.

[0075] Comparative Example 4

[0076] (1) Mix 39 parts of N-methylpyrrolidone and 33 parts of small molecule polyethylene glycol (relative molecular mass of 400), heat the mixture to 70°C and stir until uniform, then cool to 50°C, add 14 parts of polyethersulfone (BASF E6020P), 3 parts of sulfonated polyethersulfone (sulfonation degree 10%) and 10 parts of block polyether (PE6400, relative molecular mass of 2900 g / mol) and continue stirring to dissolve. After 8 hours, a homogeneous solution is obtained. Vacuum degassing and maintain constant temperature of 30°C to obtain a homogeneous casting solution.

[0077] (2) The casting solution is applied to the release film with a doctor blade at a gap of 300 μm to obtain a solution coating.

[0078] (3) The lower surface of the solution coating is placed on a stainless steel base plate at 25°C to cool along with the release film. At the same time, the upper surface of the coating is subjected to double induction for 30 seconds with hot air at 60°C and 80%RH to obtain the nascent film.

[0079] (4) The nascent membrane is placed in a deionized water coagulation bath at 60°C to solidify into a membrane, and finally cleaned and dried to obtain a polyethersulfone antibacterial membrane.

[0080] The prepared polyethersulfone antibacterial membrane has a thickness of 110-120 μm, is a membrane with a symmetrical structure, and does not have a three-layer structure.

[0081] Performance testing

[0082] The bubble point is the gas pressure required to displace the liquid from the largest pore of a porous structure. When a sample of the material to be tested is immersed in a liquid, the liquid spontaneously fills the pores in the sample. Then, pressurized gas is applied to one side of the sample. Initially, the gas does not flow through the sample because the pores are filled with liquid. As the gas pressure increases, the gas will, under a certain pressure, empty the largest pore of the liquid, and the gas will begin to flow through the sample. The pressure at which the gas begins to flow through the sample is called the bubble point pressure.

[0083] Flux is defined as the amount of fluid that a filter can handle until the end of the filtration process.

[0084] Bubble point test: According to GB / T32361-2015 "Test method for pore size of separation membrane, bubble point and average flow rate method", the pure water flux and pure water bubble point of the PES sterilization membranes of the examples and comparative examples were tested (test pressure was 70 kPa). The test results are shown in Table 1.

[0085] Bacterial Retention Test: The PES sterilization membranes from the examples and comparative cases were used as samples for a bacterial retention challenge test. The test method followed the guidance document TR26 issued by the PDA. During the test, *Pseudomonas degenerativeae* (ATCC 19146) with a diameter of 0.3-0.4 μm was used as the retained bacteria. The bacterial retention test was conducted on the samples according to standard ASTM F838-2015ae1, and the LRV value of the filter membrane was measured. The test results are shown in Table 1.

[0086] Filtration Capacity Test: Preparation of Tryptic Soybean Liquid Culture Medium (TSB) Challenge Solution: Measure 5L of ultrapure water using a graduated cylinder, adding 4L to a 10L plastic container. Then weigh 150g of tryptic soybean liquid culture medium (TSB) and add it to the 4L water. Sonicate for 10 minutes to dissolve the solution. Add the dissolved tryptic soybean liquid culture medium (TSB) solution to a pressure vessel, rinse the plastic container with the reserved ultrapure water, and stir for 5 minutes to ensure homogeneity. Cut the PES sterile membranes from the examples and comparative examples into 47mm diameter (d) pieces, wet them, and place them in a disc filter. Filter the volume V of tryptic soybean liquid culture medium (TSB) at a constant pressure of 1 bar.

[0087] The calculation method is as follows: Filter capacity = ν / П / (d / 2) 2

[0088] The present invention characterizes the filtration capacity of the filter membrane by filtering the volume of tryptic soy peptone liquid culture medium (TSB) at a constant pressure of 1 bar. The test results are shown in Table 1.

[0089] In Table 1, K and M represent similar asymmetric PES films sold on the market.

[0090] Table 1 Performance parameters of the asymmetric PES antibacterial membranes prepared in each embodiment and comparative example.

[0091] Test object Pure water soaking point (MPa) <![CDATA[Pure water flux (mL / min / cm 2 )]]> LRV <![CDATA[Filter loading (ml / cm 2 )]]> Example 1 0.5 45 8.2 130 Example 2 0.5 42 8.1 129 Example 3 0.4 40 8.0 123 Comparative Example 1 0.5 30 8.4 107 Comparative Example 2 0.48 28 8.2 103 Comparative Example 3 0.38 20 6.8 50 Comparative Example 4 0.3 23 5.4 34 K 0.48-0.5 25 8.3 21 M 0.43-0.47 30 8.1 27

[0092] The filter loading capacity in the table above reflects the membrane's dirt holding capacity and service life.

[0093] This invention utilizes phase separation (TIPS) achieved by heating the upper surface of the coating to a temperature above its lower critical dissolution temperature, forming a nascent separation layer with a porous structure. The upper surface of the coating, in contact with steam, first undergoes phase separation dominated by VIPS, promoting pore opening and forming a nascent porous protective layer above the nascent separation layer along the steam induction direction. Simultaneously, delayed phase separation occurs on the lower surface of the coating due to cooling, and the phase separation domain gradually expands, forming a macroporous nascent pre-filtration layer. Finally, the entire nascent membrane is rapidly immersed in a non-solvent coagulation bath for LIPS curing, resulting in an inverted V-shaped highly asymmetric membrane structure. This invention creatively combines TIPS, VIPS, and LIPS. Those skilled in the art should understand that appropriate adjustments to the process conditions or formulation are within the scope of this invention.

[0094] The above-described embodiments are merely preferred embodiments provided to fully illustrate the present invention, and the scope of protection of the present invention is not limited thereto. Equivalent substitutions or modifications made by those skilled in the art based on the present invention are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the claims.

Claims

1. An asymmetric polyethersulfone filter membrane, characterized in that: The asymmetric polyethersulfone antibacterial membrane comprises, from top to bottom, a protective layer, a separation layer, and a pre-filter layer, with the average pore size relationship being: pre-filter layer > protective layer > separation layer.

2. The asymmetric polyethersulfone filter membrane according to claim 1, characterized in that: The protective layer is a porous protective layer with an average pore size of 0.8-1.5 μm; the separation layer is a separation layer composed of continuous dense small pores with an average pore size of 0.20-0.25 μm; the pre-filter layer is a double continuous gradient increasing macroporous layer with an average pore size of 5.7-6.0 μm. The asymmetry ratio between the pre-filter layer and the separation layer is 24-29.

3. The asymmetric polyethersulfone filter membrane according to claim 1, characterized in that: The thickness ratio of the protective layer, separation layer and pre-filter layer is 1:3:3-6. The three-layer structure has a continuous transition with no obvious interface and the cross-section is inverted V-shaped.

4. The method for preparing the asymmetric polyethersulfone filter membrane according to any one of claims 1 to 3, characterized in that: Includes the following steps: (1) Solution preparation: According to the weight, 10-18 parts of polyethersulfone, 3-8 parts of sulfonated polyethersulfone, 25-40 parts of solvent, 30-40 parts of non-solvent additive and 5-20 parts of pore-forming agent are mixed and dissolved to obtain a homogeneous casting solution; wherein, the content of non-solvent additive is greater than the content of solvent. (2) Debubbling and coating: The homogeneous casting solution is coated onto the support; (3) Primary film formation process: The coating accompanying the support is subjected to differential synchronous induction between the upper and lower layers; the upper surface of the coating is subjected to double induction using heated steam on the air side, with a steam temperature of 50-90℃ and a steam relative humidity of 50-90%; the lower surface of the coating is subjected to low-temperature induction through the base plate in contact with it, with a base plate temperature of 20-50℃, thus obtaining the primary film. (4) Curing: The nascent membrane is immersed in a water coagulation bath along with the support to solidify into a membrane, and then washed and dried to obtain an asymmetric polyethersulfone filter membrane.

5. The method for preparing the asymmetric polyethersulfone filter membrane according to claim 4, characterized in that: The solvent is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, 2-pyrrolidone, and dimethyl sulfoxide.

6. The method for preparing the asymmetric polyethersulfone filter membrane according to claim 4, characterized in that: The non-solvent additive is one or more of the following: ethylene glycol monomethyl ether, 2-methoxyestradiol, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, diethylene glycol monomethyl ether, and small molecule polyethylene glycol.

7. The method for preparing the asymmetric polyethersulfone filter membrane according to claim 4, characterized in that: The pore-forming agent is one or more of the following: polyacrylic acid, polyvinyl alcohol, polyvinyl acetate, polyvinylpyrrolidone, polyethylene glycol, polyvinylpyridine, polyethyleneimine, polyoxazoline, and block polyether.

8. The method for preparing the asymmetric polyethersulfone filter membrane according to claim 4, characterized in that: In step (3), the steam temperature is 50-65℃, the steam relative humidity is 60-80%, and the bottom plate temperature is 20-40℃.

9. The method for preparing the asymmetric polyethersulfone filter membrane according to claim 4, characterized in that: In step (3), the differential synchronization induction time between the upper and lower layers is 5-60s.

10. The application of the asymmetric polyethersulfone filter membrane according to any one of claims 1 to 3 in filtration and sterilization.

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