An asymmetric microfiltration membrane, its preparation method and application

Abstract

The application belongs to the technical field of membrane separation, and particularly relates to an asymmetric microfiltration membrane and a preparation method and application thereof. The application has a pore size change trend by setting a pre-filter layer, so that the flux effect of the microfiltration membrane can be improved. When a large-pore surface is used as a liquid inlet surface of the microfiltration membrane, the flux of the microfiltration membrane can be further improved. The fiber inside the communication pores in the asymmetric microfiltration membrane has pores, and the fiber has excellent buffering performance due to the pores in the fiber, so that the impact resistance of the microfiltration membrane can be improved, and the microfiltration membrane is not easy to be damaged. The fiber inside the region close to the large-pore surface is provided with pores, so that the diameter of the fiber can be increased to improve the strength, and the flux of the membrane will not be affected due to the distribution region mainly in the pre-filter layer, but the pressure resistance and shock resistance of the pre-filter layer can be improved, so that the microfiltration membrane has excellent mechanical strength as a whole, and safe and efficient filtration for a long time is provided.

Description

Technical Field

[0001] This application belongs to the field of membrane separation technology, specifically relating to an asymmetric microfiltration membrane, its preparation method, and its application. Background Technology

[0002] Microporous polymer membranes (microfiltration membranes) are widely used in industrial, pharmaceutical, and medical fields. During the separation process, the substances to be separated are not affected by pressure or heat, making them suitable for high-precision filtration. Microfiltration membranes can remove fine particles or microstructures down to the submicron level, making them suitable for pure water purification in laboratories or the semiconductor industry. Microfiltration membranes can be classified into symmetrical and asymmetrical membranes based on their structure. Symmetrical membranes have a relatively uniform average pore size along their thickness direction, while asymmetrical membranes exhibit diverse average pore size distributions.

[0003] In applications, membranes with asymmetric structures are preferred because, compared to membranes with symmetrical structures, asymmetric membranes with the same retention capacity have better flux. Existing technologies for improving filtration membrane flux without affecting its retention capacity include optimizing the membrane structure and increasing porosity. However, optimizing the membrane structure generally involves complex processes and cumbersome procedures; while increasing porosity often involves adding excessive pore-forming agents, leading to a decrease in the overall mechanical properties of the membrane. Furthermore, existing microfiltration membranes have poor shock resistance, making their structures prone to damage. Summary of the Invention

[0004] Therefore, the technical problem to be solved by this application is to overcome the above-mentioned defects of the microfiltration membrane in the prior art, thereby providing an asymmetric microfiltration membrane, its preparation method and application.

[0005] Therefore, this application provides the following technical solution:

[0006] This application provides an asymmetric microfiltration membrane, comprising a porous body, one side of which is a macropore surface and the other side is a micropore surface. The porous body includes a pre-filtration layer with gradually decreasing pore size from the macropore surface to the micropore surface, and a retention layer with uniform pore size. The fibers of the porous body near the macropore surface have pores.

[0007] This application improves the flux of the microfiltration membrane by setting a pre-filtration layer with a tendency for pore size variation. While using a macroporous surface as the inlet surface of the microfiltration membrane can further increase flux, the macroporous surface can easily damage the fiber structure near it, causing membrane pores to collapse and hindering long-term, efficient filtration. Existing fiber structures are difficult to adjust specifically. In contrast, the asymmetric microfiltration membrane of this application has internal pores within the fibers forming interconnected pores. The cross-section of the fiber shows that these pores are mainly distributed in a honeycomb pattern. Furthermore, the presence of these pores within the fibers provides excellent buffering performance, improving the microfiltration membrane's shock resistance and preventing damage. By incorporating pores within the fibers near the macroporous surface, this application not only increases fiber diameter and strength but also, because the pores are mainly distributed in the pre-filtration layer, does not affect the membrane flux. Instead, it improves the pressure resistance and shock absorption of the pre-filtration layer, resulting in superior overall mechanical strength for the microfiltration membrane, providing long-term, safe, and efficient filtration.

[0008] The number of porous fibers accounts for 0.1-60% of the total number of fibers in the porous body, or the thickness of the porous fiber layer accounts for 0.5-50% of the overall thickness of the porous body.

[0009] The microfiltration membrane of this application has a retention layer with a uniform pore size. The pore size of the retention layer is small and plays a role in filtration and retention. It does not need to have an impact resistance effect. The presence of pores inside the fiber will affect the fiber diameter of the retention layer. Therefore, it is not necessary for all fibers to have pores inside.

[0010] The porous fiber has an internal pore distribution of 4–60 pores / square micrometer. The number and distribution of pores inside the fiber affect the pressure resistance and fiber diameter. By limiting the distribution of the number of pores inside the fiber, a balance between mechanical properties and filtration performance can be achieved. For example, when the internal pore distribution of the porous fiber is greater than 60 pores / square micrometer, it will result in a large number of pores and a large fiber diameter, which will affect the flux of the microfiltration membrane.

[0011] The thickness ratio of the pre-filter layer to the retention layer is (2-7):1, preferably (2-6):1, and the overall asymmetry coefficient of the pre-filter layer and the retention layer is 0.02-0.07, preferably 0.02-0.06. By limiting the thickness ratio and overall asymmetry coefficient of the pre-filter layer and the retention layer, the aim is to ensure the high flux and excellent retention performance of the microfiltration membrane. Furthermore, the pre-filter layer in this application has a relatively large thickness, enabling the microfiltration membrane to possess a strong dirt-holding capacity and prolonging the clogging time of the microfiltration membrane. The overall asymmetry coefficient of the pre-filter layer and the retention layer is the ratio of the difference in average pore size between the two layers to the overall thickness of the pre-filter layer and the retention layer. The flux and retention performance of microfiltration membranes are mainly affected by changes in pore size and thickness. By limiting the asymmetry coefficient, both parameters can be controlled simultaneously. Furthermore, based on a determined thickness ratio between the pre-filtration layer and the retention layer, an overall asymmetry coefficient of 0.02-0.06 between the pre-filtration layer and the retention layer can ensure that the microfiltration membrane has excellent flux and retention performance.

[0012] The porous body also includes a protective layer with an average pore diameter that gradually increases from the large pore surface to the small pore surface, and the protective layer is disposed between the small pore surface and the retaining layer.

[0013] The asymmetric microfiltration membrane provided in this application consists of three regions. A retention layer with a uniform pore size plays the primary filtration role, and a protective layer is placed outside the retention layer to prevent damage during mechanical movement, which could lead to a decrease in retention efficiency. The retention layer is mainly located inside the membrane, and the regions adjacent to it have a macroporous structure, ensuring the membrane's flux performance and reducing the risk of surface scratches caused by external forces reducing retention efficiency.

[0014] The thickness of the pre-filtration layer ranges from 65% to 85% of the total membrane thickness, the thickness of the retention layer ranges from 10% to 30% of the total membrane thickness, preferably 12% to 30%, and the thickness of the protective layer ranges from 1% to 16% of the total membrane thickness, preferably 1% to 8%.

[0015] Although the average pore size of the protective layer in the microfiltration membrane of this application gradually increases, it still affects the flux of the microfiltration membrane. Therefore, the microfiltration membrane of this application ensures that it can protect the retention layer, while controlling the thickness of the protective layer to be 0.5-8% to minimize the impact of the protective layer thickness on the flux of the microfiltration membrane.

[0016] The thickness of the protective layer is 1-20 μm, preferably 1-8 μm. Optionally, the average pore diameter of the macropore surface is 3-8 μm, and the pore ratio is 23%-45%, preferably 25%-45%.

[0017] And / or, the average pore size of the microfiltration membrane is 0.5 to 1.9 μm, preferably 0.5 to 1.6 μm, and the pore size ratio is 13% to 28%;

[0018] And / or, the average pore size of the retaining layer is 0.19–0.49 μm;

[0019] Optionally, the average pore size of the pre-filter layer is 0.8–3.8 μm, preferably 0.8–3 μm;

[0020] And / or, the average pore size of the protective layer is 0.3 to 1.3 μm, preferably 0.3 to 0.9 μm.

[0021] In this application, a higher pore ratio indicates that more liquid enters the membrane at the same time point, ensuring better flux.

[0022] Optionally, the average diameter of the fibers in the pre-filter layer ranges from 0.55 to 3 μm, and the ratio of the average pore size to the average fiber diameter in the pre-filter layer is maintained at (0.25 to 5.5):1.

[0023] And / or, the average diameter of the fibers in the protective layer ranges from 0.2 to 0.5 μm, and the ratio of the average pore size in the protective layer to the average diameter of its fibers is maintained at (0.6 to 4.5):1;

[0024] And / or, the average diameter of the fibers in the microfiltration membrane retention layer ranges from 0.15 to 0.35 μm, and the ratio of the average pore size in the retention layer to the average diameter of its fibers is maintained at (0.5 to 3.1):1.

[0025] In this application, when the ratio of the pore size to the fiber diameter of the pre-filtration layer is maintained at (0.25–5.5):1, the coarser fibers and larger pore size can protect the retention layer and provide better pressure resistance, ensuring the smooth flow of feed liquid into or through the membrane. When the ratio of the average pore size to the average fiber diameter in the retention layer is maintained at (0.5–3.1):1, the smaller pore size and finer fiber diameter in the retention layer contribute to the permeability of the membrane's internal structure, ensuring retention while also ensuring good permeation performance in that area. The main function of the protective layer is to protect the retention layer. Limiting the diameter of the protective layer fibers can protect the retention layer. Moreover, controlling the ratio of the average pore size to the average fiber diameter in the protective layer to be maintained at (0.6–4.5):1 can reduce the impact of the protective layer on the flux of the microfiltration membrane.

[0026] And / or, the overall asymmetry ratio of the asymmetric microfiltration membrane is between 3 and 10, and the asymmetry ratio of the pre-filtration layer to the retention layer is between 3 and 16.

[0027] The asymmetry ratio characterizes the variation in average pore size within a selected region. It is determined by the ratio of the average pore size at the top and bottom 1µm regions of the selected area on the microfiltration membrane cross-section, typically choosing a ratio of the larger to the smaller average pore size. For example, the overall asymmetry ratio of an asymmetric microfiltration membrane is expressed as the ratio of the average pore size at the 1µm region near the larger pore surface to the average pore size at the 1µm region near the smaller pore surface. By limiting the asymmetry ratio within the region, a significant gradient distribution of pore size along the thickness direction can be achieved, ensuring the flux performance of the microfiltration membrane.

[0028] Although the asymmetric microfiltration membrane in this application has a three-layer structure, with the smallest pore size retention layer located inside the membrane, the protective layer in this application is relatively thin and has a small average pore size. Therefore, the asymmetric microfiltration membrane in this application still has a high asymmetry ratio, which makes the pore size have a significant gradient change in the thickness direction, thus ensuring the flux of the microfiltration membrane.

[0029] Optionally, the total thickness of the asymmetric microfiltration membrane ranges from 100 to 150 μm, and the porosity of the asymmetric microfiltration membrane is 70 to 85%; and / or, the initial water contact angle of the macropore surface is 15 to 40°, and the initial water contact angle of the micropore surface is 20 to 45°.

[0030] By controlling the overall thickness of the microfiltration membrane, the thickness of the retention layer (which plays a primary role in trapping pollutants) and the thickness of the pre-filtration layer (which can hold pollutants) are affected. By keeping the total thickness of the asymmetric microfiltration membrane in this application within the range of 100–150 μm, not only is excellent retention capacity and good pollutant holding effect ensured, but the microfiltration membrane also possesses good tensile properties and mechanical strength. Controlling the porosity of the asymmetric microfiltration membrane to 70–85% allows for a certain degree of visualization of the internal structure of the microfiltration membrane, ensuring excellent permeability of the internal pores. By limiting the water contact angle between the macropore and micropore surfaces, the microfiltration membrane of this application possesses strong hydrophilic properties, making it suitable for filtration in the pharmaceutical field.

[0031] Optionally, the bubble point of the asymmetric microfiltration membrane is 20–60 psi;

[0032] And / or, the microfiltration membrane has a water flux of 25–75 ml / cm at 14.5 psi. 2 ·min;

[0033] The water flux test results show that, due to the limitation of the specific structure of the microfiltration membrane in this application, the microfiltration membrane can have excellent flux performance.

[0034] And / or, the tensile strength of the asymmetric microfiltration membrane is 4.5 to 8 MPa, and the elongation at break is 13% to 70%, preferably 13% to 55%.

[0035] The average pore size, layer thickness, pore size ratio, and fiber diameter of different regions of the microfiltration membrane in this application can all be calculated by morphological characterization of the membrane structure using scanning electron microscopy, followed by measurement using computer software (such as Matlab, NIS-Elements, etc.) or manual measurement. Parts with significantly smaller or larger dimensions are excluded from the measurement. In actual measurement, the membrane surface (or cross-section) can be characterized first using an electron microscope to obtain the corresponding SEM image, and a certain area, such as 1 μm, can be selected. 2 (1μm x 1μm) or 25μm 2 (5μm x 5μm), the specific area size depends on the actual situation. Then, the morphological parameters such as the pore size and fiber diameter of all pores in this area are measured using appropriate computer software or manually, and then calculated to obtain the average value of this area. Regarding the testing of the average pore size, in addition to measurement and analysis of SEM images, the average pore size of each layer can also be directly analyzed using an average pore size distribution analyzer. For example, a membrane of a certain size is first cut, and the water in the original wet membrane is replaced with ethanol of different concentrations. Then, it is wetted with a low surface tension solvent and placed in a test tank. Finally, the average pore size of the PMI is obtained through a dry-wet line. The above measurement methods for each parameter are only examples; it is understood that those skilled in the art can obtain the above parameters through other measurement methods.

[0036] The pre-filtration layer contains porous fibers, and the analysis includes the number of pores on the fibers and the thickness of the porous fiber layer. This is also done on an SEM image by taking a cross-sectional area of ​​the entire microfiltration membrane and calculating the number of porous fibers and the total number of fibers, then determining their ratio; or by calculating the thickness of the porous fiber layer and the overall membrane thickness, then determining their ratio. The number of pores on the fibers is also obtained by calculating the number of pores per unit area of ​​the fiber cross-section.

[0037] The average pore size, layer thickness, pore ratio, fiber diameter, the proportion of porous fibers in the pre-filter layer, and the number of pores on the fibers can be controlled by factors such as the content of photocuring pore-forming agent, UV radiation intensity, irradiation time, and air humidity.

[0038] This application also provides a method for preparing the above-mentioned asymmetric microfiltration membrane, comprising the following steps:

[0039] S1, Prepare the casting solution;

[0040] S2, the casting solution is coated onto the surface of a transparent carrier and cured by ultraviolet light to obtain the virgin membrane;

[0041] S3, the original membrane is immersed in the coagulation bath to obtain an asymmetric microfiltration membrane with pores inside the fiber.

[0042] The preparation method provided in this application uses ultraviolet light curing to pre-form the asymmetric microfiltration membrane. The fiber has pores inside and a large fiber diameter. The cavities inside the fiber give it excellent buffering performance, which can improve the impact resistance of the microfiltration membrane and ensure that the microfiltration membrane is not easily damaged.

[0043] Optionally, in step S1, the polymer solid content in the casting solution is 14-20% by mass percentage, the solvent content is 40-70%, and the additive content is 20-35%; the additive includes a photocurable pore-forming agent, and the content of the photocurable pore-forming agent is 2-8%.

[0044] Specifically, the method for preparing the casting solution includes dissolving a sulfone polymer in a solvent, adding an additive after dissolution, and obtaining the casting solution.

[0045] The sulfone polymers may include at least one of polysulfone and polyethersulfone.

[0046] The solvent is selected from one or more of dimethylformamide, dimethylacetamide, tetrahydrofuran, N-methylpyrrolidone, triethyl phosphate, dimethyl sulfoxide, ethyl lactate, and γ-butyrolactone.

[0047] The additives include pore-forming agents and photocurable pore-forming agents. The pore-forming agents are selected from various polyethylene glycols, such as PEG-400 and PEG-1500; various polyvinylpyrrolidones, such as PVP-K30 and PVP-K60; and various alcohols, such as tripropylene glycol, triethylene glycol, diethylene glycol, n-butanol, and tert-amyl alcohol. The photocurable pore-forming agents contain unsaturated photosensitive groups such as acrylate, methacrylate, vinyl ether, or allyl groups on their molecular chains. Simultaneously, the photocurable pore-forming agents can also act as hydrophilic modifiers, typically including a certain number of hydrophilic groups on their molecular weight, such as carboxyl, hydroxyl, amino, quaternary ammonium, ether, and amide groups. As a further preferred option, the photocurable pore-forming agent is selected from one or more of hydroxyethyl methacrylate, hydroxyethyl acrylate, trimethylolpropane diallyl ether, polyethylene glycol dimethacrylate, acryloyloxyethyltrimethylammonium chloride, and 2-methyl methacrylate trimethylammonium chloride, but is not limited to these types.

[0048] During the preparation process, the photocurable pore-forming agent in the casting solution is excited by UV light, undergoing photophysical and photochemical reactions to generate active free radicals. This triggers the polymerization and cross-linking of monomers (photocurable pore-forming agent) to form compounds, causing a partial transformation of the liquid casting solution near the light source into a solid state. This solid state gradually weakens as the solution extends towards the air section, resulting in a solid-liquid coexistence phenomenon during the UV irradiation stage. Subsequently, in the early stage of phase transformation, the encapsulation of some liquid casting solution by the solidified photosensitive compound hinders bidirectional diffusion between solvent and non-solvent in this area. The surrounding polyethersulfone initially forms a large number of robust fibers, while the fibers retain many small-volume solvents. As the phase transformation process deepens, these small-volume solvents diffuse towards the non-solvent, forming dense pores, resulting in a large number of pores distributed within the fibers.

[0049] Optionally, in step S2, the ambient humidity is controlled to be 50-90% RH;

[0050] And / or, the UV light band for UV curing is 254–395 nm; by controlling the UV light band to change the radiation intensity, the photocurable pore-forming agent can form small voids inside the membrane, and the prepared membranes all have coarse fibers, and a large number of voids are distributed on the fibers, which helps to improve the overall pressure resistance of the membrane.

[0051] And / or, the curing time under ultraviolet light is 5 to 60 seconds.

[0052] And / or, in step S3, the coagulation bath is a solution with an organic solvent to water mass ratio of (0-0.15):1. Optionally, the organic solvent is mainly at least one of alcohols, ethers, or ketones. Preferably, the alcohol has the molecular formula C0. x H y F z O, where x = 1-10, y = 2-20, z = 0-40; more preferably, at least one of ethanol, isopropanol, and hexafluoroisopropanol. In this application, the light transmittance of the transparent carrier is above 80%, and the carrier material can be selected from polyethylene terephthalate, polymethyl methacrylate, and polyethylene, but is not limited to these.

[0053] This application also provides an application of the above-described asymmetric microfiltration membrane or the asymmetric microfiltration membrane prepared by the above-described preparation method in the fields of biopharmaceuticals, food, and water treatment.

[0054] Specifically, it can be used to remove fine particles or micro-organisms in water down to the submicron level, such as removing microorganisms from water.

[0055] The technical solution of this application has the following advantages:

[0056] The asymmetric microfiltration membrane provided in this application includes a porous body with a macropore surface on one side and a micropore surface on the other. The porous body includes a pre-filtration layer with gradually decreasing pore size from the macropore surface to the micropore surface, and a retention layer with uniformly consistent pore size. The fibers near the macropore surface of the porous body have pores within them. This application improves the flux of the microfiltration membrane by setting the pre-filtration layer to have a trend of pore size variation. While using a macropore surface as the inlet surface of the microfiltration membrane can further increase the flux, the macropore surface can easily damage the fiber structure near it, causing the membrane pores to collapse and hindering long-term efficient filtration. Existing fiber structures are difficult to adjust specifically. In contrast, the asymmetric microfiltration membrane of this application has pores within the fibers forming interconnected pores. The cross-section of the fiber shows that these pores are mainly distributed in a honeycomb pattern. Furthermore, the presence of these pores within the fibers provides excellent buffering performance, improving the shock resistance of the microfiltration membrane and ensuring it is not easily damaged. This application creates pores inside the fibers near the large pore area, which not only increases the fiber diameter and improves strength, but also, since the distribution area is mainly in the pre-filtration layer, does not affect the membrane flux. Instead, it improves the pressure resistance and shock absorption of the pre-filtration layer, giving the microfiltration membrane excellent overall mechanical strength and providing safe and efficient filtration over a long period of time. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the specific embodiments of this application or the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0058] Figure 1 This is a scanning electron microscope image of the cross-section of the asymmetric microfiltration membrane prepared in Example 2, magnified 600 times.

[0059] Figure 2 This is a scanning electron microscope image, magnified 2000 times, of the cross-section of the asymmetric microfiltration membrane pre-filtration layer prepared in Example 2.

[0060] Figure 3 This is a scanning electron microscope image of the macropore surface of the asymmetric microfiltration membrane prepared in Example 2, magnified 1000 times.

[0061] Figure 4 This is a scanning electron microscope image of the cross-section of the asymmetric microfiltration membrane prepared in Example 3, magnified 600 times.

[0062] Figure 5 This is a scanning electron microscope image, magnified 2000 times, of the cross-section of the asymmetric microfiltration membrane pre-filtration layer prepared in Example 3.

[0063] Figure 6 This is a scanning electron microscope image, magnified 800 times, of the cross-section of the pre-filtration layer of the asymmetric microfiltration membrane prepared in Comparative Example 2.

[0064] Figure 7 The image shown is a scanning electron microscope image magnified 5000 times of the cross-section of the asymmetric microfiltration membrane pre-filtration layer prepared in Comparative Example 2. Detailed Implementation

[0065] The following embodiments are provided to better understand this application and are not limited to the preferred embodiments described herein. They do not constitute a limitation on the content and scope of protection of this application. Any product that is the same as or similar to this application, derived by anyone under the guidance of this application or by combining features of this application with other prior art, falls within the scope of protection of this application.

[0066] For experiments not specifically described in the examples, the procedures or conditions should be followed according to the conventional experimental procedures described in the literature in this field. Reagents or instruments whose manufacturers are not specified are all commercially available conventional reagent products.

[0067] Example 1

[0068] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0069] First, polyethersulfone (molecular weight around 50,000) is dissolved in N,N-dimethylformamide. Then, hydroxyethyl methacrylate and PVP-K60 are added as additives. Finally, diethylene glycol, a pore-forming agent, is added and mixed. The mass ratio of polyethersulfone, dimethylformamide, hydroxyethyl methacrylate, PVP-K60, and diethylene glycol is 18:55:5:2:20. The mixture is stirred at 60°C until clear to obtain the casting solution.

[0070] In an environment with a relative humidity of 80%RH, the thickness of the scraper was adjusted to 200 micrometers, and the casting liquid was poured onto a polyethylene carrier with a transmittance of more than 80%. The side near the carrier was irradiated with a 365nm ultraviolet lamp for 30 seconds, and then immersed in a coagulation bath (10wt% ethanol aqueous solution) for complete phase separation to prepare an asymmetric microfiltration membrane (a).

[0071] Example 2

[0072] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0073] First, polyethersulfone (molecular weight approximately 55,000) is dissolved in N-methylpyrrolidone. Then, additives 2-ethyl methacrylate trimethylammonium chloride and PVP-K30 are added. Finally, diethylene glycol, a pore-forming agent, is added and mixed. The mass ratio of polyethersulfone, N-methylpyrrolidone, 2-ethyl methacrylate trimethylammonium chloride, PVP-K30, and diethylene glycol is 17:56:4:5:18. The mixture is stirred at 50°C until clear to obtain the casting solution.

[0074] In an environment with a relative humidity of 75%RH, the thickness of the scraper was adjusted to 250 micrometers, and the casting liquid was poured onto a polyethylene carrier with a transmittance of more than 80%. The side near the carrier was irradiated with a 325nm ultraviolet lamp for 30 seconds, and then immersed in a coagulation bath (5wt% ethanol aqueous solution) for complete phase separation to prepare an asymmetric microfiltration membrane (b).

[0075] Example 3

[0076] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0077] First, polyethersulfone (molecular weight approximately 48,000) is dissolved in a mixed solvent of dimethylformamide and ethyl lactate. Then, hydroxyethyl acrylate and PVP-K30 are added as additives. Finally, triethylene glycol, a pore-forming agent, is added and mixed. The mass ratio of polyethersulfone, dimethylformamide, ethyl lactate, hydroxyethyl acrylate, PVP-K30, and triethylene glycol is 16:44:10:6:2:22. The mixture is stirred at 45°C until clear to obtain the casting solution.

[0078] In an environment with a relative humidity of 80%RH, the thickness of the scraper was adjusted to 250 micrometers. The casting solution was poured onto a polymethyl acrylate carrier with a transmittance of over 90%. The side near the carrier was irradiated with a 365nm ultraviolet lamp for 40 seconds. Then, it was immersed in a coagulation bath (5wt% isopropanol aqueous solution) for complete phase separation to prepare an asymmetric microfiltration membrane (c).

[0079] Example 4

[0080] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0081] First, polyethersulfone (molecular weight around 50,000) is dissolved in a mixed solvent of dimethylacetamide and ethyl lactate. Then, the additives polyethylene glycol dimethacrylate and PVP-K60 are added. Finally, the pore-forming agent triethylene glycol is added and mixed. The mass ratio of polyethersulfone, dimethylacetamide, ethyl lactate, polyethylene glycol dimethacrylate, PVP-K60 and triethylene glycol is 15:41:10:6:3:25. The mixture is stirred at 45°C until clear to obtain the casting solution.

[0082] In an environment with a relative humidity of 70%RH, the thickness of the scraper was adjusted to 250 micrometers. The casting solution was poured onto a polymethyl acrylate carrier with a transmittance of over 90%. The side near the carrier was irradiated with a 365nm ultraviolet lamp for 35 seconds. Then, it was immersed in a coagulation bath (3wt% isopropanol aqueous solution) for complete phase separation to prepare an asymmetric microfiltration membrane (d).

[0083] Example 5

[0084] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0085] First, polyethersulfone (molecular weight approximately 55,000) is dissolved in dimethylformamide solvent. Then, hydroxyethyl acrylate and acryloyloxytrimethylammonium chloride are added as additives. Finally, triethylene glycol, a pore-forming agent, is added and mixed. The mass ratio of polyethersulfone, dimethylformamide, hydroxyethyl acrylate, acryloyloxytrimethylammonium chloride, and triethylene glycol is 15:56:2:2:25. The mixture is stirred at 50°C until clear to obtain the casting solution.

[0086] In an environment with a relative humidity of 60%RH, the thickness of the scraper was adjusted to 250 micrometers, and the casting liquid was poured onto a polyethylene carrier with a transmittance of more than 80%. The side near the carrier was irradiated with a 280nm ultraviolet lamp for 15 seconds, and then immersed in a coagulation bath (2wt% hexafluoroisopropanol aqueous solution) for complete phase separation to prepare an asymmetric microfiltration membrane (e).

[0087] Example 6

[0088] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0089] First, polyethersulfone (molecular weight around 50,000) is dissolved in dimethyl sulfoxide solvent. Then, additives ethyl 2-methacrylate trimethylammonium chloride and PVP-K30 are added. Finally, pore-forming agent tert-amyl alcohol is added and mixed. The mass ratio of polyethersulfone, dimethyl sulfoxide, ethyl 2-methacrylate trimethylammonium chloride, PVP-K30 and triethylene glycol is 20:58:3:4:15. The mixture is stirred at 60°C until clear to obtain the casting solution.

[0090] In an environment with a relative humidity of 80%RH, the thickness of the scraper was adjusted to 200 micrometers. The casting solution was poured onto a polymethyl methacrylate carrier with a transmittance of over 90%. The side near the carrier was irradiated with a 325nm ultraviolet lamp for 30 seconds. Then, it was immersed in a coagulation bath (2wt% hexafluoroisopropanol aqueous solution) for complete phase separation to prepare an asymmetric microfiltration membrane (f).

[0091] Example 7

[0092] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0093] First, polyethersulfone (molecular weight around 60,000) is dissolved in dimethylformamide and tetrahydrofuran solvent. Then, additives 2-ethyl methacrylate trimethylammonium chloride and hydroxyethyl methacrylate are added. Finally, porogen tert-amyl alcohol is added and mixed. The mass ratio of polyethersulfone, dimethylformamide, tetrahydrofuran, 2-ethyl methacrylate trimethylammonium chloride, hydroxyethyl methacrylate and tripropylene glycol is 18:55:5:2:2:18. The mixture is stirred at 60°C until clear to obtain the casting solution.

[0094] In an environment with a relative humidity of 85%RH, the thickness of the scraper was adjusted to 200 micrometers, and the casting liquid was poured onto a polyethylene carrier with a light transmittance of more than 80%. The side near the carrier was irradiated with a 395nm ultraviolet lamp for 30 seconds, and then immersed in a coagulation bath (pure water) for complete phase separation to prepare an asymmetric microfiltration membrane (g).

[0095] Example 8

[0096] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0097] First, polyethersulfone (molecular weight around 50,000) was dissolved in γ-butyrolactone solvent. Then, additives ethyl 2-methacrylate trimethylammonium chloride and PVP-K30 were added. Finally, pore-forming agent PEG-400 was added and mixed. The mass ratio of polyethersulfone, γ-butyrolactone, ethyl 2-methacrylate trimethylammonium chloride, PVP-K30 and PEG-400 was 16:54:4:4:22. The mixture was stirred at 60°C until clear to obtain the casting solution.

[0098] In an environment with a relative humidity of 80%RH, the thickness of the scraper is adjusted to 200 micrometers. The casting liquid is poured onto a polyethylene carrier with a light transmittance of more than 80%. The side near the carrier is irradiated with a 365nm ultraviolet lamp for 50 seconds. Then it is immersed in a coagulation bath (pure water) for complete phase separation to prepare an asymmetric microfiltration membrane (h).

[0099] Example 9

[0100] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0101] First, polysulfone (molecular weight around 60,000) is dissolved in N-methylpyrrolidone. Then, additives 2-ethyl methacrylate trimethylammonium chloride and PVP-K30 are added. Finally, diethylene glycol, a pore-forming agent, is added and mixed. The mass ratio of polyethersulfone, N-methylpyrrolidone, 2-ethyl methacrylate trimethylammonium chloride, PVP-K30 and diethylene glycol is 17:56:4:5:18. The mixture is stirred at 50°C until clear to obtain the casting solution.

[0102] In an environment with a relative humidity of 75%RH, the thickness of the scraper was adjusted to 200 micrometers, and the casting liquid was poured onto a polyethylene carrier with a transmittance of more than 80%. The side near the carrier was irradiated with a 325nm ultraviolet lamp for 30 seconds, and then immersed in a coagulation bath (5wt% ethanol aqueous solution) for complete phase separation to prepare an asymmetric microfiltration membrane (i).

[0103] Example 10

[0104] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0105] First, polyethersulfone (molecular weight approximately 48,000) is dissolved in a mixed solvent of dimethylformamide and ethyl lactate. Then, hydroxyethyl acrylate and PVP-K30 are added as additives. Finally, triethylene glycol, a pore-forming agent, is added and mixed. The mass ratio of polyethersulfone, dimethylformamide, ethyl lactate, hydroxyethyl acrylate, PVP-K30, and triethylene glycol is 16:44:10:6:2:22. The mixture is stirred at 45°C until clear to obtain the casting solution.

[0106] In an environment with a relative humidity of 80%RH, the thickness of the scraper was adjusted to 250 micrometers. The casting solution was poured onto a polymethyl acrylate carrier with a transmittance of over 90%. The side near the carrier was irradiated with a 395nm ultraviolet lamp for 120 seconds. Then, it was immersed in a coagulation bath (5wt% isopropanol aqueous solution) for complete phase separation to prepare an asymmetric microfiltration membrane (l).

[0107] Example 11

[0108] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0109] First, polyethersulfone (molecular weight approximately 48,000) is dissolved in a mixed solvent of dimethylformamide and ethyl lactate. Then, hydroxyethyl acrylate and PVP-K30 are added as additives. Finally, triethylene glycol, a pore-forming agent, is added and mixed. The mass ratio of polyethersulfone, dimethylformamide, ethyl lactate, hydroxyethyl acrylate, PVP-K30, and triethylene glycol is 16:44:10:6:2:22. The mixture is stirred at 45°C until clear to obtain the casting solution.

[0110] In an environment with a relative humidity of 80%RH, the thickness of the scraper was adjusted to 250 micrometers. The casting solution was poured onto a polymethyl acrylate carrier with a transmittance of over 90%. The side near the carrier was irradiated with a 280nm ultraviolet lamp for 40 seconds. Then, it was immersed in a coagulation bath (5wt% isopropanol aqueous solution) for complete phase separation to prepare an asymmetric microfiltration membrane (m).

[0111] Example 12

[0112] This embodiment provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0113] First, polysulfone (molecular weight around 60,000) is dissolved in dimethylformamide solvent. Then, hydroxyethyl acrylate and acryloyloxytrimethylammonium chloride are added as additives. Finally, triethylene glycol, a pore-forming agent, is added and mixed. The mass ratio of polyethersulfone, dimethylformamide, hydroxyethyl acrylate, acryloyloxytrimethylammonium chloride, and triethylene glycol is 15:56:2:2:25. The mixture is stirred at 50°C until clear to obtain the casting solution.

[0114] In an environment with a relative humidity of 80%RH, the thickness of the scraper is adjusted to 250 micrometers. The casting liquid is poured onto a polyethylene carrier with a light transmittance of more than 80%. The side near the carrier is irradiated with a 365nm ultraviolet lamp for 60 seconds. Then it is immersed in a coagulation bath (2wt% isopropanol aqueous solution) to carry out complete phase separation and prepare an asymmetric microfiltration membrane (o).

[0115] Comparative Example 1

[0116] This comparative example provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0117] First, polyethersulfone (molecular weight approximately 55,000) is dissolved in N-methylpyrrolidone. Then, additives 2-ethyl methacrylate trimethylammonium chloride and PVP-K30 are added. Finally, diethylene glycol, a pore-forming agent, is added and mixed. The mass ratio of polyethersulfone, N-methylpyrrolidone, 2-ethyl methacrylate trimethylammonium chloride, PVP-K30, and diethylene glycol is 17:56:4:5:18. The mixture is stirred at 50°C until clear to obtain the casting solution.

[0118] In an environment with a relative humidity of 75%RH, the thickness of the scraper was adjusted to 200 micrometers, and the casting liquid was poured onto a polyethylene carrier with a transmittance of more than 80%. The side near the carrier was irradiated with a 450nm ultraviolet lamp for 30 seconds, and then immersed in a coagulation bath (5wt% ethanol aqueous solution) for complete phase separation to prepare an asymmetric microfiltration membrane (j).

[0119] Comparative Example 2

[0120] This comparative example provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0121] First, polyethersulfone (molecular weight around 50,000) is dissolved in a mixed solvent of dimethylacetamide and ethyl lactate. Then, the additives polyethylene glycol dimethacrylate and PVP-K60 are added. Finally, the pore-forming agent triethylene glycol is added and mixed. The mass ratio of polyethersulfone, dimethylacetamide, ethyl lactate, polyethylene glycol dimethacrylate, PVP-K60 and triethylene glycol is 15:41:10:6:3:25. The mixture is stirred at 45°C until clear to obtain the casting solution.

[0122] In an environment with a relative humidity of 70% RH, the thickness of the scraper was adjusted to 250 micrometers, and the scraper was kept in the air section for 35 seconds before being immersed in a coagulation bath (3 wt% isopropanol) to perform complete phase separation and prepare an asymmetric microfiltration membrane (k).

[0123] Comparative Example 3

[0124] This comparative example provides an asymmetric microfiltration membrane, the preparation method of which includes the following steps:

[0125] First, polyethersulfone (molecular weight around 50,000) is dissolved in dimethylformamide solvent. Then, hydroxyethyl acrylate and acryloyloxytrimethylammonium chloride are added as additives. Finally, triethylene glycol, a pore-forming agent, is added and mixed. The mass ratio of polyethersulfone, dimethylformamide, hydroxyethyl acrylate, acryloyloxytrimethylammonium chloride, and triethylene glycol is 15:56:2:2:25. The mixture is stirred at 50°C until clear to obtain the casting solution.

[0126] In an environment with a relative humidity of 80% RH, the thickness of the scraper was adjusted to 250 micrometers, and it was kept in the air section for 25 seconds before being immersed in a coagulation bath (2 wt% hexafluoroisopropanol aqueous solution) to carry out complete phase separation and prepare an asymmetric microfiltration membrane (n).

[0127] Test case

[0128] The following test methods are used to evaluate the asymmetric microfiltration membranes prepared according to the above embodiments and comparative examples.

[0129] 1. Bubble Point Test

[0130] The bubble point pore size is the bubble point value in micrometers representing the maximum effective pore size in the sample, measured according to ASTM F-316-03, using IPA:H2O (60:40) with a surface energy of 23 dynes / cm as the wetting fluid, and a 47 mm disk as the sample size.

[0131] 2. Flux Testing

[0132] Membrane water flux is determined by measuring the amount of water passing through a membrane sample over a given time period. The membrane sample is cut into a 47 mm diameter disc and pre-wetted with Milli-Q grade water or IPA. The sample is placed in a negative pressure apparatus at 14.5 psi, and the time required for the membrane to pass 50 mL of water at this pressure is recorded. The flow rate per minute at this pressure is then calculated.

[0133] 3. Water contact angle test

[0134] The water contact angle was determined using a DropMeter A-100P contact angle / surface tension meter. A 2cm × 2cm square membrane was cut, fixed to a glass slide with tape, and placed on the sample stage for testing. The initial contact angle when a water droplet landed on the membrane surface was recorded. The experiment was repeated five times, and the average value was taken.

[0135] 4. Interception Test

[0136] Bacterial retention tests were performed on the prepared microfiltration membrane using *Serratia marcescens* (ATCC19146) and *Serratia marcescens* (ATCC8100). The corresponding bacteria were dissolved in 0.9% physiological saline to ensure a bacterial count of at least 10⁻⁶ per milliliter of solution. 7 CFU, select an effective area of ​​13.8cm. 2 The filtration device was tested for membrane retention. Finally, the number of microorganisms remaining in each square centimeter of effective filtration area was calculated.

[0137] 5. Average pore size and fiber diameter test

[0138] In this application, the average pore diameter of large and small pores, the pore ratio, the average pore diameter of the protective layer, the retention layer, and the pre-filtration layer, the average fiber diameter, the proportion of porous fibers in the total fiber content of the porous carrier, and the pore distribution on the fibers can all be obtained by characterizing the membrane structure using a scanning electron microscope, followed by calculation and analysis using computer software (such as Matlab, NIS Elements, etc.) or manual mapping. Parts that are significantly smaller or larger than the stated size are not considered during measurement. In the actual calculation of the pore ratio, the membrane surface can be characterized using an electron microscope to obtain the corresponding SEM image, and a certain area, such as 100 μm, can be selected. 2 (10μm x 10μm) or 25μm 2 (5μm by 5μm), the specific area size depends on the actual situation, and then the average pore size of the area is obtained by calculation using the corresponding computer software (Image J) (that is, the average pore size measured by SEM).

[0139] 6. Mechanical strength test

[0140] The tensile strength of the membrane was measured at room temperature using a universal testing machine (Instron 5943). All samples were dried at 60°C for 2 hours to eliminate the influence of residual moisture on the mechanical properties of the membrane. The membrane was cut to a size of 10 mm × 0.1 mm × 70 mm. Tensile tests were conducted at a tensile rate of 20 mm / min using the universal testing machine. The maximum and minimum values ​​were removed and the average was calculated.

[0141] The specific test results are shown in the table below:

[0142] Table 1

[0143]

[0144]

[0145] Table 2

[0146]

[0147]

[0148] Table 3

[0149]

[0150] pass Figure 1 It can be seen that the microfiltration membrane structure of Example 2 is a three-layer structure, with a small pore surface on the upper side and a large pore surface on the lower side. The smaller pore size retention layer is disposed inside the membrane, which is clearly visible. Figure 1 The protective layer inside is relatively thin. Figure 2 for Figure 1 The enlarged cross-sectional view of the pre-filtration layer shows that most of the fiber cross-section is solid with no pores inside. However, pores are present in the area near the large pore surface. Therefore, the average fiber diameter of the pre-filtration layer increases, and the pores inside give the fiber and microfiltration membrane good buffering and pressure resistance. Figure 3 The image shows an electron microscope image of the macroporous surface. As can be seen from the image, the average pore size and fiber diameter of the macroporous surface are both relatively large, thus ensuring a large flux of the microfiltration membrane and strong mechanical strength, which improves the pressure resistance of the microfiltration membrane. Figure 4 and Figure 5 With more porous fibers, the average fiber diameter of the pre-filter layer is also larger, which can further enhance the pressure resistance of the filter membrane. Figure 6 and Figure 7 The process did not use ultraviolet light irradiation for pre-forming membrane fabrication, and the resulting fibers did not have pores inside, resulting in smaller pre-filtered fiber diameters.

[0151] Based on the data above, it can be seen that by reasonably controlling the proportion of the retention layer, the thickness of the protective layer, the thickness ratio of the pre-filter layer to the retention layer, and the overall asymmetry coefficient between the pre-filter layer and the retention layer, microfiltration membranes with high flux and high retention efficiency can be obtained. Comparative Example 2 illustrates the importance of the separation layer thickness for membrane flux and retention performance. When the retention layer thickness exceeds 28% of the overall membrane thickness, the membrane flux decreases sharply, reducing production efficiency. Using a higher UV light band (Comparative Example 1) and not using UV light (Comparative Example 2) directly affects the thickness of the protective layer, the thickness ratio of the pre-filter layer to the retention layer, and the overall asymmetry coefficient between the pre-filter layer and the retention layer, thus reducing membrane flux and worsening bacterial retention. Comparative Examples 10-12 discussed the issues of an excessively thick protective layer, a high overall asymmetry coefficient, and a high ratio of pre-filter layer to retention layer thickness. An excessively thick protective layer leads to a reduced retention layer thickness, decreased tensile strength, and decreased bacterial retention capacity. A high overall membrane asymmetry coefficient causes the protective layer to disappear entirely, making the retention layer prone to tearing and reducing overall membrane flux. A high ratio of pre-filter layer to retention layer thickness can result in partial loss of flux and retention efficiency. By optimizing these parameters, better flux and retention efficiency can be achieved, balancing both aspects.

[0152] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this application.

Claims

1. An asymmetric microfiltration membrane, characterized in that, The porous body includes a porous body with a large pore surface on one side and a small pore surface on the other side. The porous body includes a pre-filter layer with a gradually decreasing pore size from the large pore surface to the small pore surface, and a retaining layer with a uniform pore size. The porous body has pores inside the fibers near the large pore surface.

2. The asymmetric microfiltration membrane according to claim 1, characterized in that, The number of porous fibers accounts for 0.1%-60% of the total number of fibers in the porous matrix; And / or, the thickness of the porous fiber layer ranges from 0.5% to 50% of the overall thickness of the porous matrix; And / or, the porous fiber has an internal pore distribution of 4 to 60 pores per square micrometer.

3. The asymmetric microfiltration membrane according to claim 1 or 2, characterized in that, The thickness ratio of the pre-filter layer to the retention layer is (2-7):1, and the overall asymmetry coefficient of the pre-filter layer and the retention layer is 0.02-0.

07. And / or, the porous body further includes a protective layer with an average pore diameter that gradually increases from the large pore surface to the small pore surface, the protective layer being disposed between the small pore surface and the retaining layer.

4. The asymmetric microfiltration membrane according to claim 3, characterized in that, The thickness ratio of the pre-filter layer to the retention layer is (2-6):1; And / or, the overall asymmetry coefficient between the pre-filter layer and the retention layer is 0.02-0.

06.

5. The asymmetric microfiltration membrane according to claim 3, characterized in that, The thickness of the pre-filtration layer ranges from 65% to 85% of the total membrane thickness; The thickness of the retaining layer ranges from 10% to 30% of the total membrane thickness; The thickness of the protective layer ranges from 1% to 16% of the total membrane thickness; And / or, the thickness of the protective layer is 1-20 μm; And / or, the average pore diameter of the large-pore surface is 3~8μm, and the pore ratio is 23%-45%; And / or, the average pore size of the microfiltration membrane is 0.5~1.9μm, and the porosity is 13%-28%; And / or, the average pore size of the retaining layer is 0.19~0.49μm; And / or, the average pore size of the pre-filter layer is 0.8~3.8μm; And / or, the average pore size of the protective layer is 0.3~1.3μm.

6. The asymmetric microfiltration membrane according to claim 5, characterized in that, The thickness of the retaining layer ranges from 12% to 30% of the total membrane thickness; And / or, the thickness of the protective layer ranges from 0.5% to 8% of the total film thickness; And / or, the thickness of the protective layer is 1-8 μm; And / or, the porosity of the large-aperture surface is 25%-45%; And / or, the average pore size of the microfiltration membrane is 0.5~1.6μm; And / or, the average pore size of the pre-filter layer is 0.8~3μm; And / or, the average pore size of the protective layer is 0.3~0.9μm.

7. The asymmetric microfiltration membrane according to claim 3, characterized in that, The average diameter of the fibers in the pre-filter layer ranges from 0.55 to 3 μm, and the ratio of the average pore size to the average fiber diameter in the pre-filter layer is maintained at (0.25 to 5.5):

1. And / or, the average diameter of the fibers in the protective layer ranges from 0.2 to 0.5 μm, and the ratio of the average pore size in the protective layer to the average diameter of its fibers is maintained at (0.6 to 4.5):1; And / or, the average diameter of the fibers in the microfiltration membrane retention layer ranges from 0.15 to 0.35 μm, and the ratio of the average pore size in the retention layer to the average fiber diameter is maintained at (0.5 to 3.1):1; And / or, the overall asymmetry ratio of the asymmetric microfiltration membrane is 2.8 to 10, and the asymmetry ratio of the pre-filtration layer to the retention layer is 3 to 16; And / or, the total thickness of the asymmetric microfiltration membrane ranges from 100 to 150 μm, and the porosity of the asymmetric microfiltration membrane is 70% to 85%; And / or, the initial water contact angle of the large orifice is 15~40°, and the initial water contact angle of the small orifice is 20~45°.

8. The asymmetric microfiltration membrane according to any one of claims 1-2 or 4-7, characterized in that, The bubble point of the asymmetric microfiltration membrane is 20~60 psi; And / or, the microfiltration membrane has a water flux of 25~75 ml / cm at 14.5 psi. 2 ·min; And / or, the tensile strength of the asymmetric microfiltration membrane is 4.5~8MPa, and the elongation at break is 13%~70%.

9. The asymmetric microfiltration membrane according to claim 8, characterized in that, The elongation at break of the asymmetric microfiltration membrane is 13% to 55%.

10. A method for preparing an asymmetric microfiltration membrane according to any one of claims 1-9, characterized in that, Includes the following steps: S1, Prepare the casting solution; S2, the casting solution is coated onto the surface of a transparent carrier and cured by ultraviolet light to obtain the virgin membrane; S3, the original membrane is immersed in the coagulation bath to obtain an asymmetric microfiltration membrane.

11. The method for preparing the asymmetric microfiltration membrane according to claim 10, characterized in that, In step S1, by mass percentage, the polymer solid content in the casting solution is 14-20%, the solvent content is 40-70%, and the additive content is 20-35%; the additive includes 2-8% of a photocurable pore-forming agent. And / or, in step S3, the coagulation bath is a solution in which the mass ratio of organic solvent to water is (0~0.15):

1.

12. The method for preparing the asymmetric microfiltration membrane according to claim 10 or 11, characterized in that, In step S2, the ambient humidity is controlled at 50-90%RH; And / or, the ultraviolet light band for UV curing is 254~395nm; And / or, the curing time under ultraviolet light is 5~60s.

13. The application of an asymmetric microfiltration membrane according to any one of claims 1-9 or an asymmetric microfiltration membrane prepared by any one of claims 10-12 in the fields of biopharmaceuticals, food or water treatment.

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