Sulfone polymer microporous filter membrane and preparation method thereof

Abstract

The invention provides a sulfone polymer microporous filter membrane and a preparation method thereof. The invention relates to a preparation method of a sulfone polymer microfiltration membrane, which comprises the following steps: preparing a membrane casting solution which comprises 13-25wt% of a sulfone polymer, 10-15wt% of a solvent and 10-15wt% of a non-solvent; measuring the cloud point of the membrane casting solution after heating treatment; scraping the membrane casting solution in the step S1 onto a preheated carrier to form a liquid membrane; the temperature of the preheated carrier is higher than the cloud point; exposing the liquid film together with the carrier in the air with the relative humidity of 30-90%; and immersing in a gel bath, and curing to obtain the sulfone polymer microporous filter membrane with a target aperture. According to the preparation method of the sulfone polymer microfiltration membrane provided by the invention, the sulfone polymer microfiltration membrane with high strength and large aperture is obtained by simultaneously adopting the preparation methods of TIPS and VIPS, and the preparation method is simple, convenient and reliable.

Description

Technical Field

[0001] This invention relates to the field of filtration materials technology, and in particular to a sulfone polymer microporous filter membrane and its preparation method. Background Technology

[0002] Microporous membranes are porous thin-film filtration media that primarily trap particulate matter through physical barriers, allowing the filtered fluid to pass through smoothly. Microporous membranes typically refer to membranes with pore sizes between 0.05 and 5 micrometers. They have wide applications in the electronics, chemical, food, beverage, and pharmaceutical industries, playing a particularly crucial role in the biopharmaceutical industry. Membranes with pore sizes of 0.22 micrometers are commonly used for sterilization; membranes smaller than this are typically used for virus or mycoplasma removal; and membranes larger than this are generally used for removing yeast and for pre-filtration in sterilization processes.

[0003] Various materials can be used to prepare microporous filter membranes, including (but not limited to) metals, ceramics, and organic polymers. Membrane materials suitable for pharmaceutical applications are primarily organic polymers, such as (but not limited to) cellulose acetate, nylon, polysulfones, polyvinylidene fluoride, polyethylene, polypropylene, polycarbonate, polyaromatic amides, and polytetrafluoroethylene. The main methods for preparing polymer filter membranes are the drawing method and the phase transition method. The drawing method is suitable for polymers that are difficult to dissolve in solvents, such as polyolefins and tetrafluoroethylene. The phase transition method is suitable for polymers that are easily soluble in solvents, such as polysulfones, cellulose acetate, and polyvinylidene fluoride. Membranes can be made in planar, mesoporous fibrous, tubular, or other shapes.

[0004] Flat-sheet microporous membranes can be used to manufacture filter cartridges, capsule filters, plate filters, or other types of filters suitable for various applications. In the pharmaceutical industry, these filters are generally for single use. The fluid being filtered flows perpendicular to the membrane surface, impurities are trapped and accumulate inside the membrane or on the surface where the fluid enters, while the fluid and product can pass through freely. This type of filtration is called "dead-end filtration," so the membrane requires high flux (the volume of fluid filtered per unit time and per unit membrane area under a given pressure) and high capacity (the volume of fluid filtered per unit membrane area before the filter becomes clogged). Flux and capacity are closely related to the membrane structure. Generally speaking, high-flux, high-capacity membranes have high porosity, a network-like pore structure, uniform pore size, and a gradually increasing, highly asymmetrical pore size distribution.

[0005] Polysulfone polymers are suitable for preparing microporous filter membranes with the aforementioned properties. Much research and product development focuses on the thermodynamics and kinetics of the film-forming process, aiming to "tailor" formulations and optimize the process to prepare membranes with desired properties. Thermodynamic studies of the film-forming process primarily focus on selecting appropriate solvents, additives, and non-solvents, as well as their contents, to achieve the formation of a network-like asymmetric porous structure during phase transition. Kinetic studies aim to control pore size, pore asymmetry, and skin thickness and pore size. Specific research and product development involve the influence of polymer content, non-solvent selection, and process parameters, including the effects of temperature, humidity, gas flow rate, and residence time during film formation on membrane performance.

[0006] US Patent 4,629,563 discovered a solvent-free phase inversion method for fabricating asymmetric, network-like microporous membranes. This method uses a low polymer concentration, adds an alcohol as a non-solvent to form a metastable casting solution, and then forms the membrane in an aqueous phase. Later patents US 5,171,445 and US 5,518,8734 also used alcohols as a non-solvent, but modified the method by controlling the exposure time of the liquid membrane to air to a very short time (less than 0.5 seconds), lowering the gel (phase transition) temperature, and claiming to obtain membranes with higher surface porosity than the former, thereby increasing membrane flux. Other patents use similar methods, but expose the liquid membrane to humid air for a period of time, within an exposure range of 5-6 inches, thus obtaining microporous membranes with larger pore sizes. US Patent 5869147 discloses another method for fabricating asymmetric microporous membranes, preparing a thermodynamically stable casting solution containing a large amount of non-solvent, but which is clear and transparent (or slightly turbid). Such non-solvents typically result in membranes with greater asymmetry and pore size than other non-solvents. The nascent membrane is held in moist air for a period of time before being placed in a gel bath for complete phase transformation. Membranes formed in this way exhibit higher asymmetry and larger pore size than those produced by previously reported methods. US 4900449A increases the residence time of the liquid membrane in moist air until the membrane surface becomes turbid, thus obtaining a microporous membrane; this method of vapor-induced phase separation is abbreviated as "VIPS". US 6045899 and US 712549 employ the VIS membrane formation method, but different formulations produce highly asymmetric microporous membranes. The patent reports the addition of a high molecular weight hydrophilic polymer (such as polyvinyl alcohol or polyvinylpyrrolidone) to the casting solution. During the phase transition, a portion of the hydrophilic polymer remains in the membrane matrix after the phase transition and washing, thus ensuring that the membrane retains permanent water-repellent properties.

[0007] In summary, all of the methods described above employ relatively low polymer concentrations (generally below 13%) to prepare microporous membranes with the desired pore size and asymmetry. However, low polymer concentrations inevitably lead to weak membrane strength, making it difficult to fabricate complete filters. Another drawback is the insufficient network structure of the membrane.

[0008] US Patent 5444097 reports a method called thermally induced phase separation (TIPS) for preparing flat sheet microporous membranes. This method selects a suitable polymer / solvent / non-solvent casting solution. The interaction between the selected polymer (e.g., polyethersulfone), solvent (e.g., N-dimethylpyrrolidone), and non-solvent (e.g., polyvinyl alcohol 200, ethylene glycol, diethylene glycol, triethylene glycol, glycerol, isopropanol, butanol, pentanol) is affected by temperature. When a non-solvent is added to the polymer solution, the solubility of the polymer decreases, eventually reaching saturation and causing phase separation. The composition of this phase separation changes with temperature and there exists a critical temperature. When the casting solution temperature rises to the critical temperature, a phase transition occurs, resulting in turbidity; below this critical temperature, the casting solution remains clear. This temperature is called the minimum critical temperature (also known as the cloud point). When a clear casting solution is scraped onto a substrate with a temperature above its cloud point, the liquid membrane undergoes a phase change due to heating, and then completely solidifies into a film in a gel bath. This method successfully prepared a microporous membrane with an asymmetric pore structure. Chinese patent CN103055724A also reported a similar method for preparing polysulfone-based microporous membranes. Polyethersulfone was dissolved in N-dimethylacetamide, and then diethylene glycol or polyethylene glycol was added to form a transparent casting solution with a minimum critical temperature. When the casting solution was scraped onto a heated glass plate, it became turbid, and then a film was formed in a gel bath.

[0009] Recent US patents US8727136 and US9844625 and Chinese patents CN101227965B and CN103608092B report a method for preparing hydrophilic polyethersulfone microporous filter membranes for industrial production using the VIPS method. The method is characterized by preparing a high-viscosity casting solution containing a large amount of hydrophilic polymer (the hydrophilic agent also acts as a pore-forming agent). The scraped liquid membrane is then contacted with humid air to solidify its surface, and then cured in a gel bath. Specifically, the patent involves dissolving polyethersulfone resin at high temperature in a mixed solvent of γ-butyrolactone and ε-caprolactam (these two solvents are chosen to increase the membrane's hydrophilicity), and then adding a high content (greater than 10%) of polyvinylpyrrolidone (K30 or K90) and polyvinyl alcohol (PEG200) to form the casting solution. The casting solution is scraped onto a high-temperature metal roller, where the liquid membrane undergoes a surface phase change upon contact with high-temperature, high-humidity air, and then is cured in a high-temperature gel bath. The patent shows that the formed membrane has large pore sizes on both the humid air contact surface and the metal roller surface, while a separation layer with gradually increasing pore sizes exists between the two surfaces. Recently, Chinese patents CN113117538B and CN114130202A have used similar formulations and film-forming processes to prepare membranes with similar pore structures: a large pore size layer on the humid air contact surface, a separation layer with gradually increasing pore sizes on the other side of the membrane, and the pore size shrinking on the other side. Membranes prepared by this method have good hydrophilicity and mechanical strength. However, their disadvantages include the need to control the casting solution temperature, roller surface temperature, humid air temperature and humidity, and film-forming tank temperature, resulting in a complex production process with many factors affecting membrane pore size. Another disadvantage is that the added hydrophilic agent precipitates during use, resulting in high leaching content, and the hydrophilic membrane has poor thermal stability.

[0010] Current technologies reporting methods for preparing asymmetric microporous membranes by directly fabricating membranes that have reached their cloud point or by using thermally induced polarization (TIPS) to achieve the cloud point are all based on low polymer content (solid content less than 13%) to achieve the desired pore size and structure. It is known that increasing the mechanical strength is achieved by increasing the polymer content, also known as the solid content, in the casting solution. Membranes with low solid content lack sufficient mechanical strength to form complete, defect-free filters. Although patent CN103055724 uses a casting solution with high solid content, the maximum pore size of the membrane prepared is only 0.1 micrometers. Therefore, the methods reported in these patents are limited in preparing high-strength, large-pore-size (e.g., above 0.45 micrometers) microporous membranes. Patents US8727136, CN113117538B, and CN114130202A have successfully fabricated microporous filter membranes for industrial use using casting solutions with high solids content (around 16%). However, this method has drawbacks such as complex processes, the need for numerous controllable parameters, high membrane leachate content, and low hydrophilicity. The thickness and size of the pores in the retained layer are difficult to control. Summary of the Invention

[0011] The purpose of this invention is to provide a sulfone polymer microporous filter membrane and its preparation method. By using TIPS and VIPS simultaneously in a casting solution with high solids content, a sulfone polymer microporous filter membrane with high strength and large pore size is obtained. This preparation method is simple and reliable.

[0012] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0013] This invention provides a method for preparing a sulfone polymer microporous filter membrane, the method comprising the following steps:

[0014] S1: Prepare a casting solution comprising a sulfone polymer, a solvent, and a non-solvent, wherein the sulfone polymer is present in a mass percentage of 13-25 wt%, and the casting solution is stable and transparent at room temperature;

[0015] S2: The turbidity point of the casting solution is determined after heating treatment, wherein the turbidity point is the temperature at which phase separation occurs in the casting solution;

[0016] S3: The casting solution from step S1 is scraped onto a preheated carrier to form a liquid film; the temperature of the preheated carrier is higher than the cloud point.

[0017] S4: Expose the liquid membrane along with the carrier to air with a relative humidity of 30-90%;

[0018] S5: The liquid membrane after step S4 is immersed in a gel bath along with the carrier, and after solidification, a sulfone polymer microporous filter membrane with the target pore size is obtained.

[0019] In a preferred embodiment, the sulfone polymer includes polyethersulfone, polysulfone, and polyarylsulfone, but is not limited to these polymers. The method is also suitable for other polymers that can be used to prepare films by phase transition methods. These polymers can be in powder or particulate form.

[0020] In a preferred embodiment, the sulfone polymer is 15-20 wt% by mass to ensure that the prepared membrane has sufficient mechanical strength.

[0021] In a preferred embodiment, the solvent includes a combination or one of N-dimethylpyrrolidone, dimethylacetamide, dimethylformamide, triethyl phosphate, tributyl phosphate, γ-butyrolactone, and ε-caprolactam.

[0022] In a preferred embodiment, the non-solvent includes a combination or one of alcohols, ketones, esters, organic acids, ethers and water.

[0023] In a preferred embodiment, the alcohols include a combination or one of methanol, ethanol, propanol, butanol, pentanol, ethylene glycol, diethylene glycol, triethylene glycol, and glycerol; the ketones include a combination or one of acetone and butanone; the esters include a combination or one of butyl acetate, ethyl acetate, ethyl propionate, butyl propionate, and amyl acetate; the organic acids include a combination or one of formic acid, acetic acid, lactic acid, citric acid, and tartaric acid; and the ethers include a combination or one of polyvinyl alcohol PEG200, polyvinyl alcohol PEG400, polyacryl alcohol, and diethanolmethyl ether.

[0024] In a preferred embodiment, the casting solution further includes additives, including a combination of lithium chloride and zinc chloride, or one of them. The resulting casting solution is bubble-free and clear at room temperature, but becomes cloudy (tIPS) when the temperature rises (preferably between 40 and 60 degrees Celsius). However, it does not immediately separate into solid and liquid phases, but forms a temporarily stable cloudy suspension. The viscosity of the casting solution should not be too high to avoid difficulties in the casting process. The casting solution can be cast onto a carrier with a temperature exceeding the cloud point of the casting solution using a doctor blade, extrusion head, or other methods.

[0025] In a preferred embodiment, step S3 further includes the following step: scraping the casting liquid onto a preheated carrier using a doctor blade or extrusion head to form a liquid film; the temperature of the preheated carrier is higher than the cloud point. The temperature of the liquid film at the carrier contact point has reached or exceeded the cloud point before entering the gel bath, and a decreasing temperature gradient is formed from the heated surface to the air contact surface. The temperature distribution in the film depends on the temperature of the carrier and the air temperature; a larger temperature gradient usually leads to a higher asymmetry in the film.

[0026] In a preferred embodiment, the carrier is selected from one or more of the following: glass plate, nonwoven fabric, PET or polyethylene film, stainless steel roller or steel strip.

[0027] In a preferred embodiment, the air in step S4 is selected from stationary air or flowing air. Before entering the gel bath, the liquid membrane is exposed to humid air to induce a phase change (VIPS). The humid air can be stationary or flowing; fluid contact can increase the phase change rate at the membrane surface. Generally speaking, humid air induction can lead to an increase in the pore size of the air-contact surface and a decrease in the asymmetry of the membrane.

[0028] In a preferred embodiment, the gel bath comprises water, or a mixture of water and a non-solvent or solvent; the non-solvent comprises alcohols and ketones, and the solvent comprises a combination or one of N-dimethylpyrrolidone, dimethylacetamide, dimethylformamide, triethyl phosphate, tributyl phosphate, γ-butyrolactone, and ε-caprolactam. The liquid membrane completely solidifies into a film after entering the gel bath.

[0029] In a preferred embodiment, in step S3, the temperature of the preheated carrier is higher than the turbidity point, but does not exceed the turbidity point + 20°C. The temperature of the preheated carrier depends on the pore size of the filter membrane to be produced; the higher the temperature, the larger the pore size.

[0030] In a preferred embodiment, in step S4, the liquid membrane is exposed together with the carrier to air with a relative humidity of 30-90%, preferably 50-90%; the temperature of the air is 20-40°C, preferably 25-30°C; the exposure time is 1-100 seconds, preferably 1-60 seconds, and the exposure time is determined according to the target pore size of the microporous filter membrane.

[0031] The present invention also provides a sulfone polymer microporous filter membrane, which is prepared according to the sulfone polymer microporous filter membrane preparation method described above.

[0032] In a preferred embodiment, the sulfone polymer microporous filter membrane is an asymmetric microporous filter membrane.

[0033] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0034] (1) The method for preparing sulfone polymer microporous filter membranes provided by the present invention combines the TIPS and VIPS methods to prepare sulfone polymer microporous filter membranes. This method has greater operational flexibility than other methods in preparing microporous filter membranes with different pore sizes and asymmetries. All of them can be adjusted and controlled. It is not only suitable for preparing filter membranes with large pore sizes (greater than 0.45 micrometers), but also suitable for preparing 0.22 micrometer filter membranes with complete bacterial retention. By adjusting the operating parameters of the TIPS and VIPS methods, asymmetric membranes with complete retention layers can be prepared to ensure complete bacterial retention.

[0035] (2) The method for preparing sulfone polymer microporous filter membrane provided by the present invention does not require the addition of any polymer hydrophilic agent, thus eliminating the defect of high solubility. The surface-modified filter membrane is very suitable for use in biopharmaceuticals. The method is simple and easy to operate.

[0036] (3) The sulfone polymer microporous filter membrane provided by the present invention has high solid content, high mechanical strength and large pore size, which will improve the quality of the filter and reduce the production cost. It will play a positive role in promoting the research and development and production of biopharmaceuticals.

[0037] (4) This invention provides a method for preparing sulfone polymer microporous filter membranes using both TIPS and VIPS, and employs a simple casting solution formulation without any additives. Microporous membranes with different pore sizes and asymmetries can be prepared simply by controlling the air temperature and humidity, exposure time, and carrier temperature. The membrane preparation process of this invention is simple and easy to operate, and it is suitable for the industrial production of high-quality microporous membranes. Attached Figure Description

[0038] Figure 1 This is a scanning electron microscope (SEM) cross-sectional image of a polyethersulfone microporous filter membrane prepared by the TIPS and VIPS methods in a specific embodiment of the present invention. Detailed Implementation

[0039] The technical solution of the present invention will be described in detail below with reference to the embodiments. Unless otherwise specified, all reagents and biological materials used below are commercial products.

[0040] Example 1:

[0041] A 1L multi-necked glass flask was placed in a constant-temperature water bath at 50°C. 313.6g of N-dimethylpyrrolidone (NMP) and 180g of diethylene glycol (DEG) were added to the flask. Stirring was started, followed by the addition of 126.4g of polyethersulfone (PES) resin (purchased from Sumitomo, Japan, 5900P). Stirring continued until the polymer was completely dissolved. The temperature of the water bath was then lowered to approximately 35°C, and 180g of DEG was slowly added. The mixture was stirred for 24 hours. After degassing at room temperature, a clear and transparent casting solution was obtained, with a PES solids content of 15.8% (by weight). A 20mL glass vial containing the degassed casting solution was placed in a constant-temperature water bath and the temperature was slowly increased. The cloud point of the casting solution was measured to be 47.5°C.

[0042] The glass plate was preheated to a preset temperature in an oven, as shown in Table 1. An appropriate amount of casting solution was placed on the heated glass plate, and a liquid film with a thickness of approximately 180 micrometers was manually scraped out using a metal scraper roller. The liquid film was exposed to air at a temperature of 25°C and a relative humidity of 85% for a preset time, as shown in Table 1. Then, it was placed in a temperature-controlled gel bath to solidify into a film, as shown in Table 1. The solidified polyethersulfone microporous filter membrane was thoroughly washed with clean water and then air-dried at room temperature. Take a dried polyethersulfone microporous filter membrane and immerse it in a solvent containing 70% (by weight) isopropanol and 30% water. After removal, measure the pressure required for the first bubble to appear, defined as the initial bubble point pressure. This pressure corresponds to the maximum pore size of the polyethersulfone microporous filter membrane. When the initial bubble point pressure is 0.25 MPa, the corresponding pore size of the polyethersulfone microporous filter membrane is approximately 0.05 μm; when the initial bubble point pressure is 0.15 MPa, the corresponding pore size is approximately 0.22 μm; when the initial bubble point pressure is 0.1 MPa, ... The pore size of the polyethersulfone microporous filter membrane is approximately 0.45 micrometers; when the initial bubble point pressure is 0.07 MPa, the pore size of the polyethersulfone microporous filter membrane is approximately 0.65 micrometers; when the initial bubble point pressure is 0.05 MPa, the pore size of the polyethersulfone microporous filter membrane is approximately 1 micrometer. After the polyethersulfone microporous filter membrane was thoroughly washed in pure water, the filtration time of 50 mL of pure water was measured at a vacuum of 0.075 MPa and 25°C. The results are shown in Table 1. The different experimental conditions and results in Example 1 are shown in Table 1 below.

[0043] Table 1

[0044]

[0045]

[0046] The results shown in Table 1 are analyzed as follows:

[0047] (1) To investigate the effects of different humid air exposure times on the initial bubble point pressure (pore size) and pure water filtration time of polyethersulfone microporous membranes, experimental groups 1-3 were conducted under conditions where the glass plate temperature and gel bath temperature were both 25°C. The initial bubble point pressure and filtration time of 50 mL of pure water were measured after different exposure times (1 s, 30 s, and 60 s) of the liquid membrane in air at 25°C and 85% relative humidity. Table 1 shows that, under the same operating conditions (glass plate temperature, gel bath temperature, etc.), the initial bubble point pressure of the polyethersulfone microporous membrane decreased with increasing air exposure time, meaning the pore size of the polyethersulfone microporous membrane increased with increasing air exposure time, corresponding to a decrease in pure water filtration time, leading to increased flux. In experimental groups 1-3, the liquid membrane temperature of 25°C was lower than the measured casting liquid turbidity point (47.5°C). Therefore, experimental groups 1-3 exhibited the humid air-induced phase separation (VIPS) effect.

[0048] (2) To investigate the effects of different gel bath temperatures on the initial bubble point pressure (pore size) and pure water filtration time of the polyethersulfone microporous filter membrane, the results of experimental groups 2 and 4, and experimental groups 5 and 7 were compared.

[0049] Experimental groups 2 and 4 were conducted with a glass plate temperature of 25℃, gel bath temperatures of 25℃ and 55℃ respectively, and an exposure time of 30s in air with a relative humidity of 85%, to determine the initial bubble point pressure and filtration time of 50mL of pure water. Table 1 shows that, under the same operating conditions (glass plate temperature, exposure time in air, etc.), different gel bath temperatures had little effect on the initial bubble point pressure (0.16 and 0.15 MPa) of the polyethersulfone microporous membranes in experimental groups 2 and 4, indicating that the gel bath temperature had little effect on the membrane pore size.

[0050] Experiments 5 and 7 were conducted with a glass plate temperature of 55℃, higher than the cloud point of the casting solution (47.5℃). The initial bubble point pressure and filtration time of 50 mL of pure water were measured after exposure to air at 85% relative humidity for 30 seconds at gel bath temperatures of 25℃ and 55℃, respectively. Table 1 shows that, under the same operating conditions (glass plate temperature, air exposure time, etc.), different gel bath temperatures had little effect on the initial bubble point pressure (0.065 MPa and 0.06 MPa) of the polyethersulfone microporous membrane in experiments 5 and 7 (0.06 MPa), indicating that the gel bath temperature had little effect on the membrane pore size.

[0051] (3) To investigate the effects of different glass plate temperatures on the initial bubble point pressure (pore size) and pure water filtration time of the polyethersulfone microporous membrane, experimental groups 2 and 5 were tested under the conditions of glass plate temperatures of 25℃ and 55℃, respectively, gel bath temperature of 25℃, and air exposure time of 30s at a relative humidity of 85%. The initial bubble point pressure and filtration time of 50mL of pure water were measured. Table 1 shows that, under the same operating conditions such as gel bath temperature and air exposure time, the initial bubble point pressure of the polyethersulfone microporous membrane decreased significantly with increasing glass plate temperature (0.16 and 0.065 MPa), indicating that the glass plate temperature has a significant impact on the pore size of the polyethersulfone microporous membrane.

[0052] In experimental group 5, the temperature of the glass plate was 7.5°C higher than the cloud point of the casting liquid (47.5°C). At this temperature, the glass plate heated the liquid film above the cloud point, causing a phase change. Therefore, the initial bubble point pressure measured in experimental group 5 (0.065 MPa) was significantly lower than that measured in experimental group 2 (0.16 MPa). Thus, the comparison results of experimental groups 2 and 5 clearly demonstrate the role of thermally induced phase change (TIPS) in the preparation of polyethersulfone microporous filter membranes.

[0053] (4) To investigate the effect of different exposure times in air on the initial bubble point pressure (pore size) and pure water filtration time of the polyethersulfone microporous filter membrane when both the glass plate temperature and the gel bath temperature are higher than the cloud point of the casting solution, test groups 6-8 were conducted with both the glass plate temperature and the gel bath temperature at 55℃, higher than the cloud point of the casting solution, and the liquid membrane was exposed to air with a relative humidity of 85% for 1s, 30s, and 45s, respectively. Table 1 shows that the results of test groups 6-8 clearly demonstrate that under the condition of thermally guided phase change (TIPS), the initial bubble point pressure of the polyethersulfone microporous filter membrane decreases with the extension of the exposure time in humid air, that is, the pore size of the polyethersulfone microporous filter membrane increases with the extension of the exposure time in humid air.

[0054] Figure 1 These are SEM cross-sectional images of the polyethersulfone microporous filter membranes prepared using the TIPS and VIPS methods in experimental group 8. Figure 1 The results show that the polyethersulfone microporous filter membranes prepared by the TIPS and VIPS methods have asymmetry and excellent porosity.

[0055] Compared to experimental groups 1-3 which only used the moist air-induced phase separation (VIPS) method, experimental groups 6-8 demonstrated that in the presence of thermally guided phase change (TIPS), the combined use of moist air-induced phase separation (VIPS) can significantly alter the initial bubble point pressure of the polyethersulfone microporous filter membrane, thus significantly changing the pore size of the polyethersulfone microporous filter membrane. Table 1 shows the feasibility of fabricating microporous membranes with different pore sizes using the combined effect of TIPS and VIPS, and clearly demonstrates that the combined effect of TIPS and VIPS yields microporous membranes with larger pore sizes than either effect alone.

[0056] Example 2

[0057] The casting solution in Example 2 was prepared using the same method as in Example 1, with the differences being the non-solvent, solid content, and cloud point. In this example, ethylene glycol methyl ether (PFS) was used as the non-solvent, the PFS solid content was 16%, and the cloud point of the casting solution was measured to be 49°C. The different experimental conditions and results in Example 2 are shown in Table 2 below.

[0058] Table 2

[0059]

[0060] * indicates that in this test group, the liquid film was exposed to flowing humid air, and the flowing humid air was obtained by blowing with a fan.

[0061] In Example 2, the glass plate temperature and gel bath temperature of experimental groups 1-3 were both 55°C, higher than the cloud point of the casting solution (49°C). The results in Table 2 further verify that, in the presence of thermally induced phase transition (TIPS), contacting the liquid membrane surface with humid air for an appropriate time can prepare polyethersulfone microporous filter membranes with the desired pore size. Furthermore, the results of experimental group 3 show that the phase change induced by flowing humid air is more effective than that induced by static humid air. The polyethersulfone microporous filter membranes obtained in experimental groups 2 and 3 have a pore size of approximately 1 micrometer, indicating that the method provided by this invention is feasible for preparing large-pore polyethersulfone microporous filter membranes.

[0062] The above are merely some preferred embodiments of the present invention, and the present invention is not limited to the contents of these embodiments. For those skilled in the art, various changes and modifications can be made within the scope of the present invention's technical solutions, and any such changes and modifications are within the protection scope of the present invention.

Claims

1. A method for preparing a sulfone polymer microporous filter membrane, characterized in that, The preparation method includes the following steps: S1: Prepare a casting solution, wherein the casting solution comprises a sulfone polymer, a solvent and a non-solvent, wherein the sulfone polymer has a mass percentage of 13-25 wt%; S2: The turbidity point of the casting solution is determined after heating treatment, wherein the turbidity point is the temperature at which phase separation occurs in the casting solution; S3: The casting solution from step S1 is scraped onto a preheated carrier to form a liquid film; the temperature of the preheated carrier is higher than the cloud point. S4: Expose the liquid membrane along with the carrier to air with a relative humidity of 30-90%; S5: The liquid membrane after step S4 is immersed in a gel bath along with the carrier, and after solidification, a sulfone polymer microporous filter membrane with the target pore size is obtained.

2. The preparation method according to claim 1, characterized in that, The sulfone polymers include polyethersulfone, polysulfone, and polyarylsulfone.

3. The preparation method according to claim 1, characterized in that, The sulfone polymer has a mass percentage of 15-20 wt%.

4. The preparation method according to claim 1, characterized in that, The solvent includes a combination or one of N-dimethylpyrrolidone, dimethylacetamide, dimethylformamide, triethyl phosphate, tributyl phosphate, γ-butyrolactone, and ε-caprolactam.

5. The preparation method according to claim 1, characterized in that, The non-solvents include combinations or one of alcohols, ketones, esters, organic acids, ethers and water.

6. The preparation method according to claim 5, characterized in that, The alcohols include a combination or one of methanol, ethanol, propanol, butanol, pentanol, ethylene glycol, diethylene glycol, triethylene glycol and glycerol; The ketones include a combination of acetone and butanone or one thereof; The esters include a combination or one of butyl acetate, ethyl acetate, ethyl propionate, butyl propionate, and amyl acetate; The organic acids include combinations or one of formic acid, acetic acid, lactic acid, citric acid and tartaric acid; The ethers include combinations or one of polyvinyl alcohol PEG200, polyvinyl alcohol PEG400, polyacryl alcohol and diethanol methyl ether.

7. The preparation method according to claim 1, characterized in that, The casting solution also includes additives, which include a combination of lithium chloride and zinc chloride or one of them.

8. The preparation method according to claim 1, characterized in that, Step S3 further includes the following steps: The casting solution is scraped onto a preheated carrier using a scraper or extrusion head to form a liquid film; the temperature of the preheated carrier is higher than the cloud point.

9. The preparation method according to claim 1 or 8, characterized in that, The carrier is selected from one or more of the following: glass plate, non-woven fabric, PET or polyethylene film, stainless steel roller or steel belt.

10. The preparation method according to claim 1, characterized in that, The air used in step S4 is selected from stationary air or flowing air.

11. The preparation method according to claim 1, characterized in that, The gel bath comprises water, or a mixture of water and a non-solvent or solvent; the non-solvent comprises alcohols and ketones, and the solvent comprises a combination or one of N-dimethylpyrrolidone, dimethylacetamide, dimethylformamide, triethyl phosphate, tributyl phosphate, γ-butyrolactone, and ε-caprolactam.

12. The preparation method according to claim 1, characterized in that, In step S3, the temperature of the preheated carrier is higher than the cloud point, but does not exceed the cloud point + 20°C.

13. The preparation method according to claim 1, characterized in that, In step S4, the liquid membrane is exposed together with the carrier to air with a relative humidity of 30-90%, preferably 50-90%; the temperature of the air is 20-40°C, preferably 25-30°C; and the exposure time is 1-100 seconds, preferably 1-60 seconds.

14. A sulfone polymer microporous filter membrane, characterized in that, Prepared according to any one of the preparation methods described in claims 1-13.

15. The sulfone polymer microporous filter membrane according to claim 14, characterized in that, The sulfone polymer microporous filter membrane is an asymmetric microporous filter membrane.

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