Asymmetric hourglass type polysulfone microporous membrane and preparation method thereof

Abstract

The invention provides an asymmetric hourglass type polysulfone microporous membrane and a preparation method thereof.The preparation method comprises the steps that at the first temperature, polysulfone resin is added into a solvent to be stirred and dissolved, and a polymer solution is obtained; adding a pore-foaming agent and a strong-polarity non-solvent into the polymer solution, continuously stirring to a uniform state, and defoaming to obtain a membrane casting solution at a second temperature; coating the pretreated base material with the membrane casting solution to form a liquid membrane; performing phase inversion on the liquid film for a first time at a third temperature and a preset humidity; transferring the liquid membrane subjected to phase conversion into a solidification liquid for solidification for a second time to obtain an intermediate membrane; and cleaning and drying the intermediate membrane to obtain the microporous membrane. According to the asymmetric hourglass type polysulfone microporous membrane and the preparation method thereof provided by the invention, the polysulfone microporous membrane with high flux, excellent interception performance, ultrahigh pollutant holding capacity and high asymmetric hourglass type structure is obtained, and the process is simple, feasible and environment-friendly, and the cost is reduced.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer membrane materials, and particularly relates to an asymmetric hourglass-shaped polysulfone microporous membrane and a preparation method thereof. Background Art

[0002] Polysulfone resins are one of the most widely used polymer membrane materials, which have excellent processability, mechanical stability, physicochemical stability and thermal stability. Obtaining microfiltration membranes from polysulfone resins has also become the preferred membrane material for the separation of aqueous solution systems due to its good chemical stability, thermal stability and application reliability. With the continuous increase in application requirements and scenarios, the demand for asymmetric microfiltration membranes with high fouling capacity has become more explicit. A higher fouling capacity means that the filter membrane has a longer service life and can effectively reduce application costs.

[0003] Currently, the most common asymmetric membranes mainly include V-shaped and hourglass-shaped ones, and their cross-sections both contain a macroporous layer and a small-pore retention layer. Among them, the pore size of the V-shaped asymmetric membrane shows an increasing trend from one surface to the other. For example, Patent US4629563A describes a V-shaped asymmetric membrane. Among them, the macroporous region can carry more fouling capacity, while the small-pore region on the other side can ensure the retention of smaller particles. However, the separation layer of this membrane is close to the skin layer, which causes the separation layer of the membrane sheet to be easily damaged during actual application. In Patent CN117398865A, an asymmetric hourglass structure is obtained by performing segmented treatment on the liquid membrane. However, the preparation process of this membrane is relatively complex and requires multi-stage segmented treatment of the liquid membrane. The liquid membrane will pass through a pretreatment bath and a re-treatment bath, and finally solidify into a membrane through a coagulation bath. This process is relatively complex and has strict requirements for equipment. Moreover, the media in the pretreatment bath and the re-treatment bath are mostly solvents, which increases the working environment and the cost of membrane preparation. Therefore, the current application of asymmetric membranes is poor, or the preparation method is complex and the production cost is high. Summary of the Invention

[0004] The present invention provides an asymmetric hourglass-shaped polysulfone microporous membrane and a preparation method thereof. Through the asymmetric hourglass-shaped polysulfone microporous membrane and the preparation method provided by the present invention, a polysulfone microporous membrane with a highly asymmetric hourglass structure is obtained. The microporous membrane has high flux, excellent retention performance and extremely high fouling capacity. Moreover, a multi-layer structure is formed by a one-step method without a multi-stage treatment bath, and the coagulation bath is only water. The process is simple and feasible, very easy to industrialize, avoids the consumption of organic solvents, is environmentally friendly and reduces costs.

[0005] To solve the above technical problems, the present invention provides a preparation method for an asymmetric hourglass-shaped polysulfone microporous membrane, which at least includes the following steps:

[0006] At a first temperature, add a polysulfone resin to a solvent and stir to dissolve it to obtain a polymer solution;

[0007] Add a pore-forming agent and a strongly polar non-solvent to the polymer solution, continuously stir until it reaches a homogeneous state, and defoam to obtain a casting solution at a second temperature;

[0008] Coat the casting solution on the pretreated substrate to form a liquid film;

[0009] At a third temperature and a preset humidity, subject the liquid film to phase inversion for a first time;

[0010] Transfer the liquid film after phase inversion to a coagulation liquid for a second coagulation time to obtain an intermediate film; and

[0011] Wash and dry the intermediate film to obtain a microporous membrane.

[0012] In one embodiment of the present invention, the strongly polar non-solvent includes at least one of water, n-butanol, ethanol, ethylene glycol, n-propanol, glycerol or formamide.

[0013] In one embodiment of the present invention, the polysulfone resin includes at least one of polysulfone, polyphenylene sulfone or polyethersulfone;

[0014] And / or, the solvent includes at least one of N-methylpyrrolidone, dimethylacetamide or dimethylformamide;

[0015] And / or, the pore-forming agent includes at least one of polyvinylpyrrolidone K30, polyethylene glycol 400 or polyethylene glycol 800.

[0016] In one embodiment of the present invention, the first temperature is 70°C to 90°C, and the second temperature is 20°C to 30°C.

[0017] In one embodiment of the present invention, the casting solution includes 48 parts to 65 parts of the solvent, 12 parts to 18 parts of the polysulfone resin, 12 parts to 18 parts of the pore-forming agent, and 3 parts to 10 parts of the strongly polar non-solvent.

[0018] In one embodiment of the present invention, the third temperature is 35°C to 45°C, the preset humidity is 50RH% to 80RH%, and the first time is 10s to 40s.

[0019] In one embodiment of the present invention, the coagulation liquid is water, and the temperature of the coagulation liquid is 25°C to 40°C;

[0020] And / or, the second time is 30s to 60s;

[0021] And / or, the pretreatment of the substrate includes cleaning and drying, and the temperature of the substrate is 20°C to 30°C.

[0022] In an embodiment of the present invention, the viscosity of the casting solution is 2000 mPa·s to 3000 mPa·s.

[0023] The present invention also provides an asymmetric hourglass-shaped polysulfone microporous membrane obtained by the above method. The microporous membrane comprises a skin layer, a separation layer, and a support layer in sequence from the top layer to the bottom layer. The pore size of the skin layer is larger than that of the separation layer, and the pore size of the skin layer is smaller than that of the support layer.

[0024] In an embodiment of the present invention, the thickness ratio of the skin layer, the separation layer, and the support layer is 1-2:1-2:7-8.

[0025] In summary, the present invention provides an asymmetric hourglass-shaped polysulfone microporous membrane and a preparation method thereof. A polysulfone microporous membrane with a high asymmetric hourglass structure is successfully prepared. This structure enables the microporous membrane to have excellent rejection performance and an extremely high fouling capacity while maintaining high flux. Moreover, by regulating the phase separation rate through the vapor-induced phase inversion method, a multi-layer structure is formed in one step without a multi-stage treatment bath, and the coagulation bath is only water. The process is simple and feasible, extremely easy to industrialize, avoids the consumption of organic solvents, is environmentally friendly and reduces costs. It can control the quality of the formed liquid membrane and obtain a high-quality asymmetric hourglass-shaped polysulfone microporous membrane. The microporous membrane has the characteristics of embedded protection of the separation layer, high flux, high rejection rate, and anti-fouling. Moreover, the microporous membrane has been improved in terms of pore size distribution, porosity, mechanical strength, etc. Especially in specific separation fields, it shows higher separation efficiency and longer service life, obtaining a high-performance microporous membrane. The obtained microporous membrane can be widely applied to multiple fields such as industry, biology, medicine, and water treatment, meeting the requirements of different industrial processes for the performance of membrane materials. Description of the Drawings

[0026] To more clearly illustrate the technical solutions of the embodiments of the present invention, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0027] Figure 1 It is a scanning electron microscope image of the cross-section of the microporous membrane in Example 1.

[0028] Figure 2 It is a scanning electron microscope image of the skin layer plane of the microporous membrane in Example 1.

[0029] Figure 3 It is a scanning electron microscope image of the support layer plane of the microporous membrane in Example 1.

[0030] Figure 4It is a scanning electron microscope image of the cross-section of the microporous membrane in Example 2.

[0031] Figure 5 It is a scanning electron microscope image of the cross-section of the microporous membrane in Example 3.

[0032] Figure 6 It is a scanning electron microscope image of the cross-section of the microporous membrane in Comparative Example 1.

[0033] Figure 7 It is a scanning electron microscope image of the cross-section of the microporous membrane in Comparative Example 2.

[0034] Figure 8 It is a scanning electron microscope image of the cross-section of the microporous membrane in Comparative Example 3.

[0035] Figure 9 It is a scanning electron microscope image of the cross-section of the microporous membrane in Comparative Example 4.

[0036] Figure 10 It is a scanning electron microscope image of the cross-section of the microporous membrane in Comparative Example 5.

[0037] Figure 11 It is a scanning electron microscope image of the cross-section of a commercially available PES membrane in Comparative Example 6. Detailed implementation manners

[0038] The following uses specific specific examples to illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0039] It should be understood that the present invention can be implemented in different forms and should not be construed as limited to the embodiments presented herein. On the contrary, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the present invention to those skilled in the art.

[0040] The following further elaborates on the technical solutions of the present invention in conjunction with several embodiments. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the scope of protection of the present invention.

[0041] The present invention provides a method for preparing an asymmetric hourglass-shaped polysulfone microporous membrane, which at least includes: at a first temperature, adding a polysulfone resin into a solvent and stirring to dissolve, obtaining a polymer solution; adding a pore-forming agent and a strongly polar non-solvent into the polymer solution, continuously stirring until a homogeneous state is achieved, and defoaming to obtain a casting solution at a second temperature; coating the casting solution on a pretreated substrate to form a liquid film; at a third temperature and a preset humidity, subjecting the liquid film to phase inversion for a first time; transferring the phase-inverted liquid film to a coagulation liquid for coagulation for a second time to obtain an intermediate film; cleaning and drying the intermediate film to obtain a microporous membrane. Through the preparation method of the present application, the obtained asymmetric hourglass-shaped polysulfone microporous membrane includes a skin layer, a separation layer, and a support layer arranged in sequence, wherein the pore sizes of the skin layer and the support layer are larger than those of the separation layer, thereby having excellent retention performance and an ultra-high fouling capacity, and the preparation method is simple and feasible, the film-forming process has high controllability, and it is extremely easy to industrialize.

[0042] In an embodiment of the present invention, the polysulfone resin includes, for example, at least one of polysulfone (PSU), polyphenylene sulfone resins (PPSU), or polyethersulfone (PES), etc., and the solvent includes, for example, at least one of N-methylpyrrolidone (NMP), N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), etc. The first temperature is, for example, 70°C to 90°C. Specifically, at the first temperature, the polysulfone resin is slowly added into the solvent, and stirred while adding until completely dissolved to obtain a polymer solution, wherein the stirring speed is, for example, 200 rpm / min to 300 rpm / min.

[0043] In an embodiment of the present invention, without changing the stirring speed, a pore-forming agent and a strongly polar non-solvent are added, and then stirring is continued until a homogeneous state is obtained. Among them, the pore-forming agent includes, for example, at least one of polyvinylpyrrolidone K30 (PVP-K30), polyethylene glycol 400 (PEG400), or polyethylene glycol 800 (PEG800), etc., and the strongly polar non-solvent includes, for example, at least one of water, n-butanol, ethanol, ethylene glycol, n-propanol, glycerol, or formamide, etc. In a specific embodiment of the present invention, after adding the pore-forming agent and the strongly polar non-solvent, the stirring speed remains unchanged, and for example, the continuous stirring time is, for example, 4 h to 6 h to obtain a homogeneous and transparent solution. Then, the solution is defoamed to obtain a casting solution at a second temperature. In a specific embodiment of the present invention, defoaming is carried out, for example, by vacuum degassing, etc., and the defoaming time is, for example, 2 h to 3 h. During the defoaming process, the temperature of the solution decreases from the first temperature to the second temperature to obtain a casting solution, and the second temperature is, for example, 20°C to 30°C.

[0044] In an embodiment of the present invention, in the casting solution, for example, it includes 48 parts to 65 parts of a solvent, 12 parts to 18 parts of a polysulfone resin, 12 parts to 18 parts of a pore-forming agent, and 3 parts to 10 parts of a strongly polar non-solvent, where parts are mass fractions. By adjusting the ratio of the solvent to the non-solvent, the viscosity and stability of the casting solution are controlled. Among them, the viscosity of the casting solution is, for example, 2000 mPa·s to 3000 mPa·s. By controlling the viscosity of the casting solution, the quality of the formed liquid film can be controlled, and during the phase inversion and solidification processes, it is possible to prevent the problem that the exchange rate between the solvent and the non-solvent is too fast due to too low viscosity, resulting in the easy formation of large permeable pores, and at the same time prevent problems such as difficult exchange between the solvent and the non-solvent due to too high viscosity, so as to obtain a high-quality asymmetric hourglass-shaped polysulfone microporous membrane.

[0045] In an embodiment of the present invention, the substrate is, for example, selected from one of non-woven fabric or release film, etc., and the present application does not further limit the materials of the non-woven fabric or the release film. Among them, before using the substrate, the substrate is pretreated. The pretreatment includes, for example, cleaning and drying with deionized water, absolute ethanol, or isopropanol, etc., to ensure that the surface of the substrate is flat, clean, and dry, so as to improve the quality of the subsequent formed liquid film. For example, a doctor blade is used to coat the casting solution on the pretreated substrate to form a liquid film. Among them, the film scraping distance between the doctor blade and the substrate is, for example, 200 μm to 400 μm, and the temperature of the substrate is, for example, 20°C to 30°C.

[0046] In an embodiment of the present invention, after the liquid film is formed, the liquid film is placed in an environment with a third temperature and a preset humidity for steam-induced phase inversion for a first time. Among them, the third temperature is, for example, 35°C to 45°C, the preset humidity is, for example, 50RH% to 80RH%, and the first time is, for example, 10 s to 40 s. Controlling the conditions of steam-induced phase inversion can control the pore size and quality of the formed top layer.

[0047] In an embodiment of the present invention, the phase-converted liquid membrane is transferred to a coagulation liquid for coagulation for a second time to obtain an intermediate membrane. Wherein, the coagulation liquid is, for example, water, and the temperature of the coagulation liquid is, for example, 25°C to 40°C, and the second time is, for example, 30 s to 60 s. The coagulated intermediate membrane detaches and separates from the substrate. Wherein, during the vapor-induced phase inversion process of the liquid membrane, due to contact with water vapor in the air, the liquid membrane contains a high content of strongly polar non-solvent and exchanges with the high-humidity air to form a skin layer with a certain pore size, and then enters the coagulation liquid. A dense separation layer is formed due to the rapid exchange between the solvent and the coagulation bath in the intermediate layer, and a porous support layer is formed due to the slow diffusion of the solvent in the inner layer. By controlling the temperature of the coagulation liquid, the pore size of the separation layer can be controlled, thereby controlling the filtration performance of the microporous membrane.

[0048] In the present invention, the liquid membrane first undergoes vapor-induced phase inversion and then is solidified by a coagulation liquid. The solvent and non-solvent in the casting solution exchange, resulting in phase separation of the membrane layer and forming an asymmetric hourglass structure. By introducing a strongly polar non-solvent and utilizing the solvent and coagulation bath exchange mechanism during the phase inversion process, a polysulfone-based microporous membrane with a highly asymmetric hourglass structure is successfully prepared. This structure enables the microporous membrane to have excellent retention performance and extremely high fouling capacity while maintaining high flux. And by regulating the phase separation rate through the vapor-induced phase inversion method, a multi-layer structure is formed in one step, without the need for a multi-stage treatment bath, and the coagulation bath is only water. The process is simple and feasible, avoiding the consumption of organic solvents, being environmentally friendly and reducing costs.

[0049] In an embodiment of the present invention, after obtaining the intermediate membrane, the intermediate membrane is washed and dried to obtain a microporous membrane. Specifically, for example, the intermediate membrane is taken out from the coagulation liquid, placed in deionized water at 70°C to 80°C and washed for 10 min to 30 min, taken out and dried. The drying temperature and time are not required, just dried, to obtain a highly asymmetric hourglass-shaped polysulfone-based microporous membrane.

[0050] The present invention also provides an asymmetric hourglass-shaped polysulfone-based microporous membrane obtained by the above preparation method. Among them, the microporous membrane sequentially includes a skin layer, a separation layer and a support layer from the top layer to the bottom layer. That is, along the thickness direction of the microporous membrane, the pore size of the whole microporous membrane gradually decreases first and then gradually increases, presenting a "hourglass-shaped" structure of loose-dense-loose. By forming a highly asymmetric microporous membrane, the overall structure of the microporous membrane is more loose and the flux is higher. That is, compared with the polysulfone-based microporous membrane prepared by the traditional method, the polysulfone-based microporous membrane obtained by the preparation method of the present application has both embedded protection of the separation layer, high flux, high rejection rate and anti-fouling characteristics, and the microporous membrane has been improved in terms of pore size distribution, porosity, mechanical strength, etc. Especially in specific separation fields, it shows higher separation efficiency and longer service life, obtaining a high-performance microporous membrane.

[0051] In an embodiment of the present invention, the thickness of the microporous membrane is, for example, 110 μm to 130 μm, and the thickness ratio of the skin layer, the separation layer and the support layer is, for example, 1 - 2:1 - 2:7 - 8. The support layer has an appropriate thickness. Considering the pore size relationship of each layer of the microporous membrane, it ensures that the overall support layer has high mechanical strength, and the support layer has a low density, so as to further ensure that when the support layer is introduced, the internal resistance of the microporous membrane only increases slightly while the external resistance decreases significantly, and the flux of the microporous membrane is significantly improved. In a specific embodiment of the present invention, the bubble point of the microporous membrane is, for example, 0.4 MPa to 0.45 MPa, and the pure water flux of the microporous membrane is, for example, 35 mL / min / cm 2 ~40 mL / min / cm 2 , and the dirt holding capacity is, for example, 95 g / cm 2 ~115 g / cm 2 The microporous membrane of the present invention can be widely used in multiple fields such as industry, biology, medicine, and water treatment to meet the performance requirements of membrane materials for different industrial processes.

[0052] Hereinafter, the present invention will be more specifically explained by reference to embodiments, which should not be construed as restrictive. Appropriate modifications can be made within the scope consistent with the gist of the present invention, and all of them fall within the technical scope of the present invention.

[0053] Example 1

[0054] At 80 °C, 16 parts of polyethersulfone resin were slowly added to 63 parts of dimethylacetamide, stirred at 250 rpm / min until the polyethersulfone resin was completely dissolved, 5 parts of water and 16 parts of PVP-K30 were added, and then stirred for another 5 h and degassed under vacuum for 2 h to obtain a casting solution at a temperature of 25 °C. The casting solution was blade-coated onto a release film to form a liquid film, the blade coating distance was 300 μm, and the temperature of the release film was 25 °C. The liquid film was left standing in a constant temperature and humidity chamber for 30 s, the temperature of the constant temperature and humidity chamber was 30 °C, the humidity was 60 RH%, and then immersed in a 25 °C water bath for curing for 1 min. The cured intermediate film was taken out, washed in deionized water for 50 min and then taken out and dried to obtain a microporous membrane.

[0055] Example 2

[0056] At 80 °C, 16 parts of polyethersulfone resin were slowly added to 63 parts of dimethylacetamide, and stirred at 250 rpm / min until the polyethersulfone resin was completely dissolved. 5 parts of glycerol and 16 parts of PVP-K30 were added, and then stirring was continued for 5 h, followed by vacuum degassing for 2 h to obtain a casting solution at 25 °C. The casting solution was blade-coated onto a release film to form a liquid film, with a blade gap of 300 μm and the temperature of the release film being 25 °C. The liquid film was left standing in a constant temperature and humidity chamber for 30 s, with the temperature of the constant temperature and humidity chamber being 30 °C and the humidity being 60 RH%. It was then immersed in a 25 °C water bath for curing for 1 min. The cured intermediate film was taken out, washed in deionized water for 50 min and then taken out and dried to obtain a microporous membrane.

[0057] Example 3

[0058] At 80 °C, 16 parts of polyethersulfone resin were slowly added to 58 parts of dimethylacetamide, and stirred at 250 rpm / min until the polyethersulfone resin was completely dissolved. 10 parts of glycerol and 16 parts of PVP-K30 were added. The remaining operations and steps were the same as those in Example 2.

[0059] Comparative Example 1

[0060] The liquid film was left standing in a constant temperature and humidity chamber for 60 s, and the remaining operations and steps were the same as those in Example 2.

[0061] Comparative Example 2

[0062] The liquid film was left standing in a constant temperature and humidity chamber for 30 s and then immersed in a 50 °C water bath for curing for 1 min, and the remaining operations and steps were the same as those in Example 2.

[0063] Comparative Example 3

[0064] The casting solution was blade-coated onto a release film to form a liquid film. The side surface of the release film away from the liquid film was preheated using a 50 °C heating pad for 30 s, and then the liquid film was left standing in a constant temperature and humidity chamber for 30 s, with the temperature of the constant temperature and humidity chamber being 35 °C and the humidity being 60 RH%. The remaining operations and steps were the same as those in Example 2.

[0065] Comparative Example 4

[0066] At 80 °C, 16 parts of polyethersulfone resin were slowly added to 56 parts of dimethylacetamide, and stirred at 250 rpm / min until the polyethersulfone resin was completely dissolved. 12 parts of water and 16 parts of PVP-K30 were added. The remaining operations and steps were the same as those in Example 1.

[0067] Comparative Example 5

[0068] Replace 5 parts of water with a mixture of 5 parts of polyethylene glycol, lithium chloride, and water, with the mass ratio of polyethylene glycol, lithium chloride, and water being 10:2:1. The remaining operations and steps are the same as those in Example 1.

[0069] Comparative Example 6

[0070] Select a PES membrane from 3M Company in the United States, with the model being Micro series - 022.

[0071] In one embodiment of the present invention, the thickness of the microporous membrane at multiple positions is manually measured by a thickness gauge, and the thickness ranges of the microporous membranes prepared in Examples 1 - 3 and Comparative Examples 1 - 6 are recorded.

[0072] In one embodiment of the present invention, for the bubble point test of the microporous membrane, the microporous membrane is cut into a 40 - mm round piece and pure water is used as the wetting agent. According to "GB / T32361 - 2015 Test Method for Separation Membrane Pore Size - Bubble Point and Average Flow Method", the bubble point pressure of the microporous membranes in Examples 1 - 3 and Comparative Examples 1 - 6 is detected.

[0073] In one embodiment of the present invention, for the pure water flux test of the microporous membrane, the membrane sheet is cut into a round piece with a diameter of 47 mm. The round piece is placed under a flux test device at 25°C and a pressure of 10 psi. The effective filtration diameter of the membrane sheet is 42 mm. The time required for 100 mL of water to pass through the filter membrane is measured, and then the water flux of the filter membrane is calculated through the following calculation formula:

[0074]

[0075] Where J is the pure water flux, with the unit mL / min / cm 2 ; V is the volume of the permeated water, with the unit mL; A is the effective filtration area of the membrane, with the unit cm 2 ; t is the time required for filtering water, with the unit min.

[0076] In one embodiment of the present invention, for the fouling capacity test, according to the usage of the culture medium (tryptic soy broth liquid medium), 1000 mL of pure water is added to every 30 g of the culture medium to prepare the solution required for the test. The membrane sheet is cut into a round piece with a diameter of 47 mm (the effective filtration diameter is 42 mm). After being wetted with water, it is loaded into the membrane filter. The solution is added to the pressure vessel and connected to the membrane filter through the inlet valve. The inlet valve is opened to start the test, and the pressure of the liquid entering the membrane filter is controlled at 0.1 MPa. The test ends when the filtrate starts to drip in droplets, and the value shown on the balance at this time is recorded as the fouling capacity of the membrane sheet.

[0077] Table 1. Performance of the asymmetric hourglass - shaped polysulfone - based microporous membrane and lithium - ion battery in Examples 1 - 3 and Comparative Examples 1 - 6

[0078]

[0079] See also Figures 1 to 3 As shown, the cross-section, cortex plane and support layer plane of the microporous membrane obtained in Example 1 are respectively scanning electron microscope (SEM) images. It can be seen from the figure that the cross-section of the microporous membrane presents a highly asymmetric three-layer structure, the upper layer is the cortex, and the pore size of the cortex is smaller than the pore size of the support layer, and larger than the pore size of the separation layer, that is, the cortex is a mesoporous layer, which can provide protection for the intermediate separation layer without affecting the flux. The middle layer is a separation layer, which plays a role in interception and can ensure the interception accuracy. The lower layer is a support layer, and the pore size is the largest among the three layers, and there is enough space to achieve high flux and high pollution holding capacity.

[0080] See also Figures 4 to 5 As shown in the figure, the cross-sections of the microporous membranes obtained in Example 2 and Example 3 are respectively shown. It can be seen from the figure that by using different strong polar non-solvents, a highly asymmetric three-layer structure can be obtained, and the upper cortex layer is of medium pore diameter, the middle separation layer is of small pore diameter, and the bottom support layer is of large pore diameter, which can achieve a microporous membrane with high flux, high retention and high dirt holding capacity. And as the content of the strong polar non-solvent increases, the pore diameter of the cortex decreases, the pore diameter of the support layer increases, and the thickness of the separation layer decreases. Therefore, by controlling the content of the strong polar non-solvent, the pore diameter and thickness of each layer can be adjusted to meet the use requirements of different environments.

[0081] See also Figures 6 to 11 The cross sections of the microporous membranes obtained in Comparative Examples 1-6 are shown. Figure 6 It can be seen that the skin layer of the microporous membrane obtained in Comparative Example 1 has a larger pore size, while the pore sizes of the lower separation layer and the support layer are smaller than the pore size of the upper skin layer. This is because the steam-induced phase conversion time is too long, resulting in a larger pore size of the formed skin layer. Figure 7 It can be seen that the skin layer of the microporous membrane obtained in Comparative Example 2 has a larger pore size, while the pore sizes of the lower separation layer and the support layer are smaller than the pore size of the upper skin layer. This is because the water bath curing temperature is too high and the exchange rate of the solvent and non-solvent is fast, resulting in smaller pore sizes of the separation layer and the support layer. Figure 8 It can be seen that the skin layer of the microporous membrane obtained in Comparative Example 3 becomes thicker, the skin layer cavity becomes larger, the support layer shrinks and the pore size becomes smaller. This is because the liquid membrane is heated, which causes the support layer to shrink and the pore size to become smaller, and the liquid membrane is affected by the heating, and the steam-induced temperature increases, resulting in the skin layer becoming thicker and the skin layer cavity becoming larger. Figure 9 It can be seen that the microporous membrane obtained in Comparative Example 4 has a symmetrical structure as a whole, with thick upper and lower skin layers and support layers, a larger internal cavity, and significantly thicker fibers, indicating that the content of the highly polar non-solvent needs to be controlled. If the content is too high, it will affect the structure of the microporous membrane. Figure 10It can be seen that the porosity of the upper epidermal layer of the microporous membrane obtained in Comparative Example 5 is very low, and a honeycomb structure appears in the upper layer, and finger-like large cavities appear in the lower support layer, indicating that selecting other substances to replace the strongly polar non-solvent cannot achieve the purpose of obtaining the highly asymmetric three-layer structure of the present application. From Figure 11 It can be seen that the asymmetry of the PES membrane in Comparative Example 6 is relatively low, which results in its flux and fouling resistance being lower than those of the examples of the present invention.

[0082] Referring to Table 1, by comparing Examples 1-3 and Comparative Examples 1-6, it can be seen that the comprehensive performance of the microporous membranes prepared in the examples is better. Combining Figures 1 to 10 It can be seen that the pore size and structure of the microporous membrane obtained by using the preparation process and conditions of the present invention are completely different from those of the microporous membrane obtained by the present invention. And in the case where there is a large gap in the pore size between the comparative examples and the products of a certain competitor, the fouling capacity of the microporous membrane of the present invention is equivalent to or better than that of the comparative examples and the commercially available products, the bubble point is equivalent, and the pure water flux is generally high. That is, the performance of the microporous membrane of the present invention has been greatly improved.

[0083] In summary, the present invention provides an asymmetric hourglass-shaped polysulfone microporous membrane and a preparation method thereof. By appropriate raw material ratios, suitable film-forming temperatures, simple induction methods such as steam induction temperature and time, etc., a polysulfone microporous membrane with a highly asymmetric hourglass-shaped structure is successfully prepared. This structure enables the microporous membrane to have excellent rejection performance and extremely high fouling capacity while maintaining high flux. And by regulating the phase separation rate through the steam-induced phase inversion method, a multi-layer structure is formed in one step, without the need for a multi-stage treatment bath, and the coagulation bath is only water. The process is simple and feasible, very easy to industrialize, avoids the consumption of organic solvents, is environmentally friendly and reduces costs. It can control the quality of the formed liquid film and obtain a high-quality asymmetric hourglass-shaped polysulfone microporous membrane. The microporous membrane has the characteristics of embedded protection of the separation layer, high flux, high rejection rate and anti-fouling, and the microporous membrane has been improved in terms of pore size distribution, porosity, mechanical strength, etc. Especially in specific separation fields, it shows higher separation efficiency and longer service life, and obtains a high-performance microporous membrane. The obtained microporous membrane can be widely applied to many fields such as industry, biology, medicine and water treatment, meeting the requirements of different industrial processes for the performance of membrane materials.

[0084] The above description is only for the preferred embodiments of the present application and the explanation of the applied technical principles. Those skilled in the art should understand that the scope of the invention involved in the present application is not limited to the technical solutions formed by the specific combination of the above technical features. At the same time, it should also cover other technical solutions formed by any combination of the above technical features or their equivalent features without departing from the inventive concept, such as the technical solutions formed by mutually replacing the above features with the (but not limited to) technical features with similar functions disclosed in the present application.

[0085] Except for the technical features described in the specification, the remaining technical features are well-known to those skilled in the art. To highlight the innovative features of the present invention, the remaining technical features will not be elaborated herein.

Claims

1. A method for preparing an asymmetric hourglass-shaped polysulfone microporous membrane, characterized in that: At least the following steps are included: At a first temperature, adding a polysulfone resin into a solvent and stirring to dissolve the polysulfone resin to obtain a polymer solution; adding a porogen and a strong polar non-solvent to the polymer solution, continuously stirring until the solution is uniform, and performing defoaming to obtain a casting solution at a second temperature; Applying the casting liquid on the pretreated substrate to form a liquid film; performing a phase transformation of the liquid film at a third temperature and a preset humidity for a first time; Transferring the phase-inverted liquid film to a coagulation liquid for coagulation for a second time to obtain an intermediate film; as well as The intermediate membrane is washed and dried to obtain a microporous membrane.

2. The method for preparing the asymmetric hourglass-shaped polysulfone microporous membrane according to claim 1, characterized in that: The highly polar non-solvent includes at least one of water, n-butanol, ethanol, ethylene glycol, n-propanol, glycerol or formamide.

3. The method for preparing the asymmetric hourglass-shaped polysulfone microporous membrane according to claim 1, characterized in that: The polysulfone resin includes at least one of polysulfone, polyphenylene sulfone or polyether sulfone; and / or, the solvent comprises at least one of N-methylpyrrolidone, dimethylacetamide or dimethylformamide; And / or, the porogen includes at least one of polyvinyl pyrrolidone K30, polyethylene glycol 400 or polyethylene glycol 800.

4. The method for preparing an asymmetric hourglass-shaped polysulfone microporous membrane according to claim 1, characterized in that: The first temperature is 70°C to 90°C, and the second temperature is 20°C to 30°C.

5. The method for preparing an asymmetric hourglass-shaped polysulfone microporous membrane according to claim 1, characterized in that: The casting solution comprises 48 to 65 parts of the solvent, 12 to 18 parts of the polysulfone resin, 12 to 18 parts of the porogen and 3 to 10 parts of the highly polar non-solvent.

6. The method for preparing an asymmetric hourglass-shaped polysulfone microporous membrane according to claim 1, characterized in that: The third temperature is 35° C. to 45° C., the preset humidity is 50RH% to 80RH%, and the first time is 10s to 40s.

7. The method for preparing an asymmetric hourglass-shaped polysulfone microporous membrane according to claim 1, characterized in that: The coagulation liquid is water, and the temperature of the coagulation liquid is 25°C to 40°C; And / or, the second time is 30s to 60s; And / or, the pretreatment of the substrate includes washing and drying, and the temperature of the substrate is 20°C to 30°C.

8. The method for preparing an asymmetric hourglass-shaped polysulfone microporous membrane according to claim 1, characterized in that: The viscosity of the casting solution is 2000mPa·s to 3000mPa·s.

9. An asymmetric hourglass-shaped polysulfone microporous membrane, characterized in that: The microporous membrane is obtained by the preparation method according to any one of claims 1 to 8, wherein the microporous membrane comprises a skin layer, a separation layer and a support layer from the top layer to the bottom layer, the pore size of the skin layer is larger than the pore size of the separation layer, and the pore size of the skin layer is smaller than the pore size of the support layer.

10. The asymmetric hourglass-shaped polysulfone microporous membrane according to claim 9, characterized in that: The thickness ratio of the skin layer, the separation layer and the support layer is 1-2:1-2:7-8.

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