Preparation method of asymmetric polyethersulfone microfiltration membrane and microfiltration membrane

Abstract

The invention provides a preparation method of an asymmetric polyethersulfone microfiltration membrane, which comprises the following steps: dissolving polyethersulfone in a solvent, adding an additive and a pore-foaming agent, uniformly mixing to obtain a membrane casting solution, vacuumizing, scraping the membrane casting solution at high temperature, carrying out induction treatment by a low-temperature cold roller, and then conveying the membrane casting solution to a constant-temperature and constant-humidity environment for steam induction treatment to obtain the asymmetric polyethersulfone microfiltration membrane. Finally, performing water-bath curing to form a wet film; and soaking the wet membrane in an ethanol water solution, and drying to obtain the asymmetric polyethersulfone microfiltration membrane. According to the method, the temperature difference is formed through high-temperature film scraping and low-temperature cold roller induction, the relative viscosity of the film casting liquid is regulated and controlled through the temperature difference, the viscosity of the film casting liquid at the bottom of the film is increased, phase splitting is difficult, viscosity difference of the upper face and the lower face of the liquid film is caused, and the controllability of non-solvent movement is achieved by controlling the phase splitting rate of the liquid film in the steam induction stage; therefore, an integrated asymmetric microporous filter membrane structure is formed, the surface has high porosity, the pollutant holding capacity is increased, and the service life is prolonged.

Description

Technical Field

[0001] The invention relates to the technical field of microporous membranes, in particular to a preparation method of an asymmetric polyethersulfone microporous filter membrane and the microporous filter membrane. Background Art

[0002] Polyethersulfone (PES) is a polymer membrane material with excellent comprehensive performance, including excellent blood compatibility, corrosion resistance, heat resistance and other properties. Since the structure of the membrane prepared by polyethersulfone material is very sensitive to various film forming conditions during the membrane making process, it is currently difficult to obtain a high-precision PES asymmetric membrane by only using the phase inversion method of the membrane making solution, the formula of the coagulation bath, the temperature and the environmental conditions. Therefore, it is necessary to make major improvements to the existing phase inversion process.

[0003] For example, the patent application number CN1759924B discloses a multi-layer composite asymmetric ultrafiltration membrane, which is made by co-casting at least two different casting solutions by a coating machine. The layered structure formed is not integrally formed, and the adhesion between the layers is required to be high, otherwise the layers are easy to separate, affecting the filtering effect. In addition, the preparation process requires the co-configuration of multiple casting solutions, which is relatively cumbersome to operate. At the same time, the composite process is complex, resulting in high economic costs. Therefore, the market urgently needs to develop a simpler preparation process that can prepare a high-precision, integrally structured asymmetric PES membrane. Summary of the invention

[0004] In view of the above-mentioned shortcomings of the prior art, the object of the present invention is to:

[0005] In the first aspect, a method for preparing an asymmetric polyethersulfone microporous filter membrane is provided, the key of which is to prepare it according to the following steps:

[0006] S1, dissolving polyethersulfone in a solvent and adding an additive and a porogen, and mixing them uniformly to obtain a casting solution, wherein the additive comprises one of polyethylene glycol, glycolic acid and 2-pyrrolidone and a polyol, and the mass ratio of the polyethylene glycol, glycolic acid or 2-pyrrolidone to the polyol is (1-7):1;

[0007] S2. After vacuum treatment, the casting liquid is scraped at a high temperature of 50-80°C, then subjected to a low temperature cold roller induction treatment at -10-20°C, and then sent to a constant temperature and humidity environment for steam induction treatment, and finally cured in a water bath to form a wet film;

[0008] S3, the wet membrane is soaked in an ethanol aqueous solution and then dried to obtain an asymmetric polyethersulfone microporous filter membrane.

[0009] In combination with the first aspect, in one implementation, the mass ratio of the additive to the polyethersulfone is (1-4):1.

[0010] In combination with the first aspect, in one implementation, in step S2, the vacuum treatment time is 20 to 40 minutes.

[0011] In combination with the first aspect, in one implementation, in step S2, the high-temperature scraping film is in a constant temperature environment, the thickness of the scraping film is 100 to 120 um, and the traction speed of the scraping film is 1 to 4 m / s.

[0012] In combination with the first aspect, in one implementation, in step S2, the time of low-temperature cold roller induction is 5 to 30 seconds.

[0013] In combination with the first aspect, in one implementation, in step S2, the temperature of the constant temperature and humidity environment is 20° C. to 45° C., and the relative humidity is 40RH% to 90RH%.

[0014] In combination with the first aspect, in one implementation, in step S2, the steam temperature of the steam induction treatment is 20-45°C, the steam induction time is 5-60 seconds, and / or the temperature of the water bath curing is 25-45°C.

[0015] In combination with the first aspect, in one implementation, the solvent includes one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide, and the mass ratio of the solvent to the polyether sulfone is (3 to 7):1; the porogen includes polyvinyl pyrrolidone having a weight average molecular weight of 30,000-58,000 Da, and the mass ratio of the porogen to the polyether sulfone is 1:(5 to 15).

[0016] In the second aspect, a microporous filter membrane is also provided, the key of which is: it is prepared by the preparation method of the asymmetric polyethersulfone microporous filter membrane described in any implementation method of the first aspect, the microporous filter membrane includes a first porous layer, an intermediate porous layer, and a second porous layer stacked along the thickness direction, the pore size of the microporous filter membrane decreases gradually from one side to the other along the thickness direction, and the pore size of the first porous layer decreases gradually along the thickness direction; the average pore size of the first porous layer is 460~3500nm, and the average pore size of the second porous layer is 135~325nm.

[0017] In combination with the second aspect, in one implementation, the pore size of the middle porous layer decreases in a gradient along the thickness direction, and the pore size of the second porous layer decreases in a gradient along the thickness direction.

[0018] As described above, the preparation method of an asymmetric polyethersulfone microporous filter membrane and the microporous filter membrane of the present invention include at least the following beneficial effects: high-temperature scraping and low-temperature cold roller induce a temperature difference, and the relative viscosity of the casting liquid is regulated by the temperature difference, so that the viscosity of the casting liquid at the bottom of the membrane increases and phase separation is difficult, resulting in a difference in viscosity between the upper and lower surfaces of the liquid membrane, which is beneficial to the formation of an asymmetric microporous filter membrane structure and can also ensure high interception precision; and by controlling the phase separation rate of the liquid membrane in the steam induction stage, the controllability of non-solvent movement is achieved, further assisting in the formation of a gradient, integrated asymmetric microporous filter membrane structure, the surface has a high porosity, the dirt holding capacity is increased, and the service life is increased. Description of the drawings:

[0019] Figure 1 This is a cross-sectional electron microscope photograph of the asymmetric polyethersulfone microporous filter membrane of Example 1 of the present invention;

[0020] Figure 2 This is a cross-sectional electron microscope photograph of the asymmetric polyethersulfone microporous filter membrane of Example 2 of the present invention;

[0021] Figure 3 This is a cross-sectional electron microscope photograph of the asymmetric polyethersulfone microporous filter membrane of Example 3 of the present invention;

[0022] Figure 4 This is a cross-sectional electron microscope photograph of the asymmetric polyethersulfone microporous filter membrane of Example 4 of the present invention;

[0023] Figure 5 This is a cross-sectional electron microscope photograph of the asymmetric polyethersulfone microporous filter membrane of Example 5 of the present invention;

[0024] Figure 6 This is a cross-sectional electron microscope photograph of the asymmetric polyethersulfone microporous filter membrane of Example 6 of the present invention;

[0025] Figure 7 This is a cross-sectional electron microscope photograph of the asymmetric polyethersulfone microporous filter membrane of Example 7 of the present invention. DETAILED DESCRIPTION

[0026] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention, not for limiting the scope of protection of the present invention.

[0027] It should be noted that the raw materials used in the technical solution of the present invention: polyethersulfone (PES for short), polyol, polyethylene glycol, glycolic acid, 2-pyrrolidone, N,N-dimethylacetamide (DMAC for short), N,N-methylformamide (DMF for short), N-methylpyrrolidone (NMP for short), dimethyl sulfoxide, polyvinylpyrrolidone, etc. are all commercially available products.

[0028] The polyol is one of propylene glycol, triethylene glycol, diethylene glycol and ethylene glycol.

[0029] First, the technical solution of the present invention provides a method for preparing an asymmetric polyethersulfone microporous filter membrane, which is prepared according to the following steps:

[0030] S1. Dissolve polyethersulfone in a solvent and add additives and porogens, mix well to obtain a casting solution, wherein the additives include one of polyethylene glycol, glycolic acid and 2-pyrrolidone and a polyol, and the mass ratio of the polyethylene glycol, glycolic acid or 2-pyrrolidone to the polyol is (1-7):1; the two additives form a composite additive system, and the additives have different migration rates in the steam induction stage due to their different hydrophilic and hydrophobic properties, so that it is easier to obtain a microporous filter membrane with a gradient distribution of pore sizes. In addition, in order to ensure that the temperature of the casting solution can quickly reach the ideal temperature during the scraping process, the raw materials are preheated simultaneously during the mixing process.

[0031] S2. After the vacuum treatment, the casting liquid is scraped at a high temperature of 50 to 80°C, then subjected to a low temperature cold roller induction treatment at -10 to 20°C, and then sent to a constant temperature and humidity environment for steam induction treatment, and finally cured in a water bath to form a wet film. The temperature is constant during the high temperature scraping process, so that the overall temperature of the casting liquid is constant. When the casting liquid is subjected to low temperature cold roller induction by the cooling roller, the temperature of one side of the casting liquid drops rapidly, and a temperature difference is formed between the upper and lower sides of the membrane. The viscosity of the side with a low temperature increases and phase separation is difficult, resulting in different viscosities on the upper and lower sides of the membrane, which is conducive to the formation of an asymmetric PES microporous filter membrane; in addition, during the steam induction process, the above-mentioned additives are combined to control the phase separation rate during the steam induction process, achieve the controllability of non-solvent movement, and further enhance the one-piece molding of the asymmetric PES microporous filter membrane.

[0032] S3, the wet membrane is soaked in ethanol water solution and then dried to obtain an asymmetric polyethersulfone microporous filter membrane, wherein the temperature of the ethanol water solution is optimally controlled at about 30°C, the drying speed is controlled at 1.5 m / s, and the drying temperature is controlled at about 70°C.

[0033] In some embodiments, the mass ratio of the additive to the polyethersulfone is (1-4):1.

[0034] In some embodiments, in step S2, the vacuum treatment time is 20 to 40 minutes to reduce the formation of pores inside the casting solution.

[0035] In some embodiments, in step S2, the high-temperature scraping film is in a constant temperature environment, the thickness of the scraping film is 100-120 um, and the pulling speed of the scraping film is 1-4 m / s.

[0036] In some embodiments, in step S2, the low-temperature cold roller induction time is 5 to 30 seconds. The low-temperature cold roller induction time of the film is ensured in accordance with the speed of film scraping.

[0037] In some embodiments, in step S2, the temperature of the constant temperature and humidity environment is 20° C. to 45° C., and the relative humidity is 40 RH% to 90 RH%. The quality of the film forming environment is guaranteed.

[0038] In some embodiments, in step S2, the steam temperature of the steam induction treatment is 20-45°C, the steam induction time is 5-60 seconds, and / or the temperature of the water bath curing is 25-45°C.

[0039] In some embodiments, the solvent includes one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide, and the mass ratio of the solvent to the polyether sulfone is (3-7):1; the porogen includes polyvinyl pyrrolidone with a weight average molecular weight of 30000-58000Da, and the mass ratio of the porogen to the polyether sulfone is 1:(5-15).

[0040] Secondly, a microporous filter membrane is also provided, which is prepared by the preparation method of the asymmetric polyethersulfone microporous filter membrane described in any of the above embodiments, and the microporous filter membrane includes a first porous layer, an intermediate porous layer, and a second porous layer stacked along the thickness direction, and the pore size of the microporous filter membrane decreases gradually from one side to the other along the thickness direction, and the pore size of the first porous layer decreases gradually along the thickness direction; the average pore size of the first porous layer is 460~3500nm, and the average pore size of the second porous layer is 135~325nm.

[0041] In some embodiments, the pore size of the middle porous layer decreases in a gradient along the thickness direction, and the pore size of the second porous layer decreases in a gradient along the thickness direction.

[0042] The present invention is described in detail below by specific examples. It should also be understood that the following examples are only used to specifically illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Some non-essential improvements and adjustments made by those skilled in the art based on the above content of the present invention belong to the scope of protection of the present invention. The specific process parameters and the like in the following examples are also only examples within a suitable range, that is, those skilled in the art can make a selection within a suitable range through the description herein, and are not limited to the specific values ​​​​exemplified below.

[0043] Example 1

[0044] The additives were prepared in a mass ratio of 1:1 between triethylene glycol and polyethylene glycol, and then 52g of N-methylpyrrolidone and 30g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, and after vacuuming for 0.5h, it was placed in an 80°C constant temperature box, and the film thickness was controlled at 110um, the traction speed was 2.5m / s, and after 20s of cold roller induction at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 40°C steam for 20s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, and the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C.

[0045] Example 2

[0046] The additives were prepared in a mass ratio of 1:1 between ethylene glycol and polyethylene glycol, and then 60g of N-methylpyrrolidone and 16g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, and after vacuuming for 0.5h, it was placed in an 80°C constant temperature box, and the film thickness was controlled between 110um, the traction speed was 2.5m / s, and after 20s of cold roller induction at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 40°C steam for 20s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, and the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C.

[0047] Example 3

[0048] The additives were prepared in a mass ratio of 1:7 between triethylene glycol and polyethylene glycol, and then 45g of N-methylpyrrolidone and 60g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 50°C and stirred for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, vacuumed for 0.5h, and placed in a 50°C constant temperature box, the film thickness was controlled at 100um, the pulling speed was 1m / s, and after 5s of cold roller induction at -10°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 20°C steam for 60s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C.

[0049] Example 4

[0050] The additives were prepared in a mass ratio of 1:5 between triethylene glycol and polyethylene glycol, and then 105g of N-methylpyrrolidone and 15g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 70°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, vacuumed for 0.5h, and then placed in a 70°C constant temperature box, and the film thickness was controlled at 120um, the traction speed was 4m / s, and after 20s of cold roller induction at 20°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 45°C steam for 30s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C.

[0051] Example 5

[0052] The additives were prepared in a mass ratio of 1:3 between triethylene glycol and polyethylene glycol, and then 52g of N-methylpyrrolidone and 30g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, vacuumed for 0.5h, and placed in an 80°C constant temperature box, the film thickness was controlled at 110um, the pulling speed was 1m / s, and after 40s of cold roller induction at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 30°C steam for 5s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C.

[0053] Example 6

[0054] The additives were prepared in a mass ratio of 1:1 between glycerol and glycolic acid, and then 52g of N, N-dimethylacetamide and 30g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, vacuumed for 0.5h, and placed in an 80°C constant temperature box, the film thickness was controlled at 110um, the traction speed was 2.5m / s, and after 20s of cold roller induction at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed at 40°C for 20s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C.

[0055] Example 7

[0056] The additives were prepared in a mass ratio of 1:1 between diethylene glycol and 2-pyrrolidone, and then 52g of dimethyl sulfoxide and 30g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, and after vacuuming for 0.5h, it was placed in an 80°C constant temperature box, and the film thickness was controlled at 110um, the traction speed was 2.5m / s, and after 20s of cold roller induction at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 40°C steam for 20s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, and the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C.

[0057] Example 8

[0058] The final products of Examples 1 to 7 were tested: 1. The electron microscope scanning images were as follows: Figures 1 to 7 2. The test results of the pure water flux, the first bubble point pressure and the pollutant holding capacity of the membrane at 0.7 MPa are shown in Table 1.

[0059] Table 1 is the test data of PES microporous membrane in Examples 1 to 7

[0060]

[0061]

[0062] Comparative Example 1

[0063] The additives were prepared in a mass ratio of triethylene glycol to polyethylene glycol of 2:1, and then 52g of N-methylpyrrolidone and 30g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, vacuumed for 0.5h, and placed in an 80°C constant temperature box, and the film thickness was controlled between 110um, the traction speed was 2.5m / s, and after 0°C cold roller induction for 20s, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 40°C steam for 20s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C. The pore size of the prepared polyethersulfone microporous filter membrane is 0.22μm, and the pure water flux of the polyethersulfone microporous filter membrane at 0.7MPa is 14ml / cm 2 ·min, the first bubble point pressure is 0.42MPa, and the dirt holding capacity is 80g.

[0064] Analysis: Comparative Example 1 is different from Example 1 in that the mass ratio of the raw materials triethylene glycol and polyethylene glycol of the additives is different, and the other steps and methods are the same. The comparative example method can form an asymmetric PES microporous filter membrane, but the pure water flux of the membrane is slightly poor and the dirt holding capacity does not meet the standard. Reason: The molecular weight of triethylene glycol is relatively small, and its proportion is relatively large, resulting in a large amount of retention in the membrane after induction, and the overall pore size is small after molding.

[0065] Comparative Example 2

[0066] The additives were prepared in a mass ratio of 1:1 between triethylene glycol and polyethylene glycol, and then 52g of N-methylpyrrolidone and 30g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, vacuumed for 0.5h, and placed in an 80°C constant temperature box, and the film thickness was controlled between 110um, the traction speed was 2.5m / s, and after 20s of cold roller induction at 30°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 40°C steam for 20s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C. The pore size of the prepared polyethersulfone microporous filter membrane is 0.22μm, and the pure water flux of the polyethersulfone microporous filter membrane at 0.7MPa is 17ml / cm 2 ·min, the first bubble point pressure is 0.38MPa, and the dirt holding capacity is 110g.

[0067] Analysis: The difference between Comparative Example 2 and Example 1 is that the temperature induced by the cold roller is different, and the other steps are the same. The comparative method can form an asymmetric PES microporous filter membrane, and the pure water flux of the membrane is barely qualified, but the membrane's dirt holding capacity does not meet the standard. Reason: The temperature of the cold roller is relatively high, and a large viscosity difference cannot be formed on both sides of the liquid membrane, resulting in a smaller pore size at the bottom and poor performance.

[0068] Comparative Example 3

[0069] The additives were prepared in a mass ratio of 1:1 between triethylene glycol and polyethylene glycol, and then 52g of N-methylpyrrolidone and 30g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, and after vacuuming for 0.5h, it was placed in an 80°C constant temperature box, and the film thickness was controlled between 110um, the traction speed was 2.5m / s, and after 20s of cold roller induction at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 40°C steam for 90s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, and the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C. After testing, the pore size of the prepared polyethersulfone microporous filter membrane is 0.22μm, and the pure water flux of the polyethersulfone microporous filter membrane at 0.7MPa is 11ml / cm 2 ·min, the first bubble point pressure is 0.52MPa, and the dirt holding capacity is 45g.

[0070] Analysis: The difference between Comparative Example 3 and Example 1 is that the steam induction time is different, and the other steps are the same. The comparative method can form an asymmetric PES microporous filter membrane, but the pure water flux of the membrane is too low, and the pollutant holding capacity is far from meeting the standard. Reason: The steam induction time is too long, resulting in a large amount of non-solvent migration, thus forming a symmetrical structure.

[0071] Comparative Example 4

[0072] The additives were prepared in a mass ratio of 1:1 between triethylene glycol and polyethylene glycol, and then 52g of N-methylpyrrolidone and 30g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, and after vacuuming for 0.5h, it was placed in an 80°C constant temperature box, and the film thickness was controlled between 110um, the traction speed was 2.5m / s, and after 20s of cold roller induction at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 50°C steam for 20s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, and the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C. After testing, the pore size of the prepared polyethersulfone microporous filter membrane is 0.22μm, and the pure water flux of the polyethersulfone microporous filter membrane at 0.7MPa is 16ml / cm 2 ·min, the first bubble point pressure is 0.48MPa, and the pollution holding capacity is 105g.

[0073] Analysis: The difference between Comparative Example 4 and Example 1 is that the steam temperature during steam induction is different, and the other steps are the same. This comparative method can form an asymmetric PES microporous filter membrane, but the pure water flux and the dirt holding capacity do not meet the standards. Reason: The induction temperature is too high, which leads to an accelerated non-solvent migration speed, thereby forming a symmetrical structure.

[0074] Comparative Example 5

[0075] The additives were prepared in a mass ratio of 1:1 between triethylene glycol and polyacrylate, and then 52g of N-methylpyrrolidone and 30g of additives were weighed in a stirring kettle, and then 15g of polyethersulfone and 3g of polyvinylpyrrolidone were added to the stirring kettle, and the casting solution was kept at 80°C for 6h. After the casting solution was completely stirred, it was poured into a pressure vessel, and after vacuuming for 0.5h, it was placed in an 80°C constant temperature box, and the film thickness was controlled between 110um, the traction speed was 2.5m / s, and after 20s of cold roller induction at 0°C, the humidity in the constant temperature and humidity box was adjusted to 80%, and steam induction was performed with 40°C steam for 20s, and the film was cured in a 30°C water bath; the prepared wet film was immersed in an aqueous solution containing 25% ethanol, and the solution temperature was controlled at 30°C, the drying speed was 1.5m / s, and the roller temperature was dried at 70°C. After testing, the pore size of the prepared polyethersulfone microporous filter membrane is 0.22μm, and the pure water flux of the polyethersulfone microporous filter membrane at 0.7MPa is 8ml / cm 2 ·min, the first bubble point pressure is 0.58MPa, and the pollution holding capacity is 17g.

[0076] Analysis: Compared with Example 1, Comparative Example 5 differs in the additive raw materials, and the other steps are the same. The comparative method can form an asymmetric PES microporous filter membrane, but the pure water flux and the pollutant holding capacity do not meet the standards. Reason: The liquid membrane phase separation speed is slow in the induction stage, and the surface open porosity is low, resulting in low flow rate and high bubble point.

[0077] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the technology may modify or change the above embodiments without violating the spirit and scope of the present invention. Therefore, all equivalent modifications or changes made by a person of ordinary skill in the art without departing from the spirit and technical ideas disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing an asymmetric polyethersulfone microporous filter membrane, characterized in that Prepare as follows: S1, dissolving polyethersulfone in a solvent and adding an additive and a porogen, and mixing them uniformly to obtain a casting solution, wherein the additive comprises one of polyethylene glycol, glycolic acid and 2-pyrrolidone and a polyol, and the mass ratio of the polyethylene glycol, glycolic acid or 2-pyrrolidone to the polyol is (1-7):1; S2. After vacuum treatment, the casting liquid is scraped at a high temperature of 50-80°C, then subjected to a low temperature cold roller induction treatment at -10-20°C, and then sent to a constant temperature and humidity environment for steam induction treatment, and finally cured in a water bath to form a wet film; S3, the wet membrane is soaked in an ethanol aqueous solution and then dried to obtain an asymmetric polyethersulfone microporous filter membrane.

2. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1, characterized in that: The mass ratio of the additive to the polyethersulfone is (1-4):

1.

3. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1 or 2, characterized in that: In the step S2, the vacuum treatment time is 20 to 40 minutes.

4. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1 or 2, characterized in that: In the step S2, the high temperature scraping film is in a constant temperature environment, the thickness of the scraping film is 100-120 um, and the pulling speed of the scraping film is 1-4 m / s.

5. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1 or 2, characterized in that: In the step S2, the low temperature cold roller induction time is 5 to 30 seconds.

6. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1 or 2, characterized in that: In step S2, the temperature of the constant temperature and humidity environment is 20°C to 45°C, and the relative humidity is 40RH% to 90RH%.

7. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1 or 2, characterized in that: In the step S2, the steam temperature of the steam induction treatment is 20-45°C, the steam induction time is 5-60 seconds, and / or the temperature of the water bath curing is 25-45°C.

8. The method for preparing the asymmetric polyethersulfone microporous filter membrane according to claim 1 or 2, characterized in that: The solvent includes one of N-methylpyrrolidone, N,N-dimethylformamide, N,N-dimethylacetamide and dimethyl sulfoxide, and the mass ratio of the solvent to the polyether sulfone is (3-7):1; the porogen includes polyvinylpyrrolidone with a weight average molecular weight of 30000-58000Da, and the mass ratio of the porogen to the polyether sulfone is 1:(5-15).

9. A microporous filter membrane, characterized in that: The asymmetric polyethersulfone microporous filter membrane is prepared by the preparation method of any one of claims 1 to 8, wherein the microporous filter membrane comprises a first porous layer, an intermediate porous layer, and a second porous layer stacked along the thickness direction, the pore size of the microporous filter membrane decreases gradually from one side to the other along the thickness direction, and the pore size of the first porous layer decreases gradually along the thickness direction; the average pore size of the first porous layer is 460 to 3500 nm, and the average pore size of the second porous layer is 135 to 325 nm.

10. The microporous filter membrane according to claim 9, characterized in that: The pore size of the middle porous layer decreases in a gradient along the thickness direction, and the pore size of the second porous layer decreases in a gradient along the thickness direction.

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