A polyvinylidene fluoride microporous filter membrane and a method for preparing the same

Abstract

The application belongs to the technical field of microporous filter membranes, and provides a polyvinylidene fluoride microporous filter membrane and a preparation method thereof, the method comprising the following steps: dissolving polyvinylidene fluoride in a solvent and adding an additive at a first temperature, mixing to obtain a feed liquid, and cooling the feed liquid to a second temperature to obtain a casting solution; preparing the casting solution to form a liquid membrane; after steam-induced phase separation of the liquid membrane, immersing the liquid membrane in a coagulation bath to coagulate and form a polyvinylidene fluoride microporous filter membrane. The application can prepare a polyvinylidene fluoride (PVDF) microporous filter membrane with excellent performance by using a simple low-temperature and low-humidity non-solvent steam-induced phase separation method without a complex process.

Description

Technical Field

[0001] This application relates to the field of microporous filter membrane technology, and in particular to a polyvinylidene fluoride microporous filter membrane and its preparation method. Background Technology

[0002] Polyvinylidene fluoride (PVDF) is one of the most commonly used polymers for membrane manufacturing due to its excellent chemical, thermal, and mechanical stability. PVDF membranes can be widely used in wastewater treatment, food processing, and healthcare applications, including microfiltration (MF), ultrafiltration (UF), and membrane bioreactors (MBR). Because of its strong hydrophobicity and electrostatic adsorption properties, PVDF membranes exhibit a strong non-specific adsorption capacity for proteins, making them promising for applications in the biomedical field. Currently, PVDF membranes are being used in laboratory Western blotting (protein immunoblotting). Furthermore, due to their excellent physical strength and solvent resistance, PVDF membranes offer significant advantages over other transfer materials.

[0003] Furthermore, PVDF is readily soluble in common organic solvents such as N,N-dimethylacetamide (DMAc), N,N-dimethylformamide (DMF), and N,N-dimethyl sulfoxide (DMSO). Therefore, those skilled in the art can produce porous PVDF membranes using a simple phase inversion method.

[0004] Currently, commonly used methods for preparing PVDF microporous membranes include non-solvent-induced phase separation (NIPS) and non-solvent vapor-induced phase separation (VIPS). For example, Chinese patent application CN112495197A discloses a polyvinylidene fluoride (PVDF) filter membrane and its preparation method and applications, which uses the VIPS method to prepare PVDF microporous membranes. European patent EP0037836 discloses a polyvinylidene fluoride hollow fiber microfiltration membrane and its manufacturing method, which uses an immersion gel bath for phase precipitation to form an asymmetric membrane structure. Chinese patent application CN 114849489A discloses a method for preparing a hydrophilic polyvinylidene fluoride microfiltration membrane, which involves pre-evaporating a liquid membrane under constant temperature and humidity conditions, followed by immersion in a coagulation bath for phase separation precipitation to prepare a PVDF microfiltration membrane.

[0005] Furthermore, the use of membranes as carriers for Western blotting experiments has been reported before. For example, Chinese patent CN1851462B discloses a method for preparing cellulose adsorption and transfer membranes, which produces nitrocellulose membranes for protein adsorption. However, the adsorption capacity is low, the protein binding strength is low, and the cellulose membrane has poor strength and is easily broken.

[0006] PVDF membranes are ideal for immunoblotting due to their high strength, strong protein binding, and large adsorption capacity. For example, patent CN101850217B discloses a method for preparing a skinless, uniform PVDF transfer membrane. However, this membrane has a large pore size, which cannot retain small amounts of protein, and the protein transfer bands are relatively blurry.

[0007] Therefore, how to prepare PVDF membranes with stable performance and effective application in protein transfer using a simple process has become a research focus in this field. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the present invention provides a polyvinylidene fluoride microporous filter membrane and its preparation method, so as to solve the problems of complex PVDF membrane preparation process, difficulty in industrialization, and poor protein transfer effect of the prepared PVDF membrane in the prior art.

[0009] To achieve the above and related objectives, the present invention employs the following technical means:

[0010] The first aspect of this invention provides a method for preparing a polyvinylidene fluoride microporous filter membrane, comprising the following steps:

[0011] (1) At the first temperature, polyvinylidene fluoride is dissolved in a solvent and additives are added and mixed to obtain a liquid. The liquid is then cooled to the second temperature to obtain a casting solution.

[0012] (2) Prepare a liquid film from the casting solution;

[0013] (3) After the liquid membrane is subjected to steam-induced phase separation, it is immersed in a coagulation bath to solidify and form a polyvinylidene fluoride microporous filter membrane.

[0014] In one embodiment of this application, in step (1), the first temperature is 40-80°C;

[0015] And / or, the second temperature is 30–60°C.

[0016] In one embodiment of this application, the mass fraction of polyvinylidene fluoride in the liquid in step (1) is 10-30 wt%.

[0017] And / or, the solvent mass fraction is 50–80 wt%;

[0018] And / or, the mass fraction of the additive is 0–20 wt%.

[0019] In one embodiment of this application, the solvent in step (1) includes one or more of N,N-dimethylacetamide, N,N-methylformamide, N-methyl-2-pyrrolidone, triethyl phosphate, and 2-pyrrolidone.

[0020] In one embodiment of this application, the additive in step (1) includes one or more of methanol, ethanol, glycerol, isopropanol, n-butanol, diethylene glycol, triethylene glycol, tetraethylene glycol, ethylene glycol methyl ether, ethylene glycol dimethyl ether, and water.

[0021] In one embodiment of this application, step (3) includes: placing the liquid membrane in a low-temperature and low-humidity environment for vapor-induced phase separation, wherein the temperature of the low-temperature and low-humidity environment is 10-30°C and the relative humidity is 40-80%RH.

[0022] In one embodiment of this application, the steam induction time in step (3) is 120 to 600 s.

[0023] In one embodiment of this application, the second temperature is further preferably 30-50°C.

[0024] In one embodiment of this application, step (3) includes: immersing in a coagulation bath to solidify and form a membrane, washing, drying, and obtaining a polyvinylidene fluoride microporous filter membrane.

[0025] A second aspect of the present invention is a polyvinylidene fluoride microporous filter membrane prepared according to the above preparation method.

[0026] The beneficial technical effects of this invention are as follows:

[0027] This invention requires no complex processes; a simple low-temperature, low-humidity, solvent-free vapor-induced phase separation method can be used to prepare high-performance polyvinylidene fluoride (PVDF) microporous filter membranes. Specifically, this invention first lowers the feed solution temperature to ensure the feed solution system is in a metastable state; then, under low-temperature and low-humidity conditions, solvent-free vapor induces crystallization and phase separation in the membrane, generating spherulites and rod-shaped short fiber crystals; finally, the membrane is immersed in a coagulation bath to exchange the solvent and other components, thereby obtaining the polyvinylidene fluoride microporous filter membrane.

[0028] This invention can effectively adjust the structure and properties of the final film by adjusting the parameters of each component in the feed solution and the low-temperature, low-humidity, non-solvent vapor-induced environment.

[0029] The preparation method of this invention is simple, the film-forming process is highly controllable, and it is very easy to industrialize. The polyvinylidene fluoride microporous filter membrane prepared by this invention has excellent stiffness and support properties, as well as good protein transfer effect.

[0030] It should be understood that the above general description and the following detailed description are exemplary and explanatory only, and do not limit this application. Attached Figure Description

[0031] The accompanying drawings, incorporated in and forming part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application. It is obvious that the drawings described below are merely some embodiments of this application, and those skilled in the art can obtain other drawings based on these drawings without inventive effort. In the drawings:

[0032] Figure 1 Here is an electron microscope image of the surface of the PVDF microporous filter membrane in Example 1;

[0033] Figure 2 Here is an electron microscope image of the surface of the PVDF microporous filter membrane in Example 2;

[0034] Figure 3 Here is an electron microscope image of the surface of the PVDF microporous filter membrane in Example 3;

[0035] Figure 4 Electron micrograph of the surface of the PVDF microporous filter membrane in Comparative Example 1;

[0036] Figure 5 Electron micrograph of the surface of the 2PVDF microporous filter membrane (comparative example);

[0037] Figure 6 This is an electron microscope image of the surface of a 3PVDF microporous filter membrane, which is a comparative example. Detailed Implementation

[0038] Unless otherwise defined, all technical and / or scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should be understood that certain features of the invention (described in the context of separate embodiments for clarity) may also be provided in combination in a single embodiment. Conversely, multiple features of the invention (described in the context of a single embodiment for brevity) may also be provided separately or in any suitable combination or, where appropriate, in any other described embodiment of the invention. Certain features described in the context of various embodiments will not be considered essential features of those embodiments unless the embodiment is inoperable without those elements. The invention is further illustrated below by specific examples; however, it should be noted that the specific process conditions and results described in the embodiments of the invention are merely illustrative and should not be construed as limiting the scope of protection of the invention. All equivalent changes or modifications made in accordance with the spirit and essence of the invention should be covered within the scope of protection of the invention.

[0039] First, it should be noted that the raw materials used in the technical solution of this invention, including polyvinylidene fluoride (PVDF), N,N-dimethylacetamide (DMAC), N,N-methylformamide (DMF), N-methyl-2-pyrrolidone (NMP), triethyl phosphate (TEP), 2-pyrrolidone, methanol, ethanol, glycerol, isopropanol, n-butanol, diethylene glycol, triethylene glycol, tetraethylene glycol, ethylene glycol methyl ether, and ethylene glycol dimethyl ether, are all commercially available products.

[0040] This invention provides a method for preparing a polyvinylidene fluoride microporous filter membrane, comprising the following steps:

[0041] (1) At the first temperature, polyvinylidene fluoride is dissolved in a solvent and additives are added. The mixture is stirred and mixed evenly to obtain a liquid. The liquid is then cooled to the second temperature and kept warm to obtain a casting solution.

[0042] In this step, the first temperature is 40-80℃, preferably 50-80℃;

[0043] In this step, the second temperature is 30-60°C, preferably 30-50°C;

[0044] In this step, the mass fraction of polyvinylidene fluoride in the feed solution is 10-30 wt%, preferably 15-25 wt%.

[0045] In this step, the mass fraction of the solvent is 50-80 wt%, preferably 50-60 wt%.

[0046] In this step, the mass fraction of the additive is 0-20 wt%, preferably 10-20 wt%.

[0047] In this step, the solvent includes one or more of N,N-dimethylacetamide, N,N-methylformamide, N-methyl-2-pyrrolidone, triethyl phosphate, and 2-pyrrolidone;

[0048] In this step, the additives include one or more of methanol, ethanol, glycerol, isopropanol, n-butanol, diethylene glycol, triethylene glycol, tetraethylene glycol, ethylene glycol methyl ether, ethylene glycol dimethyl ether, and water.

[0049] (2) The casting solution is coated onto the PES release film, and the film is scraped to form a liquid film. The scraping distance is 200-500μm, preferably 200-300μm.

[0050] (3) The liquid membrane is placed in a low-temperature and low-humidity environment for vapor-induced phase separation. The temperature of the low-temperature and low-humidity environment is 10-30℃ and the relative humidity is 40-80RH.

[0051] In this step, the preferred temperature is 20–30°C;

[0052] In this step, the relative humidity is preferably 60-80% RH;

[0053] In this step, the steam induction time is 120–600 s, preferably 180–300 s.

[0054] (4) The liquid membrane after steam-induced phase separation is immersed in a coagulation bath to exchange solvent and additives, coagulate and form, clean, and dry to obtain polyvinylidene fluoride microporous filter membrane.

[0055] In this step, the coagulation bath temperature is 20–60°C, preferably 20–40°C;

[0056] In this step, the coagulation bath treatment time is 2 to 10 minutes, preferably 4 to 8 minutes;

[0057] In this step, the cleaning time is 5 to 20 minutes, preferably 10 to 20 minutes;

[0058] In this step, the drying temperature is 50–90°C, preferably 60–80°C;

[0059] In this step, the drying time is 1 to 10 minutes, preferably 2 to 8 minutes.

[0060] The present invention also provides a polyvinylidene fluoride microporous filter membrane prepared according to the above preparation method.

[0061] The present invention will be described in detail below through specific examples and embodiments. It should also be understood that the following embodiments are only for specific illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the appropriate range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below.

[0062] Example 1

[0063] (1) Dissolve 60g of polyvinylidene fluoride in 180g of N,N-dimethylacetamide and add 60g of ethylene glycol dimethyl ether. Stir at 70°C for 8 hours until the polyvinylidene fluoride is evenly dissolved to obtain the liquid.

[0064] The liquid material is cooled to 30°C and kept at that temperature to obtain the casting solution.

[0065] (2) The casting solution is coated onto the PES release film, and the film is scraped to form a liquid film with a scraping distance of 300 μm.

[0066] (3) The liquid membrane was placed in a low-temperature and low-humidity environment for vapor-induced phase separation for 180s. The temperature of the low-temperature and low-humidity environment was 25℃ and the relative humidity was 80%RH.

[0067] (4) The liquid membrane after steam-induced phase separation is immersed in a coagulation bath at 25°C. The coagulation bath is pure water. After treatment for 8 minutes, it is solidified and formed to obtain a gel membrane.

[0068] The gel membrane was washed with pure water for 10 minutes and then dried at 70°C for 8 minutes to obtain a polyvinylidene fluoride microporous filter membrane.

[0069] Example 2

[0070] (1) Dissolve 54g of polyvinylidene fluoride in 216g of N,N-dimethylacetamide, add 27g of ethylene glycol dimethyl ether and 3g of water, stir at 80℃ for 8h until the polyvinylidene fluoride is evenly dissolved to obtain the liquid.

[0071] The liquid material is cooled to 40°C and kept at that temperature to obtain the casting solution.

[0072] (2) The casting solution is coated onto the PES release film, and the film is scraped to form a liquid film with a scraping distance of 350 μm.

[0073] (3) The liquid membrane was placed in a low-temperature and low-humidity environment for vapor-induced phase separation for 240s. The temperature of the low-temperature and low-humidity environment was 20℃ and the relative humidity was 60RH.

[0074] (4) The liquid membrane after steam-induced phase separation is immersed in a coagulation bath at 30°C. The coagulation bath is pure water. After 5 minutes of treatment, it is solidified and formed to obtain a gel membrane.

[0075] The gel membrane was washed with pure water for 5 minutes and then dried at 80°C for 5 minutes to obtain a polyvinylidene fluoride microporous filter membrane.

[0076] Example 3

[0077] (1) Dissolve 60g of polyvinylidene fluoride in 180g of N,N-dimethylacetamide, add 30g of ethylene glycol dimethyl ether and 30g of diethylene glycol, stir at 70°C for 8h until the polyvinylidene fluoride is evenly dissolved to obtain the liquid.

[0078] The liquid material is cooled to 30°C and kept at that temperature to obtain the casting solution.

[0079] (2) The casting solution is coated onto the PES release film, and the film is scraped to form a liquid film with a scraping distance of 350 μm.

[0080] (3) The liquid membrane was placed in a low-temperature and low-humidity environment for vapor-induced phase separation for 240s. The temperature of the low-temperature and low-humidity environment was 20℃ and the relative humidity was 70%RH.

[0081] (4) The liquid membrane after steam-induced phase separation is immersed in a coagulation bath at 40°C. The coagulation bath is pure water. After treatment for 10 minutes, it is solidified and formed to obtain a gel membrane.

[0082] The gel membrane was washed with pure water for 10 minutes and then dried at 80°C for 10 minutes to obtain a polyvinylidene fluoride microporous filter membrane.

[0083] Comparative Example 1

[0084] The difference between this comparative example and Example 1 is as follows:

[0085] (1) Dissolve 60g of polyvinylidene fluoride in 180g of N,N-dimethylacetamide and add 60g of ethylene glycol dimethyl ether. Stir at 70°C for 8 hours until the polyvinylidene fluoride is evenly dissolved to obtain the casting solution.

[0086] Comparative Example 2

[0087] The difference between this comparative example and Example 1 is as follows:

[0088] (3) The liquid membrane was placed in a high temperature and high humidity environment (relative conditions) for vapor-induced phase separation for 180s. The temperature of the high temperature and high humidity environment was 35℃ and the relative humidity was 85RH.

[0089] Comparative Example 3

[0090] The difference between this comparative example and Example 1 is as follows:

[0091] (1) Dissolve 60g of polyvinylidene fluoride in 180g of N,N-dimethylacetamide and stir at 70℃ for 8h until the polyvinylidene fluoride is evenly dissolved to obtain the liquid.

[0092] The liquid material is cooled to 30°C and kept at that temperature to obtain the casting solution.

[0093] Performance testing

[0094] Bubble point pressure and flux: The bubble point pressure (test liquid: anhydrous ethanol) and flux (test liquid: anhydrous ethanol) of the membranes prepared in Examples 1-3 and Comparative Examples 1-3 were tested according to GB / T32361-2015 "Test Method for Pore Size of Separation Membranes: Bubble Point and Average Flow Rate Method". The test results are shown in Table 1.

[0095] Protein adsorption capacity: The protein adsorption capacity of the membranes prepared in Examples 1-3 and Comparative Examples 1-3 was determined using the following methods:

[0096] The membrane cross-section was determined by the sample fracturing in liquid nitrogen, and the surface to be observed was gold-coated in a vacuum environment using a sputtering coating instrument. After processing, the sample was scanned and imaged under an accelerating voltage of 10 kV. The dried transfer membrane was then placed in a protein solution of a certain concentration for static adsorption for 24 hours. The change in absorbance of the solution before and after adsorption was measured, and the amount of protein adsorbed by the membrane was calculated. The results are shown in Table 1.

[0097] Microstructure: The microstructure of the membranes prepared in Examples 1-3 and Comparative Examples 1-3 was observed using a scanning electron microscope, such as... Figures 1-6 As shown.

[0098] The experimental data and analysis are as follows:

[0099] Table 1 shows the properties of the membranes prepared in Examples 1-3 and Comparative Examples 1-3.

[0100]

[0101] As shown in Table 1, the bubble point pressures of the PVDF microporous filter membranes in Examples 1 to 3 of this application are all lower than those of the PVDF membranes in Comparative Examples 1 to 3. This indicates that the pore size of the PVDF microporous filter membranes in this application is relatively large, and it is not easy to form a dense structure on the film-forming surface.

[0102] The flux of the PVDF microporous filter membranes in Examples 1 to 3 of this application is greater than that of the PVDF membranes in Comparative Examples 1 to 3, which indicates that the PVDF microporous filter membranes in this application have relatively large and uniform pore sizes.

[0103] The protein adsorption capacity of the PVDF microporous membranes in Examples 1-3 of this application is greater than that of the PVDF membranes in Comparative Examples 1-3, indicating that the PVDF microporous membranes in this application can be used for protein immunoblotting and have a better protein transfer effect.

[0104] In contrast, in Comparative Example 1, no cooling and heat preservation treatment was performed on the casting solution. Due to the high temperature of the solution, liquid-liquid phase separation and film formation occurred. As a result, the final film surface was dense, the film had a high bubble point pressure, and the flux was low.

[0105] Comparative Example 2 involves non-solvent vapor induction of a liquid membrane under high temperature and high humidity (relative conditions), which accelerates membrane phase separation, causing liquid-liquid phase separation, resulting in a relatively high bubble point pressure and low flux.

[0106] No additives were added to the casting solution of Comparative Example 3, resulting in a solution containing only polyvinylidene fluoride and solvent. DMAc is a good solvent for PVDF. Therefore, the casting solution was much more stable than that of Example 1. Consequently, when induced by low temperature and low humidity non-solvent vapor, the liquid membrane could not undergo phase separation in a short time. After the liquid membrane was placed in the coagulation bath, severe liquid-liquid phase separation occurred, resulting in a dense membrane surface, relatively high bubble point pressure, and low flux.

[0107] Furthermore, such as Figure 1 As shown, in Example 1 of this application, spherulites and rod-shaped short fiber crystals are generated on the surface of the PVDF microporous filter membrane, and there is no dense skin layer, which can be used for protein transfer and the protein transfer effect is better.

[0108] like Figure 2 As shown, in Example 2 of this application, spherulites and rod-shaped short fiber crystals are generated on the surface of the PVDF microporous filter membrane, and there is no dense skin structure. It can be used for protein transfer and the protein transfer effect is better.

[0109] like Figure 3 As shown, in Example 3 of this application, spherulites and rod-shaped short fiber crystals are generated on the surface of the PVDF microporous filter membrane, and there is no dense skin structure. It can be used for protein transfer and the protein transfer effect is better.

[0110] like Figure 4 As shown, due to the high temperature of the liquid, liquid-liquid phase separation occurs, resulting in less crystallization in the final film of Comparative Example 1. At the same time, the film surface is relatively dense, making it unsuitable for protein transfer printing.

[0111] like Figure 5 As shown, high temperature and high humidity induction will accelerate the phase separation of the membrane, causing liquid-liquid phase separation. The membrane surface of Comparative Example 2 does not form a typical crystalline spherical structure and is dense, making it unsuitable for protein transfer.

[0112] like Figure 6 As shown, the casting solution in Comparative Example 3 is stable. When steam is induced, the liquid film cannot undergo phase separation in a short time. When the liquid film is placed in the coagulation bath, a violent liquid-liquid phase separation occurs, resulting in a dense film surface, which is not suitable for protein transfer.

[0113] In summary, this invention controls the process conditions such as non-solvent vapor induction temperature and time by using appropriate raw material ratios, suitable film-forming temperatures, and simple induction methods, thereby controlling the film-forming process and preparing high-performance PVDF microporous filter membranes. These membranes are stable and can be effectively applied in the field of protein transfer with good protein transfer results.

[0114] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing a polyvinylidene fluoride microporous filter membrane, characterized in that, Includes the following steps: (1) At a first temperature, polyvinylidene fluoride is dissolved in a solvent and additives are added, and the mixture is mixed to obtain a liquid. The liquid is then cooled to a second temperature to obtain a casting solution. The first temperature is 40~80℃, and the second temperature is 30~60℃. The solvent includes one or more of N,N-dimethylacetamide, N,N-methylformamide, N-methyl-2-pyrrolidone, triethyl phosphate, and 2-pyrrolidone. The additives include one or more of methanol, ethanol, glycerol, isopropanol, n-butanol, diethylene glycol, triethylene glycol, tetraethylene glycol, ethylene glycol methyl ether, ethylene glycol dimethyl ether, and water. (2) The casting solution is used to prepare a liquid film; (3) After the liquid membrane is placed in a low temperature and low humidity environment for steam-induced phase separation, it is immersed in a coagulation bath to solidify and form the polyvinylidene fluoride microporous filter membrane, which has spheroids and rod-shaped short fiber crystals on its surface and no dense skin layer; the temperature of the low temperature and low humidity environment is 10~30℃, the relative humidity is 40~80RH%, and the steam induction time is 120~600s.

2. The preparation method according to claim 1, characterized in that, In step (1), the mass fraction of polyvinylidene fluoride in the feed solution is 10~30 wt%; And / or, the solvent has a mass fraction of 50~80 wt%; And / or, the mass fraction of the additive is 0~20wt%.

3. The preparation method according to claim 1, characterized in that, The second temperature is 30~50℃.

4. The preparation method according to claim 1, characterized in that, Step (3) includes: immersing in a coagulation bath to solidify and form, washing, drying, and obtaining the polyvinylidene fluoride microporous filter membrane.

5. The polyvinylidene fluoride microporous filter membrane prepared by the preparation method according to any one of claims 1 to 4.

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