A polyvinylidene fluoride film and a method for producing the same

Abstract

The application belongs to the technical field of structural materials, and particularly relates to a polyvinylidene fluoride film and a preparation method thereof, the preparation method comprising S1. adding polyvinylidene fluoride, a pore former and a surfactant into a mixed solvent, stirring to obtain a casting solution, the mixed solvent comprising a first solvent and a second solvent, the first solvent comprising at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide, and the second solvent comprising an ester, S2. casting the casting solution obtained in step S1 onto a release film, scraping the film with a doctor blade to form a liquid film, S3. placing the liquid film in a constant-temperature and constant-humidity environment for treatment, and then placing the liquid film in a coagulation bath for coagulation to obtain a gel film, and drying the gel film after cleaning in a cleaning bath to obtain the polyvinylidene fluoride film. The application can significantly improve the flux of the prepared polyvinylidene fluoride film by selecting a mixed solvent composed of specific types.

Description

Technical Field

[0001] This invention belongs to the field of structural materials technology, specifically relating to a polyvinylidene fluoride membrane and its preparation method. Background Technology

[0002] Polyvinylidene fluoride (PVDF) is a highly non-reactive thermoplastic fluoropolymer, soluble in strong polar solvents such as dimethylacetamide. It possesses excellent properties such as anti-aging, chemical corrosion resistance, weather resistance, UV radiation resistance, oxidation resistance, and ease of processing, making it widely used in electronics, pigments and coatings, chemical equipment, and solar cells. Furthermore, PVDF exhibits good thermal stability and excellent chemical stability, and its microporous membranes are widely used in ultrafiltration, microfiltration, and membrane distillation. Particularly in microfiltration for sterilization, where the membrane pore size must be smaller than that of bacteria, membranes with uniform surface pore size have a greater competitive advantage.

[0003] In related technologies, non-solvent-induced phase separation (NIPS) and non-solvent vapor-induced phase separation (VIPS) methods are commonly used to prepare polyvinylidene fluoride (PVDF) microporous membranes. However, PVDF microporous membranes prepared by NIPS and VIPS methods have large pores on their surface and a very uneven pore size distribution, resulting in low flux. Summary of the Invention

[0004] In view of this, the purpose of the present invention is to provide a polyvinylidene fluoride membrane and a method for preparing the same, so as to improve the flux of the polyvinylidene fluoride membrane.

[0005] In a first aspect, the present invention provides a method for preparing a polyvinylidene fluoride (PVDF) membrane, comprising:

[0006] S1. Add polyvinylidene fluoride, a pore-forming agent, and a surfactant to a mixed solvent, stir, and obtain a casting solution. The mixed solvent includes a first solvent and a second solvent. The first solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide. The second solvent includes an ester.

[0007] S2. The casting liquid obtained in step S1 is cast onto the release film, and the film is scraped with a doctor blade to form a liquid film. The liquid film is then treated in a constant temperature and humidity environment, and then treated in a coagulation bath to obtain a gel film. The gel film is then cleaned in a cleaning bath and dried to obtain the polyvinylidene fluoride film.

[0008] Optionally, in step S1, the ester includes triethyl phosphate or butyl acetate or a combination of both.

[0009] Optionally, in step S1, the pore-forming agent includes polyvinylpyrrolidone, polyethylene glycol, or a combination of both.

[0010] Optionally, in step S1, the surfactant includes a nonionic surfactant.

[0011] Optionally, in the mixed solvent of step S1, the proportion of the first solvent is 10wt%-90wt%, preferably 15wt%-90wt%.

[0012] Optionally, in the casting solution of step S1, the content of polyvinylidene fluoride is 10wt%-15wt%, preferably 12wt%-15wt%.

[0013] Optionally, in the casting solution of step S1, the content of the surfactant is 5wt%-10wt%, preferably 8wt%-10wt%.

[0014] Optionally, in the casting solution of step S1, the content of the pore-forming agent is 5wt%-10wt%, preferably 8wt%-10wt%.

[0015] Optionally, in step S1, the weight-average molecular weight of the polyvinylpyrrolidone is 250,000-350,000.

[0016] Optionally, in step S1, the weight-average molecular weight of the polyethylene glycol is 370-460.

[0017] Optionally, in step S1, the nonionic surfactant includes a polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer.

[0018] Optionally, during the film scraping process in step S2, the distance between the scraper and the release film is 200-500 μm, preferably 250-500 μm.

[0019] Optionally, the temperature of the constant temperature and humidity environment is 25-40℃, preferably 30-40℃; the relative humidity of the constant temperature and humidity environment is 50RH%-90RH%, preferably 60RH%-90RH.

[0020] Optionally, in step S2, the liquid membrane is placed in a constant temperature and humidity environment for 30-300 seconds, preferably 60-300 seconds.

[0021] Optionally, in step S2, the temperature of the coagulation bath is 30-60℃, preferably 40-60℃.

[0022] Optionally, in step S2, the liquid membrane is placed in a coagulation bath for 1-5 minutes, preferably 2-5 minutes.

[0023] Optionally, in step S2, the temperature of the cleaning bath is 40-70℃, preferably 45-70℃.

[0024] Optionally, in step S2, the gel membrane is placed in a cleaning bath for 5-10 minutes, preferably 6-10 minutes.

[0025] Optionally, in step S2, the drying temperature is 40-70℃, preferably 50-60℃; the drying time is 1-5 min, preferably 3-4 min.

[0026] Secondly, the present invention also provides a polyvinylidene fluoride membrane prepared according to the preparation method described above.

[0027] As described above, the polyvinylidene fluoride membrane and its preparation method of the present invention have the following beneficial effects:

[0028] This invention significantly improves the flux of the prepared polyvinylidene fluoride membrane by selecting a mixed solvent of a specific type. Attached Figure Description

[0029] Figure 1 This is a scanning electron microscope image of the polyvinylidene fluoride membrane prepared in Example 1;

[0030] Figure 2 This is a pore size distribution diagram of the polyvinylidene fluoride membrane prepared in Example 1. Detailed Implementation

[0031] The present invention will be further illustrated below through specific examples. However, it should be noted that the specific material ratios, process conditions, and results described in the embodiments of the present invention are only for illustrative purposes and should not be used to limit the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention. It should be noted that, unless otherwise specified, "wt%" in the present invention refers to mass percentage.

[0032] This invention provides a method for preparing a polyvinylidene fluoride (PVDF) membrane, comprising:

[0033] S1. Add polyvinylidene fluoride, a pore-forming agent, and a surfactant to a mixed solvent, and stir to obtain a casting solution with a polyvinylidene fluoride concentration of 10wt%-15wt%, a pore-forming agent concentration of 5wt%-10wt%, and a surfactant concentration of 5wt%-10wt%. The mixed solvent includes a first solvent and a second solvent, and the proportion of the first solvent in the mixed solvent is 10wt%-90wt%.

[0034] The first solvent includes at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and dimethyl sulfoxide;

[0035] The second solvent includes an ester, which includes triethyl phosphate or butyl acetate or a combination of both.

[0036] Pore-forming agents include polyvinylpyrrolidone with a weight average molecular weight of 250,000-350,000, polyethylene glycol with a weight average molecular weight of 370-460, or a combination of the two.

[0037] Surfactants include nonionic surfactants, and nonionic surfactants include polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymers;

[0038] S2. The casting liquid obtained in step S1 is cast onto the release film, and the film is scraped with a scraper to form a liquid film. During the scraping process, the distance between the scraper and the release film is 200-500μm.

[0039] The liquid membrane is treated in a constant temperature and humidity environment of 25-40℃ and 50%-90%RH% for 30-300 seconds. Then, the liquid membrane is treated in a coagulation bath of 30-60℃ for 1-5 minutes to obtain a gel membrane. The gel membrane is then cleaned in a cleaning bath of 40-70℃ for 5-10 minutes, and then dried at 40-70℃ for 1-5 minutes to obtain a polyvinylidene fluoride membrane.

[0040] The present invention will be described in detail below through specific examples. It should also be understood that the following examples are only for specific illustration of the present invention and should not be construed as limiting the scope of protection of the present invention. Non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are all within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are only 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. It should be understood that the following examples only list the specific case of N,N-dimethylacetamide as the first solvent and triethyl phosphate as the second solvent. Those skilled in the art may also select N,N-dimethylformamide, N-methylpyrrolidone, or dimethyl sulfoxide, or a mixture of at least two of these as the first solvent, or a mixture of N,N-dimethylacetamide with at least one of N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide as the first solvent, and butyl acetate or a combination of butyl acetate and triethyl phosphate as the second solvent.

[0041] Example 1

[0042] A polyvinylidene fluoride membrane is prepared according to the following steps:

[0043] S1. Add 75g of polyvinylidene fluoride (PVDF, weight average molecular weight 1,458,000, the same below), 50g of pore-forming agent polyvinylpyrrolidone (PVP, weight average molecular weight 300,000, the same below), and 25g of surfactant polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer (weight average molecular weight 2,900, the same below) to 350g of mixed solvent. Stir at 80℃ for 8h, and then let stand at 80℃ for 2h to obtain casting solution. The mixed solvent is composed of the first solvent N,N-dimethylacetamide (DMAc) and the second solvent triethyl phosphate (TEP) in a mass percentage of 50wt%:50wt%.

[0044] S2. The casting liquid obtained in step S1 is cast onto the release film (the stretching speed of the release film is 2m / min), and the film is scraped with a doctor blade to form a liquid film. During the scraping process, the distance between the doctor blade and the release film is 300μm.

[0045] The liquid membrane was treated in a constant temperature and humidity environment of 35℃ and 80% RH for 90s. Then, the liquid membrane was treated in pure water coagulation bath at 45℃ for 5min to obtain a gel membrane. The gel membrane was then washed in pure water cleaning bath at 60℃ for 10min. Then, it was washed at room temperature with a mixed ethanol / water solution (ethanol to water mass ratio of 2:8), followed by washing with pure water for 5min. Finally, it was dried at 60℃ for 3min to obtain a polyvinylidene fluoride membrane.

[0046] Example 2

[0047] A polyvinylidene fluoride membrane is prepared according to the following steps:

[0048] S1. Add 50g of polyvinylidene fluoride (PVDF), 25g of pore-forming agent polyvinylpyrrolidone (PVP), and 50g of surfactant polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer to 350g of mixed solvent, stir at 80℃ for 8h, and then let stand at 80℃ for 2h to obtain casting solution. The mixed solvent is composed of the first solvent N,N-dimethylacetamide (DMAc) and the second solvent triethyl phosphate (TEP) in a mass percentage ratio of 10wt%:90%.

[0049] S2. The casting liquid obtained in step S1 is cast onto the release film (the stretching speed of the release film is 2m / min), and the film is scraped with a doctor blade to form a liquid film. During the scraping process, the distance between the doctor blade and the release film is 300μm.

[0050] The liquid membrane was treated in a constant temperature and humidity environment of 35℃ and 80% RH for 180s. Then, the liquid membrane was treated in pure water in a coagulation bath at 45℃ for 5min to obtain a gel membrane. The gel membrane was then washed in pure water in a cleaning bath at 60℃ for 10min. Then, it was washed at room temperature with an ethanol / water mixed solution (ethanol to water mass ratio of 2:8), followed by washing with pure water for 5min. Finally, it was dried at 50℃ for 3min to obtain a polyvinylidene fluoride membrane.

[0051] Example 3

[0052] A polyvinylidene fluoride membrane is prepared according to the following steps:

[0053] S1. Add 75g of polyvinylidene fluoride (PVDF), 25g of pore-forming agent polyvinylpyrrolidone (PVP), and 50g of surfactant polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer to 350g of mixed solvent, stir at 80℃ for 8h, and then let stand at 80℃ for 2h to obtain casting solution. The mixed solvent is composed of the first solvent N,N-dimethylacetamide (DMAc) and the second solvent triethyl phosphate (TEP) in a mass percentage of 35wt%:65wt%.

[0054] S2. The casting liquid obtained in step S1 is cast onto the release film (the stretching speed of the release film is 2m / min), and the film is scraped with a doctor blade to form a liquid film. The distance between the doctor blade and the release film is 300μm.

[0055] The liquid membrane was treated in a constant temperature and humidity environment of 35℃ and 90% RH for 60s. Then, the liquid membrane was treated in pure water coagulation bath at 40℃ for 5min to obtain a gel membrane. The gel membrane was then washed in pure water cleaning bath at 60℃ for 10min. Then, it was washed at room temperature with a mixed ethanol / water solution (ethanol to water mass ratio of 2:8), followed by washing with pure water for 5min. Finally, it was dried at 60℃ for 4min to obtain a polyvinylidene fluoride membrane.

[0056] Example 4

[0057] A polyvinylidene fluoride membrane is prepared according to the following steps:

[0058] S1. Add 75g of polyvinylidene fluoride (PVDF), 50g of pore-forming agent polyvinylpyrrolidone (PVP), and 25g of surfactant polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer to 350g of mixed solvent, stir at 80℃ for 8h, and then let stand at 80℃ for 2h to obtain casting solution. The mixed solvent is composed of the first solvent N,N-dimethylacetamide (DMAc) and the second solvent triethyl phosphate (TEP) in a mass percentage of 50wt%:50wt%.

[0059] S2. The casting liquid obtained in step S1 is cast onto the release film (the stretching speed of the release film is 0.5 m / min), and the film is scraped with a doctor blade to form a liquid film. During the scraping process, the distance between the doctor blade and the release film is 500 μm.

[0060] The liquid membrane was treated in a constant temperature and humidity environment of 35℃ and 80% RH for 300s. Then, the liquid membrane was treated in pure water in a coagulation bath at 40℃ for 5min to obtain a gel membrane. The gel membrane was then washed in pure water in a cleaning bath at 60℃ for 10min. Then, it was washed at room temperature with an ethanol / water mixed solution (ethanol to water mass ratio of 2:8), followed by washing with pure water for 5min. Finally, it was dried at 60℃ for 3min to obtain a polyvinylidene fluoride membrane.

[0061] Comparative Example 1

[0062] Except for the following conditions, the polyvinylidene fluoride membrane was prepared in the same manner as in Example 1:

[0063] S1. Add 75g of polyvinylidene fluoride (PVDF), pore-forming agent polyvinylpyrrolidone (PVP), and surfactant polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer to 350g of solvent N,N-dimethylacetamide (DMAc). Stir at 80°C for 8 hours, and then let stand at 80°C for 2 hours to obtain casting solution.

[0064] Comparative Example 2

[0065] Except for the following conditions, the polyvinylidene fluoride membrane was prepared in the same manner as in Example 1:

[0066] S1. Add 75g of polyvinylidene fluoride (PVDF), pore-forming agent polyvinylpyrrolidone (PVP), and surfactant polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer to 350g of solvent N-methylpyrrolidone (NMP), stir at 80°C for 8h, and then let stand at 80°C for 2h to obtain casting solution.

[0067] Comparative Example 3

[0068] The difference between this comparative example and the previous example is that the second solvent used is N-methylpyrrolidone (NMP).

[0069] Performance testing

[0070] The polyvinylidene fluoride membrane prepared in Example 1 was scanned by electron microscopy, and the results are as follows: Figure 1 As shown;

[0071] The pore size distribution of the membrane prepared in Example 1 was tested according to GB / T32361-2015 "Separation Membrane Pore Size Test Method - Bubble Point and Average Flow Rate Method". The results are as follows: Figure 2 As shown;

[0072] The bubble point (liquid is ethanol) and flux (liquid is ethanol) of the membranes prepared in Examples 1-4 and Comparative Examples 1-3 were tested according to GB / T32361-2015 Separation Membrane Pore Size Test Method Bubble Point and Average Flow Rate Method. The results are shown in Table 1.

[0073] Depend on Figure 1 It can be seen that the polyvinylidene fluoride membrane prepared in Example 1 has a number of pores with uniform pore size distributed on its surface.

[0074] Depend on Figure 2 It can be seen that the pore size distribution of the polyvinylidene fluoride film surface prepared in Example 1 is uniform, and the proportion of pores with a pore size of about 250 nm is 80%.

[0075] Table 1 Test Results

[0076]

[0077] As shown in Table 1, compared with Comparative Examples 1-3, the flux of the polyvinylidene fluoride membrane prepared in Example 1 was significantly improved. This result indicates that a mixed solvent of a specific type can significantly improve the flux of the prepared polyvinylidene fluoride membrane.

[0078] 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 producing a polyvinylidene fluoride film, characterized by, The method comprises the following steps: S1. Adding polyvinylidene fluoride, a pore-forming agent and a surfactant into a mixed solvent to obtain a casting solution by stirring, wherein the mixed solvent comprises a first solvent and a second solvent, the first solvent accounts for 10wt%-50wt%, the first solvent comprises at least one of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and dimethyl sulfoxide, and the second solvent comprises an ester, the ester comprises triethyl phosphate, butyl acetate or a combination of the two; the content of the polyvinylidene fluoride, the surfactant and the pore-forming agent in the casting solution is 10wt%-15wt%, 5wt%-10wt% and 5wt%-10wt% respectively; S2. Casting the casting solution obtained in step S1 on a release film, scraping the film with a doctor blade to form a liquid film, and then placing the liquid film in a constant temperature and humidity environment for 30-300s, and then placing the liquid film in a coagulation bath of pure water for 1-5min to obtain a gel film, and then placing the gel film in a cleaning bath for cleaning and drying to obtain the polyvinylidene fluoride film, wherein the polyvinylidene fluoride film has a plurality of pores with uniform pore size distribution on the surface; The temperature of the constant temperature and humidity environment is 25-40℃, and the relative humidity is 50RH%-90RH%; The temperature of the coagulation bath is 30-60℃.

2. The preparation method according to claim 1, wherein In step S1, the pore-forming agent comprises polyvinylpyrrolidone, polyethylene glycol or a combination of the two; And / or, in step S1, the surfactant comprises a non-ionic surfactant.

3. The preparation method according to claim 2, characterized in that, In step S1, the weight average molecular weight of the polyvinylpyrrolidone is 250000-350000; And / or, in step S1, the weight average molecular weight of the polyethylene glycol is 370-460; And / or, in step S1, the non-ionic surfactant comprises a polyethylene glycol-polypropylene glycol-polyethylene glycol triblock copolymer.

4. The method of claim 1, wherein, In the film scraping process of step S2, the distance between the doctor blade and the release film is 200-500μm.

5. The preparation method according to claim 1, characterized in that, In step S2, the temperature of the cleaning bath is 40-70℃; And / or, in step S2, the gel film is placed in the cleaning bath for 5-10min; And / or, in step S2, the drying temperature is 40-70℃, and the drying time is 1-5min.

6. A polyvinylidene fluoride film produced by the production method according to any one of claims 1 to 5, characterized by, The polyvinylidene fluoride film is prepared by the following steps: S1. To 350 g of a mixed solvent, 75 g of polyvinylidene fluoride with a weight average molecular weight of 1458000, 50 g of a porogen polyvinylpyrrolidone with a weight average molecular weight of 300000 and 25 g of a surfactant polyethylene glycol with a weight average molecular weight of 2900 were added Polypropylene glycol The polyethylene glycol triblock copolymer was stirred at a temperature of 80 °C for 8 h and then left to stand at a temperature of 80 °C for 2 h to obtain a casting solution, and the mixed solvent consisted of a first solvent N,N-dimethylacetamide and a second solvent triethyl phosphate in a mass percentage of 50 wt%: 50 wt%. S2. Casting the casting solution obtained in step S1 on a release film, scraping the film with a doctor blade to form a liquid film, and then placing the liquid film in a constant temperature and humidity environment for 30-300s, and then placing the liquid film in a coagulation bath of pure water for 1-5min to obtain a gel film, and then placing the gel film in a cleaning bath for cleaning and drying to obtain the polyvinylidene fluoride film, wherein the polyvinylidene fluoride film has a plurality of pores with uniform pore size distribution on the surface; In the film scraping process of step S2, the distance between the doctor blade and the release film is 200-500μm. In step S2, the temperature of the cleaning bath is 40-70℃; And / or, in step S2, the gel film is placed in the cleaning bath for 5-10min; And / or, in step S2, the drying temperature is 40-70℃, and the drying time is 1-5min. The polyvinylidene fluoride film is prepared by the following steps: S2. Casting the casting solution obtained in step S1 on a release film, scraping the film with a doctor blade to form a liquid film, and then placing the liquid film in a constant temperature and humidity environment for 30-300s, and then placing the liquid film in a coagulation bath of pure water for 1-5min to obtain a gel film, and then placing the gel film in a cleaning bath for cleaning and drying to obtain the polyvinylidene fluoride film, wherein the polyvinylidene fluoride film has a plurality of pores with uniform pore size distribution on the surface; In the film scraping process of step S2, the distance between the doctor blade and the release film is 200-500μm. In step S2, the temperature of the cleaning bath is 40-70℃; And / or, in step S2, the gel film is placed in the cleaning bath for 5-10min; And / or, in step S2, the drying temperature is 40-70℃, and the drying time is 1-5min.

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