A method for preparing microporous membrane based on PTFE emulsion

Abstract

The present invention relates to a method for preparing a microporous membrane based on PTFE emulsion. The method comprises using PTFE emulsion as the main component, mixing a water-soluble polymer material as a structural carrier, applying a scraper to form a membrane, utilizing freezing to induce pores, and then heat-treating the membrane. The PTFE membrane prepared by the present invention has a unique pore structure, and the membrane material thickness, porosity, cross-sectional pore structure, and membrane mechanical properties can be controlled by regulating the composition of the structural carrier, coating conditions, freezing, and sintering parameters. Compared to PTFE membranes prepared by mechanical stretching, the present invention has the advantages of a simple preparation process, a uniform pore structure, and uniform membrane thickness, making it suitable for the precise separation of heterogeneous materials in harsh separation environments.

Description

Technical Field

[0001] The invention belongs to the field of separation membrane materials and preparation thereof, and particularly relates to a method for preparing a microporous membrane based on PTFE emulsion. Background Art

[0002] PTFE membrane has excellent high temperature resistance, solvent resistance and acid and alkali corrosion resistance, and has good hydrophobicity, and has unique application advantages in the field of membrane separation. However, the high temperature resistance and solvent resistance of PTFE make it difficult to process and form membranes by melting, dissolving, etc. At present, PTFE membranes are mainly prepared by mechanical stretching. For example, invention patent CN115216042B discloses a hydrophobic and oleophobic PTFE composite membrane prepared by processes such as biaxial stretching and surface fluorosilane coating with PTFE resin, aviation kerosene and nano-silica as materials. However, the traditional mechanical stretching method often faces some limitations in the preparation process, such as membrane pore structure, thickness is not easy to control uniformly, and the process is complex, energy consumption is high and the environmental impact is large. With the advancement of industrial separation technology, the performance requirements of filtration membrane materials are increasing, especially in harsh separation environments, which require membrane materials to have not only good mechanical strength and chemical corrosion resistance, but also a controllable pore structure to achieve accurate separation of heterogeneous materials. However, existing PTFE membrane material preparation methods have limited capabilities in regulating membrane thickness, porosity, pore structure, etc., and are difficult to meet the needs of complex separation environments. Summary of the Invention

[0003] The present invention aims to provide a PTFE emulsion-based microporous membrane and its preparation method. The PTFE membrane prepared by the present invention has a unique pore structure. The membrane thickness, porosity, cross-sectional pore structure, and mechanical properties can be controlled by regulating the structural carrier composition, doctor blade coating conditions, and freezing and sintering parameters. It is suitable for the precise separation of heterogeneous materials in demanding separation environments.

[0004] The technical solution of the present invention is:

[0005] A method for preparing a microporous membrane based on PTFE emulsion, using PTFE emulsion as the main material and a water-soluble polymer material as a structural carrier, is carried out by freezing to form pores and sintering to form a membrane. The specific steps are as follows:

[0006] (1) Slowly pour the water-soluble polymer material (WSP) into deionized water, heat it at 60-90 °C, and stir it thoroughly to obtain a water-soluble polymer solution. Mix the commercial PTFE emulsion and the water-soluble polymer solution in a certain proportion, stir them evenly at room temperature, and cast them on a flat plate after degassing to form a film by blade coating.

[0007] (2) placing the flat plate and the membrane described in step (1) in a low-temperature environment, and adjusting the position of the flat plate and the freezing conditions to obtain a PTFE membrane green body;

[0008] (3) The green body of step (2) is dried under certain conditions to obtain a PTFE membrane green body with a porous structure, and then subjected to heat treatment in a muffle furnace to obtain a microporous PTFE membrane.

[0009] In step (1) of the present invention, the water-soluble polymer material (WSP) includes PVA, CMC, PEG, PAM, and gelatin, and the mass fraction of the water-soluble polymer material solution is 10wt% to 20wt%; the molecular weight of PTFE in the PTFE emulsion is 1×10 5 ~1×10 8 The particle size is 0.05~0.5 μm, the solid content is 30wt%~60wt%, and the mixture is mixed at a PTFE / WSP mass ratio of (4~30):1.

[0010] The flat plate used in step (1) of the present invention is a glass plate with a thermal conductivity of 0.6-1.4 W / (m·K) or a metal plate with a thermal conductivity of 15-400 W / (m·K); the film thickness during the scraping process is 10-300 μm, the scraping speed is 10-50 mm / s, and the standing time after scraping is 0-40 min.

[0011] In step (2) of the present invention, the low-temperature environment includes low-temperature nitrogen, low-temperature air, low-temperature liquid nitrogen, and a low-temperature aluminum plate, and the temperature is -196 to -10°C; the position of the plate includes the front, back, and side surfaces contacting the low-temperature environment, and the contact method is surface contact, or partial to complete immersion in the low-temperature environment; the freezing condition is set to cool and freeze at a freezing rate of 1°C / min to 100°C / s.

[0012] The drying conditions in step (3) of the present invention are vacuum drying or freeze drying, the freeze drying time is 6 to 48 hours, and the drying temperature is -50 to 10°C.

[0013] The muffle furnace heat treatment process in step (3) of the present invention is specifically to heat the sample from room temperature to 340-380°C, control the heating rate at 0.1-10°C / min, keep the temperature for 0-10 h, and control the cooling rate at 0.1-10°C / min.

[0014] The PTFE microporous membrane prepared by the present invention can realize unique pore structures of dendritic pores, columnar pores, sponge-like pores and lamellar pores.

[0015] Beneficial Effects: The PTFE membrane of the present invention has a unique pore structure. Compared with mechanically stretched PTFE membranes, the present invention offers advantages such as a simpler preparation process, a uniform pore structure, and uniform membrane thickness. It is suitable for the precise separation of heterogeneous materials under harsh separation environments, providing a reference for the future preparation of high-performance PTFE microporous membranes. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 1 is a SEM image of the columnar pore PTFE microporous membrane prepared in Example 1 (the attached figure is a cross-sectional view of the membrane surface).

[0017] Figure 2 This is a SEM image of the layered PTFE microporous membrane prepared in Example 2 (the attached figure is a cross-sectional view of the membrane surface).

[0018] Figure 3 3 is a SEM image of the sponge-like PTFE microporous membrane prepared in Example 3 (the attached figure is a cross-sectional view of the membrane surface).

[0019] Figure 4 This is an SEM image of the lamellar PTFE lamellar microporous membrane prepared in Example 4 (the attached figure is a cross-sectional view of the membrane surface).

[0020] Figure 5 1 is a SEM image of the dendritic pore PTFE microporous membrane prepared in Example 5 (the attached figure is a cross-sectional view of the membrane surface).

[0021] Figure 6 1 is a SEM image of the dendritic pore PTFE microporous membrane prepared in Example 6 (the attached figure is a cross-sectional view of the membrane surface).

[0022] Figure 7 1 is a SEM image of the dendritic pore PTFE microporous membrane prepared in Example 7 (the attached figure is a cross-sectional view of the membrane surface).

[0023] Figure 8 1 is a SEM image of the dendritic pore PTFE microporous membrane prepared in Example 8 (the attached figure is a cross-sectional view of the membrane surface).

[0024] Figure 9 This is a SEM image of the dendritic pore PTFE microporous membrane prepared in Example 9.

[0025] Figure 10 This is a SEM image of the sponge-like PTFE microporous membrane prepared in Example 10.

[0026] Figure 11 This is a SEM image of the sponge-like PTFE microporous membrane prepared in Example 11.

[0027] Figure 12 This is a SEM image of the columnar pore PTFE microporous membrane prepared in Example 12.

[0028] Figure 13 1 is a pore size distribution diagram of the PTFE microporous membranes prepared in Examples 1 to 4.

[0029] Figure 14 5 is the pore size distribution diagram of the PTFE microporous membranes prepared in Examples 5 to 8. DETAILED DESCRIPTION Example 1

[0030] 20 g of 2488 polyvinyl alcohol (PVA) particles were slowly poured into a conical flask containing 180 g of deionized water. After stirring at room temperature for approximately 5 hours, the mixture was stirred at 90°C for another 5 hours until the solids were completely dissolved. The mixture was then placed in a 90°C oven for 12 hours and cooled to room temperature to obtain a 10 wt% PVA solution. To this solution, 10 g of the 10 wt% PVA solution (PTFE / PVA mass ratio of 15:1) was added 25 g of a PTFE emulsion with a solid content of 60 wt% and a particle diameter of 0.23 μm. The mixture was stirred at room temperature for 3 hours at 300 rpm. The mixture was then poured into a vacuum filtration flask and evacuated for 8 hours to obtain the casting solution. The casting solution was poured onto a glass plate and scraped with a 250 μm-thick scraper. The scraped glass plate was immediately placed in an insulated box and completely immersed in low-temperature nitrogen at -110°C. The reverse surface was simultaneously exposed to liquid nitrogen at -196°C until fully frozen. The film was then freeze-dried at -50°C for 24 hours to obtain a freeze-dried membrane on a glass plate. The membrane-coated glass plate was then sintered in a 380°C muffle furnace for 1 hour. The muffle furnace sintering program was as follows: heating from room temperature to 380°C at a rate of 1°C / min, then holding at that temperature for 1 hour, and then cooling at a rate of 1°C / min. Once the film reached room temperature, it was removed from the glass plate to obtain the prepared membrane.

[0031] Figure 1 : is a SEM image of the PTFE microporous membrane prepared in this example, wherein the upper right corner is a cross-sectional view of the membrane surface, from which it can be seen that its pore structure is columnar pores with an average pore diameter of about 6.76 μm. Example 2

[0032] The freezing method is changed to placing the plate in an insulated box, with the back of the plate contacting the low-temperature nitrogen volatilized from liquid nitrogen at a temperature of -110°C, and waiting for it to be fully frozen. The other steps are exactly the same as in Example 1.

[0033] Figure 2 : is a SEM image of the PTFE microporous membrane prepared in this example, wherein the upper right corner is a cross-sectional view of the membrane surface, from which it can be seen that its pore structure is layered pores with an average pore diameter of about 5.18 μm. Example 3

[0034] 20 g of gelatin particles were slowly poured into a conical flask containing 180 g of deionized water. After soaking for 10 minutes, the solution was stirred in a 60°C oil bath for 20 minutes to obtain a 10 wt% gelatin solution. To this solution, 10 g of the 10 wt% gelatin solution (PTFE / gelatin mass ratio of 15:1) was added 25 g of a PTFE emulsion with a solid content of 60 wt% and a particle diameter of 0.23 μm. The mixture was stirred in a 60°C oil bath at 300 rpm for 12 hours to obtain a casting solution. The casting solution was poured onto a glass plate and the film was scraped using a 250 μm-thick scraper. The scraped glass plate was immediately placed in an insulated container with the back surface exposed to liquid nitrogen at -196°C until fully frozen. The solution was then freeze-dried at 10°C for 24 hours to obtain a freeze-dried film. The coated glass plate was then placed in a 380°C muffle furnace and fired for 1 hour. The muffle furnace sintering program was to increase the temperature from room temperature to 380°C at a rate of 1°C / min, then hold for 1 hour and cool at a rate of 1°C / min. Once the film reached room temperature, it was removed from the bottom of the glass plate to obtain the prepared film.

[0035] Figure 3 : is a SEM image of the PTFE microporous membrane prepared in this example, wherein the upper right corner is a cross-sectional view of the membrane surface, from which it can be seen that its pore structure is sponge-like pores with an average pore diameter of about 8.16 μm. Example 4

[0036] During the film scraping process, an iron plate was used as the flat plate. The freezing method was changed to placing the plate in an insulated box and immersing it in -30°C low-temperature air until it was fully frozen. The other steps were completely consistent with Example 1.

[0037] Figure 4 : is a SEM image of the PTFE microporous membrane prepared in this example, wherein the upper right corner is a cross-sectional view of the membrane surface, from which it can be seen that its pore structure is layered pores with an average pore diameter of about 3.76 μm. Example 5

[0038] The thickness of the scraper used in the film scraping process was changed to 100 μm, and the freezing method was changed to placing the plate in an insulated box with the reverse surface of the plate contacting a low-temperature aluminum plate at a temperature of -50°C. The other steps were exactly the same as in Example 1.

[0039] Figure 5 : is a SEM image of the PTFE microporous membrane prepared in this example, wherein the upper right corner is a cross-sectional view of the membrane surface, from which it can be seen that its pore structure is dendritic pores with an average pore diameter of about 0.5 μm. Example 6

[0040] After the film scraping process was completed, the plate was placed at room temperature for 10 minutes. The freezing method was changed to placing it in an insulated box with the back surface of the plate contacting a low-temperature aluminum plate at a temperature of -50°C. The other steps were exactly the same as in Example 1.

[0041] Figure 6 : is a SEM image of the PTFE microporous membrane prepared in this example, wherein the upper right corner is a cross-sectional view of the membrane surface, from which it can be seen that its pore structure is dendritic pores with an average pore diameter of about 0.32 μm. Example 7

[0042] The sintering procedure steps were as follows: the sintering temperature was changed to 340°C, the freezing method was changed to placing the plate in an insulated box with the reverse surface of the plate contacting a low-temperature aluminum plate at a temperature of -50°C, and the other steps were exactly the same as in Example 1.

[0043] Figure 7 : is a SEM image of the PTFE microporous membrane prepared in this example, wherein the upper right corner is a cross-sectional view of the membrane surface, from which it can be seen that its pore structure is dendritic pores with an average pore diameter of about 0.42 μm. Example 8

[0044] The water-soluble polymer material was changed to 0588 PVA, the PTFE / PVA mass ratio was changed to 20:1, and the freezing method was changed to placing the plate in an insulated box with the back surface of the plate contacting a low-temperature aluminum plate at a temperature of -50°C. The other steps were exactly the same as in Example 1.

[0045] Figure 8 : is a SEM image of the PTFE microporous membrane prepared in this example, wherein the upper right corner is a cross-sectional view of the membrane surface, from which it can be seen that its pore structure is dendritic pores with an average pore diameter of about 0.51 μm. Example 9

[0046] The water-soluble polymer material was changed to 1788 PVA with a mass fraction of 20 wt %. An iron plate was used for the scraping process. The freezing method was changed to placing the film in an insulated box and immersing it in -30°C low-temperature air until it was fully frozen. The other steps were exactly the same as in Example 1.

[0047] Figure 9 3 is a SEM image of the PTFE microporous membrane prepared in this example, from which it can be seen that its pore structure is dendritic. Example 10

[0048] The water-soluble polymer material was changed to 1788 PVA, the PTFE / PVA mass ratio was changed to 4:1, and the other steps were exactly the same as in Example 1.

[0049] Figure 103 is a SEM image of the PTFE microporous membrane prepared in this example, from which it can be seen that its pore structure is sponge-like. Example 11

[0050] The water-soluble polymer material was changed to 1788 PVA, the solid content of the PTFE emulsion was changed to 30 wt %, the PTFE / PVA mass ratio was changed to 10:1, and the other steps were exactly the same as in Example 1.

[0051] Figure 11 3 is a SEM image of the PTFE microporous membrane prepared in this example, from which it can be seen that its pore structure is sponge-like. Example 12

[0052] The water-soluble polymer material was changed to 2488 PVA, the PTFE / PVA mass ratio was changed to 30:1, and the other steps were exactly the same as in Example 1.

[0053] Figure 12 3 is a SEM image of the PTFE microporous membrane prepared in this example, from which it can be seen that its pore structure is columnar pores.

Claims

1. A method for preparing a microporous membrane based on PTFE emulsion, characterized in that: Using PTFE emulsion as the main material and water-soluble polymer material as the structural carrier, the film is formed by freezing to form pores and sintering. The specific operation steps are as follows: (1) Slowly pour the water-soluble polymer material WSP into deionized water, heat it at 60-90 °C, and stir it thoroughly to obtain a water-soluble polymer solution. Mix the commercial PTFE emulsion and the water-soluble polymer solution in a certain proportion, stir them evenly at room temperature, and cast them on a flat plate after degassing to form a film by blade coating. The water-soluble polymer material WSP includes PVA or gelatin. (2) placing the flat plate and the membrane in step (1) in a low-temperature environment, and regulating the position of the flat plate and the freezing conditions to obtain a PTFE membrane green body; the low-temperature environment includes low-temperature nitrogen, low-temperature air, low-temperature liquid nitrogen or a low-temperature aluminum plate, and the temperature is -196~-10°C; the position of the flat plate includes the front, back and side contacting the low-temperature environment, and the contact mode is surface contact, or partial to complete immersion in the low-temperature environment; the freezing conditions are set to cool and freeze at a freezing rate of 1°C / min~100°C / s; (3) The green body of step (2) is dried under certain conditions to obtain a PTFE membrane green body with a porous structure, and then subjected to heat treatment in a muffle furnace to obtain a microporous PTFE membrane.

2. A method for preparing a microporous membrane based on PTFE emulsion according to claim 1, characterized in that: The mass fraction of the water-soluble polymer solution in step (1) is 10 wt% to 20 wt%; the molecular weight of PTFE in the PTFE emulsion is 1×10 5 ~1×10 8 The particle size is 0.05~0.5 μm, the solid content is 30wt%~60wt%, and the mixture is mixed at a PTFE / WSP mass ratio of (4~30):

1.

3. A method for preparing a microporous membrane based on PTFE emulsion according to claim 1, characterized in that: The flat plate used in step (1) is a glass plate with a thermal conductivity of 0.6-1.4 W / (m·K) or a metal plate with a thermal conductivity of 15-400 W / (m·K); the film thickness during the scraping process is 10-300 μm, the scraping speed is 10-50 mm / s, and the standing time after scraping is 0-40 min.

4. A method for preparing a microporous membrane based on PTFE emulsion according to claim 1, characterized in that: The drying conditions in step (3) are vacuum drying or freeze drying, the freeze drying time is 6 to 48 hours, and the drying temperature is -50 to 10°C.

5. A method for preparing a microporous membrane based on PTFE emulsion according to claim 1, characterized in that: The porous structure in step (3) is one of dendritic pores, columnar pores, sponge-like pores, and layered pores.

6. A method for preparing a microporous membrane based on PTFE emulsion according to claim 1, characterized in that: The muffle furnace heat treatment process in step (3) is specifically to heat the temperature from room temperature to 340-380°C, control the heating rate at 0.1-10°C / min, keep the temperature for 0-10 h, and control the cooling rate at 0.1-10°C / min.

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