Preparation method of microporous membrane based on PTFE emulsion

Abstract

The invention relates to a preparation method of a microporous membrane based on PTFE (polytetrafluoroethylene) emulsion. The microporous membrane is obtained by taking the PTFE emulsion as a main body, mixing a water-soluble polymer material as a structural carrier, performing blade coating to form a membrane through a scraper blade, performing freeze pore forming and performing heat treatment. The PTFE membrane prepared by the method has a unique pore structure, and the thickness, porosity, section pore structure, membrane mechanical properties and the like of a membrane material can be regulated and controlled by regulating and controlling the composition of a structural carrier, blade coating conditions and freezing and sintering parameters. Compared with a PTFE membrane prepared through mechanical stretching, the method has the advantages of being simple in preparation process, uniform in pore structure, uniform in membrane thickness and the like, and can be suitable for precise separation of heterogeneous materials in a harsh separation environment.

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 characteristics of PTFE's high temperature resistance and solvent resistance make it difficult to process and make 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, requiring membrane materials not only to have good mechanical strength and chemical corrosion resistance, but also to have 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 purpose of the present invention is to provide a microporous membrane based on PTFE emulsion and a preparation method thereof. The PTFE membrane prepared by the present invention has a unique pore structure, and the thickness, porosity, cross-sectional pore structure, and membrane mechanical properties of the membrane material can be regulated by regulating the composition of the structural carrier, the coating conditions, and the freezing and sintering parameters. It can be applied to the precise separation of heterogeneous materials under harsh separation environments.

[0004] The technical solution of the present invention is: A method for preparing a microporous membrane based on PTFE emulsion, using PTFE emulsion as the main material, using water-soluble polymer materials as structural carriers, and forming pores by freezing 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 after degassing, pour them on a flat plate and apply them by scraping to form a film. (2) placing the flat plate and the membrane 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; (3) Drying the green body in step (2) under certain conditions to obtain a PTFE membrane green body with a porous structure, and subjecting the green body to heat treatment in a muffle furnace to obtain a microporous PTFE membrane.

[0005] 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 it is mixed according to the PTFE / WSP mass ratio = (4~30):1.

[0006] 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.

[0007] 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~-10°C; the position of the plate includes the front, back and side 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~100°C / s.

[0008] 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.

[0009] The muffle furnace heat treatment process in step (3) of the present invention is specifically to increase 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.

[0010] The PTFE microporous membrane prepared by the invention can realize a unique pore structure of dendritic pores, columnar pores, sponge-like pores and lamellar pores.

[0011] Beneficial effects: The PTFE membrane of the present invention has a unique pore structure. Compared with the PTFE membrane prepared by mechanical stretching, the present invention has the advantages of simple preparation process, uniform pore structure, uniform membrane thickness, etc. It can be applied to the precise separation of heterogeneous materials under harsh separation environments, and provides a reference for the preparation of high-performance PTFE microporous membranes in the later stage. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 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).

[0013] 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).

[0014] Figure 3 This 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).

[0015] Figure 4 This is a SEM image of the lamellar pore PTFE microporous membrane prepared in Example 4 (the attached figure is a cross-sectional view of the membrane surface).

[0016] Figure 5 This 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).

[0017] Figure 6 This 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).

[0018] Figure 7 This 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).

[0019] Figure 8 This 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).

[0020] Fig. 9 This is a SEM image of the dendritic pore PTFE microporous membrane prepared in Example 9.

[0021] Fig.10 This is a SEM image of the sponge-like PTFE microporous membrane prepared in Example 10.

[0022] Fig.11 This is a SEM image of the sponge-like PTFE microporous membrane prepared in Example 11.

[0023] Fig.12 This is a SEM image of the columnar pore PTFE microporous membrane prepared in Example 12.

[0024] Fig.13 1 is a pore size distribution diagram of the PTFE microporous membranes prepared in Examples 1 to 4.

[0025] Fig.14 5 is the pore size distribution diagram of the PTFE microporous membrane prepared in Examples 5 to 8. DETAILED DESCRIPTION Example 1

[0026] Take 20 g of 2488 polyvinyl alcohol PVA particles and slowly pour them into a conical flask containing 180 g of ionized water. After stirring and swelling at room temperature for about 5 h, continue stirring at 90 °C for 5 h until the solid is completely dissolved, put it into a 90 °C oven and let it stand for 12 h, and cool it to room temperature to obtain a 10wt% PVA solution. According to the PTFE / PVA mass ratio of 15:1, weigh 10 g of 10wt% PVA solution and add 25 g of PTFE emulsion with a solid content of 60wt% and a particle diameter of 0.23 μm. Stir at room temperature for 3 h at a speed of 300 rpm. Then pour it into a vacuum filtration bottle and evacuate for 8 h to obtain a casting solution. Pour the casting solution on a glass plate, use a 250 μm thick scraper to scrape the film, and immediately place the scraped glass plate with the film in an incubator, immerse it in low-temperature nitrogen at a temperature of -110 °C, and at the same time, the reverse surface is in contact with liquid nitrogen at a temperature of -196 °C until it is fully frozen. After that, freeze-dry at -50℃ for 24 hours to obtain a freeze-dried film on the glass plate. Then, the glass plate with the film was placed in a 380℃ muffle furnace for high temperature sintering for 1 hour. The sintering procedure of the muffle furnace was to increase the temperature from room temperature to 380℃ at 1℃ / min, then keep it warm for 1 hour, and the cooling rate was 1℃ / min. After reaching room temperature, it was peeled off from under the glass plate to obtain the prepared film.

[0027] 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

[0028] The freezing method is changed to placing the plate in an incubator, with the back side of the plate contacting the low-temperature nitrogen volatilized from liquid nitrogen at a temperature of -110°C until it is fully frozen. The other steps are completely consistent with Example 1.

[0029] 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 size of about 5.18 μm. Example 3

[0030] Take 20 g of gelatin particles and slowly pour them into a conical flask containing 180 g of ionized water. After soaking for 10 min, stir in a 60°C oil bath for 20 min to obtain a 10wt% gelatin solution. Weigh 10 g of 10wt% gelatin solution according to the PTFE / gelatin mass ratio of 15:1, add 25 g of PTFE emulsion with a solid content of 60wt% and a particle diameter of 0.23 μm, stir in a 60°C oil bath for 12 h at a speed of 300 rpm to obtain a casting solution. Pour the casting solution onto a glass plate, scrape the film with a 250 μm thick scraper, and immediately place the scraped glass plate with the film in an incubator so that the reverse surface contacts liquid nitrogen at a temperature of -196°C until it is fully frozen. Then freeze-dry at 10°C for 24 h to obtain a freeze-dried film on the glass plate. Then the film-bearing glass plate was placed in a muffle furnace at 380 °C for 1 h. The sintering procedure of the muffle furnace was to increase the temperature from room temperature to 380 °C at a rate of 1 °C / min, then keep the temperature for 1 h, and cool down at a rate of 1 °C / min. After reaching room temperature, the film was peeled off from the bottom of the glass plate to obtain the prepared film.

[0031] 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

[0032] During the film scraping process, an iron plate is used for the flat plate, and the freezing method is changed to placing it in an incubator and immersing it in -30°C low-temperature air until it is fully frozen. The other steps are completely consistent with Example 1.

[0033] 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 size of about 3.76 μm. Example 5

[0034] 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 incubator with the reverse surface of the plate contacting a low-temperature aluminum plate at a temperature of -50°C. The other steps were completely consistent with Example 1.

[0035] 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

[0036] After the film scraping process was completed, the plate was placed at room temperature for 10 minutes, and the freezing method was changed to placing it in an incubator with the reverse surface of the plate contacting a low-temperature aluminum plate at a temperature of -50°C. The other steps were completely consistent with Example 1.

[0037] 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

[0038] 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 incubator, the reverse surface of the plate contacting a low-temperature aluminum plate, the temperature being -50°C, and the other steps were completely consistent with Example 1.

[0039] 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

[0040] The water-soluble polymer material was changed to 0588 PVA, the PTFE / PVA mass ratio was changed to 20:1, the freezing method was changed to placing the plate in an incubator with the reverse surface of the plate contacting a low-temperature aluminum plate at a temperature of -50°C, and the other steps were completely consistent with Example 1.

[0041] 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

[0042] The water-soluble polymer material was changed to 1788 PVA with a mass fraction of 20 wt %. An iron plate was used for the film scraping process. The freezing method was changed to placing the film in an incubator and immersing the film in -30 ° C low-temperature air until it was fully frozen. The other steps were completely consistent with Example 1.

[0043] Fig. 9 : is a SEM image of the PTFE microporous membrane prepared in this example, and it can be seen that its pore structure is dendritic pores. Example 10

[0044] 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 completely consistent with Example 1.

[0045] Fig.10: is a SEM image of the PTFE microporous membrane prepared in this example, and it can be seen that its pore structure is sponge-like pores. Embodiment 11

[0046] 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 completely consistent with Example 1.

[0047] Fig.11 : is a SEM image of the PTFE microporous membrane prepared in this example, and it can be seen that its pore structure is sponge-like pores. Example 12

[0048] 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 completely consistent with Example 1.

[0049] Fig.12 : is a SEM image of the PTFE microporous membrane prepared in this example, and 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 after degassing, pour them on a flat plate and apply them by scraping to form a film. (2) placing the flat plate and the membrane 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; (3) After drying the green body in step (2) under certain conditions, a PTFE membrane green body with a porous structure is obtained, and then heat-treated 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: In step (1), 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 it is mixed according to the PTFE / WSP mass ratio = (4~30):

1.

3. A method for preparing a microporous membrane based on PTFE emulsion according to claim 1, characterized in that: The 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: In step (2), the low-temperature environment includes low-temperature nitrogen, low-temperature air, low-temperature liquid nitrogen, and low-temperature aluminum plate, and the temperature is -196~-10°C; the position of the plate includes the front, back and side 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~100°C / s.

5. 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.

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

7. 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 increase 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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