Method for preparing microporous membrane based on PTFE emulsion

Abstract

The present invention relates to a method for preparing a microporous membrane based on a PTFE emulsion. The microporous membrane is obtained by using a PTFE emulsion as a main body, mixing same with a water-soluble polymer material serving as a structural carrier, forming a membrane by means of blade coating, forming pores by means of freezing, and performing a heat treatment. The PTFE membrane prepared in the present invention has a unique pore structure, and the thickness, porosity, sectional pore structure, membrane mechanical properties, etc. of the membrane material can be adjusted by adjusting the composition of the structural carrier, blade coating conditions, and freezing and sintering parameters. Compared with the preparation of a PTFE membrane by means of mechanical stretching, the present invention has the advantages of a simple preparation process, uniform pore structure, uniform membrane thickness, etc., and is suitable for accurate separation of heterogeneous materials in a harsh separation environment.

Description

A method for preparing microporous membranes based on PTFE emulsion Technical Field

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

[0002] PTFE membranes possess excellent high-temperature resistance, solvent resistance, and acid and alkali corrosion resistance, along with good hydrophobicity, giving them unique advantages in membrane separation. However, the high-temperature and solvent resistance of PTFE makes it difficult to process into membranes through melting or dissolution. Currently, PTFE membranes are mainly prepared using mechanical stretching. For example, invention patent CN115216042B discloses a hydrophobic and oleophobic PTFE composite membrane prepared from PTFE resin, aviation kerosene, and nano-silica through biaxial stretching and surface fluorosilane coating. However, traditional mechanical stretching methods often face limitations in the preparation process, such as difficulty in uniformly controlling membrane pore structure and thickness, as well as drawbacks such as complex processes, high energy consumption, and significant environmental impact. With the advancement of industrial separation technology, the performance requirements for filtration membrane materials are increasing, especially in harsh separation environments. Membrane materials must not only possess good mechanical strength and chemical corrosion resistance but also have a controllable pore structure to achieve precise separation of heterogeneous materials. However, existing PTFE membrane material preparation methods have limited ability to control membrane thickness, porosity, and pore structure, making it difficult to meet the needs of complex separation environments. Summary of the Invention

[0003] The purpose of this invention is to provide a microporous membrane based on PTFE emulsion and its preparation method. The PTFE membrane prepared by this invention has a unique pore structure, and the membrane material thickness, porosity, cross-sectional pore structure, and mechanical properties can be controlled by adjusting the composition of the structural carrier, coating conditions, and freezing and sintering parameters. It is suitable for the precise separation of heterogeneous materials under harsh separation environments.

[0004] The technical solution of the present invention is as follows: a method for preparing a microporous membrane based on PTFE emulsion, using PTFE emulsion as the main material and water-soluble polymer material as the structural carrier, and forming a membrane by freezing and sintering. The specific operation steps are as follows: (1) slowly pour water-soluble polymer material (WSP) into deionized water, heat at 60-90 ℃, and stir thoroughly to obtain a water-soluble polymer solution. Mix commercial PTFE emulsion and water-soluble polymer solution in a certain proportion, stir evenly at room temperature, and after degassing treatment, pour it onto a plate and coat it to form a membrane; (2) place the plate and membrane in a low temperature environment, adjust the plate position and freezing conditions to obtain a PTFE membrane preform; (3) dry the preform in step (2) under certain conditions to obtain a PTFE membrane preform with a porous structure, and obtain a microporous PTFE membrane by heat treatment in a muffle furnace.

[0005] In step (1) of this 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%~20wt%; the PTFE emulsion has a molecular weight of 1×105~1×108, a particle size of 0.05~0.5 μm, and a solid content of 30wt%~60wt%, and is mixed at a mass ratio of PTFE / WSP = (4~30):1.

[0006] The plate used in step (1) of this 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 coating process is 10~300 μm, the coating speed is 10~50 mm / s, and the standing time after coating is 0~40 min.

[0007] In step (2) of this invention, the low-temperature environment includes low-temperature nitrogen, low-temperature air, low-temperature liquid nitrogen, and low-temperature aluminum plate, with a temperature of -196 to -10 ℃; the plate is positioned to contact the low-temperature environment from the front, back, and sides, and the contact method is surface contact or partial to complete immersion in the low-temperature environment; the freezing conditions are set to a cooling rate of 1 ℃ / min to 100 ℃ / s.

[0008] In step (3) of this invention, the drying conditions are vacuum drying or freeze drying, the freeze drying time is 6~48 h, and the drying temperature is -50~10 ℃.

[0009] The muffle furnace heat treatment process in step (3) of this invention specifically involves heating from room temperature to 340~380 ℃, with the heating rate controlled at 0.1~10 ℃ / min, holding at the temperature for 0~10 h, and the cooling rate controlled at 0.1~10 ℃ / min.

[0010] The PTFE microporous membrane prepared by this invention can achieve unique pore structures such as dendritic pores, columnar pores, sponge-like pores, and layered pores.

[0011] Beneficial effects: The PTFE membrane of this invention has a unique pore structure. Compared with the mechanical stretching method for preparing PTFE membranes, this invention has the advantages of simple preparation process, uniform pore structure, and uniform membrane thickness. It can be applied to the precise separation of heterogeneous materials under harsh separation environments, and provides a reference for the subsequent preparation of high-performance PTFE microporous membranes. Attached Figure Description

[0012] Figure 1 is a SEM image of the columnar PTFE microporous membrane prepared in Example 1 (the attached figure is a cross-sectional view of the membrane surface).

[0013] Figure 2 is a SEM image of the layered porous PTFE microporous membrane prepared in Example 2 (the attached figure is a cross-sectional view of the membrane surface).

[0014] Figure 3 is a SEM image of the sponge-like porous PTFE microporous membrane prepared in Example 3 (the attached figure is a cross-sectional view of the membrane surface).

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

[0016] Figure 5 is a SEM image of the dendritic PTFE microporous membrane prepared in Example 5 (the attached figure is a cross-sectional view of the membrane surface).

[0017] Figure 6 is a SEM image of the dendritic PTFE microporous membrane prepared in Example 6 (the attached figure is a cross-sectional view of the membrane surface).

[0018] Figure 7 is a SEM image of the dendritic PTFE microporous membrane prepared in Example 7 (the attached figure is a cross-sectional view of the membrane surface).

[0019] Figure 8 is a SEM image of the dendritic PTFE microporous membrane prepared in Example 8 (the attached figure is a cross-sectional view of the membrane surface).

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

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

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

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

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

[0025] Figure 14 is a pore size distribution diagram of the PTFE microporous membranes prepared in Examples 5-8. Detailed Implementation

[0026] Example 1

[0027] 20 g of 2488 type polyvinyl alcohol (PVA) particles were slowly poured into an Erlenmeyer flask containing 180 g of deionized water. The mixture was stirred at room temperature until it swelled for approximately 5 hours. Then, stirring was continued at 90 °C for another 5 hours until the solid was completely dissolved. The flask was then placed in a 90 °C oven and allowed to stand for 12 hours. After cooling to room temperature, a 10 wt% PVA solution was obtained. 10 g of the 10 wt% PVA solution was weighed at a PTFE / PVA mass ratio of 15:1. 25 g of PTFE emulsion with a solid content of 60 wt% and a particle diameter of 0.23 μm was added. 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 a casting solution. The casting solution was poured onto a glass plate, and a 250 μm thick doctor blade was used to scrape a film. The coated glass plate was immediately placed in an insulated box, completely immersed in low-temperature nitrogen gas at -110 °C, while the reverse side was in contact with liquid nitrogen at -196 °C, until fully frozen. The glass plate was then freeze-dried at -50℃ for 24 h to obtain a freeze-dried film. The film-coated glass plate was then sintered in a muffle furnace at 380℃ for 1 h. The muffle furnace sintering program was as follows: heating from room temperature to 380℃ at a rate of 1℃ / min, holding at that temperature for 1 h, and then cooling at a rate of 1℃ / min. After cooling to room temperature, the film was peeled off from under the glass plate to obtain the prepared film.

[0028] Figure 1 is a SEM image of the PTFE microporous membrane prepared in this embodiment, with the upper right corner showing a cross-sectional view of the membrane surface. It can be seen that its pore structure is columnar, with an average pore diameter of approximately 6.76 μm. Example 2

[0029] The freezing method was changed to placing it in an insulated box, with the back of the plate in contact with the low-temperature nitrogen gas volatilized from the liquid nitrogen at a temperature of -110 ℃, until it was fully frozen. The other steps were completely the same as in Example 1.

[0030] Figure 2 is a SEM image of the PTFE microporous membrane prepared in this embodiment, with the upper right corner showing a cross-sectional view of the membrane surface. It can be seen that its pore structure is layered, with an average pore size of approximately 5.18 μm. Example 3

[0031] 20 g of gelatin granules were slowly poured into an Erlenmeyer flask containing 180 g of deionized water. After soaking for 10 min, the solution was stirred in a 60 ℃ oil bath for 20 min to obtain a 10 wt% gelatin solution. 10 g of the 10 wt% gelatin solution was weighed at a PTFE / gelatin mass ratio of 15:1, and 25 g of PTFE emulsion with a solid content of 60 wt% and a particle diameter of 0.23 μm was added. The mixture was stirred in a 60 ℃ oil bath for 12 h at 300 rpm to obtain a casting solution. The casting solution was poured onto a glass plate, and a 250 μm thick doctor blade was used to scrape a film. The coated glass plate was immediately placed in an incubator, with its reverse surface in contact with liquid nitrogen at -196 ℃, until fully frozen. Then, it was freeze-dried at 10 ℃ for 24 h to obtain a freeze-dried film on the glass plate. The glass plate with the film was then placed in a muffle furnace at 380 °C for 1 hour. The muffle furnace sintering program was as follows: the temperature was increased from room temperature to 380 °C at a rate of 1 °C / min, then held at that temperature for 1 hour, and the temperature was decreased at a rate of 1 °C / min. After cooling to room temperature, the film was peeled off from under the glass plate to obtain the prepared film.

[0032] Figure 3 is a SEM image of the PTFE microporous membrane prepared in this embodiment, where the upper right corner shows a cross-sectional view of the membrane surface. It can be seen that its pore structure is sponge-like, with an average pore diameter of approximately 8.16 μm. Example 4

[0033] The flat plate used in the film coating process is an iron plate. The freezing method is changed to placing it in an insulated box and immersing it completely in -30 ℃ low temperature air until it is fully frozen. The other steps are completely the same as in Example 1.

[0034] Figure 4 is a SEM image of the PTFE microporous membrane prepared in this embodiment, with the upper right corner showing a cross-sectional view of the membrane surface. It can be seen that its pore structure is layered, with an average pore size of approximately 3.76 μm. Example 5

[0035] The thickness of the scraper used in the film coating process was changed to 100 μm, and the freezing method was changed to placing it in an insulated box with the reverse side of the flat plate in contact with a low-temperature aluminum plate at a temperature of -50 °C. Other steps were completely consistent with those in Example 1.

[0036] Figure 5 is a SEM image of the PTFE microporous membrane prepared in this embodiment, with the upper right corner showing a cross-sectional view of the membrane surface. It can be seen that its pore structure is dendritic, with an average pore diameter of approximately 0.5 μm. Example 6

[0037] After the film coating process is completed, the plate is left to stand at room temperature for 10 minutes. The freezing method is changed to placing it in an insulated box, with the reverse side of the plate in contact with a low-temperature aluminum plate at a temperature of -50 ℃. The other steps are completely consistent with those in Example 1.

[0038] Figure 6 is a SEM image of the PTFE microporous membrane prepared in this embodiment, with the upper right corner showing a cross-sectional view of the membrane surface. It can be seen that its pore structure is dendritic, with an average pore size of approximately 0.32 μm. Example 7

[0039] The sintering procedure was changed, the sintering temperature was changed to 340 ℃, the freezing method was changed to placing it in an insulated box, with the reverse surface of the flat plate in contact with a low-temperature aluminum plate at a temperature of -50 ℃, and the other steps were completely consistent with Example 1.

[0040] Figure 7 is a SEM image of the PTFE microporous membrane prepared in this embodiment, with the upper right corner showing a cross-sectional view of the membrane surface. It can be seen that its pore structure is dendritic, with an average pore size of approximately 0.42 μm. Example 8

[0041] The water-soluble polymer material was changed to type 0588 PVA, the PTFE / PVA mass ratio was changed to 20:1, and the freezing method was changed to placing it in an insulated box with the reverse side of the plate in contact with a low-temperature aluminum plate at a temperature of -50 ℃. The other steps were completely consistent with those in Example 1.

[0042] Figure 8 is a SEM image of the PTFE microporous membrane prepared in this embodiment, with the upper right corner showing a cross-sectional view of the membrane surface. It can be seen that its pore structure is dendritic, with an average pore size of approximately 0.51 μm. Example 9

[0043] The water-soluble polymer material was changed to type 1788 PVA with a mass fraction of 20 wt%. The film coating process used an iron plate. The freezing method was changed to placing it in an insulated box and immersing it completely in -30 ℃ low temperature air until it was fully frozen. The other steps were completely the same as in Example 1.

[0044] Figure 9 is a SEM image of the PTFE microporous membrane prepared in this embodiment, showing that its pore structure is dendritic. Example 10

[0045] The water-soluble polymer material was changed to type 1788 PVA, the PTFE / PVA mass ratio was changed to 4:1, and the other steps were completely consistent with Example 1.

[0046] Figure 10 is a SEM image of the PTFE microporous membrane prepared in this embodiment, showing that its pore structure is sponge-like. Example 11

[0047] The water-soluble polymer material was changed to type 1788 PVA, the PTFE emulsion solid content was changed to 30wt%, the PTFE / PVA mass ratio was changed to 10:1, and the other steps were completely consistent with Example 1.

[0048] Figure 11 is a SEM image of the PTFE microporous membrane prepared in this embodiment, showing that its pore structure is sponge-like. Example 12

[0049] The water-soluble polymer material was changed to type 2488 PVA, the PTFE / PVA mass ratio was changed to 30:1, and the other steps were completely consistent with Example 1.

[0050] Figure 12 is a SEM image of the PTFE microporous membrane prepared in this embodiment, which shows that its pore structure is columnar.

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 membrane is formed by freezing and sintering. The specific operation steps are as follows: (1) Slowly pour water-soluble polymer material (WSP) into deionized water, heat at 60-90 ℃, and stir thoroughly to obtain water-soluble polymer solution. Mix commercial PTFE emulsion and water-soluble polymer solution in a certain proportion, stir evenly at room temperature, and after degassing treatment, pour it onto a plate and coat it to form a membrane; (2) Place the plate and membrane in the low temperature environment, adjust the plate position and freezing conditions to obtain PTFE membrane preform; (3) Dry the preform in step (2) under certain conditions to obtain PTFE membrane preform with porous structure, and obtain microporous PTFE membrane by heat treatment in a muffle furnace.

2. The 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%~20wt%; the PTFE emulsion has a molecular weight of 1×105~1×108, a particle size of 0.05~0.5 μm, and a solid content of 30wt%~60wt%, and is mixed at a mass ratio of PTFE / WSP = (4~30):

1.

3. The 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 coating process is 10~300 μm, the coating speed is 10~50 mm / s, and the standing time after coating is 0~40 min.

4. The 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, with a temperature of -196 to -10 ℃; the plate is positioned to contact the low-temperature environment from the front, back, and sides, and the contact method is surface contact or partial to complete immersion in the low-temperature environment; the freezing conditions are set to a freezing rate of 1 ℃ / min to 100 ℃ / s for cooling and freezing.

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

6. The 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 the following: 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) specifically involves heating from room temperature to 340~380 ℃, with the heating rate controlled at 0.1~10 ℃ / min, holding at that temperature for 0~10 h, and the cooling rate controlled at 0.1~10 ℃ / min.

Images