A method for hydrophilic modification of polytetrafluoroethylene microporous separation membranes

Abstract

This application discloses a method for hydrophilic modification of a polytetrafluoroethylene (PTFE) microporous separation membrane, comprising: removing impurities from the PTFE microporous separation membrane to be treated to obtain a pretreated PTFE microporous separation membrane; treating the pretreated PTFE microporous separation membrane with an amphiphilic polymer to obtain a PTFE microporous separation membrane loaded with an amphiphilic substance; immersing the PTFE microporous separation membrane loaded with the amphiphilic substance in an acidic aqueous solution of a crosslinking agent for hydrolysis and crosslinking to form a crosslinked PTFE microporous separation membrane; immersing the crosslinked PTFE microporous separation membrane in an alkaline aqueous solution for further hydrolysis, followed by rinsing and drying to complete the modification of the PTFE microporous separation membrane and obtain a hydrophilic PTFE microporous separation membrane.

Description

Technical Field

[0001] This invention relates to the field of separation membrane materials technology, and in particular to a method for hydrophilic modification of polytetrafluoroethylene microporous separation membranes. Background Technology

[0002] In existing technologies, the hydrophilic modification methods for polytetrafluoroethylene (PTFE) membranes are mainly divided into etching modification, grafting modification, and physical modification. Etching modification involves breaking the CF or CC bonds of PTFE through intense chemical oxidation or high-energy particle beam treatment, and introducing polar chemical groups to achieve hydrophilic modification. However, chemical oxidation often uses highly corrosive hazardous chemicals, resulting in difficult wastewater recovery and poor environmental friendliness; while high-energy particle beam equipment is expensive, difficult to mass-produce continuously, and the hydrophilic effect is limited to the outer surface of the membrane. Grafting modification involves constructing a hydrophilic layer on the material through the coupling or polymerization of functional monomers. Due to the intrinsic chemical inertness of PTFE, it is often necessary to introduce active sites on the membrane surface as grafting initiation sites before grafting modification. PTFE membranes prepared by grafting can maintain hydrophilicity for a long time, but it still suffers from drawbacks such as long processing time and high cost. Physical modification primarily uses surfactants as modifiers. The hydrophobic ends of surfactants adsorb onto the surface and pore walls of the polytetrafluoroethylene (PTFE) membrane through hydrophobic interactions, while the hydrophilic ends help enhance the membrane's hydrophilicity. This method is simple and easy to implement, but the modifier is easily lost during membrane use, making the hydrophilic modification effect difficult to sustain.

[0003] Therefore, it is necessary to develop a new method for hydrophilic modification of polytetrafluoroethylene microporous separation membranes. Summary of the Invention

[0004] This application provides a method for hydrophilic modification of polytetrafluoroethylene microporous separation membranes to solve the above-mentioned technical problems.

[0005] This application provides a method for hydrophilic modification of a polytetrafluoroethylene microporous separation membrane, the modification method comprising:

[0006] Impurities are removed from the polytetrafluoroethylene microporous separation membrane to be treated to obtain a pretreated polytetrafluoroethylene microporous separation membrane.

[0007] The pretreated polytetrafluoroethylene microporous separation membrane is treated with an amphiphilic polymer to obtain a polytetrafluoroethylene microporous separation membrane loaded with an amphiphilic polymer.

[0008] The polytetrafluoroethylene microporous separation membrane loaded with the amphiphilic polymer is treated with a crosslinking agent to form a crosslinked polytetrafluoroethylene microporous separation membrane.

[0009] The cross-linked polytetrafluoroethylene microporous separation membrane is treated with an alkaline aqueous solution by soaking, rinsing and drying to complete the modification of the polytetrafluoroethylene microporous separation membrane and obtain a hydrophilic polytetrafluoroethylene microporous separation membrane.

[0010] This application provides a method for hydrophilic modification of a polytetrafluoroethylene (PTFE) microporous separation membrane. By loading an amphiphilic polymer, poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), onto the PTFE microporous separation membrane, and sequentially performing acidic hydrolysis / crosslinking and alkaline hydrolysis, a hydrophilic network is constructed that interpenetrates and intersperses with the PTFE membrane fibrils and nodes. This overcomes the drawbacks of existing technologies, such as damage to the intrinsic membrane structure and easy loss of hydrophilic agents. Compared to the original membrane, the modified PTFE microporous separation membrane exhibits a significantly reduced water contact angle and a significantly increased pure water flux. The technical solution proposed in this invention involves only immersion treatment, requires no complex equipment, and is simple to operate; it does not involve hazardous chemicals, and the modified solution can be reused multiple times, resulting in low cost and environmental friendliness. Attached Figure Description

[0011] Figure 1 This is a schematic diagram of the hydrophilic modification method for the polytetrafluoroethylene microporous separation membrane provided in the embodiments of this application;

[0012] Figure 2 This is a schematic diagram showing the wetting results of the polytetrafluoroethylene microporous separation membranes corresponding to Example 2 and Comparative Example 1 in pure water.

[0013] Figure 3 This is a schematic diagram showing the oxygen distribution in the cross-section of the polytetrafluoroethylene microporous separation membrane corresponding to Example 2 of this application. Detailed Implementation

[0014] To better understand the technical solution of the present invention, the following embodiments will further illustrate the method provided by the present invention. However, the present invention is not limited to the listed embodiments, but should also include any other well-known modifications within the scope of the claims of the present invention.

[0015] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0016] Materials used in this invention: There are no special restrictions on the source of all raw materials in this invention and the following embodiments and comparative examples; they can be commercially available.

[0017] Figure 1 This is a schematic diagram of a method for modifying the hydrophilicity of a polytetrafluoroethylene (PTFE) microporous separation membrane according to an embodiment of this application. Figure 1 As shown, the modification methods include:

[0018] Step S101: Remove impurities from the polytetrafluoroethylene microporous separation membrane to be treated to obtain a pretreated polytetrafluoroethylene microporous separation membrane.

[0019] In this embodiment of the application, the step of removing impurities from the polytetrafluoroethylene microporous separation membrane to be treated, and obtaining a pretreated polytetrafluoroethylene microporous separation membrane, specifically includes:

[0020] The polytetrafluoroethylene microporous separation membrane to be treated was immersed in ethanol for 2 hours to wash out impurities on the surface and in the pores of the polytetrafluoroethylene microporous separation membrane to be treated, thereby obtaining a pretreated polytetrafluoroethylene microporous separation membrane.

[0021] Step S103: The pretreated polytetrafluoroethylene microporous separation membrane is treated with an amphiphilic polymer to obtain a polytetrafluoroethylene microporous separation membrane loaded with an amphiphilic polymer.

[0022] In the embodiments of this application, the amphiphilic polymer is poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), and the mass concentration of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) is 1 wt% to 5 wt%.

[0023] In a specific embodiment, the mass concentration of the poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) is preferably 1 wt%, 3 wt%, or 5 wt%, with the most preferred being 3 wt%.

[0024] In this embodiment of the application, the step of using an amphiphilic polymer to perform amphiphilic treatment on the pretreated polytetrafluoroethylene microporous separation membrane to obtain a polytetrafluoroethylene microporous separation membrane loaded with an amphiphilic substance specifically includes:

[0025] The pretreated polytetrafluoroethylene microporous separation membrane was immersed in poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) for 2 h to 6 h.

[0026] After draining the residual solution at room temperature, a polytetrafluoroethylene microporous separation membrane loaded with an amphiphilic substance is obtained.

[0027] In a specific embodiment, the treated polytetrafluoroethylene microporous separation membrane is immersed in poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) for a soaking time of 2 h, 4 h, or 6 h, preferably 4 h.

[0028] In the embodiments of this application, in the chemical structure of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), the butyral and vinyl acetate units exhibit hydrophobicity, while the vinyl alcohol units exhibit hydrophilicity. Poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) is loaded onto a polytetrafluoroethylene (PTFE) microporous separation membrane through hydrophobic interactions. This process is essentially the first modification of the PTFE microporous separation membrane.

[0029] Step S105: The polytetrafluoroethylene microporous separation membrane loaded with the amphiphilic polymer is treated with a crosslinking agent to form a crosslinked polytetrafluoroethylene microporous separation membrane.

[0030] In the embodiments of this application, the crosslinking agent is an aqueous solution of glutaraldehyde.

[0031] In this embodiment, the treatment of the polytetrafluoroethylene microporous separation membrane loaded with the amphiphilic polymer using a crosslinking agent to form a crosslinked polytetrafluoroethylene microporous separation membrane specifically includes:

[0032] The polytetrafluoroethylene microporous separation membrane loaded with amphiphilic substances was immersed in an aqueous solution of glutaraldehyde, wherein the mass concentration of glutaraldehyde was 1 wt% to 5 wt%, the immersion time was 8 h to 24 h, and the pH of the aqueous solution of glutaraldehyde was 2.0.

[0033] The residual solution was drained at room temperature to form a cross-linked polytetrafluoroethylene microporous separation membrane.

[0034] In specific embodiments, the concentration of glutaraldehyde is 1 wt%, 3 wt%, or 5 wt%, preferably 3 wt%.

[0035] In a specific embodiment, a polytetrafluoroethylene microporous separation membrane loaded with an amphiphilic substance is immersed in a glutaraldehyde aqueous solution for a soaking time of 8 h, 12 h, or 24 h, preferably 12 h.

[0036] Immersing a polytetrafluoroethylene microporous separation membrane loaded with amphiphilic substances in a glutaraldehyde aqueous solution for 8 to 24 hours can achieve the purpose of hydrolyzing butyral units and releasing hydroxyl groups. Furthermore, the released hydroxyl groups form a cross-linking network with the glutaraldehyde aqueous solution, thus completing the cross-linking.

[0037] Continuing from the previous example, based on the first modification of the polytetrafluoroethylene (PTFE) microporous separation membrane, the membrane was immersed in an acidic aqueous solution of glutaraldehyde. During this process, the butyral units were hydrolyzed and released hydroxyl groups, while the exposed hydroxyl groups reacted with glutaraldehyde to form a cross-linked network. This process constitutes the second modification of the PTFE microporous separation membrane.

[0038] Step S107: The cross-linked polytetrafluoroethylene microporous separation membrane is treated with an alkaline aqueous solution. After soaking, rinsing and drying, the polytetrafluoroethylene microporous separation membrane is modified to obtain a hydrophilic polytetrafluoroethylene microporous separation membrane.

[0039] In this embodiment of the application, the alkaline aqueous solution is a sodium hydroxide aqueous solution, and the pH value of the sodium hydroxide aqueous solution is 13.0.

[0040] In this embodiment, the treatment of the cross-linked polytetrafluoroethylene (PTFE) microporous separation membrane with an alkaline aqueous solution, including soaking, rinsing, and drying, to modify the PTFE microporous separation membrane and obtain a hydrophilic PTFE microporous separation membrane, specifically includes:

[0041] The cross-linked polytetrafluoroethylene microporous separation membrane was immersed in an aqueous sodium hydroxide solution for 4 h to 12 h.

[0042] After rinsing three times with pure water, the membrane was air-dried at room temperature to complete the modification of the polytetrafluoroethylene microporous separation membrane and obtain a hydrophilic polytetrafluoroethylene microporous separation membrane.

[0043] When the cross-linked polytetrafluoroethylene (PTFE) microporous separation membrane is immersed in an aqueous sodium hydroxide solution for 4 to 12 hours, the vinyl acetate units are hydrolyzed and the remaining hydroxyl groups are released. After rinsing and drying, the PTFE microporous separation membrane is modified to obtain a hydrophilic PTFE microporous separation membrane.

[0044] In a specific embodiment, the cross-linked polytetrafluoroethylene microporous separation membrane is immersed in an aqueous sodium hydroxide solution for 4 h, 8 h, or 12 h, preferably 8 h.

[0045] Continuing from the previous example, based on the second modification of the polytetrafluoroethylene microporous separation membrane, the membrane material was treated with an alkaline solution to hydrolyze the vinyl acetate unit and release the remaining hydroxyl groups, thus completing the third modification of the polytetrafluoroethylene microporous separation membrane.

[0046] To further illustrate the present invention, the following detailed description of the hydrophilic modification method for polytetrafluoroethylene microporous separation membrane provided by the present invention is provided in conjunction with embodiments, but these should not be construed as limiting the scope of protection of the present invention.

[0047] Example 1

[0048] The steps of the hydrophilic modification method for the polytetrafluoroethylene microporous separation membrane in this embodiment are as follows:

[0049] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0050] (2) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (1) in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 1 wt% for 4 h, and drain the residual solution at room temperature after completion.

[0051] (3) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (2) in a glutaraldehyde aqueous solution with a mass concentration of 3 wt% and a pH of 2.0 for 12 h. After completion, drain the residual solution at room temperature.

[0052] (4) The polytetrafluoroethylene microporous separation membrane treated in step (3) was immersed in a sodium hydroxide aqueous solution with a pH of 13.0 for 8 hours, then rinsed with pure water 3 times and dried at room temperature to complete the hydrophilic modification.

[0053] Example 2

[0054] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0055] (2) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (1) in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 3 wt% for 4 h, and drain the residual solution at room temperature after completion.

[0056] (3) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (2) in a glutaraldehyde aqueous solution with a mass concentration of 3 wt% and a pH of 2.0 for 12 h. After completion, drain the residual solution at room temperature.

[0057] (4) The polytetrafluoroethylene microporous separation membrane treated in step (3) was immersed in a sodium hydroxide aqueous solution with a pH of 13.0 for 8 hours, then rinsed with pure water 3 times and dried at room temperature to complete the hydrophilic modification.

[0058] Example 3

[0059] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0060] (2) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (1) in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 5 wt% for 4 h, and drain the residual solution at room temperature after completion.

[0061] (3) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (2) in a glutaraldehyde aqueous solution with a mass concentration of 3 wt% and a pH of 2.0 for 12 h. After completion, drain the residual solution at room temperature.

[0062] (4) The polytetrafluoroethylene microporous separation membrane treated in step (3) was immersed in a sodium hydroxide aqueous solution with a pH of 13.0 for 8 hours, then rinsed with pure water 3 times and dried at room temperature to complete the hydrophilic modification.

[0063] As can be seen, the content of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) is different in Examples 1-3. To verify the effect, an unmodified polytetrafluoroethylene (PTFE) microporous membrane was used as Comparative Example 1. The PTFE microporous membranes corresponding to Examples 1-3 and Comparative Example 1 were used as samples for pure water flux testing. The testing method is as follows: Three PTFE microporous membrane materials were placed in a Φ8×250 mm membrane shell, and the ends were sealed with epoxy resin. After curing for 24 h, a membrane filter was obtained. External pressure filtration was used, and the flux was stabilized by filtering at 1 bar for 2 h. Then, the amount of water passing through a unit membrane area per unit time was calculated at a test pressure of 1 bar. The measured pure water flux data are shown in Table 1 (water contact angle and pure water flux results of PTFE microporous membranes corresponding to Examples 1-3 and Comparative Example 1). Each sample was measured three times in parallel according to the above method, and the average value was taken as the final result.

[0064] Table 1

[0065]

[0066] As shown in Table 1, after hydrophilic modification, the water contact angle of the polytetrafluoroethylene microporous separation membrane was significantly reduced compared with the original membrane before modification in Comparative Example 1, the hydrophilicity was significantly improved, and the pure water flux was significantly increased. Among them, the ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 3 wt% showed the best effect (i.e., Example 2).

[0067] Further verification of the wetting effect was conducted. A pure water immersion experiment was performed on the polytetrafluoroethylene microporous separation membranes corresponding to Example 2 and Comparative Example 1: a section of membrane material was placed in pure water, and its wetting condition was observed. The wetting results are shown in [the table below]. Figure 2 .

[0068] Depend on Figure 2 It can be seen that the polytetrafluoroethylene microporous separation membrane corresponding to Example 2 can be completely wetted in pure water. After wetting, the membrane material sinks to the bottom of the water and its appearance is semi-transparent, demonstrating good hydrophilicity. However, the original membrane in Comparative Example 1 before modification cannot be wetted at all. The membrane material floats on the water surface and its appearance is still opaque white.

[0069] Elemental analysis was performed on the cross-section of the polytetrafluoroethylene (PTFE) microporous separation membrane corresponding to Example 2: The PTFE microporous separation membrane material was wetted with pure water, then frozen and fractured with liquid nitrogen to obtain the cross-section; after complete drying, it was sputter-coated with gold for 30 seconds, and then subjected to energy dispersive spectroscopy (EDS). The measured oxygen distribution is shown in the figure. Figure 3 .

[0070] Depend on Figure 3 It can be seen that oxygen is evenly distributed in the cross-section of the polytetrafluoroethylene microporous separation membrane corresponding to Example 2, indicating that the hydrophilic modification is applied to the entire membrane medium and is not limited to the membrane surface.

[0071] To further verify the immersion time of the polytetrafluoroethylene microporous separation membrane in poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), it was immersed in a 3 wt% ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) for 2 h, 4 h and 6 h respectively.

[0072] Example 4

[0073] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0074] (2) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (1) in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 3 wt% for 2 h, and drain the residual solution at room temperature after completion.

[0075] (3) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (2) in a glutaraldehyde aqueous solution with a mass concentration of 3 wt% and a pH of 2.0 for 12 h. After completion, drain the residual solution at room temperature.

[0076] (4) The polytetrafluoroethylene microporous separation membrane treated in step (3) was immersed in a sodium hydroxide aqueous solution with a pH of 13.0 for 8 hours, then rinsed with pure water 3 times and dried at room temperature to complete the hydrophilic modification.

[0077] Example 5

[0078] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0079] (2) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (1) in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 3 wt% for 6 h, and drain the residual solution at room temperature after completion.

[0080] (3) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (2) in a glutaraldehyde aqueous solution with a mass concentration of 3 wt% and a pH of 2.0 for 12 h. After completion, drain the residual solution at room temperature.

[0081] (4) The polytetrafluoroethylene microporous separation membrane treated in step (3) was immersed in a sodium hydroxide aqueous solution with a pH of 13.0 for 8 hours, then rinsed with pure water 3 times and dried at room temperature to complete the hydrophilic modification.

[0082] Examples 2, 4, 5 and Comparative Example 1 were tested, and the test results are shown in Table 2 (the water contact angle and pure water flux of the polytetrafluoroethylene microporous separation membranes corresponding to Examples 2, 4, 5 and Comparative Example 1).

[0083] Table 2

[0084]

[0085] According to Table 2, the optimal soaking time for the polytetrafluoroethylene microporous separation membrane in poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) is 4 hours.

[0086] To further verify the amount of crosslinking agent used, the concentration of glutaraldehyde was verified at 1 wt%, 3 wt%, or 5 wt%.

[0087] Example 6

[0088] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0089] (2) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (1) in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 3 wt% for 4 h, and drain the residual solution at room temperature after completion.

[0090] (3) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (2) in a glutaraldehyde aqueous solution with a mass concentration of 1 wt% and a pH of 2.0 for 12 h, and drain the residual solution at room temperature after completion.

[0091] (4) The polytetrafluoroethylene microporous separation membrane treated in step (3) was immersed in a sodium hydroxide aqueous solution with a pH of 13.0 for 8 hours, then rinsed with pure water 3 times and dried at room temperature to complete the hydrophilic modification.

[0092] Example 7

[0093] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0094] (2) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (1) in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 3 wt% for 4 h, and drain the residual solution at room temperature after completion.

[0095] (3) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (2) in a glutaraldehyde aqueous solution with a mass concentration of 5 wt% and a pH of 2.0 for 12 h, and drain the residual solution at room temperature after completion.

[0096] (4) The polytetrafluoroethylene microporous separation membrane treated in step (3) was immersed in a sodium hydroxide aqueous solution with a pH of 13.0 for 8 hours, then rinsed with pure water 3 times and dried at room temperature to complete the hydrophilic modification.

[0097] Comparative Example 2

[0098] Comparative Example 2 uses the case without treatment with glutaraldehyde aqueous solution and sodium hydroxide aqueous solution. The operation steps are as follows:

[0099] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0100] (2) The polytetrafluoroethylene microporous separation membrane treated in step (1) was immersed in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 3 wt% for 4 h, and then dried at room temperature to complete the modification.

[0101] Examples 2, 6, and 7, and Comparative Examples 1 and 2 were tested, and the test results are shown in Table 3 (the water contact angle and pure water flux of the polytetrafluoroethylene microporous separation membranes corresponding to Examples 2, 6, and 7, and Comparative Examples 1 and 2).

[0102] Table 3

[0103]

[0104] As shown in Table 3, treatment with glutaraldehyde aqueous solution can enhance the hydrophilicity of the corresponding membrane material. The effect of Example 7 is not significantly different from that of Example 2. Considering the need for cost-effectiveness, the concentration of glutaraldehyde aqueous solution is optimal at 3 wt% in this application.

[0105] To further verify the soaking time of glutaraldehyde aqueous solution, different soaking times were set, including 8h, 12h and 24h.

[0106] Example 8

[0107] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0108] (2) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (1) in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 3 wt% for 4 h, and drain the residual solution at room temperature after completion.

[0109] (3) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (2) in a glutaraldehyde aqueous solution with a mass concentration of 3 wt% and a pH of 2.0 for 8 h, and drain the residual solution at room temperature after completion.

[0110] (4) The polytetrafluoroethylene microporous separation membrane treated in step (3) was immersed in a sodium hydroxide aqueous solution with a pH of 13.0 for 8 hours, then rinsed with pure water 3 times and dried at room temperature to complete the hydrophilic modification.

[0111] Example 9

[0112] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0113] (2) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (1) in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 3 wt% for 4 h, and drain the residual solution at room temperature after completion.

[0114] (3) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (2) in a glutaraldehyde aqueous solution with a mass concentration of 3 wt% and a pH of 2.0 for 24 h. After completion, drain the residual solution at room temperature.

[0115] (4) The polytetrafluoroethylene microporous separation membrane treated in step (3) was immersed in a sodium hydroxide aqueous solution with a pH of 13.0 for 8 hours, then rinsed with pure water 3 times and dried at room temperature to complete the hydrophilic modification.

[0116] Examples 2, 8, and 9, and Comparative Examples 1 and 2 were tested, and the test results are shown in Table 4 (the water contact angle and pure water flux of the polytetrafluoroethylene microporous separation membranes corresponding to Examples 2, 8, and 9, and Comparative Examples 1 and 2).

[0117] Table 4

[0118]

[0119] As shown in Table 4, the optimal soaking time is 12 hours, and the membrane effect is not improved by extending the soaking time.

[0120] To further verify the effect of immersing the cross-linked polytetrafluoroethylene microporous separation membrane in an alkaline aqueous solution, the following comparative example 3 was set up.

[0121] Comparative Example 3

[0122] Comparative Example 3 uses the case without sodium hydroxide aqueous solution treatment. The operation steps are as follows:

[0123] (1) Soak the polytetrafluoroethylene microporous separation membrane in ethanol for 2 h to wash out impurities on the membrane surface and in the membrane pores;

[0124] (2) Immerse the polytetrafluoroethylene microporous separation membrane treated in step (1) in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) with a mass concentration of 3 wt% for 4 h, and drain the residual solution at room temperature after completion.

[0125] (3) The polytetrafluoroethylene microporous separation membrane treated in step (2) was immersed in a glutaraldehyde aqueous solution with a mass concentration of 3 wt% and a pH of 2.0 for 12 h, then rinsed with pure water 3 times and dried at room temperature to complete the modification.

[0126] The polytetrafluoroethylene microporous separation membranes corresponding to Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3 were used as samples for water contact angle testing. The results are shown in Table 5 (Water contact angle and pure water flux results of the polytetrafluoroethylene microporous separation membranes corresponding to Example 2, Comparative Example 1, Comparative Example 2, and Comparative Example 3).

[0127] Table 5

[0128]

[0129] As shown in Table 5, compared with the original membrane before modification in Comparative Example 1, the membrane prepared in Comparative Example 2 without treatment with glutaraldehyde aqueous solution and sodium hydroxide aqueous solution, and the membrane in Comparative Example 3 without treatment with sodium hydroxide aqueous solution, the water contact angle of the polytetrafluoroethylene microporous separation membrane was significantly reduced and the hydrophilicity was significantly improved after hydrophilic modification. It should be noted that although the membrane material in Comparative Example 2 was loaded with the amphiphilic polymer poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), the amphiphilic polymer was quickly lost under the scouring of water flow, and the stable pure water flux was only slightly higher than that of the original membrane before modification; compared with Example 2, Comparative Example 3 was not treated with sodium hydroxide aqueous solution, and the hydroxyl groups were not completely released, so the hydrophilicity of the corresponding membrane material was not as good as that of Example 2, and therefore the water flux was also lower.

[0130] This application provides a method for hydrophilic modification of a polytetrafluoroethylene (PTFE) microporous separation membrane. By loading an amphiphilic polymer, poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), onto the PTFE microporous separation membrane, and sequentially performing acidic hydrolysis / crosslinking and alkaline hydrolysis, a hydrophilic network is constructed that interpenetrates and intersperses with the PTFE membrane fibrils and nodes. This overcomes the drawbacks of existing technologies, such as damage to the intrinsic membrane structure and easy loss of hydrophilic agents. Compared to the original membrane, the modified PTFE microporous separation membrane exhibits a significantly reduced water contact angle and a significantly increased pure water flux. The technical solution proposed in this invention involves only immersion treatment, requires no complex equipment, and is simple to operate; it does not involve hazardous chemicals, and the modified solution can be reused multiple times, resulting in low cost and environmental friendliness.

[0131] The above description is merely a preferred embodiment of the present invention and is not intended to limit the implementation. It should be noted that those skilled in the art can make other variations or modifications without departing from the principles of the present invention, and any obvious variations or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A method for hydrophilic modification of a polytetrafluoroethylene microporous separation membrane, characterized by, The modification method includes: Impurities are removed from the polytetrafluoroethylene microporous separation membrane to be treated to obtain a pretreated polytetrafluoroethylene microporous separation membrane. The pretreated polytetrafluoroethylene (PTFE) microporous separation membrane is treated with an amphiphilic polymer to obtain a PTFE microporous separation membrane loaded with the amphiphilic polymer. Specifically, the amphiphilic polymer is poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate). The pretreated PTFE microporous separation membrane is immersed in an ethanol solution of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate), where the mass concentration of poly(vinyl butyral-co-vinyl alcohol-co-vinyl acetate) is 1 wt% to 5 wt%, and the immersion time is 2 h to 6 h. The membrane is then drained of the residual solution at room temperature to obtain the PTFE microporous separation membrane loaded with the amphiphilic polymer. The polytetrafluoroethylene microporous separation membrane loaded with the amphiphilic polymer is treated with a crosslinking agent to form a crosslinked polytetrafluoroethylene microporous separation membrane, wherein the crosslinking agent is glutaraldehyde. The cross-linked polytetrafluoroethylene (PTFE) microporous separation membrane is treated with an alkaline aqueous solution by soaking, rinsing, and drying to modify the PTFE microporous separation membrane and obtain a hydrophilic PTFE microporous separation membrane. The alkaline aqueous solution is a sodium hydroxide aqueous solution.

2. The modification method of claim 1, wherein, The process of treating the polytetrafluoroethylene microporous separation membrane loaded with the amphiphilic polymer using a crosslinking agent to form a crosslinked polytetrafluoroethylene microporous separation membrane specifically includes: The polytetrafluoroethylene microporous separation membrane loaded with amphiphilic substances was immersed in an aqueous solution of glutaraldehyde, wherein the mass concentration of glutaraldehyde was 1 wt% to 5 wt%, the immersion time was 8 h to 24 h, and the pH of the aqueous solution of glutaraldehyde was 2.

0. The residual solution was drained at room temperature to form a cross-linked polytetrafluoroethylene microporous separation membrane.

3. The modification method of claim 1, wherein, The pH value of the sodium hydroxide aqueous solution is 13.

0.

4. The modification method of claim 1, wherein The process involves treating the cross-linked polytetrafluoroethylene (PTFE) microporous membrane with an alkaline aqueous solution, followed by soaking, rinsing, and drying to modify the PTFE microporous membrane and obtain a hydrophilic PTFE microporous membrane. Specifically, this includes: The cross-linked polytetrafluoroethylene microporous separation membrane was immersed in an aqueous sodium hydroxide solution for 4 h to 12 h. After rinsing three times with pure water, the membrane was air-dried at room temperature to complete the modification of the polytetrafluoroethylene microporous separation membrane and obtain a hydrophilic polytetrafluoroethylene microporous separation membrane.

5. The modification method of claim 1, wherein The process of removing impurities from the polytetrafluoroethylene (PTFE) microporous separation membrane to obtain a pretreated PTFE microporous separation membrane specifically includes: The polytetrafluoroethylene microporous separation membrane to be treated was immersed in ethanol for 2 hours to wash out impurities on the surface and in the pores of the polytetrafluoroethylene microporous separation membrane to be treated, thereby obtaining a pretreated polytetrafluoroethylene microporous separation membrane.

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