Hydrophilic modification method of PTFE microporous membrane

Abstract

The invention discloses a hydrophilic modification method of a PTFE microporous membrane, which comprises the following steps: (1) vacuum plasma treatment: placing a PTFE membrane in a vacuum plasma reaction chamber, and carrying out double-sided treatment; (2) monomer grafting: immersing the membrane subjected to plasma treatment into a perfluorosulfonyl fluoride monomer solution for heat treatment; and (3) post-treatment: taking out the membrane, sequentially washing the membrane with a solvent, soaking the membrane in a KOH solution, washing the membrane with deionized water, soaking the membrane in an HCl solution again, finally washing the membrane with deionized water, and drying the membrane to obtain the hydrophilic modified PTFE membrane. Free radicals are generated on the surface of PTFE through plasma activation, efficient grafting of perfluorosulfonyl fluoride monomers is achieved, and the contact angle of the PTFE membrane can be reduced to 100 degrees from 140 degrees. The PTFE membrane prepared by the method is lasting in modification effect and excellent in chemical resistance, and the technical problem of poor hydrophilicity of the PTFE membrane is solved.

Description

Technical Field

[0001] This invention belongs to the field of PTFE membrane material surface modification technology, specifically involving a method for achieving long-lasting hydrophilic modification of PTFE microporous membranes through plasma activation and in-situ grafting of perfluorinated monomers. This method is suitable for improving the liquid permeability and durability of PTFE membranes in applications such as filtration and separation, and is especially suitable for filtering highly corrosive fluids (such as concentrated sulfuric acid and hydrogen peroxide mixtures, SPM solutions). Background Technology

[0002] PTFE microporous membranes possess excellent chemical stability, corrosion resistance, and thermal stability, making them widely used in water treatment, biomedicine, and microelectronics. However, PTFE's low surface energy and strong hydrophobicity (water contact angle exceeding 130°) result in poor fluid permeability and high filtration pressure drop, limiting its applications. While existing technologies have improved hydrophilicity through modification, shortcomings remain. CN105885081B discloses a plasma treatment modification strategy to improve membrane hydrophilicity, but this method still carries the risk of short-lived modification effects and degradation over time. EP3130394B1 discloses a modification strategy involving coating a PTFE substrate with a perfluorosulfonic acid (PFSA) polymer. This achieves physical adhesion of PFSA to the PTFE surface through low-temperature curing of the coating. However, this method significantly reduces membrane flux, and the low physical adsorption force makes PFSA prone to detachment, potentially contaminating subsequent fluids. CN105315479A discloses a method for modifying PTFE using a sodium naphthalene treatment solution. However, this method damages the mechanical properties of PTFE and has poor environmental friendliness, making it particularly unsuitable for modifying PTFE microporous membranes with low mechanical strength. US7611629B2 discloses a UV treatment strategy, but this method suffers from poor modification results. CN104998562B discloses a strategy of grafting acrylic monomers onto the PTFE surface and combining it with titanium dioxide self-assembly technology to improve the hydrophilicity of the membrane. However, the grafted monomers in this method have the disadvantage of being susceptible to strong acid and corrosion environments, limiting its application in the filtration of highly corrosive fluids. Therefore, there is a need to develop a hydrophilic modification method for PTFE microporous membranes that combines durability, strong adhesion, environmental friendliness, and resistance to strong acid and corrosion environments. Summary of the Invention

[0003] The purpose of this invention is to provide a method for hydrophilic modification of PTFE microporous membranes, so as to solve the problems of short-lasting hydrophilicity, poor environmental performance and poor resistance to strong acid and strong corrosion environments in the prior art.

[0004] To achieve the above-mentioned objectives, the technical solution of the present invention is as follows:

[0005] A method for hydrophilic modification of PTFE microporous membranes, the specific steps of which are as follows:

[0006] (1) Vacuum plasma treatment: The PTFE membrane is placed in the vacuum plasma reaction chamber and treated on both sides;

[0007] (2) Monomer grafting: The plasma-treated membrane is immersed in a perfluorosulfonyl fluoride monomer solution for heat treatment;

[0008] (3) Post-processing: Take out the membrane, rinse it with solvent in sequence, then soak it in KOH solution, rinse it with deionized water, and then soak it in HCl solution again. Finally, rinse it with deionized water and dry it to obtain hydrophilic modified PTFE membrane.

[0009] Preferably, in step (1), the atmosphere is selected from at least one of air, nitrogen, oxygen, argon, ammonia or helium, preferably argon or helium, and the gas flow rate is 30-250 mL / min.

[0010] Preferably, in step (1), the vacuum plasma reaction apparatus can be purchased through commercial channels, such as Dongguan Shengding Precision Instruments Co., Ltd.

[0011] Preferably, in step (1), the power of the vacuum plasma reaction chamber is 50-300W.

[0012] Preferably, in step (1), the processing time of the vacuum plasma reaction chamber is 10s-30min, more preferably 1-10min.

[0013] Preferably, in step (2), the perfluorosulfonyl fluoride monomer is perfluoro(4-methyl-3,6-dioxa-7-octene)sulfonyl fluoride (CAS: 16090-14-5), the concentration of the perfluorosulfonyl fluoride monomer solution is 1%-95wt%, preferably 10%-60wt%, and the solvent is perfluorotributylamine or perfluorotripropylamine.

[0014] Preferably, in step (2), the heat treatment is carried out under oxygen-isolated conditions, the heat treatment temperature is 40-120℃, preferably 80-110℃, and the heat treatment time is 1-24h, preferably 10-24h.

[0015] Preferably, in step (3), the rinsing solvent is selected from one or more of perfluorotributylamine solution, methanol solution and deionized water.

[0016] Preferably, in step (3), the concentration of the KOH solution is 1-20 wt%, and the soaking time in the KOH solution is 2-6 h; the concentration of the HCl solution is 5-20 wt%, and the soaking time in the HCl solution is 1-4 h.

[0017] Preferably, in step (3), the final rinsing time with deionized water is 10-40 min, the drying temperature is 40-80℃, and the drying time is 0.5-10 h.

[0018] The beneficial effects of this invention are that, through the synergistic effect of vacuum plasma pretreatment, perfluorosulfonyl fluoride monomer grafting, alkaline hydrolysis, and acid activation, the comprehensive performance of PTFE membranes is significantly improved: after plasma activation, the membrane surface is bonded with perfluorosulfonyl fluoride monomers through heat treatment, and stable hydrophilic sulfonic acid groups are introduced after acid and alkali treatment, reducing the water contact angle to 100° and maintaining the hydrophilic effect for a long time; at the same time, it has excellent acid resistance and can remain stable for a long time in strong acid and strong corrosion environments; the process is both environmentally friendly and economical, and is suitable for subsequent industrial scale-up production; in addition, this method is universally applicable to various types of PTFE microporous membranes. Attached Figure Description

[0019] Figure 1 This is a technical roadmap for the present invention.

[0020] Figure 2 This is a graph showing the flux change trend of the modified and unmodified samples after the dehumidification resistance test in this invention.

[0021] Figure 3 This is a graph showing the trend of contact angle changes during long-term monitoring of different samples in this invention. Detailed Implementation

[0022] To facilitate understanding of the present invention, the following description, in conjunction with embodiments, will further illustrate the invention. It should be understood that the following embodiments are merely for a better understanding of the invention and do not imply that the invention is limited to these embodiments.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items. Locational terms such as top and bottom, mentioned or possibly used in this specification, are defined relative to the constructions shown in the accompanying drawings; they are relative concepts and may therefore vary depending on their location and usage.

[0024] Main raw material sources

[0025] PTFE microporous membrane: purchased from Gore, GMM600 microporous membrane, average pore size 30nm, thickness 15μm;

[0026] Perfluorosulfonyl fluoride monomer: purchased from Shanghai Titan Technology Co., Ltd. (Adamas), full name perfluoro(4-methyl-3,6-dioxa-7-octene)sulfonyl fluoride (CAS: 16090-14-5), purity ≥98%, structural formula as follows:

[0027]

[0028] Perfluorotributylamine: Purity ≥ 95% (Beijing Inokai Technology Co., Ltd.);

[0029] Perfluorotripropylamine: Purity ≥ 95% (Beijing Inokai Technology Co., Ltd.)

[0030] All other conventional raw materials used in this invention can be purchased from reagent companies such as Aladdin and Inokai.

[0031] Main testing methods

[0032] Contact angle test: After the membrane is dried, it is placed on a clean glass slide, flattened, and the water contact angle is measured using a contact angle meter with a water droplet volume of 4 μL.

[0033] Flux test: The membrane was placed in the vacuum filtration device and fixed. After pre-wetting with ethanol, the time t for 100 mL of pure water to pass through the membrane was measured under a negative pressure of 20 kPa. The effective area of ​​the membrane was S, and the flux Q = 100 / (t·S).

[0034] Acid resistance test: 96% concentrated sulfuric acid and 10% hydrogen peroxide solution were mixed at a volume ratio of 4:1 to obtain SPM solution. The prepared sample was immersed in SPM solution for 16 hours. After rinsing with deionized water and drying in an oven, the contact angle and flux were tested.

[0035] Dehumidification resistance test: The membrane was placed and fixed in a vacuum filtration device, pre-wetted with ethanol, and under a negative pressure of 20 kPa, the time t for 50 mL of pure water to pass through the membrane was measured. The effective area of ​​the membrane was S. The membrane flux under wetted conditions was Q0 = 50 /

[0036] (t·S); then evacuate for 2 minutes, add 50 mL of pure water again, and measure the water flux Q1; repeat this step, and perform a total of 5 dehumidification experiments; by measuring the water flux after different dehumidification times and comparing it with the water flux of the first time, the percentage decrease in flux after each dehumidification can be calculated.

[0037] Example

[0038] Example 1:

[0039] PTFE microporous membranes with a diameter of 70 mm were cut, fixed with an annular gasket, and placed in a plasma reaction chamber for vacuum plasma treatment. The treatment atmosphere was argon, power 300 W, time 5 min, gas flow rate 150 mL / min, frequency 13.56 MHz, and double-sided treatment was performed. A 50% (w / w) solution of perfluorosulfonyl fluoride monomer (solvent: perfluorotributylamine) was prepared. The plasma-treated membrane was immersed in the above solution, isolated from oxygen, and then heat-treated in a 100℃ oven for 10 h. It was then rinsed sequentially with perfluorotributylamine, methanol, and deionized water for 10 min each, then immersed in a 10 wt% KOH solution for 3 h, rinsed with deionized water, and then immersed again in a 10 wt% HCl solution for 3 h. Finally, it was rinsed with deionized water for 30 min and dried in a 60℃ oven for 1 h.

[0040] Example 2:

[0041] PTFE microporous membranes with a diameter of 70 mm were cut, fixed with an annular gasket, and placed in a plasma reaction chamber for vacuum plasma treatment. The treatment atmosphere was air, power 200 W, time 10 min, gas flow rate 75 mL / min, frequency 40 kHz, and double-sided treatment was performed. A 20% (w / w) solution of perfluorosulfonyl fluoride monomer (solvent: perfluorotributylamine) was prepared. The plasma-treated membrane was immersed in the above solution, isolated from oxygen, and then heat-treated in an oven at 110 °C for 16 h. It was then rinsed sequentially with perfluorotributylamine, methanol, and deionized water for 10 min each, then immersed in 10 wt% KOH solution for 3 h, rinsed with deionized water, and then immersed again in 10% HCl solution for 3 h. Finally, it was rinsed with deionized water for 30 min and dried in an oven at 60 °C for 1 h.

[0042] Example 3:

[0043] The atmosphere was adjusted to helium, the plasma power was 200W, the processing time was 10min, the gas flow rate was 100mL / min, and the rest was the same as in Example 1.

[0044] Example 4:

[0045] The plasma power was adjusted to 50W, the treatment time to 10min, the gas flow rate to 30mL / min, and the concentration of the perfluorosulfonyl fluoride monomer solution to 30%. The rest was the same as in Example 1.

[0046] Example 5:

[0047] The concentration of the perfluorosulfonyl fluoride monomer solution was adjusted to 10%, the heat treatment temperature was 60°C, and the heat treatment time was 16 hours. The rest was the same as in Example 1.

[0048] Example 6:

[0049] The concentration of the perfluorosulfonyl fluoride monomer solution was adjusted to 60%, the heat treatment temperature was 80°C, and the heat treatment time was 24 hours. The rest was the same as in Example 1.

[0050] Comparative Example

[0051] Comparative Example 1: Plasma treatment only; the specific steps are as follows: cut a PTFE microporous membrane with a diameter of 70 mm, fix it with a circular gasket, and place it in the plasma reaction chamber for vacuum plasma treatment. The treatment atmosphere is argon, the power is 300 W, the time is 5 min, the gas flow rate is 150 mL / min, the frequency is 13.56 MHz, and the treatment is performed on both sides.

[0052] Comparative Example 2: Without plasma treatment, the membrane was directly immersed in a monomer solution followed by heat treatment. The specific steps were as follows: a 70mm diameter PTFE microporous membrane was cut and fixed with a circular gasket; a 50% perfluorosulfonyl fluoride monomer solution (using perfluorotributylamine as the solvent) was prepared; the fixed membrane was immersed in the solution; after isolating it from oxygen, it was heat-treated in a 100℃ oven for 10 hours. It was then rinsed sequentially with 100% perfluorotributylamine solution, 100% methanol solution, and deionized water for 10 minutes each; then immersed in 10% KOH solution for 3 hours; rinsed with deionized water; and then immersed again in 10% HCl solution for 3 hours. Finally, it was rinsed with deionized water for 30 minutes and dried in a 60℃ oven for 1 hour.

[0053] Comparative Example 3: Activation without acid / alkali treatment; the specific steps were as follows: a 70mm diameter PTFE microporous membrane was cut, fixed with a circular gasket, and placed in a plasma reaction chamber for vacuum plasma treatment. The treatment atmosphere was argon, power 300W, time 5min, gas flow rate 150mL / min, frequency 13.56MHz, and double-sided treatment was performed. A 50% (w / w) perfluorosulfonyl fluoride monomer solution (solvent: perfluorotributylamine) was prepared. The plasma-treated membrane was immersed in the above solution, isolated from oxygen, and then heat-treated in a 100℃ oven for 10h. It was then rinsed sequentially with 100% perfluorotributylamine solution and 100% methanol solution for 10min each, and finally rinsed with deionized water for 30min, and dried in a 60℃ oven for 1h.

[0054] Comparative Example 4: Grafting monomers intolerant to SPM corrosion; the specific steps were as follows: 70mm diameter PTFE microporous membranes were cut, fixed with an annular gasket, and placed in a plasma reaction chamber for vacuum plasma treatment. The treatment atmosphere was argon, power 300W, time 5min, gas flow rate 150mL / min, frequency 13.56MHz, and double-sided treatment was performed. A 50% (w / w) aqueous solution of acrylic monomer was prepared, and the plasma-treated membrane was immersed in the solution. After isolating it from oxygen, it was heat-treated in an 80℃ oven for 10h. Finally, it was rinsed with deionized water for 30min and dried in a 60℃ oven for 1h.

[0055] Comparative Example 5: Untreated PTFE base film.

[0056] The products obtained in the examples and comparative examples were tested.

[0057] The test results are shown in Table 1:

[0058] Table 1: Evaluation Results

[0059]

[0060] As shown in Table 1, the contact angle of the hydrophilic modified PTFE membrane prepared in this invention can be reduced from 140° to 100°, and the pure water flux is increased by 9% compared with the base membrane. Moreover, it can still maintain good performance and meet the filtration requirements after being soaked in a highly corrosive SPM solution for 16 hours. It can be seen from Comparative Example 1 and Example 1 that the membrane modification effect of plasma treatment alone is slightly poor, and the flux improvement is limited. According to Comparative Example 2, no modification effect can be achieved without plasma treatment, indicating that plasma treatment is a key step in opening the CF bond, otherwise subsequent grafting cannot be carried out. According to Comparative Example 3, without acid and alkali activation, the hydrophilicity of the modified membrane is limited, and the water contact angle is still relatively high. After SPM treatment, the hydrophilicity and flux are slightly improved due to the generation of some sulfonic acid groups. According to Comparative Example 4, the hydrophilicity of the membrane is significantly improved after grafting polyacrylic acid. However, polyacrylic acid is not resistant to strong oxidizing and corrosive solutions. After SPM treatment, the hydrophilic groups are destroyed, and the hydrophilicity drops sharply, resulting in poor hydrophilic modification effect. In addition, anti-dehumidification experiments were conducted on Example 1 and Comparative Example 5, such as... Figure 2 As shown, the unmodified base membrane exhibits poor resistance to dehumidification. With each dehumidification cycle, the flux decreases more significantly, reaching a 70% reduction after the fifth dehumidification treatment. This indicates that the membrane pores are largely filled with gas, leading to flux loss. In contrast, in Example 1, the flux remained almost unchanged throughout the dehumidification resistance test, demonstrating excellent hydrophilicity and resistance to dehumidification.

[0061] Finally, long-term testing was conducted on Example 1 and Comparative Example 1. Specifically, the two types of membranes were placed at room temperature and atmospheric pressure for six months, and the changes in contact angle at different time points were measured. The experimental results are as follows: Figure 3 As shown, over time, only the plasma-treated sample (Comparative Example 1) exhibited a slow rebound in contact angle, increasing from an initial 129° to 134° after six months. This is because the spontaneous rotation of the PTFE chains buries the surface polar groups internally, re-exposing the CF bonds to the outside, resulting in a decrease in the proportion of hydrophilic groups on the membrane surface. In contrast, the contact angle of Example 1 remained stable throughout the process, indicating that the steric hindrance effect after monomer grafting ensures that the hydrophilic groups are always on one side of the membrane surface, thus guaranteeing a more durable hydrophilic modification effect.

[0062] It is readily understood that the above embodiments are merely illustrative examples for clear explanation and do not imply that the invention is limited thereto. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for hydrophilic modification of a PTFE microporous membrane, characterized by, The method comprises the following steps: (1) vacuum plasma treatment: PTFE film is placed in a vacuum plasma reaction chamber and treated on both sides; (2) monomer grafting: the film treated by plasma is immersed in a perfluorosulfonyl fluoride monomer solution and subjected to heat treatment; (3) post-treatment: the film is taken out, washed with a solvent, immersed in a KOH solution, washed with deionized water, then immersed in an HCl solution, finally washed with deionized water and dried to obtain a hydrophilic modified PTFE film.

2. The hydrophilic modification method according to claim 1, wherein In step (1), the atmosphere is at least one selected from air, nitrogen, oxygen, argon, ammonia or helium, preferably argon or helium, and the gas flow rate is 30-250 mL / min.

3. The hydrophilic modification method according to claim 1 or 2, wherein In step (1), the power of the vacuum plasma reaction chamber treatment is 50-300 W; and / or, the time of the vacuum plasma reaction chamber treatment is 10 s-30 min, preferably 1-10 min.

4. The hydrophilic modification method according to any one of claims 1 to 3, wherein In step (2), the perfluorosulfonyl fluoride monomer is perfluoro(4-methyl-3,6-dioxa-7-octene)sulfonyl fluoride (CAS: 16090-14-5), the concentration of the perfluorosulfonyl fluoride monomer solution is 1%-95wt%, preferably 10%-60wt%, and the solvent is perfluorotributylamine or perfluorotripropylamine.

5. The hydrophilic modification method according to any one of claims 1 to 4, wherein In step (2), the heat treatment is carried out in an oxygen-free condition, the heat treatment temperature is 40-120℃, preferably 80-110℃, and the heat treatment time is 1-24 h, preferably 10-24 h.

6. The hydrophilic modification method according to any one of claims 1 to 5, wherein In step (3), the washing solvent is selected from one or more of perfluorotributylamine solution, methanol solution and deionized water.

7. The hydrophilic modification method according to any one of claims 1 to 6, wherein In step (3), the concentration of the KOH solution is 1-20wt%, and the time of immersion in the KOH solution is 2-6 h; the concentration of the HCl solution is 5-20wt%, and the time of immersion in the HCl solution is 1-4 h.

8. The hydrophilic modification method according to any one of claims 1 to 7, wherein In step (3), the time of washing with deionized water is 10-40 min, the drying temperature is 40-80℃, and the drying time is 0.5-10 h.

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