A method for modifying a fluoropolymer film

Abstract

This invention discloses a method for modifying fluoropolymer membranes, belonging to the field of membrane separation technology. The method includes the following steps: (1) wetting the fluoropolymer membrane with a low surface energy liquid; (2) transferring the wetted fluoropolymer membrane to pure water for immersion; (3) transferring the immersed fluoropolymer membrane to a container containing a photosensitizer and irradiating it with ultraviolet light; (4) transferring the irradiated fluoropolymer membrane to pure water for rinsing. This invention, through the synergistic effect of ultraviolet irradiation and photosensitizer, can significantly improve the membrane's resistance to desiccation and chemical stability, and also enhance the fluoropolymer membrane's retention effect on particulate matter, without damaging the membrane's skeletal structure and mechanical properties. This method is simple, low-cost, environmentally friendly, and easy to implement in continuous production, making it suitable for filtration applications of strong acids, strong alkalis, and strong oxidizing liquids in industries such as semiconductors and microelectronics.

Description

Technical Field

[0001] This invention relates to the field of polymer film surface modification technology, and specifically to a method for modifying fluoropolymer films. Background Technology

[0002] Fluoropolymer membranes are widely used in liquid filtration, gas separation, and membrane distillation due to their excellent chemical stability, high-temperature resistance, and mechanical strength. Among them, polytetrafluoroethylene (PTFE) microporous membranes are particularly important in filtration applications in the semiconductor, pharmaceutical, and fine chemical industries due to their excellent chemical corrosion resistance and thermal stability. However, PTFE and other fluoropolymer membranes have extremely strong hydrophobicity. While this characteristic is advantageous in some applications, it becomes a major obstacle limiting their application in aqueous liquid filtration. During filtration, due to the pressure difference between the upstream and downstream of the membrane, gases dissolved in the filtrate gradually escape and grow, forming gas nuclei that adhere to the membrane's pore structure. As these gas nuclei grow, the pore structure can become completely blocked, preventing the filtrate from passing through and reducing the overall flux of the membrane—a phenomenon known as dehumidification. Therefore, it is necessary to modify fluoropolymer membranes to improve their resistance to dehumidification. Currently, methods for improving the dehumidification resistance of fluoropolymer membranes mainly fall into two categories: physical modification and chemical modification. Physical modification methods mainly involve coating the surface of a fluoropolymer film with hydrophilic monomers or polymers, and then using methods such as heating or light irradiation to physically entangle the hydrophilic molecular chains on the surface or within the pores of the fluoropolymer film, increasing the adhesion between the hydrophilic coating and the fluoropolymer film. Chemical modification methods mainly include plasma treatment, high-energy irradiation, and immersion in strongly oxidizing liquids. CN1147350C discloses a surface-modified porous membrane and its manufacturing method. This method involves contacting a porous membrane matrix with a perfluorinated carbon copolymer component, so that the membrane surface is completely modified by the perfluorinated carbon copolymer while maintaining the membrane's permeability essentially unchanged. CN1159091C provides a method for preparing a surface-modified porous membrane using a perfluorinated carbon copolymer. This method includes contacting a porous membrane matrix with a solution containing a perfluorinated carbon copolymer composition, allowing the composition to bind to the matrix surface, then applying mechanical force to remove excess composition and performing heat treatment.

[0003] Secondly, the retention mechanism of fluoropolymer membranes for particulate matter in filtrate mainly consists of pore sieving and adsorption retention. Pore sieving primarily relies on the physical size and tortuosity of the internal pores of the membrane, while adsorption retention mainly relies on the interaction force between the membrane and the particulate matter. By coating or grafting new functional groups onto the surface of the fluoropolymer through anti-wetting modification methods, the zeta potential of the membrane can be altered, thereby increasing the interaction force between the membrane and the particulate matter and improving the membrane's particulate matter retention performance.

[0004] However, existing modification methods have many problems. First, the hydrophilicity of existing hydrophilic modification methods is easily degraded after cleaning with high-concentration acids, alkalis, or oxidants. In the semiconductor industry, most liquid chemicals possess one or more of the following properties: strong acid, strong alkali, and strong oxidizing agent. Examples include SC-1 cleaning solution (composed of ammonia, hydrogen peroxide, and water), SC-2 cleaning solution (composed of hydrochloric acid, hydrogen peroxide, and water), SPM solution (composed of sulfuric acid, hydrogen peroxide, and water), hydrofluoric acid, sulfuric acid, phosphoric acid, and hydrogen peroxide. This requires not only excellent acid and alkali resistance, oxidation resistance, and corrosion resistance of the film itself, but also extremely high stability of the modified groups. If the modified groups react and detach during filtration, it will cause serious contamination. Common hydrophilic groups such as hydroxyl and carboxyl groups are difficult to withstand harsh conditions; for example, they undergo dehydration and cross-linking reactions in 96% sulfuric acid, and the grafted hydrophilic groups detach in SC-1 cleaning solution. CN113230910B discloses a method for improving the desiccation resistance of polytetrafluoroethylene (PTFE) microporous membranes using gamma ray irradiation. While this method can reduce the F / C ratio of the PTFE membrane and introduce oxygen atoms to increase hydrophilicity, it fails to address the stability issue under harsh chemical environments. CN105536556A discloses an oleophobic separation membrane by modifying the porous base membrane surface with a coating rich in perfluoroalkyl compounds to improve the membrane's oleophobic properties and antifouling performance. However, this method also fails to solve the balance problem between hydrophilicity and chemical stability. Furthermore, the strength of CF bonds is much higher than that of CC bonds. Plasma technology and high-energy ray irradiation can break CF bonds to graft hydrophilic groups, but they also break CC bonds, damaging the skeletal structure of fluoropolymer films and reducing mechanical properties. Therefore, there is an urgent need to develop a modification method that can stably introduce hydrophilic groups onto the surface of fluoropolymer films, possess excellent desiccation resistance, and not affect the strength of the film's skeletal structure. Summary of the Invention

[0005] To address the limitations of fluoropolymer membranes in the field of aqueous liquid filtration, as well as the technical problems of existing modification methods such as high cost, damage to membrane mechanical properties, and poor chemical stability, this invention provides a method for modifying fluoropolymer membranes to improve their desiccation resistance, retention performance, and chemical stability.

[0006] The technical solution adopted by the present invention to solve the above-mentioned technical problems is as follows:

[0007] A method for modifying a fluoropolymer film includes the following steps:

[0008] (1) Wet the fluoropolymer film with a low surface energy liquid;

[0009] (2) Transfer the moistened fluoropolymer film to pure water for immersion;

[0010] (3) Transfer the fluoropolymer film soaked in pure water to a container containing a photosensitizer and irradiate it with ultraviolet light;

[0011] (4) Transfer the fluorinated polymer film after irradiation with ultraviolet light to pure water for immersion and cleaning.

[0012] In the preparation method of the present invention, the fluoropolymer in the fluoropolymer film includes one or more of polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer (PFA), fluorinated ethylene propylene copolymer (FEP), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-trifluorochloroethylene copolymer (ECTFE), and polytrifluorochloroethylene (PCTFE).

[0013] Preferably, the thickness of the fluoropolymer film is 5-200 μm, for example, it can be a range of 5, 10, 30, 50, 70, 90, 100, 120, 150, 180, 200 μm or any combination thereof, preferably 10-100 μm, more preferably 10-50 μm; the pore size of the fluoropolymer film is 1-200 nm, for example, it can be a range of 5, 35, 40, 55, 80, 90, 100, 120, 150, 170, 180 nm or any combination thereof, preferably 10-50 nm.

[0014] The low surface energy liquid in step (1) includes one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, tert-butanol, acetone, butanone, tetrahydrofuran, and dioxane, preferably at least one of ethanol, isopropanol, and n-butanol.

[0015] In step (1), a low surface energy liquid is used to wet the fluoropolymer film for a wetting time of 0.1-120 min, for example, a range of 2, 3, 5, 10, 30, 40, 60, 70, 80, 90, 100, 110 min or any combination thereof, preferably a wetting time of 5-30 min.

[0016] In step (2), the wetted fluoropolymer film is immersed in pure water for 0.1-120 min, for example, it can be a range of 2, 3, 5, 10, 30, 40, 60, 70, 80, 90, 100, 110 min or any combination thereof, preferably the immersion time is 5-30 min.

[0017] The photosensitizer in step (3) comprises one or more of potassium iodide, sodium iodide, sodium sulfite, potassium sulfite, potassium bisulfite, sodium bisulfite, potassium ferrocyanide, sodium sulfide, potassium sulfide, sodium phenolate, potassium phenolate, triethylamine, tryptophan, tyrosine, dimethyl sulfide, titanium dioxide, and zinc oxide; preferably, the photosensitizer is selected from at least one of potassium iodide, sodium sulfite, and sodium bisulfite.

[0018] Preferably, the photosensitizer-containing container can be a liquid tank, a sealed container, etc., and the container also contains water to dissolve or disperse the photosensitizer. The photosensitizer content is 0.01-0.5 mol / L, based on the total volume of water and photosensitizer. Preferably, the photosensitizer content is 0.05-0.3 mol / L.

[0019] The ultraviolet light source in step (3) includes at least one of deuterium lamp, low-pressure mercury lamp, medium-pressure mercury lamp, high-pressure mercury lamp, xenon lamp, excimer laser, and LED. The preferred light source includes at least one of low-pressure mercury lamp, medium-pressure mercury lamp, and LED.

[0020] Preferably, the wavelength of the ultraviolet light is 170-280nm, for example, it can be a range of 170, 180, 200, 230, 250, 270, 280nm or any combination thereof;

[0021] Preferably, the ultraviolet irradiance is 20-300 mW / cm². 2 For example, it can be 20, 50, 80, 100, 120, 150, 180, 200, 230, 250, 280, or 300 mW / cm². 2 Or any combination of the two, preferably 20-100 mW / cm 2 ;

[0022] Preferably, the ultraviolet radiation dose is 1-50 J / cm². 2 For example, it can be 2, 5, 10, 15, 20, 25, 30, 35, 40, 45, or 50 J / cm³. 2 Or any combination of the two, preferably 20-40 J / cm 2 .

[0023] Preferably, in step (4), the fluoropolymer film is soaked in water for 1-48 hours, more preferably 2-24 hours, and even more preferably 5-12 hours.

[0024] In step (4) of the present invention, after soaking and cleaning in pure water, the modified fluoropolymer film is obtained by drying.

[0025] The modification method for fluoropolymer films described in this invention is simple, low-cost, environmentally friendly, and easy to scale up for continuous production. It is suitable for filtration applications of strong acids, strong bases, and strong oxidizing liquids such as sulfuric acid, phosphoric acid, ammonia, hydrogen peroxide, SC-1, and SC-2 in industries such as semiconductors and microelectronics.

[0026] The beneficial effects of this invention are as follows:

[0027] 1. Through the synergistic effect of ultraviolet irradiation and photosensitizer, hydrophilic groups are stably introduced into the surface of fluoropolymer films, which significantly improves the anti-wetting performance of the films and overcomes the original hydrophobicity and low wettability problems of fluoropolymer films.

[0028] 2. The modification method proposed in this invention can also improve the retention effect of the membrane on particulate matter in the filtrate by increasing the interaction force between the fluoropolymer membrane and the particulate matter;

[0029] 3. The method proposed in this invention does not significantly affect the skeleton structure and mechanical properties of the film. Compared with common plasma treatment and high-energy ray irradiation, the photosensitizer and ultraviolet irradiation conditions used in this invention are relatively mild and will not affect the skeleton structure of the fluoropolymer film, thus preserving the excellent mechanical properties of the fluoropolymer film;

[0030] 4. The modified fluoropolymer film prepared by this invention has excellent acid and alkali resistance, and can maintain stable filtration performance in strong acid and strong alkali environments, meeting the stringent requirements of the semiconductor filtration field for membrane materials;

[0031] 5. The modification method of the present invention is simple, easy to operate, low in cost, and easy to scale up for production, overcoming the problems of complex processes and high costs in the prior art. Attached Figure Description

[0032] Figure 1 This refers to the water contact angle of the modified film in Example 1 of the present invention. Detailed Implementation

[0033] 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.

[0034] <Source of Raw Materials>

[0035] Polytetrafluoroethylene (PTFE) film, polyvinylidene fluoride (PVDF) film, and ethylene-tetrafluoroethylene copolymer (ETFE) film are commercially available products.

[0036] The photosensitizer, low surface energy liquid, and gold nanoparticles were all purchased from Beijing Innocare Technology Co., Ltd.

[0037] <Testing Methods>

[0038] Maximum tensile strength: The fluoropolymer film was cut into rectangular strips 1 cm wide and 10 cm long, and the maximum tensile strength was tested using an electronic tensile testing machine. The initial test spacing was 5 cm, and the tensile rate was 100 mm / min.

[0039] Water contact angle: The contact angle of the film was tested using a water contact angle meter. Five points were tested for each sample and the average value was taken. 4 μL of pure water was added each time.

[0040] Flux: The fluoropolymer membrane was completely wetted with isopropanol and then inserted into the filter. A pressure of 20 kPa was applied, allowing pure water at 20°C to pass through continuously. Starting from the 10th minute, the mass of the filtered water was recorded at 1-minute intervals, and this was continued until the 30th minute. The mass of water passing through a unit area of ​​the membrane per minute was calculated and recorded as the flux.

[0041] Anti-dehumidification flux loss: After completely wetting the fluoropolymer membrane with isopropanol, it was placed in the filter. A pressure of 40 kPa was applied, and 100 mL of pure water was passed through. The time t0 for the pure water to completely pass through was recorded. Then, while maintaining a pressure of 40 kPa, air was passed through for 1 min, followed by another 100 mL of pure water. The time t1 for the pure water to completely pass through was recorded as the first cycle. After 10 consecutive cycles, t1, t2, ..., t9, t... were obtained respectively. 10 The calculation method for the flux loss due to dehumidification is (t) 10 -t0) / t 10 .

[0042] Retention rate: After the fluoropolymer film was completely wetted with isopropanol, it was placed in the filter and a pressure of 150 kPa was applied. An aqueous dispersion containing 1 ppm (C0) gold nanoparticles with a particle size of 30 nm was passed through, and the mixture was continuously filtered for 30 min. The filtrate after 30 min was collected, and the content of gold particles (C1) was tested. The retention rate was calculated as 1 - (C1 / C0).

[0043] Chemical stability: The fluoropolymer membrane was completely wetted with isopropanol and then immersed in pure water for 1 hour. It was then placed in a reactor containing SC-1 cleaning solution, and the reactor temperature was maintained at 70°C for 7 consecutive days. After removal, the membrane was immersed in pure water for 24 hours. The difference in flux loss before and after immersion was compared.

[0044] Example 1

[0045] A polyvinylidene fluoride (PVDF) film with a pore size of 30 nm and a thickness of 30 μm was immersed in isopropanol for 10 min, and then transferred to pure water for immersion for 10 min. The immersed film was then transferred to a 0.1 mol / L sodium bisulfite aqueous solution and irradiated with a wavelength range of 200-280 nm and an irradiation intensity of 50 mW / cm². 2 Irradiation with a medium-pressure mercury lamp for 10 minutes resulted in a total radiation dose of 30 J / cm². 2 After irradiation, the film was removed, immersed in pure water for 12 hours, removed, and allowed to dry naturally at room temperature to obtain the modified polyvinylidene fluoride film.

[0046] Example 2

[0047] A polytetrafluoroethylene (PTFE) film with a pore size of 30 nm and a thickness of 40 μm was immersed in isopropanol for 10 min, and then transferred to pure water for immersion for 10 min. The immersed film was then transferred to a 0.15 mol / L potassium iodide aqueous solution and irradiated with a wavelength of 185 nm and an intensity of 30 mW / cm². 2 Irradiation with a low-pressure mercury lamp for 15 minutes resulted in a total radiation dose of 27 J / cm². 2 After irradiation, the film was removed, immersed in pure water for 12 hours, removed, and allowed to air dry at room temperature to obtain the modified polytetrafluoroethylene film.

[0048] Example 3

[0049] An ethylene-tetrafluoroethylene copolymer film with a pore size of 30 nm and a thickness of 45 μm was immersed in ethanol for 10 min, and then transferred to pure water for immersion for 10 min. The immersed film was then transferred to a 0.05 mol / L sodium sulfite aqueous solution and irradiated with a 254 nm LED lamp for 20 min at an irradiation intensity of 20 mW / cm². 2 The total radiation dose was 24 J / cm². 2 After irradiation, the film was removed, immersed in pure water for 12 hours, removed, and naturally dried at room temperature to obtain the modified ethylene-tetrafluoroethylene copolymer film.

[0050] Example 4

[0051] A polytetrafluoroethylene (PTFE) film with a pore size of 30 nm and a thickness of 45 μm was immersed in ethanol for 10 min, and then transferred to pure water for 10 min. The immersed film was then transferred to a 0.1 mol / L sodium sulfite aqueous solution and irradiated with an LED lamp with an effective wavelength of 254 nm for 30 min at an irradiation intensity of 20 mW / cm². 2 The total radiation dose was 36 J / cm². 2 After irradiation, the film was removed, immersed in pure water for 12 hours, removed, and allowed to air dry at room temperature to obtain the modified polytetrafluoroethylene film.

[0052] Comparative Example 1

[0053] A 45 μm thick polytetrafluoroethylene (PTFE) film with a pore size of 30 nm was immersed in ethanol for 10 min, and then transferred to pure water for 10 min. The immersed film was then transferred to pure water and irradiated with an LED lamp with an effective wavelength of 254 nm for 30 min at an irradiation intensity of 20 mW / cm². 2 The total radiation dose was 36 J / cm². 2 After irradiation, the film is removed, immersed in pure water for 12 hours, then removed and allowed to air dry at room temperature.

[0054] Comparative Example 2

[0055] A 30 nm pore size and 30 μm thickness polyvinylidene fluoride (PVDF) film was immersed in isopropanol for 10 min, then transferred to pure water for 10 min. The immersed film was then transferred to a 0.1 mol / L sodium bisulfite aqueous solution and irradiated with gamma rays at an intensity of 0.2 Mrad / h for 10 h, with a total irradiation dose of 2 Mrad. After irradiation, the film was removed, immersed in pure water for 12 h, and then allowed to air dry at room temperature.

[0056] The test results of the films in each embodiment and comparative example are shown in the table below.

[0057]

[0058] Compared to the initial films, the modified films in Examples 1-4 all showed significantly reduced contact angles and flux losses after dehumidification tests, demonstrating excellent dehumidification resistance. Furthermore, the tensile properties of the films treated with this method decreased by less than 5%. The gold nanoparticle retention rate of the original films was 50%-60%, while the retention rate after treatment with this method increased to over 90%. Immersion in SC-1 did not significantly change the flux loss due to dehumidification, exhibiting excellent chemical stability.

[0059] Comparative Example 1 used only UV irradiation on the film without adding a photosensitizer; the film's hydrophilicity, desiccation resistance, retention rate, and chemical stability remained unchanged. Comparative Example 2 treated the film with gamma rays. The test results showed that although the hydrophilicity improved significantly, the maximum tensile strength decreased from 58.4 MPa to 41.3 MPa, a 29% decrease, indicating a significant deterioration in mechanical properties. The retention rate of the film treated in Comparative Example 2 decreased to 31%, indicating that gamma rays disrupted the film's pore structure, leading to increased pore size. After immersion in SC-1, the desiccation flux loss of the modified film in Comparative Example 2 increased from 6% to 20%, indicating that the modified film could not withstand SC-1 and underwent structural changes during immersion, resulting in a decrease in desiccation resistance.

[0060] 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 modifying a fluoropolymer film, characterized in that: Includes the following steps: (1) Wet the fluoropolymer film with a low surface energy liquid; (2) Transfer the wetted fluoropolymer film to pure water for immersion; (3) Transfer the fluoropolymer film soaked in pure water to a container containing a photosensitizer and irradiate it with ultraviolet light; (4) Transfer the fluorinated polymer film after irradiation with ultraviolet light to pure water for immersion and cleaning.

2. The method for modifying fluoropolymer films according to claim 1, characterized in that: The fluoropolymers in the fluoropolymer film include one or more of the following: polytetrafluoroethylene (PTFE), perfluoroalkoxy polymer (PFA), fluorinated ethylene propylene copolymer (FEP), polyvinylidene fluoride (PVDF), ethylene-tetrafluoroethylene copolymer (ETFE), ethylene-trifluorochloroethylene copolymer (ECTFE), and polytrifluorochloroethylene (PCTFE).

3. The method for modifying fluoropolymer films according to claim 2, characterized in that: The thickness of the fluoropolymer film is 10-100 micrometers, preferably 10-50 micrometers; the pore size is 1-200 nanometers, preferably 10-50 nanometers.

4. The method for modifying fluoropolymer films according to claim 1, characterized in that: Low surface energy liquids include one or more of methanol, ethanol, isopropanol, n-propanol, n-butanol, isobutanol, tert-butanol, acetone, butanone, tetrahydrofuran, and dioxane, preferably at least one of ethanol, isopropanol, and n-butanol.

5. The method for modifying fluoropolymer films according to claim 1, characterized in that: The ultraviolet light source includes at least one of the following: deuterium lamp, low-pressure mercury lamp, medium-pressure mercury lamp, high-pressure mercury lamp, xenon lamp, excimer laser, and LED. The wavelength of the ultraviolet light is 170-280nm.

6. The method for modifying fluoropolymer films according to claim 5, characterized in that: Ultraviolet radiation intensity is 20-300 mW / cm 2 Preferably 20-100mW / cm 2 The irradiation dose is 1-50 J / cm. 2 Preferably 20-40 J / cm 2 .

7. The method for modifying fluoropolymer films according to claim 1, characterized in that: The photosensitizer comprises one or more of potassium iodide, sodium iodide, sodium sulfite, potassium sulfite, potassium bisulfite, sodium bisulfite, potassium ferrocyanide, sodium sulfide, potassium sulfide, sodium phenolate, potassium phenolate, triethylamine, tryptophan, tyrosine, dimethyl sulfide, titanium dioxide, and zinc oxide, preferably at least one of potassium iodide, sodium sulfite, and sodium bisulfite.

8. The method for modifying fluoropolymer films according to claim 7, characterized in that: The container containing the photosensitizer contains water, and the photosensitizer content, based on the total volume of water and photosensitizer, is 0.01-0.5 mol / L, preferably 0.05-0.3 mol / L.

9. The method for modifying fluoropolymer films according to any one of claims 1-8, characterized in that: The modification method satisfies at least one of the following conditions: A. Step (1) Wet the fluoropolymer film with a low surface energy liquid for a wetting time of 0.1-120 min, preferably 5-30 min; B. In step (2), the wetted fluoropolymer film is soaked in pure water for 0.1-120 min, preferably for 5-30 min; C. In step (4), the fluoropolymer film is soaked in water for 1-48 hours, preferably 2-24 hours, and more preferably 5-12 hours; D. Step (4) After soaking and cleaning in pure water, the modified fluoropolymer film is obtained by drying.

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