A method for hydrophilic modification of polytetrafluoroethylene membrane

Abstract

The present invention discloses a method for hydrophilic modification of a polytetrafluoroethylene membrane, belonging to the field of polytetrafluoroethylene membrane modification. The method comprises the following steps: preparing a mixed solution containing a polymerizable hydrophilic monomer, a photoinitiator, and a crosslinking agent, wherein the polymerizable hydrophilic monomer is one or more of acrylic acid, acrylamide, and hydroxyethyl methacrylate; completely immersing the polytetrafluoroethylene membrane in the mixed solution; removing the immersed polytetrafluoroethylene membrane and irradiating it with ultraviolet light to induce a crosslinking polymerization reaction of the polymerizable hydrophilic monomer on the surface of the polytetrafluoroethylene membrane and within the micropores; rinsing the photopolymerized polytetrafluoroethylene membrane with deionized water, and then drying. The method is simple to operate, does not require complex equipment or harsh reaction conditions, and can be completed through conventional steps such as solution preparation, immersion, photopolymerization, and post-processing, making it suitable for large-scale industrial production.

Description

Technical Field

[0001] The invention relates to the technical field of polytetrafluoroethylene membrane modification, in particular to a method for hydrophilic modification of a polytetrafluoroethylene membrane. Background Art

[0002] Polytetrafluoroethylene (PTFE) membranes are widely used in a variety of technical fields, including filtration, clothing, biology, and medicine, due to their excellent chemical stability, high and low temperature resistance, chemical corrosion resistance, and low surface tension and friction coefficient. However, the hydrophobic nature of PTFE membranes, such as low surface tension and poor wettability, makes them highly susceptible to membrane fouling in aqueous processes such as sewage treatment, leading to a rapid decrease in membrane flux and severely restricting their application in water treatment and other fields.

[0003] At present, the methods for hydrophilic modification of PTFE membranes at home and abroad are mainly divided into chemical methods and physical methods, but the existing technologies have many defects:

[0004] The patented method of CN114832634A improves hydrophilicity through the preparation of specific modifiers, but the preparation process is complicated, involving multi-step reactions and special reagent synthesis. It is not only not conducive to large-scale industrial production, but may also destroy the original structure of the PTFE membrane, affecting its mechanical properties and chemical stability.

[0005] Patented method CN114405296A: Although it achieves a super-hydrophilic effect, the preparation process relies on special equipment and strict reaction conditions (such as specific temperature range, pressure control, etc.), which increases production costs and difficulty, and has stringent environmental requirements, limiting its promotion and application.

[0006] Common problems of existing methods: Some modification methods have the problem of poor hydrophilic stability, and the hydrophilic effect will weaken with prolonged use or environmental changes.

[0007] Therefore, it is of great practical significance to develop a modification method that is simple to operate, low in cost, causes little damage to the membrane structure, and can effectively improve the hydrophilicity and hydrophilic stability of the PTFE membrane. Summary of the Invention

[0008] In view of the deficiencies of the prior art, the present invention provides a method for hydrophilic modification of polytetrafluoroethylene membranes, which solves the problems raised in the above-mentioned background technology.

[0009] Technical solution: To solve the above technical problems, according to one aspect of the present invention, more specifically, a method for hydrophilic modification of polytetrafluoroethylene membranes comprises the following steps:

[0010] S1. Prepare mixed solution

[0011] Component composition: Contains polymerizable hydrophilic monomers, photoinitiators, cross-linking agents, and organic solvents can be added as needed.

[0012] Polymerizable hydrophilic monomer: one or more combinations of acrylic acid, acrylamide, and hydroxyethyl methacrylate are selected to introduce hydrophilic groups on the surface of the PTFE membrane by utilizing their good hydrophilicity and polymerizability.

[0013] Photoinitiator: The mass fraction of the photoinitiator in the mixed solution is 0.1%-5%. Common types include benzoin dimethyl ether, 2-hydroxy-2-methyl-1-phenyl-1-propanone, benzophenone, etc. Its function is to generate free radicals under ultraviolet light irradiation, initiating the polymerization reaction of hydrophilic monomers.

[0014] Cross-linking agent: The mass fraction is 0.05%-2%, including N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, divinylbenzene, etc. The cross-linking agent can form a cross-linked network structure in the hydrophilic polymer after polymerization, thereby enhancing the bonding strength between the hydrophilic layer and the PTFE membrane and the stability of the hydrophilic layer itself.

[0015] Organic solvent: One or more of ethanol, acetone, and N,N-dimethylformamide can be selected to adjust the solubility and volatility of the solution, promote uniform mixing of the components, and help the solution infiltrate the PTFE membrane.

[0016] Concentration control: The mass fraction of the polymerizable hydrophilic monomer in the mixed solution is 5%-20%. This concentration range can ensure that sufficient monomers participate in the polymerization to form an effective hydrophilic layer, while avoiding excessive monomer concentration causing excessive polymerization reaction and affecting membrane performance.

[0017] S2. Pretreatment: Before infiltration, the PTFE membrane is placed in a plasma environment for 1-5 minutes, with the plasma power controlled at 50-200W. Plasma pretreatment can introduce active groups onto the surface of the PTFE membrane, increase surface roughness, and improve the affinity between the membrane and the components of the mixed solution, laying the foundation for subsequent infiltration and polymerization reactions.

[0018] S3, Immersion treatment: The polytetrafluoroethylene membrane is completely immersed in the mixed solution for 10-60 minutes. Through this process, the mixed solution fully penetrates the microporous structure and surface of the PTFE membrane, providing material support for the polymerization reaction.

[0019] S4. Photopolymerization: Remove the soaked PTFE membrane and irradiate it with ultraviolet light at a wavelength of 250-400nm for 5-30 minutes. This wavelength effectively excites the photoinitiator to produce free radicals, which trigger cross-linking polymerization of hydrophilic monomers on the membrane surface and within the micropores, forming a hydrophilic polymer layer with a cross-linked structure.

[0020] S5. Post-treatment: Rinse the photopolymerized PTFE membrane with deionized water for 3-5 times to remove impurities such as unreacted monomers, photoinitiators and cross-linking agents, and then dry it at 40-80°C for 1-3 hours to further solidify the hydrophilic polymer layer on the membrane surface and improve the performance stability of the membrane.

[0021] Furthermore, the cross-linking agent matching strategy is as follows: when the polymerizable hydrophilic monomer contains acrylic acid or acrylamide, N,N'-methylenebisacrylamide is preferably used as the cross-linking agent; when it contains hydroxyethyl methacrylate, ethylene glycol dimethacrylate is preferably used as the cross-linking agent to achieve a better cross-linking effect.

[0022] Furthermore, pretreatment enhancement: plasma treatment parameters can be optimized according to the membrane material and thickness. The higher the power and the longer the treatment time, the more significant the surface modification effect. However, excessive treatment should be avoided to cause damage to the membrane structure.

[0023] The beneficial effects of the hydrophilic modification method of a polytetrafluoroethylene membrane of the present invention are:

[0024] (1) The method of the present invention is simple to operate and does not require complex equipment and harsh reaction conditions. It can be completed through conventional steps such as solution preparation, infiltration, photopolymerization and post-processing, and is suitable for large-scale industrial production.

[0025] (2) The present invention adopts a light-initiated polymerization method, the reaction conditions are mild, the damage to the original structure of the PTFE membrane is small, and its excellent properties such as chemical stability and mechanical properties can be well preserved.

[0026] (3) The present invention forms a cross-linked network structure by adding a cross-linking agent, which greatly improves the bonding force between the hydrophilic layer and the PTFE membrane and the stability of the hydrophilic layer itself, so that the hydrophilic effect of the modified PTFE membrane is not easily weakened with time and environmental changes. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0028] Figure 1 It is a structural schematic diagram of the present invention. DETAILED DESCRIPTION

[0029] The present invention will be described in detail below with reference to the accompanying drawings and in combination with embodiments. It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other.

[0030] In order to make the technical solution of the present invention clearer, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0031] Example 1

[0032] Reference Figure 1 A method for hydrophilic modification of polytetrafluoroethylene membrane (based on acrylic acid) comprises the following steps:

[0033] Prepare the mixed solution:

[0034] Weigh 5 g of acrylic acid (polymerizable hydrophilic monomer), 0.2 g of photoinitiator benzoin dimethyl ether, and 0.05 g of cross-linker N,N'-methylenebisacrylamide;

[0035] The above components were added to 100 g of ethanol (organic solvent) and magnetically stirred at room temperature for 30 minutes until they were completely dissolved to form a uniform and transparent mixed solution.

[0036] Infiltration treatment:

[0037] Take a polytetrafluoroethylene (PTFE) membrane with a diameter of 10 cm and an average pore size of 0.2 μm and place it in a clean glass culture dish;

[0038] Slowly pour the prepared mixed solution into the culture dish to completely cover the PTFE membrane and ensure that the membrane surface and micropores are fully infiltrated;

[0039] Allow to soak at room temperature for 30 minutes, gently shaking the dish to promote solution penetration.

[0040] Light aggregation:

[0041] Use tweezers to remove the soaked PTFE membrane and drain the excess solution on the surface;

[0042] The membrane was spread on a quartz plate of a UV polymerization device and irradiated with a UV lamp (power 100 W) with a wavelength of 365 nm for 15 minutes;

[0043] During the irradiation process, the distance between the film surface and the light source was kept at 10 cm to ensure uniform lighting.

[0044] Post-processing:

[0045] The PTFE membrane after light exposure was rinsed with deionized water three times, each rinse lasting 1 minute to remove unreacted monomers and reagents;

[0046] The membrane was placed in a vacuum drying oven and dried at 60° C. for 2 hours to solidify the hydrophilic polymer layer.

[0047] The hydrophilicity of this example: the water contact angle test result is 42°, and the carboxyl group (-COOH) of acrylic acid forms a strong hydrophilic group;

[0048] Stability: After 30 days of storage, the water contact angle becomes 45°, with a variation of less than 5°, and the cross-linked network structure is stable;

[0049] Membrane flux: The initial flux was 1800L / (m²・h), which dropped to 1650L / (m²・h) after 10 hours of continuous operation, a decrease of 8.3%.

[0050] The carboxyl group in this embodiment has strong polarity and high density of hydrophilic groups, and is suitable for filtering acidic wastewater.

[0051] Example 2

[0052] A method for hydrophilic modification of polytetrafluoroethylene membrane (based on hydrophilic modification of acrylamide) comprises the following steps:

[0053] Plasma pretreatment:

[0054] A PTFE flat membrane with an average pore size of 0.2 μm was selected, cut into 5 cm × 5 cm squares, and placed in the plasma treatment equipment chamber;

[0055] Evacuate to a pressure of <10 Pa, introduce argon (flow rate 50 mL / min), set the power to 100 W, and process for 3 minutes;

[0056] After the treatment is completed, wait until the cavity pressure returns to normal pressure and take out the membrane for use.

[0057] Prepare the mixed solution:

[0058] Weigh 8 g acrylamide (polymerizable hydrophilic monomer), 0.5 g photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 0.1 g crosslinker ethylene glycol dimethacrylate;

[0059] The above components were added to 100 g of acetone (organic solvent) and ultrasonically vibrated for 15 minutes until they were completely dissolved to form a mixed solution.

[0060] Infiltration treatment:

[0061] Place the pretreated PTFE membrane into a conical flask and pour in the mixed solution to ensure that the membrane is completely immersed;

[0062] The membrane was shaken on a shaker at 100 rpm for 40 minutes to promote the solution to penetrate into the membrane micropores.

[0063] Light aggregation:

[0064] The membrane was taken out, the excess solution on the surface was gently absorbed with filter paper, and then placed in a UV reactor with a wavelength of 300 nm;

[0065] The light irradiation distance was controlled at 8 cm and irradiation was performed for 20 minutes to induce acrylamide polymerization and cross-linking.

[0066] Post-processing:

[0067] Rinse the membrane with deionized water 4 times, soaking for 5 minutes each time to completely remove residual reagents;

[0068] The membrane was placed in a forced air drying oven and dried at 50°C for 2.5 hours to complete the modification.

[0069] The pretreatment effect in this embodiment is: after plasma treatment, the surface roughness of the film increases, the contact angle decreases from the initial 110° to 85°, and the wetting effect is improved;

[0070] Hydrophilicity: After modification, the water contact angle is 40°, and the amide group (-CONH2) forms a hydrogen bond with water, making it hydrophilic and long-lasting;

[0071] Membrane performance: Initial flux was 1750 L / (m²・h), and after 10 hours, the flux was 1600 L / (m²・h), a decrease of 8.6%. The interfacial bonding strength was better than that of the untreated sample.

[0072] The amide group has hydrogen bonding effect and excellent salt resistance, making it suitable for separation of electrolyte solutions.

[0073] Example 3

[0074] A method for hydrophilic modification of polytetrafluoroethylene membrane (based on hydrophilic modification of hydroxyethyl methacrylate) comprises the following steps:

[0075] Prepare the mixed solution:

[0076] Weigh 10 g of hydroxyethyl methacrylate (polymerizable hydrophilic monomer), 0.8 g of photoinitiator benzophenone, and 0.15 g of cross-linking agent divinylbenzene;

[0077] The above components were added to 100 g of N,N-dimethylformamide (DMF, organic solvent) and magnetically stirred for 45 minutes until the mixture became homogeneous and transparent.

[0078] Infiltration treatment:

[0079] Select a PTFE flat membrane with an average pore size of 0.2 μm, place the PTFE membrane in a horizontal glass tank, and slowly pour the mixed solution into it to cover the membrane surface;

[0080] Let it soak at room temperature for 50 minutes, shaking the glass tank gently every 10 minutes to avoid local uneven concentration.

[0081] Light aggregation:

[0082] Remove the membrane, hang it to drain for 30 seconds, and place it in a UV curing device with a wavelength of 380 nm;

[0083] The light intensity was controlled at 50 mW / cm² and irradiated for 25 minutes to initiate cross-linking polymerization of hydroxyl and ester groups.

[0084] Post-processing:

[0085] Rinse the membrane with deionized water five times, ultrasonically cleaning for 3 minutes each time to remove deep residual reagents;

[0086] The film was dried in a vacuum drying oven at 70°C for 1.5 hours to solidify the hydrophilic layer.

[0087] Monomer characteristics of this example: The hydroxyl group (-OH) of hydroxyethyl methacrylate directly provides hydrophilicity, and the water contact angle is 38°, the lowest among the three examples;

[0088] Cross-linked structure: Divinylbenzene forms a dense network, the hydrophilic layer has a tensile strength of 2.3MPa, and has the best mechanical stability;

[0089] Filtration performance: Initial flux 1850L / (m²・h), flux 10 hours later 1700L / (m²・h), a decrease of 8.1%, excellent pore patency.

[0090] The hydroxyl group in this embodiment has good compatibility with the membrane and high mechanical strength, and is suitable for high-pressure filtration or long-term use scenarios.

[0091] The above-described embodiments merely illustrate several implementations of the present invention, and while their descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make numerous variations and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for hydrophilic modification of polytetrafluoroethylene membrane, characterized in that: The following steps are involved: S1. Preparing a mixed solution: Preparing a mixed solution containing a polymerizable hydrophilic monomer, a photoinitiator, and a crosslinking agent, wherein the polymerizable hydrophilic monomer is one or more of acrylic acid, acrylamide, and hydroxyethyl methacrylate; and the crosslinking agent is one or more of N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, and divinylbenzene; When the polymerizable hydrophilic monomer contains acrylic acid or acrylamide, the crosslinking agent is N,N'-methylenebisacrylamide; when the polymerizable hydrophilic monomer contains hydroxyethyl methacrylate, the crosslinking agent is ethylene glycol dimethacrylate; S2, immersion treatment: completely immerse the polytetrafluoroethylene membrane in the above mixed solution; S3, photopolymerization: The infiltrated polytetrafluoroethylene membrane is taken out and irradiated with ultraviolet light to initiate a cross-linking polymerization reaction of the polymerizable hydrophilic monomer on the surface of the polytetrafluoroethylene membrane and in the micropores; S4. Post-treatment: Rinse the photopolymerized polytetrafluoroethylene membrane with deionized water and then dry it.

2. The method for hydrophilic modification of polytetrafluoroethylene membrane according to claim 1, characterized in that: The mixed solution further includes an organic solvent, which is one or more of ethanol, acetone, and N,N-dimethylformamide.

3. The method for hydrophilic modification of polytetrafluoroethylene membrane according to claim 1, characterized in that: Before the infiltration treatment step, the method further includes a step of pre-treating the polytetrafluoroethylene film. The pre-treatment method is to treat the polytetrafluoroethylene film in a plasma environment.

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