Hydrophilic modification method for polytetrafluoroethylene membrane

Abstract

The invention discloses a hydrophilic modification method for a polytetrafluoroethylene membrane, which belongs to the field of polytetrafluoroethylene membrane modification and comprises the following steps: preparing a mixed solution containing polymerizable hydrophilic monomers, a photoinitiator and a cross-linking agent, wherein the polymerizable hydrophilic monomer is one or a combination of more of acrylic acid, acrylamide and hydroxyethyl methylacrylate; completely immersing a polytetrafluoroethylene film into the mixed solution; taking out the infiltrated polytetrafluoroethylene membrane, and under the irradiation of ultraviolet light, initiating a cross-linking polymerization reaction of the polymerizable hydrophilic monomer on the surface of the polytetrafluoroethylene membrane and in micropores; and washing the polytetrafluoroethylene film subjected to illumination polymerization with deionized water, and then drying. The method provided by the invention is simple to operate, does not need complex equipment and harsh reaction conditions, can be completed only through conventional steps such as solution preparation, infiltration, photopolymerization and post-treatment, and is suitable for large-scale industrial production.

Description

Technical Field

[0001] The present invention relates to the technical field of polytetrafluoroethylene membrane modification, and particularly to a hydrophilic modification method for polytetrafluoroethylene membranes. Background Art

[0002] Due to its excellent chemical stability, high and low temperature resistance, chemical corrosion resistance, low surface tension and friction coefficient, polytetrafluoroethylene (PTFE) membranes are widely used in multiple technical fields such as filtration, clothing, biology, and medicine. However, the hydrophobic characteristics of PTFE membranes, such as low surface tension and poor wettability, make them prone to membrane fouling in aqueous processes such as sewage treatment, resulting in a rapid decline in membrane flux, which severely restricts their application in the field of water treatment and other fields.

[0003] Currently, the hydrophilic modification methods for PTFE membranes at home and abroad are mainly divided into chemical methods and physical methods, but there are many defects in the existing technologies: The patent method of CN114832634A: Improve hydrophilicity through the preparation of a specific modifier, but the preparation process is complex, involving multiple steps of reactions and the synthesis of special reagents. This not only is not conducive to large-scale industrial production but may also damage the original structure of the PTFE membrane, affecting its mechanical properties and chemical stability.

[0004] The patent method of CN114405296A: Although it achieves a superhydrophilic effect, the preparation process depends on special equipment and strict reaction conditions (such as a specific temperature range, pressure control, etc.), increasing the production cost and difficulty, and having strict environmental requirements, which limits its popularization and application.

[0005] Common problems of existing methods: Some modification methods have the problem of poor hydrophilic stability, and the hydrophilic effect will weaken with the extension of use time or environmental changes.

[0006] Therefore, it is of great practical significance to develop a modification method that is simple to operate, low in cost, has little damage to the membrane structure, and can effectively improve the hydrophilicity and hydrophilic stability of PTFE membranes. Summary of the Invention

[0007] In view of the deficiencies of the prior art, the present invention provides a hydrophilic modification method for polytetrafluoroethylene membranes, which solves the problems raised in the above background art.

[0008] Technical Solution: To solve the above technical problems, according to one aspect of the present invention, more specifically, a hydrophilic modification method for polytetrafluoroethylene membranes includes the following steps: S1. Prepare a mixed solution Component composition: It contains polymerizable hydrophilic monomers, photoinitiators, crosslinking agents, and organic solvents can be added according to requirements.

[0009] Polymerizable hydrophilic monomers: One or a combination of acrylic acid, acrylamide, and 2-hydroxyethyl methacrylate is selected. Utilizing their good hydrophilicity and polymerizability, hydrophilic groups are introduced onto the surface of the PTFE membrane.

[0010] Photoinitiator: Its mass fraction 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.

[0011] Crosslinking agent: Its mass fraction is 0.05% - 2%, including N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, divinylbenzene, etc. The crosslinking agent can make the polymerized hydrophilic polymer form a crosslinked network structure, enhancing the binding force between the hydrophilic layer and the PTFE membrane and the self-stability of the hydrophilic layer.

[0012] Organic solvent: One or more of ethanol, acetone, and N,N-dimethylformamide can be selected, which are used to adjust the solubility and volatility of the solution, promote the uniform mixing of each component, and help the solution infiltrate the PTFE membrane.

[0013] Concentration control: The mass fraction of the polymerizable hydrophilic monomer in the mixed solution is 5% - 20%. This concentration range can not only ensure that enough monomers participate in the polymerization to form an effective hydrophilic layer but also avoid the too violent polymerization reaction caused by too high monomer concentration, which affects the membrane performance.

[0014] S2. Pretreatment: Before the infiltration treatment, the polytetrafluoroethylene membrane is placed in a plasma environment for 1 - 5 minutes, and the plasma power is controlled at 50 - 200 W. Plasma pretreatment can introduce active groups onto the surface of the PTFE membrane, increase the surface roughness, and improve the affinity of the membrane with each component of the mixed solution, laying a foundation for the subsequent infiltration and polymerization reactions.

[0015] S3. Infiltration treatment: The polytetrafluoroethylene membrane is completely immersed in the mixed solution, and the infiltration time is 10 - 60 minutes. Through this process, the mixed solution fully penetrates into the microporous structure and surface of the PTFE membrane, providing a material guarantee for the polymerization reaction.

[0016] S4. Photo-polymerization: The infiltrated PTFE membrane is taken out and irradiated with ultraviolet light with a wavelength of 250 - 400 nm for 5 - 30 minutes. The ultraviolet light in this wavelength range can effectively excite the photoinitiator to generate free radicals, initiating the crosslinking polymerization reaction of hydrophilic monomers on the membrane surface and in the micropores, forming a hydrophilic polymer layer with a crosslinked structure.

[0017] S5. Post-treatment: Rinse the photo-polymerized PTFE membrane with deionized water 3 - 5 times to remove impurities such as unreacted monomers, photoinitiators, and crosslinking agents. Then dry it at 40 - 80 °C for 1 - 3 hours to further cure the hydrophilic polymer layer on the membrane surface and improve the performance stability of the membrane.

[0018] Furthermore, the crosslinking agent matching strategy: When the polymerizable hydrophilic monomer contains acrylic acid or acrylamide, N,N'-methylenebisacrylamide is preferably used as the crosslinking agent; when it contains 2-hydroxyethyl methacrylate, ethylene glycol dimethacrylate is preferably used as the crosslinking agent to achieve a better crosslinking effect.

[0019] Furthermore, pre-treatment enhancement: The 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, but over-treatment that may cause damage to the membrane structure should be avoided.

[0020] The beneficial effects of the hydrophilic modification method of the polytetrafluoroethylene membrane of the present invention are as follows: (1). The method of the present invention is simple to operate, without the need for complex equipment and harsh reaction conditions. It can be completed only through conventional steps such as solution preparation, infiltration, photo-polymerization, and post-treatment, and is suitable for large-scale industrial production.

[0021] (2). The present invention adopts a photo-initiated polymerization method with mild reaction conditions, which causes little damage to the original structure of the PTFE membrane and can better retain its excellent properties such as chemical stability and mechanical properties.

[0022] (3). The present invention forms a crosslinked network structure by adding a crosslinking agent, greatly improving the binding force between the hydrophilic layer and the PTFE membrane and the self-stability of the hydrophilic layer, so that the hydrophilic effect of the modified PTFE membrane is not easily weakened over time and with environmental changes. Description of the Drawings

[0023] The following further elaborates the present invention in detail with reference to the drawings and specific implementation methods.

[0024] Figure 1 It is a schematic structural diagram of the present invention. Detailed Embodiments

[0025] The present invention will be described in detail below with reference to the drawings and in combination with embodiments. It should be noted that, without conflict, the embodiments in the present application and the features in the embodiments can be combined with each other.

[0026] To make the technical solution of the present invention clearer, the following further elaborates the present invention in detail with reference to the drawings and specific embodiments.

[0027] Example 1 Refer to Figure 1, A hydrophilic modification method for polytetrafluoroethylene membrane (hydrophilic modification based on acrylic acid), comprising the following steps: Prepare a mixed solution: Weigh 5 g of acrylic acid (polymerizable hydrophilic monomer), 0.2 g of photoinitiator benzoin dimethyl ether, and 0.05 g of crosslinking agent N,N'-methylenebisacrylamide; Add the above components to 100 g of ethanol (organic solvent), and stir magnetically at room temperature for 30 minutes until completely dissolved to form a uniform and transparent mixed solution.

[0028] Infiltration treatment: 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 petri dish; Slowly pour the prepared mixed solution into the petri dish to completely cover the PTFE membrane, ensuring that the membrane surface and micropores are fully infiltrated; Let it stand at room temperature for 30 minutes, and gently shake the petri dish during this period to promote the penetration of the solution.

[0029] Photo-polymerization: Use tweezers to take out the infiltrated PTFE membrane and drain the excess solution on the surface; Lay the membrane flat on the quartz plate of the ultraviolet light polymerization device, and irradiate it with an ultraviolet lamp (power 100 W) with a wavelength of 365 nm for 15 minutes; During the irradiation, keep the distance between the membrane surface and the light source at 10 cm to ensure uniform illumination.

[0030] Post-treatment: Rinse the irradiated PTFE membrane 3 times with deionized water, with each rinsing time being 1 minute, to remove unreacted monomers and reagents; Put the membrane into a vacuum drying oven and dry it at 60 °C for 2 hours to cure the hydrophilic polymer layer.

[0031] 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; Stability: The water contact angle becomes 45° after 30 days of placement, and the change range < 5°, and the crosslinked network structure is stable; Membrane flux: The initial flux is 1800 L / (m²·h), and it drops to 1650 L / (m²·h) after continuous operation for 10 hours, with a decrease of 8.3%.

[0032] This example has a strong carboxyl polarity and a high density of hydrophilic groups, and is suitable for filtering acidic sewage.

[0033] Example Two A hydrophilic modification method for polytetrafluoroethylene membrane (hydrophilic modification based on acrylamide), comprising the following steps: Plasma Pretreatment: Select a PTFE flat membrane with an average pore size of 0.2 μm, cut the PTFE membrane into a 5 cm × 5 cm square, and place it in the cavity of the plasma treatment equipment; Vacuum to a pressure < 10 Pa, introduce argon (flow rate 50 mL / min), set the power to 100 W, and treat for 3 minutes; After the treatment, wait for the cavity pressure to return to atmospheric pressure, and take out the membrane for standby.

[0034] Prepare the mixed solution: Weigh 8 g of acrylamide (polymerizable hydrophilic monomer), 0.5 g of photoinitiator 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 0.1 g of crosslinking agent ethylene glycol dimethacrylate; Add the above components to 100 g of acetone (organic solvent), and ultrasonically oscillate for 15 minutes until completely dissolved to form a mixed solution.

[0035] Infiltration treatment: Put the pretreated PTFE membrane into a conical flask, pour in the mixed solution, and ensure that the membrane is completely immersed; Oscillate and infiltrate at a speed of 100 rpm on a shaker for 40 minutes to promote the penetration of the solution into the membrane micropores.

[0036] Photo-polymerization: Take out the membrane, gently suck the excess solution on the surface with filter paper, and place it in a UV photoreactor with a wavelength of 300 nm; Control the illumination distance at 8 cm and irradiate for 20 minutes to initiate the polymerization and crosslinking of acrylamide.

[0037] Post-treatment: Rinse the membrane 4 times with deionized water, soak for 5 minutes each time, and thoroughly remove the residual reagents; Put the membrane into a forced-air drying oven and dry at 50 °C for 2.5 hours to complete the modification.

[0038] Function of the pretreatment in this example: After plasma treatment, the surface roughness of the membrane increases, the contact angle decreases from the initial 110° to 85°, improving the infiltration effect; Hydrophilicity: The water contact angle after modification is 40°, and the amide group (-CONH2) forms hydrogen bonds with water, with long-lasting hydrophilicity; Membrane performance: The initial flux is 1750 L / (m²·h), the flux after 10 hours is 1600 L / (m²·h), and the decrease is 8.6%. The interfacial bonding force is better than that of the untreated sample.

[0039] Due to the hydrogen bond action of the amide group, it has excellent salt resistance and is suitable for the separation of electrolyte solutions.

[0040] Example Three A hydrophilic modification method for polytetrafluoroethylene membrane (hydrophilic modification based on 2-hydroxyethyl methacrylate), comprising the following steps: Prepare a mixed solution: Weigh 10 g of 2-hydroxyethyl methacrylate (polymerizable hydrophilic monomer), 0.8 g of photoinitiator benzophenone, and 0.15 g of crosslinking agent divinylbenzene; Add the above components to 100 g of N,N-dimethylformamide (DMF, organic solvent), and stir magnetically for 45 minutes until homogeneous and transparent.

[0041] Infiltration treatment: 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 to cover the membrane surface; Let it stand and infiltrate at room temperature for 50 minutes, and gently shake the glass tank every 10 minutes during this period to avoid uneven local concentration.

[0042] Photo-polymerization: Take out the membrane, hang it to drain for 30 seconds, and put it into an ultraviolet curing device with a wavelength of 380 nm; Control the light intensity at 50 mW / cm² and irradiate for 25 minutes to initiate cross-linking polymerization of hydroxyl groups and ester groups.

[0043] Post-treatment: Rinse the membrane 5 times with deionized water, and ultrasonically clean for 3 minutes each time to remove residual reagents deep inside; Dry it in a vacuum drying oven at 70 °C for 1.5 hours to cure the hydrophilic layer.

[0044] The monomer characteristics of this example: The hydroxyl group (-OH) of 2-hydroxyethyl methacrylate directly provides hydrophilicity, and the water contact angle is 38°, which is the lowest among the three examples; Cross-linking structure: Divinylbenzene forms a dense network, and the tensile strength of the hydrophilic layer reaches 2.3 MPa, with the best mechanical stability; Filtration performance: The initial flux is 1850 L / (m²·h), and the flux after 10 hours is 1700 L / (m²·h), with a decrease of 8.1%, and the pore channel permeability is excellent.

[0045] The hydroxyl groups in this example have good compatibility with the membrane and high mechanical strength, and are suitable for high-pressure filtration or long-term use scenarios.

[0046] The above-described embodiments only represent several implementation manners of the present invention. The description is relatively specific and detailed, but it should not be construed as a limitation on the scope of the patent of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention should be subject to the appended claims.

Claims

1. A hydrophilic modification method for a polytetrafluoroethylene membrane, characterized in that It includes the following steps: S1. Prepare the mixed solution: Prepare a mixed solution containing a polymerizable hydrophilic monomer, a photoinitiator, and a crosslinking agent, where the polymerizable hydrophilic monomer is one or a combination of acrylic acid, acrylamide, and 2-hydroxyethyl methacrylate; S2. Impregnation treatment: Immerse the polytetrafluoroethylene membrane completely in the above-mentioned mixed solution; S3. Photo-polymerization: Take out the impregnated polytetrafluoroethylene membrane and irradiate it under ultraviolet light to initiate the crosslinking polymerization reaction of the polymerizable hydrophilic monomer on the surface and in the micropores of the polytetrafluoroethylene membrane; S4. Post-treatment: Rinse the photo-polymerized polytetrafluoroethylene membrane with deionized water and then dry it.

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

3. The hydrophilic modification method of a polytetrafluoroethylene membrane according to claim 1, characterized in that, Before the impregnation treatment step, there is also a step of pre-treating the polytetrafluoroethylene membrane, and the pre-treatment method is to treat the polytetrafluoroethylene membrane in a plasma environment.

4. A hydrophilic modification method of a polytetrafluoroethylene membrane according to claim 1, characterized in that, The crosslinking agent is one or more of N,N'-methylenebisacrylamide, ethylene glycol dimethacrylate, and divinylbenzene.

5. A hydrophilic modification method of a polytetrafluoroethylene membrane according to claim 4, characterized in that: When the polymerizable hydrophilic monomer contains acrylic acid or acrylamide, the crosslinking agent is N,N'-methylenebisacrylamide; when the polymerizable hydrophilic monomer contains 2-hydroxyethyl methacrylate, the crosslinking agent is ethylene glycol dimethacrylate.

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