Hydrophilic modified polytetrafluoroethylene oil removal film and preparation method thereof

Abstract

The invention provides a hydrophilic modified polytetrafluoroethylene oil removal film and a preparation method thereof. A modified layer of the hydrophilic modified polytetrafluoroethylene oil removal film is mainly prepared from the following raw materials in percentage by mass: 8-12 wt% of a hydrophilic vinyl monomer, 0.3-0.6 wt% of a cross-linking agent, 0.2-0.5 wt% of an initiator and the balance of a deionized water solvent. A new chemical grafting modification strategy is adopted, the surface of the PTFE membrane is activated through low-temperature plasma, co-grafting and cross-linking polymerization of a hydrophilic monomer and a cross-linking agent on the surface of the PTFE membrane are initiated, and a layer of firm hydrophilic polymer brush with a three-dimensional network structure is constructed on the surface of the membrane; a stable hydration layer is formed on a membrane-water interface, the PTFE membrane is endowed with excellent underwater super-oleophobic property, the oil-water separation efficiency, flux and anti-pollution capacity of the PTFE membrane are remarkably improved, the technological process is simple, and the product performance is stable.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and more specifically, to a hydrophilic modified polytetrafluoroethylene degreasing membrane and its preparation method. Background Technology

[0002] Oily wastewater widely originates from industries such as petrochemicals, machinery processing, and food manufacturing, and its efficient separation is a major challenge in the field of industrial water treatment. Membrane separation technology, due to its advantages of high efficiency, energy saving, and ease of operation, has shown great potential in oil-water separation. Polytetrafluoroethylene (PTFE) membranes possess excellent chemical stability, thermal stability, and mechanical strength, making them an ideal candidate material for treating oily wastewater under harsh conditions.

[0003] However, the inherent strong hydrophobicity of PTFE materials is a major obstacle to their application in oil-water separation. On the one hand, the hydrophobic surface easily leads to oil droplet adsorption and membrane pore blockage, resulting in severe membrane fouling and a sharp decline in flux. On the other hand, hydrophobic membranes require a high transmembrane pressure difference to drive the aqueous phase through, resulting in high energy consumption and a complex pre-wetting process before operation.

[0004] Therefore, hydrophilic modification of PTFE membranes to impart oil-resistant properties is crucial for their efficient application in oil-water separation. However, existing hydrophilic modification methods for PTFE membranes, such as surfactant coating and physical blending, often suffer from problems like unstable modified layers, easy detachment, and poor durability, leading to severe performance degradation during long-term operation or in complex chemical environments. While chemical grafting can construct a robust hydrophilic layer on the PTFE surface, traditional methods primarily focus on improving general hydrophilicity, neglecting to specifically enhance the membrane surface's "underwater superoleophobic" properties (i.e., anti-oil adhesion), thus failing to achieve high-throughput, long-term stable oil removal. Summary of the Invention

[0005] Therefore, the first objective of this invention is to provide a hydrophilic modified polytetrafluoroethylene (PTFE) oil removal membrane. A novel chemical grafting modification strategy is employed, using low-temperature plasma to activate the PTFE membrane surface, thereby initiating co-grafting and cross-linking polymerization of hydrophilic monomers and cross-linking agents on its surface. This constructs a robust hydrophilic polymer brush with a three-dimensional network structure on the PTFE membrane surface. This polymer brush, through strong hydration, forms a stable hydration layer at the membrane-water interface, endowing the PTFE membrane with excellent underwater superoleophobic properties. This significantly improves the oil-water separation efficiency, flux, and antifouling ability of the PTFE membrane, resulting in a high-efficiency PTFE oil removal membrane with high flux, strong antifouling properties, and long service life.

[0006] The second objective of this invention is to provide a method for preparing the above-mentioned hydrophilic modified polytetrafluoroethylene degreasing film, which has a simple process flow and is convenient for field application.

[0007] In order to achieve the above-mentioned objectives of the present invention, the following technical solution is adopted: This invention provides a hydrophilic modified polytetrafluoroethylene degreasing film. The modified layer of the hydrophilic modified polytetrafluoroethylene degreasing film is mainly made from the following raw materials by mass percentage: 8-12 wt% hydrophilic vinyl monomer, 0.3-0.6 wt% crosslinking agent, 0.2-0.5 wt% initiator, and the remainder is deionized water solvent.

[0008] Hydrophilic vinyl monomers enhance hydrophilicity and promote oil adsorption. A three-dimensional network structure is formed through crosslinking agents, improving the stability of the modified layer and preventing monomer shedding. Initiators activate the monomer polymerization reaction. The modified surface energy is significantly increased, the contact angle is reduced, and hydrophilicity is enhanced, enabling more effective adsorption and separation of oil-water mixtures. The inherent corrosion and solvent resistance of PTFE is not compromised; after modification, it remains stable in environments with strong acids, strong alkalis, or organic solvents. The addition of crosslinking agents makes the material more heat-resistant, chemically resistant, and improves mechanical strength, resulting in greater durability and a longer lifespan, making it suitable for applications in oil-water separation and wastewater treatment.

[0009] Further, the hydrophilic vinyl monomer includes one or more of the following: acrylic acid, methacrylic acid, hydroxyethyl methacrylate, acrylamide, N-vinylpyrrolidone, and sulfobetaine methacrylate ([2-(methacryloyloxy)ethyl]dimethyl-(3-sulfonylpropyl)ammonium hydroxide).

[0010] Acrylic acid (AA) contains a carboxyl group, exhibits strong hydrophilicity, and is easily grafted polymerized, significantly improving the hydrophilicity and antifouling properties of membrane surfaces. Methacrylic acid (MAA) is suitable for modifications requiring a balance between hydrophilicity and mechanical properties. Hydroxyethyl methacrylate (HEMA) contains hydroxyl groups and has excellent hydrophilicity. Acrylamide (AM) contains amide groups, is hydrophilic, and readily polymerizes. N-vinylpyrrolidone (NVP) contains pyrrolidone groups and exhibits outstanding hydrophilicity. Sulfobetaine methacrylate (SBMA) has an amphoteric structure and strong anti-protein adsorption properties.

[0011] Furthermore, the crosslinking agent is a bifunctional reagent containing at least two vinyl groups, including: N,N'-methylenebisacrylamide (MBA) and polyethylene glycol diacrylate.

[0012] N,N'-Methylenebisacrylamide (MBA) is a white crystalline powder, readily soluble in water and organic solvents. It contains two active acrylamide groups, enabling efficient crosslinking of monomers such as acrylamide and acrylic acid. Polyethylene glycol diacrylate is prepared by esterification of polyethylene glycol (PEG) with acrylic acid; its molecular weight is adjustable, and it forms a flexible network after crosslinking.

[0013] Preferably, the hydrophilic vinyl monomer contains a combination of monomers with carboxyl and hydroxyl groups or the zwitterionic monomer SBMA.

[0014] Furthermore, when the hydrophilic vinyl monomer is a combination of acrylic acid (AA) and hydroxyethyl methacrylate (HEMA), an acrylic acid and hydroxyethyl methacrylate co-grafted modified layer is formed. The acrylic acid and hydroxyethyl methacrylate co-grafted modified layer is mainly prepared from the following raw materials in the following mass percentages: 4-6 wt% acrylic acid (AA), 4-6 wt% hydroxyethyl methacrylate (HEMA), 0.4-0.6 wt% N,N'-methylenebisacrylamide (MBA), 0.2-0.4 wt% potassium persulfate (KPS), and the remainder is deionized water solvent.

[0015] The synergistic effect of acrylic acid (AA) and hydroxyethyl methacrylate (HEMA) significantly improves the hydrophilicity of the membrane surface, reduces the contact angle, and facilitates the adsorption and separation of oil-water mixtures. The inherent corrosion and solvent resistance of PTFE is retained, allowing it to remain stable in strong acid, strong alkali, or organic solvent environments after modification. N,N'-methylenebisacrylamide (MBA), as a crosslinking agent, enhances the material's heat resistance and mechanical strength, making the modified layer more durable. Deionized water is primarily used as a solvent in the preparation of modified PTFE membranes to ensure the purity of the reaction system and prevent impurities from interfering with the polymerization process. All raw materials used in the formulation (such as AA, HEMA, and MBA) meet environmental protection requirements, making the production and use process safer.

[0016] Furthermore, the acrylic acid and hydroxyethyl methacrylate co-grafted modified layer is mainly prepared from the following raw materials by mass percentage: 5 wt% acrylic acid (AA), 5 wt% hydroxyethyl methacrylate (HEMA), 0.5 wt% N,N'-methylenebisacrylamide (MBA), 0.3 wt% potassium persulfate (KPS), and the remainder is deionized water solvent.

[0017] Acrylic acid (AA) provides strongly hydrophilic carboxyl groups (-COOH), and hydroxyethyl methacrylate (HEMA) provides hydroxyl groups (-OH). The copolymerization of these two forms a polymer network rich in various hydrophilic groups (such as P(AA-co-HEMA)), which can strongly bind water molecules through hydrogen bonding and other interactions, forming a dense hydration layer and significantly improving surface hydrophilicity. N,N'-methylenebisacrylamide (MBA), as a crosslinking agent, covalently links the long chains of AA and HEMA into a three-dimensional network structure during polymerization. This greatly enhances the mechanical strength and chemical stability of the modified layer, making it resistant to rinsing and washing, less prone to dissolution or detachment, and with a longer service life. Potassium persulfate (KPS), as an initiator, decomposes under heating conditions to generate free radicals, effectively initiating the graft copolymerization reaction. The increased hydrophilicity effectively reduces the adsorption of hydrophobic contaminants (such as oil stains and proteins). This formulation achieves a good balance between hydrophilicity, stability, and processability, making it suitable for a wider range of demanding applications.

[0018] Furthermore, when the hydrophilic vinyl monomer is sulfobetaine methacrylate, a sulfobetaine methacrylate graft-modified layer is formed. The sulfobetaine methacrylate graft-modified layer is mainly prepared from the following raw materials in the following mass percentages: 7-9 wt% sulfobetaine methacrylate (SBMA), 0.3-0.5 wt% N,N'-methylenebisacrylamide (MBA), and 0.3-0.5 wt% potassium persulfate (KPS), with the remainder being deionized water solvent.

[0019] The introduction of sulfobetaine methacrylate (SBMA) significantly improves the hydrophilicity of the membrane surface and reduces the contact angle, making it more conducive to the adsorption and separation of oil-water mixtures, suitable for applications such as oil-water separation and wastewater treatment. N,N'-methylenebisacrylamide (MBA), as a crosslinking agent, enhances the heat resistance and mechanical strength of the material, making the modified layer more durable.

[0020] Furthermore, the sulfobetaine methacrylate grafted modified layer is mainly prepared from the following raw materials in the following mass percentages: 8 wt% sulfobetaine methacrylate (SBMA), 0.4 wt% N,N'-methylenebisacrylamide (MBA) and 0.4 wt% potassium persulfate (KPS), with the remainder being deionized water solvent.

[0021] The zwitterionic structure of SBMA (containing both sulfonic acid and quaternary ammonium groups) strongly binds water molecules through electrostatic interactions, forming a dense "hydration layer" on the material surface. This water layer acts as a barrier, effectively preventing the non-specific adsorption of substances such as proteins, oil, and bacteria. N,N'-methylenebisacrylamide (MBA), as a crosslinking agent, establishes strong covalent bonds between SBMA polymer chains, forming a three-dimensional network. This significantly enhances the mechanical strength and chemical stability of the modified layer, making it less susceptible to hydrolysis or physical erosion, thus ensuring the durability of its performance. Potassium persulfate (KPS), as a thermal decomposition initiator, efficiently generates free radicals at suitable temperatures, initiating the polymerization and grafting reactions of SBMA monomers. Its dosage, in the ratio of SBMA to MBA, is optimized to help form a uniform and complete grafted layer.

[0022] This invention also provides a method for preparing a hydrophilic modified polytetrafluoroethylene (PTFE) degreasing film, which is used to prepare the hydrophilic modified PTFE degreasing film as described above, and includes the following steps: Pretreatment: The PTFE membrane is ultrasonically cleaned in an organic solvent to remove surface impurities; Plasma activation: The cleaned PTFE membrane is subjected to plasma treatment using oxygen plasma to introduce oxygen-containing active groups on its surface; Grafting solution preparation: Dissolve hydrophilic vinyl monomers, crosslinking agents and initiators in water to form a homogeneous grafting solution; Interfacial grafting polymerization: The activated PTFE membrane is immersed in the grafting solution and a free radical grafting copolymerization reaction is carried out under heating conditions; Post-processing: After the reaction is complete, the membrane is removed, cleaned and dried to obtain the modified PTFE degreasing membrane.

[0023] Oxygen plasma treatment bombards the PTFE surface, introducing oxygen-containing active groups (such as hydroxyl and carboxyl groups) onto the PTFE membrane surface. On one hand, physical etching increases nanoscale roughness, enlarges the specific surface area, significantly improves surface energy, reduces contact angle, and enhances hydrophilicity. On the other hand, high-energy particles can break some CF and CC bonds in the PTFE molecular chain, introducing oxygen-containing polar groups such as hydroxyl (-OH) and carboxyl (-COOH) groups onto the surface. These groups act like countless active "anchor points" on the "inert" PTFE surface, providing reaction sites for subsequent grafting reactions. In the subsequent graft polymerization reaction, the free radicals of hydrophilic vinyl monomers react with these "anchor points," firmly attaching to the PTFE backbone through covalent bonds. This bonding method is far stronger than physical coating or adsorption, ensuring that the modified layer is not easily detached or lost during use, thus guaranteeing the durability of the modification effect and helping the PTFE membrane to more effectively adsorb and separate oil-water mixtures.

[0024] Furthermore, the reaction temperature for the interfacial graft polymerization is 40-70°C, and the reaction time is 1-6 hours.

[0025] The 40-70℃ temperature range falls within the medium-low temperature range, which can rapidly initiate free radical polymerization, shortening reaction time (1-6 hours) and reducing energy consumption. This temperature range avoids polymer degradation caused by high temperatures, ensuring uniform molecular weight distribution, strong grafted layers, and resistance to detachment. For example, grafting acrylic monomers is more effective at 50-70℃. It is particularly suitable for temperature-sensitive materials, such as PTFE, maintaining the original properties of the substrate while enhancing surface hydrophilicity.

[0026] Furthermore, the post-treatment cleaning temperature is 50-70℃, and the drying temperature is 40-60℃.

[0027] Warm water at 50-70℃ effectively dissolves and removes residual unreacted monomers, initiators, and homopolymers. Increasing the temperature enhances the thermal motion and solubility of water molecules, resulting in more thorough cleaning and helping to prevent these impurities from clogging the membrane pores or slowly dissolving later, thus affecting product purity and membrane performance. This temperature range is far below the decomposition temperature of most hydrophilic polymers, avoiding the thermal shock or structural damage to the modified layer that could be caused by extreme conditions such as boiling water. Gentle hot cleaning relaxes the polymer network, helping to release internal stress and making the modified layer more stable. A drying temperature of 40-60℃ promotes moderate rearrangement and relaxation of hydrophilic polymer segments and helps to further complete the crosslinking reaction, making the bond between the hydrophilic layer and the PTFE base membrane stronger. This drying temperature is far below the boiling point of water, allowing moisture to evaporate slowly. If the drying temperature is too high (e.g., above 80℃), rapid vaporization of moisture may damage the microstructure of the modified layer and even the pore structure of the PTFE base membrane. Gentle drying effectively maintains the integrity of the membrane structure. The 0-70℃ cleaning water and 40-60℃ drying environment are easy to achieve and control in actual production, and the energy consumption is low. Compared with the prior art, the beneficial effects of the present invention are as follows: The hydrophilic modified polytetrafluoroethylene (PTFE) oil-removing membrane and its preparation method provided by this invention employ a novel chemical grafting modification strategy. The PTFE membrane surface is activated by low-temperature plasma, which then initiates co-grafting and cross-linking polymerization of hydrophilic monomers and cross-linking agents on the surface. This constructs a robust hydrophilic polymer brush with a three-dimensional network structure on the PTFE membrane surface. This polymer brush is stable, dense, and possesses excellent underwater superoleophobic properties. Through strong hydration, a stable hydration layer is formed at the membrane-water interface, endowing the PTFE membrane with excellent underwater superoleophobic properties. This significantly improves the oil-water separation efficiency, flux, and antifouling ability of the PTFE membrane, resulting in a high-efficiency PTFE oil-removing membrane with high flux, strong antifouling properties, and long service life. This method is simple, operates under mild conditions, is applicable to PTFE membranes of different configurations, is convenient for field application, and produces stable products with broad application prospects in various oily wastewater treatment fields. Detailed Implementation

[0028] The embodiments of the present invention will be described in detail below with reference to examples. However, those skilled in the art will understand that the following examples are for illustrative purposes only and should not be considered as limiting the scope of the invention. Unless otherwise specified in the examples, conventional conditions or conditions recommended by the manufacturer are followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0029] Example 1 PTFE degreasing film co-grafted with acrylic acid (AA) and hydroxyethyl methacrylate (HEMA): 1) Pretreatment of PTFE membrane: The PTFE membrane was ultrasonically cleaned in anhydrous ethanol for 20 minutes, rinsed with deionized water, and then dried at room temperature. 2) Plasma activation: The dried membrane was placed in an oxygen plasma treatment instrument and treated for 3 minutes at a power of 50 W and a pressure of 20 Pa. 3) Grafting solution preparation: Prepare an aqueous solution containing 5 wt% acrylic acid (AA), 5 wt% hydroxyethyl methacrylate (HEMA), 0.5 wt% N,N'-methylenebisacrylamide (MBA) and 0.3 wt% potassium persulfate (KPS), and stir well; 4) Grafting reaction: The activated PTFE membrane is completely immersed in the above grafting solution, nitrogen gas is passed through to remove oxygen for 5 minutes, and then it is placed in a 60℃ water bath for 3 hours to react. 5) Post-processing: After the reaction is complete, the membrane is removed, washed thoroughly with 60℃ hot water, and then dried in a 50℃ vacuum oven to obtain the modified membrane PTFE-g-(AA-co-HEMA).

[0030] Example 2 PTFE degreasing film co-grafted with acrylic acid (AA) and hydroxyethyl methacrylate (HEMA): 1) Pretreatment of PTFE membrane: The PTFE membrane was ultrasonically cleaned in anhydrous ethanol for 20 minutes, rinsed with deionized water, and then dried at room temperature. 2) Plasma activation: The dried membrane was placed in an oxygen plasma treatment instrument and treated for 3 minutes at a power of 50 W and a pressure of 20 Pa. 3) Grafting solution preparation: Prepare an aqueous solution containing 6 wt% acrylic acid (AA), 6 wt% hydroxyethyl methacrylate (HEMA), 0.6% N,N'-methylenebisacrylamide (MBA) and 0.4 wt% potassium persulfate (KPS), and stir well; 4) Grafting reaction: The activated PTFE membrane is completely immersed in the above grafting solution, nitrogen gas is passed through to remove oxygen for 5 minutes, and then it is placed in a 60℃ water bath for 3 hours to react. 5) Post-processing: After the reaction is complete, the membrane is removed, washed thoroughly with 60℃ hot water, and then dried in a 50℃ vacuum oven to obtain the modified membrane PTFE-g-(AA-co-HEMA).

[0031] Example 3 PTFE degreasing film co-grafted with acrylic acid (AA) and hydroxyethyl methacrylate (HEMA): 1) Pretreatment of PTFE membrane: The PTFE membrane was ultrasonically cleaned in anhydrous ethanol for 20 minutes, rinsed with deionized water, and then dried at room temperature. 2) Plasma activation: The dried membrane was placed in an oxygen plasma treatment instrument and treated for 3 minutes at a power of 50 W and a pressure of 20 Pa. 3) Grafting solution preparation: Prepare an aqueous solution containing 4 wt% acrylic acid (AA), 4 wt% hydroxyethyl methacrylate (HEMA), 0.4% N,N'-methylenebisacrylamide (MBA) and 0.2 wt% potassium persulfate (KPS), and stir well; 4) Grafting reaction: The activated PTFE membrane is completely immersed in the above grafting solution, nitrogen gas is passed through to remove oxygen for 5 minutes, and then it is placed in a 60℃ water bath for 3 hours to react. 5) Post-processing: After the reaction is complete, the membrane is removed, washed thoroughly with 60℃ hot water, and then dried in a 50℃ vacuum oven to obtain the modified membrane PTFE-g-(AA-co-HEMA).

[0032] Example 4 PTFE degreasing film grafted with sulfobetaine methacrylate (SBMA): 1) Pretreatment: Same as in Example 1; 2) Plasma activation: Same as in Example 1; 3) Grafting solution preparation: Prepare an aqueous solution containing 8 wt% sulfobetaine methacrylate (SBMA), 0.4 wt% MBA and 0.4 wt% KPS; 4) Grafting reaction: Immerse the activated membrane in the grafting solution and react at 60°C for 4 hours; 5) Post-processing: Same as in Example 1, to obtain the modified film.

[0033] Example 5 PTFE degreasing film grafted with sulfobetaine methacrylate (SBMA): 1) Pretreatment: Same as in Example 1; 2) Plasma activation: Same as in Example 1; 3) Grafting solution preparation: Prepare an aqueous solution containing 9 wt% sulfobetaine methacrylate (SBMA), 0.5 wt% MBA and 0.5 wt% KPS; 4) Grafting reaction: Immerse the activated membrane in the grafting solution and react at 60°C for 4 hours; 5) Post-processing: Same as in Example 1, to obtain the modified film.

[0034] Example 6 PTFE degreasing film grafted with sulfobetaine methacrylate (SBMA): 1) Pretreatment: Same as in Example 1; 2) Plasma activation: Same as in Example 1; 3) Grafting solution preparation: Prepare an aqueous solution containing 7 wt% sulfobetaine methacrylate (SBMA), 0.3 wt% MBA and 0.3 wt% KPS; 4) Grafting reaction: Immerse the activated membrane in the grafting solution and react at 60°C for 4 hours; 5) Post-processing: Same as in Example 1, to obtain the modified film.

[0035] Example 7 The steps for preparing the grafting solution, the grafting reaction, and the post-treatment are the same as in Example 1, except that the pretreatment and plasma activation steps are different from those in Example 1: 1) Pretreatment of PTFE membrane: The PTFE membrane was ultrasonically cleaned in anhydrous ethanol for 15 minutes, rinsed with deionized water, and then dried at room temperature. 2) Plasma activation: The dried membrane was placed in an oxygen plasma treatment instrument and treated for 2 minutes at a power of 50 W and a pressure of 20 Pa. Example 8 The pretreatment, plasma activation, and grafting solution preparation steps are the same as in Example 1, except that the grafting reaction and post-treatment steps are different from those in Example 1: 4) Grafting reaction: The activated PTFE membrane is completely immersed in the above grafting solution, nitrogen gas is passed through to remove oxygen for 5 minutes, and then it is placed in a 60℃ water bath for 2 hours to react. 5) Post-treatment: After the reaction is complete, the membrane is removed, washed thoroughly with 60℃ hot water, and then dried in a 40℃ vacuum oven to obtain the modified membrane PTFE-g-(AA-co-HEMA).

[0036] Comparative Example 1 The process steps for preparing the hydrophilic modified polytetrafluoroethylene degreasing film are the same as in Example 1, except that the mass percentages of acrylic acid (AA) and hydroxyethyl methacrylate (HEMA) in the raw materials are 3 wt%.

[0037] Comparative Example 2 The process steps for preparing the hydrophilic modified polytetrafluoroethylene degreasing film are the same as in Example 1, except that the mass percentage of N,N'-methylenebisacrylamide (MBA) in the raw materials is 0.2 wt%.

[0038] Comparative Example 3 The process steps for preparing the hydrophilic modified polytetrafluoroethylene degreasing film are the same as in Example 1, except that the mass percentage of potassium persulfate (KPS) in the raw materials is 0.1 wt%.

[0039] Comparative Example 4 The process steps for preparing the hydrophilic modified polytetrafluoroethylene degreasing film are the same as in Example 1, except that the reaction temperature for interfacial graft polymerization is 30°C and the reaction time is 0.8 hours.

[0040] Comparative Example 5 The process steps for preparing the hydrophilic modified polytetrafluoroethylene degreasing film are the same as in Example 1, except that the post-treatment cleaning temperature is 40°C and the drying temperature is 30°C.

[0041] Test Results The processing results of the above embodiments and comparative examples were subjected to performance tests. The performance tests for Examples 1-3 are as follows: Surface wettability: Measured using a contact angle meter: the air water contact angle (WCA) of the unmodified PTFE membrane was 125° (hydrophobic), and the underwater oil contact angle (UOCA, with dichloroethane as the test oil) was 130°.

[0042] The modified PTFE membrane (as shown in Table 1) has a water contact angle (WCA) in air that is reduced to 55° and an oil contact angle (UOCA) underwater that is increased to 132° (underwater superoleophobic).

[0043] Oil-water separation performance: A 1 g / L stable peanut oil / water emulsion (average oil droplet size approximately 2 µm) was prepared as the feed liquid. Under a transmembrane pressure of 0.1 MPa, the pure water flux of the modified membrane was 850 L / m²·h, the rejection rate of the above emulsion oil was >95%, and the permeate turbidity was <1 NTU, as shown in Table 1.

[0044] Antifouling and flux recovery rate: Five consecutive cycles of oil-water separation were conducted (1 hour of filtration per cycle). After each cycle, the membrane surface was simply rinsed with deionized water for 2 minutes. The modified membrane maintained a flux recovery rate (FRR) of over 88% in the fifth cycle, while the unmodified membrane experienced a flux drop of over 70% after the second cycle and was difficult to recover.

[0045] The performance tests for Examples 4-6 are as follows: Surface wettability: 50° for WCA and 135° for UOCA of the modified film.

[0046] Oil-water separation performance: For emulsions containing 1 wt% mineral oil, at 0.08 MPa, with an initial flux of 780 L m⁻²h⁻¹, the rejection rate is >95%.

[0047] Long-term stability test: After the modified membrane was continuously operated to treat emulsified oily wastewater containing surfactants for 100 hours, its UOCA and separation performance did not decrease significantly, indicating that the grafted layer has excellent chemical stability and anti-fouling durability.

[0048] The measurement results are shown in Table 1 below: Table 1

[0049] As can be seen from the measurement results in Table 1, after a reasonable design of the mass percentage of the raw material components in the modified layer of the hydrophilic modified polytetrafluoroethylene degreasing film, the water treatment effect of Examples 1-8 is better than that of Comparative Examples 1-5.

[0050] This is because when performing co-grafting and cross-linking polymerization on the surface of PTFE membranes, there is an optimal range of dosage for hydrophilic vinyl monomers, cross-linking agents, and initiators, and their dosage needs to be controlled within an appropriate range.

[0051] When the crosslinking density is too low, the modified layer will be incomplete, with insufficient hydrophilic groups, leading to a significant decrease in hydrophilicity and water flux. Insufficient crosslinking density will cause the modified layer to become a linear structure, which is prone to swelling and peeling, resulting in poor durability. Low initiation efficiency will lead to incomplete graft polymerization reaction.

[0052] Excessive hydrophilicity can lead to an overly thick modified layer, which is prone to swelling and clogging of membrane pores, resulting in a decrease in water flux. Excessive hydrophilicity can also weaken underwater oleophobicity. Excessive crosslinking density makes the membrane brittle and hard, significantly reducing water flux; it also decreases the flexibility of the modified layer, making it prone to cracking and detachment. Overly rapid or aggressive reactions can cause an increase in homopolymers, uneven grafting, and a rough, unstable modified layer.

[0053] The proportions of the hydrophilic vinyl monomer, crosslinking agent, and initiator in this invention are scientifically sound and reasonable. Furthermore, considering all examples 1-8, the metal oxide catalyst particles in Examples 1 and 4 produce the best results when added at the middle percentage range by weight.

[0054] Comparing Comparative Example 1 with Example 1, when the mass percentage of hydrophilic vinyl monomers in the raw material is too low, the modified layer is discontinuous and incomplete, unable to effectively cover the PTFE substrate, with insufficient hydrophilic groups, low water flux, and poor underwater oleophobicity (UOCA), thus reducing the oil-water separation treatment effect.

[0055] Comparing Comparative Example 2 with Example 1, when the mass percentage of N,N'-methylenebisacrylamide (MBA) in the raw material is too low, a sufficient three-dimensional network structure cannot be formed, and the modified layer degenerates from an ideal, stable network into a loose linear or branched structure. This results in a significant decrease in the crosslinking density of the entire modified layer, thus reducing the oil-water separation effect.

[0056] Comparing Comparative Example 3 with Example 1, when the mass percentage of potassium persulfate (KPS) in the raw material is too low, it cannot effectively attack the active sites (such as oxygen-containing free radicals) generated on the PTFE membrane surface after plasma activation, and it is also difficult to open the double bonds of vinyl monomers. This results in a slow start-up of the graft polymerization reaction or even its ineffectiveness. Even if the reaction occurs partially, the grafting rate of monomers will be very low due to the lack of active centers. This may lead to the inability to form a continuous and dense hydrophilic polymer layer on the PTFE surface, instead forming some sparse and isolated grafting points. The modified layer coverage is uneven, and complete hydrophilization cannot be achieved, directly affecting the efficiency of the graft polymerization reaction and thus reducing the oil-water separation treatment effect.

[0057] Comparing Comparative Example 4 with Example 1, when the reaction temperature and reaction time of the interfacial graft polymerization are too low, the monomers are difficult to fully graft onto the PTFE surface, resulting in insufficient grafting rate, poor hydrophilic modification effect, and low grafting rate. Insufficient grafting reduces the introduction of hydrophilic groups (such as hydroxyl and carboxyl groups), decreases hydrophilicity, and keeps the membrane surface hydrophobic, affecting its oil removal performance and thus reducing the oil-water separation effect.

[0058] Comparing Comparative Example 5 with Example 1, when the post-treatment cleaning temperature is too low, the solubility of the cleaning agent and surfactant decreases, making it difficult to effectively remove unreacted monomers, grafting byproducts, or impurities from the membrane surface. Incomplete removal of residues affects the membrane's hydrophilicity and oil removal performance. Similarly, when the drying temperature is too low, water or solvent cannot evaporate completely, resulting in residual water inside the membrane. Insufficient drying leads to decreased hydrophilicity or membrane structural instability, thus reducing the oil-water separation efficiency.

[0059] Application examples Application in the treatment of high-salt and oily wastewater: The PTFE-g-(AA-co-HEMA) membrane prepared in Example 1 was used to treat simulated high-salt oily wastewater containing 3 wt% NaCl and 1000 mg / L emulsified lubricating oil.

[0060] Separation performance: At 0.1 MPa, the membrane flux is 520 L m⁻² h⁻¹, the oil rejection rate is >95%, and the oil content in the effluent is <5 mg / L.

[0061] Salt fouling resistance: After 48 hours of continuous operation, the membrane flux stabilized at about 88% of the initial flux, demonstrating good resistance to salt ion fouling.

[0062] In summary, the efficient hydrophilic modified PTFE degreasing membrane preparation method of this invention utilizes plasma activation and controlled interfacial graft polymerization to firmly construct a strongly hydrophilic polymer brush with a three-dimensional network structure on the PTFE membrane surface. This modified layer, through effective hydration, endows the membrane with excellent underwater superoleophobic properties, achieving efficient, high-flux, and high-retention separation of emulsified oils, while exhibiting superior antifouling performance and operational stability. This method is simple, operates under mild conditions, and is applicable to PTFE membranes of different configurations, showing broad application prospects in various oily wastewater treatment fields.

[0063] Although the invention has been illustrated and described with reference to specific embodiments, it should be understood that many other changes and modifications can be made without departing from the spirit and scope of the invention. Therefore, it is intended that all such changes and modifications falling within the scope of the invention be included in the appended claims.

Claims

1. A hydrophilic modified polytetrafluoroethylene degreasing film, characterized in that, The modified layer of the hydrophilic modified polytetrafluoroethylene degreasing film is mainly made from the following raw materials by mass percentage: 8-12 wt% hydrophilic vinyl monomer, 0.3-0.6 wt% crosslinking agent, 0.2-0.5 wt% initiator, and the remainder is deionized water solvent.

2. The hydrophilic modified polytetrafluoroethylene degreasing film according to claim 1, characterized in that, The hydrophilic vinyl monomers include one or more combinations of acrylic acid, methacrylic acid, hydroxyethyl methacrylate, acrylamide, N-vinylpyrrolidone, and sulfobetaine methacrylate.

3. The hydrophilic modified polytetrafluoroethylene degreasing film according to claim 1, characterized in that, The crosslinking agent is a bifunctional reagent containing at least two vinyl groups, including: N,N'-methylenebisacrylamide and polyethylene glycol diacrylate.

4. The hydrophilic modified polytetrafluoroethylene degreasing film according to claim 2, characterized in that, When the hydrophilic vinyl monomer is a combination of acrylic acid and hydroxyethyl methacrylate, an acrylic acid and hydroxyethyl methacrylate co-grafted modified layer is formed. The acrylic acid and hydroxyethyl methacrylate co-grafted modified layer is mainly prepared from the following raw materials in the following mass percentages: 4-6 wt% acrylic acid, 4-6 wt% hydroxyethyl methacrylate, 0.4-0.6 wt% N,N'-methylenebisacrylamide, 0.2-0.4 wt% potassium persulfate, and the remainder is deionized water solvent.

5. The hydrophilic modified polytetrafluoroethylene degreasing film according to claim 4, characterized in that, The acrylic acid and hydroxyethyl methacrylate co-grafted modified layer is mainly prepared from the following raw materials in the following mass percentages: 5 wt% acrylic acid, 5 wt% hydroxyethyl methacrylate, 0.5 wt% N,N'-methylenebisacrylamide, 0.3 wt% potassium persulfate, and the remainder is deionized water solvent.

6. The hydrophilic modified polytetrafluoroethylene degreasing film according to claim 2, characterized in that, When the hydrophilic vinyl monomer is sulfobetaine methacrylate, a sulfobetaine methacrylate graft-modified layer is formed. The sulfobetaine methacrylate graft-modified layer is mainly prepared from the following raw materials in the following mass percentages: 7-9 wt% sulfobetaine methacrylate, 0.3-0.5 wt% N,N'-methylenebisacrylamide, and 0.3-0.5 wt% potassium persulfate, with the remainder being deionized water solvent.

7. The hydrophilic modified polytetrafluoroethylene degreasing film according to claim 6, characterized in that, The sulfobetaine methacrylate grafted modified layer is mainly prepared from the following raw materials in the following mass percentages: 8 wt% sulfobetaine methacrylate, 0.4 wt% N,N'-methylenebisacrylamide and 0.4 wt% potassium persulfate, with the remainder being deionized water solvent.

8. A method for preparing a hydrophilic modified polytetrafluoroethylene (PTFE) degreasing membrane, used to prepare the hydrophilic modified PTFE degreasing membrane as described in any one of claims 1-7, characterized in that, Includes the following steps: Pretreatment: The PTFE membrane is ultrasonically cleaned in an organic solvent to remove surface impurities; Plasma activation: The cleaned PTFE membrane is subjected to plasma treatment using oxygen plasma to introduce oxygen-containing active groups on its surface; Grafting solution preparation: Dissolve hydrophilic vinyl monomers, crosslinking agents and initiators in water to form a homogeneous grafting solution; Interfacial grafting polymerization: The activated PTFE membrane is immersed in the grafting solution and a free radical grafting copolymerization reaction is carried out under heating conditions; Post-processing: After the reaction is complete, the membrane is removed, cleaned and dried to obtain the modified PTFE degreasing membrane.

9. The method for preparing the hydrophilic modified polytetrafluoroethylene degreasing film according to claim 8, characterized in that, The reaction temperature for the interfacial graft polymerization is 40-70℃, and the reaction time is 1-6 hours.

10. The method for preparing the hydrophilic modified polytetrafluoroethylene degreasing film according to claim 8, characterized in that, The post-treatment cleaning temperature is 50-70℃, and the drying temperature is 40-60℃.

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