A hydrophilic-oleophobic polytetrafluoroethylene membrane, its preparation method and application

Abstract

This invention discloses a hydrophilic-oleophobic polytetrafluoroethylene (PTFE) membrane, its preparation method, and its application, belonging to the field of PTFE membrane processing and manufacturing technology. The invention first prepares graphene oxide using a modified Hummers method, then oxidizes it with chloroacetic acid to obtain carboxylated graphene oxide. Polyvinylidene fluoride (PVDF) is used as a crosslinking agent and mixed with CGO in different proportions and dispersed in N,N-dimethylformamide. After ultrasonic dispersion, the mixture is poured into a mold containing a PTFE membrane for reaction. A dopamine-tris(hydroxymethyl)aminomethane / hydrochloric acid solution is then prepared and slowly poured into the mold containing the PTFE membrane for further crosslinking reaction to obtain the hydrophilic-oleophobic PTFE membrane. The hydrophilic-oleophobic PTFE membrane has a rougher surface structure and exhibits strong negative charge properties, demonstrating asymmetric wettability and high water affinity, effectively solving the problems of shortened service life and reduced retention effect caused by wettability in existing membrane materials.

Description

Technical Field

[0001] This invention belongs to the field of polytetrafluoroethylene membrane processing and manufacturing technology, specifically relating to a hydrophilic-oleophobic polytetrafluoroethylene membrane, its preparation method and application. Background Technology

[0002] Polytetrafluoroethylene (PTFE) microporous membranes are made from PTFE resin particles mixed with additives and matured, then expanded, stretched, and heat-set at temperatures below their melting point to form a microporous membrane with excellent filtration performance. PTFE microporous membranes have a microporous structure with interwoven fibers, offering advantages such as high porosity, low resistance, high particle rejection rate, good temperature resistance, resistance to strong acids and alkalis, resistance to organic solvents, antioxidants, and aging. Filter bags, cartridges, and filters made by coating PTFE microporous membranes onto support materials such as polyester felt, PET, and PTFE fiber felt have shown good performance in flue gas and dust treatment and recovery in the cement, metallurgy, petrochemical, and plastics industries. Filter sheets and filters made by coating PTFE microporous membranes onto support materials such as PET and PP nonwoven fabrics also have promising applications in the chemical, pharmaceutical, and electronics industries.

[0003] Furthermore, polytetrafluoroethylene (PTFE) is considered a promising material for seawater treatment due to its excellent chemical stability, corrosion resistance, high mechanical strength, and separation efficiency. However, the strong hydrophobic properties of PTFE make the membrane material susceptible to fouling during use, limiting its application prospects. To improve the application rate of PTFE membranes in various scenarios, the hydrophilicity of the membrane material can be enhanced, thereby reducing its wettability when in contact with organic matter, extending its service life, and improving its efficiency. Therefore, modification treatments such as dual-hydrophobicity modification, superhydrophobicity modification, and antifouling modification of PTFE membranes have become a hot research topic both domestically and internationally.

[0004] Currently, methods for surface hydrophilic modification of polytetrafluoroethylene (PTFE) membranes are divided into physical and chemical methods. The most commonly used physical modification method suffers from low coating adhesion after modification, while chemical methods such as plasma treatment and radiation grafting are limited by their significant damage to the membrane surface, expensive equipment, and complex operation procedures. Therefore, to better utilize PTFE membranes in the purification of seawater with high organic content, research is needed on a PTFE membrane that is hydrophilic in air and oleophobic underwater, along with its modification methods. Improving its surface wettability and enhancing its surfactant rejection rate is of great practical significance and has broad application prospects.

[0005] The invention disclosed in CN110743396A presents a porous graphene composite pervaporation membrane material for preferential alcohol permeation and its preparation method. The main steps include preparing porous graphene using a combination of Hummers redox and hydrothermal methods, further hydrophobically modifying it, and then composite it with PDMS to prepare the pervaporation membrane for preferential alcohol permeation. The resulting porous graphene composite pervaporation membrane for preferential alcohol permeation exhibits good film-forming properties and mechanical properties, achieving preferential alcohol permeation and can be used in pervaporation systems. However, this pervaporation membrane is mainly composed of porous graphene, offering no technical inspiration for polytetrafluoroethylene (PTFE) materials. Furthermore, its excellent separation performance is primarily for the permeation separation of alcohols and cannot be applied to reducing the wettability of organic matter. The invention disclosed in CN112452159A provides a method for preparing a superhydrophilic-underwater superoleophobic microfiltration membrane. The method utilizes an interfacial assembly approach. First, a nanostructured composite coating is formed on the surface of the microfiltration membrane through electrostatic co-assembly of tannic acid / polyethyleneimine composite nanoparticles. Second, using the composite nanostructured coating as a template, metal ions are introduced to form a metal-polyphenol network with tannic acid, further enhancing the hydrophilicity of the nanostructured composite coating and preparing the superhydrophilic-underwater superoleophobic microfiltration membrane. However, this microfiltration membrane requires the simultaneous construction of a dual cross-linked network structure of metal-polyphenol coordination and tannic acid-polyethyleneimine electrostatic complexation within the nanostructured composite coating. The membrane itself has a complex structure, and the preparation process is challenging. Summary of the Invention

[0006] To address the problems existing in the prior art, this invention utilizes a surface deposition strategy to improve the hydrophilicity of the membrane surface, transforming the initial surface of the membrane material, which is hydrophobic in air and superoleophilic underwater, into a surface that is hydrophilic in air and oleophobic underwater.

[0007] The technical solution of the present invention is as follows:

[0008] One objective of this invention is to provide a method for preparing a hydrophilic-oleophobic polytetrafluoroethylene membrane, comprising the following steps:

[0009] (1) Graphene oxide was prepared by a modified Hummers method;

[0010] (2) The graphene oxide obtained in step (1) was oxidized with chloroacetic acid to obtain carboxylated graphene oxide;

[0011] (3) Carboxylated graphene oxide and polyvinylidene fluoride were mixed and dispersed in N,N-dimethylformamide solution in a certain proportion, and ultrasonically dispersed to obtain a dispersion.

[0012] (4) Pour the dispersion into a sand core filter device with a polytetrafluoroethylene membrane, and after the reaction, rinse the surface with acetone solution to remove excess dispersion.

[0013] (5) Prepare a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution and add dopamine to the solution;

[0014] (6) Pour the solution prepared in (5) back into the sand core filter device with a polytetrafluoroethylene membrane, and vacuum dry it after the reaction to obtain a hydrophilic-oleophobic polytetrafluoroethylene membrane.

[0015] Further, in step (1), concentrated sulfuric acid is added to a beaker, and after the temperature drops, graphite powder is added and stirred evenly. Then, potassium permanganate granules are slowly added, and after stirring and reacting, the temperature inside the beaker is raised to 45°C and stirred continuously. After the solution turns dark brown and becomes viscous, deionized water and hydrogen peroxide are poured into the beaker and the reaction is continued until the solution turns golden yellow and the reaction ends. The solution is centrifuged until the pH of the supernatant is neutral, and graphene oxide is obtained after freeze-drying.

[0016] Furthermore, the mass ratio of concentrated sulfuric acid, graphite powder, and potassium permanganate particles is 20:1:6, and the volume ratio of deionized water and hydrogen peroxide is 1:1.

[0017] Furthermore, in step (2), the graphene oxide powder is ultrasonically dispersed with deionized water until uniform, and then chloroacetic acid is added and ultrasonically stirred. After the reaction is completed, the graphene oxide powder is centrifuged and washed with deionized water, and then freeze-dried to obtain carboxylated graphene oxide.

[0018] Furthermore, the mass ratio of the graphene oxide powder to chloroacetic acid is 1:10.

[0019] Furthermore, in step (3), the mass ratio of carboxylated graphene oxide to polyvinylidene fluoride is 10 to 40:1.

[0020] Furthermore, in step (4), the sand core filtration device consists of a suction cup, a filter head, and a conical flask from top to bottom. The filter cup interface between the suction cup and the filter head is fixed with a clamp, and the polytetrafluoroethylene membrane is placed at the filter cup interface.

[0021] Furthermore, the concentration of the dopamine solution in step (5) is 2-5 g / L.

[0022] The second objective of this invention is to provide a hydrophilic-oleophobic polytetrafluoroethylene membrane, wherein the hydrophilic-oleophobic polytetrafluoroethylene membrane has a rough surface structure and forms a hydration layer structure on the rough membrane surface when in contact with water.

[0023] The third objective of this invention is to provide an application of a hydrophilic-oleophobic polytetrafluoroethylene membrane in seawater with a high organic content.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] 1. This invention innovatively prepares a hydrophilic-oleophobic polytetrafluoroethylene (PTFE) membrane. It utilizes carboxylated graphene oxide (CGO) to modify the traditional PTFE membrane, giving it a rougher surface structure. Then, dopamine is used to crosslink the deposited CGO layer. The addition of dopamine not only connects the CGO layer to the PTFE membrane but also further enhances the membrane's hydrophilicity. Compared to unmodified PTFE membrane materials, the surface-modified PTFE membrane exhibits higher hydrophilicity and roughness, displaying asymmetry in wettability. It transforms from a surface that is hydrophobic in air and superoleophilic underwater into a surface that is hydrophilic in air and oleophobic underwater. This effectively solves the problems of shortened service life and reduced retention efficiency of existing PTFE membranes when treating seawater with high organic content due to poor wettability. Furthermore, it achieves a 99% retention rate for organic solvents.

[0026] 2. To obtain a hydrophilic-underwater superoleophobic microfiltration membrane with excellent anti-oil adhesion properties, this invention provides a method for preparing a hydrophilic-oleophobic polytetrafluoroethylene (PTFE) membrane. First, graphene oxide is prepared using a modified Hummers method. Then, chloroacetic acid is used to oxidize the graphene oxide to prepare carboxylated graphene oxide, providing more active sites for subsequent modification of the PTFE membrane material. Second, compared to conventional blending methods, this method employs a surface deposition modification strategy, allowing the modifier to act more directly on the surface of the membrane material, improving its performance. Furthermore, this method uses PVDF as a crosslinking agent to modify the carboxylated graphene oxide on the surface of the PTFE membrane, and adds a dopamine layer to the membrane surface, enhancing the crosslinking effect and hydrophilicity, further improving the membrane material's anti-wetting and oleophobic properties. Finally, this invention places the PTFE membrane in a sand core filter device for pressure deposition, increasing the crosslinking degree between CGO and PDA and the PTFE membrane, resulting in a tighter bond between the crosslinked layer and the PTFE membrane, reducing detachment problems during use and minimizing impact on service life.

[0027] 3. The hydrophilic-oleophobic polytetrafluoroethylene membrane disclosed in this invention has unique advantages in treating seawater with high organic content. It has the advantages of low oil adhesion, high flux, high separation efficiency and excellent structural stability. It can overcome the problems of low selectivity, low separation efficiency and short membrane life of conventional microfiltration membrane products. Moreover, the preparation method is simple, easy to operate and environmentally friendly. The structure is controllable and has prospects for industrial application.

[0028] Figure Labels

[0029] Figure 1 The diagram shows the structure of the hydrophilic-oleophobic polytetrafluoroethylene membrane prepared according to Examples 1-3 of the present invention; wherein, 1, CGO / PDA layer, 2, PTFE membrane, 3, PTFE membrane;

[0030] Figure 2 This is a schematic diagram of the sand core filtration device for preparing hydrophilic-oleophobic polytetrafluoroethylene membranes in Examples 1-3 of the present invention. Detailed Implementation

[0031] The present invention will be further described below with reference to the accompanying drawings and preferred embodiments. The embodiments given are only for illustrating the present invention and are not intended to limit the scope of the present invention.

[0032] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0033] In the quantitative experiments in the following examples, three replicate experiments were set up, and the average value of the results was taken.

[0034] Unless otherwise specified, the experimental methods in the following examples are conventional methods;

[0035] Example 1

[0036] This embodiment provides a hydrophilic-oleophobic polytetrafluoroethylene membrane, the preparation method of which includes the following steps:

[0037] S1. Add 120mL of concentrated sulfuric acid to a beaker. When the temperature drops to 0℃, add 5g of graphite powder to the beaker. After stirring continuously for 1 hour, slowly add 30g of potassium permanganate to the beaker and stir for 3 hours.

[0038] S2. After the reaction is complete, heat the temperature inside the beaker to 45°C and continue stirring for 1 hour. When the solution gradually becomes thick and dark brown, slowly pour 100 mL of deionized water into the beaker. After stirring for 10 minutes, add 100 mL of hydrogen peroxide into the beaker until the solution turns golden yellow. The reaction is then complete.

[0039] S3. Centrifuge the graphene oxide (GO) suspension until the pH of the GO solution supernatant is neutral, stop centrifugation, and freeze-dry the graphene oxide (GO) solution in a dryer.

[0040] S4. Disperse 0.1g of graphene oxide (GO) powder evenly with 500mL of deionized water by ultrasonication, then add 1g of chloroacetic acid and stir ultrasonically for 3h. After the reaction is completed, wash with deionized water by centrifugation and freeze-dry to obtain carboxylated graphene oxide (CGO).

[0041] S5. Mix 10 mg of carboxylated graphene oxide (CGO) with 1 mg of polyvinylidene fluoride (PVDF) powder and place the mixture in a 250 mL beaker. Add 100 mL of N,N-dimethylformamide solution to the mixture and sonicate to disperse the mixture evenly for 6 hours to obtain a uniform dispersion.

[0042] S6. Pour the dispersion into a sand core filter device with a polytetrafluoroethylene membrane sandwiched in, react at room temperature for 4 hours, and then rinse the surface with acetone solution to remove excess CGO and PVDF.

[0043] S7. Prepare a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, add dopamine to the solution to a concentration of 2 g / L, pour the prepared solution back into a sand core filter device with a polytetrafluoroethylene membrane, and vacuum dry at room temperature for 24 h to obtain a hydrophilic-oleophobic polytetrafluoroethylene membrane.

[0044] Example 2

[0045] This embodiment provides a method for preparing a hydrophilic-oleophobic polytetrafluoroethylene membrane, comprising the following steps:

[0046] S1. Add 120mL of concentrated sulfuric acid to a beaker. When the temperature drops to 0℃, add 5g of graphite powder to the beaker. After stirring continuously for 1 hour, slowly add 30g of potassium permanganate to the beaker and stir the reaction for 3 hours.

[0047] S2. After the reaction is complete, heat the temperature inside the beaker to 45°C and continue stirring for 1 hour. When the solution gradually becomes thick and dark brown, slowly pour 100 mL of deionized water into the beaker. After stirring for 10 minutes, add 100 mL of hydrogen peroxide into the beaker until the solution turns golden yellow. The reaction is then complete.

[0048] S3. Centrifuge the graphene oxide (GO) suspension until the pH of the GO solution supernatant is neutral, stop centrifugation, and freeze-dry the graphene oxide (GO) solution in a dryer.

[0049] S4. Disperse 0.1g of graphene oxide (GO) powder evenly with 500mL of deionized water by ultrasonication, then add 1g of chloroacetic acid and stir ultrasonically for 3h. After the reaction is completed, wash with deionized water by centrifugation and freeze-dry to obtain carboxylated graphene oxide (CGO).

[0050] S5. Mix 20 mg of carboxylated graphene oxide (CGO) with 5 mg of polyvinylidene fluoride (PVDF) powder and place the mixture in a 250 mL beaker. Add 100 mL of N,N-dimethylformamide solution to the mixture and sonicate to disperse the mixture evenly for 6 hours to obtain a uniform dispersion.

[0051] S6. Pour the dispersion into a sand core filter device with a polytetrafluoroethylene membrane sandwiched in, react at room temperature for 6 hours, and then rinse the surface with acetone solution to remove excess CGO and PVDF.

[0052] S7. Prepare a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, add dopamine to the solution to a concentration of 2 g / L, pour the prepared solution back into a sand core filter device with a polytetrafluoroethylene membrane, and vacuum dry at room temperature for 24 h to obtain a hydrophilic-oleophobic polytetrafluoroethylene membrane.

[0053] Example 3

[0054] This embodiment provides a method for preparing a hydrophilic-oleophobic polytetrafluoroethylene membrane, comprising the following steps:

[0055] S1. Add 120mL of concentrated sulfuric acid to a beaker. When the temperature drops to 0℃, add 5g of graphite powder to the beaker. After stirring continuously for 1 hour, slowly add 30g of potassium permanganate to the beaker and stir the reaction for 3 hours.

[0056] S2. After the reaction is complete, heat the temperature inside the beaker to 45°C and continue stirring for 1 hour. When the solution gradually becomes thick and dark brown, slowly pour 100 mL of deionized water into the beaker. After stirring for 10 minutes, add 100 mL of hydrogen peroxide into the beaker until the solution turns golden yellow. The reaction is then complete.

[0057] S3. Centrifuge the graphene oxide (GO) suspension until the pH of the GO solution supernatant is neutral, stop centrifugation, and freeze-dry the graphene oxide (GO) solution in a dryer.

[0058] S4. Disperse 0.1g of graphene oxide (GO) powder evenly with 500mL of deionized water by ultrasonication, then add 1g of chloroacetic acid and stir ultrasonically for 3h. After the reaction is completed, wash with deionized water by centrifugation and freeze-dry to obtain carboxylated graphene oxide (CGO).

[0059] S5. Mix 20 mg of carboxylated graphene oxide (CGO) with 5 mg of polyvinylidene fluoride (PVDF) powder and place the mixture in a 250 mL beaker. Add 100 mL of N,N-dimethylformamide solution to the mixture and sonicate to disperse the mixture evenly for 6 hours to obtain a uniform dispersion.

[0060] S6. Pour the dispersion into a sand core filter device with a polytetrafluoroethylene membrane sandwiched in, react at room temperature for 6 hours, and then rinse the surface with acetone solution to remove excess CGO and PVDF.

[0061] S7. Prepare a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution, add dopamine to the solution to a concentration of 5 g / L, pour the prepared solution back into a sand core filter device with a polytetrafluoroethylene membrane, and vacuum dry at room temperature for 24 h to obtain a hydrophilic-oleophobic polytetrafluoroethylene membrane.

[0062] Performance testing

[0063] 1. Membrane contact angle test

[0064] The water and oil contact angles of the modified hydrophilic-oleophobic polytetrafluoroethylene (PTFE) membranes of Examples 1-3 of this invention and the unmodified PTFE membrane materials were measured using a DSA*20 instrument from Kruss Inc. First, small volumes of water (5 μL) and cyclohexane were respectively transferred onto the test membrane materials using a microsyringe. Then, images of the droplets remaining on the surface were recorded using a digital camera. Finally, the contact angles in water and oil were measured using the image analysis software included with the DSA*20 instrument. The test results are shown in Table 1.

[0065] As shown in Table 1, the water contact angle of the modified hydrophilic-oleophobic polytetrafluoroethylene membranes in Examples 1-3 of the present invention is significantly smaller than that of the unmodified polytetrafluoroethylene membrane material, exhibiting moderate hydrophilicity. At the same time, the oil contact angle of the modified hydrophilic-oleophobic polytetrafluoroethylene membranes in Examples 1-3 is significantly higher than that of the unmodified polytetrafluoroethylene membrane material, demonstrating higher anti-wetting and oleophobic properties.

[0066] Table 1. Membrane contact angle test results

[0067]

[0068] 2. Membrane retention rate test

[0069] After homogenization, the water samples were filtered through the modified hydrophilic-oleophobic polytetrafluoroethylene membranes of Examples 1-3 of this invention and the unmodified polytetrafluoroethylene membrane materials. The total carbon content (TOC) of dissolved and suspended organic matter in the water before and after filtration was measured as the organic matter retention value. The test results are shown in Table 2.

[0070] Test method: Add a small amount of organic water sample to be tested into a small combustion furnace, heat it to 600-980℃, and then use platinum metal as a catalyst to oxidize the organic pollutants. The organic matter is completely oxidized by instantaneous combustion.

[0071] As shown in Table 2, the modified hydrophilic-oleophobic polytetrafluoroethylene membranes of Examples 1-3 of the present invention have a higher total carbon (TOC) rejection rate for dissolved and suspended organic matter in water than the unmodified polytetrafluoroethylene membrane material. This indicates that the hydrophilic-oleophobic polytetrafluoroethylene membrane prepared by the present invention can alleviate the problems of shortened service life and reduced rejection effect in the current treatment of seawater with high organic content.

[0072] Table 2 Membrane retention rate test results

[0073]

[0074] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a hydrophilic-oleophobic polytetrafluoroethylene membrane, characterized in that, Includes the following steps: (1) Graphene oxide was prepared by a modified Hummers method; (2) The graphene oxide obtained in step (1) is oxidized with chloroacetic acid to obtain carboxylated graphene oxide; (3) Carboxylated graphene oxide and polyvinylidene fluoride were mixed and dispersed in N,N-dimethylformamide solution in a certain proportion, and ultrasonically dispersed to obtain a dispersion; (4) Pour the dispersion into a sand core filter device with a polytetrafluoroethylene membrane, and after the reaction, rinse the surface with acetone solution to remove excess dispersion. (5) Prepare a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution and add dopamine to the solution; (6) Pour the solution prepared in (5) back into the sand core filter device with polytetrafluoroethylene membrane sandwiched in it. After the reaction, vacuum dry it to obtain a hydrophilic-oleophobic polytetrafluoroethylene membrane. In step (3), the mass ratio of carboxylated graphene oxide to polyvinylidene fluoride is 10 to 40:

1.

2. The method for preparing a hydrophilic-oleophobic polytetrafluoroethylene membrane as described in claim 1, characterized in that, In step (1), concentrated sulfuric acid is added to a beaker. After the temperature drops, graphite powder is added and stirred evenly. Then, potassium permanganate granules are slowly added. After stirring and reacting, the temperature inside the beaker is raised to 45 °C and stirred continuously. When the solution turns dark brown and becomes viscous, deionized water and hydrogen peroxide are poured into the beaker and the reaction is continued until the solution turns golden yellow. The reaction is then stopped. The solution is centrifuged until the pH of the supernatant is neutral. After freeze-drying, graphene oxide is obtained.

3. The method for preparing a hydrophilic-oleophobic polytetrafluoroethylene membrane as described in claim 2, characterized in that, The mass ratio of concentrated sulfuric acid, graphite powder, and potassium permanganate granules is 20:1:6, and the volume ratio of deionized water and hydrogen peroxide is 1:

1.

4. The method for preparing a hydrophilic-oleophobic polytetrafluoroethylene membrane as described in claim 1, characterized in that, In step (2), graphene oxide powder is ultrasonically dispersed with deionized water until uniform, and then chloroacetic acid is added and ultrasonically stirred. After the reaction is completed, deionized water is used for centrifugal washing, and carboxylated graphene oxide is obtained after freeze drying.

5. The method for preparing a hydrophilic-oleophobic polytetrafluoroethylene membrane as described in claim 4, characterized in that, The mass ratio of the graphene oxide powder to chloroacetic acid is 1:

10.

6. The method for preparing a hydrophilic-oleophobic polytetrafluoroethylene membrane as described in claim 1, characterized in that, In step (4), the sand core filtration device consists of a suction cup, a filter head, and a conical flask from top to bottom. The filter cup interface between the suction cup and the filter head is fixed with a clip, and the polytetrafluoroethylene membrane is placed at the filter cup interface.

7. The method for preparing a hydrophilic-oleophobic polytetrafluoroethylene membrane as described in claim 1, characterized in that, The concentration of dopamine solution in step (5) is 2-5 g / L.

8. A hydrophilic-oleophobic polytetrafluoroethylene membrane prepared by the method according to any one of claims 1 to 7, characterized in that, The hydrophilic-oleophobic polytetrafluoroethylene membrane has a rough surface structure, and when it comes into contact with water, a hydration layer structure is formed on the rough membrane surface.

9. The application of a hydrophilic-oleophobic polytetrafluoroethylene membrane prepared by the method according to any one of claims 1 to 7 in the purification and treatment of seawater with high organic content.

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