Filter membrane and preparation method thereof

Abstract

The invention provides a filter membrane and a preparation method thereof, and belongs to the technical field of microporous filter membranes. The filter membrane comprises a base membrane and a coating. Wherein the base membrane is a polytetrafluoroethylene porous membrane; the coating comprises a polymer containing a hydrophobic group, a silicon-oxygen bond and a hydrophilic group, and the hydrophobic group comprises a fluorine substituent group; the polymer is cross-linked through the silicon-oxygen bond, and the hydrophilic group is grafted on the silicon-oxygen bond. According to the filter membrane, a coating is formed on the surface of a base membrane, and polymers in the coating are polymerized and crosslinked through silicon-oxygen bonds to form the membrane. The coating structure effectively enhances the chemical stability of the surface of the filter membrane, so that the surface of the filter membrane has hydrophilicity and oxidation resistance, thereby prolonging the service life of the filter membrane, expanding the use scene of the filter membrane and ensuring that the filter membrane can still keep the surface hydrophilicity in a strong oxidant environment.

Description

Technical Field

[0001] The present invention relates to the technical field of microporous membranes, and particularly to a filter membrane and a preparation method thereof. Background Art

[0002] Polytetrafluoroethylene (PTFE) porous membranes have excellent chemical resistance, thermal stability and aging resistance, and are often used in separating and filtering liquids and gases, and encapsulating semiconductors and electronic components.

[0003] The inherently extremely low surface energy and strong hydrophobicity of PTFE porous membranes hinder the penetration of water through the membrane pores, resulting in the need for higher pressure to achieve effective filtration when using PTFE porous membranes in filtration equipment. Therefore, when applied in water filtration equipment, modifying the surface of the PTFE porous membrane with hydrophilic substances to create a hydrophilic coating becomes a necessary means. However, most current hydrophilic PTFE porous membranes are prone to losing their hydrophilicity in a relatively short time in water bodies with a high content of oxidants such as ozone, which in turn leads to performance degradation (such as poor wettability and reduced flux) and shortened service life of the PTFE porous membranes. Such PTFE porous membranes exhibit poor oxidant tolerance, greatly limiting their application in related fields.

[0004] Therefore, it is necessary to design a filter membrane and a preparation method thereof to improve the above problems. Summary of the Invention

[0005] In view of the above disadvantages of the prior art, the present invention provides a filter membrane and a preparation method thereof to improve the technical problem of poor oxidation tolerance of the currently hydrophilic modified PTFE porous membranes.

[0006] To achieve the above and other related purposes, the present invention provides a filter membrane, which includes a base membrane and a coating.

[0007] Wherein, the base membrane is a polytetrafluoroethylene porous membrane; the coating includes a polymer containing a hydrophobic group, a silicon-oxygen bond and a hydrophilic group, and the hydrophobic group includes a fluorine-substituted group; the polymer is cross-linked through the silicon-oxygen bond.

[0008] In an example of the present invention, the polymer is a block copolymer of the hydrophobic group, the silicon-oxygen bond and the hydrophilic group.

[0009] In an example of the present invention, the hydrophobic group is a perfluoro-substituted group.

[0010] In an example of the present invention, the hydrophilic group includes at least one of hydroxyl, carboxyl and amino.

[0011] In an example of the present invention, the hydrophobic group includes -[CF2-CF3] xand at least one of -[CF2]5-CF3, where x≥1.

[0012] In an example of the present invention, the hydrophilic group includes a hydroxyl group and a carboxyl group.

[0013] In an example of the present invention, in the coating, the polymer is adsorbed on the surface of the base film through the hydrophobic group, the polymer forms a network structure through polymerization crosslinking by the siloxane bond, and the hydrophilic group is grafted onto the network structure.

[0014] In an example of the present invention, one side of the coating has the hydrophobic group, the hydrophobic group is adsorbed to the carbon-fluorine bond on the base film, and the other side of the coating includes the network structure and the hydrophilic group grafted onto the network structure.

[0015] The present invention also provides a preparation method of the filter membrane according to any one of the above examples. The preparation method of the filter membrane includes:

[0016] Providing a base film, the base film is a polytetrafluoroethylene porous membrane;

[0017] Attaching a modifying substance to the surface of the base film to obtain a precursor filter membrane; the modifying substance is a polymer containing a hydrophobic group and a siloxane bond, and the hydrophobic group includes a fluorine-substituted group;

[0018] Crosslinking the modifying substance on the surface of the precursor filter membrane and performing hydrophilic modification on the precursor filter membrane to obtain a filter membrane.

[0019] In an example of the present invention, the attaching the modifying substance to the surface of the base film includes:

[0020] Obtaining a modifying substance formed by condensation of a surfactant and silanol; wherein, the surfactant is an amphiphilic copolymer, and the hydrophilic end of the surfactant condenses with the silanol to form the siloxane bond to form the modifying substance;

[0021] Immersing the base film in a solution containing the modifying substance so that the modifying substance is adsorbed on the surface of the base film.

[0022] In an example of the present invention, the surfactant includes at least one of Zonyl FSN-100, Zonyl FSO-100, Capstone FS-30, and Capstone FS-31.

[0023] In an example of the present invention, before the step of obtaining the modifying substance formed by polymerization of a surfactant and silanol, it further includes:

[0024] Hydrolyze the silane in a hydrolysis solution to obtain silanol; wherein, the silane includes at least one of tetraethoxysilane, tetramethoxysilane, methyltrimethoxysilane, methyltriethoxysilane, and tetrapropoxysilane.

[0025] In an example of the present invention, crosslinking the modifying substances on the surface of the precursor filter membrane and performing hydrophilic modification on the surface of the precursor filter membrane includes:

[0026] Prepare a hydrophilic modification solution, which includes an initiator, an ester substance, a second acidic substance, and a solvent;

[0027] Apply the hydrophilic modification solution to the surface of the precursor filter membrane and heat the precursor filter membrane so that the modifying substances crosslink on the surface of the precursor filter membrane to form a coating, and hydrophilic groups are attached to the coating.

[0028] In an example of the present invention, in the hydrophilic modification solution, the mass ratio of the initiator is 5% - 15%, the mass ratio of the ester substance is 5% - 10%, and the mass ratio of the second acidic substance is 40% - 55%; wherein, the initiator includes at least one of ammonium persulfate and potassium persulfate, the ester substance includes at least one of dimethyl carbonate and diethyl carbonate, and the second acidic substance includes at least one of formic acid and glacial acetic acid.

[0029] The present invention provides a filter membrane, on the surface of the base membrane of which a coating is formed. The polymer in the coating is polymerized and crosslinked into a film through silicon-oxygen bonds, and the hydrophilic groups in the coating are stably grafted onto the silicon-oxygen bonds. The above coating structure effectively enhances the chemical stability of the filter membrane surface, enables the filter membrane surface to have both hydrophilicity and antioxidant properties, thereby extending the service life of the filter membrane, expanding the usage scenarios of the filter membrane, and ensuring that the filter membrane can still maintain surface hydrophilicity in a strong oxidant environment. Description of the Drawings

[0030] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other embodiments can also be obtained according to these drawings.

[0031] Figure 1 is the optical photo of the PTFE membrane before and after modification;

[0032] Figure 2 is the scanning electron microscope image of the PTFE membrane before and after modification;

[0033] Figure 3Schematic diagram of the filter membrane structure in an embodiment of the present invention;

[0034] Figure 4 Schematic flow chart of the preparation method of the filter membrane in an embodiment of the present invention;

[0035] Figure 5 Schematic process flow diagram of the preparation of the filter membrane in an embodiment of the present invention;

[0036] Figure 6 Graph of the change in pure water flow rate measured for the filter membranes prepared in Example 1 and Comparative Example 2 in an ozone environment. Detailed implementation manners

[0037] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts belong to the scope of protection of the present invention.

[0038] It should be noted that the diagrams provided in this embodiment only illustrate the basic concept of the present invention in a schematic manner. Therefore, only the components related to the present invention are shown in the diagrams, rather than being drawn according to the number, shape, and size of the components in actual implementation. The type, quantity, and ratio of each component in actual implementation can be arbitrarily changed, and the component layout type may also be more complex.

[0039] In the present invention, it should be noted that when terms such as "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc. appear, the orientation or positional relationship indicated is based on the orientation or positional relationship shown in the accompanying drawings. This is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation to the present application. In addition, when terms such as "first" and "second" appear, they are only used for descriptive and distinguishing purposes, and cannot be understood as indicating or implying relative importance.

[0040] On the one hand, the present application provides a filter membrane, the surface of which has both hydrophilicity and antioxidant properties and can be used in common with oxidants without being easily oxidized.

[0041] The above filter membrane includes a base membrane and a coating. The base membrane is a polytetrafluoroethylene (PTFE) porous membrane, and the chemical formula of the PTFE porous membrane is -[CF2-CF2] n -, and due to the strong electronegativity and low polarizability of fluorine atoms in the PTFE porous membrane, it exhibits extremely low surface tension. For example, the surface tension of the PTFE porous membrane is 25 - 33×10 -3N / m. Moreover, due to the completely symmetric carbon-fluorine bond structure (C-F bond) of the perfluorocarbon chains in the PTFE porous membrane, the two side surfaces of the PTFE porous membrane exhibit strong hydrophobicity.

[0042] The coating is adsorbed on the surface of the base membrane. The coating includes a polymer containing hydrophobic groups, silicon-oxygen bonds, and hydrophilic groups. In the coating, the polymers are cross-linked by polymerization through silicon-oxygen bonds, and the silicon-oxygen bonds polymerize to form a three-dimensional network structure; the hydrophilic groups are connected to the network structure and stably adhere to the surface of the coating. The network structure formed by the polymerization of silicon-oxygen bonds can establish an antioxidant layer on the surface of the coating. The chemical properties of the antioxidant layer are stable, which can effectively prevent the coating from being oxidized and damaged by oxidants and avoid the exposure of the hydrophobic surface of the PTFE porous membrane to the external environment. Since the hydrophilic groups are connected to the network structure, they can be exposed on the surface of the filter membrane and are not easily oxidized and damaged by oxidants. While bringing hydrophilicity to the surface of the coating, the hydrophilic groups effectively ensure the tolerance of their own structure to oxidants, thereby making the surface of the coating exhibit both hydrophilicity and antioxidant properties.

[0043] The hydrophobic groups on the polymer include fluorine-substituted groups, and the polymer is evenly and firmly adsorbed on the hydrophobic surface of the base membrane through the hydrophobic groups. The hydrophobic groups are adsorbed to the carbon-fluorine bonds on the base membrane through intermolecular forces, thereby driving the polymer to be tightly adsorbed and evenly distributed on the surface of the base membrane, making the polymer cross-linked to form a network structure evenly distributed on the surface of the base membrane, and making the hydrophilic groups connected to the network structure exposed on the surface of the filter membrane, thereby making the coating structure formed by the cross-linking of the polymer on the base membrane more dense and uniform.

[0044] It should be noted that the hydrophobic groups include at least one fluorine-substituted group. The type of the fluorine-substituted group in this application is not limited. The fluorine-substituted group can be a partially fluorinated group. For example, the partially fluorinated group can be selected from at least one of fluoromethyl, 1-fluoroethyl, 2-fluoroethyl, difluoromethyl, difluoroethyl, fluoromethoxy, and difluoromethoxy; the fluorine-substituted group can also be a perfluorinated group. For example, the perfluorinated group can be selected from at least one of perfluoroalkyl (such as trifluoromethyl, pentafluoroethyl, heptafluoropropyl), perfluorocycloalkyl (such as perfluorocyclohexyl), perfluoroaryl (such as pentafluorophenyl), and perfluoroether group (such as trifluoromethoxy). In some embodiments, the fluorine-substituted group can be selected from at least one of -[CF2-CF3] x and -[CF2]5-CF3, where x≥1.

[0045] In addition, it should be noted that in this application, the type of hydrophilic group on the polymer may not be limited. The hydrophilic group can be any group that can be connected to the network structure and has hydrophilicity. For example, in some embodiments, the hydrophilic group can be selected from at least one of hydroxyl group, carboxyl group, and amino group. That is, the hydrophilic group can be any one of the types listed above, such as hydroxyl group, carboxyl group, or amino group. Optionally, the hydrophilic group can be carboxyl group or hydroxyl group; the hydrophilic group can also include any combination of the types listed above, such as the hydrophilic group can include hydroxyl group and carboxyl group, or hydroxyl group and amino group, or carboxyl group and amino group, or hydroxyl group, carboxyl group, and amino group.

[0046] The polymer in the coating is a block copolymer containing hydrophobic groups, siloxane bonds, and hydrophilic groups. The block copolymer can be a triblock copolymer (such as hydrophobic group - siloxane bond - hydrophilic group), or a multiblock copolymer (such as (hydrophobic group - siloxane bond - hydrophilic group)n). In some embodiments, the polymer is a triblock copolymer of hydrophobic groups, siloxane bonds, and hydrophilic groups. The triblock copolymer adsorbs on the surface of the base film through the hydrophobic group at one end and polymerizes and cross-links with each other by the siloxane bonds between them, thereby forming a three-dimensional network structure covering the surface of the base film and exposing the hydrophilic group at the other end to the surface of the coating.

[0047] As Figure 3 shown, in some embodiments, in the coating, the chemical formula of the cross-linked polymer can be represented as shown in structural formula (1), and structural formula (1) is as follows:

[0048]

[0049] In the formula, Rh represents a hydrophilic group, and Rf represents a hydrophobic group. It should be noted that formula (1) only represents the connection relationship between the Si atom and the hydrophobic group Rf and between the Si atom and the hydrophilic group Rh, and does not limit the connection structure between the Si atom and the hydrophobic group Rf and between the Si atom and the hydrophilic group Rh, nor does it limit the number of siloxane bonds connected to the hydrophobic group Rf and the number of hydrophilic groups Rh connected to the Si atom in the connection relationship. Among them, the Si atom and the hydrophobic group Rf can be directly connected by a covalent bond or can be connected through other intermediate groups, such as connected through an ether bond (-O-), a carbon-oxygen bond (-C-O-), or a carbon-carbon bond (-C-C-); similarly, the Si atom and the hydrophilic group Rh can be directly connected by a covalent bond or can be connected through other intermediate groups, such as connected through a methylene group, a carbon-oxygen bond (-C-O-), or a carbon-carbon bond (-C-C-).

[0050] As Figure 3As shown, in the filter membrane, the side of the coating adsorbed to the base membrane has a hydrophobic group (Rf), and the hydrophobic group (Rf) is adsorbed to the carbon-fluorine bond (C-F) on the base membrane through hydrophobic interaction. The side of the coating facing away from the base membrane includes a network structure (-Si-O-Si-) and a hydrophilic group (Rh) connected to the network structure. The network structure and the hydrophilic group constitute the surface of the coating exposed to the outside. As Figure 1 and Figure 2 shown, compared with the uncoated PTFE original membrane, a dense and uniform coating structure is formed on the surface of the PTFE porous membrane modified by this application. The coating structure uniformly and highly covers the surface of the PTFE porous membrane, and the coating structure can still maintain the integrity of the membrane layer after being tested and used in an ozone oxidant environment without being damaged by the ozone oxidant.

[0051] As Figure 6 shown, in the filtration test of the PTFE porous membrane modified by this application in an ozone environment, the pure water flow rate filtered by the modified PTFE porous membrane does not show obvious attenuation with the extension of the use time, which proves that the hydrophilic group on the surface of the filter membrane coating is not easily damaged by the oxidant.

[0052] On the other hand, the present invention also provides a method for preparing a filter membrane. As Figure 4 and Figure 5 shown, the method for preparing the filter membrane includes the following steps:

[0053] S1. Provide a base membrane, and the base membrane is a polytetrafluoroethylene porous membrane;

[0054] S2. Attach a modifying substance to the surface of the base membrane to obtain a precursor filter membrane; the modifying substance is a polymer containing a hydrophobic group and a silicon-oxygen bond, and the hydrophobic group includes a fluorine-substituted group;

[0055] S3. Crosslink the modifying substance on the surface of the precursor filter membrane and perform hydrophilic modification on the precursor filter membrane to obtain a filter membrane.

[0056] In some embodiments, step S1 further includes performing a pre-wetting treatment on the base membrane to facilitate the coating and attachment of the modifying substance on the surface of the base membrane in subsequent steps. Specifically, the base membrane is wetted with an alcohol solution for 2 to 5 minutes. Among them, the alcohol solution is selected from one or more combinations of methanol, ethanol, and isopropanol.

[0057] In some embodiments, step S2 includes the following steps:

[0058] S21. Obtain a modifying substance formed by the condensation of a surfactant and silanol.

[0059] The surfactant is an amphiphilic copolymer. The surfactant has a hydrophilic end and a hydrophobic end. The hydrophilic end includes hydrophilic groups such as ether bond (-O-), hydroxyl group (-OH), etc. The hydrophobic end includes hydrophobic groups such as fluorine-substituted groups. For example, the hydrophobic group can be a perfluoro-substituted group, such as it can be selected from -[CF2-CF3] x and at least one of -[CF2]5-CF3, where x≥1.

[0060] The hydrophilic end of the surfactant condenses with silanol to form a stable silicon-oxygen bond, thereby forming a modified substance. One end of the formed modified substance has a hydrophobic group, and the other end has a silicon-oxygen bond. For example, the ether bond (C-O-C) and hydroxyl group (-OH) in the hydrophilic end of the surfactant undergo a condensation reaction with silanol, and after removing water molecules, a stable silicon-oxygen bond (≡Si-O-C or ≡Si-O-Si) is formed. The specific reaction formula example is ≡Si-OH + R-OH → ≡Si-O-R + H2O.

[0061] Specifically, in step S21, the prepared silanol solution is heated to 70-90 °C; then the surfactant is slowly added to the silanol solution, and during the addition, the concentration of the surfactant in the silanol solution is maintained at 0.5-1 g / L. After continuing to stir for 10-20 minutes, heating and stirring are stopped, thereby obtaining a solution containing the modified substance.

[0062] It should be noted that the surfactant can be any amphiphilic copolymer whose hydrophilic end includes an ether bond and / or a hydroxyl group and whose hydrophobic end includes a perfluoro-substituted group. For example, in some embodiments, the surfactant is selected from at least one of Zonyl FSN-100, Zonyl FSO-100, Capstone FS-30, and Capstone FS-31. The structural formulas of Zonyl FSN-100, Zonyl FSO-100, Capstone FS-30, and Capstone FS-31 are shown as follows:

[0063]

[0064] In the formula, x≥1 and y≥1.

[0065] In addition, in some embodiments, the silanol in step S21 is obtained by hydrolyzing silane. Specifically, a hydrolysis solution is prepared and stirred evenly, for example, the hydrolysis solution is stirred evenly at a rotation speed of 800 to 1000 rpm. Among them, the hydrolysis solution can be an acid solution or a base solution, and the specific type is adjusted based on the type of silane. The acidic environment or basic environment in the hydrolysis solution is used to accelerate the hydrolysis reaction of silane; then, the evenly stirred hydrolysis solution is heated to 40 to 90 °C, and silane is slowly added to the hydrolysis solution. During the addition process, the concentration of silane in the hydrolysis solution is maintained at 0.15 to 0.25 mol / L, and continuous stirring is carried out for 20 to 40 min, so that the silane in the hydrolysis solution is continuously hydrolyzed, thereby hydrolyzing and converting silane into silanol.

[0066] Among them, the silane includes at least one of tetraethoxysilane (TEOS), tetramethoxysilane (TMOS), methyltrimethoxysilane (MTMS), methyltriethoxysilane (MTES), and tetrapropoxysilane (TPOS).

[0067] It should be noted that in step S21, the pH value and heating temperature of the prepared hydrolysis solution can be adaptively adjusted based on the type of silane to be hydrolyzed. For example, when the silane is TMOS, the hydrolysis temperature to which the hydrolysis solution is heated is 50 to 80 °C, and the hydrolysis solution can be an acid solution or a base solution; when the silane is TEOS, the hydrolysis temperature to which the hydrolysis solution is heated is 60 to 90 °C, and the pH value of the hydrolysis solution is 2 to 8; when the silane is MTMS, the hydrolysis temperature to which the hydrolysis solution is heated is 20 °C to 60 °C, and the hydrolysis solution is an acidic solution; when the silane is MTES, the hydrolysis temperature to which the hydrolysis solution is heated is 40 °C to 70 °C, and the hydrolysis solution can be an acid solution or a base solution. Optionally, the hydrolysis solution is a base solution, and the pH value of the hydrolysis solution is 8 to 10; when the silane is TPOS, the hydrolysis temperature to which the hydrolysis solution is heated is 70 °C to 100 °C, the hydrolysis solution is an acid solution, and the pH value of the hydrolysis solution is 2 to 5. In addition, when the hydrolysis solution is an acid solution, the first acidic substance in the acid solution includes at least one of glacial acetic acid and hydrochloric acid; when the hydrolysis solution is a base solution, the base solution can be ammonia water.

[0068] S22. Immerse the base film in a solution containing a modifying substance so that the modifying substance is adsorbed on the surface of the base film. Among them, the modifying substance has a hydrophobic end inherited from the surfactant, and the hydrophobic end can be adsorbed on the surface of the base film through hydrophobic interaction, thereby driving the uniform adsorption of the modifying substance on the surface of the base film.

[0069] Specifically, in step S22, the base film is immersed in a solution containing a modifying substance and left to soak for 14 to 18 hours, so that the modifying substance in the solution adheres to the surface of the base film; after the base film soaking is completed, the base film is taken out and dried, and the drying temperature and time are not required, just dry it.

[0070] In some embodiments, step S3 includes the following steps:

[0071] S31. Configure the hydrophilic modification solution;

[0072] Specifically, add the initiator, ester substance, and second acidic substance to the solvent in sequence, and stir well until the initiator, ester substance, and second acidic substance are completely dissolved to obtain the hydrophilic modification solution.

[0073] In the hydrophilic modification solution, the mass proportion of the initiator is any value in the range of 5% to 15%, for example, it can be 5%, 7%, 9%, 10%, 12%, 14%, or 15%; if the dosage of the initiator in the hydrophilic modification solution is too small, it will lead to insufficient grafting of hydrophilic groups on the surface of the filter membrane, resulting in insufficient improvement of the hydrophilicity of the filter membrane; if the dosage of the initiator in the hydrophilic modification solution is too large, it will cause excessive cross-linking on the surface of the filter membrane, thereby causing membrane pore blockage.

[0074] In the hydrophilic modification solution, the mass proportion of the second acidic substance is 40% to 55%, for example, it can be 40%, 43%, 45%, 47%, 50%, 53%, or 55%. The second acidic substance can generate hydrophilic groups in the hydrophilic modification solution and use the acidic environment to dominate the grafting of hydrophilic groups on the surface of the precursor filter membrane.

[0075] In the hydrophilic modification solution, the mass proportion of the ester substance is any value in the range of 5% to 10%, for example, it can be 5%, 6%, 7%, 8%, 9%, or 10%. The alcohol substance, as a co-solvent, can promote the uniform dispersion of the initiator and the second acidic substance in the hydrophilic solution, thereby regulating the reaction rate of the modification substance and the hydrophilic group and the generation of by-products; at the same time, the alcohol substance can also partially hydrolyze to generate hydroxyl (-OH) or carbonate groups under acidic high-temperature conditions, thereby participating in the surface modification of the precursor filter membrane.

[0076] Among them, the initiator is selected from at least one of ammonium persulfate and potassium persulfate; the ester substance is selected from at least one of dimethyl carbonate and diethyl carbonate; the second acidic substance is selected from at least one of formic acid and glacial acetic acid; the solvent can be selected as water.

[0077] S32. Coat the hydrophilic modification solution on the surface of the precursor filter membrane, and heat the precursor filter membrane with the hydrophilic modification solution coated on its surface so that the modification substance cross-links on the surface of the precursor filter membrane to form a coating, and the hydrophilic groups adhere to the coating.

[0078] In step S32, immerse the precursor filter membrane in the hydrophilic modification solution, after impregnating for 5 to 10 minutes, then take it out and place it in a steam environment at 90 to 110 °C for heating reaction for 5 to 10 minutes.

[0079] When the current body filter membrane is infiltrated with a hydrophilic modification solution and placed in a steam environment for heating reaction, for the areas on the base membrane not covered by the modified substance, the sulfate radicals decomposed by the initiator in the acidic environment will attack the exposed C-F bonds on the surface molecular chains of the precursor filter membrane, so that the hydrophilic groups of the acid in the hydrophilic solution (such as carboxyl groups) are grafted onto the surface of the base membrane not covered by the modified substance through the reaction of sulfate radicals, forming a -PTFE-hydrophilic group structure, such as -PTFE-COOH; for the areas of the modified substance attached to the base membrane, the modified substance undergoes a cross-linking reaction in the high-temperature steam environment, and the modified substances polymerize through the siloxane bonds between each other to form a three-dimensional cross-linked network structure, and the hydrophilic groups combine with the network structure under the promotion of the acidic environment. For example, the hydrophilic groups combine with the siloxane bond (-Si-O-Si-) or combine with the unreacted -Si-OH bond, so as to adhere to the coating surface, such as -Si-O-Si-OH, -Si-O-Si-(CH2)3-NH2 or -Si-O-Si-(CH2)3-COOH.

[0080] In addition, it should be noted that the hydrophilic groups on the finally formed coating, in addition to the hydrophilic groups bound to the network structure in the acidic environment, also include the hydroxyl groups carried by the incompletely condensed silanols. Such groups exist in the coating in the form of -Si-O-Si-OH structure.

[0081] The technical solutions of the present invention will be described in detail below through several specific examples and comparative examples. Unless otherwise specified, the raw materials and reagents used in the following examples are all commercially available products or can be prepared by conventional methods in the art.

[0082] Example 1

[0083] This example provides a filter membrane, and the preparation method of the filter membrane includes the following steps:

[0084] (1) Using a PTFE porous membrane as the base membrane, the pore size of the PTFE porous membrane is 0.22 μm, and the base membrane is wetted with an ethanol solution for 3 minutes;

[0085] (2) Prepare a solution containing a modified substance: Configure an acetic acid solution with a pH value of 3, stir the acetic acid solution evenly at a speed of 1000 rpm, and heat it to 80 °C for standby; Slowly add tetramethoxysilane to the acetic acid solution so that its concentration remains at 0.20 mol / L, and continuously stir for 30 minutes to effectively hydrolyze the tetramethoxysilane; Continue to add the surfactant Zonyl FSO-100 to the acetic acid solution, adjust the surfactant concentration to 1.5 g / L, stop heating and stirring after stirring for 20 minutes;

[0086] (3) Immerse the base film obtained in step (1) into the solution containing the modifying substance, and let it stand for deposition for 18 hours; after the immersion is completed, take it out and place it in an oven to dry and heat at 70 °C for 10 minutes to obtain a precursor filter membrane;

[0087] (4) Prepare a hydrophilic modification solution: sequentially add ammonium persulfate as an initiator with a mass fraction of 10%, glacial acetic acid with a mass fraction of 50%, and diethyl carbonate with a mass fraction of 5% to water as a solvent, and stir well at a rotation speed of 500 rpm at room temperature for about 30 minutes. After the solute is completely dissolved, a hydrophilic modification solution is obtained;

[0088] (5) Immerse the precursor filter membrane obtained in step (3) into the hydrophilic modification solution. After impregnation for 8 minutes, take it out and place it in a steam environment at 100 °C to heat and react for 8 minutes;

[0089] (6) Take out the filter membrane obtained in step (5) and wash it. First, wash it in hot water at 60 °C for 5 minutes, then wash it in cold water at 20 °C for 5 minutes, and finally dry it to obtain a modified filter membrane.

[0090] Example 2

[0091] This example provides a filter membrane, and the preparation method of this filter membrane includes the following steps:

[0092] (1) Use a PTFE porous membrane as the base film. The pore size of this PTFE porous membrane is 0.22 μm, and wet the base film with an isopropanol solution for 5 minutes;

[0093] (2) Prepare a solution containing a modifying substance: configure a hydrochloric acid solution with a pH value of 2, stir the hydrochloric acid solution evenly at a rotation speed of 800 rpm, and heat it to 70 °C for standby; slowly add tetraethoxysilane to the hydrochloric acid solution to keep its concentration at 0.25 mol / L, and continuously stir for 40 minutes to effectively hydrolyze tetraethoxysilane; continue to add the surfactant Zonyl FSN-100 to the hydrochloric acid solution, adjust the surfactant concentration to 1.0 g / L, and stop heating and stirring after stirring for 30 minutes;

[0094] (3) Immerse the base film obtained in step (1) into the solution containing the modifying substance, and let it stand for deposition for 16 hours; after the immersion is completed, take it out and place it in an oven to dry and heat at 70 °C for 10 minutes to obtain a precursor filter membrane;

[0095] (4) Prepare a hydrophilic modification solution: sequentially add potassium persulfate as an initiator with a mass fraction of 5%, formic acid with a mass fraction of 55%, and dimethyl carbonate with a mass fraction of 5% to water as a solvent, and stir well at a rotation speed of 500 rpm at room temperature for about 30 minutes. After the solute is completely dissolved, a hydrophilic modification solution is obtained;

[0096] (5) Immerse the precursor filter membrane obtained in step (3) in the hydrophilic modification solution for 5 minutes, then take it out and place it in a 90°C steam environment for heating reaction for 10 minutes;

[0097] (6) The filter membrane obtained in step (5) is taken out and cleaned, first in 60°C hot water for 3 minutes, then in 30°C cold water for 3 minutes, and finally dried to obtain the modified filter membrane.

[0098] Example 3

[0099] This embodiment provides a filter membrane, and the preparation method of the filter membrane comprises the following steps:

[0100] (1) Using a PTFE porous membrane as a base membrane, the pore size of the PTFE porous membrane is 0.22 μm, and wetting the base membrane with a methanol solution for 2 minutes;

[0101] (2) Prepare a solution containing a modified substance: prepare a glacial acetic acid solution with a pH value of 2.5, stir the glacial acetic acid solution at a speed of 900 rpm, and heat it to 90° C. for standby use; slowly add tetramethoxysilane to the glacial acetic acid solution to keep its concentration at 0.15 mol / L, and continue stirring for 20 minutes to effectively hydrolyze the tetramethoxysilane; continue to add surfactant Capstone FS-30 to the glacial acetic acid solution, adjust the surfactant concentration to 2.0 g / L, stir for 20 minutes, and then stop heating and stirring;

[0102] (3) Immerse the base membrane obtained in step (1) into a solution containing a modified substance, and allow to stand for 14 hours; take it out after immersion, and place it in an oven for drying and heating at 70° C. for 10 minutes to obtain a precursor filter membrane;

[0103] (4) preparing a hydrophilic modification solution: adding 15% by mass of an initiator potassium persulfate, 40% by mass of glacial acetic acid, and 10% by mass of diethyl carbonate to a solvent water, stirring the mixture at 500 rpm for about 30 minutes at room temperature, and obtaining a hydrophilic modification solution after the solute is completely dissolved;

[0104] (5) Immerse the precursor filter membrane obtained in step (3) in the hydrophilic modification solution for 10 minutes, then take it out and place it in a 110° C. steam environment for heating and reaction for 5 minutes;

[0105] (6) The filter membrane obtained in step (5) is taken out and cleaned, first in 70°C hot water for 5 minutes, then in 20°C cold water for 3 minutes, and finally dried to obtain the modified filter membrane.

[0106] Comparative Example 1

[0107] This comparative example provides a PTFE porous membrane without surface modification, and the pore size of the PTFE porous membrane is 22 μm.

[0108] Comparative Example 2

[0109] In this comparative example, a filter membrane was prepared. The filter membrane was only hydrophilically modified on the surface of the PTFE porous membrane. The preparation process of the filter membrane included the following steps:

[0110] (1) Using the PTFE porous membrane as the base membrane, the pore size of the PTFE porous membrane was 0.22 μm, and the base membrane was wetted with an ethanol solution for 3 minutes;

[0111] (2) Preparing a hydrophilic modification solution: successively adding ammonium persulfate as an initiator with a mass fraction of 10%, glacial acetic acid with a mass fraction of 50%, and diethyl carbonate with a mass fraction of 5% into the solvent water, and fully stirring at a speed of 500 rpm at room temperature for about 30 minutes. After the solute was completely dissolved, a hydrophilic modification solution was obtained;

[0112] (3) Immersing the base membrane into the hydrophilic modification solution. After impregnation for 8 minutes, it was taken out and placed in a steam environment at 100 °C for heating reaction for 8 minutes;

[0113] (4) Taking out the filter membrane obtained in step (3) for cleaning, first cleaning in hot water at 60 °C for 5 minutes, then cleaning in cold water at 20 °C for 5 minutes, and finally drying to obtain the modified filter membrane.

[0114] Comparative Example 3

[0115] In this comparative example, a filter membrane was prepared. In the preparation process of the filter membrane, hydrophilic treatment was first performed on the surface, and then a silane deposition film was formed on the surface. The preparation method of the filter membrane included the following steps:

[0116] (1) Using the PTFE porous membrane as the base membrane, the pore size of the PTFE porous membrane was 0.22 μm, and the base membrane was wetted with an ethanol solution for 3 minutes;

[0117] (2) Preparing a hydrophilic modification solution: successively adding ammonium persulfate as an initiator with a mass fraction of 10%, glacial acetic acid with a mass fraction of 50%, and diethyl carbonate with a mass fraction of 5% into the solvent water, and fully stirring at a speed of 500 rpm at room temperature for about 30 minutes. After the solute was completely dissolved, a hydrophilic modification solution was obtained;

[0118] (3) Immersing the filter membrane obtained in step (3) into the hydrophilic modification solution. After impregnation for 8 minutes, it was taken out and placed in a steam environment at 100 °C for heating reaction for 8 minutes;

[0119] (4) Preparation of a solution containing a modifying substance: Prepare an acetic acid solution with a pH value of 3, stir the acetic acid solution evenly at a speed of 1000 rpm, and heat it to 80 °C for standby; slowly add tetramethoxysilane to the acetic acid solution to keep its concentration at 0.20 mol / L, and continuously stir for 30 minutes to enable the effective hydrolysis of tetramethoxysilane; continue to add the surfactant Zonyl FSO-100 to the acetic acid solution, adjust the surfactant concentration to 1.5 g / L, stir for 20 minutes, and then stop heating and stirring;

[0120] (5) Immerse the filter membrane obtained in step (3) into the solution containing the modifying substance, and let it stand for deposition for 18 hours; after the immersion is completed, take it out and place it in an oven to dry and heat at 70 °C for 10 minutes;

[0121] (6) Take out the filter membrane obtained in step (5) and wash it. First, wash it in hot water at 60 °C for 5 minutes, then wash it in cold water at 20 °C for 5 minutes, and finally dry it to obtain the modified filter membrane.

[0122] To further verify the efficacy of the present invention, first, perform wettability, filtration flow rate, and bubble point tests on the filter membranes prepared in Examples 1 to 3 and Comparative Examples 1 to 3. The test results are shown in Table 1.

[0123] Wettability test: Take filter membrane samples of Examples 1 to 3 and Comparative Examples 1 to 3 with a certain area (generally a circular piece with a diameter of 46 mm), immerse them in pure water, observe the wetting situation, and record the time when the membrane is completely wetted by pure water.

[0124] Flow rate and bubble point tests: According to GB / T 32361-2015 "Test Method for Separation Membrane Pore Size - Bubble Point and Average Flow Method", for the filter membrane samples of Examples 1 to 3 and Comparative Examples 1 to 3, first perform pure water flux tests (test pressure is 70 KPa) on the filter membrane samples that are not ozone oxidation resistant; then place the filter membrane samples in an ozone oxidant environment, store them for 9 days, and then perform pure water flux tests (test pressure is 70 KPa) to obtain the flow rate test and bubble point test results of the filter membrane samples before and after oxidation resistance.

[0125] Table 1: Performance test results of the filter membranes prepared in Examples 1 to 3 and Comparative Examples 1 to 2

[0126]

[0127] Compare the test results of Examples 1 to 3 and Comparative Example 2 and Figure 6, it can be seen that for the filter membrane prepared in Comparative Example 2, only hydrophilic modification was carried out on the surface of the PTFE porous membrane and it does not have antioxidant ability. The surface hydrophilicity of the filter membrane will be greatly damaged after storage in an oxidant environment, resulting in a significant reduction in the pure water flow rate filtered by the filter membrane after storage in an oxidant environment, and the filtration performance of the filter membrane decays severely. For the filter membranes prepared in Examples 1 to 3, an antioxidant layer formed by cross-linking of siloxane bonds is first adsorbed on the surface of the PTFE porous membrane, and then hydrophilic groups are firmly grafted onto the antioxidant layer, thereby ensuring that the hydrophilic groups on the surface of the filter membrane are not easily damaged by oxidants. As shown in the test results, after the filter membranes prepared in Examples 1 to 3 are stored in an ozone oxidant environment for 9 days, there are only slight changes in their surface hydrophilic properties and the pure water flow rate of filtration, and no significant attenuation occurs, which effectively proves that the filter membrane of the present application has both antioxidant and hydrophilic properties.

[0128] Comparing the test results of Examples 1 to 3 and Comparative Example 3, it can be seen that for the filter membrane prepared in Comparative Example 3, hydrophilic modification was first carried out on the surface of the PTFE porous membrane, and then a silane antioxidant layer was deposited on the PTFE porous membrane. During the hydrophilic modification process, due to the lack of cross-linking anchor points provided by the surfactant on the surface of the PTFE porous membrane, only a small amount of active sites formed by the attack of initiator free radicals on the C-F bonds of the PTFE porous membrane are bonded to the hydrophilic groups, and the silane deposition layer mainly provides antioxidant support and will continue to form a network structure on the surface of this weak hydrophilic layer, and cannot provide antioxidant protection for the hydrophilic groups on the surface of the filter membrane. Therefore, even if the filter membrane prepared in Comparative Example 3 is not used in an oxidant environment, its hydrophilicity and the pure water flow rate of filtration are much lower than those of the filter membranes in Examples 1 to 3; after the filter membrane prepared in Comparative Example 3 is stored in an oxidant environment, its hydrophilicity and the pure water flow rate of filtration will still show a large degree of attenuation.

[0129] In summary, the present invention provides a filter membrane and a preparation method thereof. The coating adsorbed on the surface of the filter membrane has both antioxidant and hydrophilic properties, greatly extending the service life of the filter membrane and effectively expanding the use scenarios of the filter membrane, enabling the filter membrane to be used in a strong oxidant environment while still maintaining surface hydrophilicity.

[0130] The above embodiments are only illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Any person familiar with this technology can modify or change the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or changes completed by those with ordinary knowledge in the technical field without departing from the spirit and technical ideas disclosed by the present invention should still be covered by the claims of the present invention.

Claims

1. A filter membrane, characterized in that, Comprising: A base film, the base film being a polytetrafluoroethylene porous film; A coating, the coating comprising a polymer containing a hydrophobic group, a silicon-oxygen bond and a hydrophilic group, the hydrophobic group including a fluorine-substituted group; Wherein, the polymer is crosslinked through the silicon-oxygen bond.

2. The filter membrane according to claim 1, wherein The polymer is a block copolymer of the hydrophobic group, the silicon-oxygen bond and the hydrophilic group; wherein, the hydrophobic group is a perfluoro-substituted group; and / or, the hydrophilic group includes at least one of a hydroxyl group, a carboxyl group and an amino group.

3. The filter membrane according to claim 1 or 2, characterized in that, The hydrophobic group includes -[CF2-CF3] x and at least one of -[CF2]5-CF3, where x≥1; and / or, the hydrophilic group includes a hydroxyl group and a carboxyl group.

4. The filter membrane according to claim 1 or 2, characterized in that, In the coating, the polymer is adsorbed on the surface of the base film through the hydrophobic group; and / or, the polymer forms a network structure through polymerization crosslinking of the silicon-oxygen bond, and the hydrophilic group is grafted on the network structure.

5. The filter membrane according to claim 4, characterized in that, One side of the coating has the hydrophobic group, the hydrophobic group is adsorbed to the carbon-fluorine bond on the base film, and the other side of the coating includes the network structure and the hydrophilic group grafted on the network structure.

6. A method for preparing a filter membrane, characterized in that, Comprising: Providing a base film, the base film being a polytetrafluoroethylene porous film; Attaching a modifying substance to the surface of the base film to obtain a precursor filter membrane; The modifying substance is a polymer containing a hydrophobic group and a silicon-oxygen bond, the hydrophobic group including a fluorine-substituted group; Crosslinking the modifying substance on the surface of the precursor filter membrane and performing hydrophilic modification on the precursor filter membrane to obtain a filter membrane.

7. The preparation method according to claim 6, characterized in that, The attaching a modifying substance to the surface of the base film includes: Obtaining a modifying substance formed by condensation of a surfactant and silanol; wherein, the surfactant is an amphiphilic copolymer, and the hydrophilic end of the surfactant condenses with the silanol to form the silicon-oxygen bond to form the modifying substance; Immersing the base film in a solution containing the modifying substance so that the modifying substance is adsorbed on the surface of the base film.

8. The preparation method according to claim 7, characterized in that, The surfactant includes at least one of Zonyl FSN-100, Zonyl FSO-100, Capstone FS-30 and Capstone FS-31.

9. The preparation method according to claim 6, wherein Before the step of obtaining the modifying substance formed by polymerization of a surfactant and silanol, it further includes: Hydrolyzing silane in a hydrolysis solution to obtain silanol; wherein, the silane includes at least one of tetraethoxysilane, tetramethoxysilane, methyltrimethoxysilane, methyltriethoxysilane and tetrapropoxysilane.

10. The preparation method according to claim 6, characterized in that, The crosslinking the modifying substance of the precursor filter membrane and performing hydrophilic modification on the surface of the precursor filter membrane includes: Preparing a hydrophilic modification solution, the hydrophilic modification solution including an initiator, an ester substance, a second acidic substance and a solvent; Coating the hydrophilic modification solution on the surface of the precursor filter membrane and heating the precursor filter membrane so that the modifying substance crosslinks on the surface of the precursor filter membrane to form a coating, and the hydrophilic group attaches to the coating.

11. The preparation method according to claim 10, characterized in that, In the hydrophilic modification solution, the mass ratio of the initiator is 5% - 15%, the mass ratio of the ester substance is 5% - 10%, and the mass ratio of the second acidic substance is 40% - 55%; wherein, the initiator includes at least one of ammonium persulfate and potassium persulfate, the ester substance includes at least one of dimethyl carbonate and diethyl carbonate, and the second acidic substance includes at least one of formic acid and glacial acetic acid.

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