Polyethylene hydrophilic separation membrane as well as preparation method and application thereof

Abstract

The invention discloses a polyethylene hydrophilic separation membrane and a preparation method and application thereof, the polyethylene hydrophilic separation membrane comprises a polyethylene membrane main body, an active middle layer is deposited on the surface of the polyethylene membrane main body, the active middle layer is an interwoven network structure polymer, and at least a chain segment of the active middle layer enters a chain segment gap of the polyethylene membrane main body. At least chain segments form an interwoven network structure on the surface of the polyethylene film main body, the surface of the active middle layer is also provided with a surface hydrophilic layer formed by reaction of a hydrophilic polymer, and the surface hydrophilic layer at least has hydrophilic polymer chain segments which are wound and connected with the interwoven network structure of the active middle layer. The interwoven network structure of the active middle layer plays a connecting role, so that the hydrophilic polymer can be wound and connected with the active middle layer, the hydrophilic polymer can be combined with the polyethylene film in a cross-linked network form to form a stable three-layer structure, and the problem that a hydrophilic substance is easy to fall off in a hydrophilic modification process is solved; the characteristic that the polyethylene film is not wet when encountering water can be effectively changed.

Description

Technical Field

[0001] The present invention relates to the field of membrane separation technology, in particular to a polyethylene hydrophilic separation membrane and a preparation method and application thereof. Background Art

[0002] In recent years, with the continuous expansion of industrial scale and the increasing environmental protection requirements, the industrial filter material industry has shown a significant market size worldwide. High-performance filter materials have become a key area for future development. Through the application of high-efficiency filtration technology and regeneration technology, not only can environmental pollution be reduced, but also discarded filter elements can be recycled, thereby reducing operating costs and meeting the requirements of sustainable development.

[0003] The research and development of high-performance filtration materials is one of the key factors driving the development of the industry. Materials such as PTFE membranes, PE membranes, PES membranes, ceramic membranes and metal membranes, due to their high precision at the micron level and below, can achieve multiple functions such as filtration, separation, purification and concentration, and cover many fields of modern industry. Therefore, the research and development and application of these materials not only improve the filtration efficiency, but also meet the needs of different industries for high-quality products, which is of great significance and application value for promoting industrial development and environmental protection.

[0004] Among them, polyethylene film (PE film) is known for its excellent mechanical strength. It still maintains good flexibility and chemical stability under low temperature conditions, can withstand strong acid and strong alkali environments, and exhibits good solvent stability at room temperature. Therefore, it is suitable for filtering various liquid environments such as strong acid and alkaline liquids with complex components, oily liquids and organic liquids. However, due to the surface properties of PE film, it is difficult to be wetted by water. The carbon atoms in the PE molecular chain are connected by single bonds, resulting in a close arrangement between molecules, which is not conducive to the penetration of water molecules. This poor surface hydrophilicity has become the main limiting factor for its application in the separation and filtration industry, and needs to be improved through surface modification.

[0005] At present, the commonly used modification methods all have corresponding limitations. For example, plasma polymerization can introduce a large number of hydrophilic groups on the membrane surface to improve hydrophilicity, but it is costly and complicated to operate, making it difficult to apply on a large scale; ultraviolet irradiation can make the membrane obtain good hydrophilicity in a short time, but it is complicated to operate and difficult to achieve industrial production; chemical coating method is easy to operate and low in cost, but the surface modified coating material is easy to swell or decompose in water, resulting in a decrease in coating performance and easy to fall off. Therefore, it is urgent to prepare a surface modified polyethylene membrane by a method with simple process and appropriate cost, and the hydrophilic layer of the polyethylene membrane is not easy to fall off and has long-lasting excellent hydrophilicity.

[0006] In view of this, the present invention is proposed. Summary of the invention

[0007] The object of the present invention is to provide a polyethylene hydrophilic separation membrane and a preparation method and application thereof, so as to improve the above technical problems.

[0008] The present invention is achieved in that:

[0009] In the first aspect, the present invention provides a polyethylene hydrophilic separation membrane, which includes a polyethylene membrane main body, an active intermediate layer deposited on the surface of the polyethylene membrane main body, the active intermediate layer is an interwoven network structure polymer, and the active intermediate layer has at least segments entering the segment gaps of the polyethylene membrane main body, at least segments forming an interwoven network structure on the surface of the polyethylene membrane main body, the surface of the active intermediate layer also has a surface hydrophilic layer formed by the reaction of a hydrophilic polymer, and the surface hydrophilic layer has at least hydrophilic polymer segments entangled and connected with the interwoven network structure of the active intermediate layer.

[0010] In an optional embodiment, the active intermediate layer is a polymer having a hydrophilic group obtained by polymerizing and cross-linking a high molecular polymer and an additive on the surface of the polyethylene film body.

[0011] In an optional embodiment, the high molecular polymer includes at least one of polyacrylic acid, polyethyleneimine, polyethersulfone, polyacrylonitrile and polyvinyl chloride, and preferably, the average molecular weight of the high molecular polymer is 5000 to 500000;

[0012] The additive includes at least one of N-ethylpropylamine, dopamine, dopa and catechol.

[0013] In an optional embodiment, the hydrophilic polymer includes at least one of polyethyleneimine, polyethylene glycol, polypropylene glycol and polyacrylic acid. Preferably, the average molecular weight of the hydrophilic polymer is 200-50,000.

[0014] In a second aspect, the present invention provides a method for preparing a polyethylene hydrophilic separation membrane as described in any of the aforementioned embodiments, which comprises: contacting one side of the polyethylene membrane body with air and the other side with a reaction liquid, and then subjecting the air-liquid interface to ultrasonic treatment to form an active intermediate layer on the surface of the polyethylene membrane body to obtain an intermediate membrane body; and then contacting the intermediate membrane body with a hydrophilic polymer to react to form a surface hydrophilic layer on the surface of the intermediate membrane body.

[0015] In an optional embodiment, the reaction liquid is a homogeneous suspension system formed by mixing and dissolving the high molecular polymer and additives described in the above embodiment in a solvent; preferably, the solvent is water or ethanol, the temperature of the mixed dissolution is 30°C to 50°C, and the mixed dissolution is performed for at least 24 hours; preferably, in the homogeneous suspension system, the mass concentration of the high molecular polymer is 0.1% to 2%, and the mass concentration of the additive is 0.1% to 2%; preferably, the temperature of the reaction liquid is controlled to be 60°C to 80°C, and the time of ultrasonic treatment of the gas-liquid interface is 1min to 5min.

[0016] In an optional embodiment, the contact reaction between the intermediate film body and the hydrophilic polymer is to immerse the polyethylene film body with the active intermediate layer in a solution containing the hydrophilic polymer and perform ultrasound; preferably, the temperature of the solution containing the hydrophilic polymer is controlled to be 60°C to 80°C, and the ultrasound time is 1min to 5min; preferably, in the solution containing the hydrophilic polymer, the mass concentration of the hydrophilic polymer is 0.5% to 5%, and the solution is deionized water.

[0017] In an optional embodiment, the method for preparing a polyethylene hydrophilic separation membrane further comprises reacting the polyethylene membrane after forming a surface hydrophilic layer with an acidic coupling agent solution;

[0018] Preferably, the acidic coupling agent solution contains 1% to 6% by weight of coupling agent and 5% to 20% by weight of dilute acid, and the pH of the acidic coupling agent solution is 4 to 6; more preferably, the dilute acid is 1wt% to 10wt% of acetic acid;

[0019] Preferably, the coupling agent is selected from at least one of glutaraldehyde and silane coupling agent;

[0020] Preferably, the temperature for reacting with the acidic coupling agent solution is room temperature, and the reaction time is 5 min to 10 min.

[0021] In an optional embodiment, before subjecting the polyethylene membrane body to the air-liquid interface ultrasonic treatment, the polyethylene membrane body is subjected to a wetting treatment;

[0022] Preferably, the wetting agent used in the wetting treatment includes at least one of ethanol, isopropanol, dimethylacetamide, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone.

[0023] In a third aspect, the present invention provides the use of the polyethylene hydrophilic separation membrane as described in any of the aforementioned embodiments as a filtration membrane in a liquid environment of a strong acid or alkaline liquid, an oily liquid or an organic liquid.

[0024] The present invention has the following beneficial effects: an active intermediate layer is deposited on the surface of the polyethylene film body, the active intermediate layer is an interwoven network structure polymer, and at least a segment of the active intermediate layer enters the segment gap of the polyethylene film body, and at least a segment forms an interwoven network structure on the surface of the polyethylene film body, and the structure plays a connecting role, so that the hydrophilic polymer can be entangled and connected with it, and then the hydrophilic polymer can be combined with the polyethylene film in the form of a cross-linked network to form a stable three-layer structure, which solves the problem of easy detachment of hydrophilic substances in the hydrophilic modification process, and the active intermediate layer and the surface active layer can contain a variety of hydrophilic groups, which can effectively change the non-wetting property of the polyethylene film when it meets water, and greatly improve the hydrophilicity of the polyethylene film surface. In addition, the polyethylene hydrophilic separation membrane of this structure can be prepared by a simple process, without expensive equipment, rich raw material selection, easy large-scale continuous production, and can save energy consumption and reduce cost space. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0026] Figure 1 This is a schematic diagram of the principle of preparing an intermediate active layer on the surface of a polyethylene film body according to an embodiment of the present invention;

[0027] Figure 2 This is the SEM image of the surface of the PE microporous membrane before modification;

[0028] Figure 3 This is a SEM image of the surface of the PE modified hydrophilic membrane obtained in Example 4;

[0029] Figure 4 This is the SEM image of the cross section of the PE microporous membrane before modification;

[0030] Figure 5 This is a SEM image of the cross section of the PE modified hydrophilic membrane obtained in Example 4. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical scheme and advantages of the embodiments of the present invention clearer, the technical scheme in the embodiments of the present invention will be described clearly and completely below. If the specific conditions are not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments used is not specified, they are all conventional products that can be purchased commercially.

[0032] The following is a detailed description of a polyethylene hydrophilic separation membrane provided by the present invention and its preparation method and application.

[0033] Some embodiments of the present invention provide a polyethylene hydrophilic separation membrane, which includes a polyethylene membrane main body, an active intermediate layer deposited on the surface of the polyethylene membrane main body, the active intermediate layer is an interwoven network structure polymer, and the active intermediate layer has at least segments entering the segment gaps of the polyethylene membrane main body, at least segments forming an interwoven network structure on the surface of the polyethylene membrane main body, the surface of the active intermediate layer also has a surface hydrophilic layer formed by the reaction of a hydrophilic polymer, and the surface hydrophilic layer has at least hydrophilic polymer segments entangled and connected with the interwoven network structure of the active intermediate layer.

[0034] Through research, the inventors found that although the existing chemical coating method is simple, the surface modified coating is easy to fall off. Based on this, the inventors, through a lot of research and practice, creatively proposed to first in-situ reaction deposit an active intermediate layer on the surface of the polyethylene membrane body. The active intermediate layer is a polymer with an interwoven network structure, and at least the active intermediate layer has chain segments entering the chain segment gaps of the polyethylene membrane body, and at least the chain segments form an interwoven network structure on the surface of the polyethylene membrane body. Such structural characteristics enable the active intermediate layer to be fully and firmly connected to the polyethylene membrane body. At the same time, its interwoven network structure is also conducive to further connecting the surface hydrophilic layer formed by the hydrophilic polymer. The surface hydrophilic polymer segments can be combined with the interwoven network of the active intermediate layer to be entangled and connected, so that the hydrophilic polymer can be fully and firmly connected to the polyethylene membrane body, effectively achieving the hydrophilic modification of the polyethylene membrane body while also having a long-lasting firmness, and the hydrophilic substance is not easy to fall off.

[0035] It should be noted that the active intermediate layer can also be made of materials with hydrophilic groups when selecting raw materials. On the one hand, the active intermediate layer can also achieve hydrophilic modification to a certain extent and can also play a connecting role, while the hydrophilicity of the surface hydrophilic layer can enhance the hydrophilicity of the active intermediate layer.

[0036] Specifically, in order to achieve good connection between the active intermediate layer and the polyethylene film and a certain hydrophilicity of the corresponding interwoven network structure, in some embodiments, the active intermediate layer is a polymer having hydrophilic groups obtained by polymerizing and cross-linking high molecular polymers and additives on the surface of the polyethylene film body.

[0037] Further, for reference, the high molecular polymer includes but is not limited to at least one of polyacrylic acid (PAA), polyethyleneimine (PEI), polyethersulfone (PES), polyacrylonitrile (PAN) and polyvinyl chloride (PVC), that is, any one of the above substances can be selected, or a mixture of two or more thereof can be selected. In order to achieve a better polymerization effect, the average molecular weight of the high molecular polymer is 5000 to 500000. Too small or too large a molecular weight will affect the pore morphology of the interwoven network structure formed by the polymer to a certain extent.

[0038] For reference, the additives include but are not limited to at least one of N-ethylpropylamine, dopamine, DOPA and catechol. For example, the additives can be selected from N-ethylpropylamine, dopamine, DOPA or catechol alone, or a mixture of two or three of them can be selected, and the mixing ratio is not limited.

[0039] In some embodiments, in order to make the surface hydrophilic layer have better hydrophilicity, the hydrophilic polymer includes but is not limited to at least one of polyethyleneimine, polyethylene glycol, polypropylene glycol and polyacrylic acid, and the average molecular weight of the hydrophilic polymer is 200-50,000.

[0040] It should be noted that in some preferred embodiments, the active intermediate layer should have hydrophilic groups in the selection of high molecular weight polymers. At the same time, the selection of hydrophilic polymers should correspond to the groups of the high molecular weight polymers, that is, some groups of the hydrophilic polymers can react with some groups of the active intermediate layer to achieve chemical bonding, so that the hydrophilic polymers can be more firmly connected, thereby improving the stability of the surface hydrophilic layer.

[0041] Furthermore, some embodiments of the present invention also provide a method for preparing a polyethylene hydrophilic separation membrane as described in any of the aforementioned embodiments, which comprises: contacting one side of the polyethylene membrane body with air and the other side with a reaction liquid, and then subjecting the air-liquid interface to ultrasonic treatment to form an active intermediate layer on the surface of the polyethylene membrane body to obtain an intermediate membrane body; and then contacting the intermediate membrane body with a hydrophilic polymer to react to form a surface hydrophilic layer on the surface of the intermediate membrane body.

[0042] The above preparation method has a rapid reaction process, which improves the efficiency of the hydrophilic modification process. The whole process is simple, does not require expensive equipment, has a rich selection of raw materials, and is easy for large-scale continuous production, providing a large space for saving energy and reducing costs in future production.

[0043] Specifically, in some embodiments, the method for preparing the polyethylene hydrophilic separation membrane comprises the following steps:

[0044] S1. Expose one side of the polyethylene film body to air and the other side to reaction liquid, and then perform ultrasonic treatment on the air-liquid interface to form an active intermediate layer on the surface of the polyethylene film body to obtain an intermediate film body.

[0045] The active intermediate layer is formed by ultrasonic treatment of the gas-liquid interface. Ultrasonic vibration can decompose the agglomerated particles in the reaction liquid, so that the polymer can be crushed evenly to improve the uniformity of the active intermediate layer. At the same time, the ultrasonic action can clean the membrane surface to remove impurities and pollutants, and enhance the bonding force between the coating and the membrane. The ultrasonic action can also produce microscopic roughness on the membrane surface, enhance the contact area between the coating and the membrane, and improve the bonding strength. In addition, the high energy generated when the ultrasonic cavitation bubble collapses is enough to break chemical bonds, promote polymerization reactions, and increase reaction rates and yields.

[0046] In some embodiments, the polyethylene film body is wetted before being subjected to ultrasonic treatment at the gas-liquid interface. Wetting can improve the contact between the gas and liquid and the PE film, reduce the surface tension, and allow the liquid to be better distributed on the film surface, which is beneficial to the subsequent chemical reaction and coating adhesion at the gas-liquid interface.

[0047] For reference, the wetting agent used in the wetting treatment includes, but is not limited to, at least one of ethanol, isopropyl alcohol, dimethylacetamide, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone.

[0048] In some embodiments, the reaction solution is a homogeneous suspension system formed by mixing and dissolving the polymer and additives described in the above embodiments in a solvent, wherein the polymer and additives have hydrophilic groups such as hydroxyl groups and amino groups. Figure 1 Under the condition of ultrasound at the air-liquid interface, the long polymer chains in the oligomeric state and the hydrophilic modified additives are subjected to the action of O2 to form a stable interwoven network structure with hydrophilic groups such as hydroxyl and amino groups on the surface of the PE film, which becomes the intermediate active layer. The copolymer generated by the reaction is deposited on the surface of the film to form an active intermediate layer, in which at least some segments enter the segment gaps of the polyethylene film body, and at least some segments form an interwoven network structure on the surface of the polyethylene film body.

[0049] Specifically, the solvent forming the reaction solution is water or ethanol, the temperature for mixed dissolution is 30°C to 50°C, for example, 30°C, 35°C, 40°C, 45°C, 50°C, etc., and the mixed dissolution is performed for at least 24 hours.

[0050] Furthermore, in order to achieve better reaction polymerization effect, in the homogeneous suspension system, the mass concentration of the high molecular polymer is 0.1% to 2%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%, etc., and the mass concentration of the additive is 0.1% to 2%, for example, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9% or 2%, etc.

[0051] Furthermore, during the ultrasonic treatment of the gas-liquid interface, the temperature of the reaction liquid is controlled to be 60°C to 80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C, and the time of the ultrasonic treatment of the gas-liquid interface is 1min to 5min, for example, 1min, 2min, 3min, 4min, 5min, etc.

[0052] S2. The intermediate film body is contacted with a hydrophilic polymer to react so as to form a surface hydrophilic layer on the surface of the intermediate film body.

[0053] Specifically, in some embodiments, the contacting reaction between the intermediate film body and the hydrophilic polymer is performed by immersing the polyethylene film body having the active intermediate layer in a solution containing the hydrophilic polymer and performing ultrasound.

[0054] The solution containing the hydrophilic polymer is prepared by adding the hydrophilic polymer into deionized water. Specifically, in the solution containing the hydrophilic polymer, the mass concentration of the hydrophilic polymer is 0.5% to 5%, for example, the mass concentration is 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5% or 5%.

[0055] Furthermore, during the ultrasonic reaction, the temperature of the solution containing the hydrophilic polymer is controlled to be 60°C to 80°C, for example, 60°C, 65°C, 70°C, 75°C or 80°C, and the ultrasonic time is 1 min to 5 min, for example, 1 min, 2 min, 3 min, 4 min, 5 min, etc.

[0056] It should be noted that after the ultrasonic reaction formed the surface hydrophilic layer, the polyethylene film was taken out and rinsed in water.

[0057] S3, reacting the polyethylene film after forming the surface hydrophilic layer with an acidic coupling agent solution.

[0058] Specifically, in some embodiments, the polyethylene film is immersed in the acidic coupling agent solution, and after the reaction is completed, it is taken out, washed and dried.

[0059] Through the action of the coupling agent under acidic conditions, the surface hydrophilic layer will undergo further cross-linking reaction, thereby strengthening the cross-linking and interpenetration of the network structure with the active intermediate layer, thereby further improving the durability of the surface hydrophilicity of the polyethylene film.

[0060] Furthermore, the acidic coupling agent solution is prepared by adding a coupling agent to deionized water and adding dilute acid to adjust the pH to 4-6; in some embodiments, the acidic coupling agent solution contains 1% to 6% by mass of the coupling agent and 5% to 20% by mass of the dilute acid.

[0061] In some embodiments, the dilute acid is 1 wt % to 10 wt % acetic acid.

[0062] For reference, the coupling agent includes, but is not limited to, at least one of glutaraldehyde and a silane coupling agent.

[0063] In some embodiments, in order to allow the surface hydrophilic layer to further react fully under the action of the coupling agent, during the reaction, the temperature of the acidic coupling agent solution is controlled to room temperature, and the reaction time is 5 min to 10 min, for example, 5 min, 6 min, 7 min, 8 min, 9 min or 10 min.

[0064] It should be noted that, in the preparation process, the solvent can be water or ethanol, both of which are green and clean solvents, which greatly reduce the generation of industrial organic waste liquid. Compared with the traditional hydrophilic modification process that uses too much organic solvent, it is more conducive to the construction of a clean and safe production system.

[0065] Furthermore, some embodiments of the present invention also provide the use of the polyethylene hydrophilic separation membrane as described in any of the above embodiments as a filter membrane in a liquid environment of a strong acidic or alkaline liquid, an oily liquid or an organic liquid. In view of the above liquid environment with complex components, the polyethylene hydrophilic separation membrane has a better separation effect due to its better hydrophilicity, and its sustained hydrophilicity is excellent.

[0066] The features and performance of the present invention are further described in detail below in conjunction with the embodiments.

[0067] The PE microporous membrane in the following embodiments and comparative examples is a PE membrane produced by Shanghai Enjie New Material Technology Co., Ltd., with a thickness of 20 um and a pore size of about 40 nm.

[0068] Example 1

[0069] This embodiment provides a polyethylene hydrophilic separation membrane, which is prepared by the following steps:

[0070] 1) Wet the PE microporous membrane with DMAC.

[0071] 2) Using deionized water as solvent, a mixed solution of 0.2 wt% PEI and 0.2 wt% catechol was prepared, wherein the molecular weight of PEI was 25000. One side of the wetted PE film was exposed to air and the other side was exposed to the mixed solution, and an air-liquid interface ultrasonic treatment was performed at 60° C. for 3 min (ultrasonic frequency was 40 KHz and power was 480 W).

[0072] 3) The treated PE membrane was immersed in a 0.2 wt % PEI aqueous solution, wherein the molecular weight of PEI was 25,000, and ultrasonically treated at 60° C. for 5 min (ultrasonic frequency was 40 KHz, power was 480 W), and then rinsed in water.

[0073] 4) The rinsed PE membrane is immersed in a 1% glutaraldehyde aqueous solution at room temperature for 10 minutes, and finally taken out, washed and dried to obtain a PE modified hydrophilic membrane containing an active intermediate layer and a surface hydrophilic layer, namely a polyethylene hydrophilic separation membrane.

[0074] Example 2

[0075] This embodiment provides a polyethylene hydrophilic separation membrane, which is prepared by the following steps:

[0076] 1) Wet the PE microporous membrane with ethanol.

[0077] 2) Using ethanol as solvent, a mixed solution of 0.4 wt% PAA and 0.4 wt% N-ethylpropylamine was prepared, wherein the molecular weight of PAA was 10000. One side of the wetted PE film was exposed to air and the other side was exposed to the mixed solution, and an air-liquid interface ultrasonic treatment was performed at 80° C. for 1 min (ultrasonic frequency was 40 KHz and power was 480 W).

[0078] 3) The treated PE film was immersed in a 2 wt % PAA aqueous solution, wherein the molecular weight of PAA was 3000, and ultrasonically treated at 80° C. for 3 min (ultrasonic frequency was 40 KHz, power was 480 W), and then rinsed in water.

[0079] 4) The rinsed PE membrane is immersed in a 2% KH792 aqueous solution adjusted to pH 5 for 5 minutes at room temperature, and finally taken out, washed and dried to obtain a PE modified hydrophilic membrane containing an active intermediate layer and a surface hydrophilic layer, namely a polyethylene hydrophilic separation membrane.

[0080] Example 3

[0081] This embodiment provides a polyethylene hydrophilic separation membrane, which is prepared by the following steps:

[0082] 1) Wet the PE microporous membrane with ethanol.

[0083] 2) Using deionized water as solvent, a mixed solution of 0.2 wt% PAN and 0.2 wt% dopamine was prepared, wherein the molecular weight of PAN was 5000. One side of the wetted PE film was exposed to air and the other side was exposed to the mixed solution, and an air-liquid interface ultrasonic treatment was performed at 60° C. for 5 min (ultrasonic frequency was 40 KHz and power was 480 W).

[0084] 3) The treated PE film was immersed in a 2 wt% PPG aqueous solution with a molecular weight of 400, and subjected to ultrasonic treatment at 60° C. for 5 min (ultrasonic frequency of 40 KHz and power of 480 W), and then taken out and rinsed in water.

[0085] 4) The rinsed PE membrane is immersed in a 5 wt % KH550 aqueous solution adjusted to pH 5 for 5 min at room temperature, and finally taken out, washed and dried to obtain a PE modified hydrophilic membrane containing an active intermediate layer and a surface hydrophilic layer, namely a polyethylene hydrophilic separation membrane.

[0086] Example 4

[0087] This embodiment provides a polyethylene hydrophilic separation membrane, which is prepared by the following steps:

[0088] 1) Wet the PE microporous membrane with DMAC.

[0089] 2) Using deionized water as solvent, a mixed solution of 1 wt% PEI and 1 wt% catechol was prepared, wherein the molecular weight of PEI was 3000. One side of the wetted PE film was exposed to air and the other side was exposed to the mixed solution, and an air-liquid interface ultrasonic treatment was performed at 70° C. for 5 min (ultrasonic frequency was 40 KHz and power was 480 W).

[0090] 3) The treated PE membrane was immersed in a PEG aqueous solution with a molecular weight of 6000 and a 5 wt% concentration, and subjected to ultrasonic treatment at 70° C. for 5 min (ultrasonic frequency of 40 KHz and power of 480 W), and then taken out and rinsed in water.

[0091] 4) The rinsed PE membrane is immersed in a 5 wt % KH550 aqueous solution adjusted to pH 5 for 10 min at room temperature, and finally taken out, washed and dried to obtain a PE modified hydrophilic membrane containing an active intermediate layer and a surface hydrophilic layer, namely a polyethylene hydrophilic separation membrane.

[0092] Example 5

[0093] This embodiment provides a polyethylene hydrophilic separation membrane, which is prepared by the following steps:

[0094] 1) Wet the PE microporous membrane with DMAC.

[0095] 2) Using deionized water as solvent, a mixed solution of 2 wt% PES and 2 wt% DOPA was prepared, wherein the molecular weight of PES was 5800. One side of the wetted PE film was exposed to air and the other side was exposed to the mixed solution, and an air-liquid interface ultrasonic treatment was performed at 80° C. for 3 min (ultrasonic frequency was 40 KHz and power was 480 W).

[0096] 3) The treated PE film was immersed in a 1 wt% PAA aqueous solution with a molecular weight of 2000, and subjected to ultrasonic treatment at 80° C. for 3 min (ultrasonic frequency of 40 KHz and power of 480 W), and then taken out and rinsed in water.

[0097] 4) The rinsed PE membrane is immersed in a 2 wt % glutaraldehyde aqueous solution at room temperature for 5 minutes, and finally taken out, washed and dried to obtain a PE modified hydrophilic membrane containing an active intermediate layer and a surface hydrophilic layer, namely a polyethylene hydrophilic separation membrane.

[0098] Example 6 (Comparative Example 2)

[0099] This embodiment provides a polyethylene hydrophilic separation membrane, which is prepared by the following steps:

[0100] 1) Wet the PE microporous membrane with ethanol.

[0101] 2) Using ethanol as solvent, a mixed solution of 0.4 wt% PAA and 0.4 wt% N-ethylpropylamine was prepared, wherein the molecular weight of PAA was 10000. One side of the wetted PE film was exposed to air and the other side was exposed to the mixed solution, and an air-liquid interface ultrasonic treatment was performed at 70° C. for 5 min (ultrasonic frequency was 40 KHz and power was 480 W).

[0102] 3) The treated PE membrane was immersed in a 0.2 wt% PEI aqueous solution with a molecular weight of 5000, and subjected to ultrasonic treatment at 70° C. for 5 min (ultrasonic frequency of 40 KHz and power of 480 W), and then taken out and rinsed in water.

[0103] 4) After being taken out, it is dried to obtain a PE-modified hydrophilic membrane containing an active intermediate layer and a surface hydrophilic layer, namely a polyethylene hydrophilic separation membrane.

[0104] Example 7

[0105] This embodiment provides a polyethylene hydrophilic separation membrane, which is prepared by the following steps:

[0106] 1) Wet the PE microporous membrane with ethanol.

[0107] 2) Using deionized water as solvent, a 2wt% PES and 2wt% DOPA mixed solution was prepared, wherein the molecular weight of PES was 5800. One side of the wetted PE film was exposed to air and the other side was exposed to the mixed solution, and an air-liquid interface ultrasonic treatment was performed at 80° C. for 5 min (ultrasonic frequency was 40 KHz and power was 480 W).

[0108] 3) The treated PE film was immersed in a 2 wt% PAA aqueous solution with a molecular weight of 100,000, and subjected to ultrasonic treatment at 80° C. for 5 min (ultrasonic frequency of 40 KHz and power of 480 W), and then rinsed in water.

[0109] 4) The rinsed PE membrane is immersed in a 5% KH550 aqueous solution adjusted to pH 5 for 5 minutes at room temperature, and finally taken out, washed and dried to obtain a PE modified hydrophilic membrane containing an active intermediate layer and a surface hydrophilic layer, namely a polyethylene hydrophilic separation membrane.

[0110] Comparative Example 1

[0111] This comparative example provides a PE modified hydrophilic membrane, which is completed by the following steps:

[0112] 1) Wet the PE microporous membrane with ethanol.

[0113] 2) Using deionized water as solvent, prepare a mixed solution of 0.2 wt% PEI and 0.2 wt% catechol, wherein the molecular weight of PEI is 10000. Immerse the wetted PE film in the solution, heat it at 60° C. for 10 min, and then rinse it in water.

[0114] 3) The rinsed PE membrane was immersed in a 2 wt % KH792 aqueous solution adjusted to pH 5 at room temperature for 30 min, and finally taken out, washed, and dried to obtain a hydrophilically modified PE membrane.

[0115] Comparative Example 2

[0116] This comparative example provides a PE modified hydrophilic membrane, which is completed by the following steps:

[0117] 1) Wet the PE microporous membrane with DMAC.

[0118] 2) Using deionized water as solvent, prepare a mixed solution of 0.2wt% PAN and 0.2wt% dopamine, wherein the molecular weight of PAN is 5000. Immerse the wetted PE film in the solution, perform ultrasonic treatment at 70°C for 10 min (ultrasonic frequency of 40KHz, power of 480W), and then rinse in water.

[0119] 3) The rinsed PE membrane was immersed in a 2 wt % KH550 aqueous solution adjusted to pH 5 at room temperature for 10 min, and finally taken out, washed, and dried to obtain a hydrophilically modified PE membrane.

[0120] Comparative Example 3

[0121] This comparative example provides a PE modified hydrophilic membrane, which is completed by the following steps:

[0122] 1) Wet the PE microporous membrane with DMAC.

[0123] 2) Using deionized water as solvent, a mixed solution of 0.4 wt% PEI and 0.4 wt% catechol was prepared, wherein the molecular weight of PEI was 3000. One side of the wetted PE film was exposed to air and the other side was exposed to the mixed solution, and an air-liquid interface ultrasonic treatment was performed at 80° C. for 5 min (ultrasonic frequency was 40 KHz and power was 480 W).

[0124] 3) The treated PE film was immersed in a 2.5 wt% PVP aqueous solution with a molecular weight of 24,000, and subjected to ultrasonic treatment at 80° C. for 5 min (ultrasonic frequency of 40 KHz and power of 480 W), and then taken out and rinsed in water.

[0125] 4) The rinsed PE membrane was immersed in a 5 wt % KH550 aqueous solution adjusted to pH 5 at room temperature for 5 minutes, and finally taken out, washed, and dried to obtain a hydrophilically modified PE membrane.

[0126] Comparative Example 4

[0127] This comparative example provides a PE modified hydrophilic membrane, which is completed by the following steps:

[0128] 1) Wet the PE microporous membrane with DMAC.

[0129] 2) Using deionized water as solvent, a mixed solution of 1 wt% PEI and 0.2 wt% catechol was prepared, wherein the molecular weight of PEI was 25000. One side of the wetted PE film was exposed to air and the other side was exposed to the mixed solution, and an air-liquid interface ultrasonic treatment was performed at 60° C. for 3 min (ultrasonic frequency was 40 KHz and power was 480 W).

[0130] 3) The treated PE membrane was immersed in a 0.2 wt % PEI aqueous solution, wherein the molecular weight of PEI was 25,000, and ultrasonically treated at 60° C. for 5 min (ultrasonic frequency was 40 KHz, power was 480 W), and then rinsed in water.

[0131] 4) The rinsed PE membrane is immersed in a 1% glutaraldehyde aqueous solution at room temperature for 10 minutes, and finally taken out, washed and dried to obtain a PE modified hydrophilic membrane containing an active intermediate layer and a surface hydrophilic layer, namely a polyethylene hydrophilic separation membrane.

[0132] Comparative Example 5

[0133] This comparative example provides a PE modified hydrophilic membrane, which is completed by the following steps:

[0134] 1) Wet the PE microporous membrane with DMAC.

[0135] 2) Using deionized water as solvent, a mixed solution of 1 wt% PEI and 1 wt% catechol was prepared, wherein the molecular weight of PEI was 3000. One side of the wetted PE film was exposed to air and the other side was exposed to the mixed solution, and an air-liquid interface ultrasonic treatment was performed at 70° C. for 3 min (ultrasonic frequency was 40 KHz and power was 480 W).

[0136] 3) The treated PE membrane was immersed in a PEG aqueous solution with a molecular weight of 6000 and a 5 wt% concentration, and subjected to ultrasonic treatment at 70° C. for 5 min (ultrasonic frequency of 40 KHz and power of 480 W), and then taken out and rinsed in water.

[0137] 4) The rinsed PE membrane was immersed in a 5wt% KH550 aqueous solution adjusted to pH 5 for 10 minutes at room temperature, and finally taken out, washed and dried to obtain a PE modified hydrophilic membrane containing an active intermediate layer and a surface hydrophilic layer, i.e., a polyethylene hydrophilic separation membrane. As shown in Tables 1 and 2, they are various process parameters of the PE modified hydrophilic membranes of various embodiments and comparative examples.

[0138] Table 1

[0139]

[0140]

[0141] Table 2

[0142]

[0143]

[0144] The PE modified hydrophilic membranes prepared in the above-mentioned embodiments and comparative examples were subjected to (1) pure water flux test, specifically, the membrane was placed in a test device, and negative pressure suction was performed at a pressure of -0.02MPa to measure the amount of pure water permeation within a certain period of time, and the parameter results obtained by three measurements were averaged, wherein the test device was a self-made negative pressure suction flux detection device, in which two membranes were clamped with a fixture, separated by a guide net in the middle, and there was a water outlet on the fixture. The fixture was placed in a water tank, and pure water was sucked in from the surface membrane holes and flowed out from the water outlet, flowing through the negative pressure gauge and the peristaltic pump, and then returned to the water tank. And (2) hydrophilicity test, specifically, deionized water was injected into the corresponding modified membrane to measure the static contact angle of the modified membrane, and the parameter results obtained by three measurements were averaged. As shown in Table 3 below, the test results of pure water flux and contact angle of the PE modified hydrophilic membranes of each embodiment and comparative example are shown.

[0145] Table 3. Test results of pure water flux and contact angle of PE modified membranes in various embodiments

[0146]

[0147]

[0148] Some of the examples and comparative examples were immersed in pure water for several days, and then taken out to perform pure water flux and static contact angle performance tests to verify the durability of the prepared membranes. As shown in Table 4 below, the durability test results of the PE modified hydrophilic membranes of some of the examples and comparative examples are shown.

[0149] Table 4. Durability test results of PE modified films of some examples

[0150]

[0151] The PE microporous membrane before modification and the PE modified hydrophilic membrane in Example 4 were observed by scanning electron microscope. The SEM images of their surfaces are as follows: Figure 2 and Figure 3 The SEM images of its cross section are shown in Figure 4 and Figure 5 As shown. Figure 2 It can be seen that the surface morphology of the PE microporous membrane is a stretched polyethylene polymer long chain, which is staggered to form pores of different sizes. Figure 3 As shown in the figure, the membrane surface is covered with a layer of interwoven network structure, which makes the pores smaller (the red frame part is more obvious in the figure). Figure 4 It can be seen that the surface of the PE microporous membrane is very smooth and flat, but after modification, such as Figure 5 As shown, the membrane surface has protruding undulations, which are caused by the embedding of hydrophilic polymer segments in the surface of the base membrane.

[0152] In summary, the polyethylene hydrophilic separation membrane containing an active intermediate layer and a surface hydrophilic layer and the preparation method thereof according to the embodiment of the present invention have the following advantages:

[0153] 1) Through the interwoven network structure copolymer formed by high molecular polymer and additive under the action of ultrasonic resonance at the air-liquid interface, various hydrophilic polymers can be combined with PE film in the form of a cross-linked network to form a solid three-layer structure, which solves the problem of easy detachment of hydrophilic substances in the hydrophilic modification process and becomes a more effective hydrophilic substance connection medium. The rich amino and hydroxyl groups in the hydrophilic polymer change the non-wetting property of the PE film when it comes into contact with water, making the surface of the PE film more hydrophilic.

[0154] 2) The process has a rapid reaction process, which improves the efficiency of the hydrophilic modification process. The entire process is simple, does not require expensive equipment, has a rich selection of raw materials, and is easy to produce on a large scale, providing a large space for saving energy and reducing costs in future production.

[0155] 3) The solvent in this process is water or ethanol, both of which are green and clean solvents, which greatly reduces the generation of industrial organic waste liquid. Compared with the traditional hydrophilic modification process that uses too much organic solvent, it is more conducive to the construction of a clean and safe production system.

[0156] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A polyethylene hydrophilic separation membrane, characterized in that: It includes a polyethylene film main body, an active intermediate layer is deposited on the surface of the polyethylene film main body, the active intermediate layer is an interwoven network structure polymer, and at least a segment of the active intermediate layer enters the segment gap of the polyethylene film main body, at least a segment forms an interwoven network structure on the surface of the polyethylene film main body, and the surface of the active intermediate layer also has a surface hydrophilic layer formed by the reaction of a hydrophilic polymer, and the surface hydrophilic layer has at least a hydrophilic polymer segment entangled and connected with the interwoven network structure of the active intermediate layer.

2. The polyethylene hydrophilic separation membrane according to claim 1, characterized in that: The active intermediate layer is a polymer having a hydrophilic group obtained by polymerizing and cross-linking a high molecular polymer and an additive on the surface of the polyethylene film body.

3. The polyethylene hydrophilic separation membrane according to claim 2, characterized in that: The high molecular polymer includes at least one of polyacrylic acid, polyethyleneimine, polyethersulfone, polyacrylonitrile and polyvinyl chloride. Preferably, the average molecular weight of the high molecular polymer is 5000 to 500000; The additive includes at least one of N-ethylpropylamine, dopamine, dopa and catechol.

4. The polyethylene hydrophilic separation membrane according to claim 1, characterized in that: The hydrophilic polymer includes at least one of polyethyleneimine, polyethylene glycol, polypropylene glycol and polyacrylic acid. Preferably, the average molecular weight of the hydrophilic polymer is 200-50,000.

5. The method for preparing a polyethylene hydrophilic separation membrane according to any one of claims 1 to 4, characterized in that: It includes: One side of the polyethylene film body is contacted with air, and the other side is contacted with the reaction liquid, and then the air-liquid interface is ultrasonically treated to form the active intermediate layer on the surface of the polyethylene film body to obtain an intermediate film body; then the intermediate film body is contacted with the hydrophilic polymer to react to form the surface hydrophilic layer on the surface of the intermediate film body.

6. The method for preparing a polyethylene hydrophilic separation membrane according to claim 5, characterized in that: The reaction liquid is a homogeneous suspension system formed by mixing and dissolving the high molecular polymer and additives described in claim 2 in a solvent; Preferably, the solvent is water or ethanol, the temperature of mixed dissolution is 30°C to 50°C, and the mixed dissolution is performed for at least 24 hours; Preferably, in the homogeneous suspension system, the mass concentration of the high molecular weight polymer is 0.1% to 2%, and the mass concentration of the additive is 0.1% to 2%; Preferably, the temperature of the reaction liquid is controlled to be 60° C. to 80° C., and the time of the gas-liquid interface ultrasonic treatment is 1 min to 5 min.

7. The method for preparing a polyethylene hydrophilic separation membrane according to claim 5, characterized in that: The middle film body is contacted with the hydrophilic polymer to react by immersing the polyethylene film body having the active middle layer in a solution containing the hydrophilic polymer and performing ultrasound; Preferably, the temperature of the solution containing the hydrophilic polymer is controlled to be 60° C. to 80° C., and the ultrasonic time is 1 min to 5 min; Preferably, in the solution containing the hydrophilic polymer, the mass concentration of the hydrophilic polymer is 0.5% to 5%, and the solution is deionized water.

8. The method for preparing a polyethylene hydrophilic separation membrane according to any one of claims 5 to 7, characterized in that: The method further comprises reacting the polyethylene film after forming the surface hydrophilic layer with an acidic coupling agent solution; Preferably, the acidic coupling agent solution contains 1% to 6% by weight of coupling agent and 5% to 20% by weight of dilute acid, and the pH of the acidic coupling agent solution is 4 to 6; more preferably, the dilute acid is 1wt% to 10wt% of acetic acid; Preferably, the coupling agent is selected from at least one of glutaraldehyde and silane coupling agent; Preferably, the temperature for reacting with the acidic coupling agent solution is room temperature, and the reaction time is 5 min to 10 min.

9. The method for preparing a polyethylene hydrophilic separation membrane according to any one of claims 5 to 7, characterized in that: Before subjecting the polyethylene film body to the air-liquid interface ultrasonic treatment, subjecting the polyethylene film body to a wetting treatment; Preferably, the wetting agent used in the wetting treatment includes at least one of ethanol, isopropanol, dimethylacetamide, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone.

10. Use of the polyethylene hydrophilic separation membrane according to any one of claims 1 to 4 as a filtration membrane in a liquid environment of a strong acid or alkaline liquid, an oily liquid or an organic liquid.

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