Stimuli-responsive hydrophilic-oleophobic film, preparation method and application thereof

Abstract

The present application relates to the field of oil-water separation, and discloses a stimulus-responsive hydrophilic and oleophobic film, a preparation method and application thereof.The stimulus-responsive hydrophilic and oleophobic film comprises a polymer matrix, a polymer connecting segment grafted on the polymer matrix, a hydrophilic segment grafted on the polymer connecting segment, and a hydrophobic segment grafted on the hydrophilic segment, wherein the structural unit of the polymer connecting segment is derived from a double-bond-containing olefinic acid compound, the hydrophilic segment is derived from polyethyleneimine, and the hydrophobic segment is derived from a fluorine-containing anhydride compound.According to the present application, a novel stimulus-responsive hydrophilic and oleophobic film, a preparation method and application thereof can be provided, the method is low in cost, can avoid the film layer from falling off after multiple uses caused by coating and the like, is suitable for industrialized production, and has strong emulsified oil demulsification separation capacity in addition to the ability of separating and chromatographing oil.

Description

Technical Field

[0001] This invention relates to the field of oil-water separation, specifically to a stimulus-responsive hydrophilic-oleophobic membrane, its preparation method, and its application. Background Technology

[0002] Modern industrial production and urban life generate large amounts of oily wastewater, including produced water from oil and gas field development in the petrochemical industry, cleaning wastewater from petrochemical production and transportation, surface cleaning wastewater from machinery manufacturing and metal product manufacturing, cutting fluids used in cutting and grinding, emulsified wastewater from rolling processes in the metallurgical industry, food processing wastewater, and oily wastewater from kitchens. If this oily wastewater is discharged directly into the environment without treatment, it will cause serious environmental pollution and ecological damage: for example, it will cover water surfaces, prevent oxygen from the air from diffusing into the water, hinder algal photosynthesis, and oil will also affect the growth of aquatic organisms, ultimately causing water bodies to turn black and smelly, reducing the usability of water resources. Pollutants in oil may also re-enter the food chain and threaten human health.

[0003] With increasing emphasis on environmental protection and ever-stricter emission standards, the green and safe treatment of oily wastewater has become an urgent priority. Traditional oil-water separation technologies are based on gravity separation, mechanical oil skimming, flotation (including electrolytic flotation), flocculation, adsorption, and oxidation. Each of these processes has its own inherent drawbacks. For example, gravity separation and mechanical oil skimming are only effective for chromatographic oils; flotation and flocculation introduce new impurities and generate hazardous waste such as scum; adsorbents are costly and generate large amounts of hazardous waste; and oxidation methods are energy and material-intensive and cannot treat excessively high concentrations of oily wastewater. Compared to these traditional oil-water separation methods, membrane separation is a physical process with advantages such as high efficiency, no phase change, no secondary pollution, low energy consumption, and small footprint, and has gradually gained widespread attention. However, membrane fouling remains a major obstacle to its large-scale application.

[0004] Membrane separation mechanisms mainly consist of three types: the sieving effect of the membrane pores themselves, adsorption on the membrane surface, and electrostatic interactions. The sieving effect refers to the membrane's retention of particles larger than the pore size. Adsorption refers to the hydrophobic / hydrophilic interaction between the target pollutant (oil) and the membrane. Electrostatic interactions refer to the attraction or repulsion of the target substance's charge on the membrane surface. In the field of oil-water separation, the sieving and adsorption effects play a decisive role in the separation process. Compared to the relatively mature membrane pore formation control technology, research on the regulation of the hydrophobicity / hydrophilicity of the membrane surface in oil-water separation is still in its early stages.

[0005] From the perspective of surface wetting, oil-water separation membrane materials can be classified into hydrophobic-oleophilic, hydrophilic-underwater oleophobic, hydrophilic-oleophobic, amphiphilic, dual-repellent, smart, and Janus types. Currently, hydrophobic-oleophilic membranes suffer from high mass transfer resistance and membrane fouling due to oil adsorption, which is difficult to solve from a filtration principle standpoint, leading to frequent replacements and high operating costs. Amphiphilic, smart, and Janus types are still in the conceptual design stage. Dual-repellent membranes, due to their repulsion of both oil and water, are mainly used in membrane distillation. Hydrophilic-underwater oleophobic and hydrophilic-oleophobic membranes are the two main development directions. However, hydrophilic-underwater oleophobic membranes are easily permeated by oil if not pre-wetted or if they are in prolonged contact with oil without contact with water. Hydrophilic-oleophobic membranes avoid the above-mentioned drawbacks and have strong anti-fouling capabilities; however, in principle, oil has a lower surface energy than water, making the fabrication of hydrophilic-oleophobic membranes more difficult.

[0006] CN103601826A discloses a method for preparing a humidity-responsive hydrophilic and oleophobic fabric mesh film. The preparation process is complex and involves multiple steps. Furthermore, the crosslinking agents used are dialdehyde, dicarboxylic acid, and diisocyanate, which have poor adhesion to the fabric substrate, resulting in the surface hydrophilic and oleophobic coating being easy to peel off.

[0007] CN105148563A discloses a method for preparing a humidity-responsive hydrophilic and oleophobic film. The method first constructs a hybrid coating by mixing oleophobic nanoparticles and hydrophilic coating, and then coats it onto a screen by spraying or UV curing. The synthesis process uses a lot of toxic and harmful solvents, and the coating method makes the film easy to fall off. Summary of the Invention

[0008] The purpose of this invention is to provide a novel stimulus-responsive hydrophilic and oleophobic membrane, its preparation method, and its application. This method is low in cost, avoids membrane peeling after repeated use caused by coating and other methods, is suitable for industrial production, and has a strong ability to demulsify and separate emulsions in addition to separating chromatographic oils.

[0009] To achieve the above objectives, the present invention provides a stimulus-responsive hydrophilic-oleophobic film, wherein the stimulus-responsive hydrophilic-oleophobic film comprises a polymer matrix, polymer linking segments grafted onto the polymer matrix, hydrophilic segments grafted onto the polymer linking segments, and hydrophobic segments grafted onto the hydrophilic segments, wherein the structural units of the polymer linking segments are derived from double-bonded olefinic compounds, the hydrophilic segments are derived from polyethyleneimine, and the hydrophobic segments are derived from fluoroanhydride compounds.

[0010] Preferably, the double-bonded acrylic acid compound is one or more selected from acrylic acid, methacrylic acid, dimethacrylic acid, 2-ethylacrylic acid, butenoic acid, 3-amino-2-butene, and 3-methoxybutenoic acid, and more preferably one or more selected from acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

[0011] Preferably, the average molecular weight of the polymer linker segments is 500,000 to 700,000.

[0012] Preferably, the average molecular weight of the polyethyleneimine is 500-3000.

[0013] Preferably, the fluoroanhydride compound is one or more of trifluoroacetic anhydride, pentafluoropropionic anhydride, heptafluorobutyric anhydride, and nonafluorovalerate anhydride.

[0014] Preferably, the polymer matrix is ​​one or more of polysulfone, polyethersulfone, and polyvinylidene fluoride.

[0015] Preferably, the pore size of the polymer matrix is ​​1-30 nm, more preferably 4-20 nm.

[0016] A second aspect of the present invention provides a method for preparing a stimulus-responsive hydrophilic-oleophobic film, wherein the method includes the following steps:

[0017] 1) The step of irradiating polymer powder with γ-rays to form active groups on the surface of the polymer powder;

[0018] 2) The polymer powder with active groups on the surface obtained in step 1) is polymerized and grafted with a compound containing double-bonded olefins to obtain polymer powder A with polymer linking segments grafted onto the polymer matrix.

[0019] 3) The step of casting a film using a casting solution containing the polymer powder A, a pore-forming agent and a solvent to obtain a substrate film A with polymer connecting segments on the surface of the substrate film;

[0020] 4) In the presence of a crosslinking agent, the carboxyl groups on the substrate membrane A are crosslinked with the amino groups of polyethyleneimine to obtain a substrate membrane B with hydrophilic segments grafted onto the polymer linking segments.

[0021] 5) In the presence of a catalyst, the amino group in the hydrophilic segment is reacted with a fluorinated anhydride compound to obtain a matrix membrane C with a hydrophobic segment grafted onto the hydrophilic segment.

[0022] Preferably, the polymer powder is one or more of polysulfone powder, polyethersulfone powder, and polyvinylidene fluoride powder.

[0023] Preferably, the polymer powder has a particle size of 0.05-0.2 mm.

[0024] Preferably, the gamma rays used are from... 60 Co, radiation dose is 15-25 kGy.

[0025] Preferably, the double-bonded acrylic acid compound is one or more selected from acrylic acid, methacrylic acid, dimethacrylic acid, 2-ethylacrylic acid, butenoic acid, 3-amino-2-butene, and 3-methoxybutenoic acid, and more preferably one or more selected from acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

[0026] Preferably, the polymerization grafting comprises: polymerizing and grafting a mixture containing polymer powder with active groups formed on its surface, the double-bonded olefin compound, and a solvent.

[0027] Preferably, the weight ratio of the polymer powder with active groups formed on its surface to the compound containing double bonds is 1:3-5.

[0028] Preferably, the amount of solvent used is 2-4 times the total weight of the polymer powder with active groups formed on its surface and the compound containing double-bonded olefins.

[0029] Preferably, the conditions for the polymerization grafting include: a temperature of 60-80°C and a time of 4-20 hours.

[0030] Preferably, the solvent is water.

[0031] Preferably, the weight ratio of the polymer powder A, the pore-forming agent, and the solvent is 10:1-2:60-80.

[0032] Preferably, the pore-forming agent is one or more of diethylene glycol butyl ether, polyethylene glycol, polyvinylpyrrolidone, lithium chloride, and lithium bromide.

[0033] Preferably, the solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

[0034] Preferably, the thickness of the substrate film A is 40-120 μm.

[0035] Preferably, the molar ratio of the matrix film A, calculated as carboxyl groups, to the polyethyleneimine, calculated as amino groups, is 1:2-4.

[0036] Preferably, the molar ratio of the matrix film A, calculated based on the carboxyl groups, to the crosslinking agent is 1:2-4.

[0037] Preferably, the crosslinking agent is one or more of dicyclohexylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and diisopropylcarbodiimide.

[0038] Preferably, the molar ratio of the polyethyleneimine to the fluoroanhydride compound is 1:2-4.

[0039] Preferably, the catalyst is triethylamine and / or pyridine.

[0040] Preferably, the molar ratio of the fluorinated anhydride compound to the catalyst is 100:1-5.

[0041] Preferably, the reaction is carried out in an organic solvent, which is one or more of ethanol, ethyl acetate, and dichloroethane.

[0042] Preferably, the reaction conditions include: a reaction temperature of 25-35°C and a reaction time of 0.5-1.5 h.

[0043] The third aspect of the present invention provides a method for preparing a stimulus-responsive hydrophilic and oleophobic film according to the second aspect of the present invention.

[0044] The fourth aspect of the present invention provides the application of the stimulus-responsive hydrophilic-oleophobic membrane prepared by the method of preparing the stimulus-responsive hydrophilic-oleophobic membrane of the first aspect of the present invention or the method of preparing the stimulus-responsive hydrophilic-oleophobic membrane of the second aspect of the present invention in oil-water separation.

[0045] According to this invention, a pre-grafting followed by phase transfer method is used to form a film, and hydrophilic polymers and hydrophobic / oleophobic long-chain molecules are modified separately through a two-step chemical grafting method to form an oleophobic-hydrophilic film. The film surface has a large number of hydrophobic / oleophobic long-chain molecules, which can maintain oleophobicity in air and gradually change from superhydrophobic to superhydrophilic under continuous water immersion (because the hydrophobic / oleophobic long-chain molecules are all under flexible hydrophilic polymers). Compared with the prior art, this method does not use substrates such as fabrics or metal meshes, but controls the surface groups from the synthesis of the film; because phase transfer film formation is used, the film pores are controllable, and it has a stronger sieving effect compared with oleophobic / hydrophilic films using fabrics or metal meshes; and the film modification is carried out by chemical bonding rather than coating, which has better stability and will not age and peel off after repeated use. In addition, this patent uses inexpensive commercial reagents and solvents, resulting in low preparation costs.

[0046] Furthermore, the stimulus-responsive hydrophilic-oleophobic membrane of the present invention exhibits excellent hydrophobic and oleophobic properties in air, but transforms into a hydrophilic membrane upon immersion in water. It is a stimulus-responsive oil-water separation membrane with excellent oil-water separation effect. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the molecular structure on the membrane surface.

[0048] Figure 2This is a scanning electron microscope image of the surface of the membrane obtained in Example 1.

[0049] Figure 3 This is a graph showing the water contact angle of the membrane obtained in Example 1.

[0050] Explanation of reference numerals in the attached figures

[0051] 1. Carboxyl groups on the membrane surface form amide bonds with PEI.

[0052] 2. Bonds formed by the condensation of PEI and heptafluorobutyric anhydride Detailed Implementation

[0053] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0054] According to a first aspect of the present invention, a stimulus-responsive hydrophilic-oleophobic film is provided, wherein the stimulus-responsive hydrophilic-oleophobic film comprises a polymer matrix, polymer linking segments grafted onto the polymer matrix, hydrophilic segments grafted onto the polymer linking segments, and hydrophobic segments grafted onto the hydrophilic segments, wherein the structural units of the polymer linking segments are derived from double-bonded olefinic compounds, the hydrophilic segments are derived from polyethyleneimine, and the hydrophobic segments are derived from fluoroanhydride compounds.

[0055] According to the present invention, the polymer linking segment is a segment for connecting with the hydrophilic segment. The structural unit of the polymer linking segment is derived from a compound containing a double bond olefin. By using a compound containing a double bond olefin to form the polymer linking segment, the polymer linking segment has a carboxyl group, through which it can connect with the hydrophilic segment.

[0056] Preferably, the compound containing double bonds is one or more selected from acrylic acid, methacrylic acid, dimethacrylic acid, 2-ethylacrylic acid, butenoic acid, 3-amino-2-butene, and 3-methoxybutenoic acid; more preferably, the compound containing double bonds is one or more selected from acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

[0057] According to the present invention, preferably, the average molecular weight of the polymer linker segment is 500,000 to 700,000; more preferably, the average molecular weight of the polymer linker segment is 600,000 to 650,000.

[0058] According to the present invention, the hydrophilic segment is derived from polyethyleneimine, and the amino groups of the polyethyleneimine can react with the carboxyl groups of the polymer segment to form the hydrophilic segment by grafting onto the polymer linking segment.

[0059] According to the present invention, preferably, the polyethyleneimine is dendritic. Furthermore, the average molecular weight of the polyethyleneimine is preferably 500-3000; more preferably, the average molecular weight of the polyethyleneimine is 1500-2000.

[0060] According to the present invention, the hydrophobic segment is derived from a fluoroanhydride compound, which forms the hydrophobic segment by reacting with the amino group of the hydrophilic segment.

[0061] According to the present invention, preferably, the fluoroanhydride compound is one or more selected from trifluoroacetic anhydride, pentafluoropropionic anhydride, heptafluorobutyric anhydride and nonafluorovalerate anhydride.

[0062] According to the present invention, preferably, the polymer of the polymer matrix is ​​one or more of polysulfone, polyethersulfone, and polyvinylidene fluoride.

[0063] According to a first aspect of the invention, preferably, the pore size of the polymer matrix is ​​1-30 nm, more preferably 4-20 nm.

[0064] According to a second aspect of the present invention, a method for preparing a stimulus-responsive hydrophilic-oleophobic film is provided, wherein the method includes the following steps:

[0065] 1) The step of irradiating polymer powder with γ-rays to form active groups on the surface of the polymer powder;

[0066] 2) The polymer powder with active groups on the surface obtained in step 1) is polymerized and grafted with a compound containing double-bonded olefins to obtain polymer powder A with polymer linking segments grafted onto the polymer matrix.

[0067] 3) The step of casting a film using a casting solution containing the polymer powder A, a pore-forming agent and a solvent to obtain a substrate film A with polymer connecting segments on the surface of the substrate film;

[0068] 4) In the presence of a crosslinking agent, the carboxyl groups on the substrate membrane A are crosslinked with the amino groups of polyethyleneimine to obtain a substrate membrane B with hydrophilic segments grafted onto the polymer linking segments.

[0069] 5) In the presence of a catalyst, the amino group in the hydrophilic segment is reacted with a fluorinated anhydride compound to obtain a matrix membrane C with a hydrophobic segment grafted onto the hydrophilic segment.

[0070] The preparation method of the stimulus-responsive hydrophilic and oleophobic film of the present invention will be described step by step below.

[0071] Step 1)

[0072] Step 1) is a step of irradiating polymer powder with γ-rays to form active groups on the surface of the polymer powder.

[0073] In this invention, the polymer powder is preferably one or more of polysulfone powder, polyethersulfone powder, and polyvinylidene fluoride powder.

[0074] Furthermore, the particle size of the polymer powder is preferably 0.05-0.2 mm, more preferably 0.1-0.15 mm. By ensuring that the particle size of the polymer powder is within the above range, it has the advantage of uniform grafting.

[0075] According to the present invention, preferably, the γ-rays used are from... 60 Co, with a radiation dose of 15-25 kGy, is more preferably 18-22 kGy to further improve its hydrophobic and oleophobic properties in air and enhance oil-water separation.

[0076] According to the present invention, step 1) can form active groups such as carboxyl groups and peroxy groups on the surface of the polymer powder, and the peroxy groups can generate free radicals to initiate the polymerization of monomers.

[0077] Step 2)

[0078] Step 2) involves polymerizing and grafting the polymer powder with active groups on its surface obtained in Step 1) with a compound containing double-bonded olefins to obtain polymer powder A with polymer linking segments grafted onto the polymer matrix.

[0079] According to the present invention, preferably, the compound containing double bonds is one or more selected from acrylic acid, methacrylic acid, dimethacrylic acid, 2-ethylacrylic acid, butenoic acid, 3-amino-2-butene, and 3-methoxybutenoic acid; more preferably, the compound containing double bonds is one or more selected from acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

[0080] In a preferred embodiment of the present invention, the polymerization grafting includes: polymer grafting a mixture containing the polymer powder with active groups formed on its surface, the double-bonded olefin compound, and a solvent.

[0081] Preferably, the weight ratio of the polymer powder with active groups formed on its surface to the compound containing double bonds is 1:3-5, for example, it can be 1:3, 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4, 1:4.2, 1:4.4, 1:4.6, 1:4.8, 1:5, etc.

[0082] Preferably, the amount of solvent used is 2-4 times the total weight of the polymer powder with active groups formed on its surface and the compound containing double-bonded olefins, for example, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, etc.

[0083] Preferably, the conditions for polymerization grafting include: a temperature of 60-80°C and a time of 4-20 hours; more preferably, the conditions for polymerization grafting include: a temperature of 65-75°C and a time of 6-10 hours.

[0084] Preferably, the solvent is one or more of water, formamide, and methanol; more preferably, the solvent is water.

[0085] In a preferred embodiment of the present invention, the polymerization grafting includes: dissolving the polymer powder containing the active groups formed on the surface and the double-bonded olefin compound in a solvent, purging nitrogen / argon gas to remove air during the dissolution process, sealing the reaction system after 15-30 minutes, maintaining the reaction at 60-80°C for polymerization grafting, and maintaining the reaction under continuous stirring for 6-8 hours.

[0086] According to the present invention, preferably, the method further includes, after the polymerization grafting, performing solid-liquid separation on the polymerization grafting product (e.g., filtration or centrifugation) to obtain a solid, washing it 4-6 times with 1-3M sodium hydroxide or potassium hydroxide to remove unpolymerized grafted monomers, washing it 1-2 times with deionized water, then wetting it 4-6 times with 1-2M hydrochloric acid, sulfuric acid, or nitric acid to re-acidify the surface of the grafted solid powder, and finally rinsing it with deionized water until the pH of the rinsing water is 7. The rinsed solid powder is dried in a vacuum drying oven at a constant temperature (50-70°C) to a constant weight.

[0087] Step 3)

[0088] Step 3) is to cast a film using a casting solution containing the polymer powder A, a pore-forming agent, and a solvent to obtain a substrate film A with polymer linkages on the surface of the substrate film.

[0089] Preferably, the weight ratio of the polymeric powder A, the pore-forming agent, and the solvent is 10:1-2:60-80; more preferably, the weight ratio of the polymeric powder A, the pore-forming agent, and the solvent is 10:1.5-1.8:65-70. By using the polymeric powder A, the pore-forming agent, and the solvent within the above range, the membrane has the advantage of uniform pore distribution and pore size.

[0090] Preferably, the pore-forming agent is one or more of diethylene glycol butyl ether, polyethylene glycol, polyvinylpyrrolidone, lithium chloride, and lithium bromide; more preferably, the pore-forming agent is one or more of diethylene glycol butyl ether, lithium chloride, and lithium bromide.

[0091] Preferably, the solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide, and dimethyl sulfoxide; more preferably, the solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, and dimethylacetamide.

[0092] Preferably, the thickness of the substrate membrane A is 40-120 μm, and more preferably 60-100 μm to further improve its hydrophobic and oleophobic properties in air and enhance oil-water separation.

[0093] According to the present invention, the method for forming a substrate film A using the casting solution is a phase transfer method. The phase transfer method preferably includes the following steps:

[0094] (1) The casting liquid is coated onto a clean and flat glass plate using a casting knife, and the casting thickness is 40-120 μm;

[0095] (2) The glass plate is transferred to a phase transfer agent for phase transfer.

[0096] Preferably, the phase transfer method further includes degassing the casting solution before step (1). The degassing is preferably performed ultrasonically for 0.5-2 hours.

[0097] Preferably, the phase transfer agent is one or more of water, ethanol, and glycerol, more preferably water.

[0098] Preferably, the phase transfer temperature is 25-45℃ and the phase transfer time is 3-6h.

[0099] Preferably, after the phase transfer is completed, the glass plate with the membrane is removed from the water, the membrane is washed with deionized water 6-8 times, the membrane is peeled off the glass plate, and then washed repeatedly with deionized water 6-8 times.

[0100] Step 4)

[0101] Step 4) involves crosslinking the carboxyl groups on the substrate membrane A with the amino groups of polyethyleneimine in the presence of a crosslinking agent to obtain a substrate membrane B with hydrophilic segments grafted onto the polymer linking segments.

[0102] According to the present invention, preferably, the molar ratio of the matrix film A, calculated as carboxyl groups, to the polyethyleneimine, calculated as amino groups, is 1:2-4, for example, it can be 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8, 1:3, 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4, etc.

[0103] The carboxyl content per unit area of ​​the substrate membrane A can be determined by titration, i.e., by taking a sample of 0.5 × 0.5 cm. 2 Take 3-5 membrane sheets and place them in 50 ml of deionized water. Add phenolphthalein as an indicator and titrate until the phenolphthalein changes color. Calculate the carboxyl content per unit area of ​​the membrane. Based on the carboxyl content per unit area of ​​the membrane, calculate the amount of carboxyl groups in the matrix membrane A, which is the amount of carboxyl groups per unit area of ​​the membrane multiplied by the membrane area.

[0104] Preferably, the carboxyl content per unit area of ​​the substrate membrane A is 0.1-1.0 μmol / cm². 2 .

[0105] According to the present invention, preferably, the molar ratio of the matrix film A, based on the carboxyl groups, to the crosslinking agent is 1:2-4; more preferably, the molar ratio of the matrix film A, based on the carboxyl groups, to the crosslinking agent is 1:2.5-3.5.

[0106] Specific examples of the molar ratio of the matrix film A to the crosslinking agent, based on the carboxyl groups, include 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8, 1:3, 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4, etc.

[0107] As the crosslinking agent, any agent that can achieve the grafting purpose is acceptable, and preferably one or more of dicyclohexylcarbodiimide (DCC), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride (EDC), and diisopropylcarbodiimide.

[0108] Preferably, to further promote crosslinking, a crosslinking accelerator is used in conjunction with the crosslinking agent. Various accelerators commonly used in the art can be used as the crosslinking accelerator, preferably N-hydroxysuccinimide (NHS) and / or thiosuccinimide (Sulfo-NHS).

[0109] In a preferred embodiment of the present invention, the crosslinking agent and the crosslinking promoter are used in combination as follows: dicyclohexylcarbodiimide / N-hydroxysuccinimide (DCC / NHS), 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride / N-hydroxysuccinimide (EDC / NHS), and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride / thiosuccinimide (EDC / Sulfo-NHS).

[0110] In this invention, the amount of the crosslinking accelerator can be selected according to the amount of carboxyl groups in the matrix membrane A. Preferably, the molar ratio of the matrix membrane A to the crosslinking accelerator, based on the carboxyl groups, is 1:4-8; more preferably, the molar ratio of the matrix membrane A to the crosslinking accelerator, based on the carboxyl groups, is 1:5-7.

[0111] According to the present invention, preferably, the polyethyleneimine is dendritic. Furthermore, the average molecular weight of the polyethyleneimine is preferably 500-3000; more preferably, the average molecular weight of the polyethyleneimine is 1500-2000.

[0112] In a preferred embodiment of the present invention, a 0.05-0.1 mol / L aqueous solution is prepared using (2-(N-morpholino)ethanesulfonic acid (MES) as a buffer substance, and the pH is adjusted to between 5 and 6. DCC, EDC, DCC / NHS, EDC / NHS, or EDC / Sulfo-NHS are dissolved in the MES solution, respectively. The substrate membrane A is immersed in the MES solution containing DCC, EDC, DCC / NHS, EDC / NHS, or EDC / Sulfo-NHS and activated at 30-40°C for 30-60 min. Then, the activated carboxyl group substrate membrane A is removed and immersed in the MES solution containing polyethyleneimine and the reaction continues at 30-40°C for 6-12 h. After the reaction is completed, the pH is adjusted to 7.5, and the substrate membrane A is repeatedly washed with deionized water (e.g., 6-8 times). It is then dried at a constant temperature (50-70°C) in a vacuum drying oven until constant weight.

[0113] Step 5)

[0114] Step 5) involves reacting the amino group in the hydrophilic segment with a fluorinated anhydride compound in the presence of a catalyst to obtain a matrix membrane C with a hydrophobic segment grafted onto the hydrophilic segment.

[0115] According to the present invention, in step 5), the amount of the fluoroanhydride compound can be selected according to the amount of polyethyleneimine in step 4). Preferably, the molar ratio of the polyethyleneimine to the fluoroanhydride compound is 1:2-4, for example, 1:2, 1:2.2, 1:2.4, 1:2.6, 1:2.8, 1:3, 1:3.2, 1:3.4, 1:3.6, 1:3.8, 1:4, etc.

[0116] According to the present invention, preferably, the catalyst is triethylamine and / or pyridine; more preferably, the catalyst is triethylamine.

[0117] According to the present invention, the amount of catalyst can be selected according to the amount of the fluoro anhydride compound. Preferably, the molar ratio of the fluoro anhydride compound to the catalyst is 100:1-5, for example, 100:1, 100:2, 100:3, 100:4, 100:5, etc.

[0118] According to the present invention, in order to promote the rapid progress of the reaction, the reaction is preferably carried out in an organic solvent, which may be one or more of methanol, acetonitrile, ethanol and ethyl acetate; preferably, the organic solvent is ethanol and / or ethyl acetate.

[0119] According to the present invention, preferably, the reaction conditions include: a reaction temperature of 25-35°C and a reaction time of 0.5-1.5 h.

[0120] According to the present invention, the method further includes the steps of repeatedly rinsing the substrate membrane C with deionized water until the pH of the rinsing water is 7, and drying the substrate membrane C in a vacuum drying oven at a constant temperature (50-70°C) until constant weight.

[0121] In this invention, the substrate membrane C is the stimulus-responsive hydrophilic and oleophobic membrane of this invention.

[0122] According to a third aspect of the present invention, a stimuli-responsive hydrophilic-oleophobic film prepared by the method of the second aspect of the present invention is also provided.

[0123] According to a fourth aspect of the present invention, the application of the stimulus-responsive hydrophilic-oleophobic membrane prepared by the method of preparing the stimulus-responsive hydrophilic-oleophobic membrane of the first aspect of the present invention or the method of preparing the stimulus-responsive hydrophilic-oleophobic membrane of the second aspect of the present invention in oil-water separation is also provided.

[0124] The present invention will be described in detail below through embodiments, but the present invention is not limited to the following embodiments.

[0125] In the following examples, the average molecular weight of the polymer was determined using a gel permeation chromatography system (Agilent 1260MDS, USA); the surface scanning electron microscope images of the membrane were taken using an S-4800 scanning electron microscope (Hitachi, Japan); and the water contact angle of the membrane was determined using a DSA100S contact angle meter (KRUSS, Germany).

[0126] Example 1 (PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic film)

[0127] 1) Polysulfone (PSF) powder was irradiated with gamma rays in air at room temperature. The purity of the powder was above 98% by weight, and the particle size was approximately 0.1 mm. The gamma rays used were from... 60 Co, radiation dose of 20 kGy. The irradiated powder was stored at -20°C for future use.

[0128] 2) Mix the powder obtained in step 1) with acrylic acid at a weight ratio of 1:4, and dissolve it in deionized water at 70°C. The mass of deionized water is three times the combined weight of the powder and acrylic acid obtained in step 1). Nitrogen gas is bubbled in during the dissolution process to remove air. After 20 minutes, the reaction system is sealed and the reaction polymerization grafting is carried out at 70°C. The reaction is maintained for 8 hours with continuous stirring. Acrylic acid polymerizes under the condition of free radicals generated by peroxy groups, forming grafted double bond polymers (average molecular weight of polymer is 600,000) on the surface of the high molecular weight PSF. After the above reaction, the grafted solid powder is obtained by filtration. It is washed five times with 2M sodium hydroxide to remove unpolymerized grafted monomers (each wash uses a volume three times the volume of powder). Then it is washed twice with deionized water (each wash uses a volume three times the volume of powder). Then it is soaked five times with 1.5M hydrochloric acid to acidify the surface of the acrylic acid grafted PSF solid powder. Finally, it is rinsed with deionized water until the pH of the water after washing is 7. The rinsed PSF solid powder was dried at a constant temperature (60°C) in a vacuum drying oven until it reached a constant weight.

[0129] 3) The acrylic acid-grafted PSF solid powder, pore-forming agent, and solvent from step 2) are mixed in a mass ratio of 10:1:60 and stirred at 80°C to form a casting solution. The pore-forming agent used is diethylene glycol butyl ether, and the solvent is N-methylpyrrolidone. The casting solution is ultrasonically degassed for 1 hour before use. After degassed, the casting solution is coated onto a clean, flat glass plate using a casting knife, resulting in a film thickness of 80 μm. After completing the above steps, the glass plate is transferred to a phase transfer agent. Water is typically chosen as the phase transfer agent, and the temperature is maintained at 30°C for 4 hours. After phase transfer, the glass plate with the film is removed from the water, washed 7 times with deionized water, and then peeled off the glass plate. The film is then washed 7 more times with deionized water, resulting in a membrane with a pore size of 8 nm. The carboxyl content per unit area of ​​the membrane is determined by titration, i.e., taking a 0.5 × 0.5 cm... 2 Five membrane sheets were placed in 50 ml of deionized water, and phenolphthalein was added as an indicator. Titration continued until the phenolphthalein changed color. The carboxyl content per unit area of ​​the membrane was calculated, and the calculated carboxyl content was 0.18 μmol / cm³. 2 .

[0130] 4) DCC was used as a crosslinking agent for the carboxyl groups and amino groups of polyethyleneimine on the membrane surface, and NHS was used as a crosslinking promoter. The selected polyethyleneimine was dendritic (average molecular weight 1800, purchased from Sigma).

[0131] Calculate the amount of carboxyl groups based on the titration results in step 3), which is the amount of carboxyl groups per unit area of ​​the membrane multiplied by the area of ​​the membrane. Take a membrane of a certain area and calculate the amounts of DCC, NHS, and polyethyleneimine (calculated as amino) used according to the above-mentioned amount of carboxyl groups. Specifically, the amount of carboxyl groups: DCC: NHS: polyethyleneimine (calculated as amino) = 1:3:6:2.

[0132] Prepare the DCC / NHS solution according to the above proportions: Prepare a 0.1 mol / L aqueous solution using MES (2-(N-morpholino)ethanesulfonic acid) as a buffer, adjust the pH to 5, and ensure the volume of the MES solution is 400 times the volume of the membrane. Dissolve DCC and NHS separately in the MES solution. Immerse the membrane in the MES solution containing DCC and NHS and activate it at 30°C for 40 min. Remove the activated carboxyl group membrane and immerse it in an MES solution containing polyethyleneimine (the volume of the MES solution containing polyethyleneimine is 400 times the volume of the membrane). Continue the reaction at 30°C for 8 h. After the reaction is complete, adjust the pH to 7.5. Wash the membrane repeatedly with deionized water 7 times and then dry it at a constant temperature (60°C) in a vacuum drying oven until constant weight.

[0133] 5) Take the membrane grafted with polyethyleneimine in step 4), and calculate the amount of fluoroanhydride to be used according to the amount of polyethyleneimine (calculated as amino) used in step 4). The amount of fluoroanhydride is 3 times the molar amount of polyethyleneimine (calculated as amino). The fluoroanhydride used is pentafluoropropionic anhydride.

[0134] The polyethyleneimine-grafted membrane from step 4) was immersed in a solution containing the aforementioned acid anhydride and catalyst. The catalyst used was triethylamine, and the molar ratio of acid anhydride to catalyst was 100:2. Ethanol was used as the solvent (the amount of solvent used was just enough to completely submerge the membrane). The reaction time was 1 hour, and the reaction temperature was 30°C. After the reaction was complete, the membrane was repeatedly rinsed with deionized water until the pH of the rinsing water reached 7. Finally, the membrane was placed in a vacuum drying oven and dried at a constant temperature (60°C) until constant weight.

[0135] The electron micrograph of the above membrane is shown below. Figure 2 As shown; the water and oil contact angles after immersion in water and oil for 0 min, 15 min, 30 min, and 1 h, respectively, are as follows. Figure 3 As shown in the figure, the water contact angles after immersion in water for 0 min, 15 min, 30 min, and 1 h were 146.9°, 120.5°, 71.9°, and 0°, respectively; the oil contact angles after immersion in diesel fuel for 0 min, 15 min, 30 min, and 1 h were 146.4°, 145.3°, 144.1°, and 144.6°, respectively. This indicates that the membrane is hydrophobic and oleophobic in air, but becomes hydrophilic when immersed in water, making it a stimulus-responsive oil-water separation membrane.

[0136] In addition, water and diesel oil were mixed at a volume ratio of 1:1, stirred evenly, and poured into an oil-water separator. The above-mentioned PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic membrane was used as the filter membrane and filtered under a pressure of 0.15 MPa. Water could be seen passing through the filter membrane, while yellow diesel oil remained on the membrane. No visible floating oil was found in the water that passed through. The oil content was measured to be 0.32 mg / L by an infrared oil analyzer.

[0137] Example 2 (PES / Methacrylic Acid / PEI / Hepenofluorobutyric Anhydride)

[0138] 1) Polyethersulfone (PES) powder was irradiated with gamma rays in air at room temperature. The purity of each powder used was greater than or equal to 98% by weight, and the particle size was approximately 0.05 mm. The gamma rays used were from... 60 Co, radiation dose of 20 kGy. The irradiated powder was stored at -20°C for future use.

[0139] 2) Mix the powder obtained in step 1) with methacrylic acid at a weight ratio of 1:4, and dissolve in deionized water at 70°C. The mass of deionized water is three times the combined weight of the powder and methacrylic acid obtained in step 1). Nitrogen gas is bubbled in during the dissolution process to remove air. After 20 minutes, the reaction system is sealed and the reaction is maintained at 70°C for polymerization and grafting. The reaction is maintained for 8 hours with continuous stirring. Methacrylic acid polymerizes under the condition of free radicals generated by peroxy groups, forming grafted double bond polymers (average molecular weight of polymer is 620,000) on the surface of polymeric PES. After the above reaction, the grafted solid powder is obtained by filtration. It is washed five times with 2M sodium hydroxide to remove unpolymerized grafted monomers (each wash uses a volume three times the volume of powder). Then it is washed twice with deionized water (each wash uses a volume three times the volume of powder). Then it is soaked five times with 1.5M hydrochloric acid to acidify the surface of the methacrylic acid grafted PES solid powder. Finally, it is rinsed with deionized water until the pH of the water after washing is 7. The rinsed PES solid powder was dried at a constant temperature (60°C) in a vacuum drying oven until it reached a constant weight.

[0140] 3) The methacrylic acid-grafted PES solid powder, pore-forming agent, and solvent from step 2) are mixed in a mass ratio of 10:1:60 and stirred at 80°C to form a casting solution. Lithium bromide is used as the pore-forming agent, and dimethylacetamide is used as the solvent. The casting solution is ultrasonically degassed for 1 hour before use. After degassed, the casting solution is coated onto a clean, flat glass plate using a casting knife, resulting in a film thickness of 80 μm. After completing the above steps, the glass plate is transferred to a phase transfer agent. Water is typically chosen as the phase transfer agent, and the temperature is maintained at 30°C for 4 hours. After phase transfer, the glass plate with the film is removed from the water, washed 7 times with deionized water, and then peeled off the glass plate. The film is then washed 7 more times with deionized water, resulting in a membrane with a pore size of 7 nm. The carboxyl content per unit area of ​​the membrane is determined by titration, i.e., a 0.5 × 0.5 cm⁻¹ sample is used. 2 Five membrane sheets were placed in 50 ml of deionized water, and phenolphthalein was added as an indicator. Titration continued until the phenolphthalein changed color. The carboxyl content per unit area of ​​the membrane was calculated, and the calculated carboxyl content was 0.23 μmol / cm³. 2 .

[0141] 4) DCC was used as the crosslinking agent for the carboxyl groups and amino groups of polyethyleneimine on the membrane surface, and NHS was used as the crosslinking promoter. The selected polyethyleneimine was dendritic (average molecular weight 2000, purchased from Sigma-Aldrich).

[0142] Calculate the amount of carboxyl groups based on the titration results in step 3), which is the amount of carboxyl groups per unit area of ​​the membrane multiplied by the area of ​​the membrane. Take a membrane of a certain area and calculate the amounts of EDC, NHS, and polyethyleneimine (calculated as amino) used according to the above-mentioned amount of carboxyl groups. Specifically, the amount of carboxyl groups: EDC: NHS: polyethyleneimine (calculated as amino) = 1:3:6:3.

[0143] Prepare the EDC / NHS solution according to the above proportions, specifically: Prepare a 0.1 mol / L aqueous solution using MES as a buffer, with the volume of the MES solution being 400 times the volume of the membrane. Adjust the pH to 5. Dissolve EDC and NHS separately in the MES solution. Immerse the membrane in the MES solution containing EDC and NHS and activate it at 30°C for 40 min. Remove the activated carboxyl group membrane and immerse it in an MES solution containing polyethyleneimine (the volume of the MES solution containing polyethyleneimine is 400 times the volume of the membrane). Continue the reaction at 30°C for 8 h. After the reaction is complete, adjust the pH to 7.5. After repeatedly washing the membrane with deionized water 7 times, dry it at a constant temperature (60°C) in a vacuum drying oven until constant weight.

[0144] 5) Take the membrane grafted with polyethyleneimine from step 4), and calculate the amount of fluoroanhydride to be used based on the amount of polyethyleneimine (calculated as amino) used in step 4). The amount of fluoroanhydride should be three times the molar amount of polyethyleneimine (calculated as amino). The fluoroanhydride used is heptafluorobutyric anhydride.

[0145] The polyethyleneimine-grafted membrane from step 4) was immersed in a solution containing the aforementioned acid anhydride and catalyst. The catalyst used was triethylamine, and the molar ratio of acid anhydride to catalyst was 100:2. The solvent used was ethyl acetate. The reaction time was 1 hour, and the reaction temperature was 30°C. After the reaction was complete, the membrane was repeatedly rinsed with deionized water until the pH of the rinsing water was 7. Finally, the membrane was placed in a vacuum drying oven and dried at a constant temperature (60°C) until constant weight.

[0146] The contact angle test results of the above membrane are similar to those of Example 1. The water contact angles after immersion in water for 0 min, 15 min, 30 min, and 1 h were 145.3°, 118.7°, 69.5°, and 0°, respectively; the oil contact angles after immersion in diesel fuel for 0 min, 15 min, 30 min, and 1 h were 146.3°, 145.8°, 145.6°, and 145.3°, respectively. This indicates that the membrane is hydrophobic and oleophobic in air, but becomes hydrophilic when immersed in water, making it a stimulus-responsive oil-water separation membrane.

[0147] In addition, water and rapeseed oil were mixed at a volume ratio of 1:1, stirred evenly, and poured into an oil-water separation device. The above-mentioned PES / methacrylic acid / PEI / heptafluorobutyric anhydride hydrophilic and oleophobic membrane was used as the filter membrane and filtered under a pressure of 0.15 MPa. Water could be seen passing through the filter membrane, while yellow rapeseed oil remained on the membrane. No visible floating oil was found in the water that passed through. The oil content was measured to be 0.25 mg / L by an infrared oil analyzer.

[0148] In addition, such as Figure 1 As shown, in Example 2, a base film (with carboxylic acid groups already on its surface) is first formed using a phase transfer method. Then, polyethyleneimine and the carboxylic acid groups on the film surface are crosslinked (the carboxyl groups on the film surface and PEI form amide bonds 1). Subsequently, an anhydride and the amino group of polyethyleneimine are condensed (PEI and heptafluorobutyric anhydride condense to form bond 2).

[0149] Example 3 (PVDF / 2-ethylacrylic acid / PEI / nonafluorovalerate anhydride hydrophilic and oleophobic film)

[0150] 1) Polyvinylidene fluoride (PVDF) powder was irradiated with gamma rays in air at room temperature. The powder used had a purity of ≥98% by weight and a particle size of approximately 0.1 mm. The gamma rays used were from... 60 Co, radiation dose of 20 kGy. The irradiated powder was stored at -20°C for future use.

[0151] 2) The powder obtained in step 1) and 2-ethylacrylic acid are mixed at a weight ratio of 1:4 and dissolved in deionized water at 70°C. The mass of the deionized water is three times the combined mass of the powder and 2-ethylacrylic acid obtained in step 1). Nitrogen / argon gas is bubbled in during the dissolution process to remove air. After 20 minutes, the reaction system is sealed and the reaction polymerization grafting is carried out at 70°C. The reaction is maintained for 8 hours with continuous stirring. 2-ethylacrylic acid is polymerized under the condition of free radicals generated by peroxy groups, forming a grafted double bond polymer (average molecular weight of the polymer is 650,000) on the surface of the PVDF polymer. After the above reaction, the grafted solid powder is obtained by filtration. It is washed five times with 2M sodium hydroxide to remove unpolymerized grafted monomers (each wash uses a volume three times the volume of the powder). Then it is washed twice with deionized water (each wash uses a volume three times the volume of the powder). Then it is soaked five times with 1.5M hydrochloric acid to acidify the surface of the PVDF solid powder grafted with 2-ethylacrylic acid. Finally, it is rinsed with deionized water until the pH of the water after washing is 7. The rinsed PVDF solid powder was dried at a constant temperature (60℃) in a vacuum drying oven until it reached a constant weight.

[0152] 3) The grafted solid powder, pore-forming agent, and solvent from step 2) are mixed in a ratio of 10:1:60 and stirred at 80°C to form a casting solution. Lithium bromide is used as the pore-forming agent, and N,N-dimethylformamide is used as the solvent. The casting solution is ultrasonically degassed for 1 hour before use. After degassed, the casting solution is coated onto a clean, flat glass plate using a casting knife, resulting in a film thickness of 80 μm. After completing the above steps, the glass plate is transferred to a phase transfer agent. Water is typically chosen as the phase transfer agent, and the temperature is maintained at 30°C for 4 hours. After phase transfer, the glass plate with the film is removed from the water, washed 7 times with deionized water, and then peeled off the glass plate. The film is then washed 7 more times with deionized water, resulting in a membrane with a pore size of 9.5 nm. The carboxyl content per unit area of ​​the membrane is determined by titration, i.e., a 0.5 × 0.5 cm⁻¹ sample is used. 2 Five membrane sheets were placed in 50 ml of deionized water, and phenolphthalein was added as an indicator. Titration continued until the phenolphthalein changed color. The carboxyl content per unit area of ​​the membrane was calculated, and the calculated carboxyl content was 0.26 μmol / cm³. 2 .

[0153] 4) EDC was used as a crosslinking agent for the carboxyl groups and amino groups of polyethyleneimine on the membrane surface, and NHS was used as a crosslinking promoter. The selected polyethyleneimine was dendritic (average molecular weight 1800, purchased from Sigma).

[0154] Calculate the amount of carboxyl groups based on the titration results in step 3), which is the amount of carboxyl groups per unit area of ​​the membrane multiplied by the area of ​​the membrane. Take a membrane of a certain area and calculate the amounts of EDC, NHS, and polyethyleneimine (calculated as amino) used according to the above-mentioned amount of carboxyl groups. Specifically, the amount of carboxyl groups: EDC: NHS: polyethyleneimine (calculated as amino) = 1:3:6:3.

[0155] Prepare the EDC / NHS solution according to the above proportions, specifically: Prepare a 0.1 mol / L aqueous solution using MES as a buffer, with the volume of the MES solution being 400 times the volume of the membrane. Adjust the pH to 5. Dissolve EDC and NHS separately in the MES solution. Immerse the membrane in the MES solution containing EDC and NHS and activate it at 30°C for 40 min. Remove the activated carboxyl group membrane and immerse it in an MES solution containing polyethyleneimine (the volume of the MES solution containing polyethyleneimine is 400 times the volume of the membrane). Continue the reaction at 30°C for 8 h. After the reaction is complete, adjust the pH to 7.5. Wash the membrane repeatedly with deionized water 7 times and then dry it at a constant temperature (60°C) in a vacuum drying oven until constant weight.

[0156] 5) Take the membrane grafted with polyethyleneimine in step 4), and calculate the amount of fluoroanhydride to be used according to the amount of polyethyleneimine (calculated as amino) used in step 4). The amount of fluoroanhydride is 3 times the molar amount of polyethyleneimine (calculated as amino). The fluoroanhydride used is nonafluoropentanoic acid anhydride.

[0157] The polyethyleneimine-grafted membrane from step 4) was immersed in a solution containing the aforementioned acid anhydride and catalyst. The catalyst was triethylamine, and the molar ratio of acid anhydride to catalyst was 100:2. Ethanol was used as the solvent (the amount of solvent used was just enough to completely submerge the membrane). The reaction time was 1 hour, and the reaction temperature was 30°C. After the reaction was complete, the membrane was repeatedly rinsed with deionized water until the pH of the rinsing water was 7. Finally, the membrane was placed in a vacuum drying oven and dried at a constant temperature (60°C) until constant weight.

[0158] The contact angle test results of the above membrane were similar to those in Example 1. The water contact angles after immersion in water for 0 min, 15 min, 30 min, and 1 h were 148.3°, 125.7°, 74.1°, and 0°, respectively; the oil contact angles after immersion in diesel fuel for 0 min, 15 min, 30 min, and 1 h were 147.1°, 147.1°, 145.8°, and 145.3°, respectively.

[0159] In addition, water and dyed hexadecane (Sudan Red dye) were mixed at a volume ratio of 1:1, and Tween 20 was added and stirred evenly to form an emulsion oil. The emulsion oil was poured into an oil-water separation device, and the above-mentioned PVDF / 2-ethylacrylic acid / PEI / nonafluorovalerate anhydride hydrophilic and oleophobic membrane was used as a filter membrane. The filter was filtered at a pressure of 0.15 MPa. Water could be seen passing through the filter membrane, while the red hexadecane remained on the membrane. No red color was visible in the water. The oil content was measured to be 0.65 mg / L by an infrared oil analyzer.

[0160] Example 4 (PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic film)

[0161] 1) Polysulfone (PSF) powder was irradiated with gamma rays in air at room temperature. The purity of the powder was above 98% by weight, and the particle size was approximately 0.1 mm. The gamma rays used were from... 60 Co, radiation dose of 20 kGy. The irradiated powder was stored at -20°C for future use.

[0162] 2) The powder obtained in step 1) and acrylic acid are mixed at a weight ratio of 1:5 and dissolved in deionized water at 75°C. The mass of the deionized water is three times the combined weight of the powder and acrylic acid obtained in step 1). Nitrogen gas is bubbled in during the dissolution process to remove air. After 25 minutes, the reaction system is sealed and the reaction is maintained at 70°C for polymerization and grafting. The reaction is maintained for 6 hours with continuous stirring. Acrylic acid polymerizes under the condition of free radicals generated by peroxy groups, forming grafted double bonds on the surface of the polymer PSF. After the above reaction, the grafted solid powder is obtained by filtration. It is washed five times with 2M sodium hydroxide to remove unpolymerized grafted monomers (each wash uses a volume three times the volume of the powder). Then it is washed twice with deionized water (each wash uses a volume three times the volume of the powder). Then it is soaked five times with 1.5M hydrochloric acid to re-acidify the surface of the acrylic acid-grafted PSF solid powder. Finally, it is rinsed with deionized water until the pH of the water after washing is 7. The rinsed PSF solid powder is dried at a constant temperature (60°C) in a vacuum drying oven to constant weight.

[0163] 3) The acrylic acid-grafted PSF solid powder, pore-forming agent, and solvent from step 2) are mixed in a mass ratio of 10:1.5:68 and stirred at 80°C to form a casting solution. The pore-forming agent used is diethylene glycol butyl ether, and the solvent is N-methylpyrrolidone. The casting solution is ultrasonically degassed for 1 hour before use. After degassed, the casting solution is coated onto a clean, flat glass plate using a casting knife, resulting in a film thickness of 90 μm. After completing the above steps, the glass plate is transferred to a phase transfer agent. Water is typically chosen as the phase transfer agent, and the temperature is maintained at 30°C for 4 hours. After phase transfer, the glass plate with the film is removed from the water, washed 7 times with deionized water, and then peeled off the glass plate. The film is then washed 7 more times with deionized water, resulting in a membrane with a pore size of 8.5 nm. The carboxyl content per unit area of ​​the membrane is determined by titration, i.e., taking a 0.5 × 0.5 cm... 2 Five membrane sheets were placed in 50 ml of deionized water, and phenolphthalein was added as an indicator. Titration continued until the phenolphthalein changed color. The carboxyl content per unit area of ​​the membrane was calculated, and the calculated carboxyl content was 0.23 μmol / cm³. 2 .

[0164] 4) DCC was used as a crosslinking agent for the carboxyl groups and amino groups of polyethyleneimine on the membrane surface, and NHS was used as a crosslinking promoter. The selected polyethyleneimine was dendritic (average molecular weight 1500, purchased from Sigma).

[0165] Calculate the amount of carboxyl groups based on the titration results in step 3), which is the amount of carboxyl groups per unit area of ​​the membrane multiplied by the area of ​​the membrane. Take a membrane of a certain area and calculate the amounts of DCC, NHS, and polyethyleneimine (calculated as amino) used according to the above-mentioned amount of carboxyl groups. Specifically, the amount of carboxyl groups: DCC: NHS: polyethyleneimine (calculated as amino) = 1:3.5:7:3.

[0166] Prepare the DCC / NHS solution according to the above proportions: Prepare a 0.1 mol / L aqueous solution using MES (2-(N-morpholino)ethanesulfonic acid) as a buffer, with the volume of the MES solution being 400 times the volume of the membrane. Adjust the pH to 5. Dissolve DCC and NHS separately in the MES solution. Immerse the membrane in the MES solution containing DCC and NHS and activate it at 30°C for 40 min. Remove the activated carboxyl group membrane and immerse it in an MES solution containing polyethyleneimine (the volume of the MES solution containing polyethyleneimine being 400 times the volume of the membrane). Continue the reaction at 30°C for 8 h. After the reaction is complete, adjust the pH to 7.5. Wash the membrane repeatedly with deionized water 7 times and then dry it at a constant temperature (60°C) in a vacuum drying oven until constant weight.

[0167] 5) Take the membrane grafted with polyethyleneimine in step 4), and calculate the amount of fluoroanhydride to be used according to the amount of polyethyleneimine (calculated as amino) used in step 4). The amount of fluoroanhydride is twice the molar amount of polyethyleneimine (calculated as amino). The fluoroanhydride used is pentafluoropropionic anhydride.

[0168] The polyethyleneimine-grafted membrane from step 4) was immersed in a solution containing the aforementioned acid anhydride and catalyst. The catalyst used was triethylamine, and the molar ratio of acid anhydride to catalyst was 100:2. Ethanol was used as the solvent (the amount of solvent used was just enough to completely submerge the membrane). The reaction time was 0.5 h, and the reaction temperature was 35 °C. After the reaction was complete, the membrane was repeatedly rinsed with deionized water until the pH of the rinsing water reached 7. Finally, the membrane was placed in a vacuum drying oven and dried at a constant temperature (60 °C) until constant weight.

[0169] The contact angle test results of the above membrane are similar to those of Example 1. The water contact angles after immersion in water for 0 min, 15 min, 30 min, and 1 h were 147.3°, 118.6°, 65.9°, and 0°, respectively; the oil contact angles after immersion in diesel fuel for 0 min, 15 min, 30 min, and 1 h were 147.0°, 146.5°, 144.9°, and 145.1°, respectively. This indicates that the membrane is hydrophobic and oleophobic in air, but becomes hydrophilic when immersed in water, making it a stimulus-responsive oil-water separation membrane.

[0170] In addition, water and diesel oil were mixed at a volume ratio of 1:1, stirred evenly, and poured into an oil-water separator. The above-mentioned PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic membrane was used as a filter membrane and filtered under a pressure of 0.15 MPa. Water passed through, while yellow diesel oil remained on the membrane. No visible floating oil was found in the water. The oil content was measured to be 0.35 mg / L by an infrared oil analyzer.

[0171] Example 5 (PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic film)

[0172] 1) Polysulfone (PSF) powder was irradiated with gamma rays in air at room temperature. The purity of the powder was above 98% by weight, and the particle size was approximately 0.12 mm. The gamma rays used were from... 60 Co, radiation dose of 20 kGy. The irradiated powder was stored at -20°C for future use.

[0173] 2) The powder obtained in step 1) and acrylic acid were mixed at a weight ratio of 1:3.5 and dissolved in deionized water at 60°C. The mass of the deionized water was twice the combined weight of the powder and acrylic acid obtained in step 1). Nitrogen gas was bubbled in during the dissolution process to remove air. After 30 minutes, the reaction system was sealed and the reaction polymerization grafting was carried out at 60°C. The reaction was maintained for 8 hours with continuous stirring. Acrylic acid polymerized under the condition of free radicals generated by peroxy groups, forming grafted double bonds on the surface of the polymer PSF. After the above reaction, the grafted solid powder was obtained by filtration. It was washed 5 times with 2M sodium hydroxide to remove unpolymerized grafted monomers (each wash used a volume 3 times the volume of the powder). It was then washed 2 times with deionized water (each wash used a volume 3 times the volume of the powder). Then, it was soaked 5 times with 1.5M hydrochloric acid to re-acidify the surface of the acrylic acid grafted PSF solid powder. Finally, it was rinsed with deionized water until the pH of the water was 7. The rinsed PSF solid powder was dried at a constant temperature (60°C) in a vacuum drying oven to constant weight.

[0174] 3) The acrylic acid-grafted PSF solid powder, pore-forming agent, and solvent from step 2) are mixed in a mass ratio of 10:1.8:70 and stirred at 80°C to form a casting solution. The pore-forming agent used is diethylene glycol butyl ether, and the solvent is N-methylpyrrolidone. The casting solution is ultrasonically degassed for 1 hour before use. After degassed, the casting solution is coated onto a clean, flat glass plate using a casting knife, resulting in a film thickness of 70 μm. After completing the above steps, the glass plate is transferred to a phase transfer agent. Water is typically chosen as the phase transfer agent, and the temperature is maintained at 30°C for 4 hours. After phase transfer, the glass plate with the film is removed from the water, washed 7 times with deionized water, and then peeled off the glass plate. The film is then washed 7 more times with deionized water, resulting in a membrane with a pore size of 10.5 nm. The carboxyl content per unit area of ​​the membrane is determined by titration, i.e., taking a 0.5 × 0.5 cm... 2 Five membrane sheets were placed in 50 ml of deionized water, and phenolphthalein was added as an indicator. Titration continued until the phenolphthalein changed color. The carboxyl content per unit area of ​​the membrane was calculated, and the calculated carboxyl content was 0.26 μmol / cm³. 2 .

[0175] 4) DCC was used as a crosslinking agent for the carboxyl groups and amino groups of polyethyleneimine on the membrane surface, and NHS was used as a crosslinking promoter. The selected polyethyleneimine was dendritic (average molecular weight 2000, purchased from Sigma).

[0176] Calculate the amount of carboxyl groups based on the titration results in step 3), which is the amount of carboxyl groups per unit area of ​​the membrane multiplied by the area of ​​the membrane. Take a membrane of a certain area and calculate the amounts of DCC, NHS, and polyethyleneimine (calculated as amino) used according to the above-mentioned amount of carboxyl groups. Specifically, the amount of carboxyl groups: DCC: NHS: polyethyleneimine (calculated as amino) = 1:3:5:2.

[0177] Prepare the DCC / NHS solution according to the above proportions: Prepare a 0.1 mol / L aqueous solution using MES (2-(N-morpholino)ethanesulfonic acid) as a buffer, with the volume of the MES solution being 400 times the volume of the membrane. Adjust the pH to 5. Dissolve DCC and NHS separately in the MES solution. Immerse the membrane in the MES solution containing DCC and NHS and activate it at 30°C for 40 min. Remove the activated carboxyl group membrane and immerse it in an MES solution containing polyethyleneimine (the volume of the MES solution containing polyethyleneimine being 400 times the volume of the membrane). Continue the reaction at 30°C for 8 h. After the reaction is complete, adjust the pH to 7.5. Wash the membrane repeatedly with deionized water 7 times and then dry it at a constant temperature (60°C) in a vacuum drying oven until constant weight.

[0178] 5) Take the membrane grafted with polyethyleneimine in step 4), and calculate the amount of fluoroanhydride to be used according to the amount of polyethyleneimine (calculated as amino) used in step 4). The amount of fluoroanhydride is 4 times the molar amount of polyethyleneimine (calculated as amino). The fluoroanhydride used is pentafluoropropionic anhydride.

[0179] The polyethyleneimine-grafted membrane from step 4) was immersed in a solution containing the aforementioned acid anhydride and catalyst. The catalyst used was triethylamine, and the molar ratio of acid anhydride to catalyst was 100:3. Ethanol was used as the solvent (the amount of solvent used was just enough to completely submerge the membrane). The reaction time was 1.5 h, and the reaction temperature was 30 °C. After the reaction was complete, the membrane was repeatedly rinsed with deionized water until the pH of the rinsing water reached 7. Finally, the membrane was placed in a vacuum drying oven and dried at a constant temperature (60 °C) until constant weight.

[0180] The obtained membrane exhibited water contact angles of 146.5°, 121.7°, 72.9°, and 0° after immersion in water for 0 min, 15 min, 30 min, and 1 h, respectively; and oil contact angles of 145.3°, 144.8°, 145.0°, and 144.9° after immersion in diesel fuel for 0 min, 15 min, 30 min, and 1 h, respectively. This indicates that the membrane is hydrophobic and oleophobic in air, but becomes hydrophilic upon immersion in water, making it a stimulus-responsive oil-water separation membrane. Furthermore, when water and diesel fuel were mixed at a 1:1 volume ratio and stirred thoroughly, the mixture was poured into an oil-water separation device. Using the aforementioned PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic membrane as the filter, filtration was performed at a pressure of 0.15 MPa. Water passed through, while yellow diesel fuel remained on the membrane; no visible floating oil was observed in the water. Infrared oil content analysis showed an oil content of 0.25 mg / L.

[0181] Example 6 (PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic film)

[0182] The process was carried out according to Example 1, except that the casting film thickness was 40 μm, and a PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic film was obtained in the same way.

[0183] The obtained membrane exhibited water contact angles of 133.2°, 99.6°, 30.2°, and 0° after immersion in water for 0 min, 15 min, 30 min, and 1 h, respectively; and oil contact angles of 133.0°, 129.8°, 129.9°, and 128.9° after immersion in diesel fuel for 0 min, 15 min, 30 min, and 1 h, respectively. This indicates that the membrane is hydrophobic and oleophobic in air, but becomes hydrophilic upon immersion in water, making it a stimulus-responsive oil-water separation membrane.

[0184] In addition, water and diesel oil were mixed at a volume ratio of 1:1, stirred evenly, and poured into an oil-water separator. The above-mentioned PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic membrane was used as a filter membrane. Water passed through, while yellow diesel oil remained on the membrane. No visible floating oil was found in the water. The oil content was measured to be 7.62 mg / L by an infrared oil analyzer.

[0185] Example 7 (PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic film)

[0186] The procedure was carried out as in Example 1, except that the selected gamma rays were from... 60 Co, with a radiation dose of 15 Gy, similarly yielded a PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic film.

[0187] The obtained membrane exhibited water contact angles of 130.5°, 102.3°, 37.8°, and 0° after immersion in water for 0 min, 15 min, 30 min, and 1 h, respectively; and oil contact angles of 128.9°, 129.6°, 130.0°, and 127.8° after immersion in diesel fuel for 0 min, 15 min, 30 min, and 1 h, respectively. This indicates that the membrane is hydrophobic and oleophobic in air, but becomes hydrophilic when immersed in water, making it a stimulus-responsive oil-water separation membrane.

[0188] In addition, water and diesel oil were mixed at a volume ratio of 1:1, stirred evenly, and poured into an oil-water separator. The above-mentioned PSF / acrylic acid / PEI / pentafluoropropionic anhydride hydrophilic and oleophobic membrane was used as a filter membrane and filtered under a pressure of 0.15 MPa. Water passed through, while yellow diesel oil remained on the membrane. No visible floating oil was found in the water. The oil content was measured to be 9.17 mg / L by an infrared oil analyzer.

[0189] Comparative Example 1 (PVDF / 2-ethylacrylic acid / PEI membrane)

[0190] Steps 1) to 4) of Comparative Example 1 are the same as those of Example 3, except that step 5) is omitted, where a fluorinated compound is grafted onto the surface to obtain a PVDF / 2-ethyl acrylic acid / PEI film. The surface of the film is amphiphilic and does not have oleophobic properties, as determined by contact angle testing.

[0191] Comparative Example 2 (PVDF / 2-Ethyl Acrylic Acid)

[0192] Steps 1) to 3) of Comparative Example 2 are the same as those of Example 3, except that phase transfer film is formed. The surface of the film is amphiphilic according to the contact angle test, but it does not have oleophobic ability.

[0193] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A stimulus-responsive hydrophilic-oleophobic film, characterized in that, The stimulus-responsive hydrophilic-oleophobic film includes a polymer matrix, polymer linking segments grafted onto the polymer matrix, hydrophilic segments grafted onto the polymer linking segments, and hydrophobic segments grafted onto the hydrophilic segments. The structural units of the polymer linking segments are derived from double-bonded olefin compounds, the hydrophilic segments are derived from polyethyleneimine, and the hydrophobic segments are derived from fluoroanhydride compounds.

2. The stimulus-responsive hydrophilic-oleophobic film according to claim 1, wherein, The double-bonded acrylate compounds are one or more selected from acrylic acid, methacrylic acid, dimethacrylic acid, 2-ethylacrylic acid, butenoic acid, and 3-methoxybutenoic acid.

3. The stimulus-responsive hydrophilic-oleophobic film according to claim 2, wherein, The double-bonded acrylic acid compound is one or more of acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

4. The stimulus-responsive hydrophilic-oleophobic film according to claim 1, wherein, The average molecular weight of the polymer linker segments is 500,000 to 700,000.

5. The stimulus-responsive hydrophilic-oleophobic film according to claim 1, wherein, The average molecular weight of the polyethyleneimine is 500-3000.

6. The stimulus-responsive hydrophilic-oleophobic film according to claim 1, wherein, The fluoroanhydride compound is one or more of trifluoroacetic anhydride, pentafluoropropionic anhydride, heptafluorobutyric anhydride, and nonafluorovalerate anhydride.

7. The stimulus-responsive hydrophilic-oleophobic film according to claim 1, wherein, The polymer matrix is ​​one or more of polysulfone, polyethersulfone, and polyvinylidene fluoride.

8. The stimulus-responsive hydrophilic-oleophobic film according to claim 1, wherein, The polymer matrix has a pore size of 1-30 nm.

9. The stimulus-responsive hydrophilic-oleophobic film according to claim 8, wherein, The polymer matrix has a pore size of 4-20 nm.

10. A method for preparing a stimulus-responsive hydrophilic-oleophobic film, characterized in that, The method includes the following steps: 1) The step of irradiating polymer powder with γ-rays to form active groups on the surface of the polymer powder; 2) The polymer powder with active groups on its surface obtained in step 1) is polymerized and grafted with a compound containing double-bonded olefins to obtain polymer powder A with polymer linking segments grafted onto the polymer powder. 3) The step of casting a film using a casting solution containing the polymer powder A, a pore-forming agent and a solvent to obtain a substrate film A with polymer connecting segments on the surface of the substrate film; 4) In the presence of a crosslinking agent, the carboxyl groups on the substrate membrane A are crosslinked with the amino groups of polyethyleneimine to obtain a substrate membrane B with hydrophilic segments grafted onto the polymer linking segments. 5) In the presence of a catalyst, the amino group in the hydrophilic segment is reacted with a fluorinated anhydride compound to obtain a matrix membrane C with a hydrophobic segment grafted onto the hydrophilic segment.

11. The method according to claim 10, wherein, The polymer powder is one or more of polysulfone powder, polyethersulfone powder, and polyvinylidene fluoride powder.

12. The method according to claim 10, wherein, The polymer powder has a particle size of 0.05-0.2 mm.

13. The method according to claim 10, wherein, The gamma rays used are from 60 Co, radiation dose is 15-25 kGy.

14. The method of claim 10, wherein, The double-bonded acrylate compounds are one or more selected from acrylic acid, methacrylic acid, dimethacrylic acid, 2-ethylacrylic acid, butenoic acid, and 3-methoxybutenoic acid.

15. The method according to claim 14, wherein, The double-bonded acrylic acid compound is one or more of acrylic acid, methacrylic acid, and 2-ethylacrylic acid.

16. The method of claim 10, wherein, The polymerization grafting includes: polymerizing and grafting a mixture containing polymer powder with active groups formed on its surface, the double-bonded olefin compound, and a solvent.

17. The method according to claim 10, wherein, The weight ratio of the polymer powder with active groups formed on its surface to the compound containing double bonds is 1:3-5.

18. The method according to claim 16, wherein, The amount of solvent used is 2-4 times the total weight of the polymer powder with active groups formed on its surface and the compound containing double-bonded olefins.

19. The method according to claim 10, wherein, The conditions for the polymerization grafting include: a temperature of 60-80℃ and a time of 4-20 hours.

20. The method of claim 16, wherein, The solvent is water.

21. The method according to any one of claims 10-20, wherein, The weight ratio of the polymer powder A, the pore-forming agent, and the solvent is 10:1-2:60-80.

22. The method according to any one of claims 10-20, wherein, The pore-forming agent is one or more of diethylene glycol butyl ether, polyethylene glycol, polyvinylpyrrolidone, lithium chloride, and lithium bromide.

23. The method according to any one of claims 10-20, wherein, The solvent is one or more of N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide, and dimethyl sulfoxide.

24. The method according to any one of claims 10-20, wherein, The thickness of the substrate film A is 40-120 μm.

25. The method according to any one of claims 10-20, wherein, The molar ratio of the matrix membrane A, calculated as carboxyl groups, to the polyethyleneimine, calculated as amino groups, is 1:2-4.

26. The method according to any one of claims 10-20, wherein, The molar ratio of the matrix film A (based on carboxyl groups) to the crosslinking agent is 1:2-4.

27. The method according to claim 26, wherein, The crosslinking agent is one or more of dicyclohexylcarbodiimide, 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and diisopropylcarbodiimide.

28. The method according to any one of claims 10-20, wherein, The molar ratio of the polyethyleneimine to the fluoroanhydride compound is 1:2-4.

29. The method according to any one of claims 10-20, wherein, The catalyst is triethylamine and / or pyridine.

30. The method according to any one of claims 10-20, wherein, The molar ratio of the fluorinated anhydride compound to the catalyst is 100:1-5.

31. The method according to any one of claims 10-20, wherein, The reaction is carried out in an organic solvent, which is one or more of ethanol, ethyl acetate, and dichloroethane.

32. The method according to any one of claims 10-20, wherein, The reaction conditions include: a reaction temperature of 25-35℃ and a reaction time of 0.5-1.5h.

33. The stimuli-responsive hydrophilic and oleophobic film prepared by the method of any one of claims 10-32.

34. The application of the stimulus-responsive hydrophilic-oleophobic membrane prepared by the method of any one of claims 1-9 or any one of claims 10-32 in oil-water separation.

Images