Ultrafiltration membrane, its preparation method and application

Abstract

The embodiment of the present application discloses an ultrafiltration membrane and a preparation method and application thereof. The ultrafiltration membrane comprises a porous channel support layer and a functional layer on the outer surface of the porous channel support layer; wherein the porous channel support layer comprises a hot melt type resin and a polytetrafluoroethylene dispersion resin, and the functional layer comprises a hydrophilic colloidal crystal structure formed by arranging hydrophilic colloidal microspheres in an array form on the outer surface of the porous channel support layer. The porous channel support layer and the functional layer in the ultrafiltration membrane of the present application form hierarchical filtration, and the nanoscale gap between adjacent microspheres with the same size in the hydrophilic colloidal crystal structure can realize the rejection of the ultrafiltration level. The hydrophilicity of the hydrophilic colloidal crystal structure can not only improve the anti-pollution property of the ultrafiltration membrane, but also effectively solve the 'Trade-off' effect between the rejection rate and the water flux.

Description

Technical Field

[0001] This application relates to the field of membrane filtration technology, specifically to an ultrafiltration membrane, its preparation method, and its application. Background Technology

[0002] Membrane separation based on filtration and sieving mechanisms is an effective way to purify water. Ultrafiltration (membrane pore size 1-100 nm), as a highly efficient and stable low-pressure membrane separation technology, features low energy consumption, simple equipment operation, and low risk of secondary pollution. It can effectively remove particulate matter, microorganisms, colloids, oils, and other organic matter from water. In recent years, significant progress has been made in the application of ultrafiltration membranes to oil-water separation, making it an important development direction for wastewater treatment technology.

[0003] However, for oily wastewater with complex composition, high organic concentration, and difficult treatment, such as oily wastewater generated during textile scouring, dyeing, and softening processes, traditional ultrafiltration membranes struggle to achieve effective oil-water separation, thus hindering water purification and reuse. Combining chemical demulsification and microbial treatment with ultrafiltration membranes promises better oil-water separation results, but this introduces new problems such as high energy consumption, high operating costs, low reuse rates, and unavoidable secondary pollution. From an environmental protection and economic perspective of oil-water reuse, new technologies and processes are needed for the in-depth treatment of complex oily wastewater.

[0004] Traditional ultrafiltration membranes alone often fail to achieve the desired results, primarily due to technical bottlenecks such as the "trade-off" effect between flux and selectivity, membrane fouling, and difficulty in achieving precise separation. Improving retention rate, increasing water flux, mitigating membrane fouling, and enhancing separation accuracy have become popular research topics for the application of ultrafiltration membranes in complex oil-water separation. However, there are currently no reports on how to prepare ultrafiltration membranes that combine strong antifouling properties, high retention rate, and high filtration accuracy.

[0005] In view of this, the present invention is hereby proposed. Summary of the Invention

[0006] One object of this application is to provide an ultrafiltration membrane that enables tiered filtration and ultrafiltration-level retention, achieving strong antifouling properties, high retention rate, and high filtration accuracy.

[0007] The purpose of this application is not limited to the above-mentioned purposes. Other purposes and advantages of this application not mentioned above can be understood from the following description and will become clearer through the embodiments of this application. Furthermore, it is readily understood that the purposes and advantages of this application can be achieved through the features disclosed in the claims and combinations thereof.

[0008] In one aspect of this application, an ultrafiltration membrane is provided, comprising:

[0009] A porous support layer and a functional layer located on the outer surface of the porous support layer;

[0010] The porous support layer comprises a hot-melt resin and a polytetrafluoroethylene dispersion resin, and the functional layer comprises a hydrophilic colloidal crystal structure formed by hydrophilic colloidal microspheres arranged in a lattice on the outer surface of the porous support layer.

[0011] In one embodiment, the hot-melt resin is selected from at least one of tetrafluoroethylene-hexafluoropropylene binary copolymer and tetrafluoroethylene-vinylidene fluoride-hexafluoropropylene terpolymer.

[0012] In one embodiment, the hydrophilic colloidal microspheres have a hard core and soft shell structure, and the soft shell has self-adhesive properties;

[0013] Optionally, the hydrophilic colloidal microspheres are silica@polydopamine microspheres;

[0014] Optionally, the hydrophilic colloidal microspheres have a particle size of 185-325 nm.

[0015] In one embodiment, the porous support layer is loaded with hydrophilic nanoparticles.

[0016] In one embodiment, the hydrophilic nanoparticles are at least one of silica sol particles and titanium dioxide sol particles;

[0017] Optionally, the hydrophilic nanoparticles have a particle size of 15-20 nm.

[0018] In one embodiment, the average pore size of the functional layer is 1 to 30% of the average pore size of the porous support layer; and / or, the thickness of the functional layer is 40 to 50% of the thickness of the porous support layer.

[0019] In one embodiment, the porous support layer is in the form of hollow fibers or a flat plate.

[0020] In another aspect of this application, a method for preparing the ultrafiltration membrane as described above is provided, comprising the following steps:

[0021] A porous support layer is obtained by sequentially extruding, stretching and sintering heat setting of materials containing hot melt resin and polytetrafluoroethylene dispersion resin.

[0022] The outer surface of the porous support layer is brought into contact with hydrophilic colloidal microspheres, and after drying, an ultrafiltration membrane is obtained.

[0023] In one embodiment, before contacting the outer surface of the porous support layer with the hydrophilic colloidal microspheres, the method further includes:

[0024] Hydrophilic nanoparticles are filled into the porous support layer and then dried to obtain a porous support layer loaded with hydrophilic nanoparticles.

[0025] In another aspect of this application, the application of the ultrafiltration membrane described above in water purification is also provided.

[0026] The technical solutions provided by the embodiments of this application may include the following beneficial effects:

[0027] The porous support layer and functional layer in the ultrafiltration membrane of this application form a layered filtration. The nanoscale voids between adjacent microspheres of uniform size in the hydrophilic colloidal crystal structure can achieve ultrafiltration-level retention. The hydrophilicity of the hydrophilic colloidal crystal structure can not only improve the antifouling properties of the ultrafiltration membrane, but also effectively solve the "trade-off" effect between retention rate and water flux.

[0028] The method for preparing ultrafiltration membranes in this application is simple, controllable, and has good universality. The prepared ultrafiltration membranes have strong antifouling properties, high rejection rate, high flux, and high filtration accuracy, and can be applied to the field of oil-water separation. Attached Figure Description

[0029] Other features, objects, and advantages of this application will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0030] Figure 1 This is a flowchart illustrating the preparation process of the ultrafiltration membrane according to an embodiment of this application. Detailed Implementation

[0031] The present application will now be described in further detail with reference to the embodiments. It is to be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit the invention.

[0032] It should be noted that, unless otherwise specified, the embodiments and features described in this application can be combined with each other.

[0033] It should be noted that 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.

[0034] Where specific techniques or conditions are not specified in the examples, they shall be performed in accordance with the techniques or conditions described in the literature in this field or in accordance with the product instructions. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products.

[0035] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with that embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0036] Polytetrafluoroethylene (PTFE), polymerized from tetrafluoroethylene monomers, possesses outstanding chemical stability, resistance to acid and alkali corrosion, high heat resistance, and high fracture toughness, earning it the title of "King of Plastics." PTFE membranes, with their high porosity, good recoverability, and small footprint, are irreplaceable as a filtration medium in numerous filtration and purification fields. However, research on the preparation and application of PTFE ultrafiltration membranes is still very limited both domestically and internationally. This is mainly due to the extreme difficulty in controlling process parameters during the preparation of PTFE hollow fiber ultrafiltration membranes, and the difficulty in meeting the pore size requirements of ultrafiltration.

[0037] Based on this, this application provides a polytetrafluoroethylene ultrafiltration membrane that has the good properties of a PTFE membrane and achieves ultrafiltration-level retention. The ultrafiltration membrane includes a porous support layer and a functional layer located on the outer surface of the porous support layer.

[0038] The porous support layer comprises a hot-melt resin and a polytetrafluoroethylene dispersion resin, and the functional layer comprises a hydrophilic colloidal crystal structure formed by hydrophilic colloidal microspheres arranged in a lattice on the outer surface of the porous support layer.

[0039] This application begins with the membrane-forming raw materials, using a polymer alloy composed of a melt-processable hot-melt resin and a conventional, refractory polytetrafluoroethylene (PTFE) dispersion resin. A PTFE-based porous support layer is then prepared using conventional membrane-forming methods (including but not limited to stretching). The resulting support layer has a "node-fiber" microporous structure, with fibers connected by nodes, interwoven into a network, forming orderly arranged elongated channels that enable the sieving of large-diameter oil droplets. Next, a functional layer is constructed on the outer surface of the porous support layer using hydrophilic colloidal microspheres with uniform particle size distribution, excellent monodispersity, and good sphericity as structural units. This functional layer contains a regularly arranged, highly hydrophilic colloidal crystal structure, achieving ultrafiltration-level retention through the nanoscale gaps between adjacent microspheres. Thus, layered filtration and ultrafiltration separation are achieved in the prepared membrane. Furthermore, the "trade-off" effect can be solved by adjusting the porosity of the colloidal crystal array. At the same time, the regularly arranged colloidal microspheres will form gaps of uniform size, which also lays the foundation for high-precision filtration of the filter membrane.

[0040] The addition of hot-melt resin can effectively improve the non-stickiness of conventional PTFE resin and enhance the interfacial compatibility between the support layer and the functional layer to a certain extent. Furthermore, the hydrophilicity of the colloidal crystal structure not only improves the antifouling properties of the ultrafiltration membrane, but its hydrophilicity and high porosity can also effectively resolve the "trade-off" effect between retention rate and water flux, resulting in an ultrafiltration membrane that combines strong antifouling properties, high retention rate, and high filtration accuracy ("one strong and two high").

[0041] This application proposes for the first time that by composite a hydrophilic colloidal microsphere array on the surface of a polytetrafluoroethylene support layer, ultrafiltration-level filtration of the filter membrane can be easily achieved by utilizing the nanoscale pores between the colloidal microspheres, while simultaneously achieving hydrophilic modification of the polytetrafluoroethylene support layer.

[0042] Furthermore, in one embodiment, the hot-melt resin forming the porous support layer accounts for 20-25% of the mass of the polytetrafluoroethylene (PTFE) dispersion resin, within which the hot-melt resin and PTFE dispersion resin exhibit good compatibility. In addition, functionally, the PTFE dispersion resin acts as a skeleton, forming the main body of the support layer, while the hot-melt resin acts as an adhesive.

[0043] Furthermore, in one embodiment, the hot-melt resin is selected from at least one of tetrafluoroethylene-hexafluoropropylene binary copolymer and tetrafluoroethylene-vinylidene fluoride-hexafluoropropylene terpolymer.

[0044] Furthermore, in one embodiment, the hydrophilic colloidal microspheres have a hard-core, soft-shell structure, and the soft shell is self-adhesive. This allows the connection between the functional layer and the porous support layer to be achieved without the need for additional adhesives.

[0045] Preferably, the hydrophilic colloidal microspheres are silica@polydopamine microspheres. With silica as the core and polydopamine as the shell, they possess excellent hydrophilicity and self-adhesive properties.

[0046] Preferably, the hydrophilic colloidal microspheres have a particle size of 185-325 nm. The particle size of the hydrophilic colloidal microspheres will affect the filtration pore size of the formed functional layer, and the hydrophilic colloidal microspheres with the corresponding particle size can be selected according to the desired filtration pore size of the functional layer.

[0047] Furthermore, in one embodiment, the porous support layer is loaded with hydrophilic nanoparticles.

[0048] In this embodiment, hydrophilic nanoparticles can be "embedded" in the pores of the porous support layer using hydrophilic finishing technology, i.e., embedded between the fibrils of the porous support layer. This adjusts the filtration pore size of the support layer while increasing its hydrophilicity, thereby improving the membrane's wettability, pure water flux, and filtration accuracy. Furthermore, the synergistic effect of the highly hydrophilic PTFE-based support layer and the colloidal crystal array can further contribute to obtaining a "strong and high" ultrafiltration membrane.

[0049] Furthermore, in one embodiment, the hydrophilic nanoparticles are at least one of silica sol particles and titanium dioxide sol particles.

[0050] Preferably, the hydrophilic nanoparticles have a particle size of 15-20 nm, which helps to enhance hydrophilicity without causing the filter pore size of the support layer to be at an appropriate level. The amount of hydrophilic nanoparticles is determined based on the desired filter pore size and hydrophilicity of the support layer.

[0051] Furthermore, in one embodiment, the average pore size of the functional layer is 10-30% of the average pore size of the porous support layer; and / or, the thickness of the functional layer is 40-50% of the thickness of the porous support layer.

[0052] Furthermore, in one embodiment, the porous support layer is in the form of hollow fibers or a flat plate. Exemplarily, the hollow fiber shape can be obtained by uniaxial stretching, and the flat plate shape can be obtained by biaxial stretching.

[0053] When a hollow fiber support layer is used, the functional layer is attached to the outer surface of the support layer to form a hollow tubular ultrafiltration membrane. The ultrafiltration membrane can be used in the following ways: wastewater enters the tube and passes through the support layer and the functional layer in sequence under pressure for tiered filtration, and the purified wastewater flows out from the tube wall; or wastewater enters the tube through the outer wall and passes through the functional layer and the support layer in sequence under pressure, and the purified wastewater flows out from the tube.

[0054] In another aspect of this application, a method for preparing the ultrafiltration membrane as described above is provided, comprising the following steps:

[0055] A porous support layer is obtained by sequentially extruding, stretching and sintering heat setting of materials containing hot melt resin and polytetrafluoroethylene dispersion resin.

[0056] The outer surface of the porous support layer is brought into contact with hydrophilic colloidal microspheres, and after drying, an ultrafiltration membrane is obtained.

[0057] In this embodiment, extrusion involves pressing a material comprising a hot-melt resin and a polytetrafluoroethylene dispersion resin into a blank, and then extruding the blank to form a support layer, for example, in the form of a hollow tube. In this process, the material may also include lubricating oil commonly used in the art.

[0058] As an optional embodiment of this application, the billet is extruded at 200-280°C.

[0059] As an optional embodiment of this application, the extrusion speed is 150-300 cm / min. Typical but limiting extrusion speeds are 150 cm / min, 200 cm / min, 250 cm / min, 280 cm / min, or 300 cm / min.

[0060] In this embodiment, stretching is used for the generation and further growth of fibrils, ensuring that the support layer has a high porosity and small pore size with uniform pore size distribution.

[0061] As an optional embodiment of this application, the stretching temperature is 200-280°C, and the stretching ratio is 0.5-8 times. Typical but non-limiting stretching temperatures are 200°C, 210°C, 220°C, 230°C, 250°C, 260°C, or 280°C, and typical but non-limiting stretching ratios are 0.5 times, 1.0 times, 1.5 times, 2.0 times, 2.5 times, 3.0 times, 3.5 times, 4.0 times, 5.0 times, 6.0 times, 7.0 times, or 8.0 times.

[0062] In this embodiment, the sintering heat setting temperature is 320-360℃, and the sintering heat setting time is 10-40s. Typical but non-limiting sintering heat setting temperatures are 320℃, 325℃, 330℃, 340℃, 350℃, 355℃, or 360℃, and typical but non-limiting sintering heat setting times are 10s, 15s, 20s, 25s, 30s, or 40s.

[0063] In some embodiments, the process of contacting the outer surface of the porous support layer with hydrophilic colloidal microspheres and drying the ultrafiltration membrane specifically includes the following steps: dispersing the hydrophilic colloidal microspheres in a dispersant, centrifuging to remove the supernatant to obtain a slurry, scraping the slurry onto the outer surface of the support layer, and drying it at 50-70°C to form a functional layer with a hydrophilic colloidal crystal structure on the support layer.

[0064] In one embodiment, before contacting the outer surface of the porous support layer with the hydrophilic colloidal microspheres, the method further includes:

[0065] Hydrophilic nanoparticles are filled into the porous support layer and then dried to obtain a porous support layer loaded with hydrophilic nanoparticles.

[0066] In this embodiment, drying after filling with hydrophilic nanoparticles allows the hot-melt resin to melt. The molten hot-melt resin can "anchor" the hydrophilic nanoparticles to the fibrils of the porous support layer through a "riveting" effect, preventing the particles from falling off and thus ensuring the strong hydrophilicity of the support layer. The drying temperature and time are determined based on the melting temperature of the hot-melt resin.

[0067] The hydrophilic nanoparticles can be filled into the porous support layer by means such as vacuum suction.

[0068] In another aspect of this application, the application of the ultrafiltration membrane described above in water purification is also provided.

[0069] Specifically, it can be used as a water treatment membrane to remove turbidity, bacteria, and viruses from river water, seawater, alkaline water, sewage, and wastewater; a medical membrane for artificial kidneys and plasma separation; a food / beverage industry membrane for fruit juice concentration; a gas separation membrane for separating exhaust gases and carbon dioxide; an electronics industry membrane for fuel cell separators; and a textile industry membrane for textile scouring, dyeing, and softening. Among the aforementioned water treatment membranes, ultrafiltration is preferred, and oil-water separation is more preferred.

[0070] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0071] Example 1

[0072] Please see Figure 1 This embodiment provides a high-efficiency polytetrafluoroethylene ultrafiltration membrane, and the preparation steps are as follows:

[0073] (1) Preparation of porous support layer: Polytetrafluoroethylene hollow fiber membrane was prepared by uniaxial stretching using a polymer alloy composed of a binary copolymer (FEP) formed by tetrafluoroethylene (TPE) and hexafluoropropylene (HFP) and conventional refractory polytetrafluoroethylene dispersion resin (the content of FEP is 20 wt% of the polytetrafluoroethylene dispersion resin) as raw materials. The process of obtaining hollow fiber membrane by uniaxial stretching is as follows: after pressing the above raw materials into a blank, the blank is extruded at 200°C at an extrusion speed of 150 cm / min to form a hollow tubular support layer; then it is stretched at 200°C with a stretch ratio of 2, and then sintered at 360°C for 10 s to obtain the polytetrafluoroethylene hollow fiber membrane.

[0074] Using this hollow fiber membrane as the base membrane, hydrophilic silica sol particles with a particle size of 15 nm are loaded onto the base membrane under a vacuum environment of -0.1 MPa. The base membrane loaded with nanoparticles is then dried at 260°C for 15 minutes to obtain a hydrophilic polytetrafluoroethylene fiber membrane.

[0075] (2) Preparation of functional layer: The silica@polydopamine (silica as the core layer and polydopamine as the shell layer) microsphere emulsion with excellent monodispersity, solid content of 10% and particle size of 250nm was placed in a centrifuge at 5000r / min and centrifuged for 30min. After centrifugation, the supernatant was discarded and the lower slurry was scraped onto the hydrophilic polytetrafluoroethylene fiber membrane prepared in step (1). After drying at 70℃, it can be deposited on the hydrophilic polytetrafluoroethylene fiber membrane to form a hydrophilic colloidal crystal structure.

[0076] Characterization revealed that the obtained ultrafiltration membrane had an average pore size of 55 nm. When applied to the treatment of oil-in-water emulsions, it achieved an oil droplet interception rate of 96%; after five cycles of repeated use, the interception rate remained above 90%, indicating its excellent antifouling properties.

[0077] Example 2

[0078] This embodiment provides a high-efficiency polytetrafluoroethylene ultrafiltration membrane, and the preparation steps are as follows:

[0079] (1) Preparation of porous support layer: Polytetrafluoroethylene (TPE), vinylidene fluoride (VDF) and hexafluoropropylene (HFP) terpolymer and conventional refractory polytetrafluoroethylene dispersion resin (the content of terpolymer is 25 wt% of polytetrafluoroethylene dispersion resin) were used as raw materials, and then polytetrafluoroethylene flat fiber membrane was prepared by biaxial stretching method. The stretching parameters were the same as in Example 1.

[0080] Using this fiber membrane as the base membrane, hydrophilic titanium dioxide sol particles with a particle size of 20 nm were loaded onto the base membrane under a vacuum environment of -0.1 MPa. The base membrane loaded with nanoparticles was then dried at 270 °C for 10 min to obtain a hydrophilic polytetrafluoroethylene fiber membrane.

[0081] (2) Preparation of functional layer: The silica@polydopamine (silica as the core layer and polydopamine as the shell layer) microsphere emulsion with excellent monodispersity, solid content of 10% and particle size of 185nm was placed in a centrifuge at 7000r / min and centrifuged for 30min. After centrifugation, the supernatant was discarded and the lower slurry was scraped onto the hydrophilic polytetrafluoroethylene fiber membrane prepared in (1). After drying at 70℃, it can be deposited on the hydrophilic polytetrafluoroethylene fiber membrane to form a hydrophilic colloidal crystal structure.

[0082] Characterization revealed that the obtained ultrafiltration membrane had an average pore size of 20 nm. When applied to the treatment of oil-in-water emulsions, it achieved an oil droplet interception rate of 97%; after five cycles of repeated use, the interception rate remained above 90%, indicating its excellent antifouling properties.

[0083] Example 3

[0084] This embodiment provides a high-efficiency polytetrafluoroethylene ultrafiltration membrane, and the preparation steps are as follows:

[0085] (1) Preparation of porous support layer: Polytetrafluoroethylene (TPE), vinylidene fluoride (VDF) and hexafluoropropylene (HFP) terpolymer and conventional refractory polytetrafluoroethylene dispersion resin (the content of terpolymer is 20 wt% of polytetrafluoroethylene dispersion resin) were used as raw materials, and then polytetrafluoroethylene flat fiber membrane was prepared by biaxial stretching method. The stretching parameters were the same as in Example 1.

[0086] Using this fiber membrane as the base membrane, hydrophilic silica sol particles with a particle size of 18 nm are loaded onto the base membrane under a vacuum environment of -0.1 MPa. The base membrane loaded with nanoparticles is then dried at 270°C and removed after 10 min to obtain a hydrophilic polytetrafluoroethylene fiber membrane.

[0087] (2) Preparation of functional layer: The silica@polydopamine (silica as the core layer and polydopamine as the shell layer) microsphere emulsion with excellent monodispersity, solid content of 10% and particle size of 325nm was placed in a centrifuge at 4000r / min and centrifuged for 30min. After centrifugation, the supernatant was discarded and the lower slurry was scraped onto the hydrophilic polytetrafluoroethylene fiber membrane prepared in (1). After drying at 70℃, it can be deposited on the hydrophilic polytetrafluoroethylene fiber membrane to form a hydrophilic colloidal crystal structure.

[0088] Characterization revealed that the obtained ultrafiltration membrane had an average pore size of 80 nm. When applied to the treatment of oil-in-water emulsions, it achieved an oil droplet interception rate of 95%; after five cycles of repeated use, the interception rate remained above 90%, indicating its excellent antifouling properties.

[0089] Example 4

[0090] This embodiment provides a high-efficiency polytetrafluoroethylene ultrafiltration membrane, and the preparation steps are as follows:

[0091] (1) Preparation of porous support layer: A polymer alloy composed of a binary copolymer (FEP) formed by tetrafluoroethylene (TPE) and hexafluoropropylene (HFP), a terpolymer formed by tetrafluoroethylene (TPE), vinylidene fluoride (VDF) and hexafluoropropylene (HFP), and conventional refractory polytetrafluoroethylene dispersion resin (the content of the terpolymer is 23 wt% of the polytetrafluoroethylene dispersion resin) was prepared by biaxial stretching method to obtain polytetrafluoroethylene flat fiber membrane, with the same stretching parameters as in Example 1;

[0092] Using this fiber membrane as the base membrane, hydrophilic silica sol particles with a particle size of 15 nm are loaded onto the base membrane under a vacuum environment of -0.1 MPa. The base membrane loaded with nanoparticles is then dried at 270°C for 15 minutes to obtain a hydrophilic polytetrafluoroethylene fiber membrane.

[0093] (2) Preparation of functional layer: The silica@polydopamine (silica as the core layer and polydopamine as the shell layer) microsphere emulsion with excellent monodispersity, solid content of 10% and particle size of 230nm was placed in a centrifuge at 5000r / min and centrifuged for 30min. After centrifugation, the supernatant was discarded and the lower slurry was scraped onto the hydrophilic polytetrafluoroethylene fiber membrane prepared in (1). After drying at 70℃, it can be deposited on the hydrophilic polytetrafluoroethylene fiber membrane to form a hydrophilic colloidal crystal structure.

[0094] Characterization revealed that the obtained ultrafiltration membrane had an average pore size of 45 nm. When applied to the treatment of oil-in-water emulsions, it achieved an oil droplet interception rate of 96%; after five cycles of repeated use, the interception rate remained above 90%, indicating its excellent antifouling properties.

[0095] Example 5

[0096] This embodiment provides a high-efficiency polytetrafluoroethylene ultrafiltration membrane, and the preparation steps are as follows:

[0097] (1) Preparation of porous support layer: Polytetrafluoroethylene hollow fiber membrane was prepared by uniaxial stretching method using a polymer alloy composed of a binary copolymer (FEP) formed by tetrafluoroethylene (TPE) and hexafluoropropylene (HFP) and conventional refractory polytetrafluoroethylene dispersion resin (the content of the terpolymer is 21 wt% of the polytetrafluoroethylene dispersion resin) as raw material. The stretching parameters are the same as in Example 1.

[0098] Using this fiber membrane as the base membrane, hydrophilic silica sol particles with a particle size of 15 nm and hydrophilic titanium dioxide sol particles with a particle size of 20 nm are loaded onto the base membrane under a vacuum environment of -0.1 MPa. The base membrane loaded with nanoparticles is then dried at 260°C for 15 min to obtain a hydrophilic polytetrafluoroethylene fiber membrane.

[0099] (2) Preparation of functional layer: The silica@polydopamine (silica as the core layer and polydopamine as the shell layer) microsphere emulsion with excellent monodispersity, solid content of 10% and particle size of 280nm was placed in a centrifuge at 5000r / min and centrifuged for 30min. After centrifugation, the emulsion was removed, the supernatant was discarded, and the lower slurry was scraped onto the hydrophilic polytetrafluoroethylene fiber membrane prepared in (1). After drying at 70℃, the hydrophilic colloidal crystal structure was formed on the hydrophilic polytetrafluoroethylene fiber membrane.

[0100] Characterization revealed that the obtained ultrafiltration membrane had an average pore size of 70 nm. When applied to the treatment of oil-in-water emulsions, it achieved an oil droplet interception rate of 97%. After five cycles of repeated use, the interception rate remained above 90%, indicating its excellent antifouling properties.

[0101] Example 6

[0102] This embodiment provides a high-efficiency polytetrafluoroethylene ultrafiltration membrane, and the preparation steps are as follows:

[0103] (1) Preparation of porous support layer: Polytetrafluoroethylene hollow fiber membrane was prepared by uniaxial stretching method using a polymer alloy composed of a binary copolymer (FEP) formed by tetrafluoroethylene (TPE) and hexafluoropropylene (HFP) and conventional refractory polytetrafluoroethylene dispersion resin (the content of FEP is 20wt% of polytetrafluoroethylene dispersion resin) as raw material, and the stretching parameters were the same as in Example 1.

[0104] (2) Preparation of functional layer: The silica@polydopamine (silica as the core layer and polydopamine as the shell layer) microsphere emulsion with excellent monodispersity, solid content of 10% and particle size of 260nm was placed in a centrifuge at 5000r / min and centrifuged for 30min. After centrifugation, the supernatant was discarded and the lower slurry was scraped onto the hydrophilic polytetrafluoroethylene fiber membrane prepared in (1). After drying at 70℃, it can be deposited on the hydrophilic polytetrafluoroethylene fiber membrane to form a hydrophilic colloidal crystal structure.

[0105] Characterization revealed that the obtained ultrafiltration membrane had an average pore size of 65 nm. When applied to the treatment of oil-in-water emulsions, it achieved an oil droplet interception rate of 90%; after five cycles of repeated use, the interception rate remained above 88%, indicating its excellent antifouling properties.

[0106] Comparative Example 1

[0107] This comparative example provides a high-efficiency polytetrafluoroethylene ultrafiltration membrane, and the preparation steps are as follows:

[0108] Polytetrafluoroethylene hollow fiber membranes were prepared by a uniaxial stretching method using a polymer alloy composed of a copolymer (FEP) formed by tetrafluoroethylene (TPE) and hexafluoropropylene (HFP) and a conventional refractory polytetrafluoroethylene dispersion resin (the content of FEP is 23 wt% of the polytetrafluoroethylene dispersion resin) as raw materials. The stretching parameters were the same as in Example 1.

[0109] Characterization showed that the obtained ultrafiltration membrane had an average pore size of 70 nm. When applied to the treatment of oil-in-water emulsions, it achieved an oil droplet rejection rate of 58%. After five cycles of repeated use, the rejection rate dropped to below 38%, indicating poor retention rate and antifouling properties.

[0110] As can be seen from the above experiments, the method of the present invention can prepare a polytetrafluoroethylene ultrafiltration membrane with high filtration efficiency, which can be used to achieve oil-water separation.

[0111] The above description is merely a preferred embodiment of this application and an explanation of the technical principles employed. Those skilled in the art should understand that the scope of disclosure in this application is not limited to technical solutions formed by specific combinations of the above-described technical features, but should also cover other technical solutions formed by arbitrary combinations of the above-described technical features or their equivalents without departing from the foregoing disclosed concept. For example, technical solutions formed by substituting the above features with (but not limited to) technical features with similar functions disclosed in this application.

Claims

1. An ultrafiltration membrane, characterized in that, include: A porous support layer and a functional layer located on the outer surface of the porous support layer; The porous support layer comprises a hot-melt resin and a polytetrafluoroethylene dispersion resin. The hot-melt resin is selected from at least one of tetrafluoroethylene-hexafluoropropylene binary copolymer and tetrafluoroethylene-vinylidene fluoride-hexafluoropropylene terpolymer. The porous support layer is a structure in which the hydrophilic nanoparticles are loaded into the pores by filling the pores with hydrophilic nanoparticles and then drying the hot-melt resin to melt it. The functional layer comprises a hydrophilic colloidal crystal structure formed by hydrophilic colloidal microspheres arranged in a lattice on the outer surface of the porous support layer. The hydrophilic colloidal microspheres have a hard core and soft shell structure, and the soft shell has self-adhesive properties. The hydrophilic colloidal microspheres are selected from silica@polydopamine microspheres with silica as the core and polydopamine as the shell.

2. The ultrafiltration membrane according to claim 1, characterized in that, The hydrophilic colloidal microspheres have a particle size of 185-325 nm.

3. The ultrafiltration membrane according to claim 1, characterized in that, The hydrophilic nanoparticles are at least one of silica sol particles and titanium dioxide sol particles.

4. The ultrafiltration membrane according to claim 1, characterized in that, The hydrophilic nanoparticles have a particle size of 15-20 nm.

5. The ultrafiltration membrane according to claim 1, characterized in that, The average pore size of the functional layer is 10-30% of the average pore size of the porous support layer; And / or, the thickness of the functional layer is 40-50% of the thickness of the porous support layer.

6. The ultrafiltration membrane according to any one of claims 1-5, characterized in that, The porous support layer is in the form of hollow fibers or flat plates.

7. A method for preparing an ultrafiltration membrane as described in any one of claims 1-6, characterized in that, Includes the following steps: A porous support layer is obtained by sequentially extruding, stretching and sintering heat setting of materials containing hot melt resin and polytetrafluoroethylene dispersion resin. Hydrophilic nanoparticles are filled into the pores of the porous support layer and then dried to obtain a porous support layer in which the hydrophilic nanoparticles are loaded in the pores. The outer surface of the porous support layer is brought into contact with hydrophilic colloidal microspheres, and after drying, an ultrafiltration membrane is obtained.

8. The application of the ultrafiltration membrane as described in any one of claims 1-6 in water purification.

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