A hydrophilic polyethylene ultrafiltration membrane with a small pore size and its preparation method

Abstract

The present invention discloses a hydrophilic polyethylene ultrafiltration membrane with a small pore diameter and a preparation method thereof, relating to the technical field of ultrafiltration membrane separation. The polyethylene-based membrane is treated by plasma in an oxygen atmosphere, so that the surface of the polyethylene-based membrane contains hydroxyl and / or carboxyl active groups; a hydrophilic polyelectrolyte is dissolved in deionized water under stirring conditions to obtain a polyelectrolyte solution; the polyelectrolyte solution is coated on the polyethylene-based membrane treated by plasma and dried to obtain the polyethylene ultrafiltration membrane. The present invention can increase the hydrophilicity of the polyethylene membrane, reduce the membrane pore diameter, and reduce the material and process costs of the ultrafiltration membrane separation technology.

Description

Technical Field

[0001] The present invention relates to the technical field of ultrafiltration membrane separation, and specifically to a small-aperture hydrophilic polyethylene ultrafiltration membrane and a preparation method thereof Background Technique

[0002] Ultrafiltration membrane separation technology has the advantages of low energy consumption, high efficiency, no secondary pollution, and small equipment floor area, and is widely used in separation and purification processes such as urban sewage treatment, seawater desalination pretreatment, and fruit juice concentration. Polymer membranes are the core of ultrafiltration membrane separation technology, with a pore size range of 2 to 100 nm, and can retain macromolecular organic substances with a molecular weight of 1 to 100 kDa. Polymer ultrafiltration membranes are often prepared into membranes from materials such as polyethersulfone, polysulfone, and polyvinylidene fluoride through non-solvent induced phase separation or thermally induced phase separation methods. However, the above several materials generally have a high cost, and the use of toxic solvents and diluents in the processing process results in a high process cost, further restricting the widespread application of ultrafiltration membrane separation technology

[0003] Polyethylene is a low-cost polymer material that can be processed into a porous membrane with a highly interconnected pore structure through a thermally induced phase separation method using non-toxic white oil as a diluent, and has broad development potential in the technical field of ultrafiltration membrane separation. However, the polyethylene material itself is relatively hydrophobic, and there are problems of low flux and easy contamination when directly used in the water treatment field. Secondly, due to process limitations, the prepared polyethylene porous membranes generally have a pore size greater than 100 nm and are not suitable for the ultrafiltration separation field. Adding a hydrophilic layer through processes such as coating is an effective method to improve the hydrophilicity of polyethylene porous membranes and reduce the pore size

[0004] Patent CN112044281A discloses a hydrophilic polyethylene microporous membrane and its preparation method. The polyethylene membrane is wetted with a wetting agent and then coated with a hydrophilic substance and a crosslinking agent on the membrane. Finally, a hydrophilic polyethylene microporous membrane is obtained through a heat treatment and a cleaning step. However, the wetting agent used is a toxic organic solvent. Patent CN112295405A discloses a high-flux and highly anti-pollution polyethylene ultrafiltration membrane. By using an electric field to array carbon nanotubes, an arrayed carbon nanotube / polyethylene ultrafiltration membrane is prepared, and a hydrophilic reagent is coated on the surface of the base membrane to make it have hydrophilic properties. The bovine serum albumin rejection rate of the polyethylene ultrafiltration membrane prepared by this patent can be increased to more than 97.0%. However, the hydrophilic reagent still needs to be dissolved in a toxic organic solvent (such as N,N-dimethylacetamide). Patent CN111672334A discloses a dual-hydrophilic polyethylene ultrafiltration membrane and its preparation method. By using the combination of amine and hydroxyl groups in polysaccharide polymers, a chitosan (or its derivative) / nano-silica polyethylene ultrafiltration membrane is prepared based on the thermally induced phase separation method using an organic-inorganic sol-gel, significantly increasing the bovine serum albumin rejection rate to more than 97.0%. However, this method still needs to use the toxic solvent tetrahydrofuran. Patent CN109126483A uses plasma to treat the polyethylene membrane, then coats it with a PVA solution, and finally performs thermal crosslinking to improve the hydrophilicity and water flux of the polyethylene membrane. However, the thermal crosslinking step is relatively complex and is not conducive to industrial application. Summary of the Invention

[0005] The object of the present invention is to provide a small-aperture hydrophilic polyethylene ultrafiltration membrane and its preparation method. By performing plasma treatment and coating with an aqueous polyelectrolyte solution on a polyethylene base membrane, the hydrophilicity of the polyethylene membrane is increased, the membrane aperture is reduced, and the material and process costs of the ultrafiltration membrane separation technology are reduced.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] A preparation method of a small-aperture hydrophilic polyethylene ultrafiltration membrane, comprising the following steps:

[0008] Treat the polyethylene base membrane with plasma in an oxygen atmosphere to make the surface of the polyethylene base membrane contain hydroxyl and / or carboxyl active groups;

[0009] Dissolve a hydrophilic polyelectrolyte in deionized water under stirring conditions to obtain a polyelectrolyte solution;

[0010] Coat the polyelectrolyte solution on the polyethylene base membrane that has been treated with plasma, and dry it to obtain a polyethylene ultrafiltration membrane.

[0011] Further, the conditions of the plasma treatment include: an excitation frequency of 13.56 MHz, a radio frequency power of 10-70 W, and a treatment time of 10-60 seconds.

[0012] Furthermore, the polyvinyl film is a commercial polyethylene separator for lithium-ion batteries with a thickness of 5-25 μm and a porosity of 30%-60%.

[0013] Furthermore, the polyelectrolyte is selected from one or more of poly(diallyldimethylammonium chloride) (PDDA), polyethyleneimine (PEI), and polyacrylamine (PAH).

[0014] Furthermore, the polyelectrolyte is dissolved in deionized water under stirring conditions of 25-60 °C and 50-800 rpm.

[0015] Furthermore, the concentration of the polyelectrolyte solution is 1-25 wt%.

[0016] Furthermore, the coating process used is one of dip coating, wire bar coating, or microgravure coating.

[0017] Furthermore, the drying conditions are: temperature 40-60 °C, duration 6-12 h.

[0018] A small-aperture hydrophilic polyethylene ultrafiltration membrane is prepared by the above preparation method.

[0019] The beneficial effects of the present invention are as follows:

[0020] The polyvinyl film is treated with plasma to make its surface rich in active groups such as hydroxyl and carboxyl groups, and then a cationic polyelectrolyte is further coated. By using the stable non-covalent bond binding between the polyelectrolyte and the active groups on the surface of the polyolefin film, the hydrophilic polyelectrolyte is loaded on the hydrophobic polyethylene film to improve its hydrophilicity. By using different coating processes, the pore size of the polyethylene film is optimized and reduced, realizing the preparation of a small-aperture hydrophilic polyethylene ultrafiltration membrane without solvent and in a green way. The method of the present invention is simple, the conditions are mild, the cost is low, and the controllability is strong, which is beneficial to reducing the application cost of the existing ultrafiltration membrane separation technology. Specific Embodiments

[0021] To make the above features and advantages of the present invention more obvious and understandable, the following specific embodiments are given for detailed description.

[0022] For all raw materials of the present invention, there is no special limitation on their sources, and they can be purchased on the market or prepared by conventional methods well-known to those skilled in the art.

[0023] For all raw materials of the present invention, there is no special limitation on their purity. The present invention preferably uses analytical pure or the purity commonly used in the field of separation membrane materials.

[0024] Example 1

[0025] A polyethylene diaphragm with a thickness of 5 μm and a porosity of 30% was treated with oxygen plasma at a radio frequency power of 10 W for 60 seconds to obtain a functionalized polyethylene film. A 1 wt% PDDA solution was prepared at 60 °C and 50 rpm. The PDDA solution was dip-coated onto the polyethylene film and dried at 40 °C for 12 h to obtain a small-pore hydrophilic polyethylene ultrafiltration membrane.

[0026] Example 2

[0027] A polyethylene diaphragm with a thickness of 9 μm and a porosity of 40% was treated with oxygen plasma at a radio frequency power of 50 W for 30 seconds to obtain a functionalized polyethylene film. A 12.5 wt% PDDA solution was prepared at 40 °C and 400 rpm. The PDDA solution was dip-coated onto the polyethylene film and dried at 50 °C for 8 h to obtain a small-pore hydrophilic polyethylene ultrafiltration membrane.

[0028] Example 3

[0029] A polyethylene diaphragm with a thickness of 25 μm and a porosity of 60% was treated with oxygen plasma at a radio frequency power of 70 W for 10 seconds to obtain a functionalized polyethylene film. A 25 wt% PDDA solution was prepared at 25 °C and 800 rpm. The PDDA solution was dip-coated onto the polyethylene film and dried at 60 °C for 6 h to obtain a small-pore hydrophilic polyethylene ultrafiltration membrane.

[0030] Example 4

[0031] A polyethylene diaphragm with a thickness of 9 μm and a porosity of 40% was treated with oxygen plasma at a radio frequency power of 50 W for 30 seconds to obtain a functionalized polyethylene film. A 12.5 wt% PEI solution was prepared at 40 °C and 400 rpm. The PDDA solution was coated onto the polyethylene film by a wire bar and dried at 50 °C for 8 h to obtain a small-pore hydrophilic polyethylene ultrafiltration membrane.

[0032] Example 5

[0033] A polyethylene diaphragm with a thickness of 9 μm and a porosity of 40% was treated with oxygen plasma at a radio frequency power of 50 W for 30 seconds to obtain a functionalized polyethylene film. A 12.5 wt% PAH solution was prepared at 40 °C and 400 rpm. The PDDA solution was coated onto the polyethylene film by microgravure and dried at 50 °C for 8 h to obtain a small-pore hydrophilic polyethylene ultrafiltration membrane.

[0034] Comparative Example 1

[0035] A polyethylene diaphragm with a thickness of 9 μm and a porosity of 40% was treated with oxygen plasma at a radio frequency power of 50 W for 30 seconds to obtain a functionalized polyethylene film.

[0036] Product testing:

[0037] The pure water flux of the membrane was tested at a pressure of 0.1 MPa using a cross-flow membrane performance evaluation device. A phosphate buffer solution (PBS) containing 1.0 g / L bovine serum albumin (BSA) was used as the feed solution to test the BSA rejection of the membrane to evaluate the change in membrane pore size. The concentration of the BSA solution was detected by an ultraviolet-visible spectrophotometer. The calculation formula for the membrane flux (J) is: J = V / (A·t), where V is the volume of the permeate (L), A is the effective membrane area (m 2 ), and t is the test time (h). The calculation formula for the membrane rejection rate (R) is: R = (1 - C p / C f ) * 100%, where C f is the BSA concentration of the feed solution, and C p is the BSA concentration of the permeate. The static water contact angle of the membrane surface was tested using a contact angle analyzer, and the test results are shown in Table 1.

[0038] Table 1 Performance test data of polyethylene membranes

[0039]

[0040] The test results in Table 1 show that under certain test conditions, the pure water flux of the polyethylene ultrafiltration membrane prepared by the present invention is 600 - 1200 L / (m 2 ·MPa), the BSA rejection rate is 90% - 99%, the water contact angle is 37° - 45°, and it remains stable after long-term placement.

[0041] Although the present invention has been disclosed as above with examples, it is not intended to limit the present invention. Any appropriate modification or equivalent replacement of the technical solutions of the present invention by those of ordinary skill in the art shall be covered by the protection scope of the present invention, and the protection scope of the present invention shall be defined by the claims.

Claims

1. A preparation method of a hydrophilic polyethylene ultrafiltration membrane with a small pore size, characterized in that, The method includes the following steps: Treat a polyethylene film in an oxygen atmosphere using plasma so that the surface of the polyethylene film contains hydroxyl and / or carboxyl active groups. The polyethylene film is a commercial polyethylene separator for lithium-ion batteries with a thickness of 5 - 25 μm and a porosity of 30% - 60%. Dissolve a hydrophilic polyelectrolyte in deionized water under stirring conditions to obtain a polyelectrolyte solution with a concentration of 12.5 - 25 wt%. The polyelectrolyte is selected from one or more of poly(diallyldimethylammonium chloride), polyethyleneimine, and polyacrylamine. Coat the polyelectrolyte solution on the polyethylene film treated with plasma, and then dry it to obtain a polyethylene ultrafiltration membrane.

2. The preparation method according to claim 1, wherein The conditions of the plasma treatment include: an excitation frequency of 13.56 MHz, a radio frequency power of 10 - 70 W, and a treatment time of 10 - 60 seconds.

3. The preparation method according to claim 1, characterized in that, The polyelectrolyte is dissolved in deionized water under stirring conditions at 25 - 60 °C and 50 - 800 rpm.

4. The preparation method according to claim 1, characterized in that, The coating process used is one of dip coating, wire bar coating, or microgravure coating.

5. The preparation method according to claim 1, characterized in that, The drying conditions are: a temperature of 40 - 60 °C and a duration of 6 - 12 h.

6. A hydrophilic polyethylene ultrafiltration membrane with a small pore size, characterized in that, It is prepared by the preparation method according to any one of claims 1 - 5.

Images