Hydrophilic modified polyolefin base material for reverse osmosis membrane, preparation method of hydrophilic modified polyolefin base material and reverse osmosis membrane

Abstract

The invention discloses a hydrophilic modified polyolefin base material for a reverse osmosis membrane, a preparation method of the hydrophilic modified polyolefin base material and the reverse osmosis membrane. The first hydrophilic coating is arranged on one side of the polyolefin base material; the second hydrophilic coating is arranged on the other side of the polyolefin base material; the contact angle of the first hydrophilic coating is theta A, the contact angle of the second hydrophilic coating is theta B, and theta A is smaller than theta B; the theta A ranges from 50 degrees to 80 degrees, and the theta B ranges from 70 degrees to 90 degrees; the first hydrophilic coating and the second hydrophilic coating are formed by thermal crosslinking curing. The hydrophilic coating on the hydrophilic modified polyolefin base material has strong adhesive force and is not easy to fall off, and when the hydrophilic coating is used as the support body of the reverse osmosis membrane, the reverse osmosis membrane can have high water flux and desalination rate at the same time.

Description

Hydrophilic modified polyolefin substrate for reverse osmosis membrane and its preparation method, reverse osmosis membrane Technical Field

[0001] This invention relates to the field of reverse osmosis membrane technology, specifically to a hydrophilic modified polyolefin substrate for reverse osmosis membranes, its preparation method, and a reverse osmosis membrane. Background Technology

[0002] Polyethylene microporous membranes are widely used in lithium-ion batteries due to their relatively low cost, excellent mechanical strength, thermal stability, and chemical inertness. The relatively uniform and interconnected pore structure of polyethylene microporous membranes facilitates the formation of a uniform and highly cross-linked polyamide separation layer, which can further improve the performance of reverse osmosis membranes. If polyethylene microporous membranes replace nonwoven fabrics and polysulfones as the support for reverse osmosis membranes, production costs can be significantly reduced. Furthermore, the thinner polyethylene microporous membranes can increase the membrane area per unit volume, thereby improving the packing density of membrane elements.

[0003] Polyethylene microporous membranes have a strong hydrophobic surface. If used directly as a support, phase separation will occur between the hydrophilic m-phenylenediamine monomer and the hydrophobic membrane surface during interfacial polymerization, forming an uneven polyamide layer and reducing the performance of the reverse osmosis membrane. Therefore, hydrophilic modification of polyethylene microporous membranes is a necessary step before the preparation of polyethylene-based reverse osmosis membranes.

[0004] Methods for hydrophilic modification of polyethylene microporous membranes include blending polyethylene with hydrophilic substances, surface treatment (plasma / corona treatment), and surface coating with hydrophilic substances. While blending improves hydrophilicity, it leads to a decrease in the membrane's mechanical properties. Plasma or corona treatment of polyethylene microporous membranes has a limited lifespan for hydrophilic modification, and the substrate surface structure is easily damaged, resulting in closed pores or holes. Directly coating the surface of polyethylene microporous membranes with hydrophilic substances results in poor adhesion between the hydrophilic layer and the base membrane, making it prone to detachment and affecting the long-term performance of the reverse osmosis membrane separation layer. Therefore, there is a need to develop a new hydrophilic-modified polyolefin substrate to improve the performance of reverse osmosis membranes. Summary of the Invention

[0005] This invention aims to at least partially solve one of the technical problems in the related art. Therefore, one object of this invention is to provide a hydrophilic modified polyolefin substrate for reverse osmosis membranes, wherein the hydrophilic coating on the hydrophilic modified polyolefin substrate has strong adhesion and is not easily detached. When used as a support for a reverse osmosis membrane, it enables the reverse osmosis membrane to achieve both high water flux and desalination rate.

[0006] Specifically, a first aspect of the present invention provides a hydrophilic modified polyolefin substrate for reverse osmosis membranes, comprising: a polyolefin substrate; a first hydrophilic coating disposed on one side of the polyolefin substrate; and a second hydrophilic coating disposed on the other side of the polyolefin substrate; wherein the contact angle of the first hydrophilic coating is θ.A The contact angle of the second hydrophilic coating is θ B , and θ A <θ B ;θ A θ is 50°-80°. B 70°-90°;

[0007] Both the first and second hydrophilic coatings are formed by thermal crosslinking and curing.

[0008] This invention forms a hydrophilic coating on both sides of a substrate through thermal crosslinking and curing. The epoxy and amino groups in the hydrophilic coating undergo a thermal crosslinking reaction to generate hydrophilic groups, increasing the hydrophilicity of the substrate. The coating also exhibits good adhesion and is not easily peeled off, achieving durable hydrophilic modification of the polyolefin substrate. This facilitates the uniform formation of the polyamide layer and improves the performance of the reverse osmosis membrane. Furthermore, this invention controls the different hydrophilicities on the two sides of the hydrophilic-modified polyolefin substrate, while simultaneously controlling the contact angles of the hydrophilic coatings on both sides within a specific range. This reduces the amount of hydrophilic monomers used to synthesize polyamide in the substrate pores during reverse osmosis membrane preparation, minimizing interfacial polymerization reactions within the pores and preventing pore blockage. When the polyolefin substrate of this invention is used as a support for a reverse osmosis membrane, it enables the membrane to achieve both high water flux and high desalination rate. It is important to note that the contact angles of the hydrophilic coatings on both sides of the substrate should not be too small, i.e., the hydrophilicity on both sides should not be too high. Otherwise, during reverse osmosis membrane preparation, a large amount of hydrophilic monomers used to synthesize polyamide will remain in the substrate pores and undergo interfacial polymerization reactions, clogging the pores. The contact angle of the hydrophilic coating on both sides of the substrate should not be too large, that is, the hydrophilicity on both sides should not be too low. Otherwise, the hydrophilic monomers used to synthesize polyamide during the reverse osmosis membrane preparation process will be difficult to spread on the substrate surface, resulting in uneven polyamide layer and reduced performance of reverse osmosis membrane.

[0009] According to some embodiments of the present invention, the first hydrophilic coating is formed by thermal crosslinking and curing of a first substance containing epoxy groups and a second substance containing amino groups; the second hydrophilic coating is formed by thermal crosslinking and curing of a third substance containing epoxy groups and a fourth substance containing amino groups.

[0010] According to some embodiments of the present invention, the first substance containing epoxy groups and the third substance containing epoxy groups respectively include one or more of ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, butylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol triglycidyl ether, and trimethylolpropane triglycidyl ether; the second substance containing amino groups and the fourth substance containing amino groups respectively include one or more of aminosulfonic acid, ethanolamine, polyetheramine, and polyethyleneimine.

[0011] According to some embodiments of the present invention, the mass ratio of the first substance containing an epoxy group to the second substance containing an amino group is 1:(0.5-3); the mass ratio of the third substance containing an epoxy group to the fourth substance containing an amino group is 1:(2-5).

[0012] According to some embodiments of the present invention, the areal densities of the first hydrophilic coating and the second hydrophilic coating are both 0.5 g / m³. 2 -2g / m 2 .

[0013] According to some embodiments of the present invention, the thickness of the polyolefin substrate is 9μm-50μm and the porosity is 40%-70%.

[0014] According to some embodiments of the present invention, the polyolefin substrate includes any one of PE substrate and PP substrate.

[0015] The second aspect of this invention provides a method for preparing a hydrophilic modified polyolefin substrate for reverse osmosis membranes according to the first aspect of this invention, comprising the following steps: mixing a first substance containing epoxy groups, a second substance containing amino groups, and a solvent to obtain a first coating liquid; wherein the mass ratio of the first substance containing epoxy groups to the second substance containing amino groups is 1:(0.5-3); mixing a third substance containing epoxy groups, a fourth substance containing amino groups, and a solvent to obtain a second coating liquid; wherein the mass ratio of the third substance containing epoxy groups to the fourth substance containing amino groups is 1:(2-5), and the mass ratio of the third substance to the fourth substance is less than the mass ratio of the first substance to the second substance; coating one side of the polyolefin substrate with the first coating liquid and drying it; coating the other side of the polyolefin substrate with the second coating liquid, drying it, and then performing thermal crosslinking and curing to obtain the hydrophilic modified polyolefin substrate for reverse osmosis membranes.

[0016] The preparation method of this invention is simple to operate, has a short process, and is highly repeatable, making it suitable for large-scale industrial application. The hydrophilic modified polyolefin substrate prepared by the method of this invention has good hydrophilicity and high coating adhesion, making it difficult to peel off; when used as a support for reverse osmosis membranes, it can significantly improve the water flux and desalination rate of the reverse osmosis membrane.

[0017] According to some embodiments of the present invention, the solvent includes a mixture of ethanol and water; the drying temperature is 60°C-80°C; the thermal crosslinking curing temperature is 60°C-80°C; and the thermal crosslinking curing time is 6h-20h.

[0018] A third aspect of the present invention provides a reverse osmosis membrane, comprising a hydrophilic modified polyolefin substrate for reverse osmosis membranes according to the first aspect of the present invention or a hydrophilic modified polyolefin substrate for reverse osmosis membranes obtained by the preparation method of the second aspect of the present invention.

[0019] Because of the use of the above-mentioned hydrophilic modified polyolefin substrate, the reverse osmosis membrane of the present invention has better water flux and desalination rate, and its performance is significantly improved.

[0020] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0021] Figure 1 is a scanning electron microscope (SEM) image of the hydrophilic modified PE substrate prepared in Example 3.

[0022] Figure 2 shows the contact angle images of the hydrophilic modified PE substrate prepared in Example 3. a: Contact angle image of surface A; b: Contact angle image of surface B.

[0023] Figure 3 is a SEM image of the PE substrate in Comparative Example 1.

[0024] Figure 4 shows the contact angle image of the PE substrate in Comparative Example 1.

[0025] Figure 5 is a SEM image of the reverse osmosis membrane prepared using the hydrophilic modified PE substrate of Example 3.

[0026] Figure 6 is a SEM image of the reverse osmosis membrane prepared using the PE substrate of Comparative Example 1. Detailed Implementation

[0027] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0028] In the description of this invention, unless otherwise stated, "a plurality of" means two or more. "Multiple" means two or more. Throughout this document, the terms "comprising" or "including" are open-ended expressions, meaning they include the contents specified in this invention but do not exclude other aspects.

[0029] 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.

[0030] The terms "first," "second," "third," and "fourth" used in this document are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first," "second," "third," or "fourth" may explicitly or implicitly include one or more of that feature.

[0031] Hydrophilic modification technology for polyethylene microporous membranes includes membrane preparation by blending polyethylene with hydrophilic substances, surface treatment (plasma / corona treatment), and surface coating with hydrophilic substances. While blending improves hydrophilicity, it leads to a decrease in the membrane's mechanical properties. Plasma or corona treatment of polyethylene microporous membranes has a limited lifespan for hydrophilic modification, and the substrate surface structure is easily damaged, resulting in closed pores or holes. Directly coating the surface of polyethylene microporous membranes with hydrophilic substances results in poor adhesion between the hydrophilic layer and the base membrane, making it prone to detachment and affecting the long-term performance of the reverse osmosis membrane separation layer. Furthermore, the hydrophilicity of the polyethylene microporous membrane also significantly impacts the performance of the reverse osmosis membrane separation layer (such as the polyamide layer). During the preparation of the reverse osmosis membrane separation layer, a substrate with excessively high hydrophilicity carries more aqueous solution, which easily undergoes interfacial polymerization within the pores, increasing the total transport path length of water and solutes and reducing water flux. Conversely, a substrate with insufficient hydrophilicity carries less aqueous solution, making it more likely to react rapidly with the oil phase monomers, resulting in a thicker and rougher separation layer, leading to reduced water flux and desalination rate. Therefore, as the supporting layer of the reverse osmosis membrane, the polyethylene microporous membrane should also have suitable hydrophilicity.

[0032] To address the above problems, this invention proposes a hydrophilic modified polyolefin substrate for reverse osmosis membranes. The hydrophilic coating on the hydrophilic modified polyolefin substrate has strong adhesion and is not easily detached. When used as a support for reverse osmosis membranes, it can significantly improve the water flux and desalination rate of the reverse osmosis membranes.

[0033] Specifically, a first aspect of the present invention provides a hydrophilic modified polyolefin substrate for reverse osmosis membranes, comprising: a polyolefin substrate; a first hydrophilic coating disposed on one side of the polyolefin substrate; and a second hydrophilic coating disposed on the other side of the polyolefin substrate; wherein the contact angle of the first hydrophilic coating is θ. A The contact angle of the second hydrophilic coating is θ B , and θ A <θ B ;θ A θ is 50°-80°. B The angle is 70°-90°; both the first and second hydrophilic coatings are formed by thermal crosslinking and curing.

[0034] This invention forms a hydrophilic coating on both sides of a substrate through thermal crosslinking and curing. The epoxy and amino groups in the hydrophilic coating undergo a thermal crosslinking reaction to generate hydrophilic groups, increasing the hydrophilicity of the substrate. The coating also exhibits good adhesion and is not easily peeled off, achieving durable hydrophilic modification of the polyolefin substrate. This facilitates the uniform formation of the polyamide layer and improves the performance of the reverse osmosis membrane. Furthermore, this invention controls the different hydrophilicities on the two sides of the hydrophilic-modified polyolefin substrate, while simultaneously controlling the contact angles of the hydrophilic coatings on both sides within a specific range. This reduces the amount of hydrophilic monomers used to synthesize polyamide in the substrate pores during reverse osmosis membrane preparation, minimizing interfacial polymerization reactions within the pores and preventing pore blockage. When the polyolefin substrate of this invention is used as a support for a reverse osmosis membrane, it enables the membrane to achieve both high water flux and high desalination rate. It is important to note that the contact angles of the hydrophilic coatings on both sides of the substrate should not be too small, i.e., the hydrophilicity on both sides should not be too high. Otherwise, during reverse osmosis membrane preparation, a large amount of hydrophilic monomers used to synthesize polyamide will remain in the substrate pores and undergo interfacial polymerization reactions, clogging the pores and reducing water flux. The contact angle of the hydrophilic coating on both sides of the substrate should not be too large, that is, the hydrophilicity on both sides should not be too low. Otherwise, the hydrophilic monomers used to synthesize polyamide during the reverse osmosis membrane preparation process will be difficult to spread on the substrate surface, resulting in uneven polyamide layer and reduced performance of reverse osmosis membrane.

[0035] In some embodiments, θ A It can be 50°, 55°, 60°, 65°, 70°, 75°, or 80°. θ B The contact angle can be 70°, 75°, 80°, 85°, or 90°. The smaller the contact angle of the hydrophilic coating to water, the better its hydrophilicity. The contact angles of both the first and second hydrophilic coatings must be within a reasonable range; they should not be too large or too small.

[0036] In some embodiments, the first hydrophilic coating is formed by thermal crosslinking and curing of a first substance containing epoxy groups and a second substance containing amino groups. The second hydrophilic coating is formed by thermal crosslinking and curing of a third substance containing epoxy groups and a fourth substance containing amino groups. Epoxy groups and amino groups themselves have a certain degree of hydrophilicity, and at the same time, epoxy groups and amino groups can undergo a thermal crosslinking reaction to generate hydrophilic groups, thereby improving the hydrophilicity of the substrate.

[0037] In some embodiments, the first substance containing epoxy groups and the third substance containing epoxy groups respectively include one or more of ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, butylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol triglycidyl ether, and trimethylolpropane triglycidyl ether. Thus, it can undergo thermal crosslinking and curing with amino groups to form a hydrophilic coating with high strength.

[0038] In some embodiments, the second amino-containing substance and the fourth amino-containing substance respectively include one or more of aminosulfonic acid, ethanolamine, polyetheramine, and polyethyleneimine. This allows for thermal cross-linking and curing with epoxy groups, forming a hydrophilic coating with high strength.

[0039] In some embodiments, the mass ratio of the first substance containing epoxy groups to the second substance containing amino groups is 1:(0.5-3), for example, 1:0.5, 1:1, 1:1.5, 1:2, 1:2.5, or 1:3. The mass ratio of the first substance to the second substance is related to the contact angle of the first hydrophilic coating. By controlling the mass ratio, the contact angle of the first hydrophilic coating can be controlled within the range of 50°-80°.

[0040] In some embodiments, the mass ratio of the third substance containing epoxy groups to the fourth substance containing amino groups is 1:(2-5), for example, 1:2, 1:2.5, 1:3, 1:3.5, 1:4, 1:4.5, or 1:5. The mass ratio of the third substance to the fourth substance is related to the contact angle of the first hydrophilic coating. By controlling the mass ratio, the contact angle of the second hydrophilic coating can be controlled within the range of 70°-90°.

[0041] In some specific embodiments, the mass ratio of the third substance to the fourth substance is less than the mass ratio of the first substance to the second substance, thereby enabling control of θ. A <θ B .

[0042] In some embodiments, the areal densities of the first hydrophilic coating and the second hydrophilic coating are both 0.5 g / m³. 2 -2g / m 2 For example, 0.5g / m 2 1g / m 2 1.5g / m 2 or 2g / m 2 This can improve the performance of the reverse osmosis membrane. If the areal density is too low, a continuous and uniform hydrophilic membrane layer cannot be formed, exposing the hydrophobic regions of the polyolefin substrate. This results in an uneven polyamide layer during reverse osmosis membrane preparation, reducing the salt rejection performance of the reverse osmosis membrane. If the areal density is too high, the coating thickness is too large, causing severe pore blockage in the polyolefin substrate. This significantly increases the resistance to water molecule mass transfer, leading to a decrease in the water flux of the reverse osmosis membrane.

[0043] In some embodiments, the thickness of the polyolefin substrate is 9 μm-50 μm, for example, 9 μm, 10 μm, 20 μm, 30 μm, 40 μm, or 50 μm. This improves the performance of the reverse osmosis membrane. If the thickness is too large, the mass transfer path is too long, and the fluid resistance inside the pores (friction resistance) increases significantly, resulting in a lower overall water flux of the membrane module. If the thickness is too small, the mechanical properties of the substrate are poor, which is not conducive to the fabrication of reverse osmosis membrane modules.

[0044] In some embodiments, the porosity of the polyolefin substrate is 40%-70%, for example, 40%, 45%, 50%, 55%, 60%, 65%, or 70%. This improves the performance of the reverse osmosis membrane. If the porosity is too low, the separation layer formed during the interfacial polymerization reaction has a low degree of cross-linking, a smooth surface, and a thin thickness, resulting in a decrease in the salt rejection performance of the reverse osmosis membrane. If the porosity is too high, the separation layer formed during the interfacial polymerization reaction has an excessive degree of cross-linking, a rough surface, and a thick thickness, resulting in a decrease in the water flux of the reverse osmosis membrane.

[0045] In some embodiments, the polyolefin substrate includes either a PE substrate or a PP substrate. Preferably, the polyolefin substrate is a PE substrate. PE substrates have relatively low cost, excellent mechanical strength, thermal stability, and chemical inertness.

[0046] The second aspect of this invention provides a method for preparing a hydrophilic modified polyolefin substrate for reverse osmosis membranes according to the first aspect of this invention, comprising the following steps: mixing a first substance containing epoxy groups, a second substance containing amino groups, and a solvent to obtain a first coating liquid; wherein the mass ratio of the first substance containing epoxy groups to the second substance containing amino groups is 1:(0.5-3); mixing a third substance containing epoxy groups, a fourth substance containing amino groups, and a solvent to obtain a second coating liquid; wherein the mass ratio of the third substance containing epoxy groups to the fourth substance containing amino groups is 1:(2-5), and the mass ratio of the third substance to the fourth substance is less than the mass ratio of the first substance to the second substance; coating one side of the polyolefin substrate with the first coating liquid and drying it; coating the other side of the polyolefin substrate with the second coating liquid, drying it, and then performing thermal crosslinking and curing to obtain the hydrophilic modified polyolefin substrate for reverse osmosis membranes.

[0047] The preparation method of this invention is simple to operate, has a short process, and is highly repeatable, making it suitable for large-scale industrial application. The hydrophilic modified polyolefin substrate prepared by the method of this invention has good hydrophilicity and high coating adhesion, making it difficult to peel off; when used as a support for reverse osmosis membranes, it can significantly improve the water flux and desalination rate of the reverse osmosis membrane.

[0048] In some embodiments, the solvent comprises a mixture of ethanol and water. The mass ratio of ethanol to water is 1:(0.1-2.5), for example, 1:0.1, 1:0.5, 1:1, 1:1.5, 1:2, or 1:2.5.

[0049] In some embodiments, the drying temperature is 60°C-80°C, for example, 60°C, 65°C, 70°C, 75°C, or 80°C. This allows the solvent to evaporate sufficiently.

[0050] In some embodiments, the temperature for thermal crosslinking and curing is 60°C-80°C, for example, 60°C, 65°C, 70°C, 75°C, or 80°C. This allows the epoxy groups and amino groups to react fully.

[0051] In some embodiments, the thermal crosslinking curing time is 6h-20h, for example 6h, 8h, 10h, 12h, 14h, 16h, 18h or 20h. This allows the epoxy groups and amino groups to react fully.

[0052] A third aspect of the present invention provides a reverse osmosis membrane, comprising a hydrophilic modified polyolefin substrate for reverse osmosis membranes according to the first aspect of the present invention or a hydrophilic modified polyolefin substrate for reverse osmosis membranes obtained by the preparation method of the second aspect of the present invention.

[0053] Because of the use of the above-mentioned hydrophilic modified polyolefin substrate, the reverse osmosis membrane of the present invention has better water flux and desalination rate, and its performance is significantly improved.

[0054] The present invention will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be considered as limiting the scope of the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0055] Example 1 for preparing hydrophilic modified PE substrate (1) Mix 20g of ethanol with 40g of deionized water, add 2.4g of ethylene glycol diglycidyl ether and 1.8g of polyethyleneimine (Aladdin, model MW 1200) to the above mixture, stir evenly to obtain the first coating liquid; (2) Mix 20g of ethanol with 40g of deionized water, add 1.1g of propylene glycol diglycidyl ether and 3.1g of polyetheramine (Hunsmay, model ED-900) to the above mixture, stir evenly to obtain the second coating liquid; (3) Coat the first coating liquid on the A side of a PE substrate with a thickness of 25μm (porosity of 60%) and dry it at 60℃, then coat the B side of the PE substrate with the second coating liquid, dry it at 60℃ to remove moisture, and then perform thermal crosslinking curing at 60℃ for 20h to obtain a hydrophilic modified PE substrate with a first hydrophilic coating and a second hydrophilic coating.

[0056] Example 2 (1) Take 20g of ethanol and 40g of deionized water and mix them. Add 2.0g of butanediol diglycidyl ether and 2.2g of aminosulfonic acid to the above mixture and stir evenly to obtain the first coating liquid; (2) Take 20g of ethanol and 40g of deionized water and mix them. Add 1.0g of polyethylene glycol diglycidyl ether (Aladdin, model Mn 520-550) and 3.2g of ethanolamine to the above mixture and stir evenly to obtain the second coating liquid; (3) Coat the first coating liquid on the A side of a PE substrate with a thickness of 25μm (porosity of 60%) and dry it at 60℃. Then coat the second coating liquid on the B side of the PE substrate, dry it at 80℃ to remove moisture, and then perform thermal crosslinking curing at 80℃ for 8h to obtain a hydrophilic modified PE substrate with a first hydrophilic coating and a second hydrophilic coating.

[0057] Example 3 (1) Mix 20g of ethanol with 40g of deionized water, and mix 2.8g of polypropylene glycol diglycidyl ether (Aladdin, model Mn 500) with 1.4g of polyethyleneimine (Aladdin, model MW). 1200) was added to the above mixture and stirred evenly to obtain the first coating liquid; (2) 20g of ethanol and 40g of deionized water were mixed, and 1.2g of glycerol triglycidyl ether and 3.0g of polyetheramine (Hunsmay, model ED-2000) were added to the above mixture and stirred evenly to obtain the second coating liquid; (3) The first coating liquid was coated on the A side of a PE substrate with a thickness of 25μm (porosity of 60%) and dried at 60℃. Then the second coating liquid was coated on the B side of the PE substrate, dried at 60℃ to remove moisture, and then thermally crosslinked and cured at 70℃ for 15h to obtain a hydrophilic modified PE substrate with a first hydrophilic coating and a second hydrophilic coating. Its SEM image is shown in Figure 1, and the contact angles of the A side and the B side are shown in Figure 2a and Figure 2b.

[0058] Example 4 (1) Take 20g of ethanol and 40g of deionized water and mix them. Add 1.3g of trihydroxymethane triglycidyl ether and 2.9g of polyetheramine (Hunsman, model ED-600) to the above mixture and stir evenly to obtain the first coating liquid; (2) Take 20g of ethanol and 40g of deionized water and mix them. Add 0.8g of trihydroxymethane triglycidyl ether and 3.4g of polyetheramine (Hunsman, model ED-600) to the above mixture and stir evenly to obtain the second coating liquid; (3) Coat the first coating liquid on the A side of a PE substrate with a thickness of 25μm (porosity of 60%) and dry it at 60℃. Then coat the second coating liquid on the B side of the PE substrate, dry it at 60℃ to remove moisture, and then perform thermal crosslinking curing at 80℃ for 6h to obtain a hydrophilic modified PE substrate with a first hydrophilic coating and a second hydrophilic coating.

[0059] Comparative Example 1 provides a PE substrate with a thickness of 25 μm and a porosity of 60%. The SEM image of the PE substrate is shown in Figure 3, and its contact angle image is shown in Figure 4.

[0060] Comparative Example 2 prepared a hydrophilic modified PE substrate according to the method described in Example 3, except that step (2) was not performed, and the first coating liquid prepared in step (1) was coated on the A and B sides of the PE substrate respectively.

[0061] Comparative Example 3 prepared a hydrophilic modified PE substrate according to the method described in Example 3, except that step (1) was not performed, and the second coating liquid prepared in step (2) was coated on the A and B sides of the PE substrate respectively.

[0062] Comparative Example 4 (1) Take 20g of ethanol and 40g of deionized water and mix them. Add 3.0g of polypropylene glycol diglycidyl ether (Aladdin, model Mn 500) and 1.2g of polyethyleneimine (Aladdin, model MW 1200) to the above mixture and stir evenly to obtain the first coating liquid; (2) Take 20g of ethanol and 40g of deionized water and mix them. Add 2.0g of butanediol diglycidyl ether and 2.2g of aminosulfonic acid to the above mixture and stir evenly to obtain the second coating liquid; (3) Coat the first coating liquid on the A side of a PE substrate with a thickness of 25μm (porosity of 60%) and dry it at 60℃. Then coat the second coating liquid on the B side of the PE substrate, dry it at 60℃ to remove moisture, and then perform thermal crosslinking curing at 70℃ for 15h to obtain a hydrophilic modified PE substrate with a first hydrophilic coating and a second hydrophilic coating.

[0063] Comparative Example 5 (1) Take 20g of ethanol and 40g of deionized water and mix them. Add 0.8g of polypropylene glycol diglycidyl ether (Aladdin, model Mn 500) and 3.4g of polyethyleneimine (Aladdin, model MW 1200) to the above mixture and stir evenly to obtain the first coating liquid; (2) Take 20g of ethanol and 40g of deionized water and mix them. Add 0.6g of glycerol triglycidyl ether and 3.6g of polyetheramine (Hunsmay, model ED-2000) to the above mixture and stir evenly to obtain the second coating liquid; (3) Coat the first coating liquid on the A side of a PE substrate with a thickness of 25μm (porosity of 60%) and dry it at 60℃. Then coat the second coating liquid on the B side of the PE substrate, dry it at 60℃ to remove moisture, and then perform thermal crosslinking curing at 70℃ for 15h to obtain a hydrophilic modified PE substrate with a first hydrophilic coating and a second hydrophilic coating.

[0064] The reverse osmosis membrane was prepared using the hydrophilic modified PE substrate prepared in the above examples and comparative examples, and the reverse osmosis membrane was prepared by the general method described below.

[0065] (1) Preparation of aqueous solution: Weigh 2.0g of m-phenylenediamine, 2.0g of triethylamine hydrochloride and 0.01g of camphor sulfonic acid and add them to 95.9g of deionized water and stir to dissolve.

[0066] (2) Preparation of oil phase solution: Weigh 0.1g of trimesoyl chloride and add it to 99.9g of n-hexane, and stir to dissolve.

[0067] (3) Fix the hydrophilic modified PE substrate flat in the glass frame, then pour the aqueous solution into the tank so that the aqueous solution completely covers the surface of the first hydrophilic coating. After 60 seconds, pour out the excess aqueous solution and use filter paper to absorb the aqueous phase on the substrate surface. After there are no obvious water droplets on the film surface, pour the oil phase solution onto the surface of the first hydrophilic coating after removing the aqueous phase. After reacting for 30 seconds, remove the oil phase solution, drain it, and cure it in an oven at 80°C for 2 minutes.

[0068] Figure 5 shows the SEM image of the reverse osmosis membrane prepared using the hydrophilic modified PE substrate of Example 3. Figure 6 shows the SEM image of the reverse osmosis membrane prepared using the PE substrate of Comparative Example 1.

[0069] Test Method (1) Water Contact Angle Test of Hydrophilic Modified PE Substrate: The contact angle of the membrane surface was tested using a static contact angle meter (JC2000C1, Shanghai Zhongchen). During the test, the hydrophilic modified PE substrate was cut into strips and fixed to a glass slide with double-sided tape. The volume of the water droplet dropped by the syringe was 2.0 μL. All data are the average values ​​after 3 tests.

[0070] (2) Pure water flux test of hydrophilic modified PE substrate: A flat-panel membrane analyzer (Shandong Bona) was used. The test solution was pure water, the temperature was 25℃±2℃, the test pressure was 0.1MPa, and the effective membrane tank area was 60.00 cm². 2 After 30 minutes of stable operation, the pure water flux of the membrane was tested. The specific formula is: J = V / (S×t), where J is the pure water flux in L / (m³). 2 •h); V is the permeate volume in L; S is the effective membrane area in m². 2 t represents the running time, in hours (h).

[0071] (3) Coating loss rate test of hydrophilic modified PE substrate: After cutting the hydrophilic modified PE substrate into a shape of 10cm×10cm, the weight of the substrate m0 was recorded. After soaking the substrate in pure water for 30 days, it was dried and the weight m0 was recorded. p The coating loss rate is A = (m0 - m) / ( ... p ) / m0×100%. After immersing the substrate in pure water for 30 days, test the pure water flux according to the method in (2) above.

[0072] (4) Surface density test of the first and second hydrophilic coatings on the hydrophilic modified PE substrate: The PE substrate, the substrate coated with the first hydrophilic coating, and the substrate coated with the first and second hydrophilic coatings were cut into 10cm×10cm shapes, and their weights were measured as m, m1, and m, respectively. 12 The surface density (m) of the first hydrophilic coating Δ1 = m1-m; Surface density of the second hydrophilic coating m Δ2 = m 12 -m1.

[0073] (5) Water flux and desalination rate test of reverse osmosis membrane: A flat-plate membrane analyzer (Shandong Bona) was used. The test solution was 250±5 mg / L NaCl, pH=7.5~8, temperature was 25℃±2℃, test pressure was 0.41MPa, and the effective area of ​​the membrane tank was 60 cm². 2 After 30 minutes of stable operation, the water flux and desalination rate of the membrane were tested. The water flux formula is: J = V / (S×t), where J is the water flux in L / (m³). 2 •h); V is the permeate volume in L; S is the effective membrane area in m². 2 t represents the running time in hours (h). The desalination rate formula is: R = (1 - Cp / Cf) × 100%, where R is the desalination rate (%), Cp is the salt content of the permeate in g / L, and Cf is the salt content of the feed solution in g / L.

[0074] The test results are shown in Tables 1 and 2.

[0075] Table 1: Performance of hydrophilic modified PE substrate

[0076] Table 2: Performance of Reverse Osmosis Membranes

[0077] Results and Discussion: By comparing the above examples and comparative examples, it can be seen that the present invention forms a hydrophilic coating on both sides of the substrate through thermal crosslinking and curing, thereby improving the hydrophilicity of the substrate. The coating also exhibits good adhesion and is not easily peeled off, achieving durable hydrophilic modification of the polyolefin substrate. Furthermore, the present invention controls the different hydrophilicities of the two surfaces of the hydrophilically modified polyolefin substrate, while simultaneously controlling the contact angle of the hydrophilic coating on both sides within a specific range. This improves the spreadability of the aqueous monomers during reverse osmosis membrane preparation, controls the amount of aqueous phase carried in the substrate, and facilitates the uniform formation of the polyamide layer, thus enabling the reverse osmosis membrane to achieve both high water flux and high desalination rate.

[0078] 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 the present invention. 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.

[0079] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A hydrophilic modified polyolefin substrate for reverse osmosis membranes, characterized in that, include: Polyolefin substrate; A first hydrophilic coating is disposed on one side of the polyolefin substrate; And a second hydrophilic coating disposed on the other side of the polyolefin substrate; the contact angle of the first hydrophilic coating is θ. A The contact angle of the second hydrophilic coating is θ B , and θ A <θ B ;θ A θ is 50°-80°. B The angle is 70°-90°; both the first and second hydrophilic coatings are formed by thermal crosslinking and curing.

2. The hydrophilic modified polyolefin substrate for reverse osmosis membranes according to claim 1, characterized in that, The first hydrophilic coating is formed by thermal crosslinking and curing of a first substance containing epoxy groups and a second substance containing amino groups; the second hydrophilic coating is formed by thermal crosslinking and curing of a third substance containing epoxy groups and a fourth substance containing amino groups.

3. The hydrophilic modified polyolefin substrate for reverse osmosis membranes according to claim 2, characterized in that, The first substance containing epoxy groups and the third substance containing epoxy groups respectively include one or more of ethylene glycol diglycidyl ether, propylene glycol diglycidyl ether, butylene glycol diglycidyl ether, polyethylene glycol diglycidyl ether, polypropylene glycol diglycidyl ether, glycerol triglycidyl ether, and trimethylolpropane triglycidyl ether; the second substance containing amino groups and the fourth substance containing amino groups respectively include one or more of aminosulfonic acid, ethanolamine, polyetheramine, and polyethyleneimine.

4. The hydrophilic modified polyolefin substrate for reverse osmosis membranes according to claim 2, characterized in that, The mass ratio of the first substance containing an epoxy group to the second substance containing an amino group is 1:(0.5-3); the mass ratio of the third substance containing an epoxy group to the fourth substance containing an amino group is 1:(2-5).

5. The hydrophilic modified polyolefin substrate for reverse osmosis membranes according to claim 1, characterized in that, The areal densities of the first hydrophilic coating and the second hydrophilic coating are both 0.5 g / m³. 2 -2g / m 2 .

6. The hydrophilic modified polyolefin substrate for reverse osmosis membranes according to claim 1, characterized in that, The thickness of the polyolefin substrate is 9μm-50μm, and the porosity is 40%-70%.

7. The hydrophilic modified polyolefin substrate for reverse osmosis membranes according to claim 1, characterized in that, The polyolefin substrate includes either PE substrate or PP substrate.

8. A method for preparing a hydrophilic modified polyolefin substrate for a reverse osmosis membrane according to any one of claims 1-7, characterized in that, Includes the following steps: A first coating liquid is obtained by mixing a first substance containing epoxy groups, a second substance containing amino groups, and a solvent; wherein the mass ratio of the first substance containing epoxy groups to the second substance containing amino groups is 1:(0.5-3); a second coating liquid is obtained by mixing a third substance containing epoxy groups, a fourth substance containing amino groups, and a solvent; wherein the mass ratio of the third substance containing epoxy groups to the fourth substance containing amino groups is 1:(2-5), and the mass ratio of the third substance to the fourth substance is less than the mass ratio of the first substance to the second substance; the first coating liquid is coated on one side of a polyolefin substrate and dried; the second coating liquid is coated on the other side of the polyolefin substrate, dried, and then thermally crosslinked and cured to obtain the hydrophilic modified polyolefin substrate for reverse osmosis membranes.

9. The preparation method according to claim 8, characterized in that, The solvent includes a mixture of ethanol and water; the drying temperature is 60℃-80℃; the thermal crosslinking curing temperature is 60℃-80℃; and the thermal crosslinking curing time is 6h-20h.

10. A reverse osmosis membrane, characterized in that, The reverse osmosis membrane hydrophilic modified polyolefin substrate according to any one of claims 1-7 or the reverse osmosis membrane hydrophilic modified polyolefin substrate obtained by the preparation method according to claim 8 or 9.

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