A method for modifying the surface hydrophobicity of a hyperbranched polyolefin polymer microporous membrane

Abstract

The application relates to a method for modifying the surface hydrophobicity of a hyperbranched polyolefin polymer microporous membrane, belonging to the field of functional materials and membrane separation technology. First, a low-crystallinity highly branched polyolefin is dissolved in a hydrocarbon solvent to prepare a coating solution with a concentration of 1-200 g / L; then a clean polymer microporous membrane is immersed in the coating solution for 1-300 minutes and taken out; finally, the polymer microporous membrane is washed and dried in a cleaning agent, and further heat treatment is carried out, so that a polymer microporous membrane with a stable polyolefin dense hydrophobic coating layer on the surface is obtained. The modified polymer microporous membrane has a reduced surface pore size and a significantly improved water contact angle, and presents high-performance water-blocking and air-permeating characteristics, and has a wide application in the fields of membrane water degassing, ink degassing, ammonia removal, membrane distillation, membrane extraction, membrane absorption and the like.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of functional materials and membrane separation technology, and particularly relates to a method for modifying the surface hydrophobicity of a hyperbranched polyolefin modified polymer microporous membrane. BACKGROUND

[0002] Membrane technology is widely used in water treatment, energy, environment, electronics and biological medicine and other fields due to its high efficiency, energy saving, no pollution and no post-treatment process, and is suitable for various separation processes such as filtration, distillation, absorption, desorption, extraction and the like. As the core of the technology, the development of membrane materials and membrane preparation technology seriously restricts the progress and expansion of the technology. Therefore, actively researching and developing new membrane materials and technology will greatly promote the wide application of the technology in various fields.

[0003] Due to different application fields, different requirements are presented for the performance of the membrane. For example, in water treatment, the membrane surface is required to have high hydrophilicity so that water can quickly permeate the membrane and the treatment capacity of the membrane is maximized. However, for membrane distillation, membrane degassing and membrane extraction, the more hydrophobic the membrane is, the more conducive to the efficient operation of the process. Currently commonly used membrane materials, such as polyethylene, polypropylene, polyvinyl chloride, polyvinylidene fluoride, polysulfone, polyethersulfone, polyacrylonitrile and the like, due to the continuous innovation and development of membrane preparation and modification technology, all show good hydrophilicity and have been widely used in water treatment field. However, due to the material itself and the membrane surface structure, the hydrophobicity of these membranes needs to be improved, which has seriously restricted the application expansion of them in other fields. Therefore, this research is committed to improving the hydrophobicity of the membrane material, promoting the development of the separation field required by the hydrophobic membrane, reducing energy consumption and improving efficiency, which will bring huge economic benefits.

[0004] So far, many works have been carried out on hydrophobic membranes. The main method is to first construct micro-nano structure on the surface and then implant hydrophobic groups or low surface energy polymers. Patent CN101463140A discloses a preparation method of super-hydrophobic polyvinylidene fluoride and its product, which first constructs micro-nano structure on the polyvinylidene fluoride membrane by plasma treatment, and then performs hydrophobic modification by chemical vapor deposition of organosilane to obtain super-hydrophobic polyvinylidene fluoride membrane. Patent 103191855A discloses a super-hydrophobic composite membrane and a preparation method thereof, which blends nano-particles and polyorganosiloxane, then sprays on the membrane surface, and finally obtains a super-hydrophobic porous membrane by drying. Patent CN104014259A first grafts fluorine-containing hydrophobic material on the commonly used membrane material polymer by γ irradiation, and then coats on the surface of the porous membrane to prepare a hydrophobic porous membrane. Although the above-mentioned methods can prepare super-hydrophobic porous membranes, the materials used, such as polysiloxane, have low adhesion to the membrane surface and are not stable and easy to fall off; in addition, the surface structure technology such as plasma or γ irradiation is not suitable for practical application. Therefore, it is crucial and urgent to find a simple and practical method for modifying the hydrophobicity of the membrane. SUMMARY

[0005] In view of the above problems existing in the prior art, the purpose of the present application is to provide a technical solution of a method for modifying the surface hydrophobicity of a hyperbranched polyolefin modified polymer microporous membrane, which is simple in process and reagents, suitable for industrial production, and has a high water-blocking and air-permeable property after modification, thus having a wide application prospect in the fields of membrane degassing, distillation, absorption, and extraction.

[0006] The method for modifying the surface hydrophobicity of a hyperbranched polyolefin modified polymer microporous membrane comprises the following steps:

[0007] 1) Dissolving a highly branched polyolefin in a solvent to obtain a coating solution, wherein the concentration of the branched polyolefin is 1-200 g / L; the polyolefin is long-chain branched polyethylene or long-chain branched polypropylene, the branching degree of the branched polyolefin is 0.1-0.3, and the branching structure of the branched polyolefin is a carbon-hydrogen chain with a carbon atom number of 5-10 and is in any one of a brush shape, a star shape, or a comb shape; and the solvent is any one of n-hexane, n-heptane, or n-octane;

[0008] 2) Soaking a clean polymer microporous membrane in the coating solution for 1-300 minutes and then taking it out, wherein the material of the polymer microporous membrane is any one of polyethylene, polypropylene, or poly-4-methyl-1-pentene;

[0009] 3) Soaking the polymer microporous membrane in a cleaning agent for 1-300 minutes, taking it out, and naturally air-drying it;

[0010] 4) Heat-treating the clean modified membrane to obtain a polymer microporous membrane with a stable polyolefin hydrophobic coating layer on the surface.

[0011] The method for modifying the surface hydrophobicity of a hyperbranched polyolefin modified polymer microporous membrane, wherein in step 1), the concentration of the branched polyolefin is 50-150 g / L, preferably 100-120 g / L.

[0012] The method for modifying the surface hydrophobicity of a hyperbranched polyolefin modified polymer microporous membrane, wherein in step 1), the branching degree of the branched polyolefin is 0.15-0.2, and the branching structure of the branched polyolefin is a carbon-hydrogen chain with a carbon atom number of 6-8.

[0013] The method for modifying the surface hydrophobicity of a hyperbranched polyolefin modified polymer microporous membrane, wherein in step 2), the shape of the polymer microporous membrane is a flat membrane or a hollow fiber membrane.

[0014] The method for improving the hydrophobicity of the surface of a hyperbranched polyolefin modified polymer microporous membrane is characterized in that, in step 2), the soaking time is 50-250 minutes, preferably 100-200 minutes, and more preferably 120-150 minutes.

[0015] The method for improving the hydrophobicity of a microporous membrane surface modified by hyperbranched polyolefin is characterized in that, in step 2), the average pore size of the polymer microporous membrane is 0.1-0.45 micrometers, preferably 0.2-0.3 micrometers.

[0016] The method for improving the hydrophobicity of the surface of a hyperbranched polyolefin modified polymer microporous membrane is characterized in that, in step 3), the cleaning agent is any one of methanol, ethanol, isopropanol, and n-butanol.

[0017] The method for improving the hydrophobicity of the surface of a hyperbranched polyolefin modified polymer microporous membrane is characterized in that, in step 3), the soaking time is 10-200 minutes, preferably 30-150 minutes.

[0018] The method for improving the hydrophobicity of the surface of a hyperbranched polyolefin modified polymer microporous membrane is characterized in that, in step 4), the heat treatment temperature is 100℃-120℃, preferably 105℃-115℃; and the heat treatment time is 10-15 minutes, preferably 12-13 minutes.

[0019] The above-described method for modifying the surface of a hyperbranched polyolefin-modified polymer microporous membrane involves selecting a branched polyolefin with low crystallinity and solubility in hydrocarbon solvents. The low surface energy of the polyolefin provides hydrophobicity. Under natural conditions, rapid drying with the hydrocarbon solvent leads to surface self-assembly, forming a micro / nano structure. Finally, a polymer microporous membrane coated with a hydrophobic polyolefin coating is obtained. Because the modified polymer used in this invention maintains a high degree of consistency with the structural units of the polymer membrane substrate, based on the principle of compatibility, the two exhibit excellent adhesion. The coating can be easily applied to the substrate surface and exhibits stable and reliable adhesion, resisting peeling. Furthermore, this invention adds a heat treatment step. During this process, the temperature is controlled near the polymer's crystallization temperature, allowing local molecular chains to have a certain degree of mobility, embedding the hyperbranched polyolefin on the surface of the polymer microporous membrane, further improving the coating's stability. Testing shows that the pore size of the hydrophobically modified polymer microporous membrane is reduced, and the water contact angle is significantly increased, exhibiting high-performance water-blocking and air-permeable characteristics, demonstrating significant performance in membrane degassing processes. Attached Figure Description

[0020] Figure 1 Scanning electron microscope image of a cross section of an unmodified polypropylene hollow fiber membrane;

[0021] Figure 2A scanning electron microscope image of the inner surface of an unmodified polypropylene hollow fiber membrane;

[0022] Figure 3 A scanning electron microscope image of the outer surface of an unmodified polypropylene hollow fiber membrane;

[0023] Figure 4 This is a scanning electron microscope image of the cross-section of the polypropylene hollow fiber membrane after hydrophobic modification in Example 2 of the present invention.

[0024] Figure 5 This is a scanning electron microscope image of the inner surface of the polypropylene hollow fiber membrane after hydrophobic modification in Example 2 of the present invention.

[0025] Figure 6 This is a scanning electron microscope image of the outer surface of the polypropylene hollow fiber membrane after hydrophobic modification in Example 2 of the present invention. Detailed Implementation

[0026] The technical solutions of the present invention will now be clearly and completely described with reference to the embodiments and accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0027] Example 1:

[0028] First, a certain amount of hyperbranched polyethylene with alkyl chains of 5 carbons, a branching degree of 0.3, and a brush-like structure was dissolved in n-hexane to prepare a hydrophobic modification coating solution with a concentration of 1 g / L. Then, a clean polyethylene sheet membrane with a pore size of 0.1 μm was immersed in the coating solution for 300 minutes, removed, washed in methanol for 1 minute, and air-dried. Finally, it was heat-treated at 100℃ for 10 minutes to obtain a polyethylene sheet membrane with a hydrophobic polyethylene coating. Testing showed that the obtained hyperbranched, hydrophobically modified polyethylene sheet membrane had a water contact angle of 150°; a surface pore size of 50 nm; and oxygen, nitrogen, and carbon dioxide fluxes of 31, 30, and 34 L / min, respectively, with an oxygen removal efficiency of 83% in water.

[0029] Example 2:

[0030] First, a certain amount of hyperbranched polyethylene with alkyl chains of 10 carbons, a branching degree of 0.1, and a comb-like structure was dissolved in n-heptane to prepare a hydrophobic modification coating solution with a concentration of 200 g / L. Then, a clean polypropylene hollow fiber membrane with a pore size of 0.2 μm was immersed in the coating solution for 1 minute, removed, washed in ethanol for 10 minutes, and air-dried. Finally, it was heat-treated at 100℃ for 10 minutes to obtain a polypropylene microporous membrane with a hydrophobic coating of hyperbranched polyethylene. Testing showed that the obtained hyperbranched polyethylene hydrophobic modified polypropylene hollow fiber membrane had a water contact angle of 154°; a surface pore size of 40 nm; and oxygen, nitrogen, and carbon dioxide fluxes of 27, 25, and 30 L / min, respectively. The oxygen removal efficiency in water reached 85%.

[0031] Example 3:

[0032] First, a certain amount of hyperbranched polypropylene with alkyl chains of 6 carbons, a branching degree of 0.2, and a star-shaped structure was dissolved in n-octane to prepare a hydrophobic modification coating solution with a concentration of 200 g / L. Then, a clean poly(4-methyl-1-pentene) hollow fiber membrane with a pore size of 0.2 μm was immersed in the coating solution for 300 minutes, removed, washed in isopropanol for 300 minutes, and air-dried. Finally, it was heat-treated at 120℃ for 15 minutes to obtain a poly(4-methyl-1-pentene) hollow fiber microporous membrane with a surface modified by hydrophobic modification of hyperbranched polypropylene. Testing showed that the obtained hyperbranched polypropylene hydrophobic modified poly(4-methyl-1-pentene) hollow fiber membrane had a water contact angle of 149°; a surface pore size of 60 nm; and oxygen, nitrogen, and carbon dioxide fluxes of 35, 32, and 40 L / min, respectively. The oxygen removal efficiency in water reached 80%.

[0033] Example 4:

[0034] First, a certain amount of hyperbranched polypropylene with alkyl chains of 8 carbons, a branching degree of 0.15, and a brush-like structure was dissolved in n-heptane to prepare a hydrophobic modification coating solution with a concentration of 100 g / L. Then, a clean polypropylene hollow fiber membrane with a pore size of 0.45 μm was immersed in the coating solution for 150 minutes, removed, and washed in n-butanol for 100 minutes. After air drying, it was heat-treated at 110℃ for 15 minutes to obtain a polypropylene hollow fiber membrane with a hyperbranched polypropylene hydrophobic coating. Testing showed that the obtained hyperbranched polypropylene hydrophobic modified polypropylene hollow fiber membrane had a water contact angle of 160°; a surface pore size of 30 nm; and oxygen, nitrogen, and carbon dioxide fluxes of 42, 5, and 50 L / min, respectively, with an oxygen removal efficiency of 92%.

[0035] Example 5:

[0036] First, a certain amount of hyperbranched polyethylene with alkyl chains of 7 carbons, a branching degree of 0.1, and a star-shaped structure was dissolved in n-heptane to prepare a hydrophobic modification coating solution with a concentration of 50 g / L. Then, a clean polyethylene sheet membrane with a pore size of 0.3 μm was immersed in the coating solution for 100 minutes, removed, washed in ethanol for 50 minutes, and air-dried. Finally, it was heat-treated at 100℃ for 10 minutes to obtain a polyethylene sheet membrane with a hyperbranched polyethylene hydrophobic coating. Testing showed that the obtained hyperbranched polyethylene hydrophobic modified polyethylene sheet membrane had a water contact angle of 158°; a surface pore size of 45 nm; and oxygen, nitrogen, and carbon dioxide fluxes of 35, 30, and 45 L / min, respectively, with an oxygen removal efficiency of 88% in water.

[0037] Example 6:

[0038] First, a certain amount of hyperbranched polyethylene with alkyl chains of 6 carbons, a branching degree of 0.2, and a brush-like structure was dissolved in n-octane to prepare a hydrophobic modification coating solution with a concentration of 200 g / L. Then, a clean poly(4-methyl-1-pentene) hollow fiber membrane with a pore size of 0.2 μm was immersed in the coating solution for 30 minutes, removed, and washed in isopropanol for 30 minutes. After air drying, it was heat-treated at 120℃ for 15 minutes to obtain a poly(4-methyl-1-pentene) hollow fiber membrane with a hydrophobic coating of hyperbranched polyethylene. Testing showed that the obtained hydrophobic modified poly(4-methyl-1-pentene) hollow fiber membrane had a water contact angle of 155°, a surface pore size of 55 nm, and oxygen, nitrogen, and carbon dioxide fluxes of 32, 29, and 35 L / min, respectively, with an oxygen removal efficiency of 85% in water.

[0039] Example 7:

[0040] First, a certain amount of hyperbranched polyethylene with alkyl chains of 9 carbons, a branching degree of 0.15, and a comb-like structure was dissolved in n-octane to prepare a hydrophobic modification coating solution with a concentration of 100 g / L. Then, a clean polypropylene hollow fiber membrane with a pore size of 0.15 micrometers was immersed in the coating solution for 50 minutes, removed, washed in ethanol for 10 minutes, and air-dried. Finally, it was heat-treated at 110℃ for 15 minutes to obtain a polypropylene hollow fiber membrane with a hydrophobic coating of hyperbranched polyethylene. Testing showed that the obtained hyperbranched polyethylene hydrophobic modified polypropylene hollow fiber membrane had a water contact angle of 160°; a surface pore size of 35 nanometers; and oxygen, nitrogen, and carbon dioxide fluxes of 45, 8, and 48 L / min, respectively. The oxygen removal efficiency in water reached 97%.

[0041] Figures 4-6The images show scanning electron microscope (SEM) images of the cross-section, inner surface, and outer surface of the hydrophobically modified polypropylene hollow fiber membrane of Example 2 of this invention. The images show that the hyperbranched polyolefin coating densifies the modified microporous membrane and is tightly bonded to the support layer, with no detachment or separation. Similar structures can also be obtained from SEM images of the modified polypropylene hollow fiber membranes of Examples 1 and 3-7 of this invention.

[0042] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for modifying the surface hydrophobicity of a microporous membrane by hyperbranched polyolefin modification, characterized in that... Includes the following steps: 1) A highly branched polyolefin is dissolved in a solvent to obtain a coating solution, wherein the concentration of the branched polyolefin is 1-200 g / L; the polyolefin is long-chain branched polyethylene or long-chain branched polypropylene, the degree of branching of the branched polyolefin is 0.1-0.3, and the branching structure of the branched polyolefin is a hydrocarbon chain with 5-10 carbon atoms and the distribution type is any one of brush-shaped, star-shaped or comb-shaped; the solvent is any one of n-hexane, n-heptane, and n-octane. 2) After immersing the clean polymer microporous membrane in the coating solution for 1-300 minutes, remove it. The polymer microporous membrane is made of any one of polyethylene, polypropylene, or poly4-methyl-1-pentene. 3) Soak the polymer microporous membrane in the cleaning agent for 1-300 minutes, then remove and air dry naturally; 4) The clean modified membrane is heat-treated to obtain a polymer microporous membrane with a stable polyolefin hydrophobic coating on the surface.

2. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefin as described in claim 1, characterized in that... In step 1), the concentration of the branched polyolefin is 50-150 g / L.

3. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefins as described in claim 1, characterized in that... In step 1), the concentration of the branched polyolefin is 100-120 g / L.

4. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefin as described in claim 1, characterized in that... In step 1), the branching degree of the branched polyolefin is 0.15-0.2, and the branched structure of the branched polyolefin has 6-8 carbon atoms.

5. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefins as described in claim 1, characterized in that... In step 2): the polymer microporous membrane is in the shape of a flat sheet membrane or a hollow fiber membrane.

6. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefin as described in claim 1, characterized in that... In step 2), the soaking time is 50-250 minutes.

7. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefins as described in claim 1, characterized in that... In step 2), the soaking time is 100-200 minutes.

8. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefin as described in claim 1, characterized in that... In step 2): the average pore size of the polymer microporous membrane is 0.1-0.45 micrometers.

9. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefin as described in claim 1, characterized in that... In step 2): the average pore size of the polymer microporous membrane is 0.2-0.3 micrometers.

10. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefin as described in claim 1, characterized in that... In step 3): the cleaning agent is any one of methanol, ethanol, isopropanol, and n-butanol.

11. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefin as described in claim 1, characterized in that... In step 3), the soaking time is 10-200 minutes.

12. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefin as described in claim 1, characterized in that... In step 3), the soaking time is 30-150 minutes.

13. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefin as described in claim 1, characterized in that... In step 4): the heat treatment temperature is 100℃-120℃ and the heat treatment time is 10-15 minutes.

14. The method for improving the hydrophobicity of a microporous membrane surface modified with hyperbranched polyolefin as described in claim 1, characterized in that... In step 4): the heat treatment temperature is 105℃-115℃, and the heat treatment time is 12-13 minutes.

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