METHOD FOR PREPARING THE NETWORK-PORE POLYVINYLIDENE FLUORIDE MEMBRANE BASED ON POLYVINYL ALCOHOL GEL

Abstract

A method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol (PVA) gel includes the steps of (1) mix and stir PVA, masking agent and solvent, heat and dissolve the mixture evenly under 105 degree Celsius to obtain a PVA solution; (2) in the PVA solution, add PVDF and pore-forming agent, where the rest shall be added with the solvent until the total mass fraction sum is 1, stir, heat and dissolve the solution evenly to obtain the homogeneous casting solution; (3) the casting solution is filtered, deaerated, phase-separated and solidified as membrane A; (4) removes the PVA gel from membrane A to obtain membrane B; (5) membrane B is washed with water to remove the residual solvent to obtain the PVDF membrane with network-pore structure. The resulting PVDF membrane is an asymmetric membrane with an ultra-thin cortex and an interpenetrating network-pore sub-cortex structure.

Claims

1. A method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol gel, which mainly comprises: (1) Mix and stir PVA, masking agent and solvent according to a certain mass ratio, i.e. 0.5-5%, 1-8%, 30-60%, heat and dissolve the mixture evenly under 105 degree Celsius, to obtain the PVA solution; (2) In the aforementioned PVA solution, add PVDF of 10-30% and pore-forming agent of 1-10%, where the rest shall be added with the solvent until the total mass fraction sum is 1, stir, heat and dissolve the solution evenly under 80 degree Celsius, to obtain the homogeneous casting solution; (3) The casting solution is filtered, deaerated and coated on a smooth clean glass plate with the coating thickness of 250 ?m in a closed environment for membrane making with a temperature of 20-40 degree Celsius and a humidity of 40-70%, and then after staying in the air for 10-45 s, it is placed in the gel bath of 20-50 degree Celsius to be phase-separated and solidified as the membrane A; (4) The membrane A is treated by the post-treatment process to remove the PVA gel, to obtain the membrane B; (5) The membrane B is washed with water to remove the residual solvent, to obtain the PVDF membrane with network-pore structure.

2. The method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol gel according to claim 1, which is characterized in: that the polymerization degree of PVA in said step (1) is 300-2400 and the alcoholysis degree is 70%-100%.

3. The method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol gel according to claim 1, which is characterized in: that the masking agent in said step (1) is one or several of lithium perchlorate, lithium chloride, lithium nitrate, zinc chloride and calcium chloride.

4. The method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol gel according to claim 1, which is characterized in: that the solvent in said step (1) is one or a combination of several of formamide, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide.

5. The method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol gel according to claim 1, which is characterized in: that the weight-average molecular weight of PVDF in said step (2) is 300-800 thousand Dalton and the intrinsic viscosity is 1.65-1.90.

6. The method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol gel according to claim 1, which is characterized in: that the pore-forming agent in said step (2) is one or a combination of several of polyethylene glycol, hydroxymethyl cellulose, methyl acrylate, polyvinylpyrrolidone, inorganic salt, glycerin and octanol.

7. The method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol gel according to claim 1, which is characterized in: that the solvent in said step (2) is one or a combination of several of triethyl phosphate, formamide, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone and dimethyl sulfoxide.

8. The method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol gel according to claim 1, which is characterized in: that the gel bath in said step (3) is one or a combination of several of pure water gel bath, isopropanol/water mixed solution and solvent/water mixed solution.

9. The method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol gel according to claim 1, which is characterized in: that the post-treatment process in said step (4) is a soaking treatment for 8-36 h in pure water of 40-100 degree Celsius or a treatment for 2-12 h in a sodium hypochlorite solution of 30-60 degree Celsius and 100-5000 ppm, or a combination of the aforementioned two methods.

10. The method for preparing the network-pore polyvinylidene fluoride membrane based on polyvinyl alcohol gel according to claim 9, which is characterized in: that said sodium hypochlorite solution adopts a sodium hypochlorite solution of 30 degree Celsius and 500 ppm.

Description

BRIEF INTRODUCTION OF THE DRAWINGS

[0024] FIG. 1 is a scanning electronic microscope image of cross section of PVDF membrane prepared in embodiment 1 of this Invention;

[0025] FIG. 2 is a scanning electronic microscope image of cross section of PVDF membrane prepared in embodiment 2 of this Invention;

[0026] FIG. 3 is a scanning electronic microscope image of cross section of PVDF membrane prepared in embodiment 3 of this Invention;

[0027] FIG. 4 is a scanning electronic microscope image of cross section of PVDF membrane prepared in embodiment 4 of this Invention;

[0028] FIG. 5 is a scanning electronic microscope image of cross section of PVDF membrane prepared in embodiment 5 of this Invention;

[0029] FIG. 6 is a scanning electronic microscope image of cross section of PVDF membrane prepared in embodiment 6 of this Invention;

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] This Invention will be described in further detail in conjunction with specific embodiments as follows

Embodiment 1

[0031] Firstly, dissolve 2 g PVA in 18 g DMSO organic solvent and stir it under 105 degree Celsius, dissolved evenly. Then, add 54 g DMF and 8 g lithium chloride and continue stirring until dissolved evenly, cooled to the normal temperature. Then, add 15 g PVDF and 3 g polyethylene glycol pore-forming agent, and stir for 12 h under 80 degree Celsius, dissolved evenly and placed for deaeration; on a smooth clean glass plate, make the coating in an air environment with a temperature of 30 degree Celsius and a humidity of 60% by a scraper with a thickness of 250 ?m, where the time for staying in the air shall be controlled as 10 s, and place it in the pure water gel bath of 30 degree Celsius to be phase-separated and solidified as the membrane; then, the obtained membrane is soaked for 24 h in hot water of 70 degree Celsius; finally, remove the residual solvent to obtain the polyvinylidene fluoride membrane with network-pore structure, which has a good network penetrability and a pure water flux of 915 LMH (1 bar, 25 degree Celsius).

Embodiment 2

[0032] Firstly, dissolve 0.5 g PVA in 18 g DMSO organic solvent and stir it under 105 degree Celsius, dissolved evenly. Then, add 54 g DMF and 1 g lithium chloride and continue stirring until dissolved evenly, cooled to the normal temperature. Then, add 10 g PVDF, 10 g PVP pore-forming agent and 6.5 g DMF, and stir for 12 h under 80 degree Celsius, dissolved evenly and placed for deaeration; on a smooth clean glass plate, make the coating in an air environment with a temperature of 30 degree Celsius and a humidity of 60% by a scraper with a thickness of 250 ?m, where the time for staying in the air shall be controlled as 10 s, and place it in the pure water gel bath of 30 degree Celsius to be phase-separated and solidified as the membrane; then, the obtained membrane is soaked for 24 h in hot water of 70 degree Celsius; finally, remove the residual solvent to obtain the polyvinylidene fluoride membrane with network-pore structure, which has a pure water flux of 1007 LMH (1 bar, 25 degree Celsius).

Embodiment 3

[0033] Firstly, dissolve 5 g PVA in 33.5 g DMSO organic solvent and stir it under 105 degree Celsius, dissolved evenly. Then, add 33.5 g DMF and 5 g lithium chloride and continue stirring until dissolved evenly. Then, add 20 g PVDF and 3 g PVP pore-forming agent, and stir for 12 h under 80 degree Celsius, dissolved evenly and placed for deaeration; on a smooth clean glass plate, make the coating in an air environment with a temperature of 20 degree Celsius and a humidity of 40% by a scraper with a thickness of 250 ?m, where the time for staying in the air shall be controlled as 10 s, and place it in the pure water gel bath of 20 degree Celsius to be phase-separated and solidified as the membrane; then, the obtained membrane is soaked for 8 h in hot water of 100 degree Celsius; finally, remove the residual solvent to obtain the polyvinylidene fluoride membrane with network-pore structure, which has a pure water flux of 374 LMH (1 bar, 25 degree Celsius).

Embodiment 4

[0034] Firstly, dissolve 2 g PVA in 22 g DMSO organic solvent and stir it under 105 degree Celsius, dissolved evenly. Then, add 43 g DMF and 2 g lithium chloride and continue stirring until dissolved evenly. Then, add 30 g PVDF and 1 g PVP pore-forming agent, and stir for 12 h under 80 degree Celsius, dissolved evenly and placed for deaeration; on a smooth clean glass plate, make the coating in an air environment with a temperature of 30 degree Celsius and a humidity of 70% by a scraper with a thickness of 250 ?m, where the time for staying in the air shall be controlled as 30 s, and place it in the pure water gel bath of 30 degree Celsius to be phase-separated and solidified as the membrane; then, the obtained membrane is soaked for 8 h in a NaCl0 solution of 30 degree Celsius and 500 ppm; finally, remove the residual solvent by pure water soaking to obtain the polyvinylidene fluoride membrane with network-pore structure, which has a pure water flux of 458 LMH (1 bar, 25 degree Celsius).

[0035] The NaCl0 solution in this Embodiment may also be 60 degree Celsius and 100 ppm; or 30 degree Celsius and 5000 ppm

[0036] The soaking time of NaCl0 solution in this Embodiment may also be 2 h.

Embodiment 5

[0037] Firstly, dissolve 2 g PVA in 31 g DMSO organic solvent and stir it under 105 degree Celsius, dissolved evenly. Then, add 47 g DMF and 2 g lithium chloride and continue stirring until dissolved evenly. Then, add 15 g PVDF and 3 g PVP pore-forming agent, and stir for 12 h under 80 degree Celsius, dissolved evenly and placed for deaeration; on a smooth clean glass plate, make the coating in an air environment with a temperature of 30 degree Celsius and a humidity of 40% by a scraper with a thickness of 250 ?m, where the time for staying in the air shall be controlled as 30 s, and place it in the pure water gel bath of 50 degree Celsius to be phase-separated and solidified as the membrane; then, the obtained membrane is soaked for 24 h in hot water of 60 degree Celsius; finally, remove the residual solvent to obtain the polyvinylidene fluoride membrane with network-pore structure, which has a pure water flux of 547 LMH (1 bar, 25 degree Celsius).

Embodiment 6

[0038] Firstly, dissolve 2 g PVA in 31 g DMSO organic solvent and stir it under 105 degree Celsius, dissolved evenly. Then, add 47 g DMF and 2 g lithium chloride and continue stirring until dissolved evenly. Then, add 15 g PVDF and 3 g PVP pore-forming agent, and stir for 12 h under 80 degree Celsius, dissolved evenly and placed for deaeration; on a smooth clean glass plate, make the coating in an air environment with a temperature of 40 degree Celsius and a humidity of 50% by a scraper with a thickness of 250 ?m, where the time for staying in the air shall be controlled as 45 s, and place it in the 40% isopropanol/water gel bath of 50 degree Celsius to be phase-separated and solidified as the membrane; the obtained membrane is soaked for 36 h in hot water of 40 degree Celsius at first and then it is soaked for 12 h in a NaCl0 solution of 30 degree Celsius and 500 ppm; finally, remove the residual solvent to obtain the polyvinylidene fluoride membrane with network-pore structure, which has a pure water flux of 682 LMH (1 bar, 25 degree Celsius).

[0039] In this Embodiment, the alcohol/water gel bath selects the isopropanol/water gel bath, and other alcohol/water gel baths applicable to this Invention are included in the protection range of this Invention.

[0040] In the aforementioned Embodiments 1-6, the polymerization degree of PVA is 300-2400 and the alcoholysis degree is 70%-100%.

[0041] In the aforementioned Embodiments 1-6, the weight-average molecular weight of PVDF is 300-800 thousand Dalton and the intrinsic viscosity is 1.65-1.90.

[0042] In the aforementioned Embodiments 1-6, the masking agent adopts the preferred lithium chloride, and the others such as lithium perchlorate, lithium nitrate, zinc chloride, calcium chloride or their combinations are applicable to this Invention and are included in the protection range of this Invention.

[0043] In the aforementioned Embodiments 1-6, the solvent prefers DMSO and DMF, and the others such as formamide, N,N-dimethylacetamide, N-methylpyrrolidone, triethyl phosphate or their combinations are applicable to this Invention and are also included in the protection range of this Invention.

[0044] In the aforementioned Embodiments 1-6, the pore-forming agent prefers polyvinylpyrrolidone and polyethylene glycol, and the others such as hydroxymethyl cellulose, methyl acrylate, inorganic salt, glycerin and octanol are applicable to this Invention and are also included in the protection range of this Invention.

[0045] In the aforementioned Embodiments 1-6, the gel bath prefers pure water gel bath and isopropanol/water mixed solution, and the other alcohol/water mixed solutions and solvent/water mixed solutions are also applicable to this Invention and are also included in the protection range of this Invention.

[0046] Although the aforementioned Embodiments have described the technical proposals of this Invention in detail, the technical proposals of this Invention shall not be limited in the aforementioned Embodiments. Without departing from ideas and purposes of this Invention, any modification to the technical proposals of this Invention will be included in the range limited by the Claims of this Invention.