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 comprising: (1) preparing a polyvinyl alcohol (PVA) solution by heating and stirring a mixture under 105 degree Celsius, wherein the mixture comprises a PVA, a masking agent, and a solvent, wherein the PVA has a polymerization degree of 300-2400 and an alcoholysis degree of 70%-100%, and wherein the masking agent is selected from the group consisting of lithium perchlorate, lithium chloride, lithium nitrate, zinc chloride, calcium chloride, and mixtures thereof; (2) adding a polyvinylidene fluoride (PVDF) and a pore-forming agent to the PVA solution, stirring and heating the PVA solution under 80 degree Celsius to obtain a casting solution; (3) filtering and deaerating the casting solution; coating the casting solution on a smooth clean glass plate to form a film having a thickness of 250 m at a temperature of 20-40 degree Celsius and a humidity of 40-70%; drying the film in air for 10-45 s; placing the film in a gel bath at 20-50 degree Celsius to phase-separate and solidify the film to form a membrane A; (4) treating the membrane A in a post-treatment process to remove PVA gel from the membrane A to obtain membrane B; and (5) washing the membrane B with water to obtain the PVDF membrane, wherein the casting solution comprises, based on mass percentage, 0.5-5% of the PVA, 1-8% of the masking agent, 10-30% of the PVDF, 1-10% of the pore-forming agent, and the solvent being the balance of the casting solution.

2. The method of claim 1, wherein the solvent in said step (1) is selected from the group consisting of formamide, N,N-dimethylacetamide, N,N-dimethylformamide, N-methylpyrrolidone, dimethyl sulfoxide, and mixtures thereof.

3. The method of claim 1, wherein the PVDF in said step (2) has a weight-average molecular weight of 300-800 thousand Dalton an intrinsic viscosity of 1.65-1.90.

4. The method of claim 1, wherein the pore-forming agent in said step (2) is selected from the group consisting of polyethylene glycol, hydroxymethyl cellulose, methyl acrylate, polyvinylpyrrolidone, inorganic salt, glycerin, octanol, and mixtures thereof.

5. The method of claim 1, wherein the gel bath in said step (3) is a pure water gel bath or an isopropanol/water mixed solution.

6. The method of claim 1, wherein the post-treatment process in said step (4) comprises soaking the membrane A in pure water at 40-100 degree Celsius for 8-36 hrs or in a 100-5000 ppm sodium hypochlorite solution at 30-60 degree Celsius for 2-12 hrs.

7. The method of claim 6, wherein the post-treatment process in said step (4) comprises soaking the membrane A in a 500 ppm hypochlorite solution at 30 degree Celsius for 2-12 hrs.

Description

BRIEF INTRODUCTION OF THE DRAWINGS

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

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

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

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

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

(6) 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

(7) This Invention will be described in further detail in conjunction with specific embodiments as follows

(8) Embodiment 1

(9) 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).

(10) Embodiment 2

(11) 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).

(12) Embodiment 3

(13) 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).

(14) Embodiment 4

(15) 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).

(16) The NaCl0 solution in this Embodiment may also be 60 degree Celsius and 100 ppm; or 30 degree Celsius and 5000 ppm

(17) The soaking time of NaCl0 solution in this Embodiment may also be 2 h.

(18) Embodiment 5

(19) 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).

(20) Embodiment 6

(21) 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).

(22) 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.

(23) In the aforementioned Embodiments 1-6, the polymerization degree of PVA is 300-2400 and the alcoholysis degree is 70%-100%.

(24) 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.

(25) 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.

(26) 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.

(27) 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.

(28) 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.

(29) 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.