Preparation of polymer membranes with highly porous surface structure by non-solvent induced phase separation method
Date Issued
2007
Date
2007
Author(s)
Lee, Wan-Yu
DOI
zh-TW
Abstract
The present work was to prepare polymer membranes with highly porous surface structure by non-solvent induced phase separation method, including wet process and vapor induced phase separation. Three highly applied materials, PEI, PSf and CA were chosen. In some systems or during the membrane preparation process, because the solvents were hard to be removed, the coarsening rate was important for controlling the pore size. Therefore the present work was to reduce the coarsening phenomena by additives or changing solvents in the casting solution.
In first part, wet process method was used. Ethanol was chosen as coagulant to prevent the formation of dense surface. In PEI/NMP system, a porous surface with 30.8% porosity was obtained. In PSf/NMP system, because of further coarsening a denser surface was obtained. By adding non-solvent in the casting solution, while the viscosity was lower than 100cp, the coarsening phenomenon was reduced and a porous surface with 35.7% porosity was obtained. In CA/NMP system, during phase separation process the polymer concentration on the surface decreased, therefore the interfacial tension between two phases was smaller. Also the viscosity was higher than 1500 cp, as a result a slower coarsening rate and the porosity reached 46.5%.
In second part, the vapor induce phase separation method was used. By controlling different VIPS time, the growth of polymer poor phase could be controlled. Then water was chosen as coagulant to solidify the structure to prepare membranes with different pore sizes. Because the solvents were harder to be removed compared the wet process, it would be necessary to reduce the coarsening rate and a micron porous surface membrane could be prepared. In PEI/NMP system, by adding non-solvent 2P, the viscosity increased efficiently ( about 196cp ) compared the casting solution by adding non-solvent GBL. Also in PSf system, 2P was chosen as solvent, the viscosity could increase efficiently ( about 588cp ). Therefore the coarsening rate was slower, and hence it was easier to control the membrane structure. Finally, the method combining the VIPS process and wet process with coagulant ethanol could obtain porous surface approaching 49.6% porosity, suppress the formation of macrovoids, and have chance to improve the application of membranes.
Subjects
非溶劑誘導相分離法
聚醚醯亞胺
聚碸
醋酸纖維素
合併速度
high porosity
non-solvent induced phase separation process method
polyetherimide
polysulfone
cellulose acetate
coarsening rate
Type
thesis
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