以非溶劑誘導相轉換法製備高孔隙度膜面結構之探討

Abstract

本研究主要工作是以非溶劑誘導相分離法製備高孔隙度膜面結構之探討，製程方法包括濕式法（Wet process）以及蒸氣誘導式法（VIPS process）。選用三種高應用性之材料分別為PEI ( polyetherimide)、PSf ( polysulfone )及CA ( cellulose acetae )；由於所使用之系統或製程中溶劑移除較慢，因此合併速度在薄膜孔洞控制方面極為重要，而本研究則透過添加物或改變溶劑來控制合併行為。 第一部份為濕式法，以乙醇為凝聚劑以避免緻密皮層產生；於PEI/NMP(N-Methyl-Pyrrolidone)系統，可得多孔膜面，孔隙度為30.8%；於PSf/NMP系統中，由於過度成長，膜面轉為緻密，因此透過添加物於鑄模液中，在黏度提升不高時（100cp以下），抑制孔洞合併，孔隙度為35.7%。在CA/NMP系統中，相分離過程表面高分子濃度大幅下降，因而相分離後高分子貧相與富相間的界面張力差異小，此外鑄膜液黏度高於1500cp，抑制孔洞合併，最終膜面孔隙度為46.5%。 第二部份為蒸氣誘導式相分離法，此部份控制不同的VIPS時間，使孔洞成長，再入水固定結構，而達到控制孔洞大小之目的。由於VIPS中溶劑移除較濕式法為慢，因此需設法抑制合併以製備多孔結構。在PEI/NMP系統中相較添加非溶劑GBL(γ-butyrolactone)於鑄膜液中，添加劑2P(2-Pyrrolidinone)較可有效提升黏度(約196cp以上)，此外於PSf系統以2P為溶劑，也可大幅提升黏度(約588cp)，因此抑制合併速度，利於製程上控制孔洞大小。在後續研究中結合VIPS程序再以乙醇為凝聚劑固定結構，最終膜面孔隙度可高達49.6%，且抑制巨型孔洞之生成，並有機會提升薄膜之應用性。

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.