利用超臨界二氧化碳為非溶劑之相分離方法製備多孔性高分子薄膜之研究

Abstract

本研究以超臨界二氧化碳為非溶劑，取代傳統濕式相分離法(phase inversion method)中的有機非溶劑，使高分子溶液進行相分離，製備出非對稱性(asymmetric)的多孔性高分子薄膜。本實驗所選取的高分子為三醋酸纖維素(cellulose triacetate)以及聚醚醯亞胺(polyetherimide)，所選取的溶劑為1,4-dioxane。實驗主要目的為探討不同的操作變因對形成薄膜的孔隙度、平均孔徑大小、及孔徑大小分佈的影響，而本實驗探討的操作變因分別為壓力、溫度以及鑄膜液的濃度。實驗結果顯示，操作壓力高以及操作溫度低時，形成的膜材孔隙度較高，平均孔徑較小且孔徑分佈較窄。本研究在操作溫度為35℃，操作壓力為40 MPa以及鑄膜液濃度10 wt%時，可達膜孔孔徑最小值為0.29μm。 本研究又針對另一種高分子材料聚醚醯亞胺(polyetherimide)進行實驗，藉由改變聚醚醯亞胺鑄的濃度，觀察不同成膜途徑分相後形成的不同膜結構。實驗結果顯示，當鑄膜液濃度由20 wt%減少至2 wt%，所製備出的膜結構由多孔型結構(cellular structure)改變為小球狀堆積結構(nodular structure)。

Porous polymer membranes of cellulose triacetate and polyetherimide have been prepared using a supercritical fluid phase inversion process. 1,4-Dioxane and carbon dioxide were used as the solvent and non-solvent respectively. The dry membranes were directly obtained without post-treatment after the pressure was diminished. Series of experiments were performed at various pressures, temperatures and polymer concentrations. Their effects on the average pore size, pore size distribution and porosity of membranes were investigated. It is concluded that high pressure and lower temperature favor the formation of high porosity and smaller pore size of porous polymer membranes. At the optimal operation temperature (T=35℃), pressure (P=40 MPa) and initial polymer solution concentration (10 wt%), the minimum pore size and maximum porosity were observed as 0.29μm and 88%, respectively. Moreover, we also observed membrane structures via changing polymer solution concentration for poyetherimide/1,4-dioxane/SC-CO2 system in this study. Concentration influences the change in membrane structures from cellular structure to nodules structure.