聚乙烯醇多孔膜之製備

Preparation of Porous PVA Membranes

吳思樺(Szu-Hua Wu)

指導教授 ： 王大銘

國立臺灣大學/工學院/化學工程學研究所/碩士(2006年)

https://doi.org/10.6342/NTU.2006.02820

摘要

本研究將聚乙烯醇（polyvinyl alcohol，PVA）的水溶液浸入凝聚槽中利用溼式相轉換法來製備親水性多孔膜。所選用的凝聚劑可分為兩種：(1) 飽和鹽類水溶液；(2) 醇類，包括甲醇、乙醇、正丙醇及正丁醇。
實驗結果顯示，以氯化鈉水溶液作為凝聚劑所製備而成的多孔膜，在乾燥時會因水與高分子界面張力的影響而收縮，導致多孔結構的破壞而成為緻密膜。此收縮現象與乾燥時膜中所含水份所造成的 Tg下降效應（Tg depression）有關，這是由於膜孔中的水對PVA具有塑化效應（plasticization），造成高分子鏈容易運動而導致的現象。要避免乾燥時的收縮，除了可利用冷凍乾燥來固化膜結構之外，亦可以利用醇類將膜孔中的水份置換出來，由於醇類是PVA的非溶劑，可以減少Tg下降的效應而固化膜結構。
研究中亦探討以醇類作為非溶劑的成膜過程，結果顯示不同碳數的醇類所製備出的膜結構也不同。藉由分析高分子和非溶劑間的親和性，並利用傅立葉轉換顯微紅外線光譜儀（FT-IR microscope）量測成膜過程中各成份的濃度變化，來探討醇類碳數對膜結構的影響。在PVA/H2O/強非溶劑的系統中，成膜時表面溶劑會快速被移除而形成高分子濃度較高的膠化層（gel layer），進而形成較緻密的表面結構。而在PVA/H2O/弱非溶劑的系統中，成膜時表面溶劑與非溶劑的質傳交換會使得非溶劑濃度提高而進入相分離區，進而形成多孔的表面結構。

關鍵字

聚乙烯醇 ； 濕式相轉換法 ； 孔洞膜

並列摘要

Porous hydrophilic poly (vinyl alcohol) (PVA) membranes were prepared by the phase inversion method. Two kinds of coagulant were used in the present work: sodium chloride aqueous solution and alcohols, including methanol, ethanol, 1-propyl alcohol, 1-butyl alcohol.
Experimental results showed that porous membranes, using NaCl(aq) as coagulant, contracted to form dense structure at the drying stage because of Tg depression resulted from plasticization caused by the remaining water in the membrane before drying. The contraction during drying stage can be presented either by freeze drying or by replacing water with appropriate alcohols, which have lower degree of plasticization.
We have also investigated the possibility of using alcohols as coagulant because of their nonsolvency to PVA to prepared membranes. Analysis of the affinity between polymer and measurement of concentration change during membrane forming provide insight into how the porous structure was formed. For a PVA/H2O/strong nonsolvent system, the high solvent outflux resulted in a of high polymer concentration layer (gel layer), and then turned into a dense skin. On the other hand, for a PVA/H2O/weak nonsolvent system, the influx of coagulant to the cast film dominated, resulting in phase separation near the surface and a porous surface structure.

並列關鍵字

polyvinyl alcohol ； immersion precipitation ； porous membrane

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