Effects of Different Ionic Liquids as Green Solvents on the Formation and Ultrafiltration Performance of CA Hollow Fiber Membranes
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- 作者：Ding Yu Xing ; Wen Yi Dong ; Tai-Shung Chung
- 刊名：Industrial & Engineering Chemistry Research
- 出版年：2016
- 出版时间：July 13, 2016
- 年：2016
- 卷：55
- 期：27
- 页码：7505-7513
- 全文大小：566K
- 年卷期：0
- ISSN：1520-5045
文摘
In this work, we have examined and compared the interactions between cellulose acetate and different ionic liquids at a molecular level and explored their effects on dope rheology, hollow fiber morphology, and performance. Ionic liquid, 1-ethyl-3-methylimidazolium acetate ([EMIM]OAc), was found to interact with cellulose acetate (CA) more closely with intensive hydrogen bonds than 1-ethyl-3-methylimidazolium thiocyanate ([EMIM]SCN). Thus, the CA/[EMIM]OAc solution exhibits a more pronounced charge-ordered network than the CA/[EMIM]SCN solution. In addition, the former does not obey the Cox–Merz rule, whereas the latter obeys the rule with its shear viscosity η identical to its complex viscosity |η*| at the equivalent shear rate and angular frequency. These dissimilar factors have contributed to an instantaneous liquid–liquid demixing and resulted in a dense outer skin surface and a porous cross-sectional structure comprising macrovoids for the CA/OAc membrane. In contrast, the CA/SCN membrane has a looser interconnected nodular structure resulting from the delayed liquid–liquid demixing. The effects of spinning conditions on membrane properties have been determined. The higher dope flow rate and take-up speed result in smaller pore size. [EMIM]OAc is a more practical solvent than [EMIM]SCN to fabricate CA hollow fibers with a broader choice of spinning parameters. The newly developed CA/OAc membranes have PWP values of 230 and 260 L/(m2 bar h) and pore sizes of 10–27 nm. This work may provide useful insights to develop polymeric membranes using ionic liquids as solvents and facilitate a greener fabrication method in the membrane industry.