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.
ASJC Scopus subject areas
- Chemical Engineering(all)
- Industrial and Manufacturing Engineering