Cellulose and cellulose acetate membranes were fabricated by phase inversion from their solutions in 1-ethyl-3-methylimidazolium acetate ([EMIM] OAc), or its mixture with dimethyl sulfoxide (DMSO). Inclusion of DMSO in the solution decreased crystallinity and rejection for both polymers. When cellulose solutions were coagulated in ethanol crystallinity and rejections were lower, and cellulose acetate membranes coagulated in ethanol had a loose, macroporous morphology, which was attributed to the poor nonsolvent strength of ethanol for this polymer. All cellulose membranes, when dried, performed similarly in rejecting Blue Dextran (20 kDa) by over 90% and Bromothymol Blue by around 80%. On the other hand, when these membranes were used without drying, Bromothymol Blue rejections decreased with increasing DMSO content in solution and with changing of nonsolvent from water to ethanol, implying the presence of a microporous structure which collapses to a similar dense structure upon drying for all cases. Phase inversion rate of both polymers was slower in ethanol, which was attributed to the lower diffusivity of ethanol compared to water due to its larger size. The viscosity of the solvent media, which differed by an order of magnitude between [EMIM]OAc and [EMIM]OAc-DMSO mixtures, on the other hand, did not have a measurable influence on the phase inversion rate. (C) 2017 Elsevier Ltd. All rights reserved.