This work reports for the first Lime the degradation mechanism of cellulose triaccrate membranes exposed to ethanol-water mixtures. The process of membrane degradation is elucidated by XPS, ATR-FTIR, NMR to proceed via a classical Claisen-type condensation followed by water condensation reactions leading to the formation of the acetoacetate and ether pendant groups in the polymeric matrix. This work provides vital insight into the chemical stability and durability of the cellulose ester-based membranes for long term operation in liquid separation applications involving ethanol solutions. (C) 2013 Elsevier B.V. All rights reserved