Thermally Triggered Phase Separation of Organic Electrolyte–Cellulose Solutions

Organic electrolyte solutions (OES)—binary mixtures of an ionic liquid (IL) with a neutral polar aprotic co‐solvent—are being recognized as excellent candidate solvents for the dissolution, derivatization, and sustainable processing of cellulose. These solutions exhibit the beneficially combined properties of rapid‐to‐instantaneous cellulose dissolution, raised thermal stability, and reduced viscosity, compared to cellulose solutions in the parent ILs. Herein, we report the reversible, thermally triggered phase separation of cellulose solutions in 1‐ethyl‐3‐methylimidazolium acetate with 1,3‐dimethyl‐2‐imidazolidinone. In these solutions, cellulose drives the process of phase separation, resulting in a lower, IL‐rich layer in which the biopolymer is segregated. In turn, the upper phase is enriched in the neutral co‐solvent. We show that the temperature of phase separation can be fine‐tuned by modification of mole fractions of IL, co‐solvent, and cellulose. This finding holds promise for the design of strategies for separation and solvent recycling in cellulose chemistry.