Phase diagram, solubility limit and hydrodynamic properties of cellulose in binary solvents with ionic liquid

Cellulose solubility phase diagrams in two binary solvents based on 1-ethyl-3-methylimidazolium acetate (EmimAc) mixed with water and with dimethylsulfoxide (DMSO) were built. The minimal amount of EmimAc molecules needed to dissolve cellulose is 2.5–3 moles per anhydroglucose unit. This proportion allows calculation of the maximal cellulose concentration soluble in EmimAc–DMSO at any composition; in EmimAc it is around 25–27 wt%. Water forms hydrogen bonds with EmimAc and thus competes with cellulose for ionic liquid; the solubility of cellulose in EmimAc–water is much lower than that in EmimAc–DMSO. Hydrodynamic properties of cellulose in two solvent systems were compared. In EmimAc–DMSO cellulose intrinsic viscosity practically does not depend on DMSO content as predicted by the phase diagram. The intrinsic viscosity in EmimAc–water first increases with water content due to cellulose self-aggregation and then abruptly decreases due to coagulation.