Thermo‐Reversible Cellulose Micro Phase‐Separation in Mixtures of Methyltributylphosphonium Acetate and γ‐Valerolactone or DMSO

Abstract

We have identified cellulose solvents, comprised of binary mixtures of molecular solvents and ionic liquids that rapidly dissolve cellulose to high concentration and show upper-critical solution temperature (UCST)-like thermodynamic behaviourupon cooling and micro phase-separation to roughly spherical microparticle particle-gel mixtures. This is a result of an entropy-dominant process, controllable by changing temperature, with an overall exothermic regeneration step. However, the initial dissolution of cellulose in this system, from the majority cellulose I allomorph upon increasing temperature, is also exothermic. The mixtures essentially act as 'thermo-switch-able' gels. Upon initial dissolution and cooling, micro-scaled spherical particles are formed, the formation onset and size of which are dependent on the presence of traces of water. Wideangle X-ray scattering (WAXS) and 13 C cross-polarisation magicangle spinning (CP-MAS) NMR spectroscopy have identified that the cellulose micro phase-separates with no remaining cellulose I allomorph and eventually forms a proportion of the cellulose II allomorph after water washing and drying. The rheological properties of these solutions demonstrate the possibility of a new type of cellulose processing, whereby morphology can be influenced by changing temperature.

The dialkylcarbonate route to ionic liquids: purer, safer, greener?

“…cellulose concentration, solvent composition, temperature and cooling rate, etc. 102,103 Guglielmero et al synthesized and studied the thermal properties of several dicarboxylate ionic liquids. Although the majority of them were made from halide-based ionic liquid precursors, with an expensive anion exchange step (based on silver salt, or ion exchange resin), those with a butylmethylimidazolium cation were reached thanks to the DMC route.…”