Abstract: Ionic liquids (ILs) have been used for dissolution of cellulose with its further regeneration in a form of fibers, for example, in the textile production. Organic electrolyte solutions (OESs) are used instead of pure ILs in some cases. OESs are binary mixtures of an IL and a polar aprotic co-solvent, which can show better dissolution capacity for cellulose than that of pure ILs. We have used OESs consisting of tetraalkylphosphonium acetate IL and dimethyl sulfoxide (DMSO) or γ-valerolactone (GVL) as co-solvents. Cellulose is first dissolved in these OESs at 120°C and then regenerated upon cooling in the course of micro and macro phase separation. This phenomenon resembles the upper-critical solution temperature (UCST) type thermodynamic transition though it is much slower, which allows for the cellulose crystallization. The regeneration process is a consequence of multi-parameter interdependence, where the polymer characteristics, OES composition, temperature, cooling rate and equilibration time all play their roles. Depending on the experimental conditions, cellulose regenerates in the form of either individual spherical particles/aggregates, or multi particles clusters or macroscopic gels. The formation of the spherical multi molecular aggregates below the phase separation boundary was systematically investigated. The regenerated cellulose particles are semi-crystalline and composed of Cellulose II and amorphous cellulose.

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