Cellulose Preferentially Dissolved over Xylan in Ionic Liquids through Precise Anion Interaction Regulated by Bulky Cations

Due to its crystallinity, cellulose is one of the least soluble natural polymers. There are no solvents that can dissolve cellulose while not dissolving its readily soluble analogues, such as xylan. In this study, ionic liquids were selected as the solvent because the solvent–polysaccharide interaction can be precisely regulated by bulky cations. The bulky ionic liquids dissolved cellulose but not xylan at 100 °C within 60 min. Further investigation revealed that difference in dissolution behavior, and while the dissolution time of cellulose depended only on diffusivity, that of xylan depended on cation bulkiness as well as diffusivity. Molecular dynamics simulations and subsequent analyses showed that polysaccharides cannot form the most stable state in bulky ionic liquids because of the disorder of hydrogen bonds, supporting the difference in dissolution behavior. Our protocol for preferential dissolution is applicable to other natural materials.