Cellulose Dissolution in a Mixed Solvent of Tetra(n-butyl)ammonium Hydroxide/Dimethyl Sulfoxide via Radical Reactions

9.19 wt % of microcrystalline cellulose (MCC) could be dissolved in a new mixed solvent of tetra(n-butyl)ammonium hydroxide (TBAH; 20 wt %) and dimethyl sulfoxide (DMSO; 80 wt %) within 5 min at room temperature. The ratio of TBAH in the mixed solvent (WTBAH) is found to exert great influence on the solubility of cellulose. Dissolution mechanism relative to radical reactions has been proposed according to electron spin resonance (ESR) and UV–vis results, showing positive correlation between cellulose solubility and the radical amount produced in the mixed solvent (i.e., WTBAH). Partial degradation of the reducing AGU terminals via radical attack could be observed, followed by recombination of cellulose chain radicals, resulting in amorphous structures of all regenerated cellulose with higher average degree of polymerization values. Therefore, dissolution mechanism with regard to radical reactions has been proposed in this letter, supplementing the predominant electron donor–acceptor complexation theory.