Direct dissolution of cellulose in NaOH/thiourea/urea aqueous solution.

Untreated cellulose was directly and quickly dissolved in NaOH/thiourea/urea aqueous solution. The mechanism of dissolution was investigated by SEM, WXRD and (13)C NMR. The components of this solvent cannot dissolve cellulose on their own, and the interactions between NaOH and urea, as well as between NaOH and thiourea, play an important role in improving the dissolution of cellulose. Moreover, (13)C NMR spectra proved that NaOH, thiourea, and urea were bound to cellulose molecules, which brings cellulose molecules into aqueous solution to a certain extent and prevents cellulose macromolecules from associating. (13)C NMR spectra of the cellulose solution show that this novel mixture is a direct solvent. Optical microscopy and CP MAS (13)C NMR were used to study the process of dissolution. The results reveal that cellulose is dissolved completely and that cellulose I (cotton linter) first changes to amorphous cellulose chains in solution, and then to cellulose II during regeneration. Moreover, a new, more effective dissolution method is proposed, as confirmed by dynamic rheology measurements.