Dissolution behaviour and solubility of cellulose in NaOH complex solution

Aqueous mixture of NaOH/urea/thiourea at a 8/8/6.5 composition and pre-cooled at −10 °C readily dissolved cellulose to produce stable solutions at relatively high concentrations. The exothermic dissolution process was favored at −2 to 0 °C. Aqueous NaOH/urea/thiourea solution as non-derivatizing solvent broke the intra- and inter-molecular hydrogen bonding of cellulose and prevented the approach toward each other of the cellulose molecules, leading to the good dispersion of cellulose to form solution. The strength of the solvent network structure as well as the interaction between cellulose and solvent decreased as a function of increasing solution temperature. In the semi-dilute entangled solutions (>3.5% concentration), the entropy-driven gelation occurred, and the gel temperature dropped with increasing cellulose contents in the solution. The NaOH/urea/thiourea/H2O was demonstrated to be the most powerful solvent among all aqueous NaOH solutions and this novel solvent does not degrade cellulose even after storage times of up to 1 month.