Activation of cellulose by 1,4-dioxane for dissolution in N,N-dimethylacetamide/LiCl

N,N-Dimethylacetamide/lithium chloride (DMAc/LiCl) mixture is a popular solvent system used for cellulose dissolution, analysis, and derivatization. However, a pre-treatment (activation) procedure is needed for most celluloses to dissolve readily in DMAc/LiCl. Here, an optimized version of the activation protocol based on solvent exchange to 1,4-dioxane was introduced. Its universality was demonstrated by successful activation and dissolution of six different celluloses (AVICEL, Sigmacell, cotton linters, Encell, Lincell, and Whatman paper). Dissolution times varied significantly for different cellulose types and also depended on factors such as the drying method employed or the water removal step inclusion/omission. Dioxane-activated celluloses were analyzed with a variety of methods. SEC measurements indicated low destructivity of the dioxane activation method. The infrared spectroscopy analysis showed that dioxane remained adsorbed on cellulose even after rigorous drying. In addition, upon dioxane activation, stagnation or a slight increase in the total order index of celluloses was observed. This observation was in accordance with the crystallinity index changes determined by solid-state NMR. Finally, scanning electron microscopy revealed disintegration of AVICEL particles and defibrillation of fibrous celluloses upon dioxane activation; Sigmacell remained apparently unchanged.