Probing cellulose–solvent interactions with self-diffusion NMR: Onium hydroxide concentration and co-solvent effects

The molecular self-diffusion coefficients were accessed, for the first time, in solutions of microcrystalline cel-lulose, dissolved in 30 wt% and 55 wt% aqueous tetrabutylammonium hydroxide, TBAH (aq), and in mixtures of 40 wt% TBAH (aq) with an organic co-solvent, dimethylsulfoxide (DMSO), through pulsed field gradient stim-ulated echo NMR measurements. A two-state model was applied to estimate alpha (i.e., average number of ions that "bind" to each anhydroglucose unit) and Pb (i.e., fraction of "bound" molecules of DMSO, TBAH or H2O to cellulose) parameters. The alpha values suggest that TBA+ ions can bind to cellulose within 0.5 TBA+ to 2.3 TBA+/ AGU. On the other hand, the Pb parameter increases when raising cellulose concentration for TBA+, DMSO and water in all solvent systems. Data suggests that TBAH interacts with the ionized OH groups from cellulose forming a sheath of bulky TBA+ counterions which consequently leads to steric hindrance between cellulose chains.