Cellulose–solvent interactions from self-diffusion NMR

Molecular self-diffusion coefficients were measured in solutions of microcrystalline cellulose (MCC) and dissolving pulp, in 40 wt% aqueous tetrabutylammonium hydroxide (TBAH), using pulsed field gradient stimulated echo NMR. From the cellulose diffusion coefficients, a weight averaged radius of hydration < R-h >(w) = 6.1 nm for MCC and < R-h >(w) = 15 nm for pulp were obtained. Water and TBA(+) ions show a significantly different dependence on the cellulose concentration, revealing different molecular interactions with the polymer. Water-cellulose are essentially excluded volume. TBA(+) ions, on the other hand, bind to cellulose with approximately 1.2 TBA(+) ions per glucose unit.