The effect of pressure on cation-cellulose interactions in cellulose/ionic liquid mixtures

Cation-cellulose interactions in binary mixtures of [EMIM][OAc] and cellulose have been investigated using high-pressure infrared spectroscopy. At low concentrations of cellulose, almost no changes were observed in the imidazolium C(2)-H frequency; on the other hand, at high concentrations of cellulose, increases in the C(2)-H vibration frequency were observed under ambient pressure. As the pressure was elevated, the imidazolium C(2)-H absorption of the [EMIM][OAc]/cellulose mixtures underwent band-narrowing and blue-shifts in the frequency. These observations suggest that high pressures may strengthen the hydrogen bonds formed between C(2)-H and cellulose, possibly forcing the cellulose to dissociate clusters of ionic liquid through enhanced cation-cellulose interactions. In contrast to the cation-cellulose interaction results, the COO(-) absorption of the anion does not show dramatic changes under high pressures. Our results indicate the possibility of enhanced cation-cellulose interactions through pressure elevation, demonstrating that high pressures may have the potential to tune the relative contributions of cation-cellulose and anion-cellulose interactions in cellulose/ionic liquid mixtures.