(729f) Physical State of Dry Native Cellulose in Solution with Ionic Liquids

Cellulose is the most abundant renewable natural polymer on earth that does not easily dissolve in common solvents. There has been a hunt on novel solvents that can dissolve cellulose completely, and certain ionic liquids (ILs) are found to be capable of doing so. Ionic liquids dissolve native cellulose by breaking hydrogen bonds without derivatizing it. Their low vapor pressure and ability to be regenerated and reused for many process cycles make ionic liquids strong candidates in replacing traditional solvents for cellulose. It was assessed previously that solutions of cellulose in 1-Ethyl-3-methylimidazolium acetate (EMImAc) and 1-Ethyl-3-butylimidazolium chloride (BMImCl) can be dried by placing solutions at 80℃ for 20 minutes [1]. The intrinsic viscosities of these dried solutions measured in 2 RH% environment propose less cellulose swelling at higher temperatures. Contrary to the previous findings that reported 50% decrease in intrinsic viscosity over the span of 100℃, intrinsic viscosity in low moisture environment does not drop as much and this indicates the probable elimination of water effects. The time-temperature-superposition mastercurves of cellulose/IL solutions demonstrate that the amount of associations cellulose has with ionic liquids depends on multiple factors including ionic liquid’s anion size. Mastercurves of these solutions also show the mobility of ionic liquids chain, that is also reflected in the changing glass transition temperature of solutions with different cellulose content. Perturbing the ionic regularity of strongly-coupled systems like ionic liquids by cellulose addition causes the glass transition temperature to decrease before entanglement effect of cellulose chains take off. Aging of cellulose/IL solutions are quantified through the zero-shear viscosity drop with time, indicating cellulose chain scission when stored at elevated temperatures. Depolymerization of cellulose in EMImAc and BMImCl happens during storage at 80℃ and 40℃, causing a decrease in intermolecular entanglement and friction that translates to reduction in zero-shear viscosity.

[1] Nazari, B.; Utomo, N. W.; Colby, R. H. Biomacromolecules 2017, 18(9), 2849–2857.