Transition of cellulose crystalline structure in biodegradable mixtures of renewably-sourced levulinate alkyl ammonium ionic liquids, γ-valerolactone and water

Abstract

In this work, we report that combination of levulinate as a renewably sourced anion with short chain alkyl ammonium as a cation yields room temperature ionic liquids that are capable of dissolving up to 10 wt% of microcrystalline cellulose. This dissolution results in a change of the cellulose crystalline structure from cellulose I to cellulose II, a pre-requisite step known to significantly improve the accessibility of cellulose to enzymes. As compared to previous methodologies, such ILs tolerate the presence of up to 18 wt% of water. Hence technical grade ILs can be used, thus avoiding the energy-consuming drying process generally required with traditional ILs before dissolution experiments. In addition, such ILs can be mixed with 20 wt% of γ-valerolactone, a renewably-sourced co-solvent, resulting in an improvement of the cellulose dissolution up to 20 wt% while concomitantly increasing the sustainability of these media. Finally, prepared ILs were proved to be biodegradable according to the OCDE 301F directive, thus opening a promising route for the pre-treatment of cellulose with a higher eco-efficiency.