Dissolution of Cellulose: Are Ionic Liquids Innocent or Noninnocent Solvents?

Cellulose is a naturally abundant and readily accessible substrate for large scale biorefinery technologies. There has been a significant focus on ionic liquids as alternative solvents for the valorization of cellulosic substances. Ionic liquids dissolve cellulose in varying degrees, facilitating ready chemical transformations. However, there is no self-contained set of knowledge and information on the influence (or not) of the simple dissolution process on the cellulose molecule. Herein, we detail the dissolution, recovery, and characterization of cellulose in various classes of ionic solvents in a systematic study. This provides a view of the stability of cellulose in each solvent. We consider the major classes of ionic liquids commonly employed for cellulose chemistry, the dissolution in zinc chloride hydrate systems, quaternary ammonium salts, and deep eutectic solvents under varied processing conditions. We regenerate cellulosic material from the solvent and characterize the polymer employing gravimetric analysis, IR spectroscopy, and size exclusion chromatography. Surprisingly, most ionic liquids employed caused reduction in the MW of the cellulose.