Microcrystalline cellulose processing with supercritical CO2 in alkylmethlimidazolium chloride ionic liquids

Cellulose processing with ionic liquids (ILs) in supercritical media has been investigated. ILs are a group of salts consisting only of cations and anions with environmentally friendly features: e.g. negligible vapour pressure, non-flammable and high thermal stability. In particular, ILs of the alkylmethylimidazolium chloride family are able to solubilise high amounts of cellulose. Nevertheless these solutions present challenges related to the high viscosities and melting points of these ILs. In this work CO2 was used to reduce the melting point and viscosity of the ILs, thereby improving acetylation reactions. The production of cellulose acetate polymer was achieved by acetylation of microcrystalline cellulose dissolved in [Amim]Cl using acetic anhydride as reagent. The degree of substitution has been studied in different reaction medium: absence of CO2, supercritical CO2 media (scCO2), with a catalyst scandium III triflate (sc(OTf)3) and scCO2 + sc(OTf)3.