IONIC LIQUID AS SOLVENT FOR A BIOPOLYM ER: ACETYLATION OF HEMICELLULOSES

Ionic liquids (ILs) are designated as "green" solvents because they have extremely low vapor pressure, are noninflammable, and thermally and chemically stable. In view of these distinct advantages, ionic liquids have become an exciting area of research recently. In particular, ionic liquids are capable of dissolving complex macromolecules and polymeric materials with high efficiency. In the context of the combination of the renewable raw material hemicelluloses with the recyclable ionic liquid which can yield a contribution to environment protection, the aim of our work was to investigate the acetylation of wheat straw hemicelluloses reacted with anhydrides in the presence of iodine as a novel catalyst using 1-butyl-3-methylimidazolium chloride ([C4mim]Cl ionic liquid as solvent. The characterization of the acetylated hemicelluloses and unmodified hemicelluloses was comparatively studied by nuclear magnetic resonance (NMR) spectroscopy. Significantly, the dissolution mechanism of hemicelluloses in 1-butyl-3-methylimidazolium chloride ([C4mim]Cl ionic liquid was investigated in detail. Factors of the hemicelluloses dissolution in [C4mim]Cl ionic liquid such as the amount of hemicelluloses and the dissolution temperature were considered. The process of hemicelluloses dissolved in [C4mim]Cl ionic liquid was monitored by polarizing microscope, and the characterization of regenerated hemicelluloses was characterized by various techniques such as Fourier transform infrared (FT-IR), gel permeation chromatography (G PC), and thermo-gravimetry (TG). It was found that [C4mim]Cl ionic liquid actually acted as a non-derivatizing solvent in its dissolution of hemicelluloses. That is to say, hemicelluloses were not involved in a reaction with [C4mim]Cl ionic liquid.