Solubility of starch and microcrystalline cellulose in 1-ethyl-3-methylimidazolium acetate ionic liquid and solution rheological properties

This study compared the solubility of starch (G50) and microcrystalline cellulose (MCC) in an ionic liquid (IL), 1-ethyl-3-methylimidazolium acetate ([Emim][OAc]), at different temperatures. From SAXS and WAXS analysis, polysaccharides could be totally dissolved in [Emim][OAc]. Fourier-transform infrared (FTIR) spectra showed a similar dissolution mechanism for starch and MCC, which was related to the formation of hydrogen bonds between polysaccharide hydroxyls and acetic anions, causing the breakage of the hydrogen bonding network of the polysaccharide. The polysaccharide-[Emim][OAc] solutions displayed viscosity in the order of G50-[Emim][OAc] < G50/MCC-[Emim][OAc] < MCC-[Emim][OAc], which led to speculation that the molecular chain of G50 and MCC existed concordantly in [Emim][OAc]. The intrinsic viscosity study showed that G50 was much less temperature-sensitive than MCC, and G50/MCC solutions showed intermediate and tuned behaviors. Steady-shear measurements indicated that for dilute solutions, there was a slightly shear-thinning behavior at low shear rates, and high concentration solutions presented an apparent shear-thinning behavior at high shear rates. These characteristics also reflect the different conformation of polysaccharide chains in the solution, which guides the processing of polysaccharide materials and composites for the desired structure and properties.