Steady state shear flow of different types of cellulose (microcrystalline, spruce sulfite and bacterial) dissolved in 1-ethyl-3-methylimidazolium acetate was studied in a large range of concentrations (0-15%) and temperatures (0-100 degrees C). Newtonian flow was recorded for all experimental conditions; these viscosity values were used for detailed viscosity-concentration and viscosity-temperature analysis. The exponent in the viscosity-concentration power law was found to be around 4 for temperatures from 0 to 40 degrees C, which is comparable with cellulose dissolved in other solvents, and around 2.5-3 for 60-100 degrees C. Intrinsic viscosities of all celluloses decreased with temperature, indicating a drop in solvent thermodynamic quality with heating. The data obtained can be reduced to a master plot of viscosity versus (concentration x intrinsic viscosity) for all celluloses studied in the whole temperature range. Mark-Houwink exponents were determined: they were lower than that for cellulose dissolved in LiCl/N,N-dimethylacetamide at 30 degrees C and close to theta-value. Viscosity-inverse temperature plots showed a concave shape that is dictated by solvent temperature dependence. The values of the activation energies calculated within Arrhenius approximation are in-line with those obtained for cellulose of comparable molecular weights in other solvents.

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In the past decade, ionic liquids (ILs) have received enormous interest as solvents for cellulose. They have been studied intensively for fractionation and biorefining of lignocellulosic biomass, for dissolution of the polysaccharide, for preparation of cellulosic fibers, and in particular as reaction media for the homogeneous preparation of highly engineered polysaccharide derivatives. ILs show great potential for application on a commercial scale regarding recyclability, high dissolution power, and their broad structural diversity. However, a critical analysis reveals that these promising features are combined with serious drawbacks that need to be addressed in order to utilize ILs for the efficient synthesis of cellulose derivatives. This review presents a comprehensive overview about chemical modification of cellulose in ILs. Difficulties encountered thereby are discussed critically and current as well as future developments in this field of polysaccharide research are outlined.