Rheological Properties of Cellulose/Ionic Liquid Solutions: From Dilute to Concentrated States

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 °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 °C, which is comparable with cellulose dissolved in other solvents, and around 2.5−3 for 60−100 °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 × 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 °C and close to θ-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.