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

摘要

Steady state shear flow of different types of cellulose (microcrystalline, spruce sulfite and bacterial) dissolved in l-ethyl-3-methylimidazolium acetate was studied in a large range of concentrations (0-15%) and temperatures (0-100％). 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℃, which is comparable with cellulose dissolved in other solvents, and around 2.5-3 for 60-100℃. 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/A^N-dimethylacetamide at 30℃ and close to 0-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.