Viscosity-temperature dependence and activation energy of cellulose solutions

The dependence of cellulose solution shear viscosity as a function of temperature and measurements of solution activation energy are reviewed based on results obtained in our laboratory and elsewhere. Cellulose is not easy to solubilize. Solutions are often forming aggregates and are not stable in time and with temperature variations. This can be highlighted by the calculation of the activation energy of the shear viscosity, a parameter which is very sensitive to any change in the state of the solution during the shear experiments. Changes in the organization of the solution like gelation or cellulose or solvent degradation are phenomena which are strongly influencing the values of activation energy. Cellulose solutions in three classes of solvent, ionic liquids, N-methylmorpholine-N-oxide-monohydrate and (7-9)% NaOH-water with and without additives, were analyzed. Cellulose was of various molecular weights. The plot of the reduced activation energy versus cellulose concentration shows that most points fall within a narrow range of values, with a low downward curved shape, not in agreement of the predictions developed for flexible chains in semi-dilute regime.