Steady-shear rheology of concentrated chitosan solutions

The rheological properties of 0.5 - 2.0% (wt/wt) chitosan solutions in steady-shear were investigated as a function of temperature (25C - 45C), acid type (acetic, lactic, and hydrochloric), and ionic strength (0 and 0.2 M NaCI) to determine their flow behavior. Viscosity and normal forces have been determined over a wide range of shear rates and the results are presented using appropriate master curves for the temperature and concentration effects. For the experimental conditions studied, chitosan solutions behaved like non-Newtonian viscoelastic shear-thinning fluids. They show a low-shear rate Newtonian plateau and a high-shear rate non-Newtonian region. All material functions (viscosity and primary normal stress) decrease with an increase in temperature and a decrease in chitosan concentration. The most important parameter affecting the rheology of the solutions has been found to be salt addition, particularly for chitosans dissolved in weak acids where electrostatic effects are believed to be important.