RHEOLOGICAL CHARACTERISTICS OF SEMIDILUTE CHITOSAN SOLUTIONS

The present work is concerned with experimental results on rheological characteristic properties of semi-dilute chitosan solutions in weakly acetic acid. The flow measurements were conducted on solutions of chi tosan of various deacetylation degrees DD (62.8%-86.7%) with changing experimental conditions such as concentration (up to 5 g/100 mL), temp erature (20 degrees C-41 degrees C) and shear rate applied (up to 10(3 ) s(-1)). Chitosan solutions behave generally as a typical non-Newtoni an shear-thinning fluid with a characteristic n-parameter lower than 1 . The rheological n-parameter decreases with decreasing deacetylation degree and increasing solution concentration but it increases with inc reasing temperature. Because of strong intermolecular hydrogen bonding even at low concentration the chitosan macromolecules have a tendency to entangle and to network formation. The density of the molecular en tanglements in the chitosan solution depends on concentration, tempera ture and shear rate applied. An effect of the deacetylation degree on the Huggins viscosity constant related to polymer solvent interaction is found. The most important results refer to the activation energy of viscous flow found from Arrhenius plots. The dependence of the activa tion energy on solution concentration, shear rate and DD is discussed.