Rheological characteristics of semi‐dilute chitosan solutions

Abstract 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 chitosan of various deacetylation degrees DD (62.8%–86.7%) with changing experimental conditions such as concentration (up to 5 g/100 mL), temperature (20°C–41°C) and shear rate applied (up to 103s−1). Chitosan solutions behave generally as a typical non‐Newtonian 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 increasing 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 entanglements in the chitosan solution depends on concentration, temperature 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 activation energy on solution concentration, shear rate and DD is discussed.