The kinetics of chitosan depolymerisation at different temperatures

The stability (in terms of molar mass) of chitosan potentially plays an important role in its behaviour and functional properties in a wide range of applications and therefore any changes over time must be understood. The weight-average molar masses and intrinsic viscosities of chitosan solutions at different temperatures (4, 25 and 40 °C) have been investigated using size exclusion chromatography coupled to multi-angle laser light scattering (SEC-MALLS) and a "rolling ball" viscometer respectively. The weight-average molar mass (M_w) and the intrinsic viscosity ([η]) both decrease with increased storage time, although this phenomenon is more pronounced at elevated temperatures. Good correlation was found between the changes in molar mass and intrinsic viscosity with time and these parameters were used to determine the depolymerisation constant (k) and the activation energy (E_a). Knowledge of the effect of storage conditions (e.g. temperature) is important in the understanding the stability of chitosan solutions, but whether or not chitosan depolymerisation will be detrimental to its intended application will depend on the functional significance of the changes that occur.