Characteristic Features of Chitosan/Glycerol Blends Dynamics

Abstract

Abstract Summary: The phase relaxation behavior of chitosan and its blends with glycerol has been studied by dynamic mechanical thermal analysis (DMTA) and differential scanning calorimetry (DSC) techniques. The analysis of DMTA spectra of chitosan leads to recognition of two molecular relaxations in chitosan and its blends. The analysis of enthalpic and entropic contributions suggest that both processes involve a large degree of cooperativity. At high temperature, the α ‐relaxation has been assigned to its glass transition temperature T g on the basis of the stiffness of the chitosan backbone, the high activation energy, and the plasticization with glycerol. T g may be originated by torsional oscillations between two glucopyranose rings across a β ‐1,4‐glycosidic oxygen and a cooperative hydrogen bond reordering. The other is a low temperature β ‐relaxation that, in chitosan, has been associated to motions of lateral pendant groups in the glucopyranose rings and in the blends to the movements of a glycerol hydrogel bonded to the lateral groups of chitosan. Its composition dependence has been modeled by means of the Schneider‐Riegel‐Penzel equation in which the interactions among functional groups when a glass‐forming liquid is adsorbed to a stiff, highly functionalized macromolecule such as chitosan are taken into account. A three‐dimensional plot representing the tan δ for a series of chitosan and chitosan/glycerol blends as a function of temperature and composition. magnified image A three‐dimensional plot representing the tan δ for a series of chitosan and chitosan/glycerol blends as a function of temperature and composition.