Differences in the interaction of water with starch and chitosan films as revealed by infrared spectroscopy and differential scanning calorimetry

A comparison of starch and chitosan, with respect to the state of absorbed water at low water content was carried out using infrared spectroscopy and differential scanning calorimetry (DSC). The infrared water deformation ban d appears as a simple, symmetric band at 1647 cm(-1) in the case of starch while it is a doublet band (1647-1582 cm(-1)) for chitosan. The band splitt ing observed for chitosan would indicate a stronger interaction of water mo lecules with the hydroxyl group than with the amine group. The observed DSC endotherm is more symmetric for chitosan than for starch samples equilibra ted with air. The differences observed between the thermograms of the two p olymers are explained by means of a molecular mechanism of water removal, u pon heating, based on the different strengths of the interaction of water w ith hydroxyl and amine groups. (C) 1999 Elsevier Science Ltd. All rights re served.