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 band 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 splitting observed for chitosan would indicate a stronger interaction of water molecules with the hydroxyl group than with the amine group. The observed DSC endotherm is more symmetric for chitosan than for starch samples equilibrated with air. The differences observed between the thermograms of the two polymers are explained by means of a molecular mechanism of water removal, upon heating, based on the different strengths of the interaction of water with hydroxyl and amine groups.