Thermal behavior of zein-based biodegradable films

In previous work, zein was plasticized with oleic acid to obtain flexible films. However, it was observed that film properties were affected by the preparation method employed. Our objective was to investigate the effect of processing methods on thermal behavior of zein films by differential scanning calorimetry (DSC). Films containing 41% oleic acid were prepared by casting ethanol solutions of its components on flat surfaces or by extrusion of zein resins prepared by cold water precipitation of ethanol solutions of zein and oleic acid. Extrusion was carried out in single-screw or twin-screw extruders. Zein films were finished by hot rolling or heated in a Carver press. DSC thermograms showed large oleic acid melting peaks for cast films, smaller peaks for resin films, and no apparent peaks for heat-treated samples. It was suggested that the resin formation process enhanced zein-oleic acid interactions and promoted plasticization. All samples showed glass transitions at low temperatures.