Thermal behavior of zein sheets plasticized with oleic acid

Zein, extracted from underutilized corn gluten meal may serve as an alternative starting material for fabrication of biodegradable packaging. Zein plasticized with oleic acid may be formed into flexible and water-resistant sheets. Our objective was to investigate the effect of plasticization on thermal behavior of zein sheets employing differential scanning calorimetry (DSC). Zein sheets were rolled from a resin prepared by dispersing zein and oleic acid in aqueous alcohol followed by the recovery of the formed moldable compound by precipitation with water. Sheets were later replasticized with additional oleic acid to increase ductility. DSC thermograms were used to investigate zein-oleic acid interactions in zein sheets. DSC endotherms were attributed to melting of free oleic acid or to the dissociation of zein-oleic acid bonds. Plasticized sheets contained bound and free oleic acid. Further heat-treatment of plasticized sheets apparently resulted in zein absorption of free oleic acid. However, high temperatures were believed to cause dissociation of some zein-oleic acid bonds formed during replasticization.