Improving physical properties and retrogradation of thermoplastic starch by incorporating agar

To develop functional and sustainable packaging materials from starch and to enhance their properties, agar was added to thermoplastic corn starch (TPS) in a wide concentration range and the products were prepared either by casting or melt blending with a high glycerol content. The role of agar in the mechanical and barrier performance of films, as well as the compatibility of TPS and agar was systematically evaluated. In addition, the retrogradiation of starch in various blends after long storage periods was widely characterized. Results proved that the addition of agar to TPS resulted in films with promising barrier and tensile properties. Stiffness and strength increased considerably by increasing agar content, while deformability of blends was better than those of pure TPS. Agar incorporation decreased water permeability and solubility and improved light transmittance. Retrogradation of the dry blends was significantly smaller than that of pure TPS owing to the strong starch/agar interaction.