The influence of maltodextrins on the structure and properties of compression-molded starch plastic sheets

Starch plastic sheets were prepared by compression molding of starch-based plastic granulates. The granulates were prepared by extrusion processing of mixtures of granular potato starch and several maltodextrins (5% w/w) in the presence of glycerol and water as plasticizers and lecithin as melt flow accelerator. The materials were semicrystalline, containing B-type, Vh-type, and Eh-type crystallinity. The properties were dependent on water content. For the materials, a brittle-to-ductile transition occurred at a water content in the range of 11-12%, which was in accordance with the observed glass transition temperature. The structural and mechanical properties were a function of starch composition and maltodextrin source as well as molding temperature. The amount of granular remnants and residual B-type crystallinity decreased with increasing processing temperature. The amount of recrystallized single-helical amylose increased with increasing temperature. At molding temperatures in the range of 180-200°C, a sharp decrease in starch molecular mass occurred. The influence of molding temperature was reflected in a sharp increase in elongation at molding temperature above 160°C and a gradual decrease in elastic modulus. The tensile strength showed an initial small increase up to 160°C and a sharp decrease at higher molding temperatures.