Oxidized potato starch based thermoplastic films: Effect of combination of hydrophilic and amphiphilic plasticizers

Different combinations of hydrophilic (glycerol and water) and amphiphilic (isoleucine) plasticizers were studied in the production of thermoplastic starch (TPS) powders and films from oxidized potato starch. All powder samples had an irregular and shrivelled morphology. In all mixtures containing isoleucine, this additive exuded from the starch matrix and re-crystallized during spray drying, resulting in hollow particles. The crystallinity and moisture sensitivity of freshly prepared films depended on the isoleucine content in the plasticizer formulation. Increasing the content led to a decrease in moisture absorption. Isoleucine formulated films showed the best tensile strength, whereas glycerol-rich ones showed better strain at break values. All glycerol plasticized formulations and the spray dried non-modified starch were amorphous. Glycerol reduced the glass transition temperature to 128°C and glycerol formulated films showed the highest moisture uptake due to its hydrophilic nature. At a relative humidity (RH) of 50%, the rate of retrogradation was low, but at RH 100% all TPS films showed a high rate of retrogradation.