Aging effects on sorbitol- and non-crystallizing sorbitol-plasticized tapioca starch films

The effect of aging on the properties of tapioca starch films plasticized with either sorbitol (S) or non-crystallizing sorbitol (NCS) was investigated in this study. Tapioca starch, plasticizer and deionized water were mixed, heated, cast on high-density polyethylene plates and dried at ambient conditions. The results showed that S was more effective in plasticizing fresh starch film than NCS. However, sorbitol crystallization was observed in S-plasticized starch film after one month of storage, while there was no crystallization observed in NCS-plasticized starch film after two months of storage. Mechanical properties of both S- and NCS-plasticized starch films changed significantly with time, but with less change in the NCS-plasticized films. Tensile strength, elastic modulus and toughness increased over time; conversely, elongation decreased. Additionally, the water vapor transmission rate decreased as storage time increased. The fact that mechanical properties of both S- and NCS-plasticized films changed is likely due to an increase in crystallinity of the starch in the films with time.