Plasticized waxy maize starch: effect of polyols and relative humidity on material properties.

The plasticizing effect of different polyols such as glycerol, xylitol, sorbitol, and maltitol on waxy maize starch was investigated. The concentration of plasticizer was fixed at 33 wt % (dry basis of starch). The structure and mechanical performance of resulting films conditioned at different relative humidity levels were studied in detail. The effect of the plasticizer on the glass-rubber transition temperature (T(g)) and crystallinity was characterized using differential scanning calorimetry. It was found that T(g) decreases with increasing moisture content and decreasing molecular weight of the plasticizer. The water resistance of starch increased steadily with the molecular weight of the plasticizer and was directly proportional to the ratio of the end to total hydroxyl groups. As the molecular weight of the plasticizer increased, the brittleness of the dry system increased. However, the use of high molecular plasticizer allowed good mechanical properties of the moist material to be obtained in terms of both stiffness and elongation at break.