Formation of starch films with varying crystallinity

Self-supporting, smooth and translucent films were prepared by drying starch gels at various temperatures and air humidities. Light microscopy showed different structures among the films dried at elevated temperatures compared with those dried at room temperature. B-type crystallinity, varying from almost none to 23%, developed upon film formation, as determined by wide-angle X-ray diffraction. Attenuated total reflectance infrared spectroscopy (ATR-FTIR) revealed an increasing absorbance ratio of the peaks at 1047 cm(-1) and 1032 cm(-1), which correlates with an increasing crystallinity in the films. The water content of the films was found to increase with increasing B-type crystallinity, which is partly explained by the higher water content of the B-type crystalline areas as compared with the amorphous areas. The glass transition temperature, T(g), decreased linearly as a calculated amount of water in the amorphous phase increased. An interesting observation was made in the second DSC scan, where the T(g) decreased relative to the first scan. This decrease was found to be proportional to the amount of crystallinity in the films. (C) 1997 Published by Elsevier Science Ltd. All rights reserved.