The influence of polyols on the molecular organization in starch-based plastics

Abstract

The effect of processing temperature and time on the B-type crystallinity of thermoplastic starch was studied by recording X-ray diffractograms of conditioned, compression molded starch systems containing glycerol and water as plasticizers at a ratio of 100 : 30 : 56 (w/w/w). Initial recrystallization, developed during molding, was investigated further on similar amorphous potato starch and potato amylopectin systems. The crystallinity prior to processing does not influence the recrystallization, though residual (granular) crystallinity, present due to incomplete melting, increases the total crystallinity. After molding at high temperatures (>160 °C), amylose is mainly responsible for initial recrystallization in the B-type lattice. The observed degree of recrystallization, however, cannot be due to amylose crystallization alone. Amylose seems to serve as a nucleus for crystallization of amylopectin or amylose–amylopectin co-crystallization takes place. Thermally induced starch polysaccharide–glycerol interactions were investigated on mixtures of dried starch and glycerol using differential scanning calorimetry and solid-state nuclear magnetic resonance spectroscopy. An exothermal transition was observed after which the mobility of glycerol was decreased significantly. This indicated the development of a strong polysaccharide–glycerol interaction in the absence of water. Copyright © 1999 John Wiley & Sons, Ltd.