The role of water during plasticization of native starches

Flexible, starch-based plastics of native corn, potato, waxy corn and wheat starch were produced by compression moulding mixtures of native starch and glycerol in the weight ratio 0.30 (W-glycerol/W-dry starch). In these premixes, the weight ratio water/dry starch was varied between 0.112 and 0.422. The mechanical properties of these compression moulded starches, with a glass-rubber transition temperature below room temperature, were strongly dependent on the water content of the premix. Varying the water content in the premixes led to large changes in strain and stress at break. This effect could be explained by a dependence of the polysaccharide mobility on the water content in the premix. The mechanical properties of the materials were also dependent on starch source, and hence on the composition of the native starch and the structure of the constituting polysaccharides. From the results it could be concluded that both amylose and amylopectin formed chain interactions or entanglements in the materials. (C) 1998 Elsevier Science Ltd. All rights reserved.