Microhardness and water sorption in injection-molded starch

The microhardness of injection-molded potato starch was investigated in relation to the water sorption mechanism. The creep behavior under the indenter and the temperature dependence of the microhardness are reported. The influence of the drying time on microhardness, weight loss and density changes for materials with different injection-molding temperatures is highlighted. Results reveal the role of the various mechanisms of water evaporation involved. The occurring structural mechanisms are discussed in terms of the gradual transformation of single helices of amylose and amylopectin into a network structure of double helices and the partial destruction of this structure. Experiments on starch samples, heated at 200degreesC, suggested the occurrence of an extreme densification of the network hindering the water adsorption in a humid atmosphere. (C) 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1246-1252, 2002.