On the Stress-Strain Behavior of Thermoplastic Starch Melts

Different grades of starch, glycerol, and water were blended in order to produce a series of thermoplastic starch materials. The starch grades used included native potato starch and modified grades of native potato starch, high amylose potato starch, and amylopectin potato starch. The modification of the latter three grades involved hydroxypropylation and oxidation. The main focus of the study was on the stress-strain properties or the drawability of the thermoplastic starch melts at 120° or 140°C. At these temperatures, the ultimate strain of the starch materials was found to be significantly lower than that of a high-density polyethylene reference at 180°C. In general, the strain at break of the melts based on the native potato starch and the modified native potato starch tended to increase when increasing the glycerol content (and the corresponding amount of water) but decreased as the melt temperature was increased from 120° to 140°C. The chemical modification of the native potato starch appe...