SUB-T-G THERMAL-PROPERTIES OF AMORPHOUS WAXY STARCH AND ITS DERIVATIVES

The sub-T-g thermal properties of aged amorphous waxy starch, beta-limit dextrin, and amylopectin triacetate at low moisture contents were studied by differential scanning calorimetry (DSC). When T-g was above 50 degrees C (similar to 5-14% moisture), a 50 degrees C endothermic peak was observed in waxy starch and beta-limit dextrin samples. The Delta H of the 50 degrees C peak was proportional to the moisture content. At a similar moisture content the Delta H of beta-limit dextrin was greater than that of waxy starch. No 50 degrees C peak was observed in the amylopectin triacetate samples at the moisture contents studied (similar to 0.5-5% moisture). All amylopectin triacetate samples showed an endothermic overshoot associated with the glass transition. It is suggested that water-hydroxyl group interactions may be required for the formation of the sub-T-g peak. The 50 degrees C endotherm is a separate event different from the aging peak associated with the glass transition seen in many polymers.