Pressure-volume-temperature relationships of soy protein isolate/starch plastic

The use of pressure-volume-temperature (PVT) studies in processing of a biodegradable plastic composition made from soy protein isolate and corn starch is described. The ability of PVT measurements to predict the combined effects of pressure, volume, and temperature effects is demonstrated. The results show that the PVT relations of the plastic can be predicted by using a regression analysis similar to the Tait equations of state. A change in slope of the PVT curves was observed at around 80 degrees C, which is ascribed to the glass-transition process of the plastic. Evidence of onset of thermal degradation of the plastic was observed at ca. 160 degrees C under 0 to 200 MPa isobaric pressure. This thermal degradation precluded determination of the crystal melting point of the plastic.