Pressure-Volume-Temperature Relationships of Soy Protein Isolate/Starch Plastic

Otaigbe, J. U. and J. Jane

Dep. Material Sci. Eng.

Iowa State Univ., Ames, IA, USA

Abstract

The use of pressure-vol.-temp. (PVT) studies in processing of a biodegradable plastic compn. made from soy protein isolate and corn starch is described. The ability of PVT measurements to predict the combined effects of pressure, vol., and temp. effects is demonstrated. The results show that the PVT relations of the plastic can be predicted by using a regression anal. similar to the Tait equations of state. A change in slope of the PVT curves was obsd. at around 80 ° C, which is ascribed to the glass-transition process of the plastic. Evidence on onset of thermal degrdn. of plastic was obsd. at ca. 160 ° C under 0 to 200 MPa isobaric pressure. This thermal degrdn. precluded detn. of the crystal m.p. of the plastic.