Poly(3-hydroxybutyrate-co-11 mass%3-hydroxyvaleate) molded part during the solidification step

Abstract

The numerical simulation of the temperature and relative crystallinity developed across the thickness of a poly(3-hydroxybutyrate-co-11 mass%3-hydroxyvaleate) (PHBV) part upon cooling from the melt as a function of the temperature of the cooling fluid (water) is presented. A modified form of the Avrami equation was used to predict the crystallinity as a function of the temperature. A simple expression was used to relate the kinetic constant k with the temperatures. Temperature profiles were predicted by coupling the above mentioned equations to the one-dimensional unsteady-state thermal energy equation through a heat term describing the crystallization heat. Cooling temperatures were in the range between 20 to 80°C and were restricted by the glass transition temperature of the material and the degree of under-cooling, respectively. Even degrees of crystallinity were predicted for part- thicknesses lower than 10 mm cooled at 60°C, while a fluid temperature of 40°C was more appropriate for a 20 mm - thick part. The model predicted uneven crystallinity profiles for part-thicknesses higher than 30 mm.