The use of master curves to describe the simultaneous effect of cooling rate and pressure on polymer crystallization

Abstract

In a previous work a master-curve approach was applied to experimental density data to explain isotactic polypropylene (iPP) behaviour under pressure and high cooling rates. Suitable samples were prepared by solidification from the melt under various cooling rate and pressure conditions with the help of a special apparatus based on a modified injection moulding machine. The approach here reported is more general than the case study previously shown, and is suitable to be applied to several materials and for different measures related to crystalline content. The proposed simple model is able to predict successfully the final polymer properties (density, micro-hardness, crystallinity) by superposition of the effect of cooling rate and the effect of pressure in a wide range of experimental conditions. For this purpose three semi-crystalline polymers were studied [iPP, polyamide-6 (PA6) and poly(ethyleneterephthalate) (PET)], which exhibited remarkably different behaviour when crystallized under pressure and high cooling rates