Influence of temperature changes on crystallization of an ethylene-propylene random copolymer

Unconventional procedures were used to crystallize an ethylene/propylene copolymer, with the aim of investigating the effect of temperature changes on crystallization kinetics and spherulitic morphology. The solidification process of specimens crystallizing under isothermal conditions was cyclically stopped for a while, by increasing the temperature, and afterward re-established by cooling at the original temperature. The resulting morphology characterized by rings within spherulites was compared to that obtained by continuous isothermal crystallization. The different temperature dependencies of the thermal expansion coefficient of liquid and solid phases account for the presence of rings within spherulites grown in a temperature field.