Thermal and Dynamic Mechanical Properties of a Polypropylene Random Copolymer

Isothermal crystallization kinetics, melting, structure and dynamic mechanical properties of a polypropylene (PP) random copolymer with low ethylene content were studied. In order to study the effect of cooling rate on melting, two different cooling rates were applied to the samples. While water-cooled samples revealed a broad single melting endotherm with a-crystalline structure, slow-cooled samples showed a shoulder at lower temperature followed by a sharp melting endotherm and a mixture of a and 7-crystalline phases. The effect of annealing on log E' of the beta-relaxation for the PP copolymer showed that the beta-transition increased in intensity with increasing annealing temperature. No considerable difference was found in the activation enthalpy of relaxation, DeltaH, values for the annealed compared to that of the water-cooled samples using the Arrhenius equation. The isothermal crystallization kinetics was also studied for PP and the values of nucleation constant, Kg, and end-surface free energy of the crystal growth, sigmae, were calculated using Lauritzen-Hoffman theory.