Relation of crystalline structure and mechanical properties of nucleated polypropylene

Four heterogeneous nucleating agents were added to polypropylene (PP) homo-, block and random copolymers. Melting and crystallization of the polymers were studied by differential scanning calorimetry (DSC), and characteristics derived from the crystallization exotherms were related to the mechanical properties of injection molded bars. A very close correlation was found between the crystallization characteristics and Youngs modulus of the polymers. The general correlation proved to be valid for all three polymers studied and also for each nucleating agent. The developed empirical correlation makes possible the approximate prediction of stiffness from a simple DSC trace. Further study is needed to give the relationship better physical meaning and to extend it to other mechanical properties.