Influence of aging on the mechanical properties of smectic polypropylene

Isotactic polypropylene (iPP) was quenched to the smectic state and analyzed during aging at room temperature for very long times, up to five years. Calorimetric differential scanning calorimetry (DSC) curves, dynamic mechanical behavior, and mechanical properties were used to analyze the aged samples and data were compared with the results for the fresh sample. The obtained results can be explained by a reduction of free volume of the amorphous phase, as well as a concomitant increase of the smectic domains' dimensions. A good correlation was found between some calorimetric and mechanical parameters.