On isotactic polypropylene annealing: Difference in final properties of neat and β-nucleated polypropylene

The effect of isotactic polypropylene (iPP) molecular weight and thermal treatment on final crystalline structure and mechanical properties were investigated by X-ray scattering, differential scanning calorimetry, tensile testing, and scanning electron microscopy. Neat and beta-nucleated isotactic polypropylene were subjected to annealing above melting temperature of beta-phase but still below melting temperature of alpha-phase, which caused both improvement of alpha crystallites and beta to alpha-recrystallization, in case of nucleated material. As a consequence, the final mechanical properties like tensile strength and stiffness improved significantly. The increase is much more pronounced in the case of beta to alpha-transformed materials with lower molecular weight. This phenomenon can also be attributed to the partial preservation of the specific structure of the amorphous phase present in beta-nucleated polypropylene, in addition to the perfection of the crystalline phase. The amorphous phase comprises many interconnecting chains passing through several lamellae whereby providing a long-range effect.

Automated summary

This study investigates the influence of isotactic polypropylene (iPP) molecular weight and thermal treatment on the crystalline structure and mechanical properties. The results indicate that under specific conditions, thermal treatment can improve the crystalline and mechanical properties of the polymer.