Spherulitic isotactic polypropylenes (iPPs) having a wide range of β-phase contents were prepared by adding β-nucleators, and the effects of the β-phase modification on the mechanical properties of the iPP were investigated. This chapter described the tensile properties of β-nucleated iPP, while key structural parameters, such as spherulite size and crystallinity, were controlled. The increase in the β-phase content led to broader yield peaks and an enhancement in the yield toughness but to a reduction in the yield strength. On the other hand, the initial elastic modulus was found to be independent of the β-contents. Furthermore, the deformation of the β-spherulites, which have a sheaflike structure, was anisotropic and depended on the stretching direction with respect to the sheaf axis. Consequently, the improved drawability and ductility of β-iPP compared to α-iPP are thus associated with the enhanced toughness resulting from the multiple deformation processes in the sheaflike spherulites.
Part of the book: Polypropylene