Polymorphism in Sheared Isotactic Polypropylene Containing Nucleant Particles

This study explored the combined influence of shear flow and nucleating agents on isotactic polypropylene (iPP) crystallisation. The study showed that oriented alpha-iPP crystals were not necessary to form beta-iPP crystals, contrary to the accepted view that the surface of oriented alpha-iPP crystals provides nucleation sites for an alpha-iPP to beta-iPP growth transition. Instead it was proposed that flow-induced mesomorphic point-like nuclei preferentially nucleates beta-iPP. The combined effect of shear flow and nucleant was found to promote gamma-iPP crystals. The surprising gamma-iPP nucleation effect was explained by the high density of flow-induced and heterogeneous nuclei present at the start of crystallisation.