On row-structures in sheared polypropylene and a propylene–ethylene copolymer

The crystallisation of polymers such as polyethylene or polypropylene from the melt is greatly influenced by the flow-thermal history prior to the crystallisation. We explore the influence of the chemical configuration of polypropylene based chains on the formation of row structures on crystallisation. We use a combination of in situ time resolved small-angle X-ray scattering, ex situ wide angle X-ray scattering with optical and scanning electron microscopy to show that row nuclei are formed in random copolymers of propylene with a limited amount of ethylene subjected to modest shear flow fields. We contrast observations performed using two homopolymers of isotactic polypropylene and one random copolymer of propylene and ethylene. We propose that it is not strictly necessary to argue that the row nuclei are already crystalline nor to invoke epitaxial crystallisation as the mechanism for the nucleation of lamellae, as similar structures can be formed on carbon nanotubes and fibrils of dibenzylidene sorbitol. The combination of microscopy and scattering provides a powerful approach to investigating these phenomena, especially as compared to either technique used in isolation.