The molecular weight dependence of crystal growth process of isotactic polypropylene under shear flow

In this research, we aim to clarify the oriented structure growth process observed under applying shear flow with isotactic polypropylene of various molecular weights in various shear rate and temperature. It was found that, polymer chains were stretched on shearing was applied, in the case of a sample having a molecular weight of 200,000 or more. In lower shear temperature conditions, the micron-scaled oriented structure growth was observed during shear flow after polymer chain orientation with polarized optical microscopy mounted with high-speed camera. On the other hand, in the case of molecular weight of 12,000, polymer chains could not be oriented in any strong shear conditions. In the micron scaled oriented structure, the stacked lamellar crystalline aligned to the shear direction, that is the so-called shish-kebab structure, were observed with approximately 22 nm with in-situ small angle X-ray scattering measurements. The production conditions of the oriented structure growth, not only depend on orientation and relaxation of polymer chains due to strong shear, but also strongly on the supercooling. © 2019 The Society of Materials Science, Japan.