Dissolution and Re-emergence of Flow-Induced Shish in Polyethylene with a Broad Molecular Weight Distribution

Abstract

Flow-induced shish formation in semicrystalline polymers is an important phenomenon since shish can strongly influence final material properties. The formation, dissolution, and re-emergence of flow-induced shish were studied for a polyethylene system with a broad molecular weight distribution using time-resolved synchrotron small-angle X-ray scattering (SAXS). The results show that shish are generated for a critical strain of 100 at various shear rates, ranging from 25 to 200 s–1. The shish formed at 140 °C are not stable and decay during a subsequent isothermal process. The specific shish dissolution dynamics is in contrast with the shish formation, affected by the shear rate applied. Unexpectedly, when the polymer melt with dissolved shish was cooled down, shish re-emerges. It demonstrates that the shish created did not dissolve completely into relaxed random coils but relaxed only partially into some ordered precursors that are below the limit of SAXS detection. Moreover, shish dissolution dynamics wa...