Flow instabilities of highly entangled thermoplastic polymers

The flow behaviors of thermoplastic polymers in strong flows have a profound impact on the applications of polymer processing, such as extrusion and injection molding. And many phenomena, such as shark skin and spurt flow, are related to the flow instabilities of polymers. Furthermore, the understanding of how polymer structures affect the flow properties plays a key role in designing the structure-processing-property relationship. In the present work, we have self-built particle tracking/imaging devices on commercial rheometers. By directly visualizing the shear flow fields of polybutadiene (PBD) and polystyrene (PS) solutions, we investigated edge fracture and shear banding, both of which are flow instabilities that could affect the finishing of thermoplastic products. By either optimizing the surface topology or chemically modifying the surface chemistry of the rheometer plates, we were able to prevent interfacial wall slip. Under highly nonlinear viscoelastic flows (Weissenberg number > 200), our results show that there is no compelling evidence of the existence of shear banding. This is opposed to recent literature results which suggest shear banding in comparable conditions.