The Rheology of Optically Transparent Polystyrene Blends Filled With Cross-Linked Polystyrene Beads

In order to assist the understanding of the rheological properties of polymer blends, a series of polymer blends have been made where a polystyrene matrix has been blended with spherical cross-linked polystyrene particles. The blend has sufficient transparency that optical observations can be made during processing. Different concentrations of blends were prepared by one of two routes; namely mechanical blending and blending using solvent mixing. Processing data was obtained using a Cambridge Multipass Rheometer MPR [1]. Rheological data and optical observations of the blends were carried out using the MPR for an entry/exit slit flow [2]; using both flow birefringence and direct optical visualisation. The MPR pressure profile rheological data showed differences between the blends that were prepared by mechanical and solvent processing. The birefringence and direct visualisation observations provided insight into the similarities and differences in rheolgical behaviour of the matrix alone and the blended materials. In addition an unexpected cavitation phenomenon was observed for certain processing conditions of the blend and it is speculated relative flow around the cross-linked beads causes local low-pressure regimes where cavitation can occur.