A Study of the Rheology, Processing and Flow Induced Mesostructures of Glass Bead Filled Polystyrene

This paper presents some recent experimental results on the effects of the addition of glass beads (both coupled and uncoupled) on the linear and non-linear rheology, and hence processability, of a commercial polystyrene. Oscillatory, low strain, measurements showed an increase in viscosity with the addition of the glass beads, which varied depending on the testing frequency and degree of coupling. For the coupled beads, at low frequencies the increase in viscosity was well predicted by the Kreiger-Dougherty relationship, while at higher frequencies a smaller increase than this was seen, linked with a shift to lower frequencies of the lower frequency cross-over between G[ and G[. For the uncoupled beads, the viscosity was found to shift vertically with no change in the position of the G[,G[ cross-over. For the non-linear shear and extension measurements, at low shear rates and low strains the increase in viscosity agreed well with the linear results, whereas at high strain rates and strains, more disparity was seen, which in non-linear extension was been linked to voiding. For non-linear shear measurements, the plateau viscosities of the pure polystyrene were found to fit the Cox-Merz rule, while the glass bead filled materials did not. The deviations in behaviour of the filled materials were found to be closely linked to the characteristic relaxation times of the polymer, particularly the reptation time td and the Rouse time tR.