The Effects of Twin Screw Extrusion Screw Design and Screw Speed on Filler Dispersion in Polystyrene

The properties of polymer nanocomposites can be improved by greater filler dispersion. Filler dispersion in highly viscous polymers is affected by the kinetics of mixing and chemical affinity. It is challenging to quantify nano-dispersion due to the small-size features averaged over large volumes. In order to quantify dispersion, X-ray scattering data was measured as a function of filler concentration and used to calculate the pseudo-second order virial coefficient, A2. In a true thermodynamic sense, A2 is a measure of miscibility. For polymer nanocomposites, a larger A2 indicates a better dispersion. This nano-scale measure of dispersion is compared with macroscopy measures using microscopy. Nanocomposites of carbon black filled polystyrene mixed in a single and twin-screw extruder (following Schadler et al.) and in a Brabender mixer were compared. The effect of screw design and screw speed were explored for the twin screw extruder.