Morphology and Rheology of Polypropylene/Polystyrene/Clay Nanocomposites in Batch and Continuous Melt Mixing Processes

The addition of organically modified layered silicates (organoclay) to highly immiscible polypropylene/polystyrene, PP/PS, blends leads to a significant change in blend morphology and rheology. In this study, the kinetics for morphological development of the blend nanocomposites was studied by two mixing methods (internal batch mixing and continuous mixing), with a focus on the mechanism of dispersion of the silicate layers and its dependence on mixing conditions. Through the use of a twin-screw co-rotating extruder specially modified with sampling ports along its length it was possible to study, for the first time, the kinetics of morphology developed upon mixing. The results show that the evolution of silicate layer dispersion during morphology occurs by and large relatively early in the mixing process and that the most favorable breaking process of the dispersed phase occurs initially due to the breaking up of the initial silicate tactoids into thinner ones and also due to their presence inside it. As a consequence of these sequential processes, the organoclay layers end up at the interface between the PP and the polystyrene phases and stabilize the morphology.