Relationship between surface and bulk morphologies for immiscible polymer blends

Abstract

The surface morphology of compression-moulded PP/PET blends is investigated and compared to the bulk morphology. Before compression moulding the blends are prepared by melt mixing in a Brabender plastograph. Model experiments are developed to analyse the influence of the processing conditions and of the nature of the moulding surface on the surface and bulk morphologies. Films are prepared under different shear conditions with PI as the moulding surface. At low shear rates the bulk and surface morphologies (size and composition) are very similar. At high shear rates and when the PET is the dispersed phase, the nodules at the surface are highly deformed in the flow direction while the PET nodules remaining in the bulk are undeformed. The PET concentration at the surface increases above the bulk concentration. When PP is the dispersed phase, the surface concentration is much lower than the bulk concentration. The observed surface morphology for samples prepared with high shearing can be explained by an interplay between the flow field and the affinity of the dispersed phase for the moulding surface.