Effect of single screw extrusion through a round die on the morphology of POM/PP blends

Abstract

POM/PP blends of different compositions were extruded through a round die of 2 mm diameter using a single screw extruder. The morphology of the extrudates was studied using a polarized light microscope (PLM), a scanning electron microscope (SEM) and the solvent extraction technique. A cable-like structure was observed in the extrudates, consisting of circular cords surrounded by a skin layer. The number and distribution of the cords matched with the holes on the breaker plate just before the die. The composition and morphology of the cords were found to vary with the POM/PP composition ratio. For composition ratios between 10/90 and 40/60, the outer cords were rich in PP and only a small amount of POM fibres, particles or thin films were found. In contrast the inner cords contained more POM fibres and they were distributed more evenly within the PP matrix. In the 50/50 blend, both POM and PP fibres were present. In blends with more than 50% POM, the cords were made up of PP fibres in a continuous POM matrix. Cryogenically-fractured sections of the extrudates showed clean fibre/matrix interfaces under the SEM, this being a sign of poor adhesion between the polymers.