EFFECT OF SINGLE-SCREW EXTRUSION THROUGH A ROUND DIE ON THE MORPHOLOGY OF POM PP BLENDS/

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 techniq ue. A cable-like structure was observed in the extrudates, consisting of circular cords surrounded by a skin layer. The number and distribut ion of the cords matched with the holes on the breaker plate just befo re the die. The compositon and morphology of the cords were found to v ary 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 amou nt 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 fibre s were present. In blends with more than 50% POM, the cords were made up of PP fibres in a continuous POM matrix. Cryogenically-fractured se ctions of the extrudates showed clean fibre/matrix interfaces under th e SEM, this being a sign of poor adhesion between the polymers.