Effect of twin-screw extruder design and process conditions on ultrafine CaCO3 dispersion into PP

Highly filled calcium carbonate (CaCO3)/polypropylene (PP) blends were comp ounded using an intermeshing corotating twin-screw extruder. The effect of screw configuration, rotation speed, flow rate, filler feed port position a nd barrel temperature on dispersion of calcium carbonate into polypropylene was investigated. A method based on image analysis of optical transmission micrographs obtained from 25 micron thick films was found to be quick and reliable for evaluating the state of dispersion in the filled systems. The dispersion state affected the mechanical performance of the systems. In par ticular, falling weight and unnotched Izod impact resistance decreased sign ificantly as dispersion got poorer. Mechanical properties were correlated w ith the relative volume concentration of agglomerates in the blend.