Rheology of highly filled polypropylenes prepared with surface treated fillers

Highly filled polypropylene (PP) composites have been produced by extrusion of polypropylenes with surface treated fillers. The aim is to include the highest proportion of filler that can provide hardness and high density, without undue brittleness. Modification of the filler surface provided significant enhancement of the processing properties that have been studied with parallel plate rheometry. The experimental results indicated that the viscoelastic behavior of melt flow of highly filled polypropylene composites significantly depended on the following properties of the fillers: aspect ratio, specific surface area and particle size in talc, calcium carbonate and barium sulfate filled polypropylene composites. Traditional surface modifiers such as stearic acid are useful, but titanates and in particular small amounts of silicones have provided the greatest rheological modification.