Aggregation Tendency of Particulate Fillers: Determination and Consequences

Abstract

The agglomeration tendency of 11 commercial CaCO₃ fillers with different particle size and specific surface area was investigated with various techniques. Some powder characteristics were measured and also the sedimentation of treated, as well as non-treated fillers were determined in water and toluene. PP composites containing 25 vol% filler were homogenized in an internal mixer. Melting and crystallization, as well as tensile properties were determined on compression moulded plates. Unambiguous determination of aggregation is difficult, since it depends on interaction and experimental conditions. The extent of aggregation is always determined by the relative magnitude of attractive and separating forces under the given sample preparation and/or testing conditions. Observable aggregation begins at 5–7 m²/g specific surface area for the studied fillers, but its extent depends also on their particle size distribution and on surface treatment. Composites with a larger number of aggregates possess inferior mechanical properties, however, the effect depends very much on the characteristics measured.