Aggregation Tendency of Particulate Fillers: Determination and Consequences
The agglomeration tendency of 11 commercial CaCO3 fillers with different particle size
and specific surface area was investigated by means of 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. Polypropylene (PP) composites containing
25 vol% filler were homogenized in an internal mixer. Melting and crystallization, as well
as tensile properties were determined on compression molded 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.