The effect of mineral fillers on impact and tensile properties of polypropylene

Impact and tensile properties of polypropylene filled with various minerals have been measured. The minerals investigated were dolomite, calcium carbonate, mica and wollastonite. The effect of particle shape, size, content and surface treatment on mechanical properties was studied. A special interest was devoted to the measuring of impact strength, since this is an important property in many applications. The results show that, for stearic acid treated minerals, there is a marked relationship between decreasing particle size and increasing impact strength. This is especially distinct for the results from the staircase method of ASTM-D3029. Comparing the coarsest and finest fraction of particulate fillers studied, there is a 20-fold difference in impact strength at 50% filler content. The staircase method, compared to the instrumented falling weight impact test, shows a higher sensitivity to changes in impact strength, caused by, for example, variations in particle size or content.