The effect of filler nature on the crystallization behavior and mechanical properties of filled polypropylene

Nucleating activity in the crystallization of polypropylene (PP) was studied for three types of shungite fillers with a carbon content of 2.5% (Sh-2.5), 30% (Sh-30) and 98% (Sh-98) and glass beads. The shungite fillers revealed a considerable nucleating activity, whereas the glass beads turned out to be an inert filler. The nucleating activity of shungite fillers was displayed as a elevation of the PP crystallization temperature, a decrease in the spherulite size, and an increase in the proportion of the crystalline phase. The nucleating activity of shungites increases in the order Sh-2.5, Sh-98, Sh-30. The polymer affinity and ability of shungites to adsorb nonpolar macromolecules were explained by the presence of carbon-containing areas and hydrocarbon fragments on the surface of particles. The interrelation between the nucleating activity of fillers and the deformation behavior of filled PP was established. The stronger reinforcing effect of shungite fillers as compared to glass bead fillers was accounted for by the increase in the crystallinity of PP. The high adhesion between PP and shungite particles was assumed to be due to the interaction of macromolecules with surface hydrocarbon groups, as in the case of adsorption in a melt.