Tribological and percolation properties of polypropylene/nanodiamond soot composites

The relationship between surface- and bulk-related physical and mechanical characteristics of polypropylene (PP)-based composites filled with nanodiamond soot (NDS) particles was investigated. The tribological properties of a composite were considered as surface properties. Wear and friction coefficient values were measured using a steel pin-on-composite disk testing procedure under the justified set of test parameters. Loading of NDS particles to the PP matrix resulted in a drastic increase in the composite’s wear resistance. A significant increase in friction coefficient and contact temperature was observed for the composites with NDS content below a certain value assumed to be the percolation threshold for the selected processing method and components used. After the percolation threshold is reached, the friction coefficient decreases sharply and returns to the value characteristic of a filler-free PP. The effects observed were attributed to changes in properties of polymer matrix and composite melt.