Surface and electrical properties of high density polyethylene + carbon black composites near the percolation threshold

We have studied friction, scratch resistance and electrical resistivity in high density polyethylene (HDPE) + carbon black (CB) composites in relation to electric resistivity percolation threshold. Below the threshold, CB addition lowers dynamic friction by providing a smaller surface area of contact of the composites with the pin surface; the effect is stronger at higher loads. Above the percolation concentration, an increase in friction is seen due to formation of CB agglomerates and thus an increase in the area of contact. The recovery depth in scratch testing behaves similarly as dynamic friction and for the same reasons, particularly so at high loads, with a minimum at the percolation threshold. Thus, at the threshold we have simultaneously superior scratch resistance, low dynamic friction and low electric resistivity.