Electrical Properties of Carbon Black-Filled Polypropylene/Ultra-High Molecular Weight Polyethylene Composites

Abstract

This chapter discusses the electrical properties of carbon black (CB)-filled polypropylene/ultrahigh molecular weight polyethylene (PP/UHMWPE) composites. In the experiment described in the chapter, CB-tilled PP/UHMWPE composites were prepared by the conventional melt mixing method. The electrical properties of the composites including the positive temperature coefficient (PTC) effect and the CB distributions in the PP/UHMWPE matrix are studied in the chapter. The results indicate that the PP/UHMWPE weight ratio and CB content are the two main factors that can significantly influence the electrical resistivity of the CB-filled PP/UHMWPE composites. At a fixed CB content, a minimum value in resistivity was observed at the PP/UHMWPE weight ratio of 1:1. At a fixed PP/UHMWPE weight ratio (1:1), a percolation threshold of 0.008 volume fraction of CB was observed, which is much lower than that of conventional CB-filled polymer composites. The measurements of resistivity of the composites versus temperature show that the stronger double-PTC effects are observed at low CB content and low PP/UHMWPE weight ratio. The melting of UHMWPE crystallites at about 140 °C and the melting of PP crystallites at about 170 °C were responsible for the first PTC effect and the second PTC effect, respectively. The results of optical microscopy studies illustrate that CB particles are selectively localized at the interface between the PP matrix and the UHMWPE particles or in the PP matrix because of the extremely high viscosity of UHMWPE.