Ethylene-octene copolymer/graphite composites: Electrical and thermal conductivities and flame resistance

Abstract

A series of ethylene-octene copolymer (EOC) composites have been prepared by melt-mixing with different weight ratios of expandable graphite filler (0-50% by weight). Electrical conductivity [both alternating current (AC) and direct current (DC)] and thermal conductivity studies were carried out. Effect of filler loading and frequency on electrical conductivity was studied. DC conductivity has increased from 1.51x10-13 Scm-1 to 1.17x10-1 Scm-1. Percolation threshold by DC and also AC methods was observed at about 16 vol. % of the filler. Real part of permittivity was found to be decreasing with increase in frequency while conductivity was increasing. Thermal conductivity was also found to be increasing gradually from 0.196 to 0.676 Wm-1K-1 which is about 245% increase. Graphite not only increases the electrical and thermal conductivities but at and above 40 wt. %, also acts as a halogen-free, environmental friendly flame retardant. Horizontal burn rate was studied in detail with interesting results. Initially the addition of graphite increases the horizontal burn rate but above 35 wt. % of graphite the burning speed decreases. Shore-A hardness of EOC/graphite composites shows that even with high graphite loading, the hardness is increased from about 50 to 68 only so that the rubbery nature of the composite is not affected very much.