Effect of incorporating ethylene-ethylacrylate copolymer on the positive temperature coefficient characteristics of carbon black filled HDPE systems

In order to study the effect of introducing ethylene-ethylacrylate copolyme r (EEA) in carbon black-HDPE composite systems, two HDPE-EEA composites pre pared by pre-blending and masterbatch-blending processes were compared with HDPE and EEA composites in terms of positive temperature coefficient (PTC) characteristics and percolation threshold. The percolation threshold of ma sterbatch-blended composites occurred at the lowest carbon black concentrat ion among four kinds of composites. The conduction path in the masterbatch- blended composite is effectively formed as a result of the localization of carbon black distribution predominantly in the EEA phase, resulting in an i ncrease of conductivity. I-peak values, the resistivity ratio of the peak t o 25 degrees C, of two blend composites were lower than those of HDPE compo sites. The I,, values, the resistivity ratio of 85 degrees C to 25 degrees C, of masterbatch-blended composites were higher than those of pre-blended as well as HDPE composites. It is evident that since most carbon black is d ispersed in the EEA phase of the masterbatch-blended composites, the conduc tion networks are mainly broken by the crystal melting of EEA before the te mperature reaches the crystal melting temperature of HDPE.