The Conductivity Distribution in Injection Moulded LDPE and HDPE Filled with Carbon Black

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Abstract
This study of the distribution of conductivity in injection-moulded compositions (test bars) of LDPE and HDPE containing carbon black (20% Vulcan XC-72, 10% Ketjenblack EC) showed that the skin and shear zones have substantially higher resistivity levels than the core. In general, the resistivity increased with the degree of orientation, as determined by thermal shrinkage measurements. There was, however, no simple relation between resistivity and shrinkage. Regions with increased resistivity showed a pronounced frequency dependence, the resistivity decreasing with increasing frequency; in annealed samples or samples taken from the core, the resistivity was frequency independent. Annealing restored the high conductivity of isotropic samples. The results are in qualitative agreement with the assumption of a conducting CB-network changing its connectivity upon deformation and flow, and recovering when the sample is annealed.