Intelligent Processing of Carbon-Black Loaded Plastics

Abstract

The electrical conductivity of alternating current (AC) and permittivity of carbon-black (CB)-filled low density polyethylene (LDPE) has been measured as function of time at a temperature higher than the melting temperature of matrix polymer. The conductivities measured at lower frequencies (If) can be used for the characterization of the properties of the interlayer between the CB-particles. The conductivities measured at higher frequencies (hf) reflects the properties of the internal structure of the individual CB-aggregate. At a characteristic time t°, the lf AC conductivity suddenly increased up to the hf conductivity and the permittivity suddenly decreased. The CB aggregates are probably linked together by paracrystalline layers after a certain time of annealing. The time t° increases with the weight percent of CB. It was also found that t° increases as the temperature of annealing decreases. The time t° is interpreted as a relaxation of potential energy of electrostatic repulsion forces between the reversible disintegrated CB particles. The poor reproducibility and stability of CB-filled plastics can be explained by the observed changes of conductivity.