CARBON-BLACK HIGH-DENSITY POLYETHYLENE CONDUCTING COMPOSITE-MATERIALS.2. THE RELATIONSHIP BETWEEN THE POSITIVE TEMPERATURE-COEFFICIENT ANDTHE VOLUME RESISTIVITY

Carbon black/polymer composites can be used in a variety of industrial applications, where a high conductivity is an important physical para meter. The relationship between the positive temperature coefficient ( PTC) effect and the room temperature volume resistivity has been inves tigated. These are two of the more important operating parameters. Res istivity-temperature measurements were performed on a radiation crossl inked high structure (H) carbon black mixed at different concentration s in HDPE. The results obtained for composites with a range of carbon black properties showed that there was a linear relationship between l og (R-2/R-1) and log R-1, where R-2 = maximum resistivity and R-1 = ro om temperature volume resistivity. The relationship can be taken as a reference line for the assessment of the relative effect that modifyin g the carbon black structure and changing the mixing variables on the relative magnitude of the PTC effect and the room temperature volume r esistivity. The high structure (H) carbon black structural characteris tics were modified by both gas phase (carbon dioxide at 900 degrees C) and liquid phase (nitric acid) treatments. The former treatment proce dure resulted in a decrease, while the latter an increase in the volum e resistivities of the final composites. These results are discussed i n terms of the effect of surface functionality and carbon structural c haracteristics.