Thermal ageing of conducting polymeric composites

The electrical properties of polymer composites-polyethylene/carbon black (PE/CB), polyethylene/carbon black modified by polypyrrole (PE/CB-PPy), and polyethylene/carbon black modified by polyaniline (PE/CB-PANI)-were investigated during slow cyclic heating and cooling thermal ageing. Conductivity in composites was measured in heating/cooling cycles in the temperature range from 16 to 125 degreesC. Scanning electron microscopy was used for morphology study of surface of modified CB particles. It was found that the thermal treatment resulted in a conductivity increase in all composites when heated below the melting point of PE. This effect was explained by increased crystallinity in the polymer matrix of thermally treated composites and confirmed by DSC analysis. The thermal ageing during the heating above the melting point of polymer matrix caused decrease in conductivity of PE/ CB composites, but increase of conductivity in composites containing CB-PPy or CB-PANI as a filler. The modified fillers create more perfect and thermally resistant conducting network in PE matrix. The temperature of decomposition maximum of PE/CB-PPy and PE/CB-PANI composites into higher compared with PE/CB composite as observed by thermogravimetric analysis. (C) 2003 Elsevier Ltd. All rights reserved.