The mechanism of PTC effect in polyethylene/carbon black composite

Xi, B. and Chen, G. (2000) The mechanism of PTC effect in polyethylene/carbon black composite. 6th International Conference on Properties and Applications of Dielectric Materials, Xian Jiaotong Univiversity, Xi'an, China. 20 - 26 Jun 2000. pp. 995-998 .

Abstract

The positive temperature coefficient (PTC) effect in polymeric composite has a variety of applications in industry, as a result many researches have been carried out to understand the mechanisms of the PTC effect. It has been stated in the literature that the PTC effect resulting from a distribution in the continuity of conducting network is principally due to the volumetric expansion of the polymeric matrix. However, the details of mechanism are not yet known. This paper reports an investigation on the PTC effect in polyethylene/carbon black composite. A model based on phase change in the polyethylene matrix is proposed. In this model, carbon black particles mainly reside in the amorphous phase in the composite, thus forming a conductive channel below the melting point. When temperature rises near to the melting point of the polyethylene, the crystalline phase starts to melt leading to formation of new amorphous regions. The volume of the new amorphous regions is larger than that of the previous crystalline region. Some portion of the new amorphous phase will extend into the previous amorphous regions. As the newly formed amorphous phase contains no carbon black, this extension can reduce and finally break up the conducting channel in the previous amorphous phase, resulting in rapid increase in resistivity of the composite. Thus this model can be used to explain the PTC effect in semicrystalline polymeric composite.

This record has no associated files available for download.

Contributors

Download statistics