The mechanism of PTC effect in polyethylene/carbon black composite

An investigation of the positive temperature coefficient (PTC) effect in polyethylene/carbon black composite is reported. 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 the temperature rises near to the melting point of 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 portions 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 a rapid increase in resistivity of the composite. This model can explain the PTC effect in semicrystalline polymeric composite.