PTC effect of carbon fiber filled EPDM rubber composite

Conductive ethylene-propylene-diene (EPDM) rubber composites filled with carbon fiber (CF) and carbon black (CB) were prepared by the conventional melt-mixing method. Optical microscope was used to observe the formation of the conductive pathways in the CF-filled composite. A model based on thermal expansion and electron tunneling theory was proposed to explain the PTC effect of CF-filled composite. The resistivity-temperature behavior of filled EPDM composites depended on the shape of carbonaceous fillers, CF/EPDM composite showed a positive temperature coefficient (PTC) effect, while CB/EPDM composite showed a negative temperature coefficient (NTC) effect.