Positive Temperature Coefficient (PTC) Evolution of Segregated Structural Conductive Polypropylene Nanocomposites with Visually Traceable Carbon Black Conductive Network

Electrically conductive carbon black (CB)/polypropylene (PP) nanocomposites with a segregated structure are fabricated by localizing CB particles at the interfaces among the PP granules. Interesting double-peak positive temperature coefficient (PTC) effect when exposed to temperature field is observed and ascribed to the breakage of unique segregated conductive network due to the volume expansion stemming from the crystal melting of interfacial PP and the bulk PP matrix. With extending thermal treatment time, the PTC intensity first increases and then decreases obviously. Long treatment time is required for the composites with high CB loadings to reach the PTC intensity maximum value. This phenomenon is attributed to the evolution of segregated microstructure during the thermal treatment, which is traced visually in situ through an optical microscope (OM). The diffusion due to the concentration gradient and the subsequent aggregation of CB particles lead to this behavior. A model based on the OM observation is proposed to reveal the origin of this novel resistivity-temperature behavior.