Carbon black-filled polypropylene as a positive temperature coefficient material: effect of filler treatment and heat treatment

Polymer-based positive temperature coefficient (PTC) composites are of special interest because they have great potential in temperature-sensitive devices. In this work, composites based on polypropylene and carbon black (CB) particles were prepared by solution blending. The electrical and mechanical properties of composites were measured when CB particles were treated with silane coupling agent before added to the PP matrix. It was found that CB treated by coupling agent exhibited a higher filler–polymer interaction which was reflected in the improvement of the mechanical properties and the modification of electrical conductivity of composites, especially when measured against the temperature. The effect of heat treatment on the electrical conductivity, PTC behavior and mechanical properties was also studied. It turned out that the optimal heat treatment condition of composites was at 120 °C for 3 h. The differential scanning calorimetry analysis and X-ray diffraction analysis revealed that heat treatment could increase the crystallinity of composites, so that the PTC intensity increased.