The Study Of The Polypropylene/carbon Black Conductive PTC Composite

Polymeric PTC composite derived from cheap raw materials has become a very interesting research subject because of the advantages of easy processing and safety in the utilization. It has been widely used in the field of automatic temperature-control heating cable, over-current protection component, electromagnetism shield materials and sensors. Automatic temperature-control heating cable is one of the main applications of the polymeric PTC composite owing to the characters of low source temperature, easy heating at every sect of duct. Nowadays the obstructer in application of polymeric PTC composite is the high resistivity at room temperature, the poor reproducibility and the short life-span.The new PP-based composites filled with various carbon blacks were investigated in this thesis. The percolation behavior and the PTC performance of the composites were studied. The effects of the crystalline behavior, the volume expansion of the PP matrix, the types and content of CB on the conductivity, the PTC intensity, as well as PTC conversion temperature of the composites were elucidated in detail. The PTC effect of the composites was shown to be closely related to the crystalline behavior and the volume expansion around the melt point of the polymer matrix. In comparison with PE-based composites, PP-based composites exhibit a higher PTC conversion temperature. The acetyl carbon black filled composites exhibit lower percolation threshold and better PTC effect compared to those of others. The tremendous decreasing of the percolation threshold was achieved by blending FE into the PP/CB composite. The experiment results showed that the maximal PTC intensity appeared at the critical concentration and the PTC conversion temperature increased in the PP/FE/CB composites. The better reproducibility can be made by the recovery distribution of the CB particles with the repeated expansion/contraction on the change of the temperature. The improved properties are resulted from the higher viscosity of FE which was used as one of its components. A kind of automatic temperature-control heating cable was prepared on the basis of our findings. The operating temperature of the cable was 105°C and the PTC intensity was above 4 quantities. The operating temperature and power of the cable were changed less than 10% for continuous electrifying test.