| In this work, based on carbon black (CB), polypropylene (PP) conductive composites were prepared via melt mixing. The objective of present study was to investigate the effects of the third component, including ethylene-acrylic-acid (EAA), nylon6 (PA6) and carbon nanotubes on the conductive property and morphology of CB/PP system. The relationships between the conductive properties of these composites and the dispersed state of CB, microscopic morphology of the composites, crystalline behaviors of polymers and environmental temperature were discussed. The mechanisms were studied. The main works and conclusions were as follows:(1) The results of conductivity testing revealed that the adding of EAA or PA6 into the CB/PP system could significantly decrease, the volume resistivity of the composites. Among the studied composites of CB/PP-EAA, when the mass proportion of PP/EAA was 60/40, the conductivity of the composite was the best. But for CB/PP-PA6 composites the optimum mass proportion of PP/PA6 was 80/20. As for CB/PP composite, the introduction of a small quantity of CNTs was benefit to improving the conductivity.(2) According to SEM, in CB/PP system, CB particles were dispersed in PP matrix homogeneously, and did not form continuous structure at a small CB content. In CB/PP-EAA and CB/PP-PA6 systems, CB particles were selectively located in the polar EAA or PA6. In CB/PP-EAA systems, EAA formed strip structure in PP matrix and continuous structure was easy to form as the content of EAA resin increasing. In CB/PP-PA6 composites, PA6 can form fibrous structure and connected with each other to form a continuous structure in PP matrix.(3) According to Resistance-Temperature testing, the PTC intensity of CB/PP composite was up to 10~6, and the NTC effect was also strong. The PTC behavior of the composite was closely related to crystalline melting process. There was no obvious abrupt of the resistivity for CB/PP-EAA system and the biggest peak was caused by EAA. The CB/PP-PA6 system did not have PTC effect at all, it had a stable resistivity value in a wide temperature range with a good stability during thermal cycles. It indicated that CB particles were selectively located in EAA or PA6.(4) DSC results showed that the crystalline temperature increased by about 12℃for CB filled EAA or PP composites, due to the heterogeneous nucleation effect of CB particles. In CB/PP-EAA system, the crystalline temperature of PP deceased by about 7℃compared to CB/PP system, the crystallinity of EAA was decreased. It revealed that the nucleation effect of CB on PP was reduced, and the crystalline of EAA was restrained by CB. So we presumed that CB particles were mainly dispersed in EAA phase.(5) Dynamic rheological testing showed that in CB/PP system, the dependence of G' onωdecreased gradually with CB increased. The "second platform" occurred when the volume content of CB was more than 0.05, it revealed that CB formed a network structure in PP. In CB/PP-EAA system(φ=0. 025), G' of the composite was increased as the content of EAA increased in low frequency area, but the value of G' for CB/PP-EAA composite with a ratio of PP/EAA being 60/40 was higher than CB/PP-EAA composite with a ratio of PP/EAA being 50/50. The rheological behavior was closely related to the conductivity and SEM results of the composites.
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