Effects of hybrid fillers on the electrical conductivity and EMI shielding efficiency of polypropylene/conductive filler composites

In this study, the effects of hybrid fillers on the electrical conductivity and electromagnetic interference shielding efficiency (EMI SE) of the polypropylene (PP)/Ni-coated carbon fiber (NCCF) composites with the second fillers, such as multi-walled carbon nanotube (MWCNT), carbon black and TiO ₂, were investigated. The morphological behavior showed that the NCCF and the second fillers, such as MWCNT, carbon black and TiO₂, seemed to disperse evenly in the PP phase. Among the PP/NCCF composites with MWCNT, carbon black and TiO₂, the PP/NCCF/TiO₂ composites showed the higher electrical conductivity and EMI SE compared with those of the PP/NCCF/MWCNT and PP/NCCF/carbon black composites. This was the case because TiO₂ has high dielectric constant with dominant dipolar polarization. The estimated EMI SE values of the PP/NCCF composites with MWCNT, carbon black and TiO₂ are in good agreement with the experimentally obtained values of the composites. Based on the electrical properties of the composites, it was suggested that TiO₂ was the most effective second filler when it was hybridized with the NCCF of the PP/NCCF/TiO₂ composite. Based on the analysis of the flexural modulus, the PP/NCCF/MWCNT composite had a higher flexural modulus than the PP/NCCF/TiO₂ and PP/NCCF/carbon black composites because of the higher aspect ratio of the MWCNT.