Improving the electrical conductivity of a carbon nanotube/polypropylene composite by vibration during injection-moulding

An isotactic polypropylene/multi-wall carbon nanotube (iPP/MWCNT) composite was prepared by a vibration injection moulding technique. The effect of the vibration field on the electrical conductivity property of samples was investigated. The results show that the electrical conductivities of the samples prepared by vibration injection moulding was far higher than those of samples prepared by conventional injection moulding when the CNT concentration are above 2 wt.% and below 6 wt.%. Besides the electrical conductivity of vibration injection moulded samples are a little higher than those of the compression moulded samples. The higher conductivity was resulted from the MWCNT movement induced by the periodical shear during vibration injection moulding. The agglomerates or individual MWCNT were disentangled, stretched and oriented along the flow direction, resulting in better conducting paths thus greatly increased the electrical conductivity. The electrical conductivity increased with increasing vibration frequency. The difference in the voltage-current relationships among the samples prepared at different vibration frequencies suggests that the mechanism of electrical conductivity of iPP/MWCNT composite changed from a tunnel to an ohmic effect. Compared with conventional injection moulded samples, there was no loss of mechanical properties. (C) 2011 Elsevier Ltd. All rights reserved.