Electrical properties of extruded milled carbon fibre and polypropylene

Abstract

A milled carbon fibre and polypropylene polymer composite at high filler loading was developed to produce conductive polymer composites for high conductive applications. Current research of conductive polymer composite material has reported about in-plane conductivity that was often higher than through-plane conductivity, which contradicted with the target of applications that required higher electrical conductivity in the through-plane direction. Therefore, electrical conductivity in parallel and transverse to extrusion directions were investigated. The general-effective media and modified fibre contact model were adapted to predict the electrical conductivity of the composite material. The experimental conductivity data of polypropylene/milled carbon fibre composites for transverse and parallel directions were not correlated with the general-effective media model with 2.009 and 0.663 S/cm, respectively, at the highest filler loading of 80 wt.%. This disagreement was due to various critical exponential, t values (2–3.25) that were obtained in this study. However, the modified fibre contact model seemed to have good agreement with the experimental data in the parallel to extrusion direction. This model was unable to predict electrical conductivity in the transverse direction due to lack of orientation occurring in that direction. The electrical conductivity increased as the filler loading increased as explained in percolation theory. Predicting the electrical conductivity of conductive polymer composites material is still in the preliminary stages where the researcher often obtains fluctuating agreement with the experimental values. Thus, contact between filler and orientation is considered as the main factor that influences the electrical conductivity and mechanical strength of the conductive polymer composites material.