Insights to low electrical percolation thresholds of carbon-based polypropylene nanocomposites

Abstract

Electrically conductive polypropylene nanocomposites filled with carbon-based nanofillers such as carbon nanotubes, graphene and carbon black are widely being used in different applications such as electromagnetic interference shielding, wearable electronics, sensors, soft actuators, structural health monitoring and energy storage capacitors. The electrical conductivity of polypropylene nanocomposites depends on multiple factors, and can be tailored by using different processing and pre/post-processing techniques. There has been a lot of research in the past decade or so to maintain the electrical conductivity of polypropylene nanocomposites at the lowest possible filler concentration. Low percolation threshold is critically important for several technical applications as a key factor to well tailor mechanical properties, maintain optical transparency, and bring cost-effectiveness in manufacturing. This review article presents a comprehensive insight of the methodologies that have been used by different researchers to achieve low/ultralow electrical percolation thresholds in carbon-based polypropylene nanocomposites. Most importantly, different parameters that directly influence the percolation threshold and electrical conductivity such as the type, size, aspect ratio, functionalization and nucleating ability of carbon nanofillers, inter-particle interactions, density, crystallinity, viscosity of matrices, nanocomposite morphology, interaction of nanofillers with the polymer matrix, as well as post-processing techniques like annealing have also been discussed in detail. Percolation threshold and its theory, as well as the conduction phenomena such as the tunneling effects are also mentioned. The research has been characterized based on carbon filler types and critical comparisons have been made between the studies using similar methodologies.