Anisotropic multilayer conductive networks in carbon nanotubes filled polyethylene/polypropylene blends obtained through high speed thin wall injection molding

Abstract

To prepare composites with anisotropic conductive networks, electrical conductive polymer composites (CPCs) consisting of polypropylene (PP) and carbon nanotubes (CNTs) filled polyethylene (PE) are fabricated through high speed thin-wall injection molding. Morphological study demonstrates that CNTs are localized in PE phase while the alternating multilayer structure with different polymer phases elongated as well as conductive network oriented parallel to flow direction is observed. To form such alternating layered structure, the dispersed phases are firstly deformed into discontinuous layers, and finally further deformed into wide and regular continuous alternating layers. In term of the mechanism behind this, the good viscosity match, low interfacial tension between different polymer components, short relaxation time and high shear rate are thought as important issues. The anisotropic conductive behavior of these CPCs, i.e. conductive in longitudinal (parallel to flow direction) and transverse (perpendicular to flow direction) direction but non-conductive in thickness direction, is contributed by the insulating PP layer which cuts off the conductive networks in the core layer. More importantly, much better electromagnetic interference (EMI) shielding ability is obtained for these CPCs with alternating multilayer conductive networks comparing with the same polymer blends with isotropic conductive networks, despite of the fact that much lower resistivity is obtained for the later. This indicates great potential of these anisotropic CPCs for electronic applications. Moreover, this study has shed some light on the potential use of such alternating multi-layered structure to prepare a range of multi-functional materials.