Annealing-induced enhancement of electrical conductivity and electromagnetic interference shielding in injection-molded CNT polymer composites

Abstract

Carbon nanotubes (CNTs) are of great interest to polymer scientists as reinforcements in polymer matrices to produce conductive thermoplastics. Unfortunately, their orientation distributions after the injection molding process have been found to provide low interparticle contact and electrical conductivity. In this study, we attempt to improve these characteristics in CNT-reinforced polycarbonate (PC) composites produced by injection molding using both types of CNTs, namely, single- and multi-walled carbon nanotubes (SWCNTs and MWCNTs, respectively). However, electrically conductive CNT networks were found to be re-tailored through post-processing annealing at high temperatures. For example, the conductivity of SWCNT(1 wt%)/PC was improved 1012 times with annealing. Herein, the electrical network of SWCNT-based polymer composites transformed after annealing was investigated for the first time in detail. Polarized Raman mapping clearly demonstrated the transition from aligned, unconnected CNTs before annealing to a randomly oriented interconnected network after annealing. Moreover, the annealing-induced expansion of the CNT electrical network path was directly visualized using the lock-in thermography technique, which clearly showed an increase in the degree of interconnection among CNTs in all regions of the molded parts from the skin to the core. Notably, the response of the composite to electromagnetic waves changed from absorption to reflection owing to this improved conductivity. The 3 wt% SWCNT/PC, which exhibited the highest electrical conductivity of 2.37E-01 S/cm also provided the highest electromagnetic interference (EMI) shielding effectiveness of 46.7–51.1 dB, providing its wide-ranging applicability in EMI pollution protection.