Ultrasonic treatment of polycarbonate/carbon nanotubes composites

Abstract

A twin-screw extruder having an ultrasonic treatment zone in the barrel was used to prepare polycarbonate (PC)/multi-walled carbon nanotubes (MWNTs) composites. The effect of molecular weight of PC, carbon nanotubes (CNTs) concentration and ultrasonic amplitude on processing characteristics, electrical, morphological, rheological and mechanical properties of PC filled with 0.2–1.5 wt% CNTs was investigated. Ultrasonic treatment showed significant effects on improving the dispersion and distribution of CNTs especially in low molecular weight PC (LPC). The electrical and rheological percolation thresholds of low and high molecular weight PCs obtained by fitting the experimental data to classic percolation theory were significantly decreased after ultrasonic treatment. Specifically, the electrical percolation threshold of LPC/CNTs composites decreased from 0.176 vol% (0.30 wt%) for untreated samples to 0.088 vol% (0.15 wt%) for treated samples at an amplitude of 13 μm. To the best of our knowledge, this obtained value is the lowest percolation threshold, so far, achieved in melt processed PC/CNTs composites. The mechanism for the decrease of rheological and electrical percolation thresholds after ultrasonic treatment was proposed. Also, some improvements in mechanical properties (including the Young's modulus and elongation at break) of PC/CNTs composites after ultrasonic treatment at an amplitude of 13 μm were observed. The ultrasonic extrusion technology is shown to be a suitable method for manufacturing high quality products at lower CNTs concentration.