Effects of carbon nanotube dispersion methods on the radar absorbing properties of MWCNT/epoxy nanocomposites

Abstract

Radar absorbing materials (RAMs) for practical applications are expected not only to have strong microwave absorption and a wide absorption bandwidth, but also to be lightweight, to have a fine thickness and acceptable structural performance, as well as being cost-effective. Although the dispersion of carbon-nanofillers in polymer matrices is a key factor determining the microwave absorbing properties of the composites, there have few studies on these effects. To our knowledge, to date, the realization of pristine multi-walled carbon nanotube (MWCNT)/polymer composites as RAMs in industrial production has been restricted, due to high CNT contents or large composite thicknesses. Thus, in this work, two MWCNT dispersion processing methods, a solution process with surfactant-aid and a ball-milling dispersion, were investigated to fabricate pristine MWCNT/epoxy nanocomposites. The effects of the different dispersion processes, CNT loading, and composite thickness on CNT dispersion in the matrix, were observed by TEM, and the electrical conductivity and X-band absorbing performance of the composites were assessed. The use of an ionic surfactant to aid the dispersion of CNTs in solution resulted in the best RAMs, with a good compromise among effective X-band absorption, small composite thickness, and very low CNT content. The ball-milling method also resulted in materials with a low CNT content and microwave absorbing performance acceptable for industrial applications. Moreover, it offers a very simple and efficient route suitable for low-cost, mass production of RAMs. The results showed that by facile approaches of dispersing pristine commercial MWCNTs in an epoxy resin matrix, composites of only 2–3 mm thickness and as little as 0.25–0.5 wt% CNT loading could be obtained, with a relatively wide X-band operating bandwidth and maximum absorptions exceeding 18–25 dB.