Effects of Carbon Nanotube Dispersion Methods on the Radar Absorbing Properties of MWCNT/Epoxy Nanocomposites

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.