Rapid curing and additive manufacturing of thermoset systems using scanning microwave heating of carbon nanotube/epoxy composites

Here we show that the heating response of multi-walled carbon nanotube (MWCNT) fillers to applied microwave fields can provide a means to rapidly cure epoxy composites; this is useful for eliminating thermal gradients and decreasing cure times, even in the unconstrained environments common to additive manufacturing. We demonstrate this by comparing 5.0 wt% (2.2 vol.%) MWCNT-loaded epoxy samples cured in different environments: (i) in a conventional oven, (ii) under a forced thermal gradient in order to simulate industrial-scale non-uniformities, and (iii) scanned beneath a microwave waveguide. We assess both cure speed and cure uniformity in conductivity and composition. Microwave-cured samples show ∼1 order of magnitude higher conductivity than oven-cured samples, whereas the forced thermal gradient results in extreme variations in conductivity. This rapid cure allows for thermosets to be used in processing techniques that had previously been very difficult to achieve due to the long cure times necessary for a thermally curable epoxy. The concept of additive manufacturing of thermosets is demonstrated by completing a novel deposition-and-scan technique that results in a patterned structure of cured epoxy. This indicates that the microwave scanning technique is a feasible way to quickly cure multiple layers of unconstrained epoxy in an additive manufacturing context.

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