Tunable Electromechanical and Microwave Shielding Properties of Epoxy Composites With Hybrid Nanocarbon/Cobalt Fillers

Electrical and electromagnetic shielding properties of three‐phase nanocarbon/Co/epoxy composites were studied. Highly resistive composites with 2–3 wt% of graphite nanoplatelets (GNPs) and 30 wt% of Co showed an irreversible increase in electrical resistance under compression due to GNPs reorientation and partial destruction of electrical contacts in conductive chains. The significant compression‐induced decrease in electrical resistance for highly conductive composites with 5% nanocarbon/Co occurs due to sample densification, formation of new conductive pathways and improved interparticle electrical contacts. CNT‐based composites showed enhanced Young's modulus and compression strength compared to GNP/Co‐filled, however the increase of nanocarbon content to 5 wt% results in the deterioration of mechanical properties due to filler particle agglomeration. The high electromagnetic shielding efficiency (SE) of nanocarbon/Co/epoxy composites is the result of high conduction loss and multiple reflection of EM waves. The 5% CNT/Co composite achieves SE value of 36 dB at 35 GHz while maintaining a compressive strength of 162 MPa, outperforming prior binary systems. The enhanced microwave absorption in three‐layered composite structure based on GNP/Co/epoxy layers with a reflection loss |RL min | ≥ 10 dB for the whole frequency range 26–37.5 GHz can be ascribed to the improved impedance matching and EM wave multiple reflection on additional interior interfaces between layers.