Effect of foaming on the electromagnetic interference-shielding performance of exfoliated graphite nanoplatelets-filled EVA/EOC blend composites in the S-band region

Abstract

In this study, microcellular ethylene vinyl acetate (EVA) and ethylene octane copolymer (EOC) blend composites filled with exfoliated graphite nanoplatelets (xGnP) were fabricated using azodicarbonamide (ADC) as a foaming agent. Closed cell structures were obtained, which were revealed via FESEM analysis. The size, density and porosity of cells increased with an increase in foaming agent content. The thermal stability of solids and their foamed counterparts were analyzed based on TGA thermograms. The EVA/EOC/xGnP foamed system showed enhanced values of specific EMI-shielding efficiency compared to their solid counterparts. The maximum EMI-shielding (SE_T) efficiency of 34.17 dB with a specific EMI SE value of 107.79 dB cm³ g⁻¹ was achieved with 30 wt% of xGnP and 4 wt% of the foaming agent in the S-band region. The effect of xGnP loading was investigated at a constant foaming agent content (4 wt%); the results revealed that the maximum total shielding efficiency (SE_T) of 32.58 dB and a specific EMI SE of 113.51 dB cm³ gm⁻¹ were achieved with 10 wt% of xGnP, which is much better than our previously studied xGnP-loaded solid counterparts. Thus, foaming EVA/EOC/xGnP offers the advantages of high EMI-shielding efficiency, low cost, and lightweight. The study of electromagnetic properties showed that real and imaginary permittivity values increased with an increase in foaming agent content, along with enhanced electrical conductivity.