Elastomeric dielectric materials from natural rubber/copper-modified coconut-shell-derived activated carbon composite: combined experimental and density functional theory study

This study examines the enhanced dielectric and mechanical properties of natural rubber (NR) composites filled with copper-modified activated carbon (Cu-AC), employing both experimental characterization and density functional theory (DFT) simulations to explore structure-property relationships. NR composites were prepared with Cu-AC loadings of 5, 10, and 15 phr, and their performance was compared to those reinforced with neat activated carbon (AC). The effects of Cu-AC content on crosslink density, swelling behaviour, and curing characteristics were evaluated. SEM and EDX analyses confirmed good dispersion of Cu-AC particles, particularly at lower loadings. Mechanical testing revealed a significant increase in tensile strength and elongation at break, with the best balance of properties performed at 10 phr Cu-AC. Dielectric analysis showed increased interfacial polarization and charge storage, with the composite containing 15 phr Cu-AC exhibiting a dielectric constant of around 20 at 1 Hz, which is 2.68 times higher than that of neat NR. This enhancement was associated with interfacial polarization consistent with the Maxwell–Wagner–Sillars effect and the formation of conductive pathways by Cu-AC. However, due to reduced mechanical strength at higher loadings, the 10 phr Cu-AC composite was identified as the optimal formulation, offering a favourable combination of dielectric and mechanical performance. DFT calculations supported these findings, demonstrating strong NR–filler interactions, high adsorption energy (Eads) and significant charge transfer for copper-doped surfaces. These results highlight the multifunctional potential of Cu-AC as a reinforcing and functional additive in NR composites for use in flexible electronics, dielectric elastomers, and energy storage applications.