Biowax-derived epoxy composites with rGO–NZF–Al₂O₃: a green solution for enhanced EMI shielding and structural performance

This study reports the synthesis and evaluation of eco-friendly, multifunctional composites using beeswax and soyawax as sustainable alternatives to petroleum-based modifiers. These biowaxes were incorporated with epoxy resin, reduced graphene oxide (rGO), Nickel Zinc Ferrite (NZF), and alumina (Al₂O₃) to form four variants: BW–rGO–Al₂O₃, BW–rGO–NZF–Al₂O₃, SW–rGO–Al₂O₃, and SW–rGO–NZF–Al₂O₃. Characterization included FTIR, XRD, tensile testing, EMI shielding, and free vibration analysis. FTIR spectra showed improved filler dispersion in soyawax systems, particularly with rGO/NZF. XRD revealed broader crystallite sizes of 7.13–37.48 nm in BW–rGO–NZF–Al₂O₃, while SW–rGO–NZF–Al₂O₃ exhibited more uniform sizes of 4.49–25.13 nm, indicating superior structural properties. EMI shielding (8–12 GHz) showed BW–rGO–NZF–Al₂O₃ and SW–rGO–NZF–Al₂O₃ had higher transmission loss of −128 dB, −43 dB, while BW–rGO–Al₂O₃ and SW–rGO–Al₂O₃ displayed stronger reflection of −49 dB, −78 dB respectively. Free vibration analysis revealed significant increases in first-mode natural frequencies: 71.96% for BW–rGO–NZF–Al₂O₃ and 58.87% for SW–rGO–NZF–Al₂O₃ under CF boundary conditions, and 47.15% and 36.89%, respectively, under CC—indicating enhanced stiffness from filler synergy. Tensile testing showed SW–rGO–NZF–Al₂O₃ improved modulus by 17.75% and UTS by 10.36% over SW–rGO–Al₂O₃, while BW–rGO–NZF–Al₂O₃ showed marginal reductions. The results demonstrate that rGO–NZF–Al₂O₃-reinforced biowax composites offer enhanced mechanical, damping, and EMI shielding performance, highlighting their promise for sustainable structural and electronic applications.