Sustainable EMI shielding in flexible PVA matrix using Cymbopogon citratus-derived ZnO nanoparticles and natural fiber hybridization

Abstract

Due to the rapid expansion of internet-connected devices, the demand for lightweight, flexible, and effective electromagnetic interference (EMI) shielding materials has significantly increased to ensure device safety and operational efficiency. In this study, a sustainable and flexible polyvinyl alcohol (PVA) composite was developed by reinforcing zinc oxide (ZnO) nanoparticles and biocarbon derived from Cymbopogon citratus (lemon grass), along with areca microfibers. The ZnO nanoparticles were synthesized via a thermochemical route, while biocarbon was obtained through slow pyrolysis. The fillers and fiber reinforcements were incorporated into the PVA matrix using a hand layup process, and all characterizations were carried out following ASTM standards. Among the fabricated composites, PAF2 (2 vol% ZnO/biocarbon and 30 vol% areca microfiber) exhibited the highest tensile strength of 64 MPa and tear strength of 42 N/mm, representing an improvement of 68.42% and 82.60%, respectively, over the neat PVA matrix (composite P). Increasing the filler loading to 4 vol% in PAF3 enhanced hardness to 43 Shore D, a 34.37% increase compared to the control. Dielectric analysis revealed that PAF3 achieved a dielectric constant of 7.6 and dielectric loss of 0.8, which are 287% and 334% higher than those of composite P, respectively. In terms of EMI shielding performance, PAF3 demonstrated outstanding results. At frequencies of 8 GHz, 12 GHz, 16 GHz, and 20 GHz, the absorption shielding effectiveness was 10, 13.5, 20.4, and 24.2 dB, while the reflection shielding effectiveness was 3.6, 7.2, 8.6, and 12.5 dB, respectively. The corresponding total EMI shielding effectiveness reached 12.6, 16, 30.6, and 34.8 dB, marking significant improvements over the unreinforced matrix. These findings highlight the potential of ZnO/biocarbon and natural fiber hybrid-reinforced PVA composites as promising candidates for EMI shielding applications in smartphones, wearable electronics, communication devices, and electronic equipment, where flexibility, sustainability, and performance are essential.