Synergistically Enhanced EMI Shielding and Negative Permittivity in Mechanically Flexible Poly(vinyl Alcohol)-Carbon Black-Graphitic Carbon Nitride Composites

Electromagnetic interference (EMI) poses a critical challenge to the reliability and performance of modern electronic systems, necessitating the development of lightweight, flexible, and environmentally benign shielding materials. In this study, flexible ternary polymer composites based on poly(vinyl alcohol) (PVA), carbon black (CB), and graphitic carbon nitride (g-C 3 N 4 ) were fabricated using a simple and cost-effective die-casting method. The dual incorporation of CB and g-C 3 N 4 within the PVA matrix formed an interconnected conductive framework that enhanced interfacial polarization and charge carrier transport. The composites exhibited frequency-dependent dielectric behavior characterized by negative permittivity in the kHz–MHz region─consistent with Drude-type plasmonic response─and positive permittivity in the X-band (8.2–12.4 GHz). Increasing g-C 3 N 4 content significantly improved electrical conductivity and dielectric loss, leading to superior EMI shielding performance. The optimized composite achieved a maximum total shielding effectiveness of ∼40 dB, corresponding to over 99.99% attenuation of incident electromagnetic radiation, predominantly via absorption. These results highlight the significance of PVA/CB/g-C 3 N 4 ternary composites as lightweight, flexible, and sustainable materials for advanced EMI shielding applications in aerospace, flexible electronics, and portable devices.