Synergistic EMI Shielding Efficiency of Biodegradable PLA/PBS-Based Composites Reinforced with Carbon Fibers and ZnO Nanoparticles

The escalating electromagnetic pollution from modern electronics, combined with the global plastic waste crisis, demands the development of high-performance EMI shielding materials based on sustainable and biodegradable polymers. Biodegradable polyesters such as polylactic acid (PLA) and polybutylene succinate (PBS) offer a compelling solution owing to their renewable origin, low carbon footprint, and susceptibility to enzymatic degradation by proteases, lipases, and esterases under composting conditions, which enable responsible end-of-life disposal and support circular economy principles. In this context, this study focuses on the development of biodegradable PLA/PBS-based composites with exceptional electromagnetic interference (EMI) shielding effectiveness through the synergistic combination of carbon fibers (CF) and ZnO nanoparticles. A fixed CF content of 20 wt % was employed to establish a conductive backbone, while ZnO nanoparticles were incorporated at 1, 3, 5, and 7 wt % to enhance dielectric loss and absorption-based shielding. EMI shielding measurements in the X-band revealed a dramatic improvement in total shielding effectiveness (SET), increasing from 1.7 dB for the PLA/PBS matrix to 30.7 dB with CF reinforcement and reaching 70, 59, 73, and 85 dB for composites containing 1, 3, 5, and 7 wt % ZnO, respectively. The composite containing 1 wt % ZnO exhibited the most efficient EMI shielding response relative to filler content, achieving a high SET of ∼70 dB with minimal nanoparticle loading. This superior performance was attributed to the uniform dispersion of ZnO nanoparticles, which maximized interfacial polarization, dielectric loss, and multiple internal scattering within the carbon fiber-supported network. Structural, rheological, thermal, and mechanical analyses consistently showed that increasing ZnO content beyond 1 wt % led to nanoparticle agglomeration, network disruption, reduced melt elasticity, and mechanical embrittlement, despite further increases in absolute SET at higher loadings. EMI shielding in all composites was dominated by absorption (SEA > 80%), making them particularly suitable for practical EMI mitigation applications. These findings demonstrate that optimized ZnO dispersion at low loading is a key factor in achieving efficient, absorption-dominant EMI shielding in biodegradable polymer composites, offering a sustainable and environmentally responsible alternative to conventional metal-based and petroleum-derived polymer shielding materials.