Synergistic enhancement of charge transport, dielectric behavior, and impedance response in Cu/ZnO dual-nanofiller-loaded NaAlg/CMC biopolymer nanocomposites for biodegradable solid polymer electrolytes

Abstract

ZnO nanoparticles were synthesized via a sol-gel method and then incorporated as Cu/ZnO dual nanofillers into sodium alginate (NaAlg)/carboxymethyl cellulose (CMC) biopolymer composite films using the solution-casting technique. The structural, dielectric, electrical, and impedance characteristics of the prepared films were systematically evaluated. XRD analysis showed that Cu/ZnO incorporation progressively disrupted the crystalline domains of the NaAlg/CMC matrix, with the optimum effect observed at 4.0 wt.% filler content. FTIR spectra indicated strong intermolecular interaction between the functional groups of the polymers (–OH/–COO⁻) and the nanofillers through hydrogen bonding and electrostatic coordination. SEM images showed improved dispersion of nanofillers at lower concentrations, while higher loading led to partial agglomeration. The dielectric parameters (ε′ and ε″) strongly depended on the filler content, consistent with Maxwell–Wagner–Sillars (MWS) polarization arising from charge accumulation at the polymer–nanofiller interfaces. The AC conductivity increased with Cu/ZnO incorporation and reached a maximum value of ~2.1 × 10⁻⁵ S.cm⁻¹ at 4.0 wt.% filler loading at high frequency (10 MHz). The Nyquist plots exhibited depressed semicircles, indicating a non-Debye response associated with the bulk resistance of the polymer matrix and interfacial charge-transport processes. Overall, the optimized NaAlg/CMC:Cu/ZnO nanocomposite exhibited enhanced dielectric and electrical properties, indicating its potential as a biodegradable solid polymer electrolyte platform for future energy-storage and electronic applications. Cu/ZnO dual nanofillers were incorporated into NaAlg/CMC biopolymer blend via solution casting method. Structural analysis confirms enhanced amorphization and strong polymer–nanofiller interactions in the nanocomposite films. Significant improvement in AC conductivity, dielectric constant, and impedance response is achieved with optimized filler content. Interfacial polarization and charge carrier mobility are enhanced due to increased free volume and nanofiller dispersion. The developed biopolymer nanocomposites show potential for biodegradable solid-state electrolytes and energy storage applications. Cu/ZnO dual nanofillers were incorporated into NaAlg/CMC biopolymer blend via solution casting method. Structural analysis confirms enhanced amorphization and strong polymer–nanofiller interactions in the nanocomposite films. Significant improvement in AC conductivity, dielectric constant, and impedance response is achieved with optimized filler content. Interfacial polarization and charge carrier mobility are enhanced due to increased free volume and nanofiller dispersion. The developed biopolymer nanocomposites show potential for biodegradable solid-state electrolytes and energy storage applications.