Biopolymer-based dielectric nanocomposites: Green-synthesized CuO embedded in methyl cellulose for flexible energy...

The development of eco-friendly polymer-nanoparticle composites has emerged as a promising strategy to design flexible dielectric films for advanced energy storage and electronic devices. In this study, copper oxide nanoparticles (CuO-500) were synthesized via a green route using green tea extract as a reducing and stabilizing agent, followed by calcination at 500 °C. The as-prepared CuO nanoparticles were incorporated into a methyl cellulose (MC) matrix at different loadings (2, 4, and 6 wt%) through solution casting to form MC/CuO nanocomposite films. X-ray diffraction confirmed the monoclinic tenorite phase of CuO with average crystallite sizes of 24 ± 2 nm, decreasing upon incorporation into MC due to confinement and interfacial strain. FTIR spectra revealed strong hydrogen-bonding interactions between CuO and MC functional groups, while FESEM images demonstrated uniform nanoparticle dispersion up to 4 wt%. This electronic modification is directly linked to an enhanced optical dielectric constant real and imaginary parts (ε_r and ε_i) across the photon energy spectrum, with the absorption edge shifting to lower energies as the CuO content increased. All measurements were repeated in triplicate, showing deviations within ±3 %. These findings demonstrate that green-synthesized CuO embedded in MC provides a sustainable pathway for fabricating flexible dielectric films with improved energy-storage potential for supercapacitors and flexible electronic devices.