Tailoring bandgap and dielectric properties of RPET using lanthanum oxide nanofillers for UV-shielding and optoelectronic applications

This study reports the functionalization of recycled polyethylene terephthalate (RPET) with lanthanum oxide (La₂O₃) nanoparticles at loadings of 1, 2, 4, and 8 wt.% to enhance its physicochemical, optical, dielectric, and thermal properties for advanced material applications. Molecular electrostatic potential (MESP) analysis revealed enhanced charge redistribution and increased electronegativity with La₂O₃ incorporation, indicating improved chemical reactivity and potential in energy storage systems. X-ray diffraction (XRD) confirmed a transition from amorphous to semi-crystalline structures, maximized at 4 wt.% La₂O₃, while FT-IR spectra displayed characteristic peak shifts and bond formations evidencing strong RPET-La₂O₃ interactions. Optical studies revealed a marked increase in the UV-region absorption coefficient (α) with increasing La₂O₃ content, indicating enhanced photon-polymer interactions, while maintaining high transparency in the visible region. The direct optical band gap decreased from 3.98 eV (pristine RPET) to 3.77 eV at 8 wt.% loading, confirming matrix-filler interaction and tunability of optical properties. Dielectric analysis showed significant improvements in dielectric constant (ε′), dielectric loss (ε″), and AC conductivity (σ_AC), with the 4 wt.% composite exhibiting the highest σ_AC (1.12 × 10^–5 S·cm⁻¹ at 100 °C) and stable dielectric performance over a broad frequency range. Thermal analysis (TGA and DSC) confirmed enhanced thermal stability, with the 4 wt.% sample exhibiting a 12 °C increase in onset decomposition temperature and altered melting profiles, indicating strong interfacial bonding and the formation of thermally resistant phases. These findings identify 4 wt.% La₂O₃ as the optimal loading, offering a balanced improvement in optical absorption, dielectric stability, conductivity, and thermal resistance, thereby establishing La₂O₃-RPET nanocomposites as promising candidates for UV-shielding, dielectric, and thermally stable conductive materials for electronic and energy applications.