Effect of Free Radicals induced by thermal aging on electrical and optical properties of BOPP film for capacitors

Thermal aging is one of the complex problems facing the reliable performance of capacitor dielectrics. This work is to investigate the effect of thermal oxidation on the electrical and optical properties of biaxially oriented polypropylene (BOPP) film at temperatures ranging from 50$^{\circ}\mathbf{C}$to 110 °C. The chemical composition, thermal oxidation, changes in microstructural, surface topography, and morphology are confirmed by attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy, field emission electron microscopy (FE-SEM), and atomic force microscopy (AFM), respectively. In contrast, the film's electrical properties are identified with dielectric relaxation spectroscopy (DRS). Molecular dynamics (MD) simulation is performed based on density functional theory to determine the mechanisms behind it. Analysis of Three-dimension (3D) surface maps and Ultraviolet-visible (UV-Vis) spectra, as well as the calculation of energies of a highest occupied molecular orbital (HOMO) - lowest unoccupied molecular orbital (LUMO) and density of states (DOS), confirms the degradation of optical properties due to the influence of hydroxyl -OH and carbonyl$\mathbf{C}= \mathbf{O}$groups. It has been found that the long-term heat causes serious chemical-physical changes that lead to a loss of dielectric properties of BOPP film.