Structural and Optical Investigations of Radiation Damage in Transparent PET Polymer Films

Abstract

Effects of gamma irradiation at different doses up to 135 kGy on polyethylene terephthalate (PET) polymer films have been investigated by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and ultraviolet-visible (UV-VIS) spectroscopy. From XRD analysis, it was found that even at a high dose of gamma irradiation of 135 kGy, crystallinity of the PET samples remain unchanged. However, the FTIR peak at 871 cm−1 (depicting C–H bending mode of out-of-plane vibration) and another at 1303 cm−1 (representing C–H bending mode of in-plane vibration) disappear for gamma-irradiated PET. In this study, it has also been found that γ-irradiation in air enhances the optical absorption in the wavelength region 320–370 nm. This has been attributed to free radicals being produced in the polymer by the γ-radiation. Further, the free radicals react with oxygen of air to form carbonyl group and hydroxyls. With increasing γ-dose, there is a red shift of the UV—near visible cutoff for PET. XRD and FTIR observations on γ-damage have been correlated.