Reciprocity and spectral effects of the degradation of poly(ethylene‐terephthalate) under accelerated weathering exposures

Abstract

ABSTRACTExposures of poly(ethylene‐terephthalate) (PET) films were performed under xenon‐arc (full spectrum) and fluorescent UVA‐340 (UV only) irradiation to investigate the reciprocity principle and wavelength dependence of photodegradation in weathering. When the intensity of full spectral irradiance is increased from 5× to 50×, the reciprocity principle is not obeyed in this material system. The change in optical properties for PET is attributed to the corresponding longer exposure time of the 5× exposure that allows oxidative reactions to occur at lower irradiance. Full spectrum xenon‐arc and fluorescent UVA‐340 lamps have different spectral distributions and samples exhibits different material degradation mechanisms under each source. The UVA‐340 exposure leads to more pronounced degradation relative to the full spectrum xenon‐arc. This study shows that intensification of a single stressor in lab‐based weathering experiments to accelerate degradation and the use of differing light sources are not sufficient to allow reliable determination of service lifetime of polymeric materials. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47589.