WAVELENGTH SENSITIVITY OF UNSTABILIZED AND UV STABILIZED POLYCARBONATE TO SOLAR SIMULATED RADIATION

Activation spectra of bisphenol A polycarbonate based on yellowing and increase in ultraviolet (UV) absorption were obtained by the sharp cut filter technique which was shown to provide the same information as the spectrographic technique. The optical changes are caused by two distinctly separate actinic regions of borosilicate filtered xenon arc radiation, wavelengths below 300 nm and between 310 and 340 or 350 nm. They have significantly different quantum efficiencies and differ in the amount of yellowing relative to the increase in ultraviolet absorption promoted. This supports previous studies which identify different degradation mechanisms by short versus long wavelength UV radiation. The shorter wavelength region causes both more severe yellowing and greater increase in UV absorption. Inhibition of degradation by the UV absorber in the stabilized polycarbonate was shown to be more effective against the long wavelength actinic radiation. Yellowing by solar radiation is due only to the longer wavelength region, indicating that the photo-Fries pathway is insignificant during outdoor exposure, based on previous work showing that it is primarily promoted by the short wavelength UV radiation.