Quantitative ultraviolet spectroscopy in weathering of a model polyester-urethane coating

摘要

Spectroscopy was used to quantify the effects of ultraviolet light on a model polyester-urethane coating as it degraded in an accelerated exposure chamber. An explorative calculation of the effective dosage absorbed by the coatings was made and, depending on the quantum yield chosen to represent the damaging processes, was found to follow an accelerating trend with exposure period that may permit estimation of a service lifetime by spectroscopy. The accelerating trend was due to an increase in the absorption "yellowing" tail as degradation proceeded. Quantification as an "Urbach" tail, and the underlying electronic transition by an analysis due to Tauc et al., showed that the Urbach energy was consistent with values found elsewhere. It is possible that, for this urethane at least, any explanation of "yellowing" may not require the development of specifically yellow chromophores.