Facility for determining action spectra of UV photodegradation

We have developed an ultraviolet (UV) ageing facility consisting of a spectrograph which can be used to expose material samples with spectrally dispersed UV radiation at the wavelength range 273-423 nm, and an automated, high-resolution laser-based setup for measuring the induced color changes in the transmittances of the exposed samples. The samples are scanned using a suitable laser wavelength to obtain the wavelength dependence on the color change. The locations on the samples are converted to exposure wavelengths with the known dispersion of the spectrograph. We demonstrate the facility by exposing and measuring a set of atactic polystyrene sheets. By studying samples aged for different time periods we derive a complex action spectrum for the photoyellowing that is nonlinear with respect to the radiant exposure. We further derive linear activation spectra for the photoyellowing demonstrating how they depend on the selected threshold level