Comparison of laboratory accelerated weathering tests for organic coatings

Acrylic polyurethane varnish coatings were exposed in two artificial weathering environments produced by a fluorescent UV/eondensation weathering device and a xenon lamp light exposure/weathering equipment for different periods of time. The results showed that the xenon exposure program affected the thickness loss and gloss loss more seriously than the UV/condensation. However, yellow index measurements and low frequency impedance revealed that a greater degradation was caused by the UV/condensation, which was in agreement with the result obtained from FTIR analysis. In the two accelerated weathering environments, the low frequency impedance modulus of intact coatings decreased exponentially with the increase in ageing time, and correlated with the changes in other properties of ageing coatings. It can be used to predict the lifetime of the coatings.