Ultraviolet light absorber mobility in crosslinked coatings: Experiments and modeling
Date of Original Version
The diffusion of an ultraviolet absorber (UVA) across a concentration step change in an acrylic melamine clearcoat was measured via micro-ultraviolet spectroscopy. Concentration profiles were obtained after diffusion times of 4-200 h at steady temperatures of 70, 80, and 90 °C. The glass transition temperature of the coating was measured via dynamic mechanical analysis for each time-temperature pair, and Tg was observed to increase with thermal aging, with a faster rate of increase at higher aging temperatures. The change in Tg was modeled using a first-order dependence on the deviation from a long-time Tg asymptote. The diffusion coefficient was then represented by a free volume expression, and the combination provided an accurate model of the measured concentration profiles. The time-dependent increases in glass transition temperature helped to explain why UVA diffusion does not alleviate concentration gradients created by photooxidation under natural weathering conditions. © 2006 Elsevier B.V. All rights reserved.
Progress in Organic Coatings
Peters, C. A., K. R. Ellwood, Y. Srivastava, M. E. Nichols, and M. L. Greenfield. "Ultraviolet light absorber mobility in crosslinked coatings: Experiments and modeling." Progress in Organic Coatings 58, 4 (2007): 272-281. doi:10.1016/j.porgcoat.2006.12.004.