کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
694225 | 889943 | 2007 | 10 صفحه PDF | دانلود رایگان |
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.
Journal: Progress in Organic Coatings - Volume 58, Issue 4, 1 March 2007, Pages 272–281