Title

Ultraviolet light absorber mobility in crosslinked coatings: Experiments and modeling

Document Type

Article

Date of Original Version

3-1-2007

Abstract

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.

Publication Title

Progress in Organic Coatings

Volume

58

Issue

4

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