A novel adsorption method to simulate the dirt pickup performance of organic coatings

The evaluation of the dirt resistance of organic coatings according to traditional accelerated methods (e.g., the standard method GB/T 9780-2013 in China) usually provides results which deviate from their real-world performance in seriously polluted environments. As an alternative, a novel adsorption method with methyltrimethoxysilane-modified rice-straw ash as the artificial dirt standard was proposed in this paper. With this method, the ash was dispersed into the air in a testing chamber and then allowed to physically adsorb to the coating, which is believed to more accurately simulate the adsorption behavior of floating particulates outdoors. Two groups of latex coatings from Dow Chemical Company were employed to evaluate the adsorption method by monitoring the changes in color, whiteness, and reflectivity. In parallel, outdoor exposure testing of these coatings was conducted. The influences of charging method, of ash type, and panel position on the testing results were carefully investigated. Multicharging of ash (9 g × 3) and parallel panels at different positions in the testing chamber are designed for the generation of repeatable results. It was demonstrated that the adsorption method basically matched the outdoor exposure results and was more predictive of real-world results than GB/T 9780-2013.