Assessment of Various Analytical Techniques On Naturally Weathered Paints as a Predictor Of Long-Term Gloss Retention for Waterborne Acrylic Architectural Paints.

Gloss retention of waterborne acrylic architectural paints is one of many properties defining exterior durability. Assessing gloss retention is a time consuming process, and accelerated weathering protocols (Weather-Ometer®) typically have poor correlation with natural exposures for this class of paints. The recent development of new analytical techniques for assessing automotive paint durability raises the possibility of detecting subtle changes in short-term natural exposures that would be predictive of long-term gloss retention; however, extension to architectural paints has yet to be demonstrated. To test the concept, seven paints based on different aqueous emulsion polymers were exposed to natural weathering at the same time for 12 weeks at the Paint Quality Institute (PQI) test site, and were then examined using scanning probe microscopy, optical profilometry, chemiluminescence, XPS, and FTIR. These paints were also exposed for 1000 hr in a Weather-Ometer (WOM). Scanning probe microscopy, optical profilometry, chemiluminescence, FTIR, and the WOM results all showed poor correlation with 96-week natural exposure at the PQI test site. The lack of correlation for the WOM results emphasizes the crucial importance of using natural weathering to assess gloss retention. In contrast, the XPS shows some promise for qualitatively predicting subsequent gloss loss and appears worthy of further exploration. As employed here, the XPS was used to monitor the ratio of pigment (Al, Si, and Ti) to carbon coming from the TiO₂ in the top few nanometers of the paint surface. A correlation (R² = 0.731) was found between gloss retention after 96 weeks and the change (2 versus 12 weeks of exposure) in pigment to carbon ratio. This correlation is probably sufficient to rank a series of paints and allow for an assessment against well-established controls. While promising, XPS has some issues. Surface contamination, equipment expense, the considerable expertise required, and precision make utility for screening less than ideal. [ABSTRACT FROM AUTHOR]