|Thursday, February 7 Preservation Hall B, 2nd Floor 11:00 am - 11:30 am|
|Jeffrey Quill||New proposed ASTM test method for accelerated weathering of coatings|
Co-Author: Sean Fowler
Coatings designed for automotive and aerospace applications have high performance expectations. One of the challenges faced by coatings chemists is that durability testing traditionally has taken two or more years to yield useful data. In a rapidly changing economic, technological, and regulatory environment, waiting two years for data is unacceptable. Accelerated weathering test protocols offer the promise of faster results, but speed often comes at the expense of accuracy. State of the art accelerated weathering tests in the automotive coatings industry, as published in SAE J2527, have not provided sufficient correlation with outdoor results to deliver reliable data about a proposed formulation’s durability. In a multi-year, multi-stage study, a consortium of leading companies in the automotive and aerospace coatings and weathering testing industries developed a more reliable accelerated weathering test protocol. A variety of coatings systems were exposed in South Florida for a minimum of two years, and the results of these exposures were closely replicated by the new accelerated laboratory protocol. Correlation between the accelerated protocol and natural exposures was determined by advanced infrared spectroscopy to examine degradation mechanisms on a molecular level. Common laboratory methodologies were used to determine correlation of physical changes, such as delamination, gloss loss, color change, cracking, and blistering. In addition to improved correlation, the new protocol achieved 40% greater acceleration than SAE J2527 accelerated tests. The study identified three limiting factors in the existing methods and targeted them for improvement. First, optical filters that achieve a better match to sunlight in the ultraviolet region were developed. Second, water absorption in South Florida exposures and in accelerated weathering devices was carefully characterized, and significant improvements were made in the accelerated weathering protocol as a result. Finally, cyclic conditions in the accelerated weathering chambers were iteratively developed to mimic the natural environment and improve correlation of both chemical and physical degradation. The new protocol utilizes existing, commercially available weathering devices and can be performed in devices of differing architecture.