Failure of navy coating systems 1: chemical depth profiling of artificially and naturally weathered high-solids aliphatic poly(ester-urethane) military coating systems

A variety of weathering protocols are in use in industry and research laboratories to both replicate and accelerate the effects of weathering on coating systems. This work focuses on the use of two artificial and one natural weathering protocol (QUV, GM9540P, Florida beach exposure) in combination with spatially resolved transmission-mode Fourier transform infrared (FT-IR) spectroscopy for the purpose of chemically depth-profiling highly opaque high solids multi-layer poly(ester-urethane) coatings employed by the U.S. Department of Defense. Samples were prepared via subjection to 6/12-week GM9540P exposure, 7/13/25-week Florida beach exposure, or 6-/18-week QUV protocol. Thin (3 μm) cross-section samples were prepared via microtomy and depth-dependant trends in chemical evolutions were analyzed using transmission-mode micro-FT-IR. Scanning electron/energy-dispersive microscopy (SEM/EDS) was conducted on 10 μm cross-sections and spatial distribution/chemical makeup of inorganic constituents were analyzed. An apparent synergistic relationship between weathering protocols was found. It was theorized that a combination of chemistry and morphology of the inorganic fillers was primarily responsible for greater-than-expected photooxidative modification of the polymeric binder.