Pollutant-accelerated aging behaviors of fluorocarbon coating in tropical marine atmosphere

The aging behavior of polyvinylidene fluoride coatings in a tropical marine atmosphere was studied by natural exposure tests. The surface morphologies, chemical structures, and barrier effects of the coatings after natural weathering were investigated by scanning electron microscopy, attenuated total reflection Fourier transform infrared, X-ray photoelectron spectroscopy, and electrochemical impedance spectra measurements. Grey relational analysis was also performed to establish the relationship between environmental factors and degradation behaviors. It was found that the degradation of the coatings was accelerated, manifesting the breakage of CF bonds after 18 months of exposure at Hainan test site. With the aid of grey relational analysis, temperature, humidity, sunshine duration, and ammonia deposition were the most important factors that greatly affected the aging behaviors of the coatings. Therefore, a two-step degradation mechanism was proposed for the aging process. The first step was the degradation of the acrylic polyurethane resin through the photo-oxidation reactions. The second step was the dehydrogenation and defluorination of the fluorocarbon resin resulting from the ammonia-induced alkaline environment.