Accelerated weathering and chemical resistance of polyurethane powder coatings

A study of the weathering mechanism of innovative polyurethane powder coatings has been performed. UV-B irradiation and condensation cycle accelerated tests were carried out on two different polyurethane powder coating formulations for outdoor applications. Using Fourier transform infrared spectroscopy and microscope observation, it was possible to analyze the photochemical and morphological modifications. In addition, the color and gloss changes were measured. Organic coatings are often in contact with solvents in particular during cleaning actions. The chemical resistance was then studied considering the evolution of the corrosion barrier property of the coating as a function of the solvent contact time. Electrochemical impedance spectroscopy measurements were carried out. Methylethylketone (polar) and xylene (apolar) were considered as representative solvents. Due to the strong polarity, the first solvent showed a strong interaction with the hydrogen bonds between the polyurethane chains causing the solvent uptake. The amount of solvent uptake depends on the coating chains rigidity caused by the different polyester resin monomers. The apolar xylene presented no significant interaction with the coatings.