An investigation of the effect of pigment on the degradation of a naturally weathered polyester coating

A series of coil coatings based on a polyester/melamine resin formulation, incorporating different pigment systems, were naturally weathered after being exposed to the elements in Hainan, PRC, for 2 years. The surface chemistry and morphology, before and after weathering, was investigated using both traditional (i.e., gloss retention, color change) and novel (i.e., X-ray photoelectron spectroscopy [XPS], atomic force microscopy [AFM], and scanning electron microscopy [SEM]) methods. Chemical changes occurring in the coating bulk were investigated using step-scan photoacoustic Fourier transform infrared spectroscopy (SSPA-FTIR). It was found that the coating surface morphology, surface chemistry, and bulk chemistry, both before and after weathering, were all affected by the type and concentration of the pigments included in the coating formulation. Moreover, it was found that different types of pigment catalyze different coating degradation mechanisms.