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

Abstract

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.

Consideration of roles of commercial TiO2 pigments in aromatic polyurethane coating via the photodegradation of dimethyl toluene-2,4-dicarbamate in non-aqueous solution

“…Previous studies have focused on some physical property of the polymer such as weight loss, discoloration, and gloss retention, for evaluating the performance of titanium dioxide pigments through artificial weathering tests or outdoor exposure tests [18][19][20]. Changes in these physical properties, however, often take hundreds or thousands of hours to become apparent and also are easily influenced by operating conditions.…”

Depth-Resolved FTIR-ATR Imaging Studies of Coating Degradation during Accelerated and Natural Weathering─Influence of Biobased Reactive Diluents in Polyester Melamine Coil Coating

“…The degradation shown in the spectra was quantified using melamine substitution functionality loss (MSFL), sometimes denoted melamine degradation, loss of melamine, or triazine substitution index. 14 , 27 , 30 where P ref = ( I 1550 / I 1375 ) ref is the absorbance of the 1550 cm –1 triazine peak in the reference sample, normalized against the 1375 cm –1 peak assigned to the carbon chain backbone of the coating material, and P exp is the corresponding normalized peak height in the spectra for the analyzed sample area after exposure.…”

“…One example of such a study is that of Zhang et al, which reported on coatings with different pigments exposed in accelerated weathering (QUVA) and after weathering exposures at a field site in China. 14 The results showed among other things that different degradation mechanisms related to the dissolution of pigmentation in acid rain occurred for the outdoor weathering exposures as compared to that for the accelerated QUVA weathering. In addition, degradation at the surface level of the coating did not necessarily give a valid indication of the state of the bulk material.…”

Model-based analysis of photoinitiated coating degradation under artificial exposure conditions

“…If any essential special rate phenomena occur, e.g., a hydrolysis reaction 17,48,50 or reactions of photoactive pigments, 70 detailed experimental data are required prior to incorporation of these rate-influencing steps in the model. In principle, the model can be used for predicting in-service coating behavior, based on well-controlled and extensive accelerated laboratory measurements, by calibration of the model parameters.…”