Photoageing and durability of a polyester-melamine organic coating on steel: Influence of pigments and multiscale analysis

This study investigates the influence of pigments on a polyester-melamine coating subjected to accelerated artificial photooxidative ageing using different scales of analysis (from molecular to macroscopic) with different techniques (IR, DSC, AFM, etc.) to gain broad insight into the material's degradation. The samples were studied in self-standing films and in coated steel plates with a coating thickness of 25 μm. Four formulations (with and without antioxidant, with and without pigments) were characterised, with a focus on the difference in behaviour between the degradation of the whole material and the degradation of the surface only under accelerated artificial photoageing. The data show that, regardless of the scale of analysis chosen, unpigmented formulations are degraded homogeneously, while pigmented formulations show significant degradation on the surface and relatively light degradation when the whole material is considered. This result signifies that the pigments show a retardant effect on the overall degradation of the coatings but have no retardant effect on the extreme surface of the samples. In addition, the different scales of analysis showed many similarities, which led to many correlations between them, including in cases where the effect of the pigment was considered.