Advanced Spectroscopic Studies into the Degradation of Polyester Melamine Coil Coatings before and after Exposure to Natural and Accelerated Weathering Tests

Abstract

Polymeric coating research requires advanced spectroscopic techniques to perform more efficient and detailed analysis in order to improve knowledge on the component distribution and the degradation of functional groups in the coating. In this work, the advanced non-destructive Step-scan Photoacoustic (SSPA) FTIR and Confocal Raman Microscopy (CRM) techniques were developed and applied to the component distribution studies and degradation studies of polyester/melamine based coil coating. The results show that both techniques are very suitable to carry out both qualitative and quantitative analyses. The degradation of polyester/melamine coil coating exposed in various environmental conditions were studied in detail using the advanced SSPA-FTIR and CRM techniques; the results clearly show that the coating degradation is highly dependent on the weathering conditions. Acid rain was also found to significantly affect the coating durability. Moreover, different pigments incorporated into the coating formulation were also found to have a major impact on the coating durability. With the help of the powerful CRM component distribution analysis function, melamine enriched zones that were very likely to arise from the melamine self-condensation during the curing process of coil coating were clearly observed in the coatings. This finding confirms the hypothesis developed over 20 years in the coil coating research field. Moreover, the durability of the melamine enriched zones was also investigated in this work.