A non-destructive study on the degradation of polymer coating I: Step-scan photoacoustic FTIR and confocal Raman microscopy depth profiling

A polyester-melamine coating was exposed to accelerated weathering (i.e., cycle of high UV followed by condensation). The degradation depth profile in the coating was investigated using non-destructive step-scan photoacoustic fourier transform infrared spectroscopy (SSPA-FTIR) and confocal Raman microscopy (CRM). The degradation at different sampling depths was then evaluated following the method developed in this work. The results obtained using the two techniques correlate well with each other and suggest coating surface is more likely to undergo moisture enhanced photo-oxidation degradation. This may be due to the higher moisture level near the coating surface. It is also found that melamine side chains degrade prior to the melamine ring. The quantification methods developed in this work were found to be very suitable to monitor the degradation depth profile in polymeric coatings.