Polyurethane composite coatings are frequently applied to strengthen the barrier properties of various construction materials such as wood, metal and concrete. The changes of color and glossiness of the composite coatings for building materials proceeds more slowly than that of polyurethane because of containing fillers and several types of additives. However, the most critical barrier properties have not been studied directly based on the difference from the degradation mechanism of polyurethane coatings. Additionally, the difference in thermal and UV degradation mechanisms of coatings is not clear in the existing studies dealing with conventional accelerated weathering tests and outdoor exposure tests. Therefore, the behavior of the filler contained in the coatings was observed using an oven to accelerate thermal degradation. The chemical analysis of the coating surface by XPS and the analysis of the images and elemental mappings by SEM-EDS were carried out, and the mechanism of degradation progress was investigated. In addition, the temperature dependency of the degradation was studied in changing the heating temperature. It was suggested that polymer and fillers interact in promoting mass transfer at the same time as the thermal degradation reaction consequently.
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