Photo-Aging of Coating Based on Mixture of TDI and N75

The photoaging of coating based on toluene diisocyanate (TDI) and N75 was investigated though artificial light exposure. The properties of studied polyurethane coatings, such as film gloss loss and discoloration were examined at some aging interval. In addition, scanning electronic microscopy (SEM) and Fourier transform infra-red spectroscopy (FTIR) were used to measure the morphology and chemical change of coatings before and after exposed under UV light. It was found that the addition of N75 had a significant effect on the discoloration of polyurethane coating. Furthermore, SEM images showed that greater degradation occurred in the coating without N75. These findings were also supported by the results obtained from FTIR analysis and gloss loss. The above results suggested that a mixed curing agent system with a mass ratio of TDI to N75 between 5:5 and 3:7 be a possible substitute of pure N75 for weather resistance PU coatings.