Thermal yellowing and photobleaching of automotive topcoats
Thermal yellowing and photobleaching are common problems that are seen to some extent in all automotive topcoat systems today. These effects can cause difficulties in the matching of light colors in the assembly plant and then later upon delivery to the customer.
Current literature offers no clear mechanism for the thermal yellowing and photobleaching. Based on observed formulation dependencies, a mechanism is proposed based on oxidation of amine compounds. The scientists constructed a model in vitro system using a hydroperoxide to thermally oxidize amines in solution.
Nitrone formation as chromophore
In this system, a series of amines were tested and both yellowing and photobleaching were reproduced. Loss of basicity confirmed that amine oxidation occurred under these conditions. Both the location of the UV absorption peak and strong amine structure dependence indicate nitrone formation as the yellow chromophore.
The study is published in: Journal of Coatings Technology and Research January 2018, Volume 15, Issue 1, pp 131–139.
Bildquelle: Pixabay
