Effects of temperature on the weathering lifetime of coated polycarbonate

The lifetime of polycarbonate (PC) coated with silicone hardcoats containing UV absorber is shorter at elevated temperatures. The activation energy (Ea) for delamination was found to be 18 ± 2 kJ/mol (4.3 ± 0.5 kcal/mol) at the 95% confidence level in this study. This Ea is the consequence of the sensitivity of the substrate and the UV absorber to temperature. The Ea for PC photodegradation was previously found to be 17-21 kJ/mol (4-5 kcal/mol). The Ea for loss of absorbance in the second-generation silicone hardcoat was found to be 28.5 ± 5.4 kJ/mol (6.8 ± 1.3 kcal/mol) at the 95% confidence level. Results are consistent with experimental findings when these activation energies are used in published predictive models. Since the Ea for coating delamination depends on the Ea of UV absorber loss, coating systems different from the one in this study will need to be investigated separately.