Staining Behavior of an Anti-Graffiti Polyurethane Clear Coating against Accelerated Weathering Test

Apermanent anti-graffiti clear polyurethane coating, using a silicone additive,was prepared and studied. Various techniques, such as contact anglemeasurements and EDX were employed to characterize and investigate thesurface properties of the coatings. The results revealed that with inclusion of siliconadditive to clear coating, according to Wu method, surface free energy was decreasedfrom 45.13 mJ/m2 for neat clear polyurethane film to 25.25 mJ/m2 in a coating containing5% additive. With inclusion of higher mole percentage of additive, surfaceenergies remained constant as revealed by EDX technique, which was considered tobe due to the excessively covered surface by silicone additive. Ageing under UVradiation revealed that the inclusion of additive up to 5 mole percentage couldimprove the anti-graffiti property during the first few aging cycles. However, byincreasing the number of aging cycles and higher concentration of silicone additive,the rate of degradation in coatings increased. The results showed that PU5% has thebest anti-graffiti and ageing properties among other compositions