Effects of Spectral UV on Degradation of Acrylic-Urethane Coatings

摘要

Polyurethanes (PU) based on acrylic polyols are used extensively as exterior coatings. However, these materials undergo degradation during exposure to outdoor environments. Although temperature, moisture, and other weathering elements may contribute to the degradation of polymer coatings, the primary cause of PU degradation during outdoor exposure is ultraviolet (UV) light. For that reason, the photodegradation mechanism of PU and its model compounds have been studied extensively. Both aromatic and aliphatic isocyanate-based polyurethanes undergo chain scission by photo-oxidation process. It is well known that photodegradation (photolysis and photo-oxidation) of a material is determined by the absorption characteristics of radiation in that material. However, the absorption of radiation energy in polymers is controlled by their chemical structure and is dependent on radiation wavelength. Studies on wavelength sensitivities of a variety of polymers have been reviewed. However, little information is available on the photodegradation behavior of PU with respect to radiation wavelengths. The main objective of the present study is to investigate the effects of different radiation wavelengths from 290 nm to 525 nan on the degradation mechanism and quantum efficiency of acrylic polyol-based polyurethanes.