ABSTRACT
Plastics and organic coatings used outdoors are exposed to ultraviolet (UV) radiation in the range of 295-400 nm, which is often the primary cause of degradation and weathering. UV absorbers (UVAs) are commonly used in these applications to prevent UV radiation from reaching the bulk of the polymer, or from penetrating the coating and reaching a UV-sensitive substrate. Early in the development of UVAs, it was recognized that they did not perform perfectly and could be depleted during exposure. Indeed, as early as 1961 Rirt and colleagues wrote:
Although subsequent workers recognized that UVAs could be depleted from polyolefins, the insight of slow, photochemical UVA loss seemed gradually to disappear from common wisdom. Then around 1990, several groups began to rediscover that UVAs used in coatings could be lost through photochemical reactions, and that this loss was responsible for limiting the lifetime of the coatings. This has led to a resurgence in interest in UVA photostability and to an understanding of how rates of UVA loss affect the lifetime of coatings.
