Abstract
AbstractThe photo‐oxidation of PVC has been studied over the temperature range 30–150°C. Initiation with ultraviolet (2537A) radiation has been correlated with the presence of minute amounts of ozone. The contribution of atomic oxygen and singlet oxygen (1Δg) molecules to the initiation mechanism is discussed. The β‐chloroketones probably formed in the photo‐oxidation of PVC, decomposed according to a Norrish type I reaction without loss of chlorine atoms. The gaseous products of the photo‐oxidation of PVC at 30°C were carbon dioxide, carbon monoxide, hydrogen, and methane. Hydrogen chloride was obtained only when PVC was heated at high temperatures. When PVC was photo‐oxidized and then heated at high temperature, benzene was obtained in addition to hydrogen chloride. The gaseous products from the photo‐oxidations of model compounds, such as 4‐chloro‐2‐butanone and 2,4‐dichloropentane, were also compared with those from PVC. Hydrogen chloride was detected only after photo‐oxidation at temperatures of 25°C or higher. Therefore, it was concluded that hydrogen chloride is mainly a product of thermal decomposition. Since unsaturation was not observed in photo‐oxidized PVC films, the cause of discoloration is unclear. When PVC was modified by stabilizers or additives, the oxidative degradation was further complicated by side reactions with the additives.
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