Abstract
Several important classes of u.v. activator for polymers have been studied in polyethylene. The progress of the oxidation was followed by measuring carbonyl formation in polyethylene films (carbonyl index) and by following the change in dynamic modulus of the polymer with time. The two procedures gave good agreement on the rates and extents of the two degradative reactions occurring. Three different kinds of u.v. oxidative behaviour were observed. The first, typical of the efficient triplet activators such as benzophenone and its derivatives, caused an initial rapid oxidation, increasing with ketone concentration, followed by auto-retardation. The second, typical of transition metal ions, caused an auto-accelerating rate of oxidation increasing with concentration, the third, characteristic of sulphur-containing metal complexes, showed an initial induction period which increased with increasing concentration, followed by rapid autoacceleration to physical disintegration. It is shown that, in each class, the u.v. behaviour is an extension of the function of the additive in the polymer melt during processing.
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