Diffusion mechanism of the synergism of u.v.-absorbers and antioxidants

The mechanism of synergism in mixtures of u.v.-absorbers with antioxidants is considered. The synergism is attributed to diffusion of the antioxidant from the deeper-lying layers of polymer film, protected from the action of light by a u.v.-absorber, towards surface layers where the photoreaction takes place. The effect of the antioxidant diffusion process on the duration of the induction period of the unbranched chain oxidation reaction of the polymer is analysed. The experimental investigation of the polybutadiene photo-oxidation process has verified the diffusion mechanism so allowing finding of the optimum relationship between the concentrations of u.v.-absorber and antioxidant and explanation of the observed enhancement of the effect of synergism in thicker polymeric films, for higher antioxidant diffusion coefficients and lower light intensities.