Natural phenolic compounds: Anti-oxidants or pro-oxidants for biopolyesters?

In this work, different naturally occurring phenolic compounds, such as Thymol (Th), Vanillic acid (VA) and Ferulic Acid (FA), have been considered as UV stabilizers against the photo-oxidative degradation of polylactic acid (PLA). Particularly, in order to explore the effectiveness of the naturally occurring stabilizers, thin PLA-based films, containing different amount of the stabilizers, have been formulated and subjected to accelerate UVB exposure. The preliminary characterizations suggest that the all considered stabilizers exert a plasticizing action and the overall crystallinity of the samples is slightly reduced. If the considered stabilizers are added at low concentration, they exert a protection action, but if their content overcome a specific threshold, are able to exert a pronounced pro-degradation action. Overall, in this work, the concentration-dependent anti-/pro- oxidant activity of used naturally occurring phenolic compounds has been accurately investigated and reported.