Influence of the structure on the γ-irradiation of polypropylene and on the post-irradiation effects

The radiation-induced oxidative degradation of isotactic, smectic and amorphous polypropylene (PP) films was characterised after gamma-irradiation and during storage at ambient temperature. Combining IR analysis with chemical derivatisation reactions and physical treatments allowed the detection of the products formed just after exposure and in the post-irradiation period. The formation of ketones and acids was observed and the structure of hydroperoxides and alcohols was characterised. The formation of oxidative species was shown to continue in the post-irradiation period after gamma-exposure of isotactic and smectic PP. On the contrary, the oxidation was shown to occur only to a small extent after gamma-exposure of amorphous PP or after exposure to UV of amorphous, isotactic and smectic PP, indicating that the free radicals trapped in the crystalline area are the main cause for the post-irradiation oxidation observed in the case of gamma-irradiated PP. The presence of the smectic phase favours the oxidation during exposure but also enhances the resistance of PP to post-irradiation oxidation. (C) 2004 Elsevier B.V. All rights reserved.