Evolution of a polyphenolic antioxidant in electron irradiated polypropylene for a grafting purpose

Complete text of publication follows. It is known that polypropylene (PP) irradiated in O2 atmosphere will degrade due to the presence of tertiary C on the backbone. Hydroxyperoxides and radicals are induced which are responsible for the degradative oxidation during and after irradiation. PP must be suitably stabilized in order to withstand radiation sterilisation and long-term storage. This work carries on several studies that have evidenced the degradation of these polymer additives under ionizing radiation during the sterilization process. As the degradation products created are likely to migrate through the polymer matrix into the surrounding medium, their potential toxicity creates a health problem considering that the medium in contact can either be solutions, drugs or even food. One of the solutions to migration is the immobilization by radiation grafting of the additives in the polymer matrix by means of covalent bonds. We have previously evidenced by high temperature Size Exclusion Chromatography (SEC) and Differential Scanning Calorimetry that the medical grade PP chosen degrades under radiation by fragmentation of the crystalline zones. By means of IRFT, we also evidenced the formation of oxidation products during irradiation. This present work gives the results of UV studies showing the extraction kinetic of the antioxidant Irganox 1010 and of High Performance Liquid Chromatography (HPLC) study performed on extraction solutions showing that Irganox 1010 degrades into products having higher polarity and/or smaller size. One of the degradation products of Irganox 1010 is the butylated hydroxy toluene (BHT) which represents one quarter of the chemical composition of Irganox 1010. Nevertheless the chemical yield of the extraction does not give the ratio of 4 moles of BHT for one mole of Irganox 1010, which leads us to consider either the bad efficiency of the extraction either the good efficiency of the grafting