The effects of electron beam irradiation on additives present in food-contact polymers.

A range of additives (Irganox 1010, Irganox 1076, Irganox 1330, Irgafos 168 and Tinuvin 622) has been incorporated into a variety of food-contact polymers including polypropylene and low density polyethylene. Samples of these stabilized polymers were subjected to electron-beam or gamma irradiation to receive doses of 1,5,10,25 and 50 kGy. The effects of electron-beam irradiation on the amount of extractable antioxidant in polymers were determined. Using hplc techniques it was found that there was a dose-related reduction in the amount of extractable antioxidant similar to that caused by gamma irradiation. The magnitude of this reduction was found to be dependent upon the nature of both the antioxidant and the polymer type. Electron-beam irradiation was also found to cause a dose-related reduction in the levels of the antioxidants Irganox 1010 and Irganox 1076 migrating from polymers into a food simulant. This effect was similar to that caused by gamma irradiation. The extent of polymer binding of antioxidant fragments derived from Irganox 1076 following electron-beam irradiation was determined, using a radiochemical method. The amount of binding was found to be dose-related and of a similar order of magnitude to that caused by gamma-irradiation. This study has revealed the presence of many irradiation derived antioxidant transformation products in extracts from irradiated polymers. Attempts have been made to isolate and identify these compounds, and a number of possible structures are proposed following lc-ms studies. In some cases, the irradiation-derived transformation products appear to be different to those produced on thermally aging stabilized polymers. Irradiation was also found to give transformation products farmed via the cleavage of tertiary butyl groups from the parent molecules, and such compounds are not produced during the thermal aging of similar stabilized polymers, nor in model reactions between the antioxidants and t-butylperoxyl radicals. A brief examination of the effects of gamma irradiation on Tinuvin 622 in polypropylene was also carried out, and a number of UV absorbing transformation products were detected.