Chemical and physical change of packaging materials for food by γ-ray irradiation

Packaging materials for food made of polyethylene, polypropylene and polystyrene were irradiated with 60Co γ-ray. Exposure was 10, 30 and 50 kGy at 5 kGy/h exposure rate. With irradiating, all packaging materials of polyethylene and polypropylene produced volatile substances, for example, aldehydes, ketones and alcohols, especially, large amount of acetic acid and acetone. These volatile compounds were not observed in the sample unirradiated and increased with increasing exposure. Accordingly, it is concluded that they were decomposition products depend on irradiation. Polypropylene products were much more easily decomposed than polyethylene one because much more kinds and amount of volatile products were formed. However, on polystyrene products, content of styrene and ethylbenzene, monomer of raw materials, were reduced by irradiation and small amount of volatile substances were formed. These results proved its resistance to irradiation. (S.Y.)