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L. DESCHENES¹, C. Vachon², D. J. Carlsson³, M. Kzrymien³, M. Mercier³, and B. Stewart¹. (1) Food Research and Development Centre, Agriculture & Agri-food Canada, 3600 Casavant West, St-Hyacinthe, QC J2S 8E3, Canada, (2) Industrial Materials Institute, National Research Council Canada, 75 de Mortagne, Boucherville, QC J4B 6Y4, Canada, (3) Institute for Chemical Process and Environmental Technology, National Research Council Canada, Montreal Road, Ottawa, ON K1A 0R6, Canada

Irradiation could be used for cold pasteurization treatment to increase shelf-life of prepackaged food products as well as to decontaminate packaging materials prior to filling with food and beverages. If irradiation does not significantly affect plastic polymers at doses of 60 kGy or less, it has a determinant effect on smaller molecules such as additives.

This work was undertaken to (1) better understand the degradation of tris(2,4-di-tert-butylphenyl) phosphite (Irgafos 168), a widely used antioxidant for polyhydrocarbons, and (2) identify the degradation products and potential migrants from irradiated polyethylene (PE) packaging materials.

Irgafos 168 was irradiated with Cobalt 60 at doses between 0 and 100 kGy. Samples under solid form were analyzed by NMR, FT-IR, dynamic headspace GC-MS and DSC. Extractives were analyzed by GC-MS, HPLC and LC-MS. Several experiments were also conducted on 1,3-di-tert-butyl benzene (1,3-DTBB) and 2,4-di-tert-butyl phenol to estimate their potential of grafting on PE and their stability to irradiation.

The results showed that, under solid dry form, Irgafos 168 resists well to irradiation. However, in solution and in PE matrix, it is easily destroyed, even at low doses. The structural analysis of the extracts of irradiated samples indicated that the degradation mechanism started by the conversion of phosphite to phosphate form. Thereafter, the phosphate is broken in smaller entities containing one or two 2,4-di-tert-butyl phenyl groups and in 2,4-di-tert-butyl phenol. Under irradiation, 2,4-di-tert-butyl phenol was converted in dimer or degraded in 1,3-di-tert-butyl benzene and smaller compounds. A dose of 100 kGy decreased the PE Tonset by 48°C.

This study suggests that Irgafos 168 contained in PE food trays is converted in several different chemical compounds (new indirect additives) under irradiation treatment. These compounds should be assessed for their migration into food simulants and for their toxicity.