Phosphite additives and their transformation products in polyethylene packaging for gamma-irradiation

Infrared (IR) spectroscopy has been used to identify and quantify the phosp hite antioxidant, tris(2,4-di-tert,butylphenyl) phosphite, and its correspo nding phosphate in high density polyethylene (HDPE) food trays, both in the original, commercial trays and also as a function of gamma -irradiation an d post-irradiation, storage conditions. This direct method of inhibitor ana lysis complements time-consuming (some times non-quantitative) extraction m ethods, which for organo-phosphites are complicated by their facile convers ion to phosphates by peroxidic impurities in the solvent. Because of the co mplete destruction of phosphite to give mainly phosphate at quite low gamma -irradiation doses (similar to5 kGy) and phosphate formation during melt p rocessing and radiation sterilization of these HDPE trays must take into ac count products from the irradiation of phosphate. Any residual phosphite is lost progressively in post-irradiation reactions, which are complex, produ cing a less than-quantitative yield of phosphate.