A comparison of phenolic antioxidant performance in HDPE at 32–80°C

Abstract

The effects of several phenolic antioxidants on the thermal and γ-initiated oxidation of HDPE has been studied. Antioxidants included both di-tert.butyl hindered phenols and vitamin E. For equivalent concentrations of phenol groups, vitamin E was comparable to or better than the hindered phenols in limiting the oxidation of HDPE exposed to γ-rays. The poorer antioxidant activity in γ-irradiated HDPE at ∼32°C of a clustered, quadri-functional phenol, may stem from one group grafting through a peroxide link to the HDPE backbone. The activity of the three remaining phenolic groups will then be impaired because of restricted mobility. In thermo-oxidation at 80°C, vitamin E showed quite good performance at 80°C at low concentration, but clearly inferior to the clustered hindered phenol, present at a somewhat higher molar equivalent level. A small hindered phenol had poor performance because of its facile volatilisation from the polymer.