Antioxidant effectiveness of vitamin E in HDPE and tetradecane at 32°C

Abstract

Vitamin E was found to be a very effective antioxidant both in a model, liquid alkane, (teradecane) and in HDPE when oxidations at close to room temperature were initiated with g-radiation. FTIR was used to follow changes in vitamin E in oxidising tetradecane and HDPE, even at very low concentrations of the antioxidant. Formation of isolated hydroperoxide groups as a direct result of the vitamin E-peroxyl radical reaction were clearly visible. Quinone products from vitamin E were formed during g-irradiation, but different quinones were formed depending on the vitamin E concentrations. Vitamin E quite effectively retarded the oxidation of HDPE during g-irradiation and so should be useful in polyethylene intended for radiation sterilisation, as packaging materials or medical devices. Crown

Grafting of α-tocopherol upon γ-irradiation in UHMWPE probed by model hydrocarbons

“…The antioxidant effect of α-tocopherol on PE upon γ-irradiation has been studied extensively [2,3,5,7,[10][11][12][13]25]. Most of those studies concentrated on the formation of oxidation products in PE, radical formation or cross linking.…”

“…Only a few studies, however, have investigated the chemical transformation or degradation of α-tocopherol. Typically, degradation of α-tocopherol was observed in terms of loss of the IR absorption of the phenolic OH group [2] or by polymer extraction studies [25].…”

“…Nowadays, stabilisation by this antioxidant is used in many PE foils used for food contact. Concentrations of α-tocopherol for such applications are in the range of 100 to 300 ppm, including pouches intended for γ sterilisation [2,3]. Around the year 2000, α-tocopherol was postulated as antioxidant to be used in UHMWPE for orthopaedic implants [4] and extensive investigations initiated on the mechanical, physical, chemical and wear behaviour of such stabilised UHMWPE.…”

“…In the experiments of Mallégol et al [2], HDPE was irradiated step by step and the polymer was analysed immediately after each irradiation by FTIR. An exhaustion of the phenolic function of α-tocopherol with increasing irradiation dose was observed.…”

“…As postulated before by Al-Malaika et al [13] it is concluded that the α-tocopherol molecule is grafted to the polymer back chain. Mallégol and co-workers report a "grafted quinone" and suggest that the α-tocopherol is grafted to the macromolecule by a peroxide bond on the site of the former phenol group [2].…”