Hindered Amines as an Alternative of α-Tocopherol for Polyethylene Stabilization

Abstract

Ultra-high molecular weight polyethylene (UHMWPE) is used as a bearing material in total joint replacements. These joint replacements are in contact with the body fluids during their lifetime, resulting in material degradation. Due to the limited flow behaviour and the large number of physical entanglements of UHMWPE, some measurements (rheological measurements, determination of the gel content and extractable fraction, etc.) cannot be properly evaluated. Therefore, we have focused on accelerated aging of high density polyethylene (HDPE) in the hydrogen peroxide oxidation environment, allowing complete evaluation of degradation damage by monitoring mechanical, rheological, thermal and spectroscopic changes of the material. Perspective amine antioxidants (HALS) and the classical phenolic stabilizer α-tocopherol were used for HDPE stabilization and their effects compared. The aim of the work was to find an effective and rapid method of evaluating the antioxidant effect of newly developed stabilizers for UHMWPE using accelerated aging tests of lower molecular weight analogues. The results have shown that radiation crosslinking of HDPE leads to materials with higher sensitivity to oxidation. All tested stabilizers effectively inhibited the oxidation of HDPE. Moreover, after irradiation and subsequent aging, the branching of HALS stabilizer-containing HDPE chains took place which resulted in increased material resistance.