Stabilization of Polyethylene against Thermo-oxidative Degradation

5 Stabilization of Polyethylene against Thermo-oxidative Degradation 

As mentioned at the beginning of the chapter, the development of a second generation of highly cross-linked polyethylenes aims at providing oxidation resistance without the 

Despite the promising results presented by other antioxidants, the main oxidation stabilizers of choice are sterically hindered phenols, among which Vitamin E and Irganox (1010, 1035, 1076) stand out. These antioxidants have been shown to be more effective in radiative processes [80, 81]. Also, advances on the mechanisms of stabilization in polymer processing have shown that vitamin E is more efficient compared to other commercial additives [82,83]. Tocopherol compounds were proposed as stabilizers for polyolefins in the 1980s [84] and currently, they are the best alternative for the oxidative stabilization of highly cross-linked UHMWPEs. 

On one hand, the chroman head is capable of donation of a hydrogen atom to free radicals leading to the stabilization of these species. On the other hand, the long lipophilic phytyl tail provides high compatibility and miscibility with UHMWPE. The stabilization mechanism of a-tocopherol in UHMWPE have been studied in depth [20, 86]. The cycle of oxidative stabilization of UHMWPE by means of this antioxidant can be found in Ref [87]. 

While the incorporation of vitamin E did not produce significant effects on the temperature point, the effects of thermal treatments were dependent of the temperature at which the thermal stabilization was carried out. Annealing at 130 °C produced a slight increase in T, while a remelting process at 150°C results in a significant reduction in independent of the radiation doses [76]. It is worth noting that this behavior 

---