Thermal stability of gamma irradiated low density polyethylene films containing hindered amine stabilizers

The thermal stability of gamma irradiated low density polyethylene (LDPE) films in presence of various structures of hindered amine stabilizers (HAS) was investigated by the oxygen uptake method under constant tempeture of 180degreesC and normal pressure conditions. The sigmodial dependency of oxygen uptake allows the calculation of the main kinetic parameters: oxidation induction time and oxidation rate on the propagation step. The various steps involved in tyhe thermal degradation process were deteched by the derived procedure applied to the dependancies of oxygen uptake on time. Itr was found that the kinetic parameters of the thermal degradation process determined by oxygen uptake, revealed the antioxidant role HAS in gamma-irradiated LDPE films by providing better stability, when compared with the unstabilized samples. Moreover, the results indicated that the dependencies of oxygen uptake on thermal degradation time involved two degradation stages: the former occuring in the ingrafted moiety and the latter taking place after the antioxidant inhibitors depletion is achieved. The stabilization efficiency of these oxidation inhibitors provides satisfactory thermal resistance to LDPE films, especially those based on an alkoyl-amine structure.