Polyethylene stabilization against thermal oxidation by a trimethylquinoleine oligomer

The thermal oxidation at 110 and 120 °C of polyethylene (PE) films stabilized by 0.1, 0.2 and 0.5% of a trimethylquinoleine (TMQ) oligomer has been studied by IR spectroscopy (carbonyl build-up) and by DSC (measurement of the oxidation induction time at 200 °C). The induction period increases almost proportionally to the TMQ concentration and the TMQ efficiency (as estimated by the ratio tind/[TMQ]0) increases when lowering the temperature. Some features of stabilizer consumption kinetics and the dependence of maximum oxidation rate with initial stabilizer concentration were compared to experimental results obtained for stabilization by hindered phenols (Irganox 1010) and to literature data for sacrificial (e.g. hindered phenols) and regenerative (Hindered Amine Stabilizers) antioxidants. These comparisons led to classify TMQ in the category of Hindered Amine Stabilizers (HAS), which was confirmed by a kinetic analysis. Only the scheme taking into account the specific features of HAS (role of NO radicals, regeneration from alkoxyamines) was able to correctly simulate the oxidation behaviour of TMQ stabilized PE.