Polymer Degradation and Stability 40 (1993) 101-107 The comparative effectiveness of some commercial antioxidants as studied by lyoluminescence S. Jipa, R. Setnescu, T. Setnescu, C. Cazac, P. Budrugeac ICPE Research Institute for Electrical Engineering, Bucharest, Romania & I. M_ihaicea University of Bucharest, Faculty of Chemistry, Department of Physical Chemistry, Bucharest, Romania (Received 6 April 1992; accepted 11 May 1992) Lyoluminescence is an interesting tool to study the reactivity of different antioxidants towards the free RO2 radicals which are frequently involved in the oxidative processes of different polymeric materials. In the present paper we have used lyoluminescence to characterize the effectiveness of the following commercial phenolic antioxidants: Topanol OC, Irganox 1076, Ionox 220, Etanox 330, Cyanox 2246 and Irganox 1010. The antioxidant efficiency of these products in the thermal oxidation of polyethylene was compared on the basis of the results of oxyluminescence and thermal analysis methods. INTRODUCTION The thermal oxidative degradation of polymers and the means of inhibiting this ageing process is still one of the most important problems of polymer chemistry. The subject has an especial significance because of the trend towards improvements in the quality and service life of polymeric materials. A number of methods are available to characterize the effectiveness of antioxidants in polymers, including spectro- photometric determination of thermal oxidative degradation (IR absorption of the carbonyl groups in the range from 1675 cm-' to 1800 cm-' or less selectively carbonyl detection in the UV range), oxygen uptake measurements, oxylumin- escence determinations, differential scanning calorimetry (DSC), differential thermal analysis (DTA) and therrnogravimetric experiments. The development of new sensitive methods of antioxidant ranking could be advantageous. In the present study we have applied the lyoluminescence method for the characterization of the effectiveness of some commercial phenolic antioxidants. Lyoluminescence (LL) is the light emitted on dissolution of pre-irradiated solids and was originally investigated from the point of view of radiation dosimetry, t For most organic compounds the light yield is proportional to the free radical concentration over a wide range, hence lyoluminescence provides the basis of a rapid method of studying the reactivity of the free radicals. 101 EXPERIMENTAL Materials The phenolic antioxidants used in the present work were commercial antioxidants as specified