Eciency assessment of additives in thermal degradation of i-PP by chemiluminescence I. Triazines Silviu Jipa*, Radu Setnescu, TantËa Setnescu, Traian Zaharescu R & D Institute for Electrical Engineering, 313 Splaiul Unirii, Bucharest 74204, Romania Received 28 July 1999; received in revised form 10 October 1999; accepted 30 October 1999 Abstract In this paper the kinetics of thermal oxidation of isotactic polypropylene with some new mercaptotriazines is presented. Iso- thermal degradation of i-PP was studied by chemiluminescence in air at 180  C on polymer samples containing various concentra- tions of stabilizers (0.15, 0.25, 0.50 and 0.75 wt%). The antioxidant eciencies in thermal protection of i-PP were assessed by means of temporal parameters (t i , t 1=2 and t max ), oxidation rates (V max ox ), relative activities (A) and relative stabilities (S) relative to a stan- dard (Irganox 565). The concentration constants that characterize the stabilization eect of triazinic antioxidants were calculated and linear correlation between OIT and s-Hammett constants could be pointed out. # 2000 Elsevier Science Ltd. All rights reserved. 1. Introduction The thermal stability of polymer materials can be improved by the addition of various antioxidants. The stabilization activity can be assessed by kinetic studies using chemiluminescence technique [1,2]. Various organic compounds similar to sterically hindered phe- nols can act as the oxidation inhibitors because during degradation the free radicals formed substitute hydro- gen belonging to phenolic hydroxyl. Thus, hydrocarbon radicals become unavailable for the reaction with mole- cular oxygen [3]. Triazines behave as antioxidants when they are added to polymers substrate [4]. It can be assumed that their mercaptoderivatives would also operate as oxidation stabilizers. In spite of the remarkable eciency of tria- zines in oxidation protection of polymers only a few studies have been devoted [4±11]. The kinetic studies on the thermal oxidation of poly- mers can be accurately performed by a very sensitive method, chemiluminescence. This procedure is based on the proportionality between the number of photons expelled by the deexcitation of carbonyls and the rate of material oxidation [12,13]. Chemiluminescence is a convenient method applicable to a large variety of studies on polymer stability and the progress in the improvement of counting performances allows the detection of low level emitters [14,15]. More- over, the proportionality between the oxidation resis- tance of polymer materials and the rate of peroxide decomposition can be successfully used in the assess- ment of the chemical strength displayed by polymers during oxidation [16]. In this paper six mercaptotriazines belonging to a new series of this class of compounds were tested relative to their stabilization eciency in the oxidation of poly- propylene by means of chemiluminescence measure- ments. 2. Experimental Isotactic polypropylene (Moplen 1 , Himont, Italy) was puri®ed by precipitation with methanol from hot o- xylene solution. After the removal of remaining solvent, i-PP mass was dried at room temperature. The additives studied in this work were synthetized by the condensation of cyanuric chloride with amines and/or 0141-3910/00/$ - see front matter # 2000 Elsevier Science Ltd. All rights reserved. PII: S0141-3910(99)00179-2 Polymer Degradation and Stability 68 (2000) 159±164 * Corresponding author. Tel.: +40-1-322-2813; fax: +40-1-321- 3769.