Chemiluminescence of Isotactic Polypropylene Induced by Photo-Oxidative Degradation and Natural Weathering Silviu Jipa, 1,2 Radu Setnescu, 1,2 Traian Zaharescu, 2 Tanta Setnescu, 1,2 Mustapha Kaci, 3 Naima Touati 3 1 Valahia University of Targoviste, Faculty of Sciences, Dept. of Chemistry, Bd. Regele Carol nr. 2, Targoviste, Romania 2 National Institute for Advanced Research in Electrical Engineering (INCDIE ICPE–CA), Splaiul Unirii 313, sector 3, Bucharest, Romania 3 Laboratoire des Mate ´riaux Organiques, De ´partement de Ge ´nie des Proce ´de ´s, Universite ´ Abderrahmane Mira, Route de Targa–Ouzemmour, Bejaia 06000, Algeria Received 19 September 2005; accepted 18 March 2006 DOI 10.1002/app.24534 Published online in Wiley InterScience (www.interscience.wiley.com). ABSTRACT: The analysis of the chemiluminescence (CL) kinetic parameters (induction time, oxidation rate, and acti- vation energy) after the UV irradiation and outdoor expo- sure of isotactic polypropylene (i-PP) films have been stud- ied. The initial CL emission intensity increased with increasing photodegradation time of i-PP films. On photo- degradation, the activation energies were found to decrease linearly with time of UV-irradiation and outdoor exposure. The slopes of these linear dependences were used to indi- cate the degree of photodegradation of the polymer and also for the characterization of the stabilizing effect of the additive. Ó 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4623–4629, 2006 Key words: chemiluminescence; photodegradation; isotac- tic polypropylene; Sanduvor PR 31 stabilizing effect INTRODUCTION The degradation of polymeric materials is determined by various factors such as heat, UV light, ozone, and mechanical stress, resulting in brittleness, cracks, color change, etc. Degradation is promoted by oxygen, hu- midity, and strain. The degradation rates are extrapo- lated to predict the service life of a material under dif- ferent conditions. The greatest damage to polymers exposed under natural conditions is caused by the UV portion of sun- light, even though this portion represents up to 10% (depending on the atmospherical conditions and lati- tude) of the total energy reaching the earth from the sun, with about 50% being visible and about 40% IR light. 1 The photo-oxidation of polypropylene has been recognized to involve the initiation of a free radical chain reaction by the photolysis of hydroperoxide groups. The homolysis of the hydroperoxide by UV irradiation is the primary initiation step (reaction 1). The photolysis of hydrogen-bonded peroxides (reac- tion 2) produces a peroxy radical as well as alcoxy radical: 2 ROOH ! hv RO  þ O  H (1) ð2Þ The most significant reaction is the b-scission of the alcoxy radical to produce a chain scission, a ketone and an alkyl radical. The chain breaking may also occur due to the reaction of the hydroxyl radical formed in reaction (1) with a carbonyl group to produce an acid end group. The carbonyl groups necessary for this reaction are formed by the termination reaction of per- oxy radicals (reaction 3): ð3Þ The resultant carbonyl group may also undergo a Nor- rish II reaction to produce a chain scission. Various types of hindered amines are largely used to protect polymers against photooxidation. Among them, hindered tertiary amines containing a-H at the nitrogen atom are very effective in hydroperoxide decomposition. Correspondence to: R. Setnescu (rsetnescu@yahoo.com). Journal of Applied Polymer Science, Vol. 102, 4623–4629 (2006) V V C 2006 Wiley Periodicals, Inc.