Chemiluminescence study on irradiated low-density polyethylene containing various photo-stabilisers Radu Setnescu a,b, ) , Mustapha Kaci c , Silviu Jipa a,b , Tanta Setnescu a,b , Traian Zaharescu b , Ghania Hebal c , Aida Benhamida c , Hocine Djedjelli c a VALAHIA University Targoviste, Bd. Castanilor nr. 2, Targoviste, Jud. Dambovita, Romania b Advanced Research Institute for Electrical Engineering (ICPE-CA), Splaiul Unirii 313, Sector 3, Bucharest, Romania c Organic Materials Laboratory, University A. Mira of Bejaia, Route de Targa-Ouzemmour, 06000, Algeria Received 7 November 2003; accepted 20 December 2003 Abstract The effect of hindered amine stabilisers (HAS) on the thermal oxidation of low-density polyethylene (LDPE) films subjected to various gamma radiation doses in the range of 68e812 kGy, was studied by chemiluminescence (CL) at 190 (C in the presence of air. Different types of HAS were used, commercially known as Tinuvin 123, Sanduvor PR31 and Uvasil 299. It was found that under CL conditions, an antioxidative effect occurs for all unirradiated samples, being more relevant in the case of Sanduvor PR31. Our results indicate a specific decrease in the stability (depending on HAS nature) of irradiated materials with increasing irradiation dose. The initial intensity of CL emission (I 0 ), which is related to the concentration of radiation-induced peroxy species was plotted as a function of dose and led to straight line dependence with the slope values placing the HAS effectiveness in the sequence: Tinuvin 123 > Sanduvor PR31 > Uvasil 299 [ none. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: Chemiluminescence; Polyethylene; Radiation induced oxidation; Hindered amine stabilisers 1. Introduction Polyethylene is widely used for various technical purposes, such as greenhouse covering, mulching and packaging films [1], clinical hip joint prostheses [2], insulating materials [3], etc. It is known that during processing or use, it is subjected to various stress factors including g-irradiation in the presence of air [4]. Exposure of PE to gamma radiation under inert atmos- phere results in crosslinking of the polymer and the formation of trapped free radicals that can be used in grafting applications [5]. In addition, it is well known that irradiation of polyethylene in air produces free radicals, mostly alkyl radicals which react with oxygen to yield ketones probably due to b scission of peroxy or alkoxy radicals [2,6]. Hydroperoxide and alcohol groups and trapped peroxy radicals are also produced in irradiated polyethylene [7]. These oxidation reactions are competitive with crosslinking, which occurs espe- cially at high dose rate or inside the thick samples, because less oxygen is available [2]. Thus, exposure of polyethylene to ionising radiation could lead to partial oxidative destruction of the polymer, resulting in a decrease of its valuable properties [8e12]. In order to retard efficiently the oxidation process, stabilisers are often used. Among them hindered phenols, amines, quinones or thiols act as radical scavengers [13]. On the other hand, the role of some additives as energy scavengers is well reported in literature, like propylfluor- anthene [14], pyrene [15,16], or several other polynuclear hydrocarbons [17]. ) Corresponding author. Advanced Research Institute for Electrical Engineering (ICPE-CA), Splaiul Unirii 313, Sector 3, Bucharest, Romania. Tel.: C40-21-346-7235; fax: C40-21-346-8299. E-mail address: rsetnescu@yahoo.com (R. Setnescu). 0141-3910/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymdegradstab.2003.12.004 Polymer Degradation and Stability 84 (2004) 475e481 www.elsevier.com/locate/polydegstab