Thermal Stability of Gamma Irradiated Low Density Polyethylene Films Containing Hindered Amine Stabilizers Traian Zaharescu, 1 Mustapha Kaci,* 2 Ghania Hebal, 2 Radu Setnescu, 1,3 Tanta Setnescu, 1,3 Rochedine Khima, 2 Che ´rifa Remili, 2 Silviu Jipa 1,3 1 Research & Development Institute for Electrical Engineering, 313 Splaiul Unirii, Bucharest 70204, Romania 2 Laboratoire des Mate ´riaux Organiques, De ´partement de Ge ´nie des Proce ´de ´s, Route de Targa-Ouzemmour, Universite ´ A. Mira, Be ´jaı ¨a 06000, Algeria Fax: 0021334216098; E-mail: kacimu@yahoo.fr 3 Valahia University of Targoviste, Faculty of Sciences, Bd. Carol I, nr. 2, 0200 Targoviste, Romania Received: September 15, 2003; Revised: January 22, 2004; Accepted: March 5, 2004; DOI: 10.1002/mame.200300275 Keywords: gamma irradiation; HAS; LDPE films; oxygen uptake; thermal stability Introduction Thermal stability is the main problem of polymer durability. The formulation of any material influences the behavior under certain operation conditions. The integrity of products depends on the material capability to delay thermal degrad- ation. Different modification routes for increase in heat resistance like crosslinking [1–3] and stabilizer addition [4,5] may be followed for long term protection. These alterna- tives offer the possibility to improve the quality of products in thermoplastics industry. The most facile alternative for chemical resistance improvement is the addition of a suit- able antioxidant. Several classes of antioxidants were inten- sively studied for various purposes: prevention of thermal degradation [6–8] or weather aging [9–12] , and radiation stability. [13–15] The majority of products reach high per- formances due to protective action of antioxidants, which confer excellent protection against the action of permanent Summary: The thermal stability of gamma irradiated low density polyethylene (LDPE) films in presence of various structures of hindered amine stabilizers (HAS) was investiga- ted by the oxygen uptake method under constant temperature of 180 8C and normal pressure conditions. The thermo- oxidation was run using air environment. The sigmoidal de- pendency of oxygen uptake allows the calculation of the main kinetic parameters: oxidation induction time and oxidation rate on the propagation step. The various steps involved in the thermal degradation process were detected by the deriv- ative procedure applied to the dependencies of oxygen uptake on time. It was found that the kinetic parameters of the ther- mal degradation process, determined by oxygen uptake, re- vealed the antioxidant role of HAS in g-irradiated LDPE films by providing better stability, when compared with the unstabilized samples. Moreover, the results indicated that the dependencies of oxygen uptake on thermal degradation time involved two degradation stages: the former occurring in the ungrafted moiety and the latter taking place after the antioxidant depletion is achieved. The stabilization efficiency of these oxidation inhibitors provides satisfactory thermal resistance to LDPE films, especially those based on an alkoxy- amine structure. Dependencies of oxygen uptake on time at the thermal de- gradation of LDPE irradiated at 812 kGy. (-&-) free of additive; (-*-) Tinuvin 123; (-~-) Sanduvor PR 31; (-}-) Uvasil 299. Macromol. Mater. Eng. 2004, 289, 524–530 DOI: 10.1002/mame.200300275 ß 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 524 Full Paper