Photooxidation of fire retarded polypropylene. I. Photoageing in accelerated conditions

The influence of fire retardant additives (decabromodiphenylether, antimony oxide) on the kinetic aspects of the photooxidation of polypropylene is re ported. The photochemical oxidation of 60 mu m thick films containing diffe rent amounts of fire retardant additives was studied and compared with that of pure polypropylene. Monitoring the variations of the infrared carbonyl absorption permitted a comparison of the oxidation curves. A significant re duction of the induction period was observed but, surprisingly, no importan t variations of the apparent oxidation rate were noted. This latter result was related to the heterogeneous distribution of the oxidation photoproduct s in the fire retarded sample. The heterogeneity of the oxidation was resul ting from the strong absorption of the flame retardant additives in the ran ge 300-350 nm. The oxidation kinetics monitored in the case of the fire ret arded films were then apparent curves that had to be corrected in order to take into account the oxidation profiles. Moreover, considering the high co ntent of fire retardant (12-47% by weight) within the samples, the oxidatio n curves had to be corrected in order to compare the oxidation of similar c oncentrations of polymer. On these bases, the influence of the fire retarda nt on the oxidation kinetics was studied in the case of thin films (thickne ss near to 10 mu m) in order to limit the heterogeneity of the photochemica l reactor constituted by the polymeric sample, and the oxidation kinetics w ere compared by plotting the variation of the ratio OD1713/c(polymer) with the irradiation time. This gave evidence that the oxidation rates increased dramatically in the presence of the fire retardant. Moreover, a significan t increase of the rate of oxygen consumption was observed in the case of th e fire retarded sample. The oxidation rates were however found to be relati vely constant for contents of fire retardant higher than 5%. (C) 1999 Elsev ier Science Ltd. All rights reserved.