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

Abstract

The influence of fire retardant additives (decabromodiphenylether, antimony oxide) on the kinetic aspects of the photooxidation of polypropylene is reported. The photochemical oxidation of 60 μm thick films containing different 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 reduction of the induction period was observed but, surprisingly, no important variations of the apparent oxidation rate were noted. This latter result was related to the heterogeneous distribution of the oxidation photoproducts in the fire retarded sample. The heterogeneity of the oxidation was resulting from the strong absorption of the flame retardant additives in the range 300–350 nm. The oxidation kinetics monitored in the case of the fire retarded films were then apparent curves that had to be corrected in order to take into account the oxidation profiles. Moreover, considering the high content of fire retardant (12–47% by weight) within the samples, the oxidation curves had to be corrected in order to compare the oxidation of similar concentrations of polymer. On these bases, the influence of the fire retardant on the oxidation kinetics was studied in the case of thin films (thickness near to 10 μm) in order to limit the heterogeneity of the photochemical reactor constituted by the polymeric sample, and the oxidation kinetics were compared by plotting the variation of the ratio OD 1713/ c polymer with the irradiation time. This gave evidence that the oxidation rates increased dramatically in the presence of the fire retardant. Moreover, a significant increase of the rate of oxygen consumption was observed in the case of the fire retarded sample. The oxidation rates were however found to be relatively constant for contents of fire retardant higher than 5%.