Qualitative and quantitative free radical transformations between polypropylene alkyl radicals, oxygen, and brominated flame retardants in the molten and gaseous phases of thermally treated samples are described. By ESR technique it has been proved that, depending on the applied pressure during pyrolysis, highly reactive peroxy radicals or less reactive radicals of the retardant are formed. For flame‐retarded samples, compared with polypropylene without additives, the concentration of the primary alkyl radicals transferred from the molten to the gaseous phase is reduced by two orders of magnitude (from 7 × 1014 to 7 × 1012 spins/0.02 g), whereas the limiting oxygen index [LOI] is raised from 17–18% to 25–26%. The great variety of physical and chemical processes proceeding in molten polymer in the preflame zone and burning gaseous phase calls for use of different retardant types with a programmed release of Br and HBr with the temperature increase. The chain oxidation of the “fuel,” a product of the endothermic decomposition of polymer, determines the temperature of self‐ignition according to the number of initiating alkyl and allyl radicals formed per unit time; the [LOI] index depends more on the length of the kinetic chain of propagation reactions in the stationary process of oxidation at a given pressure.
Abstract-Smoke evolved from burning poly-(vinylchloride) plasticized with diisooctylphthalate has been studiedusing a light absorption method. It has been shown that the quantity of smoke produced depends upon the oxygen concentration of the oxidizing gas as well as on the concentration of diisooctylphthalate present in the polymer. The results of this work have been analysed using an empirical equation proposed by the authors, which correlates the maximum smoke density (urnax) with oxygen concentration. This equation may be written where Noz is the molar concentration of oxygen in the oxidizing gas, and LO1 refers to the limiting or critical concentration of oxygen at which the polymer will just burn, as defined by the ASTM test 2863. The effect of various additives, particularly organic iodine compounds, as smoke suppressants has also been investigated. Omax = ULOI exp ( -k (Noz-LOI))
Various polymeric materials were combusted in small scale laboratory equipment and the toxicity of evolved gases evaluated by the leth ality of Drosophila melanogaster flies. The results were compared with data ob tained for the same materials in experiments with mice.
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