Synergistic action of Sb2O3 with bromine-containing flame retardant in polyolefins: 3—The relationship between certain combustion variables

The combustion of polypropylene flame-retarded by the synergistic action between Sb₂O₃ and bromine-containing flame retardants has been studied. From the relationship between a number of the variables, a parameter quantatively reflecting the flame retardant effect has been found. With the addition of flame retardant, the rate of weight loss, the CO and CO₂ emission rates and heat release all decrease while smoke density increases. These effects were considered to depend on the concentration of HBr gas in the pyrolysates released into the gas phase (i.e., dW_HBr/dW, HBr flux ensity), and the following equations were obtained: η*(dW/dt)_max, which approximately corresponds to the oxidation velocity of pyrolized hydrocarbon, is inversely proportional to the HBr flux density. As the conversion of CO to CO₂ was almost independent of the amount of flame retardants added, the flame retardant effect of bromine-containing flame retardants was considered to be a retardant effect of the initial oxidation reaction at the gas liquid interface. Moreover, η* is almost proportional to the combustion efficiency η, which was obtained from the heat release measured in the flaming region. The heat release is therefore considered to be governed by the HBr flux density.