Char formation from polyolefins. Correlations with low-temperature oxygen uptake and with flammability in the presence of metal halogen systems

The oxidative degradation and combustion of polypropylene were investigated by simultaneous thermal analysis (STA) and by flammability measurements. STA shows that, while halogen compounds and metal oxides invariably increase char formation from the polymeric substrate, metal chelates can act both as inhibitors and as promoters of carbonisation. In general, however, there appears to be a direct correlation between the effect of an additive on oxygen uptake and that on char formation. Pro-oxidants which catalyse char formation are effective condensed-phase flame retardants, as a result of their producing fewer volatile species from the polymer.