Some mechanistic aspects of the fire retardant action of red phosphorus in aliphatic nylons

The fire retardant action of red phosphorus in nylon 6 was improved by co-addition of ferric/ferrous oxides. It was found that the activity of Fe oxides depends on the product grade. Polymer formulations, non-ignitable in air were obtained by co-addition of Fe3O4/Fe2O3 = 3:2 with red phosphorus. Scanning electron microscopy showed that ferric oxide contributes beneficially to the fire retardancy, probably because it modifies the morphology of the char. Red phosphorus coated by Fe3O4 and encapsulated with phenol formaldehyde resin provided further improvements of fire retardancy and significantly decreased the rate of evolution of phosphine. Mechanistic studies did not support the hypothesis reported in the literature, that the fire retardant action of red phosphorus is due to its oxidation by oxygen of air.