The fire retardant action of red phosphorus in nylon 6 was improved by co-a
ddition of ferric/ferrous oxides. It was found that the activity of Fe oxid
es depends on the product grade. Polymer formulations, non-ignitable in air
were obtained by co-addition of Fe3O4/Fe2O3 = 3:2 with red phosphorus. Sca
nning 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 formalde
hyde resin provided further improvements of fire retardancy and significant
ly decreased the rate of evolution of phosphine. Mechanistic studies did no
t support the hypothesis reported in the literature, that the fire retardan
t action of red phosphorus is due to its oxidation by oxygen of air.