Mechanism of action of phosphorus-based flame retardants in nylon 6. III: Ammonium polyphosphate / manganese dioxide

Abstract

Partial substitution of ammonium polyphosphate (APP) by manganese dioxide (MnO2) in polyamide 6 (PA-6) fire retarded with 20% of APP strongly increases the fire retardant effect. ‘Linear pyrolysis’ experiments, which are modified cone calorimeter tests, show an increase in the amount and an improvement of the shielding properties of the intumescent char formed on the surface of burning polymer. The enhancement of the yield of aliphatic–aromatic char stable to oxidation was observed in thermogravimetry under air. The fire retardant action of an APP/MnO2 mixture in PA-6 is twofold. On the one hand, this additive promotes involvement of the polymer in the charring and, on the other, the formed manganese phosphate glasses improve the thermo-insulating properties of the intumescent char on the surface of burning PA-6