Mechanism of action of phosphorus-based flame retardants in nylon 6. I: Ammonium polyphosphate

Comparison of oxygen and nitrous oxide indices indicates that ammonium polyphosphate (APP) should act in the condensed phase when added to nylon 6 (PA-6). A detailed study of the thermal degradation mechanism of PA-6/APP mixtures is carried out. A polyphosphate ester is formed on heating, which is the precursor of an intumescent char. Evidence is given of the thermal insulating action of the intumescent char which slows down the rate of combustion of the polymer