MECHANISTIC ASPECTS OF INTUMESCENT FIRE-RETARDANT SYSTEMS

The mechanism of intumescence is studied in mixtures of ammonium polyphosphate (APP) with several polycondensates as a part of a systematic study of intumescent fire retardants. It is shown that APP reacts on heating with the polycondensate to form a precursor of the intumescent char which is obtained on further heating. The introduction of the intumescent system in polypropylene does not modify the structure of the char formed on heating. However, the polymer modifies the foaming behaviour of the system. The thermal decomposition of the char occurs with volatilisation of phosphorus moieties and formation of a relatively thermally stable residue. Effects of the thermal behaviour of the char, on fire retardance, are discussed.