Decomposition intumescent systems

Intumescent systems are a particular class of phosphorus-based flame retardant. They are characterized by the production of an expanded foamed char on exposure to heat which then protects the underlying polymer. Ideally the char volume should be large, with a thick continuous surface crust and an inner structure which should be similar to a closed-celled foam. The char structure is important in providing a good insula-tive effect and hence reducing thermal decomposition of the polymer to volatile flammable products. 

Ammonium polyphosphates, on the other hand, are relatively water insoluble, nonmelting solids with very high phosphorus contents (up to about 30%). There are several crystalline forms and the commercial products differ in molecular weights, particle sizes, solubilities, and so on. They are also widely used as components of intumescent paints and mastics where they function as the acid catalyst (i.e., by producing phosphoric acid upon decomposition). They are used in paints with pentaerythritol (or with a derivative of pentaerythritol) as the carbonific component and melamine as the spumific compound.22 In addition, the intumescent formulations typically contain resinous binders, pigments, and other fillers. These systems are highly efficient in flame-retarding hydroxy-lated polymers. 

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