Acid source, intumescent formulations

Typical acid source (dehydrating agent) used in numerous intumescent formulations. 

Le Bras and co-workers [50] developed flame retardant intumescent formulations using the association of APP as the acid source and PA-6 as the carbonisation agent in an EVA (8%) copolymer matrix. 

A patent review [4] showed that early intumescent formulations incorporated in polymers contained a precursor of phosphoric or polyphosphoric acid, a pentaerythritol type char source, and melamine, as typical formulations of intumescent coatings. Further developments tried to reduce the complexity of the additive system, for example by using a binary combination of the add precursor with nitrogen-containing compounds, which also act as a char source. While the add source is generally APP, typical examples of the second component are produds of condensation of formaldehyde with substituted ureas products of readions between aromatic diisocyanates and pentaerythritol or melamine polymers containing the piperazine ring in the main chain, also combined with substituted s-triazine, hydroxyalkyl isocyanurate etc. 

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