Intumescent flame retardant systems

Mode of action: formation of a voluminous, insulating protective layer through carbonization and simultaneous foaming

Intumescent systems puff up to produce foams. They are used to protect combustible materials such as plastics or wood, and those like steel, which lose their strength when exposed to high temperatures, against the attack of heat and fire.

Basically, intumescent flame retardant systems consist of the following:
1. "Carbon" donors (e.g. polyalcohols such as starch, pentaerythritol)
2. Acid donors (e.g. ammonium polyphosphate)
3. Spumific compounds (e.g. melamine)

Process of intumescent mechanism

1. Softening of the binder/polymer (e.g. polypropylene)

2. Release of an inorganic acid (e.g. ammonium polyphosphate)

3. Carbonization (e.g. of polyalcohols)

4. Gas formation by the spumific compound (e.g. melamine)

5. Foaming of the mixture

6. Solidification through cross-linking reactions

The picture below shows how the foam looks in the end. This coating expanded from a 1 mm layer to a 100 mm foam.