Ammonium Polyphosphate (APP, Form II) is a high-molecular-weight, non-halogenated flame retardant. It is the most important “acid source” and the backbone of modern intumescent flame retardant (IFR) systems.

Flame Retardant Mechanism APP is the “engine” of the intumescent reaction:

1. Acid Source: APP is thermally stable up to ~275°C. Above this, it decomposes to produce polyphosphoric acid (H(PO3)H) and ammonia.

2. Catalytic Charring: The polyphosphoric acid is a powerful catalyst. It “attacks” hydroxyl (-OH) groups in the system (either from a char source like PER or from the polymer itself), catalyzing a dehydration and cross-linking reaction that builds the stable, 3D carbonaceous char “backbone”.

Key Application Areas

• Intumescent Coatings: The primary active ingredient in fire-protective coatings for structural steel and wood.

• Polyolefins (PP): The core component of IFR systems for polypropylene, typically combined with a char source (PER) and gas source (Melamine).

• Polyurethanes (PU): Used in both flexible and rigid PU foams to create a charring barrier.