Intumescent flame retardants (IFRs) do not constitute a single type of flame retardant; rather, they are halogen-free composite flame retardants primarily composed of phosphorus, nitrogen, and carbon, which exhibit an inherent synergistic effect within the system. They are termed “intumescent” because they foam and expand when exposed to heat.
The flame-retardant mechanism of an intumescent system is generally understood to occur in the condensed phase. Upon heating, ammonium polyphosphate decomposes to produce phosphoric acid and pyrophosphoric acid—substances with strong dehydrating properties—which esterify pentaerythritol, subsequently leading to dehydration and carbonization. The water vapor generated during this reaction, combined with ammonia gas released from the decomposition of melamine, causes the carbonaceous layer to expand. This results in the formation of a highly porous char layer, which acts as a barrier against air and heat transfer, thereby protecting the underlying polymer and achieving a flame-retardant effect. When incorporated into polymer materials, intumescent flame retardants must possess several key properties: good thermal stability to withstand processing temperatures exceeding 200°C; the ability to undergo thermal degradation—releasing significant amounts of volatile substances while forming a solid residue—without negatively impacting the expansion and foaming process; uniform dispersion within the polymer matrix, ensuring the formation of an intumescent char layer that completely covers the material’s surface during combustion; and good compatibility with the host polymer, such that they do not interact adversely with the polymer or other additives, nor significantly degrade the material’s physical or mechanical properties. Compared to conventional flame retardants, intumescent flame retardants offer the advantages of being halogen-free and antimony-free, producing low smoke, exhibiting low toxicity, and generating no corrosive gases. Furthermore, the char layer formed by these flame retardants can capture molten, burning polymer, preventing it from dripping and spreading the fire.
Intumescent flame retardants effectively overcome many of the drawbacks associated with traditional flame-retardant technologies. Their advantages include: high flame-retardant efficiency, the absence of flaming droplets, superior resistance to prolonged or repeated flame exposure, a halogen-free and antimony-free composition, and the production of minimal smoke, low toxicity, and no corrosive gases.
Ammonium polyphosphate (APP) is an inorganic phosphorus-based flame retardant.
Phosphorus-based flame retardants exhibit synergistic effects when combined with nitrogen-based flame retardants or metal hydroxides; such combinations enhance flame retardancy and reduce smoke generation.
Inorganic phosphorus-based flame retardants have poor water resistance and typically require modification before use.
Properties: It appears as a white powder, with water absorption decreasing as the degree of polymerization increases. APP decomposes at temperatures above 250°C, releasing water and ammonia while forming phosphoric acid. Its flame-retardant mechanism involves absorbing heat to lower the temperature and diluting combustible gases. Because its molecules contain both phosphorus and nitrogen, APP offers excellent synergistic effects and superior flame-retardant performance; it is primarily used in fire-retardant coatings.
Post time: Nov-02-2026
