The flame-retardant mechanisms of phosphorus-based flame retardants primarily involve the following aspects:

Formation of phosphorus compounds: At high temperatures, phosphorus-based flame retardants decompose to produce substances such as phosphoric acid and metaphosphoric acid. These substances promote the dehydration and charring of the polymer, creating a non-flammable char layer that insulates against heat and oxygen, thereby inhibiting the spread of flames.

Endothermic effect: The decomposition process of the flame retardant is often accompanied by endothermic reactions, which help lower the material's surface temperature and slow down the rate of combustion.

Free radical scavenging: Phosphorus compounds can react with free radicals in the flame, interrupting the combustion chain reaction and reducing the generation of combustible gases.

Formation of a molten coating: Phosphates produced during the decomposition of certain phosphorus-based flame retardants (such as APP) can form a glassy coating; this layer provides an additional barrier against oxygen and enhances the flame-retardant effect.