Phosphorus and phosphorus compounds have been used as flame retardants for a long time, and their flame retardant mechanisms have been studied earlier. The flame retardant effect of phosphorus compounds in different reaction zones can be divided into condensed phase flame retardant mechanism and vapor phase flame retardant mechanism. Organic phosphorus flame retardants play a flame retardant role in condensed phase. The flame retardant mechanism is as follows:

During combustion, phosphorus compounds decompose to form a non combustible liquid film of phosphoric acid, with a boiling point of up to 300 ℃. At the same time, phosphoric acid is further dehydrated to form metaphoric acid, which then polymerizes to form polyphosphoric acid. In this process, not only does the covering layer generated by phosphoric acid have a covering effect, but also because the generated polyphosphoric acid is a strong acid and a strong dehydrating agent, it dehydrates and carbonizes the polymer, changing the mode of polymer combustion and forming a carbon film on its surface to isolate air, thereby exerting a stronger flame retardant effect.

The flame retardant effect of phosphorus based flame retardants is mainly reflected in the polymer decomposition stage in the early stage of a fire, as it can promote the dehydration and gasification of polymers, thereby reducing the amount of flammable gases produced by the thermal decomposition of polymers, and the generated carbon film can also isolate external air and heat. Generally, phosphorus based flame retardants have the best effect on oxygen-containing polymers and are mainly used in hydroxyl containing polymers such as cellulose, polyurethane, polyester, etc. For hydrocarbon polymers without oxygen, the effectiveness of phosphorus based flame retardants is relatively small.

Phosphorus containing flame retardants are also a type of free radical scavenger. Using mass spectrometry technology, it has been found that any phosphorus containing compound forms PO · during polymer combustion. It can bind with hydrogen atoms in the flame area to suppress the flame. In addition, the moisture generated by phosphorus based flame retardants during the flame retardant process can lower the temperature of the condensed phase and dilute the concentration of combustibles in the gas phase, thereby better achieving flame retardant effects.