Phosphorus-based flame retardants are a crucial class of flame-retardant additives widely used in materials such as plastics, rubber, textiles, coatings, and electronic products to enhance their fire resistance. They function primarily through chemical and physical mechanisms to reduce material flammability and the rate of flame spread. Characterized by low smoke emission, low toxicity, and low or zero halogen content, they are a preferred choice for environmentally friendly flame-retardant solutions.

Phosphorus-based flame retardants are primarily categorized into two groups:

Inorganic phosphorus-based flame retardants:

Red phosphorus: The most direct source of phosphorus, offering high flame-retardant efficiency; however, it requires special handling and encapsulation due to its color, tendency for spontaneous combustion, and corrosiveness.

Ammonium polyphosphate (APP): Commonly used in intumescent fire-retardant coatings and polymers; upon heating, it decomposes to release ammonia and water while forming a char layer that provides thermal insulation and suppresses flames.

Melamine phosphate and melamine polyphosphate: Used as flame retardants and blowing agents; they facilitate the formation of a porous char layer, thereby enhancing flame-retardant performance.

Piperazine pyrophosphate, etc.: Offer good thermal stability and flame-retardant properties.

Organic phosphorus-based flame retardants:
Phosphate esters: Such as trimethyl phosphate and triethyl phosphate; these provide flame retardancy while also functioning as plasticizers.

Phosphite esters: Used as auxiliary flame retardants in certain applications to improve material processing characteristics and flame-retardant efficiency.

Phosphonate esters: Such as triphenyl phosphonate; widely used due to their excellent thermal stability and flame-retardant effects.

Phosphorus-containing heterocyclic compounds: Such as phosphazenes and phosphaphenanthrenes; characterized by unique structures and superior flame-retardant performance.

Metal salts of organic phosphinates: Emerging flame retardants gaining attention for their favorable environmental profile and effective flame-retardant performance.