A Survey of Recent Progress in Phosphorus-Based Flame Retardants and Some Mode of Action Studies

Phosphorus-based flame retardants have diverse modes of action, Aryl phosphates can have vapor phase action in styrenic polymers but also can contribute to producing a barrier layer. Tris(dichloroisopropyl) phosphate in a flexible polyurethane foam can serve as both a vapor-phase (probably physical) flame inhibitor in bottom ignition but contributes to formation of a barrier in top-down burning. Halogen/phosphorus and nitrogen/phosphorus synergism are not general but examples are known. Red phosphorus and ammonium polyphosphate interact with nylon 6 under burning conditions to produce phosphate esters and eventually chars. The cyclic neopentyl ester of nitrilotris(methylphosphonic acid) as a flame retardant in ethylene vinyl acetate copolymer can serve as a char-former and catalyst. Attempts to find synergists for phosphorus provide clues to improved combinations.