Other Phosphorus Flame Retardants

DOPO Flame Retardant

Alfa Chemistry provides other innovative phosphorus-based flame retardants, including but not limited to organic hypophosphites, phosphates, phosphites, phosphorus oxide flame retardants, to help you make progress in the innovation of flame retardant materials.


Organic Hypophosphites

Metal organic hypophosphites have attracted much attention as an emerging flame retardant. Alfa Chemistry offers innovative organic hypophosphite flame retardants with excellent thermal and hydrolytic stability.

Organic hypophosphite flame retardants have the following advantages:

  • High flame retardant efficiency
  • Low dosage
  • Halogen-free and non-toxic
  • Less drop in mechanical properties

Phosphates and Polyphosphates

Phosphate flame retardants, such as melamine phosphate (MPP), are widely used additive flame retardants. MPP can be used for flame retardancy of fire-retardant coatings, polystyrene, rubber, nylon, epoxy resin, rigid polyurethane foam, etc.



Phosphite flame retardants are an important branch of phosphorus flame retardants, which not only have the unique flame retardant plasticizing effect of phosphate ester flame retardants, but also have antioxidant effects. For example, trimethyl phosphite (TMP(i)) and trimethyl phosphate (TMP(a)) can be used as electrolyte additives to improve the safety and electrochemical performance of lithium batteries. [1]

 Phosphorus Oxides

Phosphorus oxides have hydrolytically stable P-C bonds, and their P content is higher than that of aryl phosphates. Their diols and triols are reactive flame retardants for polyurethanes and epoxy resins.

Flame Retardant Mechanism

PFRs generally involve two modes of action, including condensed-phase and gas-phase mechanisms. When PFR burns, it generates phosphoric acid, metaphosphoric acid, polymetaphosphoric acid, etc., which are covered on the surface of the resin to promote the carbonization of the plastic surface to form a carbon film. The polymetaphosphoric acid is covered in a viscous liquid state on the surface of the plastic. The solid or liquid membrane prevents the escape of free radicals and keeps out oxygen.

In addition, PFRs are also a free radical scavenger. Using mass spectrometry technology, it was found that any phosphorus-containing compounds have PO· formed when the polymer is burned. It can combine with the hydrogen atoms in the flame area to suppress the flame.

Research Information

To investigate the effect of the oxidation state of phosphorus in flame retardants on the thermal and flame retardant properties of the polymer substrates, researchers added three different oxidation states (including +3, +5 and -1) of phosphorus to PU and EP as flame retardants. The results showed that the thermal stability of both polymers decreased with the addition of phosphorus flame retardants, regardless of the oxidation state, and a larger amount of residue was observed in the case of phosphites. [2]

DPhosphitesChemical structure of compounds: (a) preparation of polyurea and epoxy resin; (b) triphenylphosphite (TPPi); (c) triphenylphosphate (TPPa); (d) triphenylphosphine oxide (TPPO). [2]

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  1. X.L. Yao, et al. (2005). "Comparative study of trimethyl phosphite and trimethyl phosphate as electrolyte additives in lithium ion batteries," Journal of Power Sources 144(1), 170-175.
  2. Thirumal Mariappan, et al. (2013). "Influence of oxidation state of phosphorus on the thermal and flammability of polyurea and epoxy resin," European Polymer Journal 49(10), 3171-3180.
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