Ammonium Phosphate

Ammonium Phosphate

Ammonium phosphate ranks high among common flame retardant additives and is particularly effective for cellulose. Alfa Chemistry offers high quality ammonium phosphate flame retardants to meet fire safety challenges.


  • Ammonium phosphate is an inorganic compound with the chemical formula (NH4)3PO4. There are also two acid salts, diammonium hydrogen phosphate and ammonium dihydrogen phosphate. Ammonium phosphate has poor thermal stability and will decompose when heated.
  • In contrast to the unstable nature of triammonium salts, diammonium phosphate (NH4)2HPO4 and monoammonium salts (NH4)H2PO4 are stable materials that can be used as flame retardants.

Flame Retardant Mechanism

The flame retardant effect of ammonium phosphate on cellulose mainly works in the condensed phase through a char formation mechanism. Phosphate is attached to the cellulose chain through an ester group, which is easily eliminated to form a conjugated double bond, which eventually cyclizes to form carbon.

Similarly, ammonium phosphates impart flame retardancy to polymers such as polystyrene by charring. This occurs through a series of processes including initial peroxide formation, decomposition into alcohols and aldehydes, alkyl phosphate formation, dehydration and subsequent char formation. [1]

Ammonium Phosphate

Research Information

Microencapsulated Ammonium Phosphate

I. Vroman developed three types of diammonium hydrogen phosphate (DAHP) microcapsules with different polymer shells as intumescent flame retardants for polypropylene (PP) fabrics. The results showed that DAHP microcapsules with PU shells provided better results than DAHP in terms of HRR and THE reduction, while results were comparable to microcapsules with melamine-formaldehyde and PHMA shells, which were low in phosphate. [2]

HRR and THE curves of filled PP fabricsHRR and THE curves of filled PP fabrics [2]

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  1. K. Kishore, et al. (1981). "Mechanistic studies on the action of ammonium phosphate on polymer fire retardancy," Combustion and Flame 43, 145-153.
  2. I. Vroman, et al. (2010). "Polypropylene fabrics padded with microencapsulated ammonium phosphate: Effect of the shell structure on the thermal stability and fire performance," Polymer Degradation and Stability 95(9), Pages 1716-1720.
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