Table 5: Fire retardants and its function [34].

Fire retardantDescription

Phosphorous compounds
(i) Ammonium polyphosphate
(ii) Sodium phosphate
(i) An swelling material, char formers and stop the fire propagation  
(ii) Generation of solid form of phosphoric acid inhibits access to oxygen and shields it from releasing flammable gases able to feed flames

Bromine Based compounds
 Decabromodiphenyl oxide
(i) Acts in the condensed phase to direct chemical reactions inside burning. Heavy-bromine gases cover the material from touching oxygen and heat
(ii) Always used with an antimony synergist, often antimony trioxide

Antimony based  
 Antimony trioxide
The compounds alone do not work much, yet are powerful in combination with halogens forming antimony trihalide to scavenge free radicals and increase char formation

Metal hydroxides
(i) Aluminium-based
(ii) Magnesium-based
(i) An inorganic compound thus healthy and environmentally safe
(ii) More effective as hydrated compounds and provide effective flame retarding effects by releasing contained water at high temperatures, absorbing heat from the combustion zone, producing char, generating metal oxide coating that acts as insulator and reduces smoke
(iii) Mg(OH)2 has superior endothermic flame retarding reaction and is more suitable for polyolefins, polypropylene, and polyamides because it decomposes at a higher temperature (300–320°C), thus allowing it to be processed in plastics, for which Al(OH)3 (decomposition temperature: 200°C) is not thermally stable enough

Boron-based compounds  
 Zinc borate
(i) Are generally char producers.
(ii) Zinc borate compounds reduce smoke production and are mostly used as hydrates
(iii) The heat required from dehydration also contributes to its fire retardant capability

Melamine-based  
 Melamine cyanurate
(i) Aids in char formation
(ii) Compounded with phosphates to achieve a phosphorus-nitrogen synergism.
(iii) Creates endothermic reactions and scavenges free radicals.

Silica(i) Recognised as inert diluent and shows some flame retardant effect
(ii) Synergistic effect with APP, accumulate on the surface in fire and consequently forms a charred layer by combining with APP.

Halogneated compoundsFunction primarily by a vapour phase flame inhibiting mechanism through radical reaction