Recent Developments on the Use of Eco-Friendlier Phosphazenes as Flame-Retardants for Different Polymeric Materials

The study of phosphazenes as halogen free flame-retardants has gained attention in recent years to replace halogen flame retardants because of their negative impact on the environment. Most phosphazenes have a very distinctive structures which play a significant role on their excellent flame-retardant properties. They can be used as reactive flame-retardants (FRs), additives FRs or even modifiers in polymers. Researchers have synthesized and investigated their use in polymers, to observe the effect they have on the flammability properties of polymers. These investigations have successfully allowed researchers to outline the mechanisms by which phosphazenes work as effective flame-retardants, including the formation of protective char layers and restraint of volatile combustible gases. Most studies involving the use of phosphazene as a FR require curing agents on thermosets such as epoxy resin. The cone calorimeter tests, thermogravimetric analysis (TGA), vertical burning test (UL 94) and the limiting oxygen index test (LOI) have been used in most studies to evaluate the thermal stability and the flame retardancy properties of polymers. Research studies show a great improvement of flame retardancy in polymers where phosphazenes were used as FRs and this presents a promising venture that can be used to design advanced flame-retardant polymeric materials with enhanced fire safety and reduced flammability across an extensive number of industries and applications.