Additive flame retardants such as ammonium polyphosphate or phosphinates are physically dispersed and migrate to the surface over time, losing efficiency and affecting appearance.
High filler loading raises viscosity and degrades mechanical properties and transparency — especially problematic for films and coatings.
Halogenated systems face both regulatory pressure and smoke toxicity concerns.
Phosphorus works in both gas and condensed phases: decomposition produces PO· and HPO· radicals that scavenge H· and OH· in the flame, while phosphorus acids promote dehydration and char formation, creating a barrier against heat and oxygen.
Once copolymerized, phosphorus is covalently bound and cannot migrate; the phosphate group also acts as the acid source in an intumescent system with nitrogen and silicon.
More phosphorus is not automatically better — excess reduces crosslink density and water resistance, so the balance between flame retardancy and mechanics must be found empirically.