Recent progress in flame retardant strategies for polyamides

Their flammability, melt dripping, high heat release and toxic-gas generation nevertheless restrict use in fire-safety-critical applications. This review summarizes recent flame-retardant strategies for aliphatic, semi-aromatic and aromatic PAs, with emphasis on aliphatic PA systems that dominate both academic research and industrial applications.

Additive approaches are compared with nano-sized synergists, reactive/copolymer FRs and flame-retardant finishing. The mechanisms responsible for gas-phase radical quenching, condensed-phase charring, barrier formation, melt-dripping control and smoke/toxicity regulation are discussed in relation to PA structure, processing stability and end-use requirements. Nano-sized synergists are treated as supporting components rather than primary FRs, because their main role is to reinforce char, improve dispersion and reduce heat/mass transfer at low loadings.