Application of MCA–AlPi Nitrogen–Phosphorus Synergistic Flame Retardant in Nylon 11

ABSTRACT Halogen‐free flame‐retardant nylon was prepared by melting a mixture of nylon 11 (PA11), melamine cyanurate (MCA) and aluminum diethylphosphonate (AlPi) in a twin‐screw extruder. The addition amount and ratio of the synergistic formula would affect the synergistic flame‐retardant effect and degradation process of the composites. In the cone calorimetric test, when the flame‐retardant content was 35%, the total heat release (THR) of the halogen‐free flame‐retardant formula decreased by 24% to 52% compared with pure PA11. The most noteworthy finding is that the ignition time (TTI) of the flame‐retardant formula with MCA (334 s) is significantly longer than that of the pure PA11 (131 s) and AlPi (140 s) flame‐retardant formulas, and the effect of the compound formula can be better than that of the MCA single‐component formula, up to 404 s. Upon analyzing the structure and composition of the gas products and char residue of each formula, we discerned that MCA and AlPi played different roles in promoting the formation of carbon residues within the condensed phase. Based on all the test results, it was concluded that the mechanism of the nitrogen flame‐retardant MCA involves delaying the decomposition of composites and promoting the formation of an expanded carbon layer by generating refractory gas.