Preparation and flame-retardant mechanism of polyheptazine/PA6 nanocmposites

Triazine derivations, as effective non-halogen flame-retardant additives, have been widely used due to the world-wide problem of ecological and environmental safety. However, controllable adjustments for the thermal stability of triazine derivations remain challenging. The premature decomposition of the retardant will significantly reduce the thermal decomposition temperature of the composites, leading to impacts on the process temperature and service temperature. In this paper, a series of poly-heptazine flame retardants (HLCN) with tunable decomposition temperatures are synthesized by one-step thermal calcination of urea. The HLCN is uniformly composited with polyamide 6 (PA6) by melt extrusion. The composite demonstrates improved LOI for PA6 to 30.5 with 2 wt% HLCN. The results of thermal analysis and pyrolysis gaseous productions analysis reveal the flame retardant mechanism of HLCN as the synergistic effect of melam/melem oligomers inducing gas phase flame retardancy and highly condensed melon inducing condensed phase flame retardancy. The HLCN demonstrates superior flame retardant effect than that of the commercial melamine cyanurate (MCA) with much less impacts on the service temperature of PA6, providing cost-effective halogen-free flame retardants with tunable decomposition temperatures to adapt various polymer matrices.