Intumescent flame-retardant poly(1, 4-butylene terephthalate) with ammonium polyphosphate and a hyperbranched triazine charring-foaming agent: Flame retardancy performance and mechanisms

Intumescent flame-retardant poly(1, 4-butylene terephthalate) composites with ammonium polyphosphate and a hyperbranched triazine charring-foaming agent were prepared through melt blending. The flame retardancy, pyrolysis behavior, and flame-retardant mechanism of flame-retardant poly(1, 4-butylene terephthalate) were investigated using flammability tests, cone calorimeter measurements, thermogravimetric analysis including evolved gas analysis, and residue analysis (Fourier transform infrared and scanning electron microscopy). The results showed that the intumescent flame retardant with the appropriate ammonium polyphosphate/hyperbranched triazine charring-foaming agent mass ratio (4/1) could significantly improve the flame retardancy of poly(1, 4-butylene terephthalate), and the highest Limiting Oxygen Index value and UL-94 V-0 rating was reached. The peak heat release rate and total heat evolved remarkably decreased, respectively, by 84% and 76% corresponding to poly(1, 4-butylene terephthalate). Thermogravimetric analysis results showed the synergistic effect between ammonium polyphosphate and hyperbranched triazine charring-foaming agent could enhance the char formation ability of composites. The results of gaseous products and residue char structure analysis indicated intumescent flame retardant influenced the decomposition behavior and promoted the formation and accumulation of phosphorous/azotic and polyaromatic char possessing high graphitization degree, which exerted a condensed-phase flame-retardant effect on the flame-retardant composites.