Synthesis, Characterization, and Utilization of a Novel Phosphorus/Nitrogen-Containing Flame Retardant

The novel phosphorus/nitrogen-containing flame retardant hexa(phosphaphenanthrene aminophenoxyl)cyclotriphosphazene (HPAPC), which contains phosphaphenanthrene [9,10-dihydro-9-oxa-10-phosphaphenanthrene 10-oxide (DOPO)] and phosphazene (hexachlorocyclotriphosphazene) groups, was synthesized by the classic Atherton–Todd reaction, and its chemical structure was characterized by Fourier transform infrared (FTIR) and nuclear magnetic resonance (NMR) spectroscopies. Poly(lactic acid) (PLA) composites containing HPAPC were prepared by melt blending, and their fire performance and thermal behaviors were investigated in terms of limiting oxygen index (LOI), vertical burning (UL-94), cone calorimeter tests, and thermogravimetric analysis (TGA). The LOI value could reach up to 34.7%, and UL-94 could pass V-0 for the PLA composite containing only 5 wt % HPAPC. TGA results showed that the char formation of PLA could be significantly improved by the presence of HPAPC. The evolved gas of the composite was analyzed by FTIR-TGA and pyrolysis–gas chromatography/mass spectrometry (Py–GC/MS). The dispersion of fillers in PLA was observed by back-scattered electron (BSE). The char morphology was characterized by FTIR spectroscopy and scanning electronic microscopy (SEM). It was suggested that the presence of HPAPC could release ammonia gas during combustion, which was beneficial to the formation of an intumescent char structure.