The flame retardancy and thermal stability properties of poly (ethylene terephthalate)/hexakis (4-nitrophenoxy) cyclotriphosphazene systems

The aim of this work was to study the effect of hexakis(4-nitrophenoxy) cyclotriphosphazene (HNCP), which was found to be a highly efficient and intumescent flame retardant, on the thermal properties and flame retardancy of poly(ethylene terephthalate) (PET). HNCP was synthesized for use as flame retardant. PET/HNCP composites were prepared by melt blending. Three levels of HNCP (5%, 10% and 15%) were considered for the blends. Thermal stability of PET/HNCP systems was studied by thermogravimetric analysis, and the results showed that the addition of HNCP could improve char formation of this system both in nitrogen and in air atmosphere. It was found that the blends could pass UL-94 V-0 just containing 5% of HNCP. The Py-GC/MS analytical results indicated that introducing HNCP into PET would prevent the polymer pyrolysis during heating. The morphology and structure of the charred residue of these samples were evaluated by SEM and FTIR respectively. Results demonstrated that the char of PET/HNCP blends with a continuous outer surface and porous internal structure provided a good barrier to improve the thermal behaviours and decrease combustion properties of the composites during burning.