Fire retardant synergism between cyclic diphosphonate ester and melamine in poly(butylene terephthalate)

A cyclic diphosphonate ester and melamine have provided excellent fire retardant performance in poly(butylene terephthalate) (PBT). An increase of the oxygen index as well as an improvement of the UL-94 classification to V-0 rating was observed. The interaction between the fire retardant additives and PBT was studied by thermal analysis and infrared spectroscopy. Aromatic nitriles were detected in the solid residue and in high boiling products of the thermal decomposition of the fire retardant polymer. Synergism between cyclic diphosphonate ester and melamine is discussed in terms of chemical interaction of the additives with PBT.