Ammonium polyphosphate (APP) shows fire retardant activity in poly(butylene terephthalate (PBT), as the LOI values increase and the UL94 rating improves. TG, FT-IR and GC/MS data provide evidence that APP interacts with PBT. Addition of APP changes the composition of the solid, high and low boiling decomposition products as compared to those of neat PBT. The main reaction occurring on pyrolysis was shown to be ammonolysis of PBT resulting in the formation of various aromatic nitriles. The fire retardant effect was mainly attributed to the condensed-phase activity of APP.
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