Synergistic action between aryl phosphates and phenolic resin in PBT

Fire retardant efficiency of aryl phosphates in combination with phenol-formaldehyde novolac type resin was studied in poly(butylene terephthalate) (PBT). It was shown that resorcinol bis(diphenyl phosphate) or bisphenol A bis(diphenyl phosphate) in combination with novolac is an efficient fire retardant in non-glass reinforced PBT. Co-addition of triphenyl phosphate was required for glass-reinforced PBT to reach similar fire retardant performance. Apparently aryl phosphates/novolac prevent exudation of aryl phosphates to the surface and facilitate crystallization of PBT. Although the aryl phosphates/novolac are compatible with PBT and do not decompose polymer during compounding, PBT exhibited some reduction of Izod impact strength and heat distortion temperature. These phenomena were attributed to changes in the crystalline morphology, and probably also in the amorphous regions of the polymer.