An efficient halogen-free flame retardant for glass-fibre-reinforced poly(butylene terephthalate)

Compared with poly(butylene terephthalate) (PBT), glass-fibre-reinforced poly(butylene terephthalate) (GF-PBT) is difficult to flame retard with halogen-free flame retardants. In the present study, the aluminium salt of hypophosphorous acid (AP) was used as a flame retardant for GF-PBT. A series of flame-retardant GF-PBT composites was prepared via melt compounding. The flame retardance and combustion behaviour of the composites were studied by limiting oxygen index (LOI), vertical burning test (UL-94) and cone calorimetric test. Thermal behaviours and thermal decomposition kinetics were investigated by thermogravimetric analysis (TGA) under N2 atmosphere. The addition of AP to the composites could result in an increased LOI value, a UL-94 V-0 (1.6mm) classification and a better fire performance in cone calorimetric tests. The char morphology observation after flame-retardant tests, calculation of decomposition kinetics, X-ray photoelectron spectroscopy (XPS) and infra-red spectral analysis of the char residue confirmed the condensed-phase flame-retardant mechanism. Furthermore, the mechanical properties of the flame-retardant composites were not deteriorated, retaining an acceptable level.