A nano-Sb2O3 masterbatch (M-nano-Sb2O3) whose concentration was 80% was prepared.The masterbatch was added into poly(ethylene terephthalate) synchronized with aluminium diethlyphosphinate (AlPi).Different test methods such as limiting oxygen index (LOI)

vertical burning (UL 94)

cone calorimeter (CONE)

scanning electron microscope (SEM) demonstrated that the LOI of PET increased from 21.0% to 34.6% and the UL 94 vertical burning rating reached V-0; the heat release rate

total smoke release and CO production were reduced; the compact degree of the char residue was remarkably improved.All these phenomena were due to the synergism between nano-Sb2O3 and AlPi.Morever

thermal gravimetric analysis (TGA)

X-ray photoelectron spectroscopy (XPS) and Fourier transformed infrared spectroscopy (FTIR) pointed that the synergistic effect increased the char residue and its thermal stability

the char formation was promoted by the condensation of diethylphosphinic acid with the Sb-OH on the surface of nano-Sb2O3

and the char residue was mainly consisted of aluminum (antimony) phosphates

aluminum (antimony) pyrophosphate and organic compounds containing aryl cyclic structure.Differential scanning calorimetry (DSC) showed that the synergistic effect facilitated the crystallization of PET and its melting endotherm.Therefore

flame retardancy mechanisms in PET for AlPi in combination with nano-Sb2O3 were primarily cross-linking reactions

char formation in condensed phase and endothermic effect

meanwhile

gas phase mechanism was also involved.