Synergistic flame retardant effects and mechanisms of nano-Sb2O3 in combination with aluminum phosphinate in poly(ethylene terephthalate)

The synergistic flame retardant effects and mechanisms of nano-Sb2O3 in combination with aluminum diethlyphosphinate (AlPi) in poly(ethylene terephthalate) (PET) were investigated by means of limiting oxygen index (LOI), UL 94 vertical burning test, thermogravimetric analysis (TGA) and thermogravimetric analysis coupled with Fourier transform infrared spectrometer (TGA-FTIR). A good dispersion of nano-Sb2O3 and AlPi into polymer matrix was achieved as showed by high resolution transmission electron microscope (HRTEM) and scanning electron microscope (SEM). Obvious synergistic effects between nano-Sb2O3 and AlPi were observed for flame retardant PET when the mass ratio of AlPi and nano-Sb2O3 was from 1:1 (4 wt%) to 4:1 (10 wt%). LOI value of flame-retarded PET was increased to 33.6% and UL 94 rating passed V-0. Adding nano-Sb2O3 to AlPi remarkably changed the thermo and thermo-oxidative degradation behaviors of AlPi, as the initial and maximum-rate decomposition temperature of AlPi/nano-Sb2O3 shifted and more residues were obtained at 800 °C. Compared with PET/AlPi, two processes were believed to promote the formation of more carbonaceous char for PET/AlPi/nano-Sb2O3: one was the catalytic effect of nano-Sb2O3 on the cross-linking phenomenon, the other one was the condensation reaction between Sb-OH on the surface of nano-Sb2O3 and diethylphosphinic acid. Furthermore, the interaction between nano-Sb2O3 and AlPi in the condensed phase happened mainly over the temperature range of 460-600 °C. All these results were confirmed by evolved gas and residue analysis.