The pyrolysis and the flame retardancy of poly(butylene terephthalate) (PBT) containing aluminum diethylphosphinate (AlPi) and nanometric Fe2O3 were investigated using thermal analysis, evolved gas analysis (Thermogravimetry-FTIR), flammability tests (LOI, UL 94), cone calorimeter measurements and chemical analysis of residue (FTIR). AlPi mainly acts as a flame inhibitor in the gas phase, through the release of diethylphosphinic acid. A small amount of Fe2O3 in PBT promotes the formation of a carbonaceous char in the condensed phase. The combination of 5 and 8 wt% AlPi, respectively, with 2 wt% metal oxides achieves V-0 classification in the UL 94 test thanks to complementary action mechanisms. Using PBT/metal oxide nanocomposites shows a significant increase in the flame retardancy efficiency of AlPi in PBT and thus opens the route to surprisingly sufficient additive contents as low as 7 wt%.
The flame retardancy of poly(butylene terephthalate) (PBT) containing aluminium diethlyphosphinate (AlPi) and/or nanometric metal oxides such as TiO2 or Al2O3 was investigated. In particular the different active flame retardancy mechanisms were discovered. Thermal analysis, evolved gas analysis (TG-FTIR), flammability tests (LOI, UL 94), cone calorimeter measurements and chemical analyses of residues (ATR-FTIR) were used. AlPi acts mainly in the gas phase through the release of diethylphosphic acid, which provides flame inhibition. Part of AlPi remains in the solid phase reacting with the PBT to phosphinate-terephthalate salts that decompose to aluminium phosphate at higher temperatures. The metal oxides interact with the PBT decomposition and promote the formation of additional stable carbonaceous char in the condensed phase. A combination of metal oxides and AlPi gains the better classification in the UL 94 test thanks to the combination of the different mechanisms.