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Nanocomposites of bisphenol A polycarbonate with 2, 4, 6, and 15 wt% multiwall carbon nanotubes (MWNT) and their use in fire retardancy are investigated. Their thermal behavior and pyrolysis are characterized using thermogravimetry, differential scanning calorimeter, oscillatory shear rheology, and dynamic mechanical analysis. The flammability is addressed using LOI and UL 94; the fire behavior, with a cone calorimeter using different irradiation. With increasing MWNT content the storage modulus is increased (10-20%) and melt viscosity increases by several orders of magnitude, particularly for low shear rates. The melt flow, dripping, and deformation during fire are hindered, which influences UL 94 and cone calorimeter results. The peak heat release rate is reduced up to 40-50% due to an improved barrier for small amounts (2 wt%) of MWNT and for low irradiation, whereas the effect is reduced for increasing irradiation and nearly vanishes for increasing filling. Adjuvant but also deleterious mechanisms result in the complex dependency on the MWNT content. Significant flame retardancy effects are specific and limited to only some fire properties. This study allows the materials' potential for implementation in different fire scenarios and tests to be assessed and provides insight into active mechanisms.
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.