The flame retarding mechanism of the novolac as char agent with the fire retardant containing phosphorous-nitrogen in thermoplastic poly(ether ester) elastomer system

In this paper, the flame retarding mechanism of novolac as char agent and the phosphorous-nitrogen (P-N) flame retardant system was investigated in thermoplastic poly(ether ester) elastomer(TPEE) composites containing aluminum diethylphosphinic (AlPi) and melamine polyphosphate (MPP). The fire resistance of TPEE containing P-N flame retardant and novolac was analyzed by the limiting oxygen index (LOI) and the vertical burning (UL94) test. The result shows that the flame retardants containing P-N increased the LOI of the material from 17.3 to 27%. TPEE containing P-N flame retardants just got UL94 V-2 ranking, which resulted in the flaming dripping phenomenon. On the other hand, TPEE containing P-N flame retardant and novolac achieved UL94 V-0 rating. The mechanism of thermal decomposition and char formation was studied by thermal gravimetric analysis (TGA), temperature-dependent FTIR and Pyrolysis/GC/MS. TGA and SEM-EDX measurements have demonstrated that novolac results in the increase of char yield and the formation of the thermally stable carbonaceous char. The results of FTIR and Pyrolysis/GC/MS analyses indicated that cross-linking reaction between the novolac and P-N flame retardant and polyaromatisation of the novolac itself which resulted in a strong compact carbonaceous char. Therefore, novolac is a promising synergist for the P-N flame retardant in TPEE.