An urethane-based phosphonate ester for improving flame retardancy and smoke suppression of thermoplastic polyurethane

Abstract The flame-retardant thermoplastic polyurethane (TPU) with remarkable smoke suppression, anti-dripping and mechanical properties has been still a big conundrum in the field of fire safety science. In this article, an urethane-based phosphonate ester (UPE) flame retardant additive was successfully synthesized and incorporated into TPU. The fire safety, mechanical performance and flame-retardant mechanisms of TPU/UPE composites were lucubrated. With the incorporation of only 10 wt% UPE, TPU/10 wt% UPE composites passed UL-94 V-0 rating without dripping and the limited oxygen index (LOI) value reached 28.8%. Cone calorimetry tests indicated that the peak value of heat release and smoke production of TPU/10 wt% UPE composites were significantly diminished with the reduction of 70.6 and 54.1% in comparison with that of pure TPU. The analysis of flame-retarded mechanism for TPU/UPE indicated that UPE efficiently exerted free radical capture effect in gaseous phase, and stimulated the decomposition and charring of TPU composites in advance and the formation of high-quality char layer exerted isolation role in condensed phase. Therefore, the fire safety of TPU composites was enhanced by the incorporation of UPE. Meanwhile, the mechanical performance of TPU/UPE composite was well remained due to the good compatibility between UPE and TPU matrix. This work supplied a promising way for fabricating fire-safety TPU composites with preferable comprehensive properties.