Cupric ion decorated ammonium polyphosphate as an effective flame retardant for thermoplastic polyurethane

Inspired by the significant synergistic charring effect and catalytic graphitizing effect of metal ion, cupric ion decorated ammonium polyphosphate (APP@Cu) was prepared to improve the fire safety of thermoplastic polyurethane (TPU). The characterization on micromorphology, chemical composition and structure of APP@Cu confirmed that copper hydroxide was decorated on the surface of APP. Comparing for TPU/APP, TPU/APP@Cu achieved a higher LOI value of 28.2% and reached UL-94 V-0 rating. What’s more, the peak of heat release rate, total smoke production and the fire growth rate significantly reduced by 72%, 36% and 76%, respectively, in comparison with that of TPU. These results demonstrated that APP@Cu preferably magnified the flame-retardant efficiency of APP for TPU due to the synergistic charring effect of phosphorus and cupric ion, and the catalytic graphitizing effect of copper species. Therefore, the enhancing char-forming mechanism would provide a strategy for improving the fire safety of TPU.