Synergistic effect between phosphorus tailings and aluminum hypophosphite in flame-retardant thermoplastic polyurethane composites

The massive accumulation of phosphorus tailings (PT) not only occupies land resources and also causes great threat to ecological environment and human security. It is of great significance to explore the resource utilization of PT in some fields. Herein, aluminum hypophosphite (AHP) and PT are blended together to enhance the flame retardancy of thermoplastic polyurethane (TPU) composites, and the synergistic effects between AHP and PT are investigated systematically. Cone calorimeter test (CCT) results indicate that the peak heat release rate (PHRR) and total heat release (THR) of the samples containing 25 wt% AHP are decreased by 89% and 68%, respectively, and the total smoke release (TSR) show a reduction of 58.8%, in comparison with those of neat TPU. For the sample TPU/22.5AHP/2.5PT, the PHRR, THR, and TSR are decreased by 91.2%, 70%, and 63%, respectively. Scanning electron microscopy (SEM) analysis results demonstrate that the addition of PT can facilitate the generation of dense and compact char layers, preventing the release of heat and smoke effectively. All the abovementioned results indicate that the synergistic effects are existed between AHP and PT for enhancing the fire safety of TPU composites, which can provide a new way for the utilization of PT.