Phosphorus-containing Salen-metal complexes investigated for enhancing the fire safety of thermoplastic polyurethane (TPU)

Three novel phosphorus-containing Salen-based derivatives (Salen-DPCP-M: M = Ni, Zn, and Mn), which include both phenyl phosphate structures (DPCP) and Salen-metal complexes, were prepared for enhancing the fire safety of thermoplastic polyurethane (TPU). Thermogravimetric analysis (TGA) showed that Salen-DPCP-M altered the thermal degradation pathways of TPU probably due to the phosphorus-containing structure of Salen-DPCP-M. The cone calorimeter test showed that the addition of 3 wt% of Salen-DPCP-Ni, Salen-DPCP-Zn, and Salen-DPCP-Mn lowered the peak of heat release rate (PHRR) from 1495 kW/m 2 for neat TPU to 690, 875, and 813 kW/m 2 , respectively, for the TPU composites, which demonstrated that Salen-DPCP-M improved the fire safety of TPU. In addition, the release of toxic CO gas from the Salen-DPCP-Ni/TPU and Salen-DPCP-Zn/TPU composites was reduced by 78.2% and 80.0%, respectively. The results of TGA/infrared spectrometry (TG-FTIR) showed that the incorporation of Salen-DPCP-Ni promoted the release CO 2 , while reducing the formation of harmful gases. Laser Raman spectroscopy (LRS) and scanning electron microscopy (SEM) showed that Salen-DPCP-Ni/TPU and Salen-DPCP-Zn/TPU composites formed a dense and stable char layer. Herein, the mechanism of these flame retardants containing novel phosphorus-containing Salen-metal complexes is also proposed.