Smoke suppressant in flame retarded thermoplastic polyurethane composites: Synergistic effect and mechanism study

Considerable smoke and toxic volatiles generation has compromised the application of thermoplastic polyurethane (TPU) and caused a great threat to human life. Here, nano-MgFe layered double hydroxide (MgFe-LDH) with uniform particle size was synthesized to reduce smoke density and toxic gases of TPU composites using ammonium polyphosphate (APP) as a flame retardant agent. The results show that the combination of 16 wt.% APP and 4 wt.% MgFe-LDH greatly decreased the smoke density (D_20min and D_{s, max}), smoke production rate (SPR) and heat release rate (HRR) of TPU composites. Furthermore, the MgFe-LDH synergist demonstrated high efficiency in decreasing total volatiled products and toxic volatiles evolved, such as the CO, HCN and isocyanates. The reason was mainly attributed to the chemical reaction between MgFe-LDH and APP, which can promote the compactness of char layers with fine microstructure formed in the decomposition process of MgFe-LDH/APP/TPU composites. The protective char layers could act as barriers between combustion zone and matrix to protect the unburned substrate and promote smoke suppression effect.