Flame retardancy and smoke suppression effect of bis(4-nitrophenyl) phosphate modified layered double hydroxides derived from red mud in thermoplastic polyurethanes

Red mud-based layered double hydroxides (LRM) was synthesized by a co-precipitation route, and then a hybrid with bis(4-nitrophenyl) phosphate (BNPP)-modified LRM material (BRL) was prepared in this paper. Through X-ray diffraction(XRD), Fourier transform infrared spectra (FTIR), nuclear magnetic resonance spectra (NMR), transmission electron microscope (TEM) and energy dispersive spectrometer (EDS) analysis, the results show that BRL is better dispersed than LRM. Then, thermoplastics polyurethanes (TPU) was used as the base material. TPU/LRM and TPU/BRL composites were prepared by a melt-blending method. Cone calorimeter test (CCT) was used to investigate the effect on flame retardancy and smoke suppression. Specifically, the PHRR values of TPU/LRM and TPU/BRL composites were reduced by 41.6% and 52.5% compared with pure TPU sample. The main factor of improved flame retardancy and smoke suppression can be explained by the catalytic carbonization of LRM or BRL in solid phase and the P-radicals (such as PO center dot and HPO center dot) in gas phase which demonstrated by thermo-gravimetric analyzer test (TGA) and char analysis.