Synthesis and characterization of MnO2 nanosheets based multilayer coating and applications as a flame retardant for flexible polyurethane foam

MnO2 nanosheets were firstly successfully deposited on the surface of flexible polyurethane (FPU) foams through layer-by-layer technique for the purpose of improving its fire safety. The coating growth was realized by alternatively deposition of MnO2 nanosheets suspension and polyelectrolytes solutions. UV-Vis spectra exhibited positive correlation relationship between the absorption intensity and layer number. Thermogravimetric analysis results showed that the thermal stability of the coated FPU foams increased obviously after the fabrication of MnO2 nanosheets. Moreover, the peak heat release rate (pHRR) values of the coated FPU foams decreased remarkably with a relative low loading compared with the pure sample, indicating that MnO2 based coating had tremendous advantages in reducing the fire hazards of the FPU foams. Furthermore, the thermogravimetric-Fourier transform infrared tests indicated that the generation of the toxic gases was suppressed significantly, which was benefit for the fire rescue when the fire occurred. In addition, its potential flame retardancy mechanism was proposed: the MnO2 nanosheets based coating can perform as a physical insulating barrier, which can effectively delay the permeation of heat, oxygen and flammable volatiles and decrease the heat release rate. Therefore, MnO2 nanosheets based coating fabricated through layer-by-layer technique can effectively endow FPU foams with excellent thermal stability, flame retardancy and toxicity suppression properties.