Layer-by-layer assembled nanocoating containing MoS 2 nanosheets and C 60 for enhancing flame retardancy properties of flexible polyurethane foam

A novel three bilayers nanocoating containing MoS2 nanosheets and C60 was constructed on the surface of flexible polyurethane (FPU) foam by a layer-by-layer assembly method. MoS2 nanosheets were prepared by ultrasonic-assistant exfoliation method in a mixed solvent of N-Methyl-2-pyrrolidinone (NMP) and aqueous hydrogen peroxide (30% H2O2). MoS2-C60/FPU foam was prepared by alternately submerging the FPU foam into C60/guargum and MoS2/sodium alginate suspensions. Scanning electron microscopy (SEM) characterization showed that MoS2 nanosheets and C60 nanoparticles were uniformly distributed on the surface of FPU foam matrix. Thermogravimetric analysis demonstrated that MoS2-C60/FPU foam exhibited better thermal stability than the control FPU foam. Cone calorimeter test results revealed that MoS2-C60/FPU foam with the incorporation of 5.24 wt. % MoS2-C60 nanocoating had a remarkable reduction in peak heat release rate (pHRR, 47.5% reduction), total heat released (THR, 51.1% reduction) and total smoke production (TSP, 33.1% reduction) compared with those of the control FPU foam. Furthermore, the morphology and structure of char residue after cone calorimeter test were investigated by SEM and Raman spectroscopy. The possible flame-retardant mechanism of MoS2-C60/FPU foam was proposed, and this significant improvement in flame retardancy could be ascribed to the insulating barrier and adsorption effect of MoS2 nanosheets, free radicals-trapping ability of C60 in condensed phase, and the catalytic carbonization effect of the MoS2-C60 nanocoating. This work provides a new approach for producing high quality flame retardant polyurethane foam materials.