Mechanistic investigation of a flame retardant coating made by layer-by-layer assembly

Abstract

The efficiency of a flame retardant coating based on poly(allylamine) (PAH) and montmorillonite (MMT), deposited on polyamide 6 (PA6) bulk polymer was demonstrated in our previous work. In this paper we aim to investigate the mechanism of action of this flame retardant coating. To reach this objective, PA6-(PAH-MMT) at 40 bilayers was tested in a cone calorimeter and interrupted at different characteristic times: 25 s (after the fire test start), time to ignition, time of peak heat release rate and time of flameout. The condensed phases of the specimen residues obtained were characterized by scanning electron microscopy, X-ray diffraction, laser desorption ionization and solid state ¹³C nuclear magnetic resonance while the gas phase was evaluated by thermogravimetric analysis coupled with infrared spectroscopy and mass spectrometry. Finally the pyrolysis combustion flow calorimeter was used to evidence the effect of this layer-by-layer assembly in the gas phase. A possible mechanism explaining the improvement of the flame retardancy of a PA6 substrate in the presence of LbL coating made of PAH and clay is proposed.