Boron-containing intumescent multilayer nanocoating for extinguishing flame on cotton fabric

Sodium polyborate (SPB) has been employed with polyhexamethylene guanidine phosphate (PHMGP) to compose a nitrogen-phosphorus-boron intumescent coating on cotton fabric via a layer-by-layer (LBL) technique for obtaining excellent flame retardancy. The infrared spectra and atomic emission spectra indicate that the PHMGP-SPB multilayer grows gradually during the assembly process. Thermogravimetric analysis results show that the residue char of cotton is greatly enhanced after treatment with the LBL coating, which has a high char forming effect on cellulose during testing. The micro-calorimeter test finds that the assembly coating drastically decreases the peak heat release rate and total heat release of cotton fabric as a result of the catalytic charring effect. Cotton’s burning behavior is monitored by the flammability test, and the results show that ten bilayer (BL) coating with only 7.5 wt% can completely extinguish the flame on cotton samples. The oxygen index test reveals that the limiting oxygen index (LOI) of cotton samples is substantially increased by introducing the LBL coating. When the BL increases to 20, the LOI value reaches up to 41. The residual char after burning is analyzed by scanning electron microscope and infrared spectroscopy, and the results show the the LBL coating has an intumescent flame-retardant effect on cotton.