Intumescent multilayer hybrid coating for flame retardant cotton fabrics based on layer-by-layer assembly and sol–gel process

An intumescent coating composed of a nitrogen-modified silane hybrid (SiN) and phytic acid (PA) was deposited on cotton fabric through layer-by-layer assembly in order to reduce flammability. SiN was synthesized via a sol–gel process and characterized by 29Si-nuclear magnetic resonance. This intumescent coating system lowered the thermal stability of the cotton due to the catalyzed effect on degradation, but significantly improved the char formation. In a vertical flame test, fabrics coated with 15 bilayers (BLs) of SiN–PA extinguished the flame immediately upon removing the ignition source, while untreated cotton was completely burned out. Cone calorimeter data revealed that 15BL-coated cotton resulted in a 31% and 38% reduction in peak heat release rate and total heat release, respectively, relative to those of the uncoated control. This superior fire retardant performance is believed to be attributed to the formation of intumescent char layer on fibers that could effectively inhibit the oxygen and heat permeation when burning. In addition, as evidenced by thermogravimetric analysis-Fourier transform infrared spectroscopy results, the increased amount of inflammable gases and the decreased amount of flammable gases during the degradation of coated cotton fabrics was another important factor to improve the flame resistance. These results demonstrate that the combination of layer-by-layer assembly and sol–gel method will provide an effective alternative to current flame retardant treatments.