Microintumescent mechanism of flame-retardant water-based chitosan-ammonium polyphosphate multilayer nanocoating on cotton fabric

Layer-by-layer (LbL) assembly of nanocoatings on fabric substrates has been very successful in terms of reduction of flammability. In particular, an LbL system comprised ammonium polyphosphate as the polyanion and chitosan as the polycation, applied to cotton fabric, dramatically reduced cotton flammability. At this point, the fire-retardant (FR) mechanism of action of this system has never been fully elucidated. Sonicated and nonsonicated coated cotton fabrics were evaluated using a vertical flame test and mass loss calorimeter. Coating morphology was investigated before and after burning. Thermal analyses and chemical analyses in the condensed phase (and in the gas phase) were conducted to reveal the FR mechanism of action. At the cotton surface, a combination of both condensed (formation of aromatic char) and gas phase (release of water and highly flammable gases) mechanisms impart the FR behavior, promoting a kind of microintumescence phenomenon. © 2016 Wiley Periodicals, Inc.