Construction of a self-adaptive coordination catalytic system and its regulation mechanism for flame retardancy and smoke suppression of cotton fabrics

Cotton fabric is highly flammable, posing serious fire hazards. Herein, a ternary bio-based flame retardant system comprising chitosan oligosaccharide (COS), ammonium pentaborate (APB), and zinc ions is constructed via a simple pad-dry-cure process. The COS/APB/Zn 2+ coating significantly enhances the flame retardancy and smoke suppression of cotton. The treated fabric achieves a limiting oxygen index of 32.4% and zero after-flame/after-glow time in vertical burning tests. Cone calorimeter test results show that the peak heat release rate, total heat release, and total smoke production of the CBZn-treated cotton fabric are reduced by 88.4%, 73.0%, and 84.5%, respectively. Thermogravimetric analysis reveals a char yield of 35.3% at 800 °C. The flame-retardant mechanism is dominated by condensed-phase action. APB decomposes to borate and forms B-O-C crosslinks with COS and cellulose, while Zn 2+ catalyzes aromatization and char graphitization. An intumescent, dense char layer is formed, blocking heat and mass transfer. Gas-phase analysis confirms reduced combustible volatiles and increased non-flammable gases. The treatment causes only moderate changes in tensile strength and stiffness. This work provides an efficient, halogen-free, formaldehyde-free biomass boron-based flame retardant strategy for cotton textiles.