Multi-synergistic flame-retardant hydrogel coating for bamboo veneers

The urgent demand for fire-safe coatings in bamboo furniture has driven significant progress in developing halogen-free flame-retardant technologies. This study presents a new multi-synergistic flame-retardant hydrogel coating, composed of methylcellulose (MC), polyacrylamide (PAAm), and tetraethyl orthosilicate (TEOS)-pretreated ammonium polyphosphate (SiO₂@APP) for bamboo veneers. The uniformly dispersed SiO₂@APP serves as an acid catalyst and an incombustible gas source, while MC and PAAm act as carbon sources in the fire-resistant C-Si-P-N coating system. Additionally, the hydrogel containing MC and water provides significant heat absorption, improving its flame-retardant efficacy. The limiting oxygen index (LOI) of the resultant hydrogel-coated bamboo (HB) increases significantly from 22.1 % to 55.9 %. Notable reductions of 20.3 % and 53.1 % in the peak heat release rate (PHRR) and total heat release (THR) of the hydrogel-coated bamboo (HB) are observed, respectively, in comparison to the original bamboo. After combustion, the dense hybrid char layer incorporating P, N, and Si effectively impedes heat release and combustible gas diffusion. Additionally, the hydrogel coating exhibits excellent interfacial adhesive strength (125.9 kPa) on the bamboo surface. Through this simple and facile sol-gel preparation process, efficient flame-retardant coatings demonstrate promising potential for biomass-based materials in diverse applications, including furniture, commercial buildings, and industrial uses.