Ternary Biobased Flame Retardant Gives Precious Veneer Excellent Decorative and Fire Safety Properties

Precious veneer possesses exceptional decorative properties, but its inherent combustibility makes it susceptible to rapid flame spread in fire scenarios. In this study, a ternary biobased flame-retardant system comprising phytic acid (PA), cytosine (CY), and vitamin C (VC) was developed and introduced into the veneer by a one-step impregnation method. The treated veneer retained its decorative quality, exhibiting minimal color change (ΔE* = 1.86) and supporting the formation of a uniform waterborne polyurethane coating comparable to that on untreated veneer. The PA–CY–VC system significantly enhanced fire safety: it increased the high-temperature char residue to over 24%, prevented ignition in sustained flame tests, and effectively suppressed flame propagation. At the optimal CY/VC mass ratio of 1:1, the total heat release and total smoke release were reduced by 25.5% and 54.0%, respectively, compared with those of pure veneer. Mechanistic studies indicated that the system operates through a synergistic combination of condensed-phase and gas-phase actions, promoting the formation of a stable, graphitized protective char while releasing flame-inhibiting gases. This environmentally benign, biobased flame-retardant system provides a sustainable strategy for simultaneously upgrading the fire safety and preserving the aesthetic value of high-end decorative veneers, promoting their wider application in fire-sensitive settings.