Effect of APP-TA-silica sol compound flame retardant on fire resistance of Chinese fir and the fire spread numerical simulation in buildings

To develop a novel flame retardant that enhances the fire resistance of wood, a compound consisting of ammonium polyphosphate, tannic acid, and silica sol was integrated into Chinese fir. This study examined its effects on fire resistance and analyzed the dynamics of flame spread in flame-retardant wood using numerical simulations of the Fire Dynamics Simulator. The optimal flame retardant combinations, identified through orthogonal testing, were F-STA1 (Flame retardant silica sol: tannic acid: ammonium polyphosphate ratio of 2:1:1) and F-STA2 (Flame retardant silica sol: tannic acid: ammonium polyphosphate ratio of 3:1:2). Their corresponding limited oxygen index values were 34.2% and 33.6%, respectively, achieving a flame retardant classification of B1 level and a UL-94 rating of V-0. Thermogravimetric analysis revealed that the peak weight loss rates for F-STA1 and F-STA2 were substantially lower than those for the F-Ctrl (Control group), with increases in carbon residue rates of 83.33%, 114.22%, and 68.22%, at 800 °C for F-STA1, F-STA2, and F-TA (The flame retardant has no silica sol, and the tannic acid: ammonium polyphosphate ratio is 1:2), respectively. Cone calorimetric analysis indicated significant reductions in HRR (Heat Release Rate) and THR (Total Heat Release) for F-STA2, with decreases of 41.86% and 38.41% compared to the control. Raman spectroscopy demonstrated a reduction in the residual carbon ID/IG ratio by 34.63% for F-STA2. Furthermore, the addition of silica sol notably enhanced the mechanical properties of the wood; bending strength and modulus for F-STA2 improved by 55.47% and 45.33%, respectively, and compressive strength increased by 10.69%. Simulation outcomes suggest that flame retardant application reduces flame spread, smoke propagation, and the rate of temperature change in wood structure buildings, effectively inhibiting fire progression.