Magnesium silica gel crystallized in the cell lumen of Chinese fir to construct porous structure for filtering toxic fumes

This study was conducted to improve the flame retardancy and smoke suppression of fast-growing Chinese fir (Cunninghamia lanceolate) wood by using magnesium silica gel to construct porous structure in the cell lumen. This method improved the fire retardancy of the wood, enhanced the mechanical properties of the wood in flames, and filtered toxic fumes to enhance the safety of buildings. Firstly, sodium silicate solution was used to impregnate the Chinese fir cell walls to enhance the mechanical strength. Then, sodium silicate and magnesium sulfate were compounded to become magnesium silica gel, which was crystallized in the cell lumen. In this way, magnesium silicate gel modified Chinese fir wood was prepared, and its heat and smoke suppression properties were tested. The pyrolyzed residual carbon mass of modified wood in nitrogen was 20% higher than that of the natural wood. A lower pyrolysis temperature reduced the yield of combustible volatile gases and halted the appearance of the violent combustion stage. The total heat release (THR) was reduced to 15 MJ/m², reaching B1 level in the Chinese National Standard (flame-retardant material). It maintained its mechanical strength within 3 min during combustion and greatly improved its application safety. SEM images showed the pore structure of the filler in the cell lumen, which blocked heat conduction, slowed the spread of fire, and filtered and adsorbed toxic and harmful smoke when it passed through. In line with the results of CONE and TG-IR tests, the total smoke production (TSP) was reduced by 85% compared with natural wood, which greatly enhanced the application value of the modified wood.