A green inorganic flame retardant applicable for Chinese ancient wooden building

Wood is a versatile raw material and renewable building material favored for its abundance, low cost, sustainability and significant contribution to peak carbon and carbon neutrality. Wood coated with tung oil, while having a longer service life by preventing insect bites and reducing volume loss, is also more flammable in a fire. In the present study, micro- and nano-flower-shaped magnesium alkali carbonates were synthesized by solution precipitation method. The synthesized magnesium alkali carbonate was further disintegrated into nanosheets of about 10 nm thickness and mixed with tung oil. The obtained mixture was applied to the surface of tinder and pine wood and the corresponding burning behavior and flame-retardant properties were characterized. The limiting oxygen index (LOI) value of the modified wood increased from 18% to 27%, indicating a significant enhancement of its flame-retardant properties. The addition of floral magnesium alkali carbonate increased the residual carbon content by 167% compared to wood coated with tung oil, indicating a carbon-forming effect of this unique inorganic flame retardant. Both tinder and pine wood coated with both tung oil and floral magnesium alkali carbonate exhibited lower ignition propensity, self-extinguishing behavior, and lower smoke emissions. These findings open a new way for the application of inorganic flame retardants to ancient wooden buildings coated with tung oil.