Abstract: Chinese fir is the main tree species for artificial afforestation in southern forest areas of China. It is mostly used in indoor furniture and houses. It has the characteristics of wide use and fast growth. However, Chinese fir has low fire resistance and is prone to fire in high temperature or thermal radiation environment. In order to reduce the risk of fire, this paper proposes a flame retardant process to prepare flame retardant Chinese fir. Chinese fir is immersed in ammonium polyphosphate-borax composite impregnating solution, and melamine is coated on the surface to achieve flame retardant effect. The drug absorption rate, weight gain rate, combustion performance, pyrolysis and ignition characteristics of modified Chinese fir were studied by cone calorimeter, thermogravimetric analyzer and ignition experiment, and the flame retardant mechanism was explored. Compared with logs, flame retardant Chinese fir can effectively reduce the heat release rate and total heat release of Chinese fir during combustion, which plays an important role in delaying its combustion behavior in fire. The total smoke release, CO and CO2 production rate, and the smoke suppression performance was improved. At 800 ℃, the residual carbon rate of flame retardant Chinese fir increased by 160% after pyrolysis, and the thermal stability was improved. The methane torch quickly ignited the logs and burned violently. After 90 s of combustion, the surface lost its overall structure, while the flame retardant Chinese fir did not ignite within 90 s.

Key words: Chinese fir flame retardant; impregnating coating; combustion characteristics; pyrolysis characteristics