Research progress in fire warning strategies and flame retardancy of wood composites

Wood composites have been widely applied in fields of construction， decoration， furniture， and transport. The fire safety has always been concerned. In a view of the combustion characteristics of wood composites， in the past 10 years， the two strategies for safeguarding on wood composites were reviewed as active fire protection （fire warning） and passive fire protection （flame retardancy）. As noted， wooden composites have no the “smart”characteristic. The fire warning function of composites is achieved by introducing temperature-responsive functional materials on its surface， such as thermally responsive semiconductor materials， thermochromic materials， shape-memory materials， etc.， and converting the temperature signal into a receivable signal （electrical signal， color， shape deformation， etc.） to transmit to the outside world， achieving timely warning of fires. The key to flame retardant treatment of wood composites lies in limiting the heat conduction and material transfer within the solid phase and between the gas-solid phase during the combustion process. In addition， the research progress in the flame retardant and smoke suppression properties of metal systems （magnesium/aluminum oxides， magnesium/aluminum layered double hydroxides）， boron systems， phosphorus nitrogen systems， biobased flame retardant systems， etc. in plywood， particleboard， and fiberboard was further summarized. As well as its relevant construction and synergistic flame retardant mechanism of the flame retardant compound system were further clarified. Moreover， the curing process of adhesives and mechanical properties of wood composites influenced by flame retardant compound systems were also discussed. Finally， it is pointed out that adopting early warning and mid to later-stage flame retardant methods can significantly improve the flame retardant and fire resistance of wood composites.