In Situ Polymerization of Furfuryl Alcohol with Ammonium Dihydrogen Phosphate in Poplar Wood for Improved Dimensional Stability and Flame Retardancy

Fast-growing plantation wood normally possesses some undesirable intrinsic properties, such as dimensional instability, inferior mechanical strength, and flammability, limiting its usage as an engineering material. Herein, we report a green and facile approach for upgrading the low-quality poplar wood via a combined treatment with biomass-derived furfuryl alcohol (FA) and ammonium dihydrogen phosphate (ADP) acting as a flame-retardant additive. Wood/PFA/ADP composites were prepared by impregnation of the FA precursor solutions into the wood matrix, followed by in situ polymerization upon heating to form a hydrophobic FA resin/ADP network within the wood scaffold. In-depth scanning electron microscopy coupled with enregy-dispersive X-ray spectroscopy (SEM-EDX) and confocal laser scanning microscopy (CLSM) analyses reveal the wide distribution of the FA resin/ADP complexes inside the cell walls and also in the cell lumens. The incorporation of hydrophobic FA resin into wood results in reduced water uptake and remarkably enhanced dimensional stability, as well as generally improved mechanical properties. The addition of a small amount of ADP greatly enhances the flame retardancy of the modified wood and also effectively suppresses smoke generation during its combustion by reducing the heat-release rate and promoting char formation, as proven by cone calorimetry. The FA resin/ADP complexes increase phosphorus fixation in wood and reduces its leaching into water, suggesting a long-term fire protection of wood in service. Such modified poplar wood with overall enhanced properties could be potentially utilized as a reliable engineering material for structural applications.