Tough flame-retardant wood fabrication via lignin reassembly

Wood, a renewable and eco-friendly resource, holds significant potential for developing sustainable structural materials. Nevertheless, in advanced engineering applications, natural wood often fails to meet requirements for mechanical performance and flame retardancy. Herein, we present a novel, simple yet highly effective strategy to fabricate tough flame-retardant wood (TF-wood). This approach involves partial delignification using alcohol-amine-based deep eutectic solvents (DESs), followed by N/P-functionalization of the dissolved lignin that is reincorporated into the wood matrix with subsequent hot-pressing. With the incorporation of 20% functionalized lignin, the resulting TF-wood demonstrates a remarkable increase in tensile strength (425.2 MPa), strain (2.9%), and the corresponding toughness reaching 8.1 MJ/m³, 27 times higher than that of natural wood. Additionally, the peak heat release rate (pHRR) of the TF-wood is reduced by 58.3%, and the total heat release (THR) is decreased by 47.8%. Crucially, TF-wood exhibits an ultralow water migration rate, further enhancing its structural stability in humid environments. These combined properties render TF-wood highly attractive for structural applications requiring enhanced fire safety and durability. This study paves the way for designing sustainable, high-performance building materials that integrate multiple functionalities.