Phosphorylated sodium alginate-filled delignified wood-reinforced transparent wood: Crafting flame-retardant composites
Mingjie Guo, Ying Pan, Songyuan Xu, Wei Wang, Yan Zhang, Shaodan Xu, Dihua Wu, Dong Zhang, Suling Zhang, Ting Lü, Hongting Zhao
Abstract
Transparent wood (TW), an emerging sustainable material with high optical transmittance and mechanical strength, is hindered by the inherent flammability of its cellulose-lignin matrix, posing fire risks. To address this, we developed an eco-friendly flame-retardant TW by integrating phosphorylated sodium alginate (PSA)-filled delignified wood with polyurethane acrylic resin (PUA). Delignified balsa wood was freeze-dried into a porous structure, functionalized with PSA, and reinforced with UV-cured PUA. Structural characterization confirmed uniform PSA coating on delignified wood channels, introducing phosphorus groups that enhanced thermal stability and flame retardancy. Combustion tests revealed self-extinguishing behavior in PSA-modified delignified woods, reducing peak heat release rate (pHRR) by 67 % and total heat release (THR) by 80 % versus delignified wood. The final PUA/wood-PSA3 composite demonstrated a 27 % pHRR reduction and 47 % lower THR compared to pure PUA, alongside 61 % less smoke emission. Optical transmittance of composites decreased moderately due to PSA's light absorption, while tensile strengths of PUA/wood composites surged to 30 MPa owing to the aligned cellulose scaffold. The flame-retardant mechanisms were investigated using characterization of the char residue and molecular dynamics simulations. These methods demonstrated the effectiveness of phosphorus-induced char formation and radical quenching in enhancing fire safety while preserving essential material properties.