Enhanced fire-retardant, smoke-suppressing, and ultra-strong mechanical properties of non-adhesive laminated wood through borate ion crosslinking

The development of flame-retardant, smoke-suppressing, and strong structural materials is crucial for reducing energy consumption, enhancing building safety, and ensuring personal and property security. Fast-growing poplar is widely abundant in nature. However, its application in construction is limited due to its flammability, propensity to produce smoke post-combustion, and inadequate mechanical strength. To address these challenges, this study introduced a simple and feasible method to produce flame-retardant, smoke-suppressing, and robust non-adhesive wood laminate. The method involves impregnating delignified poplar veneer with a solution of boric acid and sodium tetraborate, followed by hot pressing. The surface fibers of delignified poplar wood, rich in hydroxyl groups, interacted with borate ions to form covalent bonds, significantly enhancing flame retardancy, smoke suppression, and mechanical properties. The ultimate oxygen index of the densely layered boric acid/sodium tetraborate-impregnated wood increased from 22.1 % to 47.9 % compared with untreated wood, and its vertical combustion grade was also increased from flammable grade to V-0 grade. Cone calorimetric tests demonstrated reductions of 41.1 % in total smoke emission, 54.2 % in maximum smoke generation rate, 30.8 % in maximum heat release rate, 53 % in total heat release per unit mass, 27 % in average effective heat of combustion, and a 37-second delay in ignition time compared with untreated wood. Mechanical tests revealed significant enhancements in specific tensile strength (∼ 253.55 MPa·cm 3 ·g −1 ), tensile strength (∼ 330.63 MPa), tensile modulus (∼ 5.91 GPa), flexural strength (∼ 273.36 MPa), flexural modulus (∼ 50.69 GPa), and impact strength (53.69 kJ·m 2 ). The wood laminates manufactured using this method hold promise as flame-retardant, smoke-suppressing, and high-strength structural materials, providing a convenient and feasible strategy for producing multifunctional energy-efficient building materials. • B(OH) 4 −1 can covalently cross-link with –OH of cellulose on the wood surface. • The wood laminate exhibits excellent flame retardancy and smoke suppression properties. • The wood laminate exhibits ultra-strong mechanical properties.