Nanostructured multifunctional wood hybrids fabricated via in situ mineralization of zinc borate in hierarchical wood structures

Developing feasible and eco-friendly methods to fabricate multifunctional wood remains an imperative yet challenging task. Prompted by biomineralization, this study proposes the fabrication of nanostructured wood hybrids with efficient flame retardancy, smoke suppression, mold resistance, and antitermite activity via in situ mineralization of nanosized zinc borate (ZnB) particles in a hierarchical void system of wood. ZnB was successfully deposited in the hierarchical nano/microporous cell wall structures, as confirmed by X-ray microtomography and energy-dispersive X-ray spectroscopy. The mineralized wood exhibited excellent heat insulation performance during combustion. The limiting oxygen index of the mineralized wood with 22.1 wt% ZnB (MW22) increased from 22.6% of the untreated wood to 41.2%. Cone calorimetry testing revealed reductions of 51.4%, 89.0%, and 79.5% in average CO yields, total smoke production, and maximum smoke production ratio, respectively, in MW22 relative to those in the untreated wood; the peak heat release rate and total heat release also decreased by 46.9% and 47.9%, respectively. A noncombustible film of molten ZnB covered and cross-linked the carbonaceous char layer, forming a cohesive and robust 3D residual skeleton, which endowed thermal insulation to the wood, delayed oxygen diffusion, reduced flammable gas release, and suppressed toxic smoke. Antitermite tests showed a mothproofing rating of 10 for MW22, far higher than the rating of 4 for untreated wood. Moreover, MW22 exhibited exceptional mold resistance, with an average infection of 0 and an average protective efficiency of 100%. Therefore, in situ mineralization of the wood cell wall architecture with ZnB provides a facile and feasible strategy to fabricate multifunctional integrated wood, which is suitable for scaling up and can be potentially used in modern green buildings.