Biomimetic versatile wood hybrids with gradient structure towards lightweight, high strength, fire-retardant, and deterioration-resistant materials

Abstract

The development of versatile wood-based biomaterials with integrated low density, high surface hardness, high strength, fire-resistance, anti-decay, and termite-resistance is highly desirable, yet challenging to skillfully fabricate. Inspired by the ubiquity of gradient biostructures in nature, we achieve biomimetic gradient densification structures by controlling the distribution of thermal-moisture fields within the wood, and combine this with in-situ curing of polyacrylic acid/borate supramolecular resins within the wood cells to transform bulk natural wood into lightweight, high strength, and multifunctional materials. The optimally gradient-densified hybrid wood, with a slight increase in density, demonstrates markedly improved mechanical properties (≈2.4 × increase in surface hardness, ≈52 % increase in flexural strength), excellent dimensional stability, and leaching resistance. In addition, the collaboration of the gradient-densified structure and the in-situ cured acrylic resin/borate supramolecular network provides the biomimetic wood hybrids with excellent fire resistance (V-0 rating in fire retardant grade, 74 % reduction in total smoke release, ≈2.5 × increase in fire performance index), decay and mildew resistance (mass loss of less than 10 %), as well as termite resistance (100 % protection efficiency and termite kill rate) properties. It is the first report to combine gradient densification with in-situ curing of supramolecular resins in the structural design and functionalization of wood-based composites. This new design principle provides guidance for fabricating advanced all-in-one wood materials with applications in lightweight, strong, fire-resistant, deterioration-resistant, and scalable building and furniture materials.