Green and Sustainable Wood Composites: Chain Entanglement-Driven Viscosity Modulation for Asymmetric Surface Reinforcement

Developing green and sustainable wood composites with ultralow density and excellent mechanical properties remains a major challenge. Here, we present a simple strategy to achieve asymmetric surface reinforcement of natural wood via chain entanglement-driven viscosity modulation in a polyurethane-modified epoxy system. Exploiting the multiscale chain entanglements of polyurethane, we are able to tune the viscosity of the cured resin to precisely control its penetration depth and spatial distribution from the surface inward. This in situ filling and reinforcement transforms natural wood into high-performance composites without the need for high-energy mechanical treatment or heavy mineral additives. The resulting asymmetric structural wood has a density of only 0.498 g/cm3, less than half of that of conventional impregnated wood, while achieving a specific bending strength of 262 MPa·g– 1 ·cm 3, which exceeds most engineering panels, many metal alloys, and even eight times higher than 1040 steel. Due to its simple process and no toxic and hazardous chemical waste liquids, this method has opened up a truly sustainable production route for wood structural materials and is expected to be widely used in lightweight construction and environmental protection projects.