Strong Anisotropic Transparent Wood with Large Ductility.

A longstanding challenge in processing natural wood into high-performance structural materials lies in overcoming the inherent trade-off between strength and fracture strain, compromising its work-of-fracture (toughness). Here, we report a mechanical-confinement-reinforced strategy that can transform fast-growing, low-density balsa wood into an anisotropic, fully biobased laminated wood film (LWF). The resulting LWF achieves an extraordinary synergy of mechanical properties, exhibiting a tensile strength (∼560 MPa) rivaling that of steel alloys, a large fracture strain (∼11%), and a work-of-fracture (∼30 MJ·m-3) enhanced by 300-fold over its natural precursor. This strategy is generalizable across multiple wood species to consistently obtain fracture strain near 10%, yielding a maximum strength of 710 MPa and a work-of-fracture of 41 MJ·m-3. The exceptional performance originates from a multiscale architecture featuring a cellulose-nanofiber (CNF)-reinforced core fused with dense CNF surface layers, which transforms the failure mode from brittle shear to ductile fracture via mechanical constraint. Concurrently, the LWF demonstrates excellent optical properties (∼87% transmittance, ∼80% haze), enabling anisotropic light modulation for antiglare applications. This work presents a generalizable design paradigm for creating sustainable, high-performance structural materials that transcend conventional property trade-offs.