Ultrastrong TEMPO‐Oxidized Densified Bamboo via Interface Decoupling and Hierarchical Toughening

The mechanical potential of natural fiber-based composites remains restricted by interfacial constraints, preventing them from robust structural applications. Here, an interface decoupling strategy based on selective TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) oxidation is applied to enhance the mechanical properties of densified bamboo simultaneously with thermally-assisted structural densification. The resulting compact TEMPO-oxidized densified bamboo exhibits ultrahigh tensile strength of 661 MPa and toughness of 22 MJ m^-3, representing 5.5 times higher than natural bamboo. Fracture morphologies, characterized by extensive fibril pull-out and bridging that enhance energy dissipation, align with acoustic emission data revealing frequent, low-energy microdamage events and a continuous, non-catastrophic failure process. Specifically, TEMPO-induced carboxylation disrupts orderly hydrogen bonds and increases the relative contribution of van der Waals interactions at the molecular level, enabling stress dissipation through a network of weaker, more reversible intermolecular forces. This work demonstrates that hierarchical interface engineering offers a broadly applicable strategy to endow natural composites with toughness and strength far exceeding their original mechanical paradigm.