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

ABSTRACT 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.