Decoupling Density–Strength–Toughness in Wood Modification via Molecular Compaction

Herein, we report a "molecular compaction" strategy that breaks the long-standing density-strength-toughness coupling in wood. Instead of conventional mass densification, ionic carbon quantum dots (ICQDs) are introduced into the cell wall to trigger in situ polymer reorganization. At an ultralow concentration of 0.25%, the material achieves a 62% increase in strength and a 30% increase in toughness while slightly reducing bulk density by 0.4%. Mechanistically, ICQDs serve as multifunctional nano-modifiers: hydrogen bonding with cellulose as well as hemicellulose and π-π interactions with lignin promote higher crystallinity, greater chain orientation, and tighter microfibril packing, yielding densified yet thinner cell walls. The modified wood further exhibits enhanced antifungal and UV resistance. Multiscale structural and spectroscopic analyses corroborate this compaction pathway-crystallinity and orientation increase without lumen filling or bulk densification. The solution-processable, low-additive protocol is compatible with standard impregnation routes, enabling scalable manufacturing and facile translation to other lignocellulosic substrates. This low-additive, mechanism-guided approach establishes a general route to lightweight, durable, high-performance bio-based composites for sustainable applications.