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As the most abundant natural biomass in nature, nanocellulose is emerging the ideal fundamental component for sustainable high-performance materials [1, 2]. The lack of in-depth understanding of the coupling relationship between intermolecular interactions and intrinsic microstructure in nanocellulose makes it challenging to realize the bottom-up mechanical design of cellulose-based materials [3, 4]. Herein, starting from multiscale theoretical modeling, we first reveal an anomalous stabilizing effect in cellulose nanocrystals (CNCs) by the cooperation between the non-covalent hydrogen bonds (HBs) and covalent glucosidic skeleton, namely molecular levers (MLs). The covalent-like binding of HBs in MLs at cryogenic temperature contributes to the anomalously enhanced strength and toughness of CNCs below ~77K [5]. Then, combining multiscale mechanics and experimental characterization, we demonstrate the humidity-mediated interface in hierarchical CNCs. The formation of CNC–water–CNC HBs triggers the transition of interfacial slipping mode, resulting in the arising of a pronounced strain hardening effects and the suppression of strain localization. Finally, a new method is proposed to regulate the strength and toughness of nanocellulose materials via humidity-mediated interface [6]. Our investigation indicates that HBs play a vital role in the multiscale mechanical behaviors of nanocellulose, which would provide a promising strategy for the bottom-up design of cellulose-based materials with tailored mechanical properties.

Nanocellulose; multiscale mechanics; hydrogen bond; molecular lever; humidity-mediated interface