Ultrastrong, Highly Resilient, and Humidity‐Sensitive Wood Nano‐Aerogel Composed of Resembling Native‐State Fibrils

Abstract Fast‐evolving nanotechnologies have supported traditional wood industries to breach the barriers and slip into tailor‐made functional nanomaterials that cater to the high‐tech and low‐carbon era. Here, wood cell walls are in situ nanofibrillated via reversible hemicellulose supermolecular regulation toward versatile mesoporous wood nano‐aerogels. The as‐prepared wood nano‐aerogels are composed of highly combinative high‐aspect‐ratio fibrils resembling native‐state “core (cellulose)‐shell (hemicellulose)” nanostructure, which is unreachable for conventional in situ nanofibrillation strategies involving depolymerization of non‐cellulosic phases and topochemical engineering of cellulosic phase. The hemicellulose‐induced in situ nanofibrillation mechanism is systematically elucidated via theoretical and experimental analysis: the enhanced swelling of hemicellulose supermolecules in specific polar cosolvent (e.g., ionic liquid/water) significantly weakens the fibril–fibril interactions within wood fiber cells without affecting the macromolecular structures. The desired structural features of in situ nanofibrillated fiber cells including high mesoporosity and microstructural homogeneity contribute to significant poroelastic dissipation and efficient stress transfer under external stress, which in turn leads to an exceptional combination of compressive strength and resilience for the as‐prepared wood nano‐aerogel. Furthermore, the highly hydrophilic hemicellulose “shells” of constituent nanofibrils within mesoporous cell walls endow the strong and resilient wood nano‐aerogel with superior humidity responsiveness, thereby opening up vast possibilities for applications in sensing, process monitoring, and energy management systems. This work provides a feasible and environmentally benign wood nanostructure‐engineered strategy for top‐down manufacturing of high‐performance lignocellulosic nanomaterials by leveraging the inherent functionality of wood structural constituents.