Recyclable Chitosan-Modified Cellulose Fiber Porous Structure for Sensitive and Robust Moisture-Driven Actuators and...

Moisture-driven actuators featuring programmable stimuli-responsiveness and a rapid response have garnered substantial research attention. Cellulose-based actuators face challenges, including prolonged and unstable responsiveness, along with inadequate interfacial bonding. Herein, we developed a bilayer structured moisture actuator by integrating multiscale cellulose fibers with chitosan. The protonated chitosan forms strong electrostatic attractions with negatively charged cellulose nanofibrils (CNF), achieving a robust interfacial interaction. Leveraging the hierarchically porous structure and varying hygroscopicity of microfibrillated cellulose (MFC) and CNF, the film establishes an effective wettability gradient, enabling a stable and rapid moisture actuation performance. The bilayer film exhibits large deformation toward moisture with a bending angle of 60°, a short response time of 12 s, good stability over 50 wetting and drying cycles, and promising recyclability. Harnessing these advantageous properties, the bilayer film was demonstrated for its applications in automatic cooling textiles, contactless electrical switches, and artificial moisture-activated muscles, showing great potential for practical use.