A Toughness, Reversible and Highly Sensitive Humidity Actuator Based on Cellulose Nanofiber Films by Intercalation Modulated Plasticization

Abstract

Nanocellulose was an ideal candidate for humidity actuators based on its wide availability, biocompatibility and excellent hydrophilicity. However, conventional nanocellulose-based actuators faced challenges like poor water resistance, flexibility, and sensitivity. Herein, water-resistant, flexible, and highly sensitive cross-linked cellulose nanofibers (CCNF) single-layer humidity actuators with remarkable reversible humidity responsiveness were prepared by combining the green click chemistry modification and intercalation modulated plasticization (IMP). Notably, the incorporation of phenyl ring and the crosslinked network structure in CCNF films contributed to its improved water resistance (the water absorption was only 102%) and mechanical properties (with a stress increased from 85.9 ± 3.1 MPa to 141.2 ± 21.5 MPa). SEM analysis confirmed enhanced interlaminar sliding properties facilitated by IMP. This resulted in increased flexibility and toughness of CCNF films, with a strain of 11.5% and toughness of 9.9 MJ/m3. These improvements efficiently enhanced humidity sensitivity for nanocellulose, with a 4.8-fold increase in bending curvature. Finally, the good humidity sensitivity of modified CNF can be easily imparted to carbon nanotubes (CNTs) via simple self-assembly method, thus leading to a high-performance humidity-responsive actuator. The click chemistry modification and IMP offer a new avenue to fabricate toughness, reversible and highly sensitive humidity actuator based on cellulose nanofiber.

Keywords: Nanocellulose, hydroxyl-yne click reaction, intercalation modulated plasticization, humidity sensitivity