Mechanically flexible and flame-retardant cellulose nanofibril-based films integrated with MXene and chitosan

Abstract

Remarkable flame-retardant and integrated mechanical properties are essential requirements for the potential applications of bio-based films in industrial areas. Unfortunately, the design and fabrication of such film materials that possess a good trade-off between mechanical properties and flame-retardant performance remain significant challenges. Here, phosphorylated cellulose nanofibril-based films (PCNFs) integrated with chitosan (CS) and MXene (PCNF/CS-M) are fabricated via a facile water evaporation-induced self-assembly method. An evident reinforcement of the mechanical performance can be achieved by constructing additional interactions (i.e., hydrogen bonding and nanoreinforcement) among the hybrid network, which endows the optimized films with highly improved and balanced mechanical performance (i.e., tensile strength of 172.1 MPa, tensile strain of 8.0%, Young’s modulus of 4.4 GPa and toughness of 8.5 MJ/m-3). Furthermore, the resultant films also exhibit outstanding flame resistance, as clearly illustrated by their structural integrity after cyclic testing using a butane lamp flame at 700-800 °C. The synergistic reinforcing and flame-retardant mechanisms of the films are clarified based on structural evolution and performance variation. The strategy developed herein provides an innovative concept for designing and developing advanced bio-based film materials for fireproof coatings.