Strong and flexible lignocellulosic film fabricated via a feasible molecular remodeling strategy

Biomass-derived sustainable film is a promising alternative to synthetic plastic, but hampered by strength, toughness and flexibility trade-off predicament. Here, a feasible and scalable strategy was proposed to fabricate strong and flexible lignocellulosic film through molecular reconstruction of cellulose and lignin. In this strategy, polyphenol lignin was absorbed and wrapped on the surface of cellulose fiber, forming strong interfacial adhesion and cohesion via intramolecular and intermolecular hydrogen bonding. Further, covalent ether bond was generated between the hydroxyl groups of lignocellulose to form chemical cross-linking network induced by epichlorohydrin (ECH). The synergistic effect of hydrogen bonding and stable chemical cross-linking enabled the resultant lignocellulosic film (ELCF) with outstanding mechanical strength of 132.48 MPa, the elongation at break of 9.77 %, and toughness of 9.77 MJ·m^-3. Notably, the integration of polyphenol lignin synergistically improved the thermal stability, water resistance, UV-blocking performances of ELCF. Importantly, after immersion for 30 d, ELCF still possessed high wet strength of 70.38 MPa, and elongation at break of 7.70 %, suggesting excellent and durable mechanical performances. Moreover, ELCF could be biodegraded in the natural soil. Therefore, this study provides a new and versatile approach to reconstruct highly-performance lignocellulosic films coupling strength, toughness with flexibility for promising plastic replacement.