Metal Ion Cross-Linked Cellulose/Lignin Nanocomposite Films: A Pathbreaking Approach toward High-Performance Sustainable Biomaterials

Inspired by the reinforcement mechanisms observed in biomaterials, cellulose/lignin composite membranes are prepared successfully by mixing nanolignin and nanocellulose and impregnating them with metal ion solution. Metal ion cross-linking and hydrogen bonds between cellulose and lignin create a robust cross-linking network. The composite films achieve a tensile strength of 223.8 MPa, more than twice that of pure nanocellulose films (104 MPa), and surpass commonly used commercial petroleum-based plastics. Through investigation utilizing dynamic rheological experiments and density functional theory, the interactions between cellulose fibers and lignin are elucidated, showcasing the synergistic effects of Ca²⁺ cross-linked oxygen-containing functional groups and hydrogen bonding. These interactions enhance the strength and toughness of the composite films. Capitalizing on the hydrophobic nature of nanolignin and the strong interactions between metal ions and oxygen-containing functional groups, the wet strength of the composite films reached 33.3 MPa. Moreover, the composite material demonstrates optical properties, electromechanical stability, and thermal stability, including the UV blocking rate. Compared to petroleum-based plastics such as polyethylene and poly(vinyl chloride), cellulose-based films completely degrade within 30 days. With its inherent biodegradability, the composite films have the potential to replace conventional plastics in various applications, advancing sustainable and environmentally friendly materials.