Sustainable and multifunctional metal-ion coordinated spent coffee grounds films for food preservation

This study developed a simple approach for fabricating multifunctional food packaging films from spent coffee grounds (SCG) through ionic liquid dissolution and subsequent regeneration in metal ion solutions. Metal-ion coordination with the hydroxyl groups of the polysaccharide matrix serves as the central regulatory strategy, disrupting the native hydrogen-bond network and forming coordination crosslinks that govern the film structure and properties. This structural modulation simultaneously enhances water resistance, including surface hydrophobicity, vapor barrier enhancement and retention of wet strength (tensile strength above 14.84 MPa), and introduces ion-specific functionalities such as UV-blocking, antibacterial activity, and flame retardancy. All metal-ion coordinated films completely biodegrade in natural soil within 40 days. In strawberry preservation trials, the metal-ion coordinated film effectively reduced decay, weight loss, and softening, thereby extending shelf life. This work demonstrates a feasible route for upcycling food waste into tunable, high-performance materials with potential as sustainable alternatives to non-biodegradable packaging plastics.