Lignin-Based Hydrogen-Bonded Covalent Organic Polymers as Functional “Switches” of Modified Atmosphere Packaging Membranes for Preservation of Perishable Foods

To reduce poverty and hunger in economically backward countries and regions, increasing demand for addressing severe worldwide food deterioration and wastage has triggered intensive research efforts toward modified atmosphere packaging (MAP) technology. Herein, we demonstrate that natural lignin can be used as a cheap and green monomer for preparation of hydrogen-bonded covalent organic polymers (HCOPs) with good crystallinity, permanent porosity, and high thermostability. The optimal lignin-based HCOPs (named LT-HCOPs) are synthesized by using tetrafluoroterephthalonitrile as the cross-linker, ethanol/water (7/3, v/v) as the reaction solvent, 120 °C as the reaction temperature, and ammonium persulphate and anhydrous potassium carbonate as catalysts. As-prepared LT-HCOPs can be used as promising "switches" for regulating gas permeability in the passive MAP membranes. The LT-HCOP-based passive MAP membrane, which is prepared by a simple mixing and solvent evaporation process, shows good biocompatibility, antimicrobial and antioxidant activities, improved ultraviolet light barrier property, high CO2/O2 selectivity, and suitable H2O permeation and thus is demonstrated to work well in prolonging the shelf life of perishable foods such as strawberries, waxberries, cherries, cherry tomatoes, and mangoes. This work provides a feasible way to use cheap and green natural materials to construct advanced functional materials for practical applications.