Fabrication of litchi-like lignin/zinc oxide composites with enhanced antibacterial activity and their application in polyurethane films.

Lignin has been demonstrated to be green and effective for the modification of ZnO-based materials. In this work, quaternized lignin/zinc oxide nanostructured hybrid composites (QLS/ZnO NCs) were synthesized with good dispersion and uniform particle size via a facile hydrothermal method. Sodium lignosulfonate (LS) was modified by quaternization to endow the positive charges, which effectively captured bacteria due to the electrostatic interactions. Interestingly, QLS/ZnO NCs show a litchi-like morphology consisting of nanorods with diameters of 5-10 nm, which further resulted in damage to the bacterial cell membrane. Owing to the surface charge and rough surface topology for bacterial capture, QLS/ZnO NCs exhibited greatly enhanced antibacterial activity compared with bare ZnO. After being treated with QLS/ZnO NCs for 90 min, the sterilization rates of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) reached 97.54% and 99.55%, respectively. Due to the reactive oxygen species (ROS) produced by ZnO under light irradiation, the antibacterial activity of QLS/ZnO NCs could be further enhanced. In addition, the minimal inhibition concentrations (MICs) of QLS/ZnO NCs towards E. coli and S. aureus were both 100 μg/mL, and the minimum bactericidal concentrations (MBCs) were 100 μg/mL and 200 μg/mL, respectively. Moreover, with the incorporation of QLS/ZnO NCs into polyurethane films, the composite films showed excellent antibacterial activity, strong tensile strength and enhanced ultraviolet light blocking performance.