Lignin as a multi-functional agent for the synthesis of Ag nanoparticles and its application in antibacterial coatings

Abstract

Although silver nanoparticles (AgNPs) possess broad-spectrum antimicrobial activity, their intended use may adversely affect the ecosystem. In this study, alkali lignin (AL) was modified via quaternization to synthesize amphoteric lignin (AML), which was further used as a reducing and stabilizing agent for the synthesis of amphoteric lignin@nanosilver (AML@AgNPs) composites under microwave irradiation. The AML@AgNPs were characterized via X-ray diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy measurements. The results showed that the average particle size of AgNPs was 24.7 nm. The positively charged AML@AgNPs had excellent antibacterial activity against Escherichia coli and Staphylococcus aureus, with a minimum inhibitory concentration of 30 ppm. The results of quartz crystal microbalance with dissipation monitoring and optical microscopy tests showed that the positively charged AML could effectively capture bacteria, which promoted the adhesion of the AML@AgNPs to bacteria. Furthermore, the AML@AgNPs had good compatibility with polyurethane, and when the AML@AgNPs content in the WPU–AML@AgNPs blend was 0.5 wt.% of the waterborne polyurethane (WPU), the prepared polyurethane film could completely inhibit bacteria growth.