Enhanced Antibacterial Activity in Cellulose Acetate Films with Surface Defect-Rich MgO Nanoparticles for Sustainable Active Packaging Applications

Magnesium oxide nanoparticles (MgO NPs) are one of the popular inorganic nanomaterials used for active food packaging applications, mainly due to their antimicrobial activity. Previous studies have utilized various strategies to enhance the activity by increasing surface oxygen vacancies of MgO. However, only a few of them showed competitive advantages over commercial ones. It is doubtful that when incorporated into biodegradable polymer films, these NPs still show superior antimicrobial activities and other beneficial properties. The present study synthesized a series of MgO NPs by a urea-based hydrothermal method and found that two of the surface defect-rich, {111} facet NPs released higher amounts of superoxide anions, exhibiting greater antibacterial effects against Escherichia coli and Staphylococcus aureus than those by commercial 27 nm MgO NPs. One using nitrogen calcination at 650 °C with better antibacterial activity was selected for incorporation into cellulose acetate (CA), and we found that the as-prepared 8% MgO NP-incorporated CA exhibited better antibacterial activity against S. aureus than the commercial one, while they had similar activities against E. coli. The incorporation of as-prepared MgO NPs into CA increased the tensile strength by 27% and the water vapor transmission rate (WVTR) by 29.5% compared to pristine CA, even though the tensile strength, thermal properties, and water and oxygen barrier properties, of the as-prepared nanocomposite did not further improve compared to that of the commercial one. These results suggest the use of our developed MgO NPs and the CA-MgO NP nanocomposite in sustainable active packaging applications.