Antimicrobial coating films: Development by adding zinc–melamine complex to polyvinyl alcohol and antimicrobial performance

A metal–ligand complex is a complex antimicrobial system with a 3D morphology that diversifies its antimicrobial potency. These complexes with diverse geometries can mitigate microbial resistance to biocidal agents. However, the antimicrobial potential of such complexes has not been extensively investigated. In addition, to meet the goals of the 2030 Agenda, the demand for antimicrobial packaging systems prepared from bio-based and/or biodegradable polymers has been increasing. To this end, in this study, a zinc–melamine (MA) complex was introduced into polyvinyl alcohol (PVA) using epichlorohydrin (ECH) as the epoxide crosslinker. PVA was first modified using ECH, allowing interactions between PVA–ECH and MA. Subsequently, zinc ions were introduced into PVA–ECH–MA complex to develop a metal–ligand complex in the PVA matrix and with the solutions created, film samples were obtained with the bar-coating technique. The chemical composition of a film prepared using the metal–ligand complex was assessed through Fourier transform infrared spectroscopy, which indicated the presence of the zinc–MA complex in the PVA film. The thermal properties of the samples were verified through thermogravimetric analysis. The introduction of the complex improved the flexibility, Young's modulus, and fracture resistance of PVA. Specifically, the elongation at break increased from 89.29 ± 6.63 % to 338.67 ± 14.54 %. Additionally, the Young's modulus considerably decreased from 740.40 ± 195.15 to 2.51 ± 0.26 N/mm². Furthermore, the antimicrobial properties of the metal–ligand complex against Staphylococcus aureus (S. aureus) and Escherichia coli (E. coli) were evaluated using the inhibition zone assay. The metal–ligand complex film exhibited a large inhibition zone against both microbes, with a stronger effect against E. coli than S. aureus. Indeed, the inhibition zone for E. coli was around 13/14 ± 1 mm, while the positive control obtained a zone of around 7 ± 0.5 mm. Because of its significant antimicrobial efficacy and enhanced mechanical properties, the as-prepared antimicrobial film can be applied in the production of food packaging materials and coatings for food contact paper.