Manufacture of metal-based nanoparticles and their incorporation into plastic materials for the development of active antimicrobial food packaging

Silver (Ag), copper (Cu) and zinc oxide (ZnO) nanoparticles (NPs) were synthesized and antimicrobially assessed. Ag NPs showed the best antimicrobial activity (AA) against a wide range of microorganisms: Staphylococcus aureus, Bacillus cereus, Escherichia coli and Pseudomonas fluorescens as well as microflora isolated from meat products. Ag NPs were then employed to manufacture antimicrobial films via solvent casting, extrusion or coating techniques. The resulting films were assessed in terms of their mechanical, thermal, barrier and antimicrobial properties. Surface modification of commercial polymer films using piranha solution or UV/ozone treatment was carried out to increase wettability and attachment of Ag. In general, the mechanical and thermal properties of the active films were dependent upon the type of polymer and method employed to incorporate Ag NPs. Regardless of the method used to manufacture Ag-active films, the shelf-life of CBF was significantly extended. UV/ozone treatment increased the wettability of commercial polymer films compared to piranha solution and AA of the Ag-coated LDPE films increased with increased exposure to UV/ozone. Novel methods to manufacture Ag-coated films were developed using self-assembled polystyrene-b-polyethylene (PS-b-PEO) block copolymer (BCP) and layer-by-layer process. Antimicrobial testing showed that Ag-active films had good AA against Gram-positive and Gram-negative bacteria. However, these methods were not easy to scale-up. Therefore, a simple spray coating process for producing Ag-coated films was developed using Pluronic™ surfactant and PS-b-PEO BCP. The AA of the Ag-active films were depended upon the initial concentration of Ag precursor used and the number of Ag coatings applied. Generally, Gram-negative bacteria were more susceptible to Ag NPs than Gram-positive bacteria and that pure culture bacteria were more susceptible than microflora isolated from meat products. The Ag-active films developed in this thesis have the potential to be used as antimicrobial packaging in food packaging applications