Development of palladium-based oxygen scavenger : optimization of substrate and palladium layer thickness

Abstract

Oxygen scavenging films based on vacuum deposited palladium layers were developed to remove residual oxygen remaining in food packages after modified atmosphere packaging. Palladium (Pd) was coated on to a range of packaging films and in different thicknesses using magnetron sputtering technology. To improve the substrate surface, an additional silicon oxide (SiOx) layer was also applied to the films before Pd deposition. To determine the oxygen scavenging activity, the scavenger films were placed into an airtight cell, which was flushed with a gas mixture containing 2 vol.% oxygen and 5 vol.% hydrogen. The results showed that the oxygen scavenging rate was strongly dependent on the coating substrate as well as on the Pd deposition thickness. Packaging films such as polyethylene terephthalate, aluminium oxide-coated polyethylene terephthalate, oriented polypropylene and polylactic acid were found to be the most suitable substrates for Pd-based oxygen scavengers. Moreover, it was demonstrated that the intermediate SiOx layer between the substrate and the Pd layer led to a substantial increase in the oxygen scavenging activity rate (up to 33-fold) for all applied packaging films. Additionally, it was shown that the optimal Pd layer thickness for the investigated oxygen scavenging films lies between 0.7 and 3.4 nm. The resulting scavenger films have the potential to scavenge residual headspace oxygen of sensitive foods within a matter of minutes leading to shelf life extension and overall quality improvements