Palladium-based oxygen scavenger for food packaging: Choosing optimal hydrogen partial pressure
Several packaging solutions for the food industry have to consider the harmful effects of oxygen within a pack for packaging of oxygen sensitive foods. This issue can be addressed by using oxygen scavengers. However, in adverse cases, conventional oxygen scavengers react too slowly to reduce the access of oxygen to sensible foods. Therefore, several alternative approaches for oxygen scavengers are in focus right now. In this work, an oxygen scavenger system based on vacuum-deposited palladium (Pd) on PET films was tested. Pd catalyzes the reaction of headspace oxygen, remaining in food packages, with hydrogen. The hydrogen can be provided by modified atmosphere packaging. To improve the substrate surface, an additional silicon oxide (SiOx) layer was applied to the films before Pd deposition. To determine the oxygen-scavenging activity, the Pd-metalized films were placed into airtight cells. These cells were flushed with a gas mixture containing 95 vol.-% nitrogen and 5 vol.-% hydrogen. Defined amounts of oxygen were injected into the cells. The kinetic parameters of Pd-metalized films were determined as a function of hydrogen and oxygen partial pressures and area of Pd-coated film. The effect of different cover films on Pd on the reaction rate was analyzed, too. By the results was shown that the oxygen-scavenging rate is strongly dependent on the proportion of hydrogen to oxygen. The oxygen-scavenging rate increases with a decreasing ratio of hydrogen to oxygen (with ratio 2.5:1 as the fastest tested condition). However, there has to be a sufficient hydrogen excess inside the headspace to reach overall highest oxygen-scavenging capacity (ratio up to 10.6:1 tested). For practical application in food packaging, it is important to adjust the hydrogen concentration in modified atmosphere packaging to residual oxygen present in packaging, to choose a sufficient area of Pd-metalized film as well as suitable cover film with high oxygen permeance. This publication provides recommendations for this purpose.