Retortable food containers containing a water-sensitive oxygen barrier

Multilayer food packages containing EvOH (ethylene vinyl alcohol copolymer) as the oxygen barrier are used to protect a range of oxygen-sensitive food products. Often these food packages must be steam retorted for sterilization. During retort the EvOH layer is subjected to a large water pressure resulting in substantial water sorption. A problem with EvOH is that its excellent oxygen barrier is seriously reduced at high humidity. Therefore, immediately following retort, the wet EvOH offers a reduced resistance to oxygen permeation. As the EvOH dries to a 'steady-state' profile, the barrier properties recover, but a significant amount of oxygen can pass through the package wall during the dry-out stage. This work was undertaken to develop both an experimental and theoretical understanding of multilayer EvOH structures made with both polypropylene and polycarbonate structural layers.