The Role of Polyolefins in “Protecting” Moisture Sensitive Barrier Layers in Packaging Structures, 18IFPED

It is well known that the oxygen permeation of many barrier polymers, including EVOH and polyamide (nylon), increases with increasing relative humidity (RH).  Many in the industry believe sandwiching the barrier polymer between layers of polyolefins “protects” the barrier by preventing moisture from reaching the barrier layer.  Permeation, however, is an equilibrium measurement.  The presence of a high moisture barrier polyolefin merely delays the time for the barrier layer to reach its equilibrium moisture content.  Since flexible package films are thin, the time to reach equilibrium is short, even when high moisture barrier layers are present.  In a symmetric film structure with the barrier layer in the middle, at equilibrium the barrier layer will experience an effective RH halfway between the inside and outside environments of the package, no matter what the composition of the skin layers are.  Polyolefins used in conjunction with barrier layer location, however, can shift the effective RH of the barrier layer towards that of the lower RH side of the package, reducing oxygen permeation.    Model equations are developed that highlight this effect and show how it can be used to optimize barrier packaging structures. 

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