Packaging Permeation 101

The ultimate goal of packaging is to provide a consistent barrier between a product and the surrounding environment in order to achieve the desired shelf life.

Other purposes could be to keep active ingredients inside to maintain product specifications, to keep exterior volatiles out (such as bottled soap next to water), or to encourage the exchange of oxygen and water vapor at a constant level to ensure equilibrated reaction rates for a particular product.

Permeation is defined as the movement of molecules from one side of a barrier to the other. The movement of molecules of permeant is controlled by the driving force of the test, which is the difference in concentration of molecules between the two sides of the test barrier.

The process of permeation follows a solution-diffusion mechanism where gas absorbs at the package wall (polymer), dissolves into the polymer, diffuses through the polymer due to driving force, and then desorbs/outgases on the other side.