Permeation Testing of Synthetic Polymers

A polymer's permeability is an important characteristic for packaging applications. Gas transfers through films or packaging via the process of permeation. Actually, permeation is a combination of processes involving adsorption, solubility of the permeant in the material and diffusion of the permeant through the material, and desorption. A gas will permeate through a polymer in response to a concentration gradient, which is limited by the solubility and diffusion coefficient of the gas in the polymer. Once in the polymer, Equation 5.1 shows that diffusive flux, J, of a gas molecule in a polymer is the amount (Q) passing through a unit area (A) normal to the direction of flow during time (t), that is,