Effect of water vapor on the transport properties of oxygen through polyamide packaging materials

Abstract

The barrier characteristics of polymeric packaging materials are measured by the intensity of the molecular exchange between the packaged product and its external environment. The exchange of penetrant molecules through polymeric materials is determined by the capacity of a polymer matrix to sorb the penetrant molecules, and the ability of the penetrant to diffuse through the polymeric material according to Fick's laws. However, the presence of other small relative molecular mass compounds present in the polymer matrix may change the way in which the permeant is sorbed and diffused. The case is such when water molecules are present in hydrophilic polymers affecting barrier characteristics of those polymers to penetrants such as oxygen or organic compounds. The oxygen barrier properties of hydrophilic polyamides change as a function of the amount of water in the polymer matrix. In addition, polymer morphology plays an important role in controlling the mode in which water molecules affect the transport of the penetrant. The change in oxygen barrier properties is then a function of the polymer water activity and morphology. A dual mode sorption model based on the Flory-Huggins and Langmuir equations is applied to the sorption of water by an amorphous and a semicrystalline polyamide, at three temperatures. The model provides the basis for the interpretation of the effect of water on the permeability, solubility and diffusion of oxygen within the polyamides. Different interaction mechanisms of water and oxygen within the polymers, to include self-association of water molecules and oxygen-water molecular competition, are discussed at different water activity values for both polyamides.