Gas permeabilityThe permeability of oxygen gas through a material is a critical factor when it concerns the ability of a package to prolong the lifetime of packaged food.
The most important task during development of new packaging materials for food is therefore to minimise oxygen permeability. The permeation is affected in a complex way by a number of parameters within the material, like the flexibility of the polymer chains, morphology including orientation effects, crystallinity and interaction between the permeant molecules and the polymer, and interaction with an eventual filler. Also the relative humidity has a great influence on certain materials like EVOH.
The expression ”permeation” aims at the whole transport process which simply put is a result of sorption (or condensation), diffusion and desorption (or evaporation), see figure below. The transport of gases (permeants) through a film is characterised by the permeant flow Q, which can, under the assumption that there is equilibrium, be calculated using Fick´s first law:
Q = -D (dc/dx) where D is the diffusion coefficient of the permeant and (dc/dx) is the concentration gradient.
SP has experience and a suitable equipment for measuring gas permeability. This equipment makes it possible to measure the permeability for most of the common non corrosive gases through different films and foils. The equipment requires that we measure on flat test objects with a smallest test area of Ø 10 cm and the thickness of the material should not exceed 3 - 4 mm. Determination of permeability is made with a manometer and can be performed according to ISO 2556, ASTM D 1434 and DIN 53 380.