Prediction of permeability of laminate films; new methods for ultra-thin layers and systems with solute-concentration-dependent diffusivity

Two numerical methods have been developed for the prediction of gas/vapour transmission rates in multilayer laminate films consisting of different polymers with extensive variations in relative thicknesses. The methods developed allow the use of different spatial step lengths for the different layers. The methods have been applied to experimental oxygen transmission rates through laminates based on low-density polyethylene and poly(ethylene terephthalate) and it was found that the predictions agreed with the experimental results within the experimental error limits. The methods were also used to predict the water vapour transmission rates for a three-layer laminate of low-density polyethylene and polyamide-6. Since water vapour diffusivity in polyamide-6 is a function of the water concentration, different and sometimes complex results were obtained depending on the location of the polyamide-6 layer in the laminate. Calculations showed that the only way to predict the optimum positions of different layers, in order to minimize the penetrant transmission rate through a laminate when the penetrant interacts with the material, is by rigorous simulations using these or similar methods.