Diffusion in barriers: Insights from flux tests

The performance of barriers — widely used in packaging materials to prevent undesired environmental substances from contaminating the product — can be evaluated using, for example, steady-state permeation fluxes. While this method is simpler than the standard lag-time method it does, in contrast to the latter, not provide diffusion coefficients. Furthermore, permeation flux measurements depend on test conditions (vapor pressure, barrier thickness); this limits the usefulness of the flux method because comparison between films of different type and/or thickness becomes difficult. This work attempts to overcome such limitations for the case of a single barrier layer. “Apparent” diffusion coefficients are extracted from (transient) fluxes; the time of initial exposure need not be known. Additionally, the applied approximations allow steady-state migration for different conditions to be captured by a “master line”. •Apparent diffusion coefficients are derived from permeation flux tests.•Test starting times need not be known.•Apparent diffusion coefficients relate to those from lag-time tests.•Permeation under different conditions is scaled to a “master line”.