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The effect of solvent absorption on additive migration was studied by relating the diffusion coefficient (D) of Irganox 1076 to the maximum solvent absorption of different solvents in low-density polyethylene (LDPE) film. Solvents tested were ethanol, isopropanol, isooctane, ethylacetate, cyclohexane, tributyrin, tricaprylin and olive oil. Diffusion and partition coefficients were determined by fitting the migration curves, i.e. the concentration of Irganox 1076 in solvent as a function of time, with Fick 's diffusion equation. The results for the low molecular weight solvents show that with increasing maximum solvent absorption, D of Irganox 1076 is increasing as well. This trend is not observedfor the two triglycerides and olive oil. In spite of absorption, no increase in D was observed. The obtained result is the basis of an extended predictive migration model that, besides migrant and polymer properties, is also based on the maximum solvent absorption in the polymer.

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This article describes the simultaneous diffusion of a migrant and a solvent in low density polyethylene (LDPE). The migrant (Irganox 1076) moves out of the slab, while the solvent (isooctane, n-heptane or cyclohexane) moves inwards. Solvent absorption was measured separately by following the increase of the mass of the slab in time. It can be described by the Fick diffusion equation with a diffusivity depending on the solvent concentration, and an interface concentration depending on time. The final absorptions were 12% for isooctane, 14% for n-heptane, and 29%for cyclohexane. Additive concentrations in the slab were determined at different positions by microtoming. Experiments were done for several contacting times. The concentration profiles were strongly affected by the solvent. A larger local solvent concentration increases the diffusivity of the migrant. The Fick equation with a migrant diffusivity depending on the solvent concentration gives a good description for the results with isooctane and n-heptane. The description is less good for the measurements with cyclohexane (when the polymer swells strongly).