MAGNETIC-RESONANCE-IMAGING STUDIES OF DIFFUSION IN POLYMERS

For a number of polymer/penetrant systems, for example fatty foods in direct contact with plastic wrapping, the migration of substances from the polymer is governed by the amount of penetrant entering the polym er. For food packaging this means that the rate of migration of substa nces into the food can be governed by the uptake of food into the pack aging itself. To develop predictive models of migration under various conditions there is therefore a need to understand the mechanism of th e penetration of the food into the packaging. In this paper a summary of recent Magnetic Resonance Imaging (MRI) studies is reported. Uptake of simulant, as measured by MRI is quantitative and agrees well with gravimetric uptake data. Data are shown for a comparison of olive oil and isooctane penetration into low density polyethylene at various tem peratures. Further, the rate of ingress of isooctane into a variety of commercial polyethylene plaques has been shown to differ widely. Thes e data also allow us to probe the molecular interactions between polym er and penetrant. Finally MRI is combined with a Pulsed Gradient Spin Echo (PGSE) technique to provide spatially resolved measurements of pe netrant diffusivity within a polymer. Diffusivity as a function of vol ume fraction of penetrant can also be measured. These data provide inv aluable insights into diffusion in polymers which will aid development of more accurate models of polymer/penetrant interactions and small m olecule mobility.