Diffusion of Large Molecules in Polymer Matrices

A simple radio-tracer method, based on C14 for the measurement of diffusion coefficients of solid penetrant molecules in polymer matrices has been developed. The technique has been used to determine the diffusion coefficients of 2,6-di-tertiary-butyl-p-cresol in two specific grades of polyethylene, over a small temperature range. Activation energies for this penetrant molecule were found to be 28.34 K.cals. per mole and 20.45 K.cals. per mole for the high density (0.96g. per ml.) and low density (0.92g. per ml.) materials respectively. These activation energy values have been shown to fit a linear plot of log10DO vs EA for various gas molecules. Diffusion of the penetrant molecule in polyethylene with varying morphology has been investigated, using different moulding and annealing procedures, with photomicrographic evidence, and the mechanism of diffusion has been discussed in the light of these results