A STUDY OF THE DIFFUSION OF DECANE INTO LIGHTLY CROSS-LINKED NATURAL-RUBBER BY BROAD-LINE MRI

The diffusion coefficient of decane in a lightly cross-linked peroxide vulcanizate of natural rubber (polyisoprene) has been measured by broad-line proton magnetic resonance imaging (MRI). The value of the diffusion coefficient deduced from the MRI results is higher than that obtained from conventional mass-uptake measurements. The discrepancy can be removed by assuming that the diffusion coefficient of decane increases exponentially with concentration. Proton MRI has been used for the parallel study of both the diffusing solvent and the mobility of the polymer matrix. This was achieved by exploiting the wide differences in the proton NMR relaxation times of the two components. Broad-line imaging techniques using resonant oscillating field gradients were used to overcome the short T-2 ( similar to 1 ms) of the rubber. The results show a good correlation between the ingress of the solvent and the softening of the rubber matrix.