Abstract:
Extrapolation from permeation data for pure solvents does not redict accurately their behaviour in a mixture. The purpose of this study was to examine whether the permeation of natural rubber, nitrile rubber and PVA glove materials by MEK and toluene mixtures is proportional to the degree of material swelling.
Five solvent mixtures were tested. A piece from the glove was exposed to the challenge solution and solvent concentrations permeating through the sample were monitored vs. time. For each run, the breakthrough time, the maximum permeation rate for each solvent and the degree of swelling were determined. Toluene exhibits higher permeation than MEK through natural rubber. Adding MEK to toluene decreased the permeation of toluene and increased that of MEK. This effect was proportional to the mixture compositon and the degree of swelling. The opposite was observed for nitrile rubber. Toluene, now the low permeation solvent (LPS), retarded MEK permeation and vice versa. The effect was proportional to the concentration of the mixture but not consistently proportional to the degree of swelling. No permeation was detected through PVA and swelling of the material was negligible.
In addition, natural rubber and nitrile rubber glove samples were exposed to the LPS for three periods producing no, moderate and complete swelling prior to a permeation run using the high permeation solvent (HPS). For both glove materials the decrease in the breakthrough time of the HPS was proportional to the degree of swelling caused by the LPS.
Material swelling appears to control the permeation of MEK and toluene through natural rubber. For nitrile rubber, the relationship is more complex and additional factors are apparently at work.