An Assessment of the Chemical Compatibility of Viton Fluoropolymers and Some Harsh Organic Liquid Mixtures

The molecular transport of a series of industrial solvent mixtures into O-rings of Viton fluoropolymers was studied. Sorption, diffusion, and permeation of the individual liquids toluene, cyclohexane, and methanol, and their binary and ternary mixtures, were evaluated from the solvent uptake using a gravimetric method. From the sorption results, the diffusion coefficients were calculated using Fick’s equation. A numerical method was employed to calculate the liquid concentration profiles in cylinder-shaped polymers. The desorption mechanism was also evaluated. The composition dependence of sorption, diffusion, and permeation was assessed, and the results were analysed in terms of potential interactions between polymer and penetrant molecules. Observed sorption of methanol and methanol mixtures by the polymer was very high, in some cases higher than for pure liquids. In general, the amount of methanol present in the mixture determined its diffusion coefficient. Methanol showed the smallest solubility coefficient within the polymer, but due to its high mobility and permeability, it was shown to be the liquid that flows faster through Viton fluoropolymers. Flows of toluene and cyclohexane are still considerable, notwithstanding that this fluoropolymer is usually indicated as hydrocarbon resistant. This is an important fact to keep in mind when choosing sealings for applications with a mix of solvent media.