Possible contamination of ionic liquids upon dissolution and absorption of rubber and resin components

Abstract

In this study, ionic liquids (ILs) properties of rubbers and resins dissolution and absorption were investigated, and direct and indirect potential contamination possibilities were proposed. From the trial of the direct immersion of various rubbers and resins in ILs, it was confirmed that most of the materials are dissolved in ILs resulting in contamination, with the exception of silicone rubber. On top of that, indirect contamination possibility during distillation under reduced pressure (vacuum treatment) was investigated. Following the application of vacuum to ILs, we observed a new absorption peak appear in the ultraviolet-visible spectra of various ILs in the range of 350 to 450 nm. The cause of new peak was investigated from several aspects and finally determined to result from the absorption of one or more volatilized compounds from the chloroprene rubber cap of the glass vacuum vessel, even though the IL was not in direct contact with the cap. Interestingly, although CO2 absorbed in ILs can be desorbed by the application of a vacuum, this compound could not be removed from the ILs simply by vacuum treatment conversely. These results indicate ILs contamination could be occurred through direct and indirect contact with rubbers and resins. Therefore, we need to be careful in dealing with ILs. It also follows that silicone materials should be used in conjunction with ILs where possible to avoid contamination, even in cases where the IL is not in direct contact with the material.