Solubility and Diffusivity of Water and Organic Liquids in Glassy and Rubbery Polymers

Separation processes play a major role in chemical, food and pharmaceutical industry, where they are required for the fractionation of mixtures, the recovery of high valued molecules from complex feedstock and the removal of unwanted substances that could give rise to off specific products, outflavours in food and beverages and shelf-life reduction. The industry of aromas and nutriceuticals requires to deal with feedstock with an initially low concentration of the molecules of interest. Moreover, these molecules should be treated with care, since they are frequently prone to denaturation and degradation, that can be triggered by thermal and chemical stimuli. In several of the above mentioned processes, therefore, membrane-based techniques, such as, for instance, pervaporation and organic solvent nanofiltration (OSN), can offer a viable separation method in alternative to chemical and thermal techniques. In both such processes, the solution-diffusion mechanism of transport inside the membrane plays a relevant role. Therefore, in the design of such processes, the knowledge of the fundamental transport parameters, e.g. diffusivity and solubility, of the interesting liquid components into membrane materials, is required. Indeed, the knowledge of such basic parameters can be the basis for a fundamental understanding and knowledge of the thermodynamic and of the kinetic aspects which control the separation. Unfortunately, a considerable lack of basic transport parameters of liquids in the most interesting polymers is observed in the literature. Such data are useful for the design of membrane modules, but also for the validation of models which can be used to reduce the number of experimental data required. In the present work, the solubility of a series of liquid penetrants (water, n-alkanes, alkyl-alcohols, ethyl acetate, acetone, edible oil components) has been inspected at room temperature, into dense films of both glassy (Matrimid 5218) and rubbery (crosslinked PDMS) polymers