Swelling of Nitrile Vulcanizates by Polar and Non-Polar Liquids-Part 2: Swelling Curves

Abstract

As found from previous studies, a Gaussian curve describes the swelling by various liquids of a series of nitrile rubbers containing from 0 to 50% bound acrylonitrile. The curves pass through a maximum at a value, A. While not without their shortcomings, the swelling curves do present a fairly accurate picture of how the rubbers respond to the liquids, such that the value A is a measure of the polarity of these liquids. Thus, any parameter of the liq uids that has a good correlation with A is also a good measure of the polarity. The only parameter that has a good correlation is the polarity index, which is obtained by liquid chromatography, with reference to standard liquids based on the work of Rohrschneider and Snyder. If the results for alcohols are omitted, reasonable correlation is obtained with Godfrey's miscibility index and Dimroth's molar transition energy. These three parameters have in common the fact that they are determined by reference to standard liquids. No correla tion is found between A and either the Hildebrand solubility parameter or the dielectric constant of the liquids, both of which are derived from properties of the liquids themselves.