Thermodynamic Affinity of Elastomer-Solvent System and Barrier Properties of Elastomer Materials

The aim of the study was to determine whether it is possible to correlate directly the barrier properties of elastomer materials assessed on the basis of the breakthrough time $t_{p}$ with the thermodynamic affinity of the elastomer-solvent system, characterized by their solubility parameters δ. According to EN ISO 6529:2001 standard, breakthrough time is defined as the time elapsing from the moment that the tested material sample gets in contact with the chemical to the moment in that a specified amount of the substance appears on the other side of the sample. Cured butyl rubber (IIR) in the form of flat membranes were tested in the study. For the nonpolar rubber-polar or rubber-nonpolar solvent systems it has been found that significant differences in rubber and solvent solubility parameters not in every case leads to better resistance to permeation. The properties of the permeating chemical and the rubber, including its polarity, shape, and molecule dimension of the solvent, are of considerable importance. A marked disparity of breakthrough times were observed for the permeation of polar or nonpolar solvents despite similar values of their solvent solubility parameter. The breakthrough time of the solvent from the homologous series (pentane, hexane and heptane) is determined not only by the rubber and solvent solubility parameters but by the size of the chemical molecule as well. Therefore, for the assessment of material barrier properties the thermodynamic affinity or dissimilarity of the elastomer and the permeating solvent is only semiquantitative in character.