Assessing the Transport Properties of Organic Penetrants in Low-Density Polyethylene Using Free Volume Models

Three models, two of them relying on free volume - the Cohen-Turnbull-Fujita (CTF) model and the Vrentas-Duda (VD) model, and the third being empirical using an exponential concentration dependence of the diffusivity, were applied to desorption data for a series of alkane penetrants (2,2-dimethylbutane, cyclohexane, n-hexane, n-decane, and n-tetradecane) in low-density polyethylene. The CTF model described the desorption data very well and better than the exponential diffusion law. The VD model with the attractive feature of being based on independently determined parameters was successful in describing the desorpion data. Diffusivity data indicated that the three components outside the crystal core were less accessible to n-tetradecane than to the other penetrants. This indication was further substantiated by solubility data.