Thermodynamic modeling of the sorption of organic chemicals in thermoplastics and elastomers

The amount of solute sorbed per unit weight of sorbent, qe, and the equilibrium solubility (partition) coefficient were measured using a gravimetric method for various types of organic chemicals in thermoplastics and elastomers. A thermodynamic model was derived to predict the activity‐dependent partition coefficient and qe for a wide range of organic chemicals. The thermodynamic model produced a better fit to the measured qe values than did the Flory–Huggins equation. Partition coefficients and qe increased with increase in activity. For nonpolar compounds, qe increased logarithmically but decreased for polar compounds with an increase in the saturation organic chemical vapor concentration. Elastomers had 14–28 times greater qe values than did thermoplastics. A structure–activity relationship was found to accurately predict the partition coefficient for liphophilic organic chemicals at a specific activity.