Sorption of lower alcohols in poly(ethylene terephthalate)

This paper presents equilibrium sorption and kinetics of lower alcohols in a 1.5 μ thick, biaxially oriented PET film. Methanol, ethanol, n-propanol and iso-propanol have been studied for the solubility and sorption kinetics in this film to understand how these properties change with penetrant size and branching. It is observed that n-propanol shows dual mode characteristics at all activities whereas the other three penetrants show Flory-Huggins uptake at high activities. Infinite dilution solubility is estimated and compared with that of esters, ketones and other hydrocarbons previously reported. The dispersive solubility parameter, δd is found to correlate well with the solubility of penetrants with the same functional group. The hydrogen bonding parameter, δh is observed to influence the solubility of penetrants with the same carbon number but different functional groups. This correlation with the solubility parameters may be extended to other functional groups and used to predict the infinite dilution solubility of larger penetrants in PET. Diffusion coefficients in the Fickian kinetics regime and Berens-Hopfenberg parameters in the non-Fickian kinetics regime have been evaluated. Diffusivity increases with concentration and decreases with size. Diffusion coefficient of iso-propanol is an order of magnitude lower than that of n-propanol due to branching effects.