Diffusion of hydrocarbons in polyethylene

The diffusivities of a series of aromatic hydrocarbons in semicrystalline polyethylene were obtained by the use of a modified gravimetric sorption technique with a flow system capable of a wide range of activities (or vapor pressures) and temperatures. The effects of penetrant concentration and size and temperature on the diffusivities were investigated. The experimental data can be fitted quite well by our proposed hybrid model that combines the key features of the free-volume and molecular models. In the hybrid model, polymer parameters and penetrant molecular thickness are used to determine the term equivalent to the preexponential factor of the free-volume model, and the free-volume expression is used to relate penetrant diffusivity to penetrant concentration and size. The hybrid model fitted the data better than the free-volume model, and it avoided the complexity of the molecular model.