Diffusion of toluene and n-heptane in polyethylenes of different crystallinity

Abstract

Diffusivity and solubility data for toluene and n-heptane in semi-crystalline polyethylene were obtained by gravimetric sorption experiments conducted in two different laboratories. The effects of temperature, concentration and degree of crystallinity on the diffusion and solubility behaviour were investigated at 70°C. The diffusivity data were correlated using a modification of the Vrentas–Duda free-volume theory. All the parameters in the free-volume model were estimated from pure component data except the size of the jumping units, the tortuosity, and the free-volume characteristics of the polymers. These results indicate that both the diffusivity and penetrant solubility in the polymer amorphous phase decrease with increasing crystallinity. Further, the tortuosity or the length of the diffusion path around the crystals increases with the degree of crystallinity.