Some aspects of two stage diffusion in polymer films and membranes

Ioan Mamaliga, Ciprian Negoescu

"Gheorghe Asachi" Technical University of Iasi, Faculty of Chemical Engineering and Environmental Protection, Department of Chemical Engineering, 73 Prof. dr. doc. Dimitrie Mangeron Street, 700050 Iasi, Romania


The two-stage sorption data for dichloromethane vapour in a cellulose triacetate films and membranes are analysed by the variable-surface concentration model and the diffusion relaxation model. Satisfactory fitting of the data and similar kinetic parameters are obtained using these models. The diffusion coefficient for dichloromethane is about 2.5 x 10-11 m2 s-1 in the glassy polymer at 40 C and is near 1.5 2.5 times higher as the polymer goes over the glass-rubber transition region due to solvent sorption. The relaxation rate constant is between 3.0 and 18 x 10-4 s -1 and is increased as the sorbed concentration or the vapour activity of solvent increases. When the two-stage non-Fick sorption prevails, the diffusion-relaxation model approximates the limiting cases of the both models.


cellulose triacetate membranes; non-Fickian diffusion; two stage sorption

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