Diffusion of CO2 in Bistan-AF polycarbonate til ins modified with liquid ketones
The CO2 — diffusion coefficients in PC films from Bistan AF and modified with liquid ketones have been determined. The modification of the film consisted in its swelling by means of a ketone, induction of a swelling crystallization, leaching out of the swelling agent and drying of the film. Films have been swollen by the use of acetone (MMK), methyl ethyl ketone (MEK), methyl propyl ketone (MPK), methyl butyl ketone (MBK) and methyl hexyl ketone (MHK). The highest effect on the diffusion properties of film exerted MMK, MEK and MPK, a lower effect — MBK and the lowest one — MHK. Curves showing the dependence of the CO2 — diffusion coefficient on the swelling time initially increase, and after reaching a maximum value — decrease. An increase in the diffusion coefficient is probably due to the formation of microcracks caused by internal stresses in the film accompanying the swelling-induced crystallization. This is confirmed by a decrease of the modified-film density in comparison to that of the unmodified film.
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