ISSN:
0959-8103
Keywords:
water
;
ethanol
;
crystallinity
;
concentration-dependence
;
diffusion
;
poly(vinylalcohol) membranes
;
Chemistry
;
Polymer and Materials Science
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
,
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
,
Physics
Notes:
Solvent sorption and diffusion are the key processes that control membrane performances in membrane processes. The sorption characteristic of water and ethanol vapours in poly(vinylalcohol) (PVA) membranes of different crystallinity degrees was measured by microgravimetry and the diffusion characteristic was calculated from the sorption kinetics at different water activities by curve fitting. The sorption isotherms for water vapour in membranes of 28, 37, 44 and 56% crystallinity degrees at 40°C obey the Flory equation based on the polymer lattice model. When the sorption extent was corrected by assuming that only the polymer amorphous phase is accessible to the penetrant, a unique Flory χ interaction parameter, 0.3, was obtained for all samples except for the 28% crystallinity sample. For the latter sample, the lower χ value (0.18) obtained can be explained by a change in the sorption behaviour of the original crystalline domains which may undergo partial destruction. The diffusion coefficient increases with the average water content in the membrane according to an exponential relationship characterized by a limit diffusion coefficient and a plasticization coefficient. The higher the crystallinity of the membrane, the lower the values of the limit diffusion coefficient and the plasticization coefficient. The ethanol sorption was also well described by the Flory-Huggins equation. The limit diffusion coefficient for water was two orders of magnitude larger than that for ethanol.
Additional Material:
9 Ill.
Type of Medium:
Electronic Resource
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