High-performances membranes for pervaporation I. Poly(vinyl alcohol)-poly(N-vinyl pyrrolidone) blends

• Published in: Polymers for advanced technologies 1994-06, Vol.5 (6), p.313-319
• Main Authors: Nguyen, Quang-Trong, Ping, Zhenghua, Néel, Jean
• Format: Article
• Language: English
• Subjects: Blend; Diffusion coefficient; Organic solvent dehydration; Pervaporation; Poly(N-vinyl pyrrolidone); Poly(vinyl alcohol)
• ISSN: 1042-7147; 1099-1581
• DOI: 10.1002/pat.1994.220050603

Dense membranes were prepared from poly(vinyl alcohol)–poly(N‐vinyl pyrrolidone) (PVA–PVP) blends of different compositions and studied in swelling and dehydration by pervaporation of three organic solvents contaminated by 5 wt% water. The swelling generally increases with the PVP content. No extraction occurs in water–tetrahydrofuran (THF) and water–methyl ethyl ketone (MEK) mixtures. In ethanol containing 10 wt% of water, there is no extraction for blends containing less than 40 wt% PVP and an increasing extraction beyond this PVP content. The pervaporation flux of the water–ethanol mixture increases drastically at the same threshold whereas the water permselectivity falls to a low level. The values of the diffusion and permeability coefficients determined from transient permeation of the test water–ethanol mixture exhibit a similar sudden increase at the same PVP content threshold. This singular behavior of the blend membranes is interpreted by a strong affinity of the PVP component to ethanol, combined with a disappearance of crystallites in the blend at this threshold. Consequently the amorphous membrane can swell freely according to the affinity of the PVP component, leading to the observed behavior.