Effect of solute hydrophobicity on phase behaviour in solutions of thermoseparating polymers |
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Authors: | H -O Johansson G Karlström F Tjerneld |
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Institution: | (1) Department of Biochemistry Center for Chemistry and Chemical Engineering Lund University P.O. Box 124 22100 Lund, Sweden, SE;(2) Theoretical Chemistry Center for Chemistry and Chemical Engineering Lund University P.O. Box 124 22100 Lund, Sweden, SE |
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Abstract: | Two-phase systems consisting of a polymer rich phase and polymer depleted phase, where the polymer is either ethyl(hydroxy
ethyl)cellulose (EHEC) or Ucon (a random copolymer of ethylene oxide and propylene oxide), have been studied. Both of these
polymers can be separated from an aqueous solution by either temperature increase or addition of cosolutes. The polymers are
thermoseparating and phase separate in water solutions at the cloud point temperature. Two types of EHEC have been studied:
one with a cloud point at 60 °C and the other at 37 °C. The Ucon polymer used in this study has a cloud point at 50 °C. Ternary
phase diagrams of polymer/water/cosolute systems have been investigated. When a strongly hydrophilic or hydrophobic cosolute
is added to an EHEC- or Ucon–water solution, a phase separation occurs already at, or below, room temperature. As cosolutes,
hydrophobic molecules like phenol, butyric and propionic acid, and hydrophilic molecules like glycine, ammonium acetate, sodium
carboxylates (acetate to valerate), were studied. The polymer rich phase formed when mixing polymer, water and cosolute was
strongly enriched or depleted with hydrophobic or hydrophilic cosolutes, respectively. The two phase region increased for
propionic acid, butyric acid and phenol as a result of increased cosolute hydrophobicity. The opposite occurred in the series
sodium acetate, sodium butyrate and sodium valerate. The effect of temperature on the phase behaviour has also been investigated.
Model calculations based on Flory–Huggins theory of polymer solutions are presented, in form of a phase diagram, which semiquantitatively
reproduce some experimental results.
Received: 5 July 1996 Accepted: 4 November 1996 |
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Keywords: | Polymer thermoseparation aqueous two-phase systems temperature-induced phase separation |
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