Effect of the permeants/polymer interactions on the pervaporative separation properties of the P(VDF-co-HFP) membrane

In this paper, the acetone-cast poly(vinylidene fluoride-co-hexafluoropropylene) (P(VDF-co-HFP)) membranes were prepared by isothermally vacuum-dried at 60 °C and were employed in pervaporation of methyl acetate (MeAc) or ethyl acetate (EtAc) dissolved water solutions. DSC study on the swelling process indicated that two states of both MeAc and EtAc in their swollen P(VDF-co-HFP) membranes might exist which were the ‘bound state’ and ‘bulk state’. In addition, relative to the pure EtAc, the pure MeAc had stronger interaction with the P(VDF-co-HFP) membrane, making for its higher solubility in and lower diffusivity through the membrane. However, there is a competition between the organic permeants/water interactions and the organic permeants/polymer interactions when the P(VDF-co-HFP) membrane was tested for its pervaporative separating properties. With respect to MeAc in its water mixtures, EtAc in its water mixtures had higher solubility in the membrane instead because of its weaker interaction with water. As a result, better separating properties (higher permeate flux and separation factor) when the P(VDF-co-HFP) membrane was in pervaporation of the EtAc/water mixtures were obtained.