Preparation, morphology and gas permeation properties of carbon dioxide-selective vinyl acetate-based Polymer/Poly(ethylene oxide-b-amide 6) blend membranes

Blend membranes based on the Pebax 1657 and polyvinyl acetate (PVAc) or VAc/dibutyl maleate copolymer (P(VAc-co-DBM)) were prepared via solution casting. SEM micrographs did not show any phase separation in the macro-scale. FT-IR results showed that hydrogen bonding of NH groups with carbonyl groups in the polyamide (PA) microphases or ether groups in the poly(ethylene oxide) (PEO) microphases changes towards hydrogen bonding of NH groups with the VAc-based polymers in the blends. Melting temperature and crystallinity of the both PA and PEO microphases as well as the glass transition temperature of the PEO microphase decreased by adding VAc-based polymers. It was found that P(VAc-co-DBM) copolymer chains in the blend membrane containing 50 wt% copolymer have almost a similar tendency towards both PA and PEO microphases, while those in the blend membranes containing copolymer content lower than 50 wt% are mostly located between PA microphases. It was also deduced from DSC thermograms that a separate phase of VAc-based copolymer can be formed in the membranes containing copolymer content more than 20 wt%. Despite decreased CO2 permeability, selectivity of CO2/CH4 improved significantly from 17.6 for pure Pebax to 37.5 for a blend with 30 wt% copolymer. Results obtained from permeability test revealed that in the blends containing similar amounts of VAc-based polymers, the effect of the PVAc homopolymer is far more than that of the P(VAcco- DBM) copolymer. (C) 2017 Elsevier Ltd. All rights reserved.