Poly(lactic acid) / poly(vinyl pyrrolidone) blend membranes: Effect of membrane composition on pervaporation separation of ethanol / cyclohexane mixture

Poly(vinyl pyrrolidone) (PVP) was used as an additive to modify the structure and the physical–chemical properties of poly(lactic acid) (PLA) membranes. The membranes with different PVP contents up to 21.33 wt% were employed for pervaporation separation of ethanol/cyclohexane (EtOH/CHx) azeotropic mixture. Several characterization tests were carried out on the membranes including contact angle measurements, mechanical properties before and after immersion in solvent mixtures of different compositions, swelling properties, SEM and FTIR-ATR. The membranes were able to selectively separate EtOH from the feed. The fluxes were continuously increased at higher PVP contents from 0.02 to 0.05 kg/(m2 h) due to the higher affinity to EtOH, together with the more porous structure obtained. However, this will cause the separation factor trend to level off at around 120. This behavior was expected since the addition of PVP made the membranes more hydrophilic, decreasing the water contact angle from 74æ in pure PLA to 54æ with the maximum studied PVP content (21.33 wt%). Furthermore, swelling experiments confirmed the same affinity to EtOH at higher PVP contents. The values of Young’s modulus decreased, contrary to the membrane elongation, at higher EtOH concentrations in comparison with the untreated membranes. The same trends exist for the blend membranes with higher amount of PVP.