Cellulose Nanofiber Nanocomposite Pervaporation Membranes for Ethanol Recovery

In spite of the growing interest to exploit nanocellulose in membranes for water purification, reverse osmosis, packaging, and other applications, examples of nanocellulose-containing membranes for pervaporation are rather limited. We here report the preparation of dense nanocomposite pervaporation membranes consisting of a polystyrene-block-polybutadiene-block-polystyrene (SBS) matrix and high-aspect-ratio cellulose nanofibers (CNFs). The membranes were produced by a solvent casting evaporation process, and the CNF concentration was systematically varied. At the highest CNF concentration (15 wt %), a 5-fold increase in Young’s modulus (271 MPa) and a 10-fold increase in the yield strength (18 MPa) were observed, while the elongation at break (37%) remained appreciable, suggesting that the CNFs form a reinforcing network in the SBS matrix. At the same time, the water permeability and sorption doubled and increased ten times (at relative humidity = 100%). Pervaporation experiments were carried out with a 10 wt % ethanol/water mixture at 40 °C. A 3-fold increase in mass fluxes was observed at a CNF content of 15 wt %, which was accompanied by a 40% decrease in the separation factor. This resulted in an increase of the pervaporation separation index from 66.5 g m–2 h–1 (neat SBS) to 89.4 g m–2 h–1 (15 wt % CNF nanocomposite), indicating that the relative increase in fluxes more than compensates the reduced separation efficiency.