Cellulose nanocrystals as a tunable nanomaterial for pervaporation membranes with asymmetric transport properties

Abstract

The cost-effective recovery of alcohols from aqueous fermentation broths is crucial in the production of biofuels. In this context, pervaporation processes using dense membranes have attracted remarkable interest. Cellulose nanocrystals (CNCs) have emerged as a promising renewable component for membrane applications due to their high specific surface area and tunable surface chemistry. We recently reported compositionally graded nanocomposite membranes based on a hydrophobic poly(styrene)-block-poly(butadiene)-block-poly(styrene) (SBS) matrix and CNCs that display directional water transport properties. We here explore the ethanol-recovery pervaporation performance of such graded membranes for a model ethanol-water mixture. We further decorated the CNCs with hydrophobic oleic acid moieties (OLA-CNCs) and studied the impact of this modification on the structure and pervaporation performance of SBS/OLA-CNC nanocomposite membranes. Depending on the exposure side, SBS/CNC membranes exhibit either improved or diminished mass fluxes compared to the reference SBS membranes, but also a consistent reduction of the membrane selectivity towards ethanol. By contrast, the SBS/OLA-CNC membranes display increased ethanol permeability while their separation performance is comparable to the reference SBS membranes. Thus, we show that by tuning the surface chemistry of CNCs, the pervaporation properties and the degree of asymmetry in mass transport can be tailored.