Tunable Gas Permeation Behavior in Self-Standing Cellulose Nanocrystal-Based Membranes

Biopolymers arise as environmentally benign alternatives to bio-accumulating, fossil resource-based synthetic polymers for a variety of applications, many of which require self-standing films or membranes. Novel sustainable amine-functionalized cellulose nanocrystals (CNCs) form dense films with low porosity suitable for gas barriers. Due to their brittleness, pure CNC membranes are challenging to work with but represent an attractive support material for selectivity-inducing additives. Supported ionic liquid membranes (SILMs) are promising due to their tunable properties and good performance in gas separation. In this study, we investigate the possibilities to realize such applications by applying glucose and ionic liquids (ILs) as additives with different functions in CNC-based membranes. By the choice of the plasticizer, the gas permeation behavior of the flexible self-standing films can be tuned from impermeable, using glucose as an additive, to permeable by addition of the ILs 1,3-dibutylimidazolium acetate and 1,3-ditetrahydrofurfurylimidazolium acetate. Tunability is also observed through the choice of the CNC source in the form of an inversed selectivity of the gas pair N2/O2, which was traceable to the CNCs' source-specific properties. The contributions of the matrix and additive were analyzed by comparing CNC to chitosan membranes and considering gas solubilities and diffusivities. The obtained results underline the diversity and tunability of bio-derived functional materials.