Manipulation of Fibril Surfaces in Nanocellulose-Based Facilitated Transport Membranes for Enhanced CO₂ Capture

The transition toward sustainable processing entails the use of biobased alternatives as functional materials to reduce the overall carbon footprint. Nanocellulose, due to its natural availability, biodegradability, excellent mechanical properties, tunable surface, and high aspect ratio, is attracting more and more interest as a nanoscale additive in polymeric membranes. In this work, an effective way to modify nanocellulose fibril surfaces for performance enhancement in CO₂ separation membranes has been demonstrated. The functionalization promptly triggered intrinsic property responses in favor of nanofiber dispersion and CO₂ transport. Thin composite membranes containing the modified nanofibers in water-swelling poly(vinyl alcohol) (PVA) as well as in the blend of sterically hindered polyallylamine (SHPAA) and PVA were fabricated and tested using humid gas permeation tests. Defect-free ultrathin (300 nm) hybrid selective layers containing evenly distributed nanofibers were successfully coated. The addition of nanocellulose exhibited enhanced CO₂ permeance and CO₂/N2 selectivity compared to those of the neat PVA membranes. CO₂ permeance up to 652 GPU and a CO₂/N2 selectivity of 41.3 with SHPAA/PVA blend were documented. Functionalization plays a categorical role in the dispersion of nanocellulose fibrils in the SHPAA/PVA blend, increasing the steric stabilization and interface compatibility with the polymer matrix. The tuned interface with PEG groups act as sites for water clusters retention and increased CO₂ solubility, thus creating fast diffusion pathways for CO₂ transport.