Polyol-modified biopolymer membranes of sodium alginate and chitosan for CO2/N2 and CO2/O2 separation: Linking structure and gas transport performance

• Chitosan and alginate membranes plasticized with glycerol and sorbitol • Glycerol and sorbitol increased CO2 permeability and CO2/N2 and CO2/O2 selectivity • 3 different mechanisms of gas transportation • Comprehensive characterization of membranes explaining gas transport properties • Enhanced structural, thermal, and mechanical properties of plasticized membranes This work presents a comparative assessment of two biopolymers, focusing on the relationship between structural modifications and their impact on gas separation performance. Sodium alginate and chitosan membranes were developed and thoroughly characterized after modification with varying amounts (0–60 wt.%) of CO 2 -philic polyol additives, glycerol and sorbitol, for the selective separation of carbon dioxide (CO 2 ) from light gases such as nitrogen (N 2 ) and oxygen (O 2 ). The membranes were prepared via solvent evaporation using polymer concentrations ranging from 0.5 to 1.5 wt.%. Their structural, thermal, and mechanical properties were analysed using SEM, FTIR, DSC, and tensile testing. Key gas transport parameters: permeability, diffusivity, solubility, and ideal selectivity, were systematically evaluated. The results demonstrate that the polyol content has a strong influence on membrane performance, revealing a clear correlation between structural features and gas separation efficiency. The highest CO 2 /N 2 selectivity (6.3) and CO 2 /O 2 selectivity (4.3) were obtained for the alginate membrane containing 60 wt.% sorbitol, with a corresponding CO 2 permeability of 38.6 Barrer. Although the overall separation performance remains moderate, the findings provide valuable insights into the role of polyol modifiers in biopolymer-based membranes, contributing to a deeper understanding of gas transport in bio-derived systems.