Sustainable fabrication and structure-property evaluation of chitosan-based functional membranes prepared via a CO₂-assisted process.

Emerging sustainability challenges and the need to minimise hazardous chemicals in membrane fabrication have driven the exploration of bio-based alternatives to fluorinated polymers. In this study, thin chitosan-based membranes were fabricated via a green CO₂-assisted dissolution method that eliminates the use of mineral and organic acids and integrates carbon capture directly into the fabrication process. Low-, medium-, and high-molecular-weight chitosans were investigated, both in their native form and with glycerol plasticisation, to assess their structural, sorptive, mechanical, and ion-capacity characteristics as part of an early-stage screening approach for future functional membrane development. FTIR analysis confirmed characteristic chitosan functional groups and revealed that molecular weight and glycerol addition modulate hydrogen-bonding networks. Increasing glycerol content led to thicker membranes with reduced water uptake and swelling, improving dimensional stability, while mechanical characterisation highlighted a trade-off between stiffness and flexibility. Ion-exchange capacity was strongly influenced by molecular weight and decreased with glycerol addition, likely due to partial blocking of amino groups. It is hypothesised that the CO₂-assisted dissolution of chitosan modifies the protonation dynamics and intermolecular hydrogen-bonding network within the polysaccharide matrix, enabling sustainable control over structure-property relationships essential for designing functional chitosan-based membranes.