Thymol: nature's solvent for sustainable hollow fiber fabrication†

Sustainable separation processes are crucial for industries like chemicals and pharmaceuticals and membrane technology stands out for its low energy consumption. However, membrane fabrication typically involves large amounts of solvents, which are facing tighter scrutiny due to environmental regulations. This work tackles the quest to replace toxic solvents and proposes thymol and its mixtures with other natural components as green solvents. Thymol, despite being solid at room temperature, forms homogeneous liquid solutions with a high-performance polyetherimide, exhibiting behavior analogous to deep eutectic mixtures observed for small molecules. Through spectroscopic, thermal, and rheological analyses, we elucidate the role of hydrogen bonding between carbonyl and hydroxyl groups in these solutions. We utilized the findings for membrane fabrication. Hollow fibers were spun in continuous machines using the green solvent dope solutions. These fibers coated with polyphenols were assessed for air dehumidification, showcasing the successful translation of fundamental investigation into membrane production and application.