Using Cyrene as bio-based solvent: a new greener approach in membrane fabrication

Environmental protection and climate change are current issues at the heart of global economic growth. The awareness of the real risks connected with industrial membrane production sector has been the push towards the search of new, more sustainable, solvents and raw materials [1]. In this context, dihydrolevoglucosenone (Cyrene(TM)) comes as a green biosolvent derived from waste cellulose, with enormous potentiality, which could offer the possibility to re-design manufacturing processes from the origin. The increasing interest devoted to Cyrene(TM) has its basis in the similarity with many physical-chemical properties of highly toxic organic solvents normally used for fabrication membranes (such as N-Methyl-2-pyrrolidone, N,N-Dimethylformamide and N,N-dimethyl acetamide). In fact, Cyrene(TM) is presented as a polar aprotic organic solvent, completely miscible with water, and with a relatively high boiling point (227 °C) [2]. Herein, Cyrene(TM) was employed for the preparation of polyethersulfone (PES) and poly(vinylidene fluoride) (PVDF) membranes via phase inversion [2]. By preparing PES/Cyrene(TM) and PVDF/Cyrene(TM) casting solutions, without the use of any additive, and by working at room temperature, microfiltration and ultrafiltration membranes were obtained. Non-solvent induced phase separation (NIPS) and its combination with vapour-induced phase separation (VIPS) were adopted as preparation procedure. PES and PVDF membranes were characterized in terms of thickness, porosity, pore size, contact angle and pure water permeability. The morphology was also assessed. For PVDF membranes, additional differential scanning calorimetry and Fourier transform infrared spectroscopy analysis were performed. The obtained results evidenced as, by varying the exposure time to controlled humid air and temperature during the VIPS-NIPS process, membranes with different morphology and properties can be prepared, demonstrating the applicability of Cyrene(TM) for a more sustainable membrane fabrication.