Tailoring PVDF Membranes Surface Topography and Hydrophobicity by a Sustainable Two-Steps Phase Separation Process

This work validates a sustainable way to produce customized PVDF membranes, suitable for contactors applications, in which DMSO is employed as non-hazardous solvent, in place of substances of very high concern (SVHC), by a combination of vapour-induced and liquid-induced phase separation (VIPS and LIPS) stages, and without using any chemical additive as pore forming. The experimental results highlight the key role of the kinetic and thermodynamic parameters of the phase separation processes involved in the control of the surface and transport properties of the PVDF membranes. Namely, combining VIPS and LIPS techniques in a controlled way, allowed to produce symmetric porous membranes with customized rough surface topography (root mean square roughness up to 0.67 mm) and hydrophobicity (water contact angle >140°) according to a bio-mimetic behaviour as that of lotus leaves surfaces, through an environmental friendly fabrication process. The resulting membranes are characterized by a high porosity (total porosity ³70%, mean pore size 0.08-0.4 mm), with well interconnected pores, despite no pore former additives were included in the dope solution, making them ideal candidates for application in membrane contactors. The quality of the produced membrane (permeate flux up to 12.1 Lh-1m-2 with salt rejection 99.8%) is assessed by MD tests and results comparable to commercial PVDF membranes having similar mean pore size, porosity and surface roughness, but produced using SVCH solvents