Among the major separation techniques (chromatography, crystallization, adsorption, hybrid processes), membrane technology represents an increasingly important and growing separation approach, thanks to its efficiency, modularity, flexibility and energy-saving. However, one of the main challenges lies in developing membranes using low-impact materials that provide both high performance and stability over time. However, it is very difficult to fully replace well-established petrochemical polymers such as polyvinylidene fluoride (PVDF) obtaining membranes with state-of-the-art performance. One of the strategies is to reduce the amount of petrochemical-derived polymers by blending them with bio-derived materials. In this work membranes made of PVDF and lignin blend (50/50 wt%) have been developed. Lignin was rationally selected for its amphiphilic structure, which confers high compatibility with the hydrophobic PVDF, as predicted by Hansen solubility parameters and confirmed by differential scanning calorimetry analysis. Membranes were fabricated using the non-solvent induced phase separation (NIPS) technique. A systematic study of the isothermal ternary phase diagram of polymer/solvent/non-solvent system has enabled the development of membranes with tailored structures and separation properties. As expected, membranes with lower pore size and size distribution (0.0890.002mm, 99%) were obtained in the region of delayed demixing compared to membranes prepared using conditions falling within the fast-demixing zone which showed larger pore size and size distribution (0.19 0.02 mm, 80%). The membranes with pore size of 0.19 mm (zeta potential -15.7 mV) were tested in the filtration of stabilized submicron oil-in-water emulsions (droplet’s size 0.14 0.09 mm, zeta potential -41.9 mV) obtaining enhanced pressure-normalized flux (250 Lh-1m-2bar-1) and rejection (>99.99%) compared to other hydrophilized PVDF membranes described in the literature.
Regina S, Poerio T, et al., Journal of Membrane Science Letters, 4,2 (2024), pg. 100081 https://doi.org/10.1016/j.memlet.2024.100081