Simultaneous amphiphilic polymer synthesis and membrane functionalization for oil/water separation

This work scrutinizes a versatile process during which amphiphilic copolymers (made of styrene and sulfobetaine methacrylate, ethylene glycol methacrylate or vinylpyrrolidone) are simultaneously copolymerized and coated on microporous poly (vinylidene fluoride) (PVDF) membranes. Changing the nature of the hydrophilic monomer and the reaction conditions, it is possible to regulate the wetting properties of the membranes by water and oil. The main surface physical properties of the membranes were not modified for a reaction/deposition bath containing up to 50% styrene monomer, but larger styrene amounts led to aggregate formation. A 50% molar ratio in hydrophobic/hydrophilic unit led to a suitable balance between stability and hydration, resulting in optimized water permeation and oil repellence. Gravity-driven separation of oily wastewaters was doable with all selected membranes (St50S50, St50P50 and St50V50) and oils tested (toluene, hexane, diesel). Nevertheless, it is highlighted that PEGylated surfaces offer the best overall compromise between separation kinetic and separation efficiency. Results also suggested that zwitterionization with larger amounts of zwitterionic monomers is not practical, possibly because it leads to a hydration layer too tight, which slows down the gravity-driven separation. This study demonstrates the effectiveness/versatility of this surface modification method to quickly hydrophilize PVDF membranes applied to energy-efficient separation of emulsions.