HLB-engineered superhydrophilic PVDF membranes grafted with block polyethers for high-efficiency oil-in-water emulsion separation

Oily wastewater poses a significant challenge in oilfield production, where conventional separation membranes often exhibit limited demulsification efficiency, poor antifouling performance, and inadequate separation stability. Inspired by the molecular structure of commercial poly(propylene oxide)-poly(ethylene oxide) (PPO-PEO) demulsifiers, this study introduces PPO-PEO block polyethers with varying hydrophilic-lipophilic balance (HLB) values into a polyvinylidene fluoride (PVDF) matrix to develop a high-performance ultrafiltration membrane. Graft copolymers of PPO-PEO and styrene-maleic anhydride (SMA) were synthesized and blended with PVDF to fabricate functionalized membranes via non-solvent induced phase separation (NIPS). Results indicate that increasing the HLB value of the incorporated polyether significantly enhances membrane porosity, surface hydrophilicity, underwater oleophobicity, and antifouling capability. The F68-modified membrane (M-F68) exhibited the most promising performance, with an underwater crude oil contact angle of 162.0 ± 2.9° and a pure water flux of 213.6 ± 4.8 L·m −2 ·h −1 , which is approximately 25 times that of the pristine PVDF membrane. The flux recovery rate (FRR) reached 90.9% after three cycles of BSA filtration, far exceeding the 14.0% of the unmodified membrane. Moreover, the M-F68 membrane achieved over 99.0% separation efficiency for various surfactant-stabilized oil-in-water emulsions. This work provides a facile and effective strategy for designing demulsifying ultrafiltration membranes with robust antifouling properties, demonstrating great potential for treating oily wastewater.