Polyethylenimine-Modified Glass Fiber by a Sulfur-Based Coupling Reaction for Selective Demulsification of Oil/Water Emulsions

Separating oily wastewater, especially surfactant-stabilized emulsions, is an urgent problem to solve because of its severe threats to the environment and human health. Polyethylenimine (PEI) molecules with abundant amine groups could reduce the stability of emulsions. Herein, PEI-modified glass fiber (GF) was fabricated using a facile and effective surface modification strategy: a sulfur-based three-component coupling reaction between PEI and (γ-aminopropyl)triethoxysilane-treated GF. After wet-laying the fabric, the obtained membranes presented superamphiphilicity in air, underwater superoleophobicity, and positive surface charges in water. Based on electrostatic and hydrogen-bond interactions originating from PEI, the prepared membranes exhibited different separation efficiencies from the oil-in-water emulsions prepared using anionic, nonionic, zwitterionic, and cationic surfactants. The separation efficiency was only 31.8% for the emulsion stabilized by a cationic surfactant and raised to over 94.7% for the emulsion stabilized by anionic, nonionic, and zwitterionic surfactants. In particular, it was observed that different emulsion droplets displayed various adsorption–coalescence phenomena on the prepared membranes, and a mechanism of selective demulsification was further proposed. These results suggest that the fabrication strategy is beneficial to fabricating membranes with outstanding separation efficiency.