Hydrophobic modification of a polyurethane sponge via emulsion polymerization for selective oil-water separation

A conventional polyurethane (PU) sponge shows less selectivity, which restricts its ability to favorably absorb oils. To address this limitation, the sponge surface was engineered using a simple, low-cost, and environmentally friendly emulsion polymerization approach, which produced a uniform coating and significantly improved the oil-absorption capacity. The structural formula, surface morphology and wettability of the modified sponges were characterized using Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), and contact angle measurement techniques, respectively. The key parameters influencing the modification, including the amount of monomer, selection of the water/ethanol ratio and the concentration of the cross-linker divinylbenzene, were systematically optimized. After surface treatment, the water contact angle of the sponge increased significantly from about 85° to 154°, representing strong hydrophobicity. The modified sponges exhibited excellent selectivity, efficiently removing oils and organic liquids from oil/water and organic liquid/water systems, respectively, at saturation. They delivered high absorption capacities, ranging from 21 to 75 times their weight, while suppressing water uptake by approximately 94%. Furthermore, the materials achieved separation efficiencies exceeding 98.4% for trace oil removal and retained substantial absorption capacity even after 15 reuse cycles. These results demonstrate that a simple modification strategy can yield a low-cost, high-performance, and environmentally benign sponge, making it a highly promising candidate for oil spill remediation.