Superhydrophobic ultra-high molecular weight polyethylene nanocomposite foams fabricated by supercritical CO₂ foaming for selective oil absorption

Superhydrophobic foams are promising substances for removing leaked oil from water. However, producing superhydrophobic foams with stable high performance using a low-cost, scalable, and environmentally friendly means is a challenge. Herein, superhydrophobic nanocomposite foams comprising of ultra-high molecular weight polyethylene (UHMWPE) and modified silica nanoparticles (NPs) were developed using melt blending and supercritical CO₂ foaming. Long carbon chains grafted on silica NPs formed a shell with a thickness of 100 nm, which rendered the NPs hydrophobicity and generated entanglements with UHMWPE matrix. The optimum foam with an average cell size of 41.5 μm achieved a high water contact angle of 158.2 ± 1° and a low sliding angle of 1.7 ± 0.4°, attributing to the micro-nano hierarchical structure constructed by the porous structure and the modified NPs. The foam remained superoleophilic and demonstrated high efficiency in separating both light and heavy oils from water. A relatively high oil absorption capacity of 2.8 to 7.2 g/g was achieved towards various oils and solvents, and separation efficiency of over 99 % could be maintained after ten cycles of reuse. This work provides a facile and scalable method to produce superhydrophobic UHMWPE nanocomposite foams with stable high performance for effective oil absorption from water.