Preparation of a PVA/CNF/ETOS Elastic Aerogel by Directional Freezing and Its Application in Oil–Water Separation

Nano-cellulose aerogels have low densities, high porosities, and strong absorption capacities, making them suitable for cleaning up oil and chemical spills in oceans. However, their weak lipophilicity and poor mechanical properties often limit their applications. We attempted to introduce long-chain polymers on the nanocellulose/polyvinyl alcohol (CNF/PVA) surface for the hydrophobic modification of aerogels. In this paper, PVA/CNF was silylated by introducing hydrolyzed ethyltrimethoxysilane to increase its hydrophobicity. Aerogels with interpenetrating pore structures were prepared by a directional freezing method. The aerogels had a high strength in the freezing direction and high compressive elasticity in the direction perpendicular to the freezing direction. Fourier-transform infrared spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and water contact angle (148°) tests demonstrated the successful silylation of the aerogel surface. The aerogel absorbed oil and some organic solvents 50–110 times higher than its own weight. It showed good reusability, with an absorption loss rate of 20% after 40 squeezing cycles. This green and sustainable method is inexpensive and has a short production cycle. In addition, the absorption of alcohols and lipids by aerogels can be used as a carrier for surgical drugs.