Spilled Oil Clings to Nano Sponges

Wednesday, May 14, 2014 @ 06:05 PM gHale

All industrial nations need large volumes of oil which usually ends up delivered by ocean-going tankers or via inland waterways to its destination. The most environmentally-friendly way of cleaning up nature after an oil spill accident is to absorb and recover the floating film of oil.

There is now a highly absorbent material that separates the oil film from the water and is easily recoverable in a “silylated” nanocellulose sponge, said Empa researchers Tanja Zimmermann and Philippe Tingaut, who worked in collaboration with Gilles Sèbe from the University of Bordeaux.

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In laboratory tests the sponges absorbed up to 50 times their own weight of mineral oil or engine oil. They kept their shape to such an extent that workers could remove them with pincers from the water. The next step is to fine tune the sponges so they can work on a laboratory scale but also in real disasters.

Nanofibrillated Cellulose (NFC), the basic material for the sponges, comes from cellulose-containing materials like wood pulp, agricultural by products (such as straw) or waste materials (such as recycled paper) by adding water to them and pressing the aqueous pulp through several narrow nozzles at high pressure. This produces a suspension with gel-like properties containing long and interconnected cellulose nanofibers.

When the water from the gel ends up replaced with air by freeze-drying, a nanocellulose sponge is able absorb water and oil. This pristine material sinks in water and is thus not useful for the purpose. The Empa researchers succeeded in modifying the chemical properties of the nanocellulose in just one process step by administering a reactive alkoxysilane molecule in the gel before freeze-drying. The nanocellulose sponge loses its hydrophilic properties, and only binds with oily substances.

In the laboratory the “silylated” nanocellulose sponge absorbed test substances like engine oil, silicone oil, ethanol, acetone or chloroform within seconds. Nanofibrillated cellulose sponge, therefore, reconciles several desirable properties: It is absorbent, floats reliably on water even when fully saturated and is biodegradable.

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