A team from the National University of Singapore (www.nus.edu.sg), led by assistant professor Duong Hai Minh from the Dept. of Mechanical Engineering, has succeeded in converting paper waste into cellulose aerogels that are nontoxic, ultralight, flexible, extremely strong, and water repellent. The team has produced a polysaccharide-based aerogel comprising a network of polysaccharide fibers with pores of a few micrometers. The large size of the pores enable the aerogel to absorb huge amounts of liquid.
Where the polysaccharide is cellulose, the aerogel has pores in the micrometer range, the diameters of the cellulose fibers are also in the micrometer range, and the lengths of the fibers are of the order of millimeters. For a nanocellulose aerogel, the pores are three orders smaller (in the nanometer range), the diameters and lengths are also three orders smaller — diameters of the order of nanometers and lengths in the order of micrometers.
The team developed a method for forming a polysaccharide-based aerogel by dissolving polysaccharide fibers from a recyclable material in a polysaccharide solvent in the presence of sound energy to form a polysaccharide dispersion, then forming the dispersion into an aerogel. Eventually the aerogel can be coated with an hydrophobic agent.
The team envisages many applications for the materials, including oil spill cleaning, heat insulation, packaging, coating for drug delivery, and as smart material for biomedical applications. When coated with trimethoxy-methylsilane (MTMS), the aerogels are water repellent and are capable of absorbing oil up to 90 times their dry weight, making them up to four times more effective than commercial oil sorbents.
Duong said polypropylene-based absorbents are widely used for oil absorption, but they are non-biodegradable and their absorption capabilities are low and slow.
The team has also discovered a way of expanding the weight capacity of the aerogels, by infusing the fibers of the aerogels with a solution of metallic nanoparticles. The aerogels are then hammered flat to remove most of the air, resulting in a magnetic thin film with a weight capacity of more than 28 m.t./cm2.