Tuesday, May 27, 2008

Graphene-Polymer Composite

Continued from page 1

By Prachi Patel-Predd

Brinson and her colleagues at Northwestern then found a way to evenly spread the graphene in the polymer. They disperse graphene in one solvent and dissolve the polymer in another. Then they mix the two until graphene is evenly dispersed throughout the polymer, and they evaporate the solvents.

"For all the properties we demonstrated, the graphene sheets perform equally or superior to nanotubes," Brinson says. Using the same polymer, the researchers made two composites, one containing 1 percent by weight of carbon nanotubes, and the other containing the same amount of graphene. Adding graphene to the polymer made it 80 percent stiffer, while carbon nanotubes made it a little more than 50 percent stiffer. The graphene composite could withstand 30 ºC higher temperatures compared with the polymer alone, while carbon nanotubes did not increase the temperature stability.

The Northwestern material faces a tough competitor. Based on technology that Michigan State University's Drzal developed, an East Lansing, MI, company called X G Sciences is setting up a pilot plant to manufacture various common polymers containing graphene platelets. The platelets contain stacks of about five layers of graphene, as opposed to a single sheet. Drzal, the company's chief scientist, says that stacks will not crumple or roll up during the processing methods used to make plastic products. "It's like when you have a single paper versus 10 sheets of paper . . . The stack is much stiffer and more robust." They are also cheaper to produce, he says. "The more you get towards single sheet, the more expensive the process."

One promising use for graphene composites will be to make fuel tanks and food packaging. Gas and liquid molecules can permeate through plain polymers, says Rodney Ruoff of the University of Texas at Austin, who was involved in the work. But graphene composites can form an impermeable barrier. That means fuel-tank linings would keep vapors in and dissipate static electricity. "You could keep sandwiches outside the refrigerator for six months without oxygen getting through and oxidizing [them]," suggests Ruoff.