#83: Bulletproof Paper Is Stronger Than Kevlar

New nanopaper is not only super-strong, but made from renewable materials.

By Jocelyn Rice|Monday, December 8, 2008

Bulletproof vests of the future may be constructed from an unlikely material: paper. In May a team of researchers announced a new “nanopaper”—made of tightly woven nanosize cellulose threads—proven in lab tests to be stronger and tougher than cast iron.

Cellulose fibers are hardy strands of sugar found in the cell walls of plants and algae; they are the most abundant polymer on the planet. Cellulose fibers give wood hardness and cotton toughness. But the normal papermaking process destroys the inherent strength of cellulose fibers. The wood pulp used in making paper is so coarse that the individual strings of cellulose can’t latch on tightly to their neighbors.

So the researchers, including materials scientist Lars Berglund of the Royal Institute of Technology in Sweden, used enzymes and a blender to chew standard wood pulp into a stew of much finer particles—about one-thousandth their original size. Then they filtered the stew into a goopy gel and smashed it in a press, creating sheets of nanopaper. In this form, the cellulose fibers could intertwine in strong, tight networks, just as they do in nature.

The nanopaper’s structure is a lot like that of Kevlar, Berglund says. But unlike Kevlar, it can be manufactured from renewable materials at relatively low temperature and pressure. “It’s a beautiful fiber structure,” Berglund adds. “It’s really a fantastic illustration of how biology can do things much more elegantly than commercial processes.”

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