Nanopaper made of gently processed natural cellulose nanofibers is found to have a tensile strength almost equaling that of structural steel, according to Lars Berglund of the Swedish Royal Institute of Technology.
Berglund discovered that the mechanical processes used to pulp wood damages the natural fibers, weakening them. He developed a process to extract the fibers, keeping their properties intact.
The secret to the nanopaper's performance is not only the strength of the undamaged cellulose fibers, but also the way they are arranged into networks. Although strongly bound together, they are still able to slip and slide over each other to dissipate strains and stresses. The individual cellulose fibers are also much smaller than in conventional paper.
"A regular paper network has fibers 30 micrometers in diameter, here we are at a scale three orders of magnitude smaller," says Berglund. "The material [has] very small defects compared with a conventional paper network."
Mechanical testing shows it has a tensile strength of 214 megapascals, making it stronger than cast iron (130 MPa) and nearly as strong as structural steel used in buildings and bridges (250 MPa). Normal paper is flimsy; it has a tensile strength less than 1 MPa. The tests used strips 40 millimeters long by 5mm wide and about 50 micrometers thick.
Source: Xinhua\agencies
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