CAN’T punch your way out of a paper bag? That wouldn’t be surprising if were made of a new kind of paper that’s stronger than cast iron. The super-strong paper could be used to make tough sticky tape or synthetic replacements for biological tissues.
Despite its exceptional strength, the paper is produced from cellulose, the same material as conventional paper. Cellulose fibres are the structural component of plants’ cell walls and the principal ingredient of wood.
“Despite its strength, it is made from the same stuff as conventional paper”
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“Cellulose nanofibres are characterised by high strength and toughness,” says Lars Berglund of Sweden’s Royal Institute of Technology in Stockholm. These properties mean that cellulose is increasingly being used to make novel plastics, as well as paper, but it is mostly used as a cheap “filler”, extracted from wood pulp by brute-force mechanical processes which tend to break the fibres.
Berglund and his colleagues have come up with a gentler approach. After breaking down the pulp with enzymes they fragmented it using a device that exposes the cellulose to strong shear forces, which separates it into its component fibres and leaves them suspended in water.
When the team filtered out the water using vacuum filtration, the fibres joined together in networks to form thin sheets of “nanopaper”. This turned out to have a tensile strength of 214 megapascals: more than 200 times the strength of ordinary paper, and almost as much as structural steel (Biomacromolecules, ).
The long, undamaged fibres that form the paper can slip and slide over each other while remaining strongly bound together, giving the nanopaper an effective mechanism for dissipating stresses. The individual cellulose fibres are also about 1000 times thinner than those in conventional paper, making any faults correspondingly smaller. “The material has very small defects compared with a conventional paper network,” Berglund says.
“This shows quite clearly the potential for cellulose nanofibres to provide a basis for reinforcement,” says Stephen Eichhorn, a polymer researcher at the University of Manchester, UK.
