Magnetic nanopaper shows the way for new forest products

"Magnetic nanopaper is easy to produce and has unique characteristics, but it also demonstrates the potential product research within multidisciplinary nanotechnology that has for the forest industry," says Lars Berglund, head of WWSC and professor of fibre and polymer technology at KTH.

He adds that the work has just been reported in Nature Nanotechnology and is the result of a collaboration between Finland, Spain and Sweden.

Besides the fact that magnetic nanopaper can be used to prevent the falsification of documents, there are other applications of interest, for example for implants in the human body and for small motors and sensors. Compared to metallic magnetic materials, the strong magnetic nanopaper is much more malleable. The new method of production can also be used for other forest products. Magnetic wood has already been produced in bench scale tests by researchers at WWSC.

Cellulose products are used traditionally in paper, packagings and artificial fibres, but technologies such as magnetic nanopaper open up opportunities for entirely new product areas. Previously, researchers tried to mix magnetic nanoparticles with plastics, but the properties of such materials are not particularly good. With magnetic nanopaper, you instead first create nanoparticles which remain in the paper. The particles are then magnetized. Nanopaper itself consists of very strong and flexible nanofibrils from environmentally friendly cellulose. Cellulose in the form of nanofibrils is a fibre-shaped polymer which nature produces in enormous quantities every year. The tensile strength of cellulose is therefore extremely high compared to most types of steel.

In more technical terms, you first of all produce an extremely porous so-called aerogel which consists of only 2% cellulose fibrils and 98% pores. You dip the porous cellulose aerogel into a saline solution and you then create the magnetic particles. The magnetic particles are a little more than 40 nm large and consist of cobalt ferrite. The particles bind very strongly with the cellulose. During the production process it is possible to control the amount of magnetic particles that are formed. The porous nanopaper can also be compressed to different levels of porosity, so that you can obtain the strength and the flexibility you require.

To access a summary of the work, use the following URL: http://dx.doi.org/ and specify the DOI number: 10.1038/NNANO.2010.155

For more information, contact Lars Berglund at 070 - 608 45 05 or blund@kth.se.

Peter Larsson