Wooden it be nice

Cellulose nanofibres made from wood fibre are being used to produce strong, ultralight new biomaterials that could be used in car manufacture.

Finnish researchers are exploring new avenues opened up by the manufacture of cellulose-based nanofibres, which can be used to produce extremely strong and modifiable materials. These efforts are backed by environmental concerns which lend ever stronger support to the demand for wider utilisation of natural, fibre-based materials.

“Forest cluster companies operating in Finland are on the lookout for new forest products. In order to be able to meet the challenges of these companies we need to improve the current level of know-how in wood-based products and wood processing at molecular level. New territory has been charted, for example, in the areas of composites and nanomaterials,” said Professor Janne Laine of the Helsinki University of Technology’s Department of Forest Products Technology.

Interest in cellulose-based nanofibres is primarily driven by its environmental value as a biomaterial. It is also known that nanomaterials can be used to achieve strength properties which are not attainable with larger particles. Furthermore, the smaller the particle is, the bigger the surface area, which in turn increases the desired interactivity with other materials.

“One of the main application targets for new materials is the car industry, which wants to use lightweight cellulose fibres in car interior panelling. Estimates in terms of volume of the natural fibre requirement of the European car industry in 2010 are extremely substantial,” said Laine.

Laine’s research team is one of five teams involved in examining and developing cellulose-based nanofibres as part of the Finnish-Swedish Wood Material Science and Engineering research programme.

According to Laine, the Nanostructured Cellulose Products research project has shown that wood fibre can be used to make a versatile range of materials, both for traditional wood processing industry products as well as for totally new applications.

Cellulose fibres (30 micrometers wide, 2 to 3 millimetres long) consist of nanometre-scale microfibrils (4 nm wide, 100–200 nm long).

The chief objective of the project has been to produce uniform quality nanofibre (microfibrillated cellulose, MFC) from cellulose fibres by combining enzymatic or chemical treatment with mechanical processing. Another was to attempt to functionalise the surfaces of the microfibrils, by means of polymers in order to be able to utilise the converted fibrils in as many materials as possible. A third was to demonstrate how cellulose fibrils could give totally new properties to a range of different materials.

The project has achieved an 80 per cent reduction in the energy requirement of microfibrillar cellulose manufacture compared to levels formerly claimed. In addition, enzymatic pre-treatment combined with specific mechanical treatments has produced microfibrils of extremely high and uniform quality.

“We’ve succeeded in modifying the surfaces of microfibrils by means of different polymers, which has, for instance, enabled us to make their surfaces more electrically charged. Microfibrils give considerable toughness and strength to traditional paper products even in small quantities. Correspondingly, microfibrils, as so-called nanocomposite structures, form an extremely high-strength film, the plasticity of which is possible to regulate, for example, by means of starch,” said Laine.

“Cellulose microfibrils can also be used to make ultra-light materials. By combining fibrils with conductive polymers, we’ve been able to make cellulose-based structures which conduct electricity. It’s also been possible to coat microfibrils with a thin layer of titanium dioxide, which makes the material photocatalytically active. Titanium dioxide coated microfibrillar cellulose could be used, for instance, in solar cells and applications in which self-cleaning surfaces are needed, such as filters.”