Technology whittles wooden barrier

Process promises less-energy-intensive fibril extraction.

By Seán Ottewell, editor at large

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Norwegian scientists are attempting to use some of nature’s tiniest building blocks to develop new products such as food packaging materials capable of killing bacteria and disposable duvet covers that keep infections away from hospital patients — but only if they can overcome some processing challenges.

The group is drawn from the Norwegian University for Science and Technology (NTNU), the Paper and Fibre Institute (PFI) and SINTEF, the largest independent research organisation in Scandinavia. They are based at the NTNU site in Trondheim, Norway.

Their focus is on fibrils, nature’s own mini-reinforcement rods. Consisting of long sugar molecules called cellulose and arranged in bundles, fibrils make up the walls of wood cells and give trees their characteristic toughness.

Aficionados of pulp and paper processing will be familiar with wood cells being beaten and squashed flat to become paper fibers, or being boiled to separate [okay?] the cellulose. It’s already possible to extract fibrils — measuring just nanometres in diameter — from wood cells. But the process is prohibitively expensive.

The scientists are trying to make this extraction process both more energy-efficient and cost-efficient. But this is no easy task “It has taken a lot of energy to build up these wood cells in nature, and then we come along and want to use as little energy as possible to tear them apart again,” explains Kristin Syverud, PFI scientist.

With financial support from the Research Council of Norway and in close cooperation with scientists from SINTEF and NTNU, PFI has spent the last three years on basic research into fibrils.

Fibrils are long in comparison with their diameter, which makes them good at absorbing forces. They are therefore very suitable as reinforcements for plastics, according to Bjørn Steinar Tanem, SINTEF scientist. He predicts, for example, that they could enable more plastics to be used in automotive components.

The Trondheim scientists would like to use fibrils in biopolymers, the aim being to develop composite structures whose lifecycle will have the least possible impact on the environment.

“Fibrils can give biopolymers new, improved properties which,  in conjunction with good design, could form the basis of thinner-walled molded products. This would, for example, reduce the amount of raw material needed,” says Tanem.

However, Syverud is taken by the results of a different application —  a “fibrils with attachments” variant. Here the scientists selected a chemical that kills microorganisms, which they have  made stick tightly to the fibrils.

“This is important, for substances of this sort must not leach out and end up in the wrong place,” she says.

For more on this see, issue 8 (7), pp2149-2155 of June 2007’s Biomacromolecules journal. Here Syverud and co-workers from PFI, SINTEF, the department of chemical engineering at NTNU and others outline preparation of antimicrobial films prepared from surface-modified microfibrillated cellulose. The films exhibited substantial antibacterial capacity, even at very low concentrations. Diffusion tests also confirmed that chemicals used in their manufacture hadn’t made their way into the surroundings, confirming the non-leaching nature of the films.

It’s these results that are spawning exciting product concepts such as bactericidal food wrappings, disposable duvet covers, novel water filters and more.

But there’s a down side. “Controlling the size distribution of the fibrils once they have been separated out is one of the challenges that still make us tear our hair,” says Syverud, who has been leading the project together with Per Stenius, an adjunct professor at NTNU.

Two different mechanical techniques are in use today to extract the fibrils: a mill, and a nozzle that produces a large pressure drop. Both are energy-intensive. However, according to Syverud, there’s already know-how, for example at PFI ‘s Swedish owners, that will significantly reduce energy consumption. She’s also quite certain that this research will lead to commercial products.

“However, which of the potential areas of application will take off is something we don't know yet. And I am sure that not all of our ideas will end up as products,” she says.

Syverud wouldn’t comment on the technical details of the process as a patent is pending. However, she did say that there’s been a lot of interest in the work from a number of sectors “including chemical companies.”

The western world's cellulose industry is the driving force behind fibril research. Realizing that it’s difficult to compete on price for traditional cellulose, the industry is looking for applications for processed cellulose. “They are a renewable resource that is being created by nature around us every day. And they are certainly cheap,” concludes Syverud.
 
Seán Ottewell, editor at large
sottewell@putman.net

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