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CASE STUDY: EMPA


BIOLOGICALLY REFINED


The surface of an untreated piece of wood is full of biochemical ‘connectors’. A team at Empa considers this stage the perfect opportunity to give wood exactly the features we would like it to have: surfaces that are easy to stick to, anti-fungal coatings, or even 100% ecological self-adhesive woodchips that can be compacted into fibreboards without any chemical additives whatsoever. Rainer Klose investigates. »


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ometimes innovations start with a simple run through the woods. “One particularly good idea occurred to us when we were out jogging,” explains wood expert Mark Schubert from Empa’s Applied Wood Materials laboratory. Whilst dashing around a nearby forest, Schubert − and colleague Julian Ihssen − came up with a cracking solution to an unfinished project: an antimicrobial wood surface.


Schubert, who is a qualified forestry researcher and environmental scientist, initially studied ways of combating wood-damaging fungi with other types of fungi. Then, for several years, he used fungi to specifically modify the properties of wood. He is currently studying enzymes from fungi that have specialised in ‘digesting’ wood during the course of evolution. Laccase, for instance, which is produced by many white-rot fungi, can modify the surface characteristics of wood. It converts some chemical sub-structures of


Empa


Based in Switzerland, Empa is an interdisciplinary research and services institution for material sciences and technology. Its research and development activities are oriented to meeting the requirements of industry and the needs of society, and link together applications-oriented research with the practical implementation of new ideas, science and industry. Empa offers its industrial partners


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lignin, a wood constituent, into radicals − making the surface of the wood reactive. But what can you do with a wood


solutions tailored to meet their specific needs. This encourages companies to think and act in innovative ways while helping to improve quality of life for all of us. Safety, reliability and sustainability of materials and systems are Empa’s main objectives. Empa plays a key role in the Swiss educational, research and innovation scene. For more information visit www.empa.ch


surface that is then ‘open to new ideas’? Well, you could consider a wood preservative that can be firmly anchored to the surface and will give the bare wood better protection from decay. Schubert started to run tests with isoeugenol, an antioxidant, and thymol, a herbal fungicide, which were originally used by the ancient Egyptians to preserve mummies. But his initial attempts fell on stony ground − the substances were too easy to wash off, or lost their antimicrobial punch once they interacted with the enzyme. Time to go for a jog, thought Schubert, which brings us back to the beginning of the story. During their run he told Ihssen, a researcher in the Biomaterials laboratory, about his difficulties − and got a straightforward recommendation: “Try an old home remedy.” Back in the lab, the two of them gave it a go and succeeded with, of all things, a cheap substance − which cannot at this stage be named − that can be found in any medicine cabinet. This compound stuck firmly to the surface


of the wood. By way of a trial, Schubert and Ihssen treated test-pieces of spruce and exposed them to aggressive, wood- damaging fungi. Whereas the untreated pieces were eaten away after 12 weeks in the incubator, the treated pieces withstood the fungi. The researchers are now considering patenting their discovery. The experiment proved two things: that


laccase functionalised the wood surface so profoundly that useful quantities of a desired substance could be chemically attached to it, and that applying a cheap mass-produced medicine to the wood provided antiseptic properties. These properties could be useful for


many different applications; just think about the wooden components and furniture on public transport and in public buildings, such as hospitals, kindergartens and restaurants. Now Schubert is hoping to find an


industrial partner willing to develop this antimicrobial wood treatment to a stage where it can be marketed. He is also pursuing two other projects


for which laccase modification has been the door-opener. If wood stuck to adhesives more effectively, stronger glued connections would result, even between woods such as larch and beech, which have always been difficult to glue together. After pre-treatment with an aqueous


laccase solution, functional groups such as amines could be attached as anchor molecules to the radicals that were produced. These molecules could then chemically bind to the adhesive, making the connection significantly stronger. Those opting to stay clear of chemistry


may prefer the third application for enzymatically treated wood: adhesive-free fibreboards. If pre-treated wood fibres are compacted, they can form chemical bonds with neighbouring wood fibres. There is then no need for chemical bonding agents, such as resins or isocyanates, in the manufacture of so-called medium-density fibreboards. A chemical- free, ecologically harmless fibre product suddenly becomes within reach.


September / October 2012


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