Summary
• Wood modification is driven by limits on chemical preservatives and pressure on timber species.
• Several modified woods have gone into commercial production.
• A new furfurylation plant is due for completion next year.
• Radiata pine features in many of the new processes.
Wood modification is becoming increasingly important to the timber industry, as evidenced by a European conference on the subject, during which more than 70 papers were presented by researchers, engineers and scientists from around the world. They reported on the latest processes to enhance the properties of wood, including thermal modification, acetylation, furfurylation and densification. As well as new techniques applied in the laboratory, there were updates on the successes of products that had gone into commercial production
The drive to create new wood technologies is fuelled by ever-changing legislation regarding limits to chemical preservatives, and the pressure on some species, where supply is tightening and the costs are rising.
New processes presented at the conference are designed to increase the durability or stability of different species of timber without the need for deep penetration of toxic chemicals.
This year has witnessed a growth in the use of thermally modified wood, and specifiers are beginning to regard it as an ideal product for cladding. Some companies have taken production one stage further and are offering it pre-finished with stains and colour coatings as an off-site service.
Speaking at the conference, Jukka Ala-Viikari of the Finnish Thermowood Association gave an update of the association’s work. The association’s brief is to enhance the commercial opportunities of the product on behalf of its members.
Mr Ala-Viikari said an audited system of quality control had been established which was now combined with a certification system.
The classification of Thermowood has also been developed giving end-use recommendations depending on the durability and species. Thermo-D is treated at 212°C within a range of +/- 3°C for two to three hours, giving greater durability. This classification is suitable for exterior cladding, joinery, decking and sound barriers.
Acetylated wood
Another form of wood modification to have entered the market place is acetylation. It involves treatment with acetic anhydride, which reacts with and blocks the chemical components of wood that normally absorb water and moisture. Radiata pine is now being used by Titan Wood in the production of Accoya, and the manufacturers have developed a method of analysing the correlation between acetyl percentage and quality performance to provide performance assurances to customers.
Accoya acetylated wood is being distributed in the UK by BSW Timber and is proving to be a success in the joinery market as the wood fibre retains its full strength after treatment, and is ideal for use in larger sizes for window and door frames.
Other property-enhancing technologies include furfurylation, which involves the formation of furan polymers from the condensation of furfuryl alcohol.
Per Brynildsen and Espen Myhre from Porsgrunn, Norway, described two products in commercial production since 2003: furfurylated Scots pine, and treated sapwood of various pines or temperate hardwoods such as beech or ash. A new plant, with the capacity to manufacture 20,000m³ annually of furfurylated wood, is due for completion by the summer of 2008.
The modification of wood can be achieved through chemical, thermal, impregnation or polymerisation and enzymatic treatments, and the University of Idaho’s Department of Forest Products presented a paper on a project to enhance the dimensional stability and hardness of small diameter ponderosa pine. This low-value species was improved by impregnation with a low molecular weight urea-formaldehyde resin system followed by curing. The results indicate that the process increased the material’s density and hardness and reduced swelling, offering a low-cost option for wood enhancement for flooring and furniture applications.
Radiata pine featured in many of the new processes because it readily lends itself to both heat modification and other property enhancing processes such as acetylation. As a plantation crop, supplies are well managed and forestry practices are modern, producing some high-quality dimensions. The commercial growing areas are currently in Chile, New Zealand and Australia.
In all cases, it was noted that a suitable surface coating is required to ensure radiata pine remains free from discolouration in external applications.
Selling points
Dennis Jones of Wood Knowledge Wales, based at the University of Wales Bangor in Gwynedd, summarised the presentations by saying that commercial ventures had identified a number of selling points for modified wood. These included its increased dimensional stability and durability, which had led to several claims that the product behaves in a similar fashion to tropical hardwoods. Given the sustainable source of many European species, the environmental marketing angle was a key focus.
He also cautioned that there is a fine balance between a product with excellent properties and one that can viably compete in today’s aggressive market. Finland’s Thermowood Association, he said, demonstrated the importance of a collective approach to marketing and product development.
Marketing modified wood under brand names was a major breakthrough in giving it more recognition, and the perception of a new timber product, he said.
