This is the second in our series explaining Accoya, one of the latest timber products, that we proudly use in our materials.

Accoya® is currently manufactured from radiata pine that is supplied from sustainable sources in the southern hemisphere including sources certified by the Forest Stewardship Council (FSC) or the Programme for the Endorsement of Forest Certification (PEFC). Certified timber is harvested from well-managed forests and full ‘chain of custody’ ensures that all wood used to manufacture Accoya® is sustainably sourced to the highest standards.

More information on the process of timber certification as a tool for ensuring supply of sustainable timber products is covered in TRADA WIS 2/3-58. Both FSC and PEFC certified woods meet requirements of the UK Government timber procurement policy via The Central Point of Expertise on Timber Procurement (CPET). Therefore, Accoya® is suitable for use in UK government buildings, both national and regional.

Radiata pine (also known as Monterey pine) is a native of North America, but is widely grown around the world. The largest areas of plantation are in New Zealand, Chile and Australia. Radiata pine was selected for the manufacture of Accoya® because pruning of the trees results in large volumes of clear grade wood. Modification takes place throughout its section. This allows for conversion of

Accoya® post modification without risk of exposing untreated wood, which is a real benefit over preservative treated wood. As part of the Accoya® quality control processes, sample cores

are taken from the centres of boards to confirm modification has taken place throughout the section. Figure 2 shows a sample being taken from the centre of a section of Accoya® wood.

The modification process involves impregnating wood with acetic anhydride, a colourless liquid used for the manufacture of photographic films and in the production of aspirin and other medicinal drugs. Accoya® is produced by placing dried timber in large autoclaves and then introducing and removing acetic anhydride from these vessels.

The finished Accoya® wood has a very low residual acetic acid (vinegar) level and slight associated odour. This odour dissipates naturally or can be immediately blocked by wood coatings. Acetylation causes no significant change to wood colour. Although there is darkening of the outer surface, this is insignificant compared to wood treated by thermal modification processes which considerably darken wood.

Accoya® wood is presently manufactured by Titan Wood in the Netherlands.