The technology behind Accoya™ wood is based on wood acetylation, a process that has been studied by scientists for more than 70 years and proven to be an outstanding method of improving the technical properties of wood.

The process essentially alters the actual cell structure of wood by transforming free hydroxyl groups into acetyl groups. Acetyl groups simply consist of hydrogen, oxygen and carbon and are already present in all wood species (ranging from 1% to 8% by weight) and can be derived independently from acetic acid, i.e. vinegar. Thus, the process does not introduce anything to the wood that does not naturally occur in it.

The process can be summarised as follows:

Acetic acid is ‘cracked’ by heating it to very high temperatures. Cracking breaks off a water molecule from the acetic acid leaving ketene which is used to create acetic anhydride.

Water, acetic anhydride and un-cracked acetic acid must be separated and the water/acetic acid recycled, with the acetic acid sent back for re-cracking.

Acetic anhydride is reacted with wood at high pressure. This produces acetylated wood. The by-products are un-reacted anhydride mixed with acetic acid formed in the reaction.

After the reaction, the mix of acetic anhydride and acetic acid by-product must be recycled.

The acetylated wood is washed (typically with steam) to remove residual acetic acid or anhydride and then dried.

No. All general BSW wood products are FSC certified and the company has been a pioneer of the scheme in the UK and Latvia.
Accoya™ is a new product for which we see a great affinity with the ethos of FSC. Chain of Custody for the scheme is currently being established. The target for availability of FSC Accoya™ is first half of 2007.

Unmodified wood has ‘free hydroxyl groups’ that absorb and release water as climatic conditions change, making it prone to expansion and contraction, particularly when used outdoors (windows, doors, cladding, etc), which in turn leads to splitting and rotting.

During the Accoya™ wood production process, the free hydroxyl groups within the wood are changed into acetyl groups and this reduces the ability of the wood’s cell walls to absorb water by approximately 80%, greatly improving the wood’s dimensional stability and resulting in reduced maintenance frequencies for coatings.

In addition, the change in cell structure means that fungi do not recognise Accoya™ as wood and therefore do not attack it. Insects that attempt to eat the wood die of starvation because the modified structure makes it indigestible, so that it is no longer a source of food.

Trial volumes of Accoya™ are currently available and are being used by leading joinery companies in order to evaluate it for use in the above products. Results are positive. Commercial volumes of Accoya™ are targeted for the end of the year.

Virtually all wood preserving treatments today work by impregnating toxic chemicals (such as arsenic, oils, ammonia or metal compounds) into the cell walls of the wood, filling the voids but not changing the underlying chemistry of the wood. This controls unwanted organisms, such as bacteria, viruses and fungi, by creating an inhospitable environment. However, the toxicity of such products has environmental implications, both during the serviceable life of the wood and for its safe disposal. By contrast, Accoya™ wood is non-toxic and 100% recyclable.

The main non-toxic preservative treatment available is a "thermal modification" process which works by breaking down the edible components of the wood. However, the process both discolours and weakens the wood, rendering it unsuitable for many uses. The Accoya™ production process does not weaken the original wood species – in fact, its hardness is slightly improved - nor does it compromise its bending strength.

Accoya™ Timber is modified all the way through, not just at the surface layer like many alternative treatments. This means that users can have absolute confidence in Accoya wood’s durability in a way that has not previously been possible. When Accoya wood is cut or jointed there are no exposed unacetylated surfaces in any dimension. This completely negates the need to apply additional chemical preservatives on-site, as is necessary with unmodified or envelope treated woods.

Accoya™ Timber is modified all the way through, not just at the surface layer like many alternative treatments. This means that users can have absolute confidence in Accoya wood’s durability in a way that has not previously been possible. When Accoya™ wood is cut or jointed there are no exposed surfaes in any dimension. This completely negates the need to apply additional chemical preservatives on-site, as is necessary with unmodified or envelope treated woods.

In contrast to other modification techniques, it is possible to measure the quality of Accoya™ by determining the acetyl content of the wood once it has been modified by measuring and analysing the percentage of acetyl groups present. Using an array of sophisticated and proven analytical techniques, Accoya™ wood’s producers ensure that every batch is of consistent quality and reaches the highest performance standards.

Accoya wood has been shown to deliver performance that exceeds that of even the most durable tropical hardwoods. It is ideal for exterior applications such as doors, window frames, garden decking, facades, cladding and sidings, boat decks and garden furniture where exposure to the elements means that dimensional stability, durability and UV resistance are important.

In Holland, for example, acetylated wood was used as a canal siding and removed after 10 years’ exposure to water without showing any signs of degradation.

Accoya will be exclusively supplied in UK and Ireland by BSW Timber. Titan Wood owns the intellectual property for Accoya™ and licences it to others.

There was little demand for the commercialisation of acetylated wood when there were ample supplies of tropical hardwoods and less stringent legislation governing the use of toxins in wood treatments.

Accoya's technology enables a combined and efficient process which produces the wood and recycles the by-products at a commercially viable cost for the first time.

Accoya™ wood is 100% recyclable and can be disposed of in exactly the same way as unmodified wood. The same also applies to any waste material, such as profiling waste.

No. Acetylated wood can only be glue laminated and finger-jointed after acetylation as the process would damage the glue lines and result in de-lamination.

Yes. Because the acetic anhydride used reacts with water as well as with hydroxyl groups in the wood, the lower the moisture content of the wood, the more efficient and cost effective the process.

Yes. Due to the improved dimensional stability of Accoya™ wood (significantly reduced swelling and shrinking), maintenance of the coating system can be increased to 10 to 15 years (3 to 5 years is the average for unmodified wood under normal circumstances).

Close collaboration with Sikkens, part of the world’s leading paint company Akzo Nobel, has resulted in a package of guarantees for windows and doors, inlcuding 30 years in conjunction with the Sikkens Sentinel Plus Wood Maintenance Protection Programme.

Guarantees have also been developed with Teknos (UK) Ltd.

No. Acetylation uses acetic acid which has a very low PH, meaning that the equipment used must be stainless steel, and the process itself demands special equipment.

Acetylation causes no significant change in the strength of wood. Hardness, however, is increased by up to 10%, unlike thermal modification where strength is typically reduced by 15-25%.

Whereas thermal modification significantly deepens the colour of wood to dark brown, acetylation makes no significant difference to colour.

Accoya™ wood can be machined in the same way as unmodified wood. Because, however, acetylated wood is more dimensionally stable and has lower water uptake than unmodified wood, its gluing parameters are the same as for hardwoods. Most commercially available glues can be used with Accoya™ wood.

Eve Johnson, BSW Timber: 01228 673 365 or the email address accoya@bsw.co.uk