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Green Architecture & Building Products



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Material or Product

Accoya Wood

Source

Accoya® wood can be used to replace traditional construction materials such as steel. Accoya® is a high technology wood, created from sustainably sourced softwood, that matches or exceeds the durability, stability and beauty of the very best tropical hardwoods.

The Accoya® wood production process takes sustainably-sourced, fast growing softwood and, in a non-toxic process that ‘enables nature’, creates a new durable, stable and beautiful product - that has the very best environmental credentials.

A new world of high performance, sustainable, low maintenance products - including windows, doors, decking, cladding and glulam structural beams - is opened up by Accoya® wood. The exceptional properties of durability, stability, strength and beauty have even led to Accoya® wood being used as the main construction material in a heavy traffic road bridge with a highly original design.

Accoya® - is helping to protect the world’s precious hardwood resources and is guaranteed for 50 years in exterior use and 25 years when used in the ground. This long life also provides an added benefit - helping to reduce carbon emissions.

Frequently Asked Questions

1. How is Accoya® wood made?

The technology behind Accoya® is based on wood acetylation, a process that has been studied by scientists for more than 75 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 (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.

2. What benefits does Accoya® have over unmodified wood?

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® 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.

3. How does Accoya® differ from wood that has been impregnated or modified in other ways?

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 – in fact, its hardness is slightly improved - nor does it compromise its bending strength. Indeed, no modification process exists which offers the performance benefits and retained physical properties of Accoya®.

4. Does the process affect only the surface layer of the wood or does it penetrate into the middle of the board?

Accoya® wood 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®’s durability in a way that has not previously been possible. When Accoya® 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.

5. How can the quality of Accoya® be guaranteed?

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®’s producers ensure that every batch is of consistent quality and reaches the highest performance standards.

6. What applications may Accoya® be used for?

Accoya® 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, façades, 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.

7. Can Accoya® be used in marine applications?

Yes, Accoya® wood is ideal for boat decks and trimmings and freshwater applications, such as canal sidings. Due to its lack of toxicity, however, Accoya® is not suitable for underwater use in a salt water environment.

8. Who sells Accoya®?

Please click here for information about Accoya® suppliers.

9. Why has no-one commercialised this process before?

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.

Accsys Technologies has developed a patented, proprietary process technology that, for the very first time, enables a combined and efficient process which produces the wood and recycles the by-products at a commercially viable cost.

10. Does wood need to be kiln dried before acetylation?

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.

11. How is Accoya® disposed of at the end of its life?

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.

12. Does Accoya® have different machinability and gluability?

Accoya® 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.

13. Can acetylated wood be glue laminated or finger-jointed?

Yes, acetylated wood can be glue laminated and finger-jointed. Wood cannot, however, be acetylated after it has been laminated or finger-jointed as the process would damage glue lines and result in de-lamination.

14. Does Accoya® have different paintability?

Yes. Due to the improved dimensional stability of Accoya® wood (significantly reduced swelling and shrinking), maintenance of the coating system can be increased to 3 to 5 times normal life. Extensive tests have shown better coatings adhesion and reduced costs in applying coatings in a manufacturing environment. The company is working closely with coatings manufacturers, including Teknos, Sherwin Williams and Guard Industrie, to test their systems used in conjunction with Accoya®.

15. Does the strength of the wood change during the process?

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%. This differs from most other treatments and modifications which typically adversely affect strength and brittleness.

16. Does the process affect the colour of the wood?

Acetylation causes no meaningful change to the colour of the source species. There is a slight bleaching of red colours and a slight darkening of the outer surface of other wood. This is, however, insignificant compared to other processes such as thermal modification which deepens the colour of wood to dark brown.

17. Can acetylation be achieved using standard vacuum / pressure impregnation equipment?

No. Acetylation requires specialized equipment.

 

Accoya Wood

Accoya® wood can be used to replace traditional construction materials such as steel. It was used for a unique heavy traffic road bridge at Sneek in the Netherlands. The bridge, measuring 20 metres high by 40 metres long has a cycle lane and two traffic lanes for road traffic up to 65 tonnes. Accoya® was laminated into large sections measuring 1080 x 1400 mm to create this innovative structure. ©2011 Accoya