Accoya Wood FAQs

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 90 years.  The process alters the cell structure of wood, improving its technical properties and making it much stronger and more durable.

Unmodified wood contains ‘free hydroxyl groups’ that absorb and release water as weather conditions change. This makes standard wood susceptible to expansion and contraction, particularly when used outdoors for applications such as cladding, window and door frames. The expansion and contraction of wood often leads to splitting and rotting, impacting on the service life of wood.

Hydrogen, oxygen and carbon chemicals (called acetyl groups) are created within wood after the acetylation process, changing the structure of existing free hydroxyl groups (hydrogen and oxygen). Each of these chemicals is present naturally in all woods, with acetyl created independently from acetic acid, i.e. vinegar. The process is ‘green’ meaning that the acetylation process takes effect using nothing that doesn’t occur in wood naturally.

What benefits does Accoya® have over unmodified wood?

During the Accoya® production process, the free hydroxyl groups within wood are changed into acetyl groups which reduces the ability of the wood’s cell walls to absorb water by approximately 80%. This structural change greatly improves the wood’s dimensional stability and results in a stronger, more durable wood while reducing the maintenance frequencies for coatings. 
The change in cell structure also means that the wood is virtually rot and insect-proof. Mould and fungi do not recognise Accoya® as wood and therefore don’t attack, while the modified structure is indigestible to insects.

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. This works to fill the voids within the wood but this doesn’t change the underlying chemistry. The toxicity of such products also have negative environmental implications during the serviceable life of the wood as well as during its disposal.

As an alternative, Accoya alters the wood’s structure to the core, creating an inhospitable environment and helping to control unwanted organisms, such as bacteria, viruses and fungi. The main alternative non-toxic preservative treatment to Accoya’s acetylation is “thermal modification”, a 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 and its bending strength uncompromised. Indeed, no modification process exists which offers the performance benefits and retained physical properties of Accoya®.

Does the process affect only the surface layer of the wood or does it penetrate into the middle of the

Accoya® wood is modified to its core. This means it is unlike any competitor wood products, which tend to receive surface level treatment. Those choosing to buy Accoya® can have absolute confidence in the wood’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.

How can the quality of Accoya® be guaranteed?

Thoroughly tested for dimensional stability, durability, paint retention and in-ground conditions, Accoya is so reliable that for many years it has been – and continues to be – used by scientists as the benchmark against which other treatments and modifications are measured.

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 the percentage of acetyl groups present.

Using an array of analytical techniques, Accoya®’s producers ensure that every batch is of consistent quality and reaches the highest performance standards. With such strong scientific credentials, Accoya is guaranteed for 50 years when used above ground, and 25 year when used for below-ground applications.

How environmentally friendly is Accoya®?

Accoya® wood is non-toxic and 100% recyclable. By significantly enhancing the durability and dimensional stability of fast growing, abundantly available certified wood species, Accoya® wood provides compelling environmental advantages over scarce slow growing hardwoods, woods treated with toxic chemicals, and non-renewable carbon-intensive materials such as plastics, steel and concrete. The environmental impact of Accoya can be assessed at all stages of its life cycle, from cradle to grave.

At the production stage, only abundantly available, and often fast growing source species such as Radiata pine, are used to create Accoya, safeguarding a consistent supply and preventing deforestation of tropical forests. Accoya is made from legally harvested wood from well managed sustainable sources including FSC®, PEFCTM and other regionally certified woods. The Accoya wood manufacturing process is non-toxic and adds nothing to the wood that does not already naturally occur in it. The Accoya production facility meets highest requirements with respect to health, safety and the environment and powered for over 50% by renewable energy.

Accoya remains CO2 negative over the full life cycle; therefore an environmental friendly substitute for tropical hardwood and materials from non-renewable resources. Accoya has acquired several quality certifications (e.g. KOMO, RAL, BBA, WDMA, etc) and is warranted against fungal decay for at least 50 years above ground and 25 years in ground. Outstanding dimensional stability and improved hardness results in lower maintenance frequency (lower costs) and therefore less coating use and waste over the product’s lifetime. Additionally, Accoya’s superior thermal insulation provides energy conservation advantages when used in applications such as window frames and doors.

Accoya wood is fully reusable and recyclable. Reuse is recommended but Accoya may be safely incinerated for bio-energy or composted to close the loop of the carbon cycle. Indeed, in the Cradle to Cradle® philosophy, for which it holds the prestigious Gold-level certification, Accoya wood is understood to be non-toxic and 100% biodegradable.

What applications can Accoya® be used for?

Accoya® offers a superior level of performance to traditional softwoods, often exceeding 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 – all locations where exposure to the elements and dimensional stability and durability are important. In the Netherlands for example, acetylated wood was used as a canal siding and removed after 16 years’ exposure to water without showing any signs of deterioration.

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.

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.

Does Accoya® have different machinability and gluability?

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

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.

Does Accoya® have different paintability?

Yes. Due to the improved dimensional stability of Accoya® wood and the significant reduction in swelling and shrinking, maintenance of coatings can be increased to up to 2 times the normal life of coatings applied to non-modified woods. Extensive tests have shown better coatings adhesion meaning reduced costs in applying coatings in a manufacturing environment.

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.

Does the process affect the colour of the wood?

Acetylation causes no meaningful change to the colour of wood. 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.

What benefits does Accoya® have over Wood Plastic Composite products (WPC)?

Wood Plastic Composites (WPC) are made from a mix of plastic fibres and wood products. Due to their plastic contents, WPC decking boards tend to be more slippery than Accoya decking boards.

Accoya decking boards have been thoroughly tested against a range of competitor products, including WPC, and they are found to have higher slip resistance when used across a range of applications including shower areas, swimming pools, shop entrances, exterior staircases and even public kitchens.

Additionally, recent testing has indicated the thermal gain in Accoya® is substantially less than WPC. This low level of thermal gain, combined with in-situ benefits derived from Accoya®’s dimensional stability, provides decking which is ‘barefoot friendly’. This means it remains flush and splinter-free despite prolonged weather compared to other products.

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