AccoyaThe natural beauty and versatility of wood are fundamental to its universal popularity. When properties such as high strength, light weight and good insulation are required, wood becomes the ideal choice for many applications. Unfortunately, these compelling attributes are offset by the susceptibility of many wood species to deterioration, particularly when used outdoors.

Historically, the use of inherently durable tropical hardwoods and the application of toxic chemicals to temperate climate woods have provided partial solutions to this shortcoming. Metal salts treatments, while enhancing durability, do not improve wood’s dimensional stability; plus, they create a disposal problem. If an alternative existed which offered all of the “wood is good” characteristics, was sourced from sustainable forests, had zero toxicity and provided dimensional stability and durability that exceeded even the best tropical woods, a perfect material would have been found.

Accoya® is a “new wood species”, whose performance credentials have been extensively researched and repeatedly demonstrated. Accoya® wood has properties that match those of the best tropical hardwoods, yet is manufactured using a non-toxic treatment and wood from sustainable sources. In fact, it may seem too good to be true… but Accoya® really exists.

An extraordinary new wood species

Imagine a wood that’s perfect for outdoor use, with the performance of the best tropical hardwoods and much more:

Class 1 durability – the best available
Outstanding dimensional stability which dramatically improves coatings adhesion and product performance

Lasting for 50 years above ground and 25 years in-ground Retained natural strength and beauty, plus increased hardness Consistent supply from certified, sustainably managed forests Environmental compatibility – non-toxic, 100% recyclable and naturally renewable Consistent, measurable quality all the way through the wood, not just at the surface

Accoya® wood is the result of more than 75 years research and development that have brought together a long-established and extensively researched wood modification technique, acetylation, and leading-edge technology to create and make this extraordinary “new wood species” commercially available for the first time.

Accoya® wood is set to become the material of choice for exterior applications and can be used for virtually anything, from windows to doors, decking to siding and even for applications which are presently only feasible with non-sustainable materials.

Accoya® wood is modified all the way through, not just at the surface layer like many alternative treatments. This modification technique has two key advantages:

Performance through and through

1. Users of Accoya® can have absolute confidence in the wood’s durability in a way that has not previously been possible. Accoya® wood’s durability is validated in a laboratory after the process has taken place. 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 possible performance standards.

2. When Accoya® wood is cut or jointed there are no exposed nonacetylated 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.


Dimensional stability
Swelling and shrinkage reduced by 75% or more doors and windows open effortlessly year round paints and varnishes last 3 or 4 times longer, greatly reducing maintenance costs

Class 1 durability
The most durable wood possible more durable than teak perfect for outdoor use

Barrier to insect and fungal decay
Accoya® wood is indigestible to insects and micro-organisms and is therefore not recognized as a food source durability to wood destroying fungi is dramatically increased Accoya® wood is virtually rot-proof

Accoya® wood is easy to work with and creates no challenges for product manufacturers and end users

Accoya® wood is non-toxic, protecting the environment from the harmful effects of treatment poisons leaching into the earth Accoya® wood may be safely reused and recycled

Resistance to UV degradation
Accoya® wood has superior resistance to the effects of UV exposure, meaning that the wood’s natural appearance is retained for longer Accoya® wood is the ultimate substrate

Strong and beautiful as nature intended
The process does not compromise the wood’s strength or natural beauty hardness is increased Accoya®wood’s high strength toweight ratiomakes it suitable for challenging external applications, such as traffic bridges

Naturally Insulating
Accoya® wood has reduced thermal conductivity Accoya® wood is ideal for windows and siding, where energy conservation is important

The Accoya® process under the microscope

Wood acetylation is a process that has been studied by scientists around the world for more than 75 years. This method of improving wood has been proven to deliver such superior performance that it has long been used as the “gold standard” against which other methods are measured. The Accoya® wood production process combines this work with years of proprietary research and investment to deliver consistent commercial-scale results.

Accoya chemistryThe physical properties of any material are determined by its chemical structure. Wood contains an abundance of chemical groups called “free hydroxyls”. Free hydroxyl groups absorb and release water according to changes in the climatic conditions to which the wood is exposed. This is the main reason why wood swells and shrinks. It is also believed that the digestion of wood by enzymes initiates at the free hydroxyl sites – which is one of the principal reasons why wood is prone to decay.

Acetylation effectively changes the free hydroxyls within the wood into acetyl groups. This is done by reacting the wood with acetic anhydride, which comes from acetic acid (known as vinegar when in its dilute form). When the free hydroxyl group is transformed to an acetyl group, the ability of the wood to absorb water is greatly reduced, rendering the wood more dimensionally stable and, because it is no longer digestible, extremely durable.

Acetyl groups, which are simply comprised of oxygen, hydrogen and carbon, are already naturally present in all wood species – as well as in humans and other mammals. This means that the manufacturing process adds nothing to the wood that does not already naturally occur within it. The end product, Accoya® wood, does not add toxins to the environment. Incidentally, the only by-products from the manufacture of acetic anhydride are a small amount of valuable fertilizer and trace amounts of acetic acid, which can be reused.

The effect of altering the wood’s chemical structure, as opposed to merely altering its chemical content, is essentially to create a “new species” of wood that is modified right through the cross section. By contrast, other comparable treatments merely insert chemicals (such as oils, ammonia or metal compounds) to the wood, improving durability but not dimensional stability.


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Source: “Accoya – the strength within” brochure

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