With an increased industry focus on sustainability and product performance, wood continues to be the building material of choice for durability, stability, and eco-consciousness. No other resource captures a unique warmth and beauty while providing the high-performance and adaptability sought after by architects and builders.

While the benefits of wood as a building material far outweigh the cons, natural wood is susceptible to vulnerabilities like moisture, rot, and decay. However, by modifying the wood, these vulnerabilities can be offset to enhance the durability and dimensional stability of wood without compromising its natural beauty or environmental friendliness.

What is Modified Wood?

Wood modification involves the application of a chemical, physical, or biological agent upon the wood to alter the cellular structure and enhance performance. Modified wood is stronger and more resistant to decay through reduced water absorption and expansion/contraction. There are a variety of modification techniques, including thermal modification, chemical modification, and furfurylation, which is a combination of both thermal and chemical modification. This article will focus on the benefits of chemical modification – or acetylation – a chemical reaction that has been used for over 100 years and turns softwood into hardwood by preventing the cells in the wood from absorbing water.

Acetylation: Chemical Modification of Wood

Acetylation is the most established, proven, and effective form of chemical wood modification. Unlike pressure treatment, which forces chemical preservatives into the fibers of the wood in a pressure chamber, acetylation chemically alters the biological structure of the wood.

The Acetylation Process

During the acetylation process, the wood is subjected to an organic reaction with acetic anhydride – a clear, colorless liquid with a strong scent of vinegar (essential, vinegar without the water.) Acetic anhydride reacts to a part of the wood’s cellular structure called free hydroxyls, which allow the absorption and release of water in and out of the wood. The acetylation process converts free hydroxyls into acetyl groups, which water can no longer bind to, significantly reducing the ability of the wood to absorb and retain water.

Wood Selection

Accoya® Wood is the leading example of chemically modified wood, utilizing a cutting edge, proprietary acetylation process. The acetylation of Accoya yields exceptional results for demanding exterior applications like cladding, decking, and more. The processing of producing Accoya begins by responsibly sourcing radiata pine, a high-yield, fast-growing softwood species. Accoya wood is FSC®-Certified, protecting local biodiversity and habitats through a sustainable timber supply chain.

Acetylation Reaction

Once sourced and milled, the wood is subjected to a chemical reaction with acetic anhydride, which occurs in a high-temperature, high-pressure environment, typically around 120° Celsius (248° Fahrenheit). During this phase, the hydroxyl groups (-OH) on large molecules such as lignin and hemicellulose in the plant cell wall react wiht the acetic anhydride and are replaced by acetyl groups (-COCH₃).

Post-Reaction Processing

After the acetylation reaction, the wood undergoes washing and drying to remove residual chemicals and by-products; the finished product is completely non-toxic and certified safe for humans, animals, and the environment.

The resulting acetic acid from the reaction is recovered and purified through a distillation process, which is then recycled back into the acetylation process, effectively regenerating acetic anhydride. This closed-loop system not only reduces the consumption of raw materials, but minimizes the environmental impact associated with the production and disposal of chemicals.

Benefits of Accoya Acetylated Wood

Accoya wood offers many performance, environmental, and aesthetic benefits that make it an excellent alternative to untreated or pressure-treated wood.

High Performance

• Compared to untreated wood, swelling and shrinkage in acetylated wood is reduced by 70%-80%. Its dimensional stability allows it to maintain its shape and tight joints in varying humidity and weather conditions. Accoya is highly-proven, having been tested in various environments and real-world conditions, making it an ideal choice for even the most extreme climates.
• Accoya wood is exceptionally durable; its durability, or rot resistance, is Class 1, matching and exceeding the performance of nature’s most durable wood like oak and teak.
• Accoya wood is backed by a 50 year above ground warranty, and 25 years in ground or freshwater.

Sustainability

• Accoya offers much lower lifecycle carbon emissions compared to non-renewable building materials. The acetylation process significantly increases the durability and stability of raw wood, prolonging its useful life and keeping the carbon locked in for longer.
• Accoya wood is Forest Stewardship Council® (FSC®) certified, Cradle to Cradle Gold Certified, and the only construction material in the world to achieve C2C Platinum certification for Material Health.
• Unlike other materials like PVC and plastic composites, modified wood is 100% recyclable. Accoya wood is nontoxic, safe for the environment, and sustainably sourced from fast-growing forests.

Aesthetics

• Visually, acetylated wood is just like any other wood. It maintains the natural beauty and character of unmodified wood with the added benefit of low maintenance.
• Accoya wood is ideal for a variety of textures and finishes, and weathers to a natural silver-gray if left untreated. reSAWN TIMBER co. uses proprietary finishing processes that are developed in-house. These techniques allow for:
  • Deeper penetration of finishes into the wood for enhanced durability and visual richness.
  • Consistent results across product lines due to controlled processes.
  • Customizability, allowing finishes to be tailored to specific design needs or environmental conditions.
• For those seeking a more enhanced, textured appearance and dramatic aesthetic, Shou Sugi Ban Accoya – offered by reSAWN – is a striking solution. This award-winning charring technique not only enhances exterior durability, but adds depth and richness to the wood’s appearance. The dense outer char layer develops into a uniquely weathered aesthetic over time for timeless elegance.

Acetylated wood is transforming how wood is used in a variety of applications and demanding environments, offering a smart and sustainable alternative to tropical hardwoods and synthetic materials. As the industry prioritizes sustainability, superior performance, and aesthetics, reSAWN TIMBER co., continues to craft innovative, high-performance products with Accoya wood to meet the exacting needs of any project.

Our modified wood solutions are developed in-house with proprietary finishing techniques and undergo a rigorous research and development process to ensure unmatched performance and aesthetics. We provide comprehensive technical insights and support throughout the project lifecycle to empower architects, builders, and contractors to make informed decisions and achieve desired project results.

Contact Us to find out how you can integrate reSAWN TIMBER co.’s Accoya products into your upcoming project.