Pickled wood: Chemistry transforms sustainably-grown pine into durable lumber

Posted: March 21, 2025

What do you get when you combine chemistry from old photographic film manufacturing with timber from fast-growing New Zealand pine forests? Non-toxic, sustainable, fast-growing lumber that’s durable, insect-resistant, and so impervious to rot and decay that it’s warrantied to last 25 years under water—and double that installed above ground.

The development of this Accoya wood is a story of two companies sharing knowledge to create a product that satisfies new demand and opens up new revenue streams for both of them.

For decades, Eastman Chemicals developed special expertise in producing acetic anhydride, a main component in its famous Kodak photographic film. Its Kingsport, Tennessee facility has been working with the chemical—essentially highly concentrated vinegar—for 100 years

Meanwhile, Accsys Technologies, in the UK, had been trying to solve a problem for the lumber industry. Most wood products come either from softwood or hardwood trees. Softwoods, like pine, are fast-growing and inexpensive to grow sustainably, but are vulnerable to warping and rotting. Hardwoods, like oak or teak, are much more durable, but are generally slow-growing and expensive and time-consuming to grow and harvest sustainably. The ideal commercial timber would grow quickly, cheaply and sustainably, like pine, but have the durability and water-resistance of oak and tropical hardwoods.

Other companies had tried creating such a wood by impregnating softwood lumber with various chemicals to make it more water-resistant, but this approach never gave softwoods the same durability as hardwoods, and left chemicals in the wood that could leach out over time. Accsys took a different approach. Instead of just adding chemicals into the wood, the company developed a process to chemically modify the wood itself on a molecular level using acetic anhydride—the same chemical Eastman had used for decades to make photographic film. This technique—called acetylation—essentially pickles softwood, making it even more durable than hardwoods.

Chemists have known how to create small batches of acetylated wood for nearly 100 years, but no one had figured out a way to manufacture it commercially at scale until Accsys started refining the process in the early 2000s.

What is acetylated wood? 

Wood has a large number of molecular structures called free hydroxyls. In water or moist air, water molecules bind to these hydroxyls in the wood, causing the wood to swell, change shape, and eventually rot. Soaking wood in acetic anhydride causes molecules called acetyls to bind to those free hydroxyls, changing their molecular composition—and making it impossible for water to bind to them.

Once the acetic anhydride transfers its acetyl groups to the wood’s free hydroxyls, the excess acetic anhydride and water drains away to be reused, and the wood is left free of exogenous chemicals.

The molecular changes to the wood’s structure make it more durable and dimensionally stable than even high-quality hardwoods. It’s highly resistant to warping, rot and decay. And because it’s very difficult for it to absorb water, it’s resistant to fungus and mold growth as well as to insect attacks.

Acetylation slows down decay caused by UV radiation and pollution but doesn’t completely stop it. Photochemical processes along with simple physical wear will eventually degrade the wood, but much more slowly than untreated wood. Accoya warranties its acetylated lumber for 25 years installed in water and 50 years above ground—about twice the lifespan you might expect from standard pressure-treated lumber—and it expects its lifespan to go beyond the warranty to 60-90 years.

Producing acetylated wood commercially

Accsys opened its first commercial acetylated wood plant in Arnhem, the Netherlands in 2007. It’s since expanded and refined its processes in Europe, and in September of 2024, teamed up with Eastman in a joint venture to open a new North American plant in Kingsport, Tennessee. The plant takes advantage of Eastman’s adjacent acetic anhydride facility and recycles the chemical in a closed loop between the two facilities.

The new production plant is an object lesson of companies sharing expertise to create a more sustainable, circular economy than they could working alone. The plant sources its raw timber primarily from sustainably managed FSC-certified radiata pine forests in New Zealand, which replenish in less than thirty years. Because Accoya can expect to last 60-90 years when installed above ground, the company can create new product at at least twice the rate at which it gets used up. And because acetylated wood doesn’t contain any exogenous chemicals, it can easily be recycled just like any natural forest product at the end of its life—though it will take longer for it to biodegrade.

By coordinating New Zealand timber, UK innovation, and American chemical expertise, the world has a more sustainable supply of basic building materials.