Chris Baraniuk
Technology Reporter
InventWood
Inventwood’s timber is treated to become super-strong
Could your house take a bullet for you?
Clad it with a new type of modified wood, and it might, says Alex Lau, co-founder and executive chairman of InventWood.
The US-based company has developed Superwood – a modified wood it claims is stronger than steel.
During lab tests, a gas gun fired a bullet-like projectile at thin pieces of wood, including an early version of the company’s product.
While the projectile blasted straight through the natural wood, it failed to penetrate the heavily modified version.
Mr Lau suggests that the product could have military applications, such as in battlefield shelters, but admits they “haven’t tried dropping bombs on it”.
In the race to decarbonise construction, materials such as concrete – associated with high greenhouse gas emissions – are coming under ever-greater scrutiny.
Wood-based construction, proponents say, can actually help in the fight against climate change by storing large amounts of carbon long-term.
But natural timber is not always strong enough for certain applications and it can degrade when exposed to moisture or wood-gobbling insects.
That’s where engineered wood products come in. They promise to be significantly stronger and more resilient – reliable enough, even, to form the structural frames of skyscrapers. The construction industry is increasingly pushing wood to new limits.
“You can almost massage the wood so you’re squeezing air and imperfections out,” explains Mr Lau as he describes the process of treating timber with chemicals to remove lignin, a polymer found in wood, and then compressing it extremely firmly to reduce its volume by around 80%.
This has the effect of creating additional hydrogen bonds within the material, adds Mr Lau, significantly strengthening it even though it becomes much thinner than the original timber.
A key advantage, InventWood says, is in retaining the wood’s attractive grain in the finished product.
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Wood is being used to build taller builders like this apartment block in Sweden
InventWood has spent years refining its process – it used to take more than a week. Now, staff can make a piece of Superwood in hours.
The company will use wood from poplar trees initially but Mr Lau says it’s also possible to use bamboo.
“We can grow suitable bamboo feedstock in like three or four years,” he says. “It’s really an efficient way to draw down carbon from the atmosphere.”
There are already a range of engineered and modified wood products on the market. Take glulam, or glue-laminated timber, in which layers of wood with the grain facing in the same direction are glued together to make strong, moisture-resistant beams.
Cross-laminated timber (CLT), meanwhile, involves stacking layers of wood with the grain in alternating directions, to make panels for walls and floors. Like an ultra-tough plywood.
Using CLT instead of concrete to build a community centre could reduce carbon emissions associated with the construction and operation of the building by nearly 10%, a study published in June suggested.
Superwood isn’t designed to compete with these products, says Mr Lau. But it could provide a more aesthetically pleasing, and structurally sound, finishing layer to them, for example. Or, it could function as a durable external cladding.
It’s a “promising” technology, says Morwenna Spear, research fellow at Bangor University’s BioComposites Centre.
Though she points out that, in environments such as the UK, wood that is used externally on buildings must cope with weather that cycles from wet to dry extremely frequently. “I’d want to see some data coming from them about that,” she says.
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In cross-laminated timber the wood is layered at right angles
Other companies are working on different engineered wood products.
Pollmeier in Germany, for example, has BauBuche – a laminated veneer lumber, very thin layers of wood pressed and glued together – made using beech. That’s interesting because beech is not generally considered the first choice for construction.
“By processing it into veneers, Pollmeier found a way to use it much more structurally,” explains Michael Ramage, director of the Centre for Natural Material Innovation at the University of Cambridge.
There’s also 3RT in Australia, which uses thin veneer sheets of low-value trees or “pulp logs”.
It allows them to mimic the structure and density of much more valuable hardwood. The product has recently been used in large window frames and also to make kitchen cabinets, furniture and the treads of internal staircases.
With so many wood products emerging, Dr Spear says that architects and designers today have much more choice in terms of how they use wood in a building.
“It may be that we think of these new products almost as pseudo-species,” she says. “It just increases that palette of options to people.”
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Engineered wood can replace concrete in construction
There are still barriers to wood in construction, though, says Prof Ramage: “Is the mortgage the same rate as a mortgage on a concrete building? Is the insurance the same price?”
He advocates for the wider adoption of wood products chiefly because of their ability to store carbon over many years, though he notes that there are some jobs wood can’t do. “We’re always going to need concrete in the ground for foundations,” he says.
Mr Lau points out that, after the devastating wildfires that hit Los Angeles in January, some people have questioned the wisdom of using wood as a building material. But he insists that Superwood has proved fire-resistant in tests.
Separately, the wood has also survived exposure to wood-eating insects, adds Mr Lau. While it is tougher to work with than natural timber, it can still be sawn in a traditional manner with carbide or diamond-tipped blades.
We shouldn’t forget the importance of recycling old timber amidst the rise of highly engineered wood products, though, says Dr Spear. Researchers in the UK have shown that waste wood from demolished buildings can be repurposed in CLT-style panels.
Plus, you probably already have a significant number of recycled wood products in your own home, demonstrating that novel ways of using wood really have become quite mainstream these days. “So much of our furniture is made… of particle board – a huge proportion of that comes from recycled timber,” says Dr Spear.
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