Construction Corner: ‘Superdense’ wood could revolutionize materials

A homebuilder once told me Canadians are “the greatest stick-builders in the world.”

It’s a good line, and understandable coming from a homebuilder.

After all, most Canadian homes are built primarily of wood.

Wood is probably the oldest building material in the world unless you count rocks and sod. What’s most amazing to me, is that after thousands of years of history, we are still looking for — and finding — new ways to use wood.

In recent years we’ve heard a lot about cross-laminated timber, CLT, and its growing use in highrise construction.

Now comes word of something called superdense wood that could be used to build everything from bridges to cars.

Engineers at the University of Maryland have found a way to make wood more than 10 times stronger and tougher than untreated wood. It is, apparently, stronger even than steel or many titanium alloys.

Liangbing Hu, who led the research team, says this superdense wood is comparable to carbon fiber, “but much less expensive.”

The team’s research results were published recently in the journal Nature.

The researchers developed their superdense wood using a two-step process. First, the wood is chemically treated by boiling it in a solution of sodium hydroxide and sodium sulfite. This breaks down the lignin in the wood. Lignin is a natural polymer, present in the cell walls of many rigid plants. It’s the stuff that keeps the plants stiff.

The second step is to squeeze the wood between metal plates heated to 100 C at a pressure of five megapascals, which is roughly 50 times more than atmospheric pressure.

The chemicals used to process the wood are already widely used in the pulp and paper industry and a great deal is known about them. So the researchers already know they don’t pose any significant pollution concerns says Teng Li, the paper’s co-author.

He says that means this superdense wood could provide an eco-friendly alternative to steels or alloys for constructing buildings or bridges. He says it could also be used to manufacture more lightweight, fuel-efficient cars or trains.

Not only is this new wood as strong as or stronger than steel, it weighs only about a sixth as much and takes 10 times more energy to fracture than natural wood. It can even be bent and moulded at the beginning of the manufacturing process.

There is another advantage, say the researchers. The process works well with just about any wood. That means, says Hu, that “softwoods like pine or balsa, which grow fast…could replace slower growing but denser woods like teak in furniture or buildings.”

Treating wood to improve its mechanical performance is not new. Some attempts date as far back as the 1700s. Wood has been treated with steam, heat or ammonia. It has been cold-rolled to make it stronger.

Many of these efforts enjoyed a degree of success, but none capitalized on wood’s full potential. Very often, the wood would re-expand and lose strength over time.

Huajian Gao, a professor at Brown University who was not involved in the study, says the paper “provides a highly promising route to the design of lightweight, high-performance structural materials, with tremendous potential for a broad range of applications were high-strength and toughness…are desired.”

But none of this means you can expect this superdense wood to be commercially available anytime soon. Many engineering studies remain to be done. As well, removing lignin from a natural plant material often makes that material susceptible to bacterial or fungal infections. No one knows yet whether superdense wood structures would be susceptible.

This new material, if it can be brought to market successfully, plus the growing success of CLT would mean that “stick-building” would go far beyond building homes.

Korky Koroluk is an Ottawa-based freelance writer. Send comments to editor@journalofcommerce.com.