Scientists Discover A Way To Make Wood As Hard As Steel

Stephen Moehle/Shutterstock

Madison Dapcevich 08 Feb 2018, 12:27

Get your mind out of the gutter. We’re talking about real wood – you know, from trees.

This super-hard wood is made by modifying the porous structure of natural wood using a chemical bath and hot press.

Wood is comprised of cells made of three substances: cellulose (50 percent), lignin (around 20 percent depending on the wood), and hemicellulose (the remainder).

Boiling different types of wood in a sodium hydroxide and sodium sulfite solution for seven hours left starchy cellulose mostly intact but removed surrounding lignin (a polymer that binds cellulose), creating more space. Then, researchers pressed these wood blocks “like a panini sandwich” for a day at a temperature of 100°C (212°F) and a pressure of five megapascals (50 times that of sea-level atmosphere) to squish the cellulose tubes (nanofibers) together until those cells interlocked.

“It’s a new class of materials with great potential,” said co-author Li Teng, a mechanics specialist at the University of Maryland in College Park, in a statement. The research is published in Nature

The result: a wooden plane one-fifth the thickness, 11.5 times stronger, and three times the density of natural wood.

This ultra-compact wood is as strong as steel and researchers tested it the same way they test military vehicles: by shooting stainless steel pellets from an air gun traveling about 30 meters (98 feet) per second.

The “bullets" easily broke through a typical wood plan but got lodged in the denser wood. 

They found it isn’t necessarily strong enough to protect against oncoming shelling, but researchers say they hope the lightweight wood alternative could be used to replace steel in construction and vehicle manufacturing.

In 2010, the total emissions from steel production were 2,500 million tonnes (2,750 million tons). That number is projected to rise to 2,800 million tonnes (3,000 million tons) by 2050. 

Plans to cut steel-related emissions are already underway. China – the world’s largest producer of steel – intends to reduce 150 million tonnes (165 million tons) of steel-production capacity by 2020.

Yet world crude steel output increased by 5.3 percent in 2017

Experts say emissions caused by steel production need to be reduced with more accurate and diversified building products.

Previous efforts to densify wood go back to the 1940s and some researchers say Teng’s improvements are underwhelming.

Fred Kamke with Oregon State University says other techniques, like steaming the wood before treatment and treating it with resins, achieves much of the same affect.

“These other methods are probably much less expensive than a seven-hour boil in a caustic solution,” he told Nature.

German plant biomechanics researcher Michaela Eder added that compressing wood to increase density should naturally improve strength, but it’s unclear how this new method contributed.

However, the researchers say the chemicals used in the process don’t pose any significant pollution concerns and hope the strengthened wood could be a more eco-friendly and sustainable alternative.

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