Wood treated with new method could replace steel in aeroplanes, cars and buildings
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Engineers based at the University of Maryland have developed a method for rendering wood as strong as steel and titanium alloys.
Natural wood remains one of the most popular materials for building and furniture construction, although it lacks the strength and toughness necessary to be used for more advanced works of engineering. Treating wood with steam, heat, ammonia or cold rolling followed by densification can enhance its properties.
However, this treated wood can still expand and weaken, particularly in humid environments.
Now, a group of engineers based at the University of Maryland have developed a two-step process for treating wood to render it as strong as steel and titanium alloys, while remaining far lighter and cheaper than these alloys.
Through this treatment, lignin - polymers which give plant cell walls their rigidity - and hemicellulose - another component of plant cell walls - are partially removed as the wood is boiled in chemicals. The wood is then hot pressed, entirely collapsing the rigid cell walls and leading to total densification.
According to the researchers, writing in Nature, this approach is “universally effective” for various types of wood.
The researchers compared the mechanical properties of the treated wood with those of natural wood by firing projectiles at it. While the natural wood could not withstand the projectiles, the treated wood stopped the projectiles in their paths.
The researchers found that this ‘super wood’ is just as strong as steel, but six times lighter. It takes 10 times more energy to fracture than natural wood. Unusually, for a wood, it can be bent and moulded into shape at the beginning of the treatment.
“This new way to treat wood makes it 12 times stronger than natural wood and 10 times tougher,” said Professor Liangbing Hu, the University of Maryland materials engineer who led the study. “This could be a competitor to steel or even titanium alloys, it is so strong and durable. It’s also comparable to carbon fibre, but much less expensive.”
Strength (the ability to support a load without deforming or failing) and toughness (the ability to absorb energy without fracturing) is a rare combination to find in natural materials.
“Soft woods like pine or balsa, which grow fast and are more environmentally friendly, could replace slower-growing but denser woods like teak in furniture or buildings,” said Hu. “This kind of wood could be used in cars, [aeroplanes], buildings – any application where steel is used.”