US scientists have created a high-performance structural material from wood that is stronger than steel while six times lighter.
The wood densification technique, described in Nature, has led to the creation of a material that is 12 times stronger than natural wood, as well as 10 times tougher, according to lead author Dr Liangbing Hu, an associate professor of materials science and engineering at the University of Maryland.
“This could be a competitor to steel or even titanium alloys, it is so strong and durable,” Dr Hu said.
“This kind of wood could be used in cars, airplanes, buildings – any application where steel is used.
“It’s also comparable to carbon fibre, but much less expensive.”
The densification process begins by removing a proportion of the wood’s lignin and hemicellulose, and then compressing the wood under mild heat (~66°C) to a fifth of its original size, causing the cellulose fibres to become tightly packed, with any defects like holes or knots crushed together. The study found that the cellulose fibres were pushed so close together that strong hydrogen bonds formed.
Co-lead author Dr Teng Li said the resultant material was both strong and tough, a combination of properties not typically found in nature.
“It is as strong as steel, but six times lighter,” he said.
“It takes 10 times more energy to fracture than natural wood. It can even be bent and moulded at the beginning of the process.”
Testing included shooting bullet-like projectiles at the material. Whereas bullets went straight through natural wood, the densified wood stopped the bullets in their tracks.
Dr Hu said the material breakthrough could lead to more sustainable species of wood becoming preferred.
“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,” Dr Hu said.
Environmental benefits could also be realised if the material were to replace carbon-intensive steel.
“Our processed wood has a specific strength higher than that of most structural metals and alloys, making it a low-cost, high-performance, lightweight alternative,” the paper, Processing bulk natural wood into a high-performance structural material, said.
The results of the study have been welcomed by materials scientists from across the globe.
Brown University professor Huajian Gao said there was “tremendous potential” for a broad range of applications.
“It is particularly exciting to note that the method is versatile for various species of wood and fairly easy to implement,” he said.
Harvard University mechanics and materials professor Zhigang Suo said that the paper “inspires imagination” due to the abundance of wood and other cellulose-rich plants.
Professor Orlando Rojas from Finland’s Aalto University said he was particularly impressed by the increase in strength and toughness, “two properties that usually offset each other”.
Research from the university has also created a transparent wood offering better energy efficiency than glass.