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Engineers at the University of Maryland have discovered a natural way to make a substance stronger than the titanium alloys that are commonly used in the home. By crushing together and treating wood, they have created a way to make it more than ten times stronger and more durable, and an inexpensive alternative to carbon fibers and metal alloys. The research can be found in the recently published Nature paper.
This new way to treat wood makes it twelve times stronger than natural wood and ten times tougher.
Professor Liangbing Hu, Associate Professor of Materials Science and Engineering - University of Maryland
The combination of being both tough and strong are mechanical properties that are rare to find together in nature. “It is as strong as steel, but six times lighter. It takes ten times more energy to fracture than natural wood. It can even be bent and molded at the beginning of the process,” explained Professor Teng Li, Professor of mechanical engineering at the University of Maryland.
The first stage of the process is striping the wood of its’ lignin, which gives wood its’ brown color and rigid structure. The wood mixture is then compressed under a 150 F heat, causing the cellulose fibers to become tightly packed and defects to be are crushed together. The wood was then further treated with a special coat of paint. When the fibers are pressed together tightly, they form strong hydrogen bonds, giving the wood an increase in strength, even though the compression makes the wood five times thinner than its original size.
This kind of wood could be used in cars, airplanes, buildings and any application where steel is used.
Professor Liangbing Hu, Associate Professor of Materials Science and Engineering - University of Maryland
The strength of the wood was tested by shooting bullet-like projectiles at both the new wood, and natural wood, and comparing the results. While the projectile blew straight through the natural wood, the new fully treated wood managed to stop the projectile partway through.
The crushed wood has piqued the interest of other research groups too, with both Professors at Brown and Harvard University, and other universities around the world talking about the endless possibilities. Huajian Gao, a professor at Brown University, says “The paper provides a highly promising route to the design of lightweight, high performance, structural materials. There is tremendous potential for a broad range of applications where high strength, large toughness, and superior ballistic resistance are desired.”
The limiting concentration of lignin to maximize the mechanical properties of the newly formed stronger than steel wood is an observation that has excited Professor Orlando J. Rojas from Aalto University in Finland. “Too little or too much removal of lignin lowers the strength, compared to a maximum value achieved at intermediate or partial lignin removal. This reveals a subtle balance between the hydrogen bonding, and the adhesion imparted by such a polyphenolic compound,” explains Professor Rojos. The fact that that wood densification has led to both increased strength and toughness, which are two properties that that normally offset each other, has also delighted scientists.
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.
Professor Liangbing Hu, Associate Professor of Materials Science and Engineering - University of Maryland
Professor Hu’s research group also explored the possibilities of how wood can be naturally used in nanotechnology. Nanocellulose and its relating materials is an important area of study for Hu’s group. The wooden nanotechnology research has been used for clear papers that could replace plastic, photonic paper to improved solar cell efficiency, wooden batteries, and can even be used as transparent wood for energy efficient buildings. The research shows there are many possibilities for future, natural uses of wood that are left to be explored.
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