Titanium alloys are some of the strongest materials we can build with, but they can be expensive. Now, researchers at the University of Maryland (UMD) have come up with a way to make an alternative that literally grows on trees. Using a new "densification" process, the team managed to make "super wood" that has the strength and toughness of steel.
Wood is already a pretty versatile material, but the leader of the UMD team, Liangbing Hu, has been working to give it an even longer list of uses. Over the last few years, Hu has developed transparent wood, burnt-wood water filters, and sodium-ion batteries based on wood and leaves.
The new "super wood" gets its super strength through a two-step process developed by Hu's team. First, the researchers boil samples of wood in a watery mixture of sodium hydroxide and sodium sulfite, which works to partially remove lignin and hemicellulose from the material. Then, the treated wood is hot-pressed, which causes the cell walls to collapse and forms highly-aligned cellulose nanofibers. The end result is completely densified wood, which is much stronger than the natural stuff.
"This new way to treat wood makes it 12 times stronger than natural wood and 10 times tougher," says Hu. "This could be a competitor to steel or even titanium alloys, it is so strong and durable. It's also comparable to carbon fiber, but much less expensive."
One of the experiments the team ran to test the material was to fire projectiles at it. While they blasted right through the natural wood, the super wood managed to stop the projectiles partway through.
The researchers say that the process can be applied to many different kinds of wood, and can be scaled to treat bulk amounts of the material at once. At the beginning of the process, the wood can be bent and molded into the desired shape.
The new material could allow wood to step in as a cheaper, lighter and more renewable alternative to steels and titanium alloys. And it could allow softer woods to compete with their sturdier but slower-growing cousins.
"This kind of wood could be used in cars, airplanes, buildings – any application where steel is used," says Hu. "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."
The research was published in the journal Nature.