Boiling and smushing blocks of wood can make them as strong as steel
Wood hasn’t been a big component of car design since 1912. We’ve long been accustomed to vehicles made of steel, aluminum and even plastics for their balance of strength, weight and cost, but this may change in the near future. Recent experiments with treated wood suggest that trees may have more potential than most of us would expect. As a result, we may soon be looking to wood plates as a lighter alternative to steel for our cars, trains and even infrastructure.
The strength of cellulose
The key to wood’s strength is cellulose. The natural polymer is generally structured as long, parallel fibers that not only provide strength in a tree, but also help funnel water through the plant. Researchers are looking to really maximize cellulose’s potential, starting by stripping out other components that naturally occur in a piece of wood. The latest technique involves boiling the wood for seven hours in a water-based solution of sodium hydroxide and sodium sulfite, then pressing it between heated metal plates for 24 hours. This process first removes a large portion of a a component called lignin, then eliminates the resulting gaps in the wood by smushing everything together. It’s theorized that with less lignin in the wood, the remaining cellulose can interlock, or at least form hydrogen bonds that significantly strengthen the resulting material.
The result is a remarkable block of wood with greater strength, density and relatively little weight. A block of boiled, squashed wood was only one-fifth its original width, making it three-times its original density. It was then measured as being 11.5 times stronger than before, able to stop a metal pellet moving at 67 miles-per-hour. That wouldn’t make it bulletproof, but it would be comparable to the steel found in car, just with a lot less weight to lug around.
Priced for mass production?
Impressively, the initial critiques of this engineered wood aren’t that it’s improbable, but that it should probably be even better. Other techniques focus more on steaming, heating and applying resins to wood, boosting strength almost as much as the procedure described above. Any trade-off in strength is likely made up in cost, particularly if the seven-hour boiling phase is eliminated from the process. Even if the sodium hydroxide and sodium sulfite do prove to be too expensive for mass production, the study’s authors are still happy with the knowledge gained from their work. While multiple approaches looked to remove lignin from the cellulose, we now know that leaving some lignin in wood is more effective than removing it all. As these materials continue to get refined, we’re hopefully a step closer to growing, rather than mining, the materials needed for our next car.
Source: Crushed wood is stronger than steel by Mark Zastrow, Nature