A material made from recycled wood is five times stronger than natural wood and can be made from any timber by-product, including shavings and sawdust.
Wood is a hugely versatile material, but millions of tonnes go into landfill each year. To build a truly circular economy, wood will need to be re-used on a grander scale.
Orlando Rojas at the University of British Columbia, Canada, and his colleagues have invented a process that dissolves lignin, a glue-like component inside plant cell walls, and exposes cellulose myofibrils, which are tiny fibers also found in the plant cell wall. The method involves a solvent called dimethyl, used in the presence of lithium chloride.
When two pieces of wood treated in this way are brought together, the myofibrils bind to create what the researchers call a “healed” piece of wood. Although this no longer looks like natural wood, it has better mechanical properties. Tests show it is more resistant to breaking than stainless steel or titanium alloys.
“We get a mechanical strength that supersedes the strength of the original material,” says Rojas. It works because we use the inherent properties of cellulose, which is a material that binds together very strongly by something called hydrogen bonding.
Not only can wood treated this way be re-used to create new objects, but the treatment process can be performed repeatedly on the same pieces of wood to extend their working lifetimes.
“This is a really elegant way to heal wood, using a common cellulose solvent, recovering and enhancing the mechanical properties of nature’s wonder material,” says Steve Eichhorn at the University of Bristol, UK. The approach is evidently scalable, and therein lies the challenge to take this technology to the next level.
Rojas and his team didn’t examine how much their method would cost if scaled up to an industrial level, but all the techniques used are well-established. “The processes that we use here are very typical in wood processing,” says Rojas. So scalability is not an issue. Transparent wood just got even better, moving us a step closer to windows that are far better insulators than traditional glass ones.
The standard process for making wood transparent typically involves soaking the wood in a vat of sodium chlorite – a chemical compound used in some bleaches and toothpastes – to remove a structural component of the wood called lignin. However, this takes a lot of chemicals, produces liquid waste that is tough to recycle and can weaken the wood.
Jingling He at the University of Maryland and his colleagues came up with a method that modifies the lignin instead of removing it completely. It is quicker and uses fewer materials than the standard lignin-removal process, and also leaves the wood strong. The researchers’ method stems from the recent discovery that lignin can be made transparent by removing only the parts of its molecules that give them their color. They brushed hydrogen peroxide, which is often used as a disinfectant, over the surface of the wood and then left it under a UV lamp designed to simulate natural sunlight. After soaking the wood in ethanol to remove any remaining gunk, they filled the pores in the wood with clear epoxy, a step that is also part of making lignin-free transparent wood.
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