Wood, one of the cheapest and most widely used construction materials humanity has ever employed, just had its range of uses expanded: researchers at Stockholm's KTH Royal Institute of Technology developed a method that makes wood transparent. The method is suitable for mass production, making it even more attractive.
Optically transparent wood is not a new thing, says Lars Berglund, professor at the Wallenberg Wood Science Center at KTH. But it's usually only been done in microscopic samples intended for wood anatomy studies. Their new process would allow for transparent wood production and usage on a much larger scale than anything ever before attempted.
"Wood is by far the most used bio-based material in buildings. It's attractive that the material comes from renewable sources. It also offers excellent mechanical properties, including strength, toughness, low density and low thermal conductivity," Berglund says.
"Transparent wood is a good material for solar cells, since it's a low-cost, readily available and renewable resource. This becomes particularly important in covering large surfaces with solar cells."
These transparent panels can also be employed as windows, or used to create semitransparent facades to allow light in while also maintaining privacy.
Optically transparent wood is actually a type of wood veneer from which lignin, a structurally-important component in the cellular walls of trees, is chemically removed. The resulting porous veneer substrate is saturated with a transparent polymer and the optical properties of the two materials are then matched.
"When the lignin is removed, the wood becomes beautifully white. But because wood isn't not naturally transparent, we achieve that effect with some nanoscale tailoring," Berglund adds.
"No one has previously considered the possibility of creating larger transparent structures for use as solar cells and in buildings."
Wood is a renewable resource, but that doesn't mean we're doing it substantially -- we have to grow and harvest it accordingly, not by logging away, chainsaws blazing, at the forests around us. The KTH team is now working on ways to improve the transparency of their material and on scaling-up their production method.
"We also intend to work further with different types of wood," Berglund concludes.
The full paper, titled "Optically Transparent Wood from a Nanoporous Cellulosic Template: Combining Functional and Structural Performance" was published online in the journal Biomacromolecules and can be read here.