Transparent wood holds great promise for use in energy-efficient buildings. Researchers at the University of Maryland have developed a new way to make it, and the method they used is surprisingly simple. With it, perhaps energy-efficient windows will be introduced.
Scientists have been working on making wood transparent for some time now. Such transparent wood is a new option for building houses, mainly because wood is stronger and lighter than glass. If hit with a stone, for example, wood will not break as easily as glass. However, because of the way it is produced, transparent wood has not made it into commercial use.
The cell membrane of wood consists of cellulose (about 45%), which is a very durable substance with a fibrous structure, and supporting substances: hemicellulose (about 30%), lignin (about 20%). Lignin binds cellulose and hemicellulose fibers into a strong structure. Chromophores contained in lignin prevent the penetration of light and make the wood brown.
The method previously used to make wood transparent is to completely remove the lignin from the wood using chemicals. This process is quite time-consuming, and it severely weakens the wood and creates a lot of liquid waste. An American team of researchers has found a new, easier and cheaper way to make wood transparent without removing the lignin.
What is the new method?
The new method involves changing the lignin instead of removing it. To do this, the researchers removed the lignin molecules involved in giving the wood its color. Then they applied a solution of hydrogen peroxide to the surface of the wooden planks with a regular paintbrush and exposed it to natural sunlight (or UV light). After an hour, the peroxide bleached the brown chromophores and left the lignin intact, turning the wood white. The next step was to impregnate the wood with clear epoxy resin, which filled the spaces and pores in the wood and then hardened it. This made the white wood 90% transparent.
What is the energy efficiency of transparent wood?
Scientists have found that transparent wood made with the new method is lighter and 50 times stronger than transparent wood with the lignin completely removed. The researchers also say that the transparent wood produced by their process could replace window glass because it is lighter than glass and provides much better insulation. And this is important because windows are a major source of heat loss in buildings. In addition, transparent wood is much more durable than glass, and its production using the new method does not require high temperatures.
According to the researchers, wood produced using the procedure they have developed may also find application in the construction of completely transparent houses. Thus, it could potentially serve as load-bearing walls. The researchers say that it can also be used for roofs.
The team of researchers also suggests that such wood could find applications in, for example, touch screens for use in harsh environments or in car interiors.
There is a chance that in the future we could be sitting at home or working in a building with wooden windows. However, further work and research is needed to implement this method into an industrial process.