When you think about the materials used to make window panes, wood is probably not the first thing that comes to your mind. How can this brown and opaque material create transparent windows that allow us to look out on the world? Until now, glass has been our see-through material of choice. But could this be about to change?
Wood is a cheap and strong material used to make many items, to build houses and ships, and as a source of fuel when burned. As wood is widely available around the world, it is a sustainable and renewable alternative to other common building materials.
Many types of of building materials are harmful to our planet. For example, glass is costly and environmentally harmful to make. So, scientists have been searching hard for a more sustainable choice. As well as being inexpensive and robust, wood naturally traps heat. This means that it could make an ideal alternative to glass and plastic when making window panes.
However, there is just one problem. Wood may have many valuable properties, but unfortunately it is not transparent. So, wood is not really that useful when it comes to making windows. That is, until now! Scientists have discovered an exciting new way to make wood see-through.
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The Science Behind Transparent Wood
Transparent wood first hit the news in 2016 when a group of Swedish scientists found that wood could be made transparent by removing one of its key parts, a substance known as lignin.
Wood is made up of lots of plant cells, which contain key substances including lignin, cellulose, and hemicellulose. Lignin, a glue-like material, gives wood its brown and opaque appearance. It joins up with cellulose to create a strong cell wall.
The method of creating transparent wood involves two simple steps. First, scientists soaked the wood in a heated acid bath for six hours. This reduced the amount of lignin from 25% to less than 3% and “bleached” the wood, leaving it completely white. Workers use a similar method to create paper from samples of wood.
The next step was to remove the color from the wood altogether. The team achieved this by adding a clear epoxy resin to the wood. The resin fills in the small channels and pores within the wood, stopping light from scattering around.
The result was a see-through and shatter-proof material. While a strong knock may cause glass to shatter, the new transparent wood would either splinter or bend.
Some Sticking Points
Despite transparent wood potentially being an eco-friendly replacement for glass, there were a few problems with this method of making it. Making transparent wood this way used lots of energy and some dangerous chemicals. Also, the liquid waste made during this process proved difficult to recycle. This meant that the transparent wood was not as kind to the environment as we hoped it would be.
New and Improved Process
A different team of scientists, based at the University of Maryland, found that they could change the lignin rather than removing it completely. Their improved process was quicker, used less energy, and created a stronger wood product than the earlier method.
The team painted their wood in hydrogen peroxide (commonly used to bleach hair). They then placed the wood in either direct sunlight or underneath an ultraviolet (UV) lamp for one hour. During this time, the hydrogen peroxide bleached the color-creating molecules (the brown chromophores) within the wood but left the lignin in place.
The result was a beautiful white sample of wood. As with the earlier method, the team filled the gaps in the wood with a tough resin to create a see-through material. This method produced a much stronger transparent wood. In fact, leaving the lignin in place makes the wood an amazing fifty times stronger!
A Window into the Future
The development of transparent wood paves the way for many potential uses. As transparent wood is lighter and stronger than standard wood, the University of Maryland scientists believe that it “is a promising candidate for applications in energy-efficient buildings.” The team report that their wood allows over 90% of light to pass through. This means that, in the not-so-distant future, we could be staring out of windows made entirely from transparent wood.
Experts also believe that see-through wood would be a good material to use in the making of solar panels. As we try to be kinder to our planet, this would be a big step in the right direction.
So, that image of window panes made entirely of wood is not just a dream. It is now set to become a reality! As this new method of making transparent wood is easier and cheaper, we could use it on a larger scale to make lots of exciting things. Think about how many houses are made around the world each day!
Scientists continue to work hard, trying to make wood even more transparent and stronger. They are also seeking ways to scale up the production process.
Cellulose: The main component of plant cells walls, cellulose is a complex carbohydrate
Chromophores: A substance that is responsible for giving a material its color
Epoxy Resin: A transparent and strong adhesive
Hemicellulose: A polysaccharide that forms part of the plant cell wall
Hydrogen Peroxide: An unstable compound that is commonly used as a bleaching agent and an antiseptic
Lignin: An essential component of plant cells walls, lignin helps to provide structure and strength
Flesch Kincaid Grade Level: 8.2
Flesch Kincaid Reading Ease: 60.3
Li, Y., Fu, Q., Yu, S., Yan, M. and Berglund, L. (2016). Optically Transparent Wood from a Nanoporous Cellulosic Template: Combining Functional and Structural Performance. Biomacromolecules, 17(4), pp.1358–1364. https://doi.org/10.1021/acs.biomac.6b00145
Li, Y., Vasileva, E., Sychugov, I., Popov, S., & Berglund, L. (2018). Optically Transparent Wood: Recent Progress, Opportunities, and Challenges. Advanced Optical Materials, 6(14), 1800059. doi: 10.1002/adom.201800059
Xia, Q., Chen, C., Li, T., He, S., Gao, J., Wang, X., & Hu, L. (2021). Solar-assisted fabrication of large-scale, patternable transparent wood. Science Advances, 7(5), eabd7342. https://doi.org/10.1126/sciadv.abd7342