What! Wood can become as transparent as glass?

When you think of transparent things, what do you think of? Glass, plastic, diamonds, or water?

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When you think of wood, do you think of brown and yellow wood with a textured structure?

Image source: Photo Network

Now, a team of scientists has invented a transparent wood that looks almost as transparent as glass.

Transparent wood source: Reference [2]

How is transparent wood made? Let's find out today!

01

What's in the wood?

First, let us understand the structure of wood.

Wood is one of the most abundant renewable resources on earth and mainly contains cellulose (40%~50%), hemicellulose (20%~30%) and lignin (20%~30%).

Image source: Reference [1]

Cellulose is the strength support of wood, which is highly ordered along the direction of tree growth, while hemicellulose and lignin, as small molecules and adhesives, are interwoven with cellulose through hydrogen bonds and covalent bonds to form a load-bearing network, forming a natural anti-degradation barrier to protect plant cells. Lignin is a complex organic polymer that plays an important role in the formation of cell walls, especially in wood and bark, where it gives them rigidity and prevents them from rotting.

02

How to make wood transparent?

In fact, the key to making wood transparent is to remove the chromophores in lignin and retain its aromatic skeleton . The specific operation process is simply: brush the wood with hydrogen peroxide, expose it to the sun, soak it in alcohol, and finally fill it with a transparent material epoxy resin, and then it is completed after it solidifies.

Transparent wood production flow chart

Image source: Reference [2]

In this way, we can have a transparent piece of wood!

Image source: Reference [2] The inventors of this method are Xia Qinqin and Chen Chaoji from Professor Hu Liangbing's team at the School of Materials Science and Engineering at the University of Maryland. In the specific operation of turning a 1m long and 1mm thick balsa wood board into a transparent wood board, they first brush a layer of hydrogen peroxide on the surface of the board, and then expose it to ultraviolet light (or sunlight) for one hour. At this time, the hydrogen peroxide will bleach out the chromophores of lignin, leaving only the aromatic skeleton of lignin.

Brush with hydrogen peroxide bleach

Image source: Reference [2] The wood is then immersed in ethanol to remove residues such as lignin. Finally, the wood pores are filled with a transparent epoxy resin that matches the refractive index of the wood cell wall. After the wood board is filled and cured, a 90% transparent board is created, which is much higher than the 6% to 36% transparency of natural wood.

Schematic diagram of the preparation section Source: Reference [2]

This method of preparing transparent wood has higher production efficiency, lower cost, and is more sustainable and controllable, making it a cost-effective manufacturing process.

After reading the above content, is the preparation of transparent wood very simple? If you have the conditions, you can DIY it at home! However, hydrogen peroxide is a strong oxidant, and it will hurt if it splashes on the skin. In the process of scientific exploration, you must pay attention to protection and safety first.

DIY transparent wood with different patterns Source: Reference [2] 03

What is transparent wood good for?

Transparent wood has the advantages of light weight, high light transmittance, certain haze, low thermal conductivity and high mechanical strength. Compared with the high energy consumption and high pollution industrial production mode of other transparent materials such as glass and plastic, the preparation of transparent wood is more environmentally friendly, and its raw material selection range is also relatively wide.

Compared with glass as a building material, transparent wood is lighter and stronger, has better thermal insulation, and can be used for load-bearing windows and roofs. It is suitable for places with architectural aesthetic requirements, such as wall materials in public places such as airports, libraries, and museums.

Image source: Inspiration

In addition, due to the unique hierarchical structure, high resistivity and good light management properties of transparent wood, it has the potential to be widely used in photovoltaic devices, energy-saving buildings, solar cells and touch panels. In harsh environments with sand and dust, it can also be used as a cover for solar panels, allowing them to continue to generate electricity even in sunny sand and dust weather.

Image source: Nitu.com

I believe that with these comprehensive advantages, transparent wood composite materials will have broader application scenarios in the future!

References

[1] Kong Weiqing, Hu Shufeng, Yu Senlong, Zhou Zhe, Zhu Meifang. Research progress of lignocellulose functional materials[J]. Journal of Textile Research, 2022, 43(04): 1-9.

[2] Qinqin Xia, Chaoji Chen, Tian Li, Shuaiming He, Jinlong Gao, Xizheng Wang & Liangbing Hu. "Solar-assisted fabrication of large-scale, patternable transparent wood" .Science Advances, January 2021.

[3] Ruiyu Mi, Chaoji Chen, Tobias Keplinger, Yong Pei, Shuaiming He, Dapeng Liu, Jianguo Li, Jiaqi Dai, Emily Hitz, Bao Yang, Ingo Burgert & Liangbing Hu. "Scalable aesthetic transparent wood for energy efficient buildings". Nature Communications, July 2020.

Author: Xu Yan, PhD candidate in Materials Science at Fudan University

Editor: One person

Acknowledgements: Professor Ma Ruguang from the School of Materials Science and Engineering at Suzhou University of Science and Technology provided scientific guidance for this article