Prof. Hu Liangbing is the director of the Center for Materials Innovation, University of Maryland, USA.
A study conducted by his team about the production of transparent wood has been recently published on the Science Advances journal (“Solar-assisted fabrication of large-scale, patternable transparent wood”, DOI: 10.1126/sciadv.abd7342
Image - Prof. Hu Liangbing - Credits: Center for Materials Innovation, University of Maryland, USA.
We asked Prof. Liangbing to explain better the results achieved through his study and the constraints to overcome in order to make the transparent wood a valid alternative to traditional glass used for windows.
#1: Could you please explain what are the discoveries that lead up to your current work on transparent wood?
Answer: Wood has many photolabile chromophore groups that lead to the monotonic brownish color and susceptible photo-degradation, making wood undesirable for optical management. The chromophore groups are mainly produced by lignin and can absorb the UV light.
The lignin free radicals are formed by UV excitation. Inspired by the unique UV light absorption and photo-excitation of lignin, we remove the chromophores of lignin by UV excitation and H2O2 oxidization.
Solar energy is the most abundant energy resource on earth. Much of the Sun's energy is made up of ultraviolet (UV) radiation. Thus, we use this solar UV light as a driver of wood decoloration to achieve the rapid fabrication of transparent wood.
#2: Our understanding is that the research on transparent wood is very important not only from a theoretical aspect, but also from a practical point of view. Could you please explain what are the practical benefits for businesses and people in daily life?
Answer: Compared to glass, wood has lower thermal conductivity, and it’s lighter, stronger, and more environmentally friendly, the transparent wood can be used to make energy-efficient windows, roof or even see-through buildings.
#3: What are the constraints to overcome in order to make the production process of transparent wood profitable in terms of energy, environmental impact and economy?
Answer: The tradition preparation methods of transparent wood involve the solution-based delignification process that impairs the mechanical strength of wood and is also relatively energy and chemical intensive.
Furthermore, it is necessary to fully remove the dispersed lignin from the wood scaffold, which lengthens the processing time.
Finally, the generated liquid waste is difficult to recycle and creates an additional environmental burden.
Compared with traditional solution-based immersion processes, we report a technique for rapidly fabricating transparent wood that involves chemical brushing, rather than immersion, combined with solar illumination to remove the lignin chromophore.
Our method requires fewer chemicals and energy consumptions, thus greatly reducing the preparation cost and liquid waste.
#4: What are the results that you achieved through your research and what are your research goals for the future?
Answer: We demonstrate a rapid, cost-effective, and sustainable method to fabricate patternable transparent wood based on a scalable solar-assisted chemical brushing method.
In this process, the light-absorbing chromophore groups of lignin were removed, which allowed us to improve the optical properties of the resulting transparent wood without destroying the aromatic structure of lignin entirely.
The transparent wood show a high tensile strength of 31.4–46.2 MPa, excellent optical transmittance of > 90%, low optical absorption of < 4%, and high optical haze of 60–80%.
Moreover, the solar-assisted chemical brushingmethod can selectively treat designated areas of wood samples, imparting the transparent wood with excellent designable patterning capabilities.
Compared to solution-based delignificationprocesses, our solar-assisted chemical brushing has higher production efficiency, lower cost, and is more sustainable and controllable.
This inexpensive and highly efficient fabrication of transparent wood can also use natural solar energy, expanding the technique’s application to large-scale industrial production.
We will expand the application of transparent wood. Transparent wood has emerged due to its unique hierarchical structure, high specific strength, and favorable light management properties, thus, it can be potentially used in a broad range of applications including optoelectronic devices, energy-efficient building materials, integration into solar panels, light-management layers for solar cells, and touch panels.