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article imageEssential Science: Transparent wood can transmit light

By Tim Sandle     Apr 15, 2019 in Science
Technologists have developed a transparent wood that has grabbed attention as a future material for green construction. The material is also remarkably energy efficient, in terms of its ability to release heat, thereby lowering energy costs.
The ideal material for constructing a building will be low cost and be of a low energy demand. Such a material will also have a low carbon footprint, and be efficient in terms of heating the building and maintaining it overall. While such a material may not exit in terms of meeting all expectations, the new material goes some way to achieving this.
Building are a major drain on energy and much of the world’s energy production is dedicated to running buildings. Energy is needed to light, heat and cool buildings. While glass windows can transmit light, which assist with the light levels and assists with retaining heat, glass windows cannot store energy for later use when there is no direct sunlight. These issues provided the inspiration for developing the new material.
Gherkin office block in the City of London  U.K.
Gherkin office block in the City of London, U.K.
The researchers from the KTH Royal Institute of Technology in Sweden had the idea that if walls of buildings were transparent, this would reduce the need for artificial lighting and lower the associated energy costs required to keep buildings warm.
The material is a type of transparent wood, according to The eco-friendly material is not only of a low carbon footprint, it assists with energy demand in terms of being a transmitter of light and it also requires lower energy in terms of maintaining warmth, through its ability to release heat, which will save on energy costs.
To construct the material the researchers removed lignin from samples of commercial balsa wood. Lignin is a structural polymer, and it blocks most of the light from passing through. While this step created a degree of transparency, it was not totally transparent due to a light scattering effect.
An impressive tree in Cornwall  England. The tree has several bird houses attached to it.
An impressive tree in Cornwall, England. The tree has several bird houses attached to it.
To create ‘true’ transparency, the scientists incorporated acrylic (or ‘Plexiglass’) into the structure. The end result was a transparent material twice as strong as Plexiglass, and hence tough enough to function as a wall. In a second wave of the research, the scientists have experimented with adding polyethylene glycol, which appears to improve the energy retention efficiencies even further.
The material has also been demonstrated to be capable of trapping light, which can be used for energy efficiency purposes. This is achieved by covering the transparent material with solar cells.
The wood used in the study is derive from sustainable sources. The wood offers mechanical strength, and the fusing together at the nanoscale of the wood and acrylic creates the strong transparent material that has a number of potential building applications.
With the development of the wood, one of the researchers, Céline Montanari explains: “Back in 2016, we showed that transparent wood has excellent thermal-insulating properties compared with glass, combined with high optical transmittance.”
She adds: "In this work, we tried to reduce the building energy consumption even more by incorporating a material that can absorb, store and release heat.”
The transparent wood is both bio-based and biodegradable. The video below provides more information on the development of the new material:
The early stage of the research has been published in the journal Biomacromolecules (“Optically Transparent Wood from a Nanoporous Cellulosic Template: Combining Functional and Structural Performance”). Later developments with new material will be showcased at the American Chemistry Society’s National Meeting and Expo 2019, which will be held at Orlando in Florida, U.S.
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This article is part of Digital Journal's regular Essential Science columns. Each week Tim Sandle explores a topical and important scientific issue. Last week the topic was the wonder material borophene, which has properties beyond those of graphene and has technologists excited in terms of future state electronics.
The week before Last week we considered the risk that glitter poses to the ecosystem, due to most glitters being composed of microplastics. This has led many scientists to call for a ban on glitter and related materials.
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