Transparent Wood That Stores and Releases Heat Created by Scientists

Scientists have created transparent wood that can absorb and release heat. This wood could one day be used in the construction industry to make eco-friendly buildings, researchers presenting their findings at the American Chemical Society (ACS) Spring 2019 National Meeting & Exposition said.

In 2016, a team led by Lars Berglund from the KTH Royal Institute of Technology in Stockholm announced it had developed a type of transparent wood. The research team removed a component from the cell walls of balsa wood that absorbs light and then incorporated acrylic into the wood to make it transparent. Like most woods, it could bear heavy loads, making it a promising material for construction.

"Wood is a renewable and abundant material that has been used for centuries as building material," Céline Montanari, a researcher on the project, told Newsweek. "It has many advantages, including excellent mechanical performance, low density and excellent thermal insulation properties when compared with glass.

"However, it cannot be used as light-transmitting material as it is. In a perspective of reducing artificial lighting in buildings and developing new functional wood-based material, we chemically modified wood to make it transparent without losing the mechanical properties. This suggests that it can be used for light-transmitting structures, such as windows, with the advantage of being much more insulating than glass."

Building on this research, the team then set out to improve the performance of the wood so it could absorb and emit heat—allowing it to save costs on energy if it were to be used as a building material. To do this they added polyethylene glycol (PEG) to the wood they had previously developed.

PEG is a compound that melts when it reaches 80 degrees Fahrenheit, storing energy in the process. By adding it to the wood, the team was able to boost its energy efficiency. If a house were built from the wood, it would mean that on a sunny day the material would absorb heat, keeping it cool inside. At night, this heat could then be released indoors, meaning a constant temperature could be maintained.

"In this work, we not only managed to make the wood transparent so it can transmit light, but we also added an extra functionality: heat storage," Montanari said. "This means that this transparent wood is multifunctional and fulfilled to high-demanding functions in the building sector: Transparency to reduce artificial lighting, and heat storage to reduce energy losses.

transparent wood
Laboratory image showing the transparent wood. American Chemical Society

"Transparent wood is already a great insulating material when compared with glass. However, in order to reduce the energy consumption even more we added a material that can absorb and store heat inside the wood when outdoor temperature is high, and that can release it later on when the outdoor temperature decreases."

This, she said, would allow for considerable energy savings as the wood would act as a "thermal battery" to store heat that could be redistributed later when it is needed. "Transparent wood has the advantage of transmitting light but it is also very hazy," she added. "This means that it diffuses light very well and enables privacy to be kept—such as in frosted windows where glass and plastic are used today. So in a house fully built of transparent wood, you would have a very nice natural lighting in all the rooms with maintained privacy."

Scientists involved in the research, funded by the Wallenberg Foundations and the European Research Council, are now working to scale up the production process in the hope of making it commercially viable. "We have a patent on transparent wood, which is owned by an industrial company and they are working on industrialization aspects and technology obstacles," Montanari said.

The material has the potential to be more environmentally friendly than materials like concrete and plastic. Both the wood and the PEG are biodegradable—the acrylic currently used to reduce light-scattering could potentially be replaced with another polymer, Berglund said in a statement.

"From an environmental perspective it is important to increase the use of materials coming from renewable resources and reduce the use of materials made from limited resources, which also contribute to CO2 emissions," Montanari said. "Wood is the most used bio-based material in the building sector and we show with the development of transparent wood that new applications of wood-based materials are still emerging. Research related to wood is under fast development internationally, and there will be promising renewable solutions in the future that can be applied in the building sector."