Heat-Storing Transparent Wood Could Be Skyscraper-Ready Within 5 Years

Move over, glass.

Transparent wood in action

Light-diffusing wood could boost insulation and help buildings cut down on energy usage. Researchers on Wednesday announced the development of a new kind of modified wood that could replace the glass used in skyscrapers with a strong, biodegradable, abundant material that would also the make the buildings that use it more energy efficient. It couls also be used in other technology, for example home solar panels, and the researchers tell Inverse that it could hit the market in just five years.

“Engineers developed double and triple glass structures to increase this thermal insulation, because glass is really bad,” says Céline Montanari, a PhD student at Sweden’s KTH Royal Institute of Technology who worked on the breakthrough. “But instead of going through all this process that consumes a lot of energy, you could actually just use renewable, abundant resources.”

Although the vision of the sci-fi city typically involves giant, shiny glass-scapes, the team’s material could mean a more accurate vision is something natural. Montanari’s institute announced the development of a transparent wood back in March 2016, explaining in a paper published in Biomacromolecules how the team created wood with light transmittance up to 85 percent and haze of 71 percent. The research took the lignin, which absorbs light, out of the cell walls of balsa wood. They then used acrylic to reduce the amount of light scattering.

The resultant material is not completely transparent, but its haze makes it ideal for situations where a room requires privacy without shutting out external light.

Wednesday’s research expands on this. Montanari worked with Lars Berglund, an author of the original study, to add polyethylene glycol to the wood. This is a phase-change material that stores energy when it melts at temperatures above 80 degrees Fahrenheit. That means the wood absorbs heat during a sunny day to make the indoors cooler, while releasing energy at night as it cools to make the inside hotter. The pair’s work is being presented at the American Chemical Society’s spring 2019 National Meeting and Exposition, held between March 31 and April 4 in Orlando, Florida.

With cities dominated by giant glassy towers, it’s perhaps hard to envision a world where builders move back to wood. Montanari argues that this shift is happening already, with cross-laminated timber building towers up to 18 stories high. Mjøstårnet, located near Oslo, is one of the most iconic of this new trend at 280 feet tall:

Mjøstårnet near Oslo.
Mjøstårnet near Oslo.

“I think that it would be possible to use this transparent wood for those glassy buildings, I really think so,” Montanari says. “The challenges would be having really good mechanical properties, but this is possible if you, for instance, tag several panels together, as it is done with cross-laminated timber.”

Reducing the amount of glass in use could enable more efficient use of light.

“If you add more glass, then you will have an impact on reducing the artificial lighting,” Montanari explains. “This will have a direct impact on energy consumption. But since that is a really bad insulator, then you will still consume more energy. Trying to use transparent wood, for instance, as a wall, you add more light transmitting materials, but you don’t have an impact on its insulation properties.”

The material could even play a role in boosting solar panels. Researchers are experimenting with ways to improve the amount of light hitting cells, like Insolight which is using lenses to focus light onto smaller, more efficient cells. Montanari claims a piece of wood just one millimeter thick overlaying the cells could boost yields.

“In solar cells, it’s important to diffuse very well the solar, heat and light,” Montanari says. “And right now the materials they use, they’re having difficulties with this part.”

From here, the plan is to explore mass production, as the lab can only produce pieces measuring 10 centimeters by 20. The team will also need to further explore biodegradability, as while some degree could reduce harm to the environment, the team wants to avoid windows disappearing after a couple of years.

If successful, it could help rewrite the sci-fi comic books of tomorrow.

Read the abstract of the 2016 paper below:

Optically transparent wood (TW) with transmittance as high as 85% and haze of 71% was obtained using a delignified nanoporous wood template. The template was prepared by removing the light-absorbing lignin component, creating nanoporosity in the wood cell wall. Transparent wood was prepared by successful impregnation of lumen and the nanoscale cellulose fiber network in the cell wall with refractive-index-matched prepolymerized methyl methacrylate (MMA). During the process, the hierarchical wood structure was preserved. Optical properties of TW are tunable by changing the cellulose volume fraction. The synergy between wood and PMMA was observed for mechanical properties. Lightweight and strong transparent wood is a potential candidate for lightweight low-cost, light-transmitting buildings and transparent solar cell windows.

Media via KLM, Vollark, American Chemical Society