The transparent wood developed by engineers at UMD lets in nearly as much light as glass, but provides better thermal insulation. Image: University of Maryland and Advanced Energy Materials.
The transparent wood developed by engineers at UMD lets in nearly as much light as glass, but provides better thermal insulation. Image: University of Maryland and Advanced Energy Materials.

In a new study, a team of engineers at the University of Maryland (UMD) has demonstrated that windows made of transparent wood could offer more even and consistent natural lighting and better energy efficiency than glass.

In a paper published in Advanced Energy Materials, the team, led by Liangbing Hu of UMD's Department of Materials Science and Engineering and the Energy Research Center, report that their transparent wood provides better thermal insulation and lets in nearly as much light as glass. It can also eliminate glare and provide uniform and consistent indoor lighting. These findings advance earlier published work on their development of transparent wood.

The transparent wood lets through just a little bit less light than glass, but a lot less heat, said Tian Li, the lead author of the new study. "It is very transparent, but still allows for a little bit of privacy because it is not completely see-through. We also learned that the channels in the wood transmit light with wavelengths around the range of the wavelengths of visible light, but that it blocks the wavelengths that carry mostly heat," said Li.

The team's findings were derived, in part, from tests on a tiny model house they built with a transparent wood panel in the ceiling. These tests showed that the light was more evenly distributed with a transparent wood roof than a glass roof.

The channels in the wood direct visible light straight through the material, but the cell structure that still remains bounces the light around just a little bit, a property called haze. This means the light does not shine directly into your eyes, making it more comfortable to look at. The team photographed the transparent wood's cell structure in UMD's Advanced Imaging and Microscopy (AIM) Lab.

Transparent wood still retains all the cell structures of the original piece of wood. But the wood is cut against the grain, so that the channels that drew water and nutrients up from the roots lie along the shortest dimension of the window. These natural channels then guide sunlight through the wood, making it transparent.

As sun passes over a house with glass windows, the angle at which light shines through the glass changes as the sun moves. With windows or panels made of transparent wood, however, the channels in the wood direct the sunlight in exactly the same way as the sun moves across the sky.

"This means your cat would not have to get up out of its nice patch of sunlight every few minutes and move over," Li explained. "The sunlight would stay in the same place. Also, the room would be more equally lighted at all times."

The research team recently patented their process for making transparent wood. This process starts with bleaching all the lignin from the wood; lignin is a component that makes wood both brown and strong. The wood is then soaked in epoxy, which adds strength back in and also makes the wood clearer.

Working with transparent wood is similar to working with natural wood, the researchers said. However, their transparent wood is waterproof due to its epoxy component; it is also much less breakable than glass because the cell structure inside resists shattering. So far, the team has created the transparent wood from tiny squares of linden wood about 4cm2, but the wood can be any size, the researchers said.

This story is adapted from material from the University of Maryland, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.