Materials

Transparent wood opens a window to cooler homes

Transparent wood opens a windo...
The researchers constructed a rectangular model home to put the wooden windows to the test
The researchers constructed a rectangular model home to put the wooden windows to the test
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The researchers constructed a rectangular model home to put the wooden windows to the test
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The researchers constructed a rectangular model home to put the wooden windows to the test
The wooden window was much better at eliminating glare and more evenly distributing light
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The wooden window was much better at eliminating glare and more evenly distributing light
The wooden window was much better at eliminating glare and more evenly distributing light, compared to glass window (pictured here)
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The wooden window was much better at eliminating glare and more evenly distributing light, compared to glass window (pictured here)
This more consistent lighting is a result of the haze property and is much easier on the eyes
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This more consistent lighting is a result of the haze property and is much easier on the eyes
Li tells us there is no reason the approach couldn't be scaled up to create a proper-sized window
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Li tells us there is no reason the approach couldn't be scaled up to create a proper-sized window

A few months ago, we looked at the work of material scientists who had managed to make a block of linden wood see-through. Altering the molecular makeup to turn timber transparent is an impressive bit of science to be sure, but what kind of benefits could this new material offer over its comparably opaque counterpart? The same scientists are now finding some conclusive answers to this question, using their transparent wood as a window for a model home and finding that not only does it let in a similar amount of light to glass, but it is much better at keeping the interior cool.

The research team, from the University of Maryland (UMD), create their transparent wood by bleaching it in a beaker to remove a molecule called lignin. This is the molecule that makes wood brown, but critically, also gives it its rigidity, so removing it is kind of like robbing Peter to build a see-through wall.

One research team from Sweden was able to find a way around this problem earlier in the year, removing lignin from wood and then mixing the material with acrylic glass to restore its rigidity. But the Maryland researchers took a different route, instead filling in the gaps with epoxy. Their early testing indicated that the resulting material was actually four to six times stronger than the original untreated version.

But the wood exhibited some other interesting properties too, particularly when it came to light. When the wood is treated in this way, the channels within that carry water and nutrients up and down the tree are turned into passages for light. The team reported that the material had high transparency and also high haze, a property that pertains to its ability to scatter light.

Further down the track, these characteristics could be valuable in creating advanced solar panels, with the light entering through the transparent wood and then being held in as a result of the high haze factor, allowing the panel to soak up more solar energy. But the team's latest research suggests that it could find some uses around the home, too.

The researchers constructed a rectangular model home, measuring 13.5 by 7.5 cm (5.3 x 2.95 in) and 25 cm tall (9.84 in). The ceiling consisted of the transparent wooden panel to serve as a window. The team then applied a solar simulator, which offers the same spectrum and intensity of the sun, to the top of the home to measure how the transparent wood performs as a window material.

It was found that the transparent wooden window let in nearly as much light as glass, but at the same time was much better at eliminating glare and more evenly distributing the light. This more consistent lighting is a result of the haze and is not only easier on the eyes, but also means that the direction of the incoming light doesn't change as the sun moves across the sky, as it would with regular glass.

The wooden window was much better at eliminating glare and more evenly distributing light
The wooden window was much better at eliminating glare and more evenly distributing light

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

The team also discovered that the channels in the wood allow for the wavelengths of visible light to pass, while blocking most of the wavelengths that carry heat, making for thermal insulation that is superior to traditional glass windows. They arrived at these conclusions by using a photo-detector to measure the amount of light being transmitted, and by monitoring the temperature inside the home to gauge the heat passing through.

Further adding to the material's credentials is the fact that it is waterpoof, a result of its polymer content, and much less likely to break or shatter than glass. Li tells us there is no reason the approach couldn't be scaled up to create a proper-sized window, as long as the new-age glazier has a big enough container to treat the material.

"The scalability of making the transparent wood window is only limited by how large the beaker is," she explains. "If someone were to make a real wood window, they just need to get a large enough container for the process. The chemicals to remove lignin and the polymer for filling are just the same."

The research was published in the journal Advanced Energy Materials.

Source: University of Maryland

7 comments
BartyLobethal
The "light-scattering" (diffusion) properties would make it a winner for skylights and 'privacy' glass. It would also make it a poor choice for regular windows.
zr2s10
I agree, this could really revolutionize the skylight industry. Especially being tougher than glass AND being a waterproof wood? As long as it doesn't suffer from too much UV degradation, it could last years with low risk of leaking or breakage.
KungfuSteve
As interesting as it is... glass has a superior insulating quality. Its more environmentally sound than Epoxy. And it is much harder to cut / break into - if someone decided to try to rob a place.
Douglas Bennett Rogers
The main value is that it sequesters carbon in something useful. It takes a LOT of energy to make sand into glass, and, then, to re-melt it.
ljaques
I like the diffusion. It removes the glare and distributes the light so much better than a normal skylight. That was the worst problem I've had with standard skylights and tubes. Hmm, does it let the heat in like the glass, or would the cat be frustrated because it couldn't find a warm ray of sun to lie in? What is the R rating of delignized wood? Wood is R-1. Strength, safety, & longevity are also issues.
Don Duncan
This filter of IR needs to be reversible or better yet adjustable for all through the year to compete with the new glass that can do it.
notarichman
glass doesn't exactly cut predictably. except possibly with a diamond saw. i wonder how wooden window material cuts? @Kungufusteve; the article says it has "better" insulation qualities than glass. i presume that means they tested it. whether they tested it correctly is another matter. an IR detector would work! Could it also be used for light bulbs to scatter the light? incandescent bulbs, yes! but led?