The researchers constructed a rectangular model home to put
the wooden windows to the test (Credit: Tian Li/University of
Maryland)
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.
"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