"Transparent wood" can now store and release heat
Three years ago, scientists at the Royal Institute of Technology in Sweden created "transparent wood"-a material considered to be a cheaper alternative to silica glass and solar cells currently used in windows. Now, the material can also store heat and then release it.
In order to produce the initial version of "transparent wood", the KTH team led by Professor Lars Berglund began to chemically remove the light-absorbing lignin from natural light wood fibers-lignin is an integral part of the wood cell wall.
The white fiber is then mixed with pre-polymerized methyl methacrylate (PMMA, commonly called plexiglass). This changes the refractive index of the fibers, making them transparent. The material obtained is stronger than ordinary transparent Plexiglas plates.
Recently, Berglund and doctoral student Céline Montanari added a "phase change" polymer called polyethylene glycol (PEG) to the treated wood fiber and PMMA. Usually in solid form, PEG has good compatibility with wood, and it can also store and release heat. When its temperature reaches 80ºF (27ºC), it melts and stores energy in the process. When it cools, it will return to a translucent solid, releasing the stored energy.
"On sunny days, this material absorbs heat before it reaches the indoor space, and the temperature inside will be colder than outside," Montanari said. "And at night, the opposite happens-PEG becomes strong and releases heat indoors, so you can maintain a constant temperature in the house."
As an added bonus, both wood fiber and PEG are biodegradable. Although PMMA is not, it may be replaced by a more environmentally friendly polymer, allowing the material to be completely biodegradable when discarded.
The researchers hope that the commercial version of the technology will be available within five years.
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