Seeing through trees sounds like some sort of magic trick, but it just might be the view to a greener future. Believe it or not, trees may replace the clear pane of glass in your window someday. A collaboration between Forest Products Laboratory researcher Junyong Zhu and colleagues from the University of Colorado and the University of Maryland has brought the idea to life. They developed a transparent wood material that has the potential to outperform glass in nearly every way.
Glass is the preferred material for windows because of its transparent quality. However, its use comes at a high economic and ecological price. Heat easily transfers through it, raising the energy bill when the air conditioner needs to be turned up in the summer. And the situation is just as bad in the winter because the heat indoors escapes out the window, meaning more heating is required indoors. All this extra energy use year-round means more emissions are produced, further accelerating climate change. Glass production also carries a massive carbon footprint—about 25,000 metric tons yearly. And while traditional glass remains fragile, some modern glass materials can outperform steel in hardness.
On the other hand, transparent wood is five times more thermally efficient than glass, cutting electricity costs and greenhouse gas emissions. It’s made from a renewable, sustainable resource, which further lowers its carbon footprint. That, combined with how its manufacturing is compatible with existing industrial processing equipment, and you can see why the material is considered one of the most promising future materials.
Transparent wood is made with fast-growing, low-density balsa trees and a synthetic polymer called polyvinyl alcohol (PVA). The balsa wood is treated at room temperature with an oxidizing bath that bleaches nearly all visibility. Then, it’s penetrated with PVA to create a virtually transparent product. The final product is lighter and more durable than glass. It can withstand far more substantial impacts and splinters or bends instead of shattering as glass does.
The USDA was very impressed and said, “With all of these potential benefits for consumers, manufacturing, and the environment, the case for transparent wood couldn’t be…clearer.”
Another team of researchers from Sweden’s KTH Royal Institute of Technology has taken the idea a step further by filling the transparent wood with a polymer called polyethylene glycol (PEG), giving it the ability to absorb and release heat. It could make cooling and heating homes even less costly.
Céline Montanari, a researcher involved in the KTH study, said, “During a sunny day, the material will absorb heat before it reaches the indoor space, and the indoors will be cooler than outside. And at night, the reverse occurs—the PEG becomes solid and releases heat indoors so that you can maintain a constant temperature in the house.”
PEG, a phase-change material, starts as a solid and then melts at a specific temperature—adjustable by changing the type of PEG used. When in the dissolved phase, it stores heat. As it solidifies, it releases the heat.
