Transparent wood innovation moves closer to commercial markets

MADISON, Wis. -- The idiom “You make a better door than a window” seems particularly applicable to trees, but with new innovations in transparent wood, that may someday not be the case.

It sounds like an oxymoron, but transparent wood has been around since the early 1990s when a German researcher crafted it in his lab. His general method has persisted over the years, but recent modifications show promise for a more efficient and effective process.

Turning wood transparent requires two main phases. First, scientists treat the wood with chemicals to remove the lignin, the structural tissue that gives the wood a rigid shape and strength. Next, scientists fill this wood with epoxy, or a similar chemical compound. These two steps make the wood transparent by limiting its ability to absorb or scatter light. With its low density and fast growth, balsa wood has been the chosen material for research teams, but species with higher densities, such as oak and poplar, also show promising results.

Recent improvements to the method reported by scientists at the University of Maryland early this year have taken transparent wood a step closer to the commercial market. They call their process the solar-assisted chemical brushing approach.

Traditionally, the first step has involved completely submerging the wood in chemicals for several hours. Using the new method instead, scientists brush the wood with the chemicals and then hydrogen peroxide (you may have a weaker version of this in your medicine cabinet at home!) and place it under solar light, either via the sun or a UV lamp. This process removes the color rather than the lignin itself. Once the lignin has turned white, the epoxy infiltration step follows as usual, but there is now a more robust scaffolding for it to cling to. Because the lignin is held intact, transparent wood created with this method is 50 times stronger than when lignin is completely removed.

The process also addresses some previous limitations. By brushing rather than submerging the wood, the process uses less chemicals and is less expensive. Additionally, the byproduct of the hydrogen peroxide reaction is water, so there is significantly less toxic gas and liquid waste to dispose of. Transparent wood is already compatible with existing industrial processing equipment and scaling up to the commercial market is not only possible but seems to be a promising prospect, according to the University of Maryland research team.

Transparent wood outperforms glass in multiple aspects. It is lighter and more durable than glass. When it does break, it tends to splinter or crack rather than shatter. Producing transparent wood is also less energy-intensive than producing glass, which has an annual carbon footprint of approximately 25,000 metric tons. When used for windows, glass is inefficient compared to wood due to its high thermal heat transfer. With glass, heat is more easily slipping into your house in the summer and escaping out during the winter – taking potential savings on your energy bill with it. According to a team of researchers from the University of Maryland, the University of Colorado and the Forest Products Laboratory, transparent wood is five times more thermally efficient than glass and also shields UV wavelengths, protecting both the building’s interior and human health.

Although it has a transmittance rate of over 90%, one of transparent wood’s greatest drawbacks is that it is not completely clear. Homeowners may prefer glass for their living room windows, but there are plenty of other uses for transparent wood. Potential applications include solar cells, electronic touch screens, and energy-efficient building materials for warehouses, sheds, and other non-dwellings.

Transparent wood has become increasingly more practical and efficient since its inception, and as the science continues to advance, this new forest product may soon find a key spot in the broader market.