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Earlier this year, Liangbing Hu and a team of scientists at the University of Maryland revealed their new method for turning wood transparent. Their process is more efficient, less energy-intensive, and requires the use of fewer materials and harmful chemicals. But what is motivating their research, and how does it work?
What Are the Benefits of Transparent Wood?
It’s long been accepted that glass is the most effective way to bring natural light into our homes, offices, and other buildings — and not without good reason. Glass is recyclable, weather-resistant, hardy, affordable, and a fairly good insulator.
But despite advancements in double (and triple) glazing, unmodified wood is 10 times more insulating than glass. It’s also biodegradable and can withstand heavy loads. The only problem is, it doesn’t transmit light.
In the past few years, materials scientists have been investigating ways to turn wood transparent without altering its mechanical properties. If they succeed, the material would serve as a sustainable and renewable alternative to glass windows, helping to better regulate indoor temperatures.
How Is Transparent Wood Usually Made?
Wood contains two key components that make it opaque:
- lignin, which absorbs light, and
- cellulose. Wood’s fibers mostly comprise of this light-activated compound, which is what makes the wood brown in color. The wood’s tube-like fibers scatter light and reduce transparency.
To date, research has focused on completely removing lignin from wood and replacing it with a resin material to make it transparent.
In 2019, for example, Céline Montanari and a group of scientists at the KTH Royal Institute of Technology in Sweden made some notable progress in this area. By removing lignin, they observed that light was able to effectively filter through the material.
The team subsequently soaked the wood panels in polyethylene glycol (PEG), a polymer that is most commonly found in toothpaste, to encapsulate the wood and improve its capacity as an insulator. Although PEG’s melting temperature is 30°C, the polymer stayed safely locked within the wood’s structure.
It’s an effective solution, but the process relies on using a significant amount of harmful chemicals and produces hard-to-recycle liquid waste.
Now, Hu and his team have found a way to modify the lignin in wood without having to remove it entirely.
How Does Hu’s Technique Differ?
Hu’s study effectively demonstrates how to make transparent wood without the need to remove the lignin. Instead, the team used hydrogen peroxide, a chemical often found in hair bleach or disinfectants, to alter chromophores in the wood. This changes the structure of the chromophores so they no longer absorb light.
Hu’s team used a simple three-step process:
- Firstly, the hydrogen peroxide is brushed onto the wood. It is activated with a UV light, which turns the wood white. This is the same method that is used for making bright white paper.
- Secondly, the wood is soaked in ethanol to remove any residue and filth.
- Thirdly, the cellulose fibers in the wood are filled with a resin to reduce the scattering of light. This step is mirrored from Montanari’s method.
The resulting material allows more than 90% of light to pass through, which makes it appear transparent, and it is 50 times stronger than wood that has had the lignin removed.
This modified wood doesn’t insulate as effectively as unmodified wood, but it is still four times more insulating than the top-quality double glazing available on the market today.
What Does the Future Hold for Wooden Windows?
It will take a bit of time to optimize, automate, and scale up the process, but Hu’s team is confident that their concept could ultimately be applied to large pieces of material and, in time, there will also be opportunities to incorporate decorative features.
One day soon, you might find yourself sitting in a house with wooden windows.
Image Credit: Halfpoint / Shutterstock.com
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