Wood made transparent using rice and egg whites could replace windows

Windows and smartphone screens may one day be constructed from transparent wood laced with egg whites and safely composted at the end of their life.

Researchers are interested in using wood to make biodegradable alternatives to glass with better insulating properties, or to replace plastic in electronic devices. Wood has been turned into a transparent material before by modifying or removing the organic polymer lignin from it and then injecting epoxy as a replacement, but this results in a non-biodegradable product.

Now Bharat Baruah at Kennesaw State University in Georgia and his colleagues have developed a process that replaces the synthetic epoxy with natural egg white and rice extract.

“[Previous examples of transparent wood are] very hard to synthesise, hard to make and you spend a lot of time and energy and money to make those, so that’s why we thought about creating something that we can make easily and naturally,” says Baruah.

He was inspired to use egg whites by buildings in his home state of Assam in India, which date back to the 1500s and use a cement-like mixture that included sand, sticky rice and egg whites. “That was the cement in those days, and those buildings are still there,” says Baruah. “They’re still there after more than four or five centuries and it was always fascinating to me.”

The team took sheets of balsa wood and drenched them with sodium sulphite, sodium hydroxide and diluted bleach inside a vacuum chamber to remove the lignin and hemicellulose, leaving only a paper-like cellulose structure. The voids in the material were then filled with a mixture of rice extract and egg white before being dried in an oven at 60°C (140°F) to create a semi-transparent plate with a slight brown tint. “It’s not 100 per cent transparent, but it is semi-transparent,” says Baruah. “And it’s biodegradable.”

Baruah and his colleagues built a small birdhouse fitted with a transparent wood window as a rudimentary mock-up, and found that it stayed 5 to 6°C (9 to 11°F) cooler inside when exposed to a heat lamp than the same birdhouse fitted with a glass window. The research will be presented today at the spring meeting of the American Chemical Society in San Diego, California.

Further research will investigate the strength and thermal properties of the material, as well as techniques to improve the transparency, says Baruah.