Stockholm university adds twist of orange to improve transparent wood recipe

Five years after introducing see-through wood as a building material, researchers in Sweden have found a way to make it more transparent, and entirely renewable, by adding fruit.

Researchers at KTH Royal Institute of Technology in Stockholm have been improving their recipe for transparent wood for the past five years. The basic idea is to strip out its lignin, the fibre that makes wood opaque, and filling its place in the structure with something else.

In early versions of the composite, researchers at KTH’s Wallenberg Wood Science Centre used conventional polymers. Now, they have successfully tested an eco-friendly alternative: limonene acrylate, a monomer made from citrus fruit.

"The new limonene acrylate is made from renewable citrus, such as peel waste that can be recycled from the orange juice industry," said postgraduate student Céline Montanari, the lead author of a paper on the technique published in the latest issue of the journal Advanced Science.

A 1.2mm sheet of the composite allows 90% of light to pass through, the researchers report. Unlike other transparent wood composites developed during the past five years, the material is intended for structural use. It shows heavy-duty mechanical performance: with a strength of 174MPa and elasticity of 17GPa.

Lars Berglund, the head of the KTH’s Department of Fibre and Polymer Technology, added that the material is made with no solvents, and all chemicals are derived from biological sources.

He said the latest advances could allow further developments in "smart wood", such as heat-storage and lighting – even a "wooden laser".

"We have looked at where the light goes, and what happens when it hits the cellulose," Berglund said. "Some of the light goes straight through the wood, and makes the material transparent. Some of the light is refracted and scattered at different angles and gives pleasant effects in lighting applications."

Image: KTH first announced its transparent wood research in 2016  

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