Transparent wood has been developed by researchers at KTH Royal Institute of Technology as an advanced structural material for building construction after it was first launched in 2016. It allows natural light to pass through while still storing thermal energy.

Innovating an Innovation

Researchers have brought the see-through wood construction material to a new standard five years since it was first introduced. By infusing wood with a transparent bio-plastic made from citrus fruit, they could make their composite 100% green - and more translucent.

The trick to turning wood into a translucent composite material is to remove the lignin, which is the main light-absorbing component. However, the open pores left by the lack of lignin must be filled with something that restores the wood's strength while allowing light to pass through.

The development was made possible under the KTH Royal Institute of technology.

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Fossil-Based Polymers

Researchers at KTH's Wallenberg Wood Science Centre used fossil-based polymers in earlier models of the composite. The researchers have now successfully tested an environmentally safe alternative: limonene acrylate, a limonene-derived monomer. They published their findings in the journal Advanced Science.

"The current limonene acrylate is made from organic citruses, such as peel waste from the orange juice industry," says Céline Montanari, lead author and Ph.D. student.

The polymer that restores the strength of delignified wood while allowing light to pass through is made from an extract from orange juice processing.

According to the researchers, the modern composite has a 90 percent optical transmittance at 1.2 mm thickness and a 30 percent haze. Unlike other translucent wood composites produced in the last five years, the material manufactured at KTH is intended for structural use. With a power of 174 MPa (25.2 ksi) and an elasticity of 17 GPa, it demonstrates heavy-duty mechanical efficiency (or about 2.5 Mpsi).

But, according to Professor Lars Berglund, head of the KTH's Department of Fibre and Polymer Technology, "sustainability has always been a focus for the study community."

"One of the problems we've had in producing organic translucent wood has been replacing fossil-based polymers," Berglund says.

According to him, environmental concerns and so-called green chemistry pervade the whole project. No solvents are used in the production of the products, and all additives are obtained from bio-based raw materials.

Unexplored Application Possibilities

According to Berglund, the latest developments could open up a previously unexplored variety of applications, such as wood nanotechnology. Smart glass, heat-storage timber, wood with built-in lights, and even a wooden laser are all possibilities.

Berglund explains, "We looked at where the light goes and what happens as it touches the cellulose." "Some of the light passes directly into the wood, making it translucent. In lighting systems, some light is refracted and dispersed at various angles, creating pleasing results."

Future Development

The team collaborates with Sergei Popov's photonics group at KTH to further explore nanotechnology's potential.

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