Seeing is believing

Wood you believe it: Transparent timber is stronger and greener than glass

Researchers in Sweden have developed a form of ‘invisible’ wood as a stronger, more environmentally sustainable alternative to glass or plastic.

The KTH Royal Institute of Technology produced 1mm thick, 15cm2 samples of a transparent wood composite by stripping lignin from balsa wood and replacing it with a plastic polymer.

Researchers say the material is around twice as strong as plexiglass, and much less expensive and carbon intensive to produce than glass. Current samples are about 85% transparent, but ongoing lab work is aiming to produce panels with the same transparency as the plastic polymer element.

Lars Berglund, lead researcher at KTH, told RIBA Journal: ‘The samples have roughly twice the strength of plastic alone because the wood structure reinforces the material. The main advantage is toughness: glass windows are very brittle, and as a bio-based material, in the long term it will be lower cost than glass and more sustainable. The big problem is that to make glass you need to heat it to over 1000°C, which requires a lot of energy.’

Plans to commercialise the technology are focusing on integrating solar cells into the transparent wood: ‘devices’ have been manufactured in collaboration with the Institute’s Solar Cell Group.

Berglund adds: ‘Scaling up manufacture makes it easier to focus initially on high technology applications that are less cost sensitive. Solar cells are sufficiently high value to be able to accommodate the cost of modifying the wood. We are now measuring the performance of the technology.’

The KTH team also plans to investigate the development of transparent structural panels that will simultaneously allow daylight into properties and carry loads. The same process could be used to create shatter-proof load-bearing windows.

The material is manufactured using a process similar to chemical pulping, removing strips of lignin, a form of cellulose that gives wood its brownish colour, from wood veneer pieces, then infusing them with plastic polymer.

According to Berglund, the principle challenge is matching the optical properties of the two materials. ‘Although we were always expecting the principle to work, there were several difficulties. The main challenge is that you need to match the optical properties of cellulose with those of the plastic polymer and you can't tell how well it will work until you experiment. Our first efforts were quite encouraging so we kept going.’