Transparent wood now even stronger than glass

Transparent wood has been around for some time. But a new process has made it even better. This brings us a step closer to a form of glass, which insulates much better than the windows of today.

Lignin very important

Roughly speaking, wood consists of two important components: cellulose and lignin. Lignin is a kind of 'glue' that holds the cellulose together. This makes the wood extra strong. Cellulose on its own is quite brittle. Cheap woods such as spruce and poplar consist almost entirely of cellulose. Wood-eating fungi know what to do with that. Wood species such as oak, with a lot of lignin, are much more durable.

The usually followed process for making wood, developed inter alia at the Stockholm KTH [1], involves soaking the wood in NaClO2, sodium chlorite. This is a chemical compound used in bleach and toothpastes. In this process, sodium chlorite removes the lignin. This leaves the transparent cellulose.

Lignin made transparent

However, this takes a lot of chemicals, produces liquid waste that is difficult to recycle and can weaken the wood. Liangbing Hu of the University of Maryland and his colleagues came up with something better. A method that also makes the lignin transparent, instead of removing it completely. This is faster and uses less raw materials than the standard lignin removal process. The wood was also reinforced.

The researchers' method stems from the recent discovery that you can make lignin transparent by only removing the chromatophores. These are the parts of the lignin molecules that give them their color.

They brushed hydrogen peroxide (H.2O2), a well-known disinfectant, over the surface of the wood. They then left the wood for an hour under a UV lamp designed to simulate natural sunlight. The chromatophores were opted for by the UV light, causing them to react with the hydrogen peroxide and dissolve. [2]

They then soaked the wood in ethanol (“alcohol”) to remove any residual dirt. [2]

Then they filled the pores in the wood with clear epoxy. This last step is also part of making lignin-free transparent wood.

A production process for transparent wood was developed several years earlier at the KTH University of Technology in Stockholm. Source: KTH / Peter Larsson (fair use)

Transparent wood now fifty times stronger

The final product is a 1 mm thick piece of wood, which allows more than 90 percent of the light to pass through and is more than 50 times stronger than transparent wood without lignin. The transparent wood is lighter and stronger than glass. It could be used for load-bearing windows and roofs. It could potentially be used to create a see-through house, according to discoverer Hu.

What is attractive about the material is that it allows light to pass through, but still scatters the light at greater thicknesses. And blurs images. This makes it impossible to see through the wooden glass. And it still offers a form of privacy. This material is also UV resistant, unlike polycarbonate. That makes transparent wood very interesting. Also for gardeners, contractors and for electronics designers, this is a material to keep an eye on. If you want to make it yourself, you can experiment with Hackaday's manual [3]. Hopefully, after this breakthrough, the material will now be widely available.

Sources

1. Wooden windows? New material could replace glass in solar cells and buildings, KTH Nyheter, 2016
2. Lianbing Hu et al., Solar-assisted fabrication of large-scale, patternable transparent wood, Science Advances, 2021, Vol. 7, no. 5, eabd7342, DOI: 10.1126 / sciadv.abd7342
3. Make your own transparent wood, Hackaday, 2016

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