Nalagareng Resources - Transparent wood is coming to make an energy-efficient alternative to glass

Building, Energy, Materials, Sustainability, Wood

Wood is an ancient material humans have been using for millions of years, for the construction of housing, ships and as a source of fuel for burning. It’s also a renewable source, and one way to capture excess carbon dioxide from the Earth’s atmosphere. Today, the main component of wood – cellulose – is produced annually at 20 times the volume of steel.

Could looking through woods be the view to a greener future? woods replacing the clear pane glass in your windows is not a work of science fiction. It’s happening now.

In recent years, materials scientists have been experimenting with making wood transparent. Making wood see-through, and retaining its high mechanical properties, would provide a good alternative to glass from a sustainable and renewable source. Previous methods of doing this were highly energy intensive and used harmful chemicals, but a new study has shown a way to make wood transparent without using huge amounts of energy in the process.

Forest Products Laboratory (FPL) researcher Junyong Zhu in co-collaboration with colleagues from the University of Maryland and University of Colorado, have developed a transparent wood material that may be the window of tomorrow. Researchers found that transparent wood has the potential to outperform glass currently used in construction in nearly every way.

Their findings were published in the Journal of Advanced Functional Materials in their paper, “A Clear, Strong, and Thermally Insulated Transparent Wood for Energy Efficient Windows.”

Heat easily transfers through glass, especially single pane, and amounts to higher energy bills when it escapes during cold weather and pours in when it’s warm. Glass production in construction also comes with a heavy carbon footprint. Manufacturing emissions are approximately 25,000 metric tons per year.

Now, transparent wood is emerging as one of the most promising materials of the future.

Seeing through wood

Wood’s lack of transparency comes from the combination of its two main components, cellulose and lignin. The lignin absorbs light, and the presence of chromophores – light activated compounds – in the material makes the wood look brown. The fibres in the wood, which mainly comprise cellulose, are hollow tube-like structures. The air in these hollow tubes scatters light, further reducing the material’s transparency.

The new study, by researchers at the University of Maryland, demonstrates how to make wood transparent using a simple chemical – hydrogen peroxide – commonly used to bleach hair. This chemical modifies the chromophores, changing their structure so they no longer act to absorb light and colour the wood. They have found a way to make wood transparent without having to remove the lignin.

The process involved changing the lignin rather than removing it. The researchers removed lignin molecules that are involved in producing wood color. First, they applied hydrogen peroxide to the wood surface and then exposed the treated wood to UV light (or natural sunlight). The wood was then soaked in ethanol to further clean it. Next, they filled in the pores with clear epoxy to make the wood smooth.

The final product is a piece of wood that allows more than 90 per cent of light to pass through it and is more than 50 times stronger than transparent wood with the lignin completely removed. “The transparent wood is lighter and stronger than glass. It could be used for load-bearing windows and roofs,” says Hu. “It can be potentially used to make a see-through house.”

This is not the first time someone has made wood transparent, but this is the first time researchers have been able to make 10 mm-thick piece of wood, sized 100 mm by 100 mm in area, almost completely transparent.