Researchers are working to make transparent wood, which could replace some of the glass traditionally used in buildings and cut energy costs. The wood can withstand much stronger impacts than glass, bending or splintering instead of shattering.
Engineers in Sweden and the United States have found ways to brush wood with chemicals and add polymers that turn it transparent. This process removes lignin, which gives the wood its color and prevents light from passing through.
Improved Transparency
As the world looks to reduce its carbon footprint and transition to green construction, researchers are focusing on refining wood as a sustainable material. Their efforts have resulted in insulating materials that can replace glass and also in transparent wood, which allows for a substantial amount of light to pass through it. However, the material doesn’t yet have enough strength to be used in load-bearing applications. Scientists are working to solve this problem by impregnating the wood with polymers that will strengthen it.
Transparent wood is made from two basic ingredients: cellulose, tiny fibres, and lignin, a glue-like compound that gives it its brown colour and makes it opaque. To make it transparent, scientists dissolve the lignin molecules using a hazardous chemical process known as delignification. The remaining white wood can then be coated with synthetic polymers to create a transparent material.
The mechanical properties of transparent wood depend on the alignment of the cellulose nanofibres within the cell wall. In particular, the tensile strengths of aesthetic transparent wood are enhanced along the fiber direction but lower perpendicular to it. This is a challenge for scaled-up production of the material.
To address this, a research group led by Lars Berglund from Swedish KTH University and a team at the University of Maryland developed an improved method for fabricating transparent wood. They developed a spatially selective delignification technique that preserves the original patterns of the wood while eliminating color and adding transparency. In addition, they designed a polymer with a refractive index matching that of the lignin to reduce light scattering in the material.
Self-Cleaning
Scientists have given wood a makeover, turning it into a transparent material that could be used in place of glass in green buildings. The material can also store and release heat, making it an efficient energy-saving alternative to other building materials.
Transparent wood allows more than 90 per cent of light to pass through it, and is stronger than traditional timber, researchers say. It is also more insulating than glass and may require less energy to manufacture. If it were cut thicker, the material could even be used as a structural component of a building.
To make the wood transparent, the scientists bleached the brown lignin molecules with hydrogen peroxide and removed the pigments. The result was white wood that is almost completely clear, with a high optical haze. They then infused the wood with polyethylene glycol, a phase change material that is able to absorb and store energy. This was injected into the channels and veins of the wood, which are ideal for this purpose thanks to their Nano porosity. The polyethylene glycol is encapsulated by acrylic, such as polymethyl methacrylate, which makes the transparent wood durable and waterproof.
The resulting material is able to absorb and store energy from the sun, melting when it’s heated, and hardening when temperatures fall. This means that it can be used to reduce energy consumption and carbon emissions, with the stored energy released at night when building occupants return home.
Strengthening
Researchers have discovered that they can make wood more transparent by stripping away lignin, the material that gives it its brown color and prevents light from passing through. They are able to do this using a simple bath of sodium hydroxide and additional chemicals, which is similar to the process used in paper production. This leaves them with transparent cellulose fibers, which are then filled with clear epoxy. This results in a material that has all of the strength of regular wood, but you can see through it!
The translucent material can be fabricated into structures that are incredibly strong and durable, with the potential to be used as the building materials for skylights and windows. This is a significant advancement because it allows natural sunlight to pass through the material, which can help reduce energy consumption in buildings and save on lighting costs.
This new transparent wood also boasts UV-blocking capabilities and has a lower thermal conductivity than traditional glass, which makes it an attractive alternative to standard construction materials. The research team is currently working to optimize the process and scale it up so that the transparent material can be used in real-world applications.
The research could lead to a wide variety of uses, including making solar panels more efficient, improving the transparency of electronics screens, and allowing for more efficient building insulation. But it may be several years before we actually see transparent wood in a real-life structure. Montanari admits that there is still a lot of work to be done, including replacing the acrylic with a biodegradable material for some applications, incorporating it into computer models of buildings, and conducting tests on real-life wooden structures.
Applications
Researchers at the University of Maryland have developed a way to turn ordinary wood into transparent material that is stronger and better insulating than glass. They used a chemical to strip the lignin from trees, which is the glue that holds together tiny fibres known as cellulose. Lignin contains molecules that absorb light, so without it, wood is opaque. The team then filled the resulting holes with polymer, making the material clear.
The result is a see-through material that can be moulded into windows and walls. It looks like frosted glass, but with a more natural appearance and the ability to harvest sunlight to power building lighting. The material is also more durable than glass and has the potential to be cheaper to produce.
Boitouzet has already started using the material to make acoustic panels that can absorb vibrations, and she says transparent wood could also be made into ‘smart’ windows that switch between clear and dark depending on how much electricity they receive. The technology would work by coating the transparent wood with layers of quantum dots, which can be made to fluoresce when exposed to a certain type of light.
The researchers have been working on improving the transparency of the material, and their research shows that it has the potential to become an essential engineering component in green energy-efficient buildings. Besides its aesthetic beauty, transparency and tunable haze, the material has good mechanical robustness, UV-blocking, thermal insulation and sustainable production.