Benefits of transparent wood are heating up

Since the initial creation of transparent wood three years ago, further developments have resulted in additional material benefits, including the ability to store and release heat.

In 2016, scientists from Sweden's KTH Royal Institute of Technology created specially treated timber that could transmit light, acting as a cheaper alternative to the silica-based glass traditionally used in windows and solar cells.

Now, scientists are reporting a new iteration of transparent wood with the added benefit of being able to absorb heat, before releasing it at a later time, resulting in potential energy savings.

The new material can also withstand heavy loads and is biodegradable, theoretically making it suitable for eco-friendly homes and other buildings in the future.

The researchers presented their findings at the American Chemical Society (ACS) Spring 2019 National Meeting & Exposition.

One of the PhD students who conducted the research, Céline Montanari, said as economic development has progressed worldwide, energy consumption has soared.

“Much of this energy is used to light, heat and cool homes, offices and other buildings. Glass windows can transmit light, helping to brighten and heat homes, but they don’t store energy for use when the sun goes down,” Ms Montanari said.

Building on previous work, Montanari and her team added the polymer polyethylene glycol (PEG) to the de-lignified wood.

“We chose PEG because of its ability to store heat, but also because of its high affinity for wood. In Stockholm, there’s a really old ship called Vasa, and the scientists used PEG to stabilise the wood. So we knew that PEG can go really deep into the wood cells,” Ms Montanari said.

PEG is a solid that melts at a temperature of around 27 degrees Celsius, storing energy in the process. For this reason, it is known as a ‘phase-change material’. 

“During a sunny day, the material will absorb heat before it reaches the indoor space, and the indoors will be cooler than outside. And at night, the reverse occurs. The PEG becomes solid and releases heat indoors, so that you can maintain a constant temperature in the house,” Ms Montanari said.

To prevent leakage during phase changes, the team placed PEG within the de-lignified wood scaffold. Acrylic was also added to protect the material against humidity. 

The result was a material that shared the transparent, yet slightly hazy, quality and load-bearing capabilities of the original version, but with the added advantage of heat storage and release.

In addition, PEG and wood are bio-based and biodegradable. While the acrylic element does not share this particular quality, it could ultimately be replaced by another bio-based polymer in the future.

The focus of the research team is now turning to scaling up the production process to make it industrially feasible. They are currently estimating availability for niche applications within around five years.

Source: Montanari C, Li, Y, Chen, H, Yan, M, & Berglund, L, 2019, ‘Transparent Wood for Thermal Energy Storage and Reversible Optical Transmittance’, ACS Applied Materials & Interfaces 

Photo credit: American Chemical Society