Wood may seem like a more suitable material in log cabins in forests than in modern architecture, but a team of researchers has presented at the Spring 2019 National Meeting and Exposition of the American Chemical Society – the largest scientific society the world -, a revolutionary biodegradable material : it is a new type of transparent wood that not only transmits light, but also absorbs and releases heat, which could save on energy costs in homes and buildings in general.
“In 2016, we demonstrated that transparent wood has excellent thermal insulation properties compared to glass, combined with high optical transmission,” commented Céline Montanari, a student presenting the research at the meeting. “In this work, we try to further reduce the energy consumption of the building by incorporating a material that can absorb, store and release heat.”
As economic development progresses globally, energy consumption has exploded . Much of this energy is used to light, heat and cool homes, offices and other buildings. Glass windows can transmit light, helping to illuminate and heat homes, but they don’t store energy to use when the sun goes down each day.
Three years ago, researcher Lars Berglund and his team from the Royal Institute of Technology KTH in Stockholm, Sweden, reported on an optically transparent wood in the journal Biomacromolecules . Experts made the material by removing a light-absorbing component, a polymer called lignin , from the cell walls of balsa wood. To reduce light scattering, they incorporated acrylic into the porous wood scaffold. The result was that you could see through the material, but it was vague enough to provide privacy if used as a building material. Transparent wood also had favorable mechanical properties, allowing it to withstand heavy loads.
Adding the ability to store heat
Based on this work, Montanari and Berglund added a polymer called polyethylene glycol or macrogol to the wood. “We chose macrogol because of its ability to store heat, but also because of its high affinity for wood,” says Montanari. “In Stockholm, there is a really old ship called Vasa, and the scientists used macrogol to stabilize the wood. So we knew that this polyether can really penetrate the cells of the wood.”
Known as a “phase change material”, macrogol is a solid that melts at a temperature of about 26.6 ° C, storing energy in the process. The melting temperature can be adjusted using different types of polymer. “During a sunny day, the material will absorb heat before it reaches the interior space, and the interior will be colder than the exterior,” explains Montanari. “And at night, the opposite happens: the PEG becomes solid and releases heat inside so that it can maintain a constant temperature in the house.”
The team encapsulated this polymer within the wooden scaffold, preventing leakage of the polymer during phase transitions. They also incorporated acrylic into the material to protect it from moisture. As in its previous version, the modified wood was transparent, although slightly cloudy and strong, but it had the added advantage of storing heat.
The researchers note that transparent wood has the potential to be more environmentally friendly than other building materials such as plastic, concrete and glass. In addition to its thermal storage capacity, transparent wood may be easier to dispose of after it has done its job. “Polyethylene glycol and wood are biological and biodegradable. The only part that is not biodegradable is acrylic, but this could be replaced by another bio-based polymer, ” explains Berglund.
Now the experts will focus on scaling the production process to make it industrially feasible and also more efficient in terms of energy management. The researchers estimate that transparent wood could be available for specific interior design applications in as little as five years.
Reference: This research was presented at a meeting of the American Chemical Society in the Orange County Convention Center.
Image credit: American Chemical Society
