Transparent wood can store and release heat

Wood may look more comfortable in log cabins than modern architecture, but a specially treated type of wood could be the building material of fashion tomorrow. Today, scientists are reporting a new type of transparent wood that not only transmits light, but also absorbs and releases heat, thereby saving energy. The material can withstand heavy loads and is biodegradable, opening the door to its potential use in homes and other green buildings.

The researchers will present their findings today at the 2019 Spring National Meeting and Exposition of the American Chemical Society (ACS).

"In 2016, we showed that transparent wood has excellent thermal insulation properties compared to glass, combined with high optical transmittance," says Céline Montanari, Ph.D. student presenting the research. during a meeting. "In this work, we have tried to further reduce the energy consumption of the building by incorporating a material capable of absorbing, storing and releasing heat."

As economic development progresses around the world, energy consumption has increased. Much of this energy is used to light, heat and cool homes, offices and other buildings. Glass windows can transmit light, helping to light and heat homes, but they do not store the energy needed for use when the sun goes down.

Three years ago, lead investigator Lars Berglund, Ph.D., and colleagues at KTH Royal Institute of Technology in Stockholm, Sweden, reported an optically transparent wood in the ACS journal. biomacromolecules. The researchers fabricated the material by removing a light-absorbing component called lignin from the cell walls of balsa wood. To reduce the diffusion of light, they incorporated acrylic into the porous wood scaffolding. The team could see through the material, but it was fuzzy enough to ensure the confidentiality of its use if used as a major building material. Transparent wood also had favorable mechanical properties enabling it to withstand heavy loads.

Building on this work, Montanari and Berglund have added a wood called polyethylene glycol (PEG) to delignified wood. "We chose PEG for its ability to store heat, but also for its strong affinity for wood," explains Montanari. "In Stockholm, there is a very old ship called Vasaand scientists used PEG to stabilize the wood. We therefore knew that PEG could penetrate very deeply into the cells of the wood. "

Known as "phase change material", PEG is a solid that melts at a temperature of 80 ° F and stores energy. The melting temperature can be adjusted using different types of PEG. "On a sunny day, the material will absorb heat before reaching the interior space, and the interior will be colder than outside," says Montanari. "And at night, the reverse happens: the PEG becomes solid and releases heat indoors so you can maintain a constant temperature in the house."

The team encapsulated PEG in the delignified wood scaffold, which prevented polymer leakage during phase transitions. They have also incorporated acrylic into the material to protect it from moisture. Like their previous version, the modified wood was transparent, although slightly cloudy and strong, but had the added benefit of storing heat.

The researchers point out 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 capabilities, clear wood may be easier to dispose of after performing its function. "PEG and wood are both bio-based and biodegradable," notes Berglund. "The only part that is not biodegradable is acrylic, but that could be replaced by another biobased polymer."

From now on, the objective is to intensify the process of production so that it is industrially feasible. The researchers believe that the transparent wood could be available for niche applications in interior decoration just five years ago. They are also trying to increase the storage capacity of the material to make it even more energy efficient.