New coconut, lemon material could be used to heat and cool our homes

When used in housing construction, this novel material is capable of capturing both heat and cold. Given an ambient temperature of 24°C, the team estimates that 100 kilos of this material can save about 2.5 kWh per day in heating or cooling.

The process begins with removing lignin from wood, which opens pores in the wood as well as strips the color—resulting in transparent wood. The wood gaps are then filled with citrus (limonene acrylate) and coconut-based molecules.

When heated, limonene acrylate molecules transform into a bio-based polymer, restoring the wood's strength along with allowing light to permeate. As a result, the coconut molecules can become trapped inside the material, facilitating energy storage and release.

“The elegance is that the coconut molecules can transition from a solid-to-liquid which absorbs energy; or from liquid-to-solid which releases energy, in much the same way that water freezes and melts,” said Céline Montanari, one of the authors of this study, in a statement. 

We can use this transition method to heat or cool our immediate surroundings as needed, the authors note. Furthermore, this building material is particularly useful for saving energy. 

Describing the material's applications, Peter Olsén adds: “Why not as a future material in greenhouses? When the sun shines, the wood becomes transparent and stores more energy, while at night it becomes cloudy and releases the heat stored during the day. That would help reduce energy consumption for heating and at the same time provide improved growth.”

Study abstract:

The sustainable development of functional energy-saving building materials is important for reducing thermal energy consumption and promoting natural indoor lighting. Phase-change materials embedded in wood-based materials are candidates for thermal energy storage. However, the renewable resource content is usually insufficient, the energy storage and mechanical properties are poor, and the sustainability aspect is unexplored. Here a novel fully bio-based transparent wood (TW) biocomposite for thermal energy storage, combining excellent heat storage properties, tunable optical transmittance, and mechanical performance is introduced. A bio-based matrix based on a synthesized limonene acrylate monomer and renewable 1-dodecanol is impregnated and in situ polymerized within mesoporous wood substrates. The TW demonstrates high latent heat (89 J g−1) exceeding commercial gypsum panels, combined with thermo-responsive optical transmittance (up to 86%) and mechanical strength up to 86 MPa. The life cycle assessment shows that the bio-based TW has a 39% lower environmental impact than transparent polycarbonate panels. The bio-based TW holds great potential as scalable and sustainable transparent heat storage solution.