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Summer is upon us, and many of us have already started to feel the heat of high electric bills resulting from increased air conditioning use. This means greenhouse gas emissions are increasing, too; as more people turn down the temperature inside their home or car, demand for electricity swells, putting more strain on power plants. At the same time, those with access to air conditioning are fortunate: Not everyone has the financial means or electrical access necessary to cool themselves.
A new cellulose-based material might help circumvent these environmental and accessibility concerns. Researchers at the University of Cambridge have created an innovative film that becomes cooler when exposed to direct sunlight, potentially offering an alternative to air conditioning that wouldn’t require electricity.
The film uses passive daytime radiative cooling (PDRC) to shed heat without warming the surrounding air. Cellulose is one of just a few plant-based compounds capable of PDRC. The researchers extracted cellulose nanocrystals, or CNCs, from wood and other plant sources, then dispersed the CNCs in water and allowed the suspension to evaporate. The evaporation process created a flexible arrangement of crystals that could then be applied over a white ethyl cellulose sheet to create a bi-layered iridescent film.
The Cambridge researchers presented their experimental film at the American Chemical Society’s spring 2023 meeting. When the team placed the film under direct sunlight, they found it was roughly 7 degrees Fahrenheit cooler than the surrounding air. One square meter of the film produced more than 120 watts of cooling power, nearly reproducing a residential air conditioner’s cooling effects without external resources. If the exterior of a building or vehicle was covered in the material, it could eliminate the need for conventional air conditioning.
While some white and mirrored films produce similar cooling effects via PDRC, their appearance limits usage. Like a soap bubble, the surface of the cellulose film reflects visible light to create a colorful appearance without the use of added pigment. (This is crucial, as pigments would reduce the material’s PDRC capabilities.) The result is a pleasant prismatic effect that might lend well to aesthetic-focused real-world applications like residential and automotive design. It might also be possible to mimic wood finishes, drastically expanding the film’s applications. The team is working on this next.
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