Cooling buildings with wood-based foam — ScienceDaily

Summer is almost here, a time when many people are trying to beat the heat. But running air conditioners constantly can be expensive and unnecessary. Now researchers who report in ACS’ Nano-letters have designed a lightweight foam based on wood-based cellulose nanocrystals that reflects sunlight, emits absorbed heat and is thermally insulating. They suggest the material could reduce buildings’ cooling energy needs by more than a third.

Although scientists have developed cooling materials, they have drawbacks. Some materials that passively release absorbed heat pass a lot of heat to buildings in the direct midday sun of the summer months. And other materials that reflect sunlight don’t perform well in hot, humid, or cloudy weather. So, Yu Fu, Kai Zhang and their colleagues wanted to develop a sturdy material that could reflect sunlight, passively release heat, and block wayward heat from passing through.

To generate a cooling material, the researchers connected cellulose nanocrystals with a silane bridge, before freezing and lyophilizing the material under vacuum. This process vertically aligned the nanocrystals, creating a white, lightweight foam that reflected 96% of visible light and emitted 92% of absorbed infrared radiation. When placed on a foil-lined box sitting outside at midday, the material kept the temperature inside the box 16 degrees F cooler than the outside. Additionally, the material kept the inside of the box 13 degrees F cooler when the air was humid. As the cellulose-based foam was compressed, its cooling capacity decreased, revealing adjustable cooling properties. The team calculated that placing the foam on the roof and exterior walls of a building could reduce its cooling energy needs by an average of 35.4%. Since the performance of wood-based cellulose foam can be adjusted based on weather conditions, the researcher says the technology could be applied in a wide range of environments.

The authors acknowledge funding from the German Research Foundation (DFG), Lower Saxony Ministry of Science and Culture, National Natural Science Foundation of China, Jiangsu. & Practice Innovation Program of Jiangsu Province, National First-class Disciplines (PNFD), Jiangsu Government Scholarship for Study Abroad and China Scholarship Council.

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Material provided by American chemical society. Note: Content may be edited for style and length.

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