Highly-Scattering Cellulose-Based Films for Radiative Cooling

Passive radiative cooling (RC) enables the cooling of objects below ambient temperature during daytime without consuming energy, promising to be a game changer in terms of energy savings and CO2 reduction. However, so far most RC surfaces are obtained by energy-intensive nanofabrication processes or make use of unsustainable materials. These limitations are overcome by developing cellulose films with unprecedentedly low absorption of solar irradiance and strong mid-infrared (mid-IR) emittance. In particular, a cellulose-derivative (cellulose acetate) is exploited to produce porous scattering films of two different thicknesses, L approximate to 30 mu m (thin) and L approximate to 300 mu m (thick), making them adaptable to above and below-ambient cooling applications. The thin and thick films absorb only approximate to 5%${\approx}5\%$ of the solar irradiance, which represents a net cooling power gain of at least 17 W m(-2), compared to state-of-the-art cellulose-based radiative-cooling materials. Field tests show that the films can reach up to approximate to 5 degrees C below ambient temperature, when solar absorption and conductive/convective losses are minimized. Under dryer conditions (water column = 1 mm), it is estimated that the films can reach average minimum temperatures of approximate to 7-8 degrees C below the ambient. The work presents an alternative cellulose-based material for efficient radiative cooling that is simple to fabricate, cost-efficient and avoids the use of polluting materials.