High‐Performance TPU / Al 2 O 3 @ TiO 2 Composite Coatings for Efficient Passive Daytime Radiative Cooling

ABSTRACT Passive daytime radiative cooling technique has been widely studied as an eco‐friendly and promising strategy to achieve efficient radiative cooling by reflecting sunlight and radiating heat through atmospheric windows. Currently, among various existing radiative cooling coatings, the polymeric radiative cooling coatings with dispersed inorganic particles are considered to be a promising candidate. Although TiO 2 ‐based materials possess high reflectivity and chemical stability, the limited infrared emissivity and long‐term stability still restrict their practical applications. To overcome these defects, rod‐like Al 2 O 3 coated TiO 2 (Al 2 O 3 @TiO 2 ) powders were firstly synthesized by high‐temperature calcination and acid modification processes. Moreover, considering the importance of durability in practical applications, thermoplastic polyurethane (TPU)/Al 2 O 3 @TiO 2 radiative cooling composite coatings were successfully developed by incorporating 50 wt% Al 2 O 3 @TiO 2 powders into the TPU solution. Results revealed that the tent coated with 400 μm thickness of TPU/Al 2 O 3 @TiO 2 slurry possessed a high solar reflectivity of 86.7% and infrared emissivity of 99.2% in the atmospheric window. Meanwhile, compared with the uncoated commercial tent, the tent coated with 400 μm thickness of TPU/Al 2 O 3 @TiO 2 layer obtained a temperature drop of 8.3°C under the air circulation environment. Moreover, the mechanical properties, anti‐fouling, self‐cleaning, water resistance, and flame retardancy properties of TPU/Al 2 O 3 @TiO 2 coated tents were evaluated. All these results demonstrated that the TPU/Al 2 O 3 @TiO 2 coating provides a viable solution for developing novel outdoor cooling products.