Porous Polyurethane-Based Radiative Cooling Film with Excellent Mechanical and Flame-Retardant Properties

Passive daytime radiative cooling is an electricity-free cooling technology that radiates sunlight and radiates heat to cold space. However, traditional radiation cooling materials are facing many challenges, such as poor mechanical properties or non-flame retardancy. Herein, a flame-retardant porous radiative cooling polyurethane and cellulose acetate composite film with excellent mechanical properties was successfully designed and constructed. The porous structure was achieved by low boiling point solvent volatilization and high boiling point solvent displacement. The resulting film exhibits high solar reflectivity (98.2%), high infrared emissivity (94.3%), and excellent mechanical properties (13.2 MPa). Also, it can effectively cool down 15.6 °C in an outdoor environment with 900 W m–2 sunlight radiation. In addition, good flame-retardant and color aesthetic properties facilitate their application as building materials to achieve high efficiency and energy conservation. Therefore, this work provides an approach for radiative cooling in a complex environment.