Construction of Reversible Cross-Linked Polyurethane Composite Coating with Recyclability and Passive Radiative Cooling Performance

In this work, a type of modified aluminum oxide-titanium dioxide composite filler (MAT) was employed as a high refractive index and wide electron band gap filler and incorporated into reversible cross-linked polyurethane (RCPU) with disulfide bonds to prepare passive radiative cooling coating. After modification by a 3-isocyanatopropyltrimethoxysilane coupling agent, the urethane and siloxane chains were found to covalently bond between aluminum oxide and titanium dioxide, which imparts the MAT filler a good dispersion level in the RCPU matrix. The as-prepared RCPU-MAT10 coating with 10 wt % of the MAT filler possessed desirable solar reflectance and thermal emittance in atmospheric transparency windows of 0.874 and 0.977, respectively, resulting in a subambient daytime cooling of 8.7 °C (solar light irradiation is 814 W/m2) and a nighttime cooling of 4.2 °C under outdoor environments. Taking advantage of the dynamic exchange feature of disulfide bonds, RCPU-MAT10 exhibited good recyclability behavior under heating (100 °C) for 10 min. More encouragingly, the recycling efficiency in passive radiative cooling performance for RCPU-MAT10 still remained above 95% after three cycles.