Sustainable Passive Radiative Cooling Films Based on Variable-Stiffness Poly(thiourethane) Vitrimers

Vitrimers, a class of covalent adaptable networks (CANs), combine the mechanical stability of thermosets with the reprocessability of thermoplastics via dynamic bond exchange. This offers a sustainable solution for functional films prone to outdoor degradation. Meanwhile, passive radiative cooling (PDRC) efficiently lowers temperatures by minimizing solar absorption and maximizing thermal emission through the 8-13 um atmospheric window. However, conventional PDRC films lack reprocessability and shape adaptability.
Here, we fabricated reprocessable PDRC composite films using a multifunctional poly(thiourethane) vitrimer (MFTU) matrix and hexagonal boron nitride (hBN) fillers. The MFTU matrix undergoes Zn(DTC)2-catalyzed associative exchange, enabling excellent hot-press reprocessability. Additionally, the semi-crystalline structure of MFTU provides a thermally controlled "variable stiffness." Below its melting temperature (Tm), the film remains rigid, whereas above Tm, it becomes pliable, allowing seamless adaptation to curved architectural surfaces.
To optimize performance, hBN fillers were incorporated at 10, 20, and 30 wt%. Higher hBN content improved tensile strength but decreased elongation due to filler reinforcement. Notably, FT-IR and TGA confirmed that the chemical and thermal structures remained stable even after repeated hot-press recycling. Furthermore, UV-Vis-NIR and FT-IR emittance spectra proved that the high solar reflectance and selective atmospheric window emittance were successfully preserved.
Consequently, the MFTU/hBN vitrimer films demonstrate great potential for sustainable exterior thermal management, synergizing recyclability, shape adaptability, and cooling efficiency.