Biodegradable PLA‐Bleached Pulp Composites for Sustainable Building Cooling Applications

Abstract Passive daytime radiative cooling (PDRC) has emerged as a promising strategy for energy‐efficient thermal management, particularly under direct sunlight. In this study, eco‐friendly polylactic acid (PLA)/bleached pulp composites are developed using a simple solution‐casting method to investigate their potential as high‐performance PDRC materials. The composites demonstrate exceptional emissivity in the long‐wavelength infrared range, reaching a maximum of 0.94 at a 70 wt.% cellulose content. This superior performance is attributed to the unique molecular structure of cellulose and hemicellulose in the bleached pulp, which enhances optical scattering and emissive properties across the infrared spectrum. The composites also exhibit high solar reflectance in the visible‐to‐near‐infrared region, which is critical for minimizing solar heating. Outdoor experiments revealed significant cooling effects, with the 70 wt.% bleached pulp composites achieving a surface temperature 11.1 °C below ambient and demonstrating a radiative cooling power of 110.17 W m ^{− 2} . Additionally, in the biodegradation experiments, successful biodegradation is observed, with the sample completely decomposing over 18 d. These results highlight the effectiveness of the PLA/bleached pulp composites under real‐world conditions and their potential for sustainable thermal management applications. Consequently, this study provides a foundation for the further optimization of PDRC materials using simple fabrication techniques, offering a cost‐effective and environmentally friendly solution for passive cooling systems.