Robust, stable cooling cellulose composite: Coupling nano-SiO₂ and cellulose acetate in natural cellulose

Passive radiative cooling material of cellulose by coupling inorganic nanoparticles, have demonstrated competitive advantages in sustainably cooling buildings and constructions due to their voluminous availability, biodegradability, renewability, and natural origin. However, the weak stability of cellulose-inorganic nanoparticle materials when exposed to water or external forces remains a significant challenge that impedes their practical application. In this study, we proposed an easy-to-prepare, scalable, and robust cooling cellulose composite by coupling nano-SiO₂ and cellulose acetate (CA) within cellulose fibers, using the mature pulping and paper process (filling of inorganic particles of nano-SiO₂ and subsequent sizing of polymer of CA). More importantly, the CA molecules form the strong bonding with the cellulose molecules due to the high similarity of their molecular structure, which makes CA function as a "glue" to effectively fasten nano-SiO₂ on the cellulose fibers. Correspondingly, our cellulose composite features desirable robustness and structural stability even undergoing mechanical beating and water-soaking treatments, demonstrating its excellent robustness and desirable adaptability to natural environments, such as wind and rain. As a result, despite undergoing water-soaking (for 40 days) or environmental exposure (for 90 days), the cooling cellulose composite still exhibits excellent solar reflectance (>95 %) and infrared thermal emissivity (>0.95 at 8-13 μm), enabling sub-ambient temperature (∼6.5 °C during daytime and ∼8 °C at nighttime) throughout the day. Our cooling cellulose composite demonstrates promising potential as an environmentally friendly, low-cost, and stable cooling material in our low-carbon society.