An eco-friendly fibrous membrane with birch-trunk-like fibers enabling enhanced daytime radiative cooling

Abstract

Electrospun fibrous membranes incorporating nanospheres present a promising strategy for radiative cooling, primarily due to achieving high solar reflectivity and mid-infrared emissivity. However, their practical development is often hindered by excessive use of organic solvents, susceptibility to delamination, and agglomeration of nanospheres. In this work, an eco-friendly fibrous membrane was developed via co-electrospinning of waterborne polyurethane, polyoxyethylene, and SiO₂ nanospheres (BTFM). In contrast to cellulose acetate and polytetrafluoroethylene fibrous membranes, BTFM exhibits a dense and delamination-resistant structure. The incorporation of polyoxyethylene as a thickener facilitates the uniform entanglement of SiO₂ nanospheres with polyurethane chains, resulting in birch-trunk-like fibers with an average diameter of 1.65 μm. With a thickness of approximately 531 μm and a SiO₂ content of 3.6 wt%, the BTFM membrane possesses an optimized pore structure and fiber surface ridge-groove topography, contributing to a solar reflectivity of 93.9%. Synergistic vibrational absorption from the polymer and SiO₂ endows BTFM with ∼96% of mid-infrared emissivity. These optical properties surpass those of previously reported solvent-based fibrous membranes. Under a peak solar irradiance of 980 W/m², BTFM achieved a temperature reduction of 13.4 °C and 10 °C compared to polyester with and without polyethylene film, respectively. Even under an average solar irradiance of ∼560 W/m², it provided a temperature drop of ∼4 °C relative to bare skin. BTFM outperformed traditional textiles, including polyester, cotton, synthetic leather, and leatheroid, in terms of cooling efficiency. Furthermore, BTFM exhibited excellent UV resistance, flexibility, water vapor permeability, and air permeability, underscoring its practical potential in cooling textiles. This work offers a sustainable and high-performance radiative cooling material with clearly superior properties.