From Wool Waste to Clean Air: A Green Sandwich Membrane Solution

The mitigation of air pollution caused by fine particulate matter remains an urgent global concern. To address this challenge, sustainably and bio-based air filters incorporating waste-derived natural fillers offer a promising alternative to conventional synthetic materials. In this study, innovative sandwich-structured membranes were developed by integrating a hot-pressed mat of waste wool fibers (WWFs) as a structural core, flanked by two fibrous outer layers composed of polylactic acid (PLA) and finely ground waste wool powder (WWP), produced via the solution blow spinning (SBS) technique. The resulting sandwich-structured waste wool-based membrane (S-WWM) was tested under various flow conditions and environmental humidity levels. The incorporation of 10 wt% WWP into the PLA matrix enhanced the spinnability and fiber morphology due to changes in solution viscosity. The multilayer structure, characterized by a balance between pore size and low packing density, achieved outstanding PM₁ filtration efficiency (99.5%), with a moderate pressure drop (70 Pa) at 32 L/min. In addition, the membrane showed strong performance retention over five filtration cycles and remained stable in humid conditions. These membranes are characterized by the unique properties of wool fibers, such as excellent breathability and mechanical strength, combined with high filtration efficiency achieved by PLA composite fibers. These results demonstrate the potential of upcycled wool-based materials in fabricating high-performance, reusable, and environmentally friendly air filtration systems.