Green-solvent-processable biodegradable poly(lactic acid) nanofibrous membranes with bead-on-string structure for effective air filtration: “Kill two birds with one stone”

The ultrafine particle matters (PMs) are an imminent threat to the global climate and public health because of their easy penetration through the respiratory tract and blood vessel. Tremendous efforts have been devoted by researchers on design and development of electrospun nanofibrous membranes (ENMs) for PM filtration. However, most existing ENMs suffer from the trade-off effect between removal efficiency and pressure drop, as well as non-degradability or non-recyclability, which must be settled urgently due to the ever-growing need of energy-efficient and environmentally friendly technology. Here, we report a degradable and environmentally friendly PLA bead-on-string ENM, by electrospinning with relatively green EA/DMF mixture solvent, in which the EA/DMF mixture solvent plays the role of “Killing Two Birds with One Stone”. The mixture solvent not only endows the ENM with bead-on-string structure but also improves the greenness of the ENM-making process. The air index (Ψiai) and GlaxoSmithKline (GSK) Solvent Sustainability Guide have been calculated to quantitatively illustrate the greenness of ENM-making processes. Polymer solubility experiments combined with molecular dynamics simulation (MD) demonstrate that the solvent composition plays an important role in manipulating the morphology and structure of ENM. Benefiting from the well-defined bead-on-string structure, the PLA bead-on-sting ENM could easily achieve an excellent removal efficiency over 98% for aerosol particles with an extremely low pressure drop of 29.3 Pa. Filtration progress simulation reveals that the existing beads in nanofibers are able to reduce the packing density and alleviate the pressure drop while guaranteeing the PM removal efficiency. More importantly, compared to commercial masks, the prepared PLA bead-on-string ENM (E7D3–10) presents higher filtration efficiency (PM2.5–92.6% and PM10–95.4%) in real hazy environment, which results in relatively safer PM index value (below 50 μg/m3). This work provides a platform for the design of bead-on-string ENMs via green method, thus giving access to their versatile architectural design and applications.