Implantation of web-like cellulose nanofibrils on electrospun fibrous membrane for boosting filtration performance.

Air pollution such as particulate matter is always a serious threat to public health, thus many disposable and degradable air filters were designed to deal with this severe challenge avoiding the secondary pollution after discarding. Herein, inspired by the natural spider web structure, a hierarchical porous composite fibrous membrane containing web-like cellulose nanofibrils (CNF) was developed. The implanted porous CNF membranes with web-like among the inter-fiber voids of electrospun poly(ethylene-co-viny alcohol) fibrous membrane were realized via a layer-by-layer (LBL) method followed by an elevated-temperature drying, which exhibit a smaller diameter with one or two orders of magnitude reduction comparing with the substrate fibers. The morphology of implanted CNF membranes can be regulated by changing the CNF dispersion concentration, PH, solution composition as well as the LBL times. The addition of a small amount of isopropyl alcohol to the CNF solution can efficiently facilitate the implantation of web-like CNF on substrate, resulting in both improvements on the mechanical properties and filtration capacity. The result shows that the implanted web-like CNF of as-prepared composite membrane can enhance the PM 0.3 capture ability (reaching 96.8 %) while not surge its pressure drop (225.7 Pa) exceeding N95 standard. This work presents a new design and fabrication of CNF-based filter materials directly without using freeze drying, which can not only provide a fully or partially biodegradable air filter but also give encouragement to explore new filters efficiently.