Fabricating a novel lignin@modified-cellulose-Fiber composite filter layer via layer-by-layer assembly for personal...

Commercial melt-blown filter layers, which lack antibacterial properties and are non-recyclable, are difficult to become green and sustainable materials. To overcome these challenges, this study developed a multifunctional cellulose-based filter layer using cellulose fibers (CFs) as raw material through a straightforward layer-by-layer assembly method. CFs were modified by esterification to create grafted-CFs (GCFs), then lignin was introduced via Mannich reaction to produce lignin@GCFs. Characterization methods, including FT-IR, XRD, UV-vis, and ¹³C NMR, confirmed the successful modification without disturbing the cellulose-I_β structure. The lignin@GCFs were deposited on the porous-structure high-breathable base paper to construct a lignin@GCFs-2 composite filter layer, demonstrating that its air-permeability, tensile index, and zero-span tensile strength were 72.28 μm/(Pa·s), 19.22 N·m·g^-1, and 20.25 N/cm (ROL: 24.40 N/cm/s), respectively, which completely met the physical performance standard of the middle filter layer of commercially available medical protective filters. It exhibited excellent antibacterial properties against E.coli and S.aureus with the inhibition zone of 0.60 mm and 3.00 mm, respectively. Notably, it achieved high filtration efficiency against PM_2.5, remaining above 99.00 % after being assembled into the medical protective filters and worn for 48.0 h. Furthermore, the composite filter layer was completely degraded after 120 days. This innovative, cellulose-based filter layer presents a promising alternative to the middle filter layer of commercially available medical protective filters, advancing the development of cellulose-based filtration materials.