Electrospun PCL Filtration Membranes Enhanced with an Electrosprayed Lignin Coating to Control Wettability and Anti-Bacterial Properties.

This study reports on the two-step manufacturing process of a filtration media obtained by first electrospinning a layer of polycaprolactone (PCL) non-woven fibers onto a paper filter backing and subsequently coating it by electrospraying with a second layer made of pure acidolysis lignin. The manufacturing of pure lignin coatings by solution electrospraying represents a novel development that requires fine control of the underlying electrodynamic processing. The effect of increasing deposition time on the lignin coating was investigated for electrospray time from 2.5 min to 120 min. Microstructural and physical characterization included SEM, surface roughness analysis, porosity tests, permeability tests by a Gurley densometer, ATR-FTIR analysis, and contact angle measurements vs. both water and oil. The results indicate that, from a functional viewpoint, such a natural coating endowed the membrane with an amphiphilic behavior that enabled modulating the nature of the bare PCL non-woven substrate. Accordingly, the intrinsic hydrophobic behavior of bare PCL electrospun fibers could be reduced, with a marked decrease already for a thin coating of less than 50 nm. Instead, the wettability of PCL vs. apolar liquids was altered in a less predictable manner, i.e., producing an initial increase of the oil contact angles (OCA) for thin lignin coating, followed by a steady decrease in OCA for higher densities of deposited lignin. To highlight the effect of the lignin type on the results, two grades of oak (AL-OA) of the