Lignin Particles for Multifunctional Membranes, Antioxidative Microfiltration, Patterning, and 3D Structuring

We introduce a new type of particle-based membrane based on the combination of lignin particles (LPs) and cellulose nanofibrils (CNF), the latter of which are introduced in small volume fractions to act as networking and adhesive agents. The synergies that are inherent to lignin and cellulose in plants are re-engineered to render materials with low surface energy (contact angle measurements) and can be rendered water-resistant with the aid of wet-strength agents (WSAs). Importantly, they are most suitable for antioxidative separation (ABTS^•+ radical inhibition): membranes with uniform porous structures (air permeability and capillary flow porosimetry) allow effluent oxidation at 95 mL/cm², demonstrating, for the first time, the use of unmodified lignin particles in flexible membranes for active microfiltration. Moreover, the membranes are found to be nonfouling (protein adhesion and activity rate). The inherent properties of lignin, including UV radiation blocking capacity (UV transmittance analysis) and reduced surface energy, are further exploited in the development of tailorable and self-standing architectures that are almost entirely comprised of nonbonding LP (solids content as high as 92 w/w%). Despite such composition, the materials develop high toughness (oscillatory dynamic mechanical analysis), owing to the addition of minor amounts of CNF. Multifunctional materials based on thin films (casting), 3D structures (molding), and patterned geometries (extrusion deposition) are developed as a demonstration of the potential use of lignin particles as precursors of new material generation. Remarkably, our observations hold for spherical LPs since a much poorer performance was observed after using amorphous powder, indicating the role of size and shape in related applications.