Extensive efforts to valorize lignin have led to isolating them as nanoscale particles, which unlocked their enormous potential for advanced applications. Numerous methods for preparing lignin nanoparticles (LNPs) were proposed but a method that can easily be adapted on an industrial scale remains a challenge. In this study, we demonstrated a green, rapid and direct method for preparing LNPs from alkaline pulping liquor (APL) by combining acid-precipitation and ultrasonication. The mild ultrasonication, which only required 5 min, was achieved by sonicating directly without prior drying the acid-precipitated and dialyzed lignin. The process enabled the production of monodispersed, spherical LNPs (Fig. 1) with an average hydrodynamic diameter (DH) of 80 nm and with a zeta potential of -63 mV. The nanostructure of the LNPs in aqueous system studied by small-angle x-ray scattering showed hierarchical structure (Fig. 1) consisting of mass fractal aggregates, with radius of gyration of 23-27 nm, of compact, smaller subunits. Based on the FTIR and 2D-HSQC NMR spectra of the LNPs, the chemical structure remained the same after ultrasonication. Optimization of the method showed the potential for minimizing acid consumption, shortening the dialysis time, and processing directly the APL with as much as 20 wt% lignin. The LNPs were stable during storage for 180 days, at a pH range of 4-7 and in a dispersing medium below 0.1 M NaCl. Furthermore, the isolated LNPs without additional surfactant can emulsify oil in water and form stable emulsions for several days. Thus, the developed method, which does not use hazardous organic solvents or intensive ultrasonication, opens a sustainable and highly scalable approach to producing LNPs directly from APL. The organic solvent-free LNPs can be further explored as bio-based interfacial stabilizers in the food and medical industries.

Green, rapid and direct preparation of lignin nanoparticles from alkaline pulping liquor

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.