A Facile Preparation of Super Long-Term Stable Lignin Nanoparticles from Black Liquor

With the increase in lignin availability, materials derived from micro- and nano-scale lignin developed rapidly. However, the tedious processes of raw-lignin pretreatment and poor stability seriously restrict the large-scale applications of lignin nanoparticles. To overcome these problems, in this work, a novel green and simple approach was developed to produce super long-term stable lignin nanoparticles (LTSL NPs). The LTSL NPs were prepared directly from black liquor via an acid precipitation method. The obtained LTSL NPs exhibited well uniformity, excellent dispersibility, controllable size, and super long-term stability in aqueous media (no apparent size increase or any particle precipitation for 90 days in neutral water medium). Analyses of nuclear magnetic resonance and ion chromatography revealed that LTSL NPs exhibited higher S/G ratio and higher content of hemicellulose comparing with the lignin nanoparticles which obtained from traditional solvent exchange (ethanol/H₂ O) method. In addition, the size of the LTSL NPs can be well controlled by tuning the degree of acid precipitation (the final pH value). This work not only can promote the development of lignin-based nanomaterials, but also provides a promising utilization pathway for black liquor that simultaneously achieves the fabrication of lignin materials and hemicellulose application.