A systematic study on the processes of lignin extraction and nanodispersion to control properties and functionality

This article reviews a variety of literature-reported lignin isolation procedures that bring partly minor but important changes in the produced extracts. Five lignins were produced or acquired from various sources and characterized based on their thermal properties, molecular weights, chemical structures, as well as elemental compositions, which were all found to depend on their extraction methods. These extracts were then used to produce 5 different nanolignins using 2 similar facile solvent shifting methods with the difference being an alteration in pH. The nanolignins were characterized after the solvent shifting accounting for differences in pH. Nanolignins generated via only solvent exchange exhibited diameters ranging from 58 nm to 95 nm, while nanolignins precipitated using a solvent shifting method along with a shift in pH exhibited diameters ranging from 10 nm to 34 nm and dissimilar morphology, size, and surface charge. Those differences highlight the control options for nanolignin preparetion on the colloidal length scale. Understanding how different lignins can be used to generate nanolignins is mandatory for unlocking the possibilities of nanolignin for functional material applications. These nanolignins can be applied in construction, medical, and/or agricultural industries as renewable, biodegradable alternatives to existing polymer dispersions. This article is analyzing differences in chemistry and structure of lignins isolated using various protocols and reveals influence of their properties on nanolignins prepared at different pH.