From Grape Stalks to Lignin Nanoparticles: A Study on Extraction Scale-Up, Solubility Enhancement and Green Nanoparticle Production

To effectively valorize lignin, some challenges must be addressed. First, emerging techniques based on green methods may experience difficulties during the scale-up process. Secondly, the low solubility of lignin can hinder further valorization. This study investigated the impact of lignin extraction scale-up on yield and purity and evaluated strategies to enhance lignin solubility. Lignin from grape stalks was extracted using two previously optimized methods-alkaline and deep eutectic solvents-at a scale-up by factors of 5, 10, and 20 times. Although a slight decrease in extraction yield was observed with increasing scale, lignin purity remained consistent across all conditions. After extraction, lignin samples were subjected to solubilization tests using surfactants (Tween 20, Tween 80, and polyethylene glycol) and organic solvents (ethanol and acetic acid). Results demonstrated that surfactants were notably more effective in solubilizing lignin (up to 74.5%) compared to organic solvents. Furthermore, as an alternative to lignin solubilization, the production of lignin nanoparticles through ultrasonication with minimal chemical use was also explored. Upon optimization, spherical nanoparticles with a mean diameter of approximately 200 nm were successfully obtained. The use of surfactants was necessary to avoid nanoparticle aggregation during concentration steps and to enhance colloidal stability. This study demonstrates the feasibility of scaling up lignin extraction methods and further explores two approaches to enhancing the valorization of the obtained lignin-solubilization and the production of lignin nanoparticles-thereby contributing to the development of efficient and sustainable strategies for diverse lignin-based applications.