Green extraction of polyphenolic lignin using FeCl3-mediated tartaric acid-DES and its derived lignin nanoparticles for enhancing the application performance of PVA film in green agriculture

Abstract

Lignin nanoparticles (LNPs) address the challenges associated with the complex chemical structure and high molecular weight of lignin, thereby facilitating green value-added transformations. However, the heterogeneity of lignin significantly influences the self-assembly behavior of LNPs. To obtain lignin with optimal performance for the preparation of LNPs, a novel deep eutectic solvent (DES) featuring a robust hydrogen bond network (choline chloride/tartaric acid-FeCl₃, CC/TA-FeCl₃) was developed in this study. Extracted lignin exhibited a higher phenolic hydroxyl content and lower molecular weight. Specifically, the phenolic hydroxyl content (2.90 mmol g⁻¹) increased by 15.54% compared to that extracted using (CC/lactic acid-FeCl₃ (CC/LA-FeCl₃)). Amphiphilic nanoparticles were synthesized via layer-by-layer self-assembly utilizing van der Waals forces and π–π interactions. They had a narrow particle size distribution (21–76 nm) and a small average particle size (35.33 nm). They exhibited a highly negative zeta potential of −31.25 mV and demonstrated effective free radical scavenging efficiency (79.87%). The water dispersion stability over 72 h was improved by 200%. The LNPs significantly enhanced the UV resistance (80%), tensile strength (72%), and hydrophobic characteristics (125%) of PVA films. LNPs/PVA film provides the feasibility for the high-quality development of green agriculture. These results provide a new approach for the green transformation of lignin through the preparation of efficient extraction and preparation of high-performance LNPs.