Abstract

Lignin valorization is a key strategy for advancing sustainable biorefineries by transforming this abundant aromatic polymer into high-value chemicals, thereby reducing dependence on fossil-based resources. This study explores a novel self-sustaining Fenton-like depolymerization process operating under mild conditions, in which lignin functions simultaneously as a chelating and reducing agent. The formation of lignin-FeIII complexes, followed by in situ reduction to FeII, enables continuous hydroxyl radical (•OH) generation from H2O2 without the need for external catalysts, energy inputs, or additional FeII sources. The depolymerization mechanism was evaluated through comprehensive physicochemical and chemical characterization. Gel permeation chromatography (GPC) revealed a 49% reduction in molecular weight (Mw) under optimized conditions (FeIII 0.4mgL-1, H2O2 68mgL-1), with dispersity decreasing from 3.21 to 2.52. Kinetic modeling indicated a biphasic process, with initial depolymerization followed by partial repolymerization driven by radical dynamics, captured using empirical polynomial and rate-based models. FT-IR spectroscopy confirmed the oxidative cleavage of β-O-4 ether and C-C bonds, supported by increased carbonyl and syringyl/guaiacyl absorption bands. SEM and contact angle analyses revealed morphological disruption and reduced hydrophobicity. GC-MS identified low-molecular-weight oxidation products, including propenylguaiacol, 2,6-dimethoxyphenol, and aromatic ketones, corresponding to selective cleavage pathways and yielding 7-70% total conversion into identifiable aromatic monomers. These results provide multiple lines of evidence - molecular weight reduction, structural bond cleavage, and chemical product distribution - demonstrating the effectiveness of the lignin depolymerization approach. This work highlights the dual functional role of lignin in catalyzing its own oxidative breakdown and offers a low-energy, catalyst-free route for lignin valorization. The mechanistic insights gained herein establish a foundation for future studies investigating radical-mediated pathways using advanced techniques such as electron paramagnetic resonance (EPR), which are currently under development. © 2025 Elsevier Ltd. All rights are reserved.