Acidic Oxidative Depolymerization Towards Functionalized Low Molecular Weight Lignin and High Value-Added Aliphatic Monomers: Operating Conditions, Scale-Up, and Crosslinking

Lignin, a complex aromatic biopolymer abundant as waste in biorefineries and the pulp and paper industry, holds significant potential for valorization. This study presents the oxidative depolymerization of Lignoboost lignin (LB) using H2O2 under mild, solvent- and catalyst-free, inherently acidic conditions at temperatures from 50-70°C. The depolymerized LB was rich in aromatic dimers-trimers (68.6 wt.%) with high functionalization (2.75 mmol/g OHphen, 3.58 mmol/g OHcarb, 19.5 wt.% of H in -CH=CH-), and aliphatic dicarboxylic acids (53.4 wt.% of the monomers). Acidic conditions provided higher depolymerization and functionalization than alkaline conditions, alongside simplified product recovery. The process was also successfully applied to Kraft lignin (KL) from black liquor, demonstrating its versatility and robustness. The optimized conditions were scaled up (×25), improving efficiency and yielding a Mw and Đ of 464 g/mol and 1.3, respectively. As proof of concept, the scaled-up product underwent radical crosslinking, resulting in a new biopolymer with higher thermal stability than LB (54.2 wt.% residual mass at 600°C versus 36.1 wt.%). This green, scalable depolymerization process enhances lignin valorization, producing two high-value compounds—low molecular weight functionalized aromatics and dicarboxylic acids—that can be used independently or together, owing to their inherent capacity to form crosslinked networks.