Holistic utilization of lignin-derived oligomers and polymers from oxidative catalysis to fabricate highly swelling agro-hydrogels

Abstract

Lignin valorization typically targets either monomers for chemicals or polymers for materials, often overlooking the inevitable aromatic oligomers produced during depolymerization. This study presents a “whole-component” utilization strategy that converts the full spectrum of products derived from catalytic oxidation of alkaline lignin—including previously undervalued oligomers—into high-performance agricultural hydrogels. The obtained oligomers, with a weight-averaged molecular weight of 572 g mol⁻¹ and a carboxyl group content of 1.1 mmol g⁻¹, accounted for a 24.8 wt% yield relative to the raw alkaline lignin. By decoupling the performance contributions of specific fractions, we demonstrate that the combination of oxidized lignin polymers and oxidized oligomers exhibits a synergistic effect, significantly enhancing hydrogel swelling and water-retention capacities. In agricultural trials, soil amended with the full-spectrum hydrogel exhibits superior drought resistance, increasing the fresh weight of barley seedlings by up to 355% compared with that of untreated soil. These findings reveal that aromatic oligomers act as bioactive and structural enhancers rather than as waste, offering a practical and high-efficiency pathway for the total utilization of alkaline lignin in sustainable agriculture.