Unlocking a thioglycolic acid-mediated fractionation strategy for high-whiteness and uncondensed lignin

The efficient extraction of lignin with preserved native structure and light color remains a critical challenge in biomass refining. Here, we present a novel strategy for lignin structural stabilization and chromophore suppression using a thioglycolic acid/glycolic acid (TgA/GA) cosolvent system with moderate acidity. This approach achieved efficient delignification (>83 %) and yielded lignin with near-native structural integrity and high whiteness. The TgA/GA cosolvent functioned on the lignin through a dual mechanism: quenching benzylic carbocations to protect β-O-4 linkages against condensation, and reducing chromophores in situ to inhibit their formation. The extracted lignin retained 59.0 β-O-4 linkages per 100 C 9 units—approaching native levels—allowing efficient catalytic depolymerization to monophenols (>22 wt% yield). It simultaneously exhibited high whiteness (L* > 80, ΔE < 18) due to the suppression of chromophores such as quinone-type, demonstrating suitability for applications such as sunscreens. Simultaneously, the co-produced cellulose fraction, devoid of condensed lignin particles, retained a light color and exhibited high enzymatic digestibility (>88 % glucose yield). This work presented an effective strategy for co-producing high-yield, high-whiteness, structurally preserved lignin and highly reactive cellulose from lignocellulose, paving the way for value-added lignin utilization in optically sensitive applications.