A feasible approach to chromophores removal and color reduction in industrial lignin via deep eutectic solvent/isopropanol treatment.

The dark coloration of industrial lignin significantly limits its potential for applications in high-value products. This work reported a practical strategy for lignin color reduction through the synergistic treatment of acidic deep eutectic solvent and isopropanol (DES-IPA). The results showed that the DES-IPA treatment could effectively remove the p-coumarate units and methoxy groups in lignin. Meanwhile, the condensation reaction in lignin was effectively inhibited. The color of lignin was reduced to an acceptable range while retaining the aromatic ring structure and reactive activity of lignin. Additionally, the DES-IPA treatment endowed lignin with other superior properties, including higher relative molecular weight, narrower molecular weight distribution, and higher purity. Moreover, sunscreen containing 2 wt% light-colored lignin could effectively block ultraviolet light in the wavelength range of 200-400 nm. Overall, the process expanded the application scenarios of lignin, thereby increasing the value of lignin by-products.