# Fractionation of Wood Biomass With Thiolactic Acid and Choline Chloride‐Based Solvent Into White Lignin for Sustainable Cooling Applications

## TL;DR

A new method produces bright white lignin from wood biomass, suitable for sustainable cooling applications.

## Contribution

A novel lignin fractionation method using thiolactic acid and choline chloride yields bright white lignin with high recovery.

## Key findings

- The method produces white lignin with >90% whiteness and 70% recovery efficiency.
- White lignin shows high visible light reflectance and low solar heat gain.
- It has strong UV absorption and high emissivity for passive radiative cooling.

## Abstract

Lignin, a naturally abundant biopolymer, possesses intrinsic ultraviolet (UV) shielding capabilities, making it a promising candidate for sustainable functional materials. However, conventional lignin isolation methods often lead to dark‐colored products due to structural condensation and chromophore formation, limiting its applicability in optical and esthetic applications. In this study, we introduce a novel fractionation strategy utilizing a system composed of thiolactic acid and choline chloride to selectively extract lignin from wood biomass. This environmentally benign process yields a light‐colored lignin with exceptional whiteness (>90%) and high recovery efficiency (70%). The preservation of lignin's bright appearance is attributed to its submicron‐scale morphology and chemical stabilization via thiolactic acid modification, which suppresses chromophore formation. Remarkably, the resulting white lignin demonstrates high visible light reflectance and significantly reduced solar heat gain compared to conventional kraft lignin. Furthermore, its strong UV absorption and high emissivity in the atmospheric transparency window position it as a compelling bio‐derived material for passive radiative cooling applications. This work highlights a sustainable pathway for valorizing lignin into high‐performance, multifunctional materials aligned with green chemistry principles.

A novel and highly efficient wood biomass fractionation method was developed to produce white lignin, exhibiting the brightest color reported to date. The process yielded white lignin with high yield, excellent visible light reflectance, and elevated infrared emissivity, highlighting its potential as an active material for passive radiative cooling applications.© 2026 WILEY‐VCH GmbH