Integrating ultrafiltration fractionation and click chemistry for the construction of lignin-derived dye dispersants

• Ultrafiltration enables precise lignin purification and structure control for high‑performance dispersants. • Selective azidation yields uniform, reactive lignin blocks for tunable click‑chemistry reaction. • Designed lignin deliver strong stability, low staining, and tunable performance for eco-friendly dispersants. Lignin, the most abundant aromatic polymer from nature, represents a promising feedstock for sustainable functional materials. Yet its intrinsic structural heterogeneity and broad molecular weight distribution limit its use in performance‑sensitive applications such as dye dispersants. Here, this study reports an integrated strategy for lignin modification, combining ultrafiltration fractionation and click coupling to construct structurally well‑defined dye dispersants. As a prerequisite, we compared different lignin fractionation methods. Solvent dissolution efficiently removed carbohydrate, protein, and sulfur impurities. In contrast, ultrafiltration enabled precise control of molecular weight and size‑dependent distribution of carbohydrate residues. These structural differences strongly influenced lignin self‑assembly. They revealed that molecular weight, polarity, branching, and aromaticity collectively dictate colloidal morphology and uniformity. Selective azidation allowed controlled hydroxyl blocking, and tunable demethoxylation. It also provided predictable reactivity, generating clickable lignin building blocks with preserved aromatic frameworks. Subsequent click chemistry coupling achieved near‑quantitative triazole formation and highly efficient grafting with both small‑molecule and polymeric alkynes, resulting in significant molecular‑weight growth and narrowed dispersity. Performance evaluations showed that the click engineered lignin dispersants demonstrated excellent dispersibility and low staining. They also achieved high dye exhaustion, and strong stability at high temperatures. Among them, UL2‑S1 provided the optimal balance of phenolic‑hydroxyl capping, sulfonic‑group incorporation, and molecular‑weight characteristics. As a result, it yielded stable suspensions and robust dye affinity under industrial dyeing conditions. This work establishes a molecular‑level framework for understanding and designing lignin‑based dispersants and offers a broadly applicable platform for the scalable development of sustainable, tunable lignin‑derived functional additives.