Computationally Guided Upgrading of Lignin with Amino Acid-Based Deep Eutectic Solvents for Advanced Waterborne Polyurethanes

Abstract

Lignin, a biogenic and ubiquitous aromatic polymer, holds immense promise for enhancing the performance of waterborne polyurethanes (WPUs); however, its limited dispersibility and interfacial compatibility remain significant challenges. Herein, a novel approach is proposed for lignin functionalization and molecular weight fractionation using amino acid-based deep eutectic solvents (AADESs), effectively overcoming the challenges of poor compatibility and inadequate dispersion of lignin within the soft and hard segments of WPUs. High-throughput COSMO-RS predictions identify lysine–formic acid (Lys–F) as the optimal AADES with excellent lignin solubilization and chemical modification performances. Lignin modified with Lys–F exhibits a high content of active functional groups (5.71 mmol/g), superior thermal stability (decomposition temperature of 360°C), and a low molecular weight (Mw = 1934 g/mol), making it suitable for its homogeneous incorporation into WPU emulsions. Lys–F-modified lignin induces a more refined microphase separation structure in WPU through noncovalent interactions such as hydrogen bonding and polarity differences, leading to a 12-fold enhancement in tensile strength (8.56 MPa) and complete UV shielding (100% efficiency at 200–400 nm). The results validate this computationally guided, sustainable, and robust strategy for the development of next-generation lignin–polyurethane nanocomposites with superior mechanical resilience.

Keywords: Amino acid-deep eutectic solvent, lignin, simulation, waterborne polyurethane