Synthesis of lignin-derived polyols via deep eutectic solvent liquefaction

Abstract

Polyols, serving as core feedstocks in polyurethane production, are characterized by multiple hydroxyl groups (–OH), primarily encompassing polyether polyols (PPG) and polyester polyols (PEP). Their reaction with isocyanates yields polyurethane materials with unique properties. However, conventional petroleum-derived polyols face challenges in meeting green sustainability demands. Lignin, with its abundant phenolic and aliphatic hydroxyl groups, presents a renewable alternative to petrochemical polyols. Its global abundance provides a significant resource base. Deep eutectic solvents (DESs), offering mild reaction conditions, reusability, and high efficiency/selectivity, demonstrate significant potential for producing bio-based polyols. This study employed a modified DES (comprising lactic acid as a hydrogen bond donor and 3,4-dimethyl-1H-pyrazole as a hydrogen bond acceptor) to extract lignin from waste corn stalks, followed by solvothermal liquefaction using polyethylene glycol (MW = 400) and glycerol to synthesize lignin-derived polyether polyols. Comprehensive multiscale characterization elucidated the factors influencing composition, physicochemical properties, and production efficiency. Optimized extraction conditions yielded light-colored lignin with 80% yield, a weight-average molecular weight (Mw) of 35 647 g mol⁻¹, and a polydispersity index (PDI) of 2.221, exhibiting excellent thermal stability below 200 °C. Optimal liquefaction conditions produced polyols with a hydroxyl value of 440.7 mg KOH per g, an acid value of 37.7 mg KOH per g, a viscosity of 646.7 mPa s, and an Mw of 7429 g mol⁻¹. Structural confirmation was achieved via Gel Permeation Chromatography (GPC) and Fourier Transform Infrared Spectroscopy (FTIR). This work successfully established a high-performance lignin-based polyol system, offering a sustainable pathway for polyurethane feedstocks.