High-Lignin Polyurethane Foams via a Eutectic-Like Polyol Strategy: Enabling Scalable Processing and Enhanced Structural Performance

Abstract

Replacing petroleum-derived polyols with lignin in polyurethane foams is essential for increasing renewable carbon utilization but is hindered by lignin’s heterogeneity, poor solubility, and limited reactivity. Here, we report a hydrogen-bond-engineered, eutectic-like polyol platform based on polyethylene glycol (PEG) and salicylic acid (SA), with ethylene carbonate (EC) as a cosolvent, enabling high lignin incorporation in the polyurethane foam formulation while maintaining its processability. Structural and thermal analyses confirm the formation of a homogeneous amorphous system, in which EC disrupts intermolecular interactions and enhances chain mobility, reducing the viscosity of the foam formulation to industrially relevant levels (<5 Pa·s). This platform enables the direct substitution of up to 80 wt % of the petroleum-based polyol with kraft lignin, without chemical modification, in the foam formulation. The resulting foams exhibit uniform closed-cell morphology with reduced cell size (287 ± 154 μm), enhanced network integration, improved compressive strength (0.26 MPa) and hydrophobicity, and increased thermal stability. Notably, the foams with a high lignin content demonstrate delayed heat penetration under external heating conditions, which is associated with the formation of stable closed-cell structures. This one-pot, room-temperature strategy provides a promising pathway toward the scalable development of high-lignin polyurethane foams with substantially increased renewable carbon content.