Dispersion Methodology for Technical Lignin into Polyester Polyol for High-Performance Polyurethane Insulation Foam

The incorporation of lignin into rigid polyurethane foam (RPUF) has been explored for the last two decades for replacing petrochemical polyols and producing sustainable high-performance insulation materials. However, to date, the issues associated with the dispersion of technical lignin in the commonly used polyols for RPUF have highly limited the improvement in mechanical and thermal insulation performance. This study reports the enhanced dispersion of kraft lignin (KL) up to 75 wt % in the glycerol-substituted aromatic polyester polyol blend. The influence of significantly well-dispersed KL on RPUF in terms of loading levels, the viscosity of the polyol, the microstructure, and the thermal and mechanical properties of RPUF is discussed. The KL incorporated (0.5–6.0 wt %) in polyol afforded a remarkable reduction in thermal conductivity (32%–34%) of the resultant RPUF with minimal variation in density and insignificant change in compressive strength. The scale of this improvement, to the best of our knowledge, has not been reported to date in lignin-incorporated RPUF systems. Furthermore, the presence of the KL in the RPUF also resulted in a mild improvement in the flame retardance performance. This study provides insights into producing KL-incorporated RPUF for thermal insulation application.