The incorporation of lignin into rigid polyurethane foam (RPUF) has been explored for the last two decades for replacing petrochemical polyols and producing sustainable highperformance 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 ligninincorporated 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.

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Lignin is one of the most abundant natural polymers. Produced as a by-product from the biomass refinery industries, lignin remains largely underutilised in high-value industrial applications. The incorporation of lignin...

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Lignin, the most abundant aromatic biopolymer, is explored as a renewable polyol substituent and functional additive in rigid polyurethane foam (RPUF) for structural and insulation applications. The understanding of the complex microstructural changes in the RPUF caused by lignin micro-nanoparticles has been limited by traditional two-dimensional cross-sectional imaging methods (typically limited to the average cell diameters). This study reports the microstructural changes induced by the dispersion of kraft lignin (0−2% w/w) in RPUF as monitored using X-ray computed microtomographic (X-ray μCT) analysis. The reconstruction and quantification analysis provide greater insight into the changes induced by lignin on the microstructure of the RPUF, allowing rationalization of the microstructure with physical properties. In comparison to scanning electron microscopy, the magnitude of differences observed in spatial parameters (cell volume, cell surface area, cell ellipticity, and distribution) and skeletal parameters (thickness, length, and the distribution of cell walls and struts) is significant and the presented methodology can be applied to the in-depth analysis of other cellular plastics.