In recent years, there have been extensive efforts to replace fossil-fuel-based raw materials with bio-based materials in flexible polyurethane (PU) foams. Lignin, a natural polyol generated as a byproduct of chemical pulping and biorefineries, is an attractive compound to replace petroleum-derived polyols due to its abundant availability and bio-based nature. This thesis discusses efforts to partially replace petrochemical polyols in flexible foams with a liquid lignin polyol made by oxyalkylating lignin with propylene carbonate, a green solvent. First, a small-scale computational study using density functional theory (DFT) was used to investigate the reaction between lignin model compounds and isocyanates. The results of this computational study were consistent with experimentally obtained data. Next, a screening study was conducted to determine how different types of lignin affect the properties of the developed lignin polyols. Then, flexible PU foams were made using three different lignin polyols, derived from different biomass sources and isolation processes. Electron microscopy and reaction profile analysis of foam samples showed that the addition of the lignin polyol reduced cell sizes and decreased reaction times. It was found that a high molecular weight kraft-softwood lignin resulted in a foam with significantly better mechanical properties compared to foams made with organosolv wheat straw and acid-hydrolysis hardwood lignins. After optimization, a foam produced containing 14% kraft-softwood lignin polyol met standard requirements for automotive seating applications.
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