Pyrolytic lignin fractionation for rigid polyurethane foams: Relationship between the Pyrolysate's chemical structure and foam properties

Abstract

Pyrolytic lignin (PL) has emerged as a promising renewable material for the production of polyurethanes (PU) due to the high concentration of hydroxyl groups in its structure, being a potential substitute for petroleum-based polyols. On one hand, the high functionality and liquid form of PL favor its application as a polyol in PU formulations. On the other hand, the inherent heterogeneity of PL still imposes a challenge for the development of new materials with reproducible properties. In this work, aiming to overcome these limitations, an acetone-water fractionation process was successfully used to fractionate PL. The resulting fractions were analytically characterized by HSQC NMR, 31P NMR and rheological analysis, revealing significant structural and compositional differences. Afterwards, these fractions partially replaced an industrial polyether polyol in the formulation of rigid PU foams. Finally, microstructure and mechanical properties of these foams were evaluated by SEM and uniaxial compressive tests. The lignin-based foams exhibited reduced cell size and improved mechanical properties compared to the reference foam (based on a polyether polyol). Thus, the mechanical properties of PU foams can be enhanced through the selection of specific PL fractions. These results highlight the potential of PL fractions as a sustainable and viable alternative to industrial polyols for PU foams with improved properties.