Lignin Type and Content Influence the Foaming Dynamics and Properties of Flexible Polyurethane Foams

Flexible polyurethane (PU) foams, widely used in the mattress industry, are predominantly synthesized from polyols derived from nonrenewable crude oil, raising significant sustainability concerns. In this study, we investigated the partial replacement of polyols with technical lignins, a renewable byproduct of biomass processing typically used for energy generation. Systematic study of two softwood kraft lignins (SKL) and one hardwood organosolv lignin (HOL) revealed that lignin incorporation inhibits the gelation and foaming reactions due to increased viscosity and steric hindrance from the undissolved lignin aggregates, which can, however, be mitigated through catalyst optimization. At similar densities, higher lignin content generally enhances the support factor (SF) and thermal stability but reduces tensile strength, elongation at break, and durability. Notably, one type of SKL, at low polyol replacement levels, demonstrated enhanced support factor with increased tensile strength, elongation at break, thermal stability, and durability. These findings highlight the critical influence of lignin type and content on foam properties, paving the way for sustainable innovations in flexible PU foam materials.