Furan modified lignin: Advancing rigid, open polyurethane foam production from agricultural waste

Furan-modified lignin-rich bio-oils obtained from the lignin-first approach can substitute for polyols in rigid polyurethane foams (PUFs). The addition of furan (5-methylfurfural - MF) in the lignin extraction process significantly impacted the morphological properties of PUFs. Bio-oil derived from sugarcane bagasse (SB) was tested as a polyol substitute in different weight ratios to determine the optimal formulation for PUF production. A 50% replacement of polyol with SB-derived bio-oil resulted in PUFs with favourable morphological, thermal and mechanical properties and also exhibited no peak in the FTIR spectra representing unreacted isocyanate, indicating successful and complete urethane bonding. The study further examined PUFs with 50% polyol replacement using furan-modified bio-oils from rice husk (RH) and sunn hemp biomass (SHB). All these PUFs demonstrated comparable thermal and mechanical properties to those with 100% polyol replacement, regardless of the biomass source and did not contain residual isocyanates. PUFs with a density of over 60 kg m - ³ and an open cell content of over 80%, coupled with high thermal stability, were found to display suitable sound-absorbing properties. This research paves the way for the application of furan-modified lignin in bio-based rigid PUFs for sound-absorbing building materials. • Furan-modified lignin is an effective bio-polyol in polyurethane production • The addition of furan has a huge impact on the polyurethane foams’ cell structure • At a bio-oil content of 50%, the isocyanate reacted completely with the polyol • Lignin-based polyurethane foams have better mechanical properties • The flame retardancy mainly depend on the type of biomass and the addition of furan