Development of High-Performance Bio-Based Polyurethane Foams from Nigerian Vegetable Oils as Petroleum Polyol Replacements: Synthesis, Structure, and Multiscale Characterisation

The global push towards bio-based polyurethane foams using vegetable oil-derived polyols offers a significant opportunity for Nigeria as a major producer of palm, castor, and rubber seed oils to develop domestic capacity for renewable chemical production from indigenous agricultural resources. This research develops high-performance bio-based polyurethane foams from Nigerian vegetable oil-derived polyols as petroleum polyol replacements, conducting a systematic multiscale characterisation from molecular structure to macroscale foam properties. Palm kernel oil, castor oil, and rubber seed oil polyols were synthesised by epoxidation-ring opening and transesterification routes, fully characterised by NMR spectroscopy, gel permeation chromatography, and hydroxyl value determination. Flexible and rigid polyurethane foams were formulated at varying bio-polyol replacement levels of 25, 50, 75, and 100 percent by weight of total polyol. Foam characterisation at molecular scale employed solid-state NMR and FTIR to characterise urethane network structure and cross-link density. At the cellular scale, X-ray microtomography characterised cell size distribution, cell wall thickness, and anisotropy ratio. Macroscale properties including compressive strength, resilience, thermal conductivity, flammability, and thermal stability were determined following ISO and ASTM standards. Multiscale relationships between molecular network structure, cellular morphology, and macroscale properties were established through combined experimental analysis and finite element micromechanical modelling of idealised cell geometries. Results demonstrate that 100 percent castor oil polyol replacement achieved compressive strength within 6 percent of petroleum-based control foam, attributed to castor oil's natural primary hydroxyl functionality providing ideal polyurethane network formation. Thermal conductivity of rigid bio-foam reached 0.023 W/m.K, acceptable for insulation applications. The research establishes the scientific and technical foundation for a Nigerian bio-polyol production and polyurethane foam manufacturing industry from indigenous agricultural oil resources. Keywords: bio-based polyurethane, vegetable oil polyol, foam characterisation, palm kernel oil, castor oil