Synthesis of castor oil-based polyol and its application in flexible polyurethane foam: The role of ester groups in the foam performance

A castor oil-based polyether polyol (COP) with molecular weight comparable to that of a petroleum-based polyether polyol (PPG) was prepared via the oxypropylation of castor oil and propylene oxide. Such COP was utilized to fabricate flexible polyurethane foams (FPUs). A comparative study was conducted on foams derived entirely from PPG (FPU-0), with 50 % COP substitution (FPU-0.5), and entirely from COP (FPU-1.0). Results indicated that the introduction of COP significantly enhanced hydrogen bonding interactions between the ester groups in the soft segments and the imino groups in the hard segments, as confirmed by FT-IR, XRD and DFT calculations. These stronger hydrogen bonds promoted the physical cross-links between the soft segments and the hard segments. This led to a remarkable improvement in tensile strength (from 99.5 kPa to 124.2 kPa) and energy dissipation under cyclic compression (increasing from 2.2 kJ/m³ to 5.2 kJ/m³ at the 4th cycle) while maintaining a high fracture elongation (∼140 %). Owing to its high damping capacity and sustainable, bio-based composition, the COP-based FPU showed great potential for impact-absorbing applications such as protective packaging, automotive seating cushions, and sports equipment midsoles. This work elucidated the crucial role of ester groups in enhancing intermolecular interactions and improving the properties of FPU, providing a practical guidance for developing high-performance bio-based flexible polyurethane foams.