Novel synthesis of flexible polyurethane foams with high bio-based content derived from waste cooking oil

This study investigates the production and characterization of open-cell flexible polyurethane foams (PUFs) with high bio-based content, using waste cooking oil (WCO) as a precursor for polyols to replace conventional fossil-based polyols. WCO was epoxidized to varying degrees (66–94%) through heterogeneously catalyzed oxidation with Amberlite® IR 120, followed by ring-opening reactions with ethanol to synthesize polyols with hydroxyl numbers ranging from 132 to 177 mg KOH/g. These polyols were then used to produce PUFs through confined expansion, incorporating a partially bio-based diisocyanate, water as a blowing agent, and specifically tailored additives. An isocyanate-to-hydroxyl molar ratio (NCO/OH) of 0.9 was employed to achieve efficient foaming with different crosslinking densities. Comprehensive chemical, morphological, thermal, and mechanical analyses confirmed the successful production of open-cell flexible foams. The results indicated that cell size decreased with an increasing hydroxyl number of the polyol, corresponding to a higher crosslinking density. The foams exhibited an exceptionally high bio-based content of approximately 80 wt.%, densities ranging from 82 ± 1 to 87 ± 1 kg/m3, and compression force deflection (CFD) values at 50% deformation between 6.7 ± 0.5 and 56.5 ± 2.9 kPa. Higher hydroxyl numbers in the polyols resulted in increased CFD values, highlighting the effectiveness of hydroxyl number as a strategy to control foam cellular structure and mechanical properties. These findings demonstrate the potential of WCO-derived polyols as a sustainable and efficient alternative to fossil-based raw materials in the production of flexible PUFs, offering a customizable approach for diverse applications.