Polyurethane rigid foams formed from different soy-based polyols by the ring opening of epoxidised soybean oil with methanol, phenol, and cyclohexanol

Three polyols (Polyol-M, Polyol-P, and Polyol-C) were synthesised from epoxidised soybean oil by oxirane ring opening with methanol, phenol, and cyclohexanol, and their corresponding polyurethane rigid foams (PU-M, PU-P, and PU-C) were prepared by mixing the soy-based polyol with petroleum-based polyether polyols. At identical soy-based polyol content, PU-P had the greatest density, the smallest cell size, and the highest thermal conductivity. At 25 wt% of soy-based polyol content, the introduction of phenol resulted in the improvement of the compression strength, the thermal stability, and the glass-transition temperature of the bio-foam. However, when the soy-based polyol content was increased to 50 wt%, the poor performance of PU-P was due to the low crosslink density caused by high steric hindrance of excessive benzene rings. The introduction of cyclohexanol failed to improve the properties of the bio-foam. The aliphatic six-membered ring acted as a plasticiser and could not alleviate the drawbacks created by the dangling chains.