Synthesis of soy-polyols using a continuous microflow system and preparation of soy-based polyurethane rigid foams

A soy-polyol labeled Polyol-m was synthesized directly from soybean oil in a continuous microflow system equipped with self-designed oil-water separators and using a reported scheme for epoxidation under following the optimized conditions for hydroxylation: sulfuric acid concentration of 10 wt %, residence time of 13 min, and temperature of 75 °C. Another soy-polyol labeled Polyol-f was also synthesized in a conventional flask from commercially available epoxidized soybean oil as a raw material for the purpose of comparison. Polyol-f had a wider molecular weight distribution, higher viscosity, and lower hydroxyl number than Polyol-m because of the more substantial oligomers introduced by oligomerization, which was confirmed by Fourier transform infrared (FTIR) and gel permeation chromatography (GPC). In addition, the corresponding soy-based polyurethane rigid foams labeled PU-m and PU-f were prepared. PU-m had fine, uniform, and closed-cell morphology, and it contained higher cross-linking due to such characteristics as lower viscosity and higher hydroxyl number; these characteristics were beneficial for the foam properties, including compression strength, thermal insulation, dimensional stability, and thermostability.